Theoretical insights into the generation and reactivity of hydride on the ZnO(10(1)over-bar0) surface

ZnO is an important catalytic material for CO/CO2 hydrogenation. In this work, the pristine ZnO(10 (1) over bar0) and the surfaces with Zn-O dimer vacancies (ZnO(10 (1) over bar0)-(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(10 (1) over bar0)-(Zn-O)DiV only needs to overcome the energy barrier of similar to 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 CO2 hydrogenation by preferentially producing *HCOO intermediates at Zn-O dimer vacancies. These results may help in the design of efficient Zn-based hydrogenation catalysts.