Mechanistic Investigations on Thermal Hydrogenation of CO₂ to Methanol by Nanostructured CeO₂(100): The Crystal-Plane Effect on Catalytic Reactivity

Abstract

As a key structural parameter, a crystal plane has a distinguished impact on the catalytic performance. Different exposed crystal planes exhibit different reactivities. CeO2 nanostructured powders are usually exposed to three low-index surfaces, which are (111), (110), and (100) surfaces. Because of the unique structure and low stability of the (100) surface, the investigation of the catalytic reaction mechanism on this surface is rarely involved. Here, density functional theory calculations suggest that the CeO2(100) surface exhibits the strongest reactivity for H2 oxidation, attributed to the coordination unsaturation of surface oxygen atoms. For the hydrogenation of CO2 to methanol on the defective CeO2(100) surface, CO2 is prone to adsorb at the oxygen vacancy in a nearly linear configuration and the formate pathway was verified as the dominant one. The bi-H2COO* can easily convert to bi-H2CO* with the vacancy site filled, in which bi-H2CO* serves as the key intermediate in the methanol synthesis. This study aims at providing a better understanding of the catalytic reactivity of the CeO2(100) surface and theoretical insights into the experimental design of thermal CO2-to-methanol conversion.