Production of syngas by direct catalytic oxidation of methane

The reaction between methane and oxygen over platinum and rhodium surfaces in metalcoated ceramic monoliths can be made to produce mostly hydrogen and carbon monoxide (greater than 90% selectivity for both) with almost complete conversion of methane and oxygen at reaction times as short as 10(-3) seconds. This process has great promise for conversion of abundant natural gas into liquid products such as methanol and hydrocarbons, which can be easily transported from remote locations. Rhodium was considerably superior to platinum in producing more H(2) and less H(2)O, which can be explained by the known chemistry and kinetics of reactants, intermediates, and products on these surfaces.     

NMR studies of simple molecules on metal surfaces

In recent years, improvements in the sensitivity of nuclear magnetic resonance have made it possible to detect progressively smaller numbers of nuclei. Experiments and studies previously thought to be impractical can now be undertaken, for example, the study of phenomena at surfaces. Nuclear magnetic resonance has been applied to study simple molecules (carbon monoxide, acetylene, and ethylene) adsorbed on metal surfaces (ruthenium, rhodium, palladium, osmium, iridium, and platinum). The metals, in the form of clusters 10 to 50 angstroms in diameter, supported on alumina, are typical of real catalysts. The experiments provide information about the bonding of the molecules to the metal, the structures the molecules assume after adsorption, the motion of molecules on the surface, the breakup of molecules induced by heating, and the products of such breakup.     

Controlled Deposition of Size-Selected Silver Nanoclusters

Variable-temperature scanning tunneling microscopy was used to study the effect of kinetic cluster energy and rare-gas buffer layers on the deposition process of size-selected silver nanoclusters on a platinum(111) surface. Clusters with impact energies of 相似文献   

Imaging surface atomic structure by means of auger electrons

Measurements of the complete angular distribution of Auger electrons emitted from well-defined platinum[111] single-crystal surfaces have led to the discovery that the distributions are composed of "silhouettes" of surface atoms "back lit" by emission from atoms deeper in the solid. Theoretical simulations of Auger electron angular distributions based upon atomic point emitters and spherical atomic scatterers of uniform cross section are in close agreement with these experimental results, but opposite to previous theoretical predictions. In view of the definitive results obtained and the straightforward agreement between theory and experiment, angular distribution Auger microscopy (ADAM) is useful for direct imaging of interfacial structure and investigation of electron-solid interactions in the physical and biological sciences and engineering. Applicability of ADAM is illustrated by images obtained for monolayers of silver and iodine on platinum[111].     

Rare-Earth manganites: surface-segregated platinum increases catalytic activity

Crushed and etched lanthanum lead manganite (La(0.7)Pb(0.3)MnO(3)) crystals containing as little as 0.005 atomic percent platinum have significantly higher catalytic activity than free platinum crystals. This higher activity is due to an almost 100-fold segregation of platinum on the surface. The surface platinum concentration found, 0.5 atomic percent, is sufficient to account for the enhanced activity provided that the platinum has the same activity as platinum supported on alumina.     

Enhancing hydrogen evolution activity in water splitting by tailoring Li⁺-Ni(OH)₂-Pt interfaces

Improving the sluggish kinetics for the electrochemical reduction of water to molecular hydrogen in alkaline environments is one key to reducing the high overpotentials and associated energy losses in water-alkali and chlor-alkali electrolyzers. We found that a controlled arrangement of nanometer-scale Ni(OH)(2) clusters on platinum electrode surfaces manifests a factor of 8 activity increase in catalyzing the hydrogen evolution reaction relative to state-of-the-art metal and metal-oxide catalysts. In a bifunctional effect, the edges of the Ni(OH)(2) clusters promoted the dissociation of water and the production of hydrogen intermediates that then adsorbed on the nearby Pt surfaces and recombined into molecular hydrogen. The generation of these hydrogen intermediates could be further enhanced via Li(+)-induced destabilization of the HO-H bond, resulting in a factor of 10 total increase in activity.     

NO3-和NO2-在有机锡修饰电极上的电化学研究

通过循环伏安法、旋转圆盘电极等方法研究了有机锡化合物在铂电极上的电化学行为，以及吸附有机锡化合物的铂电校对硝酸根和亚硝酸根的催化还原性能和pH的影响。结果表明二乙基锡在铂电极上的吸附对N03^-和N02^-的还原具有催化作用。还原时过电位减少，根据其还原过程的电化学行为，提出了可能的催化机理。同时通过催化过程动力学分析由实验得到了催化速率常数。     

Atomic resolution imaging of adsorbates on metal surfaces in air: iodine adsorption on pt(111)

The adsorption of iodine on platinum single crystals was studied with the scanning tunneling microscope (STM) to define the limits of resolution that can be obtained while imaging in air and to set a target resolution for STM imaging of metal surfaces immersed in an electrochemical cell. Two iodine adlattice unit cells of slightly different iodine packing density were clearly imaged: ( radical7 x radical7) R19.1 degrees -I, surface coverage ?(I) = 3/7; and (3 x 3)-I, ?(I) = 4/9. The three iodine atoms in the ( radical7 x radical7) unit cell form a regular hexagonal lattice interatomic distance d(I) = 0.424 nanometer, with two atoms adsorbed in threefold hollow sites and one atom adsorbed at an atop site. The (3 x 3) unit cell showed two different packing arrangements of the four iodine atoms exit. In one of the (3 x 3) structures, the iodine atoms pack to form a hexagonal lattice, d(I) = 0.417 nanometer, with three of the iodine atoms at twofold adsorption sites and one atom at an atop site. Another packing arrangement of iodine into the (3 x 3) unit cell was imaged in which the iodine atoms are not arranged symmetrically.     

Inducing and viewing the rotational motion of a single molecule

Tunneling electrons from the tip of a scanning tunneling microscope were used to induce and monitor the reversible rotation of single molecules of molecular oxygen among three equivalent orientations on the platinum(111) surface. Detailed studies of the rotation rates indicate a crossover from a single-electron process to a multielectron process below a threshold tunneling voltage. Values for the energy barrier to rotation and the vibrational relaxation rate of the molecule were obtained by comparing the experimental data with a theoretical model. The ability to induce the controlled motion of single molecules enhances our understanding of basic chemical processes on surfaces and may lead to useful single-molecule devices.     

Oscillatory kinetics and spatio-temporal self-organization in reactions at solid surfaces

Chemical reactions far from equilibrium on solid surfaces may exhibit typical phenomena of nonlinear dynamics, as exemplified by the catalytic oxidation of carbon monoxide on a platinum(110) single-crystal surface. Depending on the external parameters (temperature and partial pressures of the reactants), the temporal variation of the reaction rate may become oscillatory or even chaotic. In a parallel way, the concentration distributions of the adsorbed species on the surface form spatio-temporal patterns including propagating and standing waves, rotating spirals, as well as irregular and rapidly changing structures denoted "chemical turbulence."     

Shape-Controlled Synthesis of Colloidal Platinum Nanoparticles

The shapes and sizes of platinum nanoparticles were controlled by changes in the ratio of the concentration of the capping polymer material to the concentration of the platinum cations used in the reductive synthesis of colloidal particles in solution at room temperature. Tetrahedral, cubic, irregular-prismatic, icosahedral, and cubo-octahedral particle shapes were observed, whose distribution was dependent on the concentration ratio of the capping polymer material to the platinum cation. Controlling the shape of platinum nanoparticles is potentially important in the field of catalysis.     

不同叶面肥对烤烟农艺性状的影响

本试验以云烟87为材料,研究叶面肥烟白金和锌铜大师施用效果。结果表明：与常规肥相比,烟白金对生育期、农艺性状、化学品质影响不大,使烟叶品质有提升,但能增加中上等烟叶比例和产值,中上等烟比例增加了6.82%,产值增加了447.27元/亩;锌铜大师对农艺性状有一定影响,增加了产量,但产值较低,不建议使用。     

Experience in a breeding program to create a flock of sur Karakul sheep of the new Surkhan Darya type

To increase the production of sur karakul fur of the Surkhan Darya intrabreed type, regularities in the inheritance of colors in progeny have been studied. Both with homogeneous and heterogeneous breeding of ewes and stud rams of bronze, amber, and platinum colors, a high heredity of bronze and platinum colors is noted. The color of rams has a greater effect on inheritance of colors.     

Electronic structure and catalytic behavior of tungsten carbide

Tungsten carbide has been shown to be an effective catalyst for a number of reactions that are readily catalyzed by platinum, but not at all by tungsten, and it was speculated that this behavior is due to changes in the electron distribution when carbon is added to tungsten. A test of this hypothesis, made by measuring the valence band x-ray photoelectron spectrum of tungsten carbide and comparing it with the spectra of tungsten and platinum, shows that, near the Fermi level, the electronic density of states of tungsten carbide more nearly resembles that of platinum than that of tungsten.     

Combinatorial electrochemistry: A highly parallel, optical screening method for discovery of better electrocatalysts

Combinatorial screening of electrochemical catalysts by current-voltage methods can be unwieldy for large sample sizes. By converting the ions generated in an electrochemical half-cell reaction to a fluorescence signal, the most active compositions in a large electrode array have been identified. A fluorescent acid-base indicator was used to image high concentrations of hydrogen ions, which were generated in the electrooxidation of methanol. A 645-member electrode array containing five elements (platinum, ruthenium, osmium, iridium, and rhodium), 80 binary, 280 ternary, and 280 quaternary combinations was screened to identify the most active regions of phase space. Subsequent "zoom" screens pinpointed several very active compositions, some in ternary and quaternary regions that were bounded by rather inactive binaries. The best catalyst, platinum(44)/ruthenium(41)/osmium(10)/iridium(5) (numbers in parentheses are atomic percent), was significantly more active than platinum(50)/ruthenium(50) in a direct methanol fuel cell operating at 60 degreesC, even though the latter catalyst had about twice the surface area of the former.     

Platinized chloroplasts: a novel photocatalytic material

Colloidal platinum was prepared and precipitated directly onto photosynthetic thylakoid membranes from aqueous solution and entrapped on fiberglass filter paper. This composition of matter was capable of sustained simultaneous photoevolution of hydrogen and oxygen when irradiated at any wavelength in the chlorophyll absorption spectrum. Experimental data support the interpretation that part of the platinum metal catalyst is precipitated adjacent to the photosystem I reduction site of photosynthesis and that electron transfer occurs across the interface between photosystem I and the catalyst. Photoactivity of the material was dependent on the nature of the ionic species from which the platinum was precipitated. All photoactive samples were prepared from the hexachloroplatinate(IV) ion, whereas samples prepared by precipitation of the tetraammineplatinum(II) ion showed no hydrogen evolution activity and only transient oxygen activity. This system is among the simplest known for photosynthetically splitting water into molecular hydrogen and oxygen.     

Platinum catalysts for the high-yield oxidation of methane to a methanol derivative

Platinum catalysts are reported for the direct, low-temperature, oxidative conversion of methane to a methanol derivative at greater than 70 percent one-pass yield based on methane. The catalysts are platinum complexes derived from the bidiazine ligand family that are stable, active, and selective for the oxidation of a carbon-hydrogen bond of methane to produce methyl esters. Mechanistic studies show that platinum(II) is the most active oxidation state of platinum for reaction with methane, and are consistent with reaction proceeding through carbon-hydrogen bond activation of methane to generate a platinum-methyl intermediate that is oxidized to generate the methyl ester product.     

Giant magnetic anisotropy of single cobalt atoms and nanoparticles

The isotropic magnetic moment of a free atom is shown to develop giant magnetic anisotropy energy due to symmetry reduction at an atomically ordered surface. Single cobalt atoms deposited onto platinum (111) are found to have a magnetic anisotropy energy of 9 millielectron volts per atom arising from the combination of unquenched orbital moments (1.1 Bohr magnetons) and strong spin-orbit coupling induced by the platinum substrate. By assembling cobalt nanoparticles containing up to 40 atoms, the magnetic anisotropy energy is further shown to be dependent on single-atom coordination changes. These results confirm theoretical predictions and are of fundamental value to understanding how magnetic anisotropy develops in finite-sized magnetic particles.     

杂环化合物的电化学聚合及膜的pH响应

本文研究具有类似萘环结构的杂环化合物的电化学聚合特性。对修饰介质进行了优化，以铂丝为基体制得的聚合膜修饰电极对试液ｐＨ值有较好的电位响应。电极可用于实际样品中ｐＨ值的测定。     

日光温室内各表面太阳辐射照度的模拟计算

建立了温室内各表面太阳辐照度计算模型,并对沈阳地区跨度为12 m的日光温室进行模拟,分析了温室建筑参数改变对温室内各表面太阳辐射照度的影响。结果表明:冬季最冷月(2003 12至2004 02)温室内后坡单位面积太阳辐射照度分别为土壤表面及后墙面的1.45和1.49倍;温室地面太阳辐射照度模拟结果与实际测试结果差值不超过5%。改变温室跨度和高度分别对地面及北墙面太阳辐射照度有较大影响,且呈线性关系;改变温室后坡仰角对温室内各表面太阳辐射照度的影响不显著。