On the Status of Catalytic Reaction Engineering

Carberry, James J.; Butt, John

doi:10.1080/01614947408079630

Cited by 54 publications

(61 citation statements)

References 43 publications

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“…In other words, the functionalized tubule is less stiff in the direction of the tubule axis than the clean tubule and so will deform more easily in a composite. When similar simulations were carried out on other armchair tubules ranging from a (5, 5) to a (25,25), similar results were found [21]. In addition, studies on (10, 0) and (17, 0) tubules showed no dependence of the results on helical symmetry.…”

Section: The Decoration Of Carbon Nanotubulessupporting

confidence: 66%

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Molecular dynamics simulations of the filling and decorating of carbon nanotubules

Mao¹,

Garg²,

1999

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Abstract. Carbon nanotubes (CNTs) have been proposed as excellent materials for the construction of new, precisely tailored ultrafiltration membranes and as promising fibres for the construction of new, stronger composite materials. In this paper classical molecular dynamics simulations are used to investigate the potential use of CNTs in these applications. Functional groups have been covalently attached to the walls of CNTs to provide more extensive interactions between these new fibres and a polymer matrix. We examine the effects of these attachments on the mechanical properties of the tubules. The diffusive molecular flow of methane, ethane and ethylene through single tubules at room temperature are also studied. The simulations predict normal-mode molecular diffusion for methane. However, diffusion that is intermediate between normal-mode and single-file diffusion is predicted for ethane and ethylene. These diffusion results are found to be similar to results predicted for molecular diffusion in zeolites.

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Section: The Decoration Of Carbon Nanotubulessupporting

confidence: 66%

“…However, diffusion in these nanometre-scale structures is expected to be most important for applications such as shape selective catalysis [25] and separations [26]. Nivarthi et al [27] and Gupta et al [28] have modelled the diffusion of methane and ethane, respectively, in AlPO 4 -5.…”

Section: Introductionmentioning

confidence: 99%

Molecular dynamics simulations of the filling and decorating of carbon nanotubules

Mao¹,

Garg²,

1999

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“…This can be done by considering the bimolecular Langmuir-Hinshelwood kinetic model, widely used in gas-solid catalysis, which also exhibits the same abnormal behavior mentioned above. 22 In the case when one of the reactants is present in large excess while the other is strongly adsorbed on the catalyst active sites, this kinetic model leads to the dimensionless rate expression CCC 0006-3592184l121508-03$04.00 which can be compared with the equivalent form of eq. (1):…”

Section: General Behavior Of Substrate-inhibited Reactionsmentioning

confidence: 99%

Optimal distribution of immobilized enzyme in a pellet for a substrate‐inhibited reaction

Morbidelli¹,

Servida²,

Varma³

1984

Biotech & Bioengineering

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The possibility of using nonuniform distributions of immobilized enzyme in porous supports has recently been examined by various investigators (ref. l), as an attempt to improve enzyme effectiveness. For reactions with Michaelis-Menten kinetics operating in the masstransfer controlled regime, Horvath and Engasser2y3 have shown that enzyme effectiveness could be significantly improved by locating the enzyme in an outer shell of the inert support. An enzyme distribution of this type reduces the substrate diffusion path, which enhances the overall reaction rate, by maintaining high concentration of the substrate where the enzyme is located.More recently, Park and co-workers4 have pointed out that this same nonuniform enzyme distribution is actually the best for all reactions of positive order with respect to the substrate. These authors also investigated the case of substrate-inhibited reactions, using the kinetic model proposed by Haldane.s Many reactions of practical import fall in the case,(' such as hydrolysis of sucrose by in~e r t a s e ,~ hydrolysis of benzil penicillin by amidase,8 and phenol d e g r a d a t i~n .~ A general kinetic expression for substrate-inhibited reactions can be written as followslO( 1) where k ( x ) is the reaction rate constant which depends on enzyme concentration, and thus in the case of nonuniformly distributed matrix, on position within the pellet. Parameter K is the Michaelis-Menten constant, K' is a substrate-inhibition constant, and K " is a constant which basically accounts for the residual reaction rate which some systems exhibit at very large substrate concentration. 10 It may be noted that this expression includes as particular cases several widely used kinetic models, such as the first-order ( K " = 0; K' = 0; K >> S ) , the MichaelisMenten or Monod ( K " = 0; K' = O), and the Haldane ( K " = 0) kinetics. GENERAL BEHAVIOR OF SUBSTRATE-INHIBITED REACTIONSAs indicated by eq. ( l ) , substrate-inhibited reactions exhibit the abnormal feature of a maximum in the rate as the substrate concentration is varied. Thus, for relatively low concentrations of the substrate, the reaction rate increases as the substrate concentration increases. However, as the substrate concentration increases further, the rate first reaches a maximum and then continuously decreases. This feature leads to multiple operating steady states under certain isothermal conditions, and this specific aspect of the problem has received considerable attention in the This peculiar behavior of the reaction rate function also implies that an improved pellet effectiveness can be obtained if the enzyme is located in a zone within the interior of the support, rather than on its outer shell. Such an enzyme distribution would take advantage of reaction rate enhancement that would occur purely as a result of decreased concentration of the substrate caused by diffusional resistance. This intuitive result has been confirmed by Park and c o -~o r k e r s ,~ by numerically computing the effectiveness of enzyme immobilized in ...

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“…As mentioned above, the surface heterogeneity can lead to a signiÿcant decrease of the oxidation rate since the chemisorption depends strongly on the oxygen coverage. Therefore, in agreement with the Brunauer, Love and Keenan equation for the adsorption rate constant on non-ideal surface (Carberry, 1976), activity sites distribution is introduced, assuming an exponential decrease of the rate constant with the occupied O-(Ni) sites:…”

Section: Modellingmentioning

confidence: 99%

“…(8). The physical bases for this assumption can be surface heterogeneity, lateral interaction between adsorbed-species or a combination of them (Carberry, 1976;Do, 1998).…”

Section: Modellingmentioning

confidence: 99%

Mathematical modelling of the unsteady-state oxidation of nickel gauze catalysts

Monnerat

Kiwi‐Minsker

Renken

2003

Chemical Engineering Science

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The oxidation of nickel gauze catalysts by O2 was investigated by transient response methods. Qualitative description of the experimental transient responses have shown that the oxidation of metallic nickel proceeds in two stages. The ÿrst step is a fast dissociation of gaseous oxygen on the catalytic surface, followed by oxygen di usion from the surface into the bulk. This slow second step explains the long tailing observed from the experimental transient responses. Furthermore, a rise of temperature was observed during the nickel oxidation. A kinetic model has been developed on the basis of the experimental results in order to provide quantitative information about this reaction. For nickel gauze oxidation, a non-isothermal model combining the subsurface oxygen di usion with an exponential distribution for the activity of surface sites gave a good agreement with experimental transient data. As a result, the activation energies and the pre-exponential factors of the rate constants as well as the characteristic oxygen di usion times were determined. ?

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On the Status of Catalytic Reaction Engineering

Cited by 54 publications

References 43 publications

Molecular dynamics simulations of the filling and decorating of carbon nanotubules

Molecular dynamics simulations of the filling and decorating of carbon nanotubules

Optimal distribution of immobilized enzyme in a pellet for a substrate‐inhibited reaction

Mathematical modelling of the unsteady-state oxidation of nickel gauze catalysts

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