A beta-Bi2Mo2O9 catalyst was prepared by a co-precipitation method and applied to the oxidative dehydrogenation of n-butene to 1,3-butadine. It was found that the beta-Bi2Mo2O9 catalyst retained lower oxygen mobility than gamma-Bi2MoO6. It was also revealed that the beta-Bi2MoO9 was thermally unstable and decomposed into alpha-Bi2Mo3O12 and gamma-Bi2MoO6 at a reaction temperature of 420 degrees C. However, the beta-Bi2Mo2O9 showed a higher catalytic performance than the alpha-Bi2Mo3O12 and gamma-Bi2MoO6 catalysts in the oxidative dehydrogenation of n-butene, in spite of its thermal instability and low oxygen mobility. Moreover, the beta-Bi2Mo2O9 showed a stable catalytic performance with time on stream without catalyst deactivation. The high and stable catalytic performance of beta-Bi2Mo2O9 can be attributed to the synergy effect of alpha-Bi2Mo3O12 and gamma-Bi2MoO6 formed via the decomposition of beta-Bi2Mo2O9 during the catalytic reaction, to the high intrinsic catalytic activity of beta-Bi2Mo2O9, and to the well-crystallized parts of beta-Bi2Mo2O9. (c) 2006 Elsevier B.V. All rights reserved.