The Interaction of CO2 with CeO2 Powder Explored by Correlating Adsorption and Thermal Desorption Analyses

Understanding the interplay between thermodynamics and kinetics is of high importance for the optimization of catalytic reactions involving the adsorption of CO2 on CeO2 (ceria). The present study explores the interaction of CO2 with ceria powder in near-realistic conditions by correlating adsorption and thermal desorption analyses. Activation energies for desorption, E-a, and kinetic parameters (adsorption time constants, tau, and sticking coefficients, s(0)) are determined using a new methodology based on surface science models. The sticking coefficients obtained for CO2 on ceria powder are significantly lower than those observed for CO2 on flat surfaces. CO2 is found to adsorb most rapidly on sites attributed to surface defects. CO2 adsorption is slower on nondefective active sites, leading to the formation of various carbonate species. The desorption analysis indicates that each peak in the CO2-TPD profiles is composed of several subpeaks, resulting from various binding sites for CO2 on the polycrystalline powder. The distribution of the chemisorbed CO2 species between the different sites, the corresponding adsorption energies, and the influence of coverage on those energies are thus determined. In addition, the correlation between adsorption and desorption analyses indicates the influence of heating on the distribution of the chemisorbed species.