Showing papers on "Platinum published in 1969"

Catalysis by Supported Metals

Abstract: Publisher Summary This chapter describes the interaction between metal and support, which may complicate the interpretation of data obtained with supported metals, the critical problem of determining the surface area of the metal, and illustrates the use of supported metals for the elucidation of the problem of catalyst specificity. Work on the series of platinum catalysts suggests that many reactions of hydrogenation, dehydrogenation, and hydrogenolysis are structure-insensitive. If, these same catalysts are now used in reactions involving oxygen—decomposition of hydrogen peroxide, oxidation of methanol and ethanol, oxidation of acetaldehyde—the picture is substantially altered: while specific rates are again almost the same for highly dispersed samples with percentages of dispersion between 80 and 100%, these specific rates change by at least one order of magnitude on samples with a smaller dispersion (50%) and on platinum black.

Planar Complexes Containing Metal‐Metal Bonds

Abstract: Planar complexes, and particularly those of platinum, can form structures containing linear chains of heavy metal atoms with metal-metal distances as short as 3.1 A. The bonding in these chains can be strengthened by partial oxidation, and the bond lengths can be reduced to 2.8 A in this way. Model structures for the novel nonstoichiometric products, such as K2[Pt(CN)4]Cl0·32 · 2.6 H2O, are considered. The bonding is also discussed on the basis of a one-dimensional band model.

Low‐Energy Electron‐Diffraction Studies of the Adsorption of Unsaturated Hydrocarbons and Carbon Monoxide on the Platinum (111) and (100) Single‐Crystal Surfaces

Abstract: The interaction of simple aliphatic hydrocarbons and carbon monoxide with Pt(111) and Pt(100) surfaces, at gas pressures ≤ 1 × 10−7 torr, has been studied using low‐energy electron diffraction (LEED), mass spectrometry, flash desorption, and work‐function (φ) measurements. The Pt(111) substrate was characterized by a (1 × 1) diffraction pattern while a (5 × 1) surface structure was visible on Pt(100). In contrast to the saturated hydrocarbons, all the other gases used (CO, C2H2, C2H4, C3H6, 1,3‐butadiene and the isomeric butenes) were readily chemisorbed on both substrates. Relatively large decreases in φ resulted from the chemisorption of the unsaturated hydrocarbons while a small increase in φ was measured due to the adsorption of CO. A (2 × 2) surface structure was produced on the (111) face by all of the unsaturated hydrocarbons studied, with the exception of isobutylene which exhibited a larger unit mesh. Although C2H2 and C2H4 produced a C(2 × 2) structure on the (100) face of platinum, the adsorpti...

High Performance, Platinum Activated Tungsten Oxide Fuel Cell Electrodes

Abstract: HYDROCARBON fuels (methane, propane and so on) are relatively inert and can only be electrochemically oxidized using either high loading noble metal-black electrodes in phosphoric acid at 150° C or high temperature molten carbonate (or solid oxide) electrolyte cells at 600–1,000° C (ref. 1). Alternatively the fuel may be “reformed”, producing impure hydrogen (containing carbon dioxide and some carbon monoxide) which may be fed into a low temperature (> 100° C) acid fuel cell. Carbon monoxide, however, poisons platinum black by strongly adsorbing on its surface (with high coverage) at normal fuel cell anode potentials. Little opportunity exists for water molecules to adsorb on sites adjacent to surface CO molecules—a necessary condition for the removal of the latter by anodic oxidation2

Tungsten Carbide Electrodes for Fuel Cells with Acid Electrolyte

Abstract: FUEL cells with acid electrolyte, such as dilute sulphuric acid, have the advantage over those with alkaline electrolyte that carbon dioxide is not absorbed by the electrolyte. In principle it is therefore possible to use organic fuels, either direct or by reforming them with water vapour, without removing the resultant carbon dioxide. Even if carbon-free fuels such as hydrogen or hydrazine are used, an acid electrolyte should be preferred, for carbon dioxide need not be removed from the air. In the past, however, no acid-resistant catalyst has been found that might replace expensive and easily poisoned platinum.

Protective diffusion layer on nickel and/or cobalt-based alloys

Abstract: Nickel and/or cobalt-based alloys are given a protective coating by diffusing into the surface of the alloy metallic aluminum and one or more metals of the platinum groups.

Anodic oxidation of carbohydrates and their derivatives in neutral saline solution.

Abstract: Rao and Drake1 have recently reported work on the oxidation of dextrose on platinized platinum in neutral buffer solution (pH 7.4). They have shown that anodic charging curves on platinized platinum electrodes in 0.5 M dextrose solution go through an inflexion at about 0.1 V referred to standard hydrogen electrode (SHE) (where platinum starts to adsorb oxygen in neutral solution), after which oxidation is inhibited. No square root dependence was noted for the transition time to this point, indicating that the inhibitive process was not under diffusion control. In addition, the total number of coulombs required to reach the point of inflexion decreased if increasing concentrations of gluconic acid were added to the dextrose solution. They reported open circuit potential (OCP) of + 0.3 V (SHE) in deaerated gluconic acid solution (10−4 to 10−1 M), and they detected no evidence of gluconic acid oxidation in the potential range −0.6 to 0.0 V (SHE). Their general conclusions were that the only oxidation product of glucose in these conditions is gluconic acid, which adsorbs on the electrode in the potential range −0.2 to 0.0 V (SHE), effectively inhibiting glucose oxidation.

Catalytic oxidation of methane over noble metals

Abstract: The complete oxidation of methane over palladium, platinum, rhodium and iridium has been studied using a microcalorimetric technique. The results indicated that methane may be adsorbed on two types of reaction site, one of which also adsorbs oxygen. The activation energies are proportional to the Pauling bond energies of the oxygen-metal bond in the region where the order in oxygen is low.

A study of anion adsorption on platinum by ellipsometry

Abstract: Anions adsorption at platinum determined by ellipsometry, finding perchlorate and fluoride ions adsorption below detection limit