Abstract:

Zeolite MeLTL with a micro-mesoporous composite pore structure was synthesized by using nanocrystal clusters of zeolite L prepared by the crystallization nurturing method as a precursor and [3-(trimethoxysilyl)propyl] hexadecyldimethylammonium chloride (TPHAC) as the organic mesopore directing surfactant. Several techniques including X-ray diffraction (XRD), nitrogen adsorption-desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), 27Al magic angle spinning nuclear magnetic resonance (27Al MAS NMR), and Fourier transform infrared spectroscopy of pyridine adsorption (Py-FTIR) were used to characterize the samples. Results show that zeolite MeLTL is formed by the self-assembly of zeolite L nanocrystals, and it has bimodal pore distributions with a stepwise mesoporous structure and the microporous structure of zeolite L. The BET surface area and the pore volume increased significantly and were 611 m2·g-1 and 0.696 cm3·g-1, respectively. Zeolite MeLTL was composed of zeolite L units and this was responsible for the adequate surface acid amount and acid strength. As a result, the pore diffusion ability and the catalytic performance of zeolite MeLTL are enhanced by the improvement in textural properties. For diesel hydrodesulfurization, the catalyst introduced zeolite MeLTL gave better hydrodesulfurization activity compared to the catalysts introduced zeolite L or Al-MCM-41 or used bare γ-Al2O3 as a support. The sulfur content of diesel oil after hydrotreatment was 9.3 μg·g-1 and the desulfurization rate was 99.3%.

Key words: Hydrodesulfurization, Zeolite L, Micro-mesoporous composite structure, TPHAC, Diesel oil, Hydrogenation catalyst