Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Abstract--This article discusses the effects of extra-and intraparticle mass and heat transfer in transient experiments over heterogeneous catalysts. To this purpose, the time-dependent transport in a catalyst particle when introducing a reactant in an inert gas phase has been analyzed. The analysis has led to one criterion assuring the absence of both extra-and intraparticle mass transfer limitations during steady-state experiments. Furthermore, criteria for the absence of mass and heat transport limitations during transient experiments have been developed by extending the criteria for the absence of mass and heat transport limitations during steady-state experiments. As will be shown, transient kinetics are not affected by heat transfer as long as the steady-state criteria for the absence of mass and heat transport limitations are fulfilled.

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General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Abstract CO oxidation over an alumina supported copper-chromium oxide has been studied by the stepresponse method. In this study the response of the catalyst is measured after step changes in the CO, '"CO and O2 concentration in order to reveal the reaction mechanism and the concentration of active sites. Special attention was given to the behaviour of the catalyst under conditions changing from net oxidization to net reduction, as this is representative for realistic exhaust gas conditions. It was found that the catalyst goes through an oxidation/reduction cycle under these conditions. The activity of the catalyst in an oxidizing gas feed following the reducing gas feed is initially higher than the steadystate activity. The surface reaction is rate determining under oxidizing and reducing conditions, but the removal of CO> from the catalyst surface also affects the overall rate of the reaction. It is found that 27% of the surface copper is covered with CO and CO2 in a reducing reaction mixture, i.e., 5% CO and 1.5% O2 in He. This amount is 18% in an oxidizing reaction mixture. CO readsorbs rapidly at the catalyst surface, but CO*, which desorbs via a concerted reaction mechanism with 02, hardly readsorbs at the catalyst surface.

Modelling the transient kinetics of heterogeneous catalysts. CO oxidation over supported Cr and Cu Dekker, F.H.M.; Klopper, G.; Bliek, A.; Kapteijn, F.; Moulijn, J.A. Published in:Chemical Engineering Science Link to publicationCitation for published version (APA): Dekker, F. H. M., Klopper, G., Bliek, A., Kapteijn, F., & Moulijn, J. A. (1994). Modelling the transient kinetics of heterogeneous catalysts. CO oxidation over supported Cr and Cu. Chemical Engineering Science, 49(24), 4375-4390. General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Abstract--This article illustrates the capabilities of the step response method in the determination of the mechanism and kinetics of a heterogeneously catalyzed reaction. The step response method was applied to investigate the CO oxidation over alumina-supported chromium and copper. Detailed mechanisms of this reaction were determined by measuring the isothermal reduction and oxidation of the catalysts via switching the gas-phase composition from inert (He) to either reducing (CO) or oxidizing (02) conditions, Modelling the obtained response curves has given information on the reaction rate constants of the elementary steps in the CO oxidation over the Cr and Cu catalyst. Here, only a minimum number of reaction steps and parameters have been used, but they are still physically acceptable. The reduction of the Cr catalyst was found to proceed via reaction of adsorbed CO. The activation energy of this process is 95 kJ mol -~. The dispersion of the Cr catalyst is 20%, whereas only half the metal atoms at the catalyst surface participate in the oxidation and reduction. The latter metal atoms are coordinated to about four removable oxygen atoms Reduction of the Cu catalyst takes place in three steps: first oxygen on the surface is removed via reaction of CO from the gas phase. Next the oxygen in the surface is removed via reaction of adsorbed CO, and finally the oxygen from the bulk of the catalyst that has diffused to the surface is removed. The activation energy of all three processes has been determined. The dispersion of the Cu catalyst was found to be about 22%, MODELLING THE TRANSIENT KINETICS OF H E T E R O G E N E O U S CATALYSTS. CO-OXIDATION OVER I N T R O D U C T I O NIn heterogeneous catalysis much effort is put into est...