Solvent- and additive-free liquid-phase oxidation of toluene using molecular oxygen catalyzed by CeO2–MnOx/C3N4

Abstract

The selective oxidation of toluene is critical for synthesizing oxygenated compounds from aromatic hydrocarbons, in which catalysts play an irreplaceable and decisive role. In the present work, the CeO₂–MnO_x/C₃N₄ catalyst was successfully prepared using a co-precipitation method, and its structure was systematically characterized using a combination of analytical techniques, including FT-IR, SEM, XRD, nitrogen adsorption–desorption test, XPS, TGA, H₂-TPR, and O₂-TPD. The characterization results confirmed successful doping and uniform dispersion of CeO₂ and MnO_x into the C₃N₄ support. Subsequently, the catalytic performance of the CeO₂–MnO_x/C₃N₄ catalyst was evaluated for the liquid-phase oxidation of toluene, employing molecular oxygen as the oxidant in a system free of solvents and additives. To obtain the optimal reaction efficiency, the influence of four key parameters—catalyst dosage, oxygen pressure, reaction time and temperature—on the reaction was systematically investigated. Under optimal conditions, toluene conversion reached 5.1%, while the combined selectivity for benzaldehyde (Bz-CHO) and benzyl alcohol (Bz-OH) was 67.9%. Furthermore, recyclability tests demonstrated that the catalyst retained good stability after 5 cycles. Additionally, a preliminary speculation on the mechanism of CeO₂–MnO_x/C₃N₄ was proposed. Owing to its favorable catalytic activity and low preparation cost, this catalyst offers a novel, promising strategy for the selective oxidation of aromatic compounds to high-value oxygenated derivatives.