Mechanism Study On Alkali Resistance Of SCR Vanadium-titanic-based Catalyst

As the core of SCR technology,catalysts are the main factor affecting the NOx removal efficiency and economical efficiency of the whole SCR system.The commercial VWTi catalyst used in coal-fired power plants is decorated in high temperature and high dust region due to its active temperature at present.Therefore,it will inevitably encounter alkali metals in the fly ash and cause poisoning deactivation.Alkali metal has various forms in dust,in literatures,the comparative study and of different form alkali metals and alkali poisoning resistance are less.Therefore,it is important and meaningful to study the poisoning mechanism of alkali metal in different form and to develop a catalyst with promotional effect as well as good alkali poisoning resistance.The work is taking VWTi catalyst as research object,studying the poisoning laws and mechanisms.On the basis of this,the VWTi catalyst was modified to enhance the performance of alkali poisoning resistance performance and the mechanism of alkali poisoning resistance was analyzed.First,the poisoning catalyst with different content of KCl,K2 O,NaCl and Na2 O loading was prepared by impregnation method and the effect denitrification efficiency and structural characteristics were studied.The denitrification efficiency of the catalyst decreases with the increase of the form of alkali metals oxide or chloride salt loading.The effect of K is stronger than that of Na,and the effect of chloride salt is stronger than that of oxide.SO2 has a significant mitigation effect for alkali poisoning.Alkali metal deposited on the catalyst will block the pores,decreasing the specific surface area and pore volume.The introduction of alkali metal has no noticeable effect for the pore structure and anatase phase of catalyst.Second,the poisoning mechanism of alkali metal in different forms was summarized.The alkali metal adsorption on the Br?nsted and Lewis acid sites decreased the amount of acid sites.Furthermore the reducibility of V and surface chemisorbed oxygen were increased,but the ratio of V5+ was decreased.The metal ions(K+ or Na+)of alkali metal oxide combine with V-OH to form V-O-K+(Na+);The metal ions(K+ or Na+)of chloride salt combine with V-OH to form V-O-K+(Na+)and HCl,and VO(OH)(Cl)2 was formed from HCl and VO2,which can increase the ratio of V5+.Finally,the mechanism of CeVWTi catalyst for alkali poisoning resistance was studied.The introduction of Ce can enhance denitrification efficiency and alkali metal poisoning resistance performance,and Na poisoning resistance performance is stronger than K.The V-O-Ce structure of resistance to alkali metal effect was formed from cerium and VOx.The introduction of Ce can improve surface acidity,the Ce3+-NH4+ as increase Br?nsted acid sites could be resulted by the transformation of Ce3+and Ce4+ under the action of surface hydroxyl and O2.Ce3+-NH4+ can evolve into-NH2(a),and then reaction with gas phase NO.The introduction of Ce can improve the chemisorbed oxygen concentration,redox cycle(V5++Ce3+?V4++Ce4+)exists over CeVWTi catalyst based on the electron transfer between Ce and V active sites.The redox cycle resulted in a decrease in the energy required,promoting the activation of NH3 and NO.