Showing papers on "Platinum published in 1984"
TL;DR: In this paper, the authors studied the reaction kinetics of CO, C 3 H 6, 1-hexene, and toluene under excess O 2 and found that the olefin oxidation is strongly self-inhibited by HC and more than first-order in O 2, whereas the opposite was found for Rh.
346 citations
TL;DR: In this article, the hydrogenation of ethylene with both hydrogen and deuterium was studied over (111) platinum single-crystal surfaces under a total pressure of 110 torr and a temperature range of 300-370 K.
Abstract: The hydrogenation of ethylene with both hydrogen and deuterium was studied over (111) platinum single-crystal surfaces under a total pressure of 110 torr and a temperature range of 300-370 K. An activation energy (E/sub a/) of 10.8 +/- 0.1 kcal/mol and kinetic orders with respect to hydrogen and ethylene partial pressure of 1.31 +/- 0.05 and -0.60 +/- 0.05, respectively, were observed. The deuterium atom distribution in the product from the reaction with D/sub 2/ peaks at 1-2 deuterium atoms per ethane molecule produced, similar to what has been reported for supported catalysts. The reaction takes place on a partially ordered carbon covered surface, where the carbonaceous deposits have a morphology similar to that of ethylidyne. However, this ethylidyne does not directly participate in the hydrogenation of ethylene, since both its hydrogenation and its deuterium exchange are much slower than the ethane production. A mechanism is proposed to explain the experimental results.
321 citations
TL;DR: In this article, the shape of the voltammogram is distorted by the ohmic iR drop, and a two-electrode, rather than a potentiostated three-electron measuring system, is recommended to minimize noise.
269 citations
Journal Article•
TL;DR: In vitro studies with plasma and urine demonstrated that, in contrast to cisplatin, CBDCA is a stable complex [t 1/2 - 37 degrees; plasma, 30 hr, and urine, 20 to 460 hr].
Abstract: cis-Diammine-1,1-cyclobutane dicarboxylate platinum(II) (CBDCA, JM8) is a nonnephrotoxic analogue of cisplatin currently undergoing clinical evaluation. Pharmacokinetic studies have been performed in patients receiving CBDCA (20 to 520 mg/sq m) as a 1-hr infusion without hydration or diuresis. Following the end of the infusion, plasma levels of total platinum and ultrafilterable (Mr less than 50,000) platinum (free platinum) decayed biphasically with first-order kinetics (total platinum t alpha 1/2 = 98 min; t beta 1/2 range, 399 to greater than 1440 min; free platinum t alpha 1/2 = 87 min; t beta 1/2 = 354 min). During the first four hr, binding of platinum to plasma protein was limited (24%), with most of the free platinum in the form of unchanged CBDCA (94%). However, by 24 hr, the majority of platinum was protein bound (87%). The major route of elimination was renal, 65% of the platinum administered being excreted in the urine within 24 hr, with 32% of the dose excreted as unchanged CBDCA. No evidence was found from studies on the renal clearance of free platinum to indicate renal tubular secretion (mean free platinum renal clearance, 69 ml/min). However, the plasma clearance of free platinum did correlate positively with glomerular filtration rates (p = 0.005). None of the pharmacokinetic parameters determined were dose dependent. In vitro studies with plasma and urine demonstrated that, in contrast to cisplatin, CBDCA is a stable complex [t 1/2 - 37 degrees; plasma, 30 hr, and urine (range), 20 to 460 hr]. The differences in the pharmacokinetics of cisplatin and CBDCA may explain why the latter complex is not nephrotoxic.
241 citations
TL;DR: In this paper, various adlayers were grown on the surface of a platinum crystal by four different oxidizing treatments and the resulting surface phases were characterized by X-ray photoelectron spectroscopy.
202 citations
TL;DR: In this paper, a closed system between 200 and 300 °C was used for redispersion of carbon monoxide layer over the platinum crystallites, and isotopic dilution experiments using 12CO13CO mixtures showed that the CO molecules are free of dipole-dipole coupling after the redispersive treatment.
185 citations
TL;DR: In this article, the activation energy for desorption of this oxygen state was estimated from the thermal de-noising spectra to be about 163 kJ mol−1, and the chemisorbed oxygen atoms and the oxygen associated with silicon were distinguished by different binding energies (529.2 and 532.3 eV respectively).
181 citations
TL;DR: In this article, basic properties of polyaniline (PA) deposited anodically on platinum electrodes have been studied on the following points: 1) Effect of the mode of electrolysis and supporting electrolytes in the film forming process, 2) Characteristics of charging-discharging processes.
Abstract: Basic behaviors and properties of polyaniline(PA) deposited anodically on platinum electrodes have been studied on the following points. 1) Effect of the mode of electrolysis and supporting electrolytes in the film forming process. 2) Characteristics of charging-discharging processes. 3) Electric conductivity and elemental composition of PA. The different modes of electrolysis do not affect the characteristics of the PA electrode obtained. The growth rate of PA film is 2.7–2.8 times faster in sulfuric acid than in perchloric, nitric or hydrochloric acid. It is indicated that there are two types of doping; one is associated with the acid-base equilibrium between amino or imino group in the film and proton in the solution and the other is associated with the excess charge in the film produced by anodic oxidation. The electric conductivity of PA markedly decreases by the immersion in alkali solutions. The release of doped anion from PA by treating with an alkali solution is confirmed by the elemental analysi...
163 citations
TL;DR: Transparent PZT thin films with perovskite structure were successfully obtained by thermal decomposition of organometallic compounds at the temperatures of 500 to 700° C as discussed by the authors.
Abstract: Transparent PZT thin films with perovskite structure were successfully obtained by thermal decomposition of organometallic compounds at the temperatures of 500 to 700° C. The films deposited on platinum substrates were smooth and uniform, but microcrackings were observed in the films deposited on fused silica substrates. The ratio of metal composition in the PZT film agreed with that in the mixture of starting materials. Films obtained at 700° C on platinum substrate showed a hysteresis loop. A spontaneous polarization was 35.65μC cm−2, a saturation remanent polarization was 30.56μC cm−2 and a coercive field was 45 kV cm−1. Dielectric constant and dielectric loss angle were about 300 and 0.05, respectively.
162 citations
TL;DR: In this paper, the authors described the preparation and optimization of a water-cleavage catalyst consisting of Pt/TiO/sub 2/ (P-25 Degussa) and two different methods were used to prepare the catalyst: impregnation followed by reduction and exchange.
Abstract: This article describes the preparation and optimization of a water-cleavage catalyst consisting of Pt/TiO/sub 2/ (P-25 Degussa). Two different methods were used to prepare the catalyst: impregnation followed by reduction (calcination in certain cases) and exchange. H/sub 2/PtCl/sub 6/ and Pt(NH/sub 3/)/sub 4/(OH)/sub 2/ were used as base materials. The efficiency of the catalyst was tested in relation to its ability to mediate H/sub 2/ evolution for water under UV light. The influence of pH, temperature, concentration of Pt, as well as preparation temperature and time of reduction are described. Characterization by electron microscopy (EM), surface area measurements (BET), diffuse reflectance spectroscopy (DRS), hydrodynamic particle radius R/sub h/, and electrophoresis is carried out. It is shown that metal islands with a particle size below 8 Angstrom deposited onto TiO/sub 2/ agglomerates of 3000 < R/sub h/ < 6000 Angstrom are the most active catalytic species. The fate of oxygen produced by conduction band holes is also investigated.
160 citations
TL;DR: The effects of knowledge of the solution chemistry of the platinum metals on their separation by solvent extraction and ion-exchange methods are reviewed, for the period 1950-1983, and those areas which need more investigation or interpretation to provide adequate separational methods are indicated.
TL;DR: A survey of the coagulation of the platinum sols induced by mono-, di-and tri-valent cations was made in this paper, where it was found that the smaller platinum particles required higher concentrations of added electrolyte before being destabilized.
Abstract: Stable aqueous colloidal platinum sols have been prepared by the citrate reduction of chloroplatinic acid. Particle size at the completion of the reaction was found to increase with increased heat input during reduction. The u.v.–visible spectrum of the platinum sols depends upon particle size up to 4 nm. A stirring–centrifugation procedure was used to identify the extent of coagulation induced by added electrolytes. It was found that the smaller platinum particles required higher concentrations of added electrolyte before being destabilized. A survey was made of the coagulation of the platinum sols induced by mono-, di- and tri-valent cations.Hydrogen treatment of platinum sols leads to growth of particles up to a maximum size of ca. 5 nm and substantial linkage of primary particles to form extensive aggregates. Such growth and aggregation lead to significant changes in the u.v.–visible spectra and reduced resistance to electrolyte-induced coagulation.
TL;DR: The surface structure and temperature dependence of n-hexane skeletal rearrangement was investigated near atmospheric pressure and at 520-700 K over a series of five platinum single crystal surfaces with variable terrace, step, and kink structures as discussed by the authors.
TL;DR: In this paper, the structural change of an atomically smooth Pt (111) surface induced by oxidation has been followed by an electrochemical method in a sulfuric acid solution, and a sample cleaned by cycles of ion bombardment and annealing for LEED observation could also give atomically clean surfaces if the sample was not exposed to a vacuum for too long and was appropriately protected against contamination from filling pure gas.
TL;DR: The electrochemical polymerization of pyrrole on a platinum electrode covered with a film of poly(vinyl chloride) produces a dark brown, ductile, and flexible composite polymer film with an electrical conductivity comparable to polypyrrole, and mechanical properties very simllar to poly(vineyl chloride as mentioned in this paper.
Abstract: The electrochemical polymerization of pyrrole on a platinum electrode covered with a film of poly(vinyl chloride) produces a dark brown, ductile, and flexible composite polymer film with an electrical conductivity comparable to polypyrrole, and mechanical properties very simllar to poly(vinyl chloride).
TL;DR: In this paper, the monohydroxo-bridged complex (Pt(NH)(HO))(μ-OH) has been obtained in solution by reaction of [Pt[Pt]-Pn(NH) with acid or as an intermediate in the formation of these oligomers from cis-Pn[Ptn[Pn](NH)-OH)(HO), which is quite soluble in water.
Abstract: Reactions in aqueous solution between cis-[Pt(NH)(HO)] (C1O) and anions A (C1O , OH, NO , SO , HPO , CHCO ) have been studied with use of Pt, N, and, for phosphate, P NMR. The monohydroxo-bridged complex (Pt(NH)(HO))(μ-OH) has been obtained in solution by reaction of [Pt(NH)(μ-OH)] with acid or as an intermediate in the formation of these oligomers from cis-Pt(NH)(OH)(HO). Perchlorate does not coordinate. Nitrate and sulfate each gives a complex cis-Pt(NH)(A)(HO), with A unidentate. In acidic solution (pH 1.5), phosphate gives only cis-Pt(NH)(OPOH)(HO). When deprotonated, this complex is in equilibrium with (Pt(NH))(μ-OH)(μ-POH) and other complexes containing bridging phosphate. Reaction with oxygen gives blue solids and solutions. Analogous phosphate complexes are formed with methylamine and ethylenediamine, although blue solutions with methylamine are obtained only after prolonged exposure to light. In solution, acetate gives cis-P(NH)(OCCH)(HO), and Pt(NH)(OCCH), with smaller amounts of (Pt(NH))(μ-OH)(μ-OCCH). With perchlorate, a solid [Pt(NH)(OCCH)]C1O-HO crystallizes, which probably contains bridging acetate. Solutions turn blue-black when heated, indicating that oligomers with mixed oxidation states of platinum form. Solid cis-Pt(NH)(OCCH)-2HO may be isolated. It is quite soluble in water.
TL;DR: The surface of a platinum electrode was anodically polarized at 3 V vs standard hydrogen electrode in 1 N H2SO4 at 300 K for 16 h so that a thick uniform oxidation layer was formed as discussed by the authors.
TL;DR: In this paper, the effect of tin impregnation on catalysts was investigated with X-ray Photoelectron Spectroscopy (XPS), temperature-programmed reduction, and reaction measurements.
TL;DR: In this paper, the reducibility of platinum on γ-Al2O3- and TiO2 was studied with the aid of temperature programmed reduction, and the reduction peak temperature was found to be dependent on the temperature of the primary oxidation after impregnation and drying.
TL;DR: In this paper, the authors investigated the bending of benzene to a chromium tricarbonyl fragment and to cluster models of silver, nickel, and platinum (111) surfaces by means of molecular orbital calculations.
TL;DR: Complexes formed in solution between Pt(H 2O)4 2+ (I) and anionic ligands Am-, Pt(A)n(H2O) 4-n (2-mn)+, have been characterized by 195Pt NMR spectra as mentioned in this paper.
Abstract: Complexes formed in solution between Pt(H2O)4 2+ (I) and anionic ligands Am-, Pt(A)n(H2O)4-n (2-mn)+, have been characterized by 195Pt NMR spectra (Am- = Cl- (n = 1-4), ONO2 - (n = 1-3), OSO3 2- (n = 1, 2), OPO3H2 - (n = 1-4), and O2CCH3 - (n = 1)). No distinct perchlorato complexes were observed. An alkaline solution gave a single resonance assigned to Pt(OH)4 2-. Concentrated solutions disproportionated to Pt and Pt(OH)6 2-. Peroxide oxidation of acid and alkaline solutions gave respectively "PtO2·3H2O" and Pt(OH)6 2-.
TL;DR: In this paper, the authors studied the oxidation of l -ascorbic acid in sulphuric acid solutions at a bright platinum electrode, by employing cyclic voltammetry, controlledpotential electrolysis and potential-step measurements.
TL;DR: In this paper, the deactivation effect depends markedly on temperature and the number of chlorine atoms in the molecule; moreover, bromine is a more effective inhibitor than chlorine, whereas platinum catalysts are more resistant to poisoning than palladium catalysts.
TL;DR: Platinum microelectrodes of radius less than 1μm enable steady state voltammetric measurements to be made using a two electrode configuration at temperatures down to the freezing point of the solvent (eutectic mixtures) in solvents such as acetonitrile and acetone as mentioned in this paper.
TL;DR: In this paper, the high temperature oxidation behavior of the six platinum group metals (ruthenium, rhodium, palladium, osmium, iridium and platinum) is reviewed and the dependence on temperature, pressure and experimental conditions as well as the oxidation mechanism are discussed.
Abstract: The high temperature behaviour of the platinum group metals in oxidizing atmospheres is characterized by the formation of volatile oxides in addition to the evaporation of pure metal. The pressure- and temperature-dependent oxide evaporation can considerably increase the metal losses when compared with high vacuum or inert atmosphere conditions. Solid or liquid oxides are not formed on the surface because of their high dissociation pressure. In this paper the high temperature oxidation behaviour of the six platinum group metals (ruthenium, rhodium, palladium, osmium, iridium and platinum) is reviewed and the dependence on temperature, pressure and experimental conditions as well as the oxidation mechanism are discussed.
TL;DR: In this article, a 1 atm of flowing hydrogen and then examined by ESCA, it was shown that the Group VIII metal is present in a metallic state in the reduced catalyst and that the majority of the tin is in a valence state higher than Sn(0).
TL;DR: In this article, the results were as follows: electrodeposition took place in two narrow, overlapping underpotential deposition linear scan voltammetric peaks followed by one conventional bulk copper deposition peak.
Abstract: Studies by low energy electron diffraction (LEED) and Auger spectroscopy of copper electrodeposited on well‐characterized platinum (111) surfaces from aqueous sodium perchlorate solutions are reported. Prior to electrodeposition, the platinum (111) surface was pretreated with vapor in ultrahigh vacuum to form a Pt(111) R19.1°‐I superlattice, which protected the platinum surface and the surface of the electrodeposit from attack by the electrolyte and contamination by residual gases. The results were as follows: electrodeposition took place in two narrow, overlapping underpotential deposition linear scan voltammetric peaks followed by one conventional bulk copper deposition peak. Underpotential deposition produced an ordered layer. The first underpotential deposition peak formed a superlattice in which the unit cell contained four iodine atoms and a comparable number of Cu atoms per nine surface Pt atoms . At completion of the underpotential deposition process a coincidence lattice was present in which and . The iodine Auger signal was not appreciably affected by Cu deposition, indicating that the iodine atoms were present in the topmost layer of the surface at all Cu coverages.