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 co mponents (V6Mo4O25, MoO3, V2O5, TiO2). Particular attention was direct ed to the behaviour of arsenic. The spectrometer energy scale was cali brated by gold vapour deposition samples. The Au4f7/2 signal can also be used to determine the effects of slight signal shifts which influen ce 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 r ates 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 t itanium. Molybdenum in V6Mo4O25 is Present in oxidation number +6 and vanadium in oxidation numbers +4 and +5. Formation of a composite oxid e which contains arsenic can largely be ruled out on the basis of the FWHMs of the As3d signals.