Combustion synthesized WO3-ZrO2 nanocomposites as catalyst for the solvent-free synthesis of coumarins

Nanosized ZrO2 and WO3-ZrO2 particles were prepared by solution combustion synthesis using urea as fuel. These materials were characterized by X-ray diffraction, infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. XRD study indicates the presence of a mixture of tetragonal and monoclinic phases in the synthesized ZrO2 particles. The tetragonal phase content is enhanced in the WO3-ZrO2 nanocomposite oxide. IR study indicates the presence of well-dispersed WO, species grafted on to the surface of the tetragonal ZrO2. TEM analysis of the sample shows the presence of uniform particles with size in the range of 10-25 nm. The catalytic activity of the WO3-ZrO2 nanocomposite catalyst was evaluated for the synthesis of coumarins by Pechmann condensation of phenols with beta-ketoesters. It was observed that the composite oxide catalyst was highly active for the reaction. Grafting Of WO3 species on the surface of ZrO2 has a beneficial effect on the catalytic activity of the WO3-ZrO2 nanocomposite catalyst, (C) 2007 Elsevier B.V. All rights reserved.