Hydrogenation of edible oil over Pd-Me/Al 2O 3 catalysts (Me = Mo, V and Pb)

Abstract

This work presents the performance of supported Pd and Pd-Me (Me = Mo, V and Pb) catalysts in the hydrogenation of sunflower oil. The catalysts were prepared using alumina as support, and were following two different methods of preparation: wet impregnating and sol–gel techniques. The samples were characterized by atomic absorption, N 2 adsorption isotherm, temperature-programmed reduction and hydrogen chemisorption. For Pd monometallic catalysts prepared by wet impregnation (WI) of γ-Al 2O 3 and alumina sol–gel (SG), for the same iodine value (IV) and Pd surface, Pd-SG generates more trans-isomers than Pd-WI sample. This could be attributed to differences in the support morphology. Regarding bimetallic catalysts, for a smaller amount of exposed Pd, the Pd-Mo/γ-Al 2O 3 and Pd-V/γ-Al 2O 3 catalysts show the same activity compared with the respective monometallic catalyst, and increase the selectivity to trans-isomers. The molybdenum and vanadium promoting effect could be a consequence of the formation of an adsorbed initial state, after which the hydrogenation would take place on the Pd surface. On the other hand, Pd-Pb/γ-Al 2O 3 showed the lowest hydrogenation activity. This would be result of a certain dimensional limitations on the space lattice of Pd for hydrogenation of double bonds due to the formation of a Pd–Pb alloy. The sol–gel Pd-Mo sample was the most effective catalyst regarding the cis-isomers selectivity and reveals the route for future research.