Ppm Of Pt Research Articles

Magnéli Phases Doped with Pt for Photocatalytic Hydrogen Evolution

Defined substoichiometric titanium oxides (Ti$_x$O$_{2x-1}$ with $3 < x < 10$) called Magneli phases have been investigated mostly for their unusual high conductivity and metal-like behavior. In photocatalysis, Magneli phase containing titania particles have been reported to provide favorable charge separation resulting in enhanced reaction efficiency. In the current work we describe a one-step synthesis of Magneli-containing mixed phase nanoparticles that carry directly integrated minute amounts of Pt. Phase optimized nanoparticles that contain only a few hundred ppm Pt are very effective photocatalysts for H$_2$ evolution (they provide a 50-100 times higher H$_2$ evolution than plain anatase loaded with a similar amount of Pt). These photocatalysts are synthesized in a setup combining a hot-wall reactor that is used for TiOx synthesis with a spark generator producing Pt nanoparticles. Different reactor temperatures result in various phase ratios between anatase and Magneli phases. The titania nanoparticles (ca. 24 - 53 nm) were characterized using XRD, HRTEM, XPS and EPR spectra as well as ICP-OES analysis. The best photocatalyst prepared at 900$^\circ$C (which consists of mixed phase particles of 32% anatase, 11% rutile and 57% Magneli phases loaded with 290 ppm of Pt) can provide a photocatalytic H$_2$ evolution rate of ca. 5432 micromol h$^{-1} g$^{-1}$ for UV and ca. 1670 micromol h$^{-1} g$^{-1}$ for AM1.5 illumination. For powders converted to higher amounts of Magneli phases (1000$^\circ$C and 1100$^\circ$C), a drastic loss of the photocatalytic H$_2$ generation activity is observed. Thus, the high photocatalytic efficiency under best conditions is ascribed to an effective synergy between multi-junctions of Magneli titania and Pt that enable a much more effective charge separation and reaction than conventional Pt/anatase junctions.

Atomically Dispersed Pt on the Surface of Ni Particles: Synthesis and Catalytic Function in Hydrogen Generation from Aqueous Ammonia–Borane

The development of cost-effective and highly efficient catalysts is of scientific importance and practical need in the conversion and utilization of clean energy. One of the strategies fulfilling that demand is to achieve high exposure of a catalytically functional noble metal to reactants to maximize its utilization efficiency. We report herein that the single-atom alloy (SAA) made of atomically dispersed Pt on the surface of Ni particles (Pt is surrounded by Ni atoms) exhibits improved catalytic activity on the hydrolytic dehydrogenation of ammonia–borane, a promising hydrogen storage method for onboard applications. Specifically, an addition of 160 ppm of Pt leads to ca. 3-fold activity improvement in comparison to that of pristine Ni/CNT catalyst. The turnover frequency based on the isolated Pt is 12000 molH2 molPt–1 min–1, which is about 21 times the value of the best Pt-based catalyst ever reported. Our simulation results indicate that the high activity achieved stems from the synergistic effect bet...

Suppression Effect and Mechanism of Platinum and Nitrogen-Containing Silane on the Tracking and Erosion of Silicone Rubber for High-Voltage Insulation.

How to effectively improve the tracking and erosion resistance of silicone rubber (SR) was an urgent topic in the field of high-voltage insulation. In this work, the tracking and erosion resistance of SR was significantly improved by incorporating platinum (Pt) catalyst and nitrogen-containing silane (NS). The suppression effect and mechanism of Pt/NS on tracking and erosion were studied by inclined plane (IP) test, thermogravimetry (TG), thermogravimetry-Fourier transform infrared spectrometry, laser Raman spectroscopy, and scanning electron microscopy. It revealed that when 1.4 phr of NS and 6.7 ppm of Pt were added, the tracking resistance of SR was improved from 2.5 to 4.5 kV level in the IP test, and the eroded mass was significantly reduced. This might be attributed to the synergistic effect of Pt/NS on silicone chains. At a high temperature produced by arc discharge, Pt/NS would catalyze radical cross-linking, meanwhile suppressing oxidation and depolymerization of silicone chains. Hence, a tightly cross-linked network was formed and protected inner materials from arc ablation. Moreover, carbon deposit during pyrolysis was suppressed by Pt/NS, which served as the secondary mechanism of tracking suppression.

Synergistic effect and mechanism of platinum catalyst and nitrogen-containing silane on the thermal stability of silicone rubber

Platinum (Pt) catalyst and nitrogen-containing silane (NS) were introduced to improve the thermal stability of silicone rubber. The effects of Pt and NS on thermal stability and degradation mechanism of silicone rubber were investigated by thermogravimetry (TG), thermogravimetry-Fourier transform infrared spectrometry (TG-FTIR), scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDXS) and Fourier transform infrared spectrometry (FTIR). A significant synergism was found between Pt and NS for improving the thermal stability of silicone rubber. When 6.67ppm of Pt and 1.4 phr of NS were introduced, the temperature of 10% and 20% weight loss under nitrogen atmosphere were respectively increased by 36°C and 119°C. Meanwhile, the residue weight at 900°C was doubled to 68% in the presence of Pt/NS. The synergistic mechanism might be that the nitrogen atom coordinated with Pt and improved the catalytic efficiency of Pt. Additionally, NS preserved the catalytic activity of Pt under air atmosphere. Hence, Pt/NS efficiently catalyzed thermal crosslinking and suppressed degradation of silicone chains. Moreover, it revealed that the presence of Pt/NS protected silicone chains from oxidation. Thus, the unzipping depolymerization by silanol groups was reduced significantly.

Determination of Platinum, Palladium, and Rhodium in Automotive Catalysts Using High-Energy Secondary Target X-ray Fluorescence Spectrometry

A fast and direct determination procedure for precious metals in spent automotive catalyst was developed using the novel high-energy polarized-beam XRF. A sample preparation method working directly on the ground material was optimized. The material was pressed as a pellet using wax as a binder; no internal standard was added. The standards for this application were available spent automotive catalyst, previously analyzed by ICP-OES to verify their concentration, prepared in the same way as the unknown samples. The investigated concentration ranged from nearly 0 to approximately 2700 ppm for Pt, to 500 ppm for Rh, and to 7500 ppm for Pd. The repeatability of the XRF measurement appeared to be better than 0.5%, while the precision of the whole method was approximately 1%. The accuracy of the XRF method was verified with the well-established (but very time-consuming) ICP-OES method; a good agreement (no difference when using the 95% confidence interval) was found for the results. When using an irradiation time of 500 s for the CsI secondary target and the Zr secondary target, the detection limits for Pt, Pd, and Rh were found to be better than 5 ppm.

Platinum-group elements in sulfide minerals and the whole rocks of the J-M Reef (Stillwater Complex): Implication for the formation of the reef

The concentration of platinum-group elements (PGE), Co, Ni, Cu, Re, Au and Ag was determined in base metal sulfides (BMS) minerals and whole rocks of the J-M Reef (footwall, reef and hanging wall) of the Stillwater Complex (U.S.A.). The aims of the study were to establish: (i) whether the BMS minerals (pyrrhotite, pentlandite, and chalcopyrite) are the principal host of these elements; (ii) whether these elements preferentially partition into a specific BMS mineral. The results of this study allowed us to consider and evaluate: the possible parental magma composition, the role of sulfide liquid and the role of alteration in the formation of the J-M Reef. Only a minor quantity of PGE (∼ 10 to 140 ppb) were found in the footwall and hanging wall samples of the J-M Reef, which contain only small amounts of sulfur (∼ 140 to 400 ppm). In contrast, the reef samples enriched in sulfides contain higher values of PGE (49 to 419 ppm). The S, Ni, Cu, and PGE contents follow the same trends indicating that BMS minerals are the principal phases controlling these elements. Palladium and Pt are the more abundant PGE (up to 244 ppm for Pd and 166 ppm for Pt) with an average Pd/Pt ratio of 3.3. Similarly, the Pd/Ir ratio and the mantle normalized PGE patterns indicate that Pd is more strongly enriched in the reef relative to surrounding rocks than the other PGE. Pentlandite is the BMS mineral that contains the largest weight fraction of PGE. Palladium represents ∼ 95% of the PGE found in solution in BMS minerals and is mainly partitioned in pentlandite. In contrast, Pt is almost exclusively found as platinum-group minerals and do not partition in any BMS minerals. The other PGE are largely found in the BMS minerals, mainly pentlandite. The variation of S/Se ratios and the presence of secondary magnetite in some samples indicate that these samples may have lost 20 to 50% of their original S. The highest Pd (and by analogy PGE contents) are found in samples containing secondary magnetite, but these are not necessarily those which have experienced the highest S removal. This indicates that the processes which caused the removal of S and the alteration to magnetite are probably distinct. Our modeling results suggest that PGE (and to a greater extent Pd) enrichment may be summarized into two different steps. First, an immiscible sulfide liquid interacted with a large volume of magma with PGE composition close to high-Mg basalt and collected the PGE. The sulfide liquid percolated down through the crystal mush to collect at a level where the porosity did not permit any further migration. During cooling, magma chamber instabilities triggered the partial desulfurization of the sulfides. Finally, in some parts of reef, a fluid deposited Pd (possibly removed from the footwall) and altered the BMS minerals to magnetite. During this step, Pd was precipitated as an alloy in the most Pd-enriched samples and Pd possibly diffused into pentlandite forming a high-Pd bearing pentlandite. The different contributions of each of the above processes may explain the variability of the Pd grade observed along the J-M Reef.

Noble metals in carbon-rich metamorphic rocks of the Khanka terrane, Primorie

Carbon-rich metamorphic rocks of Riphean age in the northern part of the Khanka terrane were first analyzed for concentrations of noble metals (Au, Ag, Pt, Pd, Ir, Os, and Ru). According to the data of various physicochemical analytical techniques, the Au and Pt concentrations broadly vary: from 0.01 to 52 ppm for Pt and from 0.1 to 30 ppm for Au. Various techniques of sampling and analysis variably affect the losses of these metals because of difficulties in the decomposition of metal-carbon chemical bonds. The carbon isotopic composition (13C from −8.5 to −8.7‰) of the graphitized amphibolite-facies rocks widespread in the core of the Ruzhino paleodiapir suggest that their carbon is of mantle provenance. The Early Cambrian metaterrigenous rocks metamorphosed to the greenschist facies have 13C from −19.9 to −26.6‰, which testifies to its organic origin. The elevated concentrations of noble metals in these rocks suggest that the sources of carbon and metals were polygenetic and that the ore-forming system evolved over a long time span.

EXTRACTION OF PLATINUM(IV) VIA LIQUID EMULSION MEMBRANE CONTAINING CYANEX-923 FROM BROMIDE MEDIA

Transport behavior of Pt(IV) from bromide media through a liquid emulsion membrane has been studied using Cyanex-923 as a mobile carrier. Platinum(IV) was quantitatively extracted from external bromide (feed phase) media and stripped in perchloric acid as an internal (strip) phase. The important variables governing the permeation of Pt(IV) through LEM studied are membrane viscosity, concentration of mobile carrier, treatment ratio, speed of agitation, and internal (strip) phase concentration. The optimum condition for extraction of Pt(IV) via liquid emulsion membrane are—internal phase: 4.0 mol dm−3 HClO4; organic phase: 12% span-80, 7% 1-octanol, and 0.8% Cyanex-923 in xylene; feed phase: 10 ppm of Pt(IV) in 5.0 mol dm−3 HBr in presence of 0.005 mol dm−3 SnCl2.

Study on the occurrence of platinum in Xinjie CuNi sulfide deposits by a combination of SPM and NAA

A combination of neutron-activation analysis (NAA) and scanning proton microprobe (SPM) was used to study the distribution of platinum-group elements (PGEs) in rocks and ores from Xinjie CuNi deposit. The minimum detection limits of PGEs by NAA had been much improved by means of a nickel-sulfide fire-assay technique for pre-concentration of PGEs in the ore samples. A simple and effective method was developed for true element mapping in SPM experiments. A pair of moveable absorption filters was set up in the target chamber for high sensitivities of both major and trace elements. The bulk analysis results by NNA indicated that the PGE mineralization occurred at the base of Xinjie layered intrusion in clinopyroxenite rocks and the CuNi sulfide minerals disseminated within the rocks had high abundance level of PGEs. However, the micro-PIXE analysis of the CuNi sulfide mineral grains did not find PGEs above the MDL of 6–9 ppm for Rh, Ru and Pd, and 60 ppm for Pt. The search for platinum occurrence in sulfide minerals was followed by scanning analysis of SPM when some smaller platinum enriched grains were found in the sulfide minerals. The microscopic analysis results suggested that platinum occurred in the CuNi sulfide matrix as independent arsenide mineral grains. The chemical formula of the arsenide sperrylite was PtAs 2. The information of the platinum occurrence was helpful to future mineralogical research and mineral processing and beneficiation of the CuNi deposit.

Compared activities of platinum and high specific surface area Mo 2C and WC catalysts for reforming reactions : I. Catalyst activation and stabilization: Reaction of n-hexane

The catalytic properties of high specific surface area (>150 m 2/g) molybdenum and tungsten carbides are studied in hydrocarbon-reforming reactions and compared to conventional platinum supported on alumina. The isomerization of n-hexane is used as a test reaction. TPR and XPS analyses show that the raw materials are contaminated by oxygen and need an activation process to become reactive. These analyses also show that Mo 2C is decomposed by pure hydrogen at 800°C to form methane and metallic molybdenum. Different methods of reductive activation are tested: high-temperature reduction (800°C) by hydrogen leads to metallic Mo and W on the surface (catalytically unreactive for reforming); coreduction by a mixture of pentane and hydrogen (700°C) gives active catalysts but less so than conventional platinum, probably because of the presence of carboneous residues formed by decomposition of the n-pentane. Trace amounts of different group VIII transition metals (≤500 ppm) can catalyze the activation process, probably by preventing the formation of the carboneous residues. Mo 2C activated by 500 ppm of Pt, Ir, or Ru can reach total specific activities 6 to 7 times higher than the conventional Pt catalyst. However in terms of yield, the best carbide, activated by Ir, only doubles the performance of conventional platinum, with a high amount of cracked molecules formed in parallel. Clean surfaces of Mo 2C or WC can be much more reactive than conventional Pt catalysts in terms of specific activity, isomerization, plus cracking; however, the best selectivity in isomers never exceeds 30% while selectivity on Pt is usually in the range 75 to 85%.

Rapid Extraction Spectrophotometric Determination of Platinum Using Anisaldehyde-4-Phenyl-3-Thiosemicarbazone as a Chromogenic Reagent

Abstract The synthesis, spectral characteristics and analytical applications of anisaldehyde-4-phenyl-3-thiosemicarbazone (APT) are described. A simple, rapid, selective and sensitive spectrophotometric method for the determination of platinum was developed based on the colour reaction between platinum (IV) and anisaldehyde-4-phenyl-3-thio-semicarbazone (APT) in the pH range 1.7 - 3.0. The yellow coloured species has an absorption maximum at 360 nm. The complexation is complete within 1 min. A five-fold excess of the reagent is required for complete complex formation. Beer's law is obeyed over the concentration range 0.1 -20 ppm of Pt(IV). The mtilar absorptivity and Sandell's sensitivity are 1.58 × 104 l. mol−1 cm−1 and 0.0123 ug of Pt(IV) cm−2, respectively. The effects of pH, time concentration of reagent, order of addition of reagents and the interference from various ions were investigated. The method has been employed for the determination of platinum in synthetic mixtures whose composition correspo...

The extraction of noble metals with n-octylaniline

The extraction of noble metals with n-octylaniline at varying concentrations of different mineral acids was studied, and optimum conditions for their separation from the base metals commonly present in platinum-bearing materials were established. The successful application of the procedure to the analysis of mattes, sludges, and flotation concentrates is shown. The lower limit of determination in such materials is 100 ppm for Pt and Ir, 40 ppm for Ru, and 10 ppm for Pd and Rh.

Effects of the Pt content of La 0.7Pb 0.3MnO 3 on its catalytic activity for the oxidation of CO in the presence of SO 2

The catalytic activity of La 0.7Pb 0.3MnO 3, prepared by various methods and supported on monoliths of cordierite, for the oxidation of CO in the presence of 50 ppm of SO 2 is observed to increase with increasing Pt content of the samples. Crushed single crystals with Pt contents of 0–5200 ppm and polycrystalline materials with 0–2400 ppm behaved qualitatively similar in this respect. As little as 200 ppm of Pt imparted a significant resistance to poisoning by SO 2.

The activity of La 0.7Sr 0.3MnO 3 without Pt and La 0.7Pb 0.3MnO 3 with varying Pt contents for the catalytic oxidation of CO

Catalytic activities of La 0.7Pb 0.3MnO 3 and La 0.7Sr 0.3MnO 3 for the oxidation of CO were determined for unsupported samples and for samples supported on corrugated monoliths of cordierite. Pt free La 0.7Sr 0.3MnO 3 was produced with a high surface area. It is stable to ≥ 1000°C and has been used to prepare supported devices having overall activities comparable to commercial Pt catalysts. In contrast, the “intrinsic” activity of La 0.7Pb 0.3MnO 3 is in most samples markedly reduced at ≥ 400°C. The effects of Pt on the activity for CO oxidation were studied. Single crystals of La 0.7Pb 0.3MnO 3 having 0–5200 ppm of Pt were grown. Polycrystalline samples having 0–2200 ppm of Pt were prepared, mainly by freeze-drying techniques. Samples with ≤ 570 ppm Pt were not significantly more active than the “intrinsic” freshly prepared perovskite surfaces without Pt showing that the activity of the perovskite is not directly connected with Pt. Samples with ≥ 1600 ppm Pt showed markedly enhanced activity and a higher activation energy similar to that of Pt.

Cellular growth in BaFe 12O 19 crystals solidified from flux solvent

Single crystals of BaFe 12O 19 grown from a BaO-B 2O 3-PbO flux show the classical hexagonal cells hitherto reported to occur in constitutionally supercooled solidified metallic alloys. The size of the cells varies from 10–20 μm increasing with the amount of PbO in the flux. Electron microprobe analysis across both longitudinal (10 1 0) and transversal (0001) slices of the cells shows as strong periodical variation of the concentration of Ca and Sr impurities as well as a slight periodical variation of the concentration of Ba, Pb, and Fe at the cell boundaries. About 120 ppm of Pt have been found by emission spectroscopy in the crystals but this amount is much below the detection limit of our electron microprobe apparatus. It is assumed that the redistribution of the impurities of Ca and Sr, and possibly also Pt, dissolved from the crucible walls cause the cellular growth. Curie points and magnetic moment measurements of the grown crystals do show that about 10 mole% is the maximum amount of Pb 2+ which substitutes for Ba 2+ in BaFe 12O 19.

CARBON-13 NUCLEAR MAGNETIC RESONANCE OF METAL COMPLEXES. I.

Abstract Carbon-13 chemical shifts were measured for 15 cyanometallate complexes in aqueous solution with Fourier-Transform NMR spectroscopy. The chemical shift values are distributed between −50.33 ppm (from external benzene standard) for Fe(CN)64− and +2.66 ppm for Pt(CN)42−. The coupling constant 1JC-Co was found to be 126 ± 4 Hz for Co(CN)63−.