alpha-Bi2MO3O12 and gamma-Bi2MoO6 catalysts were prepared by a co-precipitation method for use in the oxidative dehydrogenation Of C-4 raffinate-3 to 1,3-butadiene. A series of mixed catalysts composed of alpha-Bi2Mo3O12 and gamma-Bi2MoO6 were also prepared by a mechanical mixing method to investigate any synergistic effects of alpha-Bi2Mo3O12 and gamma-Bi2MoO6 catalysts in the oxidative dehydrogenation Of C4 raffinate-3. The alpha-Bi2Mo3O12 and,gamma-Bi2MoO6 catalysts were formed successfully, as confirmed by XRD, FT-IR, Raman spectroscopy, and ICP-AES analyses. The gamma-Bi2MoO6 catalyst exhibited a better catalytic performance than the (alpha-Bi2Mo3O12 Catalyst due to its facile oxygen mobility. The conversion of n-butene and the yield for 1,3-butadine over the mixed catalysts showed volcano-shaped curves with respect to gamma-Bi2MoO6 content due to the synergistic effect of the alpha-Bi2Mo3O12 and gamma-Bi2MoO6 catalysts. Among the mixed catalysts, the catalyst composed of 10 wt.% (alpha-Bi2Mo3O12 and 90 wt.% gamma-Bi2MoO6 showed the best catalytic performance. The gamma-Bi2MoO6 catalyst retained a higher oxygen mobility than the alpha-Bi2Mo3O12 catalyst, while the (alpha-Bi2Mo3O12 catalyst retained much more adsorption sites for n-butene than the gamma-Bi2MoO6 Catalyst. The synergistic effect of the alpha-Bi2Mo3O12 and gamma-Bi2MoO6 catalysts in the oxidative dehydrogenation Of C4 raffinate-3 was due to a combination of the facile oxygen mobility of gamma-Bi2MoO6 and the abundant adsorption sites of alpha-Bi2Mo3O12 for n-butene. (C) 2007 Elsevier B.V. All rights reserved.