晶化温度对ZSM-5铝分布的影响及其在苯-稀乙烯烷基化中的应用

采用晶种导向的方法,在不同晶化温度(80~170℃)下水热合成了b轴厚度为50 nm的ZSM-5分子筛;采用XRD、SEM、NH_(3)-TPD、Py-IR、XPS、ICP-AES、^(27)Al MAS NMR和UV-vis-DRS等手段对ZSM-5分子筛进行表征,研究了晶化温度对ZSM-5分子筛晶体生长和铝分布的影响,并考察了不同晶化温度制备的ZSM-5分子筛催化剂在苯-稀乙烯烷基化反应中的催化性能。结果表明:晶化温度改变了ZSM-5分子筛的铝分布,从而影响分子筛的酸性质和烷基化反应性能;低晶化温度80℃下制备的ZSM-5分子筛具有酸性弱,总酸量少、Lewis酸以及外表面酸中心少,骨架铝(Al_(F))主要分布在直孔道和交叉孔道处;在反应温度360℃、压力1.4 MPa、苯/稀乙烯摩尔比1、稀乙烯质量空速1.5 h^(-1)、反应时间35 h的条件下,H-ZSM-5-80分子筛催化苯-稀乙烯烷基化反应,乙基选择性最高为95.4%,副产物二甲苯选择性最低为0.09%。

Correlation between H-ZSM-5 crystal size and catalytic performance in the methanol-to-aromatics reaction

The porosity of H‐ZSM‐5zeolite is known to facilitate the diffusion of molecules in the methanol‐to‐aromatics(MTA)reaction.The activity and selectivity of the H‐ZSM‐5catalyst in the MTAreaction has been studied as a function of crystal size.ZSM‐5zeolites with different crystal sizeswere successfully synthesized by conventional hydrothermal methods.Tailoring ZSM‐5particle sizewas easily controlled by changes to the sol‐gel composition,and in particular,the deionized waterto tetrapropylammonium hydroxide ratio,and crystallization time.The structure of the H‐ZSM‐5zeolites were characterized by X‐ray diffraction and the morphology of the zeolite particles wasdetermined by scanning electron microscopy.N2adsorption‐desorption measurements establishedchanges to the textural properties,and compositional properties were characterized by X‐ray fluorescencespectroscopy.Acidity measurements of the catalysts were measured by pyridine‐adsorbedFourier transform infrared spectroscopy and the temperature‐programmed desorption of ammonia.After subjecting the catalysts to the MTA reaction,the total amount of coke formed on the spentdeactivated catalysts was determined by thermal gravimetric analysis.The results show that theSiO2/Al2O3molar ratios and acidic properties of the H‐ZSM‐5samples are similar,however,thenano‐sized hierarchical ZSM‐5zeolite with an additional level of auxiliary pores possesses a higher

Zn/NaHZSM-5沸石在C5～C8链烷烃芳构化反应中的催化性能

采用氨气程序升温脱附(NH3-TPD)、紫外-可见光谱和小型固定床反应器,重点研究了碱金属钠离子和过渡金属锌离子改性对纳米H-ZSM-5沸石表面酸性及其催化C5~C8链烷烃芳构化反应性能的影响。结果表明,用碱金属钠离子改性能够有效地消除沸石表面的强酸中心,适当降低催化剂表面酸量,从而减少甲烷、乙烷和丙烷等低值副产物的生成,优化芳构化反应产物分布。适宜的Zn^2+负载量为3%(质量分数),过高的Zn^2+负载量会使产物中干气生成量增大,不利于芳烃收率的提高。C5~C8链烷烃芳构化的适宜反应温度为530℃。