母液中Na_2O和Na_2SO_4对无模板剂合成ZSM-5分子筛的影响

Effect of Na_2O and Na_2SO_4on the Synthesis of ZSM-5 by Template-free Crystallization Method

以水玻璃为硅源在无模板剂条件下合成ZSM-5分子筛,体系中Na2O含量通过加入硫酸进行调变。实验详细考察了不同水硅比条件下母液中Na2O和Na2SO4对ZSM-5分子筛合成的影响,并采用XRD、SEM等手段对合成样品进行表征。结果表明,母液中Na2O的比例不仅起到调节碱度的作用,同时对ZSM-5的形成具有结构导向性。当Na2O含量过高时,产物易出现MOR杂晶相,而Na2O含量过低则产生无定形物质。另外,随着母液中水硅比的减小,合成ZSM-5体系所需Na2O/SiO2的范围也相应变窄。合成体系中的Na2SO4对ZSM-5分子筛的晶相影响不大,然而对ZSM-5分子筛的结晶速度有着显著的影响。

ZSM-5 was synthesized by template-free method using sodium silicate as a silica source and the content of Na2O in mother liquid was controlled by H2SO4.The effects of Na2O and Na2SO4 on the synthesis of ZSM-5 were systematically studied.The produced samples were investigated using XRD,SEM.The results showed that the content of Na2O in mother liquid played an important role as a structure directing agent.Mordenite phase was obtained if the content of Na2O is too high while an amorphous phase was obtained if its content was too low.The Na2O composition window for ZSM-5 phase was narrowed as the molar ratio of H2O/SiO2 decreased.It was found that the content of Na2SO4 in mother liquid had no evident effect on the phase of ZSM-5,while the crystallization time decreased for the enhanced condensation reaction by the oxyanion effect of Na2SO4.