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

The oxidation of CO with oxygen over (0.25–6.4)% CuO/CeO 2 catalysts in excess H 2 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/CeO 2 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 Cu 2 O clusters and is oxidized by the oxygen of these clusters, whereas it is neither adsorbed nor oxidized on Cu 0 of the reduced catalysts. The activity of the catalysts is recovered after the dissociative adsorption of O 2 on Cu 0 at T ∼ 150°C. The activation energies of CO, CO 2 , and H 2 O desorption are estimated, and the activation energy of CO adsorption yielding CO-Cu + carbonyls is calculated in the framework of the Langmuir-Hinshelwood model.