Development of Highly Efficient and Durable Three-Dimensional Octahedron NiCo₂O₄ Spinel Nanoparticles toward the Selective Oxidation of Styrene

Herewith, we have prepared poly(vinylpyrrolidone)-assisted water-based synthesis of the nanocrystalline spinel NiCo₂O₄ nanocatalyst by a one-pot hydrothermal route. The formation of the synthesized spinel NiCo₂O₄ nanoparticle has been confirmed by X-ray diffraction, scanning electron microscopy (SEM), energy-dispersive spectrometry, transmission electron microscopy, X-ray photoelectron spectroscopy, and extended X-ray absorption fine structure (EXAFS) analyses. The SEM results confirmed the formation of the three-dimensional octahedron structure with an average size of 20-30 nm. The EXAFS results further confirmed that the spinel NiCo₂O₄ nanoparticles exist in a pure phase. The catalytic activity of the synthesized spinel NiCo₂O₄ octahedron nanoparticles was evaluated for the conversion of styrene to styrene oxide by the oxidation reaction. It was found that the conversion of styrene was 78% with 67% of styrene oxide selectivity in the presence of hydrogen peroxide as an oxidant. The catalyst has also proven to be truly heterogeneous as it does not lose its phase and catalytic activity even after five consecutive cycles.