Synergistic Co Single Atoms and Co3O4 Nanoparticles for Catalytic Fractionation of Lignocellulose

Abstract

Lignocellulose is the most abundant and sufficiently available resource for the development of the bio-economy. Although the reductive catalytic fractionation (RCF) represents a promising pretreatment strategy to valorize lignin into phenolic monomers, significant challenges are to be addressed, including high reaction temperatures, excessive hydrogen pressures, and reliance on noble metal catalysts. Herein, we develop a synergistic catalyst comprising Co single atoms and Co3O4 nanoparticles supported on oxidized activated carbon (Co1+NPs/OAC), which delivers high yields of phenolic monomers during the RCF of diverse sawdust feedstocks at 200 oC and 10 bar H2, with ethanol serving as the solvent. For example, the RCF of poplar sawdust under these optimized conditions affords 46.1 wt % phenolic-monomer yield together with 92.5 wt % carbohydrate retention. Mechanistic studies reveal a synergistic interplay wherein Co3O4 nanoparticles facilitate H2 dissociation into hydrogen species (H*), while Co single atoms adsorb the Cα-OH group in lignin. Meanwhile, ethanol is presumed to serve as a mediator that effectively accelerates the H* transfer from Co3O4 sites to Co single atoms, thereby promoting the efficiency of lignin hydrogenolysis. This catalyst-solvent synergetic strategy enables the depolymerization of diverse natural sawdust feedstocks under relatively mild conditions, which may provide a route toward the efficient valorization of lignocellulosic resources.