| Résumé | Novel Ni–Mo/activated carbon (AC) hydrotreating catalysts were prepared and evaluated for upgrading heavy vacuum gas oil (HVGO). The AC supports were derived from Alberta oil sand petroleum coke, i.e. fluid coke and/or delayed coke, hereafter referred to as OSP coke, through a chemical process. The BET surface area was as high as 2194 m2/g for the fluid coke derived AC and 2357 m2/g for the delayed coke derived AC. Both ACs contained a large number of micropores with pore volume as high as 1.2 cm3/g. Ni and Mo based active component precursors could be easily loaded on the activated carbon supports by chemical impregnation of nickel nitrate and ammonium molybdate followed by calcination in nitrogen at 773 K without further modification or oxidation treatment to the activated carbons. Scanning electron microscopy (SEM) observation showed highly porous surface structure of the bare activated carbon supports and well dispersed metal (oxide) precursor nanoparticles of 30–50 nm loaded on the AC supports. For comparison, two reference catalysts were also prepared by the same procedure but using commercial activated carbon and porous alumina as supports. After catalyst activation by sulfiding, the hydrotreating performance of the prepared catalysts was evaluated in a magnetically stirred autoclave with a HVGO feedstock to examine their hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities. Two commercial hydrotreating catalysts were also tested and compared under similar conditions with the same feed. The results showed that the catalysts based on the activated carbon supports prepared from OSP coke had better hydrotreating performance than the other catalysts. Scanning transmission electron microscopy (STEM) characterization of the catalysts after activation showed that small particles of nanostructure (2–5 nm in size) were evenly embedded in the carbon matrix except for some bigger particles that were located on the catalyst surface. Energy dispersive X-ray (EDX) spectroscopy revealed that these particles were composed of Ni, Mo and S elements. The dispersed nanoparticles formed the active sites and were responsible for the observed high HDS and HDN activity. Elemental analysis and surface characterization of the spent catalysts showed that the formation of coke precursors was favored on the alumina supported catalyst, which resulted in catalyst deactivation. |
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