Hydrodeoxygenation of guaiacol to bio-hydrocarbons in alkaline condition on the Ni/AC catalyst with an "acid-switch"

Due to the mass manufacturing of global papermaking black liquor, lignin remained in strong-alkaline black liquor is a promising raw material for bulk hydrocarbons production with huge carbon-neutral value. In this work, the alkaline in reactant is proved to inhibit the hydrodeoxygenation reaction of guaiacol severely due to the formation of phenates and cyclohexadienones. A hydroxyl interventional Ni/AC catalyst, on which an "acidswitch" is built with combination of hydroxyl groups and Ni nanoparticles, achieves 4-fold bio-hydrocarbons yield in alkaline condition compared to conventional Ni/AC catalyst. It is implied that hydroxy groups promote the C(sp2)-O reaction route with the aid of activated hydrogen on Ni nanoparticles, while acidic groups on catalyst reduce the size of Ni nanoparticles, thus further enhances the HDO efficiency. It is the first time we propose a reaction mechanism of HDO of guaiacol on Ni-based catalyst in alkaline condition to give insight into HDO reaction of lignin compounds in black liquor. This work gives insights into the relationship between catalyst surface properties and HDO efficiency, and provides a promising approach for green utilization of lignin in alkaline black liquor.