Tungstophosphoric and tungstosilicic acids on carbon as acidic catalysts

Abstract

Tungstophosphoric (TPA) and tungstosilicic acid (TSA) catalysts supported on carbon were studied. They were prepared by equilibrium and incipient wetness impregnation techniques. Solutions of TPA and TSA in 50% v/v ethanol-water were used to impregnate carbon at 20 °C. The Fourier transform infrared and 31P nuclear magnetic resonance spectroscopies of TPA and TSA supported catalysts dried at 70 °C showed that the species present were the undegraded [PW12O40]3- and [SiW12O40]4- anion, respectively. X-ray diffraction of the impregnated solids showed the same diffraction patterns as the supports, possibly owing to a high dispersion of non-crystalline species. The scanning electron microscopy with energy dispersive X-ray analysis of the supported acids showed a uniform distribution of TPA and TSA in the carbon particles with low heteropolyacid content. In the samples with high content or prepared by incipient wetness method small grains of TPA and TSA were found. These grains showed to be nearly inactive for isopropanol dehydration. The specific conversion of the catalysts for this reaction increases regularly with the increase of the adsorbed heteropolyacid content.