Amines are essential intermediates in chemical industries. To obtain them from alcohols is an alternative to the current processes that opens the road to the utilization of biomass-sourced alcohols. When catalyzed by metal supported catalysts, this reaction follows the H-borrowing mechanism. It starts with the alcohol dehydrogenation, followed by the addition of the amine on the intermediated aldehyde. Then, the resulting imine is hydrogenated into amine. This hydrogen transfer from the alcohol to the imine is an elegant route that limits the utilization of an external source of H2. In this context, we focus on the challenging amination of aliphatic alcohol by ammonia where the selectivity issue is prominent. In the quest of the best catalyst, we propose here to perform a detailed DFT study of the reaction mechanism on two metals, namely Pd and Ni. We based our study on the hydrogen-borrowing mechanism, using methanol as a simple model of alcohol. We computed the various possible reaction paths for the methanol dehydrogenation and then the imine hydrogenation using periodic DFT calculations with the PBE functional. Since the C-N coupling does not require any metal supported catalyst to proceed efficiently, we didn’t consider the elementary steps of this reaction. Comparing the energetic span obtained on Pd(111) and Ni(111), we predicted that Pd was slightly more active than Ni (1.26eV vs. 1.31eV). However, according to recent experimental studies[Shimizu et al. ACS Catal. 2013, 3, 112−117], Ni supported catalysts are clearly more active than Pd to perform the amination of aliphatic alcohol with ammonia. Since this reaction occurs in liquid phase but under a pressure of ammonia, we evaluate the coverage of ammonia at around 1/9ML at the working pressure and temperature (4 bar, 160°C). Then, we re-investigated the reaction paths including the effect of the co-adsorbed ammonia. On Pd(111), it pushes up slightly the first CH bond breaking in methanol and destabilizes also the strongly adsorbed amine leading to a reduced energetic span of 1.05eV. On Ni(111), the results are even more contrasted: ammonia stabilizes the initial OH scission transition state and strongly destablizes the amine. Then, the energetic span of the overall reaction is reduced to 0.78eV. Ni is then predicted being much more active than Pd. This is a clear example of the importance of co-adsorbed species on the activity of metallic catalysts in hydrogenation/dehydrogenation reactions.