Kinetics of selective CO oxidation in hydrogen-rich streams over Pt-Co-Ce/Al2O3 catalyst

Abstract

Kinetics of low temperature CO oxidation was studied in hydrogen-rich streams witha realistic gas composition using cobalt and ceria promoted Pt/Al2O3 catalyst prepared byincipient-to-wetness impregnation. All plausible elementary reactions constituting the CO oxidation mechanism were determined and five alternative mechanisms based on thoseelementary reactions were constructed. The mechanisms comprise of two single sitemonofunctional paths proceeding on the platinum sites, and three dual site bifunctionalpaths proceeding on the platinum sites and the cobalt-ceria sites. Both the cobalt and the ceria sites are referred to by a single site for simplicity. H2, CO2 and H2O in the feedstream were not included in the reaction mechanisms, as their effect on the reaction rateswere considered to be through the rate parameters, but not through the reactionmechanism. Intrinsic kinetic data were obtained in the initial rate region in a microflow reactor operating in differential mode using eight different sets of CO and O2concentrations each at two space times, i.e. two catalyst loadings, at 110 °C both in thepresence of 25 per cent CO2 and 10 per cent H2O, and in the absence of CO2 and H2O. Theeffect of temperature on the reaction rates was also investigated in the range of 110-130°C. The experimental rate data were used to estimate the kinetic parameters of the modelequations for the mechanisms proposed in this study, and for six alternative mechanismsfrom other studies in the literature. Model discrimination between all the model equationstested was carried out by comparing the calculated data with the experimental data. Five models, i.e. one monofunctional, three bifunctional models and one model without aproposed mechanism, were chosen as the plausible kinetic models among the elevenmodels, as no distinction could be made between them statistically.