Chemisorption model representation

The different contributions to the HF, BLYP and B3LYP interaction energy of CO on the Pt 3(7,3,3) cluster model representation of the Pt(lll) surface as obtained at the various steps of the CSOV method are reported on Figure 2. The most important result of this comparison is that the qualitative picture of the chemisorption bond arising from ab initio HF and DFT quantum chemical approaches is essentially the same the relative importance of the different mechanisms remaining unchanged. This is an important conclusion because it validates many previous analysis of the chemisorption bond carried out in the framework of Hartree-Fock cluster model wave functions. " ... 

Chemisorption is a phenomenon of importance in catalysis which may be treated by MO theory. Experimental studies have been carried out for a variety of systems, but theoretical descriptions of the electronic features of chemisorption beyond simple considerations are in a primitive stage. There are several factors responsible for this state of affairs. One is, of course, the complexity of the substrate system to be modeled, which has forced theorists to work with a small-size representation for the surface, as implied by the surface molecule concept of localized interactions. Although some early work has been done by... 

Figure 5. Schematic representation of the bridge, BS, tetrahedral hollow site, HS, and octahedral, FS, active sites considered for H2 dissociative chemisorption. The M o cluster model depicted in the figure can either represent Pd o, Cuio, Pd4Cu6 or the two first layers of PdCun. In the two former cases all atoms are equal. In Pd4Cu6 the first layer central atom and those on the second layer are Pd and the six remaining atoms on the first layer are Cu and, finally, in PdCui2 the first layer central atom is Pd and all remaining atoms are Cu.

Fig. 3.11. Schematic representation of the reverse-spillover for gas molecules impinging on a Pd/MgO model catalyst. (1) Reflection from the MgO, (2) adsorption-desorption from the MgO, (3) direct chemisorption on the Pd cluster, (4) capture by a Pd cluster of a molecule physisorbed on the MgO...

In this paper, I review the recent advances and developments of first-principle quantum chemical methods and discuss their application to modelling chemisorption, surface reactivity of reactants/intermediates, and the catalytic behavior for a series of relevant commercial chemistries. We focus primarily on the static representation of the surface. 

For the interlayer transition probabilities in the model of chemisorption with precursor (Dubrovskiy and Zyryanov 1987) one can use a simple representation (with / ,/ = 1,2,3 standing for the chemisorption, physisorption, and gas phase layers respectively)... 

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