G. Hopfengartner et al., XPS STUDIES OF OXIDIC MODEL CATALYSTS - INTERNAL STANDARDS AND OXIDATION NUMBERS, Journal of electron spectroscopy and related phenomena, 63(2), 1993, pp. 91-116
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.