Electrochemical biomass upgrading: degradation of glucose to lactic acid on a copper(ii) electrode

Homogeneous and Heterogeneous Catalysis of Glucose to Lactic Acid and Lactates: A Review

The current societal demand to replace polymers derived from petroleum with sustainable bioplastics such as polylactic acid (PLA) has motivated industry to commercialize ever-larger facilities for biobased monomers like lactic acid. Even though most of the lactic acid is produced by fermentation, long reaction times and high capital costs compromise the economics and thus limit the appeal of biotechnological processes. Catalytic conversion of hexose from biomass is a burgeoning alternative to fermentation. Here we identify catalysts to convert glucose to lactic acid, along with their proposed mechanisms. High Lewis acidity makes erbium salts among the most active homogeneous catalysts, while solvent coordination with the metal species polarize the substrate, increasing the catalytic activity. For heterogeneous catalysts, Sn-containing bimetallic systems combine the high Lewis acidity of Sn while moderating it with another metal, thus decreasing byproducts. Hierarchical bimetallic Sn-Beta zeolites combine a high number of open sites catalyzing glucose isomerization in the mesoporous regions and the confinement effect assisting fructose retro-aldol in microporous regions, yielding up to 67% lactic acid from glucose. Loss of activity is still an issue for heterogeneous catalysts, mostly due to solvent adsorption on the active sites, coke formation, and metal leaching, which impedes its large scale adoption.

Cation Incorporation into Copper Oxide Lattice at Highly Oxidizing Potentials

Electrolyte cations can have significant effects on the kinetics and selectivity of electrocatalytic reactions. We show an atypical mechanism through which electrolyte cations can impact electrocatalyst performance─direct incorporation of the cation into the oxide electrocatalyst lattice. We investigate the transformations of copper electrodes in alkaline electrochemistry through operando X-ray absorption spectroscopy in KOH and Ba(OH)2 electrolytes. In KOH electrolytes, both the near-edge structure and extended fine-structure agree with previous studies; however, the X-ray absorption spectra vary greatly in Ba(OH)2 electrolytes. Through a combination of electronic structure modeling, near-edge simulation, and postreaction characterization, we propose that Ba2+ cations are directly incorporated into the lattice and form an ordered BaCuO2 phase at potentials more oxidizing than 200 mV vs the normal hydrogen electrode (NHE). BaCuO2 formation is followed by further oxidation to a bulk Cu3+-like BaxCuyOz phase at 900 mV vs NHE. Additionally, during reduction in Ba(OH)2 electrolyte, we find both Cu-O bonds and Cu-Ba scattering persist at potentials as low as -400 mV vs NHE. To our knowledge, this is the first evidence for direct oxidative incorporation of an electrolyte cation into the bulk lattice to form a mixed oxide electrode. The oxidative incorporation of electrolyte cations to form mixed oxides could open a new route for the in situ formation of active and selective oxidation electrocatalysts.

Selective production of formate over a CuO electrocatalyst by electrochemical and photoelectrochemical biomass valorisation

CuO acts as a selective (a) electrocatalyst for electrochemical formate production from various biomass wastes and (b) a cocatalyst on a hematite photoanode for photoelectrochemical formate production from glucose.