Synergistic effect between Cu–Cr bimetallic oxides supported on g-C3N4 for the selective oxidation of toluene to benzaldehyde

Abstract

A well-defined catalyst with Cu–Cr bimetallic oxides supported on g-C₃N₄ was prepared via direct heating treatment of metallic precursors incipiently decorated with melamine. The obtained catalysts were used in the selective oxidation of toluene to benzaldehyde with H₂O₂ as the oxidant, the prepared bimetallic Cu–Cr catalysts outperformed their monometallic counterparts, and the highest benzaldehyde yield can reach 42.9% within 5 h under mild reaction conditions. It was found that some metal oxides were coated with g-C₃N₄ to form a core/shell-like structure, which hindered the metal leaching. XPS analysis indicated the presence of some low valence Cu species and the electronic interactions between the Cu and Cr species. The bimetallic Cu–Cr catalysts had a larger specific surface area and pore volume compared to the monometallic ones. Besides, the effects of the reaction parameters on catalytic activity were investigated in detail. The kinetics study indicated that toluene oxidation was a first order reaction and the apparent activation energy was calculated to be 24.3 kJ mol⁻¹. The recycling tests verified the good reusability of the prepared catalyst, making it promising in the future practical catalysis application. Finally, a possible reaction mechanism for the selective oxidation of toluene over the supported catalyst was proposed.