Synthesis Ang Catalytic Activities Of Copper Series Rare Earth Double Perovskite-Type Catalysts For Methane Combustion

Due to low carbon content and small amount of greenhouse gas CO₂ generated during the combustion process,methane,the main component of natural gas,has become into a promising clean fuel.But there is a problem of inefficiency and lots of pollution in the conventional flame combustion.It is an efficient pathway to resolve the question by catalytic combustion,in which the catalysts used are the key factor in carrying out the combustion processe.In this thesis,the rare-earth double perovskite-type catalysts La₂CuB0₆?B=Mn?Ni?Co?were prepared successfully by the sol-gel method using citric acid as a complex agent and La₂CuMn0₆ was also synthesized by other methods as comparison.Furthermore,compared with the corresponding single perovskite-type catalyst LaMnO₃ under the same conditions and a series of perovskite oxide catalysts La₂-xCuxMnO₆?x=0,0.05,0.1,0.15,0.2?which replaced with Ba on the performance of methane combustion was tested.The XRD,H₂-TPR,BET,SEM,TEM,XPS and magnetic properties techniques were used to determine the structures,surface morphology,valence of ions of these materials.In addition,We also evaluated the catalytic activity of the samples toward methane combustion.The results obtained are followed below:?1?La₂CuBO₆?B=Mn?Ni?Co?forms a single-phase rare-earth double perovskite-type oxide by the sol-gel method at 1100? under air atmosphere for 3h.During the three catalysts,The La₂CuMn0₆ reveals the best catalytic activity for methane combustion.It shows light off temperature T₁₀of 437.5? and T₉₀ of 649.2?.Combined with the results of XRD and H₂-TPR,the excellent catalytic activity for methane combustion which the La₂CuMn0₆ shows could be probably related to its prefect crystal structure and the lower reduction temperature.?2?It shows that La₂CuMnO₆ forms a single-phase rare-earth double perovskite-type oxide by the sol-gel method,morphous alloy and ionic liquids method at 1100?under air atmosphere for 3h.The basic surface morphologies of La₂CuMn0₆ which prepared by the sol-gel method are spherical,the particles are relatively smaller.Moreover it reveals the lower hydrogen reduction temperature and prefect crystal structure.These results are in the accord with its best catalytic activity of methane combustion.?3?A series of perovskite oxide catalysts La₂-xCuxMn0₆?x=0,0.05,0.1,0.15,0.2?which replaced La with Ba on the performance of methane combustion was tested.The results shows that,double perovskite La_1.9Ba_0.1CuMnO₆ has the best activity for methan combustion,its light off temperature T₁₀and T₉₀ were 400.1? and 618.9 ?,respectively.?4?Compared with the single perovskite-type oxide LaMn0₃ under the same conditions,The La₂CuMn0₆ reveals the better catalytic activity for methane combustion.The lower light-off temperature T₁₀decreases 53.1 ? and total conversion T₉₀ decreases 116.5?,respectively.The results of FT-IR show that the synthesized oxides all possess perovskite-type structures and H₂-TPR indicate that an increasing in the oxygen mobility existe in La₂CuMnO₆.Furthermore,The SEM?TEM and the magnetic properties results also tesfitied that,the two catalysts have different surface feature and magnetic property,In addition,XPS shows that La₂CuMnO₆ have more oxygen vacancies than LaMnO₃.These results are in accord with its catalytic activity of methane combustion.