Tungstophosphoric and tungstosilicic acids on carbon as acidic catalysts

Tungstophosphoric (TPA) and tungstosilicic acid (TSA) catalysts supported o n carbon were studied. They were prepared by equilibrium and incipient wetn ess impregnation techniques. Solutions of TPA and TSA in 50% v/v ethanol-wa ter were used to impregnate carbon at 20 degreesC. The Fourier transform in frared and P-31 nuclear magnetic resonance spectroscopies of TPA and TSA su pported catalysts dried at 701 degreesC showed that the species present wer e the undegraded [PW12O40](3-) and [SiW12O40](4-) anion, respectively. X-ra y diffraction of the impregnated solids showed the same diffraction pattern s as the supports, possibly owing to a high dispersion of non-crystalline s pecies. The scanning electron microscopy with energy dispersive X-ray analy sis of the supported acids showed a uniform distribution of TPA and TSA in the carbon particles with low heteropolyacid content. In the samples with h igh content or prepared by incipient wetness method small grains of TPA and TSA were found, These grains showed to he nearly inactive for isopropanol dehydration. The specific conversion of the catalysts for this reaction inc reases regularly with the increase of the adsorbed heteropolyacid content. (C) 2001 Elsevier Science B.V. All rights reserved.