Electrocatalytic hydrogenation of mono- and dimeric lignin to hydrocarbons in fluidized electrocatalytic system

Abstract

Herein, we reported a simple ECH process for preparing hydrocarbons from lignin monomers, dimers, and lignin oil in a fluidized electrocatalytic hydrogenation (FECH) system. The FECH system contained low redox potential H3O40PW12 (PW12) solution as an electrolyte, suspended Pt/C as catalyst, and NaBH4 as reductant. The introduction of NaBH4 reduced PW12 to a negative voltage in aqueous phase, and then hydrogenation of lignin-derived substrates. Meanwhile, NaBH4 as a hydrogen source could be directly combined with PW12 to achieve hydrogenation of substrates (non-electrocatalytic process). This co-driven catalytic process could realize high-performance hydrogenation of lignin oil into hydrocarbon fuels. Results demonstrated that almost complete conversion of 2-methoxy-4-propylphenol (MPP) was achieved with a higher faraday efficiency (92%), and the selectivity of the main products (propylcyclohexane and 4-propylcyclohexanol) was up to 87% at mild conditions (80 °C, 30 min and 50 mA/cm2 current density). Dimer model compounds, Phenethoxybenzene (β-O-4 linkage), also afforded over 90% hydrogenated C6, C8, and coupling products via CO scission and aromatic rings hydrogenation. By integrating depolymerization and ECH upgrading of lignin from different biomass species, lignin could be valorized to hydrocarbons with high yield.