Component-Specific Functions of Cu, Zn, and Zr in Inverse ZnZrO_x/Cu Catalysts for CO₂ Hydrogenation to Methanol

Cu-based ternary catalysts often outperform their binary counterparts in the hydrogenation of CO₂ to methanol. Unraveling the underlying synergistic effects among multiple components remains challenging and requires comprehensive operando characterization. In this study, we present a detailed investigation into the synergistic Cu-Zn-Zr interactions in inverse ZnZrO_x/Cu catalysts, which show strong promise for enhancing the synthesis of methanol from CO₂. In situ X-ray diffraction revealed that ZrO₂ clusters effectively stabilize Cu nanoparticles against sintering during the H₂ reduction. Operando X-ray absorption spectroscopy at the Cu, Zn, and Zr K-edges demonstrated that the enhanced reducibility of Zn and Zr species arises from synergistic Cu-Zn-Zr interactions. Upon H₂ reduction, partially reduced ZrO₂ facilitated CO₂ adsorption and activation. Initially dispersed Zn²⁺ species were partially transformed into the CuZn alloy, which remained stable under reaction conditions. Notably, the CuZn alloy significantly enhanced the hydrogenation of key formate reaction intermediates to methanol. Moreover, Zn incorporation in Cu inhibited methanol decomposition to CO. The combined effects of efficient H₂ activation on highly dispersed metallic Cu, enhanced CO₂ activation by reduced ZrO₂ clusters, and rapid formate hydrogenation facilitated by the CuZn alloy rendered inverse ZnZrO_x/Cu catalysts superior in methanol formation rates as compared to inverse ZnO_x/Cu, ZrO_x/Cu catalysts, a commercial CuZnAl catalyst, and previously reported CuZnZr catalysts.