| As a major atmospheric pollutant,NOx is an important cause of acid rain,photochemical smog,fog weather and ozone hole,and its emission has great harm to the ecosystem and human health.NH3 selective catalytic reduction of NOx technology(NH3-SCR)can effectively remove NOx from flue gas.Now,V2O5-WO3/TiO2 system is the most widely used catalyst commercially,but there are still many problems in this system,such as relatively narrow operating temperature window,SO2 easy oxidation to SO3,and low N2 selectivity at high temperature.Therefore,many studies have focused on the development of environmentally friendly SCR catalysts to replace V-based denitrification catalysts.MnCe oxide catalyst is a kind of efficient denitrification catalyst for flue gas,but it has some problems,such as poor thermal stability,narrow active temperature window and weak sulfur toxicity resistance,which limit its application.In this paper,a series of MnCe oxide catalysts were designed and prepared,and their denitrification performance was evaluated.The relationship between catalyst structure and NH3-SCR performance was investigated by TEM,XRD,BET,XPS,H2-TPR and NH3-TPD characterization techniques.In this paper,a series of manganese-cerium composite oxide catalysts with different exposed crystal surfaces were prepared by a one-pot hydrothermal method and their NH3-SCR performances were evaluated.The results showed that the activity of Manganese-ceric nanorods(Mn0.25Ce0.75Ox-R)was the highest when the molar ratio was 25:75.The activity of NH3-SCR excessed 90%in the temperature range of 125～200℃.The Mn0.25Ce0.75Ox-R had larger pore size and pore volume,abundant chemical surface adsorption oxygen(Oα)and Mn4+ species and strong redox ability.The water and sulfur resistance performances were tested on the Mn0.25Ce0.75Ox-R catalyst,and the results showed that the catalytic conversion decreased slightly with the addition of water vapor,and then recovered after cutting off water vapor.the presence of SO2 caused the catalyst deactivated seriously and irreversibly.The poisoning was exacerbated under the coexistence of vapor and SO2.In order to widen the temperature range of Mn0.25Ce0.75Ox-R catalyst,a series of W-modified Mn0.25Ce0.7sOx-R catalysts were prepared by impregnation method and tested for NH3-SCR reaction.The results showed that the NH3-SCR activity temperature window was widest(190-450℃,NOx conversion>80%)when the WO3 loading was 15%.The catalyst had the lowest activation energy and good resistance to SO2 and H2O at 250℃.The reasons for the best activity of 15%WO3/Mn0.25Ce0.75Ox-R catalyst were abundant Ce3+,Mn3+active species,oxygen vacancy,strong redox capacity and more medium strong acid content on its surface.In order to improve the resistance of 15%WO3IMn0.25Ce0.75Ox-R catalyst to vapor and sulfur,a 15%WO3/Mn.25Ce0.75Ox-R@TiO2 core-shell catalyst was prepared by liquid deposition method.The activity results showed that although the activity of the catalyst was decreased after TiO2 coating,the resistance to water and SO2 poisoning was significantly improved.TiO2 coating can properly inhibit the redox ability and acidity amount of the catalyst,causing the decreasing adsorption of water and SO2 molecules on catalyst surface and occurrence of SO2 oxidation to SO3 side reaction.Therefore,the 15%WO3/Mn0.25Ce0.7sOx-R@TiO2 catalyst possessed good resistance to water and sulfur. |
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