HCl Oxidation for Sustainable Cl₂ Recycle over the Ce_<i>x</i>Zr_1–<i>x</i>O₂ Catalysts: Effects of Ce/Zr Ratio on Activity and Stability

Abstract

Ce x Zr 1– x O 2 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 x Zr 1– x O 2 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 x Zr 1– x O 2 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 0.5 Zr 0.5 O 2 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 O 2 and HCl competed for the active sites rendering desorption of surface Cl as the rate-determining step. Accelerating the replacement of surface Cl by O 2 is essential for improving the activity of Ce 0.5 Zr 0.5 O 2 .