Gold on titania : effect of preparation method in the liquid phase oxidation

The effect of prepn. method (deposition-pptn. vs. sol immobilization method) and redn. method (calcination vs. chem. redn.) on Au/TiO2 catalysts for the liq. phase oxidn. of glycerol has been studied. It was revealed that a different trend existed in terms of activity and distribution of products. The catalytic activity is shown to be dependent not only on the choice of the redn. method but also on the use of protective agent (PVA, THPC) for the stabilization of the gold colloids. In fact, the highest activity was found when a low temp. chem. redn. was employed on a Au/TiO2 sample synthesized by the deposition-pptn. method. The use of a higher pre-treatment temp. or of a protective agent resulted in a lower activity but could be used to direct selectivity in oxidn. reactions. The structural data (HRTEM and XPS) along with the catalytic results indicate that the combination of metallic Au0 species with small particle size (2-5 nm) are responsible for the high activity obsd. in the liq. phase oxidn. of glycerol.