The Pt/TiO2, Pt/ZrO2, and Pt/Al2O3 catalysts submitted to low-temperature reduction (LTR, 200 degrees C) and high-temperature reduction (HTR, 500 degrees C) and exposed to hydrogen and carbon monoxide at room temperature were studied by infrared spectroscopy. There is a strong loss of transmission in the entire infrared spectra on Pt/TiO2 after its exposure to hydrogen, which is related to the reducibility of the support. A typical SMSI behavior (strong metal-support interaction), such as the decrease in carbon monoxide adsorption capacity, was detected on Pt/TiO2 and Pt/ZrO2 after exposure to hydrogen, even for the catalysts submitted to LTR treatment. Also a carbonyl band shift to lower wavenumber was observed on LTR-treated Pt/TiO2, Pt/ZrO2, and Pt/Al2O3 after exposure to hydrogen. We interpreted this SMSI behavior as an electronic rather than morphological effect, which was induced by the presence of hydrogen spillover.