Study of the surface composition of vanadyl pyrophosphate catalysts by XPSand ISS - Influence of Cs+ and water vapor on the surface P/V ratio of (VO)(2)P2O7 catalysts

The investigation of the surface composition of vanadyl pyrophosphate catal ysts and the influence of Ca ions and of water vapor on the surface PIV rat io were described and discussed. The characterization was carried out by XP S (X-ray Photoelectron Spectroscopy) and ISS (Ion Scattering Spectroscopy). It was concluded that the P/V ratio on the surface of equilibrated and non equilibrated (VO)(2)P2O7 catalysts prepared in aqueous solution was betwee n 1.3 and 1.4 (XPS) based on calibrations with different VPO glasses as sta ndard materials having uniform composition of surface and bulk. In the oute rmost layer of the catalyst the PIV ratio was much higher and laid between 2 and 3 as verified by ISS. Different in fluences, i.e. addition of alkali metall ions (Cs+) or a treatment with water vapor of the catalyst, caused a further increase in the concentration of phosphorus on the surface.