HCl oxidation for sustainable Cl₂ recycle over the Ce_xZr_{1- x}O₂ catalysts: Effects of Ce/Zr ratio on activity and stability

Ce_xZr_1-xO₂ oxides prepared by a soft reactive grinding (SRG) procedure have been investigated as the catalysts for HCl oxidation. The results show that the catalytic activities and stabilities of Ce_xZr_1-xO₂ oxides are remarkably dependent on the Ce/Zr ratio. A correlation between the physicochemical properties and catalytic performances of these samples reveals that the cubic phase in Ce_xZr_1-xO₂ with higher oxygen storage capacity (OSC) is more active for HCl oxidation, but the tetragonal phase is crucial to the stability of the catalysts. The Ce_0.5Zr_0.5O₂ catalyst with mixed phases and the highest OSC (80 μmol_O2·g_cat^-1) exhibits an excellent activity (1.89 g_Cl2·g_cat^-1·h^-1 at 430 °C) and stability (300 h) in the target reaction. Kinetic studies show that both O₂ and HCl competed for the active sites rendering desorption of surface Cl as the rate-determining step. Accelerating the replacement of surface Cl by O₂ is essential for improving the activity of Ce_0.5Zr_0.5O₂.