Novel Micro- and Mesoporous Composite Molecular Sieve Assembled by Zeolite L Nanocrystal and Its Performance for the Hydrodesulfurization (HDS) of Fluid Catalytic Cracking (FCC) Gasoline

A novel micro- and mesoporous composite molecular sieve (denoted as LMC) was synthesized by using the nanocrystal clusters of zeolite L as the precursor and a cation surfactant cetyltrimethylammonium bromide (CTAB) as the template. The physicochemical properties of samples were characterized by means of X-ray diffraction (XRD), nitrogen-adsorption isotherms, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Al-27 and Si-29 magic angle spinning nuclear magnetic resonance (MASNMR), Fourier transform infrared spectroscopy (FTIR), and Fourier transform infrared spectroscopy of pyridine adsorption (Py-FTIR). The results showed that composite molecular sieve LMC was synthesized by the self-assembly of zeolite L nanocrystal clusters under the template effect of CTAB. In addition, surface area, pore volume, and pore size of LMC significantly increased in comparison to those of conventional microporous zeolite L. The results measured by Py-FTIR showed that LMC had an appropriate acid amount and acid distribution. For evaluation of fluid catalytic cracking (FCC) gasoline hydrodesulfurization (HDS), the catalyst that introduced material LMC exhibited the excellent performances of desulfurization, isomerization, aromatization, olefin retention, and preserving the research octane number (RON) value compared to the catalyst that introduced ordinary microporous zeolite L or mesoporous Al-MCM-41 and used bare alumina as the support. The excellent catalytic performances of the catalyst should be attributed to the appropriate acidity distribution and open pore structure of material LMC.