Oxidation of perchloroethylene—Activity and selectivity of Pt, Pd, Rh, and V2O5 catalysts supported on Al2O3, Al2O3–TiO2 and Al2O3–CeO2. Part 2

Pt, Pd, Rh and V2O5 metallic monolith catalysts supported on Al2O3, Al2O3–CeO2 and Al2O3–TiO2 were examined in the oxidation of perchloroethylene (PCE). The H2-TPR experiments proved that the enhanced reducibility is the key feature of the catalyst in PCE oxidation: both the activity and the selectivity followed the orders of catalysts’ reducibility. The NH3-TPD measurements showed that the acidity is not the determining property of the catalyst in the PCE oxidation. After the 40.5 h stability test, no carbonaceous species were seen on the Pt/Al2O3–CeO2 catalyst's surface. Instead, some chlorine was detected on the surface which at this point did not alter the catalysts’ performance. During the oxidation strong correlation between the water concentration in the feed and the HCl yield was seen. In the absence of oxygen, i.e. during destructive adsorption, the presence of water had even more pronounced effect on the HCl formation and on the catalysts’ stability. The oxidation of PCE over the Pt/Al2O3 and Pt/Al2O3–CeO2 catalysts and in the presence of excess hydrogen proceeds via detaching the chlorine atoms before the breakage of the carbon–carbon double bond, and hence following the order of the lowest bond energy in each step.

Figure optionsDownload as PowerPoint slideHighlights▸ The total acidity did not correlate with the oxidation activity of the catalysts. ▸ The enhanced reducibility was the key property of the catalyst in PCE oxidation. ▸ After 40.5 h in PCE oxidation the Pt/Al2O3–CeO2 catalyst proved to be stable. ▸ In destructive adsorption water enhanced the HCl yield and catalysts’ stability. ▸ PCE decomposed by detaching the chlorine atoms prior carbon–carbon bond breakage.