Bonding Eley-Rideal mechanism

Other DFT calculations have shown that co-adsorption of H2O and O2 on Aug clusters, free or supported on MgO(lOO), leads to the formation of an 02- -H20 complex involving partial proton sharing or proton transfer, and leading to a hydroperoxy-like complex (HO2) [178]. This favors the activation of the 0—0 bond, i.e. the bond extension to values characteristic of a peroxo- or superoxo-Uke state. Consequently, the reaction with CO can occur with a small activation barrier of -0.5 eV, either through an Eley-Rideal mechanism if O2 is adsorbed on the top face of Aug clusters or through a Langmuir-Hinshelwood mechanism if O2 is adsorbed on the periphery of the cluster. 

It is assumed that this is also a rate determining step for the overall reaction. The activation energy of reaction (4) and the site density of oxygen active centers were the only adjustable parameters of the model. In general, a C-H bond scission for reactants and products of the methane dimerization process occurs by an Eley-Rideal (E-R) type mechanism to form a gas-phase alkyl radical and a hydroxyl surface site (HO ) ... 

An oxidation mechanism of the carbon monoxide following the Eley-Rideal model is realistic if we consider the existence of a weakly bonded oxygen species and, subsequently, extremely reactive oxygen species. Nevertheless, it seems that... 

Many catalyzed surface reactions can be treated as a two-step process with an adsorption equilibrium followed by one rate-determining step (diffusion, surface reaction, or desorption). The surface reaction kinetics are usually discussed in terms of two limiting mechanisms, the Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms. In the LH mechanism, reaction takes place directly between species which are chemically bonded (chemisorbed) on the surface. For a bimolecular LH surface reaction. Aawith competitive chemisorption of the reactants, the rate of reaction is given by the following expression ... 

D2 may also be considered to be in some kind of a weakly adsorbed state. It will be noted that one D atom is never bonded to the surface in any minimum Gibbs energy intermediate. It is recommended that the term Rideal or Rideal-Eley mechanism be reserved for this particular elementary process. However, the term has been used for analogous processes in which there is a reactant molecule and a product molecule of nearly the same energy in the fluid phase or in some weakly adsorbed state and in which one or more atoms are never bonded to the surface. An example is the following elementary process... 

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. ... 

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