A low-energy electron diffraction study of oxygen, water and ice adsorption on Pt(111)

Starke, Ulrich; Materer, Nicholas F.; Barbieri, A.; Döll, R.; Heinz, K.; Hove, M.A. Van; Somorjai, Gábor A.

doi:10.1016/0039-6028(93)90818-5

Cited by 67 publications

(55 citation statements)

References 15 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Ethylidyne on Pt(111) occupies the same threefold fcc metal site as di--ethylene, as shown by LEED crystallography (Fig. 2b) (27). Its C-C bond is normal to the metal surface and the nearest-and next-nearestneighbor metal atoms change their locations as compared with their positions on the metal surface before C-H bond dissociation occurs.…”

Section: C-h Bond Activation Of Ethylene Over the Platinum (111) Crysmentioning

confidence: 82%

Clusters, surfaces, and catalysis

Somorjai¹,

Contreras

Montano

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

245

187

View full text Add to dashboard Cite

The surface science of heterogeneous metal catalysis uses model systems ranging from single crystals to monodispersed nanoparticles in the 1-10 nm range. Molecular studies reveal that bond activation (C-H, H-H, C-C, CAO) occurs at 300 K or below as the active metal sites simultaneously restructure. The strongly adsorbed molecules must be mobile to free up these sites for continued turnover of reaction. Oxide-metal interfaces are also active for catalytic turnover. Examples using C-H and CAO activation are described to demonstrate these properties. Future directions include synthesis, characterization, and reaction studies with 2D and 3D monodispersed metal nanoclusters to obtain 100% selectivity in multipath reactions. Investigations of the unique structural, dynamic, and electronic properties of nanoparticles are likely to have major impact in surface technologies. The fields of heterogeneous, enzyme, and homogeneous catalysis are likely to merge for the benefit of all three.catalytic bond activation ͉ high selectivity catalyst design ͉ molecular ingredients of catalysis M etal containing catalysts are clusters of 1-10 nm in size. These are grouped into three types: heterogeneous catalysts that are embedded in high surface area supports, usually oxides, to optimize their surface area and thus the number of molecules they produce per second and also to optimize their thermal and chemical stability. They are used mostly at high temperatures (400-800 K) and in the presence of vapor phase reactants and product molecules. Enzyme catalysts operate in solution, mostly in water near 300 K, and the metal-containing active sites are surrounded by proteins that maintain structural mobility (1). Homogeneous catalysts function in the same solution in which the reactant and product molecules are dissolved, mostly in organic solvents, and used in the 300-500 K temperature range. Because of the different operating conditions and for reasons of history, the three fields of catalysis developed independently and became separate fields of science within different subdisciplines of chemistry. Heterogeneous catalysis was practiced mostly by physical chemists and chemical engineers, enzyme catalysis by biochemists, and homogeneous catalysis by inorganic and organometallic chemists.Catalytic reactions are distinguished from stoichiometric reactions by having many turnovers per reacting active site producing 10 2 to 10 6 molecules per site. Some of these catalytic reactions are very fast. For instance, the catalytic oxidation of carbon monoxide (CO) produces thousands of CO 2 molecules per metal surface site per second above ignition where the exothermicity of the process makes it self-sustaining in temperature and the reaction rate is only limited by the speed of transport of molecules to and from the catalyst surface (2-4). Ethylene hydrogenation, another exothermic reaction, turns over to produce ethane Ϸ10 times per metal surface site per second at 300 K on Pt(111) (5). The catalytic conversion of n-hexane to benzene or to branched...

show abstract

Section: C-h Bond Activation Of Ethylene Over the Platinum (111) Crysmentioning

confidence: 82%

Clusters, surfaces, and catalysis

Somorjai¹,

Contreras

Montano

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

245

187

View full text Add to dashboard Cite

show abstract

“…Among the simplest optimization algorithms is the simplex method [53,37]. It does not require derivatives at all, but uses a "simplex" (set of vertices) of N + 1 points in parameter space, if there are N parameters to fit.…”

Section: Simplex Methodsmentioning

confidence: 99%

“…A more effective algorithm is the direction-set method [53,57,37], which minimizes the R-factor along a set of independent directions which are updated as the search proceeds. The minimization along each direction is done independently, by parabolic interpolation if the function is tested to be parabolic in the region of interest, or by simple bracketing if such a test fails.…”

Section: Direction-set Methodsmentioning

confidence: 99%

“…Recent work is pointing to the need to pay closer attention than heretofore to the atomic scattering amplitude (phase shifts) used in LEED, when trying to optimize many structural parameters with high accuracy [37]. It is, however, not yet possible to systematically quantify the effects of theoretical uncertainties on the best-fit atomic coordinates.…”

Section: Atomic Scattering Amplitudementioning

confidence: 99%

“…The integer-order beams are often relatively insensitive to relaxations induced by adatoms, while fractional-order beams are strongly affected. In fact, optimizing the structure on the basis of integer-order beams only may yield a poor fit for the fractional-order beams, whereas an all-beam optimization can give good fits in all beams [37].…”

Section: Use Of Subsets Of Datamentioning

confidence: 99%

See 2 more Smart Citations