Essential role of B metal species in perovskite type catalyst structure and activity on toluene oxidation

Abstract

The perovskite type materials with transition metals are getting more attention especially as catalysts in total oxidation reaction. This work explores the B metal effect on the catalytic activity of LaBO3 structured perovskites in total oxidation of toluene. The perovskite type oxides were obtained by Pechini method and characterized by X-ray diffraction, nitrogen adsorption/desorption isotherms, thermogravimetric analysis and differential scanning calorimetry, temperature-programmed reduction (H2-TPR), Raman spectroscopy, Fourier transform infrared spectroscopy and particle size analysis. The results showed that LaFeO3 catalyst contained a single orthorhombic LaFeO3 phase, while LaMnO3 contained LaMn2O5 species besides cubic LaMnO3 phase. Both catalysts show very narrow distributions and average values of 55.59 μm and 51.43 μm for LaMnO3 and LaFeO3, respectively. With regard to the H2-TPR profile for the LaMnO3, Mn4+ to Mn3+ reduction and Mn3+ to Mn2+ reduction. Consequently, the redox performance of ABO3 perovskites was found as mainly driven by the B-site transition-metal element character. According to the catalytic tests, the LaMnO3 catalyst was more active for toluene oxidation than LaFeO3 and achieved the lowest light-off temperatures. An excellent agreement between the experimental data and the proposed one-dimensional pseudo-homogeneous model was achieved and corresponding kinetic parameters (estimated rate constants, k, activation energies, EA, and frequency factors, Ar) were estimated. Lower activation energy was estimated for LaMnO3 catalyst (84 kJ mol−1 vs. 99 kJ mol−1 for LaFeO3) confirming that LaMnO3 catalyst was more active for toluene oxidation under reaction conditions presented in this paper.