Quantitative analyses of oxygen release/storage and CO2 adsorption on ceria and Pt–Rh/ceria

The CO/O2 and CO2 pulse experiments were carried out to acquire useful information about oxygen release/storage and CO2 adsorption on ceria and Pt–Rh/ceria. In the CO pulse experiments at 500 °C, ca. 60% of CO uptake was released as CO2 while the rest of CO uptake was retained as carbon residuals on the surfaces of both samples. The carbon residuals could be removed when O2 was provided. In the CO2 pulse experiments, the adsorption of CO2 was found to relate to the temperatures and the oxidation states of surface cerium. The reduced Ce3+ sites (O vacancies) were responsible for the adsorption of CO2 at the temperature of 500 °C. In addition, the molar ratios of CO2 adsorption to O vacancies (38–39%) were in agreement with the ratios of carbon residuals to CO uptake ( ca. 40%) measured in the CO pulse experiments. Quantitative analyses of oxygen release/storage and CO2 adsorption implied that in the process of oxygen release, carbon residuals were possibly in the form of a carbonate-like species due to the adsorption of CO2 onto the reduced Ce3+ sites.