Niobium oxide prepared through a novel supercritical-CO₂-assisted method as a highly active heterogeneous catalyst for the synthesis of azoxybenzene from aniline

Abstract

High-surface area Nb2O5 nanoparticles synthesised by a novel supercritical-CO2-assisted method displayed extremely high activity as heterogeneous catalyst in the oxidative coupling of aniline to azoxybenzene using the green oxidant H2O2.

Nb2O5‐Based Photocatalysts

“…For instance, the supercritical‐CO 2 ‐assisted approach was introduced into catalyst preparation. [ 75 ] The hydrolyzed mixture of NbCl 5 dissolved in ethanol solution and aged in the supercritical CO 2 under 80 °C for 3 h. After the calcination under 200 °C, amorphous Nb 2 O 5 particles with a high surface area (≈340 m 2 g −1 ) were obtained. [ 75 ] In addition, the ball‐milling process was reported for the low‐temperature synthesis.…”

“…For instance, the Nb 2 O 5 particles can be further calcinated to prepare the bulk counterpart. [ 75 ] Besides, the resorcinol, formaldehyde, and ammonium niobate oxalate were utilized in the hydrothermal process for the synthesis of Nb 2 O 5 @polymer materials, which were further calcinated to remove the polymer and obtain the hollow Nb 2 O 5 microspheres. [ 80 ]…”

Catalytic selective oxidation of aromatic amines to azoxy derivatives with an ultralow loading of peroxoniobate salts

“…37) have also been employed for the selective oxidation of aromatic amines, and the TOF values obtained were about 0.3–74 h −1 . In particular, a high-surface area Nb 2 O 5 –scCO 2 catalyst prepared via a supercritical-CO 2 -assisted method exhibited good catalytic performance for the synthesis of azoxy compounds from aromatic amines with a TOF of 305 h −1 , 38 which affords the highest activity among state-of-the-art heterogeneous catalysts. Although great development has been achieved, the highly efficient synthesis of azoxy derivatives from the oxidation of aromatic amines is still subject to low or moderate TOF values, relatively high reaction temperatures, and the use of a high loading of catalysts.…”

Hydroperoxo on the Niobium Oxyhydroxide Surface as the Active Species in the Catalyzed Oxidation of Organic Sulfide by Hydrogen Peroxide

“…Niobium compounds have been investigated as catalysts for a set of important oxidation reactions. − An interesting example of this class of reactions is the oxidative desulfurization of liquid fuels for which different oxidants such as hydrogen peroxide, peracids, and so forth have been investigated. − de Oliveira and co-workers have reported the use of niobium oxyhydroxide (NbO 2 OH) as a catalyst for the oxidation of dibenzothiophene by hydrogen peroxide (Scheme ). In their report, the sulfur compound is transformed to the corresponding sulfoxide and sulfone, which are more polar and can be extracted from an apolar medium via partition equilibrium using acetonitrile as the solvent.…”