Carbon monoxide on metal

There has been a general updating of the material in all the chapters the treatment of films at the liquid-air and liquid-solid interfaces has been expanded, particularly in the area of contemporary techniques and that of macromolecular films. The scanning microscopies (tunneling and atomic force) now contribute more prominently. The topic of heterogeneous catalysis has been expanded to include the well-studied case of oxidation of carbon monoxide on metals, and there is now more emphasis on the flexible surface, that is, the restructuring of surfaces when adsorption occurs. New calculational methods are discussed. 

Carbon monoxide on metals forms the best-studied adsorption system in vibrational spectroscopy. The strong dipole associated with the C-O bond makes this molecule a particularly easy one to study. Moreover, the C-0 stretch frequency is very informative about the direct environment of the molecule. The metal-carbon bond, however, falling at frequencies between 300 and 500 cm1, is more difficult to measure with infrared spectroscopy. First, its detection requires special optical parts made of Csl, but even with suitable equipment the peak may be invisible because of absorption by the catalyst support. In reflection experiments on single crystal surfaces the metal-carbon peak is difficult to obtain because of the low sensitivity of RAIRS at low frequencies [12,13], EELS, on the other hand, has no difficulty in detecting the metal-carbon bond, as we shall see later on. 

Surface groups consisting of atoms foreign to the structure can be formed on a great variety of substances. It is not intended to discuss all possibilities this would surpass the scope of an article limited in volume. Furthermore, research in this field has but begun surface compounds have been studied only on a selected group of substances. Most of the investigated substances, however, are very important from an industrial viewpoint. Therefore, in this article the chemistry of surface compounds will be described for a few characteristic and well-known examples. Borderline cases, such as the chemisorption of carbon monoxide on metals, will not be considered. 

Catalytic activation of carbon monoxide on metal surfaces. Chemisorption on nonmetallic surfaces. 

Amorphous (rapidly quenched) metals and alloys have been investigated as catalysts (Schlogl, 1985). It has been found that adsorption characteristics of carbon monoxide on metallic glasses are different from those on crystalline materials. For example CO is found to dissociate readily on the surface of Ni76Bi2Si,2 metglass, but it is always molecularly adsorbed on metallic nickel (Prabhakaran Rao, 1985). 

Carbon monoxide on metals forms the best-studied adsorption system in vibrational spectroscopy. The strong dipole associated with the C-O bond makes this molecule a particularly easy one to study. Moreover, the C-O stretch frequency is... 

E. E. Donath History of Catalysis in Coal Liquefac-tioa - G. K Boreskov Catalytic Activation of Dioxygen. - M. A. Wannice Catalytic Activation of Carbon Monoxide on Metal Surfaces. - S.R. Morrison Chemisorption on Nonmetallic Surfaces. - Z. Knor Chemisorption of Dihydrogen. - P.N.lfylander Catalytic Processes in Organic Conversions. 

Two models will be postulated for the adsorption of carbon monoxide on metal—one in which CO is adsorbed as molecules, CO,... 

The adsorption of carbon monoxide on metal surfaces can be qualitatively understood using a model originally formulated by Blyholder [45]. A simplified molecular orbital picture of the interaction of CO with a transition metal surface is given in Figure 6. The CO frontier orbitals 5a and 2n interact with the localized d metal states by splitting into bonding and antibonding hybridized metal-... 

The spectrum of carbon monoxide adsorbed on nickel oxide prepared at 200° may be divided into two regions (Table I, la) (60). The first includes two bands at 2060 and 1960-1970 cm i, the second three bands at 1620, 1575, and 1420-1440 cm-i. Bands at 2060 and 1960-1970 cm- are typical of carbonyl structures and are found in the spectrum of carbon monoxide on metallic nickel (61). It has been suggested by some authors (62) that, in our experiments, these bands were also produced by the adsorption on the metal, the oxide being supposed oxygen-deficient. Chemical analyses (30) have shown, however, that, NiO(200°) contains an excess of oxygen and magnetic susceptibility measurements (33) have demonstrated that the quantity of metal is very small. Since the intensity of these bands is strong, we believe that they are not produced exclusively by the chemisorption of carbon monoxide on the metal but mainly by the adsorption on exposed nickel ions. 

Work on metal carbonyl clusters adds to the understanding of chemisorption phenomena of carbon monoxide on metals. 

The vibrational spectrum of carbon monoxide on metal surfaces has been studied from both theoretical and experimental spectroscopic perspectives. Althou it is not necessary to review these results within the scope of tUs chapter, a summary of the most important aspects will serve as a guide for the application of the technique to colloidal metals. 

It is thus clear that a rigorous study of the chemical shift anisotropy, combining theory and experiment, is essential to understand at the molecular level the variation of coordination of a ligand on a metal center. This can in fact be used to understand the mode of absorption of carbon monoxide on metallic particles and metallic clusters. ... 

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