Crystal-facet-dependent, electron sink effect for the enhanced selective oxidation of polyols at the secondary hydroxyl position

In-depth understanding and precise tuning of the crystal facet-dependent catalytic properties of supported catalysts are critical for polyol oxidation. Herein, we report a crystal-facet-dependent study of Au-ZnO interfaces for the selective promotion of the oxidation of various polyols and alcohols (glycerol, 1,2-propanediol, 1,2-butanediol, and isopropanol) at the secondary hydroxyl position to produce the corresponding ketones. Three facets of the zinc oxide support, ZnO(1   0   1), ZnO(1   0   0) and ZnO(0   0   1), associated with nanoparticles of various morphologies (spherical (S), rod (R) and disk (D), respectively), were found to induce different electronic local environments and surface oxygen vacancy contents at the Au-ZnO interface. In particular, the ZnO(0   0   1) facet dominating in the Au/ZnO-D nanoparticles can store more electrons from Au, and such electron sink effect, together with the generation of oxygen vacancies (Zn-O v ), synergistically enhances the adsorption of O 2 and polyols at the secondary hydroxyl position. Moreover, it was determined that the as-formed Au δ+ -OH* site resulting from O 2 activation can efficiently extract the hydrogen of the C-H bond of the key RCHO*CH 2 OH intermediate on the Zn-O v site of ZnO(0   0   1) surfaces. Consequently, the Au/ZnO-D catalyst exhibits unprecedented catalytic activity (turnover frequency >500 h −1 ) and ketone selectivity (>80 %) for glycerol oxidation.