Adsorption on metal clusters

The quantitative analysis of adsorption on metal clusters, as discussed earlier, can be sensitive to the cluster chosen to model the chemisorption site. In a systematic series of studies, we examined the adsorption of various atomic and molecular adsorbates on different metal surfaces. We found that it was important to optimize 1) size, 2) structural configuration, 3) spin state, and... 

From the theoretical standpoint the above issues are addressed by quantum chemistry. On the basis of calculations of various cluster models [191] the properties of surfaces of solid body are being studied as well as issues dealing with interaction of gas with the surface of adsorbent. However, fairly good results have been obtained in this area only to calculate adsorption on metals. The necessity to account for more complex structure of the adsorption value as well as availability of various functional groups on the surface of adsorbent in case of adsorption on semiconductors geometrically complicates such calculations. 

Adsorption of ions or molecules on metal clusters markedly affects their optical properties. It was shown that the intensity and the shape of the surface plasmon absorption band of silver nanometric particles, which is close to 380 nm, change upon adsorption of various substances [125]. The important damping of the band generally observed is assigned to the change of the electron density of the thin surface layer of the... 

This area has received special attention from theoreticians. The most commonly used methodology for the calculation of the particle(ion)-metal interaction is to approximate the metal surface with a cluster of several atoms with the crystallographic organization typical of the metal studied. Although such an approach has many limitations and introduces certain difficulties, cluster-model calculations are becoming more popular in studies of interfacial interactions. Section 3.10.2 gives a brief review of quantum studies related to adsorption on metal surfaces in the cluster model approximation. In Section 3.10.3 a more detailed analysis of some aspects of this methodology is described, and is related to some recently published work on the problem of specific adsorption phenomenon. 

The reasons for studying the adsorption of atoms and molecules on metal clusters are twofold. First, supported metal catalysts may involve rather small metal crystallites, although usually not... 

There have been a number of calculations of adsorption of atoms on metal clusters which aim to rationalise or supplement the results of experiments on single metal crystals. Many of these concern the electronic distribution at the surface, particularly whether there is charge transfer between the surface and adsorbate. 

Table 19.2 Adsorption energies E ) of TMA onto model metal clusters, gross MuUiken charges on metal clusters, and intermolecular distances between metal cluster and N atom in TMA...

The adsorption of molecules by microporous solids is discussed here within six categories, according to the nature of the adsorption sites, and without considering adsorption by metal clusters introduced within the pores. Tables 7.3-7.5 give enthalpies of adsorption for examples within these categories, which vary from the interaction of neutral frameworks with small molecules to strong adsorption on acid or basic sites. 

In addition, hydrogen bonding was still observed at 3,583 cm (Fig.l A). IR peaks in VC.O region (Fig.l B) shifted to lower frequency after adsorption due to precursor-support interaction and differed from that of cluster solution implying that precursor was not intact after adsorption on support but still in the form of metal carbonyl species. 

---