Ion Irradiation-Induced Coordinatively Unsaturated Zn Sites for Enhanced CO Hydrogenation

Abstract

Defect engineering critically influences metal oxide catalysis, yet controlling coordinatively unsaturated metal sites remains challenging due to their inherent instability under reaction conditions. Here, we demonstrate that high-flux argon ion (Ar⁺) irradiation above recrystallization temperatures generated well-defined coordinatively unsaturated Zn (CUZ) sites on ZnO(101̅0) surfaces that exhibited enhanced stability and activity for CO hydrogenation. Combining low-temperature scanning probe microscopy, ambient pressure X-ray photoelectron spectroscopy, and surface–ligand infrared spectroscopy with density functional theory calculations, we identified <12̅10> step edges exposing CUZ sites as the dominant active sites. These sites facilitate hydrogen-assisted CO dissociation through a mechanism distinct from formate-mediated pathways on stoichiometric ZnO. The ion-irradiation approach effectively addressed instability of Zn species, a major problem in ZnO catalysis, enabling stable performance in syngas conversion when combined with zeolites. Our atomic scale investigation provided spectroscopic fingerprints for active sites on the ZnO catalyst and insights into the structure–activity relationships of ZnO for CO hydrogenation. Our approach for engineering thermally stable defect sites in oxide catalysts provided opportunities for rational catalyst design beyond traditional preparation methods.