Effective deoxygenation of fatty acids over Ni(OAc)2 in the absence of H2 and solvent

Abstract

Different metal acetate salts were systematically examined for the catalytic deoxygenation of stearic acid in the absence of H₂ and solvent for the first time. Ni(OAc)₂ exhibited the highest activity with 62% yield achieved at 350 °C for 4.5 h with only 1 mol% (0.2 wt%) of the catalyst. Even with 0.25 mol% (0.05 wt%) catalyst, around 28% yield was achieved within 2 h at 350 °C with 89% selectivity to C17 hydrocarbons. The activity based on C17 yields per Ni was 14.5 mol mol⁻¹ h⁻¹, considerably higher than that in previous reports. The catalytically active species were identified to be in situ generated Ni nanoparticles (8–10 nm) formed from the decomposition of the metal precursor with stearic acid as a stabilizer. A new reaction pathway of alkane formation from stearic acid via anhydride intermediate decarbonylation under an inert gas atmosphere was proposed. The excellent stability of the catalyst was demonstrated by re-adding a substrate to the system, during which the activity remained constant through four consecutive runs. The novel catalytic system was found to be applicable to a range of fatty acids and triglycerides with varying activities.