Ga改性ZSM-5分子筛催化丙烷芳构化性能研究

用离子交换法制备Ga改性ZSM-5双功能催化剂,并结合XRD、SEM、BET、NH₃-TPD、Py-IR及ICP、XPS等多种技术进行表征,考察分子筛硅铝比(Si/Al)和催化剂氧化还原预处理条件对分子筛的酸性质、Ga物种的存在状态及其丙烷芳构化催化性能的影响。研究表明,硅铝比不仅可以改变分子筛的酸性,也会影响分子筛中非骨架Ga物种与分子筛表面的相互作用程度,进而影响含Ga分子筛的丙烷芳构化性能。在质量空速1.0 h^-1、反应温度550℃ 下,Si/Al比为30的Ga-HZSM-5分子筛丙烷转化率和芳烃收率最高。Ga物种的引入可以提高丙烷的转化率和芳烃的选择性,并抑制烷烃、烯烃的裂解。H₂还原处理,将分子筛表面Ga₂O₃还原为低价的Ga⁺和GaH⁺₂物种,促进了Ga物种向分子筛微孔迁移;还原-氧化处理后,Ga⁺和GaH⁺₂物种氧化成GaO⁺,占据分子筛孔道离子交换位,显著提高了催化剂的芳构化活性。

Aromatization of propane over Ga-modified ZSM-5 catalysts

H-ZSM-5 was modified with gallium by the ion-exchange method and characterized with XRD, SEM, BET, NH₃-TPD, Py-IR, ICP, and XPS techniques. The influences of the Si/Al mol ratios and the pretreatment conditions of the Ga-modified ZSM-5 ((Ga-H)-ZSM-5) on their acidity, gallium species state, and aromatization performance of propane were investigated. It was found that the Si/Al mol ratio had significant effects on the catalyst acidity and the interaction of non-framework Ga species with zeolite, and hence, the catalytic activity and selectivity for propane aromatization. At 550℃ and WHSV of 1.0h^-1, (Ga,H)-ZSM-5 with a Si/Al mol ratio of 30 showed the highest catalytic activity. It was shown that Ga species improved the aromatics selectivity and inhibited cracking reactions. After being reduced in hydrogen, Ga₂O₃ was most likely transformed into Ga⁺ and GaH⁺₂ species, and migrated into the zeolite channels. Subsequent air-oxidation treatment of the reduced (Ga,H)-ZSM-5 led to formation of GaO⁺ species, thus greatly increasing the aromatization activity.