Abstract
The correlation between catalytic activity and particle microstructure is examined for hydrocarbon hydrogenolysis and for CO hydrogenation on Rh and Ni supported on SiO 2 using TEM, XPS, reactivity, and H 2 chemisorption. It is found that C 2 H 6 hydrogenolysis is more than 10 2 higher on Rh after oxidation and low temperature reduction at 250°C than after high temperature reduction at 650°C. Catalyst activity can be restored repeatedly by oxidation and low temperature redyction. TEM shows that 100Å single crystal particles are converted into ∼10Å clusters of particles upon oxidation-reduction treatment. XPS shows that oxide particles are completely reduced to metal by 200°C. Propane hydrogenolysis shows a comparable effect of oxidation-reduction on Rh. Ni on SiO 2 exhibits a factor of two reversible decrease in activity for CO hydrogenation upon low temperature reduction. These results show that the properties of low dispersion catalysts can be altered reversibly by oxidation-reduction treatments because of the variation in surface microstructure Droduced on the metastable surfaces created by low temperature reduction of oxide.
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