Effect of Dopants on the Adsorption of Carbon Dioxide on Ceria Surfaces

High-surface-area nanosized CeO₂ and M-doped CeO₂ (M=Cu, La, Zr, and Mg) prepared by a surfactant-templated method were tested for CO₂ adsorption. Cu, La, and Zr are doped into the lattice of CeO₂, whereas Mg is dispersed on the CeO₂ surface. The doping of Cu and La into CeO₂ leads to an increase of the CO₂ adsorption capacity, whereas the doping of Zr has little or no effect. The addition of Mg causes a decrease of the CO₂ adsorption capacity at a low Mg content and a gradual increase at a higher content. The CO₂ adsorption capacity follows the sequence Cu-CeO₂>La-CeO₂>Zr-CeO₂≈CeO₂>Mg-CeO₂ at low dopant contents, in line with the relative amount of defect sites in the samples. It is the defect sites on the surface, not in the bulk of CeO₂, modified by the dopants that play the vital role in CO₂ chemisorption. The role of surface oxygen vacancies is further supported by an in situ IR spectroscopic study of the surface chemistry during CO₂ adsorption on the doped CeO₂.