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Issue 21, 2001
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Influence of support and promotor on the catalytic activity of Rh/VOx/SiO2 model catalysts

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A comparative study of the catalytic activities of a polycrystalline Rh foil with Rh/SiO2 and Rh/VOx/SiO2 model catalysts was carried out using the CO and CO2 hydrogenation to methane as a test reaction. The model systems consisted of a thin silicon oxide layer, prepared by chemical vapor deposition on a Si(100) substrate, and a nominal load of about one monolayer of rhodium (Rh/SiO2). The influence of the promotor material vanadium oxide on the catalytic activity was studied for a system with two monolayers of vanadium oxide (Rh/VOx/SiO2). The reactions of CO/H2 and CO2/H2 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 VOx-promoted catalyst is more active at equal temperatures than the unpromoted and the activity for methane in CO2/H2 reactions for both catalysts is much higher than in CO/H2 reactions. The activity of the rhodium clusters on SiO2 with a size of 1 to 2 nm was found to be on average 4 times higher for CO/H2 and 27 times higher for CO2/H2 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 VOx oxidation state during CO and CO2 adsorption and reaction.

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Publication details

The article was received on 10 Apr 2001, accepted on 25 Jul 2001 and first published on 05 Oct 2001

Article type: Paper
DOI: 10.1039/B103225A
Phys. Chem. Chem. Phys., 2001,3, 4639-4643

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    Influence of support and promotor on the catalytic activity of Rh/VOx/SiO2 model catalysts

    A. Kohl, C. Linsmeier, E. Taglauer and H. Knözinger, Phys. Chem. Chem. Phys., 2001, 3, 4639
    DOI: 10.1039/B103225A

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