Highly efficient Co-based catalysts supported on K-modified alumina for selective hydrodeoxygenation of lignin-derived phenols to alkyl cyclohexanols

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. As high as 99.99% guaiacol conversion and 96.70% cyclohexanol selectivity are obtained over optimized Co/1 K–Al2O3 catalyst, which are better than those Co-based catalyst reported in previous studies. Highly dispersed Co particles provide more metal active sites and better chemisorption of guaiacol molecules, which promotes HDO activity. Importantly, with the increase amount of K species doped in Al2O3 support, the total amount of acid sites on catalyst decreases and the strong acid site disappear, which inhibits unwanted conversion of cyclohexanol to the byproduct cyclohexane. It can be found that with proper amount of acid sites and strength, the selectivity of cyclohexanol can be maximized during selective HDO reaction of guaiacol. The kinetic study also shows that the activation energy from cyclohexanol to cyclohexane increases from 62.08 kJ/mol over Co/Al2O3 catalyst to 86.11 kJ/mol over Co/1 K–Al2O3 catalyst, implying that the reaction barrier improves, which hinders further removal of hydroxyl group on cyclohexanol. Besides, selective HDO reactions using other typical phenols as substrates over Co/1 K–Al2O3 catalyst were performed and good alkyl cyclohexanols selectivities are observed.