气相转移法与水热合成法合成ZSM-5/SAPO-5核壳结构复合分子筛的比较

以磷酸、拟薄水铝石和硅溶胶为原料,三乙胺为模板剂,在不同晶化温度和晶化时间的实验条件下,分别采用水热合成法和气相转移法合成了一系列ZSM-5/SAPO-5核壳结构复合分子筛,并用X射线衍射、扫描电镜、X射线能量散射谱、红外光谱和N2吸附等手段对其进行了表征.结果表明,所合成的分子筛是以ZSM-5为核,以SAPO-5为壳的双结构复合分子筛.晶化温度的提高和晶化时间的延长有利于分子筛结晶度的提高.与水热合成法相比,采用气相转移法可以减小壳层SAPO-5的颗粒尺寸,减少脱离ZSM-5表面独立生长的SAPO-5的量,改善SAPO-5在ZSM-5表面的分布.重油裂化结果表明,核壳结构复合分子筛对生成低碳烯烃的催化性能优于机械混合的样品.

Comparison of Core/Shell Binary Structure Zeolite ZSM-5/SAPO-5 Synthesized by Vapor-Phase Transport and Hydrothermal Synthesis

A series of ZSM-5(core)/SAPO-5(shell)binary structure zeolite samples were synthesized by hydrothermal synthesis and vapor-phase transport at different crystallization temperatures for different time.Phosphoric acid,pseudoboehmite,and silica sol were used as phosphorus,aluminum,and silicon sources,respectively.Triethylamine was used as template.The zeolite samples were characterized by means of X-ray diffraction,scanning electron microscopy,X-ray energy dispersive spectroscopy,Fourier transform infrared spectroscopy,and N2 adsorption.The zeolite samples had binary structure with a ZSM-5 core and a SAPO-5 shell.The crystallinity of the zeolite samples increased as the crystallization temperature was increased and the crystallization time was protracted.Using the vapor-phase transport technique for synthesis of binary structure zeolite could reduce the SAPO-5 particle size and the amount of self-existent SAPO-5 zeolite and improve the distribution of SAPO-5 on the ZSM-5 surface.The experiments of heavy oil cracking showed that the core/shell binary structure zeolite samples were more favorable for the formation of light olefins than the mechanical mixture.