无孪晶片状ZSM-5分子筛的合成及MnO_(x)改性后的物化性质与烷烃裂解性能

Synthesis of plate-like twin-free ZSM-5 zeolite and its physicochemical properties and alkane cracking performance after MnO_(x) modification

在无有机胺(铵)体系中,分别以纳米薄层ZSM-5和silicalite-1为晶种合成了无孪晶片状ZSM-5分子筛(EZ-NS)和有孪晶棺状ZSM-5分子筛(EZ-S1),并用Mn_(2)O_(3)对分子筛进行水热改性,利用SEM、XRD、FTIR、TEM、N_(2)吸附-脱附、NH_(3)-TPD、Raman光谱等对分子筛进行了表征,考察了分子筛的己烷催化裂解反应性能。实验结果表明,EZ-NS相比EZ-S1具有更大的微孔比表面积和微孔体积、更多强酸位,暴露的直通孔道与正弦孔道的比例高,导致两种分子筛晶内扩散性能存在差异。调节晶种用量和乙醇添加量可实现片状分子筛的可控合成。Mn_(2)O_(3)水热改性分子筛时,片状分子筛EZ-NS更有利于金属物种的均匀分布及保持反应过程中的酸性质和骨架结构,有利于提高低碳烯烃选择性和反应稳定性。

Plate-like twin-free ZSM-5 zeolites(EZ-NS) and coffin-shape ZSM-5 zeolites with twin structure(EZ-S1) were synthesized in a no-organic amine(ammonium) system by using nanosheet ZSM-5and silicalite-1 as crystal seed respectively,and hydrothermal modified with Mn_(2)O_(3).The zeolites were characterized by SEM,XRD,FTIR,TEM,N_(2) adsorption-desorption,NH_(3)-TPD and Raman.Their catalytic performances for n-hexane cracking were investigated.Results show that compared with EZ-S1,EZ-NS has larger micropore surface area and micropore volume,more strong acid site and higher ratio of straight channel to sinusoidal channel,causing the difference in diffusion properties of the two zeolites.The synthesis of plate-like zeolites can be controlled by adjusting the amounts of seed and ethanol.In hydrothermal modification of zeolites with Mn_(2)O_(3),EZ-NS is more conducive to the uniform distribution of metal species and the preservation of acid properties and framework structure during the reaction process,which is beneficial to improve the light olefins selectivity and reaction stability.