Green synthesis and performance of micro-mesoporous ZSM-5/Y composite zeolite with hierarchical pore structure for vacuum gas oil (VGO) catalytic cracking

To increase the yield of light olefins from the catalytic cracking of vacuum gas oil (VGO), a ZSM-5/Y composite has been synthesized via an in-situ quasi-solid-phase method in the absence of organic structural directing agents. ZSM-5/Y composite has a gradient distribution of acid strength and hierarchical pore structure. The proportion of Y and ZSM-5 in the composites can be adjusted by altering the amount of NaOH. Hierarchical pore structure increases the accessibility of cracking intermediates over acid sites and decreases the diffusion resistance. When employed as catalysts in the cracking of VGO, the acid synergy from ZSM-5 and Y is fabricated in ZSM-5/Y composites. Composite catalyst (CHZY(1.12)) exhibits a higher VGO conversion and olefin selectivity than mechanically mixed catalysts (CMHZY). Formation mechanism of ZSM-5/Y composites shows that the incorporation of Y crystal seeds shortens the induction period and generates hierarchical pore structure in situ during the crystallization process. These findings offer a straightforward preparation approach for composite zeolites with adjustable porosity and acidity and develop potential candidates for the catalytic cracking of heavy oil.