Bond order conservation - Morse

In addition to reaction energies, activation barriers are also important in interpreting reaction processes. It is, of course, difBcult to locate transition states for surface reactions. In order to circumvent the problem, Shustorovich [78] and Shustorovich and Sellers [82] have developed the bond order conservation-Morse potential (BOC-MP) and UBI-QEP methods, respectively, to predict accurately activation energies for dissociations or combinations of adsorbates on metal surfaces. For the dissociation reaction of CHxOHads or H2O, the activation energy is given by... 

Bond Order Conservation-Morse Potential (BOC-MP) formalism is used to study the change in activation energy for different elementary steps involving all possible chemical species on any metallic smrface in order to identify optimum catalysts for the production of methane, methanol or ethylene from synthesis gas. All possible steps are analyzed for the methanation reaction. It is assumed that the reaction occurs on pure metallic surfaces, thus, the influence of the support or promoters is not taken into account. The method suggests that Ni is a more selective for methanation reaction, in agreement with the fact that Ni/SiOz is the real catalyst used industrially. On the other hand on the surface of Fe or W the reaction may residt in the formation of adsorbed C, also in agreement with experiment. 

The semi-empirical methods referred to as bond-order conserving Morse potential (BOC-MP) or the unity bond index quadratic exponential potential (UBI-QEP) method have been reviewed extensively by Shustorovich and Sellers [145]. The UBI-QEP method is, like some of the empirical methods mentioned above, also based on the use of atom-atom interaction potentials, and here again a Morse form is convenient... 

H. Sellers. A bond order conservation-Morse potential model of adsorbate-surface interactions Dissociation of H2, 02, and F2 on the liquid mercury surface. J. Chem. Phys. 99,1993, 650-655. 

Before leaving this section, we should mention the application of simple bond-order conservation models (Shustorovich 1985, 1986, 1987, 1988) to molecule-surface PESs. In this model, one assumes that each gas atom-surface atom bond is a simple Morse potential, yielding the total interaction between A-S as ... 

A second approach which may be attractive for more complex surface systems involves the application of the Bond Order Conservation model that was developed by Shustorovich and co-workers . The BOC model treats the interaction between the adsorbate and the surface atom through the use of a Morse potential. The total heat of adsorption is then described by summing all interactions. The BOC model is based on the concept that the bonding potential for every atom in the system is conserved. The heat of adsorption for an atomic species A is described by the following expression ... 

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