Restructuring chemisorption-induced

An extreme case of chemisorption-induced restructuring of metal surfaces is coirosive chemisorption as observed by SFG. In this circumstance, metal atoms break away from step or kink surface sites and form bonds with several adsorbate molecules. Carbon monoxide can form several carbonyl ligand bonds with platinum atoms leading to the creation of metal-carbonyl species. Thus, metal-metal bonds are broken in favor of forming metal-carbonyl clusters that are more stable at high CO pressures. The SFG vibrational spectra detect the reversible formation of new adsorb carbon monoxide species above 1(X) Torr on Pt(l 11), that appear to be platinum-carbonyl clusters Pt (CO) , with (m/n) > 1 and a CO commensurate overlayer. 

TABLE 2.6. Surface Structures Formed by Chemisorption-Induced Restructuring... 

Chemisorption-induced restructuring can be very well seen using a small metal tip and field ion microscopy. In Figure 6.1 lb the field ion microscope picture of a rhodium tip is shown when clean and after exposure to carbon monoxide at 420 K at low pressures ( 10 Pa) [8]. The metal tip has been completely reshaped as a result of CO chemisorption. The tip becomes faceted and rougher, the step density is reduced, and extended low-Miller-index terraees are formed. 

Restructuring occurs in order to maximize the bonding and stability of the adsorbate-substrate complex. Thus it is driven by thermodynamic forces and is most likely to occur when the stronger adsorbate-substrate bonds that form compensate for the weakening of bonds between the substrate atoms, an inevitable accompaniment to the chemisorption-induced restructuring process. 

Ethylidyne restructures the Rh(l 11) crystal face [30], sulfur restructures the Fe(l 10) face [7], and carbon restructures the Ni(lOO) face [6, 46]. The surface metal atoms move into new equilibrium p>ositions upon chemisorption in different ways, and there is evidence of restructuring even in the second substrate layer under the surface. Review the available data and point out the important electronic and structural parameters that influence the nature and magnitude of chemisorption-induced surface restructuring. 

Oxygen chemisorption on Cu(llO) and Cu(lOO) exhibits two types of surface restructuring, in which the mass transport for the O-induced reconstructions differs... 

Ad.sorplion-induced restructuring can occur on the chemisorption time scale (isf 10 see for charge transfer or — lO" see for vibrational times). There is evidence, however, (hat adsorbate-induced restmeturing can occur on the lime scale of catalytic reactions (seconds). CO oxidation to CO or ammonia reacting with NO to produce nnd H O show osciliaiiiry behavior under certain cireumsiance.s of temperature and renctant partial pressures. The rcuction rate alternates periodically bc-... 

Adsorbate-induced restructuring of surfaces could explain the formation of cluster-like bonding of adsorbates on metal surfaces. Discuss how the strength of the chemisorption bond is likely to influence the restructuring of metal surfaces. 

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