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A comparative study of the catalytic activities of a polycrystalline Rh foil with Rh/SiO(2) and Rh/VO(x)/SiO(2) model catalysts was carried out using the CO and CO(2) hydrogenation to methane as a test reaction. The model systems consisted of a thin silicon oxide layer, prepared by chemical vapour deposition on a Si(100) substrate, and a nominal load of about one mono-layer of rhodium (Rh/SiO(2)). The influence of the promoter material vanadium oxide on the catalytic activity was studied for a system with two mono-layers of vanadium oxide (Rh/VO(x)/SiO(2)). The reactions of CO/H(2) and CO(2)/H(2) over the model catalysts and the Rh foil were performed at atmospheric pressure and elevated temperatures up to 773 K in a flow-reactor system. In both reactions the VO(x) promoted catalyst is more active at equal temperatures than un promoted and the activity for methane in CO(2)/H(2) reactions for both catalyst is much higher than in CO/H(2) reactions. The activity of the rhodium clusters SiO(2) with a size of 1 to 2 nm was found to be on average 4 times higher for CO/H(2) and 27 times higher for CO(2)/H(2) as compared to the Rh foil. The reasons for the difference in activity are discussed with respect to the Rh cluster size, the total CO coverage, the CO dissociation and the VO(x) oxidation state during CO and CO(2) adsorption and reaction.

Additional information

Authors: KOHL A, Max-Planck-Institut fur Plasmaphysic, Garching bei Munchen (DE) and Universitat Munchen, Department Chemie (DE);LINSMEIER C, Max-Planck-Institut fur Plasmaphysic, Garching bei Munchen (DE);TAGLAUER E, Max-Planck-Institut fur Plasmaphysic, Garching bei Munchen (DE);KNÖZINGER H, Universitat Munchen, Department Chemie (DE)
Bibliographic Reference: An article published in: Physical Chemistry Chemical Physics, Vol.3 (2001), pp.4639-4643
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