Pt-FeOx catalysts have been showing excellent performance on several catalytic reactions involving bifunctional mechanisms. Here, Chini's carbonyl oligomers were used as a precursor to obtain Pt nanoparticles (Pt-NP) anchored on maghemite, gamma-Fe2O3. The Pt-NP diameter were in the range of 1.5 nm and the catalysts were active in preferential oxidation of CO under H-2 rich atmosphere (PROX-CO reaction), without pretreatments. The catalytic behavior after the first heating ramp, under consecutive cycles, improved, almost triplicating the CO conversion at lower temperatures, around 353 K. A detailed characterization was performed and showed that the support, due the presence of Pt -NP, went through a phase transformation under reaction conditions, from gamma-Fe2O3 (Fe(III)) to Fe3O4 (Fe(II,III)), indicating that the presence of Fe(II) species are stabilized under PROX-CO and contribute to overall performance of the catalyst. As comparison, the bare Fe2O3 support as well as a catalyst prepared by depositing the same Chini's carbonyl oligomers on SiO2 support showed negligible activity at these low temperatures.