Catalytic ozonation of toluene over amorphous Cu-Mn bimetallic oxide: Influencing factors, degradation mechanism and pathways.

Herein, amorphous catalysts were employed to investigate the catalytic ozonation system, revealing the degradation mechanism and influencing factors (O3 concentration, temperature, and humidity) for toluene catalytic ozonation. Cu0.2MnOx exhibited the highest toluene oxidized and excellent stability (∼85% at 60 h) based on the suitable value of Oads/Olat and potent synergy between Cu with Mn. To explore the effect of factors, the change of fresh and post-reaction samples was compared as revealed in the relevant characterization results (SEM, XRD, BET, XPS, TGA), DRIFTS and GC-MS identified the intermediates and byproducts. The results show that appropriate temperature (100 °C) and O3 concentration (2100 ppm) can effectively enhance the number of reactive oxygen species. Although H2O can increase the production of ·OH to promote degradation, it is easier to quench the active sites on the surface of amorphous catalysts. During the reaction, the main role of Cu in Cu-Mn bimetallic oxides is adsorption of toluene and O3, formation of benzoic acid, and oxidation of short-chain products. As for the adjacent Mn, it works on the cleavage of O-O in O3 and the ring-opening of benzene. Then, the mainly catalytic ozonation pathway of toluene was proposed and followed the order: toluene, benzoic acid, benzene, maleic anhydride, short-chain carbon species, CO2, and H2O.