Nickel, surface modes

Polymer films were produced by surface catalysis on clean Ni(100) and Ni(lll) single crystals in a standard UHV vacuum system H2.131. The surfaces were atomically clean as determined from low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). Monomer was adsorbed on the nickel surfaces circa 150 K and reaction was induced by raising the temperature. Surface species were characterized by temperature programmed reaction (TPR), reflection infrared spectroscopy, and AES. Molecular orientations were inferred from the surface dipole selection rule of reflection infrared spectroscopy. The selection rule indicates that only molecular vibrations with a dynamic dipole normal to the surface will be infrared active [14.], thus for aromatic molecules the absence of a C=C stretch or a ring vibration mode indicates the ring must be parallel the surface. 

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 vibrational density of states was calculated for nickel slabs up to 50 layers thick [8], For the first and second layers, the vibrational density of states was different from that of the bulk reflecting their surface configuration. The calculated surface modes for the various surface planes were compared with experiment. The best agreement was for the (111) surface, see Fig. 7.4, evidence for predominant (111) faceting of the micro particles. Although by today s standards the spectra and the fits are poor, the work is of interest as an example of the use of INS in surface characterisation. 

Describe briefly why a clean nickel surface (fee structure) should not be regarded as comprising a perfect close-packed array of atoms. Indicate the arrangements of atoms that an adsorbate might encounter on the surface, and suggest possible modes of attachment for CO. 

Beck R, Maroni P, Papageorgopoulos DC, Dang TT, Schmid MP, Rizzo TR (2003) Vibrational mode-spedflc reaction of methane on a nickel surface. Science 302 98-100... 

Figure 2 shows the SEM image of the flake at a magnification of 350 x, as it was mounted on the conductive carbon tape. If there is a polymeric film covering the sample, the SEM will only show the surface topography of the film, not the structure residing below the polymeric film. EDS was conducted on two areas on the sample as indicated in Figure 2. The EDS analysis was conducted in square spot mode, approximately 1 pm by 1 pm in size. The elemental results are shown in Table 2. Based on these data sets it is apparent that the Type A defect is an iron-rich particle. Based on the lack of chromium or nickel the Type A defect is a particle of steel, not stainless steel.

In this section a method for the direct calorimetric determination of heats of adsorption on evaporated metal films is described and results for the heals of adsorption of hydrogen on nickel, iron, and tungsten are reported. In all cases the heats of adsorption decrease with the fraction of surface covered in a mode that can satisfactorily be explained by interaction of adsorbed atoms. A criterion for mobility of the adsorbed atoms is developed... 

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... 

The use of a functionalized silica-supported salen-nickel complex has allowed Kumada cross-couplings to be performed in flow the corresponding polystyrene supported complex was shown to be inferior for a number of reasons. Catalyst 33 (Figure 4.7) with the longer tether was found to be more active than the benzyl ether tether used for catalyst 34. This was postulated to be due to the fact that catalyst 33 resided further away from the silica surface and hence was more available for reaction. Under the conditions used a maximum conversion of 65% was found for the 1 1 reaction of 4-bromoanisole and phenylmagnesium chloride, which was found to be comparable to that obtained in batch mode. However, during the reaction catalyst degradation was observed and the conversion reduced from 60% in the first hour to 30% in the fifth hour of the reaction [155,156]. 

Figure 13 Typical FTIR spectra obtained from nickel electrodes polarized to 0.2 V (Li/Li+) in LiBF4 1 M solution and measured ex situ, external reflectance mode (after being washed and dried), (a) The electrode was taken out of solutions soon after the surface films were formed, (b) The spectrum was measured after the electrode was stored for 1.5 h at open circuit for 1.5 h. (c) Same as (b), storage for 3.5 h at OCV before the spectroscopic measurement [34]. (With copyright from The Electrochemical Society Inc.)...

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