The multifunctional nature of biomass-derived feedstocks demands intricate interaction between the reactant molecule and the catalyst surfaces to remove the excess oxygen and partially hydrogenate specific unsaturated groups for many relevant chemicals and fuels, a process known as hydrodeoxygenation (HDO). In doing so, one needs to avoid over-hydrogenation and unselective cracking the C-C bonds of the molecule. A selective route to remove excess oxygen-containing functional groups in biomass-derived feedstocks is via catalytic transfer hydrogenation (CTH), which employs renewable organic compounds such as alcohols and organic acids as the hydrogen donor. Since biomass is typically available in remote areas that lack a transportation system, CTH is an attractive alternative to alleviate the need for high-pressure hydrogen that requires large-scale infrastructure, available only in integrated chemical plants. CTH has been demonstrated in the upgrade of various biomass molecules, including cellulose, sugars, and furanics often employing a supported metal or metal oxides as a hydrogenation catalyst. Herein, we present a combined experimental and computational study on the reaction pathways in the CTH of furfural over a mildly oxidized Ru/C catalyst, referred to as Ru/RuOx/C, by detailed mass fragmentation analysis with isotopically labeled chemicals and rigorous kinetic studies. Furfural is an ideal biomass derived “platform” chemical and its hydrogenolysis product, MF, has a high octane number and can be employed for the production of renewable toluene. We show that the intermolecular hydride transfer is the dominant pathway for the hydrogenation of the carbonyl group of furfural to furfuryl alcohol (FA). Further, hydrogenolysis via ring activation is a major, if not the dominant, pathway in the C-OH bond cleavage in the conversion of FA to MF. Our results provide molecular level understanding of the role of the cooperativity of metal and Lewis acid sites in mediating the CTH of biomass derivatives, which can guide the rational design of efficient bifunctional catalysts by suitable choice and proper atomic level arrangement of Lewis acid and metal sites. Further, we demonstrate that detailed mass fragmentation analysis is a powerful technique in mechanistic investigations of complex reactions involving biomass-derived molecules.

Mechanistic insights into metal Lewis acid-mediated catalytic transfer hydrogenation reactions

254th National Meeting (2017)

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