Conjugated linoleic acid formation via heterogeneous hydrogenation/isomerization of safflower oil over mesostructured catalysts

Abstract

Aluminum-containing SBA-15 mesoporous molecular sieves with different nominal molar ratios Si/Al = 5, 10, 20, 50 and 100 were prepared via direct synthesis by adjusting the pH of gel synthesis just below the isoelectric point of silica (pH = 1.9 < 2). The aluminum incorporation yield in all of those materials is about 80% which is one of the highest ever reported. The calcined materials were characterized by XRD, N 2 physisorption, TEM, and 27Al NMR methods. These investigations confirm that the 2-D hexagonal mesoporous structure is maintained for all Si/Al ratios, and 27Al NMR analysis indicates that aluminum is almost in tetrahedral coordination. Among metals investigated, rhodium in metallic state, highly dispersed on Al_SBA-15(1 0 0) with a pore size ranging from 4 to 7 nm, BET-specific surface of 1000 m 2 g −1, and metal nominal total loading of 1% w/w, was revealed as a new active catalyst for the chemocatalytic vegetable oils modification inducing health-beneficial conjugated linoleic acids (CLA) formation by hydrogenation/isomerization. Time course profiles of (9- cis, 11- trans)-; (10- cis, 12- trans)-octadecadienoic CLA isomers as well as the other fatty acids traditionally encountered during the hydrogenation of vegetable oils are presented and discussed for the Rh-catalyst supported on Al_SBA-15 using Si/Al ratio of 100 under selected process conditions. The results show that it is possible to tailor characteristics of the hydrogenation catalyst in such a way to confer it bifunctional activity: hydrogenation and conjugated isomerization.