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

4 years ago

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

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

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.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/smll.201701354