Toluene oxidation process and proper mechanism over Co3O4 nanotubes: Investigation through in-situ DRIFTS combined with PTR-TOF-MS and quasi in-situ XPS

Improving catalytic efficiency is a yet still challenge in thermal catalytic oxidation. One of the key issues is to understand its catalytic oxidation mechanism. Here, a series of Co3O4 samples were prepared by solvothermal method. The characterization records showed that nanotubular Co3O4-NTs-2 for its rough surface, low temperature reducibility, abundance of Co3+ ions and surface adsorption oxygen species, thus exhibited high efficiency (T90 = 240℃, Ea = 67.42 kJ/mol) in catalytic oxidation of toluene. In-situ DRIFTS combined PTR-TOF-MS were applied to investigate the reaction process of toluene oxidation. These results revealed that the catalytic oxidation of toluene followed the listed way: toluene → benzyl alcohol → benzaldehyde → benzoate → benzene → phenol → benzoquinone → maleic anhydride and other ring opening by-products like ethanol, acetaldehyde, acetic acid, acetone etc., then ultimately mineralized to CO2 and H2O. Furthermore, the results of quasi in-situ XPS in C7H8/N2, toluene conversion in O2-free evaluation and UV–vis-DRS analysis further confirmed that surface lattice oxygen played an important role in toluene oxidation, and gas-phase oxygen facilitated the reaction. The combination of a series of instruments provided a promising means for further understanding the oxidation mechanism of toluene.