Adsorption on nickel

In a more recent RAIR study of ferrocenylhexyl isocyanide (2) adsorbed on polycrystalline Ni [63], the Ni surface was pretreated electrochemically by 

The SAM was obtained by immersing the clean substrate for 48 h in an ethanol solution of ferrocenylhexyl isocyanide. The strong v(N=C) peak at 2147cm observed in FTIR spectra of free ferrocenylalkyl isocyanide (on a KBr plate) is not present in the RAIR spectra of this isocyanide on a nickel surface. Considering the surface selection rules for RAIR spectroscopy, the absence of a v(N=C) peak in the RAIR spectrum indicates that the chemisorbed isocyanides are bonded through both their carbon and nitrogen atoms, and they adopt an orientation in which the N=C bond is parallel to the surface. 

In all reported studies of isocyanides adsorbed on Ni, the isocyanide is proposed to adsorb with both the carbon and nitrogen atoms bonded to the surface. 

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It has been suggested that the rate limiting step in the mechanism is the chemisorption of propionaldehyde and that the hydrogen undergoes dissociative adsorption on nickel. Determine if the rate expression predicted by a Hougen-Watson model based on these assumptions is consistent with the experimentally observed rate expression. 

The effect of other surface impurities may be more severe than that of oxygen. For instance, adsorbed sulfur strongly inhibits hydrogen adsorption on nickel 58), while chlorine adsorbed on nickel is also likely to be a tenaciously held surface contaminant. 

Evidence for a marked difference between the surface and bulk compositions of dilute copper-nickel alloys has been reported recently by a number of investigators (82, 87-90). Much of the experimental evidence comes from hydrogen adsorption data (74, 82, 87, 90). The conclusions of van der Plank and Sachtler were based on the premise that nickel chemisorbs hydrogen while copper does not (82, 87). The total adsorption of hydrogen at room temperature was taken as a measure of the amount of nickel in the surface. However, in hydrogen adsorption studies on the catalysts used to obtain the catalytic results in Fig. 6, the amount of adsorption on the copper catalyst, while small compared to the adsorption on nickel, is not negligible (74) However, the amount of strongly adsorbed... 

Galea NM, Kadantsev ES, and Ziegler T. Studying reduction in solid oxide fuel cell activity with density functional theory-effects of hydrogen sulfide adsorption on nickel anode surface. JPhys Chem C 2007 111 14457-14468. 

The co-existence of at least two modes of ethylene adsorption has been clearly demonstrated in studies of 14C-ethylene adsorption on nickel films [62] and various alumina- and silica-supported metals [53,63—65] at ambient temperature and above. When 14C-ethylene is adsorbed on to alumina-supported palladium, platinum, ruthenium, rhodium, nickel and iridium catalysts [63], it is observed that only a fraction of the initially adsorbed ethylene can be removed by molecular exchange with non-radioactive ethylene, by evacuation or during the subsequent hydrogenation of ethylene—hydrogen mixtures (Fig. 6). While the adsorptive capacity of the catalysts decreases in the order Ni > Rh > Ru > Ir > Pt > Pd, the percentage of the initially adsorbed ethylene retained by the surface which was the same for each of the processes, decreased in the order... 

In other cases the adsorption of hydrogen atoms results in surface hydride dipoles pointing with their negative ends away from the metal, as is observed in the adsorption on nickel,... 

Experimental Heats oj H2S Adsorption on Nickel Compared to Heats of Formation for Bulk Sulfides... 

Results of previous investigations 23,110, 111, 113, 141, 157-165) show that hydrogen adsorption on nickel at room temperature is lowered by preadsorbed sulfur. Moreover, the fraction by which hydrogen adsorption is reduced in polycrystalline and supported nickel catalysts is generally proportional to the mean fractional coverage of sulfur. This is illustrated by data in Fig. 16 from Bartholomew and co-workers 112, 113, 141, 157-162). 

Infrared mcasurcnienls of CO adsorption on nickel surfaces by Martin er qL gave some further insight on the formation mechanism of surface carbide. 

The former is called molecular or nondissociated (e.g., CO) adsorption and the latter is called dissociative adsorption. Whether a molecule adsorbs nondis-sociatively or dissociatively depends on the surface. For example, CO imder-goes dissociative adsorption on iron and molecular adsorption on nickel. ... 

This view is supported by the statistical-mechanical interpretation of the adsorption isotherm at such low coverages that the differential heat of adsorption of hydrogen is nearly constant at 26 kcal./mole. From the agreement between the surface fraction calculated by means of equation (18) with n = 2, and the experimentally found value 0ob., for the hydrogen adsorption on nickel, Kwan et al. concluded that the surface of reduced nickel is homogeneous, or that every surface element is equally available for the chemisorption of hydrogen. 

Figure 3 shows FTIR spectra of CO adsorption on nickel magnesia catalysts. On Nim Mg(,2>oO and Ni/MgO catalysts, linear (2100-2000 cm ), bridge (2000-1850 cm ) and physisorbed Ni(CO)4 (2057 cm ) were mainly observed. In contrast, on NidojMgo O nickel monomer and dimer carbonyl species which are interacted with MgO were mainly observed as previously reported[10]. These species were increased with the CO pressure, therefore they are found to be formed via CO induced structural change. On NioojMgj O solid solution, Ni metal particles seem to be highly dispersive. 

Ensemble effects are useful when adsorption requires a special grouping of surface atoms. To explain this, let us examine the simple example of ethylene adsorption on nickel, which occurs in a dt-adsorbed mode. Two nickel atoms, the right distance apart, are needed to bond a pair of carbon atoms. The bonds must be stable, but not too strong or subsequent reaction is difficult. Figure 4.2 shows symmetry and distances for tow index planes of the face centered cubic nickel surface. 

The experimental results suggest the following sequence first, a carbon monoxide and water species adsorption on nickel, second, the electrodissolution of nickel is inhibited by the adsorbed carbon monoxide, third, the anodic stripping of the adsorbate occurs at the rising branch of the current vs. potential profile, and this is finally followed by the oxidation of the underlying nickel layers. Thus, the carbon monoxide mass-current intensity signal reaches its maximum before the voltammetric peak that is almost totally determined by the bulk electrodissolution-precipitation process of nickel. A small portion of the remaining adsorbate is oxidized to carbon dioxide induced by the co-adsorbed hydroxyl present at the nickel interface. 

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