The Transient Method and Elementary Steps in Heterogeneous Catalysis

Bennett, C. O.

doi:10.1080/00087647608069936

Cited by 171 publications

(38 citation statements)

References 52 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…This phenomena was shown to occur through diffusion of oxygen abstracted from N 2 O at the surface of the catalyst into subsurface oxygen vacancies. As a result, the concentration of surface oxygen vacancies increases during the period under Ar, and consequently the rate of oxidation of the surface upon recontacting the catalyst with N 2 O is higher than the rate at the end of the previous period under N 2 O. This behavior cannot be described by a simple shrinking core model, for which there is no effect on the rate of oxidation of the catalyst when it contacts an inert gas, since there is no possible equilibration of the concentrations of solid species (lattice oxygen and lattice oxygen vacancies) during this period.…”

Section: Resultsmentioning

confidence: 99%

“…In this work, the step-response methodswhich consists of measuring the response of a catalytic system to a square like change in concentration of the reactantsswas chosen for its simplicity of application and for the substantial amount of mechanistic information that it provides (Kobayashi 1974(Kobayashi , 1982Bennett, 1976;Tamaru, 1983;Kiperman, 1991;Renken, 1993). We found it important to perform step changes in a wide range of state variables such as temperature, flow rate, and CO concentration, in order to obtain a meaningful kinetic model with reliable values of its parameters.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Modeling CO Oxidation on Silica-Supported Iron Oxide under Transient Conditions

Randall

Doepper

Renken

1997

Ind. Eng. Chem. Res.

View full text Add to dashboard Cite

The oxidation of CO on silica-supported hematite (Fe 2 O 3 ) was studied by the step-response method in a tubular fixed-bed reactor, at temperatures ranging between 270 and 350°C. The oxidation process appeared to proceed through two stages. Firstly, oxygen atoms adsorbed on the surface of hematite react with gas phase CO according to an Eley-Rideal mechanism. Once that adsorbed oxygen has been consumed to some extent, surface oxygen from the lattice of iron oxide is removed in a second stage involving CO adsorption and CO reactive desorption steps, thus generating surface oxygen vacancies. Further reduction of hematite proceeds through diffusion of subsurface oxygen into surface oxygen vacancies. On this basis, a kinetic model was developed, which quantitatively describes the transient behavior of the oxidation process. The activation energies and pre-exponential factors of the rate constants and characteristic subsurface oxygen diffusion time could be determined.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Modeling CO Oxidation on Silica-Supported Iron Oxide under Transient Conditions

Randall

Doepper

Renken

1997

Ind. Eng. Chem. Res.

View full text Add to dashboard Cite

show abstract

“…This method has been reviewed by Kobayashi and Kobayashi (1974) and by Bennett (1976). Their analyses showed that performing even some few transient experiments enables one to obtain considerable information on the reaction mechanism.…”

Section: Introductionmentioning

confidence: 97%

Transient Response Study of the Ammoxidation of Propene and Propane on an Sb−V−Oxide Catalyst

Nilsson

Andersson

1997

Ind. Eng. Chem. Res.

View full text Add to dashboard Cite

The reaction pathways in the ammoxidation of propene and of propane over an Sb-V-oxide catalyst were studied by analyzing the modes of transient responses of reactants and products resulting from step changes from inert gas to reactant feed. The pathway from propane to acrylonitrile begins with the oxidative dehydrogenation of propane to form propene. After readsorption, the propene is then transformed into adsorbed acrolein, which eventually reacts with an NH x surface species to form acrylonitrile. The adsorption of propane is rate limiting for the propane conversion, but the desorption of water formed from the propene is slow and determines the product distribution. The response modes for the direct oxidation and ammoxidation of propene are consistent with the desorption of water being rate limiting. A comparison of the experimental responses with responses simulated under the assumption that the formation of an allylic intermediate is rate determining reveals an important difference in profiles, indicating this step to not be rate determining. The results show that substantial qualitative information concerning the reaction pathways can be obtained from the analysis of transient profile modes.

show abstract

“…The simplest way of changing the concentration is in the form of a step. The basis of this so-called step response technique as applied to heterogeneous catalysis was originally laid down by Tamaru (1964) and reviewed by Kobayashi and Kobayashi (1974), Bennett (1976) and Biloen (1983) and more recently by Mirodatos (1991) and Tamaru (1991). The present study aims to illustrate the capability of the step response method in the determination of the reaction mechanism and reaction kinetics of the C O oxidation over an aluminasupported Cr and Cu catalyst.…”

Section: Introductionmentioning

confidence: 99%

Modelling the transient kinetics of heterogeneous catalysts. CO-oxidation over supported Cr and Cu

Dekker

Klopper

Bliek

et al. 1994

Chemical Engineering Science

View full text Add to dashboard Cite

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...

show abstract

The Transient Method and Elementary Steps in Heterogeneous Catalysis

Cited by 171 publications

References 52 publications

Modeling CO Oxidation on Silica-Supported Iron Oxide under Transient Conditions

Modeling CO Oxidation on Silica-Supported Iron Oxide under Transient Conditions

Transient Response Study of the Ammoxidation of Propene and Propane on an Sb−V−Oxide Catalyst

Modelling the transient kinetics of heterogeneous catalysts. CO-oxidation over supported Cr and Cu

Contact Info

Product

Resources

About