Study Of Decomposition Mechanism Of ABS On Surface Of SCR Catalyst And Catalyst Modification

Selective Catalytic Reduction（SCR）is the mainstream technology for flue gas denitrification in coal-fired power plants.When the flue gas is denitrated,the formed ammonium bisulfate（ABS）will stick the fly ash and cause the catalyst to clog.With the full implementation of ultra-low emission and full-load denitration policies,it is extremely urgent to solve the problem of ABS blockage.Domestic and foreign scholars focus on the impact of ABS on catalysts from a macro level.The mechanism of adsorption and decomposition of ABS on the catalyst surface has not been discussed in depth.The adsorption and decomposition mechanism of ABS on the catalyst surface has not been discussed in depth.The existing research has contradictions on the effect of active substances on ABS decomposition,and lacks the ability and mechanism of different additives to solve the ABS blockage problem.In this paper,the adsorption and decomposition characteristics of ABS on the catalyst surface were studied by density functional theory（DFT）and related experiments.It is studied that ABS is preferentially dissociated and adsorbed on the surface of TiO2（001）on the surface of the carrier.The SO₄^2-ion generated by decomposition and the Ti atom are strongly bonded,resulting in an increase in the thermal decomposition peak temperature of ABS.Vanadium oxide inhibits the adsorption of ABS,forming a protective layer to isolate SO₄^2-ions and Ti atoms,thereby promoting ABS decomposition.The results show that the stronger the bonding strength between ABS and catalyst surface,the higher the decomposition temperature,which provides a theoretical basis for catalyst modification research.From a microscopic point of view,ABS will produce sulfur species and high-density vanadium oxide to increase catalyst activity after adsorption on the catalyst surface;At the macroscopic level,when the ABS content increases,the catalyst pore size will be blocked and the catalyst activity will decrease.The modification of the catalyst by DFT was carried out.Compared with W,Mo,Sb and Nb,it was found that W and Mo can improve the activity of the catalyst while ensuring the oxidation rate of SO₂.Only V₂O₅-MoO₃/TiO₂ has strong resistance of ABS plugging performance.V₂O₅-Sb₂O₅/TiO₂ can not form B acid,and will directly react with SO₂ to form SO₃;L acid of V₂O₅-Nb₂O₅/TiO₂ has weak attraction to electrons,and has higher SO₂oxidation rate.The activity experiments,TPDC and TPSR experiments show that V-5Mo/T catalysts have the strongest reaction at low temperature compared with V/T and V-5W/T catalysts,and can release SO₂ at lower temperature and reacts most strongly with NO after loading ABS.Through a series of characterizations,it is proved that after the dissociation adsorption of ABS on the surface of V-5Mo/T catalyst,the charge of S atom is basically unchanged,which promotes the thermal decomposition temperature to be greatly advanced.NH₄⁺mainly exists in the form of L acid adsorption,which enhances its low temperature reaction activity and promotes the decomposition of ABS.