Graphene Oxide-Supported Chromium-Containing Polyoxometalate as an Efficient Heterogeneous Catalyst for Nitroarene Reduction Under Mild Conditions.

Selective hydrogenation of nitroarenes is a valuable organic reaction that has attracted significant interest from researchers in recent years. Herein, a new nanocomposite (GO@POM-Cr) was prepared via an electrostatic assembly method. The surface of graphene oxide (GO) was modified with ammonium groups, and the chromium-containing polyoxomolybdate anion, Na4[PCr(H2O)Mo11O39] (POM-Cr), was subsequently immobilized on GO as the counter anion to the ammonium cation through a simple ion-exchange process. The Fourier- transform infrared (FT-IR) spectroscopy confirmed the successful immobilization of POM-Cr, with the P-Oa peak at ∼1118 cm-1 appearing as a single, unsplit band, directly evidencing chromium incorporation into the Keggin framework. The surface properties of GO@POM-Cr were further investigated using Raman spectroscopy, X-ray diffraction (XRD) analysis, and elemental analysis. Remarkably, the GO@POM-Cr nanocomposite demonstrated high catalytic efficiency for nitroarene reduction (99% conversion) under mild reaction conditions. The reactions were performed in ethanol as a green solvent in the presence of hydrazine hydrate as the reducing agent. Mechanistic investigations suggested that the reduction proceeds via a direct pathway involving nitroso and hydroxylamine intermediates, affording the corresponding anilines with excellent selectivity and catalyst stability over multiple reaction cycles.