Study Of Sulphur Poisoning And Regeneration Mechanism On Cu/SAPO-34 Catalysts

The Selective Catalytic Reduction?SCR?is one of the most efficient technologies to decrease the NO_x in the exhaust gas of mobile source,especially for diesel vehicle.Compared with the V₂O₅-WO₃-TiO₂,the Cu/SAPO-34 is a promising catalyst when facing the strict emission regulation.This paper is focused on how the different sulfated gasoues,including SO₃ and ammonia,and regeneration conditions affect the structure and the activity of Cu/SAPO-34 catalyst,aming to investigate the deactivation mechanism by SO₃ and different sulfate species as well as the recovery mechanism.Meanwhile,the sulfur poisoning and regernation on molinith was also investigated.In this way,we hope that it will supply principles for researching and developing new zeolites SCR catalysts.The deactivation mechanism by SO₃ in poisoning feed was investigated and a Cu/SAPO-34 catalyst was treated with 50 ppm SO₂ alone or SO_x at 250 ?.The SO_x sulfated catalysts show lower NOx conversions at kinetic region compared with the SO₂sulfated catalyst due to reduced number of active sites.More transformation of isolated Cu²⁺to copper sulfate arising from SO₃ poisoning is considered as the reason for the deactivation of Cu/SAPO-34 catalyst at kinetic region as their turnover frequencies?TOFs?are identical.Meanwhile,the phenomenon of dealumination,appearing different Si environments and non-framework Al,also occurs in the presence of SO₃.Our study reveals that both the decreased number of active sites and the breakage of Si-O-Al bonds contribute to the reduced SCR activity at high temperature.The deactivation mechanism by different types of sulfate was investigated and a Cu/SAPO-34 catalyst was treated with 50 ppm SO₂ alone at 150 and 250 ? or in the presence of a SCR feed at 250 and 350 ?.Copper sulfate was found on all sulfated catalysts,but ammonia sulfate was found only on the catalyst sulfated in the SCR feed at 250 ?.In situ DRIFTs results show that both copper sulfate and ammonia sulfate species are formed on the isolated Cu²⁺sites.All sulfated catalysts have lower NO_x conversions compared with the unsulfated catalysts due to reduced number of active sites.Since their turnover frequencies are identical,the deactivation mechanism is similar regardless of the type of sulfate species.On the other hand,it was found that ammonia sulfate was easier to remove than copper sulfate by a desulfation treatment at600 ?,resulting in a larger extent of activity recovery.The effect of regeneration conditions on sulfated catalyst were also investigated and a sulfated Cu/SAPO-34 was treated at different temperatures?500,600,650 or 750??or times?0.5,4,8 or 12 hours?.The results show that regerenation conditions do not affect Cu/SAPO-34's framework structure.TGA results show that sulfur amount decline as temperature and time increase.When sulfated sample treated at 750 ? for 8hours,the activity can be fully regenerated because of the amount isolated Cu²⁺can be restored to the initial content upon regeneration condition.Finally,the sulfur poisoning and regeneration method were treated on Cu/SAPO-34 molinith.The results show that the phenomenon about poisoning and regeneration on molinith is similar to that on Cu/SAPO-34.Besides,the effect of pore-forming agent on Cu/SAPO-34 molinith was also investigated.The forming pore benefit to the activity on fresh sample,however,the severe deactivation can be seen on the sulfated molinith.