Modular calcination strategy to construct defect-rich nitrogen-doped Nb2O5 for boosting photocatalytic oxidation of cyclohexane to cyclohexanone in solvent-free conditions
Kuan Wang, Dan Wang, Xiaoyong Zhang, Junlei Wang, Shengli Lv, Zhen‐Hong He, Huan Wang, Weitao Wang, Yang Yang, Zhao‐Tie Liu
Abstract
The partial oxidation of cyclohexane (CHA) with oxygen to cyclohexanone (CHA-one) is one of the most transformation in the chemical industry in view that CHA-one is an irreplaceable raw material in the production of nylon. Herein, hydrogen, vacuum and air modules combined with ammonia module, respectively, were used to construct defect-rich nitrogen-doped Nb 2 O 5 . And, the calcination order and temperature were also considered to establish a modular calcination strategy. A series of modified N-doped Nb 2 O 5 were prepared by the proposed strategy, which were used to catalyze the photo-oxidation of CHA in solvent-free and room temperature conditions. Among these modified N-doped Nb 2 O 5 samples, the HN-Nb 2 O 5 possessed abundant chemical defects of oxygen vacancies and Nb 4+ , and achieved the best photocatalytic performance. Surprisingly, HN-Nb 2 O 5 achieved an amount of 130.35 μmol for CHA-one, which was approximately 2.2 and 26 times that of the pure Nb 2 O 5 and commercial Nb 2 O 5 , respectively, with up to 96.68% selectivity to CHA-one. The outstanding photocatalytic performance of the HN-Nb 2 O 5 can be ascribed to the presence of chemical defect-rich and the NO x species, enhanced light absorption and effective electron-hole separation. DFT calculations explained the promotion of the chemical defects and N doping on Nb 2 O 5 photocatalytic activity in terms of the band electron and band-gap level. The results of EPR analysis and scavenger tests found that e − is the main active species resulted in photocatalytic activity, while O 2 − is the dominant active species for producing CHA-one in the photo-oxidation of CHA. The present work developed an efficient strategy to construct the defect-rich N-doped metal oxide for the improved photocatalytic oxidation of hydrocarbon.