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sReactivation of CeO 2 ‐based Catalysts in the HCl Oxidation Reaction: In situ Quantification of the Degree of Chlorination and Kinetic Modeling
Author(s) -
Sun Yu,
Hess Franziska,
Djerdj Igor,
Wang Zheng,
Weber Tim,
Guo Yanglong,
Smarsly Bernd M.,
Over Herbert
Publication year - 2020
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.202000907
Subject(s) - catalysis , kinetics , nucleation , chlorine , chemistry , oxygen , redox , in situ , inorganic chemistry , heterogeneous catalysis , chemical kinetics , chemical engineering , organic chemistry , physics , quantum mechanics , engineering
Deactivation of CeO 2 ‐based catalysts in the HCl oxidation reaction proceeds via selective bulk chlorination of the active CeO 2 component to form CeCl 3 ×nH 2 O. We study the reactivation of two bulk‐chlorinated CeO 2 ‐based Deacon catalysts by oxygen treatment at 430 °C, namely pure CeO 2 and 20 mol % of CeO 2 supported on preformed ZrO 2 particles (20CeO 2 @ZrO 2 ), with a dedicated experiment. In the flow reactor setup we determine in‐situ the degree of chlorination of the catalyst by quantifying down‐stream with in‐situ UV‐Vis spectroscopy the total amount of chlorine in the catalyst that is exchanged by reoxidation at 430 °C. The activity of deactivated 20CeO 2 @ZrO 2 can be fully restored by oxygen exposure at 430 °C, while that of pure CeO 2 declines steadily. Since the UV‐Vis analytics is fast and sensitive, we can follow the kinetics of reoxidation. To rationalize the observed kinetics, we develop a modified Johnson‐Mehl‐Avrami‐Kolmogorov (JMAK) model based on a nucleation‐and‐growth approach for the reoxidation of the catalyst starting from the chlorinated phase. The fast reoxidation kinetics of chlorinated 20CeO 2 @ZrO 2 is traced to a fast nucleation rate.