XPS STUDIES OF OXIDIC MODEL CATALYSTS - INTERNAL STANDARDS AND OXIDATION NUMBERS

X-ray photoelectron spectroscopy was used to investigate the behaviour of model systems representing DeNOx catalysts and their individual components (V6Mo4O25, MoO3, V2O5, TiO2). Particular attention was directed to the behaviour of arsenic. The spectrometer energy scale was calibrated by gold vapour deposition samples. The Au4f7/2 signal can also be used to determine the effects of slight signal shifts which influence the full widths at half maximum (FWHMs) of the investigated signal. It can be established that As2O3 exhibits typical oxidation behaviour on TiO2 (anatase) surfaces. The As5+ formed is reduced at different rates as a function of the radiation used (Mg Kalpha1.2, Al Kalpha1,2). Neither oxidation nor reduction are observed in the absence of TiO2 (anatase). Although these redox processes are coupled on TiO2 (anatase), no chemical change from pure TiO2 (anatase) can be established for titanium. Molybdenum in V6Mo4O25 is Present in oxidation number +6 and vanadium in oxidation numbers +4 and +5. Formation of a composite oxide which contains arsenic can largely be ruled out on the basis of the FWHMs of the As3d signals.