As a biodiesel by-product, glycerol is a potential re-newable building block for sustainable chemistry.[1] It is a C3 platform molecule, potentially leading to several interesting iso-carbon chemicals such as propanediols, lactic acid, acrylic acid, etc. It can also be seen as a prototypical polyalcohol: results achieved with this substrate could be extended to higher polyols such as glucose, starch, etc. The hydrogenolysis reaction catalyzed by a transition metal solid catalyst in basic conditions is a potential way to transform glycerol into important chemicals.[2] The two main hypothesis on the first step is either a dehydrogenation step, either a dehydration step. In agreement with experimental results, theoretical studies at the DFT level sustain the first step being a dehydrogenation step in basic conditions. We will detail the glycerol dehydrogenation mechanism on Rh(111). Comparing with simpler alcohols, we will discuss the important role of the environment on the C-H and O-H bonds dissociation. As illustrated by the following picture, the activation energy can be drastically reduced by the presence of additional OH groups. [1] A. Behr, J. Eilting, K. Irawadi, J. Leschinski, F. Lindner, Green Chemistry, 2008, 10, 13-30 [2] J. Chaminand, L. Djakovitch, P. Gallezot, P. Marion, C. Pinel and C. Rosier, Green Chemistry, 2004, 6, 359-361.