Catalytic oxidation of carbon monoxide on rhodium/silica: a rapid-response Fourier-transform infrared transient study

The catalytic oxidation of CO has been studied over Rh/SiO/sub 2/ by using a rapid transient response FTIR-mass spectrometric technique. The reactivity of linearly adsorbed CO was found to be considerably greater than that of the dicarbonyl species at both 85 and 200/sup 0/C. The frequency of linearly adsorbed CO was observed to undergo a continuous red shift during the duration of the transient, suggesting the formation of a mixed CO-oxygen adlayer. Induction times required for the formation of gas-phase CO/sub 2/ were found to be nearly 2 orders of magnitude lower than those observed for Pt/SiO/sub 2/ and Pd/SiO/sub 2/. Self-sustained CO-O/sub 2/ oscillations reinforce the greater reactivity of linearly adsorbed CO. H/sub 2/-CO-O/sub 2/ transient studies also suggest the formation of mixed hydrogen-CO adlayers. Hydrogen was observed to react with the dicarbonyl species to form a hydridocarbonyl species. The CO which is displaced by hydrogen reacts rapidly with chemisorbed oxygen to form CO/sub 2/.