用于乙烯芳构化反应的Zn/HZSM-5催化剂失活机制研究

采用浸渍法制备了Zn负载量（质量分数）分别为1%、2%、3%的Zn/HZSM-5分子筛催化剂，通过XRD、N₂吸附-脱附、NH₃-TPD、Py-FTIR、XPS、TG-DTA等技术，系统考察Zn/HZSM-5分子筛在乙烯芳构化反应的失活机制。结果表明，积炭是催化剂失活的主要原因，HZSM-5中Zn的添加在较大程度上抑制了催化剂的积炭行为；低Zn含量时催化剂失活缓慢，但Zn含量较高时，由于催化剂比表面积和孔体积极剧下降，催化剂失活加剧。反应过程中，分子筛上Zn物种存在迁移和流失行为，迁移行为体现为催化剂表面Zn的富集和相对比例的变化；Zn流失速率在不同反应阶段保持恒定，但受到Zn含量的影响，Zn含量越高、流失速率越大。外表面ZnO是分子筛催化剂Zn流失的主要物种，且随Zn负载量升高变化趋势愈加明显，其含量与积炭速率存在一定关联。

The deactivation mechanism of Zn/HZSM-5 zeolites in ethylene aromatization reaction

Zn/HZSM-5 zeolites, with zinc contents of 1%, 2%, and 3%, were prepared by impregnation method and characterized by XRD, N₂ adsorption, NH₃-TPD, Py-FTIR, XPS, and TG-DTA techniques to investigate the deactivation mechanism in ethylene aromatization reaction. It shows that coking is the main reason for catalysts deactivation, which is considerably depressed with the presence of Zn in the HZSM-5 catalysts. The deactivation is slow for the catalysts with low Zn loading. However, high content of Zn in the catalysts brings in problems such as decrease of surface area and microporous volume, and hence accelerates the deactivation. In the reaction, zinc species lose from the catalysts, accompanied with the migration and redistribution of Zn from bulk to surface of zeolite. The losing rate was constant with the time on stream, but influenced by the zinc content of the catalyst. ZnO on the external surface of the catalyst are the main species leaching from zeolite. Zn leaching is accelerated with the increase of zinc content, and has correlation with coking rate to some extent.