Controlled immobilization of Keggin-type heteropoly acids on the surface of silica encapsulated γ-Fe2O3 nanoparticles and investigation of catalytic activity in the oxidative esterification of arylaldehydes with methanol

Preparation, leaching and solid acidity measurements of H3PW12O40, H3PMo12O40 and H(4)SiWi(2)O(40) supported on silica-encapsulated gamma-Fe2O3 nanoparticles were performed. The impregnating solvent and calcination temperature were optimized using various techniques. Catalytic activity of samples was examined by carrying out oxidative esterification of benzaldehyde with methanol under the same conditions. The acidity of the catalysts that was determined by NH3-temperature-programmed desorption technique and chemisorption of pyridine. The best catalyst was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and laser particle size analyzer. Finally, a mild, simple and clean procedure was presented for the one-pot oxidative esterification of arylaldehydes with methanol using magnetically recoverable nanocatalyst and hydrogen peroxide as a green oxidant. (C) 2013 Elsevier B.V. All rights reserved.