Roles of the A-Site Ca Dopant in Modifying Surface Properties of a Co-Based Perovskite Catalyst for Selective Oxidation of Cyclohexane

Abstract

Selective catalytic oxidation of cyclohexane into cyclohexanol and cyclohexanone (KA oil) is an important but challenging reaction in the modern chemistry industry, which is characterized by a low KA oil selectivity under high conversion of cyclohexane. To solve the contradictory issue between cyclohexane conversion and KA oil selectivity, A-site-doped Co-based perovskite oxides (La1–xAxCoO3, A = Mg, Ca, Sr, and Ba) as catalysts are used for solvent-free cyclohexane oxidation using molecular oxygen as an oxidant. Among all selected perovskite catalysts, Ca element-modified La0.5Ca0.5CoO3 exhibits the best catalytic performance with a cyclohexane conversion of 7.7% and a KA oil selectivity of 86.5% under optimal reaction conditions. The characterization results show that doping the Ca element into the A-site can effectively regulate the surface properties of LaCoO3 by changing the molar ratio of Co2+/Co3+ ions, creating more oxygen vacancies, and altering the acidity and basicity, which play essential roles in promoting the activation of O2 and the reduction/decomposition of cyclohexyl hydroperoxide (CHHP). This work demonstrates that the catalytic performance of LaCoO3 in the aerobic oxidation of cyclohexane can be further modified by optimizing its A-site compositions, which opens a large space for the design of highly active and selective perovskite-type catalysts for partial oxidation of saturated alkanes.