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Defective Tungsten Oxide Hydrate Nanosheets for Boosting Aerobic Coupling of Amines: Synergistic Catalysis by Oxygen Vacancies and Bronsted Acid Sites
2017-10-27
Small 13(31):UNSP 1701354 Aug 2017

Zhang, Ning; Li, Xiyu; Liu, Yifei; Long, Ran; Li, Mengqiao; Chen, Shuangming; Qi, Zeming; Wang, Chengming; Song, Li; Jiang, Jun; Xiong, Yujie

Abstract:
Adsorption and activation of molecules on a surface holds the key to heterogeneous catalysis toward aerobic oxidative reactions. To achieve high catalytic activities, a catalyst surface should be rationally tailored to interact with both organic substrates and oxygen molecules. Here, a facile bottom-up approach to defective tungsten oxide hydrate (WO3·H2O) nanosheets that contain both surface defects and lattice water is reported. The defective WO3·H2O nanosheets exhibit excellent catalytic activity for aerobic coupling of amines to imines. The investigation indicates that the oxygen vacancies derived from surface defects supply coordinatively unsaturated sites to adsorb and activate oxygen molecules, producing superoxide radicals. More importantly, the Brønsted acid sites from lattice water can contribute to enhancing the adsorption and activation of alkaline amine molecules. The synergistic effect of oxygen vacancies and Brønsted acid sites eventually boosts the catalytic activity, which achieves a kinetic rate constant of 0.455 h−1 and a turnover frequency of 0.85 h−1 at 2 h, with the activation energy reduced to ≈35 kJ mol−1. This work provides a different angle for metal oxide catalyst design by maneuvering subtle structural features, and highlights the importance of synergistic effects to heterogeneous catalysts.

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