The methane decomposition over cobalt molybdenum catalysts (CoMo100-x; x = 0, 25, 50, and 75) carburized at temperatures of 700-973 K was performed using a microreactor at 973 K. The active species for the production of hydrogen during the methane decomposition was studied on the basis of XRD, TPC, TPR, and XPS. The Co50W50C-800 catalyst exhibits a higher conversion and hydrogen production rate compared to the Mo100C-, Co25Mo75C-, and Co75Mo25C-800 catalysts. The XRD measurement showed the presence of beta-Mo2C and cobalt molybdenum oxycarbides in the catalyst before and after 6-h reaction. Cobalt molybdenum carbutized at 800 K produced a surface oxycarbide based on the formation of H2O during the TPC and production of CH4 and H2O during the TPR. The active species of the cobalt molybdenum carbide catalyst for the CH4 decomposition was the cobalt molybdenum oxycarbide (Co1.0Mo5.6C0.3O0.7 by XPS analysis) on the surface that was formed during the carburization. The catalyst also exhibited a longer lifetime during methane decomposition. (c) 2006 Elsevier B.V. All rights reserved.