Kinetics of CO and H2 oxidation over CuO-CeO2 catalyst in H2 mixtures with CO2 and H2O

The kinetics of CO and H-2 oxidation over a CuO-CeO2 catalyst were simultaneously investigated under reaction conditions of preferential CO oxidation (PROX) in hydrogen-rich mixtures with CO2 and H2O. An integral packed-bed tubular reactor was used to produce kinetic data for power-law kinetics for both CO and H-2 oxidations. The experimental results showed that the CO oxidation rate was essentially independent of H-2 and O-2 concentrations, while the H-2 oxidation rate was practically independent of CO and O-2 concentrations. In the CO oxidation, the reaction orders were 0.91, -0.37 and -0.62 with respect to the partial pressure of CO, CO2 and H2O, respectively. In the H-2 oxidation, the orders were 1.0, -0.48 and -0.69 with respect to the partial pressure Of H-2, CO2 and H2O, respectively. The activation energies of the CO oxidation and the H-2 oxidation were 94.4 and 142 kJ/mol, respectively. The rate expressions of both oxidations were able to predict the performance of the PROX reactor with accuracy. The independence between the CO and the H-2 oxidation suggested different sites for CO and H-2 adsorption on the CuO-CeO2 catalyst. Based on the results, we proposed a new reaction model for the preferential CO oxidation. The model assumes that CO adsorbs selectively on the Cu+ sites; H-2 dissociates and adsorbs on the Cu-0 sites; the adsorbed species migrates to the interface between the copper components and the ceria support, and reacts there with the oxygen supplied by the ceria support; and the oxygen deficiency on the support is replenished by the oxygen in the reaction mixture. (C) 2007 Elsevier B.V. All rights reserved.