Analysis of simple kinetic models in heterogeneous catalysis

Lynggaard, H.; Andreasen, Anders; Stegelmann, Carsten; Stoltze, Per

doi:10.1016/j.progsurf.2004.09.001

Cited by 108 publications

(76 citation statements)

References 69 publications

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“…Information about the kinetics of the conversion process can be found in the values of ∆t, the delay between the beginning of the reaction and the half constant conversion rate (see Table 5). This phenomenon was predicted in the case of the Langmuir-Hinshelwood mechanism [43].…”

Section: Catalytic Activitymentioning

confidence: 58%

Synthesis and microstructure of cobalt ferrite nanoparticles

Ajroudi

Villain

Madigou

et al. 2010

Journal of Crystal Growth

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Cobalt ferrites (Co x Fe 3-x O 4 ) nanoparticles with various compositions were synthesized by a new non-aqueous synthesis method. The cobalt ferrites were characterized by X-rays diffraction, and transmission electron microscopy coupled with energy dispersive spectroscopy. The nanoparticles are highly crystallized, with a homogeneous chemical composition. The particle size varies from 4 nm up to 7.5 nm, depending on the cobalt content. The smallest particles, with a size of 4 nm, are obtained for high cobalt content.These particles have also the highest micro-structural strain. Catalytic measurements were realized using Fourier Transform Infrared Spectroscopy. The lowest activation energy and the highest conversion rate are obtained for Co 1.8 Fe 2.4 O 4 , in the 400-500 °C temperature range.

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Section: Catalytic Activitymentioning

confidence: 58%

Synthesis and microstructure of cobalt ferrite nanoparticles

Ajroudi

Villain

Madigou

et al. 2010

Journal of Crystal Growth

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“…However, whereas the observed reaction kinetics are controlled by a limited number of transition states and adsorbed species, it is typically required to carry out detailed microkinetic analyses to identify the nature of these key transition states and adsorbed species. Thus, a general strategy to elucidate how the reaction kinetics are controlled by a proposed reaction mechanism is first to carry out density functional theory (DFT) calculations to determine the thermodynamic properties of all adsorbed species and transition states, and then to build a microkinetic model to determine the surface coverages by all adsorbed species and the forward and reverse rates of all elementary steps for a range of reaction conditions (1)(2)(3)(4)(5). Sensitivity analyses are then carried out using this microkinetic model to identify those transition states and adsorbed species that control the predicted reaction kinetics for reaction conditions of interest.…”

mentioning

confidence: 99%

Analysis of reaction schemes using maximum rates of constituent steps

Motagamwala

Dumesic

2016

Proc. Natl. Acad. Sci. U.S.A.

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We show that the steady-state kinetics of a chemical reaction can be analyzed analytically in terms of proposed reaction schemes composed of series of steps with stoichiometric numbers equal to unity by calculating the maximum rates of the constituent steps, r max,i , assuming that all of the remaining steps are quasi-equilibrated. Analytical expressions can be derived in terms of r max,i to calculate degrees of rate control for each step to determine the extent to which each step controls the rate of the overall stoichiometric reaction. The values of r max,i can be used to predict the rate of the overall stoichiometric reaction, making it possible to estimate the observed reaction kinetics. This approach can be used for catalytic reactions to identify transition states and adsorbed species that are important in controlling catalyst performance, such that detailed calculations using electronic structure calculations (e.g., density functional theory) can be carried out for these species, whereas more approximate methods (e.g., scaling relations) are used for the remaining species. This approach to assess the feasibility of proposed reaction schemes is exact for reaction schemes where the stoichiometric coefficients of the constituent steps are equal to unity and the most abundant adsorbed species are in quasi-equilibrium with the gas phase and can be used in an approximate manner to probe the performance of more general reaction schemes, followed by more detailed analyses using full microkinetic models to determine the surface coverages by adsorbed species and the degrees of rate control of the elementary steps.chemical kinetics | catalysis | microkinetics C hemical reactions take place through sequences of elementary steps, and the dynamics of the overall stoichiometric reaction are typically controlled by key steps in this sequence of steps. For example, in the case of a catalytic reaction, the reaction kinetics are controlled by the energetics of the transition states for the rate-controlling steps and by the energetics of species that are abundant on the active sites (i.e., the Gibbs free energies of these transition states and adsorbed species relative to the reactants and products of the overall stoichiometric reaction). However, whereas the observed reaction kinetics are controlled by a limited number of transition states and adsorbed species, it is typically required to carry out detailed microkinetic analyses to identify the nature of these key transition states and adsorbed species. Thus, a general strategy to elucidate how the reaction kinetics are controlled by a proposed reaction mechanism is first to carry out density functional theory (DFT) calculations to determine the thermodynamic properties of all adsorbed species and transition states, and then to build a microkinetic model to determine the surface coverages by all adsorbed species and the forward and reverse rates of all elementary steps for a range of reaction conditions (1-5). Sensitivity analyses are then carried out using this microkineti...

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“…With all other steps then at QE, appropri- (24) For these steps at QE, the corresponding site fractions, thus, following the LHHW methodology, are …”

Section: Constructing the Rr Graphmentioning

confidence: 99%

“…16 This, despite the fact that accurate prediction of kinetic and thermodynamic parameters on a given catalyst based on first-principles [17][18][19] and/or semi-empirical 20,21 approaches is a significantly more daunting task than it is for gas-phase reactions. Typically, via the microkinetic approach, 1,[22][23][24] these step kinetics are incorporated in species mass balance differential equations for a given reactor, and solved numerically for the unknown concentrations of the surface intermediates, from which the individual rate of each step as well as that of the OR is obtained. The numerical predictions may be finally compared to experimental data, for example, in a parity plot under a variety of operating conditions, 25 to determine if the proposed mechanistic steps and their computed kinetics are valid.…”

Section: Introductionmentioning

confidence: 99%

Ockham's razor for paring microkinetic mechanisms: Electrical analogy vs.Campbell's degree of rate control

2015

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Elucidation of the key molecular steps and pathways in an overall reaction is of central importance in developing a better understanding of catalysis. Campbell's degree of rate control (DRC) is the leading methodology currently available for identifying the germane steps and key intermediates in a catalytic mechanism. We contrast Campbell's DRC to our alternate new approach involving an analysis and comparison of the "resistance" and de Donder "affinity," that is, the driving force, of the various steps and pathways in a mechanism, in a direct analogy to electrical networks. We show that our approach is as just rigorous and more insightful than Campbell's DRC. It clearly illuminates the bottleneck steps within a pathway and allows one to readily discriminate among competing pathways. The example used for a comparison of these two methodologies is a DFT study of the water-gas shift reaction on Pt-Re catalyst published recently.

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Analysis of simple kinetic models in heterogeneous catalysis

Cited by 108 publications

References 69 publications

Synthesis and microstructure of cobalt ferrite nanoparticles

Synthesis and microstructure of cobalt ferrite nanoparticles

Analysis of reaction schemes using maximum rates of constituent steps

Ockham's razor for paring microkinetic mechanisms: Electrical analogy vs.Campbell's degree of rate control

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