OXIDATION OF GLYCEROL USING TITANIA SUPPORTED Au-Pd BIMETALLIC CATALYSTS: EFFECT OF Au-Pd RATIOS ON CATALYTIC PERFORMANCE

Oxidation of glycerol to form various types of short chain oxygenated derivative compounds became an important reaction to support biodiesel industries. In this study, bimetallic Au-Pd catalysts supported on TiO2 with different Au/Pd atomic ratios have been successfully prepared by deposition-precipitation method with urea decomposition. The catalysts were tested in the glycerol oxidation reactions in order to examine the effect of Au-Pd ratio on the conversion and selectivity. Catalytic activity of all the catalysts were as follow: Au7Pd3/TiO2 > Au5Pd5/TiO2 > Au8Pd2/TiO2 > Au9Pd1/TiO2 > Au6Pd4/TiO2. Analysis by XRD revealed the presence of metallic Au and gold-enriched Au-Pd alloy phase which were located between the [111] and [200] peaks of Au and Pd in the Au-Pd bimetallic catalysts. XPS analysis ascertained the formation of Au-0, Au3+, Pd-0 and PdO species together with Au-Pd alloy phase in the bimetallic Au-Pd catalysts. This shows that the catalytic activity of the catalysts was depended to the formation of mixture of active species namely Au-0, Au3+, Pd-0 dan PdO together with the presence of synergistic effect in the Au-Pd alloy. The reactions were performed at low and high temperatures (50 degrees C and 100 degrees C) and it was found that the selectivity to tartronic acid was enhanced at lower reaction temperature. The highest selectivity to tartronic acid (55% at 99% conversion) was obtained by using Au9Pd1/TiO2 at 50 degrees C and after 8 h of reaction time.