Effect of Ligands within Vanadium Complex Encapsulated in Y Zeolite Catalysts on Liquid-phase Benzene Oxidation

Vanadium-loaded catalysts used in direct liquid-phase oxidation of benzene have low reusability attributable to the elution of V species into the reaction solution. Herein, V complexes were encapsulated in Y zeolite to prevent the elution of V species in the catalyst used for phenol formation during the direct oxidation of benzene in the liquid phase. V complex catalysts encapsulated in Y zeolite were prepared by mixing Y zeolite loaded with V species using solutions containing different ligands. Using acetic acid as the solvent improved the reusability of the encapsulated V complex catalyst. The catalytic activity of the V complex catalyst for phenol formation was influenced by the ligand effect. Density functional theory (DFT) calculations indicated that the type of ligand also affected the energy gap between V3+ and V4+, which is directly related to phenol formation in the present reaction. DFT calculations were further used to identify the mechanism for the liquid-phase oxidation of benzene.