Molybdophosphoric acid adsorption on titania from ethanol-water solutions

A. CONCELLÓN; P. VÁZQUEZ; M. BLANCO; C. CÁCERES

JOURNAL OF COLLOID AND INTERFACE SCIENCE

Academic Press

Lugar: Florida; Año: 1998 vol. 204 p. 256 - 267

0021-9797

The equilibrium adsorption at 207C of molybdophosphoric acid solvent (6). Bartoli et al. (4) used supports such as SiC tosolutions, using ethanol?water as solvent, on titania was studied. take advantage of its high thermal conductivity and zirco-The molybdenum adsorption isotherm showed a sigmoidal shape; nium oxide and cerium oxide to prevent HPA over-reduclowvalues of molybdenum adsorbed were observed for final equition.The use of these supports improves the stability of librium concentrations lower than 50 mg Mo/ml, and for higherthe H4PMo11VO40 active phase in the oxydehydrogenation concentrations, the adsorbed molybdenum amount almost reachedreaction of isobutyric acid. In the vapor phase synthesis of a plateau. From this isotherm it could be concluded that the solmethyltert-butyl ether, the activity of silica-supported MPA ute?support interaction was not strong. UV?visible and NMRis higher than that of MPA supported on silica?alumina, spectra of the solutions before and after the adsorption on titaniashowed that the species PMo12O3?40 was present. This species also alumina, and magnesium oxide (7). This is related to thewas observed by DRS in the wet samples and by NMR, FT-IR, acidic or basic characteristics of the supports. In particular,and DRS, in the solid samples dried at room temperature and silica has a low-level interaction with the HPA, but reportscalcined at 255, 310, 365, and 4257C, showing that the thermal indicate that MPA becomes stable up to 6007C when supstabilityof molybdophosphoric acid adsorbed on titania is similar ported on SiO2 (8). Alkaline salts of HPA are also usedto that of the bulk acid. The impregnating solutions and the im- as modifiers of the acidic and thermal properties of theirpregnated solid changed with the time to a bluish color as a consecorrespondingheteropolyacids (9, 10) . quence of the formation of heteropoly blues which presented Mo6/On the other hand, with the objective to obtain new gener- partially reduced to Mo5/. The XRD patterns indicated that theations of hydrodesulfurization (HDS) and hydrodenitrogen- species adsorbed onto the support surface are highly dispersed likeation (HDN) catalysts, our research group has begun studies a noncrystalline form.