Applied Catalysis A: General 245 (2003) 257–275 Isomerization of linoleic acid over supported metal catalysts Andreas Bernas a , Narendra Kumar a , Päivi Mäki-Arvela a , Natalya V. Kul’kova b , Bjarne Holmbom c , Tapio Salmi a , Dmitry Yu. Murzin a,∗ a Process Chemistry Group, Laboratory of Industrial Chemistry, Åbo Akademi University, FIN-20500 Åbo/Turku, Finland b Karpov Institute of Physical Chemistry, Moscow, Russia c Process Chemistry Group, Laboratory of Wood Chemistry, Åbo Akademi University, FIN-20500 Åbo/Turku, Finland Received 16 August 2002; received in revised form 29 November 2002; accepted 4 December 2002 Abstract Heterogeneous supported metal catalysts were applied for the isomerization reaction of linoleic acid (cis-9,cis-12-octade- cadienoic acid) to conjugated linoleic acid (CLA) between 80 and 120 ◦ C in a diluted system. Ru, Ni, Pd, Pt, Rh, Ir, Os, and bimetallic Pt-Rh supported by activated carbon, Al 2 O 3 , SiO 2 Al 2 O 3 , MCM-22, H-MCM-41, H-Y, and H- were screened. Cat- alyst characterization was done by XRD, X-ray fluorescence, XPS, H 2 -TPD, DCP-AES, and nitrogen adsorption techniques. The isomerization reaction was conducted batchwise in both 1-octanol and n-decane as solvents. Reactions taking place were the isomerization of linoleic acid to CLA, hydrogenation of linoleic acid and CLA to monounsaturated octadecenoic acids (oleic acid, elaidic acid, cis-vaccenic acid, and trans-vaccenic acid), as well as the further hydrogenation of monounsaturated acids to stearic acid (n-octadecanoic acid) with isomerization and hydrogenation being two competing parallel reactions. The isomerization reaction was enhanced by catalyst preactivation under hydrogen. The presence of chemisorbed hydrogen in- creased the conversion but reduced the isomerization selectivity. Ru and Ni showed the best isomerization properties whereas Pd favored the double bond hydrogenation reaction. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Functional food; Linoleic acid; Conjugated linoleic acid (CLA); Supported metal catalysts; Double bond migration; Isomerization; Hydrogenation 1. Introduction Conjugated linoleic acid (CLA), a first in 1987 positively identified mutagen inhibitor [1], is being sold as a panacea that has the capability of reducing or even eliminating cancer, preventing heart disease, improving immune function, and altering the body composition in order to treat obesity or build lean body mass [2]. The term functional food is increas- ∗ Corresponding author. Tel.: +358-2-215-4985; fax: +358-2-215-4479. E-mail address: dmurzin@abo.fi (D.Yu. Murzin). ingly used as a generic description for the beneficial effects of ingested foods that go beyond their tradi- tional nutritive value [3]. Unfortunately, there exists very little published human research on CLA. Conju- gated linoleic acid is a collective term describing the positional and geometric conjugated dienoic isomers of linoleic acid (cis-9,cis-12-octadecadienoic acid). Linoleic acid (C 18:2 ) has double bonds located on car- bons 9 and 12, both in the cis configuration, whereas CLA has either the cis or trans configuration or both located along the carbon chain [1]. CLA exhibits 13 C NMR signals for its four olefinic carbon atoms and chemical shifts have been identified for 20 different 0926-860X/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0926-860X(02)00646-4