Supported CeO2 catalysts in technical form for sustainable chlorine production

Authors: M. Moser, C. Mondelli, T. Schmidt, F. Girgsdies, M.E. Schuster, R. Farra, L. Szentmiklósi, D. Teschner, J. Pérez-Ramírez

Abstract:
Bulk CeO₂ has been recently reported as a promising catalyst for the oxidation of HCl to Cl₂. In order to undertake the scale up of this system, various oxides (TiO₂, Al₂O₃, and low- and highsurface area ZrO₂) have been evaluated as carriers. Supported CeO₂ catalysts (3–20 wt.% Ce) prepared by dry impregnation were isothermally tested at the lab scale. Their performance was ranked as: CeO₂/ZrO₂ CeO₂/Al₂O₃ ≥ CeO₂/TiO₂. Kinetic data revealed a lower activation energy and a similar activity dependence on the partial pressure of O₂ for CeO₂/ZrO₂ compared to bulk CeO₂. Pilot-scale testing over 3-mm pellets of this catalyst evidenced outstanding stability for 700 h on stream. In-depth characterization of the carriers and fresh catalysts by N₂ sorption, Hg porosimetry, X-ray diffraction, temperature-programmed reduction with H₂, Raman spectroscopy, electron microscopy, and in situ prompt gamma activation analysis, enabled to rationalize the different catalytic behavior ofthe materials. ZrO₂ stabilizes nanostructures of CeO₂ and a Ce–Zr mixed oxide phase, which offer high dispersion and improved oxidation properties. The catalyst also shows reduced chlorine uptake, and overall stands as a better Deacon material compared to bulk CeO₂ and other supported systems. CeO₂ is present on Al₂O₃ predominantly as well-distributed nanoparticles. Still, alumina does not induce any electronic effect, thus the supported phase behaves similarly to bulk ceria. TiO₂, likely due to the structural collapse and dramatic sintering suffered during calcination, leads to the formation of very large ceria particles. Based on our results, CeO₂/ZrO₂ appears as a robust and cost-effective alternative to the current RuO₂-based catalysts for large-scale chlorine recovery.

Keywords:
Chlorine production
HCl oxidation
Ceria Support
CeO₂/ZrO₂
Technical catalyst
Pilot test

Published in: Applied Catalysis B: Environmental (Volumes 132–133, Pages 1-552, 27 March 2013)

Publisher: Elsevier  

ISSN Information: 0926-3373

Supported CeO2 catalysts in technical form for sustainable chlorine production

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