Synthesis Optimization And Application Of SSZ-13 Zeolite

With the rapid growth of the social economy,environmental problems have become increasingly prominent.Air pollution such as haze,acid rain,and ozone pollution has hindered sustainable development.The study found that the treatment of nitrogen oxides is the key to solving the problem of air pollution.Therefore,the denitration technology of industrial flue gas and diesel exhaust has been continuously developed.Currently,the NH3-SCR reaction is regarded as one of the more popular denitration technologies because of its excellent nitrogen oxide conversion rate.The small pore SSZ-13 zeolite has high stability and excellent water-resistant and low-temperature NH3-SCR performance.The classic SSZ-13 zeolite hydrothermal synthesis process requires the use of a large amount of expensive template agent N,N,N-trimethyl-l-adamantyl ammonium hydroxide(TMAdaOH),which not only increases the production cost but also limits its application.In summary,it is of great economic and social significance to find an economical industrial production method for SSZ-13 zeolite.Based on the background,this article carried out three aspects of work:(1)Tetramethylammonium hydroxide(TMAOH),choline chloride,and KOH were used to partially replace TMAdaOH.The purpose was to explore the role of the double template in the synthesis of SSZ-13 zeolite.The experimental results show that the synthesis of SSZ-13 zeolite with TMAdaOH single template can not be achieved when the amount n(TMAdaOH/Al(OH)3)is less than 0.4.Appropriate amount of TMAOH,choline chloride or KOH combined with TMAdaOH can be used as a mixed template to synthesize SSZ-13 zeolite.According to XRD,FT-IR and BETcharacterization,SSZ-13 zeolite with high crystallinity,high specific surface area and perfect pore structure can be synthesized under these optimized conditions:n(TMAdaOH)/n(TMAOH)=0.4/0.6,n(TMAdaOH)/n(TMAOH)=0.3/0.7 and n(TMAdaOH)/n(KOH)=0.4/1.6.(2)In the mixed template agent system,through the adjustment of water content,the effect of water amount on the synthesis of SSZ-13 zeolite was studied to explore its optimal water content.The results show that:In the synthesis system of n(TMAdaOH)/n(TMAOH)=0.4/0.6,when the water content is less than n(H2O)=480,some balance of silicon,aluminum and templating agent is broken,and the crystal quality of the sample was reduced and SOD zeolite was synthesized.With the further reduction of water content,it is obvious that the crystal quality of the sample begins to improve when n(H2O)=240,indicating that the equilibrium in the reaction system will be re-formed at a new critical point.In the TMAdaOH/KOH synthesis system,K+ can still be used to synthesize SSZ-13 zeolite with TMAdaOH at low water content.At this ratio n(H2O)=180 n(TMAdaOH)/n(KOH)=1.0/2.0,the synthesized samples have higher relative crystallinity and better pore structure properties.(3)Based on the synthesized SSZ-13 zeolite sample,Cu-SSZ-13 and Cu/M-SSZ-13 bimetallic catalysts were prepared by ion exchange to explore their NH3-SCR performance.The results show that the activity of Cu-SSZ-13 catalyst will be improved with the increase of Cu loading,and the optimal value is Cu4.31-SSZ-13.The excessive Cu loading of the sample Cu8.06-SSZ-13 resulted in poor catalytic performance,indicating that excessive Cu would inhibit the catalytic activity.After adding new metals(Fe,Mn,Co)to prepare Cu/M-SSZ-13 bimetallic catalyst,the catalytic activity has been improved.Mn0.82/Cu-SSZ-13 showed excellent activity in the low temperature region,and Fe1.29/Cu-SSZ-13 showed high activity in the high temperature region.