Showing papers on "Platinum published in 1983"

Importance of Interatomic Spacing in Catalytic Reduction of Oxygen in Phosphoric Acid

Abstract: A correlation between the nearest-neighbor distance and the oxygen reduction activity of various platinum alloys is reported. It is proposed that the distance between nearest-neighbor Pt atoms on the surface of a supported catalyst is not ideal for dual site absorption of O2 or 'HO2' and that the introduction of foreign atoms which reduce the Pt nearest-neighbor spacing would result in higher oxygen reduction activity. This may allow the critical 0-0 bond interatomic distance and hence the optimum Pt-Pt separation for bond rupture to be determined from quantum chemical calculations. A composite analysis shows that the data on supported Pt alloys are consistent with Appleby's (1970) data on bulk metals with respect to specific activity, activation energy, preexponential factor, and percent d-band character.

Electrochemical synthesis of electrically conducting polymers from aromatic compounds

Abstract: Amorphous, electrically conducting polymeric films can be deposited from acetonitrile solutions of specific aromatic compounds containing an appropriate electrolyte. Free-standing films peeled off a platinum electrode have electrical conductivities between 10-3 and 1 Ω-1 -cm-1. Polymers resembling the better-known polypyrrole have been obtained from benzenoid, nonbenzenoid, and heterocyclic monomers. A few characteristic examples are discussed to highlight the characterization efforts. Also discussed are the chemical investigations which have provided some insight into the mechanism of formation and the structure of these conducting polymers.

Electrodeposition of Conducting Transition Metal Oxide/Hydroxide Films from Aqueous Solution

Abstract: Donnees sur une methode generale de depot electrolytique de couches minces d'oxyde-hydroxyde de Cu, Ni, Co, Fe et Mn, a partir d'une solution aqueuse, sur une electrode a disque tournant de Pt, soit sous tension constant, soit sous tension variant cycliquement

Synthesis of SS'-bis(4'-benzo[15-crown-5]dithioglyoxime and its complexes with copper(II), nickel(II), cobalt(II), cobalt(III), palladium(II), platinum(II), and platinum(IV)

Abstract: NN′-Bis(4′-benzo[15-crown-5])diaminoglyoxime (H2L) has been prepared as a bis(sodium chloride) salt from anti-dichloroglyoxime, 4′-aminobenzo[15-crown-5], and sodium bicarbonate in ethanol. Copper(II), nickel(II), and cobalt(II) complexes of H2L·2NaCl have a metal–ligand ratio of 1 : 2 and the ligand co-ordinates through the two N atoms, as do most of the vic-dioximes. [Pt(HL)2·4NaClO4] and [Pd(HL)2·4NaClO4] complexes form six-membered chelate rings and co-ordinate through N and O atoms. [Co(HL)2(L′)Cl·4NaClO4] has been prepared with L′= triphenylphosphine or pyridine, together with a chloride ion, as axial ligands. H2L·2NaX (X = Cl– or ClO4–) reacts with UO2(O2CMe)2·2H2O to give complexes with a metal–ligand ratio of 1 : 1. All these complexes are soluble in water; n.m.r., i.r., and u.v.–visible data are presented.

Acetylene, ethylene, and arene chemistry of palladium surfaces

Abstract: The chemisorption behavior of acetylene, ethylene, and benzene on the low Miller index planes of palladium is described. This behavior is very sensitive to the surface composition, particularly to sulfur and phosphorus adatoms. Most complex was the acetylene chemistry where decomposition to carbon, reversible desorption, reversible C-H bond scission, trimerization to benzene, and hydrogenation to ethylene were five readily characterizable, competing reactions. In this context of acetylene chemistry, the palladium surfaces behave quite differently from those of nickel and platinum under ultrahigh vacuum conditions. Also, unlike nickel and platinum, palladium under ultrahigh vacuum conditions effected hydrogenation reactions such as the conversion of acetylene to ethylene.

Platinum/titanium dioxide catalysts. A photoconductivity study of electron transfer from the ultraviolet-illuminated support to the metal and of the influence of hydrogen

Abstract: Photoconductivity measurements have been carried out for a series of powder Pt/TiO2 catalysts containing from 0.05 to 10 wt% Pt as well homodispersed particles (mean diameter ca. 2 nm). The presence of platinum, at least for contents ca. 1 wt%, caused a decrease in the anatase photoconductance σeq at equilibrium under vacuum and this decrease was more pronounced for the highest loadings (5 and 10 wt%). In addition, differences in the times required to reach the steady state were observed, and an attenuation of the u.v. light flux lowered σeq of the Pt-loaded samples, whereas it did not affect that of TiO2 alone. These phenomena can be rationalized in terms of electron transfer from the titania to the platinum. Accordingly, the existence of such a withdrawal by small metal crystallites is substantiated. Conversely, in H2 the Pt deposits decreased the resistance of TiO2, illuminated or not, and this is tentatively attributed to a migration of adsorbed hydrogen atoms from Pt to TiO2 where they form OH– ions and release electrons.

Oxygen Transfer on Substituted ZrO2, Bi2O3, and CeO2 Electrolytes with Platinum Electrodes : II. A-C Impedance Study

Abstract: An equivalent electrical circuit that describes the electrode processes on different electrolytes, using porous Pt electrodes,is given. Diffusional processes are important and have to be presented by Warburg components in the circuit. Theoverall electrode process is rate limited by diffusion of atomic oxygen on the electrode surface for stabilized zirconia andsubstituted ceria (low PO2). On stabilized bismuth sesquioxide diffusion of atomic oxygen on the electrolyte surface is ratelimiting at high PO2 while at low PO2 another process, probably diffusion of electronic species in the electrolyte, is dominant.One of these processes plays a role too on substituted ceria at high PO2, where a charge transfer process is dominant. Theseresults are consistent with the mechanisms developed in part I of this paper.

Hydrogen generation by photocatalytic oxidation of glucose by platinized n-titania powder

Abstract: The photocatalytic reaction of glucose in aqueous solution containing suspended platinized n-TiO/sub 2/ (anatase) powder was found to occur in mildly acidic media, pH 4.5. The gaseous products were determined to be H/sub 2/ and CO/sub 2/ when conducted under an inert atmosphere and CO/sub 2/ alone under an O/sub 2/ atmosphere. For a 2.8 m glucose solution and a temperature of 60/sup 0/C, the initial H/sub 2/ to CO/sub 2/ ratio was near 1 and decreased to a value near 3 for times greater than 100 h. Initial rates of gas evolution were near 1.0 mL/h (volume at STP) and declined with time. Mott-Schottky plots on flamed TiO/sub 2/ electrodes determined in solutions containing glucose were found to yield flat-band potential values 210-mV more negative than measurements made in its absence; such a shift would enhance the capability for H/sub 2/ evolution. Isotopic experiments using D/sub 2/O were found to support the occurrence of conventional H/sub 2/ evolution without glucose involvement. 39 references, 3 figures, 4 tables.

Electrochemistry of Polyphenylene Films Deposited Anodically on Platinum or Glassy Carbon Electrodes in HF ‐ Benzene System

Abstract: Polyphenylene films were deposited on Pt or glassy carbon electrodes by anodically oxidizing benzene in liquid hydrogen fluoride. The polymer is electroactive in liquid , with a remarkably low oxidation potential. It can also undergo electrochemical oxidation‐reduction in dry propylene carbonate containing , and charging/discharging curves of the system are presented. The polymer film is shown to be suitable for electrode surface modification by means of simple chemical reactions performed on the coated electrodes.

Head-to-head and head-to-tail isomers of binuclear complexes of platinum(I) and palladium(I) involving 2-(diphenylphosphino)pyridine as a bridging ligand

Abstract: Preparation et etude RMN de 31 P{ 1 H} et 195 Pt{ 1 H} des complexes PtPd(μ-Ph 2 Ppy) 2 Cl 2 ou Pt 2 (μ-Ph 2 Ppy) 2 Cl 2

Ternary fuel cell catalysts containing platinum, cobalt and chromium

Abstract: An improved ternary noble metal-containing, alloy catalyst which has a catalytic activity for the electrochemical reduction of oxygen greater than two and one-half times that of the supported unalloyed noble metal alone. In addition, a disclosure of the method of preparing said catalyst is by intimately contacting two metallic elements with a supported noble metal, then heating this material to form the ternary alloy catalyst. This catalyst has particular utility for the electrochemical reduction of oxygen which makes it particularly useful as a cathode in acid fuel cells. The preferred embodiment of this catalyst is finely divided platinum alloyed with chromium and cobalt supported on an electrically conductive carbon-black support material.