Equilibrium adsorption of keggin heteropolyacids on different supports?

P. VILLABRILLE, L. PIZZIO, P. VÁZQUEZ, C. CÁCERES, M. BLANCO

Current Topics in Colloid and Interface Science

Research Trends

Lugar: Trivandum; Año: 2003 vol. 6 p. 43 - 60

0972-4494

The equilibrium adsorption of tungstophosphoric, molybdophosphoric, tungstosilicic or molybdosilicic heteropolyacids on activated zirconia, silica, titania, alumina andior carbon from solutions was studied al 20 °C. It was fornid that the adsorption characteristics depended on dic heteropolyacid and dic support. The equilibrium adsorption isotherms fitted dic classical Langmuir modo! for tungstophosphoric acid on zirconia asid alumina, for molybdophosphoric acid on alumina asid for ah dic studied heteropolyacids on carbon. The equilibrium adsorption constant and dic nwnber of adsorption sites were estimated. The grcatest solutesupport interaction was displayed by tungstophosphoric acid Qn alumina and caibon, in accordance with its higjiest acidity. The malo species in dic solutions was the undegraded anion of the corresponding acid, characterized by Uy-visible asid nuclear magnetic resonance spectroscopies. The dried solids presented a high dispersion of tSe adsorbed species and/or amorpbous heteropolyacid by X-ray diffi-action. ha addition, the [P(Si)W(Mo)j2O43 anion was dic main specics in solid samples of dic heteropohyacids adsorbed Qn Zr02, Si02, Ti01 and C, as shown by 31P MAS nuclear magnetic resonance, diffi,se reflectance asid Fourier fransformer infrared spectioscopics. llis spccies kept stable dtuing thermal treatmcnt up to 250- 365 °C, depending on dic system. For tungstophosphoric acid adsorbed on A1203, dic present specics werc tSe fP2W210,j]? asid [P2W12OÓ2]&anions. Keywords: ?equihibrirnn adsorption, Keggin hetcropolyacids, carbon, titania, zirconia, nuca, alinnina, supported catalysts