Preparation And Performance Research Of Y@ZSM-5 Core/Shell Composite Zeolite

Y zeolite has been widely used in the petrol-processing industrial fields including catalytic cracking and hydrocracking because of its excellent property in activity, selectivity and stability. And it which is the primary active component in the heavy oil cracking can lead petrol and diesel to be the mian product. ZSM-5 zeolite which has strong acidity, high thermal stability and three-dimensional pore structure can give rise to the increase of olefin in the heavy oil cracking. We can adjust the ratio of light oil to olefin in the product of heavy oil cracking effectively through changing the relative quantity of Y and ZSM-5 zeolite. However, there are many problems of the mechanical mixture, such as poor controllability and rapid loss of activity.Based on the above analysis, the Y@ZSM-5 composite zeolites which have the core of industrial NaY and the shell of highly acidic ZSM-5 were researched in present work. The structural, crystalline and textural properties of the as-synthesized materials, as well as the reference Y and ZSM-5 samples, were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), nitrogen adsorption-desorption techniques, scanning electron microscopy (SEM) and NH3 temperature programmed desorption (NH3-TPD).Firstly, industrial NaY zeolite was used as the aluminium source in the preparation of conventional ZSM-5 zeolite, which leads to the formation of the composites composed of MFI-type and FAU-type. The composites in which the ZSM-5 zeolite is smaller than the conventional ZSM-5 do not have core-shell structure though SEM. The relative quantity of Y and ZSM-5 zeolite in composites can be adjusted by the addition of NaY zeolite and silicon resource, the concentration of OH- and the crystallization time effectively. The results of FT-IR showed that the interfacial effect existed between the two kinds of zeolite through the frequency shift of the asymmetric stretching vibration of Y zeolite. The acidic property of the composites had great differences with this of pure zeolite though NH3-TPD.The composites with core-shell structure denoted as Y@NanoZSM-5 were prepared by employing Y zeolite as the aluminium source of NanoZSM-5. The XRD characteristic diffraction peaks of Y zeolite in the composites almost have no change with the extend crystallization time, indicating the core is well protected by the shell. While, the extend crystallization time lead to the change of characteristic diffraction peaks of ZSM-5 zeolite, indicating that the morphology of shell gradually changed. The thickness of the shell can be adjusted by the addition of Y zeolite availably. We can observe that the core keep the morphology of pure Y zeolite and the shell is composed of tiny crystals with the size of 100nm which can be judged as NanoZSM-5 combining with the XRD spectrum though SEM. The results of FT-IR showed that the silica-alumina ratio of ZSM-5 zeolite in composites is higher than that of pure ZSM-5 zeolite. There are unconspicuous hysteresis loop in N2 adsorption curves of the composites, indicating that the OH-turn the mesoporous of NaY into macropores. The results of NH3-TPD indicate that the acidic property of Y@NanoZSM-5 composites which is different with pure phase zeolite can be modulated effectivity by the addition of Y zeolite.