Waste cooking oil transformation into third generation green diesel catalyzed by nickel - Alumina catalysts

Three nickel-alumina catalysts were prepared with nickel content 60, 80 and 90 wt % (symbols: 60NiAl, 80NiAl, 90NiAl) following a co-precipitation methodology. The catalysts were characterized and evaluated in the selective deoxygenation of waste cooking oil for the production of third generation green diesel under solvent free conditions. Metallic Ni, NiO, and NiAl2O4 were detected in the 60NiAl catalyst. NiAl2O4 is hardly detected in the 80NiAl catalyst but not at all in the 90NiAl catalyst. The extent of reduction of NiO to metallic Ni upon activation is considerably higher in the 80NiAl and 90NiAl samples with respect to the 60NiAl sample resulting in much higher active site population. The Increase in the nickel content causes a change in the porous structure and a decrease in the specific surface area. The catalytic performance increases considerably from the 60NiAl catalyst to the 80NiAl one due to the increase in the active site population. The higher catalytic performance of the 80NiAl catalyst with respect to that of the 90NiAl catalyst, exhibiting almost equal active site population, is due to convenient porous structure of 80NiAl catalyst, which hinder the insertion of deleterious bulky compounds present in the waste cooking oil, as well as to its strong acid sites.