Preparation and Evaluation of the Composite Containing USL Zeolite-Supported NiW Catalysts for Hydrotreating of FCC Diesel

Two different ways, including an in situ synthetic method and a mechanical mixing method, were used to combine zeolite USL (ultra stable L) with alumina for preparation of a new composite support material of hydrotreating catalyst. The physicochemical properties of samples were characterized by means of XRD, N2 physisorption, SEM, FT-IR, 27Al MAS NMR, NH3-TPD, H2-TPR, and UV−vis DRS. Composite supports containing different contents of zeolite USL and Al2O3 were prepared by in situ synthetic method based on a modified pH-swing method, which showed a higher specific surface area, pore volume, as well as average pore diameter compared with the supports prepared via a mechanical mixing method. Corresponding NiW/γ-Al2O3−USL series catalysts were obtained by the incipient-wetness impregnation method, and the activities of these catalysts for FCC diesel hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) were evaluated in a high-pressure microreactor system. The assessment results indicated that the catalyst with 10 m% USL in the support prepared by the in situ method showed the highest HDS and HDN conversions, which reached a maximum of 99.3% and 94.1% for HDS and HDN, respectively. In addition, the swing pH method plays an important role in preparation of the Al2O3 support, and NiW/γ-Al2O3(P) (prepared by the swing pH method) catalyst also gave better performance for the HDS and HDN of diesel oil. These activities were much higher than those over a kind of industrial catalyst of RN10 and were also better than the corresponding catalyst in which the support was obtained by the mechanical mixing method.