Electrocatalysis Cα–Cβ and Cβ–O bond cleavage of lignin model compound using Ni-Co/C as catalyst electrode in deep eutectic solventx

Abstract

In this study, Cα–Cβ and Cβ–O bond cleavage of β-O-4 model compound (2-phenoxy-1-phenylethanol) were accomplished by electrocatalysis depolymerization process in deep eutectic solvents (DES) systems. We have investigated the application of Ni-Co/C catalysts on working electrode, which were synthesized with impregnation method. The Ni-Co/C with porous structure and abundant active sites, was shown an excellent electrocatalysis activity. Specific structure of Ni-Co/C could provide greatly efficient adsorption and desorption capacity to promote Cα–Cβ and Cβ–O bond cleavage. Therefore, in this electrocatalysis depolymerization process, the highest depolymerization rate exceeded 90%. And the yields (and conversion rates) of products (including benzaldehyde, acetophenone, benzoic acid, phenol) can reach to 124.08 mg/g (25.05%), 23.29 mg/g (4.15%), 44.64 mg/g (7.83%), 30.3 mg/g (6.9%). Furthermore, the electrocatalysis mechanism of Cα–Cβ and Cβ–O bond was investigated. The cleavage of Cα–Cβ and Cβ–O bond was initiated by in situ generated free radicals through Ni-Co/C. Then, the cleavage of Cα–Cβ and Cβ–O bond were occurred by ·OH and ·O2−. The results were showed that the Cα–Cβ bond cleavage was more in line with the β-C elimination and free radical pathways, and Cβ–O bond cleavage was consistent with direct oxidative addition. The enhanced electrocatalytic efficiency of the low-cost Ni-Co/C electrocatalyst combined with its good chemical stability and selectivity, which offer a promising route for developing an efficient lignin depolymerization technology.