Superior performance of Cu-Ce binary oxides for toluene catalytic oxidation: Cu-Ce synergistic effect and reaction pathways

Abstract

A series of Cu-Ce binary oxides were synthesized via a facile co-precipitation method for toluene catalytic oxidation. The physicochemical properties of these samples were characterized by BET, XRD, SEM, TEM, H2-TPR, O2-TPD, and XPS. It reveals that Cu1Ce3 catalyst possesses a higher specific surface area, stronger Cu-Ce synergistic effect, and better low-temperature reducibility than other samples. Moreover, Cu1Ce3 catalyst exhibited superior toluene oxidation activity with 99.10% toluene removal efficiency and 97.28% CO2 selectivity at 200 °C, as well as satisfactory stability and moisture resistance. Therefore, Cu1Ce3 catalyst indicates a huge potential for practical applications, such as coal-fired flue gas and spray coating industry. The reaction pathways for toluene catalytic oxidation over the Cu1Ce3 catalyst were further illuminated by in-situ DRIFTs. In the main pathway, toluene molecules were firstly in contact with the interface lattice oxygen, then the abstraction of H atoms occurred on the methyl group, and benzyl alcohol is considered as the primary intermediate, during which the rate-determining step is the oxidation of benzyl alcohol. In the secondary pathway, a little proportion of toluene molecules were directly oxidized into benzoic acid by the chemisorbed oxygen species. In subsequent steps, all the intermediates were converted into CO2 and H2O. At last, it is confirmed that the toluene oxidation over Cu1Ce3 catalyst involves a Mars-van-Krevelen mechanism via this study.