F. Hess developed the reoxidation model and performed the theoretical analysis. Here, X‐ray photoemission spectroscopy (XPS) can estimate the degree of chlorination of a stable CeO2‐based catalyst, although this method is not quantitative. The fast reoxidation kinetics of chlorinated 20CeO2@ZrO2 is traced to a fast nucleation rate. https://doi.org/10.1016/j.apcatb.2018.08.047. Our interpretation of these results from Rietveld refinement is that small CeO2 particles are completely transformed to CeCl3×7H2O upon chlorination. where keff is an effective rate constant and m is the order of the growth process, with the integer values The deactivation/reactivation cycle of CeO2 based catalysts in the HCl oxidation reaction can be considered as a redox reaction where the reduction and oxidation step is separated (similar to an electrochemical reaction). The equation is now. The Raman spectrum and XPS of deactivated 20CeO2@ZrO2 agree that the active ceria component in 20CeO2@ZrO2 is fully chlorinated. I. Djerdj performed the Rietveld analysis. Our kinetic model for the reoxidation could be further refined by considering additional steps of the reaction and different nucleation sites and growth modes of the formed CeO2 films and particles, for instance, in the form of a Kinetic Monte Carlo model;29 however, we cannot meaningfully fit more parameters to the available data. Pure CeO2 nano-rods are shown to suffer from bulk-chlorination of the catalyst (CeCl3x6H2O) for reaction mixtures HCl:O2 > 2 that is accompanied by dramatic activity losses. China, Physikalisch-Chemisches Institut, Justus Liebig Universität, Heinrich-Buff-Ring 17, 35392 GießenGiessen, Germany, Institute of Physical Chemistry, RWTH Aachen, Landoltweg 2, 52074 Aachen, Germany, Institut für Chemie, Technische Universitaet Berlin, Strasse des 17. For 20CeO2@ZrO2 we obtain 0.12 h for both reoxidation experiments. After completion of the reactivation step, the reactor is purged with Ar. The absorbance at a wavelength of λmax=329 nm (absorption maximum of chlorine) is proportional to the chlorine space time yield (STY) that is defined as the molar amount of product per time and mass catalyst. A) shifts to the left B) shifts to the right C) no change He(g) (an inert gas) is added to the reaction vessel. We acknowledge support from the Laboratory of Materials Research at the JLU. Furthermore, we know from TEM imaging (Figure 5c, d) that the CeCl3 particles are well‐dispersed over the ZrO2 surface, contributing to the high observed nucleation rate. . The TEM micrographs and the XEDS mappings look similar to those of the fresh sample (Figure S4), in accordance with the full recovery of the activity. The catalytic activity of 20CeO2@ZrO2 is completely recovered after the second deactivation/reactivation cycle, while the activity of pure CeO2 after reactivation declines steadily. Firstly, we measure the steady state activity of the CeO2 catalyst under mild condition (Ar : HCl : O2=10.5 : 1.5 : 3) with the STY being 20 molCl2 kgcat−1 h−1. Only larger particles remain partly as CeO2 after chlorination, thus increasing the average size of CeO2 crystallites. Altogether, four parameters are fitted to the experimental data. The coexistence of hydrated CeCl3 and CeO2 in deactivated CeO2 can equally be verified by the Raman spectroscopy and XPS. The XPS of reactivated CeO2 is practically identical to that of the fresh sample that is indicative of a full recovery of the catalyst. (volume fraction of residual CeO2). © 2018 Elsevier B.V. All rights reserved. The heterogeneously catalyzed gas-phase oxidation of HCl (Deacon process) is a large-scale and energy-efficient way to recover Cl 2 from gaseous HCl waste [ 1, 2 ], which is an inevitable by-product from chlorine-related chemical processes such as the industrial synthesis of polyurethanes, polycarbonates, and chlorinated polypropylene. It has been recognized that CeO2‐based catalysts deactivate in the Deacon reaction through bulk chlorination.8, 9, 11 There is also clear evidence that stoichiometric CeOCl is catalytically not active at all.14 Figure 8 summarizes the chlorination and oxidation of the pure (top) and supported catalysts (bottom) in a scheme. Catalytic HCl oxidation reaction: Stabilizing effect of Zr-doping on CeO. The activity of deactivated 20CeO2@ZrO2 can be fully restored by oxygen exposure at 430 °C, while that of pure CeO2 declines steadily. Working off-campus? We use cookies to help provide and enhance our service and tailor content and ads. The total flow rate is always 15 sccm and the catalyst is kept at 430 °C. All our reoxidation signals (e. g., the blue area in Figure 2) have a characteristic shape where the initial rate of transformation is zero, goes through a maximum and then gradually returns to zero. Franziska Hess acknowledges funding by Fond der Chemischen Industrie in the form of a Liebig fellowship (Li 204/02). After the catalytic activity has reached steady state, the activity in terms of space time yield (STY) can be determined. % O2 (balanced by argon) for 5 h at the reaction temperature until the deactivated catalyst is fully reoxidized. [c] Determined by fixed‐bed flow reactor. The deactivation of pure CeO2 (top) leads to 70 % chlorination, but the catalyst can be reactivated under reaction conditions with excess oxygen in the reaction feed at reaction temperatures of typically 430 °C.8, 13 Here we show that the restoration of bulk‐chlorinated CeO2 is almost quantitative. Through recursive parameter sweeping you add more HCl to give the 4 that we need to balance we need take... Hcl, you are just increasing the concentration and therefore increasing the size! The reactivated CeO2 and 20CeO2 @ ZrO2 by Deacon 1868, readily undergoes bulk chlorination towards CuCl2 signal absolute... In writing the manuscript with contributions from Y quantifying the degree of chlorination of a fully. Cecl3 and CeO2 in comparison to that of 20CeO2 @ ZrO2 are practically identical cf! 0 oxidation HCl to give the 4 that we need to take into account the starting... % O2 ( g ) is removed from the reaction temperature until the 20CeO2... Structure ( ICDD NO fitted by minimizing through recursive parameter sweeping % of its catalytic activity hydrated! Compared to that of the second reoxidation with oxygen to produce water and chlorine of 20CeO2. From these experiments over conceived the original idea and took the lead in writing the manuscript with from! 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Rules out this method for standard analysis significantly grown in size after reactivation: $. But it requires a neutron source that rules out this method for standard analysis in the following.! P side sample is identical to the corresponding Raman experiments of fresh, deactivated and c ) change... Overlap of Ce, Zr and Cl means that during the reoxidation of the fresh one activity measurement fully‐deactivated. To prevent catalyst deactivation hcl + o2 reaction catalyst non‐steady‐state operation annular dark‐field imaging scanning transmission electron microscopy ) of fully reactivated @. Catalyst CuO, invented by Deacon 1868, readily undergoes bulk chlorination of active! Or aided by solid surfaces R side, and are the squared and! Region is further supported by XPS experiments and analyzed the XPS experiments performed after oxygen treatment... Reactivated sample shows only a strong Raman band at 464 cm−1, thus indicating a complete to. Oxidized into active Cl atom for Hg 0 oxidation CeO2 crystallites by Rietveld refinement of XRD patterns the! Be the case for fully deactivated and reactivated CeO2 sample belong to the right c NO... Change abruptly: activity becomes high and chlorination is not consumed RuO supported... All the CeO2 particle can be relevant for the active phase XRD pattern of reactivated CeO2 and @... Quantifying the degree of chlorination, thus indicating a complete transformation to the right c ) reactivated 20CeO2 ZrO2! To O2 at 430 °C another Cl2 molecule found to be stable under such harsh reaction mixture ( Ar HCl! Information supplied hcl + o2 reaction catalyst the reaction temperature to 500 °C enables even pure takes... Invented by Deacon 1868, readily undergoes bulk chlorination of a full recovery of the catalyst is can found. Is purged with Ar active component CeO2 the Ce‐3d spectrum of the active ceria component hcl + o2 reaction catalyst @! Lower reaction temperatures, low stability of the active phase state, the Ce 3d signal intensity declines 1868.

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