Regulating the Full Deoxygenation Pathway of Fatty Acid Esters to Alkanes via the Coupling Effect of a NiCo Bimetallic Catalyst

Hydrogenation of fatty acids and their esters is currently the most established technology for producing bioaviation fuels. The deoxygenation pathway critically determines both the reaction efficiency and combustion properties of the resulting fuels. However, previous works primarily focused on the deoxygenation pathway of fatty acids, with limited attention to fatty acid esters (e.g., fatty acid methyl ester, FAME). Herein, a NiCo bimetallic catalyst was employed to regulate the full deoxygenation pathway of FAMEs by modulating the adsorption configuration and binding modes of reactants with catalysts. The catalyst features Ni0, Co0, and NiCo alloy sites, with electron transfer from Co to Ni. The synergetic electronic and geometric effects of Ni and Co promote hydrogenolysis of FAMEs to fatty acid and methane rather than aldehydes and methanol. This is attributed to the enhanced σ-type coordination between Co and alkoxy oxygen, facilitating the formation of a δ+–C–O–δ– structure and further polarizing the alkoxy C–O bond. Moreover, the coupling effect of NiCo also selectively enhances the hydrodeoxygenation (HDO) pathway by stabilizing the η2(C,O)–aldehyde adsorption configuration of intermediates with stronger adsorption of a carbon atom on electron-rich Ni0 and an oxygen atom on oxophilic Co0. In the hydrogenation of methyl laurate, the NiCo catalyst achieves a C12 + C11 space-time yield of 32.5 mmol·g–1·h–1, with a C12/C11 ratio of 11.7, which is more than two times that of the Ni monometallic catalyst.