Steps in CH<sub>4</sub> oxidation on Pt and Rh surfaces: High‐temperature reactor simulations

Hickman, Daniel A.; Schmidt, L.D.

doi:10.1002/aic.690390708

Cited by 332 publications

(219 citation statements)

References 49 publications

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“…The CRR mechanism is also supported by Ashcroft and co-workers, Lunsford and co-workers, and other researchers [1,2,8-10,]. However, Hickman and Schmidt, Hu, Qin and Shen et al claimed [11][12][13][14][15][16] that the POM reaction should follow a direct oxidation route, in which methane first dissociates to generate hydrogen and carbon, then H 2 desorbs and carbon is oxidized to carbon monoxide by surface oxygen species. Thus, H 2 and CO are the primary products in the DPO mechanism.…”

Section: Introductionmentioning

confidence: 74%

Mechanism for catalytic partial oxidation of methane to syngas over a Ni/Al2O3 catalyst

2002

Fuel and Energy Abstracts

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The mechanism of catalytic partial oxidation of methane to syngas (POM) over a Ni/␣-A1 2 O 3 catalyst was studied by using a pulse reactor and temperature-programmed surface reaction (TPSR) techniques. Over a reduced nickel catalyst (Ni 0 /A1 2 O 3 ), methane activation follows the dissociation mechanism; while on oxidic nickel catalysts (NiO/Al 2 O 3 ), methane is first oxidized to carbon dioxide and water, and simultaneously, NiO is reduced to Ni 0 . CH 4 dissociation occurs over Ni 0 active sites, generating hydrogen and surface C species. A transient process was observed during the CH 4 /O 2 reaction. The nickel valence was transformed from NiO to Ni 0 at a certain critical temperature and simultaneously, the reaction was transformed rapidly from the complete oxidation of methane to the partial oxidation of methane. It has been found that the POM reaction takes place over a thin layer of the catalyst bed. This reaction zone is nearly isothermal, over which almost 100% of oxygen and more than 90% of methane are converted. The temperature drop in the downstream of the catalyst bed does not imply that the steam or carbon dioxide reforming reaction occurs in the lower part of the bed. Ni 0 species constitute the active sites for the partial oxidation of methane to syngas. Both methane and oxygen are activated on Ni 0 sites, generating surface Ni· · · C and Ni δ+ · · · O δ− species. These two kinds of intermediates have been proposed to account for the mechanism of methane partial oxidation. The Ni δ+ · · · O δ− species over Ni 0 catalyst surface is considered to be a kind of weakly bounded, mobile oxygen species. The reaction between Ni δ+ · · · O δ− and Ni· · · C intermediates generate the primary product of CO. However, the presence of NiO over the catalyst surface significantly reduces the CO selectivity. Thus, the NiO species are not possible to be the intermediate for the POM reaction. The mechanism of partial oxidation of methane should follow the direct oxidation route.

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Section: Introductionmentioning

confidence: 74%

Mechanism for catalytic partial oxidation of methane to syngas over a Ni/Al2O3 catalyst

2002

Fuel and Energy Abstracts

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“…Beginning with the work of Hickman and Schmidt (1993), kinetic models for reactions of methane on rhodium have been developed via a combination of theoretical methods, fits to available experimental data, and previous analyses of related species. (Deutschmann et al, 2001;Hartmann et al, 2010;McGuire et al, 2011).…”

Section: Proposed Elementary Reactionsmentioning

confidence: 99%

Bayesian inference of chemical kinetic models from proposed reactions

Galagali

Marzouk

2015

Chemical Engineering Science

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Bayesian inference provides a natural framework for combining experimental data with prior knowledge to develop chemical kinetic models and quantify the associated uncertainties, not only in parameter values but also in model structure. Most existing applications of Bayesian model selection methods to chemical kinetics have been limited to comparisons among a small set of models, however. The significant computational cost of evaluating posterior model probabilities renders traditional Bayesian methods infeasible when the model space becomes large. We present a new framework for tractable Bayesian model inference and uncertainty quantification using a large number of systematically generated model hypotheses. The approach involves imposing point-mass mixture priors over rate constants and exploring the resulting posterior distribution using an adaptive Markov chain Monte Carlo method. The posterior samples are used to identify plausible models, to quantify rate constant uncertainties, and to extract key diagnostic information about model structuresuch as the reactions and operating pathways most strongly supported by the data. We provide numerical demonstrations of the proposed framework by inferring kinetic models for catalytic steam and dry reforming of methane using available experimental data.

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“…In particular oxidation reactions over noble metals have been modeled extensively such as of hydrogen [38][39][40][41][42][43][44] , CO [45][46][47] , and methane [31,[48][49][50][51][52] and ethane [22,26,53,54] over Pt, formation of synthesis gas over Rh [52,55] . Lately, mechanisms have been established for more complex reaction systems, for instance, three-way catalysts [56] or Chemical Vapor Deposition (CVD) reactors for the formation of diamond [57,58] , silica [59] , and nanotubes [60] .…”

Section: B Development Of Multi-step Surface Reaction Mechanismsmentioning

confidence: 99%

Computational Fluid Dynamics Simulation of Catalytic Reactors

Deutschmann

2008

Handbook of Heterogeneous Catalysis

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Catalytic reactors are generally characterized by the complex interaction of various physical and chemical processes. Monolithic reactors can serve as example, in which partial oxidation and reforming of hydrocarbons, combustion of natural gas, and the reduction of pollutant emissions from automobiles are frequently carried out. Figure 1 illustrates the physics and chemistry in a catalytic combustion monolith that glows at a temperature of about 1300 K due to the exothermic oxidation reactions. In each channel of the monolith, the transport of momentum, energy, and chemical species occurs not only in flow (axial) direction, but also in radial direction. The reactants diffuse to the inner channel wall, which is coated with the catalytic material, where the gaseous species adsorb and react on the surface. The products and intermediates desorb and diffuse back into the bulk flow. Due to the high temperatures, the chemical species may also react homogeneously in the gas phase. In catalytic reactors, the catalyst material is often dispersed in porous structures like washcoats or pellets. Mass transport in the fluid phase and chemical reactions are then superimposed by diffusion of the species to the active catalytic centers in the pores. The temperature distribution depends on the interaction of heat convection and conduction in the fluid, heat release due to chemical reactions, heat transport in the solid material, and thermal radiation. If the feed conditions vary in time and space and/or heat transfer occurs between the reactor and the ambience, a non-uniform temperature distribution over the entire monolith will result, and the behavior will differ from channel to channel.Today, the challenge in catalysis is not only the development of new catalysts to synthesize a desired product, but also the understanding of the interaction of the catalyst with the surrounding reactive flow field. Sometimes, the exploitation of these interactions can lead to

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Steps in CH₄ oxidation on Pt and Rh surfaces: High‐temperature reactor simulations

Abstract: The direct oxidation of CH, to H, and CO

Cited by 332 publications

References 49 publications

Mechanism for catalytic partial oxidation of methane to syngas over a Ni/Al2O3 catalyst

Mechanism for catalytic partial oxidation of methane to syngas over a Ni/Al2O3 catalyst

Bayesian inference of chemical kinetic models from proposed reactions

Computational Fluid Dynamics Simulation of Catalytic Reactors

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Steps in CH4 oxidation on Pt and Rh surfaces: High‐temperature reactor simulations

Abstract: The direct oxidation of CH, to H, and CO

Cited by 332 publications

References 49 publications

Mechanism for catalytic partial oxidation of methane to syngas over a Ni/Al2O3 catalyst

Mechanism for catalytic partial oxidation of methane to syngas over a Ni/Al2O3 catalyst

Bayesian inference of chemical kinetic models from proposed reactions

Computational Fluid Dynamics Simulation of Catalytic Reactors

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Steps in CH₄ oxidation on Pt and Rh surfaces: High‐temperature reactor simulations