Due　to　escalating　carbon　emissions,　increasing　attention　is　being　focused　on　the　synthesis　of　biomass-derived　liquid　fuels　with　a　low　CO2　footprint.　Currently,　the　dominant　biobased　liquid　fuel　in　the　diesel　range　is　green　diesel,　which　is　produced　via　deoxygenation　of　non-edible　natural/waste　oils　and　their　free　fatty　acid　components　into　engine-compatible　diesel-range　alkanes.　Industrially,　sulfided　NiMo　or　CoMo　catalysts　are　typically　used,　leading　to　total　hydrocarbon　yields　of　70–80　wt%.　However,　their　inevitable　sulfur　leaching　often　contaminates　the　products　and　requires　the　addition　of　sulfur-containing　agents.　Here,　we　developed　a　highly　selective　sulfur-free　Ni–Cu　alloy　catalyst　by　disentangling　the　electronic　and　size　effects,　to　enable　green　diesel　synthesis　through　the　decarbonylation　of　palmitic　acid—the　most　common　fatty　acid　in　these　feedstocks.　An　unprecedented　decarbonylation　product　(pentadecane)　yield　of　98%　(on　a　molar　basis)　was　achieved　using　a　Ni–Cu　alloy　catalyst　with　a　Ni/Cu　ratio　of　1:1　under　mild　reaction　conditions　(2　MPa　H2,　250　°C).　Minimal　metal　sintering　or　leaching　was　observed　after　multiple　reuses.　Kinetic　studies　showed　that　incorporating　Cu　into　Ni　markedly　reduced　both　the　apparent　activation　energy　and　the　reaction　order　for　the　conversion　of　palmitic　acid.　These　results,　combined　with　catalyst　characterization,　reveal　that　introducing　Cu　into　Ni　not　only　facilitates　the　adsorption　and　activation　of　the　carboxylic　hydroxyl　group　to　promote　the　reductive　deoxygenation　of　palmitic　acid　into　aldehyde/alcohol　intermediates—the　slow　step　in　decarbonylation—but　also　weakens　the　adsorption　of　C–C　bonds　on　Ni　by　enhancing　its　electron　density.　©　2025　Institute　of　Process　Engineering,　Chinese　Academy　of　Sciences.