Probing the synergistic ratio of the NiMo/γ-Al2O3 reduced catalysts for the transformation of natural triglycerides into green diesel

Abstract

The synergistic atomic ratio, NiNi+Mo, of the NiMo/γ-Al2O3reduced catalysts was investigated for the transformation of natural triglycerides into green diesel. A series of catalysts with different atomic ratios 0≤NiNi+Mo≤1 and constant atomic surface density (Mo+Ni)=4 atoms/nm2 was prepared and characterized using adsorption–desorption isotherms, XRD, SEM-EDS, XPS and H2-TPR. The catalysts were evaluated in the selective deoxygenation of sunflower oil performed by hydrotreatment using a semi-batch reactor. For comparison, two additional NiMo/γ-Al2O3sulphided catalysts were synthesized and tested. The most active reduced catalyst was also tested in the selective deoxygenation of waste cooking oil.MoO3/MoOx (Mo oxidation number between 5 and 4) and Ni0, NiO, NiAl2O4 phases very well dispersed on the support surface and uniformly distributed on the catalysts extrudates have been detected in all cases. The high dispersion of these phases does not practically disturb the texture of the support which exhibits a single peak pore volume distribution centered at about 8–9nm. The Ni, Mo composition of the catalysts somehow affects the relative amounts of these phases of the same element.It was found that the aforementioned NiNi+Mo ratio is located at about 0.8. This is very different to that of the sulphided catalysts which is located at about 0.3 for both the hydrodesulphurization of petroleum fractions and the selective deoxygenation of sunflower oil. An impressive increase of the% yield to hydrocarbons in the diesel range by a factor of 4.77 was achieved by a simple change of the NiNi+Mo atomic ratio in the NiMo/γ-Al2O3reduced catalysts from 0.3 to 0.8. A complete transformation of both sunflower oil and waste cooking oil into hydrocarbons in the diesel range was obtained over the most active catalyst at 310°C, hydrogen pressure 40bar, reactant volume to catalyst mass ratio equal to 10ml/g and reaction time equal to 5h.