Electrochemical Oxidation and Bond Cleavage of Lignin-Derived Model Compounds with Nanoparticle Catalysts

Abstract

Electrochemistry offer an environmentally friendly approach to convert biomass or biomass derived material into valuable organic chemicals, petrochemical substitutes, and energy-intensive chemicals. Monomers could be generated by cleaving ether (C-O-C) linkages in lignin via thermal decomposition process such as reductive catalytic fraction (RCF). However, this process leaves behind a significant portion of soluble lignin oligomers with recalcitrant C-C linkages. Monomer yields from the RCF pathway are approaching theoretical limits based on ether bond cleavage. Therefore, with broader goal of improving lignin utilization within a biorefinery, we probed the electrocatalytic oxidation of model dimer compounds with C-C linkages representative of RCF oligomers. Electrochemical studies offer several advantages including operation at low temperatures and pressures, applied potentials can be used to control reaction rates and selectivities, and renewable electricity can be used, thus lowering overall greenhouse gas emissions. According to previous studies, several metals such as nickel, cobalt, copper, and platinum can be used to build electrocatalysts for biomass conversion. Therefore, we have synthesized a series of low-cost nickel and molybdenum nanoparticle catalysts for the electrocatalytic oxidation of model compounds. Besides the high surface and high stability advantages of supported nanoparticles in general, these candidates exhibit interesting catalytic activities resembling that of noble metal catalysts such as platinum in oxygen reduction reaction (ORR) which could also be beneficial in bond cleavage reactions in biomass or biomass derived material. The focus of this talk will be on the electrochemical studies of the selected nanoparticle catalysts toward C-C bond cleavage in RCF dimer model compounds. The results from the studies also lead to some insights we may be able to use to guide the future development of electro-oxidation of RCF oil/ biomass stream. Besides metallic, phosphide and carbide nanoparticles on carbon support, metal foils were also tested and were used as a comparison. Notably, a MoC catalyst on carbon support showed C-C and C-O bond cleavage activities in aqueous alcoholic solution with sodium hydroxide as the electrolyte.