oa South African Journal of Chemistry - Infrared diffuse reflectance study of CO chemisorption on supported rhodium catalysts
A spectroscopic facility which is capable of obtaining DRIFT spectra of adsorbed species at high sensitivity and in situ operating conditions has been established. This technique has been used to study the adsorption of CO on titania- and alumina-supported rhodium catalysts. By using various combinations of the three parameters: reduction temperature, metal loading, and support material, several different species of surface-bonded CO on Rh have been identified. The three main species are: geminal dicarbonyl, linear CO, and bridging CO. As each of these species is associated with a specific Rh site, conclusions concerning the oxidation state and dispersion of the Rh on the surface could be made. It has been found that higher Rh loadings lead to Rh site distributions resembling those found on Rh(III) single crystals, whereas low Rh loadings produce isolated Rh sites preferentially. It was found that the AI2O3 support enables more facile reduction of the Rh precursor material to Rh metal than does the TiO2 support. This is probably due to strong metal-support interaction for Rh-TiO2.
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