Platinum-Bismuth-Catalyzed Oxidation of Glycerol: Kinetics and the Origin of Selective Deactivation

The selective oxidation of glycerol to dihydroxyacetone is still a challenging task for heterogeneous catalysis and important to the chemical industry. Especially bimetallic Pt-Bi catalysts show a high initial selectivity to dihydroxyacetone in acidic media but exhibit a strong deactivation during reaction as well. This deactivation decreases activity as well as selectivity to dihydroxyacetone. Thus, only moderate yields may be achieved. In this work, product adsorption was identified as a major cause. In particular, glyceric acid, all oxidation product of the primary hydroxyl group, selectively blocks those kinds of active sites that are predominantly responsible for dihydroxyacetone formation. This could be confirmed by means of kinetic modeling. It has been proven that all catalytic experiments taken into account for the parameter estimation are free from external and internal transport limitations. A mechanism characterized by two different active sites has been derived. Glyceric acid selectively inhibits one of them, causing the observed decrease in dihydroxyacetone selectivity and catalyst activity.