环状ZSM-5分子筛的合成与表征

Synthesis and characterization of cyclic ZSM-5 zeolite

低温条件下,以四丙基氢氧化铵(TPAOH)为模板剂、偏铝酸钠为铝源、正硅酸乙酯为硅源,采用水热合成法合成环状ZSM-5分子筛,考察了陈化温度、硅铝比和模板剂用量对分子筛环状结构形成的影响。利用XRD,SEM,TEM,N_(2)吸附-脱附等方法对环状ZSM-5与常规ZSM-5分子筛的形貌、晶体结构和孔结构进行表征。实验结果表明,较低的陈化温度(0℃)、低硅铝比(n(SiO_(2))∶n(Al_(2)O_(3))≤60)、n(TPAOH)∶n(SiO_(2))=(10~13)∶30的条件有利于形成环状结构的ZSM-5分子筛;与常规ZSM-5分子筛相比,环状ZSM-5分子筛形貌规整、结晶度高、分散更均匀,且由于环状中空结构的存在,环状ZSM-5分子筛的比表面积略高于常规ZSM-5分子筛;所得环状ZSM-5分子筛在催化苯和乙醇制乙苯反应中表现出较好的乙苯选择性。

Cyclic ZSM-5 zeolite was synthesized at low temperature by hydrothermal synthesis method using tetrapropylammonium hydroxide(TPAOH)as template,sodium aluminate as aluminum source and tetraethoxysilane as silicon source.The effects of aging temperature,silica/alumina ratio and the amount of template on the formation of cyclic structure of the zeolite were investigated.XRD,SEM,TEM and N_(2) adsorption-desorption,and other methods were used to characterize the morphology,crystal structure and pore structure of cyclic ZSM-5 zeolite and routine ZSM-5 zeolite.The experimental results show that the conditions of lower aging temperature(0℃),lower silica/alumina ratio(n(SiO_(2))∶n(Al_(2)O_(3))≤60)and n(TPAOH)∶n(SiO_(2))=(10-13)∶30 are beneficial to the formation of cyclic ZSM-5 zeolite.Compared with routine ZSM-5 zeolite,cyclic ZSM-5 zeolite has regular morphology,high crystallinity and more uniform dispersion.Due to the existence of cyclic structure,the specific surface area of cyclic ZSM-5 zeolite is higher than that of routine ZSM-5 zeolite.The cyclic ZSM-5 zeolite shows good selectivity in the catalytic reaction of benzene and ethanol to ethylbenzene.