Selectively Upgrading Lignin Derivatives to Carboxylates through Electrochemical Oxidative C(OH)−C Bond Cleavage by a Mn‐Doped Cobalt Oxyhydroxide Catalyst

Abstract

Oxidative cleavage of C(OH)ÀCb onds to afford carboxylates is of significant importance for the petrochemical industry and biomass valorization. Here we report an efficient electrochemical strategy for the selective upgrading of lignin derivatives to carboxylates by am anganese-doped cobalt oxyhydroxide (MnCoOOH) catalyst. Awide range of ligninderived substrates with C(OH)-C or C(O)-C units undergo efficient cleavage to corresponding carboxylates in excellent yields (80-99 %) and operational stability (200 h). Detailed investigations reveal atandem oxidation mechanism that base from the electrolyte converts secondary alcohols and their derived ketones to reactive nucleophiles,which are oxidized by electrophilic oxygen species on MnCoOOH from water.A s proof of concept, this approachwas applied to upgrade lignin derivatives with C(OH)-C or C(O)-C motifs,a chieving convergent transformation of lignin-derived mixtures to benzoate and KA oil to adipate with 91.5 %a nd 64.2 %y ields, respectively.

Selective Electrooxidation of Biomass‐Derived Alcohols to Aldehydes in a Neutral Medium: Promoted Water Dissociation over a Nickel‐Oxide‐Supported Ruthenium Single‐Atom Catalyst

“…[21,22] On the other hand, it is proposed that base promotes the conversion of aldehyde into reactive geminal diol, and thus facilitates subsequent electrocatalytic dehydrogenation to produce carboxylate. [23] In this context, it is considered that the neutral/near-neutral electrolyte would circumvent these issues and enable selective BDAOR to aldehydes. Indeed, as reported by Wang et al, at neutral pH, oxidation of aldehyde groups of HMF can be largely suppressed, as evidenced by the formation of 2,5-diformylfuran (DFF) intermediate and the accumulation of formyl-2furancarboxylic acid (FFCA), indicating that neutral pH is more favorable for aldehyde synthesis.…”

“…On one hand, aldehydes suffer from base‐catalyzed dimerization or aldol condensation reactions at high pH value [21, 22] . On the other hand, it is proposed that base promotes the conversion of aldehyde into reactive geminal diol, and thus facilitates subsequent electrocatalytic dehydrogenation to produce carboxylate [23] . In this context, it is considered that the neutral/near‐neutral electrolyte would circumvent these issues and enable selective BDAOR to aldehydes.…”

Green Carbon Science: Efficient Carbon Resource Processing, Utilization, and Recycling towards Carbon Neutrality

“…For instance, the β‐O‐4 linkages in lignin can be selectively cleaved using cadmium sulfide quantum dots as catalyst, generating functionalized aromatics under visible light in excellent yields [196] . A manganese‐doped cobalt oxyhydroxide catalyst can promote the electrochemical oxidation of lignin derived secondary alcohols and ketones to carboxylic acids [197] . In comparison with thermochemical routes, biological strategies enable lignin depolymerization to be carried out at much lower temperature and pressure, while offering improved selectivity.…”

Co-electrolysis toward value-added chemicals

“…The coelectrolysis strategy can also be used to lower energy consumption and obtain value-added chemicals for biomass upgrading. Zhou et al [24] reported the co-electrolysis of ligninderived substrates and water, by which benzoate/adipate and hydrogen were obtained efficiently. Chong et al [25] reported that the integration of hydrogen production/hydrogenation with Se promoted α-nitrotoluenes electrooxidation, by which hydrogen/hydrogenation products and E-nitroethenes were obtained at a lowered potential.…”