Copper single crystal surfaces

Barnes et al. (44) observed similar results on copper single-crystal surfaces near the (100) face below 10-mV ridges, 40- to 70-mV platelets, 70- to 100-mV blocks, and fine platelets and above 100 mV, polycrystaUine depKJsit. The four basic structural forms are shown in Figure 7.19. Less frequently observed growth forms are p5namids, spirals, whiskers, and dendrites. The structure of depKJsits is discussed further in Chapter 16. 

The temperature-programmed desorption of H2 turned out to be a new tool for the determination of Cu metal surface areas [6]. For industrial purposes, the interaction of hydrogen with copper surfaces is a significant elementary step in methanol synthesis. Moreover, adsorp-tion/desorption kinetics on copper single crystal surfaces is an interesting topic in surface physics... 

Surface-science studies using copper single-crystal surfaces of (110) and (310) orientation onto which ZnO islands had been deposited indicate that CO and CO2 chemisorption can be used to identify the metal and the oxide sites, respectively. Methanol chemisorption produces both formate and methoxy species. The concentration of formate is enhanced by the presence of ZnO-copper interfaces, implicating these species as a reaction intermediate. 

Kolb D M, Kdtz R and Yamamoto K 1979 Copper monolayer formation on platinum single crystal surfaces Optical and... 

Other vicinal planes of copper single crystals and polycrystalline copper have been investigated and are also found to synthesize methanol in similar amounts as the Cu(lOO) surface [H. Nakano, I. Nakamura, T. Fujitani and J. Nakamura,/. Phys. Chem. B 105 (2001) 1355 Yoshihara and C.T. Campbell, J. Catal. 161 (1996) 776],... 

The drawback of the nitride/Cu(100) approach is its narrow application while the principle is sound, the nanoscale nitride corrals only work on copper and a limited number of other single-crystal surfaces. For more realistic applications, a more generic approach is needed. The obvious place to start is to make use of intermolecular forces to control the arrangement of molecules... 

Potter HC, Blakeley JM (1975) LEED, Auger spectroscopy, and contact potential studies of copper-gold alloy single crystal surfaces. J Vac Sci Technol 12 635-642... 

A paper by Szanyi and Goodman [56] on the synthesis of methanol over a copper single crystal provides a good example of how AES is often used in surface science studies of catalytic reactions. These authors investigated the formation of methanol from a mixture of CO2, CO and H2 on Cu(100) at tempera-... 

A question which has occupied many catalytic scientists is whether the active site in methanol synthesis consists exclusively of reduced copper atoms or contains copper ions [57,58]. The results of Szanyi and Goodman suggest that ions may be involved, as the preoxidized surface is more active than the initially reduced one. However, the activity of these single crystal surfaces expressed in turn over frequencies (i.e. the activity per Cu atom at the surface) is a few orders of magnitude lower than those of the commercial Cu/ZnO/ALO catalyst, indicating that support-induced effects play a role. Stabilization of ionic copper sites is a likely possibility. Returning to Auger spectroscopy, Fig. 3.26 illustrates how many surface scientists use the technique in a qualitative way to monitor the surface composition. 

This j taper describes equipment, procedures and results for investigation of transition metal surface reactivity. Specifically, the surface reactivity of copper single crystals was examined under conditions relevant to the electrochemistry and corrosion of copper. 

In order to recognize the pattern of reactivity of alcohols on modified nickel surfaces, it is essential to know the reaction pathways exhibited by less reactive surfaces. Initially the dehydrogenation of CH3OH was studied on copper (4 ) and silver (5 ) single crystal surfaces. On Cu(110), following the preadsorption of submonolayer quantities of atomic oxygen, methanol reacted via the following sequence (4,6) ... 

The preparation of well-defined single-crystal surfaces of copper oxides in UHV or of well-sintered powders, starting from polycrystalline materials, is difficult. Consequently, structure-catalytic property correlations remain to be established. 

Mechanism and Kinetics. The most detailed study of the reaction mechanism has been made by Wachs and Madix. They used isotopic tracers and flash desorption to study the species produced when methanol is adsorbed on an oxygen-doped copper (110) single-crystal surface. While the results of such a study are of considerable interest, they are not necessarily representative of a copper catalyst continuously exposed to reaction conditions. From the desorption spectra, methanol shows exchange only of the hydroxy-hydrogen surface methoxide was identified as the most populous surface intermediate. As formaldehyde and hydrogen also appeared to be produced from the same intermediate, the mechanism (21)—(24) was proposed for the selective reaction ... 

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