Theoretical insights into the generation and reactivity of hydride on the ZnO(101̄0) surface.

ZnO is an important catalytic material for CO/CO hydrogenation. In this work, the pristine ZnO(101̄0) and the surfaces with Zn-O dimer vacancies (ZnO(101̄0)-(Zn-O)) and oxygen vacancies are calculated. We find that the hydride (H) species can be generated heterolytic H dissociation on these surfaces, and that ZnO(101̄0)-(Zn-O) only needs to overcome the energy barrier of ∼0.10 eV. This is because the ZnO system has flexible orbitals for electron storage and release and the low-coordinated Zn atoms at the defect sites can form stable Zn-H covalent bonds with high symmetry. Flexible Zn orbitals also impart the unique feature of activating multiple electrophilic adsorbates simultaneously as excess electrons exist. Moreover, we show that the covalent Zn-H species can regulate the catalytic activity and selectivity for CO hydrogenation by preferentially producing *HCOO intermediates at Zn-O dimer vacancies. These results may help in the design of efficient Zn-based hydrogenation catalysts.