Shape-Controlled CeO<sub>2</sub> Nanoparticles: Stability and Activity in the Catalyzed HCl Oxidation Reaction

CeO<sub>2</sub> is a promising catalyst for the HCl oxidation (Deacon process) in order to recover Cl<sub>2</sub>. Employing shape-controlled CeO<sub>2</sub> nanoparticles (cubes, octahedrons, rods) with facets of preferential orientations ((100), (111), (110)), we studied the activity and stability under two reaction conditions (harsh: Ar:HCl:O<sub>2</sub> = 6:2:2 and mild: Ar:HCl:O<sub>2</sub> = 7:1:2). It turns out that both activity and stability are structure-sensitive. In terms of space time yield (STY), the rods are the most active particles, followed by the cubes and finally the octahedrons. This very same trend is reconciled with the complete oxygen storage capacity (OSCc), indicating a correlation between the observed activity STY and the OSCc. The apparent activation energies are about 50 kJ/mol for cubes and rods, while the octahedrons reveal an apparent activation energy of 65 kJ/mol. The reaction order in O<sub>2</sub> is positive (0.26–0.32). Under mild reaction conditions, all three morphologies are stable, consistent with corresponding studies of CeO<sub>2</sub> powders and CeO<sub>2</sub> nanofibers. Under harsh reaction conditions, however, cubes and octahedrons are both instable, forming hydrated CeCl<sub>3</sub>, while rods are still stable. The present stability and activity experiments in the catalytic HCl oxidation reaction over shape-controlled CeO<sub>2</sub> nanoparticles may serve as benchmarks for future ab initio studies of the catalyzed HCl oxidation reaction over well-defined CeO<sub>2</sub> surfaces.