Kinetically coupled reactions of glycerol in water over bifunctional Pt/Al₂O₃ catalysts are explored as a function of the Pt particle size and the reaction conditions. Detailed analysis of the reaction network shows that “reforming” and hydrodeoxygenation require the presence of a bifunctional catalyst, i.e., the presence of an acid–base and a metal function. The initial reaction steps are identified to be dehydrogenation and dehydration. The dehydrogenation of hydroxyl groups at primary carbon atoms is followed by decarbonylation and subsequent water gas shift or by disproportionation to the acid (and the alcohol) followed by decarboxylation. Hydrogenolysis of the C–O and C–C bonds in the alcohols does not occur under the present reaction conditions. Larger Pt particles favor hydrodeoxygenation over complete deconstruction to hydrogen and CO₂.