DOCSLIB.ORG

Continuous 2-Methyl-3-Butyn-2-Ol Selective Hydrogenation on Pd/Γ-Al2o3 As a Green Pathway of Vitamin a Precursor Synthesis

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Continuous 2-Methyl-3-Butyn-2-Ol Selective Hydrogenation on Pd/Γ-Al2o3 As a Green Pathway of Vitamin a Precursor Synthesis catalysts Article Continuous 2-Methyl-3-butyn-2-ol Selective Hydrogenation on Pd/γ-Al2O3 as a Green Pathway of Vitamin A Precursor Synthesis Antonio J. Fernández-Ropero 1 , Bartosz Zawadzki 1 , Emil Kowalewski 1, Izabela S. Pieta 1 , Mirosław Krawczyk 1 , Krzysztof Matus 2 , Dmytro Lisovytskiy 1 and Anna Sr˛ebowata´ 1,* 1 Institute of Physical Chemistry, Polish Academy of Sciences, ul. Kasprzaka 44/52, 01-224 Warsaw, Poland; [email protected] (A.J.F.-R.); [email protected] (B.Z.); [email protected] (E.K.); [email protected] (I.S.P.); [email protected] (M.K.); [email protected] (D.L.) 2 Materials Research Laboratory, Silesian University of Technology, Konarskiego 18A, 44-100 Gliwice, Poland; [email protected] * Correspondence: [email protected]; Tel.: +48-22-343-3320 Abstract: In this work, the effect of pretreatment conditions (10% H2/Ar flow rate 25 mL/min and ◦ ◦ 400 C, 3 h or 600 C, 17 h) on the catalytic performance of 1 wt.% Pd/γ-Al2O3 has been evaluated for hydrogenation of 2-methyl-3-butyn-2-ol in continuous-flow mode. Two palladium catalysts have been tested under different conditions of pressure and temperature and characterized using ◦ various physicochemical techniques. The catalytic performance of red(400 C)-Pd/γ-Al2O3 and ◦ red(600 C)-Pd/γ-Al2O3 are affected by the coexistence of several related factors like the competition between PdH and PdCx formation during the reaction, structure sensitivity, hydrogen spillover Citation: Fernández-Ropero, A.J.; to the alumina support and presence or absence of Pd–Al species. High-temperature reduction Zawadzki, B.; Kowalewski, E.; Pieta, leads to formation of Pd–Al species in addition to pure Pd. The Pd–Al species which reveal unique I.S.; Krawczyk, M.; Matus, K.; δ− Lisovytskiy, D.; Sr˛ebowata,A.´ electronic properties by decreasing the Pd surface concentration via electron transfer from Pd Continuous 2-Methyl-3-butyn-2-ol to Al, leading to a weaker Pd–Alkyl bonding, additionally assisted by the hydrogen spillover, are Selective Hydrogenation on the sites of improved semi-hydrogenation of 2-methyl-3-butyn-2-ol towards 2-methyl-3-buten-2-ol Pd/γ-Al2O3 as a Green Pathway of (97%)—an important intermediate for vitamin A synthesis. Vitamin A Precursor Synthesis. Catalysts 2021, 11, 501. https:// Keywords: heterogeneous catalysis; flow chemistry; selective hydrogenation; green chemistry doi.org/10.3390/catal11040501 Academic Editors: Kei Manabe and Nicola Della Ca 1. Introduction Many chemical conversions in the pharmaceutical industry involve stoichiometric Received: 29 January 2021 amounts of reagents and, thus, generate large amounts of waste [1]. However, imple- Accepted: 12 April 2021 mentation of catalytic methods (especially in the continuous-flow mode) in this highly Published: 15 April 2021 competitive industry increases the process efficiency, improves energy efficiency and re- cyclability, reduces costs and improves sustainability. The continuous method allows Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in fine-tuning of the contact time between intermediates and the active catalytic phase, which published maps and institutional affil- may result in high selectivity without using additives or a purification step, and turns into iations. a decrease of the E-factor (kg of generated waste/kg of product) [2,3]. In consequence, the pharmaceutical industry’s application of continuous-flow practices is considered one of the most strategic fields of innovation towards greener manufacturing methods, and complies with twelve principles of green chemistry [2,4]. One of the desired products in the pharmaceutical industry is 2-methyl-3-buten-2-ol Copyright: © 2021 by the authors. (MBE) which is obtained by means of partial reduction of 2-methyl-3-butyn-2-ol (MBY) Licensee MDPI, Basel, Switzerland. This article is an open access article (Scheme1). distributed under the terms and MBE is an important intermediate for the industrial synthesis of vitamins A (Scheme S1)[6] conditions of the Creative Commons and E and are present in a large variety of perfumes as aroma compounds [7]. Attribution (CC BY) license (https:// The current manufacturing processes in batch set-ups of this alcohol avoids the com- creativecommons.org/licenses/by/ plete hydrogenation by using, for instance, Lindlar-type catalyst containing Pd (5 wt.%) 4.0/). Catalysts 2021, 11, 501. https://doi.org/10.3390/catal11040501 https://www.mdpi.com/journal/catalysts Catalysts 2021, 11, 501 2 of 19 and Pb (2–3 wt.%) deposited on CaCO3 [8]. However, lead toxicity entails an environmen- tal concern that should not be ignored [9] and the addition of additives to enhance the selectivity results in additional costs due to the necessary separation processes [7]. While it is true that other Pb-free Pd-based catalysts are being used in the synthesis of MBE with Catalysts 2021, 11, x FOR PEER REVIEW 2 of 20 yields of 95–97%, they suffer from high catalyst deactivation due to degradation of the support or sintering of the metal particles [10]. Scheme 1. PathwayScheme 1.ofPathway catalytic of2-methyl-3 catalytic-butyn-2-ol 2-methyl-3-butyn-2-ol hydrogenation hydrogenation [5]. [5]. MBE is an importantHydrogenation intermediate of MBY for hasthe beenindustrial investigated synthesis in of continuous vitamins A flow, (Scheme with a good yield, S1) [6] and E bothand are in gaspresent and in liquid a large conditions variety of [5 ,perfumes11–16]. Most as aroma of these compounds studies have [7]. been carried out The currentusing manufacturing Pd-based catalysts, processes where in batch the metal set-ups particles of this werealcohol supported avoids the on com- a large variety of materials. Yields of 89% and 92% were reached in capillary microreactors using bimetallic plete hydrogenation by using, for instance, Lindlar-type catalyst containing Pd (5 wt.%) Pd25Zn75 [11] and pure Pd nanoparticles [12] both supported on TiO2 and using methanol and Pb (2–3 wt.%) deposited on CaCO3 [8]. However, lead toxicity entails an environmen- as the solvent. Non-negligible values were obtained by Kundra et al., in a 3D printed tal concern that should not be ignored [9] and the addition of additives to enhance the catalytic static mixer. In a solution of 30% isopropanol and 70% water, with colloidal selectivity results in additional costs due to the necessary separation processes [7]. While palladium on titanium silicate as a catalyst [13], 96% conversion and 91% alkene selectivity it is true that other Pb-free Pd-based catalysts are being used in the synthesis of MBE with were achieved at a moderate pressure of 4 bars and a relatively high temperature of 100 yields of 95–97%, they suffer from high catalyst deactivation due to degradation of the ◦C. On the other hand, in the same study, the performance was much lower when using support or sintering of the metal particles [10]. Lindlar catalyst. MBE selectivity over 90% was shown in Al O -coated metallic monolithic Hydrogenation of MBY has been investigated in continuous flow, with2 3 a good yield, reactors featuring hybrid hexadecyl(2-hydroxyethyl)dimethyl ammonium dihydrogen- both in gas and liquid conditions [5,11–16]. Most of these studies have been carried out phosphate HHDMA-modified Pd nanoparticles during a three-phase continuous-flow MBY using Pd-based catalysts, where the metal particles were supported on a large variety of hydrogenation in relatively low pressure and temperature ranges (1–8 bar, 30–90 ◦C) [15]. materials. YieldsPromising of 89% resultsand 92% were were also reached obtained in capillary for the isolated microreactors Pd atoms using confined bimetallic into the six-fold Pd25Zn75 [11] and pure Pd nanoparticles [12] both supported on TiO2 and using methanol cavities of mpg-C3N4, in similar conditions. This single-site Pd catalyst showed higher as the solvent.activity Non-negligible than conventional values were heterogeneous obtained by Kundra catalysts et andal., in >90% a 3D ofprinted the selectivity cat- toward alytic static mixer.MBE [In16 ].a solution of 30% isopropanol and 70% water, with colloidal palla- dium on titanium silicate as a catalyst [13], 96% conversion and 91% alkene selectivity Furthermore, Pd supported on MgO, CeO2, ZnO and Al2O3 and bimetallic Pd–Zn were achieved at a moderate pressure of 4 bars and a relatively high temperature of 100 supported on Al2O3 were investigated for gas-phase 2-methyl-3-butyn-2-ol hydrogena- °C. On the other hand, in the same study, the performance was much lower when using tion [5]. Pd/ZnO and Pd–Zn/Al2O3 exhibited improved selectivity (c.a. 90%) as compared Lindlar catalyst.to the MBE other selectivity catalysts. over The 90% enhancement was shown wasin Al explained2O3-coated by metallic the modification monolithic of electronic reactors featuringproperties hybrid of hybrid Pd by electronhexadecyl(2-hydroxyethyl)dimethyl transfer from Pd to Zn and formationammonium of dihy- Pd–Zn alloy that drogenphosphateblocks HHDMA-modified unselective active sites.Pd nanoparticles during a three-phase continuous- flow MBY hydrogenationThe latter in revealsrelatively the low importance pressure ofand metal-support temperature interactionranges (1–8 andbar, the30– pretreatment 90 °C) [15]. Promisingmethod. Higherresults were activity also of obta Pd–Zn/Alined for2 theO3 asisolated compared Pd atoms to Pd/ZnO confined while into maintaining the six-fold cavitieshigh selectivity of mpg-C3 toN4 MBE, in similar was explained conditions. by This the single-site effect of hydrogen Pd catalyst spillover showed in the case of higher activityalumina than conventional supported catalyst heterogeneous [5]. Moreover, catalysts Pd/Al and2 O>90%3 catalytic of the performanceselectivity to- for the alkane ward MBE [16].isomerization strongly depends on the pretreatment conditions [17–20]. To the best of our Furthermore,knowledge, Pd supported although on Pd/Al MgO,2O 3CeOhas2, been ZnO commonly and Al2O studied3 and bimetallic in the MBY Pd–Zn hydrogenation in supported onflow Al2O mode3 were [ 5investigated,15] and in batch for gas-phase systems [2-methyl-3-butyn-2-ol21], the influence of this hydrogenation phenomenon has not been [5].
Load more

Recommended publications
  • Electronic Structure and Crystal Phase Stability of Palladium Hydrides
    Electronic structure and crystal phase stability of palladium hydrides Abdesalem Houari∗ Theoretical Physics Laboratory, Department of Physics, University of Bejaia, Bejaia, Algeria Samir F. Matar† CNRS, ICMCB, Universit´ede Bordeaux, 33600 Pessac, France Volker Eyert‡ Materials Design SARL, 92120 Montrouge, France (Dated: November 4, 2014) The results of electronic structure calculations for a variety of palladium hydrides are presented. The calculations are based on density functional theory and used different local and semilocal approximations. The thermodynamic stability of all structures as well as the electronic and chemical bonding properties are addressed. For the monohydride, taking into account the zero-point energy is important to identify the octahedral Pd-H arrangement with its larger voids and, hence, softer hydrogen vibrational modes as favorable over the tetrahedral arrangement as found in the zincblende and wurtzite structures. Stabilization of the rocksalt structure is due to strong bonding of the 4d and 1s orbitals, which form a characteristic split-off band separated from the main d-band group. Increased filling of the formerly pure d states of the metal causes strong reduction of the density of states at the Fermi energy, which undermines possible long-range ferromagnetic order otherwise favored by strong magnetovolume effects. For the dihydride, octahedral Pd-H arrangement as realized e.g. in the pyrite structure turns out to be unstable against tetrahedral arrangemnt as found in the fluorite structure. Yet, from both heat of formation and chemical bonding considerations the dihydride turns out to be less favorable than the monohydride. Finally, the vacancy ordered defect phase Pd3H4 follows the general trend of favoring the octahedral arrangement of the rocksalt structure for Pd:H ratios less or equal to one.
    [Show full text]
  • Dehydrogenation by Heterogeneous Catalysts
    Dehydrogenation by Heterogeneous Catalysts Daniel E. Resasco School of Chemical Engineering and Materials Science University of Oklahoma Encyclopedia of Catalysis January, 2000 1. INTRODUCTION Catalytic dehydrogenation of alkanes is an endothermic reaction, which occurs with an increase in the number of moles and can be represented by the expression Alkane ! Olefin + Hydrogen This reaction cannot be carried out thermally because it is highly unfavorable compared to the cracking of the hydrocarbon, since the C-C bond strength (about 246 kJ/mol) is much lower than that of the C-H bond (about 363 kJ/mol). However, in the presence of a suitable catalyst, dehydrogenation can be carried out with minimal C-C bond rupture. The strong C-H bond is a closed-shell σ orbital that can be activated by oxide or metal catalysts. Oxides can activate the C-H bond via hydrogen abstraction because they can form O-H bonds, which can have strengths comparable to that of the C- H bond. By contrast, metals cannot accomplish the hydrogen abstraction because the M- H bonds are much weaker than the C-H bond. However, the sum of the M-H and M-C bond strengths can exceed the C-H bond strength, making the process thermodynamically possible. In this case, the reaction is thought to proceed via a three centered transition state, which can be described as a metal atom inserting into the C-H bond. The C-H bond bridges across the metal atom until it breaks, followed by the formation of the corresponding M-H and M-C bonds.1 Therefore, dehydrogenation of alkanes can be carried out on oxides as well as on metal catalysts.
    [Show full text]
  • The Pennsylvania State University
    The Pennsylvania State University The Graduate School Energy and Geo-environmental Engineering ROLES OF ZEOLITE SUPPORT AND NOBLE METAL IN SULFUR-TOLERANT CATALYST FOR LOW TEMPERATURE HYDROGENATION OF AROMATICS A Dissertation in Energy and Geo-environmental Engineering by Hyun Jae Kim 2011 Hyun Jae Kim Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy August 2011 The dissertation of Hyun Jae Kim was reviewed and approved* by the following: Chunshan Song Distinguished Professor of Fuel Science and Professor of Chemical Engineering Dissertation Advisor Chair of Committee Yaw D. Yeboah Professor of Energy and Mineral Engineering Department Head of Energy and Mineral Engineering Yongsheng Chen Assistant Professor of Energy and Mineral Engineering Adri van Duin Associate Professor of Mechanical Engineering *Signatures are on file in the Graduate School iii ABSTRACT This dissertation focuses on fundamental understanding of the roles of supports and noble metals in the sulfur-tolerant catalysts for low-temperature hydrogenation of aromatics in the presence of sulfur. Emphasis was placed on investigating the effect of supports and supported metals for high sulfur tolerance and verifying a catalyst design concept for the sulfur-tolerant noble metal catalyst based on shape selective exclusion of sulfur and hydrogen spillover for low- temperature hydrogenation of aromatics [C.S. Song, Chemtech, 29 (1999) 26-30]. The effect of supports was explored for sulfur tolerance of the supported Pd catalyst on tetralin hydrogenation in the presence of benzothiophene by varying the Pd catalysts on different supports (mordenite, zeolite Y, zeolite A, amorphous silica-alumina). The pore structures and pore sizes were both found to be the important factors in determining the catalytic activity of sulfur-tolerant metal catalyst.
    [Show full text]
  • Hydrogen Spillover Through Matryoshka-Type (Zifs@)Nвˆ'1zifs
    ARTICLE DOI: 10.1038/s41467-018-06269-z OPEN Hydrogen spillover through Matryoshka-type (ZIFs@)n−1ZIFs nanocubes Guowu Zhan 1,2 & Hua Chun Zeng 1,2 Hydrogen spillover phenomenon is well-documented in hydrogenation catalysis but still highly disputed in hydrogen storage. Until now, the existence of hydrogen spillover through metal–organic frameworks (MOFs) remains a topic of ongoing debate and how far the split 1234567890():,; hydrogen atoms diffuse in such materials is unknown. Herein we provide experimental evi- dence of the occurrence of hydrogen spillover in microporous MOFs at elevated tempera- tures, and the penetration depths of atomic hydrogen were measured quantitatively. We have made Matryoshka-type (ZIFs@)n−1ZIFs (where ZIFs = ZIF-8 or ZIF-67) nanocubes, together with Pt nanoparticles loaded on their external surfaces to produce atomic hydrogen. Within the (ZIFs@)n−1ZIFs, the ZIF-8 shell served as a ruler to measure the travelling distance of H atoms while the ZIF-67 core as a terminator of H atoms. In addition to the hydrogenolysis at normal pressure, CO2 hydrogenation can also trace the migration of H atoms over the ZIF-8 at high pressure. 1 Department of Chemical and Biomolecular Engineering, Faculty of Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260, Singapore. 2 Cambridge Centre for Advanced Research in Energy Efficiency in Singapore, 1 Create Way, Singapore 138602, Singapore. Correspondence and requests for materials should be addressed to H.C.Z. (email: [email protected]) NATURE COMMUNICATIONS | (2018) 9:3778 | DOI: 10.1038/s41467-018-06269-z | www.nature.com/naturecommunications 1 ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/s41467-018-06269-z ydrogen spillover is a well-known phenomenon in het- cobalt-containing ZIF-67 framework is susceptible to degradation erogeneous catalysis since the first observation in 1964 on by the exposure H atoms at a much lower temperature (e.g., 180 ° H 1 a supported WO3/Pt system, where migration of C) while ZIF-8 framework remains almost intact (vide infra).
    [Show full text]
  • The Response of Work Function of Thin Metal Films to Interaction with Hydrogen
    Vol. 114 (2008) ACTA PHYSICA POLONICA A Supplement Proceedings of the Professor Stefan Mr¶ozSymposium The Response of Work Function of Thin Metal Films to Interaction with Hydrogen R. Du¶s¤, E. Nowicka and R. Nowakowski Institute of Physical Chemistry, Polish Academy of Sciences Kasprzaka 44/52, 01-224 Warszawa, Poland The aim of this paper is to summarize the results of experiments carried out at our laboratory on the response of the work function of several thin ¯lms of transition metals and rare earth metals to interaction with molecular hydrogen. The main focus concerns the description of surface phenomena accompanying the reaction of hydride formation as a result of the adsor- bate's incorporation into the bulk of the thin ¯lms. Work function changes ¢© caused by adsorption and reaction concern the surface, hence this ex- perimental method is appropriate for solving the aforementioned problem. A di®erentiation is made between the work function changes ¢© due to cre- ation of speci¯c adsorption states characteristic of hydrides, and ¢© arising as a result of surface defects and protrusions induced in the course of the reaction. The topography of thin metal ¯lms and thin hydride ¯lms with defects and protrusions was illustrated by means of atomic force microscopy. For comparison, the paper discusses work function changes caused by H2 in- teraction with thin ¯lms of metals which do not form hydrides (for example platinum), or when this interaction is performed under conditions excluding hydride formation for thermodynamic reasons. Almost complete diminishing of ¢© was observed, in spite of signi¯cant hydrogen uptake on some rare earth metals, caused by formation of the ordered H{Y{H surface phase.
    [Show full text]
  • An X-Ray Study of Palladium Hydrides up to 100 Gpa: Synthesis and Isotopic Effects Bastien Guigue, Grégory Geneste, Brigitte Leridon, Paul Loubeyre
    An x-ray study of palladium hydrides up to 100 GPa: Synthesis and isotopic effects Bastien Guigue, Grégory Geneste, Brigitte Leridon, Paul Loubeyre To cite this version: Bastien Guigue, Grégory Geneste, Brigitte Leridon, Paul Loubeyre. An x-ray study of palladium hydrides up to 100 GPa: Synthesis and isotopic effects. Journal of Applied Physics, American Institute of Physics, 2020, 127 (7), pp.075901. 10.1063/1.5138697. hal-03024503 HAL Id: hal-03024503 https://hal.archives-ouvertes.fr/hal-03024503 Submitted on 11 Dec 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. An x-ray study of palladium hydrides up to 100 GPa: Synthesis and isotopic eects. Bastien Guigue,1, 2 Grégory Geneste,2 Brigitte Leridon,1 and Paul Loubeyre2, a) 1)LPEM, ESPCI Paris, PSL Research University, CNRS, Sorbonne Université, 75005 Paris, France 2)CEA, DAM, DIF, F-91297 Arpajon, France (Dated: 10 December 2020) The stable forms of palladium hydrides up to 100 GPa were investigated using the direct reaction of palladium with hydrogen (deuterium) in a laser-heated diamond anvil cell. The structure and volume of PdH(D)x were measured using synchrotron x-ray diffraction.
    [Show full text]
  • Hydrogen Storage Overview
    HYDROGEN STORAGE (Materials) Arturo Fernandez Madrigal Instituto de Energias Renovables-UNAM [email protected] Questions ¿what is the state of the art on hydrogen as energy storage? ¿Which are the main challenges of involved technologies? Hydrogen Economic Hydrogen and other fuels [Sørensen, 2005]. Propiedad Hidrógeno Metanol Metano Propano Gasolina Unidad Mínima energía de 0.02 ---- 0.29 0.25 0.24 mJ ignición Temperatura de 2045 ---- 1875 ---- 2200 °C flama Temperatura de 585 385 540 510 230-500 °C autoignición Máxima velocidad 3.46 ---- 0.43 0.47 ---- m/s de flama Rango de 4-75 7-36 5-15 2.5-9.3 1.0-7.6 Vol. % flamabildad Rango de 13-65 ---- 6.3-13.5 ---- 1.1-3.3 Vol. % explosividad Coeficiente de 0.61 0.16 0.20 0.10 0.05 10-3 m2/s difusión Energy Content of Comparative Fuels Physical storage of H2 •Compressed •Metal Hydride (“sponge”) •Cryogenically liquified •Carbon nanofibers Chemical storage of hydrogen •Sodium borohydride •Methanol •Ammonia •Alkali metal hydrides New emerging methods •Amminex tablets •Solar Zinc production •DADB (predicted) •Alkali metal hydride slurry Compressed •Volumetrically and Gravimetrically inefficient, but the technology is simple, so by far the most common in small to medium sized applications. •3500, 5000, 10,000 psi variants. Liquid (Cryogenic) •Compressed, chilled, filtered, condensed •Boils at 22K (-251 C). •Slow “waste” evaporation •Gravimetrically and volumetrically efficient •Kept at 1 atm or just slightly over. but very costly to compress 9 Metal Hydrides (sponge) •Sold by “Interpower” in Germany •Filled with “HYDRALLOY” E60/0 (TiFeH2) •Technically a chemical reaction, but acts like a physical storage method •Hydrogen is absorbed like in a sponge.
    [Show full text]
  • University of Southampton Research Repository Eprints Soton
    University of Southampton Research Repository ePrints Soton Copyright © and Moral Rights for this thesis are retained by the author and/or other copyright owners. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the copyright holder/s. The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the copyright holders. When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given e.g. AUTHOR (year of submission) "Full thesis title", University of Southampton, name of the University School or Department, PhD Thesis, pagination http://eprints.soton.ac.uk UNIVERSITY OF SOUTHAMPTON FACULTY OF NATURAL AND ENVIRONMENTAL SCIENCES SCHOOL OF CHEMISTRY Nanostructured Palladium Hydride Microelectrodes: from the Potentiometric Mode in SECM to the Measure of Local pH during Carbonation Mara Serrapede Thesis for the degree of Doctor of Philosophy March 2014 UNIVERSITY OF SOUTHAMPTON ABSTRACT FACULTY OF NATURAL AND ENVIRONMENTAL SCIENCES SCHOOL OF CHEMISTRY Doctor of Philosophy NANOSTRUCTURED PALLADIUM HYDRIDE ELECTRODES: FROM THE POTENTIOMETRIC MODE IN SECM TO THE MEASURE OF LOCAL PH DURING CARBONATION. By Mara Serrapede The detection of local variations of the proton activity is of interest in many fields such as corrosion, sedimentology, biology and electrochemistry. Using nanostructured palladium microelectrodes Imokawa et al. fabricated for the first time a reliable and miniaturized sensor with high accuracy and reproducibility of the potentiometric-pH response.
    [Show full text]
  • Palladium Based Nanomaterials for Enhanced Hydrogen Spillover and Storage
    Materials Today Volume 00, Number 00 September 2015 RESEARCH Review Palladium based nanomaterials for enhanced hydrogen spillover and storage RESEARCH: Suresh K. Konda and Aicheng Chen* Department of Chemistry, Lakehead University, 955 Oliver Road, Thunder Bay, ON P7B 5E1, Canada Hydrogen storage remains one of the most challenging prerequisites to overcome toward the realization of a hydrogen based economy. The use of hydrogen as an energy carrier for fuel cell applications has been limited by the lack of safe and effective hydrogen storage materials. Palladium has high affinity for hydrogen sorption and has been extensively studied, both in the gas phase and under electrochemical conditions. In this review, recent advancements are highlighted and discussed in regard to palladium based nanomaterials for hydrogen storage, as well as the effects of hydrogen spillover on various adsorbents including carbons, metal organic frameworks, covalent organic frameworks, and other nanomaterials. Introduction hydrogen capacities under mild conditions, whereas chemisorp- Hydrogen has the potential to be a principal energy carrier. It has tion can occur under ambient conditions, but utilizes materials attracted significant attention not only because of its high energy that are very expensive. In some cases, the hydrogen sorption density and light weight, but also because of the technological phenomena are irreversible, albeit higher temperatures can facili- problems involved with its storage and release [1,2]. Since hydro- tate the release of the adsorbed hydrogen [11,12]. gen is gaseous at ambient temperature and pressure, its confined storage is impractical. It is clear that the key challenge in develop- Significant roles of Pd in hydrogen storage ing this technology is centered on the viable storage of hydrogen.
    [Show full text]
  • Chapter 9 Hydrogen
    Chapter 9 Hydrogen Diborane, B2 H6• is the simplest member of a large class of compounds, the electron-deficient boron hydrid Like all boron hydrides, it has a positive standard free energy of formation, and so cannot be prepared direct from boron and hydrogen. The bridge B-H bonds are longer and weaker than the tenninal B-H bonds (13: vs. 1.19 A). 89.1 Reactions of hydrogen compounds? (a) Ca(s) + H2Cg) ~ CaH2Cs). This is the reaction of an active s-me: with hydrogen, which is the way that saline metal hydrides are prepared. (b) NH3(g) + BF)(g) ~ H)N-BF)(g). This is the reaction of a Lewis base and a Lewis acid. The product I Lewis acid-base complex. (c) LiOH(s) + H2(g) ~ NR. Although dihydrogen can behave as an oxidant (e.g., with Li to form LiH) or reductant (e.g., with O2 to form H20), it does not behave as a Br0nsted or Lewis acid or base. It does not r with strong bases, like LiOH, or with strong acids. 89.2 A procedure for making Et3MeSn? A possible procedure is as follows: ~ 2Et)SnH + 2Na 2Na+Et3Sn- + H2 Ja'Et3Sn- + CH3Br ~ Et3MeSn + NaBr 9.1 Where does Hydrogen fit in the periodic chart? (a) Hydrogen in group 1? Hydrogen has one vale electron like the group 1 metals and is stable as W, especially in aqueous media. The other group 1 m have one valence electron and are quite stable as ~ cations in solution and in the solid state as simple 1 salts.
    [Show full text]
  • Promotion of Atomic Hydrogen Recombination As an Alternative To
    Promotion of atomic hydrogen recombination as an alternative to electron trapping for the role of metals in the photocatalytic production of H2 Ji Bong Joo, Robert Dillon, Ilkeun Lee, Yadong Yin, Christopher J. Bardeen, and Francisco Zaera1 Department of Chemistry, University of California, Riverside, CA 92521 Edited* by Gabor A. Somorjai, University of California, Berkeley, CA, and approved April 24, 2014 (received for review March 21, 2014) The production of hydrogen from water with semiconductor migrates to the metal and recombines to yield the final molecular photocatalysts can be promoted by adding small amounts of hydrogen product (Fig. 1B). metals to their surfaces. The resulting enhancement in photo- catalytic activity is commonly attributed to a fast transfer of the Results and Discussion excited electrons generated by photon absorption from the The dynamics of photon absorption, electronic excitation, and semiconductor to the metal, a step that prevents deexcitation electron migration was first assessed by using transient absorp- back to the ground electronic state. Here we provide experi- tion and time-resolved fluorescence spectroscopies. Time-resolved mental evidence that suggests an alternative pathway that fluorescence studies have proven to be particularly useful for the does not involve electron transfer to the metal but requires it characterization of photocatalysts, because fluorescence is one of to act as a catalyst for the recombination of the hydrogen the main channels by which the electron–hole pair recombines atoms
    [Show full text]
  • Chapter 3 Hydrogen Spillover in Platinum-Doped Superactivated
    72 Chapter 3 Hydrogen Spillover in Platinum‐Doped Superactivated Carbon 3.1 Overview Effective storage of hydrogen by physisorbent materials has remained limited to cryogenic temperatures since hydrogen binding interactions are not significantly larger ‐1 than the average thermal energy at 298 K: typically 4‐6 kJ (mol H2) . The excess adsorption capacities of known materials are less than 10 mmol g‐1 (2 wt%), and less than 5 mmol g‐1 in all but a few select cases. These figures do not include the added mass of the storage vessel and delivery apparatus, and are far from the targets suggested by the DOE for mobile vehicle applications. The volumetric density enhancement from hydrogen adsorption at room temperature has also not been shown to be significant enough to overcome the penalty in mass of including the sorbent. It was proposed that an enhancement of the hydrogen storage capacities of physisorptive materials can be gained by hydrogen spillover from a metal catalyst onto the adsorbing surface.1‐7 Hydrogen spillover is dissociative chemisorption of dihydrogen onto a metal particle followed by migration of hydrogen atoms onto the surface of the bulk material and subsequent diffusion away from the receptor site,8‐10 as shown in 73 Figure 3.1. Platinum, palladium, and nickel have been studied as metal catalysts for spillover, while materials including zeolites, metal‐organic frameworks (MOFs), and carbons were used as host materials. Figure 3.1. Spillover of the dissociated atoms of a diatomic molecule following chemisorption at the site of a catalyst particle, onto the surface of the support material.
    [Show full text]