CO irreversibly adsorbed

The spectra of CO irreversibly adsorbed at 298 K on Pd/Zr02 (Figure 3), Pd/Al203-Zr02 and Pd/Al203-Zr02-Ba0 reduced at 673 or 773 K are similar to the spectrum of CO on... 

Since CO irreversibly adsorbed on certain metal surfaces can exchange with CO in the gas phase, as illustrated by Yamada and Tamaru for polycrystalline Rh foils,the results obtained in this work suggest chat the species present on CO /K/AgClll) surfaces is different Chan isolated CO(ads). 

Figure 2. Effect of dosing H2O on CO irreversibly adsorbed on APt773 l073 (left-hand section) and ACe20Pt773l073 (right-hand section). Inset changes in the Shoh region, as a funcion of H2O coverage. [Dotted lines pure CO uptake solid lines small H2O doses added broken lines 12 T01TH2O added]...

Fig. 5 FTIR spectra for CO irreversibly adsorbed on platinum and rhodium low-index surfaces in 0.1 M HCIO4 at 0.25 V versus SCE at saturation and low CO coverages. The reference spectrum was acquired at 0.45-0.5 V after CO oxidation. (Reproduced with permission from Ref [19].)...

Feliu JM, Herrero E, Orts JM, Rodes A. 1996. CO adsorption and oxidation on Pt(lOO) single crystals modified by irreversibly adsorbed adatoms. Proc Electrochem Soc 96/98 68-82. 

Herteto E, FeUu JM, Aldaz A. 1995a. CO adsorption and oxidation on Pt(l 11) electrodes modified by irreversibly adsorbed bismuth in sulfuric acid medium. J Catal 152 264-274. 

The Pd-Sn/C catalysts (1 to 7.5% Pd containing 0 to 1% Sn) were heated under vacuum at 150°C and then exposed to hydrogen. These preactivated samples were then titrated with carbon monoxide, a veiy specific ligand for Pd, up to 800 Torr at 30°C. A general linear trend of carbon monoxide concentration with % Pd in Figure 15.3 indicates that the carbon monoxide adsorption is directly correlated to Pd concentration, as expected. The trend is independent of Sn content. This linear Pd-CO trend indicates that the particle size distribution is similar for the different catalysts. However, Figure 15.3 also indicates no relationship between % H2S irreversibly adsorbed and % Pd. 

In order to clear up whether the sorption intermediates of CO and 1 0 participating in the shift reaction are reversibly or irreversibly adsorbed a similar experiment has been accomplished with an additional stripping period of 30 min with purified N, enclosed between the testing periods. As it could be shown, this stripping phase was sufficient to remove the adsorbed 1 0 but not the CO (see (9)), therefore we like to regard the 1 0 sorption as reversible and the CO sorption as irreversible. 

Next we demonstrate that both CO and C.H.CN are irreversibly adsorbed under these conditions. To prove that CO adsorption is irreversible, we prepared a saturated CO adlayer in a solution without the nitrile, and then replaced the cell contents with the solution containing 0.2 M C2Hj.CN. The v(CO) band of the saturated adlayer remained unchanged, which shows that adsorbed CO is not displaced by solution phase C-H CN. It now follows that nitrile adsorption is also irreversible, based on the fact that the partial CO layer observed in Figure 3 is stable indefinitely. If a mixed adsorbate layer is observed in the presence of both solution phase components simultaneously, then it is impossible for one species to be irreversibly adsorbed without the adsorption of the other also being irreversible. 

Since a well-defined condition of the underpotential deposition metal at a definite coverage is better for studying its modified surface at a definite coverage, an irreversibly adsorbed underpotential deposition metal is desirable Sb on Pt(lll) for CO oxidation,Bi and Te on Pt(lOO) for formic acid oxidation, " Sb + Bi on Pt(lOO) for formic acid oxidation, and others found in these references. 

In the first study,82 it was demonstrated that ITO and FTO electrodes modified by irreversibly adsorbing a monolayer of Fe(H2DCB)32 + electrocatalyze efficiently the Co(DTB)32+ oxidation via an EC mechanism. However, while electrogenerated Fe... 

Sequence II O2—CO. Oxygen is first adsorbed on NiO(250) at 30°C. The sample is then evacuated at 30°C. (amount of irreversibly adsorbed oxygen, 1.9 cc. per gram), and carbon monoxide is adsorbed at the same temperature (Figure 3). The electrical conductivity of nickel oxide containing preadsorbed oxygen 1.8 X 10 5 (ohm cm.)"1 decreases during the adsorption of CO, and at the end of the adsorption, is identical to the conductivity of the pure oxide. Moreover, carbon dioxide is condensed in the cold trap. This shows that all ionized species are transformed into neutral species at the end of the interaction. 

A CO Sensor Based Upon Self-assembled Ferrocenyl Ferraazetine. Having demonstrated the CO dependent solid-state electrochemistry of ferrocenyl ferraazetine, we synthesized a ferrocenyl ferraazetine molecule with disulfide functionality (Id). Scheme III. The specific aim was to design a CO sensitive molecule that could be confined to the working electrode of a two-terminal device via monolayer self-assembly techniques. Disulfides have been shown to irreversibly adsorb to Au and Pt surfaces (3-10). NMR and mass spectrometry are consistent with the proposed structure for compound Id. The FTIR spectrum of Id in THF exhibits metal carbonyl bands at 2067,2024,1989,1985 cm similar to the spectra for other ferraazetine derivatives la-c (2,5-6). Like derivatives la-c. Id reacts with CO (1 atm) at 298 K in CH2C12 to form a ferrapyrrolinone complex 2d, equation (3). 

Presentation of a Reaction Mechanism. In the Na0 -CO reactions, after the reaction had achieved a steady state, the reaction gas mixture was switched into either a pure helium stream or a 02-He stream. The responses of C02 and CO were then followed. The CO(dec. , 0)-CO response obtained instantaneously responded zero with no delay, indicating that there was no reversibly adsorbed CO. Furthermore, the C0(dec.,0)-C02 response obtained was not affected by the presence of 02 in the stream, suggesting the nonexistence of irreversible adsorption of CO which could react with oxygen. Thus, a model of the direct reaction of gaseous CO with adsorbed oxygen, an Eley-Rideal type mechanism, may be proposed. 

The chemisorption studies of Parris and Klier (43) using the Cu/ZnO catalyst have been mentioned earlier. Carbon monoxide was irreversibly bonded at room temperature to the surface of the binary catalysts that were also active in methanol synthesis however, this irreversible adsorbate could be desorbed as CO, which indicates that it was not a surface carbonate but rather a strongly bonded carbonyl-type CO. Infrared studies of this chemi-sorbate are lacking and it would be very desirable to determine the structure of this surface species. 

In fact, these procedures (EMIRS or SNIFTIRS) should be used only when the system under study undergo reversible changes with potential [16]. Bipolar bands are obtained in the difference spectrum for species irreversibly adsorbed, if the band-center frequency is shifted with the potential, e.g., CO adsorbed on platinum (Fig. 8 a). But the situation is problematic when the frequency shift with potential is negligible. Then signals cancel out in the computed spectrum. This question has giv-... 

Fig. 16. Spectra of irreversibly adsorbed CO on (a) Pt(lOO) and (b) Pt(llO) at different degrees of coverage obtained by dosing different amounts of CO at -0.25 V vs. SCE in 0.1 M HCIO4. Spectra acquisition as in Fig. 15. (After [54, 55]). Reprinted by permission of the American Chemical Society and Elsevier Science.

Another important fact is that the quantity of CO exchanged on the surface is the same as that initially adsorbed. However, if the initial CO is desorbed by a switch to He, after a long time there will be a residual coverage of CO. At this coverage the activation energy of desorption has become so high that the remaining CO is irreversibly adsorbed. All this is done at constant temperature, 220°C in Ref. 17). The rest of the CO could be removed and measured by a TPD or a TPRx in H2. 

It is well known that C60 neither reacts with nor is adsorbed by bare silica, but it reacts with Si-H bonds on H-terminated silicon wafers forming covalently bonded monolayers [94]. The introduction of C60 dissolved in toluene should occur in the interfacial region between the PVFA-co-PVAm chains which are adsorbed on to silica and transform the reversibly adsorbed and flexible polyelectrolyte layer into an irreversibly adsorbed and more rigid structure. However, amino groups inside the adsorbed PVFA-co-PVAm coils are not available for surface functionalization with C60 (Scheme 5). Never-... 

The decarbonylations of iridium carbonyl clusters in NaY zeolite are reversible [12]. Infrared spectra show that [Ir6(CO)i6] in the supercages was decarbonylated by treatment in hydrogen at 300°C [12]. When CO was adsorbed at -196°C on the decarbonylated clusters formed from [Ir6(CO)i6] (or from [Ir4(CO)i2]) and the temperature raised with the sample under CO, mononuclear iridium carbonyls formed at about -30°C. These were converted at about 50°C into [Ir4(CO)i2] and at about 125°C into [Ir6(CO)i6] [12]. In contrast, the decarbonylations of the iridium cluster carbonyl anions [HIr4(CO)ii] and [Ir6(CO)i5]2 supported on MgO were found to be irreversible [13]. 

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