A nanoscale perspective on the effect of acid washing of carbon catalyst supports

Transcription

1 A nanoscale perspective on the effect of acid washing of carbon catalyst supports Emir Bouleghlimat, Philip R. Davies, Robert J. Davies, Jiri Kulahvy, David J. Morgan, School of Chemistry, Cardiff University Dennis Dowden Commemoration 3 rd April

2 Selection of papers by Dowden Title Journal Year Catalysis and the electronic structure of solids Abstracts of American chemical society 1985 Ammonia synthesis and related reactions over iron cobalt and ironnickel alloy catalysts.1. Catalysts reduced at 853 K Applied 1982 Hydrogen spillover on alumina supported Pt Re catalysts JCS Chem Comm 1977 Design of heterogeneous catalysts Chimica & lndustria 1973 Crystal and ligand field models of solid catalysts Catalysis reviews 1971 Principles for selection of catalyst carriers Chemie ingenieur technik 1968 Surface valencies chemisorption and Anales de la real sociedad espanola de fisica y quimica seria b quimica New ideas in Chemistry & industry 1962 The selective hydrogenation of acetylene Transactions of the Faraday society 1958 The significance of patterns of activity in chemisorption and Angewandte chemie 1958 Hydrogen deuterium exchange on the oxides of transition metals Advances in 1957 The testing of heterogeneous catalysts Advances in 1957 Heterogeneous.1. Theoretical basis Chemistry & industry 1949 The heat of adsorption of gases on chromium sesquioxide at low pressures and room temperatures J. Chem. Soc 1939 Heats of adsorption of gases on chromic oxide at low temperatures JACS Dennis Dowden Commemoration 3 rd April

3 Carbon as a Catalyst Support for Gold Hydrochlorination of ethyne Au/C C 2 H 2 + C 2 H 3 Cl Vinyl chloride PVC Aqua regia prepare the most efficient catalysts for the hydrochorination of acetylene by impregnation of HAuCl 4 on carbon.. due to a combination of the oxidising effect of HNO 3 on the carbon support and gold, as well as a nucleation effect of. the two acids.. act synergistically. Aqua Regia Activated Au/C Catalysts for the Hydrochlorination of Acetylene. Marco Conte, Peter Johnston, Graham J. Hutchings et al. Journal of Catalysis 297 (2013) 128 Dennis Dowden Commemoration 3 rd April

4 Preparation of Carbon Supported Metals 1. Washing:, HNO 3, Aqua Regia ( & HNO 3 ) 2. Impregnation HAuCl 4, H 2 PdCl 4 and H 2 PtCl 4 H 2 O,, HNO 3, Aqua Regia 3. Drying 290 o C 200 o C 4. Regeneration H 2 O,, HNO 3, Aqua Regia Dennis Dowden Commemoration 3 rd April

5 Direct synthesis of H 2 O 2 Switching Off Hydrogen Peroxide Hydrogenation in the Direct Synthesis Process. Edwards, Hutchings et al. Science 323 (2009) 1037 Fig. 2. STEM XEDS particle size distributions acid pretreated and non treated catalysts. Table 2. Activity and selectivity of pretreated and untreated carbon supported catalysts Dennis Dowden Commemoration 3 rd April

6 Carbon supports Dennis Dowden Commemoration 3 rd April

7 Nanoscale investigation: can we connect UHV and? HOPG Catalyst Carbon powder Preparation in air Deposition from solution Bench top surface science Graphite crystal Preparation in air Deposition from solution Surface science tools HOPG Surface Science Graphite crystal UHV Vapour deposition Surface science tools Dennis Dowden Commemoration 3 rd April

8 Experimental methods: Sample preparation: 1. Graphite peeled with sticky tape 2. Solutions added by dropper 1 drop ~ 0.2ml 3. Allowed to stand in air 30 seconds 4. Dried in clean helium stream Spectroscopic & Microscopic methods Atomic Force Microscopy X ray photoelectron spectroscopy Scanning Tunnelling Microscopy Dennis Dowden Commemoration 3 rd April

9 Control experiments Clean HOPG surface Deionised water Ultra pure water Dennis Dowden Commemoration 3 rd April

10 The effect of acid treatment on HOPG Clean HOPG surface 0.2 M, 30 min Dennis Dowden Commemoration 3 rd April

11 Low concentration 0.2 M, 30 min 0.1 M, 30 min Surface coverage of features ~ 20% surface area Dennis Dowden Commemoration 3 rd April

12 Comparison of and HNO 3: Effect of acid concentration 0.1 M, 30 min 0.1 M HNO 3, 30 min Dennis Dowden Commemoration 3 rd April

13 Comparison of and HNO 3: Effect of acid concentration II 0.5 M 10 M 0.5 M x10 10 M Dennis Dowden Commemoration 3 rd April

14 Models to account for the features Dennis Dowden Commemoration 3 rd April

15 XPS HNO 3 Clean HNO 3 Clean Dennis Dowden Commemoration 3 rd April

16 XPS HNO 3 HNO 3 No Ca, K, Na Maximum O(a) ~ 4% monolayer Dennis Dowden Commemoration 3 rd April

17 Models to account for the features Dennis Dowden Commemoration 3 rd April

18 STM Clean graphite 0.1 M treated Conclusion The graphite lattice extends over the features 0.1 M treated 0.1 M treated Bubbles not deposits Dennis Dowden Commemoration 3 rd April

19 Local delamination Dennis Dowden Commemoration 3 rd April

20 Gold deposition on acid treated surfaces 6.2 x10-5 M HAuCl 4 Sample preparation: 1. Clean graphite treated with 0.5 M 2. 6x10 5 M HAuCl 4 solution, 1 drop ~ 0.2ml 3. Stand 1 minute, blown dry in clean helium stream Gold doughnuts! Dennis Dowden Commemoration 3 rd April

21 Gold nucleation on acid treated surfaces 0.5M, 6.2 x10-6 M HAuCl 4 Au 0.5M HAuCl 4 Au nucleation on acid induced defects Dennis Dowden Commemoration 3 rd April

22 XPS of Gold on Acid Treated Carbons Au o dominates % Au o /Au + /Au 3+ similar Au nucleation greater on treated surface Dennis Dowden Commemoration 3 rd April

23 Gold deposition on acid treated surfaces 6.2 x10-6 M HAuCl 4 HNO 3 HNO 3 HNO 3 HNO 3 Dennis Dowden Commemoration 3 rd April

24 Au deposition on a treated surface Dennis Dowden Commemoration 3 rd April

25 Gold deposition on acid treated surfaces 6.2 x10-6 M HAuCl 4 HNO 3 HNO 3 HNO 3 HNO 3 Dennis Dowden Commemoration 3 rd April

26 Au deposition with an acid Sample preparation: 1. Clean graphite 2. 6x10 6 M HAuCl 4 solution in 0.5 M or HNO 3, 1 drop ~ 0.2ml 3. Stand 1 minute, blown dry in clean helium stream HNO 3 HNO 3 dosed with Au dosed with Au Dennis Dowden Commemoration 3 rd April

27 Conclusions Mild acid treatment of graphite results in local delamination Au nucleation occurs at defect sites Pretreatment with acid enhances Au nucleation & deposition HNO 3 generates larger gold nanoparticles Au depositon in acid enhances nucleation of smaller particles HNO 3 generates larger particles Dennis Dowden Commemoration 3 rd April

28 Next steps: Aqua Regia Fig. 3 Conversion ( ) after 5 h and Au 3+ ( ) for Au/C catalysts containing different amounts of Au 3+. The catalysts were obtained from impregnation using solutions containing different HNO3 volume fraction in the /HNO3 mixture. Modifications of the Metal and Support During the Deactivation and Regeneration of Au/C Catalysts for the Hydrochlorination of Acetylene. Marco Conte, Catherine J. Davies, Graham J. Hutchings et al. Catalysis Science & Technology 3, (2012) 128 Dennis Dowden Commemoration 3 rd April

29 Funded by EP/I038748/1 Cardiff University CUROP awards Dennis Dowden Commemoration 3 rd April