Carbon monoxide, adsorbed

The dynamics of fast processes such as electron and energy transfers and vibrational and electronic deexcitations can be probed by using short-pulsed lasers. The experimental developments that have made possible the direct probing of molecular dissociation steps and other ultrafast processes in real time (in the femtosecond time range) have, in a few cases, been extended to the study of surface phenomena. For instance, two-photon photoemission has been used to study the dynamics of electrons at interfaces [ ]. Vibrational relaxation times have also been measured for a number of modes such as the 0-Fl stretching m silica and the C-0 stretching in carbon monoxide adsorbed on transition metals [ ]. Pump-probe laser experiments such as these are difficult, but the field is still in its infancy, and much is expected in this direction m the near fiitiire. 

Whereas ATR spectroscopy is most commonly applied in obtaining infrared absorption spectra of opaque materials, reflection-absorption infrared spectroscopy (RAIRS) is usually used to obtain the absorption spectrum of a thin layer of material adsorbed on an opaque metal surface. An example would be carbon monoxide adsorbed on copper. The metal surface may be either in the form of a film or, of greaf imporfance in fhe sfudy of cafalysfs, one of fhe parficular crysfal faces of fhe mefal. 

Gomez R, Orts JM, Feliu JM, Clavilier J, Klein LH. 1997. The role of surface crystalline heterogeneities in the electrooxidation of carbon monoxide adsorbed on Rh(lll) electrodes in sulphuric acid solutions. J Electroanal Chem 432 1 -5. 

McCallum C, Pletcher D, 1978. An investigation of the mechanism of the oxidation of carbon monoxide adsorbed onto a smooth Pt electrode in aqueous acid. J Electroanal Chem 70 277. 

Palaikis L, Zurawski D, Hourani M, Wieckowski A. 1988. Surface electrochemistry of carbon monoxide adsorbed from electrolytic solutions at single crystal surfaces of Pt(lll) and Pt(lOO). Surf Sci 199 183-198. 

Tian ZQ, Ren B, Mao BW. 1997. Extending surface Raman spectroscopy to transition metal surfaces for practical applications. 1. Vibrational properties of thiocyanate and carbon monoxide adsorbed on electrochemically activated platinum surfaces. J Phys Chem B 101 1338-1346. 

Rice C, Tong YY, Oldfield E, Wieckowski A, Hahn F, Gloaguen F, Leger J-M, Lamy C. 2000. In situ infrared study of carbon monoxide adsorbed onto commercial fuel-cell-grade carbon-supported platinum nanoparticles correlation with C NMR results. J Phys Chem B 104 5803-5807. 

Soma-Noto Y, Sachtler WMH. 1974. Infrared spectra of carbon monoxide adsorbed on supported palladium and palladium-silver alloys, J Catal 32 315. 

Kunimatsu K, Aramata A, Nakajima N, Kita H. 1986. Infrared spectra of carbon monoxide adsorbed on a smooth gold electrode Part II. EMIRS and polarization-modulated IRRAS study of the adsorbed CO layer in acidic and alkaline solutions. J Electroanal Chem 207 293-307. 

The 5% Pd/C catalysts, with an increasing amount of tin (from 0 to 1%), were activated in the same way described above and titrated with both carbon monoxide and hydrogen sulfide, up to 800 Torr, at 30°C. Figure 15.4 indicates a constant volume of carbon monoxide adsorbed, as expected from the above relationship for a fixed amoimt of %Pd on the catalyst. However, there does appear to be a relationship between H2S adsorption and the Sn/Pd ratio at constant 5 wt% Pd concentration on the catalyst. When there is little or no tin associated with the Pd-catalyst, the H2S is irreversibly adsorbed, resulting in high voliunetric uptake of... 

As we have shown in Section 1.2.1 carbon monoxide adsorbed on platinum can be transferred from the electrochemical cell to the UHV without detectable faradaic loss (see Fig. 1.4). Therefore this system can be taken as a model for the application of ECTDMS to the analysis of organic adsorbates. 

Louie J, Hartwig JF (1996) A route to PdO from Pdll metallacycles in amination and cross-coupling chemistry. Angew Chem Int Ed Engl 35 2359-2361 Mucalo MR, Coouey RP (1989) F.T.I.R. spectra of carbon monoxide adsorbed on platinum sols. J Chem Soc Chem Commun 94—95 Munoz MP, Martin-Matute B, Fernandez-Rivas C, Cardenas DJ, Echavarren AM (2001) Palladacycles as precatalysts in Heck and cross-coupling reactions. Adv Synth Catal 343 338-342... 

Carbon monoxide adsorbed on sufficiently small palladium particles disproportionates to surface carbon and carbon dioxide. This does not occur on large particles. The CO-O2 reaction is shown to be structure-insensitive provided the metal surface available for the reaction is estimated correctly. 

R. Ryberg, Carbon-Monoxide Adsorbed on Cu(100) Studied by Infrared-Spectroscopy, Surf. Sci. 114 (1982), 627 641. 

The data for carbon monoxide adsorbed on platinum were found not to obey this equation but to conform more closely to the equation of the type... 

Two basic mechanisms have been proposed to interpret methanol formation in the CO + H2 reaction. When carbon monoxide adsorbed on the copper surface is hydrogenated by the stepwise addition of hydrogen atoms [Eq. (3.42)], the principal intermediate is a surface formyl species (5) ... 

In 1954 R. P. Eischens, W. A. Pliskin, and S. A. Francis (5) of the Texaco Research Center in New York published the first infrared spectra of chemisorbed species, namely of carbon monoxide adsorbed on the silica-supported finely divided metal catalysts of Ni, Pd, Pt, and Cu. Also, in 1956, Pliskin and Eischens (5) were the first to obtain spectra of the hydrocarbons ethylene (ethene), acetylene (ethyne), and propene adsorbed on an oxide-supported metal catalyst, Ni/Si02. Eischens and his colleagues followed this up with further studies of chemisorbed zj-alkenes and their surface-hydrogenation products on Ni/Si02 (7). 

The easy isomerization of X XI is particularly interesting since bridging and terminally bonded carbon monoxide adsorbed on platinum surfaces may be expected to undergo an analogous reaction even more easily. 

Figure 4. Infrared spectra of carbon monoxide adsorbed on H2-depleted EUROPT-l surface [5]. Spectra A-F represent 3 min exposures at progressively increasing pressures of from 1.3 x 10"5 to 15 mbar.

In some cases such information is readily interpreted and understood. For example, carbon monoxide adsorbed on a metal will show strong carbonyl absorptions (v(CO)) in the infra-red region similar to those found in molecular metal carbonyl complexes (See Al.1.3). The exact positions of the absorption, the number of bands and their shapes, can be correlated with the type of binding (to one, or more, metal atoms) and even to the strength of the bonds. 

The application of IR spectroscopy to catalysis and surface chemistry was later developed in the fifties by Eischens and coworkers at Texaco laboratories (Beacon, New York) in the USA [7] and, almost simultaneously, by Sheppard and Yates at Cambridge University in the UK [8]. Mapes and Eischens published the spectra of ammonia chemisorbed on a silica-alumina cracking catalyst in 1954 [6], showing the presence of Lewis acid sites and also the likely presence of Br0nsted acid sites. Eischens, Francis and Pliskin published the IR spectra of carbon monoxide adsorbed on nickel and its oxide in 1956 [9]. Later they presented the results of an IR study of the catalyzed oxidation of CO on nickel at the First International Congress on Catalysis, held in Philadelphia in 1956 [10]. Eischens and Pliskin also published a quite extensive review on the subject of Infrared spectra of adsorbed molecules in Advances in Catalysis in 1958, where data on hydrocarbons, CO, ammonia and water adsorbed on metals, oxides and minerals were reviewed [11]. These papers evidence clearly the two tendencies observed in subsequent spectroscopic research in the field of catalysis. They are the use of probes to test the surface chemistry of solids and the use of spectroscopy to reveal the mechanism of the surface reactions. They used an in situ cell where the catalyst sample was... 

Figure 3.25 FTIR spectra of carbon monoxide adsorbed on PdO, /y-AbOs catalyst, after previous calcination in air at 673 K (upper spectra) and after reduction in hydrogen (1 atm) at 673 K (lower spectra). The first spectra in each series has been obtained in contact with lOTorr CO at 130 K for 5 min. The other spectra were recorded upon outgassing (lO Torr) on warming to 270 K. 

Carbon monoxide adsorbed on bivalent-cation X and Y zeolites shows a cation-specific infra-red stretching band as well as two bands that are cation non-specific to a remarkable degree, occurring unchanged or almost unchanged also with univalent-cation and decationized preparations. The specific bands do not appear if even a small amount of water is present, presumably because the cations bind H2O more strongly than CO. 

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