Stability of gold nanocatalysts supported on mesoporous silica for the oxidation of 5-hydroxymethyl furfural to furan-2,5-dicarboxylic acid

The synthesis of furan-2,5-dicarboxylic acid via catalytic oxidation of 5-hydroxymethyl furfural is an important step for the production of bio-sourced polymers. We report on the activity of SiO₂-supported Au catalysts for this reaction. These catalysts reached 74% furan-2,5-dicarboxylic acid yield at 90 °C in 5 h when 5-hydroxymethyl furfural to Au molar ratio was 72. We also investigated the influence of the morphologies of the silica supports on the growth of Au nanoparticles under reaction conditions. Pronounced growth of Au nanoparticles occurred on Aerosil, SiO₂ with a disordered porosity and 50 nm average pore diameter: Au nanoparticles grew from 2.4 to 10.1 nm. However, by using ordered mesoporous supports, the growth of the gold nanoparticles was successfully minimized. Also the reaction conditions influenced the particle growth; for instance using HCO₃ ⁻ as a base led to more pronounced particle growth than using NaOH. Particle diffusion in solution, and subsequent coalescence and agglomeration was proposed to be the dominant particle growth mechanism. Our results show the importance of support morphology in mitigation of Au particle growth in liquid phase oxidation reactions.