sReactivation of CeO2-based Catalysts in the HCl Oxidation Reaction:In situQuantification of the Degree of Chlorination and Kinetic Modeling

Deactivation of CeO2-based catalysts in the HCl oxidation reaction proceeds via selective bulk chlorination of the active CeO(2)component to form CeCl(3)xnH(2)O. We study the reactivation of two bulk-chlorinated CeO2-based Deacon catalysts by oxygen treatment at 430 degrees C, namely pure CeO(2)and 20 mol % of CeO(2)supported on preformed ZrO(2)particles (20CeO(2)@ZrO2), with a dedicated experiment. In the flow reactor setup we determinein-situthe 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 degrees C. The activity of deactivated 20CeO(2)@ZrO(2)can be fully restored by oxygen exposure at 430 degrees 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.