Aerobic oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic acid over Au/Hydrotalcite catalyst − role of support and synthesis methodology on the activity and stability

Abstract

The oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is key in producing bio-based plastics like polyethylene furanoate (PEF), a sustainable alternative to petrochemical materials. This work reports a systematic study on how the hydrotalcite (HT) support precursors—specifically using Na⁺ or NH₄⁺ precursors and the choice of synthesis method (deposition–precipitation, DP, or sol immobilization, SI) influence the catalytic performance and stability of Au/HT catalysts under base-free reaction conditions. Au/HT_Na DP achieved 100 % HMF conversion and FDCA yield without an external base. This high activity is reflected in its turnover frequency (TOF), reaching 12.1 h⁻¹ per basic site and 287.4 h⁻¹ per gold site. The superior performance of Au/HT_Na DP is attributed to the strong synergy between gold nanoparticles (AuNPs) and weak basic sites (OH^– groups) of the HT, whose abundance is dictated by the choice of precursor. In contrast, Au/HT_NH4 SI, despite higher Au dispersion, showed lower activity due to reduced basicity. Magnesium leaching was identified as the primary cause of catalyst deactivation, and a regeneration strategy employing Mg(OH)₂ was developed to successfully restore both the structure and basicity of the catalyst. These findings offer practical insights into the design of recyclable, base-free catalytic systems for sustainable FDCA production.