Research On The Low Temperature Selective Catalytic Reduction Catalysts Based On SAPO-34 Zeolite

The commercial SCR catalyst V₂O₅-MoO₃?WO₃?/TiO₂ only works efficiently under300-350 ?,however,for many industrial applications,such as cement plants,steelworks and gas turbines,the suitable process temperature to arrange NO_x removal is usually below 200 ?,thus making it necessary to develop low temperature SCR catalysts to avoid reheating of the flue gas and reduce cost.Low temperature SCR catalysts xMn/SAPO and xMn-2Cu/SAPO were prepared by ion-exchange method,its crystal structure,surface area,NO oxidation capacity,chemical composition,acid site,chemical valence,redox capacity and adsorbed species was characterization by XRD,BET,TEM,NO oxidation,ICP,NH₃-TPD,H₂-TPR,UV-Vis,XPS and in-situ DRIFTS.In order to increase SO₂ resistance,doping element could be introduced into low temperature SCR catalysts,so the interactions between different supports and sulfate should be investigated to give support and evidence for screening of doping elements.The interactions between supports and sulfate were presented by the thermal decomposition reaction of NH₄HSO₄on different supports,which was characterized by TG,DSC and in-situ DRIFTS.The SCR activities of xMn/SAPO and xMn-2Cu/SAPO were evaluated using fixed-bed reactor system.They showed good activity under 120-210 ?,at 120 ? the NO conversion was above 50%for 4Mn/SAPO catalyst and above 60%for 4Mn-2Cu/SAPO.The characterization results of UV-Vis,XPS and H₂-TPR indicated that at low manganese loading manganese species mainly existed as Mn²⁺,while at high manganese loading manganese species mainly existed as Mn³⁺and Mn⁴⁺,which acted as active sites for low temperature SCR reaction.The promotion effect of Cu to xMn/SAPO for low temperature SCR activity mainly came from the increased NO oxidation capacity,the redox reaction between copper and mangenese species might be coupled into the catalytic cycle of xMn/SAPO.The characterization results of in-situ DRIFTS indicated that the catalytic mechanism on xMn/SAPO and xMn-2Cu/SAPO was Elay-Rideal mechanism and NH₃adsorbed on Br?nsted acid sites.In the catalytic cycle on xMn/SAPO,NH₃ was first adsorbed on Br?nsted acid sites,then it interacted with adjacent manganese oxides.After one of the hydrogen of NH₃ was captured by-Mn^?+-O^2-site,the remaining NH₂^-species was transferred to-Mn³⁺site and then oxidized to NH₂.At last the NO molecule from gas phase attacked the NH₂ species on-Mn²⁺site and formed NH₂NO-like transition state,which subsequently decomposed to N₂ and H₂O due to its instability.The characterization results of TG,DSC and in-situ DRIFTS indicated that the interactions between sulfate and Cr₂O₃ and activated carbon were weak,the interactions between sulfate and Al₂O₃,Co₃O₄,CuO,ZnO,MnO₂ and Mn₃O₄ were strong,the interactions between sulfate and CeO₂,Ni₂O₃ and TiO₂ were very strong.