Showing papers on "Platinum published in 1996"

Shape-Controlled Synthesis of Colloidal Platinum Nanoparticles

Abstract: 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.

Oxygen reduction of platinum low-index single-crystal surfaces in alkaline solution: Rotating ring disk{sub Pt(hkl)} studies

Abstract: The first results of a study of the oxygen reduction reaction on a rotating ring-disk electrode using single-crystal Pt disk electrodes in alkaline solution are presented. The order of activity of Pt(hkl) in 0.1 M KOH increased in the sequence (100) (100)more » > (110). 34 refs., 6 figs.« less

An amperometric microsensor for the determination of H2S in aquatic environments

Abstract: A new amperometric microsensor for detection of dissolved H2S in aquatic environments was developed The design of the microsensor is based on the same principle as the Clark-type oxygen microsensor The sensor is equipped with a glass-coated platinum working electrode and a platinum guard electrode positioned in an outer glass casing (tip diameter 20−100 μm) Both working electrode and guard electrode were polarized at a fixed value in the range from +85 to + 150 mV with respect to a counter electrode The outer casing is sealed with a thin silicone membrane and filled with a buffered electrolyte solution containing ferricyanide (K3[Fe(CN)6]) as redox mediator Hydrogen sulfide penetrates the silicone membrane and is oxidized by K3[Fe(CN)6], resulting in the formation of elemental sulfur and ferrocyanide (K4[Fe(CN)6]) The latter is electrochemically reoxidized at the exposed end of the platinum working electrode, thereby creating a current that is directly proportional to the dissolved H2S concentration

Controlled deposition of size-selected silver nanoclusters

Abstract: 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 ≤1 electron volt per atom could be landed nondestructively on the bare substrate, whereas at higher kinetic energies fragmentation and substrate damage were observed. Clusters with elevated impact energy could be soft-landed via an argon buffer layer on the platinum substrate, which efficiently dissipated the kinetic energy. Nondestructive cluster deposition represents a promising method to produce monodispersed nanostructures at surfaces.

Direct Imaging of the Atomic Configuration of Ultradispersed Catalysts

Abstract: Direct imaging of individual catalyst metal atoms on the insulating surface of an industrial support is demonstrated. Individual platinum and rhodium atoms ultradispersed on γ-Al2O3 supports were imaged by high-resolution Z-contrast (atomic number Z) microscopy in a 300-kilovolt scanning transmission electron microscope. Within small clusters, the configuration of the metal atoms was seen to be constrained to match the surface structure of the γ-Al2O3, from which likely surface adsorption sites were deduced. A thin, extended raft of rhodium atoms was observed, mostly corresponding to one monolayer. Occasional two-atom features suggested partial dissolution into the top layers of the γ-Al2O3 support.

High barrier height GaN Schottky diodes: Pt/GaN and Pd/GaN

Abstract: Platinum (Pt) and palladium (Pd) Schottky diodes on n‐type GaN grown by metalorganic chemical vapor deposition were achieved and investigated. Aluminum was used for ohmic contacts. Barrier heights were determined to be as high as ΦB=1.13 eV by the current–voltage (I–V) method and ΦB=1.27 eV by the capacitance–voltage (C–V) method for the Pt/GaN diode, and ΦB=1.11 eV, ΦB=0.96 eV, and ΦB=1.24 eV by I–V, activation energy (I–V–T), and C–V methods for the Pd/GaN diode, respectively. The ideality factors were obtained to be n∼1.10.

“Cubic” Colloidal Platinum Nanoparticles

Abstract: Cubic platinum nanoparticles (4−18 nm) have been synthesized for the first time in solution by the controlled reduction of K2PtCl4 with hydrogen gas in the presence of sodium polyacrylate as a capping material. The nanoparticles are found to have fcc structures, similar to the bulk metal with {100} facets.

Analysis of the Electrochemical Characteristics of a Direct Methanol Fuel Cell Based on a Pt‐Ru/C Anode Catalyst

Abstract: A vapor-feed direct methanol fuel cell based on a Nafion 117{reg_sign} solid polymer electrolyte was investigated. Pt-Ru/C and Pt/C catalysts were employed for methanol oxidation and oxygen reduction, respectively. The structure, surface, and morphology of the catalysts were investigated by X-ray powder diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Crystalline face-centered cubic phases were found in the Pt and Pt-Ru catalysts. The alloy composition in the Pt-Ru/C catalyst was different from the nominal composition, probably due to the formation of surface RuO{sub x} species, as indicated by X-ray photoelectron spectroscopy. Transmission electron microscopy observation showed an increase of the average particle size and particle agglomeration in the Pt-Ru/C catalyst compared to the Pt/C catalyst. The membrane/electrode assembly was prepared by using a paste process method. Scanning electron microscopy and energy dispersive X-ray analyses showed good adhesion of catalyst layers to the membrane and a homogeneous distribution of the ionomer inside the catalyst. AC-impedance and galvanostatic steady-state polarization techniques were used to investigate the electrochemical performance of the direct methanol fuel cell.

Crotonaldehyde hydrogenation over bimetallic PtSn catalysts supported on pregraphitized carbon black. Effect of the preparation method

Abstract: Three bimetallic PtSn/C catalysts have been prepared by successive impregnation of pregraphitized carbon black with an aqueous solutions of hexachloroplatinic acid and tin(II) chloride. One monometallic Pt/C sample was also prepared and studied for comparison. All catalysts were characterized by hydrogen and carbon monoxide chemisorption at room temperature and X-ray photoelectron spectroscopy and their behaviour in the gas phase hydrogenation of crotonaldehyde, at atmospheric pressure, determined. The amount of surface platinum is greatly reduced by the addition of tin, as deduced from chemisorption measurements and XPS. Both Pt0 and PtII are detected by XPS in the fresh bimetallic catalysts; after reduction in flowing hydrogen at 623 K platinum is completely reduced to the metallic state and, although a high proportion of tin remains in an oxidized state, a relatively important amount is reduced to Sn0, this allowing the possibility of PtSn alloys formation. The catalytic activity in the gas phase hydrogenation of crotonaldehyde is greatly improved by the presence of tin, in spite of the fact that the amount of surface platinum is reduced. Tin has also a very important effect on the selectivity towards the hydrogenation of the CO bond, increasing the production of crotyl alcohol in respect to the hydrogenation of the CC bond that would lead to the production of butyraldehyde. The observed results are explained on the basis of a promoting effect of oxidized tin species for the hydrogenation of the CO group, whereas the formation of a PtSn alloy or the dilution of surface platinum by metallic tin would hinder the hydrogenation of the olefinic CC bond.

A Glucose Biosensor Based on Immobilization of Glucose Oxidase in Electropolymerized o-Aminophenol Film on Platinized Glassy Carbon Electrode.

Abstract: A high-performance amperometric glucose biosensor has been developed, based on immobilization of glucose oxidase in an electrochemically synthesized, nonconducting poly(o-aminophenol) film on a platinized glassy carbon electrode. The large microscopic surface area and porous morphology of the platinized glassy carbon electrode result in high enzyme loading, and the enzyme entrapped in the electrodeposited platinum microparticle matrix is stabler than that on a platinum disk electrode surface. The response current of the sensor is 20-fold higher than that of the sensor prepared with a platinum disk electrode of the same geometric area. The experiments showed that the high sensitivity of the sensor is due not only to the large microscopic area but also to the high efficiency of transformation of H2O2 generated by enzymatic reaction to current signal on the platinized glassy carbon electrode. The response time of the sensor is 10 months.

Platinum-oxide species formed by oxidation of platinum crystallites supported on alumina

Abstract: Pt/Al2O3 samples of different platinum loadings are prepared by impregnating γ-Al2O3 with PtCl4 solution. Reduced Pt/Al2O3 samples are oxidized by dioxygen to examine the variation of PtOx (platinum-oxide) species with the oxidation temperature. Four different PtOx species are characterized according to their reduction temperature (Tr) found in the temperature-programmed reduction (TPR) experiments. They are assigned as surface platinum oxide (Tr = −25°C), PtO (Tr = 50°C), PtO2 (Tr = 100°C) and PtAl2O4 (Tr = 220°C), respectively, mainly according to their No/NPt stoichiometry found in the TPR and their desorption kinetics found in the technique of temperature-programmed desorption (TPD). These four species alternate as the dominant PtOx products on Pt/Al2O3 samples when the oxidation temperature is raised to 25°C, 300°C, 500°C and 600°C, respectively.

Complete oxidation of methane on supported palladium catalyst: support effect

Abstract: A palladium loaded catalyst was examined in order to reveal the effect of the support on the activity of oxidation of methane. The activity was declined or enhanced with time on stream, and its behavior depended upon the kind of support. The change of activity was accompanied with sintering of palladium metal. The stabilized activity of the palladium was ordered in the sequence; on SiO2 > on Al2O3 > on SiO2-Al2O3. The turn-over frequency of methane oxidation was about 50 times greater than that of platinum supported catalysts, and the activity sequence of support was opposite to that of platinum. The effect of support on the activity of palladium was smaller than on platinum from the viewpoint of activation energy as well as the turn-over frequency. The palladium dispersed on the support was less active, but the large particle which was not interacted strongly with the support was active; the behavior may be related to the small support effect on the palladium activity. Higher activity of the loaded palladium oxide than that of platinum oxide was caused by the higher reducibility of PdO chemical bonds, as confirmed by the temperature-programmed reduction. Silica deposited alumina, prepared by a method of chemical vapor deposition, was designed to create new active sites for the loading of silica-rimmed palladium; the sintering of palladium was suppressed to obtain the durable activity.

Systematic Theoretical Study of Alloys of Platinum for Enhanced Methanol Fuel Cell Performance

Abstract: The ability of substitutional atoms in the (111)Pt surface to attract a water molecule and activate the formation of OH ads on them is calculated using the ASED-MO theory. OH ads is believed to be the oxidant that removes the CO poison from Pt anode surfaces in organic fuel cells. A total of 42 alloying atoms is treated, Sc through Se from period 4, Y through Te from period 5, and La through Po from period 6. As surface substitutional atoms, no elements to the right of the Pt group are found to attract H 2 O strongly enough to activate OH dissociation. Some of these elements, including Sn, are known to be active in the electrocatalytic oxidation of CO ads but are believed to be atoms or complexes on or near the Pt surface. Of the elements to the left of the Pt group, a number from the first and second transition series attract and activate H 2 O with comparable or greater effectiveness than Ru, a known activator when present on Pt electrode surfaces. Whether these can be made stable alloy surfaces for organic fuel cell operation is an experimental issue. Past experimental work in the literature suggests promise for some of them.

Behaviour of poly(ethylene glycol) during electrodeposition of bright copper coatings in sulfuric acid electrolytes

Abstract: The interaction of poly(ethylene glycol) M n= 3000 with copper I and II ions in aqueous-acidic media was studied by investigation of the specific electrical conductivity, optical density and the cyclic voltamperometric curves in Cu+ and Cu2+ solutions. The results suggest the formation of complexes of the {Cu+(-EO-)3(x − 1)H2O} and {Cu2+(-EO-)4.(y − 1)(H2O)2} types. In the case when {−CH2CH2-O-} n and Cl− are simultaneously present in the copper electrolyte, the possibility of simultaneous complex formation between both copper ions and ethylene oxide units, and copper ions and chloride ions is considered. The strong increase in copper electrodeposition over-potential after the addition of polyethers to the electrolytes containing brighteners is explained by the formation of these complexes.

Catalyst for purifying exhaust gas

Abstract: A catalyst has a base catalyst layer containing platinum and barium as precious metal supported by alumina and an over catalyst layer containing platinum and rhodium as precious metal supported by zeolitr. The platinum and rhodium in the over catalyst layer activate NOx and HC so as to make them more reactive in terms of energy, and the barium in the base catalyst layer makes the platinum be more dispersive in the base catalyst layer. Under the existence of dispersive platinum, NOx in exhaust gas is decomposed and purified by reaction with reactive NO2 and partially oxidized HC generated in the over catalyst layer.

Synthesis and Isolation of Cuboctahedral and Icosahedral Platinum Nanoparticles. Ligand-Dependent Structures

Abstract: The reaction of Pt(dba)2 with CO (1 atm) in toluene affords a brown precipitate which can be isolated and redissolved in CH2Cl2 to give a colloidal solution of fcc platinum particles with a large s...

Platinum and Other Metal Coordination Compounds in Cancer Chemotherapy 2

Abstract: The clinical pharmacology of carboplatin, co-administered with paclitaxel, was investigated in a dose-finding and sequence-finding study in 56 previously untreated patients with non-small cell lung cancer (NSCLC). Carboplatin was administered over 30 minutes and paclitaxel over 3 hours every 4 weeks. Patients were randomized for the administration sequence, being first carboplatin (C) then followed by paclitaxel (P) or vice versa. Each patient received the alternate sequence during the second and subsequent courses. Total platinum concentrations in plasma and plasma ultrafiltrate (pUF) were measured applying flameless atomic absorption spectrometry. Ninety-five concentration-time curves were obtained in plasma and pUF. Paclitaxel doses were initially escalated from P: 100 mg/m2+ C:300 mg/m2 with 25 mg/m2 increments to P:225 mg/m2+ C:300 mg/m2. During the course of the study after six dose levels, it became clear that no sequence-depending effect on the toxicity was present, and it was decided to perform the last escalation steps with four patients per dose level. These dose levels were: level 7 (P:225 mg/m2+ C:350 mg/m2), 8 (P:250 mg/m2+ C:350 mg/m2), and 9 (P:225 mg/m2+ C:400 mg/m2). The