ZSM–5 zeolite catalysts are widely used for catalytic cracking of hydrocarbons to produce light olefins. In this study, secondary addition of Al was introduced in aluminum–silicon zeolites (ZSM–5) by impregnation to modify their acid properties. Characterizations revealed that extra–framework Al (EFAL) formed after calcinations both on the internal and external surface of the catalysts, which provided certain Lewis acid sites. Interestingly, the amount of strong Brønsted acid increased significantly in catalysts with the introduction of EFAL. In cracking of n-pentane, the modified ZSM-5 zeolites gave obviously enhanced TOF values based on Brønsted acid sites, and a significantly improved n-pentane conversion was realized than the pristine catalyst. Moreover, the isolated strong Brønsted acid sites with certain spatial barriers triggered the cracking reaction happening through monomolecular route, which inhibited the hydride transfer of light olefins. The optimized ZSM–5 with Si/Al ratio of 50 (Z–50(75)) gave 45.2 wt% yield of light olefins at 600 °C with an excellent catalytic stability.

ZSM-5 沸石催化剂广泛用于烃类催化裂化生产轻质烯烃。在这项研究中，通过浸渍在铝硅沸石 (ZSM-5) 中引入了 Al 的二次添加，以改变其酸性。表征表明，在催化剂的内表面和外表面煅烧后形成了框架外铝（EFAL），这提供了某些路易斯酸位点。有趣的是，随着 EFAL 的引入，催化剂中强布朗斯台德酸的含量显着增加。在正戊烷裂解过程中，改性 ZSM-5 沸石基于 Brønsted 酸位显着提高了 TOF 值，并且显着提高了n与原始催化剂相比，实现了-戊烷转化。此外，具有一定空间势垒的孤立强布朗斯台德酸位点通过单分子途径引发了裂解反应，从而抑制了轻烯烃的氢化物转移。Si/Al 比为 50 (Z-50(75)) 的优化后的 ZSM-5 在 600 °C 下的轻质烯烃产率为 45.2 wt%，具有优异的催化稳定性。