Unlocking Methanol Synthesis from CO2 and H2 on ZnO/ZrO2 Catalysts: Surface Hydroxyl-Mediated Activation

Abstract

ZnO/ZrO₂ catalysts show promise for CO₂-to-methanol conversion, but the challenge of effective CO₂ and H₂ adsorption and activation hinders efficiency. Herein, we address this issue by systematically adjusting the calcination temperature of m-ZrO₂ and optimizing interfacial interactions, which results in the suppression of terminal and hydrogen-bonded hydroxyl groups that hinder catalytic activity and the enrichment of interfacial and bridging hydroxyl groups that facilitate methanol synthesis. The combination of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), solid-state nuclear magnetic resonance (ssNMR), and density functional theory (DFT) calculations has elucidated that interfacial hydroxyl groups (Zn–OH–Zr) activate CO₂, forming the metastable bicarbonate species, which is essential for the formate pathway of methanol synthesis. Moreover, bridging hydroxyl groups (Zr–OH–Zr) facilitate proton transfer to intermediates, with adjacent ZnO clusters providing additional protons through H₂ dissociation, thereby emphasizing the pivotal function of hydroxyl groups in the methanol production process. Based on these insights, we prepared the 20% ZnO–ZrO₂–OG catalyst with highly dispersed ZnO and abundant bridging hydroxyl groups, achieving an 84% methanol selectivity and an ∼10% CO₂ conversion at high space velocity. This revelation offers valuable insights and guides the way for the development of more efficient catalysts, essential for the advancement of effective carbon management.