Diluted oxygen realizes high productivity of 2,5-Furandicarboxylic acid under ambient temperature

The oxidation of biomass-derived 5-hydroxymethyl furfural (HMF) into 2,5-Furandicarboxylic acid (FDCA) is a favorable reaction since FDCA is an ideal alternative to petroleum-based monomer terephthalic acid in bio-based polyester industry. However, producing FDCA with high yield under mild conditions is still challenging, especially at energy-saving near-ambient temperatures. Here, we present a Pd nanoparticles catalyst supported on Vulcan XC-72 carbon (Pd/VC) that can completely convert HMF and achieve an encouraging FDCA yield (92.4%) at 30 ℃. The most important observations include yield declines at pure oxygen bubbling, and the transformation of intermediates becomes stagnant; instead, switching to the diluted oxygen is effectively driving the tandem oxidation as the over-oxidation, and thus, rapid deactivation of the Pd surface could be alleviated. The negative effect of high oxygen concentration also occurs in the dehydrogenation and oxygenation of an extended substrate. Since the decisive influence of oxygen content has often been neglected in past investigations of oxidative transformation over Pd-based catalysts, the current study may offer a critical reminder for other liquid-phase oxidation reactions.