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

ZnO is an important catalytic material for CO/CO 2 hydrogenation. In this work, the pristine ZnO(101̄0) and the surfaces with Zn-O dimer vacancies (ZnO(101̄0)-(Zn-O) DiV ) and oxygen vacancies are calculated. We find that the hydride (H - ) species can be generated via heterolytic H 2 dissociation on these surfaces, and that ZnO(101̄0)-(Zn-O) DiV 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 3c 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 2 hydrogenation by preferentially producing *HCOO intermediates at Zn-O dimer vacancies. These results may help in the design of efficient Zn-based hydrogenation catalysts.