Gas oil hydrodesulfurization and pyridine hydrodenitrogenation over NaY-supported nickel sulfide catalysts: Effect of Ni loading and preparation method

Nickel sulfide catalysts supported on a NaY zeolite with two different meta l loadings were prepared by ion exchange and with or without a subsequent N aOH treatment. The catalysts were characterized by number of techniques and measurements, such as X-ray powder diffraction, X-ray photoelectron spectr oscopy, temperature-programmed reduction, energy-dispersive X-ray analysis using a scanning electron microscope, ion back-exchange, and acidity determ ination. The data showed that after sulfidation, nickel is homogeneously di stributed for low Ni loadings, while at high Ni loadings nickel is inhomoge neously distributed and partially located outside the zeolite pores. The Na OH pretreatment enhanced the heterogeneity of Ni distribution and its migra tion to the external surface of the zeolite, particularly for the high-Ni-c ontaining catalyst. Simultaneously, NaOH pretreatment enhanced significantl y the degree of nickel sulfidation. The activities of the catalysts for gas oil hydrodesulfurization (HDS) and pyridine hydrodenitrogenation (HDN) wer e measured simultaneously at high pressure. The results showed that low-Ni- containing catalysts, and particularly the NaOH-treated one, have the highe st intrinsic activity for gas oil HDS. This is due to the combined effect o f both their better dispersion and better sulfidation of the Ni phase. For pyridine HDN, the more active catalysts were those with higher acid site de nsity, i.e., the ones not treated with NaOH. (C) 1999 Academic Press.