Hernán Antonio Duarte

2,5-bis(hydroxymethy)lfuran (BHMF), a renewable compound with extensive industrial applications, can be obtained by selective hydrogenation of the C=O group of 5-hydroxymethylfurfural (HMF), a platform molecule derived from lignocellulosic biomass. In this work, we perform kinetic modeling of the selective liquid-phase hydrogenation of HMF to BHMF over a Cu/SiO₂ catalyst prepared by precipitation–deposition (PD) at a constant pH. Physicochemical characterization, using different techniques, confirms that the Cu/SiO₂–PD catalyst is formed by copper metallic nanoparticles of 3–5 nm in size highly dispersed on the SiO₂ surface. Before the kinetic study, the Cu/SiO₂-PD catalyst was evaluated in three solvents: tetrahydrofuran (THF), 2-propanol (2-POH), and water. The pattern of catalytic activity and BHMF yield for the different solvents was THF > 2-POH > H₂O. In addition, selectivity to BHF was the highest in THF. Thus, THF was chosen for further kinetic study. Several experiments were carried out by varying the initial HMF concentration (C⁰_HMF) between 0.02 and 0.26 M and the hydrogen pressure (P_H2) between 200 and 1500 kPa. In all experiments, BHMF selectivity was 97–99%. By pseudo-homogeneous modeling, an apparent reaction order with respect to HFM close to 1 was estimated for a C⁰_HMF between 0.02 M and 0.065 M, while when higher than 0.065 M, the apparent reaction order changed to 0. The apparent reaction order with respect to H₂ was nearly 0 when C⁰_HMF = 0.13 M, while for C⁰_HMF = 0.04 M, it was close to 1. The reaction orders estimated suggest that HMF is strongly absorbed on the catalyst surface, and thus total active site coverage is reached when the C⁰_HMF is higher than 0.065 M. Several Langmuir–Hinshelwood–Hougen–Watson (LHHW) kinetic models were proposed, tested against experimental data, and statistically compared. The best fitting of the experimental data was obtained with an LHHW model that considered non-competitive H₂ and HMF chemisorption and strong chemisorption of reactant and product molecules on copper metallic active sites. This model predicts both the catalytic performance of Cu/SiO₂-PD and its deactivation during liquid-phase HMF hydrogenation.

Synthesis of 2,5-bis(hydroxymethyl)furan (BHMF) by selective 5-hydroxymethylfurfural (HMF) hydrogenation is ecofriendly and industrially important since HMF is obtained from renewable sources, and BHMF is a raw material used for production of biodegradable polymers. Four copper-based catalysts were prepared by incipient wetness impregnation (Cu/SiO₂-I, Cu/Al₂O₃-I), precipitation–deposition (Cu/SiO₂-PD) and coprecipitation (CuMgAl), and then tested in the liquid-phase hydrogenation of HMF. Metallic phases with large copper particles were obtained by incipient wetness impregnation, while precipitation methods gave highly dispersed metal copper nanoparticles. The pattern found for the concentration and strength of surface acid sites was: CuMgAl > Cu/Al₂O₃-I > Cu/SiO₂-PD > Cu/SiO₂-I. The copper-based catalysts active in HMF hydrogenation are all highly selective to BHMF, but the intrinsic activity and stability depend on metallic copper dispersion and support nature. The catalyst stability becomes poorer in the cases that the metallic phase is formed by large copper particles or interacts with high-acidity supports. Therefore, the catalyst with the highest activity, BHMF yield and stability was Cu/SiO₂-PD. Furthermore, it was found that Cu/SiO₂-PD is reusable in the selective liquid-phase HMF hydrogenation after being submitted to a two-step thermal treatment: (1) calcination under air flow at 673 K; (2) reduction under H₂ flow at 523 K.