Ga改性ZSM-5分子筛催化丙烷芳构化性能研究

Aromatization of propane over Ga-modified ZSM-5 catalysts

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1.0h-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。

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. 0 h^-1,（ Ga,H）-ZSM-5with 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 Ga H2^＋ species,and migrated into the zeolite channels. Subsequent air-oxidation treatment of the reduced（ Ga,H）-ZSM-5 led to formation of Ga O^＋ species,thus greatly increasing the aromatization activity.