LAUSR

Lignin can be converted in useful precursors of fuels and fine chemicals by thermochemical conversion followed by catalytic hydrogenation using metal catalysts at severe reaction conditions. Thus, mild hydrogenation would significantly improve the sustainability of lignin valorization. Here, we present hydrogenation of phenols, alkylphenols and methoxyphenols at mild reaction conditions (70°C and atmospheric pressure) via H-transfer hydrogenation over Raney-Ni catalyst in 2-propanol and 2-butanol solvents. The transfer hydrogenation was feasible at the mild conditions, but the complexity of the reactant greatly decreased or even completely suppressed its reactivity. The position of the functional group (o-, m-, p- position) had a great effect on the reactivity of phenols. Moreover, 2-butanol enhanced the conversion of phenols in comparison with 2-propanol. When comparing classic hydrogenation with H-transfer hydrogenation in presence of external H2 , we found that external H2 not only regenerated H-donor solvent and ensured stable performance, but it also increased conversion of phenols and alkylphenols. On the other hand, the absence of external H2  boosted the conversion of methoxy phenols. Finally, we hydrogenated phenols extracted from a pyrolysis oil aqueous phase. We found that the conversion of phenols was greatly affected by competitive adsorption of different compounds present in the reaction mixture. External H2 promoted hydrogenation of the complex reaction mixture and prevented condensation of the reactive species in contrast to the H-transfer hydrogenation.