Deacon Process over RuO2 and TiO2-Supported RuO2

We use density functional theory (DFT) calculations to study a novel Deacon-like process over pure RuO2(110) and TiO2-supported RuO2(110), a commercial process which was recently introduced by Sumitomo Chemical. During the HCl oxidation reaction the surface becomes chlorinated, which makes this catalyst stable under the harsh reaction conditions. The reaction mechanism for the chlorination of unsupported RuO2(110) proceeds via water formation in the bridging position and the final replacement of this water species by chlorine. The actual HCl oxidation reaction takes place via a one-dimensional Langmuir-Hinshelwood mechanism. The recombination of on-top chlorine atoms to form the desired product Cl2 is identified as the rate-determining step with an activation energy E a of 114 kJ/mol. DFT calculations predict that one monolayer of RuO2(110) supported on TiO2(110) reveals catalytic activity which is almost as high as that on the unsupported RuO2(110) (E a = 124 kJ/mol). Further reduction of the Ru loading to half of a monolayer still keeps the TiO2(110)-RuO2(110) as a good catalyst for the Deacon process, with an activation barrier of the rate-determining step of 29 kJ/mol higher than at pure RuO2(110).