Comparison of γ and δ-Al2O3 supported CoMo catalysts in the hydrodesulfurization of straight-run gas oil

The effect of two different crystal species of alumina on hydrodesulfurization activity of the corresponding CoMo catalysts was studied. Cylindrical extruded alumina with two different crystal structures i.e. γ-Al2O3 and δ-Al2O3 was prepared using boehmite and nitric acid as a peptizing agent by calcination at 550 ˚C and 900 ˚C, respectively. The Al2O3 support were impregnated with 9 wt.% of Mo and 2 wt.% Co via incipient wetness impregnation method. The CoMo/Al2O3 catalysts were used for hydrodesulfurization (HDS) and hydrodenitrification (HDN) of Iranian straight-run gas oil (ISRGO). The supports and catalysts were characterized by nitrogen adsorption-desorption isotherm, XRD, UV-vis-DRS, TPD, TPR and ICP-OES. The HDS activity of CoMo/γ-Al2O3 catalyst was higher than that of CoMo/δ-Al2O3 and was found to be 95.74%. This result was due to the formation of larger CoMoO4 and MoO3 crystals in CoMo/δ-Al2O3 catalyst which reduces the active metal phase dispersion and the performance of the catalyst. The HDS activity of CoMo/γ-Al2O3 catalyst was remarkable as the metal content of the catalyst was low. The HDN activity of CoMo/γ-Al2O3 was also about 66%.