Langmuir-Hinshelwood kinetic model

Mann, Thurgood, and coworkers—Langmuir-Hinshelwood kinetic model for methanol steam reforming and WGS over Cu/Zn. Mann et al.335 published a complex Langmuir-Hinshelwood model for CuO/ZnO catalysts based on what one would encounter for a methanol steam reformer (MSR) for fuel cell applications. The water-gas shift rate, containing all MSR terms, was determined to be ... 

Wheeler, Schmidt, and coworkers—kinetic model for Pt/Ce at short contact times over medium to high T range. In 2004, Wheeler and coworkers422 reported on the water-gas shift reaction over Pt/ceria at short contact times (0.008-0.05 sec) for temperatures between 300 and 1000 °C. The reactant composition for CO, H2, and H20 was 1/2/4. A Langmuir-Hinshelwood kinetic model was used to adequately fit the medium and high temperature shift data ... 

Removal rates greater than 90% were observed for all of the phenols studied. The decay kinetics for phenol p-methoxyphenol p-cresol p-fluo-rophenol p-chlorophenol p-bromophenol 4-hydroxyacetophenone a,a,a-trifluoro-p-cresol p-cyanophenol and p-iodophenol were found to be consistent with the Langmuir-Hinshelwood kinetic model. After employing all the substituents, little variation on the Langmuir-Hinshelwood kinetic parameters was observed. 

The Langmuir-Hinshelwood kinetic model describes a reaction in which the rate-limiting step is reaction between two adsorbed species such as chemisorbed CO and 0 reacting to form C02 over a Pt catalyst. The Mars-van Krevelen model describes a mechanism in which the catalytic metal oxide is reduced by one of the reactants and rapidly reoxidizd by another reactant. The dehydrogenation of ethyl benzene to styrene over Fe203 is another example of this model. Ethyl benzene reduces the Fe+3 to Fe+2 whereas the steam present reoxidizes it, completing the oxidation-reduction (redox) cycle. This mechanism is prevalent for many reducible base metal oxide catalysts. There are also mechanisms where the chemisorbed species reacts... 

This paper shows the results of birch char gasification experiments with CO2 and CO. Kinetics for both n order model and Langmuir-Hinshelwood kinetic model have been obtained. The evolution of reactivity with degree of conversion is also studied, as well as the relevance of the ratio CO/CO2. 

CO addition has an inhibition effect on the COj gasification reaction. The Langmuir-Hinshelwood kinetics model fits well the results. 

Of course, the Eley-Rideal mechanism is a likely pathway at high reaction temperature, whereas the Langmuir-Hinshelwood mechanism is realized at low temperature, when the precursor concentration remains sufficient. The importance of reactant preadsorption on a given surface can be probed by the use of a Langmuir Hinshelwood kinetic model [91-93]. With the assumptions for this model the surface coverage (0) is related to the initial pressure of reactant (P) and to the apparent adsorption equilibrium constant K ... 

Skrzypek el al. mode (19H5) Skrzypek el al. (1985) developed this model based on the Langmuir-Hinshelwood-Hougen-Watson kinetic model to explain the non-monotonic behaviour observed by Calder-bank (1974). They suggested that the reaction rate behaviour can be related to the Langmuir-Hinshelwood kinetic model for bimolecular reactions, where the surface reaction between o-Xylene and oxygen chemisorbed on the active centers is the rate determining step. The rate of appearance of various components can be written as ... 

If the rate of degradation is identified with the trne rate constant k) of the Langmuir-Hinshelwood kinetic model, the determination of K is straightforward ... 

The Langmuir Hinshelwood kinetic model based on this reaction scheme is formulated assuming that all reactions are in equilibrium except for reaction steps (2), (4), (7) and (11). Reaction steps (2), (4) and (7) are all steps which may be slow during the shift reaction [5,6], whereas reaction step (11) represents the slow step for methanol synthesis [8], The kinetic and thermodynamic parameters are taken from available Cu single crystal experiments. We call this type of model a static microkinetic model since the number of active sites are assumed constant (i.e., independent of reaction conditions) [21]. 

Equation 5.60 demonstrates the combination of Langmuir adsorption isotherm and kinetics which are first-order in the adsorbed species, and is called the Langmuir-Hinshelwood kinetic model. 

The kinetics of the hydrodenitrogenation (HDN) of o-toluidine was studied over alumina-supported sulfided timgsten catalysts prepared from tetrathiotungstate. The Langmuir-Hinshelwood kinetic model was used to fit the data. The kinetic parameters were obtained by varying the initial reactant partial pressure and the reaction temperature. Fluorination of alumina increased the HDN rate constant, decreased the adsorption constant of o-toluidine, and increased the activation energies and the preexponential factors. 

The results from this chapter on zeolite catalysis provide a good reference point for the discussion presented later Chapter 8 where we compare heterogeneous catalysis and biocatalysis. The similarity between the Michaelis-Menten kinetic expression for enzyme catalysis and the Langmuir-Hinshelwood kinetic models for heterogeneous catalysis are noted. This ultimately derives from the conservation in the number of active reaction centers for both systems. However, the more refined synergy of the activation of molecular bonds by the enzyme will become apparent as a major difference between the two. 

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