Preexponential Factors for Elementary Surface Processes

Zhdanov, Vladimir P.; Pavlı́ček, Jan; Knor, Z.

doi:10.1080/01614948808071752

Cited by 102 publications

(58 citation statements)

References 25 publications

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“…In other words, in order to reproduce the present experimental results, both the preexponential factor and the activation energy for reaction (4) must be large, while those for reaction (5) must be small. In general, the preexponential factor for the decomposition processes on surfaces, such as reaction (4) [28,29]. The present results could not be reproduced by simulations when these typical parameters were assumed.…”

Section: Discussioncontrasting

confidence: 67%

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Catalytic Decomposition of H2O(D2O) on a Heated Ir Filament to Produce O and OH(OD) Radicals

Umemoto¹,

Kusanagi²

2009

TOCPJ

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Production of O atoms, H(D) atoms, and OH(OD) radicals was confirmed in the catalytic decomposition of H 2 O(D 2 O) on a heated Ir filament by laser spectroscopic techniques, such as vacuum-ultraviolet laser-induced fluorescence. The highest steady-state OH density achieved was 2 10 11 cm -3 . The filament temperature dependences of the radical densities were not Arrhenius-type, in contrast to the results on the decomposition of H 2 and O 2 . Especially, OH(OD) density decreased with the increase in the filament temperature over 2100 K. The decomposition process changes from the production of H+OH(D+OD) to that of 2H+O(2D+O) with the increase in the catalysis temperature. This change in the exit channel could not be reproduced by model calculations using the CHEMKIN software package when Arrhenius-type temperature dependences were assumed for the elementary-step rate constants on surfaces. It is necessary to assume that the desorption energy of OH(OD) is surface coverage dependent.

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Section: Discussioncontrasting

confidence: 67%

“…In general, activation energies depend on the surface coverage [28]. For example, the desorption energy of OH radicals from heated Pd surfaces decrease with the increase in the surface coverage [30,31].…”

Section: Discussionmentioning

confidence: 99%

Catalytic Decomposition of H2O(D2O) on a Heated Ir Filament to Produce O and OH(OD) Radicals

Umemoto¹,

Kusanagi²

2009

TOCPJ

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“…(Zhdanov et al 1988 andDumesic et al 1993) expected for rate coefficients corresponding to the elementary steps (1) to (11) in Table 1.…”

Section: Model Constructionmentioning

confidence: 99%

Kinetic modelling of multiple steady-states for the oxidation of aqueous ethanol with oxygen on a carbon supported platinum catalyst

Jelemenský

Kuster

Marin

1996

Chemical Engineering Science

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-Multiple steady-states data were used for the construction of a kinetic model for the oxidation of aqueous ethanol with oxygen on a carbon supported platinum catalyst. A model, incorporating reversible creation of oxygen adatoms on the catalyst surface from surface hydroxyl as well as reversible formation of subsurface oxygen from oxygen adatoms, couid describe quantitatively all the observations. It was essential that the reaction rate coefficients for the formation of atomic and subsurface oxygen strongly depend on the corresponding degrees of coverage introducing positive and negative feedback features. INTRODUCTIONThe selective catalytic oxidation of alcohols and carbohydrates with dioxygen has received considerable attention in the recent past ( Mallat and Balker, 1994). Supported noble metals are the favourite catalysts. The reaction can be performed selectively at relatively mild conditions i.e. in aqueous media at a pH around 7 and at temperatures around 300 K.The major bottleneck for the commercial application consists in so-called catalyst deactivation. Several causes have been put forward for the latter ( Schuurman et al., 1992b;Mallat and Baiker, 1994;Vleeming et al., 1994). There is evidence for well known deactivation mechanisms such as metal dissolution and/or sintering (Schuurman et al., 1992b) and coverage of active sites by side or intermediate products of the desired reaction ( Mallat and Baiker, 1994). A phenomenon more specific to the considered type of reactions has also been suggested. It is referred to as overoxidation of the metal surface. The term stems from the observation that the loss in activity occurs in parallel with an increase of the catalyst potential (Vleeming et al., 1994).Recently steady-state multiplicity of the selective oxidation rate of aqueous ethanol over a platinum on carbon catalyst has been reported (Jelemensky et al., 1995). Up to three stable steady-state rates could be established over a feed ethanol concentration range from 300 to 400 mol m 3 in a continuous flow stirred tank reactor. The upper steady-state was reached by a reductive start-up procedure while the two lower steady-states required an oxidative start-up. The existence of steady-state multiplicity is believed to be rather common for selective oxidations and hydrogenations by noble metals in the liquid phase.Bifurcation phenomena, such as multiple steady-states (R~zon and Schmitz,1987;Zhdanov and Kasemo, 1994), autonomous oscillations ( Gray and Scott, 1990) or chaos ( Scott, 1991) are well documented for heterogeneous catalytic reactions. In the absence of heat and/or mass transport limitations such phenomena have to be caused by purely chemical feedback features such as autocatalysis. The observations of Jelemensky et al. (1995) were free of transport limitations.The present paper concerns the development of an intrinsic kinetic model for the platinum catalyzed selective oxidation of ethanol which allows a quantitative description of the complete set of data reported by Jelemensky et al. (...

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“…(25) and (26) suggest that the chemisorption coefficient for an empty surface would amount around 40 s -1, which is somewhere in the middle of the interval proposed by Zhdanow et al [27]. A sticking coefficient So can be calculated from ra = soFco = kcKpCco(1 -Oo -0co) (27) with ra the adsorption rate and Fco the collision flux.…”

Section: Modelling Results and Interpretationmentioning

confidence: 99%

A quantitative analysis of transient kinetic experiments: The oxidation of CO by O2 over Pt

Hoebink

Huinink

Marin

1997

Applied Catalysis A: General

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Preexponential Factors for Elementary Surface Processes

Cited by 102 publications

References 25 publications

Catalytic Decomposition of H2O(D2O) on a Heated Ir Filament to Produce O and OH(OD) Radicals

Catalytic Decomposition of H2O(D2O) on a Heated Ir Filament to Produce O and OH(OD) Radicals

Kinetic modelling of multiple steady-states for the oxidation of aqueous ethanol with oxygen on a carbon supported platinum catalyst

A quantitative analysis of transient kinetic experiments: The oxidation of CO by O2 over Pt

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