The Catalytic Performance Research Of Ceria-based Catalyst In The NH₃-selective Catalytic Reduction Technique Based On The Denitration Of Coal-fired Flue Gas

The rapid development of industry need huge energy consumption,coal is dominated in the energy structure of China,which results in severe environmental pollution by the emission of coal-fired flue gas.Thus,the treatment of exhaust gas is the most crucial part.The selective catalytic reduction of NOx by NH3(NH3-SCR)is one of the most important technique for the deNOx of coal-fired flue gas.For NH3-SCR reaction,CeO2 has played an important role in the new non-vanadium-based catalysts due to its high oxygen storage-release capacity and excellent redox ability.In this thesis,we focus on studying the issue about SO2 poisoning of CeO2-based catalysts and the influence of ion mofication on the catalytic performances of CeO2,which can provide theoretical gudiance for designing the highly efficient catalysts with excellent SO2 tolerance.The details about our research as follows:(1)Investigating the influence of sulfated temperature on NH3-SCR catalytic performance of CeO2,and finding that NO conversion gradually decreased with increasing sulfated temperature.Qualitative analysis by XRD、Raman and in situ DRIFT showed that the sulfation process of CeO2 was deepened with the increase of sulfated temperature,and the sulfate species changed from surface sulfate to bulk-like sulfate to bulk sulfate.Quantitative analysis by TG-DTA、H2-TPR and XPS also indicated that the sulfation process became deepened at higher sulfated temperature.Bulk sulfate was to the disadvantage of cataltic activity in sulfated CeO2.However,bulk sulfate could be washed out by H2O and the activity could improve over sulfated CeO2 at high sulfated temperature.(2)Based on part(1),the surface modification of CeO2 was conducted by loading TiO2,and a series of inverse TiO2/CeO2 and CeO2/TiO2 catalysts were prepared by impregnation method,we found that TiO2/CeO2 had better SO2 tolerance performace than CeO2/TiO2 in NH3-SCR reaction with SO2 at 300℃.The fresh and used samples were characterized by TG-DTA,XRD,BET,in situ DRIFT,XPS and H2-TPR,the obtained results demonstrated that three different kinds of sulfate species including NH4HSO4,surface and bulk-like metal sulfates(mainly interacted with cerium species)formed over catalysts in SCR reaction with SO2.Metal sulfates blocked the active sites of Ce-O-Ti,which resulted in the deactivation of CeO2/TiO2 catalyst.Although metal sulfates also blocked the active sites of Ce-O-Ti over TiO2/CeO2,NH3-SCR could still proceed by the synergistic catalysis between surface sulfate and CeO2,which happened as the same as in the sulfated CeO2.(3)WO3 was solid acid oxide,a series of supported WO3/CeO2 catalysts were prepared by impregnation method,and investigating the influence of WO3 loading on catalytic performances.The results showed that catalytic activity firstly increased and then decreased with the increase of WO3 loading,the optimized 0.8W/Ce sample exhibited good deNOx efficiency at 200-450℃ and could keep high actvity in the presence of SO2 and H2O at 300℃.The crystalline WO3 with bad SCR activity covered on the surface of catalyst,which blocked surface active sites and resulted in the decrease of redox ability and surface acid sites.Thus,the crystalline WO3 inhibited SCR performances of WO3/CeO2 catalyst.However,the crystalline WO3 could be washed out by the NH3·H2O pretreatment at 70℃,and the catalytic activity would improve and recover.In situ DRIFT results indicated that SCR reaction proceeded by Eley-Rideal mechanism,the modificaiton of WO3 could improve the NH3 adsorption ability and inhibit nitrate species adsorption ability,which was beneficial to activating NH3 molecular,and promoting the proceeding of SCR reaction by Eley-Rideal mechanism.(4)Ceria-based composited oxides CeO2-MOx(M=Ti4+,Si4+,Al3+)were further prepared by coprecipitation method,and studying the relationships between physicochemical properties and catalytic performances.The results indicated that the catalytic performances were dependent on redox and surface acidity over ceria-based composited oxides.The order of activty was CeTi>CeSi>CeAl>CeO2 when the catalysts were calcined at 500℃,this was because the modification of MOx could improve the redox and surface acidity of CeO2,and CeO2 could obtain best redox and most surface acid sites by the modification of TiO2.The order of activty was CeSi ≈>.CeAl>CeTi when the catalysts were calcined at 750℃,this was because the anti-sintering performance of CeSi and CeAl was better than that of CeTi,and obvious phase separation happened in CeTi.In addition,ceria-based composited oxides exhibited excellent SO2 tolerance at 300℃.