On Pt surfaces

The CO oxidation occurring in automobile exhaust converters is one of the best understood catalytic reactions, taking place on Pt surfaces by dissociative chemisoriDtion of to give O atoms and chemisoriDtion of CO, which reacts with chemisorbed O to give CO, which is immediately released into the gas phase. Details are evident from STM observations focused on the reaction between adsorbed O and adsorbed CO [12]. 

It is worth noting that each Na atom appears to perturb the electron density of the Pt(lll) surface over large ( 12) atomic distances. This can explain nicely the observed long-range promotional effect of Na on Pt surfaces. It is strongly reminiscent of the IR spectroscopic work of Yates and coworkers who showed that a single adsorbed alkali atom can affect the IR spectra of up to 27 coadsorbed CO molecules.80... 

Recently, Stair and coworkers [10, 11] developed a method to produce gas-phase methyl radicals, and used this to study reactions of methyl groups on Pt surfaces [12] and on molybdenum oxide thin films [13]. In this approach, methyl radicals are produced by pyrolysis of azomethane in a tubular reactor locat inside an ulttahigh vacuum chamber. This method avoids the complications of co-adsorbcd halide atoms, it allows higher covraages to be reached, and it allows tiie study of reactions on oxide and other surfaces that do not dissociate methyl halides effectively. 

In fact, the reaction of SnEt4 on Pt surfaces covered by irreversibly adsorbed hydrogen (and in the absence of H2) leads to the same type of species, Pts[SnEt3]j, which is stable under these conditions (mechanism 13) and has... 

In conclusion, cyclovoltammetric results in CO-saturated electrolyte demonstrate that CO oxidation takes place only for > 0.55 V, and this with very low rates [Wang et al., 2001 Brankovic et al., 2002a]. Assuming a similar reaction mechanism for CO oxidation on Ru(OOOl) as for the extensively studied reaction on Pt surfaces [Santos et al., 1991 Lebedeva et al., 2000 Shubina et al., 2004], the overall oxidation... 

The kinetics of NO on Pt surfaces have been explored by many authors both in TPD and beam scattering types of experiments. In a series of sophisticated modulated beam scattering experiments, Serri efo/. (referred to subsequently in the text as STC) attempted to reconcile the apparently disparate results reported previously"- " . In their experiments they noted that for... 

Computational efforts using DPT calculations as well as kinetic modeling of reactivities based on Monte Carlo simulations or mean field mefh-ods have been employed to study elementary processes on Pt surfaces. 2 228 Unraveling systematic trends in structure versus reactivity relations remains a formidable challenge due to fhe complex nafure of sfrucfural effects in electrocatalysis. 

OH groups could appear on Pt surfaces due to the dissociation of water molecules on the surface. To estimate whether this process is energetically favorable, compare the energy of clean Pt(lll) surface and a gas-phase HzO molecule to the energy of an OH group coadsorbed on Pt(l 11) with an H atom. 

The first observations on the development of periodic modulations were made on Pt surfaces annealed in vacuum in the temperature range 920 to 1300C[9J. The 1-dimensional grating structures were made by mechanically ruling portions of gratings on polycrystalline Pt specimens. Annealing caused extensive... 

Silicide layers can also be grown on Pt surfaces.247 The preferential facets of epitaxial growth are the 111. Atom-probe data reveal that the stoichiometry of the silicide phase is Pt2Si, and the Pt-Pt2Si interface is also very sharp. However, a small fraction of silicon atoms can diffuse into the Pt matrix. Formation of silicide layers on a nickel emitter surface is much more complicated where silicide layers of varying stoichiometries are formed.246,247 Owing to the statistical nature of the atom-probe data, identification of all the silicide phases in a nickel silicide layer is at best uncertain. 

Gropen,0., Almlof,J. and Wahlgren,U. (1991) Model studies of chemisorption on Pt surfaces , in Cluster Models for Surface and Bulk Phenomena,... 

In Table V we summarize the spectra of the principal adsorbed species on Pt surface planes and include more precise band positions for the di-ct (158) and ethylidyne species (159) from RAIR spectra. The spectra are listed in the order of increasing temperatures for the adsorbed species. As we shall see, the patterns of spectra for the n- and 7i -species and for ethylidyne vary little from metal to metal, but that of the di-cr species is more variable, with other metals giving an increased wavenumber of ca. 1140 cm-1 for the strongest feature replacing 1040/980 cm 1 for Pt (17). The other surface species, except for CCH are rarely found on other metals. 

Mittal postulated that radical formation is likely due to the chemical reaction of H2 and 02 on Pt surface, this reaction is chemical in nature and shows strong dependence on the surface properties of Pt particles, and the sulfonic acid groups in the PFSA membrane maybe the key to the radical attack mechanisms.27 Cipollini28 in... 

Sulfur Trioxide Adsorption on Pt Surface Chikashi Suzuki and Toshio Nakagiri... 

Contents 1. Introduction 62 2. Calculation 63 2.1 Surface configuration 63 2.2 Electronic states 63 3. Results and Discussions 64 3.1 S03 configuration on Pt surface 64 3.2 Analysis of density of states 67 3.3 Chemical bonding states 74 3.4 Interaction between Pt surface and O atom 76 3.5 Stabilization of S02 desorption 77 4. Conclusions 78 Acknowledgment 78 References 78... 

In order to investigate the mechanism of S03 electrolysis, it was necessary to evaluate the electronic states of S03 adsorbed on Pt surface. For this purpose, by using the molecular orbital calculation with cluster models, we have evaluated the electronic states of S03 adsorbed on Pt (111) surface. Also, in order to... 

In order to calculate adsorbed SO3 configuration on Pt surface, we used the first-principles calculation code PHASE [9] with a slab model in a periodic boundary condition along the surface plane to simulate the Pt (111) surface. A four-layer slab model was used for main calculations. In these calculations, the atoms at the bottom are fixed at a bond distance d=2.83 A, which is the optimized value in Pt fee crystal with PHASE. A p(4 x 4) lateral supercell was used for the computation of the most energetically stable configuration. The p(4 x 4) surface supercell has 16 Pt atoms per layer with a lateral lattice constant of 11.31 A. 

Figure 6.2 Calculated adsorbed S03 configuration on Pt surface, (a) Configuration A (b) configuration B. For a colour version of this figure, please see the colour plate section near the end of this book.

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