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) similar to 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.