Atomic scale insights into electrochemical versus gas phase oxidation of HCl over RuO2-based catalysts: A comparative review

In this article our current understanding of the electro-catalyzed chlorine evolution reaction (CER) in comparison with that of the heterogeneously-catalyzed gas phase oxidation of HCl (Deacon process: heterogeneous catalysis) over RuO2-based catalysts will be reviewed. Both types of harsh reactions are chemically similar: The main concern is catalyst stability, and in both cases the best catalyst contains RuO2 as the catalytically active component so that a critical comparison may provide new insights into the underlying physicochemical processes. It is the primary scope of this review addresses atomic scale information on the RuO2-catalyzed HCl oxidation reaction either in electrochemical or in gas phase environment. In particular, the involved reaction mechanisms and the reason for the extraordinary stability of RuO2 under such harsh reaction conditions will be discussed, emphasizing similarities and differences in the Deacon process and the CER and what can be learnt from this comparison. The distinct properties of RuO2, which are responsible for its extraordinary catalytic performance in both the CER and the Deacon process, are highlighted.