Decarbonylation of Fatty Acids to Alkenes over Co-N-C Catalysts Derived from Co Complexes

The decarbonylation of biomass-derived fatty acids (CnH2n+1COOH) presents a sustainable method for producing high-value alkenes (CnH2n). 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 substantial phenyl 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.