Effect of the Solvent in Enhancing the Selectivity to Furan Derivatives in the Catalytic Hydrogenation of Furfural

The catalytic hydrogenation of furfural, particularly to methyl-furan, is studied on four commercial catalysts (based on Ni and Cu and alumina or silica as supports) in different aprotic solvents (n-heptane, diisopropyl ether and ethyl acetate) and two Cl-containing solvents (chlorobenzene and n-heptane containing 0.5 wt % CHCl3). The catalytic data are complemented by the estimated solvent characteristics, activity coefficients of reactants (including H-2) and products, and energy stability by the solvent on reactants and main products of reaction. The results show that the solvent plays a major role in the modification of selectivity, but strongly depending on the catalyst. In low polar solvent (n-heptane) yield up to about 50% can be obtained to methyl-furan using Cu/Al2O3, but yields nearly halve using Cu/SiO2 catalysts and become very low for Ni-based catalysts. The latter, on the contrary, show high selectivity to methyl-furan (up to about 70-80%) using n-heptane containing small amounts of CHCl3. There is a double role of the solvent, both in the stabilization of the reaction products and minor of the reactants, and in interacting with the catalyst, modifying its intrinsic reactivity, both aspects scarcely investigated, but representing a valuable option to control the selectivity in the valorization of biomass byproducts.