Hydrodeoxygenation of lignin derived phenolics over a hydrous ruthenium oxide based catalyst(s): role of surface water molecules and acidity of the support

The synthesis of efficient and engineered noble metal catalysts for selective conversion of waste renewable lignin to valuable chemical building blocks is crucial for the economic viability of current biorefineries. Motivated by the water effect in promoting catalytic activity, hydrous ruthenium oxide (HRO) incorporating acidic systems (H-ZSM5, HY zeolite, γ-Al2O3, and SiO2) were investigated for selective hydrodeoxygenation of lignin-derived phenols in the aqueous phase. The results indicated that the hydrous form (surface bonded water molecules) of ruthenium and high acidity of the support promote the hydrogenolysis activity of the as-prepared catalysts and increase the yield of alkylated cyclohexanols. Among all catalysts, HRO@Y showed the best performance and afforded the highest selectivity to cyclohexanols. Intensive catalyst characterization demonstrated that in situ metal formation, a large number of acid sites, good metal dispersion, and high adsorption capacity of HRO@Y for polar fractions were responsible for the efficient activity. Water considerably improved the selective hydrodeoxygenation activity of the catalyst by promoting hydrogenation and demethoxylation and hindering dehydration.