Three types of bismuth molybdate catalysts, alpha-Bi2Mo3O12, beta-Bi2MoO9, and gamma-Bi2MoO6, were prepared by a co-precipitation method for use in the oxidative dehydrogenation of n-butene. Unlike alpha-Bi-2-Mo3O12 and gamma-Bi2MoO6, it was found that beta-Bi2Mo2O9 was thermally unstable and decomposed into alpha-Bi2Mo3O12 and gamma-Bi2MoO6 at the reaction temperature of 420 degrees C. Therefore, beta-Bi2Mo2O9 could not serve as an efficient catalyst in the reaction. In the oxidative dehydrogenation of n-butene into 1,3-butadiene, gamma-Bi2MoO6 showed a better catalytic performance than alpha-Bi2Mo3O12. The different catalytic performance between alpha-Bi2Mo3O12 and gamma-BiN006 catalysts was elucidated by temperature-programmed reoxidation (TPRO) experiments. It was revealed that the enhanced catalytic performance of gamma-Bi2MoO6 was attributed to the facile oxygen mobility of gamma-Bi2MoO6. (c) 2006 Elsevier B.V. All rights reserved.