CHARACTERIZATION OF CHROMIUM ION-DOPED TITANIA BY FTIR AND XPS

Chromium ion-doped polycrystalline titania catalysts, mainly used in p hotoreactions, were studied by Fourier transform infrared (FTIR) spect roscopy and by X-ray photoelectron spectroscopy (XPS). Two series of c atalysts prepared by two different methods, i.e., coprecipitation and impregnation, were analysed. The FTIR spectra recorded upon adsorption of ammonia and after outgassing at increasing temperatures indicated that Cr(x)O(y)/TiO2 samples, whichever preparation method was used, ha ve two types of surface acid sites, Lewis and Bronsted sites. The Bron sted sites are associated with the presence of chromium, since they we re not detected in pure titania. According to the X-ray photoelectron study, Cr(III) and Cr(VI) species are present in both series of cataly sts, with the higher oxidation state being quite unstable under X-rays . As shown by quantitative XPS analysis, only the catalysts prepared b y coprecipiatation and containing up to 2% Cr can be described by the Kerkhof-Moulijn monolayer model. (C) 1994 Academic Press, Inc.