Surface properties of Ca, Ti-doped CeO₂ and their influence on the reverse water-gas shift reaction

CeO₂-based materials can be found in a variety of catalytic processes, including the reverse water-gas shift (RWGS) reaction. Nevertheless, the interaction of molecular gases with the surfaces of such materials is still not clear. Recently, some progress was reported on the incorporation of neodymium (Nd) and calcium (Ca) into ceria and their effect on H₂O and CO₂ adsorption. Titanium (Ti), which has a much smaller ionic radius, has the ability to change the interaction landscape, both as a co-dopant to Ca and as a sole dopant in the CeO₂ system. In this study, the interactions of environmental gases (i.e., water vapor and CO₂) on the surface of Ti-doped CeO₂ and Ca,Ti co-doped CeO₂ were investigated. Ti addition to CeO₂ was shown to decrease water vapor uptake by up to 25% all while maintaining similar heats of adsorption. In the case of CO₂ adsorption, Ti addition to CeO₂ had lowered the uptake by more than 50% as well as lowering the heat of adsorption. Co-doping with Ti and Ca showed small decrease in H₂O uptake accompanied with increased heat of adsorption. For CO₂, the changes to the uptake and energetics were small and did not indicate a specific trend. The RWGS catalytic performance showed improvement by the addition of Ti in certain levels. The relationship between the doping, surface properties, gas-surface interactions, and catalytic performance is discussed.