Research On The Activity And Tolerance To Chloride Poisoning Of The Perovskite Catalysts For VOCs Catalytic Combustion

With the rapid development of chemical industry, Volatile Organic Compounds (VOCs) are recognized as one of magjor contributors to air pollutants. Catalytic combustion is an efficient, energy-saving and environment-friendly method to control VOCs pollution. Therefore, it is necessary to find cheap, effcient and stable catalysts for VOCs catalytic combustion. In this dissertation, the activity and stability of perovskites were investigated towards catalytic combustion of VOCs. Futher, the key factors of catalytic combustion of VOCs on perovskites catalysts were also discussed.LaBO₃ (B = Cr, Mn, Fe, Co, Ni, Cu) perovskite catalysts were prepared by co-precipitation. The catalysts were characterized by XRD, BET, H₂-TPR, O₂-TPD and their catalytic performances were studied by catalytic combustion of various types of VOCs. The results show that catalytic performances of LaBO₃ depend on the oxidation - reduction capacity of the B ions. LaMnO₃ and LaCoO₃ have the best catalytic activity among all materials studied. The studies on performances of LaBO₃ perovskite catalysts for catalytic combustion of dichloromethane show the destructions of LaCoO₃, LaFeO₃, LaNiO₃ perovskite structures during the catalystic reactions, resulting in permanent deactivation. The active sites were reconstructed. Crystalline structure of LaMnO₃ catalyst has good tolerance to chlorine poisoning. The reaction activity of LaMnO₃ achieves stablity soon after the initial reconstruction of the surface. LaCrO₃ ,without any the crystalline structure destructions after reaction, gives the best tolerance to chlorine poisoning.To enhance the catalytic activity of LaMnO₃, the effects of Ce and Sr doping into A position on the structure and properties of the catalyst were investigated. The results show that when Ce doping amount is under 0.3, La1-XCeXMnO₃ catalysts have single perovskite phases. As Ce doping amount increases, the number of lattice oxygen and catalytic combustion activity increases. However, CeO₂ phase increases and the tolerance of catalysts to chlorine poisoning decreases.When Sr doping amount of La1-XSrXMnO₃ catalyst is x≤0.3, perovskite structure trends to be more complete. Meanwhile oxygen vacancies on the catalysts surface increases and activity of the catalysts is enhanced. However, when Sr doping amount reaches to 0.5, the perovskite structure is destroyed which results in the catalyst activity and tolerance to chlorine poisoning decreases.Finally, the stability of La0.8A0.2MnO₃ (A = Ce, Sr) perovskite catalysts for catalytic combustion of dichloromethane is discussed. The results show that, La0.8A0.2MnO₃ (A = Ce, Sr) catalysts have good stability for catalytic combustion of dichloromethane. After the reconstruction of catalysts, the reaction temperature and dichloromethane feed concentration have little effects on the performance of the catalysts.