Identification of Double-Chain ZnO Structure on ZrO as a Highly Active Site for CO Hydrogenation to Methanol.

ZnZrO catalysts exhibit excellent performance in the hydrogenation of CO 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 ZnO structures supported on monoclinic ZrO(1̅11) surfaces (ZnO-ZrO) are highly active and stable for methanol synthesis. The double-chain ZnO 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 ZrO(1̅11), indicating the stability of this structure. Unlike the single-atom Zn-doped ZrO(1̅11) structure (Zn-ZrO), possessing only isolated Zn-O-Zr sites, the ZnO-ZrO structure possesses both Zn-O-Zr (for CO adsorption) and Zn-O-Zn (for H dissociation) sites, enabling synergistic catalysis. Microkinetic simulations reveal an ∼4-fold higher methanol formation rate on ZnO-ZrO (2.35 s) than on Zn-ZrO (0.50 s) at 593 K. Overall, the identified ZnO-ZrO interface, with its dual functionality for CO and H activation and high methanol productivity, delivers crucial mechanistic insights into the active site over ZnZrO catalysts.