HZSM-5/SAPO-11复合分子筛的制备、表征及在异丁烷芳构化反应中的催化性能

将经聚二烯丙基二甲基氯化铵(PDDA)预处理的HZSM-5分子筛置于SAPO-11分子筛的合成母液中,在水热体系中原位制备了一系列HZSM-5/SAPO-11复合分子筛,并对分子筛的结构、形貌及酸性进行了表征,考察了其在异丁烷芳构化反应中的催化性能.结果表明,所得复合分子筛由HZSM-5表面包覆约20 nm的SAPO-11微晶组成,且通过调变SAPO-11的Si含量可以有效调变复合分子筛的酸性,提高芳构化强弱酸协同催化作用,有效抑制裂解副反应.结合异丁烷芳构化转化率及液体收率结果可知,当SAPO-11合成溶胶中硅铝摩尔比为0.6时,HZSM-5/SAPO-11复合分子筛的芳构化活性及稳定性最佳.

Preparation and Characterization of HZSM-5/SAPO-11 Composite Molecular Sieves and Their Catalytic Properties in Isobutane Aromatization?

HZSM-5/SAPO-11 composite molecular sieves with different silicon contents were synthesized hydrothermally via in situ overgrowth of SAPO-11 on ZSM-5 pretreated by polydiallyldimethylammonium chloride(PDDA), and were characterized by means of XRD, SEM, TEM, FTIR and NH3-TPD. The catalytic activity, stability and BTEX( benzene, toluene, ethylbenzene and xylenes) selectivity of HZSM-5/SAPO-11 in isobutane aromatization were also investigated. All the results were compared with those of ZSM-5, SAPO-11, and the mechanical mixtures of ZSM-5 and SAPO-11 and showed that the ZSM-5/SAPO-11 composites were composed of ZSM-5 covered by about 20 nm SAPO-11 round crystals, that modulation of ZSM-5/SAPO-11 acidity by altering Si content could effectively enhance the synergetic aromatization effect between strong and weak acids and restrain the cracking of iso-butane and the generation of C9+, thus the liquid yield and stability of aromatization were superior to HZSM-5 and mechanical mixtures when the Si content reaches 0. 6 significantly.