Theoretical insights into the generation and reactivity of hydride on the ZnO(100) surface

Abstract

ZnO is an important catalytic material for CO/CO₂ hydrogenation. In this work, the pristine ZnO(100) and the surfaces with Zn–O dimer vacancies (ZnO(100)–(Zn–O)_DiV) and oxygen vacancies are calculated. We find that the hydride (H⁻) species can be generated via heterolytic H₂ dissociation on these surfaces, and that ZnO(100)–(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 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.