ATR-SEIRAS Investigation of the Electro-oxidation Mechanism of Biomass-Derived C₅Furanics on Platinum Electrodes

The electrochemical oxidation of furfural and down-pathway intermediate and product species (furoic acid, 2(5H)-furanone, 5-hydroxy-2(5H)-furanone, and maleic acid) is investigated on platinum electrodes via attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) with modulation excitation spectroscopy (MES). Density functional theory (DFT) calculations are performed to further illuminate the elementary reaction mechanism and the surface orientations of key reaction intermediates. Evidence from these techniques suggests that oxidation selectivity of the furanic compounds is governed by a balance between several properties of the catalyst. Propensity toward C-C cleavage steps yields self-limiting accumulation of adsorbed CO at low potentials and promotes the formation of C₄products and CO₂at higher potentials. Affinity for surface carboxylates such as furoate and maleate species also leads to their accumulation on the surface at higher potentials. It is thus suggested that correlations between the various surface oxygenate binding energies represent a challenge in balancing accumulation of strongly bound intermediates against a need for the surface to bind hydroxyl to initiate O-addition steps.