Preparation And Properties Of Co-Ti Based NH₃-SCR Catalysts

Nitrogen oxides(NO_x),as one of the main atmospheric pollutants,cause acid rain and photochemical smog,which greatly damage the environment.At present,selective catalytic reduction of NO_x by NH₃(NH₃-SCR)is an effective NO_x removal method.At present,the flue gas emission temperature of various industrial furnaces and other fixed sources is lower than 300 ^? or even lower,while the active temperature window of traditional commercial vanadium catalyst(300-400 ^?)cannot meet the above denitrification requirements.Therefore,it is of great significance to prepare catalysts with good low-temperature NH₃-SCR activity.Co oxide has a strong oxidation capacity,suitable for low temperature NH₃-SCR catalyst requirements.Therefore,this paper studied Co-Ti based SCR catalyst and improved its catalytic performance by W and Ce doping to meet the requirements of low temperature flue gas denitration.XRD,N2physical adsorption,Raman spectroscopy,TEM,H₂-TPR,NH₃-TPD,XPS and in-situ DRIFTS were used to investigate the effect of W and Ce modification on the structure and performance of the catalyst.A series of Co_mTiO_x(m=0.2,0.25,0.3,0.35 and 0.4)composite metal oxide catalysts were prepared by sol-gel method.The effects of different Co contents on the SCR activity of catalysts were studied,and it was found that Co_0.4TiO_x catalyst had the best low temperature activity.However,its activity temperature window was too narrow(190-220 ^?),and N₂ selectivity was poor.In order to improve the active temperature window,a series of W-modified W_aCo_0.4TiO_x catalysts(a=0.04,0.06,0.08 and 0.10)were also prepared by sol-gel method.Compared with Co_0.4TiO_x,W_aCo_0.4TiO_x catalyst has better activity.Among them,W_0.08Co_0.4TiO_x catalyst has wider activity window(190-430 ^?),good N₂ selectivity and high temperature resistance to H₂O/SO₂ while maintaining low temperature activity.This is because W doping can increase the BET specific surface area of the catalyst and improve the surface acidity of the catalyst,especially the Br(?)nsted acid content.In-situ DRIFTS tests were carried out to investigate the reaction process on the surface of the catalyst and the mechanism of its H₂O/SO₂ resistance performance.However,the low temperature SO₂ resistance of the catalyst is still poor.In order to improve the low temperature SO₂ resistance of W_0.08Co_0.4TiO_x catalyst,a series of W_0.08Ce_nCo_0.4-nTiO_x(n=0.1,0.2 and 0.3)catalysts were synthesized by doping Ce on the basis of W_0.08Co_0.4TiO_xcatalyst.Among them,W_0.08Ce_0.1Co_0.3TiO_x catalyst not only significantly improved its catalytic activity at low temperature(160-450 ^?),but also showed good SO₂ resistance at 200 ^?.Various characterization results show that the good low temperature activity is related to the good storage and release capacity of Ce oxide.The excellent sulfur resistance is related to the fact that Ce can react with SO₂ as a sacrifice site and inhibit the formation of cobalt sulfate.Therefore,the co-modification of W and Ce regulated the surface acidity and oxidation of the catalyst,and the synergistic effect between surface acidity and oxidation of the catalyst promoted the low-temperature SCR activity.