Surface organic phosphates enhance mild oxidation of toluene by O2 to benzaldehyde over VTiOx/γ-Al2O3

The direct oxidation of toluene by O-2 to benzaldehyde with high efficiency is a bright route for the green production of benzaldehyde but still a significant challenge. In this study, we develop a ligand modification strategy by bonding organophosphonic acid (OPA) to VTiOx/gamma-Al2O3 to restructure its interface microenvironment for enhancement of toluene oxidation to benzaldehyde. The as-prepared catalyst exhibits excellent selectivity over 99 % under mild conditions. Results of comprehensive characterizations and calculations reveal that the OPA bonding in bidentate with the V6-coordinated species causes noticeable phase reconstruction between VOx and TiO2, thereby generating nearby new reactive oxygen species, which is responsible for the conversion of toluene to benzaldehyde at temperatures as low as similar to 50 degrees C, much lower than that over VOx/TiO2 (>130 degrees C). The interface microdomain around the bonding site of OPA helps to significantly weaken the methyl C-H bond of toluene molecule in reaction manifested as the significant decrease in apparent activation energy. Hence, the current work reveals a novel mechanism of the typical catalyst VOx/TiO2 under OPA bonding, which is useful to solve the classic difficult reaction of toluene to benzaldehyde by O-2 oxidation.