MOLYBDOPHOSPHORIC ACID ADSORPTION ON TITANIA FROM ETHANOL-WATER SOLUTIONS

The equilibrium adsorption at 20 degrees C of molybdophosphoric acid s olutions, using ethanol-water as solvent, on titania was studied. The molybdenum adsorption isotherm showed a sigmoidal shape; low values of molybdenum adsorbed were observed for final equilibrium concentration s lower than 50 mg Mo/ml, and for higher concentrations, the adsorbed molybdenum amount almost reached a plateau. From this isotherm it coul d be concluded that the solute-support interaction was not strong. UV- visible and NMR spectra of the solutions before and after the adsorpti on on titania showed that the species PMo12O403- was present. This spe cies also was observed by DRS in the wet samples and by NMR, FT-IR, an d DRS, in the solid samples dried at room temperature and calcined at 255, 310, 365, and 425 degrees C, showing that the thermal stability o f molybdophosphoric acid adsorbed on titania is similar to that of the bulk acid. The impregnating solutions and the impregnated solid chang ed with the time to a bluish color as a consequence of the formation o f heteropoly blues which presented Mo6+ partially reduced to Mo5+. The XRD patterns indicated that the species adsorbed onto the support sur face are highly dispersed like a noncrystalline form. (C) 1998 Academi c Press.