Evaluation of three-dimensionally ordered macroporous LaFe1−xCoxO3 perovskites and their performance for catalytic oxidation of methane

Abstract

Nowadays, excess methane emissions have caused serious environmental problems, of which catalytic oxidation is a practical and economically feasible technique for its decomposition and harm reduction. Here, three‐dimensionally ordered macroporous (3DOM) LaFe1−xCoxO3 (x = 0, 0.1, 0.3, 0.5) were prepared by colloidal crystal template (CCT) method using polynomial methacrylate (PMMA) as templates in order to evaluate their catalytic activities for methane. Numerous analytical techniques were used to characterize the physicochemical properties of as-prepared perovskite catalysts. The results showed that the morphology of the catalysts depended strongly on the PMMA template and an appropriate calcination temperature was decisive for the formation of a high-quality 3DOM structure, which affected the textural parameters, the surface compositions of the catalysts and further determined their catalytic activities for methane. Along with the doping of Co for Fe at the B site, the BET surface areas and crystallite sizes could be optimized, and the ratios of Fe4+/Fe3+, absorbed oxygen (Oads)/lattice oxygen (Olat) both increased with the increment of Co substitution, which were beneficial to improve the catalytic activity on CH4. However, the surface carbonate or hydroxide compounds also increased with the increment of Co doping and did harm to the catalytic activity in an opposite way. The final result was that the 3DOM LaFeO3 calcined at 700 ℃ (Ea = 70.9 kJ/mol, T50% = 548 ℃, T90% = 652 ℃), with the optimal pore size, pore volume, Fe4+/Fe3+ ratio, H2-TPR reducibility, on stream testing stability and carbon deposition resistance in low temperature, showed much better performance than the Co-doped 3DOM LaFe1−xCoxO3 (x = 0.1, 0.3, 0.5) in the methane catalytic process. However, it was also predictable that the performance of methane oxidation by Co-doped perovskites can be improved if the surface carbonate or hydroxide compounds can be effectively controlled in the future by surface engineering methods like acid treated or others to eliminate La segregation on its surface.