Adsorbate-induced faceting

Nevertheless, adsorbate-induced faceting of surfaces does occur under certain circumstances. An interesting and rather well-studied case is that of faceting of Cu(100) vicinal surfaces in an <010> zone to (410) as a result of atomic oxygen adsorption. The Cu(410) surface comprises (100) terraces just three atomic rows wide separated by a single atomic step, and it now seems rather well established that oxygen atoms decorate these steps in sites equivalent to those on the edges of the... 

Oscillations connected with adsorbate-induced surface restructuring were studied also in [29]. The model used was aimed at mimicking oscillations in NO reduction by H2 on a mesoscopic Pt particle containing two catalytically active (100) areas connected by an inactive (111) area that only adsorbed NO reversibly. NO diffusion on and between facets was much faster than other steps. The results obtained show that the coupling of the catalytically active sublattices may synchronize nearly harmonic oscillations observed on these sublattices and also may result in the appearance of aperiodic partially synchronized oscillations. The spatiotemporal patterns corresponding to these regimes are nontrivial. In particular, the model predicts that, due to phase separation, the reaction may be accompanied by the formation of narrow NO-covered zones on the (100) sublattices near the (lOO)-(lll) boundaries. These zones partly prevent NO supply from the (111) sublattice to the (100) sublattices. 

Linic and co-workers provided two additional examples of modifying selectivity for the ethylene epoxidation reaction. They demonstrated the promotional effect of Cs on EO formation using DFT calculations Cs atoms increase AEa by up to 0.2 eV vs. Ag only, via an induced electric field that interacts with the different dipoles of the two TS s." More recently Christopher et al. synthesized and tested (100) facet-dominated Ag nanowire catalysts, based on the DFT results that AEa is ca. 0.1 eV larger on Ag(lOO) than on Ag(lll), because of the extra elongation of the Ag-adsorbate bonds required to form the TS to AC on Ag(lOO). The Ag nanowire catalysts were indeed more selective than conventional Ag catalysts, in which Ag particles mainly exposes the (111) facet." Incidentally,... 

FT-RAIRS measurements of CO have also been used to identity facets of oxide supported Cu particles [78, 82]. The low sensitivity of RAIRS on single crystal ZnO(OOOl) prevented the observation of adsorbed CO or CO2, despite their observation in NEXAFS [78], although the local metallic dielectric allowed CO to be observed on the Cu particles. There appear to be no examples of HREELS being used to carry out vibrational spectroscopy of adsorbates on oxide supported metal particles. A HREELS study of Ag on MgO(lOO) films [95] was used only to characterise the Ag induced attenuation in the substrate Fuchs-Kliewer phonons, and the appearance of the metal/oxide interfacial plasmon at higher energies. HREELS has also been used to characterise the oxide/oxide interface between NiO and thin film MgO(lOO) [96]. Similar measurements of substrate phonon attenuation were made in HREELS studies on Pt films grown on ZnO(OOOl) [97]. 

Chen Q, Richardson NV (2003) Surface facetting induced by adsorbates. Prog Surf Sci 73 59... 

Restructuring processes involving surface diffusion of metal atoms over distances larger than one atomic distance may also be induced by adsorption at coverages near saturation. In this case, the original surface becomes unstable and breaks into new crystallographic orientations selectively stabilized by the adsorbate. This phenomenon, usually called faceting, occurs by step coalescence. The reversible... 

At o < 0.5 ML, the adsorbate starts to induce a (1 x 2) MR reconstruction of the surface. Oxygen atoms occupy every other fcc(lll) facet site along both sides of a metal row in the close-packed direction. Each adsorbate interacts with two atoms at the surface and one atom in the second substrate layer. 

Surfece facetting induced by adsorbates. Prog. Sutf. Sci., 73, 59 77. 

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