Addition Of Platinum Research Articles

Selective oxidation of CO in hydrogen-rich mixtures and kinetics investigation on platinum-gold supported on zinc oxide catalyst

A series of gold zinc oxide catalysts have been prepared using a coprecipitation procedure and selective oxidation of CO in hydrogen-rich mixtures was investigated in a fixed-bed reactor in the temperature range from 313 to 393 K. The results showed that the suitable content of Au in ZnO was about 1.5 wt.% and calcined at 573 K, shortened as Au (1.5)/ZnO-573. Stability investigation, performed at 353 K and lasted for 500 h, indicated Au (1.5)/ZnO-573 catalyst activity was slightly deteriorated as time on stream was over 350 h. Investigation indicated little addition of platinum into Au (1.5)/ZnO-573 catalyst could definitely improve its stability. However, further study showed that the selectivity of removal of CO from hydrogen-rich mixtures for Au (1.5)-Pt/ZnO-573 catalyst would be decreased with increasing content of Pt on the catalyst when Pt content was over 1.0 wt.%, which indicates that the suitable content of Pt would be 1.0 wt.% and the catalyst was indicated as Au (1.5)-Pt (1.0)/ZnO-573. Kinetic experiments performed on it were carried out in an isothermal fixed-bed microreactor under intrinsic conditions.

EPR study of ceria–silica and ceria–alumina catalysts: Localization of superoxide radical anions

Oxygen adsorption experiments were performed on evacuated and prereduced CeO 2/SiO 2 and CeO 2/Al 2O 3 catalysts with and without platinum. Considerable amounts of the superoxide radical ions were stabilized on all the samples. Signal parameters suggest Ce 4+–O 2 − positioning for all detectable superoxide species. Physisorbed oxygen broadens O 2 − signal beyond detection for all the alumina-based samples, while the same procedure for all the silica-based samples did not change signal shape of O 2 − species. Detectable O 2 − species are localized in the bulk of ceria and the nature of support (silica or alumina) determines the number of oxygen vacancies and the rate of electron transfer. XRD data suggest that for alumina-based samples small and/or thin islands of ceria dominate, while comparatively large ceria particles are stabilized on the surface of silica-based samples with the same ceria content. Average size of ceria crystallites is still not determining factor and cannot account for the observed differences. Higher concentrations of paramagnetic species may be stabilized on alumina-based samples and thus, sensor-like behavior towards gaseous oxygen at room temperature was detected for them—oxygen admission reversibly changes superoxide lineshape. For silica samples, only minor changes of O 2 − lineshapes were typical upon the change of the partial pressure of oxygen at ambient and low temperatures. Addition of platinum has little effect on parameters of the O 2 − signal, except an enhancement of the superoxide decay in the reducing media. Possible site for O 2 − stabilization inside the lattice of CeO 2 was proposed and relevance of the observed effects to the redox catalysis discussed.

Thermal Stability of NiAl-Base Coatings for High Temperature Application

Aluminide diffusion coatings act as a remedy against the aggressive environments in which modern aero-gas turbines operate. Platinum addition to basic aluminide coatings significantly improves the oxidation resistance of these coatings. The increase in operating temperatures of industrial energy systems and gas turbines, has led to the extensive use of coatings capable of providing improved service life. Interdiffusion plays a critical role in understanding the integrity of such coatings. The Danielewski-Holly model of interdiffusion which allows for the description of a wide range of processes (including processes stimulated by reactions at interfaces) is employed for studying of interdiffusion in the Pt-modified β-NiAl coatings. Using the inverse method the intrinsic diffusivities of Ni, Al and Pt were calculated. Such obtained diffusivities were subsequently used for modelling of thermal stability of Pt-modified aluminide coatings in air and in argon atmosphere.

C–C coupling of aryl groups and allyl derivatives on Pt(II)-phenanthroline fragments: crystal and molecular structure of the tbp [(η 1,η 2-2-allyl,5-methyl-phenyl)iodo(1,10-phenanthroline)platinum(II)] complex containing the N–N ligand in axial-equatorial coordination mode

The reactions between allyl compounds CH 2 CHCH 2Fn bearing electron-withdrawing functional (Fn) groups and cationic {Pt(aryl)(1,10-phenanthroline)} + fragments generated in situ are described. The aryl and platinum addition to the terminal and, respectively, internal unsaturated carbon is generally observed. The subsequent H–C aryl bond activation, followed by HFn elimination, affords the ortho organic fragment ( Pt)–aryl-CH 2CH CH 2 η 1,η 2-chelate to the platinum. This process does not occur when the regiochemistry is of Markownikov type and the Pt–CH 2CH(aryl)CH 2Fn fragment is formed. The described results are compared with those concerning the behaviour of unsubstituted α-olefins. The X-ray crystal structure of the title five-coordinate complex shows a distorted tbp arrangement of the ligands with the iodide in the equatorial plane and the unusual axial-equatorial coordination mode of the 1,10-phenanthroline.

Effects of Pt on the short-term oxidation behavior of γ-Ni+γ′-Ni3Al alloys

The aim of this study was to elucidate the beneficial role played by platinum addition in promoting the formation of a protective Al2O3 scale on γ′-Ni3Al+γ-Ni alloys during oxidation at high temperatures. To do this, the early-stage oxidation behavior of γ′-Ni3Al-based alloys of composition (in at.%) Ni–22Al and Ni–22Al with 10, 20, and 30 Pt was investigated in terms of oxidation kinetics, scale evolution and resulting composition profiles during heating to 1150°C in air. Platinum addition did not appear to affect the nature of the native oxide layer present on the γ′-based alloys at room-temperature; however, it was found that the presence of increasing Pt content aided in promoting the establishment of a continuous Al2O3 scale during heating above about 600°C. This beneficial effect can be primarily ascribed to the fact that Pt is non-reactive and its addition decreases the chemical activity of aluminum in γ′. Related to the latter, Pt partitions almost solely to the Ni sites in the ordered L12 crystal structure of γ′, which has the effect of amplifying the increase in the Al:Ni atom fraction on a given crystallographic plane containing both Al and Ni. Such an effective Al enrichment at the γ′ surface kinetically favors the formation of Al2O3 relative to NiO. A further contributing factor is that the Pt-containing γ′-based alloys showed subsurface Pt enrichment during the very early stages of oxidation. This enrichment reduces Ni availability and can increase the Al supply to the evolving scale, thus kinetically favoring Al2O3 formation.

Metal ions incorporated titania nanotubes for hydrocarbon oxidation

AbstractPresent work shows that simple, standard methods of metal addition, without the need for ion implantation or other complex and expensive processes, can dramatically improve the performance of titania based structures compared to P25 for (i.e. hydrocarbon oxidation) photocatalytic reactions. In this work, Au and Pt were incorporated into titania nanotubes, and their photocatalytic activities were investigated in detail. The samples were analyzed using a JEOL FEG-2010F field emission gun scanning transmission electron microscopy (STEM) with attached Oxford Instruments' X-ray energy-dispersive spectroscopy (EDS) system and Gatan imaging filtering (GIF) system. Both high-resolution TEM (HRTEM) images and high angle annular dark-field (HAAD) images were recorded for the specimens. The performance of the samples was tested for the oxidation of acetaldehyde using a continuous flow reactor. The pure nanotube is more photoreactive than commercial P25 titania. Both Au and Pt treated nanotube samples increased the photo reactivity. The most significant result of this work is that the activity of Pt (< 1 nm) containing nanotube is more than 10 times the rate of P25, and more than 6 times the rate of the pure nanotube. However, sizes of the Au and Pt nanoparticles on the nanotube surfaces likely affected the photo-reactivity. Large size of the Au and Pt particles decreased the photo-reactivity. Specifically, the addition of platinum without formation of obvious nanoparticles on the nanotube surfaces increased the maximum activity significantly, and increased the total yield.

Platinum‐Containing Diamond‐like Carbon Thin Films

This paper reports a composite thin film of platinum–diamond‐like carbon (Pt‐DLC). “Nonreactive” and reactive rf sputter deposition techniques were used for the preparation of these thin films under various ratios of Ar/CH4. As‐deposited thin films were characterized for microstructures using transmission electron microscopy and Raman spectroscopy, compositions using electron probe for microanalysis, surface morphology using scanning electron microscopy, and sheet resistance using four‐point probe. Correlations among the growth parameter, film composition, and structure are presented. Such correlations were found to depend on the deposition technique. Improved electrical conductivity and reduced film stress were also found due to the addition of platinum to DLC.

Catalytic decomposition of chlorodifluoromethane (HCFC-22) over platinum supported on TiO2–ZrO2 mixed oxides

Sulfated and non-sulfated TiO2–ZrO2 were promoted with platinum and the activity and selectivity of the resulting catalysts for the hydrolytic decomposition chlorodifluoromethane in air was investigated. The addition of platinum reduced the specific surface area of the catalyst slightly and lowered the catalytic activity. On the other hand, the selectivity of the catalysts towards CO2 formation was much improved. Metallic platinum was formed by the reduction of the platinum precursor with carbon monoxide produced during the hydrolysis of chlorodifluoromethane over the acidic mixed oxide and promoted the oxidation of CO. At the same time, platinum suppressed completely the formation of the fluorinated byproduct CHF3, possibly by anchoring itself on the active sites responsible for the fluorination reaction. The platinum promoted non-sulfated TiO2–ZrO2 was stable and gave more than 90% of CHClF2 conversion and 95% selectivity to CO2 for over 60h.

The role of chemical composition on the oxidation performance of aluminide coatings

The durability of aluminide bond coatings is critical to the life of thermal barrier coatings (TBCs). With service, the coating composition continues to change due to oxidation and interdiffusion. In order to better understand the effect of coating composition on its oxidation resistance, model alloys are being studied with various levels of Al, Pt and Hf. In hypostoichiometric β-NiAl, the formation of faster-growing Ni-rich oxide was observed, and this problem intensified at lower Al contents. Platinum additions were found to decrease this problem. With two-phase Ni–35Al–6Pt compositions, a phase transformation upon heating to 1100 °C caused macroscopic specimen deformation when the specimen was repeatedly cycled. The degradation of oxidation resistance with lower Al contents indicates that the loss of Al due to back-diffusion into the superalloy substrate is the critical performance-limiting problem for aluminide coatings. One strategy for improved coating performance suggested by Gleeson uses higher Pt and Hf contents and lower Al contents.

The influence of platinum on the performance of silver–platinum anti-bacterial coatings

Abstract Anti-bacterial silver coatings were deposited on thermally sensitive polymeric substrates using a combination of magnetron sputtering and neutral atom beam (Saddle Field) plasma sources. The anti-bacterial activity of silver is dependent on the release of Ag+ ions, which act by displacing other essential metal ions such as Ca2+ or Zn2+. This study reports some initial electrochemical experiments intended to evaluate the use of platinum to enhance the release of silver ions from the silver coating. In the galvanic series in seawater silver is more active than platinum and therefore probably enhances Ag+ ion formation through galvanic action when the two metals are in electrical contact. In order to evaluate this several electrochemical methods were employed using magnetron target samples as working electrodes. Cyclic voltammetric, open circuit potential measurements and potential step (chronoamperometric) experiments were performed on several silver–platinum alloys containing from 0.5% to 3.0% Pt and on a pure silver target electrode. In the case of the chronoamperometric measurements, the resulting current–time curves demonstrated that Ag+ formation was enhanced with platinum addition by up to 100%. Results of this preliminary work are discussed with reference to various reactions that can occur on the surface of silver in chloride-containing environments.

Deactivation of Pt·PdO/Al 2O 3 in catalytic combustion of methane

Catalytic combustion is being widely studied as a means of controlling the NO x of combustors. However, the poor durability of palladium-based catalysts hinders the development of catalytic combustors for the methane combustion reaction. The effects of the addition of platinum to PdO/Al 2O 3 on catalyst deactivation at 1073 K were studied using a fixed-bed flow reactor at atmospheric pressure. The adaptability of various deactivation equations to the data of methane combustion was investigated. The deactivation behavior of the catalysts could be expressed by an equation based on two kinds of deactivation species. The addition of Pt prolongs the lifetime of the PdO/Al 2O 3 catalyst by decreasing the initial activity. This is due not to the transformation of PdO to Pd–Pt but to the prevention of the growth of PdO and Pd–Pt particles during the reaction.

Carbon-based composite thin films for use as microelectrode

This paper describes a process for fabricating Pt-containing diamond-like carbon (Pt-DLC) composite thin films for use as microelectrode. Two sputter deposition techniques were used to prepare the sample thin films. In a sputter deposition process, the target used was a 99.99% pure graphite with different amounts of platinum coupons on the surface. In the other process, a reactive sputter deposition technique was employed. The target was a 99.99% pure platinum. In both cases DLC or Pt-DLC composite thin films were obtained using different deposition conditions. The resulting Pt-DLC composite thin films were subject to various analysis for the physical properties. Among them, improved electrical conductivity and reduced film stress were also found due to the addition of platinum into DLC.

Selectivity of photocatalytic oxidation of gaseous ethanol over pure and modified TiO 2

The rates of the two main stages of photocatalytic ethanol destruction—oxidation of ethanol to acetaldehyde and oxidation of acetaldehyde to CO 2—were studied under varied concentrations of ethanol and acetaldehyde and photocatalyst irradiance, at different temperatures, and over different photocatalysts. The rates followed the semiempirical three sites Langmuir–Hinshelwood model that envisages sites for ethanol and acetaldehyde adsorption and additional sites for competitive adsorption of ethanol and acetaldehyde. The increase in irradiance gave rise to higher selectivity toward CO 2 via increased concentrations of gaseous intermediate acetaldehyde. However, the rate of ethanol oxidation rose faster than the rate of acetaldehyde oxidation. The selectivity toward CO 2 monotonically decreased with temperature over TiO 2 and the rate of oxidation reached a maximum at 80 °C. Among platinum-doped catalysts, the best activity was found for 1.1% Pt/TiO 2. Platinum addition to TiO 2 resulted in a 1.5- to 2-fold increased overall rate of oxidation. The selectivity to CO 2 over Pt/TiO 2 catalyst monotonically increased with temperature. Separate studies in a batch reactor demonstrated that addition of platinum changed the product distribution. Acetic acid, instead of carbon monoxide, was formed in copious quantities over the Pt/TiO 2 catalyst.

Mechanical properties and microstructure of platinum enhanced radiopaque stainless steel (PERSS) alloys

Balloon-expandable coronary stents may be made from austenitic stainless steel conforming to ISO, BSI and ASTM specifications (UNS S31673). These stents are not sufficiently visible, radiographically, under certain operational conditions, therefore a range of platinum-enhanced radiopaque stainless steel (PERSS) alloys were developed, using UNS S31673 alloys as a base, which are more visible when used as stents. This paper gives the methodology used to develop the PERSS alloys in order to ensure that the properties are those required for coronary stents. These properties include an ability to be cold worked, mechanical strength and ductility similar to those of implant grades of austenitic stainless steel, an absence of magnetic phases, such as ferrite and martensite, as well as an absence of brittle intermetallic phases, particularly σ. Biocompatibility must also be acceptable, comparable to UNS S31673 alloys. Microscopy and X-ray diffraction analysis confirmed predictions that the microstructure of the alloys would be fully austenitic, free from potentially damaging topologically close packed intermetallic phases, and that the addition of platinum would reduce the amounts of magnetic and embrittling phases present in the alloys. Mechanical tests revealed platinum does not significantly affect the mechanical properties, except that there is about a 14% increase in ultimate tensile strength with the addition of 10 wt% platinum.

The Addition of Platinum and Palladium Groups to the Disulfido Ligand in Cyclopentadienyl Molybdenum-Manganese Carbonyl Complexes

The reaction of the complexes CpMoMn(CO)5(μ-S2), 2a, Cp=C5H5 and Cp*MoMn(CO)5(μ-S2), 2b, Cp*=C5Me5with (PPh3)2Pt(PhC2Ph) yielded the new bis-sulfido mixed metal complexes CpMoMn(CO)5Pt(PPh3)2(μ 3-S)2, 3a and Cp*MoMn(CO)5Pt(PPh3)2(μ 3-S)2, 3b by insertion of a platinum metal grouping into the S–S bond. A mono-phosphine complex, Cp*MoMn(CO)6Pt(PPh3)(μ 3-S)2, 4b was also isolated from the reaction of 2b with (PPh3)2Pt(PhC2Ph). Compounds 3b and 4b were both characterized crystallographically. Both complexes consist of open MoMnPt clusters with a Mo–Mn single bond, Mo–Mn=2.7570(16) A for 3b and Mo–Mn=2.7837(13) A for 4b, and two triply bridging sulfido ligands. The trimetallic complexes CpMo(O)MnPd(PBu t 3)(CO)5(μ 3-S), 5a and Cp*Mo(O)MnPd(PBu t 3)(CO)5(μ 3-S), 5b containing an oxo ligand bonded to molybdenum were obtained from the reaction of 2a–b with Pd(PBu t 3)2. The molecular structure of the 5a was also established crystallographically.

The influence of oversized solute additions on radiation-induced changes and post-irradiation intergranular stress corrosion cracking behavior in high-purity 316 stainless steels

The influence of oversized solute additions on the radiation-induced microstructure, radiation-induced segregation (RIS) at grain boundaries and post-irradiation intergranular stress corrosion cracking (IGSCC) behavior of model, high-purity 316 stainless alloys, doped with either 0.3 at.% platinum or 0.3 at.% hafnium, and proton-irradiated to 2.5 and 5 dpa at 400 °C was examined. Radiation-induced microstructure was characterized using both bright and dark field imaging techniques in transmission electron microscopy. Platinum addition was found to promote void nucleation and to increase both the loop density and the mean loop diameter relative to the base alloy at 2.5 dpa. Addition of hafnium was effective in reducing swelling at 2.5 and 5 dpa. Hafnium addition also significantly decreased the mean loop diameter relative to the base alloy. Both platinum and hafnium additions also resulted in significant suppression of RIS at grain boundaries at 2.5 dpa. At 5 dpa, the influence of hafnium addition on RIS was still beneficial but much less pronounced. Comparative constant elongation rate tensile tests performed in a simulated boiling water reactor environment at 288 °C demonstrated a beneficial effect of hafnium addition and to a lesser extent platinum addition on the post-irradiation IGSCC behavior of 316 stainless steel alloys. The 316SS alloy doped with platinum exhibited a slightly lower susceptibility to post-irradiation IGSCC than the 316SS base alloy at both 2.5 and 5 dpa. Most spectacularly, the 316SS alloy doped with hafnium was found to be not susceptible to post-irradiation IGSCC at both 2.5 and 5 dpa. The mechanisms by which oversized solute additions impact point defect behavior as well as the links between radiation-induced changes and irradiation-assisted stress corrosion cracking are discussed.

Structure and properties of tungstated zirconia catalysts for alkane conversion

Promoted tungstated zirconia (WZ) catalysts are active and selective for isomerization of light alkanes, offering good prospects for industrial application. This account is an abbreviated summary of what these catalysts are and how they work. WZ containing approximately a monolayer of tungstate covering the zirconia support was prepared by impregnation of zirconia, tested in a flow reactor, and characterized with a variety of spectroscopic methods. The catalytic activity is associated with interconnecting polyoxotungstate clusters on the surface of tetragonal zirconia. The polyoxotungstate species increase the acid strength of the catalyst relative to that of unmodified zirconia, but the acid strength is still less than that of zeolites and far below the superacidic range. Redox properties of WZ characterized by EPR spectroscopy suggest that alkane activation proceeds via homolytic CH bond cleavage, leading to the formation of W5+ centers and organic radicals, which can be converted to alkenes, initiating catalysis. Unpromoted WZ has a low activity; reaction intermediates remain adsorbed on the surface, where they undergo polymerization and cracking, leading to fast deactivation and poor selectivity. The addition of platinum to the catalyst and H2 to the feed drastically improves the catalytic activity, selectivity, and stability. The platinum enhances the desorption of reaction intermediates and minimizes the condensation reactions, so that monomolecular isomerization predominates. An additional promotion with iron compounds leads to further improvement in catalytic activity and selectivity.

Anti-bacterial silver coatings exhibiting enhanced activity through the addition of platinum

Anti-bacterial silver coatings were deposited on thermally sensitive polymeric substrates using a combination of magnetron sputtering and neutral atom beam (Saddle Field) plasma sources. The anti-bacterial activity of silver is dependent on the release of Ag+ ions, which act by displacing other essential metal ions such as Ca2+ or Zn+. This study evaluates the use of platinum to enhance the release of silver ions from the silver coating. In the galvanic series platinum is more active than silver and therefore Pt enhances Ag+ ion formation through galvanic action. In order to evaluate this, potential step (chronoamperometric) experiments were performed on silver/platinum alloys containing 0.5 and 3.0% Pt. The resulting current–time curves demonstrated that Ag+ formation increased with platinum addition by up to 100%. A magnetron sputtering target was fabricated consisting of 1% Pt in a Ag matrix. This was used to sputter Pt/Ag coatings with thicknesses in the range 5–12 nm onto silicone and polyurethane substrates. The bacterial adhesion and bactericidal effects of the coated polymers was assessed using Straphylococcus epidermidis and the cytotoxicity using fibroblast cells. The addition of 1% Pt was found to significantly enhance the anti-bacterial effectiveness of the Ag coatings. Up to a 2 log reduction in bacterial adhesion was achieved for 5 nm thick Ag/1% Pt coatings on silicone, which did not exhibit cytotoxicity.

Electroless Addition of Platinum to SnO2 Nanopowders

A procedure based on electroless metal deposition using Sn(II) as the reductor, previously used for the efficient addition of controlled amounts of Pd to nanoscaled SnO2 powders, is now applied to add Pt, which is also an important sensitizer of semiconductor gas sensors. This study was performed with the aim of studying the possible application of this method for the addition of other metals, regardless of the appearance of new chemical features. The characterization of these powders using XRD, Raman spectroscopy, XPS, ICP, and HRTEM is presented and discussed, showing the feasibility of the proposed catalyst addition mechanism as a useful tool for improving of existing catalytic materials for gas sensors, even using different chemical reagents because of chemical restrictions, as happens in the case of platinum. A set of platinum salt concentrations and reducing agent ratios, as well as different annealing temperatures, was used to analyze the influence of these parameters on the morphology and composit...

DLC composite thin films by sputter deposition

This paper reports a new composite thin film of Pt–DLC for used as a microelectrode for electrochemical analysis. An RF sputter deposition technique was used for the preparation of these thin films under various ratios of Ar/CH4. The microstructure of as-deposited thin films was characterized using transmission electron microscopy and Raman spectroscopy, the composition using electron probe microanalysis, the surface morphology using scanning electron microscopy, and the sheet resistance using a four-point probe. Correlation among the growth parameters, film composition, and structure are presented. Both the composition and Raman characteristics were found to be strong functions of the deposition rate. Improved electrical conductivity and reduced film stress were also found due to the addition of platinum into DLC.