Mechanism–Performance Relationships of Metal Oxides in Catalyzed HCl Oxidation

The gas-phase oxidation of HCl to Cl 2 over heterogeneous catalysts, known as the Deacon process, is a sustainable way for chlorine recycling in the chemical industry. Mechanistic aspects of this reaction over metal oxides (Cr 2 O 3, CeO 2, and MnO 2 ) have been gathered using the temporal analysis of products (TAP) reactor and compared with the outcome of previous studies over RuO 2 and CuO. The intrinsic features of the TAP technique enable investigation of this demanding reaction in a safe manner and under highly controlled conditions. We have correlated the catalytic activity measured isothermally in a continuous-flow reactor at ambient pressure with mechanistic descriptors derived from the transient responses of reaction products (Cl 2 and H 2 O) in the TAP reactor. The order of activity was RuO 2 > Cr 2 O 3 > CeO 2 ∼ CuO > MnO 2 . The oxides with lowest activity, MnO 2 and CuO, exhibited bulk chlorination detected by X-ray diffraction and a highly impeded Cl 2 evolution. Chlorination of Cr 2 O 3 and CeO 2 during reaction conditions was limited to the surface, as observed with RuO 2 . However, catalyst reoxidation over the former two catalysts is more costly. Consequently, RuO 2 possesses the two main features for a suitable Deacon catalyst: limited chlorination, conferring stability; and easier Cl 2 evolution, allowing low-temperature operation.