Volume 63, Issue 4, October 2019 Published by Johnson Matthey © Copyright 2019 Johnson Matthey

ISSN 2056-5135

Johnson Matthey’s international journal of research exploring science and technology in industrial applications

Johnson Matthey Technology Review is published by Johnson Matthey Plc.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. You may share, copy and redistribute the material in any medium or format for any lawful purpose. You must give appropriate credit to the author and publisher. You may not use the material for commercial purposes without prior permission. You may not distribute modiﬁ ed material without prior permission.

The rights of users under exceptions and limitations, such as fair use and fair dealing, are not aﬀ ected by the CC licenses. www.technology.matthey.com www.technology.matthey.com

Johnson Matthey’s international journal of research exploring science and technology in industrial applications

Contents Volume 63, Issue 4, October 2019

234 Guest Editorial: Making the Most of Our Materials By Jacqueline Edge 236 Grain Reconstruction of Palladium and Palladium-Nickel Alloys for Platinum Catchment By A. Slagtern Fjellvåg, D. Waller, J. Skjelstad and A. Olafsen Sjåstad 247 Predicting the Structure of Grain Boundaries in Fluorite-Structured Materials By Aoife K. Lucid, Aoife C. Plunkett and Graeme W. Watson 255 In the Lab: UK Research on Materials for Electrochemical Devices Featuring Samuel J. Cooper, Ainara Aguadero, Chandramohan George, Magdalena Titirici and Pooja Goddard 261 “Nanostructured Materials for Next-Generation Energy Storage and Conversion: Fuel Cells” A book review by Rob Potter 265 Exploring Microemulsion-Prepared Lanthanum Catalysts for Natural Gas Valorisation By Cristina Estruch Bosch, Stephen Poulston, Paul Collier, Joris W. Thybaut and Guy B. Marin 277 TechConnect World Innovation Conference and Expo 2019 A conference review by Debra Jones 281 “Nanocarbons for Energy Conversion: Supramolecular Approaches” A book review by Harry Macpherson 285 Oxford Battery Modelling Symposium A conference review by Giulia Mangione 289 Johnson Matthey Highlights

292 “Process Systems Engineering for Pharmaceutical Manufacturing” A book review by Michael D. Hamlin 299 Intensified Liquid-Liquid Extraction Technologies in Small Channels: A Review By Panagiota Angeli, Eduardo Garciadiego Ortega, Dimitrios Tsaoulidis and Martyn Earle https://doi.org/10.1595/205651319X15640587615677 Johnson Matthey Technol. Rev., 2019, 63, (4), 234–235

www.technology.matthey.com

Guest Editorial Making the Most of Our Materials

Recent advances in energy technology are driven Multiscale, Multifunctional Design by the need to mitigate climate change and find sustainable, non-polluting ways to power our Materials should primarily be functional at device communities. However, a large proportion of the level, fulfilling an application’s key performance impact arises from the materials used to make indicators. However, material choice should energy devices (1) and it is therefore important also consider processing costs, device lifetime, to generate and use materials effectively, while environmental impacts and safety. Device finding ways to minimise waste, energy use and performance is an inherently multiscale challenge, harmful chemicals during device fabrication. This since material properties are strongly linked to editorial describes the materials science toolbox atomistic, nanoscale and microscale structures for making the most of our resources. (4), well-structured materials often performing better than their unstructured equivalents (5). The True Value of Materials The choice of material for a particular device arises from its constituent elements and atomic Materials have value beyond their price. Raw structure, defining its electrical, mechanical, materials extraction, processing and distribution chemical and magnetic properties. Databases embody energy and costs which are not reflected of structure-property relationships of energy in their market value, such as irreversible materials are emerging from experimental and ecosystem damage, use and contamination of theoretical studies, enabling data mining for clean drinking water and pollutants produced at materials suited to a particular application, every stage. Some materials require scarce or termed rational design. Abundant elements extractively costly minerals (2, 3), for instance forming benign chemistries are indicated, for cobalt mining involves severe toxins. example sodium-ion batteries replacing lithium Worldwide population growth and rising demand (see Titirici’s work in Edge et al. (6)). makes sustainability a key consideration. Quantum effects and large surface area to volume Recycling is one way to achieve this, but it ratios at the nanoscale (1–100 nm) enhance requires considerable resources and often results or endow new properties. Integration of one- in low quality products. Therefore, techniques dimensional and two-dimensional nanostructures encouraging the best use of virgin materials into composites has led to significant advances, for are needed, for example advanced processing example carbon-based nanomaterials conferring techniques producing highly functional micro- outstanding electrochemical properties and and nanostructures from smaller quantities. strong mechanical stability (7). Other important Multifunctionality – coupling related functions into properties, such as porosity and mechanical a composite material – may increase resource strength, often rely on microstructures (100 nm efficiency across the whole supply chain. to a few cm). A whole systems perspective can ensure that One route to fabricating high precision micro- we are focussing on the right aspects and and nanostructures is additive manufacturing: account for costs and impacts over a product’s a range of processes building complex, lifecycle. Lightweighting and extending the three‑dimensional structures from the bottom lifespan of energy products are effective ways up, with minimal waste of both materials and to achieve efficiencies across the entire supply energy and few toxic chemicals. Other advanced, chain (3). resource-efficient techniques producing complex

234 © 2019 Johnson Matthey https://doi.org/10.1595/205651319X15640587615677 Johnson Matthey Technol. Rev., 2019, 63, (4) microstructures include electrospinning and and may not have immediately detectable effects, graphitising nanostructures from waste biological only influencing the long-term performance. Some matter (see Cooper and Titirici’s work (6)). studies are emerging, examining the effects of Combining single function devices into systems processes such as calendering on battery electrodes creates unnecessary complexity in manufacturing (11). There is a need for holistic studies and the and packaging, adding to weight and cost. application of green chemistry principles (12) Functional diversity, where coupled functions are throughout the supply chain, as well as studies on integrated into hybrid materials, creates efficiency degradation and its mitigation, to stretch resource opportunities across the supply chain. For example, usage. George’s work in Edge et al. (6) embeds solar cell structures into battery electrodes. JACQUELINE EDGE Modelling Real Materials: The Department of Mechanical Engineering, Imperial Importance of Defects and College London, South Kensington Campus, Heterogeneity London, SW7 2AZ, UK Email: [email protected] Advanced simulation capabilities speed up research into new materials and systems and allow technologies to be deployed safely and efficiently References (3). Rational design’s structure databases consist 1. D. Larcher and J.-M. Tarascon, Nature Chem., largely of X-ray diffraction performed on pure 2015, 7, (1), 19 crystals, while real materials are heterogeneous, for 2. C. P. Grey and J.-M. Tarascon, Nat. Mater., 2017, example through interfaces between components, 16, (1), 45 where critical reactions occur (8) and contain a 3. ‘Innovating Clean Energy Technologies in Advanced wide range of defects, such as impurities, vacancies Manufacturing’, in “Quadrennial Technology and dislocations. The heterogeneity of materials Review 2015”, Ch. 6, US Department of Energy, can define their properties, for example Lucid et Washington, USA, 2015, 53 pp al. (9) looks at how to simulate grain boundaries: 4. J. Meng, H. Guo, C. Niu, Y. Zhao, L. Xu, Q. Li and nanoscale interfaces in polycrystalline materials. L. Mai, Joule, 2017, 1, (3), 522 Defects can diminish performance, but there are 5. J. Lölsberg, O. Starck, S. Stiefel, J. Hereijgers, T. many materials, such as semiconductors, whose Breugelmans and M. Wessling, ChemElectroChem, critical qualities exist because of their impurities. 2017, 4, (12), 3309 Understanding defects is key to enhancing material properties, for example in battery electrode 6. J. S. Edge, S. J. Cooper, A. Aguadero, C. George, M. Titirici and P. Goddard, Johnson Matthey materials (10). Incorporating both defects and Technol. Rev., 2019, 63, (4), 255 heterogeneity into models will enable more accurate tuning of properties and performance. 7. Y. Li , Y.-S. Hu, M.-M. Titirici, L. Chen and X. Huang, Adv. Energy Mater., 2016, 6, (18), 1600659 8. K. T. Butler, G. S. Gautam and P. Canepa, Npj Finishing Touches Comput. Mater., 2019, 5, 19 Given that it is expensive to extract, process and 9. A. K. Lucid, A. C. Plunkett and G. W. Watson, distribute raw materials (1), particularly if they Johnson Matthey Technol. Rev., 2019, 63, (4), are scarce and particularly for energy devices (1), 247 it is important that energy materials are used as 10. K. Hoang and M. D. Johannes, J. Phys.: Condens. effectively as possible. However, materials are Matter, 2018, 30, (29), 293001 subject to a range of processes throughout the 11. H. Bockholt, M. Indrikova, A. Netz, F. Golks and A. supply chain, including the application of additives Kwade, J. Power Sources, 2016, 325, 140 or coatings and packaging, all of which may exert 12. P. T. Anastas and J. C. Warner, “Green Chemistry – mechanical stress, exposure and ageing. The Theory and Practice”, Oxford University Press Inc, effects of these processes are not well understood New York, USA, 1998, 135 pp

www.technology.matthey.com

Grain Reconstruction of Palladium and Palladium-Nickel Alloys for Platinum Catchment Effects on metal alloy composition at surface and in bulk when operated as a platinum catchment unit during high temperature ammonia oxidation

# A. Slagtern Fjellvåg PtO2 on the structural changes of the Pd-Ni gauzes. Centre for Materials Science and In addition, some samples are exposed to real Nanotechnology, Department of Chemistry, industrial conditions in an ammonia combustion University of Oslo, PO box 1126, Blindern, 0318 pilot plant reactor. Fresh and spent catchment Oslo, Norway gauzes are analysed by means of scanning electron microscopy (SEM), energy dispersive D. Waller X-ray spectroscopy (EDX), thermogravimetric Yara Technology Center, Herøya Research Park, analysis (TGA) and inductively coupled plasma Building 92, Hydrovegen 67, 3936 Porsgrunn, mass spectroscopy/optical emission spectroscopy Norway (ICP-MS/OES). By combining analysis of samples from furnace and pilot scale experiments, the main J. Skjelstad findings are that Pd-Ni gauzes undergo internal K. A. Rasmussen, Birkebeinervegen 24, 2316 oxidation to nickel(II) oxide (NiO); which in the Hamar, Norway presence of steam results in Ni depletion and that A. Olafsen Sjåstad* PtO2 vapour causes severe grain reconstruction. Centre for Materials Science and Furthermore, in laboratory-scale experiments no significant Pd loss is observed, which is in Nanotechnology, Department of Chemistry, contrast to observations from the pilot plant where University of Oslo, PO box 1126, Blindern, 0318 the samples are exposed to real post-ammonia Oslo, Norway oxidation conditions. Pd loss is likely attributed Email: *[email protected], to some gas species contained in the real post- #[email protected] ammonia oxidation gas stream.

Platinum-rhodium gauzes are frequently used to Introduction catalyse the high temperature ammonia oxidation step for production of synthetic nitrogen-based Ammonia oxidation is one of the key reaction fertilisers. The gauzes suffer from Pt loss in the steps in the production of synthetic nitrogen-based form of platinum dioxide (PtO2), due to the highly fertilisers. Industrially, the reaction is typically exothermic nature of the oxidation reaction. carried out at 900°C and a pressure of 1–13 bar Industrially this is mitigated by installing one or over metallic Pt-Rh catalytic gauzes (1). During more palladium-nickel catchment gauzes directly operation, the Pt-Rh catalyst undergoes several downstream of the combustion gauzes, to capture structural changes, such as grain growth of the wire the lost Pt. The Pd-Ni catchment gauzes undergo core, surface formation of so-called cauliflowers severe structural modification during operation. In and enrichment of Rh on the wire surface, due to a this study, we undertake a systematic study in a significant loss of Pt (2, 3). The Pt is mainly lost as laboratory-scale furnace system to determine the gaseous PtO2 and it is anticipated to be caused by role of each of the constituent gases O2, H2O and hot spots on the Pt-Rh gauze due to the extreme

236 © 2019 Johnson Matthey https://doi.org/10.1595/205651319X15597236291099 Johnson Matthey Technol. Rev., 2019, 63, (4) exothermic nature of the oxidation of ammonia to Despite the fact that the aforementioned NO (2) (selectivity ~96% (1)), Equation (i) (4): drawbacks of the Pd-Ni catchment system have been known for several decades, only a handful of 4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g) 0 –1 studies related to this topic have been published in ∆H r,298 K = −908 kJ mol (i) → the last 50 years (5–18). Ning et al. (8) report on Depending on plant conditions, the Pt loss is in the the surface reconstruction of the catchment gauze range of 0.05–0.4 g per tonne nitric acid (HNO3) and both Fierro et al. (9) and Ning et al. (10) discuss produced i.e., noble metal loss in a modern plant the catchment mechanisms. Recently, Pura et al. producing on average 1000 tonnes HNO3 per day, (11) suggested that the alloying element Ni is represents a huge financial cost for the fertiliser not participating in the catchment process, but industry (1). State of the art technology to reduce that grain boundary attack may be a mechanism this cost proceeds via catchment of the formed responsible for grain reconstruction. This was

PtO2 vapour by Pd-Ni alloy gauzes, located just further investigated by Pura et al. (18) suggesting downstream of the Pt-Rh ammonia oxidation that a rapid loss of Ni from grain boundaries causes catalyst. The predecessor of this catchment the initial porosity in the wire. Still, sufficient technology, a palladium-gold (80:20 wt%) alloy understanding of the occurring reactions is not gauze, was developed by Degussa in the late achieved and knowledge on how to improve or 1960s (5). The Pd-Au gauzes quickly outperformed modify the Pd-Ni based catchment systems is still other catchment systems, such as glass wool lacking. The common denominator between all the filters, Raschig rings and marble chips (6). Later, mentioned investigations is that they are based on cheaper metals such as Ni and cobalt replaced gauzes used in industrial operation, where several Au in the Pd-Au alloy, as they gave an enhanced different parameters such as temperature and gas catchment efficiency in addition to lower costs composition are in play simultaneously. To the (7). Still, the Pd-Ni catchment unit has several best of our knowledge, no or only minor focus has drawbacks. During operation, the Pd-Ni gauze been put on systematic, single-parameter studies wires reconstruct completely and swell in size. This to unravel the underlying reasons for the grain results in a significant loss of mechanical strength reconstruction phenomena. and additionally, it is the dominant cause of a Here we report the results of systematic studies to large pressure drop increase over the gauze pack understand the role of the individual constituents of during the campaign, see Figure 1. Furthermore, the reaction gas mixture (O2, H2O and PtO2 diluted during operation, the gauze is depleted in Ni and in N2) in the reconstruction of Pd-Ni gauzes, at depending on plant conditions, 0.2–0.4 g Pd is lost conditions relevant for high-temperature ammonia per gram Pt captured (6). oxidation. By exposing pure Pd and Pd-Ni wires and woven gauzes in a laboratory-scale furnace to the individual gas components in a systematic manner, we investigate which gas species cause 1.00 reconstruction. We will also discuss the role of Ni with respect to Pt catchment, Ni loss and the 0.95 existing Ni species during operation (metal, oxide and hydroxide). Finally, we compare the 0.90 laboratory-scale results with two samples treated in a pilot plant at the Yara Technology Center 0.85 facility (Herøya, Norway), where the samples Arb. units Arb. experience the real conditions of high temperature 0.80 ammonia oxidation in terms of gas mixture, linear Normalised pressure drop gas velocity, temperature and pressure. 0.75

0 50 100 150 200 250 Experimental

Time, days Wires and woven gauzes of the industrial alloys Fig. 1. Pressure drop from the Yara Technology Pd-Ni (95:5 wt%) and pure Pd were supplied by Center industrial facility. Data points are K. A. Rasmussen (wire diameters of 76 μm and normalised by dividing pressure by gas load to see 120 μm) which were used for the laboratory-scale the developing trend experiments. In addition, pure Pd catchment gauzes

(76 μm) were used in pilot plant experiments samples were fully dissolved in aqua regia. The Pt with a pure Pt net and a lanthanum cobaltite content was determined by ICP-MS whereas Pd and

(LaCoO3)-based ammonia oxidation catalyst, Ni concentrations were determined by ICP-OES. the latter in the form of 3 mm cylindrical pellets. The standard deviation was in the range of 1–2% For the laboratory-scale furnace experiments, of the measured value. samples were heat treated in a six-zone furnace at TGA was conducted with a NETZSCH (Germany) 900–1050°C (ambient pressure) in a quartz tube STA 449 F1 Jupiter, with an alumina TG-pin stage. (inner diameter = 6 mm) in various gas atmospheres The experiments were performed by stacking six containing synthetic air (5.0, Praxair, USA), steam (6) fresh Pd-Ni (or Pd) gauzes on top of each other and PtO2 vapour. The composition of the water and heating to 140°C to remove humidity and vapour mixture was 33 vol% H2O, 14 vol% O2 and other surface species on the sample. Thereafter, –1 53 vol% N2. PtO2 vapour was generated from a the sample was ramped to 900°C (10°C min ) rolled up Pt gauze (~0.4–0.8 g) located upstream before a 24 h dwell. After the experiment was of the sample at 1050°C, producing a p(PtO2) of completed, the same setup and temperature approximately 1 × 10−8 bar (2.5 mg Pt loss over program was rerun with a fully oxidised sample 20 days in a flow of 1 l air per min). During heat for the background correction. In all experiments treatment, samples were positioned perpendicular O2 (5.0) and N2 (5.0) from Praxair were used and to the length direction of the quartz tube to enhance the pO2 was 0.2 bar over the sample. gas exposure to the gauze and wire in the gas flow. Samples from the Yara pilot plant were treated Results and Discussion at 900°C and 5 bar in a gas mixture containing

10 vol% NH3 in compressed air, before the ammonia As-Received Palladium-Nickel and oxidation combustion catalyst. This implies that the Palladium Catchment Gauzes gas mixture contained approximately 9 vol% NO,

15 vol% H2O and 6 vol% O2, 2000 ppm or 100 ppm Prior to exposing the as-received Pd-Ni and

N2O (pure Pt or oxide catalyst) and the rest N2 Pd wires to any gases, SEM and EDX analysis when exposed to the catchment alloy. The pilot was performed on both wire surfaces and their plant samples were exposed to exactly the same cross-sections. In Figure 2, representative conditions as industrial catchment gauzes and overview images of the wire surface (Figure 2(a)) are compared with laboratory-scale samples (as and the cross‑section (Figure 2(b)) of the 120 µm described above) and industrial samples treated Pd-Ni alloy are shown. Overall, EDX analysis at 900°C at 5 bar for 47 days below an industrial confirms the cross-sections of the alloys to contain Pt-Rh (95:5 wt%) catalyst in the industrial gas minute quantities of oxygen, with slightly enhanced mixture (10 vol% NH3 in compressed air). amounts at the surface, see Table I. In addition, Various sample surfaces and cross-sections were EDX analysis of three randomly selected points examined with a high-resolution Hitachi Regulus on the Pd-Ni cross‑section reveal the Ni content 8230 field-emission scanning electron microscope to be in the range from 4.4–5.0 wt%, close to (FE-SEM). Images were obtained by collecting the the value provided by the supplier. EDX mapping secondary electrons produced by the electron beam did not reveal any obvious heterogeneities or with an acceleration voltage of 1 kV. Qualitative impurities, neither within the grains nor along the EDX analysis (mapping and point quantification) grain boundaries. Based on this we conclude the was performed on selected samples using an Pd-Ni alloy to be a homogeneous solid-solution, acceleration voltage of 30 kV. Samples were of ~95:5 wt% Pd-Ni, within the uncertainty of the mounted with carbon tape on a copper plate or EDX analysis. Finally, it should be noted that light prepared for cross-section imaging by casting the microscopy of chemically etched cross-sections wire in a conducing resin (PolyFast, Struers, UK) reveal sharp grain boundaries and a grain size of before grinding and polishing (1 µm diamond finish). 5–20 µm for 76 µm wires, of both Pd and the Pd-Ni Wet chemical etching of the polished sample was alloy, see Figure 2(c) for the Pd-Ni alloy. performed in HNO3 (heat-treated gauze) or aqua regia (unreacted gauze) for 30 seconds at room Effect of Oxygen temperature. Light microscopy was performed with a Zeiss Axio metallurgical microscope. ICP-MS/OES When the metallic Pd-Ni gauze (wire diameter analysis was performed on selected samples 76 µm) is exposed to air in the TGA instrument by SINTEF Molab AS (Norway). Prior to analysis at 900°C for 24 h, a mass gain of 1.47 wt% is

(a) (b) (c)

500 µm 40 µm 50 µm

Fig. 2. (a) SEM image of the surface of a fresh 120 µm Pd-Ni wire; (b) SEM image of the cross-section of a fresh 120 µm Pd-Ni wire; (c) light microscope image of a 76 µm Pd-Ni wire after etching in aqua regia for 30 s

Table I Qualitative EDX Results of Fresh 120 µm Pd and Pd-Ni (95:5 wt%) Alloys Sample Area Details Pd, wt% Ni, wt% O, wt% Pd-Ni Surface Large area 91.3 4.4 4.3 Pd-Ni Cross section Point, centre 95.0 5.0 0.0 Pd-Ni Cross section Point near centre 94.9 5.1 0.0 Pd-Ni Cross section Point off centre 94.5 4.4 1.1 Pd-Ni Cross section Point off centre 94.7 4.8 0.5 Pd Surface Large area 94.2 0.2a 5.6 Pd Cross section Point, centre 100.0 0.0 0.0 aPossibly overestimated value due to peak overlap between Ni and Cu (sample is mounted on Cu plate). Analysis certificate from K. A. Rasmussen shows a Ni content of <2 ppm in pure Pd wires

recorded, see Figure 3(a). The observed mass at the grain boundaries and that the grain size gain is slightly larger than the theoretical value has increased to 10–30 µm. Additionally, the NiO (1.36 wt%) for complete oxidation of Ni to NiO for precipitates are found at equal depth within the a 95:5 wt% Pd-Ni alloy. When exposing the metallic grains as in the grain boundaries, indicating that Pd gauze to similar conditions, only a minor mass oxygen diffusion is approximately equally fast in gain is observed (not shown). With reference to grains and grain boundaries (Figure 3(b)–(d)). Ning et al. (10) and Gegner et al. (19), we assign Notably, at the same time as oxygen diffuses the observed mass gain of the Pd gauze to a small towards the wire centre, EDX mapping show a oxygen solubility and formation of PdO on the Pd distinct reduction in Ni concentration in the wire surface. The minor mass gain observed for pure core (Figure 3(b)–(d)). EDX point analysis of the Pd may indeed contribute in the slightly larger wire core indicate the Ni content to be 4.2 wt% observed mass gain relative to theory for the and 2.7 wt% after 1 h and 4 h, respectively. This Pd-Ni sample. The internal oxidation of the Pd-Ni implies that during the oxidation process the Ni alloy is shown visually in Figure 3(b)–(d). Here, mobility is enhanced, causing a heterogeneous cross-sections of the Pd-Ni wire heated for 1 h distribution of Ni with more NiO at the outer part and 4 h, analysed by SEM and EDX, show small of the wire. These observations coincide well precipitated particles approaching the wire centre with reports by Gegner et al. (19) on internal with time. By EDX point analysis, the precipitated oxidation of alloys with a non-noble element in a particles are found to consist of oxygen and nickel solid solution with a more noble element. Finally, in an approximately 1:1 molar ratio, indicating NiO it should be noted that the initial grain growth formation (Figure 3(c)). is seen during the first 24 h, but no significant As shown in Figure 3(e) and Figure 3(f), grain growth is observed after another 20–30 chemical etching prior to SEM and EDX analysis days of heat treatment (see Figure S1 in the reveals that the largest NiO precipitates are located Supplementary Information).

(a) (b) (c) 1.5 800 Temperature, °C

600 1.0

400 Pd-Ni 0.5 Temperature Mass increase, % 200

0 0 5 10 15 20 Ni-KA 50 µm Ni O 50 µm Time, h

(d) (e) (f)

50 µm Ni-KA 50 µm SE Ni 50 µm

Fig. 3. (a) TGA of Pd-Ni gauze heated in air, heating rate 10°C min–1 followed by a 24 h dwell at 900°C; (b) EDX mapping of the Pd-Ni wire after 1 h exposure in the TGA experiment; (c)–(d) EDX mapping of the Pd-Ni wire after 4 h exposure in the TGA experiment; (e) SEM image of a 76 µm Pd-Ni wire heated at 900°C for 30 days in a muffle furnace (air) and etched for 30 s in a HNO3 before imaging; (f) EDX mapping of a 76 µm Pd-Ni wire heated at 900°C for 30 days in a muffle furnace (air) and etched for 30 s in a HNO3 before imaging

Palladium-Nickel Gauzes Exposed to Factsage (22, 23), which estimate a significant Pd Wet Air loss as PdOH (22, 23) in wet gas and a smaller loss as PdO2 and Pd(OH)2 (22, 23) (see Figure S2 When water vapour is included in the feed gas (wet in the Supplementary Information). This leads to air: 33 vol% H2O, 14 vol% O2, 53 vol% N2), the the conclusion that the observed mass loss of Pd- internal oxidation of Ni to NiO occurs in a similar Ni in wet air is due to NiO being hydrolysed by the manner as in dry air, see Figure 4(a). However, wet air and forming volatile Ni(OH)2, which in turn based on gravimetry, the Pd-Ni gauze has lost causes Ni depletion. This observation is in line with 2.4 wt% of its initial mass after heat treatment for Chen et al. (24). two weeks in wet air at 1050°C. ICP-MS analysis Finally, after the two weeks’ treatment in wet air of the exposed gauze give a total Ni concentration the NiO precipitates are no longer seen at the grain of only 2.7 wt% relative to Pd, compared to boundaries. Unfortunately, chemical etching prior 4.8 wt% on a comparable sample treated in dry air. to SEM analysis has not revealed the exact position In addition, SEM analysis reveal that the outer parts of the grain boundaries and thus the occurrence of the Pd-Ni wire is depleted in Ni (Figure 4(b)) of grain growth is uncertain. In many ways the and that some surface roughness has appeared situation is similar to the grain growth observed (Figure 4(c)). The data also shows that only during the initial oxidation process of Ni to NiO. 0.1 wt% Pd is lost during two weeks’ treatment in During the initial oxidation, inwards/outwards wet air; far below the industrial Pd loss observed diffusion of O-Ni increased the mobility of O-Ni, during ammonia oxidation (see below). There is just as treatment in wet air may have increased also no observed Pd loss in dry air. This correlates Ni mobility by Ni diffusion towards the surface. well with the work of Opila (20), which shows no The increased mobility may again contribute to Pd loss in wet or dry oxygen and Ar and other grain growth. However, we are currently not in literature on Pd loss in dry air (21). Notably, these position to elaborate in detail on how grain growth findings are in contradiction to the calculations of is interwoven and connected to diffusion and the

(a) (b) (c)

50 µm 50 µm 20 µm

Fig. 4. (a) SEM image of the cross section of a Pd-Ni wire (120 µm) treated in wet air at 1050°C for 3 days; (b) cross section of a Pd-Ni gauze (76 µm) treated in wet air at 1050°C for 14 days; (c) surface of a Pd-Ni gauze (76 µm) treated in wet air at 1050°C for 14 days

(a) (b) (c)

2 µm 3 µm 5 µm

(d) (e) (f)

3 µm 3 µm 5 µm

Fig. 5. SEM images of the Pd-Pt surface crystals observed on Pd-Ni (76 µm) gauzes after heat treatment at 1050°C in dry air with Pt upstream for: (a) 1 h; (b) 4 h; (c) 10 h. SEM images of the Pd-Pt surface crystals observed on Pd (120 µm) gauzes after heat treatment at 1050°C in dry air with Pt upstream for: (d) 1 h; (e) 4 h; (f) 10 h. The Pt content of the different Pd-Pt crystals are listed inTable II

oxidation process. We suggest this as a topic for surface reaction and small Pd-Pt particles or future investigations. crystals (size ~2–3 µm) are already formed on the wire surfaces after 1 h exposure, as shown in Effect of Platinum Dioxide Vapour in Figure 5(a) and Figure 5(d). The crystals show roughness and have several small ladders on their Dry and Wet Air sides, which increase in size from 4 h to 10 h

The effect of exposing Pd and Pd-Ni wires to PtO2 (Figure 5(b)–(c) and Figure 5(e)–(f)). Notably, vapour in both dry and wet air is evaluated. First, we for Pd-Ni (Figure 5(a)–(c)), some smaller (1–2 investigated if the presence of Ni in the catchment µm) and more faceted crystals appear with a darker alloy would influence reactivity of PtO2 toward Pd. contrast in the SEM images. EDX mapping and point Based on this, both materials were heat treated in analysis of these crystals indicate NiO formation, dry air at 1050°C with Pt gauzes installed upstream. in line with previous observations of Ni-oxidation The results of exposing the two catchment materials in air. From the SEM images reported in Figure 5, to PtO2 in dry air at 1 h, 4 h and 10 h are presented it appears as if Pd-Pt based crystals develop at a in Figure 5. Both materials undergo an immediate similar rate in both Pd-Ni and Pd (Figure 5). We

Table II Relative Increase in Wire Diameter and Qualitative EDX Results of Pt Concentrations in Pd-Pt Surface Crystals on Pd-Ni (120 µm) and Pure Pd (76 µm) Wires, After Heat Treatments at the Indicated Conditionsa Wire Pt content, Temperature, °C Time Gas conditions Comment swelling, % at % Pd-Ni Pd Pd-Ni Pd 1050 1 h Dry air – – 1 – Crystal as in Figure 5(a) 1050 4 h Dry air 5 ~0 – 6 On Pd-Pt crystal 1050 4 h Dry air – – – 4 Between Pd-Pt crystals 1050 10 h Dry air 5 ~0 3 4 On Pd-Pt crystals 1050 10 h Dry air – – – 2 Between Pd-Pt crystals 1050 16 h Dry air 7 ~0 12 – Regular surface crystal 1050 1 d Dry air 12 5 11 – Regular surface crystal 1050 3 d Dry air 25 15 15 19 Very exposed crystalb 1050 5 d Dry air 37 25 14 14 Regular surface crystal 1050 10 d Dry air 35–45 35 14 23 Regular surface crystal 1050 10 d Dry air – – 28 41 Very exposed crystalb 1050 20 d Dry air 45 45–60 16 22 Regular surface crystal 1050 20 d Dry air – – 44 42 Very exposed crystalb 1050 30 d Wet air 60–75 – 28 – Regular surface crystal Pilot plant, Pt 900 19 d – 45–55 – 30 Regular surface crystal catalyst Pilot plant, 900 19 d – 45–60 – 0 Regular surface crystal oxidation catalyst 900 47 d Industrial plant – 45–50 30 – Regular surface crystal aAll EDX measurements have an estimated uncertainty of ~10% of the measured value, while the values of swelling have an uncertainty of ~20% of the indicated value due to local variations in sample diameter b Crystal located on wire edge, making it subject to a large gas flow and PtO2-concentration during laboratory scale experiments therefore conclude that the NiO particles are not Selected crystals on both the Pd-Ni and the Pd participating in the reconstruction and growth wires are analysed with respect to Pt content process of the Pd-Pt crystals. by means of EDX analysis and the results are With further heat treatment (≥1 day), the summarised in Table II. Pt concentration in the interior of the Pd and Pd-Ni wires become subject average top-layered crystals increases rapidly to the earliest stage of grain reconstruction and the first day (~10–12 at%), followed by a slower ladder-like growth, as if PtO2 is penetrating accumulation. This observation goes hand in hand sub surface from the formed Pt-Pd crystal layer with the fact that the reconstruction starts to occur reacting with more fresh metal on the wire, see below the top layer of crystals, after one day on Figure 6(a) and Figure 6(b). At longer exposure stream (Figure 6(a) and Figure 6(b)), indicating time (≥3 days), the surface crystals show beautiful that Pt catchment is preferred on the Pd rich areas single crystal shapes. The ladders causing further below the outermost Pd-Pt crystals. After 20 days crystal growth (from ~10–30 µm) are large, slowly on stream, the average surface crystals reach a growing over a face of an already existing crystal Pt content of ~22 at% Pt, while the outermost (Figure 6(c)). Prolonged exposure times (20 days) exposed crystals reach a Pt content up to ~40 at% result in complete grain reconstruction to large (65 wt%). This is similar to an industrial sample surface crystals (~20–30 µm) (Figure 6(d)–(f)). treated for 47 days, where the average Pd-Pt The grain reconstruction and crystal formation crystal on the wire surface has a Pt concentration also causes significant wire swelling; the wire of ~30 at%. diameter increases by up to 60% after 20 days, At this point it is worth commenting that the Pd-Pt see Figure 6(e) and Figure 6(f) and Table II. crystal growth rate depends on how a specific part Additionally, the grain reconstruction of the wire or of the gauze or wire is directed toward the high gauze causes a significant reduction of mechanical velocity gas stream. The PtO2 molecules have strength. better access to such areas, which is reflected in a

(a) (b) (c)

50 µm 50 µm 5 µm

(d) (e) (f)

50 µm 50 µm 50 µm

Fig. 6. SEM images of Pd (76 µm) and Pd-Ni (120 µm) gauzes heat treated at 1050°C with Pt upstream for 1–20 days: (a) Pd-Ni 1 day; (b) Pd 1 day; (c) Pd-Ni 3 days; (d) Pd-Ni 5 days; (e) Pd-Ni 20 days; (f) Pd 20 days higher Pt content; more reconstruction and larger not to cause grain reconstruction or porosity crystal facets (Table II). This is more prominent in dry or wet air. Our findings coincide well with in laboratory-scale experiments, where the gas is the statement by Pura et al. (11), i.e. grain not passing equally uniformly through the gauze as reconstruction is not caused by the presence of Ni in the industrial or pilot plant. Correspondingly, on or loss of Ni from the Pd-Ni alloy, but rather by laboratory-scale samples, reconstruction is slower catchment of Pt. and Pt catchment lesser at the wire crossings and at the side(s) of the wire not directly exposed to Pilot Scale Experiments – Testing at the gas stream. These observations are applicable Industrial Conditions to both the Pd-Ni and the Pd catchment gauzes. We can now combine the two previous Finally, two samples have been exposed in experiments and perform a heat treatment with the ammonia oxidation pilot plant at the Yara both wet air and PtO2. If a Pd-Ni gauze is heated Technology Center industrial facility. Here, NH3 is for two weeks at 1050°C in wet air with PtO2, included in the gas stream (10 vol% in air) and a mass increase of 6.5 wt% is observed. From combusted over an ammonia oxidation catalyst ICP-MS/OES, the resulting Pd-Ni wire contains just upstream of the catchment unit. Two scenarios only 2.8 wt% Ni relative to Pd, at the same were explored: (i) six pure Pt ammonia combustion time as the gauze has reached a Pt content of gauzes and (ii) a bed of LaCoO3-based ammonia 9.3 wt%. This indicates simultaneous Ni loss and oxidation catalyst pellets, positioned just upstream Pt catchment. Furthermore, if the Pd-Ni gauze is of a 76 µm pure Pd catchment gauze. As Ni does heated for 30 days in total, the exterior of the wire not significantly affect Pt catchment it was chosen becomes completely reconstructed, at the same to use pure Pd and not Pd-Ni gauzes in the pilot time as the wire is almost fully depleted of Ni, see plant. The experiments were run for nineteen days Figure 7(a) and Figure 7(b). Only the wire core at 900°C at total pressure of 5 bar, during which shows the presence of NiO particles. We therefore each combustion catalyst produced ca. 28 tonnes state that Ni-loss and grain reconstruction are of nitric acid. individual effects, caused by the presence of water In the first case, when the ammonia oxidation vapour and PtO2, respectively. catalyst was a pure Pt gauze, similar features Comparing with investigations by Pura et al. (18), occurred compared to samples heat-treated in we have also observed diffusion and segregation of the laboratory scale furnace in wet air with Pt NiO in the grain boundaries. However, this seems upstream. This includes Pt catchment, grain

(a) (b) (c)

50 µm 50 µm 500 µm

(d) (e) (f)

20 µm 500 µm 10 µm

Fig. 7. SEM images of: (a) and (b) a Pd-Ni gauze (76 µm) heated for 30 days at 1050°C in wet air with PtO2; (c) and (d) a Pd catchment gauze (76 µm) used in the pilot plant for 19 days with a pure Pt combustion catalyst at 900°C; (e) and (f) a Pd catchment gauze used in the pilot plant for 19 days with an LaCoO3- based combustion catalyst at 900°C reconstruction and swelling, see Figure 7(c) still unknown and should be a relevant topic for and Figure 7(d). The Pd-Pt crystals on the wire future investigations. surface are in the range of 10–30 µm in size, with More importantly, mass change studies and an average Pt concentration of ~30 at% (44 wt%), ICP-MS analysis reveal a significant Pd loss –1 while the gauze in total had a Pt concentration of (0.033 g tonne HNO3 produced), very similar to ~14 at% (23 wt%). The Pt concentration of the the loss observed with a Pt combustion catalyst (see surface crystals obtained by EDX is similar to those above). Since the Pd loss in the pilot plant occurs found in samples treated in the laboratory scale both with a Pt and LaCoO3 combustion catalyst, it furnace, confirming the validity of the laboratory is unlikely to be connected to the Pt catchment or scale experiments on Pt catchment. In contrast to grain reconstruction caused by PtO2. In addition, our laboratory scale experiments, we now observe there is no known thermal loss mechanism for –1 a significant Pd loss (0.036 g tonne HNO3), Pd in wet or dry air that can explain such a large similar to reports by Holtzmann on Pd loss at real thermal Pd loss in the process gas (20). This leads ammonia oxidation plant conditions (5). to the conclusion that Pd loss is most probably

In the second case, with the LaCoO3-based caused by interaction with the demanding gas combustion catalyst, we can exclude effects by stream conditions of ammonia oxidation and thus

PtO2 as it is not present in the gas stream. Still, by the gas constituents that were not present in the Pd catchment gauze is subject to swelling and the laboratory-scale experiments. Identifying the pore formation, see Figure 7(e) and Figure 7(f). species or combination of species, present in the However, the wire surface does not look similar to combusted process gas that lead to Pd loss is a the Pd-Pt crystals observed previously (Figure 7) very relevant topic for future investigations. and there are no foreign elements present, hence there must be a different mechanism causing this Conclusion pore formation. This means that the observed swelling of the Pd catchment gauze, which In this work we have observed that the Pd-Ni causes the increase in pressure drop across the catchment system in a dry oxygen containing gauze pack over time, happens regardless of Pt atmosphere is subject to internal oxidation of Ni to catchment. It is an intrinsic effect of the Pd gauze NiO. Further, in a wet oxygen enriched environment, when placed in the ammonia oxidation reactor. Ni is also oxidised to NiO, but subsequently lost, most

The mechanism causing this porous structure is probably as Ni(OH)2. Furthermore, the presence of

PtO2 vapour in wet or dry air causes severe grain 6. A. E. Heywood, Platinum Metals Rev., 1973, 17, reconstruction of both Pd and Pd-Ni wires, which in (4), 118 turn causes wire swelling and pore formation similar 7. B. S. Beshty, W. R. Hatfield, H. C. Lee, R. M. Heck to industrial Pd-based catchment systems used and T. H. Hsiung, Engelhard Corporation, ‘Method during ammonia oxidation. In laboratory furnace for Recovering Platinum in a Nitric Acid Plant’, US experiments, no distinct Pd loss accompanies the Patent 4,526,614; 1985 Pt catchment. However, pilot-scale testing in an 8. Y. Ning, Z. Yang and H. Zhao, Platinum Metals ammonia oxidation atmosphere show significant Rev., 1995, 39, (1), 19 Pd loss, both with a Pt and LaCoO -based (non-Pt 3 9. J. L. G. Fierro, J. M. Palacios and F. Tomás, Surf. containing) combustion catalyst. In addition, a Interface Anal., 1989, 14, (9), 529 second type of pore formation is observed when 10. Y. Ning, Z. Yang and H. Zhao, Platinum Metals using the LaCoO3 catalyst in the pilot plant. Rev., 1996, 40, (2), 80 Therefore, we suspect the Pd loss and the second type of pore formation to be related to gas species 11. J. Pura, P. Kwaśniak, D. Jakubowska, J. Jaroszewicz, present only in the industrial gas mixture, not in J. Zdunek, H. Garbacz, J. Mizera, M. Gierej and our laboratory scale gas mixtures. We suggest this Z. Laskowski, Catal. Today, 2013, 208, 48 as a topic for further investigation. 12. Y. Ning and Z. Yang, Platinum Metals Rev., 1999, 43, (2), 62 Acknowledgements 13. Z. Yang, Y. Ning and H. Zhao, J. Alloys Compd., 1995, 218, (1), 51 The work is carried out in the industrial Catalysis 14. A. E. Heywood, Platinum Metals Rev., 1982, 26, Science and Innovation Centre (iCSI), which (1), 28 receives financial support from the Research 15. H. Holzmann, Platinum Metals Rev., 1969, 13, Council of Norway (contract No. 237922). The (1), 2 authors appreciate fruitful discussions with the iCSI 16. Z. Rdzawski, L. Ciura and B. Nikiel, J. Mater. Proc. team, the support from Ole Bjørn Karlsen (UiO) in Tech., 1995, 53, (1–2), 319 the initiation phase of the metallography work, and the assistance by Nibal Sahli on metallography 17. F. Han and X. Liu, Guijinshu, 2017, 38, (1), 31 and TGA (Yara Technology Center facility, Herøya, 18. J. Pura, P. Wieciński, P.Kwaśniak, M. Zwolińska, H. Norway). Garbacz, J. Zdunek, Z. Laskowski and M. Gierej, Appl. Surf. Sci., 2016, 388, (Part B), 670 References 19. J. Gegner, G. Hörz and R. Kirchheim, J. Mater. Sci., 2009, 44, (9), 2198 1. M. Warner, ‘The Kinetics of Industrial Ammonia 20. E. J. Opila, Materials Science and Engineering, Combustion’, PhD Thesis, School of Chemical and University of Virginia, USA, private communication, Biomolecular Engineering, University of Sydney, 1st August, 2016 Australia, May, 2013, 231 pp 21. H. Jehn, J. Less Common Metals, 1984, 100, 321 2. O. Nilsen, A. Kjekshus and H. Fjellvåg, Appl. Catal. A: Gen., 2001, 207, (1–2), 43 22. C. W. Bale, E. Bélisle, P. Chartrand, S. A. Decterov, 3. Z. M. Rdzawski and J. P. Stobrawa, J. Mater. G. Eriksson, A. E. Gheribi, K. Hack, I.-H. Jung, Y.- Process. Technol., 2004, 153–154, 681 B. Kang, J. Melançon, A. D. Pelton, S. Petersen, C. Robelin, J. Sangster, P. Spencer and M.-A. Van 4. G. Rayner-Canham and T. Overton, “Descriptive Ende, Calphad, 2016, 54, 35 Inorganic Chemistry”, 5th Edn., 2010, W. H. Freeman and Co, New York, USA, 723 pp 23. D. Cubicciotti, J. Nucl. Mater., 1988, 154, (1), 53 5. H. Holzmann, Chemie Ing. Tech., 1968, 40, (24), 24. G. Chen, G. Guan, Y. Kasai and A. Abudula, Int. J. 1229 Hydrogen Energy, 2012, 37, (1), 477

The Authors

Asbjørn Slagtern Fjellvåg is a PhD candidate in the Nanostructures and Functional Materials (NAFUMA) research group at the University of Oslo (UiO). He obtained his Masters degree in the same group in 2016, under the supervision of Professor Anja O. Sjåstad, focusing

on perovskite oxides for catalytic decomposition of N2O. The focus of his current PhD work is on platinum catchment systems for use during ammonia oxidation, in collaboration with K. A. Rasmussen and Yara International.

David Waller is a Senior Catalyst Expert and Chief Engineer at Yara Technology Centre. His doctorate, in methanol synthesis catalysts, from the University of Bath, UK, was awarded in 1993 and was supported by ICI Katalco, UK. Since then, his research has focused mainly on catalysis, in both academic and industrial environments. Areas of particular interest are catalysts associated with hydrogen, ammonia and nitric acid production. These activities have ranged from laboratory-scale production, characterisation and testing of catalysts; up to the development and commissioning of a full-scale catalyst production facility.

Johan Skjelstad has worked as Technology Manager for K. A. Rasmussen AS since 2008. He obtained his Masters degree at the Norwegian Institute of Technology (NTH), Trondheim, Norway (now Norwegian University of Science and Technology (NTNU)) in 1980 in Chemical Engineering, Unit Operations. During his employment at K. A. Rasmussen he has participated in and conducted several development projects involving the use of precious metals as catalysts for various high-temperature chemical reactions.

Anja Olafsen Sjåstad is a professor in Inorganic Chemistry and Materials Science in the research group NAFUMA at the Centre of Materials Science and Nanotechnology (SMN) at the UiO. She was awarded her doctoral degree within Materials Science at UiO in 1999. Subsequently she moved on to the research institute sector (SINTEF Materials and Chemistry, Norway) and the industry (REC Silicon, Norway and USA) with focus on catalysis and process chemistry. In 2011 she returned to UiO as a full professor and her current interest is within materials science and catalysis relevant for the chemical process industry.

www.technology.matthey.com

Predicting the Structure of Grain Boundaries in Fluorite-Structured Materials Understanding the impact of defects in crystalline materials

Aoife K. Lucid*, Aoife C. Plunkett, material properties. Furthermore, the modelling of Graeme W. Watson** materials at an atomic level is often confined to bulk School of Chemistry and Centre for Research systems which contain these point defects (1–4). on Adaptive Nanostuctures and Nanodevices Considerably less is known about extended defects (CRANN), Trinity College Dublin, The University which appear in polycrystalline systems such as of Dublin, College Green, Dublin 2, Ireland surfaces, dislocations and GBs. As nanostructuring of materials is becoming more prevalent, the Email: * [email protected] behaviour of these extended defects is becoming **[email protected] significantly more important (5–8). GBs give rise to structural discontinuities within materials which result in specific structures and potential non- Interfaces are a type of extended defect which stoichiometry and can lead to the segregation of govern the properties of materials. As the point defects to varying degrees, depending on nanostructuring of materials becomes more the specific structure (9–13). This can significantly prevalent the impact of interfaces such as grain affect the macroscopic properties, for example: boundaries (GBs) becomes more important. ionic conductivity, electronic conductivity, thermal Computational modelling of GBs is vital to the conductivity, thermal expansion, elasticity and improvement of our understanding of these defects strength – all of which are crucial for many as it allows us to isolate specific structures and applications. Therefore, the understanding of understand resulting properties. The first step to interfaces in these materials is key to optimising accurately modelling GBs is to generate accurate their performance. Despite this, relatively little is descriptions of the structures. In this paper, we known about the structure and even less of the present low angle mirror tilt GB structures for effects of these interfaces on material properties fluorite structured materials (calcium fluoride and due to the inherent complexity of the issues. ceria). We compare specific GB structures which An example of the importance of interfaces and are generated computationally to experimentally polycrystallinity is in the fluorite structured fast known structures, wherein we see excellent oxide ion conductors (14), such as yttria stabilised agreement. The high accuracy of the method which zirconia (YSZ or ZrO -Y O ) or trivalently doped we present for predicting these structures can be 2 2 3 ceria (CeO ), used in solid oxide cells, oxygen used in the future to predict interfaces which have 2 membranes and oxygen sensors (6, 15, 16). It not already been experimentally identified and can is reported that the ionic conductivity within also be applied to heterointerfaces. the GBs of these materials is several orders of magnitude lower than the bulk (17–20) with the effect attributed to a wide range of causes 1. Introduction including impurities, dopant segregation, defect When considering the properties of crystalline cluster formations and space charge layers (7, 8, materials, the impact of defects is essential. 20–25). In contradiction it has been observed Point defects such as vacancies and dopants that other materials, such as Bi2O3 (26) and are the defects most commonly considered in nanostructured YSZ, that the ionic conductivity is both computational and experimental studies of enhanced (27, 28). Much of the experimental data

(a) (b) structures are predicted and validated using high- Grain boundary quality force fields derived fromab initio data, this is discussed further in the methodology. Two fluorite-structured materials are investigated

in this study: calcium fluoride (CaF2) and CeO2. CaF is the prototypical fluorite material which Grain 2 2 Grain 1 is a super-ionic conductor at high temperatures

(>1100 K) (33). CeO2 (usually doped) is a highly technologically significant material which is both an ionic and electronic conductor with a wide range of Grain 1 Grain 2 applications including catalysis, solid oxide fuel and electrolysis cells and oxygen sensing (6, 15, 16). Fig. 1. (a) Schematic illustration of a polycrystalline We compare their predicted GB structures to material; (b) the specific structure of a GB experimental structures from the literature obtained via transmission electron microscopy (TEM). is based on average effects observed in impedence spectroscopy, where all GBs are treated equally as 2. Grain Boundary Structures: an average effect (29, 30). In fact, GBs can take on Generation and Definition specific structures, an example of this is shown in Figure 1. That is, the atomistic description of what All GBs simulated here were generated using the is happening at the GB is incomplete when obtained minimum energy techniques applied to dislocation, from macroscopic observations. Another issue interface and surface energies code (METADISE) which may arise when only considering average (34). The most stable GB structures were found effects is that it is likely that different specifically by carrying out optimisation scans of the GB. defined interfaces will behave in different ways. Surfaces with specific Miller indices were first cut As it is difficult to isolate and study the effects and then reflected to form an interface. A potential of GBs experimentally, computational studies energy surface (PES) was then calculated using a are invaluable to further our knowledge of these forcefield by scanning one surface relative to the defects and their impact on material properties. other. From this scan, a two-dimensional (2D) PES The failure to understand the basis of material for the boundary was calculated which allowed the properties in polycrystalline samples is a minimum energy structure to be identified. The significant impediment to the development of minimum energy GBs were then optimised and the new materials and the application of inexpensive most stable boundary was selected to investigate processing methods to existing materials. An using molecular dynamics. The 2D potential energy enhanced understanding of the impact of GBs and scan along with the GB structure (before and after polycrystallinity on the properties of materials optimisation) for the Σ9(221) GB in CeO2 is shown would allow us to explore alternative routes to in Figure 2. optimise their properties and ultimately enhance GBs are defined by a number of parameters: the devices. In order to model the properties of these crystallographic directions of the axes of the two interfaces we first require a method for accurate grains which come together to form the interface prediction of interfacial structures. In this paper (hi, ki, li), the rotation axis o = (ho, ko, lo), the we present a computational method for accurately misorientation angle θ around the axis o and the predicting the structure of low angle mirror tilt normal axis to the GB plane n. When n is parallel to GBs which can be applied to other interfaces o the boundary is defined as a twist GB and when and even heterointerfaces. This method utilises n is perpendicular to o the boundary is defined as both atomistic simulation and classical molecular a tilt boundary. The GBs which are studied in this dynamic simulation with sophisticated, polarisable work are high-angle mirror tilt GBs (n ⊥ o) and the force fields derived from ab initio data. Previous rotation axis is (001). theoretical studies of GB structures generally The geometric definition of the GBs used in this utilise static lattice simulations with empirical work is the coincidence site lattice model (35). A force fields and structures based on experimental coincidence lattice site can be defined when there structures (31, 32). These results often have to be exists a finite fraction of coinciding lattice sites validated using first principles due to the quality between the two lattices (grains). This model is and limitations of the force field. In this work the based on the assumption that when the energy

(a) (b) (c) –42154 10 –42155 –42156 8 –42157 Energy, eV –42158 6 –42159 4 –42160 x-direction, Å x-direction, –42161 2 –42162 –42163 0 1 2 3 4 5 6 y-direction, Å

Fig. 2. (a) The PES scan used to identify the minimum energy Σ9(221) GB; (b) the Σ9(221) GB in pure CeO2 before optimisation; (c) the Σ9(221) GB in pure CeO2 after optimisation. Cerium atoms are shown in green with oxygen atoms in red of the GB is low, the coincidence of the atomic illustrated in Figure 3, with each grain having a sites between the two grains is high, i.e. there are depth of at least ~35 Å. few bonds which are broken across the boundary. Molecular dynamics simulations were then carried The reciprocal density of coincidence lattice sites out to determine the average GB structures. is known as Σ and is used to characterise the The interaction potential used for the molecular geometry of the GB, as given in Equation (i): dynamics simulations is known as the dipole polarisable ion model (DIPPIM) (40), implemented no. lattice sites in unit cell of in the polarisable ion model aspherical ion model coincidence site lattice Σ = (i) (PIMAIM) code (41). The DIPPIM consists of four total no. lattice points in unit cell of generating lattice elements: charge-charge interactions, short-range repulsion, dispersion interactions and polarisation. For cubic lattices, the Σ value can be given by This is a highly accurate, polarisable, potential, the sum of the squares of the Miller indices of the in which the dipoles are solved self consistently symmetrical tilt boundary, given by Equation (ii): at each molecular dynamics step. This leads to a highly accurate description of the dipoles on ions Σ = δ (h2 + k2 + l2) (ii) i i i in the simulation which is of particular importance 2 2 2 – where δ = 1 if hi + ki + li is odd and δ = 0.5 if when simulating highly polarisable ions such as F 2 2 2 2– hi + ki + li is even, thus in cubic systems Σ is always and O . The data used to fit the DIPPIM potentials an odd number (35, 36). For example, the Σ9(221) GB shown above is defined by the (221) Miller GB 2 index of the surfaces which are scanned to give this boundary, i.e. (22+22+12) = 9, which is odd so δ = 1 and thus this is written as Σ9(221). The other GBs studied here are defined in the same way.

3. Methodology GB 1

Initial GB structures were generated as outlined above using METADISE with shell model interaction potentials for both CaF2 (37, 38) and CeO2 (39). z These structures were then expanded to at least y x GB 2 30 Ångström (Å) in the x-direction, 22 Å in the y-direction (parallel to the GB) and 76 Å in the Fig. 3. Schematic illustration of a GB cell used for z-direction (perpendicular to the GB). Each simulations simulation cell contained two identical GBs as

249 © 2019 Johnson Matthey https://doi.org/10.1595/205651319X15598975874659 Johnson Matthey Technol. Rev., 2019, 63, (4) used in this work were calculated using ab initio are compared to those of other fluorite materials methods (2, 42, 43). The use of ab initio data (CeO2, ZrO2 and YSZ). allows for non-equilibrium details on the PES to be accounted for which leads to a highly accurate, 4.1 Calcium Fluoride Grain transferable interatomic potential. Boundaries Often interatomic potentials for fluorite materials are derived from equilibrium experimental data The average cation structure of the ∑3(111) GB in or are formed using interatomic potentials from a CaF2 is shown in Figure 4, alongside the structure range of different sources resulting in inconsistent, identified by Feng et al. for CeO2 using high-angle non-transferable potentials which may have annular dark-field (HAADF) scanning transmission difficulties taking effects of different coordination electron microscopy (STEM) (45, 46). The structure environments into account, i.e. surfaces and obtained from our predictive method presented here interfaces. Such interatomic potentials are usually shows excellent agreement with the experimental better suited to static lattice simulations as opposed structure. Other studies of the ∑3(111) GB in fluorite to molecular dynamics simulations. In previous structured materials (ZrO2, YSZ, CeO2, uranium work on the surfaces of CeO2 (44) we have shown dioxide (UO2)) show similar levels of agreement that the DIPPIM provides an accurate description of with our predicted structure (12, 47–49). extended defects and the effect of such defects on In Figure 5 the average cation structure of the ionic transport. ∑5(210) GB in CaF2 is presented with the HAADF

The simulation cells were heated to 1473 K for STEM image of the CeO2 identified by Feng et al. 500 ps in order to simulate annealing of the GB and Hojo et al. (46, 50). The agreement seen here structures, they were then cooled to 573 K for is less striking than that observed for the ∑3(111)

500 ps and finally simulated at 300 K for 500 ps. GB. Other examples of the ∑5(210) GB in CeO2

Temperature scaling was carried out (at all (51, 52), UO2 (48) and YSZ (10, 13, 31) show very three temperatures) every 0.025 ps before data collection for analysis began. Final GB structures were generated by averaging over the frames (a) (b) of the trajectory at 300 K. The DIPPIM potential parameters used for CaF2 were previously derived by Pyper and Wilson et al. (42, 43) and those for CeO2 were obtained by Burbano et al. (2). All steps of the simulation were carried out using the isothermal-isobaric ensemble (NPT). CaF2 simulations utilised a timestep of 5 fs and a short- range cut-off of 14 Å and in the case ofCeO2 Fig. 4. (a) The average structure of the ∑3(111) simulations had a timestep of 4 fs and a short-range GB in CaF2 obtained in this work; (b) a HAADF STEM image of the ∑3(111) GB in CeO identified cut-off of 11 Å. The GBs which were simulated for 2 by Feng et al. (45, 46). Only cations are shown. CaF2 were Σ3(111), Σ5(210), Σ5(310), Σ9(221), TEM image reproduced from (46) under the Σ11(332), Σ13(320) and Σ13(510); and for CeO2 Creative Commons license are Σ3(111), Σ5(210) and Σ9(221).

4. Results and Discussion (a) (b)

Here we present the average predicted structures obtained for GBs in fluorite structured materials and compare these with TEM images obtained from experimental studies. As the F– and O2– ions present in CaF2 and CeO2 are difficult to image due to their low atomic masses we only compare the Fig. 5. (a) The average structure of the ∑5(210) cation structures obtained with the aforementioned GB in CaF2 obtained in this work; (b) a HAADF TEM images. First, we discuss the CaF2 structures STEM image of the ∑5(210) GB in CeO2 identified by Feng et al. and Hojo et al. (46, 50). Only followed by those found for CeO2. To the authors’ cations are shown. TEM image reproduced knowledge there are no experimental studies of from (46) under the Creative Commons license GB structures in CaF2 so those found in this study

similar structures which are also comparable to (a) (b) those predicted here. The ∑5(310) GB structure is compared to a

HAADF STEM image of the ∑5(310) GB in CeO2 in Figure 6. The STEM image was obtained by Tong et al. (52). Again, the structure is extremely comparable with the experimental structure shown here as well as those appearing in the literature 0.5 nm for UO2 (32, 48), YSZ (10, 31, 53–55) and other studies of CeO2 (49). Fig. 8. (a) The average structure of the ∑11(332) The ∑9(221) GB in CaF2 is given in Figure 7. GB in CaF2 obtained in this work; (b) a HAADF This is compared to the HAADF STEM image of STEM image of the ∑11(332) GB in CeO2 identified by Feng et al. (46). Only cations are shown. TEM the ∑9(221) in CeO2 studied by Feng et al. (46). image reproduced from (46) under the Creative The comparison between our predicted structure Commons license and that of Feng is excellent. Other studies have identified this GB in fluorite materials (YSZ

(10, 47), UO2 (48), CeO2 (56)) which give the (a) (b) same level of agreement. Studies of the ∑11(332) GB are far less common than others studied here with the only available comparison being that of Feng et al.’s CeO2 structure

(a) (b) Fig. 9. (a) The average structure of the ∑13(510) GB in CaF2 obtained in this work; (b) a STEM image of the ∑13(510) GB in ZrO2 identified by Dickey et al. (57). Only cations are shown. TEM image reproduced from (57) with permission from John Wiley and Sons

0.5 nm (shown in Figure 8), which displays a high level of Fig. 6. (a) The average structure of the ∑5(310) agreement with our predicted structure (46). GB in CaF obtained in this work; (b) a HAADF 2 The final structure studied for2 CaF was STEM image of the ∑5(310) GB in CeO identified 2 the ∑13(510) GB. In Figure 9 our predicted by Tong et al. (52). Only cations are shown. TEM image reproduced from (52) with permission from structure is compared with that of Dickey et al., Elsevier whose ∑13(510) GB in ZrO2 was observed using high Z-contrast STEM (57). As for the previous GBs studied here the level of agreement is extremely good. In addition to the structure from (a) (b) Dickey et al. other fluorite materials (YSZ (10, 58)

and CeO2 (39, 45)) are equally comparable to that shown here.

4.2 Ceria Grain Boundaries

Fig. 7. (a) The average structure of the ∑9(221) In the case of CeO2 three GBs were investigated: GB in CaF2 obtained in this work; (b) a HAADF the ∑3(111), ∑5(210) and ∑9(221). These three STEM image of the ∑9(221) GB in CeO2 identified GBs were selected as they span a range of stabilities by Feng et al. (46). Only cations are shown. TEM and therefore will be important going forward to image reproduced from (46) under the Creative Commons license study dynamic properties of these interfaces and because there are TEM images of these GBs in

CeO2 available for comparison (9). The levels of The GBs which were studied for both CaF2 and agreement observed for CaF2 are also seen for CeO2 (∑3(111), ∑5(210) and ∑9(221)) showed

CeO2 in Figure 10, Figure 11 and Figure 12. The largely similar structures to one another which were primary difference is that for CeO2 the structures in line with structures observed in the literature are being directly compared to experimental results for both previous computational and experimental for CeO2, which likely accounts for the improved studies. This provides significant validation for the agreement observed for the ∑5(210) GB over that method we have presented here for the prediction seen for CaF2. of interfacial structures in materials.

5. Conclusions (a) (b) We have presented a computational method for the prediction of the structure of mirror tilt GBs in fluorite structured materials. This method utilises interatomic potentials which are derived from first-principles data meaning the process is entirely predictive. The excellent level of agreement with existing experimental data on the structures of fluorite GBs highlights the power of the method. The ability to Fig. 10. (a) The average structure of the ∑3(111) accurately predict these structures is an important GB in CeO2 obtained in this work; (b) a HAADF first step into the computational investigation of the STEM image of the ∑3(111) GB CeO identified by 2 properties of these materials, which is key to future Feng et al. (45, 46). Only cations are shown. TEM image reproduced from (46) under the Creative materials and device optimisation. The method Commons license presented here can be extended to the prediction of interfaces in different materials, interfaces of different types (i.e. twist GBs) and even heterointerfaces. (a) (b) Acknowledgements

This research was supported by Science Foundation Ireland (SFI) through the Investigators Programme (Grant No. 12/IA/1414). All calculations were performed using the Kelvin (funded through grants from the Higher Education Authority, Fig. 11. (a) The average structure of the ∑5(210) through its PRTLI program), Lonsdale (funded GB in CeO2 obtained in this work; (b) a HAADF through a grant from SFI – 06/IN.1/I92/EC07) and STEM image of the ∑5(210) GB CeO2 identified by Feng et al. and Hojo et al. (46, 50). Only cations Pople (funded by SFI – 12/IA/1414) supercomputers are shown. TEM image reproduced from (46) under maintained by the Research IT at Trinity College the Creative Commons license Dublin and the Fionn supercomputer, maintained by ICHEC (tcche054b).

(a) (b) References

1. A. K. Lucid, P. R. L. Keating, J. P. Allen and G. W. Watson, J. Phys. Chem. C, 2016, 120, (41), 23430 2. M. Burbano, S. Nadin, D. Marrocchelli, M. Salanne and G. W. Watson, Phys. Chem. Chem. Phys., Fig. 12. (a) The average structure of the ∑9(221) 2014, 16, (18), 8320 GB in CeO2 obtained in this work; (b) a HAADF 3. M. Burbano, S. T. Norberg, S. Hull, S. G. Eriksson, STEM image of the ∑9(221) GB in CeO2 identified D. Marrocchelli, P. A. Madden and G. W. Watson, by Feng et al. (46). Only cations are shown. TEM Chem. Mater., 2012, 24, (1), 222 image reproduced from (46) under the Creative Commons license 4. M. Saiful Islam, J. Mater. Chem., 2000, 10, (4), 1027

5. A. Chroneos, B. Yildiz, A. Tarancón, D. Parfitt and 29. A. V. Chadwick, Phys. Status Solidi Appl. Mater. J. A. Kilner, Energy Environ. Sci., 2011, 4, (8), Sci., 2007, 204, (3), 631 2774 30. H. Inaba and H. Tagawa, Solid State Ionics, 1996, 6. A. J. Jacobson, Chem. Mater., 2010, 22, (3), 660 83, (1–2), 1 7. X. Guo and R. Waser, Prog. Mater. Sci., 2006, 51, 31. M. Yoshiya and T. Oyama, J. Mater. Sci., 2011, (2), 151 46, (12), 4176 8. G. Gregori, R. Merkle and J. Maier, Prog. Mater. 32. P. V. Nerikar, K. Rudman, T. G. Desai, D. Byler, Sci., 2017, 89, 252 C. Unal, K. J. McClellan, S. R. Phillpot, 9. T. Watanabe, J. Mater. Sci., 2011, 46, (12), 4095 S. B. Sinnott, P. Peralta, B. P. Uberuaga and C. R. Stanek, J. Am. Ceram. Soc., 2011, 94, (6), 10. B. Feng, N. R. Lugg, A. Kumamoto, Y. Ikuhara and 1893 N. Shibata, ACS Nano, 2017, 11, (11), 11376 33. B. M. Voronin and S. V. Volkov, J. Phys. Chem. 11. D. S. Aidhy, Y. Zhang and W. J. Weber, J. Mater. Solids, 2001, 62, (7), 1349 Chem. A, 2014, 2, (6), 1704 34. G. W. Watson, E. T. Kelsey, N. H. de Leeuw, 12. B. Feng, T. Yokoi, A. Kumamoto, M. Yoshiya, D. J. Harris and S. C. Parker, J. Chem. Soc. Y. Ikuhara and N. Shibata, Nature Commun., Faraday Trans., 1996, 92, (3), 433 2016, 7, 11079 35. M. L. Kronberg and F. H. Wilson, J. Miner. Metals 13. G. Sánchez-Santolino, J. Salafranca, S. T. Pantelides, Mater. Soc., 1949, 1, (8), 501 S. J. Pennycook, C. León and M. Varela, Phys. Status Solidi Appl. Mater. Sci., 2018, 215, (19), 1 36. P. Lejcek, “Grain Boundary Segregation in Metals”, eds. R. Hull, C. Jagadish, R. M. Osgood, J. Parisi, 14. H. L. Tuller, Solid State Ionics, 2000, 131, (1–2), Z. Wang and H. Warlimont, Springer Series in 143 Materials Science, Vol. 136, Springer-Verlag Berlin 15. W. Deng, C. Carpenter, N. Yi and M. Flytzani- Heidelberg, Berlin, Heidelberg, 2010 Stephanopoulos, Top. Catal., 2007, 44, (1–2), 199 37. G. W. Watson, ‘Atomistic Simulation of Minerals’, 16. A. Khodadadi, S. S. Mohajerzadeh, Y. Mortazavi PhD Thesis, Bath University, Bath, UK, 1994, 345 and A. M. Miri, Sensors Actuators B: Chem., 2001, pp 80, (3), 267 38. G. W. Watson, S. C. Parker and A. Wall, J. Phys.: 17. C. A. Leach, P. Tanev and B. C. H. Steele, J. Mater. Condens. Matter, 1992, 4, (8), 2097 Sci. Lett., 1986, 5, (9), 893 39. G. Balducci, M. S. Islam, J. Kašpar, P. Fornasiero 18. M. Aoki, Y.-M. Chiang, I. Kosacki, L. J.-R. Lee, and M. Graziani, Chem. Mater., 2003, 15, (20), H. Tuller and Y. Liu, J. Am. Ceram. Soc., 1996, 79, 3781 (5), 1169 40. M. J. Castiglione, M. Wilson and P. A. Madden, 19. X. Guo and J. Maier, J. Electrochem. Soc., 2001, J. Phys.: Condens. Matter, 1999, 11, (46), 9009 148, (3), E121 41. P. A. Madden and M. Wilson, Chem. Soc. Rev., 20. J.-S. Lee and D.-Y. Kim, J. Mater. Res., 2001, 16, 1996, 25, (5), 339 (9), 2739 42. N. T. Wilson, M. Wilson, P. A. Madden and 21. W. Lee, H. J. Jung, M. H. Lee, Y.-B. Kim, J. S. Park, N. C. Pyper, J. Chem. Phys., 1996, 105, (24), R. Sinclair and F. B. Prinz, Adv. Funct. Mater., 11209 2012, 22, (5), 965 43. N. C. Pyper, J. Phys.: Condens. Matter, 1995, 7, 22. A. Tschöpe, Solid State Ionics, 2001, 139, (48), 9127 (3–4), 267 44. M. Burbano, D. Marrocchelli and G. W. Watson, 23. A. Tschöpe, J. Electroceram., 2005, 14, (1), 5 J. Electroceram., 2014, 32, (1), 28 24. S. Kim and J. Maier, J. Electrochem. Soc., 2002, 45. B. Feng, H. Hojo, T. Mizoguchi, H. Ohta, S. D. Findlay, 149, (10), J73 Y. Sato, N. Shibata, T. Yamamoto and Y. Ikuhara, 25. X. Guo and Y. Ding, J. Electrochem. Soc., 2004, Appl. Phys. Lett., 2012, 100, (7), 073109 151, (1), J1 46. B. Feng, I. Sugiyama, H. Hojo, H. Ohta, N. Shibata 26. R. D. Bayliss, S. N. Cook, S. Kotsantonis, and Y. Ikuhara, Sci. Rep., 2016, 6, 20288 R. J. Chater and J. A. Kilner, Adv. Energy Mater., 47. N. Shibata, F. Oba, T. Yamamoto and Y. Ikuhara, 2014, 4, (10), 1301575 Philos. Mag., 2004, 84, (23), 2381 27. G. Knöner, K. Reimann, R. Röwer, U. Södervall 48. N. R. Williams, M. Molinari, S. C. Parker and and H.-E. Schaefer, Proc. Natl. Acad. Sci., 2003, M. T. Storr, J. Nucl. Mater., 2015, 458, 45 100, (7), 3870 49. P. P. Dholabhai, J. A. Aguiar, L. Wu, T. G. Holesinger, 28. U. Brossmann, G. Knoener, H.-E. Schaefer and T. Aoki, R. H. R. Castro and B. P. Uberuaga, Phys. R. Wuerschum, ChemInform, 2004, 35, (42) Chem. Chem. Phys., 2015, 17, (23), 15375

50. H. Hojo, T. Mizoguchi, H. Ohta, S. D. Findlay, 55. H. B. Lee, F. B. Prinz and W. Cai, Acta Mater., N. Shibata, T. Yamamoto and Y. Ikuhara, Nano 2010, 58, (6), 2197 Lett., 2010, 10, (11), 4668 56. X. Li, J. Sun, P. Shahi, M. Gao, A. H. MacDonald, 51. Y. Ikuhara, J. Electron Microsc., 2011, 60, Y. Uwatoko, T. Xiang, J. B. Goodenough, J. Cheng (suppl_1), s173 and J. Zhou, Proc. Natl. Acad. Sci., 2018, 115, 52. W. Tong, H. Yang, P. Moeck, M. I. Nandasiri and N. (40), 9935 D. Browning, Acta Mater., 2013, 61, (9), 3392 57. E. C. Dickey, X. Fan and S. J. Pennycook, J. Am. 53. C. A. J. Fisher and H. Matsubara, Solid State Ceram. Soc., 2004, 84, (6), 1361 Ionics, 1998, 113–115, 311 58. J. An, J. S. Park, A. L. Koh, H. B. Lee, H. J. Jung, 54. C. A. J. Fisher and H. Matsubara, J. Eur. Ceram. J. Schoonman, R. Sinclair, T. M. Gür and F. B. Prinz, Soc., 1999, 19, (6–7), 703 Sci. Rep., 2013, 3, 2680

The Authors

Aoife K. Lucid graduated from University College Cork, Ireland, in 2013 with a BSc in Chemical Physics. In 2018 she graduated with her PhD from Trinity College Dublin, Ireland, with a thesis entitled ‘Computational Modelling of Solid Oxide Electrolytes and their Interfaces for Energy Applications’. Her research interests include using first principles and classical computational methods to investigate the impact of dopants and interfaces in energy materials. She is currently a postdoctoral researcher in the Materials Theory Group at Tyndall National Institute, Cork, Ireland.

Aoife C. Plunkett obtained a BA (Mod) in Nanoscience, Physics and Chemistry of Advanced Materials at Trinity College Dublin in 2015. In 2017 she completed an MSc by research titled ‘Diffusion Within Fluorite Structured Materials and the Effect of Defects’ in the group of Professor Graeme Watson also at Trinity College Dublin.

Graeme W. Watson is a Professor of Theoretical Chemistry at Trinity College Dublin. His research interests include solid state materials and the effect of point defects, dislocations, surfaces and grain boundaries on their properties. These include reactivity, oxide and proton diffusion, electronic conductivity and thermal conductivity which are all important in a range of functional materials.

www.technology.matthey.com

In the Lab UK Research on Materials for Electrochemical Devices Johnson Matthey Technology Review features new laboratory research

Introduction learning tools will accelerate the identification of novel functional materials, composites and synthesis A select group of researchers are profiled here, techniques for a specific purpose. A comprehensive all of whom are involved in the design and materials library with powerful data mining characterisation of materials for electrochemical capabilities can also provide diagnostics for materials energy storage and conversion devices. These from a degraded device, aiding our understanding of include a broad range of battery types, fuel the mechanisms behind device ageing and failure. cells, supercapacitors, photovoltaics and devices Some of the research groups covered here have for the production, storage and utilisation of developed expertise in synthesising new energy hydrogen. materials, with provable success in controlling the Many are pioneering the use of advanced resultant materials’ properties. They make use of techniques for characterising energy materials, composites, incorporating nanostructures and other enhancing our understanding of the fundamental exotic ingredients to introduce specific properties kinetic, structural, electronic and magnetic to an already stable and reliable base material, as properties which distinguish materials as being well as a range of innovative techniques, such as well suited to a particular application. Some are electrospinning, to control microstructure. also developing novel techniques for accurately The researchers presented here engage with assessing properties which are currently not easy energy research across a range of scales, from the to measure, for example: Sam Cooper and Ainara development of atomistic mechanisms all the way Aguadero’s work on isotopic labelling for the up to techno-economics and policy. Beyond this, quantification of surface exchange and solid-state they are also all active in areas beyond energy, diffusivity of battery and fuel cell materials. including sensors, catalysts and memristors, as The performance and function of an energy material well as the development of new experimental is often strongly linked to its microstructure, both techniques and synthesis routes. in terms of its homogenised bulk properties and certain forms of heterogeneity. Understanding this JACQUELINE EDGE* link is key to enhancing manufacturing methods, Department of Mechanical Engineering, Imperial through the processing of materials to component College London, South Kensington Campus, and device construction, by tailoring materials London, SW7 2AZ, UK for optimum performance in the target device. *Email: [email protected] Experimental techniques are complemented by computational models, providing important insights About the Research into physical and chemical processes happening at the nanoscale. 1. Electrochemical Energy Storage Once reliable assessment techniques are established, it will be possible to screen materials rapidly and The most exciting aspects of Sam’s current build up a database of material properties. This research focus around two main topics within high-throughput screening and a variety of machine the realm of materials for electrochemical energy

standardise their analysis approach (5, 6), but Samuel J. Cooper more recently he is working on machine learning techniques and multiphysics parametric studies to generate design rules. In addition to his material research, Sam collaborates with Billy Wu at Imperial College London on device level characterisation to understand the state of health and optimum designs for battery cells and packs. Simplified cell models typically do not incorporate mechanisms to capture cell-to-cell variation, and yet this is known to be a key feature limiting the performance of battery packs, especially in the context of potential second-life applications. By implementing novel thermal voltammetry methods • Department: Faculty of Engineering, Dyson (7), combined with multidimensional cell grouping, School of Design Engineering they are looking to overcome this complexity with a • University: Imperial College London data-driven approach. Finally, Sam is using recurrent • Address: South Kensington Campus, London • Post Code: SW7 2AZ neural networks to predict trends in the grid-scale • Country: UK market to accelerate the implementation of next • Email: [email protected] generation electrochemical energy storage. • Website: https://www.imperial.ac.uk/people/ Much of this work is currently being funded by the samuel.cooper Faraday Institution’s Multiscale Modelling project, as well as a variety of Faraday-associated Innovate UK projects, including: Advance Battery Life storage and many of these projects are undertaken Extension (ABLE), IMproving Power bAttery Cooling in collaboration with various members of Imperial Technologies (IMPACT) and A holistic battery design College London’s Electrochemical Science and tool: From materials to packs (Mat2Bat). Engineering group. Firstly, he is using isotopic methods to characterise 2. Optimisation of Ion-Dynamics in the surface exchange and bulk diffusivity of Electrochemical Systems electrode active materials, in collaboration with Ainara Aguadero. Similar methods were deployed with great success to understand oxygen ion Ainara Aguadero transport and surface exchange for fuel cell systems (1, 2). However, battery materials present specific challenges, in particular room temperature operation and moisture sensitivity, which require these methods to be redesigned. Sam’s group is currently trialling four distinct approaches to this problem, which is a major undertaking, but the potential rewards, in terms of high throughput screening of cathodes and electrolytes, are significant. Secondly, he is looking at the analysis and design of electrode microstructures, in collaboration • Department: Faculty of Engineering, principally with Nigel Brandon, also at Imperial Department of Materials College London. X-ray and ion beam three- • University: Imperial College London dimensional (3D) imaging techniques are pushed • Address: South Kensington Campus, London to their limits by multiphase, nanoscale battery • Post Code: SW7 2AZ materials, but the last few years have seen • Country: UK significant progress in their application (3, 4), in • Email: [email protected] particular for investigating unusual microstructures • Website: https://www.imperial.ac.uk/ (5, 6). Sam has previously focused on developing people/a.aguadero open-source software to allow the community to

Ainara’s current research focuses on the study 3. Chemistry and Physics of Materials and optimisation of ion-dynamics taking place in electrochemical systems, with a special focus on Chandramohan George solid state devices, including secondary batteries, fuel cells, electrolysers and memristors. The common aim is the analysis of how the different ion dynamics affect the performance and degradation of these systems. In order to reveal this, her group uses a combination of structural, electrochemical and chemical characterisation techniques. More specifically, they use surface-sensitive analysis and isotopic labelling to reveal and differentiate different ion kinetics taking place at the bulk as well as at the surfaces and interfaces of materials. One of the biggest topics of research focuses on development of solid state batteries, in which • Department: Faculty of Engineering, Dyson Ainara studies the effect of processing on lithium School of Design Engineering dynamics (8, 9) and seeks to understand the • University: Imperial College London origin of dendrite formation (10, 11). Her group is • Address: South Kensington Campus, London also developing new isotopic labelling methods to • Post Code: SW7 2AZ • Country: UK evaluate the bulk diffusivity and surface exchange • Email: [email protected] kinetics of Li in different battery materials. This • Website: http://www.imperial.ac.uk/people/ work takes place in collaboration with Sam Cooper chandramohan.george from the Dyson School of Engineering at Imperial College and will be used to correlate battery performances with variations in the Li kinetics, for Chandra’s research activities in the broad areas instance in systems with dynamic interfaces and of chemistry and physics of materials seek to cation inter-diffusion processes (12). understand charge-carrier dynamics, ion-diffusion, Another important area of research is the charge-transport and light-matter interactions in development of fast oxygen conductors (13) solids and metal-organic frameworks for renewable and the study of the potential topotactic redox energy. Against this backdrop, shape-controlled capabilities of oxides (14) and their applications synthesis was successfully extended to battery for fuel cells, electrolysers, hydrogen production, materials via a colloidal route, producing phospho- memristive switching or catalysts (15). This work olivines in the form of thin platelet crystals, which takes place in collaboration with John Kilner and in the case of lithium iron manganese phosphate Stephen Skinner at Imperial College London and has led to a fine-tuning of metal redox energies with universities in the UK, Europe and elsewhere. due to cation intermixing (17) and in the case of Finally, in the area of surface analysis techniques, the lithium iron phosphate with an etched surface, group has a strong background in the study of energy enabled ultrafast battery charging (17). Using materials using secondary ion spectroscopy and low hierarchical carbon pre-patterned structures, ultra- energy ion scattering (16). At the moment, the group flexible Li-ion battery design capable of offering is also developing a unique, worldwide facility called fold radii down to 0.5 mm was proposed (18). By Hi5 (strategic equipment grant EP/P029914/1) with integrating solar cell materials such as organic a plasma ion source and dual positive and negative dyes (19) and organo-halide perovskites (20) in ion detection capabilities for in situ characterisation Li-ion cell configuration, new design principles of (T, bias) of electrochemical devices, from the nm to photo-rechargeable batteries are being advanced. the mm scale. Hi5 will be housed in the Department Lastly, by exploiting epitaxial growth relationships, of Materials at Imperial College London. bi-functional oxygen cathodes made of iron oxide Ainara has received funding from a number of nanoparticles and carbon nanotubes are shown to Engineering and Physical Sciences Research Council regulate the morphology of discharge products, (EPSRC) grants, the Science and Technology Facilities enabling a fully reversible Li-air battery (21). Council (STFC) Futures Early Career Award, Energy Current research into the development of next Cooperative Research Centre (CIC energiGUNE), the generation Li-ion batteries with value added Bosch Energy Research Network and The Faraday features (mechanical pliability and shape- Institution, among others. conformity) are supported by The Royal Society.

4. Sustainable Materials The group is well-funded and formed of around twenty researchers, with funds from EPSRC, the Magdalena Titirici European Union, Innovate UK, the Royal Society, the British Council, the Royal Society of Chemistry (RSC) and industry. Their publications are highly cited and recognised internationally with 18,000 citations from 160 publications, five patents, ten book chapters and one edited book. The Principal Investigator, Professor Titirici, has been recognised internationally with the RSC Corday Morgen Prize, the IOM3 Rosenheim Medal, the Chinese Academy of Science President Award and an Honorary PhD from Stockholm University, Sweden.

5. Computational Modelling of • University: Imperial College London and Fundamental Processes Queen Mary, University of London • Address: South Kensington Campus, London and Mile End Road, London Pooja Goddard • Post Code: SW7 2AZ and E1 4NS • Country: UK • Email: [email protected] • Website: https://titiricigroup.org

The research interests in Magda’s group are in sustainable materials, in particular porous carbon and hybrids produced from available resources such as bio- and plastic waste and abundant metals (i.e. iron, manganese and nickel). Her group produces carbon and carbon hybrids using hydrothermal processes which allow scale-up and • Department: Advanced Materials Modelling, continuous processes. They can produce up to Department of Chemistry 1 kg carbon per day and can control exactly the • University: Loughborough University morphology, pore structure, pore size and shape • Post Code: LE11 3TU required for each application. They have a great • Country: UK degree of control over the degree of graphitisation, • Email: [email protected] • Website: http://am2-rg.wixsite.com/home ranging from hard carbons to soft graphitic carbons. The group applies designer carbon materials to energy storage and conversion technologies, Pooja’s research group, based at Loughborough for example as anodes for sodium-ion batteries, University’s Department of Chemistry, focuses on electrodes in supercapacitors, cathodes in lithium- computational modelling of fundamental processes sulfur batteries and as electrocatalysts in fuel in complex materials at the atomic or quantum cells, electrolysers and metal-air batteries. They scale. Their multiscale modelling approach pay a great deal of attention to understanding combines inter-ionic potential-based methods the fundamentals involved in structure-function and density functional theory (DFT) simulations in relations using advanced characterisation tools synergy with experimental groups and industry. applied ex situ and operando such as: small This requires a good understanding of the angle X-ray spectroscopy (SAXS), small-angle structural, electronic, magnetic and transport neutron scattering (SANS), X-ray absorption near properties which are crucial in identifying novel edge structure (XANES), transmission electron functional materials for sustainable energy and microscopy (TEM), nuclear magnetic resonance catalytic applications. The nature of defects in (NMR) and magnetic resonance imaging (MRI), inorganic solids as well as their effect on electronic working collaboratively with experts in these areas. and transport properties is also important, not

258 © 2019 Johnson Matthey https://doi.org/10.1595/205651319X15635449482962 Johnson Matthey Technol. Rev., 2019, 63, (4) only in understanding the key structure-property 4. S. J. Cooper, D. S. Eastwood, J. Gelb, G. Damblanc, relationships, but also in the next phase of D. J. L. Brett, R. S. Bradley, P. J. Withers, P. D. Lee, materials design with enhanced performance. In A. J. Marquis, N. P. Brandon and P. R. Shearing, addition to this, a sound understanding of nano- J. Power Sources, 2014, 247, 1033 ionic properties can yield a wealth of materials with 5. X. Liu, M. Naylor Marlow, S. J. Cooper, B. Song, significant technological impact. X. Chen, N. P. Brandon and B. Wu, J. Power The computational methods range from atomistic Sources, 2018, 384, 264 potentials-based methods, where the forces 6. X. Liu, O. O. Taiwo, C. Yin, M. Ouyang, are dominated by the long-range electrostatic R. Chowdhury, B. Wang, H. Wang, B. Wu, interactions, but also includes short range, van N. P. Brandon, Q. Wang and S. J. Cooper, Adv. der Waals attractions, electron-electron repulsions Sci., 2019, 6, (5), 1801337 and polarisability, to DFT at varying levels of 7. B. Wu, V. Yufit, Y. Merla, R. F. Martinez-Botas, theory. Molecular dynamics is also used to study N. P. Brandon and G. J. Offer, J. Power Sources, 2015, 273, 495 the transport properties as a function of time and temperature. 8. R. H. Brugge, A. K. O. Hekselman, A. Cavallaro, Further to this, expansion towards more F. M. Pesci, R. J. Chater, J. A. Kilner and A. Aguadero, Chem. Mater., 2018, 30, (11), 3704 sophisticated time dependent density functional theory and embedded cluster methods is being 9. C. Bernuy-Lopez, W. Manalastas, J. M. Lopez del pursued. Amo, A. Aguadero, F. Aguesse and J. A. Kilner, Chem. Mater., 2014, 26, (12), 3610 The areas of research within the group are wide- ranging with a focus on the next generation energy 10. F. M. Pesci, R. H. Brugge, A. K. O. Hekselman, storage systems, thin film photovoltaics, fuel cell A. Cavallaro, R. J. Chater and A. Aguadero, J. Mater. Chem. A, 2018, 6, (40), 19817 materials and, more uniquely, fingerprint detection materials and biomarker detection. 11. W. Manalastas, J. Rikarte, R. J. Chater, R. Brugge, Pooja has received funding from several EPSRC A. Aguadero, L. Buannic, A. Llordés, F. Aguesse and J. Kilner, J. Power Sources, 2019, 412, 287 grants and her current collaborations include: Professor Laurence Hardwick (University of 12. G. Vardar, W. J. Bowman, Q. Lu, J. Wang, Liverpool, UK); Professor David Scanlon (University R. J. Chater, A. Aguadero, R. Seibert, J. Terry, A. Hunt, I. Waluyo, D. D. Fong, A. Jarry, College London, UK); James Cookson (Johnson E. J. Crumlin, S. L. Hellstrom, Y.-M. Chiang and Matthey Plc, UK); Professor Olle Eriksson and B. Yildiz, Chem. Mater., 2018, 30, (18), 6259 Biplab Sanyal (Uppsala University, Sweden); 13. L. Troncoso, J. A. Alonso, M. T. Fernández-Díaz and Professor Frank Tietz (Forschungszentrum Jülich, A. Aguadero, Solid State Ionics, 2015, 282, 82 Germany) and Professor Michael Walls (Centre for 14. A. Aguadero, H. Falcon, J. M. Campos-Martin, Renewable Energy Systems Technology (CREST), S. M. Al-Zahrani, J. L. G. Fierro and J. A. Alonso, Loughborough University, UK). Angew. Chemie Int. Ed., 2011, 50, (29), 6557 15. V. Celorrio, L. Calvillo, C. A. M. van den Bosch, Acknowledgements G. Granozzi, A. Aguadero, A. E. Russell and D. J. Fermín, ChemElectroChem, 2018, 5, (20), Jacqueline Edge, Department of Mechanical 3044 Engineering, Imperial College London, UK is 16. H. Téllez, A. Aguadero, J. Druce, M. Burriel, thanked for preparing the text. S. Fearn, T. Ishihara, D. S. McPhail and J. A. Kilner, J. Anal. At. Spectrom., 2014, 29, (8), 1361 References 17. A. Paolella, G. Bertoni, E. Dilena, S. Marras, A. Ansaldo, L. Manna and C. George, Nano Lett., 1. S. J. Cooper, M. Niania, F. Hoffmann and J. A. Kilner, 2014, 14, (3), 1477 Phys. Chem. Chem. Phys., 2017, 19, (19), 12199 18. S. Ahmad, D. Copic, C. George and M. De Volder, 2. M. Niania, R. Podor, T. Ben Britton, C. Li, Adv. Mater., 2016, 28, (31), 6704 S. J. Cooper, N. Svetkov, S. Skinner and J. Kilner, 19. A. Paolella, C. Faure, G. Bertoni, S. Marras, J. Mater. Chem. A, 2018, 6, (29), 14120 A. Guerfi, A. Darwiche, P. Hovington, 3. S. R. Daemi, C. Tan, T. Volkenandt, S. J. Cooper, B. Commarieu, Z. Wang, M. Prato, M. Colombo, A. Palacios-Padros, J. Cookson, D. J. L. Brett and S. Monaco, W. Zhu, Z. Feng, A. Vijh, C. George, P. R. Shearing, ACS Appl. Energy Mater., 2018, 1, G. P. Demopoulos, M. Armand and K. Zaghib, (8), 3702 Nature Commun., 2017, 8, 14643

20. A. Paolella, G. Bertoni, S. Marras, E. Dilena, Y. Li, Y.-S. Hu, M.-M. Titirici, L. Chen and X. Huang, M. Colombo, M. Prato, A. Riedinger, M. Povia, Adv. Energy Mater., 2016, 6, (18), 1600659 A. Ansaldo, K. Zaghib, L. Manna and C. George, C. Tang, H.-F. Wang, X. Chen, B.-Q. Li, T.-Z. Hou, Nano Lett., 2014, 14, (12), 6828 B. Zhang, Q. Zhang, M.-M. Titirici and F. Wei, Adv. 21. Z. Li, S. Ganapathy, Y. Xu, Q. Zhu, W. Chen, Mater., 2016, 28, (32), 6845 I. Kochetkov, C. George, L. F. Nazar and G. A. Ferrero, K. Preuss, A. Marinovic, A. B. Jorge, M. Wagemaker, Adv. Energy Mater., 2018, 8, N. Mansor, D. J. L. Brett, A. B. Fuertes, M. Sevilla (18), 1703513 and M.-M. Titirici, ACS Nano, 2016, 10, (6), 5922 J. Briscoe, A. Marinovic, M. Sevilla, S. Dunn and M. Titirici, Angew. Chemie Int. Ed., 2015, 54, Further Reading (15), 4463 S. R. Yeandel, D. O. Scanlon and P. Goddard, J. Mater. M. Qiao and M.-M. Titirici, Chem. Eur. J., 2018, 24, Chem. A, 2019, 7, (8), 3953 (69), 18374 M. J. Watts, S. R. Yeandel, R. Smith, J. Michael Walls and D.-W. Zhang, N. Papaioannou, N. M. David, H. Luo, P. M. Panchmatia, ‘Atomistic Insights of Multiple H. Gao, L. C. Tanase, T. Degousée, P. Samorì, Stacking Faults in CdTe Thin-Film Photovoltaics: A. Sapelkin, O. Fenwick, M.-M. Titirici and A DFT Study’, IEEE 7th World Conference on S. Krause, Mater. Horizons, 2018, 5, (3), 423 Photovoltaic Energy Conversion, Hawaii, USA, G.-L. Chai, K. Qiu, M. Qiao, M.-M. Titirici, C. Shang and 10th–15th June, 2018, pp. 3884–3887 Z. Guo, Energy Environ. Sci., 2017, 10, (5), 1186 S. R. Yeandel, B. J. Chapman, P. R. Slater and H. Gao, A. V Sapelkin, M. M. Titirici and G. B. P. Goddard, J. Phys. Chem. C, 2018, 122, (49), Sukhorukov, ACS Nano, 2016, 10, (10), 9608 27811

www.technology.matthey.com

“Nanostructured Materials for Next-Generation Energy Storage and Conversion: Fuel Cells” Edited by Fan Li (Beijing Key Laboratory for Catalysis and Separation, Department of Chemistry and Chemical Engineering, College of Environmental and Energy Engineering, Beijing University of Technology, China), Sajid Bashir (Department of Chemistry, Texas A&M University-Kingsville, USA), Jingbo Louise Liu (Department of Chemistry, Texas A&M University-Kingsville, USA), Springer- Verlag GmbH Germany, part of Springer Nature, Berlin Heidelberg, Germany, 2018, 556 pages, ISBN: 978-3-662-56363-2, £229.99, €282.48, US$299.00

Reviewed by Rob Potter policies of presidents Eisenhower and Trump with lots of facts and figures regarding historical energy Correspondence may be sent via use and energy vector types. The text covering Johnson Matthey Technology Review: fuel cells is PEM-centric (no SOFC or phosphoric [email protected] acid fuel cell (PAFC)) and battery vehicles are not included in the discussion. Chapter 2, ‘Concept of Hydrogen Redox Electric Introduction Power and Hydrogen Energy Generators’ by K. Ono (Kyoto University, Japan), argues that particular This Springer volume focuses on the design, bipolar electrode configurations and power supply characteristics and development potential of arrangements in coupled electrolyser or FC systems proton exchange membrane fuel cell (PEMFC) and can improve overall efficiencies markedly over solid oxide fuel cell (SOFC) technologies for both existing setups. Ono maintains one can treat the stationary and portable applications. The contents system as a combination of electrostatic energy and are organised into three themes: (a) energy electrical to chemical energy conversion. I found policy and electrical power (Chapters 1–3); the reasoning difficult to follow, perhaps because (b) optimisation of fuel cells (FCs) through design there are considerable conceptual challenges and synthesis of novel catalysts (Chapters 4–8); faced in dealing with electrostatic terms in highly (c) optimisation of FCs through modelling and condensed phases (see e.g. (1)). Unfortunately, simulation (Chapters 9–18). The book forms a no experimental data are presented to support the useful compendium of research activities across claims by Professor Ono. the globe that gives the reader a general overview Chapter 3, ‘Evaluation of Cell Performance rather than an in-depth treatment of any one and Durability for Cathode Catalysts (Platinum area. The layout and presentation are of the usual Supported on Carbon Blacks or Conducting Ceramic Springer high standard with clearly visible graphs Nanoparticles) During Simulated Fuel Cell Vehicle and illustrations; the book was compiled in 2018. Operation: Start-Up/Shutdown Cycles and Load Cycles’ by M. Uchida (University of Yamanashi, Energy Policy and Electrical Power Japan) et al., is a comprehensive work on the mechanistic details of degradation mechanisms Chapter 1, ‘Fuel Cell Technology: Policy, Features, and with proposed mitigation protocols. Different and Applications – A Mini-Review’ by S. Bashir supports are looked at, not just carbon. We are (Texas A&M University-Kingsville, USA) et al., reminded of the importance of understanding the starts with a comparative analysis of the energy practical challenges of stack design and operation

261 © 2019 Johnson Matthey https://doi.org/10.1595/205651319X15633687853085 Johnson Matthey Technol. Rev., 2019, 63, (4) in respect of membrane electrode assembly (MEA) oxidation than the previous chapter and there is degradation mechanisms. Degradation tests are a shift of emphasis towards zero-dimensional, based on voltammetric cycling to mimic start-up one-dimensional and two-dimensional materials. and shut-down automotive duty cycles. Perhaps Carbon features explicitly in the form of nanotubes not surprisingly, platinum dissolves and aggregates and graphene. and carbon corrodes and different accelerated Chapter 8, ‘Nanostructured Electrodes for High- ageing protocols give different results. This is very Performing Solid Oxide Fuel Cells’ by H. Ding important in the commercial world – you may not (Colorado School of Mines, USA), reviews solution- agree with the customers’ tests, but they are the based, ion infiltration methods of catalysing surfaces ones your product will be judged by! in electrode structures. Solution impregnation is well-known in the catalysis industries in general Design and Synthesis of Novel and it is no surprise that it has been adopted with enthusiasm by the SOFC research and development Catalysts community. Much of the know how has been Chapter 4, ‘Metal Carbonyl Cluster Complexes developed through traditional empirical methods as Electrocatalysts for PEM Fuel Cells’ by and this chapter reviews progress in the field for J. Uribe-Godinez (Centro Nacional de Metrologia, a wide variety of catalysts from base and precious Mexico) offers a general introduction and good metals to complex oxides. summary of work in the field on catalysis preparation for PEMFC systems. Carbonyl complexes can be heat Modelling and Simulation treated to produce metallic-like clusters and here the author looks at rhodium, iridium and osmium Chapter 9, ‘Modelling Analysis for Species, Pressure, species with a heat-treatment regime up to 500°C and Temperature Regulation in Proton Exchange in either nitrogen or hydrogen or thermolysed by Membrane Fuel Cells’ is written by Z. Wang (Texas redox in a suitable solvent. Unfortunately, there A&M University-Kingsville, USA). The model are no mass or specific surface area activity-based emphasis is on understanding the controlling data so although a comparison with a 30 wt% Pt factors in flooding of the MEA under steady-state on XC72R catalyst is made, it is difficult to assess conditions. The construction of the conservation specific-area based catalytic activity. equations for momentum, mass, species, charge Chapter 5, ‘Non-Carbon Support Materials Used and energy are given in some detail. in Low-Temperature Fuel Cells’ is written by X. Cao In Chapter 10, ‘The Application of Computational (Soochow University, China) et al. Traditional carbon Thermodynamics to the Cathode-Electrolyte supports used in FCs are prone to degradation in Solid Oxide Fuel Cells’ by S. Darvish and through oxidation and many attempts have been M. Asadikiya (Florida International University, made to find substitutes that can offer competitive USA), the authors use the calculation of phase performance, durability and cost. The authors give diagrams (CALPHAD) modelling approach with us a survey of the state-of-the-art. However, it is an emphasis on perovskite and fluorite structural clear that carbon is favoured as a support (for good motifs. A comprehensive summary of the materials reason) and is unlikely to be substituted in the near challenge for SOFC materials when used as term for low-temperature FCs. electrolytes and cathodes is presented. Complexity Chapter 6, ‘Noble Metal Electrocatalysts for is added wherein multiple phases can form due Anode and Cathode in Polymer Electrolyte Fuel to reaction of the components with gaseous Cells’ by S. Sharma and C. M. Branco (University impurities either in the air supply or through, of Birmingham, UK) is potentially a vast subject to for example, carbon dioxide cross-over from tackle and the chapter covers the basics of what the anode. The CALPHAD approach allows for is understood about the performance-morphology a workable description of the important defect related aspects of precious metal catalysts for chemistry of the complex oxides to be predicted PEMFC electrocatalysis. There is a particular together with ionic and electronic conductivities. emphasis on the oxygen reduction reaction (ORR). In Chapter 11, ‘Application of DFT Methods Chapter 7, ‘Nanomaterials in Proton Exchange to Investigate Activity and Stability of Oxygen Membrane Fuel Cells’ is written by Y. Zhang (Harbin Reduction Reaction Electrocatalysts’ by X. Chen Institute of Technology, China) et al. In this chapter (Southwest Petroleum University, China) et al., the PEM emphasis is a little more on direct methanol the authors describe the use of density functional

262 © 2019 Johnson Matthey https://doi.org/10.1595/205651319X15633687853085 Johnson Matthey Technol. Rev., 2019, 63, (4) theory (DFT) to model and understand the or atmospheric conditions can pose a risk to the behaviour of PEMFCs at the catalyst level with a proper functioning and longevity of the PEMFC. An focus on the ORR. Not surprisingly, the oxygen example shown is the dramatic and irreversible binding energy to (pure) metal surfaces is an drop in cathode performance when exposed to low activity descriptor of choice and its simplest levels of compounds such as hydrogen chloride exposition is in the well-known volcano plot which and bromomethane vapour. The various poisoning has platinum and palladium close to the apex. More mechanisms are discussed together with possible sophisticated approaches consider the energetics mitigation strategies. of binding of the key intermediates and a mapping Chapter 15, ‘Solid-State Materials for Hydrogen of the associated potential energy surface. As well Storage’ by R. Pedicini (Institute for Advanced as metallic-type catalysts, some metal-centred, Energy Technologies, Italy) et al., gives a general macrocyclic moieties are also investigated for introductory review covering physisorption and activity. Finally, the stabilities of these various chemisorption-based materials. The authors types of ORR catalysts are considered. describe the often conflicting requirements Chapter 12, ‘Hydrogen Fuel Cell as Range Extender that need to be met for a successful hydrogen in Electric Vehicle Powertrains: Fuel Optimization storage material, such as the storage capacity, Strategies’ is written by R. Álvarez and S. Corbera the kinetics of release and uptake and the (Universidad Nebrija, Spain). As the title suggests, resilience to mechanical degradation after many the purpose described in this chapter is to optimise duty cycles. More novel, polymeric or inorganic strategies for combining battery and FC power units hybrid materials are considered including for range extension. There is a useful summary of polyether ether ketone-manganese dioxide the current ‘competitive posturing’ between the (PEEK-MnO2) composites and the use of more various proponents of battery and FC-powered esoteric materials such as mixed metal oxides vehicles. A MATLAB®/Simulink® vehicle model, from volcanic ash. coupled with the use of genetic algorithm routines, In Chapter 16, ‘Stress Distribution in PEM Fuel has been developed to examine the interplay of Cells: Traditional Materials and New Trends’ by the electrical and mechanical components of the J. de la Cruz (CONACYT-INEEL, Mexico) et al., the system over selected drive cycles. Importantly, authors remind us that as PEMFC stack technology the FC in this case study is used to maintain the advances, more attention needs to be focused charge of the lithium ion battery rather than as an on the mechanical and electrical engineering alternative power source for coupling to the drive- aspects of cell components such as the bipolar train directly. plates and membranes to optimise performance, Chapter 13, ‘Totalized Hydrogen Energy Utilization manufacturability, durability and cost. System’ by H. Ito and A. Nakano (National Chapter 17, ‘Recent Progress on the Utilization Institute of Advanced Industrial Science and of Nanomaterials in Microtubular Solid Oxide Technology (AIST), Japan) describes a hydrogen- Fuel Cell’ is written by M. H. Mohamed (Universiti based energy storage system utilising a reversible Teknologi Malaysia) et al. Effective extension of FC/electrolyser coupled with a metal hydride tank the electrode-electrolyte-reactant interface in with fluctuating renewable electrical power inputs FCs presents material and electrode processing and heat and electrical power outputs (combined challenges. Micro-tubular SOFCs (MT-SOFCs) are heat and power (CHP)). The heat flow from the a recent development for engineering porosity system can be both positive and negative i.e. used in the ceramic anode and cathode where the for cooling or heating. The prototype demonstrator more traditional pore formers are substituted is a ten cell PEM-type stack with <1 kW output. and supplemented using tailored hollow fibres. The totalised hydrogen energy utilisation system Inevitably, there is a compromise to be had in (THEUS) was run continuously for three days on a terms of ensuring good densification of materials fixed duty cycle and data collected and analysed. to minimise ohmic drops while enabling reactant Chapter 14, ‘Influence of Air Impurities on the and product transport to function adequately at Performance of Nanostructured PEMFC Catalysts’ higher current densities. The authors present a by O. A. Baturina (Naval Research Laboratory, USA) brief review of progress in both medium and higher et al., discusses the practical issues associated temperature SOFC systems. with using PEMFC units in the real world with Chapter 18, ‘Nanostructured Materials for different environments where air-borne pollutants Advanced Energy Conversion and Storage Devices:

Safety Implications at End-of-Life Disposal’ is written by S. Bashir (Texas A&M University- Kingsville, USA) et al. It is increasingly important for manufacturers to demonstrate that they have considered and mitigated against environmental damage that may arise from the disposal of products at end of life. The conclusion from this work using iron oxide nanoparticles as a test probe of materials entering the environment is that best practice should use a combination of life cycle assessment (LCA) and risk assessment (RA) methodologies.

Conclusion In summary then, this volume brings together an interesting collection of articles covering mainly hydrogen PEM and SOFC technologies that will help build a more balanced understanding of the commercialisation and technical challenges arising from catalyst behaviour through to stack design.

Reference

1. J. S. Newman, “Electrochemical Systems”, 2nd "Nanostructured Materials for Next-Generation Edn., Prentice Hall, New Jersey, USA, 1991, 576 pp Energy Storage and Conversion: Fuel Cells"

The Reviewer

Rob Potter worked for Johnson Matthey, UK, for over thirty years on a range of topics including fuel cells, solar cells, photoelectrocatalysis and thermoelectrics, before retiring in July 2019. He completed his PhD in electrochemistry at the University of Southampton, UK, in 1986.

www.technology.matthey.com

Exploring Microemulsion-Prepared Lanthanum Catalysts for Natural Gas Valorisation Catalysts for small scale application in natural gas and biomass conversion

Cristina Estruch Bosch*, Stephen synthesised’ crystallite size and activity. However, Poulston, Paul Collier the presence of La carbonates in the materials Johnson Matthey, Blounts Court, Sonning produced was deemed to be crucial to ensure an Common, Reading, RG4 9NH, UK adequate OCM activity.

Joris W. Thybaut, Guy B. Marin 1. Introduction Laboratory for Chemical Technology (LCT), Department of Materials, Textiles and Chemical There has been significant interest in converting

Engineering, Ghent University, Technologiepark- gas, in particular CH4, into liquids (gas to liquid Zwijnaarde 125, B-9052 Gent, Belgium (GTL)) (1). Nowadays, two main GTL processes are used: (a) syngas production followed by *Email: [email protected] Fischer-Tropsch (FT) synthesis (2, 3); and (b) liquified natural gas (LNG) (4, 5). However, these processes require huge investments and their Microemulsions were used to develop a catalyst economic viability generally requires them to be with high selectivity towards ethylene and ethane carried out at very large scale (6), preferably while maintaining considerable methane (CH4) exceeding 1000 tonnes per year. Therefore, they conversion. The use of this technique to produce are mainly employed when low priced natural gas lanthanum nanoparticles was studied under is available, typically in large quantities. As of different conditions. Temperature was shown to today, the interest in exploiting small reservoirs have the most significant effect on the final material has increased significantly, particularly because properties providing a minimum crystallite size at the gas from such reservoirs is often simply burnt 25°C. The morphology observed for all the samples as no other conversion technologies are available was flake or needle like materials containing or commercially viable. On the other hand, nanocrystallites. To obtain the catalytically active interest in biomass and waste conversion (7) is materials a thermal treatment was needed and this increasing and this will require processes that are was studied using in situ X-ray diffraction (XRD). This economically viable at small scale. analysis demonstrated that the materials exhibited The development of small GTL plants based on FT significant changes in phase and crystallite size is already happening with the use of microreactors when submitted to thermal treatment and these and improved catalysts (6). On the other hand, were shown to be difficult to control, meaning efforts in finding new ways of producing liquids that the microemulsion synthesis method is a from gas are continuing. An example is the direct challenging route to produce La nanoparticles in production of ethylene from CH4 by oxidative a reproducible manner. The materials were tested coupling (8–10). Ethylene is one of the largest- for oxidative coupling of methane (OCM) and no volume petrochemicals and the building block for a correlation could be observed between the ‘as vast range of chemicals from plastics to antifreeze

265 © 2019 Johnson Matthey https://doi.org/10.1595/205651319X15613828987406 Johnson Matthey Technol. Rev., 2019, 63, (4) solutions and solvents (11). Ethylene is currently plasma reactors is also being evaluated for OCM mainly obtained from energy-intensive steam (22, 23). ADREM, a four-year EU Horizon 2020 cracking of a wide range of hydrocarbon feedstocks. project, is looking at using innovative reactor types

OCM was first investigated in the early 1980s for CH4 activation processes including a plasma by Keller and Bhasin (12). In 1985, Lunsford (2) reactor for OCM. showed that, starting from CH4, lithium/magnesium OCMOL, a five-year FP7 project, aimed to oxide (Li/MgO) could give a 19% yield for C2, with integrate energetic coupling of OCM and CO2 ethylene as the main C2 species. Since then, many reforming in a heat exchange reactor that catalyst combinations have been investigated was used to recycle CO2 produced by the for OCM with the highest obtained C2 yields in OCM reaction. The integration of OCM with the range 25–30% (13, 14). The most common other well- known processes to produce fuels catalyst formulations have been oxides based on or chemicals is another interesting approach alkaline earth metals doped with alkali metals and and, indeed, this integration seems to be more rare earth metals doped with alkali or alkaline important than the actual catalyst performance. earth metals (3). Several studies have shown A new follow up project, Methane oxidative that the activity of the OCM catalyst is affected by conversion and hydroformylation to propylene catalyst structural properties, such as morphology (C123), has recently started and will be looking

(15, 16). Also basicity and oxygen ion conductivity, at transforming CH4 into C3 products via OCM which have been identified as key parameters for which will simultaneously provide an optimum this reaction, are influenced by catalyst structural ratio of ethylene, carbon monoxide and hydrogen properties, such as particle size (17–19). for its further hydroformylation into propanal or In parallel to catalyst development and propanol. Ultimately, propanol can be dehydrated considering the challenges encountered in finding into propylene; either by an integrated approach catalysts able to perform OCM economically, efforts as part of the hydroformylation step or through a have recently been directed to the reactor design. stand-alone approach. Siluria Technologies, Inc, There have been a number of different approaches USA is promoting a catalytic process that can to novel reactor design, the common factor being transform natural or shale gas into transportation the use of membranes. In particular, for OCM, the fuels and commodity chemicals in an efficient, use of membranes has been of interest because cost effective, scalable manner using processes of its perceived ability to control the oxygen that can be seamlessly integrated into existing concentration in the gas phase and, therefore, industry infrastructure. This process is based decrease the undesired over oxidation (20, 21). around two basic chemistries: OCM and ethylene Johnson Matthey has been involved recently in to liquids. In particular, nanowires are used for four European projects working in OCM: CAtalytic the OCM reaction. membrane REactors based on New mAterials for Although process integration and reactor design

C1–C4 valorization (CARENA), MEthane activation were key for the OCMOL project, understanding via integrated MEmbrane REactors (MEMERE), on how to improve the catalyst performance to Adaptable Reactors for Resource- and Energy- obtain higher selectivity towards ethylene and

Efficient Methane Valorisation (ADREM) and higher CH4 conversion is still relevant as this Oxidative Coupling of Methane followed by will positively impact the process economics. Oligomerization to Liquids (OCMOL). The first two, The activity of the materials for OCM is closely CARENA and MEMERE, have been dealing with related to their properties and it is well known the use of membranes for this reaction. CARENA, that different properties are expected when a four-year Seventh Framework Programme for comparing nanoparticles against the bulk material Research and Technological Development (FP7) (24). Indeed, preliminary work has shown that carried out between 2011 and 2015, aimed nanomaterials with different morphologies at investigating the use of relevant process could enhance the OCM performance at low intensification and catalytic membrane reactors to temperatures (19). The present paper presents transform light alkanes (C1–C4) and CO2 to added- a summary of the work carried out within OCMOL value products. Currently running is MEMERE, a around process integration and more particularly four-year EU Horizon 2020 project that started in elaborates on the systematic study of the use of

2015 aimed at the conversion of CH4 to ethylene differently sized La-based nanoparticles for OCM using a membrane reactor with integrated air which was a main focus of the catalyst development separation. Additionally, the use of non-thermal work in OCMOL carried out by Johnson Matthey.

Flame spray pyrolysis (FSP) and microemulsion This process not only presented challenges on the were the two methods investigated to produce catalysis side but even more so on the engineering La-based nanoparticles and results from the latter side. A combination of several reactions and method will be presented and compared to data separations was required including OCM, ethylene previously reported on the materials prepared oligomerisation to liquids, membrane separation, by FSP (25). pressure swing adsorption, CH4 dry reforming, oxygenate synthesis and oxygenate to liquids 2. Oxidative Coupling of Methane conversion to establish an economically viable process. High throughput methodologies were Followed by Oligomerization to employed to more quickly overcome the challenges Liquids Project related to each of these steps and allowing, 2.1. The Process ultimately, to propose a green integrated chemical

process with near zero CO2 emissions. The aim of OCMOL was to create a laboratory An advanced process simulation toolkit and high scale demonstration of the production of liquid tech microengineering technology were developed fuels using process intensification via cutting- to aid the progress of the project. Separate units edge microreactor technologies to integrate the were used and subsequently ‘virtually’ integrated. exothermic OCM and endothermic reforming (RM). The use of process simulation tools together Oligomerisation of ethylene from the OCM step was with an economic evaluation of the integrated employed to obtain liquid fuels. Another interesting process resulted in several recommendations characteristic of the process concept was the for improving the competitiveness of the OCMOL recycle of the undesired products and unreacted process. A life cycle analysis performed during

CH4 that aimed to be converted to syngas in the project indicated that the carbon footprint the RM reactor, driven by the heat produced by was smaller compared to the conversion of the exothermic OCM. The syngas would then be natural gas to synthetic diesel via FT synthesis. converted to liquid fuels via oxygenate synthesis Remaining challenges were identified, such as and oxygenate conversion to liquids. A schematic the limited ethylene yield of the OCM process of the process can be seen in Figure 1. and, correspondingly, the significant contribution of RM to the overall product formation in the process. Considerable recycle streams resulted in a large capital expenditure required for the separation section.

CH4 O2 2.2. Oxidative Coupling of Methane – Lanthanum-Based Nanoparticles Autothermal OCM reactor RM reactor coupling As mentioned above, the activity of materials for OCM is closely related to the catalyst’s structural

CO2 CO, H2 properties. Some preliminary work can be found in the literature regarding the effect of particle Oxygenate size in OCM. Farsi et al. (27) showed that Li/MgO Separation synthesis nanoparticles had higher CH4 conversion and

C2 yield than a conventional Li/MgO catalyst.

C2H4 Noon et al. (28) obtained high C2+ selectivities

with lanthanum oxide-cerium oxide (La2O3-CeO2) Ethylene Oxygenate nanofibres obtained by electrospinning. The shape oligomerisation to liquids of the nanoparticles was also shown to be important reactor by Huang et al. (29), their study showed that

La2O3 nanorods were more active and C2 selective

at low temperatures than La2O3 nanoparticles. On Liquid fuels the other hand, La-based materials have been extensively studied for OCM and they have been Fig. 1. Simplified process flow sheet for the OCMOL identified as some of the best catalysts for this process concept (26) reaction (30, 31).

The present work more particularly elaborates achieved by modifying the process parameters and on the systematic study of the particle size the feed composition. effect of La-based nanoparticles for OCM which During OCMOL the effect of process parameters was the main focus of the catalyst development such as oxygen dispersion and feed composition work in OCMOL carried out by Johnson Matthey. were investigated for the production of La-based Catalyst development for OCM was aimed at nanoparticles. FSP was shown to be a versatile allowing the development and understanding of method that allowed tuning of its properties, not two different preparation methods for La-based only the particle size but basicity and phase. The nanomaterials: FSP and microemulsion. The two materials produced were tested for OCM and higher methods were chosen because of their versatility C2 yields were obtained with materials of higher when preparing nanomaterials and with the aim basicity. A mixture of lanthanum oxycarbonate of obtaining La-based materials with different (La2O2CO3) and La2O3 exhibited better OCM particle size. FSP allows the control of particle performance than La2O3 only (25). size and phase as a function of the conditions On the other hand, microemulsion has been used. Similarly, the microemulsion technique has extensively used to produce nanoparticles due to been used extensively to prepare oxides with the ability of this technique to control the particle different particle size and allows a finer control size (33, 48). Different types of microemulsion of the particle size (32–34). La-based materials are known, such as water in oil and oil in water. have been shown to be active for OCM (35–40), The different systems lead to the formation of particularly the variant containing 1% strontium/ reverse micelles in the first case and micelles in

La2O3 (16, 41, 42). Hence, the latter material the second. These mixtures of oil and water are was chosen as one of the standard materials for naturally unstable but can, nevertheless, be benchmarking between the OCMOL partners. The stabilised by the addition of suitable surfactants preparation method of the La-based materials has in the right proportion. By positioning themselves been shown to influence the material properties at the oil-water interface, these surfactants and, hence, their ultimate performance. Choudhary decrease the interfacial energy and help establish et al. (36) found that the catalyst precursor and a thermodynamically stable solution from the calcination conditions used to prepare La2O3 unstable oil and water mixture by creating very affected the surface properties, basicity, base small stabilised droplets (<10 nm diameter) (49). strength distribution, activity and selectivity in In diluted systems these molecules are present the OCM. A comparison of the reactivity of phases as monomers, however when their concentration was performed by Taylor et al. (43) showing that exceeds a certain threshold, the critical micelle the starting phase influenced the activity and concentration (CMC), they aggregate to form selectivity, despite La2O3 being the final phase micelles. At intermediate concentrations, following reaction, as the carbonates are not microemulsions with both aqueous and oily stable under OCM reaction conditions (44). continuous domains can exist as three-dimensional FSP is a flame aerosol technology for the (3D) interconnected sponge-like channels, also production of nanoparticles where the precursor known as bicontinuous microemulsions. is a liquid with high combustion enthalpy (>50% of total energy of combustion), usually an 3. Microemulsion organic solvent. The research group of Sotiris E. Pratsinis at ETH Zurich, Switzerland was the first 3.1. Experimental to develop the technique (45). Since then many others have followed, leading to the production A reverse micelle method modified from the method of a wide range of materials and equipment of described by Chandradass et al. (50) to prepare varying type and complexity. Johnson Matthey has lanthanum aluminate (LaAlO3) was used to prepare developed its own FSP facility which produces a the La-based nanomaterials. The microemulsion range of nanopowders. Depending on the material, was prepared by mixing 100 ml of cyclohexane and it has a capacity to produce up to 100 g h–1 of 40 ml of Igepal-520 under magnetic stirring. Once nanopowder. FSP produces nanopowders by the desired synthesis temperature was achieved spraying a liquid feed, metal precursor dissolved 5.6 ml of an aqueous lanthanum nitrate solution in an organic solvent, with an oxidising gas into a was added using a pump (24 ml min–1). Finally, flame zone. The combustion of the spray produces 2.5 ml of the precipitating agent, ammonia (35%), nanomaterials with different properties that can was added dropwise after 1 h. When the base was be controlled at a high rate (46, 47). This can be added the mixture became white and it was left

268 © 2019 Johnson Matthey https://doi.org/10.1595/205651319X15613828987406 Johnson Matthey Technol. Rev., 2019, 63, (4) under constant stirring for 22 h. The final solid nitrogen as the adsorbate. Prior to analysis, material was obtained by centrifugation for 30 min samples were outgassed at 150°C under vacuum at 4000 rpm, the temperature during centrifugation for approximately 24 h. XRD data were acquired was kept under 20°C. The sample was washed with a Bruker AXS D8 Diffractometer using copper with ethanol and centrifuged (15 min at 4000 rpm) Kα radiation and collected from 10° to 130° 2θ with three times. The material was dried at room a step size of 0.02°. Ratios of the identified phases temperature. The effects of two synthesis variables and their crystallite sizes were determined by were assessed: the synthesis temperature (7°C, Rietveld refinements using total pattern analysis 15°C, 25°C, 30°C, 40°C, 50°C and 60°C) and the solution (TOPAS) (51). The in situ XRD was water:surfactant (W:S) ratio (from 4 to 16). The performed in the same diffractometer in parallel addition rate of the reactants and the stirring speed beam mode with Anton Paar XRK 1000 sample were kept constant. A schematic of the procedure chamber and the data collected from 10° to 80° is shown in Figure 2. It was divided into three 2θ with a step size of 0.036°. The investigated stages: (a) microemulsion, (b) dried material and temperatures ranged from ambient to 900°C. (c) final powder. A summary of the results obtained Samples for transmission electron microscopy for each of these stages is presented in this work. (TEM) analysis were ground between two glass The solid materials prepared by microemulsion slides and dusted onto a holey carbon coated Cu were characterised by physisorption with TEM grid and a FEI Tecnai F20 transmission electron subsequent fitting to the Brunauer-Emmett- microscope was used to examine the samples Teller (BET) equation, XRD and high-resolution at a 200 kV accelerating voltage. Dynamic light transmission electron microscopy (HR-TEM). scattering (DLS) was measured using a Zetasizer Surface area analysis was performed using a Nano ZS from Malvern Panalytical. Quantachrome AUTOSORB-1 apparatus using OCM testing was performed with a high throughput reactor comprising eight quartz reactors (internal diameter = 4 mm, outside diameter = 8 mm). The reaction mixture consisted

of CH4, O2 and N2. Contact time, defined as catalyst weight divided by the CH flow (W/F ), Stage 1: microemulsion 4 CH4 –1 was of 2 kg s mol . CH4:O2 ratio = 2:1, 10% • Cyclohexane, Igepal-520, H2O N2 (internal standard) and a temperature and La(NO3)2 program of: 650°C, 750°C, 650°C, 850°C and • Precipitating agent: ammonia 650°C were used to test 0.04 g catalyst (particle Centrifugation size: 250–355 μm). The ramp to the different temperatures was performed under N and the + 2 first measurements were taken after 2.5 h. The Drying at room temperature temperature was controlled with a thermocouple located in one of the reactors containing quartz

Stage 2: dried powder wool, which was used as a blank reactor to assess the transformations due to gas phase reactions • La(OH)3, LaNO3(OH)2·H2O or mixtures only. A Varian CP-4900 Micro-GC was used to analyse N2, CH4 and hydrocarbons containing up to nine carbon atoms. However, the discussion

in the present work strongly focused on the C2

Thermal treatment products as only traces of C3 were observed, in

particular at high O2 conversions. The carbon balance typically amounted to about 90%.

Stage 3: powder 3.2. Characterisation • La2O3 The use of different synthesis temperatures during stage two had no effect on the phase

obtained, LaNO3(OH)2·H2O (see Figure S1 in the Fig. 2. Different stages of the microemulsion Supplementary Information). This phase differs preparation investigated during the OCMOL project from the ones obtained using FSP, in which

La2O3 and carbonates were formed. Therefore, the samples produced via microemulsion needed an extra thermal treatment to obtain the active phases (stage three). Although no change was observed with respect to the phase composition, the crystallinity of the samples was affected by the synthesis temperature as can be seen in Table I. The results are in accordance with the surface areas which decrease with the increase in synthesis temperature in the range from 25°C to 60°C. The temperature has been reported to exhibit an effect on the micelle formation, i.e., higher temperatures reduce the interfacial tension between the oil and water which enhances the diffusion of the water into the oil phase and increases the number of smaller sized 5 nm droplets (52, 53). Therefore, when increasing the temperature, a decrease in particle size would Fig. 3. TEM for sample ME-T60 be expected, however, the opposite effect was observed which can be attributed to the particles not being single crystals. The particles are the preparation of colloidal copper particles which constituted of multiple diffraction domains with were achieved using sodium bis(2-ethylhexyl) different orientations and the temperature might sulfosuccinate (AOT) as a surfactant, isooctane help the growth of these domains (Figure 3). or cyclohexane as the solvents and an aqueous The samples produced by modifying the W:S solution of hydrazine to reduce the Cu. The ratio were also shown to be poorly crystalline increase in particle size when increasing W:S ratio materials when studied in stage two and also could be observed for the two different solvents. consisted of LaNO3(OH)2·H2O (see Figure S2 in The morphology of the materials obtained by the Supplementary Information). The crystallite microemulsion was very different from that obtained size increased with W:S, as determined by XRD using FSP. The latter produced sphere like materials (Table II). The surface area measured agreed between 10–40 nm, while aggregates ranging from with this observation. This effect can be logically around 0.1 µm to 10 µm were observed for the explained because, when higher amounts of water samples prepared by microemulsion (Figure 4). are used (higher W:S ratio), bigger micelles are These were shown to be flakes or needle like created. Indeed the effect of the W:S ratio has been materials with different shapes which was confirmed shown in previous reported work to be one of the by tilting the sample at different angles Figure( 5). most defining synthesis variables for the particle This shape could be due to either aggregation after size in microemulsion (48, 54). An example of this surfactant removal or it could be due to the colloidal effect is described by Lisiecki et al. (55). These nature of the synthesis mixture and the ability for authors investigated the effect of the W:S ratio on these systems to form other shapes (56, 57).

Table I Surface Area and Crystallite Size for the Fresh Samples (Stage Two) Prepared at Different Temperature of Synthesis Catalyst name Temperature, °C Surface area, m2 g–1 Crystallite sizea, nm ME-T7 7 10.0 38.0 ME-T15 15 10.0 21.0 ME-T25 25 31.5 13.0 ME-T30 30 40.4 15.0 ME-T40 40 30.5 19.3 ME-T50 50 21.6 24.2 ME-T60 60 10.1 31.5 aCrystallite size of lanthanum nitrate hydroxide hydrate

(a) ME-T7 (b) ME-T15 (c) ME-T25

100 nm 200 nm 200 nm (d) ME-T30 (e) ME-T40 (f) ME-T50 (g) ME-T60

200 nm 200 nm 200 nm 200 nm

Fig. 4. TEM images for the samples prepared at different temperatures: (a) 7°C; (b) 15°C; (c) 25°C; (d) 30°C; (e) 40°C; (f) 50°C; (g) 60°C

Table II Surface Area and Crystallite Size for Fresh (Stage Two) Samples Prepared Using Different W:S Ratio Catalyst name W:S ratio Surface area, m2 g–1 Crystallite sizea, nm ME-W/S4 4 37.5 15.0 ME-W/S5 5 32.6 16.6 ME-W/S8 8 17.1 17.4 ME-W/S16 16 17.1 21.7 aCrystallite size of lanthanum nitrate hydroxide hydrate

To determine the origin of the flake or needle like morphology dynamic light scattering (DLS) analysis (a) alpha = 0 (b) alpha = +20 was performed on the microemulsions with and without the La precursor in the stage one at the W:S ratios used previously. The micelle size determined with DLS for the microemulsions without the La precursor in stage one followed the same trend observed previously for the materials obtained in stage two (Table II and Table III). A decrease 100 nm 100 nm of the W:S ratio resulted in an increase of micelle size. Unfortunately, the microemulsions containing (c) alpha = +40 (d) alpha = +60 the La precursor (stage one) could not be analysed with the Malvern Panalytical Zetasizer Nano ZS. This was due to the microemulsion becoming cloudy with the presence of the La precursor and not allowing the light to travel through the cuvette. The microemulsions were shown to be stable over time. Therefore, the flake or needle like morphology 100 nm 100 nm might be due to a non-spherical micelle shape. Although, the aggregation of spheres due to low Fig. 5. Images of the sample ME-W/S4 being tilted stability of the nanoparticles once removed from to 60° with steps of 20°: (a) 0°; (b) 20°; (c) 40°; (d) 60° the microemulsion cannot be eliminated.

analysis (MS-TGA). The temperature at which each Table III Micelle Size Obtained with DLS of these phases appeared depended on the starting for the Microemulsion Samples Without Precursor sample and atmosphere. Not only the transition temperature between phases was different between W:S ratio Average micelle sizea, nm the two samples, ME-T25 and ME-T60, but also the 4 2.277±0.111 evolution of the crystallite size was different. These 5 3.687±0.188 results showed that the systems are complex and 8 4.791±0.428 further experiments should be done to understand 16 7.199±0.916 the effect of the thermal treatment. aThe analysis was done after 22 h of stirring in all the samples except for sample ME-W/S5, which was stirred for 67 h. The effect of stirring time was also studied. Bigger average micelle 3.3. Oxidative Coupling of Methane size was observed for the samples stirred for longer time. However, this difference was not significant. (Average micelle Kinetics Performance size for the microemulsion with W:S = 4 after 9 days was 2.697 ± 0.0135 nm) To carry out OCM testing, the samples were treated

at 700°C for 2 h under a N2 flow. Under these

conditions Type Ia La2O2CO3 or mixtures of Type Ia

As already mentioned, the samples prepared using La2O2CO3 and La2O3 were predicted to be the main microemulsion needed an extra thermal treatment phases and these are preferred as they have been to obtain the active phase for OCM, La2O3 and shown to be beneficial for OCM activity (25). The carbonate. Therefore, the effect of the thermal XRD analysis for these materials after the thermal treatment on these samples to transform them into treatment can be seen in Figure 8 and Type Ia stage three materials was investigated using in situ La2O2CO3 mixed with La(OH)3 or pure La(OH)3. XRD on the samples ME-T25 and ME-T60 (Figure 6 The OCM activity of these samples was evaluated and Figure 7) as they represent the extremes of at 650°C, 750°C and 850°C, see Figure 9. the crystallite sizes obtained for these materials. In As expected, an increase in the CH4 conversion this analysis, the evolution of phase and crystallite and ethylene:ethane ratio and a decrease in the size was monitored during thermal treatment C2 yield are observed with increasing temperature. under two different atmospheres, air and 2N . The The overall observed activity is comparable to that of starting phase for both samples was different. the benchmark catalyst, i.e. 1% Sr/La2O3. The size • While both contained LaNO3(OH)2 H2O, ME-T60 also differences observed between the samples contained La2(OH)3. The order of appearance of prepared at different temperatures do not reflect the phases was the same for the two samples, i.e., on the activity. As already mentioned, morphology

La(OH)2NO3, unassigned phase, Type Ia La2O2CO3 was also shown to play a role in the OCM activity. and La2O3. The unassigned phase was determined However, it appears not to be the determining to be constituted of a mixture of carbonates and factor for the materials investigated in the present nitrates as a loss of CO2 and NO was observed at work. They all exhibit a flake like structure while 340°C using mass spectrometry-thermogravimetric the samples prepared by FSP are spherical and

Sample at 30°C after thermal treatment

La(OH)2NO3 Type Ia La2O2CO3 9.5 nm 9.6 nm 7.8 nm 44.3 nm 60.8 nm 60 nm N2 La2O3

9.7 nm 9.7 nm 10.3 nm 49.3 nm 49.8 nm 48.1 nm Air La2O3 30 130 230 330 430 530 630 730 830 Temperature, °C

LaNO3(OH)2•H2O Unassigned phase La2O3

Fig. 6. In situ XRD analysis for the sample prepared at 25°C (T25)

Sample at 30°C after thermal treatment

LaNO3(OH)2•H2O La(OH)2NO3 Type Ia La2O2CO3

22.9 nm 23 nm 10.3 nm 25.4 nm 35.0 nm 35.1 nm N 2 La2O3

21.9 nm 21.4 nm 11.7 nm 49.4 nm 49.0 nm 50.7 nm Air La2O3 30 130 230 330 430 530 630 730 830 Temperature, °C

La(OH)3 Unassigned phase La2O3

Fig. 7. In situ XRD analysis for the sample prepared at 60°C (T60)

Studying the effect of particle size, phase and Type Ia La2CO3O2 La(OH)3 morphology independently on the OCM activity has 'As synthesised' temperature, °C been challenging. While gaining an understanding 60 of the catalyst properties on the activity has the 50 potential to achieve higher OCM activities, it is important to consider that the integration of 40 OCM with other technologies could overcome the 30 unsatisfactory results. Process integration that includes the OCM reaction could be the solution to Intensity, arb. Intensity, 25 achieve natural gas valorisation in an economically 15 viable manner. 7 10 20 30 40 50 60 70 80 90 2θ, ° 4. Conclusions Fig. 8. XRD patterns for the samples prepared Synthesis of La-based nanomaterials using at different ‘as synthesised’ temperatures and the microemulsion technique yielded flake like calcined under N2 for 2 h at 700°C materials which contained nanocrystallites. The synthesis temperature has the most pronounced no significant difference can be observed when effect on the ultimate material properties. A comparing their activity, see Figure 9. Instead minimum crystallite size was observed at 25°C, the phase could be playing an important role however this did not affect the final OCM activity. as the activity for the microemulsion samples Other phenomena such as those occurring during is comparable to the activity obtained for the the thermal treatment play an important role for FSP materials where higher amounts of Type Ia the catalyst activity for these materials.

La2O2CO3 and Type II La2O2CO3 were observed. In situ XRD analysis demonstrated that the Characterisation of the spent catalyst could not be materials exhibit significant changes when performed due to the small amounts of catalyst submitted to thermal treatment to yield the final, used during testing. However, the phases present catalytically active materials. The changes were after the thermal treatment and before testing for difficult to control, rendering the microemulsion some of the samples are La carbonates. For some synthesis method a challenging one to produce others La(OH)3 is the only phase after thermal La nanoparticles in a reproducible manner. treatment, however this is expected to form Alternative techniques, such as FSP, seem much carbonates by reacting with CO2, atmospheric more promising in this respect. In terms of OCM or from the reaction. Therefore, again the high activity, the presence of La carbonates in the activity could be linked to the presence of La materials used was crucial. This work has put in carbonates or to the capacity of the catalyst to be evidence the challenges encountered when trying converted to La carbonate. to study the material properties, such as phase,

(a) (b) 50 100

7°C 15°C 25°C 30°C 40°C 50°C conversion, % conversion, conversion, % conversion, 4 2 60°C O CH 1%Sr/La2O3 FSP-ME2

40 80 600 700 800 900 600 700 800 900 Temperature, °C Temperature, °C (c) (d) 20 5 18 16 4 14 12 10 3 yield, % 2 8 C 6 2

4 ratio ethylene:ethane 2 0 1 600 700 800 900 600 700 800 900 Temperature, °C Temperature, °C

Fig. 9. OCM results for the samples synthesised at different temperatures by microemulsion and then calcined at 700°C for 2 h under N2: (a) CH4 conversion; (b) O2 conversion; (c) C2 yield; (d) ethylene:ethane ratio. Also included for comparation the best sample prepared by FSP (25)

particle size and morphology, independently from Cristina Estruch Bosch would like to thank Eli Van each other. de Perre and the analytical department at Johnson Optimisation of the OCM catalyst is a challenge Matthey for their assistance during this work, in and we believe the solution to achieve natural particular to Edd Bilbe and Hoi Johnson for the gas valorisation in an economically viable manner XRD work. would be a process that integrates OCM. An example is the European project currently running, References C123. 1. D. A. Wood, C. Nwaoha and B. F. Towler, J. Nat. Gas Sci. Eng., 2012, 9, 196 2. M. Nyarko, “Process Plant of Gas to Liquid (GTL): Acknowledgements Theory and Simulation”, AV Akademikerverlag GmbH and Co KG, Saarbrücken, Germany, 2012, The work was undertaken within the context of the 232 pp project ‘Oxidative Coupling of Methane followed 3. M. E. Dry, Catal. Today, 2002, 71, (3–4), 227 by Oligomerization to Liquids (OCMOL)’. OCMOL is 4. G. Venkatarathnam, ‘Natural Gas Liquefaction Processes’, in “Cryogenic Mixed Refrigerant large scale collaborative project supported by the Processes”, eds. K. D. Timmerhaus and C. Rizzuto, European Commission in the Seventh Framework Springer Science and Business Media LLC, Programme for Research and Technological New York, USA, 2008, pp. 149–220 o Development (GA n 228953). For further 5. W. Lin, N. Zhang and A. Gu, Energy, 2010, 35, information see the OCMOL website. (11), 4383

6. V. S. Arutyunov, V. I. Savchenko, I. V Sedov, 31. V. R. Choudhary, B. S. Uphade and S. A. R. Mulla, I. G. Fokin, A. V Nikitin and L. N. Strekova, Chem. Ind. Eng. Chem. Res., 1997, 36, (9), 3594 Eng. J., 2015, 282, 206 32. F. J. Arriagada and K. Osseo-Asare, J. Colloid 7. C. O. Tuck, E. Pérez, I. T. Horváth, R. A. Sheldon Interface Sci., 1999, 211, (2), 210 and M. Poliakoff,Science , 2012, 337, (6095), 695 33. J. Eastoe, M. J. Hollamby and L. Hudson, Adv. 8. J. H. Lunsford, Catal. Today, 1990, 6, (3), 235 Colloid Interface Sci., 2006, 128–130, 5 9. A. M. Maitra, Appl. Catal. A: Gen., 1993, 104, (1), 11 34. M.-P. Pileni, Nature Mater., 2003, 2, (3), 145 10. G. J. Hutchings, M. S. Scurrell and J. R. Woodhouse, 35. H. Borchert and M. Baerns, J. Catal., 1997, 168, Chem. Soc. Rev., 1989, 18, 251 (2), 315 11. M. Ghanta, D. Fahey and B. Subramaniam, Appl. 36. V. R. Choudhary and V. H. Rane, J. Chem. Soc. Petrochem. Res., 2014, 4, (2), 167 Faraday Trans., 1994, 90, (21), 3357 12. G. E. Keller and M. M. Bhasin, J. Catal., 1982, 73, 37. R. Ghose, H. T. Hwang and A. Varma, Appl. Catal. (1), 9 A: Gen., 2013, 452, 147 13. K. Machida and M. Enyo, J. Chem. Soc. Chem. 38. D. J. Ilett and M. S. Islam, J. Chem. Soc. Faraday Commun., 1987, (21), 1639 Trans., 1993, 89, (20), 3833 14. A. Galadima and O. Muraza, J. Ind. Eng. Chem., 2016, 37, 1 39. K. Otsuka, K. Jinno and A. Morikawa, J. Catal., 1986, 100, (2), 353 15. J. S. J. Hargreaves, G. J. Hutchings, R. W. Joyner and C. J. Kiely, J. Catal., 1992, 135, (2), 576 40. S. Lacombe, C. Geantet and C. Mirodatos, J. Catal., 16. T. LeVan, M. Che and J.-M. Tatibouët, Catal. Lett., 1995, 151, (2), 439 1992, 14, (3–4), 321 41. J. M. DeBoy and R. F. Hicks, J. Chem. Soc. Chem. 17. J. M. Montero, P. Gai, K. Wilson and A. F. Lee, Commun., 1988, (14), 982 Green Chem., 2009, 11, (2), 265 42. J. M. Deboy and R. F. Hicks, J. Catal., 1988, 113, 18. O. J. Durá, M. A. López de la Torre, L. Vázquez, (2), 517 J. Chaboy, R. Boada, A. Rivera-Calzada, 43. R. P. Taylor and G. L. Schrader, Ind. Eng. Chem. J. Santamaria and C. Leon, Phys. Rev. B, 2010, Res., 1991, 30, (5), 1016 81, (18), 184301 19. Y. Gambo, A. A. Jalil, S. Triwahyono and 44. T. Levan, M. Che, J. M. Tatibouet and M. Kermarec, A. A. Abdulrasheed, J. Ind. Eng. Chem., 2018, 59, J. Catal., 1993, 142, (1), 18 218 45. R. Strobel, A. Baiker and S. E. Pratsinis, Adv. 20. J. Coronas, M. Menéndez and J. Santamaria, Powder Technol., 2006, 17, (5), 457 Chem. Eng. Sci., 1994, 49, (12), 2015 46. B. Thiébaut, Platinum Metals Rev., 2011, 55, (2), 21. Y. Lu, A. G. Dixon, W. R. Moser and Y. H. Ma, 149 Chem. Eng. Sci., 2000, 55, (21), 4901 47. A. Camenzind, W. R. Caseri and S. E. Pratsinis, 22. A. Marafee, C. Liu, G. Xu, R. Mallinson and Nano Today, 2010, 5, (1), 48 L. Lobban, Ind. Eng. Chem. Res., 1997, 36, (3), 632 48. I. Capek, Adv. Colloid Interface Sci., 2004, 110, 23. S. L. Yao, F. Ouyang, A. Nakayama, E. Suzuki, (1–2), 49 M. Okumoto and A. Mizuno, Energy Fuels, 2000, 49. D. H. Everett, “Basic Principles of Colloid Science”, 14, (4), 910 The Royal Society of Chemistry, London, UK, 24. Y. Volokitin, J. Sinzig, L. J. de Jongh, G. Schmid, 1988, 243 pp M. N. Vargaftik and I. I. Moiseevi, Nature, 1996, 50. J. Chandradass and K. H. Kim, J. Cryst. Growth, 384, (6610), 621 2009, 311, (14), 3631 25. C. Estruch Bosch, M. P. Copley, T. Eralp, E. Bilbé, 51. A. A. Coelho, ‘TOPAS User Manual’, Version 3.1, J. W. Thybaut, G. B. Marin and P. Collier, Appl. Bruker AXS GmbH, Karlsruhe, Germany, 2003 Catal. A: Gen., 2017, 536, 104 26. J. W. Thybaut, J. Sun, L. Olivier, A. C. Van Veen, 52. S. Bisal, P. K. Bhattacharya and S. P. Moulik, C. Mirodatos and G. B. Marin, Catal. Today, 2011, J. Phys. Chem., 1990, 94, (1), 350 159, (1), 29 53. D. M. Zhu, K. I. Feng and Z. A. Schelly, J. Phys. 27. A. Farsi, A. Moradi, S. Ghader and V. Shadravan, Chem., 1992, 96, (5), 2382 Chinese J. Chem. Phys., 2011, 24, (1), 70 54. S. Eriksson, U. Nylén, Sergio Rojas and 28. D. Noon, B. Zohour and S. Senkan, J. Nat. Gas M. Boutonnet, Appl. Catal. A: Gen., 2004, 265, Sci. Eng., 2014, 18, 406 (2), 207 29. P. Huang, Y. Zhao, J. Zhang, Y. Zhu and Y. Sun, 55. I. Lisiecki and M. P. Pileni, J. Phys. Chem., 1995, Nanoscale, 2013, 5, (22), 10844 99, (14), 5077 30. V. I. Alexiadis, J. W. Thybaut, P. N. Kechagiopoulos, M. Chaar, A. C. Van Veen, M. Muhler and 56. K. Shinoda and B. Lindman, Langmuir, 1987, 3, G. B. Marin, Appl. Catal. B: Environ., 2014, (2), 135 150–151, 496 57. D. Langevin, Annu. Rev. Phys. Chem., 1992, 43, 341

The Authors

Cristina Estruch Bosch has a Masters degree in Catalysis from the Rovira i Virgili University, Spain. She is currently finishing her PhD in chemical engineering at Ghent University, Belgium. Cristina has been working for Johnson Matthey since 2007 and has experience in catalyst development for a variety of heterogeneous reactions including methane activation.

Stephen Poulston has a PhD in chemistry from the University of Cambridge, UK and is a research scientist at Johnson Matthey, Sonning Common, UK where he has worked since 1998. Stephen has experience of a wide range of heterogeneous catalyst systems including hydrogenation and platinum group metal catalysis.

Paul Collier is a Research Fellow at Johnson Matthey, Sonning Common, UK. He is responsible for organising Johnson Matthey’s collaborations at the Harwell site, 25 km from the Johnson Matthey Technology Centre, which hosts the world class facilities such as the UK’s synchrotron (Diamond) and the ISIS neutron spallation source. He is interested in heterogeneous and homogeneous catalysis, metal organic frameworks (MOFs), platinum group metals, oxidation, synchrotron, neutron diffraction, neutron spectoscopy, lasers, zeolite catalysts, methane and alkanes.

Joris W. Thybaut is full professor in catalytic reaction engineering at the Laboratory for Chemical Technology at Ghent University since October 2014. He obtained his master’s degree in chemical engineering in 1998 at the same university, where he continued his PhD studies on single-event microkinetic (SEMK) modelling of hydrocracking and hydrogenation. In 2003 he went to the Institut des Recherches sur la Catalyse in Lyon, France, for postdoctoral research on high throughput experimentation, before being appointed in 2005 at Ghent University.

Guy B. Marin is professor in Chemical Reaction Engineering and founding member of the Laboratory for Chemical Technology (LCT) and the Center of Sustainable Chemistry (CSC) at Ghent University. He co-founded the spinoff AVGI in 2015. The investigation of chemical kinetics, aimed at the modelling and design of chemical processes and products all the way from molecular up to industrial scale, constitutes the core of his research. He co-authored two books, “Kinetics of Chemical Reactions: Decoding Complexity” with G. Yablonsky and D. Constales (Wiley-VCH, 2nd edition 2019) and “Advanced Data Analysis and Modelling in Chemical Engineering”, as well as more than 600 papers in high impact journals and is co-inventor in four filed patents. He is co-editor of the Chemical Engineering Journal and member of the editorial boards of Industrial & Engineering Chemistry Research, Current Opinion in Chemical Engineering and the Canadian Journal of Chemical Engineering. He is member of several international scientific advisory boards and ’Master’ of 111 projects of the Chinese Government for overseas collaborations in his field.

www.technology.matthey.com

TechConnect World Innovation Conference and Expo 2019 Commercialising research in advanced materials and sustainable manufacturing

Reviewed by Debra Jones on day one of the conference. The panel consisted Johnson Matthey, Blounts Court, Sonning of Alex Fensore (Sherwin-Williams, USA), Emily Common, Reading, RG4 9NH, UK Riley (Energizer Holdings Inc, USA) and Chris van Buiten (Lockheed Martin, USA). There was E-mail: [email protected] discussion about needing both incremental and transformational innovation at different stages Introduction and in different places across an organisation and bespoke approaches and processes in place to run The TechConnect World Innovation Conference and and manage each type effectively. Expo event has been held annually for the past 20 All panel members emphasised the importance years and has alternated location between Boston, of starting incremental innovation from capturing USA and California, USA. The 2019 conference was internal and customer unmet needs, followed by held in Boston between the 17th and 19th of June looking to see what capability is already in place 2019 and attracted over 3000 participants from or can be easily sourced to solve the problems across all pillars of the ecosystem. The conference and then collaborating externally to fill any gaps will be held in Washington DC, USA for the first where necessary. There was less of a consensus on time next year. how to succeed at transformational or disruptive The aim of the conference is to connect top innovation. applied research and early-stage innovations from The panel’s top tips for innovators were: universities, laboratories and startups with industry end users and large corporates across the following • Understand what your customer needs themes, each with their own parallel stream: • Know what you want to be great at – then work out how to get there • Advanced materials • Be bold and be brave. • Advanced manufacturing • Energy and sustainability • Electronics and microsystems Innovation Spotlight: Composite • Biotechnology, medical, pharmaceutical and Materials, Films and Coatings consumer One of the highlights of each of the sessions was • Artificial intelligence (AI), machine learning, the Innovation Spotlight slot. During this time each informatics and modelling of the sponsoring companies has an opportunity to • Personal and home care, cosmetics, food and pitch to the innovators in the room and describe agriculture the company, its vision, ethos and goals and There were also two poster sessions over the three especially the types of challenges they are facing days and a large exhibition space with over 250 and where they are looking for new advanced exhibitors showcasing and demonstrating their materials. The innovators in the audience found novel technologies and inventions. these slots particularly useful to guide the areas to target their future research. If an innovative solution can be matched with a known problem Commercialisation of R&D that a large company is facing, then the route to The keynote panel discussion ‘Inspiration to commercialisation for the technology can be made Innovation Commercialization of R&D’ took place easier.

Fig. 1. Alignment of particles when exposed to an electric field in conductive films with anisotropic properties made by CondAlign, Norway (Image used with permission)

Then followed a number of seven minute selected can be insulating in one direction and electrically pitches from university technology transfer offices conductive in another. The films are usually or startups looking for seed funding, licensing comprised of conductive particles and a polymer partners or commercialisation partners. Among matrix. The mechanical properties of the films are the pitches in the Advanced Materials Innovation mainly given by the matrix, while the conductive Spotlight (sponsored by AGC, USA and Magna, properties are defined by the particles. An electric USA) were a selection summarised here. field is used to structure and align the filler particles ‘CompPair Technologies’, A. Cohades (Laboratory in a liquid matrix (Figure 1). When applying the for Processing of Advanced Composites, EPFL, electric field, electric dipoles are induced in the Switzerland) (1). Composite materials are formed particles causing chain formation. The alignment by combining materials together to form an overall occurs due to electrophoresis, therefore it is also structure with properties that differ from those possible to align non-electrically conductive or of the individual components. They are used for magnetic particles. CondAlign has demonstrated a wide range of applications from wind turbine production of films with a wide range of different blades or aircraft wings to boat hulls and masts, parameters. It is demonstrated in roll to roll surfboards and buildings. High performance and production, making the process scalable and cost lightweight composites that are composed of effective. The process is material independent and fibre and resin can be susceptible to damage by is applicable to a wide range of applications. fatigue or exposure to dust or projectiles, even ‘Surface Coating for Reduction of Aerodynamic small impacts can cause microcracks, which leads Noise and Vibrations’, C. Smith (Texas Tech to bigger cracks and potentially catastrophic part University, USA). Flow separation is a phenomenon failure. CompPair has developed a ‘prepreg’: considered to be responsible for increased vibration a fibre-based repair agent that is incorporated and drag along with higher energy consumption in directly throughout the composite materials on vehicles. The team at Texas Tech University have production and remains dormant in the part until focused on solving this problem using passive activated to enact self-repair of the composite. control via bio-inspired surfaces. Using a material The healing process requires only moderate analogous to the denticles on a shark’s skin, they temperatures of 70–85°C, easily achieved with a have developed a passive microscale fibrillar hand-held heat source and takes only one minute. coating that significantly reduced flow separation. The incorporation of the repair agent uses existing This micro-texture energises the fluid adjacent to manufacturing routes and assets, maintains the the body by creating local suction and blowing, mechanical performance of the original material delaying separation and giving a smaller wake and can extend the equipment’s lifespan by up leading to reduced noise and vibrations. A feature to three times. The company is looking to trial its of shark denticles is the asymmetric geometry repair additives in new composite materials. (Figure 2) (2). The denticles are created initially ‘Enabling New Technology for Anisotropic through a process of etching and casting, however Conductive Films’, P. M. Lindberget, CondAlign, once a mould is made it can be used almost Norway. CondAlign has a patented technology indefinitely allowing for cost-effective scale up. for producing a range of conductive films with Initially focusing on wind turbine blades, they anisotropic properties known as anisotropic managed to achieve 30% drag and noise reduction conductive films (ACFs). Anisotropic materials and are looking for partners to co-develop solutions can be described as having directionally different for specific applications where noise and vibration material properties. For instance, the material reduction are important.

between the rPET fibres and the PVA cross-linker. (a) (b) It also reinforces the rPET-PVA fibre matrix by improving its stability and mechanical properties during the curing process (Figure 3). The aerogels are very versatile and can be given different surface treatments to customise them for different applications. For example when the surface 100 µm contains terminal methyl groups, the aerogels can (c) absorb large amounts of hydrocarbons very quickly making them highly suitable for oil spill cleaning. When the surface is coated with an amine group the material can absorb carbon dioxide from the environment. The surface chemistry can be adapted to be able to incorporate the aerogels 100 µm into lightweight, breathable personal masks that filter out pollutants such as nitrogen oxides and Fig. 2. (a) Shark denticle shows a divergent shape with an asymmetry in the wall-normal and carbon monoxide in places where air quality is streamwise directions; (b) and (c) microscopy of concern. Aerogels also have incredibly poor images of the micropillar arrays, which have a heat transfer properties, which makes them ideal similar asymmetric shape (2) Creative Commons for using as insulation. When coated with fire Attribution-NonCommercial-NoDerivatives 4.0 (CC retardant chemicals, the material can withstand BY-NC-ND) temperatures of up to 450°C but weighs only about 10% of the weight of traditional thermal lining, this would allow safety equipment such as coats ‘Polyethylene Terephthalate (PET) Aerogels’, for firefighters to be made much lighter, safer and G. Wee (National University of Singapore (NUS)) cheaper and at the same time helping in the global (3). With much in the news currently about plastic fight against plastic waste. waste, the team at NUS has created a cost-effective approach to fabricating recycled polyethylene terephthalate (rPET) aerogels from waste PET fibres Awards: Thin Films, Sensors and obtained from plastic bottles. The high surface area Coatings rPET aerogels were fabricated through hydrogen and ester bonds formed between polyvinyl alcohol Each year the TechConnect Review Panel identifies (PVA) and the rPET fibres and acetal bridges from and ranks the top 15% of submitted technologies based on the potential positive impact the a glutaraldehyde (GA) cross-linker. The rPET fibres submitted technology will have on a specific were fully immersed in sodium hydroxide (NaOH) industry sector. Some of the 2019 award winners solution to produce carboxyl and hydroxyl groups are listed below. on their surface. This was heated in an oven for Click Materials Corp, Canada, is expert in thin 1 h at 80°C to accelerate the hydrolysis process. film technologies for coating highly efficient They were washed thoroughly with deionised (DI) catalysts for reduced power consumption and water to remove all the remaining NaOH before smart glass. It is commercialising electrochromic immersing them into the mixture of PVA, GA window technology that is expected to be >50% and DI water. The pH of the reaction media was lower cost than incumbent technologies. Smart controlled at pH 3 by hydrochloric acid (37%) to windows provide variable tinting capabilities that accelerate the cross-linking reaction. The resulting significantly reduce energy requirements, improve mixture was sonicated for 30 min at 220–230 W for employee productivity and enable the connected smart home. homogenisation and removal of bubbles. The cross- Chemeleon, USA, is developing a platform linking reaction was carried out in the oven for 3 h technology for a novel chemical sensor with high at 80°C and then placed into a freezer for 6–8 h sensitivity and specificity. The initial application until the sample was frozen. The frozen sample includes a smart colorimetric sensor that can be was placed into the freeze dryer for 48 h to remove embedded in drinkware to help consumers become all the solvent and produce the rPET aerogel. aware of food and drink safety to protect them Full details can be found in their publication (4). from date rape drug facilitated crime. It enables The GA cross-linker can improve the interactions instantaneous on the spot detection of many other

(a) (b) PVA

PET fibre PVA

PET fibre 100 µm 100 µm

Fig. 3. SEM images show PVA linking the PET aerogel structure (4). Creative Commons Attribution 4.0 (CC BY) analytes such as volatile organic compound (VOC), to conflicted starting materials and having a explosives or nerve agents and it can also be minimal impact on the world’s natural resources by extended to detect specific biomarkers to enable considering recycling and cradle-to-cradle lifecycles clinical diagnosis. at the start of the projects. This looks like a trend Inhibit Coatings Ltd, New Zealand, uses that is thankfully set to continue with many of the novel silver nanofunctionalisation to produce companies and institutions presenting referencing highly antimicrobial coatings. Silver is a well- the United Nations Sustainable Development Goals known antimicrobial agent effective against in their drivers and business models. over 650 different microorganisms. The novel nanotechnology allows very low biocide References concentrations (<0.1%) and exhibits an extremely –2 low leaching <0.1 ppb cm over a period of one 1. S. Aubort, ‘A Self-Healing Composite’, Ecole week fully immersed. This low leach rate and biocide polytechnique fédérale de Lausanne (EPFL), concentration gives rise to robust coatings with a Switzerland, 6th March, 2019 very long antimicrobial lifetime that withstands 2. H. Bocanegra Evans, A. M. Hamed, S. Gorumlu, wash cycles without compromising the physical A. Doosttalab, B. Aksak, L. P. Chamorro and properties of the resin system. L. Castillo, Proc. Natl. Acad. Sci., 2018, 115, (6), 1210 Conclusions 3. S. Salomo, T. X. Nguyen, D. K. Le, X. Zhang, The overarching themes across all the streams of N. Phan-Thien and H. M. Duong, Colloids Surf. A: the conference were about making things better, Physicochem. Eng. Aspects, 2018, 556, 37 smaller and cheaper but importantly also more 4. H. W. Koh, D. K. Le, G. N. Ng, X. Zhang, safely, efficiently, ethically and sustainably: using N. Phan-Thien, U. Kureemun and H. M. Duong, greener solvents and processes, finding alternatives Gels, 2018, 4, (2), 43

The Reviewer

Debra Jones joined Johnson Matthey in the Technology Centre, Sonning Common, UK in 2004 with a degree in Chemistry from the University of Birmingham, UK. She has worked across a range of sectors including Fischer Tropsch catalysis, automotive catalysis, solar thermal hydrogen production and natural gas purification. Debra currently works in the corporate innovation team and looks after Johnson Matthey’s Open Innovation activities, looking for new technologies and opportunities for Johnson Matthey to collaborate externally, particularly with startups and small to medium enterprises.

www.technology.matthey.com

“Nanocarbons for Energy Conversion: Supramolecular Approaches” Edited by Naotoshi Nakashima (Kyushu University, Japan), Nanostructure Science and Technology, Springer International Publishing AG, part of Springer Nature, Switzerland, 2019, 564 pp, ISBN: 978-3-319-92915-6, £129.99, €160.49, US$179.99

Reviewed by Harry Macpherson Nanocarbons for Fuel Cells Johnson Matthey, Orchard Road, Royston, A large portion of the book is dedicated to the role Hertfordshire, SG8 5HE, UK of nanocarbons in fuel cells (FCs), so it is worth Email: [email protected] giving a brief overview of FCs and the associated functions of nanocarbons. FCs share features with Introduction both internal combustion engines and batteries. Like an internal combustion engine fuel is oxidised, Carbon in its oxide and hydrocarbon forms is the producing exhaust gas, and like a battery chemical cause of the energy and transport sectors’ biggest energy is converted to electrical energy. In the case headache: climate change, so it is fitting that of the popular proton exchange membrane fuel cells allotropes of this most versatile element look so (PEMFCs) the fuel is commonly hydrogen, which promising to play a part in the modernisation of is split into protons and electrons at the anode. energy conversion. Naotoshi Nakashima (Kyushu Electrons are forced to flow through an external University, Japan) brings together a collection of circuit because the electrodes are separated by an chapters showcasing some impressively creative electrically insulating proton conducting polymer nanoscience, predominantly from Japan, as part of membrane such as NafionTM. Protons move Springer’s Nanostructure Science and Technology through the membrane to the cathode where they series. On reading, one is left with the impression react with oxygen and electrons that have travelled that these fascinating materials will surely play through the external circuit to form water. The some part in the coming decarbonisation of the overall reaction is the oxidation of H2 to H2O. economy. FC performance is largely determined by materials Nanocarbons, as the name implies, are performance. Looking in more detail, at the anode the allotropes of carbon that take the form side H2 diffuses through the gas diffusion layer of molecules of nanometre dimensions. The (GDL) to reach the catalyst. The GDL is often archetypal nanocarbon is graphene – a single composed of carbon fibres which allow electrons layer of sp2 hybridised atoms arranged in a two- to flow from the catalyst to the current collector dimensional hexagonal lattice. Nanotubes are and H2 to diffuse between them to the catalyst. essentially rolled up sheets of graphene, while Platinum nanoparticles catalyse the splitting of fullerenes are essentially graphene sheets curled H2 into protons which are transported across the up into spheroids. Other nanoscale carbons, such proton exchange membrane to the cathode and as nanoporous carbon, carbon black and carbon electrons which are transported along carbon fibres foams are also discussed. to the current collector.

Electric current Proton Carbon Electrically conducting supported conductive media catalyst fibres e– Fuel in Air in e– e– H O e– 2

e– O2 H+

O2 H+ H+ Unused Excess air, water fuel out H2O and heat

Anode Cathode Electrolyte PEM Catalyst GDL layer Fig. 1. The operation of a PEMFC. Creative Commons Zero 1.0 (CC0) Fig. 2. The transport of gases, electrons and protons in a PEMFC. (1) Creative Commons Attribution-Share Alike 3.0 (CC-BY-SA)

Carbons are crucial to the performance and cost effectiveness of FCs, especially as catalyst supports be more easily deposited. Chapter 1 also features where their high specific surface area enables a durability tests of membrane electrode assemblies low Pt loading for a given power density and their (MEAs) using polymer wrapped nanotubes as conductivity provides a pathway for electrons to compared to polymer wrapped carbon black. move between the Pt catalyst and the conducting Nanotube MEAs are found to maintain a significantly fibres. FC performance can be greatly enhanced by higher activity after several thousand cycles of improving the surface properties of nanocarbons durability tests compared to carbon blacks due for better gas accessibility and distribution of Pt to the inherent structural stability of the polymer nanoparticles. Their conductivity has a significant wrapped pristine nanotubes. effect on power density and their chemical and Chapter 2, which is also written by Nakashima, thermal stability has a large influence on FC follows on nicely from the first, exploring polymer durability. wrapped nanotubes as catalyst supports for direct methanol FCs. A significant problem for direct methanol PEMFCs is methanol crossover Carbon Nanotubes where methanol diffuses through the NafionTM

On the topic of FCs, some particularly interesting membrane to the cathode where it reacts with O2, work on multiwalled carbon nanotubes (MWCNTs) poisoning the Pt catalyst. While alternative transition as catalyst supports for H2 PEMFCs by Naotoshi metal cathode catalysts are more methanol Nakashima and Tsuyohiko Fujigaya of Kyushu resistant because they suppress its oxidation this University, Japan, can be found in Chapter 1. The is counterbalanced by lower oxygen reduction authors first address the difficulty of dispersing reaction (ORR) activities than Pt. Nakashima Pt nanoparticles onto nanotubes due to the lack presents a solution to this problem by coating the of binding sites for deposition. Oxidation of the polymer wrapped Pt decorated nanotubes with an nanotubes is one method of introducing hydrophilic outer layer of poly(vinylphosphonic acid) (PVPA) groups for binding, however this reduces the polymer, which increases methanol tolerance by nanotubes’ electrochemical stability. To get around the proposed mechanism of preferentially blocking this problem the authors present a protocol for diffusion of the larger molecule while only slightly wrapping MWCNTs with conjugated polymers reducing O2 accessibility. The PVPA is also found to which bind to the nanotube surface through π–π reduce carbon corrosion of nanotube and carbon interactions and on top of which the Pt catalyst can black catalyst supports.

Another highlight on the topic of FCs is the review stress tests on MEAs make it difficult to tease by Matsuhiko Nishizawa of Tohoku University, apart the contribution to performance decline from Japan, of carbon nanotube (CNT) based enzymatic different components. In order to study specifically biofuel cells in Chapter 15. Enzymatic biofuel cells Pt nanoparticle instability Arenz et al. first deposited are FCs in which an enzyme takes the place of Pt the nanotube supported catalyst onto a gold TEM nanoparticles as the electrocatalyst. At the anode, grid, initially observed the foil to define an area the enzyme oxidises fuels such as fructose or of interest, cycled the grid in a three-electrode glucose and generates electrons that are carried electrochemical cell and then re-characterised the to the current collector by a conducting carbon identical area of interest by TEM. It was found that support. At the cathode O2 is reduced to H2O by carbon corrosion of nanotubes in voltage cycling in another enzyme. An advantage of biofuel cells is which carbon is lost as carbon dioxide, converting that the incredibly high selectivity of the enzyme the hexagonal lattice to heptagon and pentagon means impure fuel feeds can be used and there rings, causes the Pt nanoparticles to move is no need for a separator, making the overall across the nanotube surface, possibly to reduce design simply a pair of enzyme functionalised interfacial energy. As the nanoparticles move on electrodes exposed to solutions containing fuel the nanotubes they make contact with each other and O2. The simplicity of the design makes them before coalescing to form larger particles. suitable for miniaturisation for use in implantable electronic devices. CNTs are presented as Nanocarbons in Hydrogen Production promising enzyme support materials due to their biocompatibility and high specific surface area. Aptly, the complementary theme of the role

Previous attempts to immobilise enzymes onto of nanocarbons in H2 production is explored nanotube electrode structures have created in Chapters 9 and 19. In Chapter 9 Yutaka nanostructure films before enzyme modification. Takaguchi and Tomoyuki Tajima of Okayama However, Nishizawa reports a method by which University, Japan and Hideaki Miyake of Yamaguchi enzyme modification precedes film production University, Japan, describe a new category of H2 so that the nanotubes pack ideally around the evolving photocatalysts based on semiconducting enzymes. This is achieved by adding an enzyme single walled carbon nanotubes (s-SWCNTs). solution to a CNT forest which shrinks to a near Nanotubes can be metallic or semiconducting, hexagonal close packed structure on drying, i.e. have or not have a band gap, depending on entrapping the enzymes between the nanotubes the rolling angle between the axis of the tube and resulting in superior activity compared to and the crystallographic directions of the rolled previous production methods. graphene sheet. The productivity of H2 from photocatalysts can be improved by expanding the Materials Characterisation range of active wavelengths from ultraviolet to near infrared (IR). The new category of nanotube A fantastic piece of FC material characterisation based photocatalyst reported promisingly shows work is presented in Chapter 5 by Somaye Rasouli H2 evolution under near IR radiation. However, and Paulo J. Ferreira working at the University of s-SWCNTs are seldom used for this application due Texas at Austin, USA. They describe the technique of to the high exciton (electron-hole pair) dissociation identical location transmission electron microscopy energy, the fact that nanotubes form bundles that (TEM) as a way to understand the mechanism of allow excitons to be transferred between tubes Pt nanoparticle growth on CNTs in PEMFCs. One of and also because they are difficult to disperse the main causes of performance decline of PEMFCs in H2O. These problems are addressed rather is the instability and coarsening of Pt nanoparticles ingeniously through the fabrication of a coaxial on carbon supports, which reduces the total surface cable composed of an s-SWCNT covered with area of active catalyst. The authors proposed a layer of C60 fullerenes, which are themselves four possible mechanisms of coarsening: Ostwald functionalised with a hydrophilic dendron moiety ripening, particle migration on the carbon support which readily complexes with Pt, the cocatalyst and coalescence, particle detachment and particle for H2 evolution. The cable is made simply by dissolution and reprecipitation. While the ideal sonicating the nanotubes in a H2O solution of the way to investigate the mechanism would be to do amphiphilic fullerodendron, which self assembles in situ TEM and concurrent voltage cycling on a around the nanotubes due to π–π interactions. MEA, the release of moisture into the vacuum This hydrophilic dendron moiety makes the chamber precludes this. Furthermore, accelerated nanotubes more easily dispersible in H2O, while

the nanotube-C60 heterojunction formed improves Kazunari Matsuda of Kyoto University, Japan and exciton dissociation. Furthermore, the problem of Nagoya University, Japan provide a clear overview bundle formation is resolved by the isolation of the of the general principles of solar cells, which nicely nanotubes from each other. sets the context for the chapter. Perhaps most intriguing is the ability of semiconducting SWCNTs Lithium-Ion Batteries and Solar Cells to generate multiple excitons from one photon, meaning they may be able to surpass the Shockley- The FC’s biggest competitor in the race to Queisser limit on the maximum efficiency of single decarbonise transport – the lithium-ion battery junction solar cells, which assumes one exciton – may also benefit from the use of nanocarbons per photon. While there are many applications in future. Of particular interest is the review of for nanotubes, from hole transport layers to nanocarbons as alternatives to graphite in anode transparent conducting electrodes, the authors materials written by Seok-Kyu Cho and Sang- Young Lee of Ulsan National Institute of Science point to a significant barrier to commercialisation: and Technology (UNIST), South Korea and the presence of metallic nanotubes in the mixtures JongTae Yoo of Korea Institute of S&T Evaluation used for studies, which increase contact resistance and Planning (KISTEP, South Korea in Chapter 18. due to their difference in work function and band The main advantage of these materials is that gap. they could potentially have significantly higher Li capacities than graphite. For example, the Conclusions capacity of C60 fullerenes was shown by Armand et al. to be 12 Li atoms per fullerene. However, this This book covers a very broad range of applications was only realised once the problem of reduced C60 for nanocarbons and while much of the underlying dissolving in liquid electrolyte was worked around chemistry and materials science transfers between by substituting for a polyethylene oxide-based chapters, it is unlikely that any single reader gel polymer electrolyte. Theoretical calculations would be familiar with all the concepts covered. of the Li storage potential of nanotubes show The reviewer would recommend this book for any them to have capacities much greater than researchers working with carbon nanomaterials, graphite, however these have yet to be realised particularly nanotubes, as well as researchers experimentally. The authors conclude that the working with PEMFCs. Overall, an interesting gap between theory and experiment motivates read that reminds the reader of the impressive more work to better understand the lithiation versatility and seemingly endless applications of mechanism of nanotubes. carbon nanomaterials. The book covers the potential roles of nanocarbons in several aspects of the future decarbonised Reference economy, covering power generation from H2 and production of H2. Chapter 20 covers the applications 1. CFA213FCE, ‘Transport of Gases, p+ and e– in of nanotubes in grid energy generation from solar PEMFC’, 23rd May 2013 cells with an emphasis on CNT-silicon solar cells and CNT based perovskite solar cells. Feijiu Wang and The Reviewer "Nanocarbons for Energy Harry Macpherson has been Conversion: working as a Materials Scientist Supramolecular in Johnson Matthey, UK, since Approaches" 2017 on the development of platinum group metal industrial products. Before that he worked on synthesising endohedral fullerene derivatives for quantum information processing in the Carbon Nanomaterials Group at the University of Oxford, UK.

www.technology.matthey.com

Oxford Battery Modelling Symposium Highlights of the latest developments in battery modelling: from atomistic length-scale to control modelling

By Giulia Mangione mechanics approach is beneficial, although Johnson Matthey, Blounts Court, Sonning computationally very demanding. Van der Ven Common, Reading, RG4 9NH, UK introduced the open-source software Cluster Approach to Statistical Mechanics (CASM) developed Email: [email protected] in his group and available from GitHub (1). In CASM, for a certain material, the thermodynamic and Introduction kinetic properties obtained from density functional theory can be fed into continuum models to realise The Oxford Battery Modelling Symposium was held fast and computationally undemanding first-principle in Oxford, UK, from 18th to 19th March 2019. The multiscale simulations for dynamic processes such conference was specifically designed to gather as electrochemical processes. This tool can be used mathematicians, chemists and engineers within to predict thermodynamic and kinetic properties the battery modelling community. It was very well of various classes of materials (such as layered, received and brought together 170 participants olivines, spinels and alloys), see Figure 1 (2). with worldwide representation from academia, In literature both accurate first-principle methods research organisations and industry involved in and continuum theories are available to predict the modelling at different scales (atomic length-scale, properties of materials and interfaces. However, continuum and control-oriented modelling). This rigorous ways to connect the two approaches are review will focus on eleven talks presented in the still lacking. In ‘Mind the Gap – Towards an Atomistic four sessions and organised as follows: Understanding of Battery Materials Interfaces’, Denis Kramer (University of Southampton, UK) • Atomistic to continuum modelling described strategies to build continuum models • Continuum modelling starting from first principle calculations and their • Continuum to control modelling application to crystallisation. The coverage effect • Control-oriented modelling. in the size-stabilisation of nanocrystals during electrochemical processes and the crystallisation Atomistic to Continuum Modelling process of manganese(IV) oxide polymorphs have been discussed (3). Finally the effect of + Li ions

Electrochemical processes can be modelled using a in the stabilisation of some MnO2 polymorphs was continuum approach (that relies on material specific described in this framework. parameters, sometimes difficult to measure) or In ‘Modeling Porous Intercalation Electrodes from first principles. As electrochemical processes with Continuum Thermodynamics and Multi-scale are thermally activated, in ‘Connecting Electronic Asymptotics’ by Manuel Landstorfer (Weierstrass Structure to Phenomenological Continuum Models Institute for Applied Analysis and Stochastics, of Electrochemical Processes’ by Anton Van der Germany), a description of the procedure for Ven (University of California Santa Barbara, USA) modelling porous cathodes was provided. For such it was shown that temperature and entropy play electrodes three scales can be identified (the double a key role for understanding the physics and layer scale, the macroscopic porous media scale the properties of materials. As such, a statistical and the microstructure scale). Landstorfer started

continuum modelling, (kinetic) Monte Carlo and (a) O1 (b) O3 molecular dynamics) and their application to B B A A the modelling of intercalation electrodes and

B C electrolytes in Li-ion batteries. He showed how A B these tools can improve understanding of the B A electrochemical processes as well as of failure A C mechanisms taking place in battery materials, B B A A helping to design high power and high energy battery materials. (c) H1-3 (d) Spinel Bob McMeeking (University of California Santa B A B Barbara, USA) presented a model for the redox A B kinetics at an interface between a solid electrolyte A C and a Li metal anode in ‘Redox Kinetics, Interface C B B Roughening and Solid Electrolyte Cracking in A C C Solid State Lithium-Ion Batteries’. This model B was based on the extension of the Butler-Volmer A B A C equation through the inclusion of the effect

A of the mechanical stress across the anode- C (e) Rock salt electrolyte interface. This method was applied to B A A the investigation of the morphological stability of C B the interface between the Li anode and the solid Li octahedra A electrolyte for various current densities and solid coordinated by O electrolyte resistivities. Moreover, the extended TM octahedra Li tetrahedra Butler-Volmer equation was used to model the coordinated by O coordinated by O evolution of cracking in ceramic solid electrolytes caused by Li insertion into pre-existing defects Fig. 1. Crystal structures relevant for layered Li on the electrolyte surface. The model showed intercalation electrodes. Blue octahedra represent how the pressure generated by Li insertion into MO6 units and green octahedra/tetrahedra represent Li sites. (Reprinted with permission the flaw causes the propagation of cracking in from (2). Copyright 2019 John Wiley and Sons) the solid electrolyte and consequent Li dendrite growth. Finally, the extended Butler-Volmer equation was used to identify the maximum Li by describing the metal-electrolyte interface and pressure and critical lengths (a1) of defects electron transfer in the double layer through a non- within a series of ceramic electrolytes to avoid equilibrium thermodynamic continuum model (4). the propagation of Li dendrites (a1 = 2 µm for

The model was scaled up to electrode particle Li7La3Zr2O12 (LLZO)) (5). scale and treated with a matched asymptotic expansion method. Finally, Landstorfer discussed a Continuum to Control Modelling third scale: the macroscopic porous media scale. He introduced homogenisation techniques for the The kinetics and uniformity of Li insertion reactions prediction of transport properties at porous scale. at the solid-liquid interface govern the rate This multiscale methodology was applied to model capability and lifetime of Li-ion batteries. Martin thermodynamic properties, diffusion processes Bazant (Massachusetts Institute of Technology, and the open circuit potentials of intercalation USA) presented a model for the prediction of cathodes for Li-ion batteries with different chemical phase transformations of intercalation materials composition and porosity. in ‘Control of Battery Phase Transformations by Electro-Autocatalysis’. The approach was based on Continuum Modelling a thermodynamic framework for chemical kinetics applied to charge transfer (namely, the Marcus and ‘Electrochemical Energy Storage’ by John extended Butler-Volmer equations) (6). Newman (University of California Berkley, USA) Reaction-driven phase transformations are was a keynote lecture on mathematical modelling common in electrochemistry, when charge transfer approaches for the design of batteries. Newman is accompanied by ion intercalation or deposition introduced various methodologies (such as in a solid phase. The model allows rationalisation

286 © 2019 Johnson Matthey https://doi.org/10.1595/205651319X15671717887271 Johnson Matthey Technol. Rev., 2019, 63, (4) of phase separation of Li-rich and Li-poor islands Control-Oriented Modelling for low discharge rates that affect the stability and cyclability of Li-ion batteries. The model also proved Gregory Plett (University of Colorado, Colorado that high discharge rates favour the formation Springs, USA) delivered a keynote lecture titled of solid-solution phases through an electro- ‘Physics-Based Reduced-Order Models of Lithium- autocatalytic mechanism, later experimentally Ion Cells for Battery Management Systems’ about confirmed for lithium iron phosphate (LFP) (7). physically-informed control models. Plett reviewed The model can be extended to the investigation of the standard physics-based model particularly electrodeposition, corrosion, chemical intercalation, focusing on how this model could be converted to precipitation and cell biology. a physics-based reduced-order model (PBROM). Göran Lindbergh (KTH Royal Institute of Battery-management systems provide a continuous Technology, Sweden) presented an extended estimate of state-of-charge, state-of-health, physics-based porous electrode model accounting available energy and available power of battery for particle surface stress that was used to packs. Traditional computational methods rely on describe ageing of nickel manganese cobalt oxide empirical equivalent circuit models of the batteries. cathode (LiNixMnyCozO2, NMC) with composition These models are computationally fast and robust. x = y = z = 0.33 (namely NMC111). In ‘An However, although accurate for many tasks, they Extended Porous Electrode Model for NMC111 cannot predict the internal electrochemical state of in Lithium-Ion Batteries’ the performances of the cell. On the other hand, physics-based models NMC111 were experimentally investigated via a that provide good predictions of the internal galvanostatic intermittent titration technique and electrochemical state are too complex to apply to two models were used to fit the experiments: (i) a battery-management systems, which are heavily standard pseudo-two-dimensional (P2D) model; parametrised and have robustness and convergence and (ii) an extended surface stress P2D model issues. PBROM is a method that, while reducing that included a stress factor depending on the computational requirement of physics-based the Li concentration gradient in the material. models, retains their prediction accuracy and can Model (ii) could accurately extract transport, be used for battery management systems. kinetic, thermodynamic and stress properties for In ‘Decoding the Electron Swelling for the whole spectrum of operative conditions (low Advanced Battery Diagnostics’ Anna and high charge-discharge rates, temperature and Stefanopoulou (University of Michigan, USA) external pressure). Although the standard model presented a conjugated experimental and works well for low potentials (less particle surface computational control model to account for battery stress), the porous electrode stress model predicts degradation. Since standard control models do not the ageing of NMC at high potentials (high surface account for swelling and ageing, during the talk stress). Stefanopoulou introduced experimental apparatus ‘Physically-Informed Models for Improved Cell to probe battery degradation and convert Design and Operation of Lithium-Sulphur Cells’ by the observables (measured terminal voltage Monica Marinescu (Imperial College London, UK) and surface temperatures) into parameters to was a lecture about the necessity of using physically- implement control models to predict swelling and informed models to predict the mechanisms ageing (11). In particular, observations of the cell and performance of batteries. The accumulated swelling during charging were used to estimate the experience on physically-informed models for loss of active material and loss of Li inventory in Li-ion was used as a starting point for engineering the anode, which is useful for avoiding Li-plating Li-S batteries. Modified equivalent circuit network during fast charge. models were used for Li-S batteries modelling The last talk was delivered by Scott in order to take into account phenomena like Trimboli (University of Colorado, Colorado Springs, shuttling, dissolution and precipitation. Moreover, USA). The ‘Model Predictive Control using Physics- simple physics-derived zero-dimensional (0D) Based Models for Advanced Battery Management’ and one-dimensional (1D) continuum models was a lecture on the model predictive control (MPC) for the prediction of open circuit voltage and developed in collaboration with Plett. Starting from of the effects of mass transport on discharge, the PBROM, Trimboli showed the mathematical degradation mechanisms and capacity fade for implementation of MPC. MPC is an effective commercially-sized Li-S batteries were presented real-time control strategy that employs a ‘look- (8–10). ahead’ approach to foresee dynamic behaviours in

287 © 2019 Johnson Matthey https://doi.org/10.1595/205651319X15671717887271 Johnson Matthey Technol. Rev., 2019, 63, (4) the battery pack before they happen. This approach 4. M. Landstorfer, C. Guhlke and W. Dreyer, can be coupled with the ability of PBROM to enforce Electrochim. Acta, 2016, 201, 187 hard constraints on internal electrochemical 5. R. M. McMeeking, M. Ganser, M. Klinsmann and variables (precursors to degradation or unsafe F. E. Hildebrand, J. Electrochem. Soc., 2019, operation conditions), making MPC appealing 166, (6), A984 for advanced battery management, where safety, lifetime and improved performance are 6. M. Z. Bazant, Faraday Discuss., 2017, 199, 423 crucial (12). 7. J. Lim, Y. Li, D. H. Alsem, H. So, S. C. Lee, P. Bai, D. A. Cogswell, X. Liu, N. Jin, Y. Yu, N. J. Salmon, Conclusions D. A. Shapiro, M. Z. Bazant, T. Tyliszczak and W. C. Chueh, Science, 2016, 353, (6299), 566 The Oxford Battery Modelling Symposium aimed to bring together the battery modelling community. It 8. T. Zhang, M. Marinescu, S. Walus and G. J. Offer, was well attended and the 12 talks as well as the Electrochim. Acta, 2016, 219, 502 25 posters were high quality. The four sessions of 9. T. Zhang, M. Marinescu, S. Walus, P. Kovacik and talks were successfully organised to provide a full G. J. Offer, J. Electrochem. Soc., 2018, 165, (1), overview of the current state of the art in Li-ion and A6001 next generation battery modelling, spanning from first-principle investigations to control-oriented 10. M. Marinescu, L. O’Neill, T. Zhang, S. Walus, approaches. T. E. Wilson and G. J. Offer, J. Electrochem. Soc., 2018, 165, (1), A6107

References 11. K.-Y. Oh, J. B. Siegel, L. Secondo, S. U. Kim, N. A. Samad, J. Qin, D. Anderson, K. Garikipati, 1. ‘CASM: A Clusters Approach to Statistical Mechanics’, prisms-centre, GitHub: https://github. A. Knobloch, B. I. Epureanu, C. W. Monroe and A. com/prisms-center/CASMcode (Accessed on 2nd Stefanopoulou, J. Power Sources, 2014, 267, 197 September 2019) 12. M. S. Trimboli, G. L. Plett, R. A. Zane, K. Smith, 2. M. D. Radin, S. Hy, M. Sina, C. Fang, H. Liu, D. Maksimovic, M. Evzelman, D. Costinett and J. Vinckeviciute, M. Zhang, M. S. Whittingham, R. D. Anderson, Utah State University, ‘Model Y. S. Meng and A. Van der Ven, Adv. Energy Mater., 2017, 7, (20), 1602888 Predictive Control and Optimization for Battery 3. W. Sun, D. A. Kitchaev, D. Kramer and C. Ceder, Charging and Discharging’, US Patent Appl. Nature Commun., 2019, 10, 573 2016/0,336,765

The Author

Giulia Mangione is a Research Scientist in the Battery Materials team of the Catalysts and Materials department at Johnson Matthey, Sonning Common, UK. Her current research interests include the computational design of high-performance materials for Li-ion and next generation battery technologies.

www.technology.matthey.com

Johnson Matthey Highlights A selection of recent publications by Johnson Matthey R&D staff and collaborators

Factors Affecting the Nucleus-Independent can be attributed to improved contact between Chemical Shift in NMR Studies of Microporous the suspended Fe3+ and the CO reducing gas. Carbon Electrode Materials Chemical Speciation and Mapping of the Si in L. Cervini, O. D. Lynes, G. R. Akien, A. Kerridge, Si Doped LFP Ingot with Synchrotron Radiation N. S. Barrow and J. M. Griffin, Energy Storage Technique Mater., 2019, 21, 335 M. Norouzi Banis, Z. Wang, S. Rousselot, Y. Liu, The factors influencing the nucleus-independent Y. Hu, M. Talebi-Esfandarani, T. Bibienne, M. chemical shift (NICS) of aqueous electrolyte Gauthier, R. Li, G. Liang, M. Dollé, P. Sauriol, T.-K. species adsorbed on polymer-derived activated Sham and X. Sun, Can. J. Chem. Eng., 2019, 97, carbon were investigated in this systematic study. (8), 2211 The observed NICS was found to be influenced by the carbon structure and the behavioural and The performance of lithium-ion batteries is chemical properties of the electrolyte species. significantly affected by small changes to the Measurement of these effects demonstrates structure of LFP. The authors aimed to understand differences in the adsorption behaviour of different the effect of silicon-doped LFP prepared using a ions in the absence of an applied potential. For melt-synthesis process by utilising XAS and XRF instance, as pore size decreases, so does the local mapping as characterisation methods. By using concentration of spontaneously adsorbed alkali these methods, the non-uniform nature of prepared ions. This research could potentially enable greater ingot samples could be better evaluated. With understanding of the mechanism of charge storage comparison to SiO2 and amorphous glass phases in capacitive devices at the molecular level. formed as impurities in Si containing undoped samples, the XAS of Si-doped LFP indicate subtle 3+ Fe Reduction During Melt-Synthesis of LiFePO4 changes in the local structure surrounding the P. Sauriol, D. Li, L. Hadidi, H. Villazon, L. Jin, dopants. Studies of this kind on the structure of B. Yari, M. Gauthier, M. Dollé, P. Chartrand, W. modified LFP will help with the design of materials Kasprzak, G. Liang and G. S. Patience, Can. J. for Li-ion batteries. Chem. Eng., 2019, 97, (8), 2196 Visualization of the Secondary Phase in LiFePO4 5 kg batches of LiFePO4 (LFP) were melt Ingots with Advanced Mapping Techniques synthesised in an induction furnace from coarse Y. Liu, M. N. Banis, W. Xiao, R. Li, Z. Wang, K. R. Fe O (509 µm). Graphite from the crucible was 2 3 Adair, S. Rousselot, P. Sauriol, M. Dollé, G. Liang, an effective reducing agent. The2+ Fe content T.-K. Sham and X. Sun, Can. J. Chem. Eng., 2019, and reaction kinetics were improved via the 97, (8), 2218 addition of metallic Fe, which is also shown to improve the lifetime of the graphite crucible. To The electrochemical performance of LFP in lithium- avoid agglomeration of the Fe powder due to ion batteries is influenced by impurity phases. the presence of a eutectic in the LiPO3-Fe-Fe2O3 Detection of such impurity phases is essential to system, a pre-mixing step is required. A Fe2+ improve the quality of LFP as a cathode material. content of 0.325 g g–1 was observed when fine The origin of the impurity and secondary phases Fe3+ (142 µm) was used with CO as the reducing can be understood through visualisation of the agent at half the holding period at 1150ºC, which impurity and secondary phase distributions

289 © 2019 Johnson Matthey https://doi.org/10.1595/205651319X15671604313083 Johnson Matthey Technol. Rev., 2019, 63, (4) immersed in the bulk LFP crystal. EDS and Raman mannitol mixture. The mixture was compared to techniques were used to observe the low melting a commercial sorbitol in aqueous phase reforming lithium phosphate phase in the LFP ingot. Further over a Pt/C catalyst. The mixtures demonstrated exploration into the LFP materials after carbon similar selectivity towards the gas-phase products coating was achieved through micro XRF mapping. and little difference in the distribution of products This technology has high sensitivity, which ensured retained in the liquid phase. The Pt/C catalysts that the secondary phases were clearly defined. displayed low efficiency regarding hydrogen production at an industrial level. It is suggested that Melt-Synthesis of LiFePO Over a Metallic Bath 4 future work should focus on increasing the amounts H. Villazon, P. Sauriol, S. Rousselot, M. Talebi- of hydrogen generated per mole of converted sugar Esfandarani, T. Bibienne, M. Gauthier, G. Liang, M. alcohols. Dollé and P. Chartrand, Can. J. Chem. Eng., 2019, 97, (8), 2287 Crystal Chemistry and Antibacterial Properties of Cupriferous Hydroxyapatite An Fe3+ precursor was used to study silver and A. Bhattacharjee, Y. Fang, T. J. N. Hooper, N. L. tin charged metallic baths for purification of the Kelly, D. Gupta, K. Balani, I. Manna, T. Baikie, P. T. melt-synthesis of LFP. Samples prepared by the Sn Bishop, T. J. White and J. V. Hanna, Materials, 2019, bath delivered up to 156 mAh g–1 of LFP, whilst Ag 12, (11), 1814 bath samples delivered 161 mAh g–1 of LFP. XRD patterns of the Ag LFP samples were also cleaner Solid-state and wet chemical processing were than those produced by the Sn bath. Ag oxides and used to produce copper-doped hydroxyapatite

Ag compounds were not present. It is suggested with the composition Ca10(PO4)6[Cux(OH)2–2xOx] that future studies should focus on investigating Ag (0.0 ≤ x ≤ 0.8). The impact of synthesis route and baths as a potential contaminant trap for the melt- mode of crystal chemical incorporation of Cu on the synthesis of LFP. antibacterial efficacy against Escherichia coli and Staphylococcus aureus strains was investigated. Synthesis of ZIF-8 Based Composite Hollow Fiber Studies revealed that the substitution site of Cu into Membrane with a Dense Skin Layer for Facilitated Biogas Upgrading in Gas-Liquid Membrane the hydroxyapatite framework is mainly controlled Contactor by the synthesis method and heat treatment process. Finer particle sizes and greater specific Y. Xu, X. Li, Y. Lin, C. Malde and R. Wang, J. Membr. surface areas were observed in the wet chemical Sci., 2019, 585, 238 material, thus leading to superior efficacy. In A composite hollow fibre membrane with an comparison to undoped hydroxyapatite, Cu-doping aminosilane-modified zeolitic imidazolate increases antibacterial efficiency by 25% to 55%. framework-8 (mZIF-8) based dense skin layer was designed and synthesised. The ZIF-8 A Robust and Precious Metal-Free High Performance Cobalt Fischer–Tropsch Catalyst nanocrystals were modified by the introduction of (3-aminopropyl)triethoxysilane. This enabled P. R. Ellis, D. I. Enache, D. W. James, D. S. Jones the ZIF-8 nanocrystals to bond with PDMS chains and G. J. Kelly, Nature Catal., 2019, 2, (7), 623 for further hydrophobicity enhancement, with Synthetic transportation fuel production commonly a contact angle of 130º. This was competitive in uses slurry-phase Fischer-Tropsch catalysis. comparison to the control membrane. The mZIF‑8 However, due to the hydrothermal and mechanical based composite membrane also demonstrated reaction conditions of such processes, the catalyst enhanced biogas upgrading performance and long- used is exposed to extreme stress. Therefore, the term stability. Biogas upgrading performance in authors demonstrate the synthesis, characterisation gas-liquid membrane contactor applications could and catalytic performance of a robust cobalt- be improved by using mZIF-8 based composite based Fischer-Tropsch catalyst. An inert alpha hollow fibre membranes. alumina support and an appropriate cobalt Hydrogen Production from Sucrose via Aqueous- addition were combined to form a mechanically Phase Reforming and hydrothermally stable material, which is easy L. I. Godina, H. Heeres, S. Garcia, S. Bennett, to reduce without precious metal additives. The S. Poulston and D. Yu. Murzin, Int. J. Hydrogen material demonstrated excellent selectivity and Energy, 2019, 44, (29), 14605 good activity in slurry-phase testing over 1000 h. Hydrogenation and aqueous phase reforming Proton Chelating Ligands Drive Improved Chemical techniques were used to produce hydrogen Separations for Rhodium from commercial sucrose. The aqueous sucrose H. Narita, R. M. Nicolson, R. Motokawa, F. Ito, solution was hydrogenated in a trickle bed reactor K. Morisaku, M. Goto, M. Tanaka, W. T. Heller, H. over 5 wt% Ru/C to produce a technical sorbitol/ Shiwaku, T. Yaita, R. J. Gordon, J. B. Love, P. A.

Tasker, E. R. Schofield, M. R. Antonio and C. A. Morrison, Inorg. Chem., 2019, 58, (13), 8720

In comparison to all elements used for technological applications, rhodium extraction has the worst carbon footprint and, unlike other elements, there are also no commercial extractants for Rh. Solvent extraction could improve current practices; however, the chemical separation stage is complicated by the presence of mixed speciation states following acid chloride leaching. Using a variety of experimental and computational techniques, 2– the dianion [RhCl5(H2O)] was shown to transfer to the organic phase in a process involving the formation of an outer-sphere assembly with the diamidoamine reagent N-n-hexylbis(N-methyl-N- Fig. 1. Reprinted with permission from H. Narita et n-octylethylamide)amine (Figure 1). The detailed al., Inorg. Chem., 2019, 58, (13), 8720. Copyright 2019 American Chemical Society knowledge gained from this work will be beneficial to the design of Rh extractants and has implications for sustainable metal extraction from both recycling Low-Temperature Studies of Propene and traditional mining. Oligomerization in ZSM-5 by Inelastic Neutron Scattering Spectroscopy High-Selectivity Palladium Catalysts for the Partial Hydrogenation of Alkynes by Gas-Phase Cluster A. P. Hawkins, A. Zachariou, P. Collier, R. A. Ewings, Deposition onto Oxide Powders R. F. Howe, S. F. Parker and D. Lennon, RSC Adv., P. R. Ellis, C. M. Brown, P. T. Bishop, D. Ievlev, 2019, 9, (33), 18785 J. Yin, K. Cooke and R. E. Palmer, Catal. Struct. Inelastic neutron scattering (INS) spectroscopy React., 2018, 4, (2), 1 was used to study the reaction between propene The bulk and fine chemical industries rely on and an activated sample of ZSM-5 at 140 K, 293 K the selective hydrogenation of alkynes, with and 373 K. The formation of linear alkyl species good selectivity to the desired product being of is observed when propene oligomerises within the particular importance. In this study, a gas-phase zeolite at 293 K, with no evidence to show branched cluster deposition method onto conventional product formation. This selective formation is support powders was used to prepare palladium attributed to confinement within the zeolite pore catalysts. These catalysts are shown to be as active structure. The reaction at 373 K yielded the same and selective as those prepared via conventional spectrum as that observed at 293 K, suggesting methods such as impregnation. Good selectivity that oligomerisation process is complete at 293 K. was observed for both support materials used. The The influence of zeolite crystallite size on the catalysts prepared by gas-phase cluster deposition product composition in technically relevant olefin are shown to contain less-active interfacial sites. oligomerisation reactions was considered.

www.technology.matthey.com

“Process Systems Engineering for Pharmaceutical Manufacturing” Edited by Ravendra Singh (Rutgers, The State University of New Jersey, USA) and Zhinhong Yuan (Tsinghua University, Beijing, China), Computer Aided Chemical Engineering, Volume 41, Elsevier, Amsterdam, The Netherlands, 2018, 674 pages, ISBN: 978-0-444-63963-9, US$187.50, £150.00, €184.57

Reviewed by Michael D. Hamlin development, covering solubility and dissolution Johnson Matthey, 25 Patton Rd, Devens, kinetics, pKa, excipient types and the standard MA 01434, USA formulation processes of direct compression as well as wet and dry granulation and capsule filling. Email: [email protected] This chapter is recommended reading for anyone not familiar with formulation of drug tablets as Introduction it provides a well-organised summary helpful in understanding the types of processes modelled “Process Systems Engineering for Pharmaceutical in the chapters on continuous manufacturing, Manufacturing” is an ambitious reference flowsheet and unit operation modelling as it relates comprising 24 chapters covering process systems to drug product. engineering (PSE) methods and case studies of I have organised this review according to general interest to engineers working in pharmaceutical topics covered rather than by sequential order of process development, model development, process the chapters. simulation, process optimisation and supply- chain or enterprise optimisation. Business model Business Model and Optimisation optimisation, including optimisation of clinical trials and supply chain, are topics covered in Chapter 1, ‘New Product Development and Supply Chapters 1 and 21–24. Continuous manufacturing Chains in the Pharmaceutical Industry’, contributed of drug product (downstream) is a key theme by Catherine Azzaro-Pantel (Université de covered in Chapters 6 and 16–20, while process Toulouse, France), introduces the pharmaceutical control, flowsheet modelling and key unit operation supply chain and summarises the product life modelling are covered in Chapters 5, 7, 8–11 and cycle of a drug starting from discovery through 13–15. Of particular interest is the topic of small clinical trials, registration and commercialisation. molecule upstream development and workup solvent This chapter provides a concise summary of clinal selection and optimisation discussed in Chapters trial phases, pre-launch and launch activities and 3–4, with case studies involving separation solvent is recommended reading for those not familiar selection presented for ibuprofen, artemisinin and with the pharmaceutical business model and drug diphenhydramine in Chapter 4. development process (Figure 1). Chapter 2, ‘The Development of a Pharmaceutical Chapter 21, contributed by Brianna Christian and Oral Solid Dosage Forms’ submitted by Rahamatullah Selen Cremaschi (Auburn University, USA), covers Shaikh, Dónal P. O’Brien, Denise M. Croker and ‘Planning of Pharmaceutical Clinical Trials Under Gavin M. Walker (University of Limerick, Ireland), Outcome Uncertainty’. The authors reference provides a summary of solid oral dosage form an increase in attrition rates in clinical trials and

Exploratory Preclinical Preclinical trials: Registration Commercialisation research trials Phases I, II and III

10,000 targeted 100 tested 10 drug candidates 1 drug molecules molecules

5 years 10 R&D years

20 years

Patent Patent deposit expiration

Fig. 1. Drug development process. Copyright (2018). Reprinted with permission from Elsevier

state “the time from discovery to product launch complex network. A takeaway from this chapter of a drug is around 10–15 years with an average is that pharmaceutical companies can anticipate research and development (R&D) cost of about improved access to software tools to compare the $2.6 billion per drug” as motivating factors driving impact of supply chain alternatives as research the need for better clinical trial optimisation. This is translated into commercial software offerings. chapter provides details of a “perfect information” deterministic mixed-integer linear programming model (MILP) problem including constraints. By Process Analytical Technology using an innovative heuristic modification to the stochastic programming model a five order of Chapter 12, ‘PAT for Pharmaceutical Manufacturing magnitude improvement is reported. Process Involving Solid Dosages Forms’ Chapter 22, ‘Integrated Production Planning contributed by Andrés D. Román-Ospino and and Inventory Management in a Multinational Ravendra Singh (Rutgers, The State University Pharmaceutical Supply Chain’ contributed by of New Jersey, USA), Vanessa Cárdenas and Naresh Susarla and Iftekhar A. Karimi (National Carlos Ortega-Zuñiga (University of Puerto Rico, University of Singapore) presents a MILP model USA), presents near-infrared (NIR) calibration for a complex supply chain and provides a models and chemometrics. For those not skilled in strategy to optimise inventory, resources and process analytical technology (PAT) and analytical production schedules in the supply chain to determination, this chapter is very informative maximise profit. The intent of the model is and provides comparison of various methods for as a tool for decision making for “production analytical data fitting to determine blend uniformity planning and scenario analysis in a multinational for real-time control of continuous pharmaceutical pharmaceutical enterprise”. To mitigate risk processes. Principal component analysis (PCA), associated with the complex, multinational partial least squares (PLS) and multivariate curve network of supply, drug inventories of 180 resolution alternating least squares (MCR-ALS) days are not atypical. However, high levels of are presented as suitable techniques for multiple inventory come at a cost. A change introduced parameter determination where linear regression in the supply network may have impact on or classical least squares methods are not inventories, lead-times and dependencies suitable. Layering of talc and lactose as a specific as impacted by other portions of the supply case study in non-homogeneity is discussed in network. In this chapter the authors describe this chapter. Finally, a process example utilising their approach to this optimisation problem. Unscrambler® X Process Pulse II (Camo Analytics While looking at the authors’ formulation of their AS, Norway) and NIR (Viavi Solutions Inc, USA) case study problem, the value of working with is presented where Unscrambler® X software is fewer strategic suppliers in a vertically integrated utilised to generate and upload a calibration model supply network is evident in that it will minimise generated via methods presented in the chapter. the complexity, delay and cost associated with a In the example the NIR data processing system is

293 © 2019 Johnson Matthey https://doi.org/10.1595/205651319X15680343765046 Johnson Matthey Technol. Rev., 2019, 63, (4) interfaced to a DeltaVTM distributed control system this method is useful for process development. (Emerson Electric Co, USA) to provide real time An interesting adaptation of the ADNC method process control of a tableting process. to a two-stage continuous mixed-suspension Chapter 19, ‘Monitoring and Control of a mixed-product removal (MSMPR) crystalliser Continuous Tumble Mixer’ contributed by Carlos system is an innovation by Yang et al. (1) where Velázquez, Miguel Florían and Leonel Quiñones, heating and cooling is performed on the jacket of a (University of Puerto Rico, USA), presents a case wet mill while the MSMPR crystalliser is maintained study for the mixing of naproxen sodium with at constant temperature. The MSMPR with wet mill excipient using a continuous mixer designed by achieves both form control and FBRM particle count Velázquez. The PAT technology implemented for this control under continuous flow operation. case study employed the use of NIR in conjunction ® with Unscrambler X in a PAT implementation Continuous Drug Product similar to that described in Chapter 12. The closed- Manufacturing (Downstream) loop control dynamics for the experimental mixer are evaluated. A finding from the study is that a Chapter 5, ‘Flowsheet Modeling of a Continuous different control scheme is required for very low Direct Compression Process’ contributed by dosage active pharmaceutical ingredient (API) vs. Seongkyu Yoon, Shaun Galbraith, Bumjoon Cha higher dosages. The authors identified flowrate and Huolong Liu (The University of Massachusetts control of API addition at very low dosage as Lowell, USA), summarises the scope of individual variable due to poor powder flow properties as well unit operation models for continuous powder as limitations of the NIR methods employed in low blending, powder feeding (and potency control), dosage applications. tablet press, feed frame and tablet compaction. Chapter 9, ‘Crystallization Process Monitoring The authors highlight both a population balance and Control Using Process Analytical Technology’ model (PBM) as well as a stirred-tanks-in-series contributed by Levente L. Simon (Syngenta modelling approach to blending. The value of the Crop Protection AG, Switzerland), Elena Simone modelling is in being able to accurately predict (University of Leeds, UK) and Kaoutar Abbou the response of perturbations on key quality Oucherif (Eli Lilly and Co, USA), introduces quality attributes of finished tablets. An accurate system- by design (QbD) and reviews online analytical wide process model allows implementation of both techniques available for crystallisation monitoring feedback and feedforward (predictive) control and control which include attenuated total methodologies which can be developed and tested reflectance Fourier-transform infrared (ATR-FTIR), offline, provided that the underlying unit operation Raman spectroscopy, acoustic spectroscopy, models are accurate. Modelling will facilitate conductivity measurement, refractive index development of continuous direct compression measurement, turbidity measurement, focused (CDC) processes and control schemes for CDC, beam reflectance measurement (FBRM) and where elimination of granulation results in simpler, particle vision and measurement (PVM). less expensive processes. Automated direct nucleation control (ADNC) along Chapter 6, ‘Applications of a Plant-Wide with polymorph determination and control via Dynamic Model of an Integrated Continuous Raman and attenuated total reflectance ultraviolet Pharmaceutical Plant: Design of the Recycle in the (ATR-UV) spectroscopy are presented for batch Case of Multiple Impurities’ submitted by Brahim and continuous crystallisation processes. The Benyahia (Loughborough University, UK), takes the ADNC method involves heating and cooling cycles continuous methodology described in Chapter 5 to control crystal count as measured by FBRM to a step further by integrating the chemical a specified target. In the batch implementation, synthesis steps (upstream) with the formulation after initial nucleation, the system automatically and tabletting steps (downstream) into a single heats to dissolve fines and heating and cooling continuous flowsheet. Of interest is the impact cycles proceed until the crystallisation endpoint of wash-factor (i.e. wash volumes) and recycle (low solution concentration). An advantage of (purge ratio) on the quantity of in-specification this method is that from PAT data collected, the product produced. The recycle of wash streams is metastable zone width (MSZW) and solubility curves not often performed in batch API but in continuous may be constructed. Since solubility curves are processing this recycle provides potential for not required prior to running ADNC experiments, optimisation and cost savings. The evaluation of

294 © 2019 Johnson Matthey https://doi.org/10.1595/205651319X15680343765046 Johnson Matthey Technol. Rev., 2019, 63, (4) wash factors and their limits as potential critical Dheeraj R. Devarampally and Rohit Ramachandran process parameters (CPP) is performed following (Rutgers, The State University of New Jersey, a model-driven QbD approach. In the case study USA), implements a hybrid computational fluid presented, plant dynamics are compared for both dynamics (CFD)/DEM approach to model the full purge and full recycle purge ratios. coupled behaviour of fluid flow and collisions. The authors transfer data from their CFD-DEM model Process Control to a PBM to provide resulting distributions from the granulation process. The DEM-CFD-PBM approach Chapter 11 ‘Process Dynamics and Control of considers residence time in the spray zone, API Manufacturing and Purification Processes’ particle collision frequency, aggregation, attrition, submitted by Maitraye Sen, Ravendra Singh particle temperatures and fluid/particle velocities. and Rohit Ramachandran (Rutgers, The State Residence time in the two zones (spray zone and University of New Jersey, USA) introduces a hybrid drying zone) is impacted by fluid flow within the model predictive control/proportional-integral- zones and the passing of particles between zones derivative (MPC-PID) controller in which a single as modelled via CFD-DEM. Results from the CFD- model based controller coupled with one PID DEM runs are exported to the PBM to investigate temperature controller replaced four separate PID sensitivity to inlet gas temperature and gas flow controllers in a continuous API/pharmaceutical rate. Excellent fit of experimental data from the intermediate process comprised of crystallisation, fluid bed granulator is achieved. filtration, drying and excipient blending operations. Chapter 15, ‘Advanced Control for the Continuous PBM and discrete element method (DEM) methods Dropwise Additive Manufacturing of Pharmaceutical were utilised to model the process while PCA Products’ was contributed by Elçin Içten (Amgen was used to generate a reduced-order model for Inc, USA), Gintaras V. Reklaitis and Zoltan K. Nagy use by the model predictive controller. Various (Purdue University, USA). In this chapter the authors control schemes can be tested and optimised describe a system and control methodology for the entirely in silico allowing investigations of system generation of solid oral dosage forms via a drop on or controller response to transient conditions and demand (DoD) additive manufacturing technique process upsets to be investigated. The authors involving dropwise deposition of API as solvent used MATLAB® (MathWorks Inc, USA) to fit data solution or as solvent/polymer melt (see Figure 2). resulting from process simulations to transfer The DoD system is particularly useful for functions useful for model predictive control. generation of personalised medicine for highly gPROMS® (Process Systems Enterprise Ltd, UK) potent (low dosage) products. The authors present was utilised for PBM calculations and EDEM® (DEM a control scheme based on image analysis of each Solutions Ltd, UK) was used to simulate the mixer drop and investigate various cooling profiles for where a PCA method was fit to six components the substrate (tablets). The authors present a from the DEM model. polynomial chaos expansion (PCE) surrogate model Chapter 13, ‘Model-Based Control System for prediction of crystallisation, total dosage and Design and Evaluation for Continuous Tablet product attributes as a function of drop attributes Manufacturing Processes (via Direct Compaction, and cooling profile. The PCE model provides a QbD via Roller Compaction, via Wet Granulation)’ approach for predictive performance of the tablets’ contributed by one of the editors of the volume, release profile. Ravendra Singh (Rutgers, The State University Chapters 16–18 present case studies for automation of New Jersey, USA), is a review of model-based of continuous pharmaceutical process plants where control for a formulation process which includes process control is the focus. Chapters 17 and 18 blending, granulation, roller compaction, milling have a bit of redundancy with Chapter 13 as all three and tableting. For the case study in Chapter 13, a chapters are based on a series of published articles PBM is employed in gPROMS®, but this time for the by one of the editors of the volume, Ravendra roller compactor. Unlike the example in Chapter 11, Singh. Chapter 18 is focused on formulation without the API crystallisation, isolation and drying steps granulation but with a control scheme to control are not included as API is taken as the input and tablet hardness by controlling tablet press punch blended with excipients prior to granulation. depth and real-time measurement of bulk density Chapter 7, ‘Advanced Multiphase Hybrid Model is used in a feedforward control scheme. Detailed Development of Fluidized Bed Wet Granulation discussion of the control hardware, sensors and Processes’ submitted by Ashutosh Tamrakar, control algorithms for the pilot plant is presented

Pump, staging, Precision P/D pump Online imaging User interface of temperature system automation system controllers Reservoir

XY-staging Substrate

Fig. 2. Dropwise additive manufacturing system. Copyright (2018). Reprinted with permission from Elsevier

in Chapter 17. Process modelling allows complex Technical University of Denmark has contributed system dynamics, interactions and control schemes to the generation of physical property estimation to be investigated and optimised in silico, as methods to address this need. enabling technology in the development of robust The author describes use of template processes continuous drug manufacturing processes. in which processes under development are fit to a template scheme based on conditions known Small Molecule Upstream to work for similar processes. For instance, a reaction step is evaluated against a process Chapter 3, ‘Innovative Process Development template for which simulation and laboratory and Production Concepts for Small-Molecule API models already exist (Figure 3). The sufficiency Manufacturing’, contributed by John M. Woodley of the template is tested and then the process is (Technical University of Denmark), summarises optimised using modelling tools already developed innovations in process systems engineering used for the template process. The author notes that to facilitate process development and optimisation. while the template process approach may only After a viable process model is developed, ‘virtual be adaptable to 80% of process candidates, for experimentation’ may be used to better focus those processes which are adapted, existing benchtop experiments. Alternative routes and knowledge may be leveraged in the development separation schemes can be evaluated if physical of the new process. Process templating is a property data is available. The CAPEC-PROCESS powerful tool in the application of PSE models for Industrial Consortium (now the Process and process integration and intensification and may be Systems Engineering Centre (PROSYS)) at the useful in evaluating process scheme alternatives

Conventional development Template approach

Reaction identified Reaction identified Develop template

Bespoke process development Fit to template process Reject those that do not fit

Slow scale-up based on Rapid scale-up based on bespoke process known template

Fig. 3. Concept of template process to accelerate process development. Copyright (2018). Reprinted with permission from Elsevier

(a) (b)

IBU-BX Et2O, IBU-CPM water, Et2O, Waste brine Waste Waste Water HCl Na SO Waste 30% 2 4 R-103 effluent HCl 30% Solvent Waste (org.) R-103 effluent

Et O, Waste 2 Waste Heptane Waste Waste carbon Waste API (aq.) API (aq.)

Batch mode Continuous mode

Fig. 4. (a) Batch (2); and (b) conceptual continuous (3, 4) separation schemes for ibuprofen (IBU). Copyright (2018). Reprinted with permission from Elsevier

when an API synthetic scheme involves multiple value of a modelling-based approach to selecting transformations. workup or extraction solvents with environmental, Chapter 4, ‘Plantwide Technoeconomic Analysis flammability and regulatory suitability. and Separation Solvent Selection for Continuous Pharmaceutical Manufacturing: Ibuprofen, Conclusions Artemisinin, and Diphenhydramine’ contributed by Samir A. Diab, Hikaru G. Jolliffe and “Process Systems Engineering for Pharmaceutical Dimitrios I. Gerogiorgis (University of Edinburgh, Manufacturing” is a diverse collection of reviews UK), provides an evaluation of continuous separation and case studies, most of which were published steps vs. their batch separation counterparts. The previously. While this book provides an excellent authors noted that for the three continuous API summary of process modelling and computing processes evaluated by others, the evaluations with a view to the increased importance of had focused on performing the chemistry steps robust simulation tools in pharmaceutical process continuously and had not implemented continuous development and manufacturing, more recent separation steps. As shown in Figure 4, the authors present a continuous liquid-liquid extraction (LLE) separation scheme as a replacement for the batch scheme found in the literature for ibuprofen (IBU). In addition, the authors evaluated additional solvents including n-heptane, cyclohexane, methylcyclohexane and isooctane and found many of the solvent choices to be suitable when a continuous LLE process is used vs. a continuous process. Using process modelling, the efficiencies of separation, the quantities of solvent and an economic comparison of alternative solvents are presented. For a continuous IBU extraction using heptane, the authors project capital savings of 58% and operating savings greater than 50% vs. the batch process utilising diethylether. The case studies presented in this chapter are based on process simulations performed by the authors and not on actual laboratory data. While it does not validate a final solvent choice, the use and “Process Systems Engineering for Pharmaceutical conclusions based on simulation data highlight the Manufacturing”

297 © 2019 Johnson Matthey https://doi.org/10.1595/205651319X15680343765046 Johnson Matthey Technol. Rev., 2019, 63, (4) journal publications may provide additional or References more in-depth information on the current state 1. Y. Yang, L. Song, Y. Zhang and Z. K. Nagy, Ind. of specific technologies or algorithms described in Eng. Chem. Res., 2016, 55, (17), 4987 the book. It is also evident that much of the key 2. A. R. Bogdan, S. L. Poe, D. C. Kubis, S. J. Broadwater work in these areas has yet to be done. One topic and D. T. McQuade, Angew. Chem. Int. Ed., 2009, missing from discussion in the book is the advent 48, (45), 8547 of quantum computing and the potential quantum computing presents in solving optimisation 3. H. G. Jolliffe and D. I. Gerogiorgis, Chem. Eng. problems in process systems engineering. I would Res. Des., 2015, 97, 175 look forward to seeing an additional volume added 4. H. G. Jolliffe and D. I. Gerogiorgis,Comput. Chem. to the series as the technology develops. Eng., 2016, 91, 269

The Reviewer

Michael Hamlin joined Johnson Matthey in November 2016 as Assistant Director, Processes Engineering at Johnson Matthey’s Devens Research Centre in Devens, MA, USA where he leads the engineering group working to establish a particle engineering capability in Devens. Prior to joining Johnson Matthey, Mike worked in engineering roles in both fine chemicals and contract pharmaceuticals for more than 20 years. Mike received a BS degree in Chemical Engineering from Bucknell University in Lewisburg, PA, USA.

www.technology.matthey.com

Intensified Liquid-Liquid Extraction Technologies in Small Channels: A Review

Panagiota Angeli*, Eduardo out approaches with appropriate manifolds is Garciadiego Ortega, Dimitrios discussed, based on the use of many channels in Tsaoulidis parallel. The combination of small channels and ThAMeS Multiphase, Department of Chemical centrifugal forces is exploited in counter-current Engineering, University College London, chromatography (CCC) systems where many Torrington Place, London, WC1E 7JE, UK mixing and settling steps are combined within the contactors. Scale up is possible via centrifugal Martyn Earle partition chromatography (CPC) configurations. The QUILL Research Centre, School of Chemistry and Chemical Engineering, The 1. Process Intensification Queen’s University of Belfast, University Road, Belfast, BT9 5AG, UK Process intensification (PI) is a design framework which aims to create smaller, safer and more *Email: [email protected] efficient processes. There have been many reviews on process intensification and attempts to define it since its inception over 20 years ago. Process Solvent extraction is a key separation process intensification approaches often involve the in several industries. Mixer-settlers and agitated reduction in the size of the process units to increase or pulsed columns are mainly used as liquid- heat and mass transfer rates and, in multiphase liquid contactors. However, these units require processes, to manipulate and control the flow large solvent inventories and long residence patterns and increase the interfacial areas. times, while flow fields are often not uniform and The benefits of operating in small scale units mixing is poor. These drawbacks can be overcome stem from the thin fluidic films and the decreased with process intensification approaches where diffusion distances, which increase the heat and small channel extractors are used instead. The mass transfer rates resulting in homogeneous reduced volumes of small units in association concentration and temperature fields. Residence with the increased efficiencies facilitate the use times can be shortened, thus avoiding side of novel, often expensive, but more efficient and reactions, increasing selectivity and reducing environmentally friendly solvents, such as ionic waste. The decrease in length scales also increases liquids. The small throughputs of intensified the importance of surface or interfacial forces over contactors, however, can limit their full usage inertial, viscous and gravitational ones; as a result, in industrial applications, thus robust scale- flow patterns in two-phase systems tend to be up strategies need to be developed. This paper regular. Channel walls with different wettabilities reviews promising intensified technologies can be fabricated to separate two-phase mixtures for liquid-liquid extractions based on small or impose certain patterns in the channels. The channels. In particular, extractions in single large interfacial area-to-volume ratios benefit mass channels and in confined impinging jets are transfer, while the large channel surface-to-volume considered. The increase in throughput via scale- ratios improve heat transfer. Flows are laminar in

299 © 2019 Johnson Matthey https://doi.org/10.1595/205651319X15669171624235 Johnson Matthey Technol. Rev., 2019, 63, (4) many cases and, combined with the regular flow 100 patterns, can be modelled more easily. The small Transitional flow regimes volumes reduce the risks of handling hazardous materials, while accidents are better contained. Drop/dispersed flow Intensification is often linked to continuous flow 10

processing. The homogeneous conditions in –1 n channels facilitate monitoring and allow modularity where the process steps are separated by , ml mi controlling, for example, the temperature or the c 1 Q addition of reactants along the channel. Annular flow

Processes involving two immiscible liquids are Segmented/plug flow widespread industrially and intensification has 0.1 already been shown to benefit emulsifications (1–3) and reactions including hydrogen peroxide oxidations and (trans-)esterifications (4, 5). 0.1 1 10 100 –1 Among two-phase liquid processes, extractions Qd, ml min are commonly used for the separation of materials Fig. 1. Diagram of a typical flow pattern map in in, among others, the pharmaceutical (proteins, 2 mm channels using water (dispersed phase) and kerosene (continuous phase). The x-axis shows the antibiotics in aqueous two-phase systems), energy volumetric flow rate of the dispersed (non-wetting) (uranium in nuclear spent fuel reprocessing; phase (Qd) and the y-axis shows the volumetric carbon dioxide or hydrogen sulfide removal) and flow rate of the continuous (wetting) phase (Qc). mining (copper and precious metals) sectors (6, The segmented flow pattern is surrounded by 7). Industrially, extractions are carried out in transitional flow regimes, where more than one mixer settler units or pulsed columns which suffer flow patterns are found in the channel from inhomogeneous and not well-characterised flow fields and large inventories. Intensified 2. Extractions in Small Channels approaches have already been applied in the extraction of bio-based chemical precursors (8, 9), When two immiscible liquids flow together in small transition metals (10) including platinum group channels, many flow patterns can form, ranging metals (11), lanthanides (12, 13) and actinides from segmented to annular and dispersed flows, (14, 15), acetone in toluene-water systems as can be seen in the example in Figure 1. Parallel (16–18). Because of the improved efficiency and flows, where the two liquids flow in continuous reduced volumes of the small units, the amount of layers next to each other, can also occur, usually solvent required is reduced; this paves the way for by modifying either the wetting properties or the the use of novel, efficient but sometimes expensive geometry of the channel walls. solvents (such as ionic liquids). In addition, The segmented, plug or slug flow pattern has external fields such as centrifugal, magnetic and been extensively studied because it appears for a ultrasonic can easily be applied to improve mixing, wide range of phase flow rates and has been linked separation or reaction rates. The majority of the to high mass transfer rates. In this pattern, the intensified demonstrations are in single channels. dispersed phase moves as drops with size larger For industrial applications it is necessary to than the channel diameter (plugs) separated by increase throughput by increasing the number of slugs of the continuous phase (see Figure 1). channels, which is presently a major challenge. Usually, there is a thin film of the continuous phase In what follows, liquid-liquid extractions in between the plugs and the channel wall. As the intensified small-scale contactors are reviewed. film is usually very thin, axial dispersion is limited. These include extractions in single channels and in In addition, within each phase, circulation patterns confined impinging jets cells as well as approaches are established which improve radial mixing to increase throughput via scale out, where many (see Figure 2). As a result, a plug-flow reactor parallel channels are combined with appropriate configuration establishes with improved radial manifolds. Developments on the use of centrifugal and decreased axial mixing that ensures uniform forces to enhance separations in small channels residence times for the reactants. in CCC systems are discussed. The combination In the small channel contactors, the flow of intensified technologies with novel ionic liquid characteristics and the mass transfer performance solvents is also considered. are closely related. The plug and slug lengths

europium (13) for spent nuclear fuel reprocessing Slug Plug Slug Plug Slug and for analysis in nuclear waste management. Channel sizes between 0.2 mm and 2 mm were used and extraction efficiencies >80% were achieved in <30 s. Pedersen et al. (26) achieved separation Fig. 2. Schematic of the circulation patterns found >90% of titanium-45 for use in positron imaging in segmented (plug) liquid-liquid flows in small in less than 15 s in 0.75 mm perfluoroalkoxy (PFA) channels tubing. The overall volumetric mass transfer coefficient determine not only the interfacial area but also for a solute being transferred from the aqueous to the mixing characteristics within the two phases. the organic phase is given by Equation (i) (15): Apart from the flow rate ratio and the properties of 1  CC−  the two phases, the plug and slug lengths depend klαε= n aq,,eq aq init  ()i Laq ττ−  CC−  significantly on the geometry of the inlet. Plug 21 aq,,eq aq fin  lengths have been reported by many investigators

(19, 20) but there is no single model to predict where εaq is the volume fraction of the aqueous them a priori. phase, Caq,eq is the concentration of the solute in

Interfacial areas can be calculated from the the aqueous phase at equilibrium, Caq,init is the measured plug and slug lengths and shapes concentration of the solute in the aqueous phase of the front and back ends of the plugs. It has at residence time τ1 and Caq,fin is the concentration been found that the specific interfacial area of the solute in the aqueous phase at residence

(interfacial area per unit volume of the contactor) time τ2. depends on the channel diameter, the flow rate High-value precious metals such as platinum ratio, the total velocity and the inlet geometry. and palladium have also been extracted using Interfacial areas ranging from 2760 m2 m–3 to intensified contactors. Yinet al. (11) and Kriel et al. 4800 m2 m–3 in 0.5 mm, 0.75 mm and 1 mm (27, 28) extracted high-value metals (Pt, Pd) internal diameter (ID) channels have been using parallel flow contactors. These metals are reported by Kashid et al. (21), whilst Li and often found in mixtures at low concentrations Angeli (13) measured specific interfacial areas up (for example, from spent automotive catalysts) to 8500 m2 m–3 for smaller channels of 0.2 mm and their extraction may not be economic using ID, using high-speed imaging. In larger channels, conventional devices. In particular, Kriel et al. (27) with a diameter of 4 mm, the specific interfacial demonstrated the extraction, scrub and stripping area decreased to values up to 880 m2 m–3. The processes in flow channels with overall recovery circulation times within the plugs or slugs can be rates over 95%. By modelling the flowsheet of calculated when the velocity fields in the phases spent nuclear fuel reprocessing using intensified are known. Velocity field measurements have extractors for the first time, Bascone et al. (29) been carried out with particle image velocimetry showed important reductions in solvent use and in (PIV) (22) or predicted from computational fluid radiolytic degradation. dynamics (CFD) simulations (23). The results have To increase throughput, large channel sizes should shown that mixing is improved as the velocity be considered that still preserve the benefits of increases and the plug and slug lengths decrease. small-scale operations, such as thin fluid films Segmented flow contactors have been used for and enhanced heat and mass transfer rates. The many liquid-liquid mass transfer and reaction extraction efficiencies and the volumetric mass operations. In the case of fast reactions, the overall transfer coefficients for channels between 0.5 mm rate of the process is primarily controlled by the and 4 mm ID were measured by Tsaoulidis and –1 rate of mass transfer and microreactors have been Angeli (25) and kLα as high as 0.06 s were found, shown to intensify processes. A typical example even at the largest channels. The kLα increased is the transesterification reaction of vegetable oils as the channel diameter decreased. In smaller to produce biodiesel, where yields over 90% can channels, however, the pressure drop increased be achieved under 30 s residence time in 240 µm and the throughput decreased. There is, therefore, hydraulic diameter channels (24). Regarding a trade-off between mass transfer performance, liquid-liquid metal extractions, combined with ionic throughput and energy requirements which needs liquids as the solvent phase, microchannels have to be carefully considered when designing plug been applied to the separation of uranium (25) and flow separators.

To integrate the small channel extractors with the a renewed interest in using confined impinging rest of the process, the separation of the two phases jets reactors (CIJR) for many applications, such at the end of the channel should be considered. as crystallisation (31), nanoparticle synthesis In small channels, wettability and interfacial using liquid precipitation (32), micromixing (33), effects are important and have been successfully extraction (15) and bioreactions (34). The high implemented for the separation of the organic and energy dissipation rates due to collision and aqueous phases. Separators with side channels redirection of the fluidic jets in the impingement or membranes that are preferentially wetted by zone make the contactor particularly suited for the organic or aqueous phases have been tested. applications where rapid mixing of the fluids is Currently, however, there are few commercially necessary. When the two jets are immiscible liquids, available options (for example, Zaiput Flow then the large energy dissipation rates result in the Technologies, USA); for parallel processing with formation of dispersions. A typical configuration of many channels (see Section 4 below) the separator a cylindrical CIJR at 180° nozzle angle is shown in capital costs would scale linearly with the number Figure 3(a). of channels. Alternatively, gravity separators can The mixing and dispersed phase size are affected still be used for systems with high throughput and by a number of geometric characteristics, such as –3 sufficient density difference (>0.1 gcm , (30)). main channel (D) and nozzle (dj) size, main channel In gravity settlers, however, the mass transfer to nozzle size ratio, inter-nozzle distance (Id), nozzle between the phases can continue and diminishes height and impingement angle. The main challenge the benefits of well-controlled conditions of the in developing confined impinging jets contactors small channel. for a particular application is the quantification of the effects of the parameters on the resulting drop 3. Intensified Impinging Jets Cells sizes. There are many studies on impinging jets with miscible liquids, which demonstrate that for An alternative option for increasing throughput improved mixing the two opposing jets should have in small channels is to increase the velocities of similar momentum so that they collide in the middle the two fluidic streams in an impinging jets inlet plane (35). Studies of impinging jets in confined configuration. In recent years, there has been spaces with immiscible liquids are very limited. The

(a) (b) Nozzle height Dispersion in the impingement zone

Liquid 1 Liquid 2

Stainless Impingement steel nozzle zone (dj)

Main channel (c) Drop size distribution inwith (D) impinging jets cell Acrylic block 40

Stainless steel 30 nozzle 20 %

0 0.0 0.1 0.2 0.3 0.4 Drop size, mm Fig. 3. (a) Typical configuration of confined impinging jets contactor; (b) photograph of dispersion in the impingement zone; (c) drop size distribution in the main channel (Photograph from (35) Creative Commons Attribution (CC BY))

302 © 2019 Johnson Matthey https://doi.org/10.1595/205651319X15669171624235 Johnson Matthey Technol. Rev., 2019, 63, (4) drop size has been related to the energy dissipation properties, while at larger ε, above 600 W kg–1, rate, while the uniformity of the dispersions depends the drop sizes converge. Similar results were also on the geometric design of the contactor, the phase found by Siddiqui (2) for aqueous/organic systems ratio and the intensity of mixing in the impingement in impinging jets contactors with the addition of zone (36). The energy dissipation rate (ε) can be emulsifiers, while in less viscous systemsa stronger described as the ratio of the power available due to dependence of drop size on energy dissipation rate kinetic energy change (K) at collision over the mixing was observed. volume of the impingement zone (Viz), according to It has been found that the dispersions formed in Equation (ii): impinging jets have low polydispersity. Tsaoulidis and Angeli (36) reported polydispersity indices K ε = ()ii (PdI) as low as 0.05, for an oil/water system, for ρV iz a wide range of jet velocities from 0.17 m s–1 to where 6.2 m s–1. Interfacial area-to-volume ratios were significantly affected by the velocities of the jets mu2 mu2 K ∝+11 22 ()iii and the values varied between 2000 m2 m–3 and 22 12,000 m2 m–3. Siddiqui (2, 3) also reported   –1 and m1 and m2 are the mass flow rates (kg s ) very narrow drop size distributions in a sunflower of Phase 1 and Phase 2 respectively, u1 and u2 are oil/water emulsification process with surfactants, the average velocities of Phase 1 and Phase 2, for dispersed phase fractions up to 10% and drop respectively, and ρ is the density of the mixture. sizes less than 10 μm. The Sauter mean diameter, given by Equation The few mass transfer studies available have also (iv): revealed high mass transfer coefficients compared

to other contactors as can be seen in Table I. kLα Σnd3 D[,32](= i i iv) can be one to two orders of magnitude higher than Σnd2 i i in conventional contactors and two to three times

(where n is the number of drops and di is the higher than in microchannels. Values are similar diameter of the drop i in the distribution) has been to those of centrifugal contactors, however, the related to the specific energy dissipation rate as specific power input for centrifugal contactors can follows (37), Equation (v): be two to three orders of magnitude higher when compared to a confined impinging jets cell (16). Dk[,32](= ε−a v) The studies revealed that high mass transfer The dependence of the average drop size on the coefficients were obtained at short residence times energy dissipation in the impingement zone is (<4 s), with values up to 1 s–1. Several parameters presented in Figure 4 for two different aqueous/ were found to affect mass transfer, including organic phase systems (15). As can be seen, at low geometric characteristics and flow rate ratio. In energy dissipation values, the drop size depends Figure 5(a), mass transfer rates were calculated on the geometry of the system and the fluid for two different main channel sizes i.e. 2 mm and

3.2 mm. It is shown that kLα depend on channel size

D = 3 mm; dj = 0.5 mm at short residence times but are independent of the Aqueous-organic system 0.50 D = 3 mm; dj = 0.25 mm γ = 32 mN m–1 channel sizes at long times. The 3.2 mm channel 0.45 D = 2 mm; dj = 0.25 mm should then be preferred because it has higher D = 3.2 mm; dj = 0.5 mm 0.40 Aqueous-organic system –1 D = 3.2 mm; dj = 0.25 mm throughput and reduced pressure drop compared 0.35 γ = 11 mN m D = 2 mm; dj = 0.25 mm to the 2 mm channel. The mass transfer coefficient 0.30 0.25 also increases with increasing collision velocities 0.20 of the two jets (shown as the sum of the two D[3,2], mm 0.15 velocities, utot in Figure 5(b)). The velocity of 0.10 the liquid jets will define the position of the point 0.05 of impingement (Figure 6) and will affect the 0 0 500 1000 1500 2000 uniformity of the flow pattern in the main channel ε, W kg–1 as well as the drop size distribution. Impinging jets systems have been used for more Fig. 4. Effect of specific energy dissipation rate (ε) on Sauter mean drop diameter D[3,2] in than four decades now but it is still not possible to confined impinging jets cells (data adapted from determine accurately the effects of the dominant Tsaoulidis et al. (15)) variables including aspect ratio of jet inlets, dead

Table I Overall Mass Transfer Coefficients (kLα) in Intensified and Conventional Contactors –1 Equipment System kLα, s Reference Intensified impinging jets

Confined impinging jets cell TBP/kerosene-U-HNO3 0.15–1.05 (15)

Two impinging jets device H2O-acetone-toluene 0.001–0.19 (18)

Impinging jets extractor Butanol–succinic acid–H2O 0.015–0.2 (16) Intensified small channels

Microchannels (D = 0.5–4 mm) TBP/ionic liquid-U-HNO3 0.05–0.3 (25) Aqueous NaOH-(butyl acetate, iso-amyl Centrifugal extractor 0.2–2 (38) acetate, hexyl acetate) Conventional contactors –5 Mixer-settler NPH-TBP-HNO3 0.5–13.3 (x 10 ) (39) –3 Rotating disc contactor Toluene-H2O-acetone 4–9.5 (x 10 ) (40)

(a) (b) 1.2 0.7 D = 3.2 mm utot 0.6 1.0 D = 2 mm 5.1 m s–1 0.5

0.8 –1 –1 –1 s s 0.4 3.4 m s 0.6 α , α , 0.3 L L k k 0.4 0.2 0.2 0.1 0 0 02468 0 2468 Residence time, s Residence time, s

Fig. 5. Overall volumetric mass transfer coefficient,L k α, as a function of residence time: (a) for two different main channel sizes (D = 3.2 mm, dj = 0.25 mm, Id = 3.2 mm; D = 2 mm, dj = 0.25 mm, Id = 2 mm); (b) for different total jet velocities totu (D = 3.2 mm, dj = 0.5 mm, Id = 3.2 mm) (data adapted from Tsaoulidis et al. (15))

K1=K2 Fluid 1 Fluid 2 K1=K2 K1≠K2

K1 K2

K1≠K2 Fluid 1 Fluid 2

K1 K2

Fig. 6. Effect of kinetic energy K( ) ratio of the two jets on the flow pattern in the impingement zone

volume at the mixing section, fluid properties on implemented industrially. These are: (a) risk of the drop size and the mass transfer performance failure by combining novel aspects; (b) scale-up of the contactors. knowledge uncertainty; (c) equipment unreliability; and (d) improved safety, health and environmental risks. The main hurdle faced by single-channel 4. Scale Out of Single Channel contactors is the scale-up uncertainty. Currently, Contactors there are no applications of small-channel Harmsen (41) identified four hurdles that any extractors at large commercial or pre-commercial PI innovation must address before it can be scales reported in the literature.

(a) (a) (b) Distribution section Split-combine Combine-split Mix W in W in out

Mix Main section out Mix O in O in Mix out out Fig. 8. Multiphase flow distribution strategies: Collection section (a) split-combine, where both phases are distributed separately and then brought into (b) contact; (b) combine-split, where the phases are brought together first and then the two-phase flow Distribution section Collection section is split into several channels

(Figure 8). Combine-split designs first bring the Main section two fluids in contact and then distribute the two- phase mixture into as many channels as necessary. Combine-split distributors do not have dead volumes and have been successfully designed by Hoang et Fig. 7. Schematics of: (a) a consecutive manifold; (b) a bifurcation manifold al. (43) at a chip-scale; the design has been tested for up to eight channels but it may be unfeasible to increase further the number of channels. While single small channel flow contactors Split-combine distributors (or double manifolds) and reactors are highly efficient, the scale-up of distribute each of the single-phase fluids the throughput without losing the small-scale independently into as many channels as necessary advantages remains a main challenge. Scale-up can and then bring them in contact. This type of be achieved by increasing the number of channels distributor can, in turn, be either a bifurcation or a operating in parallel (‘scale out’ or ‘number-up’). It consecutive manifold. is not trivial, however, to reproduce accurately the Maldistribution of gas-liquid flows in double flow conditions of a single channel in many parallel manifolds and the effects of manufacturing ones. The challenge is to design a flow distributor tolerances were studied experimentally by within the process-specific maldistribution Al-Rawashdeh et al. (44) for square main channels tolerance of the total flow rate and of the flow rate with 1 mm side. The authors achieved deviations ratio of the two phases for each channel. in the residence time below 20% by controlling Scale out for single-phase processes requires a the pressure drop in the distribution sections. flow distributor that can achieve almost the same Garciadiego Ortega et al. (45) developed a method flow rate and thus residence time, in all channels. to analyse the two-phase flow maldistribution Single-phase flow distributors are commonly and used a resistance network model to simulate encountered in multi-tubular reactors, catalytic the double manifolds. The effect of the number converters and other honeycomb catalysts. of channels on the maldistribution was also The distributors usually take one of two forms, studied and scaling-laws for the design of these bifurcation or consecutive manifolds, as shown distributors were proposed as well as a procedure in Figure 7. The consecutive manifold has a for an effective and economic double manifold small footprint compared to the bifurcation one. design. The first step is to define the single- Approaches based on resistance networks have channel size and flow rates for a particular process been used to design manifolds that reduce flow and define the sensitivity of its performance to flow non-uniformities among the channels (42). maldistribution. This defines the maldistribution In the case of multiphase systems, both the tolerances, which determine the dimensions of the residence time and the flow rate ratio of the two flow distributor. Finally, the pumping requirements phases are critical for the performance of the process are calculated. There is a trade-off between and should be constant among the many channels pumping requirements and maldistribution, with of the manifold. There are two types of two-phase low maldistribution tolerances resulting in high flow distributors: split-combine and combine-split pumping costs.

5. Counter-Current Chromatography promote solute transfer between the phases and using Ionic Liquid Solvent Systems therefore, separation of species with different partition coefficients. A promising intensified separation technology is In the last decade, the use of ionic liquids either high-performance CCC. It is a form of liquid-liquid as solvents or additives in liquid-liquid extractions extraction that achieves separation by repeated has expanded considerably because of their unique partitioning of solutes between two immiscible properties. Ionic liquids are organic salts that are liquid phases, as they interact in a continuous liquid at room temperature. The stability, phase length of coiled tubing under centrifugal and behaviour and greater solvating power of ionic Archimedean forces. The tubing is wrapped liquids, together with the ability to design their around a cylindrical drum (called a bobbin) to structure, can increase both the flexibility and form typically a three-dimensional (3D) helical performance of separations and allow separations configuration with one or several layers. Within that were not previously considered possible. The the CCC column, one of the liquid phases is held combination of the two technologies, ionic liquids stationary by a combination of hydrodynamic and and CCC, therefore represents an exciting approach hydrostatic forces generated as a result of rotating to intensified liquid-liquid separations. However, the column in planetary motion, while the other the use of ionic liquids in CCC is not a trivial task mobile phase is continuously pumped through the due to their relatively high viscosities, which can coil and serves to transport the solutes through introduce significant problems for the majority the system. The J-type CCC is the most commonly of traditional CCC machines that are mostly low used, where the bobbin is mounted on a planetary pressure. To overcome the pressure limitations axis, driven by a central axis so that the column previously encountered using the CCC technique, rotates about its own axis while it revolves around AECS-QuikPrepTM Ltd, UK in collaboration with the central axis at the same velocity in the same the QUILL Research Centre have reported on direction (Figure 9(a)). The double rotation of the design and construction of a modified high the column during its planetary motion produces backpressure CCC instrument (Figure 9(b)). a variable centrifugal force field. This force field The high solvating power of ionic liquids allows creates a unique mixing pattern in which a series of separations to be run at very high sample loadings sequential mixing and settling zones are generated which gives rise to high space-time yields for ionic simultaneously along the length of the column. liquid and CCC separations. The ability to custom These alternating mixing and settling steps are design ionic liquids allows a greater range of mobile essential to the chromatographic process as they phases to be employed and enables separations

(a) (b) Multilayer coil Settling zone on Planetary outer part of Mixing zone on gear the coil inner part of Planetary axis the coil of rotation

Sun axis of rotation

Stationary sun gear Axis of rotation

Flying lead pipe to head and tail of the coil

Fig. 9. (a) Schematics of the operation of a J-type countercurrent chromatographic column showing the coil layout and motion from as viewed from the front (left) and from the side (right); (b) The inside view of the chromatographic coil in the AECS IL-Prep instrument

306 © 2019 Johnson Matthey https://doi.org/10.1595/205651319X15669171624235 Johnson Matthey Technol. Rev., 2019, 63, (4) with pH neutral water as the mobile phase, immiscible microemulsion phase, which contains where previously toxic organic solvents (such as 75 mol% water (Figure 10). The aqueous phase acetonitrile), concentrated salt solutions (such as is composed of >99% water, which allows water to aqueous dipotassium phosphate), polymers (such be used as the mobile phase in CCC separations, as polyethylene glycol) or acids (such as nitric with the microemulsion as the stationary phase. acid) were used. Scale up can be achieved with This greatly simplifies product isolation since the the increased capacity CPC instrument (46). Ionic product does not end up mixed with large quantities liquids have been applied successfully as a major of involatile chromatography solvent constituents. solvent system component for a wide range of Also, this approach does not produce any solvent separations (47–49) including: waste (other than water) making this a very (a) Inorganic metal salt separations (cobalt chloride green and inexpensive separation to run. The full from nickel chloride from copper chloride) and lentinan process takes the freeze dried hot water more recently praseodymium(III) nitrate from extract of shiitake mushrooms (Figure 11(a)) erbium(III) nitrate both with water as the and precipitates lentinan from this crude extract

mobile phase dissolved in [C4mim]Cl, using ethanol. The (b) Separation of saccharides such as glucose from precipitated 80% lentinan (Figure 11(b)) is then sucrose and fructose from sucrose purified with the water-microemulsion solvent (c) The extraction of aromatic compounds from system shown in Figure 10 to give the off-white alkanes (such as cumene from hexane) 95% lentinan shown in Figure 11(c) on the 25 g (d) The separation of fatty acid derivatives. per run scale. Recent industrial uses of CCC and CPC The combination of ionic liquids with CCC has instruments are in the refining of galantamine from been successfully used in the separation of the daffodils (for example, BioExtractions (Wales) Ltd, anticancer drug lentinan at a scale 10–100 times UK) or the red spider lily (52), the purification of the scales of earlier separations (50). Lentinan is cannabinoids and metal ion separations associated found in shiitake mushrooms (Lentinus edodes) with the nuclear industry. and is used as an adjunct to therapy in combination with chemotherapeutic drugs such as fluorouracil 6. Conclusions to modulate the body’s immune system activity. Lentinan naturally exists in water and salt solutions Liquid-liquid extractions are widely used for the but is easily denatured by solvents. This means separation and purification of many compounds. that for the isolation and purification process Small channels (up to 4 mm in diameter) and of lentinan, water based solvent systems are a combination with external fields, such as required. The conventional purification of lentinan normally involves up to 10 steps. An ionic liquid- based aqueous biphasic solvent system (ABSS) was developed using 1-n-butyl-3-methylimidazolium salts [C4mim]Cl / 2.5 M K2[HPO4](aq) (1:1) mixture (51), which allowed lentinan separations on the 1–3 g scale, without denaturing the lentinan. Hexane This CCC process used aqueous [C4mim]Cl as the mobile phase and the lentinan was separated from Microemulsion the [C4mim]Cl solution by the addition of ethanol to the [C4mim]Cl phase. The [C4mim]Cl can be recovered and reused after the lentinan has been Water precipitated. The ethanol can also be recovered by evaporation allowing it to be reused. This leads to a separation process that does not consume solvents or reagents. An improved lentinan process has also Fig. 10. The water-[C12mim][DiIOP]-hexane been developed with a novel ABSS based on triphasic solvent system with water as the bottom microemulsions. Surface active ionic liquids phase and hexane as the top phase. The middle such as 1-dodecyl-3-methylimidazolium di(iso- microemulsion phase is composed of 75 mol% octyl)phosphinate ([C12mim][DiIOP]), when water, 23.5 mol% hexane and 1.5 mol% [C12mim] mixed with water and hexane produce a water [DiIOP]

Acknowledgements (a) (b) (c)

The research work has been supported by Engineering and Physical Sciences Research Council (EPSRC) grants (EP/P034101/1, EP/R019223, EP/ M02699X/1, EP/L018616/1). Eduardo Garciadiego Ortega also acknowledges the support from Consejo Nacional de Ciencia y Tecnología (CONACYT) Mexico and UCL for his studentship. Fig. 11. (a) Crude lentinan (30% pure); (b) lentinan precipitated from [C4mim]Cl with ethanol (80%, pure); (c) pure lentinan from CPC References and microemulsion process (95% pure) 1. A. Belkadi, D. Tarlet, A. Montillet, J. Bellettre and P. Massoli, Int. J. Multiph. Flow, 2015, 72, 11 centrifugal forces, can significantly intensify the 2. S. W. Siddiqui, Colloids Surf. A: Physicochem. process by reducing residence times, improving Eng. Asp., 2014, 443, 8 extraction and extraction efficiencies and reducing 3. S. W. Siddiqui and I. T. Norton, J. Colloid Interface the amount of solvent required. Mass transfer Sci., 2012, 377, (1), 213 coefficients up to 1s–1 have been measured in 4. K. Wang, L. Li, P. Xie and G. Luo, React. Chem. the impinging jet contactors. These characteristics Eng., 2017, 2, (5), 611 have made possible the implementation of novel 5. M. Ghasemi and A. M. Dehkordi, Ind. Eng. Chem. and often expensive solvents such as ionic liquids Res., 2014, 53, (31), 12238 with significant improvements to the separation. 6. H. Eccles, Solvent Extr. Ion Exch., 2000, 18, (4), Droplet-based flows (dispersed or plug flow 633 patterns) in particular have been shown to enhance mass transfer and increase interfacial areas. 7. L. R. de Lemos, I. J. B. Santos, G. D. Rodrigues, L. H. M. da Silva and M. C. H. da Silva, J. Hazard. However, the throughputs are small and scale Mater., 2012, 237–238, 209 out would be required before they can be applied 8. E. C. Sindermann, A. Holbach, A. de Haan and to industry. On the other hand, the fast mass N. Kockmann, Chem. Eng. J., 2016, 283, 251 transfer rates and well-characterised flow patterns render small channels suitable for analysis and for 9. K. K. R. Tetala, J. W. Swarts, B. Chen, A. E. M. Janssen and T. A. van Beek, Lab. Chip, research on new extractants. Impinging jets have 2009, 9, (14), 2085 increased throughputs and can produce dispersions with narrow size distribution and large interfacial 10. T. Vandermeersch, L. Gevers and W. De Malsche, Sep. Purif. Technol., 2016, 168, 32 areas. CCC devices with alternating mixing and settling steps allow separation of species with 11. C.-Y. Yin, A. N. Nikoloski and M. Wang, Miner. different partition coefficients and have been used Eng., 2013, 45, 18 to optimise solvent systems and conditions for 12. E. Kolar, R. P. R. Catthoor, F. H. Kriel, R. Sedev, separations. High throughputs can be achieved S. Middlemas, E. Klier, G. Hatch and C. Priest, with the increased capacity CPC which has simpler Chem. Eng. Sci., 2016, 148, 212 rotor design and fewer moving parts compared to 13. Q. Li and P. Angeli, Chem. Eng. Sci., 2016, 143, CCC (46, 53). 276 At small scales, the contactor geometry 14. C. Mariet, A. Vansteene, M. Losno, J. Pellé, significantly affects the flow and mass transfer J.-P. Jasmin, A. Bruchet and G. Hellé, Micro Nano characteristics. Possibilities are open for novel Eng., 2019, 3, 7 contactor designs that exploit interfacial and 15. D. Tsaoulidis, E. G. Ortega and P. Angeli, Chem. wettability effects to establish desirable flow Eng. J., 2018, 342, 251 patterns and enhance mass transfer. For the 16. J. Saien and V. Moradi, J. Ind. Eng. Chem., 2012, commercial application of the technology in 18, (4), 1293 production, robust scale-out designs for two- 17. J. Saien and S. A. Ojaghi, J. Ind. Eng. Chem., phase systems need to be further developed and 2010, 16, (6), 1001 the sensitivity of their performance against flow 18. J. Saien, S. A. E. Zonouzian and A. M. Dehkordi, maldistribution needs to be tested. Chem. Eng. Sci., 2006, 61, (12), 3942

19. R. Abiev, S. Svetlov and S. Haase, Chem. Eng. R. N. Patil, Chem. Eng. Res. Des., 2008, 86, Technol., 2017, 40, (11), 1985 (3), 233 20. Q. Li and P. Angeli, Chem. Eng. J., 2017, 328, 717 39. V. G. Lade, P. C. Wankhede and V. K. Rathod, 21. M. N. Kashid, Y. M. Harshe and D. W. Agar, Ind. Chem. Eng. Process. Process Intensif., 2015, 95, Eng. Chem. Res., 2007, 46, (25), 8420 72 22. V. Dore, D. Tsaoulidis and P. Angeli, Chem. Eng. 40. M. Torab-Mostaedi and M. Asadollahzadeh, Chem. Sci., 2012, 80, 334 Eng. Res. Des., 2015, 94, 90 23. L. Yang, M. J. Nieves-Remacha and K. F. Jensen, 41. J. Harmsen, Chem. Eng. Process. Process Intensif., Chem. Eng. Sci., 2017, 169, 106 2010, 49, (1), 70 24. A. Tiwari, V. M. Rajesh and S. Yadav, Energy 42. C. Amador, A. Gavriilidis and P. Angeli, Chem. Eng. Sustain. Dev., 2018, 43, 143 J., 2004, 101, (1–3), 379 25. D. Tsaoulidis and P. Angeli, Chem. Eng. J., 2015, 43. D. A. Hoang, C. Haringa, L. M. Portela, 262, 785 M. T. Kreutzer, C. R. Kleijn and V. van Steijn, Chem. Eng. J., 2014, 236, 545 26. K. S. Pedersen, J. Imbrogno, J. Fonslet, M. Lusardi, 44. M. Al-Rawashdeh, F. Yu, T. A. Nijhuis, E. V Rebrov, K. F. Jensen and F. Zhuravlev, React. Chem. Eng., V. Hessel and J. C. Schouten, Chem. Eng. J., 2012, 2018, 3, (6), 898 207–208, 645 27. F. H. Kriel, G. Holzner, R. A. Grant, S. Woollam, 45. E. Garciadiego Ortega, D. Tsaoulidis and P. Angeli, J. Ralston and C. Priest, Chem. Eng. Sci., 2015, Chem. Eng. J., 2018, 351, 589 138, 827 46. D. P. Ward, P. Hewitson, M. Cárdenas-Fernández, 28. F. H. Kriel, C. Binder and C. Priest, Chem. Eng. C. Hamley-Bennett, A. Díaz-Rodríguez, N. Douillet, Technol., 2017, 40, (6), 1184 J. P. Adams, D. J. Leak, S. Ignatova and G. J. Lye, 29. D. Bascone, P. Angeli and E. S. Fraga, Chem. Eng. J. Chromatogr. A, 2017, 1497, 56 Sci., 2019, 203, 201 47. L. Brown, M. J. Earle, M. A. Gîlea, N. V.Plechkova 30. “Handbook of Solvent Extraction”, eds. T. C. Lo, and K. R. Seddon, Top. Curr. Chem., 2017, 375, M. H. I. Baird and C. Hanson, John Wiley and Sons (5), 74 Inc, New York, USA, 1983 48. L. Brown, M. J. Earle, M. A. Gîlea, N. V Plechkova 31. M. Jiang, Y.-E. D. Li, H.-H. Tung and R. D. Braatz, and K. R. Seddon, Aust. J. Chem., 2017, 70, (8), Chem. Eng. Process. Process Intensif., 2015, 97, 923 242 49. M. Müller, M. Englert, M. J. Earle and W. Vetter, 32. R. T. Kügler and M. Kind, Chem. Eng. Process. J. Chromatogr. A, 2017, 1488, 68 Process Intensif., 2016, 101, 25 50. M. Earle and M. Gilea, K Hughes and Co Ltd, 33. K. Krupa, M. I. Nunes, R. J. Santos and ‘Lentinan Extraction Process from Mushrooms J. R. Bourne, Chem. Eng. Sci., 2014, 111, 48 Using Ionic Liquid’, World Patent Appl., 34. M. Dinarvand, M. Sohrabi, S. J. Royaee and 2013/140,185 V. Zeynali, Asia-Pacific J. Chem. Eng., 2017, 12, 51. M. J. Ruiz-Angel, V. Pino, S. Carda-Broch and (4), 631 A. Berthod, J. Chromatogr. A, 2007, 1151, (1–2), 35. G. Tu, W. Li, K. Du and F. Wang, Chem. Eng. Sci., 65 2014, 116, 734 52. C. Sun, W. Duan, X. Wang, Y. Geng, J. Li and 36. D. Tsaoulidis and P. Angeli, Chem. Eng. Sci., 2017, D. Wang, J. Liq. Chromatogr. Relat. Technol., 171, 149 2015, 38, (10), 1031 37. G. Zhou and S. M. Kresta, Chem. Eng. Sci., 1998, 53. R. Örkényi, J. Éles, F. Faigl, P. Vincze, A. Prechl, 53, (11), 2063 Z. Szakács, J. Kóti and I. Greiner, Angew. Chem. 38. B. D. Kadam, J. B. Joshi, S. B. Koganti and Int. Ed., 2017, 56, (30), 8742

The Authors

Panagiota Angeli is a Professor at UCL and leads the ThAMeS Multiphase group. She obtained a Diploma in Chemical Engineering from the National Technical University of Athens, Greece, and a PhD on Multiphase Flows from Imperial College London. She specialises in multiphase flows, particularly those involving two immiscible liquids and their applications to continuous and intensified processing. Her research combines advanced experimental studies with mechanistic modelling and numerical simulations. She co-chairs the Multiphase Flows Special Interest Group of the EPSRC-UK Fluids Network and was awarded a Leverhulme/RAEng Senior Research Fellowship in 2011. Panagiota has published over 175 peer-reviewed journal and conference papers.

Eduardo Garciadiego Ortega is a chemical engineer from Universidad Nacional Autónoma de México (UNAM), Mexico City. In 2015 he obtained an MSc in Materials for Energy and Environment in the Chemistry Department at UCL. He studied various aspects of materials science and the sustainability of technologies involving advanced materials, such as batteries and nuclear fuels. He then joined the ThAMeS Multiphase group in Chemical Engineering at UCL to study for a PhD. His research focuses on intensified multiphase reactors and contactors, and strategies to increase their throughput. He is interested in sustainability, education and science engagement in schools.

Dimitrios Tsaoulidis is a Chemical Engineer and his research interests evolve around clean energy, healthcare and manufacturing and particularly their connection with microscale technologies. He obtained his Diploma in Chemical Engineering from the Aristotle University of Thessaloniki, Greece, and his PhD in Chemical/Nuclear Engineering from University College London. He specialises in advanced multiphase flows at different scales (micro to macro) and their application to process intensification in energy, manufacturing and synthesis. Outcomes of his work have been published in over 40 peer reviewed journal and conference papers, and he received a Springer Thesis award for his PhD Thesis in sustainability.

Martyn John Earle is an Assistant Director at the QUILL Research Centre with extensive expertise in ionic liquid chemistry phase behaviour. His research is in the areas of ionic liquid phase behaviour of two, three and four phase solvent systems and their use in liquid-liquid extraction and ionic liquid-liquid chromatography. He has over 60 papers and 30 patents. He obtained his degree and doctorate at the Loughborough University of Technology, UK, in 1989 and 1992 respectively. After two years working at the Ohio State University, USA, 1992–1995, he has been working at the Queen’s University of Belfast since 1995, and the QUILL research Centre since 1999.

310 © 2019 Johnson Matthey Johnson Matthey Technology Review is Johnson Matthey’s international journal of research exploring science and technology in industrial applications www.technology.matthey.com Editorial team

Manager Dan Carter Editor Sara Coles Editorial Assistant Yasmin Stephens Senior Information OfficerElisabeth Riley

Johnson Matthey Technology Review Johnson Matthey Plc Orchard Road Royston SG8 5HE UK Tel +44 (0)1763 253 000 Email [email protected] www.technology.matthey.com