Ga、Zn改性方法对HZSM-5催化剂丙烯芳构化性能的影响

以浸渍法和水热合成法对ZSM-5分子筛进行Ga、Zn改性,制得不同酸性的分子筛催化剂。采用XRD、SEM、NH3-TPD和XPS等表征手段,研究考察了Ga、Zn和不同引入方法对催化剂的孔结构、骨架结构特性和表面酸性的影响,并以丙烯芳构化为模型反应,考察了Ga、Zn改性对ZSM-5催化剂烯烃芳构化催化性能的影响。研究结果表明,Ga、Zn改性对催化剂形貌影响较小,但能明显改变催化剂的表面酸性和烯烃芳构化性能。Zn改性能降低催化剂的酸性,而Ga改性与其引入的方式有关,浸渍法引入催化剂的中强酸位略有下降,而水热合成法引入则显著增加了催化剂的总酸量。Ga、Zn改性均提高了芳构化反应的活性和芳烃选择性,并抑制催化剂表面积炭。

Effect of Ga and Zn modification on propylene aromatization over HZSM-5 catalysts

ZSM-5 catalysts were modified with Ga and Zn by using impregnation and hydrothermal methods to obtain zeolite catalysts with different acidities. XRD, SEM, NH₃-TPD and XPS were used to characterize the effects of the modification components (Ga and Zn) and methods (impregnation and hydrothermal methods) on the pore structure, skeletal structure and surface acidity of the resultant catalysts. The performances of the Ga and Zn modified catalysts for alkene aromatization were evaluated with propylene as a model compound. The results indicated that Ga and Zn modification has little influence on the morphology of catalysts particles, but it obviously changes the surface acidity and alkene aromatization reactivity of the catalysts. Zn modification reduces the acidity of ZSM-5 catalyst, while the effect of Ga modification on the catalyst acidity depends on the Ga addition methods. Ga introduced through impregnation slightly reduces the strong acid sites, while Ga introduced via hydrothermal method apparently increases the intensity of both weak and strong acid sites. Ga and Zn modifications are able to increase the aromatization activity and the aromatics selectivity, and to suppress the carbon deposition.