Promotional effect of surface fluorine species on CeO2 catalyst for toluene oxidation

In this study, fluorine (F) modified cerium oxide (Fx-Ce) catalysts were prepared by co-precipitation method to investigate the impact of fluorine species on CeO2 catalyst for toluene oxidation. Compared to bared CeO2, the catalysis activity of Fx-Ce was further improved. The temperature of toluene conversion (T90% and T50%) for F3-Ce decreased by ΔT90% = 30°C and ΔT50% = 15°C, respectively. The characterizations of H2-TPR, O2-TPD, Raman, XPS certified that there was more chemisorbed oxygen, oxygen vacancies and Ce3+ ions on the F3-Ce than bared CeO2. DFT calculations demonstrated that the formation energy of oxygen vacancy on F3-Ce is reduced by surface-florine, which promotes the formation of oxygen vacancy. Meanwhile, Toluene-TPD indicated that fluorine-doping increased the adsorption capacity of toluene on CeO2. According to the above-mentioned results, F3-Ce has higher oxygen vacancy concentration, more active oxygen, and larger toluene adsorption capacity. Thus it has the optimal catalytic activity for toluene oxidation.