Spectra of Adsorbed Molecules

In the case of Rh on Ti02 it seems clear that raising the reduction temperature increases the proportion of linear to dicarbonyl CO species. However, this does not appear to be dependent on particle size. If it is to be attributed to the formation of rafts, as suggested by Prestridge et al., it indicates that rafts are formed after R473 for Rh/Ti02, and then disappear after reduction at a higher temperature. 

Vannice et al. have conducted a detailed investigation of Ti02-supported p 89,i36 79,137 catalysts, peaks due to both linear and 

A further interesting suggestion put forward by Vannice and co-workers is that only a small fraction of a Pt or Pd surface is active in the CO/H2 reaction. They arrived at this conclusion because it was found that only 

1-2% of the metal surface was covered by CO (detectable by infrared) under reaction conditions, and yet these catalysts had high specific activities. 

In general, metals in the SMSI state adsorb very little H2 or CO, have slightly lower activities for insensitive reactions, much lower activities for hydro-genolysis reactions, and, in some cases, significantly higher activities and different selectivities for the CO/H2 reaction. 

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L. H. Little, Infrared Spectra of Adsorbed Molecules, Academic, New York, 1966. 68a. M. L. Hair, Infrared Spectroscopy in Surface Chemistry, Marcel Dekker, New... 

Yaroslavskii N G and Terenin A N 1949 Infrared absorption spectra of adsorbed molecules Dokl. Akad. Nauk 66 885-8... 

It is desirable that the oxide chosen for an adsorption study has a high surface area. This would potentially allow a greater number of adsorbate molecules to be adsorbed and consequently more intense spectra would be obtained. In general, the observed spectra of adsorbed molecules at low coverages are weak. Further, some adsorbates (e.g. H2O) give rise to inherently weak Raman spectra even at high coverage. 

All of these facilities have special relevance in recording Raman spectra of adsorbed molecules. 

Insight into chemisorption bonds is important for the interpretation of photoemission and vibrational spectra of adsorbed molecules, as well as for the understanding of catalytic reactions. If we have a feeling for how electrons rearrange over orbitals when a molecule adsorbs, we may be able to understand why molecules dissociate or not, to what extent they are activated, or also how a promoter influences the reactions on the surface. 

The Infrared Spectra of Adsorbed Molecules R. P. Eischens and W. a. Pliskin The Influence of Crystal Face in Catalysis Allan T, Gwathmey and Robert E. Cunningham... 

Fig. 9. The infrared spectra of adsorbed molecules. The lowest line on each spectrum is the background obtained after evacuating the porous glass. Measured surface coverages (fl) are given for all spectra (133).

Interest in the vibrational spectra of adsorbed molecules is at least 40 years old. The past ten years have seen the development of many novel techniques for determining the vibrational spectra of adsorbed species and this symposium brings together a state-of-the-art survey of these techniques. In one s ethusiasm for the recent advances made in any subject there is a tendency to forget the parent technique and its steady contribution to our knowledge. In this case, the parent is simple transmission infrared spectroscopy. This paper, therefore, is an attempt to briefly present an overview of some of the developments which have occurred in the application of transmission infrared spectroscopy to surface studies with emphasis upon results generated in the past 10 years. For more detailed information on work published prior to 1967 the reader is referred to three texts which have appeared on this subject (1-3). 

VI. The Pressed-Salt Method for Obtaining Spectra of Adsorbed Molecules.. 45... 

The earliest observations of infrared bands due to hydroxyl groups on surfaces were made by workers who were primarily interested in the spectra of the solid rather than spectra of adsorbed molecules. Despite this difference in point of view, their interpretation of the hydroxyl bands is important to later studies of adsorption. 

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