模板剂种类对ZSM-22分子筛的酸性和正癸烷加氢异构化催化反应性能的影响

分别以1,6-己二胺和1-乙基溴化吡啶为模板剂,采用静态晶化法合成了不同硅铝比的ZSM-22分子筛;采用XRD、XRF、N₂物理吸附、SEM、NH₃-TPD和Py-IR等手段对分子筛的结构和酸性进行了表征;采用浸渍法制备了0.5%Pd/ZSM-22双功能催化剂,对金属Pd的分散度用H₂化学吸附进行表征,并在微型固定床反应器上考察了该催化剂对正癸烷加氢异构化反应的催化性能。结果表明,模板剂种类显著影响ZSM-22分子筛的结构和酸性,以DAH为模板剂合成的ZSM-22分子筛晶粒粒径小,异构化产物从分子筛孔道内扩散的程距更短,而且具有更高的B/L值和相对温和的酸性,在正癸烷加氢异构化反应中,金属位与分子筛的酸性位实现协同催化作用,具有更高的催化活性和异构化选择性。

Influence of different templates on the acidity of ZSM-22 zeolite and its catalytic performance for hydroisomerization of n-decane

ZSM-22 zeolites with different SiO₂/Al₂O₃ ratio were synthesized under static conditions by using 1,6-diaminohexane and 1-ethylpyridinium bromide as template, respectively.The structure and acidic properties were characterized by X-ray diffraction (XRD), X Ray Fluorescence (XRF), N₂ adsorption, Scanning electron microscopy (SEM), ammonia temperature-programmed desorption (NH₃-TPD) and FT-IR spectroscopy of pyridine adsorbed (Py-IR). The 0.5%Pd/ZSM-22 bifunctional catalysts were prepared, and the dispersions of metal Pd over bifunctional catalysts were characterized by H₂ chemical adsorption, and their catalytic performance for hydroisomerization of n-decane were investigated in the fixed reactor. The results showed that different templates have great influence on the structure and acidity of ZSM-22 zeolites. ZSM-22 zeolite synthesized with 1,6-diaminohexane as template has smaller crystallite size, and isomerization product has shorter spread distance within the molecular sieve channel. It also has high B acid/L acid ratio, medium acidity, and synergetic effect between metal site and acid site. The conversion and isomerization selectivity of n-decane were high over the bifunctional catalysts Pd/ZSM-22.