硅源对纳米级ZSM-5分子筛结构及其对甲醇转化制丙烯与丁烯反应催化性能的影响

采用低温水热晶化法,以四丙基氢氧化铵为模板剂,分别使用98%粗孔固体硅胶和30%硅溶胶为硅源,制备不同硅铝物质的量比的纳米级ZSM-5分子筛,研究硅源对其物化结构及甲醇转化制丙烯与丁烯催化性能的影响。结果表明,硅源种类影响ZSM-5分子筛的结构及铝分布,进而影响其酸性和催化性能。固体硅胶为硅源,有利于形成弱酸性位点;硅溶胶为硅源,有利于形成强酸性位点。在相同硅铝物质的量比时,以固体硅胶为硅源的ZSM-5分子筛的总酸量小于以硅溶胶为硅源的样品。无论使用何种硅源,对ZSM-5分子筛的晶型结构影响不大,且ZSM-5分子筛颗粒形貌均呈现为由小晶粒堆积成(500~1 000)nm的类球形颗粒。以硅溶胶为硅源制备的样品颗粒尺寸大于以固体硅胶为硅源制备的样品。硅铝物质的量比为400时,两种硅源合成分子筛的丙烯与丁烯的选择性相近,但以硅溶胶为硅源的ZSM-5分子筛的寿命更长。

Effects of silicon sources on structure and catalytic performance of nano-ZSM-5 zeolite for methanol to propylene and butylene

Using tetrapropyl ammonium hydroxide as the template and 98% crude solid silica and 30% silica sol,respectively,as silicon source,a series of nano-ZSM-5 zeolites with different SiO2/Al2O3 molar ratios were prepared by low temperature hydrothermal crystallization method.The effects of silicon sources on the structure and catalytic performance of the as-prepared nano-ZSM-5 zeolites for methanol to propylene and butylene reaction were investigated.The results showed that the types of silicon sources affected the structure and aluminum distribution of ZSM-5 zeolite,and then affected its acidity and catalytic performance.Using the solid silica as silicon source was beneficial to forming weak acid sites,while using the silica sol as silicon source was beneficial to forming strong acid sites.The amounts of total acid sites of ZSM-5 zeolite with solid silica as silicon source was smaller than those of ZSM-5 zeolite with silica sol as silica source under the same SiO2/Al2O3 molar ratio.No matter which silicon source was used,the crystal structure of ZSM-5 zeolite was almost the same,and the particle morphology of ZSM-5 zeolite was the large spherical particles of about (500-1 000) nm composed of the accumulation of small crystals.The size of spherical particles of ZSM-5 zeolite with silica sol as silicon source was larger than that of ZSM-5 zeolite with solid silica as silicon source.The selectivity to propylene and butylene over ZSM-5 zeolite with two types of silicon sources was similar,while the lifespan of ZSM-5 zeolite with silica sol as silicon source was longer than that of ZSM-5 zeolite with solid silica as silicon source under SiO2/Al2O3 molar ratio of 400.