Mechanism of CO oxidation in excess H2 over CuO/CeO2 catalysts: ESR and TPD studies

Abstract

The oxidation of CO with oxygen over (0.25–6.4)% CuO/CeO2 catalysts in excess H2 is studied. CO conversion increases and the temperature range of the reaction decreases by 100 K as the CuO content is raised. The maximal CO conversion, 98.5%, is achieved on 6.4% CuO/CeO2 at 150°C. At T > 150°C, the CO conversion decreases as a result of the deactivation of part of the active sites because of the dissociative adsorption of hydrogen. CO is efficiently adsorbed on the oxidized catalyst to form CO-Cu+ carbonyls on Cu2O clusters and is oxidized by the oxygen of these clusters, whereas it is neither adsorbed nor oxidized on Cu0 of the reduced catalysts. The activity of the catalysts is recovered after the dissociative adsorption of O2 on Cu0 at T ∼ 150°C. The activation energies of CO, CO2, and H2O desorption are estimated, and the activation energy of CO adsorption yielding CO-Cu+ carbonyls is calculated in the framework of the Langmuir-Hinshelwood model.