Controllable Preparation And Investigation On Sulfur Poisoning And Regeneration Of Cu/SSZ-13 NH₃-SCR 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 other zeolites catalysts,the Cu/SSZ-13 is a promising catalyst when facing the strict emission regulation.This paper focused on synthesis different particle size and the structure-acitivity relationship among particle sizes,NH₃-SCR performance,sulfur poisoning and regeneration,aming to investigate the particle sizes effect.Meanwhile,the poisoning by sulfur on molinith,coating with different particle size of Cu/SSZ-13 catalysts,was also investigated through bench test.In this way,we hope that it will supply principles for researching and developing new zeolites SCR catalysts.The preparation of different particle sizes of Cu/SSZ-13 was adjusted by controllable the amounts of seeds before crystallization.Our results reveal that adjusting of seeds amounts is the best method to synthesize uniform size with different particle size of Cu/SSZ-13 catalysts.Using different particle size of Cu/SSZ-13,the intracrystalline diffusion effect on NH₃-SCR reaction can be easily gotten.Our kinetic results justify that there is not exist intracrystalline diffusion effect on Cu/SSZ-13 catalysts because all catalysts with different particle sizes have identical Ea and TOFs values.As sulfur poisoning is a common issue in real applications,the structure-activity relationship among particle size,sulfur poisoning and regeneration should be considered.The structural characterizations show that the CHA structure is intact during sulfation.The EPR and TGA results suggest that Cu/SSZ-13 with different particle sizes gone through same sulfation condition results in same reduction of Cu²⁺ions and generation same sulfate species.Our study reveals that different particle sizes have no effect on resistance to sulfur poisoning.Besides that,the study of regeneration reveals that the different particle size does not influence the sulfur decompostition and regeneration performance.The sulfur poisoning mechanism of Cu/SSZ-13 catalyst(Si/Al=15)was investigated.Combined with the sulfur poisoning mechanism of Cu/SAPO-34 catalyst,the difference of SO₂ poisoning mechanism of Cu/Ch A catalyst was studied.Ex-situ DRIFTs results show that the CHA framework is intact after poisoning.SO₂-DRIFTs results reveal that the active sites at 8 MR could be easily poisoned,compared with that at 6 MR.The kinetic results show that a large amount of active sites decline make the decrease of NH₃-SCR performance and change of activation energy(Ea).Even though the poisoning mechanism of Cu/SSZ-13 is similar with that of Cu/SAPO-34,the degree of degration on Cu/SSZ-13 shows more serious.The regeneration mechanism of sulfur poisoned Cu/SSZ-13 and Cu/SAPO-34catalysts was investigated.The NMR results show that dealumination occur when regeneration temperature was higher than 700 ?.The H₂-TPR and EPR results show that the amounts Cu²⁺ions recovered because of decomposition of copper sulfate and copper migration during regeneration.However,the dealumination hinder the copper migration and as a result,the active sites in CHA cage amounts could not fully recover.The kinetic show that the recovered Cu²⁺ions have identical reaction rate for NH₃-SCR reaction compared with fresh ones.Compared with the good hydrothermal stability,regeneration of sulfated Cu/SSZ-13 catalysts should carfullyattent the regenerated temperature.Finally,combining with the emission standard of China VI,the sulfur poisoning and regeneration of coatings were studied in the engineering application stage by using the enlarged synthesis of Cu/SSZ-13 catalyst.The results show that the grain size has little effect on the sulfur poisoning and regeneration characteristics of the catalyst coating.The results of coatings evaluation show that sulfur poisoning mainly affected SCR activity below 250 ?,and the coating activity recovered after 600 ? treatment for 0.5 h.The bench test proves that the sulfated coating had the risk of NO_xemission exceeding the standard.However,the activity of the catalyst recovered after 600 ? high temperature activation.