Preparation Of La_1-xSr_xMnO₃/?-Al₂O₃/cordierite Catalysts And Its Catalytic Combustion Activity For VOCs

Volatile organic compounds?VOCs?are greatly emitted from industrial production process,auto exhaust and human daily life.Catalytic combustion is considered as the most promising alternative process for abatement of VOCs emissions due to its high purification efficiency,low operation temperature and low level of energy consumption.Among the catalysts used for the catalytic oxidation of VOCs,perovskite-type oxides,more specifically LaMnO₃-based perovskites,have attracted much attention due to their excellent catalytic activity and good thermal stability for catalytic oxidation of VOCs.A?-Al₂O₃ washcoat on cordierite honeycomb was prepared by an impregnation method,which was used as a support to prepare a La_1-xSr_xMnO₃?x=0,0.1,0.2,0.3,0.4?catalyst.The catalysts were synthesized by impregnation method with citrate and characterized by X-ray diffraction?XRD?,scanning electron microscopy?SEM?,BET specific surface area,and H₂-temperature program reduction?H₂-TPR?measurement.The effect of Sr doping into A position on the structure and properties of catalyst were investigated.The main results obtained in the thesis are as follows:1.At first,The powder catalysts were preparation via Sol-gel method.we found that:The thermal stability of the supports is improved by the treatment of oxalic acid.higher calcination temperature reduce the specific surface area of the catalyst.As the complexing agent and dispersant,the content of citric acid in the catalyst precursor has a great influence on the catalyst.The increase of citric acid content increases the specific surface area of the catalyst,resulting in a better catalytic activity for VOCs.The catalysts of Sr doping into A position were synthesized.It was found that the partial substitution by Sr for La could change the perovskite-type crystal structure.The above three factors have obtain a relatively good preparation process:10wt.%oxalic acid treated cordierite supports and acid content ratio?calculated as molar ratio of citric acid and La?to 1.2,and the calcination temperature is 700?.2.The catalyst washcoat on cordierite honeycomb can significantly increase the catalytic activity.When the calcination temperature is 700?,the acid content ratio?calculated as molar ratio of citric acid and La?is 1.2 and the Sr doping amount is10%,The catalyst has the highest catalytic activity.Under the concentration of toluene in the reaction feeds was set at 1000 ppm,the gas hourly space velocity?GHSV?was maintained at 15,000 ml/g h,the catalysts activity were evaluated.The temperature required for 50%and 90%toluene conversion was 123?and 164?.