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 (degrees C), have been prepared and characterized by X-ray diffraction (XRD), surface area and porosity measurements and SEM/EDX analysis. The incorporation 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 effect 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 the narrowest pore size distribution (p.s.d.), as described by its full width at half maximum (FWHM), appears in Al100P0V5 solid for which FWHM = 2.1 nm. The p.s.d. of the solids is approximated by a mixed Gaussian and Lorentzian component which varies in a controllable manner by the P and/or V addition. The XRD results show that Al100P0V0 possesses the gamma-Al2O3 structure but the samples become gradually amorphous upon addition of P and/or V up to Al100P10V10, while in the samples containing 20% P and/or V the crystal phases of AlPO4 and V2O5 become apparent. SEM shows that the surface of the crystallites becomes more fragmented by the addition of P and/or V up to 10% addition while 20% addition results in a layered appearance of the crystallite external surface. 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 mesoporous solids.