Base-free selective oxidation of 5-hydroxymethylfurfural over Pt nanoparticles on surface Nb-enriched Co-Nb oxide

Abstract

Constructing functionalized surface for heterogeneous catalysts is vital toward effective conversion of biomass. We show that Pt nanoparticles (ca. 2.1 nm) loaded on Co-Nb bimetallic oxide can efficiently catalyze the aqueous-phase base-free aerobic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid. We ingeniously construct different surface element-distributions over three Co-Nb oxides (Nb@Co, Co&Nb and Co@Nb) with the same bulk composition by changing precipitation sequence of Co and Nb precursors. This strategy allows rationally modulating synergistic interaction and surface acidity of Co-Nb oxides and in return boosts the pristine oxidation activity of loaded-Pt nanoparticles. We use kinetic investigations, comprehensive characterizations, and particularly in situ DRIFT-IR adsorption technique (CO, pyridine and furfural as probe molecules) to unravel the origin of synergistic catalysis. We disclose that Nb5+-enriched surface can formulate sufficient Lewis acidic sites and stabilize electron-rich Pt0 active centers, accelerating the tandem oxidation of HMF and the intermediates. The Co@Nb-Pt catalyst shows the highest productivity of FDCA (25 mmolFDCA molPt–1 h–1) among all Pt catalysts in the literature and achieves > 99% yield of FDCA at 110 °C and 10 bar of O2.