Support Effect and Surface Reconstruction in In₂O₃/ m-ZrO₂Catalyzed CO₂Hydrogenation

We investigate the chemical and structural dynamics at the interface of In₂O₃/m-ZrO₂and their consequences on the CO₂hydrogenation reaction (CO₂HR) under reaction conditions. While acting to enrich CO₂, monoclinic zirconia (m-ZrO₂) was also found to serve as a chemical and structural modifier of In₂O₃that directly governs the outcome of the CO₂HR. These modifying effects include the following: (1) Under reaction conditions (above 623 K), partially reduced In₂O₃, i.e., InO_x(0 < x < 1.5), was found to migrate in and out of the subsurface of m-ZrO₂in a semireversible manner, where m-ZrO₂accommodates and stabilizes InO_xby serving as a reservoir. The decreased concentration of surface InO_xunder elevated temperatures coincides with significantly decreased selectivity toward methanol and a sharp increase of the reverse water-gas shift reaction. The reconstruction-induced variation of InO_xconcentration appears to be one of the most important factors contributing to the altered catalytic performance of CO₂HR at different reaction conditions. (2) The strong interactions and reactions between m-ZrO₂and In₂O₃result in the activation of a pool of In-O bonds at the In₂O₃/m-ZrO₂interface to form oxygen vacancies. On the other hand, the high dispersity of In₂O₃nanostructures onto m-ZrO₂prevents their over-reduction under catalytically relevant conditions (up to 673 K), when bare In₂O₃is unavoidably reduced into the metallic phase (In⁰). The relationship between the extent of reduction of In₂O₃and catalytic performance (CO₂conversion, CH₃OH selectivity, or yield of CH₃OH) suggests the presence of an optimum coverage of surface InO_xand oxygen vacancies under reaction conditions. The conventional model that links catalytic performance solely to the coverage of oxygen vacancies appears invalid in the present case. In situ analysis also allows the observation of surface reaction intermediates and their interconversions, including the reduction of CO₃∗ into formate, a precursor for the formation of methanol and CO. The combinative ex situ and in situ study sheds light on the reaction mechanism of the CO₂HR on In₂O₃/m-ZrO₂-based catalysts. Our findings on the large-scale surface reconstructions, support effect, and the reaction mechanism of In₂O₃/m-ZrO₂for CO₂HR may apply to other related metal oxide catalyzed CO₂reduction reactions.