Zeolite–zeolite composite fabricated by polycrystalline Y zeolite crystals parasitizing ZSM-5 zeolite

A series of zeolite–zeolite composites were prepared by a two-step hydrothermal crystallization procedure in which the mixture of presynthesized ZSM-5 zeolite acts as nutrients for the growth of postsynthesized Y zeolite, and the as-synthesized products are denoted as MFI–FAU. The structural, crystalline, and textural properties of the as-synthesized materials, as well as the references Y, ZSM-5, and a corresponding physical mixture composed of Y and ZSM-5 zeolite, were characterized by x-ray powder diffraction (XRD), Fourier transform infrared spectrum (FTIR), temperature-programmed desorption of ammonia, N2adsorption–desorption, scanning electron microscopy, energy-dispersive spectrometry, and Thermogravimetry. The results show that the ratio of Y to ZSM-5 in the composite can be adjusted by controlling the hydrothermal treatment time of the second-step synthesis. Steric hindrance provoked by the concurrently growing crystals offers the postsynthesized Y zeolite phase, a relatively smaller size. A hierarchical pores system, which results from the extraction of silicon species from ZSM-5 and the polycrystalline accumulation of Y zeolite, has been created in the zeolite–zeolite composite. Catalytic performances of the zeolite–zeolite composite catalysts as well as the references catalysts were investigated during the catalytic cracking of isopropylbenzene. As compared with the corresponding physical mixture, the composite catalysts display the excellent catalytic performances with a higher conversion of isopropylbenzene as well as a longer catalytic life because of the introduced hierarchical pores system and the formation of special composite structure.