Titania - Supported Transition Metals Sulfides As Photocatalysts for Hydrogen Production from Propan-2-Ol and Methanol C

Titania - Supported transition metals sulfides as photocatalysts for hydrogen production from propan-2-ol and methanol C. Maheu, Eric Puzenat, Christophe Geantet, Luis Cardenas, Pavel Afanasiev To cite this version: C. Maheu, Eric Puzenat, Christophe Geantet, Luis Cardenas, Pavel Afanasiev. Titania - Supported transition metals sulfides as photocatalysts for hydrogen production from propan-2-ol and methanol. International Journal of Hydrogen Energy, Elsevier, 2019, 10.1016/j.ijhydene.2019.05.080. hal- 02935057 HAL Id: hal-02935057 https://hal.archives-ouvertes.fr/hal-02935057 Submitted on 10 Sep 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. Version of Record: https://www.sciencedirect.com/science/article/pii/S0360319919319366 Manuscript_e2d3289b89e0d9fb215783198a4bf081 1 Titania - supported transition metals sulfides as photocatalysts for hydrogen production 2 from propan-2-ol and methanol 3 Clement Maheu*, Eric Puzenat, Christophe Geantet, Luis Cardenas, Pavel Afanasiev* 4 Institut de Recherches sur la Catalyse et l’Environnement de Lyon IRCELYON, UMR 5256, 5 CNRS – Université Lyon 1, 2 av A. Einstein 69626 Villeurbanne Cedex (France); Fax: 33 04 6 7244 5399; Tel: 33 04 72 44 5466; 7 8 9 E-mail: [email protected] 10 [email protected] 11 12 13 Abstract 14 A series of transition metals sulfides deposited on anatase titania (MSx/TiO2) were prepared 15 by precipitation of transition metals salts with thioacetamide in aqueous medium under reflux. 16 The solids were characterized by XRD, XPS, temperature programmed reduction and 17 transmission electron microscopy. The properties of as obtained catalysts were compared for 18 the photocatalytic hydrogen evolution reaction (PHER) in pure methanol and water- 19 isopropanol mixture. The sequences of PHER activity were compared with electrochemical 20 HER and thiophene hydrodesulfurization (HDS) activity of the corresponding sulfides 21 prepared by the same technique. For PHER, in both alcohols the most active photocatalysts 22 contain hydrogenating sulfides of Co and Ru. However the PHER activity does not follow the 23 same trend as electrocatalytic HER and thiophene HDS. Some sulfides, such as HgS or CuS, 24 show poor activity in HDS and electrocatalytic HER, but have the PHER activity comparable 25 with that of the best samples. This difference suggests that the PHER rate is not merely 26 related to the hydrogen activating properties of the co-catalyst, but is enhanced by the transfer 27 of photogenerated electrons from TiO2 towards the sulfide. The ranking of the co-catalysts 28 and the PHER activity depend also on the nature of the alcohol molecule, the overall PHER 29 rates in water-isopropanol mixture being lower than in methanol. 30 31 Keywords: 32 Hydrogen evolution reaction; transition metal sulfides; photocatalysts; titanium oxide 33 1 © 2019 published by Elsevier. This manuscript is made available under the Elsevier user license https://www.elsevier.com/open-access/userlicense/1.0/ 1 1. Introduction 2 Direct conversion of solar energy to chemical energy of hydrogen is considered to be a very 3 promising strategy to mitigate the global warming and to address the problem of alternative 4 energy sources [1,2]. Titanium dioxide TiO 2 is by far the most studied semiconductor for the 5 artificial photosynthesis design [3,4]. Versatile aspects of surface chemistry and bulk 6 properties are important for photocatalytic hydrogen evolution reaction (PHER) using titania, 7 such as surface hydroxylation, type of exposed crystallographic facets [5], or carrier dynamics 8 [6,7]. Intense current research efforts are directed to the design of efficient co-catalysts, 9 present on the surface of TiO 2 in order to enhance the utilization of photogenerated electrons 10 and holes in redox processes involved in the targeted reactions. PHER catalysts are widely 11 studied that include proton reduction by photogenerated electrons and oxidation of organic 12 molecules by photogenerated holes. Association of titania with electron accepting and/or 13 hydrogenating materials, such as noble metals, proves favorable for PHER, one of the best 14 benchmark reference PHER catalyst being Pt/TiO 2. The relationships between the PHER 15 performance and the properties of co-catalysts are widely studied but not fully understood. 16 The improvement of PHER performance in composite catalysts vs. bare titania was attributed 17 to increased charge separation [8], plasmonic effects and increased rate of hydrogen atoms 18 recombination [9]. The impact of a co-catalyst is complex as it might simultaneously 19 influence several thermodynamic or kinetic parameters in the system, including the lifetimes 20 of charge carriers or adsorbed intermediates, which are usually unknown. Beside the efforts of 21 fundamental understanding, great number of research works report on the empirical studies of 22 novel catalysts combining titania and nanoparticles of various co-catalysts, aiming to enhance 23 PHER performance. Much attention has been recently paid to the studies of layered sulfides 24 on titania, particularly to the MoS 2/TiO 2 composites [10], which has been recently reviewed 25 [11]. MoS2 is considered as a cheap alternative to platinum, both for electrochemical HER 26 and PHER. However the specific PHER rates even for the best MoS 2/TiO 2 systems are still 27 lover than for Pt/TiO 2. 28 Other sulfides were also investigated as co-catalysts with TiO 2, though less extensively 29 studied than MoS 2. Tungsten sulfide WS 2 demonstrated PHER performance comparable to 30 MoS 2 [12,13]. Copper sulfide on Aeroxide® P25 titania (0.5-15% wt. CuS) has been prepared 31 hydrothermally using thiourea and showed good activity for methanol reforming, the best 32 catalyst containing 1wt%. CuS [14]. Core-shell composite of NiS and anatase TiO 2 was 2 1 applied for PHER using methanol as an organic substrate and demonstrate promising activity 2 [15]. Cobalt sulfide quantum dots on TiO 2 nanoparticles prepared with a precipitation- 3 deposition method were tested using ethanol as a sacrificial reagent and showed PHER rate 4 exceeding that of the pure TiO 2 by more than 35 times [16]. Cadmium sulfide CdS had been 5 widely studied for PHER, but rather as a semiconductor than as a co-catalyst [17]. Moreover 6 CdS as a semiconductor could be promoted by other TM sulfide and non-sulfide co-catalysts 7 [18,19]. However CdS value for photocatalytic applications is limited because of its 8 solubilisation by photocorrosion, releasing toxic cadmium ions. Composite materials 9 containing bismuth [20], zinc [21] and indium [22] sulfides in combination with TiO 2 showed 10 promising HER activities, as well as bimetallic and trimetallic sulfide materials as CuS/ZnS 11 [23] or ZnS–In 2S3–CuS [24]. Multi-metal titania–based composite materials have been 12 applied as photocatalysts, containing up to four metals chalcogenides such as, for instance, 13 ZnS/CdS-Mn/MoS 2/CdTe/TiO 2 [25]. Comparison of PHER efficiency measured in different 14 laboratories is always difficult because the conditions of the experiments (preparation 15 methods, reactor geometry, light source, oxidized molecule, support...) are strongly varied. 16 Despite a great number of publications on the sulfide-containing photocatalysts, systematic 17 comparison of PHER performance for a series of sulfides on titania prepared by a uniform 18 technique have never been reported. The present work aims to study an extended series of 19 sulfides prepared by means of thioacetamide precipitation technique, in an attempt to provide 20 a qualitative insight into the key properties defining their relative PHER performance. 21 22 2. Experimental 23 2.1 Preparation of catalysts 24 The series of MS x/TiO 2 supported catalysts (M= Ag, Co, Cu, Hg, Mo, Ni, Ru) were prepared 25 with the aqueous deposition method under the conditions similar to those reported by Girel et 26 al . [26] and with the same molar amount of co-catalyst metals (1.3 at % of metal). Typically, TM 27 2.0 g of commercial TiO 2 (CristalACTiV PC500) and 900 mg of thioacetamide were 28 suspended in 100 mL of deionized water. For each synthesis, transition metal precursor salt 29 was added, in an amount containing 350 µmol equivalent of metal. Then, aqueous suspension 30 was refluxed under stirring for 1 h. In the synthesis using ammonium heptamolybdate, 2.0 ml 31 of 2.5 M HCl was added to accelerate precipitation. The solid materials were isolated by 32 centrifugation, washed and dried under N 2. 3 1 Bulk transition metal sulfides were prepared in the same conditions as titania-deposited 2 catalysts, but with a tenfold increase of the precursor amount and without addition of TiO 2. 3 They were used as reference samples for characterization and phase identification of sulfide 4 phases as well as for comparison of the electrochemical HER activity. A reference catalyst 5 containing 1 wt.% Pt on P25 TiO 2 was prepared by impregnation, drying and reduction with 6 H2, as described earlier [27]. 7 8 2.2. Characterizations 9 Temperature-programmed reduction (TPR) was carried out in a quartz reactor. The samples of −1 10 sulfides (0.05–0.1 g) were heated under H 2 flow (50 ml min ) from room temperature to −1 11 1050 °C at a rate 5° min . The H 2S produced in the reduction reaction was detected by a 12 Thermo Prolab quadrupole mass-spectrometer.

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