Conversion of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid over Au-based catalysts: Optimization of active phase and metal-support interaction

In the present work, a series of Au- and Au-Cu-containing catalysts based on different carriers such as TiO2 and CeO2 were studied with a view to increasing the activity and selectivity in 5-hydroxymethylfurfural oxidation by optimizing the interaction both between the metals and with the support. The results obtained demonstrated the high activity in HMF oxidation of gold supported on ceria and titania. Nevertheless, although the particle size of gold on both supports was comparable, Au/CeO2 showed significantly higher activity than Au/TiO2, thus corroborating the theory that not only the gold particle size, but the support also, plays a key role in HMF oxidation in the aqueous phase. Indeed, pre-made uniform nanoparticles, used for catalyst preparation, were surface-bound by poly(N-vinyl-2-pyrrolidone) - the stabilizer used during nanoparticle synthesis - whose presence proved to prevent the interaction of active phases with CeO2, while worsening the catalytic activity of both monometallic and bimetallic systems. The pre-treatment of the prepared catalysts was necessary to activate the materials, by maximizing the contact between the metal and the support and thus suggesting an important role of the ceria defects on 5-hydroxymethylfurfural oxidation to 2,5-furandicarboxylic acid.