Selective electrocatalytic upgrading of lignin to aryl aldehydes and carboxylic acids over dodecyl sulfate-intercalated CoS nanocones

Abstract

Lignin is the biggest and most sustainable reservoir for aromatics, but its selective degradation is still a challenge. Herein, we report the electrocatalytic cleavage of the Cα-Cβ bonds of β-O-4, a lignin model, under mild conditions using a dodecyl sulfate-intercalated cobalt sulfide (DS-CoS) nanocone catalyst. With this noble-metal-free nanocones as an electrocatalyst, β-O-4 can be selectively oxidized to the corresponding aldehydes or carboxylates in excellent yields (90–97%) by control potential electrolysis. Moreover, the electrochemical upgrading of lignin produces aryl aldehydes or carboxylic acids in yields of 21.4 and 23.9 wt%, respectively, by controlling potential electrolysis. Mechanism studies show that the hydroxyl radicals electrogenerated on the surface of the SCo3+OH intermediate induce the cleavage of Cα-Cβ bonds to form aldehydes, which are further oxidized to carboxylic acids by superoxide radicals electrogenerated on the surface of the Co4+ intermediate. This approach features the merits of low-cost and good stability of the electrocatalyst, high conversion of β-O-4, high selectivity of products, and mild reaction conditions.