Exploring the gas-phase catalytic transfer hydrogenation as a tool for the production of fuels and chemicals from renewables

Over the past decade, great efforts have been devoted in the field of biomass valorization to the development of reductive processes for the sustainable production of bio-fuel and chemicals. Catalytic transfer hydrogenation, which uses alcohols as the hydrogen source, offers an interesting approach that avoids the use of both high H2 pressure and precious metal catalysts. In this work, the vapour-phase production of furfuryl alcohol (FAL) and 2-methylfuran (MF) from biomass-derived furfural (FU), using methanol as the H-transfer agent was studied. Two class of catalysts were employed: basic-based systems such as MgO, Mg/Fe/O, Mg/Al/O and CaO; and a mixed iron-vanadium oxide FeVO4. With the latter at the temperature of 320°C it was possible to achieve 80% yield to 2-methylfuran, with small amounts of 2,5-dimethylfuran (DMF) and 2-vinylfuran (VINFU) as by-products. The study of the reaction network permitted us to infer on the relative contribution of H-transfer and hydrogenation, to 2-methylfuran formation. On the other hand, with the basic-base catalysts, it was demonstrated that both the pristine systems MgO and CaO were totally selective towards the formation of the unsaturated alcohol FAL as the only reduction product of FU at mild temperature condition, thus allowing selective H-transfer from methanol to the substrate. Conversely, the distribution of compounds obtained with Mg/Fe/O was significantly different, with 2-methylfuran formation prevailing when the reaction was carried out between 300 and 400 °C. Furthermore the use of different hydrogen sources such as 2-propanol, acetone, acetaldehyde, formaldehyde and molecular hydrogen allow to identify the complete reaction network for the vapor-phase transformation of FU, demonstrating that both the in-situ produced molecular hydrogen and formaldehyde played a direct role in MF formation. The reported results indicate the potential application of the catalytic transfer hydrogenation reaction as an efficient process for the selective de-oxygenation of biomass-derived molecules.