Kinetics of low temperature CO oxidation over activated carbon supported Pt-CeOx catalyst

Abstract

Kinetics of low-temperature CO oxidation was studied both in the presence and in the absence of carbon dioxide and hydrogen over air-oxidized activated carbon supported Pt-CeOx catalyst prepared by sequential impregnation of aqueous cerium nitrate and hexachloroplatinic acid solution. Molar reactant concentrations in the feed were varied from 1 to 5 per cent CO and 1 to 2.5 per cent O2 in experiments conducted in the absence of carbon dioxide and hydrogen. The effect of carbon dioxide on CO oxidation mechanism was studied by changing the carbon dioxide concentration between 2-4 per cent. In preferential CO oxidation experiments, the H2 concentrations used were between 5-60 per cent. All kinetic experiments were done at 383 K and atmospheric pressure. The experimental rate data were used to estimate the kinetic parameters of the model equations in the initial rate region for the mechanisms proposed in this study. Kinetic parameters of the reaction were calculated on the basis of simple power-law expression both in the absence and presence of CO2. The reaction orders with respect to CO, O2 and CO2 partial pressures were found to be 0.29, 1.07 and 1.31, respectively, in the absence of H2 at 383 K. Langmuir-Hinshelwood rate expressions were also proposed for lowtemperature CO oxidation in the absence of both CO2 and H2 and in the presence of CO2. The results show that Langmuir-Hinshelwood mechanism gives a good fit to the data in this study. However, no single rate expression can effectively describe the CO oxidation data. The effect of the presence of H2 in the feed on CO oxidation rate was also investigated.