The effects of the carrier and pretreatment temperature on the oxidation state of Cc and Pt were evaluated in Pt/Al2O3, Pt/CeO2, and Pt/CeO2-Al2O3 catalyst samples with various CeO2 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 CeO2 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 CeO2. 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/Al2O3 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 Zn reduction temperature and increasing the CeO2 loading led to a more uniform distribution of Pt on Pt/CeO2-Al2O3. 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/CeO2 samples reduced at very high temperature (973 K).