Optimization and Reaction Kinetics of Hydrodeoxygenation of 5-Hydroxymethylfurfural to 2,5-Dimethylfuran over Ni–Co Bimetallic Catalysts

Selective production of 2,5-dimethylfuran (DMF), a promising liquid fuel, via hydrodeoxygenation (HDO) of 5-hydroxymethylfurfural (HMF) is crucial for sustainable biomass upgrading. In this study, a supported bimetallic Ni₆₀Co₄₀/SiO₂ catalyst and a reference Ni₁₀₀/SiO₂ catalyst, prepared via deposition–precipitation, were used to optimize HDO reaction conditions (temperature, 180–210 °C; hydrogen pressure, 1–3 MPa; HMF concentration, 0.15–0.3 mol/L). Results showed that the Ni₆₀Co₄₀/SiO₂ catalyst achieved complete HMF conversion with a 95% DMF yield under optimal conditions (200 °C, 2 MPa H₂ pressure, 0.23 mol/L HMF, and 180 min), surpassing the Ni₁₀₀/SiO₂ catalyst (80% DMF yield). A kinetic model for HMF conversion was developed, revealing first-order reaction kinetics. The apparent activation energy (E_a) for Ni₆₀Co₄₀/SiO₂ was 41.6 kJ/mol, which is lower than that for Ni₁₀₀/SiO₂ (60.2 kJ/mol). Quantitative analysis of the reaction pathways showed that hydrogenolysis of 2,5-bis(hydroxymethyl)furan (BHMF) to 5-methylfurfuryl alcohol (MFA) is the rate-limiting step. The model achieved excellent agreement with experimental data (R > 0.96). Moreover, the Ni₆₀Co₄₀/SiO₂ catalyst was more stable than the Ni₁₀₀/SiO₂ catalyst over five reaction cycles. The difference in stability was analyzed in detail.