Chemisorbed carbon monoxide

Yates J T and Garland C 1961 Infrared studies of carbon monoxide chemisorbed on nickel surfaces J. Catal. 65 617-24... 

Carbon monoxide chemisorbs in atop sites on the clean Nl(lOO) surface for coverages up to 0=0.50 where a well-ordered c(2x2) lattice is observed. A further Increase In CO coverage to the... 

Williams ED, Weinberg WH. 1979. The geometric structure of carbon monoxide chemisorbed on the ruthenium (001) surface at low temperatures. Surf Sci 82 93. 

CO Chemisorption on Clean Rh(lll) (23). The vibrational spectra of carbon monoxide chemisorbed on Rh(lll) at 300 K as a function of exposure are shown in Figure 2. At very low exposures (less than 0.1 L 1 L = 1 Langmuir 10-6 torr sec) only one peak at 1990 cm- - is observed in the C = 0 stretching region and no ordered LEED pattern is found. By comparison with the infrared spectra of relevant organorhodium compounds (50,... 

Study of the Metal-Carbon Bond of Carbon Monoxide Chemisorbed on... 

The details of the sample preparation and studies of the nature of the supported-metal samples have been described in a paper dealing with the effect of surface coverage on the spectra of carbon monoxide chemisorbed on platinum, nickel, and palladium (1). The samples consist of small particles of metal dispersed on a nonporous silica which is produced commercially under the names Cabosil or Aerosil.f This type of silica is suitable as a support because it is relatively inert and has a small particle size (150-200 A.). The small particle size is important because it reduces the amount of radiation which is lost by scattering. A nonporous small particle form of gamma-alumina, known as Alon-C, is also available. This material is not so inert as the silica and will react with gases such as CO and CO2 at elevated temperatures. 

Fio. 31. Spectrum of carbon monoxide chemisorbed on films of evaporated plat inum. 

Sheppard, N. and Nguyen, T.T. (1978) The vibrational spectra of carbon monoxide chemisorbed on the surfaces of metal catalysts - a suggested scheme of interpretation. Adv. Infrared Raman Spectrosc., 5, 67. 

Water adsorbs into the walls of a glass container, but that adsorption is the extent of its adhesion. Some adsorbed molecules react chemically with some types of containers in a process called chemical adsorption (chemisorption. For example, carbon monoxide chemisorbs with palladium, but not with gold). The bonds resulting from chemisorption can hold molecules to the surface with far greater force than would exist with only physical attraction. It is also possible for a molecule (that normally would not chemisorb with the container wall) to break up when hitting the wall s surface. At that point the molecule s constituent parts chemisorb with the container walls. When an adsorbed gas reacts with the materials of a container, it is called reconstruction (for example, the reconstruction of iron with oxygen is rust). 

Fig. 6. The structure of carbon monoxide chemisorbed on Ni(100) in a c(SxS) periodic arrangement. The carbon atoms are bonded to single metal atoms.

Reproducible infrared techniques for recording spectra of gases chemisorbed on metals were first developed for samples consisting of small (<10(X8) particles of metal dispersed on silica (2). This method was applied to a study of carbon monoxide chemisorbed on copper, platinum, nickel and palladium. 

Pig. 1. Spectra of carbon monoxide chemisorbed on silica-supported metals. 

Early studies of carbon monoxide chemisorbed on copper-nickel alloys were complicated by the failure to realize the importance of dissolved hydrogen when the experiments were conducted (10). However recent infrared studies have shown that addition of 1 to 2% copper to nickel causes the band to shift to lower frequencies due to linear chemisorbed carbon monoxide (11). This shift supports the idea that copper and dissolved hydrogen have similar modifying effects on the electronic properties of the nickel. An argument developed below, based on the spectral changes, shows that these modifying effects are consistent with the view that electrons are transferred to the nickel. 

On a localized ha carbonyl clusters may behave like metal surfaces with chemisorbed species. Indeed, photoemission spectra of transition metal atoms correspond well with the photoemission spectra of carbon monoxide chemisorbed on the surface of the bulk metal. Such comparisons, for instance, have been made for Ru3(CO)u. Ir4(CO),2. Os (CO)ig [6 although, of course, they bear some difficulties connected with the poor knowledge we have of metallic catalysts. 

Studies by a group at the Shell Laboratories in Amsterdam (73) have been reported as evidence of interaction between platinum and rhenium in catalysts containing these two elements. These workers, on the basis of infrared spectroscopy studies of carbon monoxide chemisorbed on platinum-rhenium catalysts, and also of X-ray photoelectron spectroscopy measurements on the catalysts, concluded that platinum-rhenium bonds are present in the surface. 

In the infrared spectroscopy studies they observed that the stretching frequency of the chemisorbed carbon monoxide was higher on a Pt-Re/Si02 catalyst than on a Pt/Si02 catalyst. When they contacted a Re/Si02 catalyst with carbon monoxide, they observed only a weak band that rapidly disappeared and could not be restored on further exposure to carbon monoxide. They concluded that the carbon monoxide in this case dissociated, with resultant irreversible poisoning of the rhenium by carbon. Consequently, they attributed the infrared band observed for the platinum-rhenium catalyst to carbon monoxide chemisorbed on platinum atoms. It was concluded that the band was shifted in frequency from that observed for the platinum catalyst because of the interaction between platinum and rhenium. 

Infrared spectra have been very fruitful in studies of relatively simple molecules, such as carbon monoxide chemisorbed on nickel where as many as five modes of chemisorption have been detected. Ultraviolet spectra, being due to electronic transitions, have been most valuable for the characterization of more complex intermediates, such... 

Assignment of Infrared Bands to Surface Species for Carbon Monoxide Chemisorbed on Supported Nickel Catalyst (66)... 

Adsorbed molecules that form chemical bonds with surface atoms exhibit vibrations of the surface chemical bond as well as within the bonds in the molecule. Carbon monoxide chemisorbed on various metal surfaces is the most frequently studied molecular adsorbate system. CO molecules, which adsorb usually with the CO... 

The vibrational spectra of carbon monoxide chemisorbed on various metal surfaces are a function of coverage and temperature [128]. Review the experimental techniques that were employed and discuss the surface structure sensitivity, the coverage and temperature dependencies of the adsorbed molecule. 

Carbon monoxide chemisorbed on various transition-metal surfaces is the most intensively studied of all adsorption systems. Thus it provides a model of how surface-science studies, using a combination of techniques, reveal the nature of the surface chemical bond in detail. 

Sheppard, N., Nguyen, T.T. (1978). The Vibrational Spectra of Carbon Monoxide Chemisorbed on the Surface of Metal Catalysts - a Suggested Scheme of Interpretation, In Advances in Infrared and Raman Spectroscopy, R.J.H. Clark, R.E. Hester, (Ed.), pp. 67-147, Heyden Son Inc, ISBN 0-85501-185-8, Philadelphia, The United States of America... 

Reflectance spectra of carbon monoxide chemisorbed on magnesium oxide show electron transfer and the development of conjugated, adsorbed (CO) species which may include the squarate dianion (335). ... 

A reaction mechanism is suggested which involves dissociative chemisorption of hydrogen and water in competition on one type of active sites and chemisorption of carbon dioxide on the other type. Chemisorption of carbon dioxide is so strong that it prevents chemisorption of carbon monoxide. Chemisorbed carbon dioxide and hydrogen are in equilibrium on the surface. Reverse shift takes place by dissociation of the reaction product into carbon monoxide and a chemisorbed hydroxyl-species. The shift reaction is taking place by reaction between carbon monoxide from the gas phase and hydroxyl-species on the surface. Methanol is formed by step-wise hydrogenation of chemisorbed carbon dioxide. 

The most common method for the estimation of the surface area of a metallic phase in a supported catalyst is by measuring the extent of the hydrogen adsorption. With iron surfaces, however, the adsorption of hydrogen often does not proceed consistently. The free iron surface area is therefore usually calculated from the extent of adsorption of carbon monoxide, measured at 90 K. In contrast to adsorption of hydrogen, which has a low boiling point, physical adsorption of carbon monoxide by oxidic surfaces present in the catalysts is appreciable at 90 K. The extent of the adsorption is therefore measured twice after the first measurement, the catalyst is evacuated at 195 K and the extent of adsorption is determined again. The amount of carbon monoxide chemisorbed by the iron surface is assumed to be the difference between the values obtained from the two adsorption isotherms. ... 

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