Hydrogenolysis of lignosulfonate into phenols over heterogeneous nickel catalysts

Abstract

We report a strategy for the catalytic conversion of lignosulfonate into phenols over heterogeneous nickel catalysts. Aryl-alkyl bonds (C-O-C) and hydroxyl groups (-OH) are hydrogenated to phenols and alkanes, respectively, without disturbing the arenes. The catalyst is based on a naturally abundant element, and is recyclable and reusable.

Heterogeneously catalyzed lignin depolymerization

“…While nickel is able to cleavage C-O aliphatic bonds, it is less active for the rupture of aromatic C-O and arene bonds. Lignin conversion to alkane-substituted guaiacols over Ni catalysts is independent of the support type (e.g., activated carbon, zeolite, or MgO) [25]. Higher conversions were obtained in the presence of diol or triol functions, such us glycerol and ethylene glycol.…”

“…Higher conversions were obtained in the presence of diol or triol functions, such us glycerol and ethylene glycol. Song and co-workers concluded that for lignosulfates, Ni(0) active sites catalyse hydrogenolysis of C-O-C bonds, C-OH bonds in side alkyl chains, and the reduction of sulfonate groups into hydrogen sulfide (H 2 S) [25]. He et al [26] studied the cleavage of aromatic ether linkages by a nickel catalyst in model lignin compounds, such as benzyl phenyl ether, 2-phenylethyl phenyl ether, and diphenyl ether, which contain b-O-4, a-O-4, and 4-O-5 bonds, respectively.…”

“…The use of noble metal catalysts favours a mixture of cyclohexane derivatives and products arising from C-C bond cleavage. Metallic nickel has shown the most promise for the production of phenolics from lignin due to its superior propensity for cleaving aryl-aryl C-O-C bonds and C-OH bonds in side chains containing CH 3 or CH 2 functions, commonly yielding C 1 -C 3 alkane-substituted guaiacols as the major product [25]. In the case of lignosulfates, Ni catalysts show good resistance to sulfur poisoning, while remaining active and selective for the transformation of lignosulfate into phenolics.…”

Lignin depolymerization (LDP) in alcohol over nickel-based catalysts via a fragmentation–hydrogenolysis process

“…41,42 We recently reported a strategy of catalytic conversion of lignosulfonate into 4-ethylguaiacol and 4-propylguaiacol over heterogeneous nickel catalysts. 43 Our study reveals that aryl-O-alkyl bonds (C-O-C) and hydroxyl groups of lignin are hydrogenated to phenols and alkanes, respectively, while preserving the aromatic structure.…”

“…On the assumption that the UV absorption of phenylpropanoid in lignin and guaiacol approximately equals each other, the dissolved lignin was calculated based on a guaiacol standard curve used in our previous study. 43 …”