Continuous Flow Synthesis of Bimetallic AuPd Catalysts for the Selective Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid

The production of 2,5-furandicarboxylic acid (FDCA) from the selective oxidation of 5-hydroxymethylfurfural (HMF) is a critical step in the production of biopolymers from biomass-derived materials. In this study, we report the catalytic performance of monometallic Au and Pd, and bimetallic AuPd nanoparticles with different Au : Pd molar ratios synthesised under continuous flow conditions using a millifluidic set-up and subsequently deposited onto titanium dioxide as the chosen support. This synthetic technique provided a better control over mean particle size and metal alloy composition, that resulted in higher FDCA yield when the catalysts were compared to similar batch-synthesised materials. A 99% FDCA yield was obtained with the millifluidic-prepared AuPd/TiO2 catalyst (Au : Pd molar composition of 75 : 25) after being calcined and reduced at 200 degrees C. The heat treatment caused a partial removal of the protective ligand (polyvinyl alcohol) encapsulating the nanoparticles and so induced stronger metal-support interactions. The catalyst reusability was also tested, and showed limited particle sintering after five reaction cycles.