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

ZnZrOx 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 ZnZrOx catalysts.