| 71% of NOx in the air pollutants of iron and steel industry came from sintering process,and nitrogen oxide emission control of sintering flue gas has attracted the attention of the scholars.Selective catalytic reduction(NH3-SCR)technology has been proven to be one of the most effective technologies for removing nitrogen oxides from coal-fired flue gas.In recent years,relevant scholars have paid more attention to the application of SCR technology in the low-temperature denitration process of sintering flue gas,and believe that it has great potential for development.Therefore,it is particularly important to find a catalyst suitable for the sintering flue gas operating temperature and with better activity.Our previous study found that Mn-Ce/AC(Activated coke)catalyst exhibited better SCR denitration activity under the condition of lower sintering flue gas temperature.However,the composition of sintering flue gas is complex,in addition to nitrogen oxides,it also contains SO2,water,alkali metals and heavy metals.Therefore,it is urgent to study the poisoning mechanism of Mn-Ce/AC catalysts by the related components in the denitration process of sintering flue gas,and to develop antipoisoning catalysts to increase the service life of the Mn-Ce/AC catalysts under complex flue gas conditions.It has important theoretical and practical significance to realize the efficient removal of NOx from sintering flue gas in China.In this paper,the effects of Nb2O5 doping on the resistance of Mn-Ce/AC catalysts to Zn and SO2 poisoning were studied.And the structural characteristics,physical and chemical properties and poisoning mechanism of Mn-Ce/AC catalysts,Zn salt poisoning catalysts,SO2 poisoning catalysts and Nb2O5 modified catalysts,as well as the anti-Zn Cl2 and SO2 poisoning mechanism of Nb2O5 doping catalysts were systematically studied.The main conclusions were as follows:(1)The SCR activity and N2 selectivity of Mn-Ce/AC catalysts were affected by zinc salt loading.The main reason was that the interaction between zinc salt and manganese oxide resulted in the zinc atoms entering the lattice of manganese oxide to form a strong chemical bond,which would occupy the acidic sites on the catalyst surface and destroy the weak acid and strong acid sites of Mn-Ce/AC catalyst,resulting in catalyst poisoning and decrease of denitrification activity.In addition,more N2 O was formed in the denitration process,which resulted in the decrease of N2 selectivity of the zinc salt poisoning catalyst.(2)Doping Nb2O5 improved the denitration activity of the Zn Cl2 poisoned catalyst.On the one hand,the doped Nb2O5 could interact with Zn Cl2 to consume a part of Zn2+,so that the amount of Zn2+ occupying the acid site of the catalyst decreased and the content of acid site increased.on the other hand,Nb2O5 loading caused the formation of new acid sites on the surface of the catalyst,and Zn-Nb-Mn-Ce/AC catalyst had more acid sites,which accelerated the adsorption and activation rate of reaction gas by the catalysts.(3)The addition of Nb2O5 significantly improved the anti-SO2 poisoning ability of Zn-Mn-Ce/AC catalyst.First,Nb2O5 preferentially reacted with SO2,slowing down the sulfation of the active metal(manganese/cerium)oxides on the catalyst.Secondly,Nb sulfate acidified by SO2 formed new acidic sites on the surface of the catalyst,which promoted the adsorption of alkaline gas NH3 by the catalysts.In addition,after doping Nb2O5,the adsorption of SO2 on the surface of the catalyst was inhibited,thereby reducing the reaction between SO2 and NH3.This process led to the blocked channel for the formation of the ammonium sulfate,and the active sites on the catalyst were not easily affected by the coating ammonium sulfate. |
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