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

摘要

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 TiO_2 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: Au_7Pd_3/TiO_2 > Au_5Pd_5/TiO_2 > Au_8Pd_2/TiO_2 > Au_9Pd_1/TiO_2 > Au_6Pd_4/TiO_2. 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°, Au~(3+), Pd° 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°, Au~(3+), Pd° dan PdO together with the presence of "synergistic" effect in the Au-Pd alloy. The reactions were performed at low and high temperatures (50℃ and 100℃) 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 Au_9Pd_1ATiO_2 at 50℃ and after 8 h of reaction time.