Chemisorption cluster models

Rdsch N, Sandl P, Gorling A and Knappe P 1988 Toward a chemisorption cluster model using the LCGTO-Xa method application to Ni(100)/Na Int. J. Ouantum Chem. Symp. 22 275... 

Duarte H A and Salahub D R 1998 Embedded cluster model for chemisorption using density functional calculations oxygen adsorption on the AI(IOO) surface J. Chem. Phys. 108 743... 

The Characterization and Properties of Small Metal Particles. Y. Takasu and A. M. Bradshaw, Surf. Defect. Prop. Solids p. 401 1978). 2. Cluster Model Theory. R. P. Messmer, in "The Nature of the Chemisorption Bond G. Ertl and T. Rhodin, eds. North-Holland Publ., Amsterdam, 1978. 3. Clusters and Surfaces. E. L. Muetterties, T. N. Rhodin, E. Band, C. F. Brucker, and W. R. Pretzer, Cornell National Science Center, Ithaca, New York, 1978. 4. Determination of the Properties of Single Atom and Multiple Atom Clusters. J. F. Hamilton, in "Chemical Experimentation Under Extreme Conditions (B. W. Rossiter, ed.) (Series, "Physical Methods of Organic Chemistry ), Wiley (Interscience), New York (1978). 

Pacchioni G, Illas F. 2003. Electronic structure and chemisorption properties of supported metal clusters model calculations. In Wieckowski A, Savinova ER, Vayenas CG. editors. Catalysis and Electrocatalysis at Nanoparticle Surfaces. New York Marcel Dekker. 

Nalewajski, R. F. and A. Michalak. 1995. Use of charge sensitivity analysis in diagnosing chemisorption clusters Minimum-energy coordinate and Fukui function study of model toluene-[V205] Systems. Int. J. Quantum Chem. 56 603-613. 

Quantum-chemical cluster models, 34 131-202 computer programs, 34 134 methods, 34 135-138 for chemisorption, 34 135 the local approach, 34 132 molecular orbital methods, 34 135 for surface structures, 34 135 valence bond method, 34 135 Quantum chemistry, heat of chemisorption determination, 37 151-154 Quantum conversion, in chloroplasts, 14 1 Quantum mechanical simulations bond activation, 42 2, 84—107 Quasi-elastic neutron scattering benzene... 

Another quite different area where ECP s have proven to be very useful for the development of transition metal cluster models. By using a very simplified description of the metal atoms, where all electrons including the d-electrons are considered as core, certain properties of the solid material such as chemisorption on metal surfaces or the reactivity of metal clusters has been studied theoretically with considerable success. 

A proposal for the proper use of pseudopotentials in molecular orbital cluster model studies of chemisorption , J.Chem.Phys. 81, 3594... 

Gropen,0., Almlof,J. and Wahlgren,U. (1991) Model studies of chemisorption on Pt surfaces , in Cluster Models for Surface and Bulk Phenomena,... 

Figure 1. Cluster models employed for the study of chemisorption of carbonate (a) Pt13(7,3,3) (b)Ptlg12,6). Darker atoms define the "local" region, see text.

For Si(l 11)-(7 x 7), various possible physisorption and chemisorption geometries have been discussed in the framework of a Si25H24PH3 cluster model.54... 

It seems of interest to compare the covalent and ionic cluster models as applied to the same system. Such a comparison was made within the scope of CNDO/2 calculations of some characteristics of surface hydroxyls of Si02 (3magnetic resonance parameters of surface sites (39), and chemisorption (40). Though somewhat different, the results obtained within these models were quite close. Nevertheless, to make a more categorical conclusion, more extensive studies are required. It is likely that in several cases the close-packed oxide structures would be better represented by stoichiometric clusters (e.g., Mg2 02n), although even in these cases it seems appropriate to take into account the Madelung field of the nearest part of the resting lattice. 

Fig. 10. Cluster model of the coordinative chemisorption of an NH3 molecule on (a) the face and (b) the edge of a silicon-oxygen tetrahedron in Si02.

The first direct quantum-chemical calculations used too simplified cluster models, sometimes as simple as a single metal ion. Such an approximation is obviously too poor for chemisorption computations. Thus, comparative calculations by Sauer et al. (54) have shown, for instance, that the neglect of the environment of a cation may result in overestimating the interaction energy by several times. 

Cluster modeling of possible chemisorption states and of possible intermediate states in surface reactions can to a first approximation be useful in guiding experiments or interpretations of experimental data for surface reactions (23-25). One important and enlightening result (6, 26, 27) in metal carbide cluster chemistry will be used here to illustrate this particular point because it bears directly on the importance of multicenter C-H-M bonding for hydrocarbon fragments in metal chemistry. 

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. " ... 

This section reports a series of examples of application of the cluster model approach to problems in chemisorption and catalysis. The first examples concern rather simple surface science systems such as the interaction of CO on metallic and bimetallic surfaces. The mechanism of H2 dissociation on bimetallic PdCu catalysts is discussed to illustrate the cluster model approach to a simple catalytic system. Next, we show how the cluster model can be used to gain insight into the understanding of promotion in catalysis using the activation of CO2 promoted by alkali metals as a key example. The oxidation of methanol to formaldehyde and the catalytic coupling of prop)me to benzene on copper surfaces constitute examples of more complex catalytic reactions. 

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.

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