Selective liquid-phase oxidation of toluene with molecular oxygen catalyzed by Mn3O4 nanoparticles immobilized on CNTs under solvent-free conditions

Abstract

The catalytic performance of Mn3O4 supported on carbon nanotubes (CNTs) in the liquid-phase oxidation of toluene to benzyl alcohol and benzaldehyde was studied. The supported catalysts were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), N2 adsorption–desorption isotherms and ICP-MS. The results demonstrate that Mn3O4 nanoparticles loaded on CNTs performed better compared with pristine Mn3O4 or CNTs. The main reason for the increased catalytic activity is the dispersion and loading of Mn3O4 in CNTs. By optimizing the reaction temperature, reaction time, catalyst quality, oxygen flow rate and initiator dosage, the optimum reaction conditions were obtained. Using tert-butyl hydroperoxide (TBHP) as the initiator and oxygen as the oxidant, the toluene conversion rate was as high as 24.63%, and benzyl alcohol and benzaldehyde selectivity was 90.49%. The good stability of the catalyst was confirmed by repeating the experiment for four cycles and observing no significant changes in its performance.