Selective hydrodeoxygenation of lignin-derived phenols to alkyl cyclohexanols over highly dispersed RuFe bimetallic catalysts

Selective hydrodeoxygenation (HDO) of phenolic compounds derived from the pyrolysis lignin-oil to desired products is a promising route in the high-value utilization of biomass-derived products. Cyclohexanol, as one of the important chemical materials, is an intermediate of catalytic HDO of guaiacol. Controllable selective HDO is conducted to improve the cyclohexanol selectivity over RuFe bimetallic catalyst prepared by ethylene glycol reduction method in this work. 99.99% guaiacol conversion and 81.35% cyclohexanol selectivity are obtained over optimized 2Ru2.5Fe/Al2O3-EG catalyst, which is better than those over 2Ru/Al2O3-EG catalyst. The mild catalyst preparation method gives it a high dispersion and uniform distribution of Ru and Fe species on the support. Various characterizations have proved that the intimate contact between Ru and Fe2O3 species contributes to the improvement of cyclohexanol selectivity. Partial blockage of Ru sites by Fe2O3 species slightly reduces the hydrogen adsorption capacity while the addition of Fe helps enhancing the hydrogenolysis of C-OMe bond. The reciprocal effect facilitates the removal of methoxyl groups and hinders the dehydroxylation of cyclohexanol to cyclohexane. Besides, other phenolic compounds and pyrolysis lignin-oil as substrates also show good selective HDO reactivity to corresponding alkyl cyclohexanols, implying potential application in the transformation from lignin-oil to high-value products.