STRUCTURE AND PROPERTIES OF MESOPOROUS ALUMINO-PHOSPHORO-VANADATES

Mesoporous solids of the general formula Al100PxVy-600, where x, y = 0 , 5, 10, 20; and 600 corresponds to the final firing temperature (degr ees C), have been prepared and characterized by X-ray diffraction (XRD ), surface area and porosity measurements and SEM/EDX analysis. The in corporation of P and/or V into the original Al100P0V0 solid results in increase of the specific surface area (ssa) from 200 to 390 m(2) g(-1 ) and the pore volume from 0.43 to 1.19 cm(3) g(-1). The maximum effec t is resulted by P rather than V while a synergistic action of the two is apparent which is maximized at ca. 15% cumulative addition of the two elements. The highest ssa appears in the Al100P10V5 solid while th e narrowest pore size distribution (p.s.d.), as described by its full width at half maximum (FWHM), appears in Al100P0V5 solid for which FWH M = 2.1 nm. The p.s.d. of the solids is approximated by a mixed Gaussi an and Lorentzian component which varies in a controllable manner by t he P and/or V addition. The XRD results show that Al100P0V0 possesses the gamma-Al2O3 structure but the samples become gradually amorphous u pon addition of P and/or V up to Al100P10V10, while in the samples con taining 20% P and/or V the crystal phases of AlPO4 and V2O5 become app arent. SEM shows that the surface of the crystallites becomes more fra gmented by the addition of P and/or V up to 10% addition while 20% add ition results in a layered appearance of the crystallite external surf ace. EDX analysis shows that phosphorus is accumulated on the surface to an amount of around 30-40% for low concentration of P and/or V and 10-20% for higher concentrations. For vanadium the emerging picture is less clear, although some accumulation is detected, a fact due to non -homogeneous distribution of V on the external surface of the mesoporo us solids.