Highly Dispersed ZnO Sites in a ZnO/ZrO ₂ Catalyst Promote Carbon Dioxide‐to‐Methanol Conversion

Abstract

Abstract ZnO/ZrO 2 catalysts have shown better activity in the CO 2 hydrogenation to methanol compared with single component counterparts, but the interaction between ZnO and ZrO 2 is still poorly understood. In particular, the effect of the ZrO 2 support phase (tetragonal vs. monoclinic) was not systematically explored. Here, we have synthesized ZnO/ZrO 2 catalysts supported on tetragonal ZrO 2 (ZnO/ZrO 2 ‐t) and monoclinic ZrO 2 (ZnO/ZrO 2 ‐m), which resulted in the formation of different ZnO x species, consisting of sub‐nanometer ZnO moieties and large‐sized ZnO particles, respectively. ZnO/ZrO 2 ‐t exhibited a higher methanol selectivity (81 vs. 39 %) and methanol yield (1.25 vs. 0.67 mmol g −1 h −1 ) compared with ZnO/ZrO 2 ‐m. The difference in performance was attributed to the redox state and degree of dispersion of Zn, based on spectroscopy and microscopy results. ZnO/ZrO 2 ‐t had a high density of ZnO x ‐ZrO y sites, which favored the formation of active HCOO* species and enhanced the yield and selectivity of methanol along the formate pathway. Such ZnO clusters were further dispersed on ZrO 2 ‐t during catalysis, while larger ZnO particles on ZnO/ZrO 2 ‐m remained stable throughout the reaction. This study shows that the phase of ZrO 2 supports can be used to control the dispersion of ZnO and the catalyst surface chemistry, and lead to enhanced catalytic performance.