Spectroscopic studies of adsorbed

Vibrational Spectroscopic Studies of Adsorbate Competition During Carbon Monoxide Adsorption on Platinum Electrodes... 

The first electron spectroscopic study of adsorbed hydrocarbons was that reported by Eastman and Demuth (78) who used He radiation to probe the valence electrons of benzene, acetylene, and ethylene. Figure 17 shows the difference spectrum of C2H4 adsorbed on Ni(lll) at 100 and 230 K compared with the results of Clarke et al. (79) for ethylene adsorption on Pt(lOO) at 290 K, propylene adsorption on Pt(lOO), and ethylene adsorption on Pt(lll). 

Compared with the gas phase, the spectroscopic studies of adsorbed CO on electrodes are still just beginning. Data are available for only a few metals. CO has been studied on single-crystal surfaces of Pt [53-58], Pd [59] and Rh(lll) [60]. 

Daniell, W., H. Landes, N. E. Fouadl and H. Knozinger, Influence of pretreatment atmospheres on the nature of silica-supported Pd generated via decomposition of Pd(acac)2 an FTIR spectroscopic study of adsorbed CO , J. Mol Catal A Chemical, vol 178, Issues 1-2,23 January 2002, pp 211-8. 

There is a continuous interest in the spectroscopic studies of adsorbed species (for instance, [EMIRS], potential modulated reflectance spectroscopy [PMRS]). The EQCM technique was used recently for the study of chemisorption and oxidation of methanol at polycrystalline (platinized) Pt. It was found that accumulation of strongly adsorbing species at the electrode surface is accompanied by a decrease in the mass, relative to the background electrolyte, and the rate of this decrease is an indication how the surface becomes covered by adsorbates. 

D. J. Greenland and M.H.B. Hayes, The Chemistry of Soil Constituents. Wiley, Chichester, U.K., 1978. Chapter 6 of this outstanding compendium, written by V. C. Fanner, reviews infrared spectroscopic studies of adsorbed water. 

Ueba H and Yamada H, eds. 1984, surf Sci 158, Proc Int Symp "Spectroscopic Studies of Adsorbates on Solid Surfaces "... 

Vibrational spectroscopic studies of heterogeneously catalyzed reactions refer to experiments with low area metals in ultra high vacuum (UHV) as well as experiments with high area, supported metal oxides over wide ranges of pressure, temperature and composition [1]. There is clearly a need for this experimental diversity. UHV studies lead to a better understanding of the fundamental structure and chemistry of the surface-adsorbate system. Supported metals and metal oxides are utilized in a variety of reactions. Their study leads to a better understanding of the chemistry, kinetics and mechanisms in the reaction. Unfortunately, the most widely used technique for determining adsorbate molecular structure in UHV,... 

In-situ ATR-FTIR spectroscopic study of electro-oxidation of methanol and adsorbed CO at Pt-Ru alloy. J. Phys. Chem. B, 108, 2654-2659. 

Currently there are four major lines of approach towards gas-phase epoxidation of propylene (1) mechanistic studies of Au/Ti02 catalysts through kinetics, spectroscopic identification of adsorbed species and... 

Kunimatsu K. 1986. Infrared spectroscopic study of methanol and formic acid adsorbates on a platinum electrode Part I. Comparison of the infrared absorption intensities of hnear CO(a) derived from CO, CH3OH and HCOOH. J Electroanal Chem 213 149 157. 

Beden B, Hahn F, Juanto S, Lamy C, Leger JM. 1987a. Infrared spectroscopic study of the methanol adsorbates at a platinum electrode Part I. Influence of the bulk concentration of methanol upon the nature of the adsorbates. J Electroanal Chem 225 215-225. 

Takasu Y, Matsuda Y, Toyoshima I. 1984. A photoelectron spectroscopic study of the effect of particle-size on the adsorbed state of carbon-monoxide over supported palladium catalysts. Chem Phys Lett 108 384-387. 

Berrodier, I., Farges, F., Benedetti, M., Winterer, M., Brown Jr, G. E., Deveughele, M. (2004). Adsorption mechanisms of trivalent gold on iron- and aluminum-(oxy)hydroxides. Part 1 X-ray absorption and Raman scattering spectroscopic studies of Au(III) adsorbed on ferrihydrite, goethite, and boehmite. Geochimica et Cosmochimica Acta, 68(14), 3019-3042. doi 10.1016/j.gca.2004.02.009... 

D. E. Sandstrom, O.N. Antzutkin, W. Forsling, A spectroscopic study of calcium surface sites and adsorbed iron species at aqueous fluorapatite by means of 1H and 31P MAS NMR, Langmuir 22 (2006) 11060-11064. 

Electrochemical reductions of CO2 at a number of metal electrodes have been reported [12, 65, 66]. CO has been identified as the principal product for Ag and Au electrodes in aqueous bicarbonate solutions at current densities of 5.5 mA cm [67]. Different mechanisms for the formation of CO on metal electrodes have been proposed. It has been demonstrated for Au electrodes that the rate of CO production is proportional to the partial pressure of CO2. This is similar to the results observed for the formation of CO2 adducts of homogeneous catalysts discussed earlier. There are also a number of spectroscopic studies of CO2 bound to metal surfaces [68-70], and the formation of strongly bound CO from CO2 on Pt electrodes [71]. These results are consistent with the mechanism proposed for the reduction of CO2 to CO by homogeneous complexes described earlier and shown in Sch. 2. Alternative mechanistic pathways for the formation of CO on metal electrodes have proposed the formation of M—COOH species by (1) insertion of CO2 into M—H bonds on the surface or (2) by outer-sphere electron transfer to CO2 followed by protonation to form a COOH radical and then adsorption of the neutral radical [12]. Certainly, protonation of adsorbed CO2 by a proton on the surface or in solution would be reasonable. However, insertion of CO2 into a surface hydride would seem unlikely based on precedents in homogeneous catalysis. CO2 insertion into transition metal hydrides complexes invariably leads to formation of formate complexes in which C—H bonds rather than O—H bonds have been formed, as discussed in the next section. 

The pressure. Spectroscopic studies of molecules adsorbed on single crystal surfaces are made in ultra-high vacuum and computations are made in the limit of zero pressure. The pressure must be extrapolated by at least 12 orders of magnitude. 

Wu, C.-H., I. Salmeen, and H. Niki, Fluorescence Spectroscopic Study of Reactions between Gaseous Ozone and Surface-Adsorbed Polycyclic Aromatic Hydrocarbons, Environ. Sci. Tech-noL, 18, 603-607 (1984). 

In most spectroscopic studies, the solids to be studied are usually compressed to form pellets under pressures around 1.5-2 kbar. From an academic point of view, the stability of MTS towards pressure is very important, since most spectroscopic studies of lattice groups or adsorbed probes might be affected by a degradation of MTS during compression. For industrial applications compaction is crucial to handle the powder. Thus the mechanical properties of MTS are a very sensitive topic if we think about the future of these materials. Solids with such high porosity and small wall thickness are very likely to be crushed. Previous studies point out a very weak mechanical strength of MTS [3,4J which can jeopardize further industrial development. It has been demonstrated that these materials have the lowest mechanical stability among the... 

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