Solvent Tunes the Selectivity of Hydrogenation Reaction over α-MoC Catalyst

Selective activation of chemical bonds in multifunctional oxygenates on solid catalysts is a crucial challenge for sustainable biomass upgrading. Molybdenum carbides and nitrides preferentially activate C=O and C-OH bonds over C=C and C-C bonds in liquid-phase hydrogenation of bioderived furfural, leading to highly selective formations of furfuryl alcohol (FA) and its subsequent hydrogenolysis product (2-methyl furan (2-MF)). We demonstrate that pure-phase alpha-MoC is more active than beta 3-Mo2C and gamma-Mo2N for catalyzing furfural hydrogenation, and the hydrogenation selectivity on these catalysts can be conveniently manipulated by alcohol solvents without significant changes in reaction rates (e.g., > 90% yields of FA in methanol solvent and of 2-MF in 2-butanol solvent at 423 K). Combined experimental and theoretical assessments of these solvent effects unveil that it is the hydrogen donating ability of the solvents that governs the hydrogenation rate of the reactants, while strong dissociative adsorption of the alcohol solvent on Mo-based catalysts results in surface which controls the reaction selectivity via enforcing steric hindrance on the formation of relevant transient states. Such solvent induced surface modification of Mo-based catalysts provides a compelling strategy for highly selective hydrodeoxygenation processes of biomass feedstocks.