The gas-phase oxidation of HCl to Cl₂ 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 (Cr₂O₃, CeO₂, and MnO₂) have been gathered using the temporal analysis of products (TAP) reactor and compared with the outcome of previous studies over RuO₂ 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 (Cl₂ and H₂O) in the TAP reactor. The order of activity was RuO₂ > Cr₂O₃ > CeO₂ CuO > MnO₂. The oxides with lowest activity, MnO₂ and CuO, exhibited bulk chlorination detected by X-ray diffraction and a highly impeded Cl₂ evolution. Chlorination of Cr₂O₃ and CeO₂ during reaction conditions was limited to the surface, as observed with RuO₂. However, catalyst reoxidation over the former two catalysts is more costly. Consequently, RuO₂ possesses the two main features for a suitable Deacon catalyst: limited chlorination, conferring stability; and easier Cl₂ evolution, allowing low-temperature operation.