Chlorine-Decorated Ceria Nanocubes for Facilitating Low-Temperature Cyclohexane Oxidative Dehydrogenation: Unveiling the Decisive Role of Surface Species and Acid Properties

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 (O2 2–) 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.

Engineering Specific Mo–O Bond Stretching to Activate Lattice Oxygen in V-Doped Bi2MoO6 for Enhanced Oxidative Dehydrogenation of 1-Butene

“…EPR measurement was performed to detect the oxygen vacancy concentration (Figure e). The spectra show that the oxygen vacancy concentration increases with the V content, demonstrating the accumulation of the defect amount. , …”

“…The spectra show that the oxygen vacancy concentration increases with the V content, demonstrating the accumulation of the defect amount. 50,51 3.3. Catalytic Performance and Kinetics Study of V− BMO Catalysts in ODH.…”

Zeolite Catalysts for Green Production of Caprolactam

“…With the aforementioned routes, green processes for the CPL production from cyclohexanone have been formed (Figure ); that is, the cyclohexanone ammoximation and then Beckmann rearrangement, where the titanosilicate (TS-1) and siliceous (S-1) zeolites were employed, ,,− respectively. For cyclohexanone production from the basic products of the petrochemical industry, such as cyclohexane dehydrogenation, − benzene semihydrogenation, − cyclohexene hydration, − and cyclohexanol dehydrogenation − have been used. In these processes, the aluminosilicate zeolite is a crucial catalyst for the cyclohexene hydration. − These facts confirm the crucial role of zeolites in the green synthesis of CPL.…”

CeO2/Ni-MOF with Synergistic Function of Enrichment and Activation: Efficient Reduction of 4-Nitrophenol Pollutant to 4-Aminophenol

“…31,32 In the chemical environment of OVs, Ce sites exhibit a functionality with a Lewis acid, which enables the efficient activation of basic 4-NP molecules. 33,34 Therefore, the integration of MOFs and CeO 2 shows a great potential for synergistically promoting the absorption and activation of 4-NP.…”

“…Li et al fabricated MOF-derived C-HK­(Cu/M), in which the porous support obviously promoted 4-NP diffusion and adsorption . MOFs possess the superiority of adsorption for substrates, but they still suffer from an inferior activity in an electrocatalysis system because of some unsatisfactory factors, involving poor conductivity and insufficient amounts of exposed sites. , According to previous reports, the insertion of a cocatalyst could address the limitation of MOFs. , As a significant cocatalyst, cerium oxide (CeO 2 ) has a nature of flexible reversibility between Ce 3+ and Ce 4+ states, which is assumed to favor the formation of abundant oxygen vacancies (OVs) in the CeO 2 matrix. , In the chemical environment of OVs, Ce sites exhibit a functionality with a Lewis acid, which enables the efficient activation of basic 4-NP molecules. , Therefore, the integration of MOFs and CeO 2 shows a great potential for synergistically promoting the absorption and activation of 4-NP.…”