| A large number of experiments showed that the complex perovskite-type oxides has excellent performance on catalytic purification of automobile exhaust. To a certain extent the catalytic ability can be equivalent to precious metal catalysts. Studies have shown that in LaBO3(B = Fe, Co, Ni, Mn, Cr, V) perovskite catalyst series, the catalytic activity of perovskite-typ LaCoO3 on CO performance is the best. So in this paper we use the LaCoO3 perovskite-type as the research object. LaCoO3 perovskite prepared by traditional methods have a small specific surface area(<20m2/g), but the mesoporous structure can improve the specific surface area of the material. So in this article, we introduced the mesoporous structure into the perovskite to increase the specific surface area.Combining with hard template method and sol-gel method, we synthesized mesoporous perovskite-type LaCoO3 by the hard-template wet impregnation sol-gel method. Using SBA-15 as hard template, citric acid as a complexing agent and various metal nitrates as inorganic sources to prepare the perovskite catalyst. Then we had a hydrothermal treatment reseach on perovskite-type LaCoO3 to study the changes on the structure and morphology. In addition, we doped Sr in the position of bit “A” to investigate their related properties. And related performance of samples were characterized by XRD, SEM, FT-IR, BET, XPS and other techniques. Finally, the catalytic conversion efficiency for CO gas were studied to reveal the catalytic performance of samples.The experimental results show that mesoporous molecular sieve SBA-15 synthesized by hydrothermal method has hexagonal ordered mesoporous structure, high specific surface area(807m2/g) and a narrow pore size distribution(most probable pore size is 5.6nm). TG-DSC and XRD analysis of dry gel suggest that the optimal calcination temperature of LaCoO3 perovskite-type is 650℃. At that temperature, samples have a single perovskite phase. The content of template agent plays a decisive role in specific surface area of LaCoO3 samples. When the molar ratio between hard template and metal ions is 2:1, LaCoO3 samples own the largest specific surface area up to 124.14m2/g and keep a single perovskite phase. Hydrothermal temperature and time have a great influence on the crystal structure, specific surface area and morphology of La CoO3 samples. Morphology have changed after samples had hydrothermal treatment in 140℃, 160℃ and 180 ℃for 6h. The ball-shaped particles change into a layered structure; Samples contain Co3O4 impurity phase; Specific surface area has greatly changed, respectively were 133.26m2/g, 136.47m2/g and 137.30m2/g. That illustrates the proper treatment temperature and time does not change the perovskite structure, on the contrary it will promote the grain refinement, inhibit structural collapse and increase the specific surface area of the samples. Experimental results on catalytic activity of CO gas show that the dual role of stability of crystalline phase and specific surface area will affect the activity of catalytic conversion. Sr doped in the position of bit “A” can affect the perovskite structure and their catalytic activity. When the Sr content x = 0.1, the sample is a single perovskite structure. But when x=0.2 or higher, there will appear perovskite-like LaSrCoO4 mixed phase and make crystallinity decrease. The catalytic activity of CO has improved with the increase of Sr content. Higher concentration of oxygen vacancy and adsorbed oxygeny caused by lattice distortion improve the catalytic conversion efficiency of CO. The XPS research shows that the content of lattice oxygen has decreased after hydrothermal treatment, but the concentration of adsorbed oxygen increase conversely. In the La0.9Sr0.1CoO3 samples, there has no impurity phase. We find that some Co3+ become into Co4+ and the concentration of adsorbed oxygen increases obviously. Studies have shown that the high concentration of adsorbed oxygeny has a promoting effect on the catalytic conversion efficiency of CO. |
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