The effects of the carrier and pretreatment temperature on the oxidation state of Ce and Pt were evaluated in Pt/Al 2 O 3 , Pt/CeO 2 , and Pt/CeO 2 -Al 2 O 3 catalyst samples with various CeO 2 loadings by applying the following spectroscopic techniques to the samples: X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy of CO adsorption. XRD showed that ceria agglomerates at high CeO 2 loadings (>3 wt %) and at a high temperature of calcination. XPS spectra showed that Ce(III) is formed more easily in the presence of Pt caused by the electron transfer between Pt and CeO 2 . A variation in the intensity and a shift in the IR bands from CO adsorbed on reduced Pt were observed, as a function of the temperature of reduction and type of the support. A heterogeneous distribution of linearly adsorbed CO on Pt at terraces and defect sites was proposed for Pt/Al 2 O 3 reduced at the lower temperature (623 K), while at the higher temperature of reduction (773 K) a complete reduction of the Pt was observed. The higher reduction temperature and increasing the CeO 2 loading led to a more uniform distribution of Pt on Pt/CeO 2 -Al 2 O 3 , related to the presence of highly unsaturated Pt caused by the strong interaction between Pt and Ce-modified alumina. The electronic effect dominates in Pt/CeO 2 samples reduced at very high temperature (973 K).

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