Electronic carbon monoxide adsorption

In carbon monoxide the bond between the atoms depends, as in the N2O molecule, on an asymmetrical electron shift, electrons of the 0 atom moving toward the C atom, and the CO molecule having a dipole character. In this case, too, metal electrons are displaced toward the adsorbed molecule and taken from the electron gas, as shown by the change of the electrical resistance of thin nickel films on carbon monoxide adsorption (18). 

Even the precovering with hydrogen is able to block the surface against electronic interaction. In Fig. 27 a nickel surface was precovered with hydrogen at 3 X 10 mm. Hg to saturation (0 = 0.39), causing an irreversible resistance decrease of 1%. After pumping off at B, carbon monoxide of 6 X 10 mm. Hg was added at Aco- At a pure nickel surface the carbon monoxide influence would have effected an increase of the resistance by 0.8%. At the surface precovered with hydrogen, neither a resistance effect nor a carbon monoxide adsorption is to be observed. 

Copper and zinc containing mesoporous molecular sieves AIMCM-41 have been studied by MAS NMR, electron spin resonance, nitrogen and carbon monoxide adsorption and temperature programmed reduction. AlMCM-41 materials with ns,/nAi = 15, 30 and x have been synthesized in the presence of copper and zinc Carbon monoxide adsorption shows the presence of Cu ions after mild activation, but Zn ions have not been detected indicating that only a ZnO phase is formed Temperature programmed reduction reveals the presence of CuO clusters of various size depending on the on the ns./n ij ratio and the zinc concentration The results of this study allow the preparation of mesoporous molecular sieves with remarkable redox properties, which are potential model catalyst for methanol synthesis... 

Other workers have not investigated the effect of decomposition products on the rate. Many of the reactions carried out in flow systems must have been concerned with a poisoned reaction with a steady-state concentration of reaction products present. The effectiveness of water and hydrogen as poisons would tend to confirm the view of Schwab (1) that the reaction involves a transfer of electrons to the nickel from the formic acid and that this process is hindered by the accumulation of electrons from adsorbed water and hydrogen. If this were the only effect, carbon monoxide adsorption, which removes electrons (16) would be expected to accelerate the de-... 

After characterization of the metal by electron microscopy and chemisorption methods such as hydrogen, oxygen, and carbon monoxide adsorption, the reaction with tetrabutyl tin was performed and followed by GC and volumetry. The reaction... 

Even if it is assumed that the reaction is ionic, Occam s Razor would lead to the conclusion that the system is too complex and that the effort to keep it ionic is too great. It is difficult to undersand why step 8c is slow and why a simple uncharged complex would not be equally reasonable. We prefer a mechanism in which the carbon monoxide molecule is adsorbed parallel to the surface and in which the oxygen orbitals as well as the carbon orbitals of C=0 bond electrons interact with the metal. It seems reasonable that hydrogenolysis occurs exclusively only because the oxygen is held in some way while the two bonds are broken and it finally desorbs as water. The most attractive picture would be (a) adsorption of CO and H2 with both atoms on the surface... 

We have undertaken a series of experiments Involving thin film models of such powdered transition metal catalysts (13,14). In this paper we present a brief review of the results we have obtained to date Involving platinum and rhodium deposited on thin films of tltanla, the latter prepared by oxidation of a tltanliua single crystal. These systems are prepared and characterized under well-controlled conditions. We have used thermal desorption spectroscopy (TDS), Auger electron spectroscopy (AES) and static secondary Ion mass spectrometry (SSIMS). Our results Illustrate the power of SSIMS In understanding the processes that take place during thermal treatment of these thin films. Thermal desorption spectroscopy Is used to characterize the adsorption and desorption of small molecules, In particular, carbon monoxide. AES confirms the SSIMS results and was used to verify the surface cleanliness of the films as they were prepared. 

The effects of tin/palladium ratio, temperatnre, pressnre, and recycling were studied and correlated with catalyst characterization. The catalysts were characterized by chemisorption titrations, in situ X-Ray Diffraction (XRD), and Electron Spectroscopy for Chemical Analysis (ESCA). Chemisorption studies with hydrogen sulfide show lack of adsorption at higher Sn/Pd ratios. Carbon monoxide chemisorption indicates an increase in adsorption with increasing palladium concentration. One form of palladium is transformed to a new phase at 140°C by measurement of in situ variable temperature XRD. ESCA studies of the catalysts show that the presence of tin concentration increases the surface palladium concentration. ESCA data also indicates that recycled catalysts show no palladium sulfide formation at the surface but palladium cyanide is present. 

Hooker, M. P., and Grant, J. T. 1977. The use of Auger electron spectroscopy to characterize the adsorption of carbon monoxide transition metals. Surf. Sci. 62 21-30. 

Figure 2. Auger electron spectrum of the surface of two Ru electrodes after deactivation by reduction of carbon monoxide and methanol at higher temperatures (75 and 90 °C respectively in 0.2 M Na2SC>4 at pH 4 and -0.545 V vs SCE ). The presence of K on the surface must result from the adsorption of K+ ions present as an impurity in the electrolyte.

The advantages of electron spectroscopy for the study of adsorbed diatomic molecules are illustrated by reference to the adsorption of carbon monoxide, nitrogen, nitric oxide, and oxygen on different metal surfaces. 

The fact that surface structure, in particular steps and coordinatively unsaturated sites, has an influence on the state and reactivity of carbon monoxide is entirely in keeping with the empirical correlation (Fig. 6) between heat of adsorption, electron binding energies, and molecular state. Elegant studies by Mason, Somorjai, and their colleagues (32, 33) have established that with Pt(lll) surfaces, dissociation occurs at the step sites only, and once these are filled carbon monoxide is adsorbed molecularly (Fig. 7). The implications of the facile dissociation of carbon monoxide by such metals as iron, molybdenum, and tungsten for the conversion of carbon monoxide into hydrocarbons (the Fischer-Tropsch process) have been emphasized and discussed by a number of people (32,34). 

If it is assumed that the mobile oxygen differs from the extralattice oxygen by the absence of an additional electron supplied by the solid, it is quite likely that modifications of the electronic levels of nickel oxide by impurities will not affect substantially the low-temperature rate of carbon monoxide oxidation. Indeed, the rate depends on surface diffusion with subsequent reaction of the adsorbed partners if our scheme is correct. On the contrary such modifications might affect the rate of the high-terapera-ture process insofar as it depends on the availability and heat of adsorption of the extralattice oxygen. As will be seen later, this prediction is correct. 

An Electron Energy Loss Spectroscopic Investigation of the Adsorption of Nitric Oxide, Carbon Monoxide, and Hydrogen on the Basal Plane of Ruthenium... 

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