Catalytic Oxidation of Carbon Monoxide over Rh/SiO2. An in Situ Infrared and Kinetic Study

Article abstract of DOI:10.1021/j150649a015

The oxidation of CO on Rh/SiO2 has been studied using an "in situ" infrared cell reactor.The catalytic activity for the rate of CO oxidation was shown to decrease in the sequence Rh(0) > Rh(I) > Rh(I-III).The results of a temperature-programmed-oxidation study show that both linearly adsorbed (2056 cm^-1) and bridge-bonded (1920 cm^-1) CO reacts with O2 at a faster rate than the CO dicarbonyl species (2092, 2033 cm^-1).A higher oxidation state of Rh, presumably Rh(I-III), which gave rise to an adsorbed CO species absorbing at 2103 cm^-1, was found to be relatively inactive.The results of a temperature-programmed-reduction study show that the adsorbed CO dicarbonyl species can be converted into the linearly adsorbed species by the addition of H2 at room temperature.Unlike Ru/SiO2 and Pt/SiO2, reaction rate hysteresis did not occur.However, in an oxygen-rich reactant gas mixture, some modification of the reaction rate did occur as a result of the formation of Rh(I).This led to modest catalytic deactivation.Both heat-transfer effects and diffusion-controlled processes occur at high CO conversions. meaningful kinetic parameters can only be obtained by considering steady-state conversion which are less than 10percent.