基于Y型沸石的解聚制备ZSM-5/Y沸石催化材料

以工业NaY沸石在碱性环境下解聚形成的硅、铝物种作为ZSM-5沸石生长的部分原料,通过补加适宜的硅物种和模板剂等,成功得到了具有核-壳结构的ZSM-5/Y沸石催化材料。采用XRD、FT-IR、NH3-TPD、SEM、EDS等对合成的材料进行表征,并以异丙苯和正庚烷的催化裂化反应评价了该复合材料作为裂解催化剂的催化活性,并与对应的机械混合物比较。结果表明,ZSM-5/Y沸石复合物的形成是一个由Y型沸石向ZSM-5沸石转变的过程,后合成的ZSM-5沸石包裹Y型沸石进行生长,形成以多晶Y型沸石为核,ZSM-5沸石为壳的复合物。ZSM-5/Y沸石复合物与对应的机械混合物的性质存在显著差异,并非两种沸石的简单加和。与对应的机械混合物相比,ZSM-5/Y沸石复合物催化正庚烷裂化反应的正庚烷转化率更高,低碳烃,特别是乙烯和丙烯的选择性更高;催化异丙苯裂化时,异丙苯转化率较低,壳层的孔道结构是其主要影响因素。

Synthesis of Core-Shell Zeolite Composite ZSM-5/Y Based on Depolymerization of Y Zeolite

Composite zeolite with ZSM-5 as shell and polycrystalline Y as core was prepared by using the depolymerized NaY zeolite as the nutrients for the growth of ZSM-5 zeolite. The prepared samples were characterized by XRD, FT-IR, NH₃-TPD, SEM and EDS. The catalytic performances of ZSM-5/Y composite zeolites were tested in the cracking of n-heptane and isopropylbenzene, and compared with the corresponding physical mixture. The results revealed that the formation of ZSM-5/Y composite zeolite was a transformation process of Y zeolite into ZSM-5 zeolite. Y zeolite was wrapped by the post-synthesized ZSM-5 zeolite, resulting in the formation of the core-shell composite. The ZSM-5/Y composite showed an outstanding difference from the corresponding physical mixture of pure Y and ZSM-5 zeolites. As compared with the corresponding physical mixture as catalyst, with ZSM-5/Y composite as catalyst a decreased conversion of isopropylbenzene in its catalytic cracking was obtained, while an enhanced conversion of n-heptane as well as an increased selectivity of light hydrocarbon, especially the selectivity of light olefins in n-heptane catalytic cracking was obtained.