Oxidation of HCl over TiO₂-Supported RuO₂: A Density Functional Theory Study

With density functional theory (DFT) calculations, we studied the oxidation of HCl with oxygen producing Cl 2 and water on the TiO 2 (110)-supported RuO 2 (110). This so-called Sumitomo—a novel Deacon—process proceeds via a one-dimensional Langmuir−Hinshelwood mechanism, in which the recombination of two adjacent chlorine atoms on the surface of the catalyst constitutes the rate-determining step. Very important for industrial application is that substantial Ru resources can be saved in the production of the Sumitomo catalyst. According to our DFT calculations already 1 ML of RuO 2 (110) supported on TiO 2 (110) suffices to maintain practically the full activity of bulk-RuO 2 in the HCl oxidation reaction. The calculated electron density differences of the TiO 2 (110)-supported 1 ML RuO 2 system in comparison with bulk RuO 2 (110) are localized at the internal interface, leaving the electronic structure of the topmost undercoordinated Ru sites (active sites) unaffected by the support. This explains naturally the invariant activity of supported 1 ML RuO 2 (110) in comparison with bulk RuO 2 (110). The stoichiometric TiO 2 (110) is not active at all in the HCl oxidation reaction. However, if the undercoordinated Ti surface atoms are substituted by Ru then the resulting 1 / 2 ML RuO 2 −TiO 2 (110) catalyst is active with an activation barrier that is 58 kJ/mol higher than for bulk-RuO 2 (110).