Effect of catalyst acidity and porosity on the catalytic isomerization of linoleic acid to obtain conjugated linoleic acids (CLAs)

The role of catalyst acidity and porosity was studied for the isomerization of linoleic acid by testing two commercial Na-zeolites (mordenite and ZSM-5) and their acid modified forms (H+, Ni2+) obtained by cation exchange. Conversion of linoleic acid increased in the presence of higher amounts of weak-moderate acid centres (Brønsted and Lewis) together with a higher accessibility of the acid sites. Additionally, the synergic effect between Brønsted and Lewis centres led to higher selectivity to the isomer cis-9, trans-11-CLA whereas higher selectivity to trans-10, cis-12-CLA was achieved with higher amounts of Brønsted acidity. Interestingly, the use of microwaves for the Ni-exchange of Na-mordenite resulted in the formation of new weak Lewis acid centres, not observed for the rest of catalysts, yielding higher conversion, and higher selectivity to cis-9, trans-11-CLA than the sample conventionally exchanged.

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► Acidity strength and type, and porosity affected linoleic acid isomerization.
► Strong acid sites were responsible for faster catalyst deactivation.
► Use of microwaves for Ni-exchange of mordenite led to new active weak Lewis acid sites.
► Higher selectivity to c9, t11-CLA associated to synergy of Brønsted and Lewis acid sites.
► Higher selectivity to t10, c12-CLA attributed to higher amounts of Brønsted acidity.