Understanding of Alcohol and Aldehyde Oxidation Behavior of Gold Nanoparticles with Carbonaceous Layers in HMF Oxidation

Biomass-derived feedstock provides a sustainable solution for biodegradable plastics production amid growing sustainability concerns. A key building block for such plastics is 2,5-furandicarboxylic acid (FDCA). FDCA is generally produced through the full oxidation of 5-hydroxymethylfurfural (HMF), which has two possible pathways due to its aldehyde and alcohol functional groups. Recently, gold-based electrocatalysts have emerged as effective catalysts for facilitating the HMF oxidation reaction (HMFOR) due to its remarkably low onset potential and great stability. However, existing literature lacks a definitive understanding of the favored reaction pathway and mechanistic details of HMFOR using gold-based catalysts. Herein, we examine the reduction-oxidation reaction of the gold surface to investigate its oxidation activity toward aldehyde groups and potential active sites of HMFOR. This gold surface under examination consists of gold nanoparticles covered with carbon film, synthesized through a facile electrochemical method and denoted as Au/C. Au/C exhibits a surface-enhanced Raman scattering (SERS) feature, enabling the use of in-situ SERS measurements as well as Au/C rotating disk electrode (RDE) experiments at varying rotating speeds. The RDE measurements provide valuable insights into the kinetics of alcohol and aldehyde oxidation, thereby revealing the favored pathway for HMF oxidation. The SERS measurements suggest that the oxidation (aldehyde or alcohol) in HMFOR depends on the coverage of hydroxyl ions on the Au surface. These findings further implicate the potential active site on this catalyst for HMF oxidation.