Preparation And Catalytic Activities Of The Rare-Earth Double Perovskite-Type Catalysts For Methane Combustion

Conventional combustion of natural gas (i.e.methane) not only causes serious air pollution,but also has low utilization efficiency.Catalytic combustion of methane as an environmentally friendly is becoming more and more attractive in recent years due to the high combustion efficiency.In this paper, the rare earth double perovskite-type catalysts La2BAlO6(B=Co,Ni,Mn) were prepared by the sol-gel method using citric acid as complex agent, and compared with the corresponding single perovskite-type catalysts LaBO3(B=Co,Ni,Mn,Al). Moreover, the influence of the calcination temperature of the double perovskite-type oxides and Sr replace La in A-site of perovskite oxide catalyst on the performance of methane combustion was studied. The catalysts were characterized by X-ray powder diffraction (XRD), H2-temperature-programmed reduction (H2-TPR), specific surface area (BET), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and magnetic property measurement, and was tested for methane combustion.Results showed that a single-phase rare-earth double perovskite oxide La2BAlO6(B=Co,Ni,Mn) could be formed by calcinations at 1100℃for 3 h. The La2NiAlO6 demonstrates the best catalytic activity for methane combustion. It has a light-off temperature (T10)of 433.1℃and a total conversion temperature (T90) of 649.7℃, then the La2CoAlO6, and La2MnA106 is the worst. Furthermore, La2NiAlO6 samples show excellent catalytic activity for methane combustion which could be related to the decrease of reduction temperature observed in H2-TPR experiments, probably due to an increased oxygen mobility promoted by the presence of aluminum.Meanwhile compared the rare earth double perovskite-type La2BAlO6(B=Co,Ni,Mn) series catalysts with the corresponding single perovskite-type catalysts LaBO3(B=Co,Ni,Mn,Al). Catalytic activity testing results showed that double perovskite series catalytic activity are superior to the corresponding single perovskite catalyst. In addition, the double perovskite still showed good catalytic activity which compared to the mixture of two kinds single perovskite catalysts. This explained that exist synergy between B-site element and Al elements in double perovskite catalyst La2BAlO6 (B= Co, Ni, Mn) structure, and this synergy effect on methane catalytic combustion reaction is favorable.Furthermore, the influence of the calcination temperature of the double perovskite-type oxides La2NiAlO6 on the physicochemical properties and the performance of methane combustion was studied. The results indicated that, La-Ni-Al-O system could be formed double perovskite-type oxides La2NiAlO6 at 800℃, with increasing the calcination temperature the structure of double perovskite La2NiAlO6 is perfectIn the end, the perovskite oxide catalysts La2NiAlO6 of A-site replaced Sr were synthesized through citric acid method. The catalytic activity of La2NiAlO6 for the performance of methane combustion was studied, appropriate replace content is beneficial to enhance catalytic activity of La2NiAlO6.The results showed that, double perovskite Lai.90Sr0.10NiAlO6 has the higher surface area, and it has the best activity for methane combustion, whose T10 and T90 were 398.7℃and 622.9℃, respectively.