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Showing papers on "Noble metal published in 1977"


Journal ArticleDOI
TL;DR: In this paper, the repulsive part of the helium-metal physisorption potential is calculated in the Hartree-Fock approximation to the lowest order in the overlap between the atomic and metallic wave functions, determined by the change in the singleparticle density of states of the metal.
Abstract: The repulsive part of the helium-metal physisorption potential is calculated in the Hartree-Fock approximation. To the lowest order in the overlap ($S$) between the atomic and metallic wave functions, this interaction is determined by the change in the single-particle density of states of the metal. Combined with a previous calculation of the Van der Waals interaction, helium-metal potentials are derived for the simple and noble metals using a jellium model for the metal. Binding energies and equilibrium positions of the helium atom are determined. For the simple metals, the binding energy decreases with increasing ${r}_{s}$. Its value for the noble metals is between 40 and 70 K. The equilibrium positions are found to be between 3 and 7 \AA{} (relative to the jellium background) for all the metals studied.

244 citations


Journal ArticleDOI
TL;DR: In this article, the catalytic effects of a submonolayer of lead on noble metals have been discussed and discussed in terms of a previously published model, and theoretical analysis of these effects is presented.

113 citations


Journal ArticleDOI
TL;DR: In this article, the photoelectron distribution curves of single-crystal faces of copper, silver and gold were measured using photon energies of 11.83, 16.85 and 21.22 eV.
Abstract: The authors have measured the photoelectron distribution curves of single-crystal faces of copper, silver and gold using photon energies of 11.83, 16.85 and 21.22 eV. The photoelectrons are collected in a narrow cone normal to the surfaces. The results show the existence of occupied surface states in the L gaps of each noble metal. The intensity of the measured surface-state peaks drastically decreases with increasing photon energy.

101 citations


Journal ArticleDOI
TL;DR: In this paper, the optical properties of aggregated noble metal films have been studied in the spectral range from 0.35 to 1.0 μm, and the effective optical constants were derived from measurements of reflectance and transmittance.
Abstract: The optical properties of aggregated noble metal films have been studied in the spectral range from 0.35 to 1.0 μm. From the measurements of reflectance and transmittance, the effective optical constants were derived. These constants were then compared to those given by a model considering the films as formed by small rotational ellipsoids. In the model, the dipole/dipole interactions between particles have been taken into account together with the influence of the substrate. Careful measurements of film structures have shown that the assumptions concerning the size and shape of particles are reasonable. When p-polarized incident light is used, the resonance wavelength observed in the visible for the noble metal films is shifted to shorter wavelengths as the angle of incidence is increased.

71 citations


Journal ArticleDOI
TL;DR: In this article, the poison resistance of supported catalysts is discussed, in which the poison reacts both with the active component and the catalyst support, and the poison reaction can be selectively manipulated with respect to the net rate of the main reaction in such a way that a catalyst with improved poison resistance is obtained.

53 citations


Book ChapterDOI
01 Jan 1977
TL;DR: In this paper, the authors defined the science of maximizing chemical reaction rates for the formation of preferred products, which is achieved by using high-surface-area materials that may have specific surface features (i.e., preferred reaction sites).
Abstract: Catalysis can be defined as the science of maximizing chemical reaction rates for the formation of preferred products. Catalysis is achieved by using high-surface-area materials that may have specific surface features (i.e., preferred reaction sites). A secondary area is the study of adsorbed species on the catalytic surface, catalyst deactivation by poisoning, and loss of surface area due to sintering.

48 citations


Patent
13 Dec 1977
TL;DR: In this paper, the authors describe a catalytic converter for use in the exhaust line of an internal combustion engine wherein the catalytically active noble metal coating is deposited only on the rearward portion of the inert carrier, with respect to the direction of flow of the exhaust gases.
Abstract: A catalytic converter for use in the exhaust line of an internal combustion engine wherein the catalytically active noble metal coating is deposited only on the rearward portion of the inert carrier, with respect to the direction of flow of the exhaust gases, said inert carrier being fully coated with a washcoat capable of absorbing catalyst poisons before application of the catalytically active noble metal coating.

32 citations


Journal ArticleDOI
TL;DR: The electrode polarization impedance of polished platinum has been analyzed on the basis of the rate determining mechanism of the oxygen electrode and has been found to follow the frequency dependence predicted by an adsorption of the electroactive species.
Abstract: The linear A. C. electrode polarization impedance of polished platinum has been analyzed on the basis of the rate determining mechanism of the oxygen electrode. The impedance has been found to follow the frequency dependence predicted by an adsorption of the electroactive species. The effects of D. C. potential and specific adsorption of anions have been studied and their effect on the electrode polarization impedance is in agreement with the adsorption mechanism.

28 citations



Patent
25 Nov 1977
TL;DR: A process for the production of 2-aryl-2H-benzotriazoles comprises reducing and cyclizing the corresponding o-nitroazobenzenes with hydrogen at a temperature in the range of about 20° C. to about 100° C as discussed by the authors.
Abstract: A process for the production of 2-aryl-2H-benzotriazoles comprises reducing and cyclizing the corresponding o-nitroazobenzenes with hydrogen at a temperature in the range of about 20° C. to about 100° C. and at a pressure in the range of about 15 psia (1 atmosphere) to about 1000 psia (66 atmospheres) in an organic solvent mixture containing an organic amine at a pH over 10 in the presence of noble metal hydrogenation catalyst, preferably palladium. High yields of pure product are obtained with a concomitant reduction of undesired by-products and a reduction in effluent pollution problems.

20 citations



Patent
Kenneth S. Wheelock1
02 Dec 1977
TL;DR: In this paper, a process for the preparation of catalysts which are highly active for oxidizing the carbon monoxide (CO) and hydrocarbon (HC) present in automobile exhaust gases, with minimum oxidation of the sulfur dioxide, by controlling the acidity of the support, or carrier, within certain critical ranges while a Group VIII noble metal component, or components, is composited with said support in forming the catalyst.
Abstract: The disclosure herein relates to (a) a process for the preparation of catalysts which are highly active for oxidizing the carbon monoxide (CO) and hydrocarbon (HC) present in automobile exhaust gases, with minimum oxidation of the sulfur dioxide, by controlling the acidity of the support, or carrier, within certain critical ranges while a Group VIII noble metal component, or components, is composited with said support in forming the catalyst; (b) a process embodying the use of the so-formed catalysts in the treatment of automotive exhaust gases; and, (c) the catalyst compositions so-formed from supports the surface acidity of which is controlled. In the formation of the catalysts the total surface acidity of the support on which the metal, or metals, component is deposited is maintained between about 0.01 to about 0.10 micromoles pyridine/m 2 , and the surface area of the metal, or metals, component ranges up to about 50 m 2 /g, preferably from about 1 m 2 /g to about 35 m 2 /g, and more preferably from about 1 m 2 /g to about 20 m 2 /g.

Patent
21 Nov 1977
TL;DR: In this article, a method and apparatus for in situ reduction of cathode overvoltage in electrolytic cells is presented, which involves introducing low overvoltages or noble metal ions into the catholyte solution and plating those ions on the cathode in situ.
Abstract: A method and apparatus for in situ reduction of cathode overvoltage in electrolytic cells. The method involves introducing low overvoltage or noble metal ions into the catholyte solution and plating those ions on the cathode in situ. The apparatus includes a low overvoltage or noble metal ion generating device for introducing low overvoltage or noble metal ions into the cathode solution so as to plate them in situ on the cathode during or prior to cell operation.

Patent
16 May 1977
TL;DR: In this paper, aqueous ammonia solution is used to rejuvenate zeolite catalysts by exchanging out at least a portion of the zeolitic mono-and/or divalent metal ions, and bringing about a desirable redistribution of the Group VIII noble metal.
Abstract: Siliceous zeolite catalysts comprising zeolitic mono- and/or divalent metal cations and a non-zeolitic Group VIII noble metal hydrogenating component supported thereon, which catalysts have undergone damage by thermal and/or hydrothermal stresses resulting in a maldistribution of the metal components, are rejuvenated in activity by treatment with an aqueous ammonia solution. The treatment has a twofold effect of exchanging out at least a portion of the zeolitic mono- and/or divalent metal ions, and bringing about a desirable redistribution of the Group VIII noble metal.

Patent
24 Jun 1977
TL;DR: In this paper, the effective concentration of an electroactive ingredient of a coating solution is determined, and may be restored to a desired level, in response to deviations in the voltammetric current sensed at an indicating electrode comprised of a noble metal.
Abstract: The effective concentration of an electroactive ingredient of a coating solution is determined, and may be restored to a desired level, in response to deviations in the voltammetric current sensed at an indicating electrode comprised of a noble metal.

Patent
11 Nov 1977
TL;DR: In this article, a process for the manufacture of resorcinols by catalytic dehydrogenation of cyclohexane diones in the liquid phase by means of a dehydrogenating mixture consisting of a solvent and of a catalyst containing a noble metal from Group VIII of the Periodic Table is described.
Abstract: The present invention is related to a process for the manufacture of resorcinols by catalytic dehydrogenation of cyclohexane diones-(1,3) in the liquid phase by means of a dehydrogenating mixture consisting of a solvent and of a catalyst containing a noble metal from Group VIII of the Periodic Table.

Patent
Ikram Morcos1
08 Jun 1977
TL;DR: In this paper, a process for obtaining electrocatalysts having a thin film of a noble metal such as palladium, platinum, gold or less noble such as silver or an alloy of noble metals or a noble one together with a less noble one such as gold or nickel is described.
Abstract: A process for obtaining electrocatalysts having a thin film of a noble metal such as palladium, platinum, gold or less noble such as silver or an alloy of noble metals or a noble metal together with a less noble one such as silver or nickel. These include metals from Group VIII of the periodic chart. The thin film is electrodeposited on nonporous pyrolytic graphite surface from an aqueous solution containing a salt of the noble metal or metals in the presence of a complexing agent. The solution is stirred mechanically or the pyrolytic graphite cathode is rotated to create conditions favorable for the electrochemical deposition to be carried out at the highest possible current densities. The electrochemical catalysts thereby obtained are useful in oxygen adsorption processes, oxygen and hydrogen evolution processes, oxide formation and oxygen reduction processes. The metal or alloy film is of a granular or nodular nature and of a depth not exceeding 7μ and has a grain size smaller than 2μ or of a filament nature with peaks each of a base size running from 0.1 to 0.2μ. The metal or the alloy is selected from the group comprising silver, palladium, gold, a gold-silver alloy and a silver-nickel alloy.

Patent
27 Dec 1977
TL;DR: A gold alloy for use in a dental restoration, and which maintains a true yellow-gold color after being cast and having a porcelain jacket fired thereon, is described in this paper.
Abstract: A gold alloy for use in a dental restoration, and which maintains a true yellow-gold color after being cast and having a porcelain jacket fired thereon. The alloy is 83-87% gold, 7-12% platinum, 1.5-3.0% rhodium, and less than 1.0% copper. Other elements are included for grain refining, strength, formation of bonding oxide for the ceramic jacket, and the like.

Journal ArticleDOI
V. B. Hughes1, Brian D. McNicol1, M. R. Andrew1, R. B. Jones1, R. T. Short1 
TL;DR: In this article, the authors compared the performance of noble metal catalysts in pure monohydrate with those in 3 M sulphuric acid and showed that the poisoning effect of acid radicals is considerably less in CF3SO3H than in H2SO4 solutions.
Abstract: Trifluoromethanesulphonic acid monohydrate CF3SO3H.H2O and its aqueous solutions have been evaluated as an electrolyte for methanol electro-oxidation. The performances of conventional noble metal catalysts in the pure monohydrate are very poor compared with those in 3 M sulphuric acid. This is contrary to previously published literature data, and possible reasons for the discrepancy are given. In aqueous solutions of CF3SO3H at concentrations between 10 and 50%wt. considerably improved performance is obtained and at 60° C the activities of the catalysts are in most cases slightly higher than in 3 M H2SO4. In addition the poisoning effect of acid radicals is considerably less in CF3SO3H than in H2SO4 solutions. Above 60° C, however, the aqueous CF3SO3 anion decomposes to produce sulphur, which poisons the noble metal catalysts.

Patent
Su Yao-Sin1
25 Apr 1977
TL;DR: In this paper, smooth surfaces of impervious zirconia-base ceramics are chemically treated to produce micropitting and/or micro-cratering therein which enables durable adherence of metal coatings applied thereon.
Abstract: Smooth surfaces of impervious zirconia-base ceramics are chemically treated to produce micropitting and/or microcratering therein which enables durable adherence of metal coatings (e.g. of noble metal) applied thereon. Treatment involves contact of the smooth surfaces with liquid leachant selected from concentrated sulfuric acid, ammonium bisulfate, alkali metal bisulfate and mixtures thereof at a temperature of at least 250° C. Leached surface is contacted with hydrochloric acid to remove reaction residue comprising sulfate of metal elements including zirconium in the ceramic.


Patent
20 Dec 1977
TL;DR: In this article, an unstable heavy hydrocarbon fraction obtained by pyrosis is reacted with hydrogen in contact with three successive catalysts: (a) a group VIII metal catalyst (b) a catalyst comprising nickel and tungsten compounds, and (c) a catalysts comprising alumina, group VIII noble metal and fluorine or chlorine.
Abstract: An unstable heavy hydrocarbon fraction obtained by pyrosis is reacted with hydrogen in contact with three successive catalysts: (a) a group VIII metal catalyst (b) a catalyst comprising nickel and tungsten compounds, and (c) a catalyst comprising alumina, a group VIII noble metal and fluorine or chlorine.

Journal ArticleDOI
TL;DR: In this paper, a simple oxidation technique was used to remove traces of iron dissolved in gold and in its homovalent alloys, which enabled an accurate determination of the low temperature thermoelectric power characteristic of the solutes copper and silver in gold.
Abstract: For pt.I see ibid., vol.4, p.256 (1974). Traces of iron dissolved in gold and in its homovalent alloys have been removed using a simple oxidation technique. This has enabled an accurate determination of the low temperature thermoelectric power characteristic of the solutes copper and silver in gold. Electron diffusion and phonon drag contributions are determined and discussed. The strongly positive diffusion thermoelectric powers of the alloys measured at low temperatures differ markedly from the apparent impurity effect determined from applying the Nordheim-Gorter rule to room temperature measurements of the alloys. Results for homovalent silver, copper and gold alloys are collected together.

Journal ArticleDOI
TL;DR: In this article, an experimental study of the relative catalytic activities of rare earth oxides for reducing nitric oxide in the presence of carbon monoxide was reported, and the results showed that the most active rare earth oxide was cerium dioxide with activity being similar to that of platinum and palladium catalysts tested under similar conditions.

Patent
Jos P Wristers1
19 Jul 1977
TL;DR: In this paper, the presence of palladium or iridium serves to extend the hydrocracking catalyst life of the metal fluoride and fluoride containing Bronsted acid, which can be described as a slurry or dispersion composed of the noble metal on a support in a liquid phase acid system.
Abstract: Hydrocarbon feedstocks are hydrocracked by contacting the feedstock in the presence of hydrogen and under hydrocracking reaction conditions with a catalyst comprised of a metal fluoride, the metal being tantalum, niobium, boron or mixtures thereof, a fluoride containing Bronsted acid and palladium or iridium, the Bronsted acid being present in at least an equimolar amount relative to the metal fluoride and sufficient to dissolve at least a portion of the metal fluoride. The presence of palladium or iridium serves to extend the hydrocracking catalyst life of the metal fluoride and fluoride containing Bronsted acid. The catalyst can be described as a slurry or dispersion composed of the noble metal on a support in a liquid phase acid system.

Patent
23 Jun 1977
TL;DR: In this article, an exhaust purifier has a housing contg. in which a first noble metal and a second non-noble metal are installed in succession in order to satisfy the higher starting temperature requirement of the second noble metal.
Abstract: Exhaust purifier has a housing contg. in succession a first catalyst of noble metal and a second catalyst of a non-noble metal. The temperature rise produced by exothermic reaction in the first catalyst assists in satisfying the higher starting temperature requirement of the second catalyst thereby making possible for use of non-noble metal. Either catalyst may be supported by a backing grid of ceramic or sintered material, wire wool, or granular material. And higher catalyst may be held in position in the housing by resilient supports acting radially and/or axially.

Patent
Andre Lecloux1, Gobillon Yves Dr1
14 Oct 1977
TL;DR: In this article, the general formula M.sub.n Me'.sub.m O.subm where n represents an integer equal to 1, 2 or 3 and m represents aninteger equal to 0.5 and 800 m 2 /g of alloy and the mean diameter of the alloy particles is between 10 and 10,000 A.
Abstract: Particles of alloys of a noble metal chosen from among iridium, osmium, palladium, platinum, rhodium and ruthenium, hereafter represented by M, with at least one non-noble metal chosen among silver, bismuth, cadmium, cobalt, copper, tin, germanium, indium, manganese, mercury, molybdenum, nickel, gold, lead, rhenium, thallium, tellurium, technetium, tungsten, vanadium and zinc, hereafter referred to as Me', and Me', representing at least one non-noble metal, characterized in that they correspond to the general formula M.sub.n Me'.sub.m where n represents an integer equal to 1, 2 or 3 and where m represents an integer equal to 1, 2 or 3, and in that their specific surface area is between 0.5 and 800 m 2 /g of alloy and in that the mean diameter of the alloy particles is between 10 and 10,000 A. The particles are prepared by reducing the mixed oxides of the corresponding formula M.sub.n Me'.sub.m O.sub.x They are used as catalyst for dehydrogenation or hydrogenation.

Journal ArticleDOI
TL;DR: Pd-C, Pt-C and Ir-C catalyse the rapid and complete hydrogenation of carbocations formed through the protonation of aromatic hydrocarbons in super acid media and of stabilised carbocations in aprotic media as mentioned in this paper.
Abstract: Pd–C, Pt–C, and Ir–C catalyse the rapid and complete hydrogenation of carbocations formed through the protonation of aromatic hydrocarbons in super acid media and of stabilised carbocations in aprotic media.

Patent
07 Oct 1977
TL;DR: The catalysts will remove oxygen from gas mixts contg. a surplus, and provide oxygen to those deficient, giving improved purificn. of the gas without accurate control of fuel mixt. as mentioned in this paper.
Abstract: Catalysts for gas oxidation and reduction processes, contg. (I) >=1 noble metal (Pt, Au, Ag, Rh, Ru, Pd, In and/or O3) and (II) >=1 base metal which can exist in at least two oxidn. states. Amt. of (II) is >=5, pref. 25.99.9%, of the wt, of active metal catalyst, which is pref. deposited on a ceramic monolith or metal carrier. Used for purifcn. of exhaust gases of petrol and diesel engines in vehicles by simultaneous oxidn. of hydrocarbons and CO, and reduction of NOx. The catalysts will remove oxygen from gas mixts contg. a surplus, and provide oxygen to those deficient, giving improved purificn. of the gas without accurate control of fuel mixt. ratio.

Patent
09 Nov 1977
TL;DR: In this paper, an electrode having good conductivity, low oxygen and chlorine overvoltage and a low corrosion rate under electrolysis conditions is disclosed, which comprises an electrically conductive substrate made of a material resistant to the electrolyte and the electrolytic products.
Abstract: An electrode having good conductivity, low oxygen and chlorine overvoltage and a low corrosion rate under electrolysis conditions is disclosed. The electrode comprises an electrically conductive substrate made of a material resistant to the electrolyte and the electrolytic products, coated on at least a portion of the surface thereof with a basic coating of a material containing 30-70% by weight of an acid insoluble metal tungstate, 15-60% by weight tantalum pentoxide and 5-15% by weight of a noble metal oxide.