Lignin Valorization: A Novel in Situ Catalytic Hydrogenolysis Method in Alkaline Aqueous Solution

Abstract

In situ catalytic hydrogenolysis of lignin is an efficient method for lignin valorization. Herein, a novel in situ lignin catalytic hydrogenolysis technique in alkaline aqueous solution over a NiAl alloy catalyst under mild conditions was systematically suited. Ni served as the active phase and could be exposed by etching Al atoms with alkaline aqueous solution. Meanwhile, H2 resources could be in situ generated and easily arrived at the adjacent exposed Ni sites to be activated. The in situ lignin hydrogenolysis system exhibits attractive depolymerization results under mild conditions, with an 86.8% conversion degree and 18.9 wt % yield of aromatic monomers at 220 °C, much higher than the traditional hydrogenolysis method using a commercial Raney Ni catalyst under high pressure external H2. The mechanism studies with lignin model compounds suggest that alkaline aqueous solution could promote the cleavage of C–O–C bonds and hinder the hydrogenation of the benzene ring. In addition, a moderate amount of exposed Ni sites as well as rich active hydrogen species are determinant for efficient lignin depolymerization.