Study On Acidity Control Of SAPO-LTA Molecular Sieve By Ion-thermal Method And Catalytic Performance Of NH₃-SCR

With the rapid development of industrial technology and the rapid increase in the number of vehicles per capita,the atmospheric pollutants of nitrogen oxides emitted by industrial processes and automobile exhaust are gradually increasing.At present,one of the most effective methods for removing nitrogen oxides from the exhaust gas of thermal power plants or automobiles is the NH3-SCR technology.The metal ion-exchanged small-pore molecular sieve has the characteristics of high low-temperature activity and good hydrothermal stability,and its application prospects are broad.In particular,the LTA structure silica-alumina molecular sieve has excellent stability in high temperature hydrothermal aging at 900℃,but the synthesis cost of the molecular sieve requires the use of expensive template agents,so commercial applications are limited.In this thesis,SAPO-LTA is synthesized by ion heat,and the influence of synthesis conditions on the acidity of molecular sieve and the catalytic performance of SCR denitrification is deeply studied.The main research results are as follows:Ion exchange conditions have an important influence on the catalytic performance of Cu-SAPO-LTA molecular sieve.Too long low-temperature water heat exchange time will easily lead to the collapse of the framework structure.The optimal ion exchange condition is determined to be 0.1 M NH4NO3 solution exchange for 1 h,then 0.01 M Cu(AC)2 solution exchange for 1 h.The reduction of fluoride ion concentration is beneficial to increase the silicon doping amount and acidity of SAPO-LTA molecular sieve,and improve the SCR catalytic performance of Cu-SAPO-LTA.This is because the reduction of fluoride ion causes the charge of the template agent to pass through the silicon doping.The formed framework has a negative charge balance,which promotes the entry of silicon and the generation of acidic centers in the molecular sieve framework.Using tetraethylorthosilicate and silica sol as silicon sources,SAPO-LTA molecular sieves with higher crystallinity can be prepared in a wide range.As the amount of silicon added increases,the SCR catalytic activity first increases and then decreases.This is because as the amount of silicon doping increases,the acidity of the molecular sieve and the exchange capacity of Cu ions have increased.However,as the amount of silicon added continues to increase,the silicon cannot be fully doped into the molecular sieve framework,resulting in a large amount of non-amorphous phase.The fixed phase is therefore not conducive to the increase of molecular sieve acidity and copper ion exchange.