Glycerol hydrogenolysis to PDOs consists of hydrogen addition and removal of one oxygen atom in the form of H2O. In order to design efficient catalysts, it is fundamental to under­stand the mechanism of this reaction. Three main reaction mechanisms have been proposed in the literature, depending on whether the reaction runs on acid or basic catalytic sites and with or without the formation of intermediate compounds:

i. dehydrogenation — dehydration — hydrogenation (glyceraldehyde route),

ii. dehydration — hydrogenation,

iii. direct glycerol hydrogenolysis.

Below, the main features of each mechanism will be discussed