Synthesis, characterization, and catalytic performance of a ZSM-5/Y composite

A ZSM-5/Y composite zeolite was prepared from Y synthesis gel by using an in-situ two-step hydrothermal crystallization process. Optimized synthetic parameters made it practical to control the transformation of zeolite Y to P, or other undesired phases during ZSM-5/Y composite formation. It was found that the pH value range of the second phase (ZSM-5 in ZSM-5/Y composite) formation is much narrower than ordinary ZSM-5 synthesis, and a lower crystallization temperature was preferred in the second step. SEM showed that the morphology of the ZSM-5/Y composite was influenced by the different synthetic methods, such as seeds and templates. The NMR data indicated that the distribution of the Si(nAl) environments are different in ZSM-5/Y composite samples that made by different methods. The composite synthesized with seeds possessed a higher ratio of Si(0A1) to Si(1A1) than that of the composite synthesized with templates. Compared to a catalyst of a mechanical mixture of ZSM-5 and Y zeolite, the catalytic cracking performance of the ion-exchanged composite zeolite catalyst showed a better yield in gasoline formation when heavy oil was used as a feedstock in a MAT reactor, and the isomerization and aromatization abilities to the gasoline fraction were better than the physical mixture of the ZSM-5 and Y. This suggested that the composite structure of the zeolite may benefit the heavy oil transformation and related reaction steps during the course of the cracking process.