Identification of Double-Chain Zn8O8 Structure on ZrO2 as a Highly Active Site for CO2 Hydrogenation to Methanol

ZnZrO_x catalysts exhibit excellent performance in the hydrogenation of CO₂ to methanol, yet the structural identification of active sites in the mixed oxide remains elusive. Herein, combining density functional theory calculations, large-scale machine-learning atomic simulations, and microkinetic modeling, we discovered that double-chain Zn₈O₈ structures supported on monoclinic ZrO₂(1̅11) surfaces (Zn₈O₈-ZrO₂) are highly active and stable for methanol synthesis. The double-chain Zn₈O₈ structure, corresponding to 50% ZnO surface coverage and featuring interconnected 8-membered rings, induces a local minimum (0.28 eV per ZnO) in the average ZnO binding energy on ZrO₂(1̅11), indicating the stability of this structure. Unlike the single-atom Zn-doped ZrO₂(1̅11) structure (Zn₁-ZrO₂), possessing only isolated Zn-O-Zr sites, the Zn₈O₈-ZrO₂ structure possesses both Zn-O-Zr (for CO₂ adsorption) and Zn-O-Zn (for H₂ dissociation) sites, enabling synergistic catalysis. Microkinetic simulations reveal an ∼4-fold higher methanol formation rate on Zn₈O₈-ZrO₂ (2.35 s^-1) than on Zn₁-ZrO₂ (0.50 s^-1) at 593 K. Overall, the identified Zn₈O₈-ZrO₂ interface, with its dual functionality for CO₂ and H₂ activation and high methanol productivity, delivers crucial mechanistic insights into the active site over ZnZrO_x catalysts.