H3PW12O40 supported on functionalized polyoxometalate organic–inorganic hybrid nanoparticles as efficient catalysts for three-component Mannich-type reactions in water

Abstract

Two new types of catalyst were synthesized by the immobilization of H₃PW₁₂O₄₀ (HPW₁₂) on the surface of organic–inorganic polyoxometalate nanoparticles of H₆Cu₂[PPDA]₆[SiW₉Cu₃O₃₇]·12H₂O (HybPOM) (PPDA = p-phenylenediamine) and Go/Fe₃O₄/HybPOM nanoparticles. These catalysts were characterized by thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and alternating gradient force magnetometry (AGFM). The IR spectroscopy as well as XRPD reveal that HPW₁₂ were immobilized on the support. The potentiometric titration with n-butylamine reveal that the catalysts can be classified as strong acids. The results show that the particles are mostly spherical in shape and have an average size in the range of 20–50 nm. The catalytic activities of the catalysts were probed through one-pot three-component Mannich-type reactions of aldehydes, amines and ketones in water at room temperature. The catalysts were re-used at least five times without any loss of their high catalytic activity.