Preparation and Characterization of Model Catalysts for the HCl Oxidation Reaction

Abstract

In this chapter we address the corrosive HCl oxidation reaction over RuO2- and CeO2-based model catalysts. Depending on the chosen model system we are able to gain in-depth information of the reaction mechanism, the catalytically active sites and the stability of the catalyst. For instance, the reaction mechanism and the molecular processes of HCl oxidation have been determined on RuO2(110) single crystalline films. The stabilization of the RuO2(110) surface against bulk-chlorination was traced to replacement of bridging surface oxygen by chlorine. Morphological stability of the catalyst has been examined by RuO2-based nanofibers which were synthesized by electrospinning. Here HCl oxidation leads to strong morphological modifications of pure RuO2 fibers, while mixed rutile TiO2–RuO2 nanofibers are shown to be much more stable under HCl oxidation conditions. A promising alternative to RuO2 constitutes CeO2. CeO2 exhibits superb reversible oxidation/reduction between Ce3+ and Ce4+, which facilitates the oxidation of HCl. The morphological stability of CeO2-based catalysts was studied by the use of nanofiber model catalysts. Pure CeO2 nanofibers are morphological unstable, while Zr doping stabilizes CeO2 nanofibers profoundly.