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 WOx 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 β-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.