Synergy of Ag and Pd in bimetallic catalysts for the selective oxidation of 5-(hydroxymethyl)furfural

Abstract

The synthesis of renewable bio-based monomers, like 2,5-furandicarboxylic acid (FDCA), is of high interest in the shift toward a circular economy. Bimetallic catalysts offer the variation of different properties, enabling the design of tailor-made catalysts. The combination of silver and palladium, both highly active for specific liquid-phase oxidation reactions, shows promise for superior performance in the selective oxidation of 5-(hydroxymethyl)furfural (HMF) to FDCA. While Ag/CBA and Ag₃Pd₁/CBA, supported on carbon black acetylene (CBA), were active only for the oxidation of the aldehyde group of HMF, increasing the Pd-fraction allowed for the oxidation of the alcohol group as well. In-depth characterization by X-ray diffraction, electron microscopy, and X-ray absorption spectroscopy revealed a synergistic effect between Ag and Pd in Pd-rich alloys, leading to an enhanced performance. Pd is particularly effective in activating oxygen, the oxidizing agent, while Ag ensures a high selectivity in the dehydrogenation reaction. Moreover, removing residual surfactants from the synthesized catalysts by increasing the calcination temperature further enhanced the activity. This study demonstrates the potential of tuning the catalytic properties of noble metal-based catalysts for optimizing liquid-phase oxidation reactions.