Phosphorus promoted trimetallic NiMoW/γ-Al2O3 sulfide catalysts in gas oil hydrotreating

A series of phosphorus promoted gamma-Al2O3-supported NiMoW sulfide catalysts consisting of 6wt.% Mo, 7wt.% W, 2.5 wt.% Ni and 0-2.5 wt.% P was synthesized by a co-impregnation method. The catalysts were characterized by N-2 adsorption, carbon monoxide chemisorption, X-ray diffraction, Raman spectroscopy, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, X-ray absorption near edge structure (XANES) and DRIFT spectroscopy of adsorbed CO. The CO uptake measurement and Raman spectroscopy showed that P addition to NiMoW improves the dispersion of Mo and W species on the gamma-Al2O3 surface. DRIFT spectra of adsorbed CO evidenced that the number of active sites on the surface of NiMoW/gamma-Al2O3 sulfide increases with increasing phosphorus concentration and reaches an optimum at 1.6wt.% of phosphorus. DRIFT spectroscopy evidenced the aluminum phosphates on the surface and also new Bronsted acid groups in P-doped catalysts. XANFS study revealed that P doping in gamma-Al2O3 does not affect the bulk electronic structure of gamma-Al2O3. The HDS and HDN of coker light gas oil derived from Athabasca bitumen in a trickle bed reactor at industrial conditions showed that phosphorus doping has a stronger promotional effect for HDN than the HDS. The enhancement in HDN activity with phosphorus addition could be attributed more to the effect of acidity than to the improvement in dispersion.The PNiMoW/gamma-Al2O3 catalyst with P loading of 1.6wt.% showed superior hydrotreating activity than the bimetallic PNiMo/gamma-Al2O3, PNiW/gamma-Al2O3 and commercial catalysts. (c) 2008 Elsevier B.V. All rights reserved.