アイテム詳細

要旨

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 high-surface 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 of the 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.