The search for environmentally correct processes is one of the greatest challenges in current energy research. Hydrogen production trough ethanol reforming emerges as a promising technology. In this work, the mechanism for ethanol decomposition over platinum was investigated by density functional theory (DFT). The various reaction intermediaries and transition states were optimized over a cluster of five Pt atoms at the B3LYP-D3/6-31+G(d,p) level of theory for ethanol with the SEWN ECP basis set for the metal atoms. This approach showed to be fully consistent with experimental observations. Two routes were considered, one leading to the formation of CH4 and CO and the other leading to C2H6. In agreement with previous calculation and experimental studies, the route forming CH4 and CO is favored. The reaction barriers were investigated by the Localized Molecular Orbital Energy Decomposition Analysis (LMOEDA) method. In general, the reaction steps that involve solely the scission of a O-H or C-H bond present elevate reaction barriers. Some other steps, however, include a concomitant strengthening of the C-O bond as the C-H bond elongates. These reaction steps present relatively low reaction barriers. For some other cases, it is the distinct interaction with the metal experienced by the transition state and the ground state that determines the energy barrier. The LMOEDA method proved to be an invaluable tool for the understanding of reaction mechanisms and for the rational design of news catalysts. (C) 2014 Elsevier B.V. All rights reserved.