Group IB metals

In this section we briefly discuss the surface expansion of the group IB metals, Cu, Ag and Au, focusing on the close-packed (111) surfaces as they have been studied in the most detail (in fact there have been no published SXS studies of the Cu(lOO) and Cu(llO) surfaces in the electrochemical environment). In terms of surface expansion effects, the IB metals are more difficult to study than Pt as no Hupd is formed, and so it is difficult to correlate stmctural changes with weU-defined adsorption processes. Furthermore, the Au(hkl) surfaces reconstruct at negative potential, which limits the potential window where the surfaces are in the unreconstructed state. Despite these difficulties, relaxation at the Au(lll) surface was recently studied by a combination of SXS and surface stress measurements. For potentials on the positive side of the potential of zero charge (pzc), where the surface is unreconstructed, increasing positive surface charge 

It was postulated that such an adsorbed monolayer would explain the high density of the water layer proposed by Toney et al. [44]. 

Recently, Ag(lll) in 0.1 M KOH was also studied by SXS [46], and, as in the previous study, the surface was characterized by measurement of the non-specular CTRs and specular CTR. In alkaline solution there is no competition between OH and anions for adsorption sites, and the SXS data can be interpreted purely on the basis of the surface coverage by OHaa. At -0.95 V (vs SCE) the best fit parameters to the CTR data indicated that the surface layer undergoes a small inward relaxation (contraction) of 0.8% of the Ag(lll) layer spacing 

For the group 1B metals there appears to be a correlation between the pzc (surface charge) and surface relaxation. In contrast to Pt(hkl) surfaces, the Ag(hkl) surfaces (Ag(lOO) and Ag(llO) also exhibit inward relaxation [46]) undergo surface contraction that increases as the coverage by OH a increases. In the case of Au(hkl), the trend toward surface relaxation is difficult to extract because of the reconstruction of the surfaces at negative potential. In the unreconstructed state, however, it appears that the surfaces also contract as the coverage 

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A short survey of information on formation, structure, and some properties of palladium and nickel hydrides (including the alloys with group IB metals) is necessary before proceeding to the discussion of the catalytic behavior of these hydrides in various reactions of hydrogen on their surface. Knowledge of these metal-hydrogen systems is certainly helpful in the appreciation, whether the effective catalyst studied is a hydride rather than a metal, and in consequence is to be treated in a different way in a discussion of its catalytic activity. 

Equilibrium conditions for the synthesis of intermetallic phases and compounds are summarized as a function of temperature and composition in the form of phase diagrams. Consequently, in the following subsections, phase relationships for group-IIA-group-IB metal systems are reviewed. Phase diagrams in ref. 1 are used as a baseline work published before this compilation is not specifically referred to, but that reported subsequently is used, as appropriate, to modify or replace these phase diagrams. 

I. Reaction of Carbonyl Aniona with Uneomplaxad Derivatives of Group-IB Metals. 

Formation of bonds between group-IB and transition metals by reacting carbonyl anions with complexed derivatives of group-IB metals is discussed in 8.3.2.1. Car-... 

These reactions give products similar to those described in 8.3.2.1. Transition-mclal hydrido complexes react with a halogen derivative of a group-IB metal to form a hydrogen halide and the required metal-metal bond ... 

The transition metals are also good conductors as they have a similar sp band as the free-electron metals, plus a partially filled d band. The Group IB metals, copper, silver and gold, represent borderline cases, as the d band is filled and located a few eV below the Fermi level. Their sp band, however, ensures that these metals are good conductors. 

Borkett, N.F., Bruce, M.I. and Walsh, J.D. (1980) Chemistry of the group IB Metals. XIV Some poly(pyrazolyl)borate derivatives containing gold. Australian Journal of Chemistry, 33, 949. 

Coates, G.E., Kowala, C. and Swan, J.M. (1966) Coordination compounds of Group IB metals. I. Triethylphosphine complexes of Au(I) mercaptides. Australian Journal of Chemistry, 19, 539-545. 

Pritchard, J. and Tompkins, F.C. (1960) Surface-potential measurements. Adsorption of hydrogen by Group IB metals. Transactions of the Faraday, Society, 56, 540-550. 

The activity of the transition metals, especially for the chemisorption of molecular hydrogen and in hydrogenation reactions has been correlated, in the past, with the existence of partially filled d bands. Many alloy studies were prompted by the expectation that catalytic activity would change abruptly once these vacancies were filled by alloying with a group IB metal. Examples of such behavior have been collected together for the Pd-Au system (1). It is to be expected also that various complications might superimpose on the simple activity patterns observed for primitive... 

Copper, and occasionally silver, have been used as catalysts for hydroformylation of a-olefins. Phosphite complexes of copper(I) chloride have been claimed as catalysts (126). Phthalocyanine complexes of Group IB metals have been stated to show a low degree of catalytic activity (127). One of the more interesting examples of copper catalysis was disclosed by McClure (128). Copper powder, with a controlled amount of water (0.2-4.0 moles H20/mole Cu), gave a slow conversion of pro-... 

For the Group VIII transition metals the d-band is partially filled and the Fermi level is in the d-band. The Group IB metals have a completely filled d-band and here the Fermi level falls above the d-levels in the s-band. Two trends in going from left to right through the metals in the periodic system are that the d-band becomes narrower and the Fermi level decreases with respect to the vacuum level. 

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