The mechanism of ethanol decomposition on alpha-Mo2C(1 0 0) surface has been systematically studied by using density functional theory (DFT) calculations. The calculation results indicate that ethanol decomposition on Mo2C catalyst starts with the scission of the O-H bond and C-H-beta bond scission, and the formation mechanism of the main products like acetaldehyde, hydrogen, and ethylene as well as the by products like methane, ethane and CO was investigated in detail. The acetaldehyde formation through the processes of CH3CH2OH -> CH3CH2O -> CH3CHO with the highest energy barrier of 0.28 eV, ethene formation via the processes of CH3CH2OH -> CH2CH2OH -> CH2CH2 + OH with the largest energy barrier of 0.45 eV, and the hydrogen formation through the reaction of 2H -> H-2 with the energy barrier of 0.76 eV. For the by-products, methane formation through the mechanism of CH3CHO -> CH3CO -> CH2CO -> CHCO -> CH -> CH2 -> CH3 -> CH4 with the highest energy barrier of 0.79 eV, ethane formation via the processes of C2H4 -> C2H5 -> C2H6 with the largest energy barrier of 1.51 eV, and CO formation controlled by its desorption energy of 2.67 eV. The formed O/OH species can act as the oxidative agent to enhance the O-H bond scission involved in ethanol, and thus complete the whole reaction processes. Moreover, it was found that the barrier of C-C bond broken decreases as the losing of H atoms in intermediate, which indicated that the C-C bond broken may become possible at the late dehydrogenation steps in the whole reaction processes. (c) 2013 Elsevier B.V. All rights reserved.