Surface Hydroxyl Species Enabled Nb2O5 for the Photocatalytic Oxidation of 5-Hydroxymethylfurfural

Abstract

Niobium oxide (Nb₂O₅), an alternative to TiO₂, has been recognized as a promising photocatalyst for the oxidation of 5-hydroxymethylfurfural (HMF) to 2, 5-diformylfuran (DFF). A series of Nb₂O₅ photocatalysts are prepared using a simple thermal approach, and their photocatalytic performance for HMF oxidation is tested. Nb₂O₅ treated at relatively lower temperatures (300–400 °C) possesses a higher surface area with abundant surface hydroxyl groups and adsorbed water species, which play a key role in the HMF oxidation, affording high DFF selectivity. In contrast, Nb₂O₅ treated at higher temperatures (500–600 °C) exhibits an adverse effect on the photocatalytic performance due to the substantial loss of surface hydroxyl groups and adsorbed water species. Various structural characterizations such as X-ray diffractometer, N₂-sorption analyses, and thermogravimetric analyser Nb₂O₅ treated at different temperatures. At the same time, CO₂-temperature programmed desorption (TPD), O₂–TPD, and diffuse reflectance infrared Fourier transform spectra disclose the nature and distribution of active sites, especially strong basic sites, which is essential for comprehending the interaction between HMF and the surface of the catalyst.