The role of Al2O3-ZrO2 and Al2O3-TiO2 sol-gel prepared supports in the activity of platinum for the NO reduction by CO under oxidizing conditions has been studied. Al-27 MAS-NMR spectra have shown the fori-nation of pentacoordinate Al-V in alumina-zirconia support. ZrO2 or TiO2 crystalline phases cannot be identified by XRD diffraction, suggesting the fort-nation of nanosized structures supported on alumina. When the reaction was carried out in presence of oxygen, large amounts of NO2 were observed on Pt/Al2O3-ZrO2 catalyst, while the formation of N2O is more pronounced on Pt/Al2O3-TiO2 catalyst. The effect of water during NO reduction is discussed.