Decarbonylation of fatty acids to alkenes over Co–N–C catalysts derived from Co complexes

Abstract

The decarbonylation of biomass-derived fatty acids (C_nH_2n+1COOH) presents a sustainable method for producing high-value alkenes (C_nH_2n). However, the development of efficient and highly selective catalysts for fatty acid decarbonylation remains challenging. In this work, we prepared a series of CoPhPhen/MWCNT-X catalysts by pyrolyzing a 4,7-diphenyl-1,10-phenanthroline (PhPhen) Co complex immobilized on multi-walled carbon nanotubes. In the model decarbonylation reaction of stearic acid, the optimized CoPhPhen/MWCNT-900 catalyst demonstrated remarkable catalytic efficacy, with 81.6% conversion of stearic acid and 58.3% yield of heptadecene. Characterization and comparative experiments demonstrated that the bulky phenyl side groups in the PhPhen ligand engage in strong π–π interactions with the MWCNT, effectively inhibiting the migration and aggregation of cobalt single atoms during pyrolysis and thus maintaining a high density of active Co single-atom sites. Further electronic structure investigation revealed that the local electron density around the cobalt species markedly rises with higher pyrolysis temperatures, and this electronic impact exhibits a distinct positive association with the decarbonylation performance of catalysts. In situ DRIFTS was employed to reveal the adsorption and reaction process of fatty acids on the Co single-atom active sites: the fatty acid molecule first coordinates to the cobalt center via the carbonyl oxygen, followed by successive dehydration and decarbonylation processes, finally yielding H₂O, CO, and olefins.