Abstract
The surface composition of (VO)2P2O7 catalysts was investigated by x-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS). The P/V ratio on the surface of (VO)2P2O7 catalysts from aqueously prepared precursors lies between 1.3 and 1.4, based on XPS calibrations with different VPO glasses as standard materials. With ISS we obtained a higher P/V ratio of (VO)2P2O7 catalysts in the outermost layer of ∽2–3. The addition of caesium (Cs+) caused a further increase in the P/V ratio of the surface of (VO)2P2O7 with increasing Cs+ concentration. Ion scattering spectroscopy indicated that Cs+ was mainly confined to the uppermost layers, and at high doping concentrations a total surface coverage with Cs+ was achieved. The influence of water vapour on the surface composition of the catalysts was also investigated. A migration and a loss of phosphorus was found after and during water vapour treatment using XPS, ISS and thermogravimetric measurements. The surface of (VO)2P2O7 is assumed to be a dynamic system influenced by the partial pressure of water vapour in the gas phase. The rate of bulk oxidation of (VO)2P2O7 was dependent on the water vapour content in the gas phase. © 1998 John Wiley & Sons, Ltd.
Published Version
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