Showing papers on "Platinum published in 1972"
TL;DR: A novel technique is described for the removal of insulation from electrode tips by embedding them in a softened bead of solder glass, producing clean fractures of the borosilicate glass at the surface of the bead; the bare, undamaged tip of the electrode is then withdrawn.
Abstract: Practical methods are described in detail for the construction of tungsten microelectrodes. Straightened 127 μm-diameter tungsten wires are etched to sharp points in KNO2 solution. The sharpened wires are insulated by collapsing borosilicate-glass capillaries onto them in a horizontal pipette puller. A novel technique is described for the removal of insulation from electrode tips by embedding them in a softened bead of solder glass. The bead is then allowed to cool, producing clean fractures of the borosilicate glass at the surface of the bead; the bare, undamaged tip of the electrode is then withdrawn. Electrodes with bare tips from 2 μm to more than 100 μm can be prepared with this method. Finally, the tips are plated with a gold cyanide solution and platinum black. The finished electrodes have tapers of less than 2° and yet are extremely strong. Electrodes with conical plated tips 20 μm long by 6 μm diameter have 1 kHz impedances of less than 1 MΨ.
581 citations
459 citations
TL;DR: In this paper, it is emphasized that metal dissolution currents should not be ignored when examining electrochemical processes on noble metals at anodic potentials, and evidence in support of an anodic mechanism for noble metal corrosion has been obtained from studies of the variation of dissolution rate with both potential and temperature.
394 citations
TL;DR: In this article, the chemisorption of hydrogen, oxygen, carbon, carbon monoxide and ethylene was studied by low-energy electron diffraction on ordered stepped surfaces of platinum which were cut at angles less than 10° from the (111) face.
309 citations
TL;DR: Crushed single crystals of perovskite-like compounds RE1-XPb5MnO3 and RECoO3 compare favorably with commercial platinum catalysts in initial activity and lifetime, and are promising substitutes for platinum in devices for the catalytic treatment of auto exhaust.
Abstract: The perovskite-like compounds RE(1-X)Pb(5)MnO(3) and RECoO(3), where RE (rare earth) is lanthanum, praseodymium, or neodymium, are active catalysts for the oxidation of carbon monoxide. Crushed single crystals of these compounds compare favorably with commercial platinum catalysts in initial activity and lifetime. Therefore, these compounds are promising substitutes for platinum in devices for the catalytic treatment of auto exhaust.
254 citations
216 citations
TL;DR: In this article, a flow method was used to measure hydrogen chemisorption on supported platinum catalysts at ambient temperature, the data were in accord with results obtained by the conventional static method.
172 citations
TL;DR: In this paper, the rate of hydrogenation of ethylene on PtSiO2 catalysts has been studied between 207 and 371 °K, and no evidence in their work for spillover of hydrogen from the metal to the alumina with enhanced rates of hydrogenated ethylene adsorbed on alumina.
149 citations
TL;DR: In this paper, current/potential curves have been obtained for the ferrous/ferric reaction at a rotating disc electrode in background electrolytes of 1 M HClO4, 0.5 M H2SO4 and 0.4 M KHSO4.
148 citations
TL;DR: In this article, the current density i+ of platinum oxide layer formation was measured in dependence on potential e, time t and coverage ϑ or the equivalent layer thickness under potentiostatic conditions in 0.5 M H2SO4.
143 citations
TL;DR: In this article, the formation and reduction of platinum oxide layers in 0.5 M H2SO4 was investigated by galvanostatic pulse measurements, and the results led to the conclusion that the properties of the layer are dependent on the formation conditions of layer, i.e. the formation rate, the ageing of layer and the method of the setting of the coverage (anodic/increase or cathodic/decrease).
TL;DR: The thermal decomposition of di-n-butylbis(triphenylphosphine)platinum(Il) (l) in methylene chloride to n-butane, l-butene, and a complex of platinum(0) is proposed to take place by an intramolecular process involving an initial dissociation of I equiv of triphenyl phosphine from 1 to yield a three-coordinate intermediate 5, elimination of platinum hydride from one butyl group of 5 with concomitant ransfer of the resulting l
Abstract: The thermal decomposition of di-n-butylbis(triphenylphosphine)platinum(Il) (l) in methylene chloride to n-butane, l-butene, and a complex of platinum(0) is proposed to take place by an intramolecular process involving an init ial dissociation of I equiv of triphenylphosphine from 1 to yield a three-coordinate intermediate 5, elimination of platinum hydride from one butyl group of 5 with concomitant ransfer of the resulting l-butene to the vacant coordination site, several cycles composed of rapid addition of platinum hydride to the coordinated butene and subsequent rapid reelimination of platinum hydride from the resulting butylplatinum complexes, and a final reductive elimination of n-butane from an intermediate having both hydride and butyl moieties bonded to platinum. Three significant conclusions concerning the mechanism of thermal decomposition of t have emerged lrom this study. First a vacant coordination site on platinum is a prerequisite for thermal decomposition under the conditions studied. Second, the identity of the rate-l imiting step for the overall decomposition reaction depends upon the concentration of triphenylphosphine added to the solution: in the absence of added triphenyiphosphine, the rate-l imiting step is the dissociation of I to 5; in the presence of ca. I equiv of added triphenylphoiphine, the rate-limiting step is the reductive elimination of butane. Third, the olefins participating in the platinum hydride addition-elimination sequence are coordinated in the intermediate platinum Complexes ufficiently firmly that they do not exchange with 1-butene free in solution. f nformat ion concerning the mechanisms of thermal r decomposi t ion of a lkyl der ivat ives of t ransi t ion metals is pert inent both to theoret ical d iscussions of the electronic structure of carbon-metal c bonds and pract ical appl icat ions of t ransi t ion metal organometal l ic compounds in organic synthesis and catalysis. ( l ) Supported' in part by The Nat ional Science Foundat ion, Grants GP-7266 and GP-142,17. (?) Nat ional Inst i tutes of Heal th Predoctoral Fel low, 1967-196g: E. B. Herschberg Fel low, 1966-1967. (3) Nat ional Inst i tutes of Heal th Predoctoral Fel low. 1967-1970, Journal ol'the Anterican Chemical Societ;' I 94:15 I Jult ' 26, 1972 Mechanisms involving both the homolytic scission of carbon-metal a bonds and the 6 elimination of metal hydrides have been proposed for these thermal decomposi t ions;{ '5 however, the lat ter course has been established as the more common for-n-alkyl derivatives (4) M. S. Kharasch and O. Reinmuth. \"Gr ignard React ions of Nonmetal l ic SubstancEs,\" Prent ice Hal l , New York, N. Y. , 1954, Chapter 5. (5) Reviews: (a) G. E. Coates, M. L. H. Creen, and K. Wadc, \"Organometal l ic Compounds,\" Vol . 2, 3rd ed, Methuen and Co., London, 1968, Chapter 7; (b) G. W. Parshal l and J. J. Mrowca, Adcan. Organometal . Chem.,7,157 (1968): (c) F. A. Cotton, Chem. Reo., 52 , 557 (1955) ; (d ) I . I . K r i t skaya , Usp . Kh im. ,35 , 167 (1966) . of platinum(Il),u rhodiur,n(I),7 and copper(I),E by ideniif ication of metal hydrides as products of the decompositions, and for derivatives of other metals by less direct techniques.s'e The nature of the factors determining both the rate of metal hydride elimination in the thermal decompositions of these classes of compounds and the reversibi l i ty of th is el iminat ion are unknown. The work reported in th is paper deals wi th an examinat ion of the mechanism of thermal decomposition of crs-di-n-butylbis(triphenylphosphine)platinum(Il) (1), a representative alkyl derivative of a dE transition metal ion, whose physical properties make it amenable to detailed mechanistic examination. The purpose of this study was to substantiate a pathway for itreimat decomposition of 1 involving platinum hydride elimination and to provide detail to the steps surrounding this elimination.
TL;DR: In this paper, the chemisorption of hydrogen, oxygen and carbon monoxide on supported platinum was studied by a pulse technique, and the resulting adsorption stoichiometries were compared with literature data which either include measurements of size or which compare the adsorptions of two or more gases on the same solid.
TL;DR: In this paper, the effects of fractional monolayers of carbon monoxide, reduced carbon dioxide and arsenic on the rates of hydrogen-oxidation and evolution were examined on unpoisoned platinum sites in 2 N H2SO4 at 25°C.
TL;DR: Complexes of 2-pyridine thiol, 4-polycyclic pyridine and 2-methyl-6 pyridine thiol with cobalt(II), nickel, zinc, cadmium, mercury, platinum, and bismu... as discussed by the authors.
Abstract: Complexes of 2-pyridine thiol, 4-pyridine thiol, and 2-methyl-6-pyridine thiol, and some of their oxygen analogs with cobalt(II), nickel(II), zinc(II), cadmium(II), mercury(II), platinum(II), bismu...
TL;DR: In this paper, the Pt particle size determinations were made from electron micrographs and from X-ray line broadening experiments following the chemisorption measurements on samples sintered in H 2 to various temperatures.
01 Jan 1972-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this paper, the diffusion coefficient of pure platinum, calculated from the time lag to reach a steady state flux, is: {065-01} in the temperature range of 1435∮ to 1504°.
Abstract: The diffusivity and solubility of oxygen in metal specimens were determined from measurements of permeation through thin wall tubes containing oxygen and heated by electrical resistance. The permeating oxygen desorbed in vacuum as monoatomic oxygen and the flux was monitored mass-spectrometrically. A known helium leak rate and experimentally-determined sensitivities of the two gases were used for flow calibration. The diffusion coefficient of oxygen in pure platinum, calculated from the time lag to reach a steady state flux, is: {fx065-01} in the temperature range of 1435∮ to 1504°. The solubility of oxygen in pure platinum was obtained from the steady-state flux using the previously determined diffusivity. The solubility is proportional to p1/2O2 and at 1 atm of oxygen the solubility is: CsO = (0.2 ± 0.1) × 1012 exp {fx065-02}, wt pct. Small amounts of nickel, less than required for internal oxidation, had a negligible effect on the oxygen solubility and diffusivity in platinum alloys.
TL;DR: In this article, it was shown that CH 3 CN occupied 3 Pt sites per molecule at adsorption saturation leaving 33% of the surface available for co-adsorption of H 2 SO 4.
TL;DR: The X-ray crystal structure analysis of the triphenyl-phosphine platinum ethylene complex (PPh3)2PtC2H4 is reported in this article.
Abstract: The X-ray crystal structure analysis of the triphenyl–phosphine platinum ethylene complex (PPh3)2PtC2H4 is reported. The crystals belong to the monoclinic system a = 16.46(3), b = 10.85(2), c = 17....
TL;DR: In this paper, the dehydrocyclization of n-heptane on platinum crystal surfaces of area less than 1 cm2 was studied in the temperature range of 100-400 °C and at pressures in the 10−4 Torr range.
TL;DR: In this article, a chain mechanism involving homolytic bond cleavage of hexachloroplatinate(IV) to yield atomic chlorine and a labile platinum(III) species is proposed to account for the observed behavior.
TL;DR: In this paper, the dependence of the non-stationary currents of formic acid, formaldehyde and methanol on the degree of coverage of the platinum electrode by adsorbed sulphur and the effect of adaption of sulphur on the electrooxidation of methenol and formaldehyde have been studied.
TL;DR: In this article, a highly dispersed platinum catalyst (platinum crystallite size less than 15Aa) on a conductive carbon support was prepared, and these doped carbons were made into Teflon-bonded fuel cell electrodes and the platinum surface area and dispersed platinum specific activity (i.e., the activity per unit area of platinum) for oxygen electroreduction in acid electrolyte was determined.
Abstract: A highly dispersed platinum catalyst (platinum crystallite size less than 15Aa) on a conductive carbon support was prepared. These doped carbons were made into Teflon‐bonded fuel cell electrodes and the platinum surface area and the dispersed platinum specific activity (i.e., the activity per unit area of platinum) for oxygen electroreduction in acid electrolyte was determined. The specific activity of the dispersed platinum was found to be approximately twenty times less than that of crystalline platinum black. The lower activity of this catalyst compared with that of platinum black may be due either to the difference in the platinum crystallite sizes, or to the influence of the support on the platinum activity, or to a combination of both these factors.
01 Jan 1972
TL;DR: The importance of the atomic structure of solid surfaces and of adsorbed molecules in heterogeneous catalysis has been advocated by many scientists throughout the years as mentioned in this paper, however, the difficulties of determining the atomic structures of catalyst surfaces proved to be almost insurmountable, mostly because of the configuration of the catalyst systems.
Abstract: The importance of the atomic structure of solid surfaces and of adsorbed molecules in heterogeneous catalysis has been advocated by many scientists throughout the years. Early studies by Balandin [l], for example, have suggested the presence of close-packed structures of adsorbed molecules that are intermediates in catalytic reactions. In his view both the atomic structure of the substrate metal surface and the structure of the adsorbed molecules were of primary importance in carrying out certain types of catalytic reactions. In the past, however, the difficulties of determining the atomic structure of catalyst surfaces proved to be almost insurmountable, mostly because of the configuration of the catalyst systems. In the case of metal catalysts most commercial catalyst systems consist of finely dispersed metal particles that are deposited on a high surface area support, most frequently silica or alumina. Even at present the atomic structure of such polydispersed systems cannot be ascertained una...
TL;DR: In this article, the electrochemical reactivity of different nitrogen oxides or their absorption products in sulfuric acid was investigated by potential scan measurements at 23°C with platinum electrodes.
Abstract: The electrochemical reactivity of different nitrogen oxides or their absorption products in sulfuric acid was investigated by potential scan measurements. Experiments were carried out at 23°C with platinum electrodes. Among the substances studied only and exhibited well‐defined oxidation and reduction currents. The electrochemical reactions of in were studied in detail by using a rotating disk electrode. Mass transport limited currents were observed for both oxidation and reduction. From the variation of the limiting current with rotation rate the diffusion coefficient of was determined to be .