Effect of cobalt substitution on LaFeO3 catalysts for propene total oxidation

SSCI-VIDE+ATARI:CARE+FPN:WZH:CFE:AGFInternational audienceIn recent years, volatile organic compounds (VOCs) have become one of the main contributors to air pollution [1]. Catalytic oxidation is one of the most efficient ways to eliminate VOCs. Perovskite oxides with the advantages of flexible composition, high thermal stability, superior redox capacities have been extensively applied in catalytic oxidation [2].In this study, a series of B-site (cobalt, copper, and manganese) substituted LaFeO3 perovskites were firstly synthesized by a citrate method and then tested in the total oxidation of propene, a model VOCs. As the outperformed dopant, the proportion of the cobalt was further varied. The physicochemical properties of the materials were fully characterized by TG/TDA, ICP analysis, FTIR, XRD, Raman, N2 adsorption, H2-TPR, and O2-TPD. In addition, water influence, long-term stability, and kinetic study were also performed over the optimal catalyst.The results showed that LaFeO3-based perovskites were successfully synthesized by the citrate method, with specific surface areas of 6–10 m2 g-1 and average crystallite sizes of 26–49 nm. All catalysts could achieve 100% conversion of propene below 450 °C. Cobalt substituted catalyst showed higher activity than other B-site substituted ones. With increasing cobalt content from 0.1 to 0.3, the structure of LaFeO3 was well maintained while the surface area decreased. Cobalt incorporation could greatly enhance the low-temperature reducibility and the oxygen mobility of the perovskite thus leading to better catalytic performance. A good correlation was established between the catalytic activity and the amount of the active oxygen species. As a cost-effective catalyst (T90 = 337 °C, Ea = 58 kJ mol–1), LaFe0.8Co0.2O3 exhibited outstanding stability in cycling and long-term tests, as well as good water resistance, being a potential candidate catalyst for industrial applications. Moreover, the Power-Law model provided fairly good fits to the kinetic data (R2 > 0.95) and suggested that the reaction order of oxygen and propene over LaFe0.8Co0.2O3 were 0.2 and 0.3, respectively. Figure 1 (a) Propene oxidation rate (r) of LaFe1-xCoxO3 perovskites as a function of temperature (b) Correlation between r at 230 °C and the amount of desorbed oxygen species below 500 °C in O2-TPD.[1]C. He, J. Cheng, X. Zhang, M. Douthwaite, S. Pattisson, Z. Hao, Chem. Rev. 119 (2019) 4471–4568.[2]S. Royer, D. Duprez, F. Can, X. Courtois, C. Batiot-Dupeyrat, S. Laassiri, H. Alamdari, Chem. Rev. 114 (2014) 10292–10368