Efficient and Selective Oxidation of 5-Hydroxymethylfurfural into 2, 5-Diformylfuran Catalyzed by Magnetic Vanadium-Based Catalysts with Air as Oxidant

Two-Dimensional NH4V3O8 Nanoflakes as Efficient Energy Conversion and Storage Materials for the Hydrogen Evolution Reaction and Supercapacitors

Herein, for the first time, we present two-dimensional (2D) NH₄V₃O₈ nanoflakes as an excellent material for both energy conversion of the hydrogen evolution reaction and storage of supercapacitors by a simple and fast two-step synthesis, which exhibit a completely sheet-like morphology, high crystallinity, good specific surface area, and also stability, as determined by thermogravimetric analysis. The 2D-NH₄V₃O₈ flakes show an acceptable hydrogen evolution performance in 0.5 M H₂SO₄ on a glassy carbon electrode (GCE) coated with 2D-NH₄V₃O₈, which results in a low overpotential of 314 mV at -10 mA cm^-2 with an excellent Tafel slope as low as 90 mV dec^-1. So far, with the main focus on energy storage, 2D-NH₄V₃O₈ nanoflakes were found to be ideal for supercapacitor electrodes. The NH₄V₃O₈ working electrode in 1 M Na₂SO₄ shows an excellent electrochemical capability of 274 F g^-1 at 0.5 A g^-1 for a maximum energy density of 38 W h kg^-1 at a power density as high as 250 W kg^-1. Moreover, the crystal structure of 2D-NH₄V₃O₈ is demonstrated by density functional theory (DFT) computational simulation using three functionals, GGA, GGA + U, and HSE06. The simple preparation, low cost, and abundance of the NH₄V₃O₈ material provide a promising candidate for not only energy conversion but also energy-storage applications.

Production of the 2,5-Furandicarboxylic Acid Bio-Monomer From 5-Hydroxymethylfurfural Over a Molybdenum-Vanadium Oxide Catalyst

2, 5-Furandicarboxylic acid (FDCA) is an important bio-monomer that can potentially replace terephthalic acid to synthesize degradable polyesters. Efficient selective oxidation of biomass-based 5-hydroxymethylfurfural (HMF) to FDCA has been a significant but challenging work in the past decades. In this study, a novel molybdenum-vanadium oxide (Mo-V-O) catalyst was prepared by a simple method and showed excellent catalytic activity for converting HMF to FDCA. A high FDCA selectivity of 94.5 and 98.2% conversion of HMF were achieved under the optimal conditions with tert-butyl hydroperoxide as the oxidant. FT-IR, SEM, XRD and TG were applied to investigate the properties of Mo-V-O catalyst. After fitting experimental data with the first-order kinetics equation, the evaluated apparent activation energies of HMF oxidation were obtained. The experimental design and study were carried out by response surface methodology (RSM) to test the effects of reaction conditions on the catalytic process.

A Carbon Catalyst Co-Doped with P and N for Efficient and Selective Oxidation of 5-Hydroxymethylfurfural into 2,5-Diformylfuran

A newly designed N and P co-doped carbon material has been developed to catalyze the conversion of 5-hydroxymethylfurfural (HMF) to 2,5-furandialdehyde (DFF) with unprecedented yield and selectivity and demonstrating a synergistic effect between the heteroatoms. The desired catalyst was first synthesized via a pyrolysis method using urea as the nitrogen and carbon source followed by calcination with phytic acid solution as the phosphorus source. The mass ratio of phytic acid to C₃ N₄ and calcination temperature were varied to investigate their effects on catalyst synthesis and microstructure as well as subsequent catalytic activity in simple reaction systems under oxygen. The effect of reaction conditions on the final HMF conversion and DFF selectivity were also investigated systematically. The P-C-N-5-800 catalyst obtained with the optimized annealing temperature of 800 °C and mass ratio of phytic acid/C₃ N₄ of 5 enabled a 99.5 % DFF yield at 120 °C for 9 h under 10 bar oxygen pressure, being the highest among any reported metal-free heterogeneous catalyst to date. The excellent performance of P-C-N-5-800 could be ascribed to the synergy between N and P heteroatoms as well as the high content of graphitic-N and the P-C species within the carbon structure. Reusability studies show that the P-C-N-5-800 catalyst was stable and reusable without deactivation. These results strongly suggest that P-C-N-5-800 is a promising catalyst for large-scale production of DFF in a green manner.