March

Picture of the Month - March 2018

Here you see current insights into the research of the LaMa groups. A collection of the former pictures can be found in the Gallery.

Shape-Controlled CeO₂ Nanoparticles: Stability and Activity in the Catalyzed HCl Oxidation Reaction

CeO₂ is a promising catalyst for the HCl oxidation (Deacon process) in order to recover Cl₂. Employing shape-controlled CeO₂ nanoparticles (cubes, octahedrons, rods) exposing facets with preferential orientations ((100), (111), (110)), we studied the activity and stability under two reaction conditions (harsh: Ar:HCl:O₂= 6:2:2 and mild: Ar:HCl:O₂=7:1:2). It turns out that both activity and stability are structure-sensitive and are not reconciled with corresponding surface energies and the formation energies of O-vacancies. 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 O₂ is positive (0.26-0.32). Under mild reaction conditions all three morphologies are stable, consistent with corresponding studies of CeO₂ powders and CeO₂ nanofibers. Under harsh reaction conditions, however, cubes and octahedrons are both instable, forming CeCl₃, while rods are still stable. The present stability and activity experiments in the catalytic HCl oxidation reaction over shape-controlled CeO₂ nanoparticles may serve as benchmarks for future ab-initio studies of the catalyzed HCl oxidation reaction over well-defined CeO₂ surfaces.

Recent Publication on this Topic:
C. Li, Y. Sun, I. Djerdj, P. Vöpel, C. Sack, T. Weller, R. Ellinghaus, J. Sann, Y. Guo, B.M. Smarsly, H. Over, Shape-controlled CeO₂ Nanoparticles: Stability and Activity in the Catalyzed HCl Oxidation Reaction, ACS Catal. 7 (2017) 6453-6463

This picture was submitted by Prof. Dr. Herbert Over.