Chlorine-Decorated Ceria Nanocubes for Facilitating Low-Temperature Cyclohexane Oxidative Dehydrogenation: Unveiling the Decisive Role of Surface Species and Acid Properties
Jinling Wang, Dang‐guo Cheng, Fengqiu Chen, Xiaoli Zhan
Abstract
Oxidative dehydrogenation (ODH) of cyclohexane over solid metal oxides is an attractive method for the production of cyclohexene, but the difficulty in selectivity control for cyclohexene due to overoxidation is considered to be one big hard nut to crack. The doping of non-metal elements is expected to tune the inherent electronic properties of metal oxides, offering a brand new train of thought for improving the catalytic performance. In this work, an efficient catalyst for cyclohexane ODH was developed by performing postsynthesis treatments of chlorine decoration on well-defined facets of cubic CeO2 nanocrystals with different levels of chloride incorporation. The catalyst obtained can significantly reduce the degrees of cyclohexane overoxidation while slightly promoting the conversion of cyclohexane and achieve 47.1% cyclohexene selectivity at a mild reaction temperature (350 °C). According to the characterization results and theoretical calculation analysis, the contribution of Cl decoration to the O-terminated surface reduces the surface defects, leading to a decrease in electrophilic peroxide species (O22–) and an increase in nucleophilic CeOCl species. The former reduces the complete oxidation of cyclohexane, while the latter is perceived to facilitate the desorption of cyclohexene. The selectivity of cyclohexene is implicated in the surface acidity of the catalyst, and the significantly improved selectivity is derived from more weak acid sites (especially Lewis acid) and fewer strong acid sites on the Cl-decorated ceria. The results verify the great potential of the proposed strategy for application in alkane-selective ODH and provide guidance for the structural optimization of CeO2-based catalysts.