Relationship between Physicochemical Properties and Toluene Oxidation Performance of the CeOx–CrOx Catalysts

A series of CeO_x–CrO_x catalysts were synthesized via the sol-gel method for the oxidation of toluene. A comprehensive set of characterization techniques, including XRD, N₂ adsorption, Raman spectroscopy, HRTEM, H₂-TPR, O₂-TPD, XPS, and in situ DRIFTS, was employed to investigate the structure-performance relationships of the catalysts. Among the catalysts, the one with a Ce/Cr molar ratio of 1:3 exhibited the best performance in toluene oxidation, with the activation energy for toluene degradation decreasing from 54.5 kJ mol⁻¹ for CeO_x to 31.3 kJ mol⁻¹ for the CeO_x–CrO_x (1:3) and CO₂ selectivity reaching 100% at temperatures above 250 °C. This enhancement was primarily attributed to an increased specific surface area, an elevated concentration of highly active Cr⁶⁺ species, and improved reducibility and mobility of surface oxygen species. During the reaction, toluene was rapidly adsorbed and converted into benzoate intermediates, which were subsequently oxidized to form the final products, CO₂ and H₂O.