Experimental Study On Low Temperature SCR Denitrification Catalyst And Molding

NH₃-SCR is one of the most effective denitration methods to control nitrogen oxides in flue gas.Catalyst is the core of SCR technology.At present,the activity of powder catalyst is superior,but powder catalyst can not be directly used in industry.The existing commercial vanadium catalyst is aimed at high temperature SCR.Therefore,to study cheap and effective molding catalyst of low temperature has a great prospect in industrial application.In the work,active carbon（AC）and fly ash（FA）,adding TiO₂,were selected as support to prepare series of catalysts by integral extrusion molding.First,the effects of different TiO₂ doping ratios of molding catalysts on low temperature activity were studied experimentally.At the same temperature,with the increase of TiO₂,NO conversion rate and denitration rate of molding catalysts increased,and NO₂ formation rate decreased.When the doping amount of TiO₂ was large,inhibition effect of the catalyst was more obvious,which decreased N₂O formation rate.Compared with 30%TiO₂,the increase trend of denitration rate on 8.5%Mn-Ce/AC-100%TiO₂ and 8.5%Mn-Ce/AC-100%TiO₂ was not obvious.Considering the cost,30%TiO₂ was the best doping amount.Then the activity of powder and molding catalyst of two carriers（FA and AC）was compared in the case of doped and undoped TiO₂.The rates of NO conversion,NO₂formation,N₂O formation and denitration of powder catalyst were all higher than those of moliding catalyst.BET showed that specific surface area of molding catalyst was larger than that of powder catalyst,while pore volume was less than powder catalyst.XRD showed that carriers with TiO₂ did not change crystal structure,and active components MnOx and CeOx highly dispersed on the surface of catalyst.SEM showed that the surface of FA was formed clusters after TiO₂ addition,and the powder catalyst which supported on AC had well-developed porous structure.However,binder covered on the surface of molding catalyst and then blocked part of pores.In addition,the low temperature catalytic activity of molding catalyst was studied under different space velocity,oxygen concentration and ammonia nitrogen ratio.The rates of NO conversion,N₂O formation and denitration decreased with the increase of space velocity.NO₂ formation rate did not change with space velocity.When oxygen concentration was over6%,rates of NO conversion and denitration increased slowly,while the amount of NO₂ and N₂O was gradually increased at 9%O₂.With the increase of ammonia nitrogen ratio,rates of NO conversion,denitration and N₂O formation of molding catalyst increased,but NO₂formation rate was not related to ammonia nitrogen ratio.The effects of 100ppm and 200ppm SO₂,3%H₂O and 6%H₂O on catalytic activity were studied.In the presence of H₂O and SO₂,rates of NO conversion and denitration decreased.The addition of SO₂ and H₂O could reduce the amount of N₂O,but had no effect on NO₂ formation rate.At last,in order to develop a more efficient molding technology,3D printer was used to"print"molding catalyst.Compared with low temperature activity of integral extrusion molding catalyst and powder catalyst,it was found that the 3D print catalyst had better activity and great industrial application prospect.