Ultra‐Dense Supported Ruthenium Oxide Clusters via Directed Ion Exchange for Efficient Valorization of 5‐Hydroxymethylfurfural

Maximizing the loading of active centers without aggregation for a supported catalyst is a grand challenge but essential for achieving high gravimetric activity, especially toward multi‐step reactions. The oxidation of 5‐hydroxymethylfurfural (HMF), a key biomass‐derived platform molecule, into 2,5‐furandicarboxylic acid (FDCA), a promising alternative to polyester monomer, is such a multi‐step reaction that involves 6 electron transfers. Herein, we devised a strategy of creating ultra‐dense supported Ru oxide clusters on a Co hydroxyanion (CoHA) support. Pyrimidine ligands were first incorporated into the CoHA interlayers, and their subsequent evacuation created porous channels for the directed ion exchange with the built‐in anions in CoHA, which allows the dense and mono‐disperse functionalization of RuCl62‐ anions and their resulting Ru oxide clusters. These ultra‐dense Ru oxide clusters not only enable high HMF electrooxidation currents under neutral conditions but also create microscopic channels in‐between the clusters for the expedited re‐adsorption and oxidation of intermediates toward highly oxidized product, such as 5‐formyl‐2‐furoic acid (FFCA) and FDCA. A two‐stage HMF oxidation process, consisting of ambient conversion of HMF into FFCA and FFCA oxidation into FDCA under 60 oC, was eventually developed to first achieve a high FDCA yield of 92.1% with significantly reduced polymerization.