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Nb 2 O 5 supported on SiO 2-Al 2 O 3 were prepared with a wide loading range (2, 5, 10, 15, 20 and 25 mass%) and analyzed by simultaneous thermogravimetric (TG) and differential thermal analysis (DTA). The materials presented a phase transition close to 1364°C. This phase transition was studied by XRD, FTIR and Raman spectroscopy. A mixture of orthorhombic (T) and monoclinic (H and M) crystalline phases was evidenced in the supported samples, which is coverage dependent, in contrast to the formation of only the monoclinic phase (H and M) when pure Nb 2 O 5 is heated under the same conditions. These results indicate the stabilization of Nb 2 O 5 on silica-alumina surface.