Effect Of Preparation Methods On Methane Catalytic Combusion Activity Of Double Perovskites LaSrFeCoO₆

The double perovskite LaSrFeCoO₆ were synthesized by different methods and characterized by means of XRD, FT-TR, H₂-TPR, SEM, XPS , magnetic properties and activity of methane catalytic combustion.We found that the LaSrFeCoO₆ catalyst calcinated at 1100℃for 3h in air was single-phase double-perovskite which was synthesized by the sol-gel methode with citric acid, glucose and sucrose as complexing agent. It showed that the catalyst with citric acid as complexing agent had the best methane combustion activity .The results showed that T₁₀ (methane conversion of 10%) and T₉₀ (methane conversion of 90%) were 432.7℃and 639.2℃. The complex agent greatly affected the catalyst surface area and surface area is proportional to methane combustion activity . We compared chemical and physical properties of LaSrFeCoO₆ catalyst with citric acid as complexing agent which was calcinaed at different temperatures. The single-phase was formed at 500℃, which indicate that the sol-gel method could synthesize double perovskites in lower calcinate temperature. Calcination temperature greatly affected catalysts surface area. And apparent activation energy is also influence catalytic activity. We also synthesized double perovskite LaSrFeCoO₆ by amorphous alloy method, sol-gel method and microemulsion method. The single-phase double perovskite LaSrFeCoO₆ calcinated 1100℃for 3h in air was synthesized by all of the three methods. The catalyst synthesized by amorphous alloy method showed good hydrogen reduction ability, electric simulation surface density and apparent activation energy. It shows better catalytic activity for methane combustion, the result showed that T₁₀ was 387.2℃and T₉₀ was 592.7℃.The perovskite-type composite oxides LaSr_1-xCe_xFeCoO₆ (x=0.05, 0.1, 0.2) and La_1-xCe_xSrFeCoO₆ (x=0.05, 0.1, 0.2) were synthesized by amorphous alloy method. The result showed the catalyst calcinated at 1100℃for 3h in air formed a single-phase when Ce doped 0.05. When x>0.05, it could formed mixed phase with a little of CeO₂. According to the experiment results,we know that the methane combustion activity is proportional to the doping ratio of Ce.