Solvent-free liquid-phase selective catalytic oxidation of toluene to benzyl alcohol and benzaldehyde over CeO2–MnOx composite oxides

Abstract

An efficient method for highly selective preparation of the high value-added benzyl alcohol (BOL) and benzaldehyde (BAL) from liquid-phase catalytic oxidation of toluene with molecular oxygen over CeO₂–MnO_x composite oxides in a solvent-free system has been successfully developed in this work. The results demonstrated that CeO₂–MnO_x composite oxides exhibited high selectivity to BOL and BAL, which benefited from the synergistic catalysis between Mn³⁺/Mn²⁺ and Ce⁴⁺/Ce³⁺ redox pairs. Under optimal reaction conditions, 6.9% toluene conversion with 64.4% selectivity to BOL and BAL and 96.8% total selectivity to BOL, BAL and benzoic acid (BAC) was achieved. The good stability of the CeO₂–MnO_x composite oxide catalyst was confirmed by a five-cycle experiment. The possible oxidation reaction mechanism for the catalytic aerobic oxidation of toluene over CeO₂–MnO_x was also suggested. This work may provide a new insight into highly selective preparation of aromatic alcohols and aldehydes from the selective aerobic oxidation of aromatic hydrocarbons employing low-cost CeO₂–MnO_x as an efficient and stable catalyst.