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

• Published in: Journal of catalysis 2024-03, Vol.431, p.115401, Article 115401
• Main Authors: Yan, Hao, Zhao, Mingyue, Cao, Yueqiang, Zhou, Xin, Liu, Yibin, Chen, Xiaobo, Feng, Xiang, Duan, Xuezhi, Zaera, Francisco, Zhou, Xinggui, Yang, Chaohe
• Format: Article
• Language: English
• Subjects: adsorption; catalysts; catalytic activity; Crystal facet; glycerol; hydrogen; Interface structure; isopropyl alcohol; Ketone; nanoparticles; oxidation; oxygen; Secondary hydroxyl oxidation; zinc oxide
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2024.115401

Three morphologies of ZnO [spherical (S), rod (R) and disk (D)] were synthesized and tested as supports for Au nanoparticles for the selective oxidation of glycerol, 1,2-propanediol, 1,2-butanediol, and isopropanol at their secondary hydroxyl group to produce the corresponding ketones. The Au-ZnO(001) interface exhibits a strong electron sink effect and abundant oxygen vacancies, greatly promoting the adsorption of O2 and the adsorption and conversion of polyols at their secondary hydroxyl moiety. Moreover, the as-formed Auδ+-OH* site resulting from O2 activation can efficiently extract the hydrogen of the C-H bond of the key RCHO*CH2OH intermediate on the Zn-Ov site of ZnO(001) surfaces. Therefore, the Au/ZnO-D exhibits superior catalytic activity (turnover frequency >500h−1) and ketone selectivity (>80 %) than other catalysts with different ZnO facets exposed. [Display omitted] •Three morphologies of ZnO [spherical (S), rod (R) and disk (D)] were synthesized to support Au nanoparticles.•Au/ZnO-D exhibits superior catalytic activity and ketone selectivity.•Au-ZnO(001) interface exhibits a strong electron sink effect and abundant oxygen vacancies.•Auδ+-OH* site can efficiently extract the hydrogen of the C-H bond of the key RCHO*CH2OH intermediate. 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(101), ZnO(100) and ZnO(001), 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(001) 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-Ov), synergistically enhances the adsorption of O2 and polyols at the secondary hydroxyl position. Moreover, it was determined that the as-formed Auδ+-OH* site resulting from O2 activation can efficiently extract the hydrogen of the C-H bond of the key RCHO*CH2OH intermediate on the Zn-Ov site of ZnO(