Langmuir-Hinselwood mechanism

MD simulations of Si film growth also have revealed a Langmuir-Hinselwood mechanism of hydrogen removal from the growth surface (Ramalingam, 2000). This mechanism involves reaction of an adsorbed SiH,... 

In other processes that involve two adsorbed species that react (for instance, Langmuir-Hinselwood mechanisms), the dependence of the reaction rate with the adsorption energy is more compKcated since two adsorption energies are involved. For this case, the ideal electrocatalyst is the one that has intermediate adsorption energy for both adsorbed species. If the chemistry of the two adsorbed species is different, which is normally the case, it is difficult to find a surface that has the right combination of adsorption energies for both species. 

CO oxidation (among other oxidation reactions of interest in electrocatalysis) belongs to this type of reactions. It has been normally proposed that adsorbed CO reacts through a Langmuir-Hinselwood mechanism with adsorbed OH from water dissociation. Therefore, this reaction... 

It is very difficult to connect the catalyst structure with reaction kinetics, however, and this remains a challenge for the XXI century. There are two main reactivity models the Langmuir-Hinselwood mechanism that involves reaction by interaction between two surface-bonded substrate atoms in the rate-determining step, and the Rideal-Eley mechanism that involves interaction between a surface-bonded substrate atom and a molecule in the gas phase in the rate-determining step. Most reactions have kinetics that are consistent with the first model. ... 

Citral has three sites of hydrogenation and as shown in (Fig. 1) the mechanism for its reduction is complex. However we have shown previously (ref. 3) that, after the elimination of time as an independent variable, the LANGMUIR-HINSELWOOD rate equation for each component in the liquid phase can be integrated. The integrated equations B = f( A ), C = g( 8 ), i01 = h ( B ), E = i ( B ) and F = j( 8 ) depend on six ratios k g/k, k /k, kgb g/k b. ... k bp/k b which have been computed simultaneously. The agrement between the calculated product compositions as a function of hydrogen consumed and the experimental data is excellent as illustrated in (Fig. 2). Therefore the computed ratio k o /kjb for each step has been used as selectivity criteria. 

Pt has been one of the most well characterized materials due to its distinguished chemical properties and outstanding performance in catalytic reactions [32, 33]. Also, CO oxidation is one of the most standard surface chemical reactions. As a standard model to explain the adsorption and dissociation processes of molecules on Pt surface, Langmuir-Hinselwood (L-H) mechanism has been widely accepted [34], In L-H mechanism, chemical reactions take place in most efficient manner when the surface remains as clean metallic state. That is, the most reactive surface is metallic surface. For example, in the case of CO oxidation, oxygen molecnles make contact to metal surface and get dissociated into surface atonfic oxygen. Then, this surface oxygen reacts to CO molecule to form CO2. During this process, surface remains clean and there is no residue remains on the surface. In the past, many stnd-ies of model system under low-pressure experiments have demonstrated the validity of L-H model. 

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