| Nitrogen oxides(NOx)are kinds of the most important air pollutants,which can participate in the formation of haze,photochemical smog,acid rain,et al.The flue gas from stationary source still accounts for the majority of NOx in China.With the implement of ultra-low emission in power industry,control of NOx from non-power industry is becoming crucial.Selective catalytic reduction of NOx by NH3(NH3-SCR)is widely used in powder industry.However,the special temperature window and complexity of flue gas in non-power industry confines the use of NH3-SCR technology.The flue gas from industry boiler comprises particulates,sulfur oxide,and nitrogen oxides.In practical applications,the pollution control in flue gas is mostly completed by combination of various separate units corresponding to one pollutant.How to design the multifunctional unit which has coupled effects of de-NOx and dust precipitation becomes more interesting.The dust precipitation modules comprise bag filters that intolerance to high temperature and SiC filter with large self-weight Therefore,a support with light weight and high dust precipitation efficiency is needed.In this thesis,the fibrous ceramic membrane(porosity-68%,apparent density-0.625 g/cm3)with high strength were used as support,and loaded with NH3-SCR catalysts in order to obtain catalytic membrane with low pressure drop and high de-NOx efficiency.The catalysts composition,microstructure,depositing method and the catalytic performance were investigated.The main research content and conclusions were as follows.(1)Using manganese and cerium nitrates as raw materials,Mn-Ce oxides catalysts were loaded on fibrous ceramic membrane with light weight,high strength and low pressure drop,in order to obtain catalytic ceramic membrane.The effects of loading weights and molar ratios of Mn/Ce on catalytic performance were investigated.The catalytic membrane with Mn/Ce molar ratio of 6/4 performed a best de-NOx performance,with more than 90%de-NOx efficiency in the temperature range of 120-250℃;mainly because the abundance of Mn4+,surface oxygen species,and acid sites facilitate the low temperature SCR.Due to a small amount of catalysts on membrane,and the poor anti-sulfur characteristics of manganese catalysts,the catalytic performance of Mn-Ce based membrane decreased when introducing SO2 in flue gas.(2)The Fe-Mn/zeolite catalysts were prepared by employing ZSM-5,25beta and 40beta as supports and iron nitrates,manganese nitrates as precursors through a co-precipitation method.The influence of support on de-NOx and its mechanism were analyzed.Fe-Mn/25beta catalyst showed the best catalytic performance,and it was loaded onto the membrane to obtain catalytic membrane with good low temperature SCR and anti-sulfur performance.Fe-Mn/25beta can obtain 100%NO conversion in a wide temperature window of 220-450℃,mainly because Fe and Mn elements can easily enter the matrix of beta zeolites.However,more metal oxides aggregated on the surface of ZSM-5,leading to poor anti-sulfur performance of Fe-Mn/ZSM-5.Fe-Mn/25beta powder were loaded onto ceramic membrane,and compared with powder catalysts,its high temperature performance increased,low temperature and anti-sulfur performance decreased.(3)The vanadium-titanium composites with large specific surface area were obtained by employing porous silica(MCM,BET=1188.7 m2/g)as supports and vanadyl acetylacetonate,tetrabutyl titanate as precursors through a sol-gel route.The powder catalysts were then loaded onto ceramic membrane to obtain vanadium titanium based catalytic membrane.The vanadium-titanium composites first filled in the channel of MCM,and then aggregated MCM sphere s’ surface.The filling of composites may lead to breakage of channels.It was shown that 5 V2O5-20TiO2/MCM(the number denoted as loading weight of V2O5 and TiO2 on MCM)performed more than 90%NO conversion in 250-450℃.The NO conversion decreased from 90%to 80%when introducing SO2 into flue gas(T=330℃).However,when loading the powder onto ceramic membrane,the NO conversion of catalytic membrane decreased to less than 50%(4)The vanadium-titanium-silicon porous composites were synthesized by using tetraethyl orthosilicate,tetrabutyl titanate and vanadyl acetyacetonate as raw materials through a sol-gel route.The catalysts with best SCR performance were loaded onto ceramic membrane by one-step sol-gel method(FC-sg),two-step sol-gel method(FC-2)and particle loading method(FC-p)to obtain catalytic membrane.The specific area of composites was increased with the contents of silica;however,more silica would lead to worse dispersion of vanadium oxide,thus leading to NO conversion decrease.The de-NOx temperature window moved to low temperature range with high vanadium loading.The catalysts with wide temperature window(230-470℃ with more than 90%NO conversion)was 10V-90Ti10Si.The influence of loading methods were investigated,and it was shown the catalytic performance followed FC-sg≈FC-p>FC-2.The FC-2 sample showed the worst catalytic performance,mainly because the vanadium species removed to membrane surface,leading to aggregated V2O5 species. |
