Unveiling the\nGold Facet Effect in Selective Oxidation\nof 5‑Hydroxymethylfurfural and Hydrogen Production

Direct oxidation of 5-hydroxymethylfurfural (HMF) to\n5-hydroxymethyl-2-furancarboxylic\nacid (HMFCA), crucial for medical supply production, is hindered by\noveroxidation. We synthesized gold nanomaterials with distinct single-crystal\nfacets, {111} in octahedra (OC), {100} in nanocubes (NCs), and {110}\nin rhombic dodecahedra (RD), to investigate the facet-dependent HMF\noxidation. The Au RD achieved the spontaneous oxidation of HMF to\nHMFCA with stoichiometric hydrogen production, maintaining 95% carbon\nbalance, 91% yield, and 98% selectivity. In contrast, Au OC and NCs\nwere inert. The superior performance is due to the absence of a C–H\nactivation energy barrier on the Au(110) facet. Furthermore, gas chromatography\nand isotope experiments supported that the intermediate is oxidized\nto produce H<sub>2</sub> via H<sup>–</sup> transfer, rather\nthan H<sub>2</sub>O via H<sup>+</sup> transfer. Oxygen was essential\nfor scavenging electrons, thereby closing the reaction loop. The Au\nRD exhibited remarkable stability, operating for 240 h without performance\ndegradation, indicating its potential for efficient HMFCA production.