Design and synthesis of core-shell Y zeolite: A tandem microreactor facilitating efficient and targeted conversion of heavy oil macromolecules

Core-shell zeolites with a single crystal Y zeolite core and a polycrystalline shell composed of loosely accumulating nano-sized Y zeolite were designed and synthesized. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, infrared spectrum, nuclear magnetic resonance, UV-Raman spectra, X-ray fluorescence (XRF) spectrometer and nitrogen adsorption-desorption characterization. The factors affecting the formation of core-shell zeolite were investigated and discussed in details. The results suggested that the properties of the starting Y zeolite core not only affect the formation of core-shell zeolite, but also decide the Si/Al ratios of the shell zeolite. The results also revealed that the initial secondary growth of primary nanocrystals in shell likes the brims rather than the faces of core crystals, and the firstly formed amorphous “fences” along the brims of the crystal faces play a vital important role in fabricating the core-shell composite because the “fences” contribute to collecting more precursors on the crystals faces. After longed by Ni, Mo active metal, the as-synthesized core-shell structured Y zeolite was evaluated during the hydrocracking of vacuum gas oil (VGO). As compared with Ni(Mo)/Y catalyst, the Ni(Mo)/Y@NY catalysts as a tandem microreactor exhibited an excellent hydrocracking performance. Specially, Ni(Mo)/Y@NY-3-24 catalyst displayed a higher conversion efficiency for VGO oil, with an increase in heavy naphtha yield by 1.47 %, a decrease in dry gas yield by 0.47 %, and a reduction in the bureau of mines correlation index (BMCI) value of tail oil by 0.7. This suggests that the fabricated core-shell microreactor holds more advantages in the hierarchically cracking and targeted conversion of macromolecules or super macromolecules.