Model Validation Through An Experimental Investigation Of Resonant Behavior For The Catalytic Oxidation Of Carbon Monoxide On Platinum

Graham, William R.C.; Lynch, David T.

doi:10.1016/s0167-2991(09)60099-9

Cited by 6 publications

(5 citation statements)

References 8 publications

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“…When T, is controlling, the same number of cycles will be required for all systems with equal values of T,,/T,. Experimental studies (Graham and Lynch, 1984;Unni et al, 1973) have shown t!iat cycle periods should be approximately the same msgnitude as, or larger than, the dominant characteristic time of the system. This is seen to hold in the rightmost region of Figure then from Equation (lo), 5/R = 1.14 x 10' cycles will be required to reach cycle invariance.…”

Section: S~i 'mentioning

confidence: 99%

“…From an examination of a model, Lynch ( l984a) has shown that the maximum time-average rate during forced cycling occurs for a cycle period which is close to the dominant characteristic time of the system. Experimental studies (Graham and Lynch, 1984;Unni et al, 1973) have shown t!iat cycle periods should be approximately the same msgnitude as, or larger than, the dominant characteristic time of the system. Thus, very small values of R should be avoided.…”

Section: Number Of Cycles To Reach Cycle Lnvariancementioning

confidence: 99%

“…The various symbols are defined in the Nomenclature section. Using the experimental results previously presented by Graham and Lynch (1984), the values of the rate constants are estimated to be K I = 1500, K -l = 0.08/Fc0, K2 = 50 and K3 = 0.06/Fc0, where Fco is the time-average fraction of carbon monoxide in the reactor feed. One result of this is that X, = 1 and Yo = 1 for steady-state operation of the reactor, instead of Fco and Fo2, respectively.…”

Section: K3mentioning

confidence: 99%

“…One result of this is that X, = 1 and Yo = 1 for steady-state operation of the reactor, instead of Fco and Fo2, respectively. As shown by Graham and Lynch (1984), the dimensionless parameters KI , K-I , K2 and K3 can be estimated by using the bifurcation behavior of the reaction system. Using the experimental results previously presented by Graham and Lynch (1984), the values of the rate constants are estimated to be K I = 1500, K -l = 0.08/Fc0, K2 = 50 and K3 = 0.06/Fc0, where Fco is the time-average fraction of carbon monoxide in the reactor feed.…”

Section: K3mentioning

confidence: 99%

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Forced cycling of catalytic reactors: Number of cycles to reach cycle invariance

Lynch

1986

Can J Chem Eng

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Section: S~i 'mentioning

confidence: 99%

Section: Number Of Cycles To Reach Cycle Lnvariancementioning

confidence: 99%

Section: K3mentioning

confidence: 99%

Section: K3mentioning

confidence: 99%

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Forced cycling of catalytic reactors: Number of cycles to reach cycle invariance

Lynch

1986

Can J Chem Eng

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“…In addition, periodic operation can be used to obtain insights into underlying reaction mechanisms. Cutlip (1 979) found that forced composition cycling of the feed stream to a CSTR (continuous stirred tank reactor) resulted in reaction rate enhancement for C O oxidation on a supported platinum catalyst, and for this reaction Cutlip et al (1 983) and Graham and Lynch (1984) have shown that reaction rate enhancement can be partially explained by using models based on Langmuir-Hinshelwood-type mechanisms. Oh et al (1978), however, have shown that a diffusionreaction model, which accounts for surface accumulation, can adequately describe the rate enhancement that was observed when a tubular reactor was used.…”

Section: Introductionmentioning

confidence: 99%

CO oxidation on Pt: Variable phasing of inputs during forced composition cycling

Graham

Lynch

1990

AIChE Journal

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A combined experimental and theoretical investigation of the effect of forced feed composition cycling for CO oxidation on platinum has been performed. A novel approach to forced composition cycling was examined, in which the phase angle between the two input streams was varied. Reaction rate enhancement is shown to occur, and by varying the phasing of the feed streams it is possible to achieve a global maximum in the time-average reaction rate. This phenomenon can be explained quantitatively by a model based on an adsorbate-induced phase change of the Pt surface combined with CO adsorption selfexclusion. This mathematical model can also quantitatively describe the complex steady-state behavior (uniqueness-multiplicity transitions) observed for this reaction. The predictions of the model have been validated further through a detailed experimental study of the effects of feed flow rate, temperature, size of catalyst charge, and cycling frequency on the instantaneous and time-average conversions during forced cycling of the feed composition. IntroductionDespite the apparent simplicity of the reaction, a complete mechanistic description of the C O oxidation on supported platinum has yet to be developed. This lack of knowledge is illustrated vividly by the variety of hypotheses proposed to explain the experimentally observed phenomena. For example, for the phenomenon of self-sustained oscillatory behavior it has been speculated that the oscillations could be due to: competitive adsorption of different types of surface CO (Hugo and Jakubith, 1972); coverage-dependent activation energies (Belyaev et al., 1974;Pikios and Luss, 1977); adsorption of inert (Eigenberger, 1978) or coreacting (Mukesh et al., 1982) species; variation of the catalyst surface temperature (Dagonnier et al., 1980;Jensen and Ray, 1982); kinetic nonlinearities in the reaction mechanism (Morton and Goodman, 198 1); catalyst oxidation/ reduction (Sales et al., 1982); variation of the oxygen sticking probability as a function of CO coverage (Ertl et al., 1982;Lynch et al., 1986); interaction of silicon impurities with the catalyst surface (Yeates et al., 1985); and diffusion of carbon to the catalyst surface (Burrows et al., 1987).Several alternative hypotheses have been postulated even for 1796December 1990 William R. C. Graham David T. LynchDepartment of Chemical Engineering University of Alberta Edmonton, Alberta, Canada T6G 2G6 the much less complex phenomenon of steady-state multiplicity. Hegedus et al. (1977) demonstrated that intrapellet diffusional resistances are important, while Chakrabarty et al. (1984) concluded that the interaction of the surface reaction with the adsorption/desorption processes, in the absence of diffusional limitations, is responsible for the multiplicities. Herskowitz and Kenney (1983) found that each of two quite different LangmuirHinshelwood-Hougen-Watson models could adequately predict the values of CO concentration at which transitions from low to high conversions occurred. Graham and Lynch (1 987) showed th...

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Catalytic oxidation of carbon monoxide under periodic operation

Silveston

1991

Can J Chem Eng

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A growing literature demonstrates resonance of the rate of CO oxidation with frequency of composition switching and that a global increase in rate under composition modulation is possible. Differences are found for the various metal catalysts used: CO oxidation is stimulated at frequencies between 0.1 and 1 .O Hz over noble metals, whereas stimulation occurs at frequencies below 0.05 Hz with oxide catalysts. Multiple resonances with an apparent harmonic relationship, "wrong-way " response, or very slow relaxation to reproducible cycles have been observed. These differences suggest mechanisms through which rate improvements arise are not the same for all catalysts.-.~ ~.Des articles de plus en plus nombreux montrent que la vitesse d'oxydation du CO entre en resonance avec la fr&quence du changement de composition et qu'il est possible d'obtenir une augmentation globale de la vitesse en modulant la composition. On a trow6 des differences en fonction des catalyseurs mktalliques utilises: I'oxydation du CO est stimulCe a des frkquences comprises entre 0, I et 1 ,O Hz sur des mktaux nobles, alors que I'on constate une stimulation a des frequences inferieures a 0,OS Hz avec des catalyseurs a base d'oxyde. On a observe des resonances multiples avec une relation harmonique apparente, une reponse (cwrong-way., ou une relaxation trks lente aux cycles reproductiblcs. Ces differences suggkrent que les mecanismes par lesquels ces augmentations de vitesse se produisent. ne sont pas les m&rnes pour tous les catalyseurs.

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Model Validation Through An Experimental Investigation Of Resonant Behavior For The Catalytic Oxidation Of Carbon Monoxide On Platinum

Cited by 6 publications

References 8 publications

Forced cycling of catalytic reactors: Number of cycles to reach cycle invariance

Forced cycling of catalytic reactors: Number of cycles to reach cycle invariance

CO oxidation on Pt: Variable phasing of inputs during forced composition cycling

Catalytic oxidation of carbon monoxide under periodic operation

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