A New Heterogeneously Catalytic Pathway for Isomerization of Linoleic Acid over Ru/C and Ni/H–MCM-41 Catalysts

The isomerization reaction of linoleic acid (cis-9,cis-12-octadecadienoic acid) to conjugated linoleic acids (CLA) was studied. A new heterogeneously catalytic pathway was developed for synthesis of CLA at mild reaction conditions (80–120°C) over Ru/C and Ni/H–MCM-41 catalysts in a diluted system. The isomerization reaction was tested in 1-octanol and n-decane. Solvents with low polarity were selected to afford good reactant adsorption on the catalyst surface and a high solvent-to-reactant ratio was used to prevent potential side reactions. Catalyst characterization was done by X-ray powder diffraction, X-ray fluorescence, X-ray photoelectron spectroscopy, hydrogen temperature-programmed desorption, direct current plasma atomic emission spectrometry, and BET techniques. The reactions taking place were isomerization of linoleic acid C18:2, hydrogenation of C18:2 acids to C18:1 monounsaturated octadecenoic acids (oleic acid, elaidic acid, cis-vaccenic acid and trans-vaccenic acid), and further hydrogenation of C18:1 acids to C18:0 stearic acid (n-octadecanoic acid) where isomerization and hydrogenation were two competing parallel reactions. The isomerization reaction was enhanced by preactivation of the catalysts under hydrogen, but such a treatment also increased the side reaction double-bond hydrogenation.