HZSM—5沸石组成及其对甲苯乙基化选择性的影响

ZSM－5是一种铝含量较低（其（Si/Ai原子比变化可连续达几个数量级）的结晶硅酸铝，对许多酸催化反应有着良好的选择性。沸石Si/Al比的必然影响它的酸性质。Auroux和Kotasthane等研究HZSM－5沸石表面酸性时指出，强酸中心数与沸石铝含量有着密切的关系，酸强度分布也与铝含量有关，即随Si/Al比增加，最高酸强度中心数减少。另外，由晶胞参数测定表明，ZSM－5沸石孔径随Si/Al比增加呈逐渐缩小的趋势。由扫描电镜对沸石晶粒形貌和大小的测定示出，随Si/Al比增加，晶粒逐渐增大。鉴此，用不同整体Si/Al比和表层Si/Al比的HZSM－5沸石对甲苯乙基化反应的选择性进行了研究，结果表明：沸石表面酸性的调度以及孔径缩小和晶粒增大都能提高p-选择性，但表面最高酸强度的降 低比孔径缩小和晶粒增大更为重要。

Composition of HZSM-5 Zeolites and Its Effect on the Selectivity of Toluene Ethylation

The shape selectivity for the alkylation of toluene with ethanol by varying Si/Al ratios of HZSM-5 and DAI HZSM-5 zeolites was studied. The results show that p-ethyltoluene selectivity increases with the zeolite Si/Al ratio increase. By treating HZSM-5 zeolite with SiCl4 vapor, the aluminium atoms were removed, indicating that the surface is deficient in aluminium obviously. At a high temperature and within short time, especially, HZSM-5 zeolites treated by SiCl4 showed obviously a higher p-selectivity, but the activity had no clear change.