Highly Dispersed ZnO Sites in a ZnO/ZrO Catalyst Promote Carbon Dioxide-to-Methanol Conversion.

ZnO/ZrO catalysts have shown better activity in the CO hydrogenation to methanol compared with single component counterparts, but the interaction between ZnO and ZrO is still poorly understood. In particular, the effect of the ZrO support phase (tetragonal vs. monoclinic) was not systematically explored. Here, we have synthesized ZnO/ZrO catalysts supported on tetragonal ZrO (ZnO/ZrO-t) and monoclinic ZrO (ZnO/ZrO-m), which resulted in the formation of different ZnO species, consisting of sub-nanometer ZnO moieties and large-sized ZnO particles, respectively. ZnO/ZrO-t exhibited a higher methanol selectivity (81 vs. 39 %) and methanol yield (1.25 vs. 0.67 mmol g h) compared with ZnO/ZrO-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-t had a high density of ZnO-ZrO 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-t during catalysis, while larger ZnO particles on ZnO/ZrO-m remained stable throughout the reaction. This study shows that the phase of ZrO supports can be used to control the dispersion of ZnO and the catalyst surface chemistry, and lead to enhanced catalytic performance.