多级孔ZSM-5性质及其对甲醇制丙烯催化性能的影响

摘要

以十六烷基三甲基溴化铵（CTAB）为介孔导向剂水热晶化法合成了介孔孔容可控的多级孔ZSM-5分子筛，并考察了其多级孔性质及表面酸性质对甲醇制丙烯（MTP）反应产物分布的影响。结果表明：CTAB的添加基本没有影响晶体的结晶度及比表面积，但明显减小了晶粒大小；介孔孔容增大，改善了分子扩散能力，抑制了氢转移二次反应，有利于丙烯及低碳烯烃（C2=~C4=）总选择性的提高；而表面酸量增加却促进了氢转移二次反应，引起丙烯及低碳烯烃的选择性降低、烷烃及C5+高碳组分选择性增加，不利于低碳烯烃的生成。%The hierarchical ZSM-5 zeolites with controllable mesopore volumes were synthesized using surfactant cetyltrimethylammonium bromide (CTAB) as mesoporous structure directing agent by the soft-template hydrothermal crystallization method, and the effects of their hierarchy and acidity on the product distribution in the reaction of methanol to propylene (MTP) were investigated. Results showed that the introduction of CTAB didn’t affect the crystallinity and specific surface area of the zeolites, but reduced the crystal size. The increased mesopore volumes enhanced the molecule diffusion and inhibited the secondary reaction of hydrogen transfer, which improved propylene selectivity and total light olefin selectivity of ethylene, propylene and butene. However, the increased acid amount promoted the hydrogen transfer reaction, resulting in decrease of the selectivities of propylene and total light olefins, and increase of the selectivities of alkanes and C5+hydrocarbons, which were unfavorable for the formation of olefins.