Synthesis Of A New Copper-based Small Pore Molecular Sieve And Study On Exhaust Gas Purification Of Diesel Vehicles

At present,diesel vehicles in my country still play an irreplaceable role in the field of traditional energy.Controlling NO_x pollution is the top priority in building a blue sky defense war.NH₃-SCR technology is one of the main technologies to solve NO_x pollution in diesel vehicle exhaust in my country.Copper-based small pore zeolite is the most attractive catalytic material in this technology.However,the traditional synthesis process conditions of this zeolite are harsh,and the preparation process The templating agent is expensive,which greatly limits its application.Therefore,the green synthesis of copper-based SSZ-13 without template is a promising research hotspot.In this paper,SSZ-13 molecular sieve was used as the seed crystal,and the low-cost high-silicon Cu-SSZ-13_seed catalyst was successfully prepared by the seed-assisted guiding method,which showed a good performance comparable to Cu-SSZ-13_con prepared by the traditional template method.It has medium and low temperature activity,and also has anti-HC/SO₂ poisoning performance and good stability.It has a better application prospect in the future diesel vehicle exhaust denitrification.The main contents and conclusions are as follows:（1）The SSZ-13_seed molecular sieve was synthesized by the seed-assisted guided method,and the molecular sieve was characterized by XRD,SEM and other technologies,and the content of seed crystals,crystallization temperature,crystallization time,silicon-to-aluminum ratio and seed state were discussed and analyzed Impact on the synthesis of molecular sieves.The results show that the optimal process conditions for the synthesis of SSZ-13_seed molecular sieve by seed assisted guiding method are:the unbaked SSZ-13molecular sieve with a content of 15%is used as the seed,and the silicon-to-aluminum ratio is 20 at 100℃for 4 days of hydrothermal treatment.（2）On the basis of the optimal process conditions,by observing the morphology and structure changes of SSZ-13_seed zeolite under different crystallization times（2 h,5 h,8 h,12h and 24 h）,reveal the seed assist Guide the crystallization kinetics of the synthesis process.The results of the study show that there are three transitional stages in the zeolite phase structure during the crystallization process:the cross promotion of amorphous silica-alumina gel and seed crystals,the growth of colloidal particles and seed crystals,and the combination and aggregation of colloidal particles and seed crystals.The whole crystallization process is consistent with The"core-shell"growth mechanism that takes the seed crystal as the core,the Si source and the Al source as the shell and continues to grow on the seed crystal matrix.（3）The SSZ-13_seed molecular sieve synthesized by the seed-assisted guided method is synthesized by ion exchange method to prepare and synthesize Cu-SSZ-13_seed,and investigate its catalytic elimination of NO_x in the simulated diesel vehicle exhaust complex environment（including CH_x,SO₂ and H₂O）performance.The results show that the Cu-SSZ-13_seed synthesized by the seed-assisted guiding method is similar in structure to Cu-SSZ-13_conprepared by the traditional template method,and the Cu-SSZ-13_seed prepared by the seed-assisted guiding method has the same structure as Cu-SSZ-13_con.In addition,the Cu-SSZ-13_seed prepared by the seed-assisted guiding method exhibits good mid-low temperature activity comparable to Cu-SSZ-13_con:that is,the NO conversion rate at 190°C reaches more than 95%,and the high activity can be maintained to 400°C.In addition,Cu-SSZ-13_seedcatalyst also has excellent anti-HC/SO₂ poisoning performance and good stability.