Adsorption of Wells–Dawson tungsten heteropolyacid on sol–gel alumina: Structural features and thermal stability

Abstract

The Wells–Dawson tungsten heteropolyacid, H 6P 2W 18O 62 supported on sol–gel and non-sol–gel alumina has been investigated by infrared spectroscopy (IR), thermal analysis (TGA/DSC), and X-ray diffraction (XRD). X-ray diffraction indicates that the heteropolyacid primary structure in bulk form holds up to 350 °C and by supporting it on the sol–gel alumina the thermal stability rose to 650 °C. UV–vis spectroscopy showed that the sol–gel alumina has a higher tendency to adsorb Wells–Dawson tungsten heteropolyacid than the non-sol–gel alumina. The heteropolyacid showed higher interaction with the sol–gel alumina than with the non-sol–gel. Esterification of propanoic acid with hexanol in the presence of alumina-supported heteropolyacid revealed that the acidic character of the heteropolyacid remains active to some extent.