Amine-functionalized metal-organic frameworks for the transesterification of triglycerides

Abstract

For the application of functionalized metal–organic frameworks (MOFs) as a solid base, amine-functionalized MOF materials are achieved by (i) dative modification of unsaturated metal sites located at the secondary building units of MOFs with diamine, and (ii) covalent modification of the amine-tagged organic linkers within the MOF by alkylation with 2-dimethylaminoethyl chloride. The resulting amine-functionalized MOFs exhibit excellent results in the liquid phase transesterification of triglycerides and methanol, with the triglyceride conversions exceeding 99%, which are important model reactions for the production of biodiesel. The relationship between the catalytic activity towards transesterification and the basicity of amine-functionalized MOFs reveals a linear correspondence in terms of turnover frequency and basic site density. The basicity of the MOFs and reaction parameters are shown to significantly affect the catalytic performance. Kinetics studies reveal that the reaction follows first-order kinetics with the calculated activation energy of 48.2 kJ mol⁻¹. This research opens up new perspectives on the postsynthetic modification of MOFs and more generally on the rational design of MOF-derived solid base catalysts.