Promoter effects in the Pt-catalysed oxidation of propylene glycol

Oxidation of aqueous solutions of propylene glycol has been performed at 333 K, pH = 8 using Pb-, Bi- and Sn-promoted Pt/graphite catalysts. Oxidation of propylene glycol towards pyruvic acid proceeds via two pathways, one via hydroxyacetone, the second via lactic acid. Experiments, performed under oxygen mass transfer limitations to avoid de-activation by over-oxidation showed significant effects of the promoters on both activity and selectivity. The addition of Pb and Bi enhances oxidation of lactic acid resulting in higher yields of pyruvic acid. The addition of Sn leads to high selectivities for both hydroxyacetone and pyruvic acid. The effect of Sn can be explained by the formation of a Sn–diol complex, where Sn is in the Sn(IV) state.