Defective Tungsten Oxide Hydrate Nanosheets for Boosting Aerobic Coupling of Amines: Synergistic Catalysis by Oxygen Vacancies and Brønsted Acid Sites

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 13; no. 31
• Main Authors: Zhang, Ning, Li, Xiyu, Liu, Yifei, Long, Ran, Li, Mengqiao, Chen, Shuangming, Qi, Zeming, Wang, Chengming, Song, Li, Jiang, Jun, Xiong, Yujie
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.08.2017
• Subjects: Activation energy; Adsorption; aerobic coupling; Amines; Brønsted acid sites; Catalysis; Catalysts; Catalytic activity; Coupling (molecular); Imines; Lattice vacancies; Nanosheets; Nanotechnology; Oxygen; oxygen vacancies; Substrates; Surface chemistry; Surface defects; synergistic catalysis; Synergistic effect; tungsten oxide hydrate; Tungsten oxides; Brønsted acid sites; synergistic catalysis; aerobic coupling; oxygen vacancies; tungsten oxide hydrate
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.201701354

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. A facile bottom‐up approach is developed to synthesize defective tungsten oxide hydrate (WO3·H2O) nanosheets. Oxygen vacancies supply coordinatively unsaturated sites to activate O2 molecules, while Brønsted acid sites efficiently adsorb amine molecules via strong hydrogen bonds. This synergistic effect boosts the catalytic activity for aerobic coupling of amines.