Boosting carbon efficiency in bio-oil upgrading over highly active Ru-Fe bimetallic catalysts

Developing efficient catalysts is crucial for maximizing biomass utilization, with high carbon efficiency being a particularly desirable attribute. Herein, a nitrogen-doped graphene-supported Ru-Fe bimetallic catalyst (RuFe/(N)C) was synthesized by a single pyrolytic step using chitosan adsorbed with Ru 3 + and Fe 3+ salts. By varying the metal loadings, the catalytic performance was effectively modulated, wherein 0.5Ru10Fe/(N)C catalyst achieved complete conversion of hexanoic acid and near 100% alkane yield under mild conditions (240 °C, 1 MPa H 2 ), outperforming its monometallic counterparts. Notably, carbon efficiency was also boosted over 0.5Ru10Fe/(N)C, and a maximum selectivity of hexane (69.3%) with high carbon efficiency (94.7%) was achieved. This unique performance arose from the suitable H₂ activation ability combined with strong hydrogenolysis capability toward C-O bonds enabled by electron-rich Ru sites, which collectively favored the hydrodeoxygenation (HDO) pathway to enhance carbon efficiency. Kinetic studies identified the hydrogenation of hexanoic acid to hexanol as the rate-determining step, and 0.5Ru10Fe/(N)C exhibited a low activation energy (76.1 kJ/mol). Furthermore, the catalyst demonstrated broad substrate applicability, enabling the conversion of diverse fatty acids. This work presents a breakthrough strategy for valorizing low-value biomass acids into high-quality biofuels with exceptional improved carbon efficiency.