The products produced by hydrogenation of biomass-derived 5-hydroxymethylfurfural (HMF) are potential sustainable substitutes for petroleum-based building blocks used in the production of chemicals. We have studied the hydrogenation of HMF over supported Ru, Pd, and Pt catalysts in monophasic and biphasic reactor systems to determine the effects of the metal, support, solution phase acidity, and the solvent to elucidate the factors that determine the selectivity for hydrogenation of HMF to its fully hydrogenated form of 2,5-di-hydroxy-methyl-tetrahydrofuran (DHMTHF). We show that the selectivity to DHMTHF is affected by the acidity of the aqueous solution containing HMF. The major by-products observed are C 6 -polyols formed from the acid-catalyzed degradation and subsequent hydrogenation of 2,5-dihydroxymethylfuran (DHMF), an intermediate hydrogenation product of HMF to DHMTHF. The highest yields (88-91%) to DHMTHF are achieved using Ru supported on materials with high isoelectric points, such as ceria, magnesia-zirconia, and γ-alumina. Supported catalysts containing Pt and Pd at the same weight percent as Ru are not as active for the selective hydrogenation to DHMTHF. † Electronic supplementary information (ESI) available: Full quantitative data for hydrogenation procedures.

The activity, selectivity, and stability of several supported acid catalysts were evaluated in tubular reactors designed to produce 5-hydroxymethylfurfural (HMF) continuously from fructose dissolved in a single-phase solution of THF and H 2 O (4:1 w/w). The reactors, packed with the solid catalysts, were operated at 403 K for extended periods, up to 190 h. The behaviors of three propylsulfonic acid-functionalized, ordered porous silicas (one inorganic SBA-15-type silica, and two ethane-bridged SBA-15-type organosilicas) were compared with that of a propylsulfonic acid-modified, nonordered, porous silica. The HMF selectivity of the catalysts with ordered pore structures ranged from 60 to 75%, whereas the selectivity of the nonordered catalyst under the same reaction conditions peaked at 20%. The latter was also the least stable, deactivating with a first-order rate constant of 0.152 h −1 . The organosilicas are more hydrothermally stable and maintained a steady catalytic activity longer than the inorganic SBA-15-type silica. The organosilica with an intermediate framework ethane content of 45 mol % was more stable, with a first-order deactivation rate constant of only 0.012 h −1 , than the organosilica containing 90 mol % ethane linkers in the framework. The catalysts were recovered and characterized after use by 13 C and 29 Si solid-state NMR, elemental analysis, nitrogen adsorption/desorption, X-ray diffraction, and SEM/TEM. Deactivation under flow conditions is caused primarily by hydrolytic cleavage of acid sites, which can be (to some) extent recaptured by the free surface hydroxyl groups of the silica surface.

No abstract

Conversion of cellulosic biomass to renewable chemicals such as 5-hydroxymethylfurfural (HMF) is of high current interest. Herein, we report a rare example of one-pot synthesis of HMF from glucose by tandem catalysis. The system is composed of a thermophilic glucose isomerase enzyme for glucose isomerization to fructose and a solid acid catalyst for fructose dehydration to HMF. A base (−NH2) functionalized mesoporous silica (aminopropyl-FMS) with large pore size was deployed successfully to immobilize and protect the thermophilic glucose isomerase in organic solvents at high temperature. The combination of this catalyst with a Brønsted acid (−SO3H) functionalized mesoporous silica (propylsulfonic acid-FMS) allowed us to conduct a one-pot transformation of glucose to HMF directly in a monophasic solvent system composed of tetrahydrofuran (THF) and H2O (4:1 v/v) with 61% yield of fructose and 30% yield of HMF at temperatures >363 K in 24 h.

Building a better dehydrator: A nanocomposite catalyst was designed and synthesized expressly for the dehydration of fructose to the platform chemical, 5‐hydroxymethylfurfural (HMF). When poly(vinylpyrrolidone) is intercalated and cross‐linked inside the acid‐functionalized mesopores of silica, the fructose tautomer equilibrium favors HMF production.