Phase Of Pt Research Articles

Improved catalytic NO oxidation over Pt supported on sulfuric acid treated TiO2

Promoting the formation of metallic Pt over the catalysts is the key to improving the NO reactivity. In general, TiO2 suppresses the oxidation of Pt by surface acidity and induces the formation of the metallic phase of Pt by Pt-Ti interaction. However, the limited number of acidic sites (–OH) contributes to the formation of large Pt particles, which may lead to the formation of Pt2+ or Pt4+, resulting in performance degradation. In this study, we further formulated the acidic sites of the TiO2 with sulfuric acid treatment (SA-TiO2) to improve catalytic NO oxidation. During the SA treatment, the TiO2 surface is positively charged by the low pH, providing an environment for well-distributed sulfate. In the subsequent introduction of Pt, the increase in acidic sites for Pt adsorption greatly enhanced the dispersion of Pt. During this process, Pt formed bonds with sulfate as [Pt(NH3)4]-SO4. The surface species combined with SO4 and NH3 were decomposed during the calcination process, thereby inhibiting the oxidation of Pt, which promotes the formation of metallic Pt. As a result, highly reactive Pt0 and Pt2+ were further formulated by increasing the acidic sites of SA-TiO2, where the low-temperature NO oxidation performance was improved, regardless of the Pt loading (0.3 to 3 wt.%).

Structural and electronic properties of Pt modified Au(100) surface

Investigations on electronic and geometric structures of platinum adsorbed on monocrystalline gold surfaces are important for understanding the remarkable catalytic properties of bimetallic Pt–Au systems. Herein, the morphology of quasi-hexagonal (hex) Au(100) surface after deposition of platinum for coverage up to 0.5 monolayer (ML) has been investigated by scanning tunneling microscopy (STM). For coverage range 0.2–0.4 ML the creation of elongated islands with mono-atomic height is observed. The islands consist of flat phase of disordered Pt-Au alloy which coexists with nanowire-like features with a hex atom arrangement and quantized width. Annealing the Pt/Au(100) system at 100–150 °C changes the surface morphology. The islands disappear and the topmost layer of the surface consists of flat phase of Pt–Au alloy which coexists with the hex-stripes. Small domains of ordered c(2 × 2) structure of Pt–Au alloy are found. The electronic properties of this structure have been investigated by ab-initio calculations. The obtained results allow to distinguish the Pt from Au atoms by their appearance in the STM images. The calculated electronic structures indicate a bonding creation between Pt and Au atoms and an electron d-states redistribution of Pt in comparison to the bare Pt(100)-(1 × 1) surface.

Kesejahteraan Ayam Petelur di PT Inti Tani Satwa Kabupaten Maros

Animal welfare relates to physical and mental states that conform to the natural behavior of animals and need to be implemented to protect animals. Laying hens are very vulnerable to violating animal welfare principles because of high production targets but demands to minimize costs. The study was conducted in the laying hens of the grower phase of PT. ITS with direct observations, interviews, and discussions. The results were analyzed descriptively according to five principles of animal welfare, namely freedom from pain, injury, and disease, freedom from hunger and thirst, freedom from heat and discomfort, freedom from fear and suffering, and freedom to express normal and natural behavior. The results show that the implementation of animal welfare at PT. ITS has been carried out, but there are also aspects that are not fulfilled, namely the aspect of being free to express normal and natural behavior that has not been fully implemented because the density of the rang or cage makes the animals very crowded so this must be corrected so that the livestock welfare aspects can be met.

A Magnetocatalytic Propelled Cobalt–Platinum@Graphene Navigator for Enhanced Tumor Penetration and Theranostics

A Magnetocatalytic Propelled Cobalt–Platinum@Graphene Navigator for Enhanced Tumor Penetration and Theranostics

Separation of Pt(IV), Pd(II), and Rh(III) from Chloride Solutions by Multistage Extraction Using Nitrogen-Containing Extractants

This article demonstrates possible separation of Pd(II), Pt(IV), and Rh(III) ions from chloride solutions by solvent extraction in rotating coiled columns (RCC). The most common reagents used for extraction of platinum metals were selected as extractants: trioctylamine (TOA), methyltrialkylammonium chloride (MTAA), tributyl phosphate (TBP), and relatively new reagent—N,N,N',N'-tetra-n-octyldiglycolamide (TODGA). The completeness of extraction of platinum metals from individual and mixed hydrochloric acid and chloride solutions has been analyzed as a function of the essence and concentration of extractant, acidity of the analyzed solutions, and other factors. Optimum conditions of quantitative extraction of the metals from model hydrochloric acid and chloride solutions into the extractant phase have been determined, including subsequent selective separation at the re-extraction stage. A flowchart has been proposed for multistage extraction of Pd(II), Pt(IV), and Rh(III) using 0.05 M MTAA solution in toluene as a stationary phase in RCC. The flowchart includes extraction of Pd(II) and Pt(IV) ions from the solution (0.1 M HCl + 30 g/L Cl–) into the organic phase upon simultaneous separation of Rh(III) remaining in the aqueous phase and consecutive re-extraction of Pd(II) and Pt(IV) from the organic phase using 0.01 M solution of thiourea in 0.1 M HCl and 1 M solution of thiourea in 0.5 M HCl, respectively. The flowchart has been verified for separation of platinum metals in the production process of preset composition. The degree of metal extraction after processing by 0.05 M solution of MTAA in in toluene and consecutive re-extraction by solutions of thiourea is 99.5% for rhodium(III), 99.9% for palladium(II), and 97.4% for platinum(IV). The extracted aqueous phases of rhodium and platinum after output from the column did not contain impurities of other platinum metals. In the aqueous fraction of palladium, the platinum content was 0.5%.

The First Heterometallic Acetate-Bridged Pt(II)–Pd(II) Complex: Synthesis, Structure, and Formation of Bimetallic PtPd2 Nanoparticles

The reaction of platinum acetate blue, empirically described as Pt(OOCMe)2.50, with palladium(II) acetate Pd3(μ-OOCMe)6 gave the first heterometallic acetate-bridged platinum(II) and palladium(II) complex Pd2Pt(μ-OOCMe)6 (I) as co-crystallizates 17Pd2Pt(μ-OOCMe)6 ⋅ 4Pd3(μ-OOCMe)6 ⋅ 42C6H6 (IIa) and 17Pd2Pt(μ-OOCMe)6 ⋅ 4 Pd3(μ-OOCMe)6 (IIb). Single crystal X-ray diffraction (CIF files CCDC nos. 1568105 and 1852744), EXAFS, and quantum chemical studies (DFT and QTAIM) of complex I revealed a slightly distorted triangular structure similar to the structure of palladium(II) acetate Pd3(μ-OOCMe)6 and hypothetical platinum(II) complex Pt3(μ-OOCMe)6. The thermal decomposition of complex IIa gives the bimetallic alloy PtPd2. A combined X-ray diffraction and EXAFS study demonstrated that the obtained material consists of core (Pt)–shell (Pd) particles with an average size of ~28 nm and a minor amount of smaller (~5 nm) PdO nanoparticles on the surface. The obtained results are useful for the understanding of the nature and structure of the supported phase of heterogeneous Pt–Pd catalysts.

Observing the oxidation of platinum

Despite its importance in oxidation catalysis, the active phase of Pt remains uncertain, even for the Pt(111) single-crystal surface. Here, using a ReactorSTM, the catalytically relevant structures are identified as two surface oxides, different from bulk α-PtO2, previously observed. They are constructed from expanded oxide rows with a lattice constant close to that of α-PtO2, either assembling into spoked wheels, 1–5 bar O2, or closely packed in parallel lines, above 2.2 bar. Both are only ordered at elevated temperatures (400–500 K). The triangular oxide can also form on the square lattice of Pt(100). Under NO and CO oxidation conditions, similar features are observed. Furthermore, both oxides are unstable outside the O2 atmosphere, indicating the presence of active O atoms, crucial for oxidation catalysts.

Efficient synthesis of PtPd/Fe3O4 nanoparticles and its magnetic recoverability and stable recyclability for the Heck and Suzuki reactions

Platinum and palladium bimetal nanoparticles on ferroferric oxide (PtPd/Fe3O4 NPs) nanocomposite catalysts were successfully synthesized with polyvinyl pyrrolidone as a stabilizing agent. The resultant samples were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, transmission electron microscopy, high-resolution transmission electron microscopy, inductively coupled plasma, and magnetic studies. The catalytic performance of the PtPd/Fe3O4 NPs in the Heck and Suzuki coupling reactions was evaluated. Results showed that the cubic phase of Pt and Pd bimetal nanoparticles coexists with that of Fe3O4. The PtPd/Fe3O4 NP catalysts, which were approximately 22 nm in size, showed excellent catalytic activity in the Heck and Suzuki reactions. Moreover, the catalyst can be recovered with a magnet and reused several times without the significant loss of catalytic activity.

Electrochemical Properties of Lithium Air Secondary Batteries with Pt100-XRux Electrocatalysts for Air Electrodes: Optimization of Pt/Ru Composition Ratio

Introduction Lithium air secondary batteries (LABs) exhibit much higher theoretical energy density than lithium ion batteries and are anticipated as one of the most promising candidates for the next generation of batteries. However, problems with LABs include their electrochemical properties, such as cyclability, overpotential, and round-trip efficiency need further improvement[1-2]. Various kinds of electrocatalysts have been studied to overcome these drawbacks [1-2]. We have reported that a battery incorporationg Pt33Ru67 electrocatalyst shows discharge capacities of more than 400 mAh/g for over 30 cycles in TEGDME-based electrolyte solution [2]. In this study, to further improve the cyclability, we prepared Pt100-x Ru x /carbon electrocatalysts with wide composition range of 0 ≤ x ≤ 100 by the soft liquid process and examined the electrochemical properties of the cells loaded with the electrocatalysts into air electrodes. Experimental Pt100-x Ru x /carbon was prepared by the formic acid reduction method [3]. KetjenBlack EC600JD (KB) was used as the carbon support material. The KB powder was dispersed in formic acid solution by sonication, and H2PtCl6¥6H2O and/or RuCl3 solution was dropped into the solution, which was then stirred overnight. The Ru content, x, in Pt100-x Ru x was 0 (Pt alone) 30, 60, 75, 83, 90, or 100 (Ru alone). Then, dried Pt100-x Ru x /KB powder was obtained by heat-treating the mixture at 300°C for 12 h in Ar. The air electrodes were prepared by coating the mixture of Pt-Ru/KB powder, and PVdF in N-methylpyrrolidone solvent, and drying it at 90°C. The composition ratio of an air electrode with a diameter of 5 mm was KB/Pt100-x Ru x /PVdF = 80: 10: 10. The LAB cell (ECC-Air, EL-Cell) was assembled, incorporating the air electrode loaded with Pt100-x Ru x /KB, an electrolyte solution (1 mol/l LiTFSA/TEGDME), a glass separator, and Li metal sheets. Electrochemical measurements were carried out under a galvanostatic condition of 0.1 mA/cm2 in a dry air atmosphere. The discharge and charge capacities were normalized by the weight of Pt100-x Ru x /KB powder and PVdF in the air electrodes. Results and discussion Figure 1 shows XRD patterns of samples with various composition ratios of Pt100-x Ru x /KB. The patterns of x = 0 and 30 corresponded to a single phase of Pt (PDF #00-004-0802), and the ones of x = 83, 90, 100 corresponded to a single phase of Ru (PDF#00-006-0663). The sample with x = 60 and 75 was identified as a mixture of the Pt and Ru phase. In addition, the XRD peaks became broad by increasing the content of Ru. This suggests that the added Ru is effective in reducing the particle size of Pt100-x Ru x alloy, and then it should enhance the electrocatalytic activities. Figure 2 shows the typical first discharge-charge curves of the cells incorporating the air electrodes loaded with Pt100-x Ru x /KB catalysts. First discharge capacities are 496, 671, 905, 1014, and 909 mAh/g in the cells with samples with x = 0, 30, 75, 90, and 100, respectively. The discharge capacities clearly increased with increasing Ru content, indicating the maximum capacity in the x = 90 sample. Moreover, the cell for the x = 90 shows the highest average voltage of 2.58 V, while the one for x = 0 shows rather low voltage of 2.43 V. In the charging process, the average charge voltages decreased with increasing Ru content and, accordingly, the charge capacities increased as a result of the smaller charge overpotentals, indicating the maximum capacity of 867 mAh/g in the x = 90 sample. Figure 3 shows the cycle properties of cells incorporating the air electrodes loaded with Pt100-x Ru x /KB catalysts. The discharge capacities of all cells gradually decreased. In particular, the cell for x = 0 shows very small capacity of less than 80 mAh/g at the 8th cycle. This result indicates the effectiveness of Ru addition for improving the cyclability. Among the cells tested, the one with the x = 90 sample showed comparatively better cycle stability with discharge capacity of over 800 mAh/g at the 8th cycle. These behaviors are very similar to the above discharge/charge properties. As a result, the x= 90 sample was confirmed to be the optimized composition as the electrocatalyst for the air electrode. From the above results, it was found that the higher Ru content leads to a higher surface area and higher dispersion state of Pt100-x Ru x electrocatalyst accompanied by inhibition of particle growth, which result in good electrochemical performance of cells incorporating Pt10Ru90/KB. [1] A. Debart et al., Angew.Chem., 120, 4597 (2008). [2] M. Hayashi et al., The 56th Battery Symposium in Japan, 3G02, (2015). [3] J. Prabhuram et al., J. Power Sources, 134, 1 (2006). Figure 1

Methanol Oxidation and Oxygen Reduction Activity of PtIrCo-Alloy Nanocatalysts Supercritically Deposited within 3D Carbon Aerogel Matrix

The comprehensive investigation of ternary PtIrCo-alloy nanoparticles supported on 3D carbon aerogel matrix toward Methanol Oxidation Reaction (MOR) and Oxygen Reduction Reaction (ORR) is focused on CO tolerance in MOR, methanol vs. oxygen selectivity in ORR, and the structural changes within the metal alloy nanoparticles caused by the heat treatment and the electrochemical conditioning. Amorphous tri-metallic Pt59Ir34Co7-nanoparticles with mean size of 1.47±0.21nm were formed within 3D CA matrix in supercritical CO2 (scCO2) from the Pt, Ir, and Co organometallic precursors. Depending on the heat-treatment temperature (600°C or 900°C), the amorphous organometallic phase of Pt, Ir and Co was transformed into a single-phase fcc PtIrCo-alloy nanoparticles with a mean particle size of 1.68±0.33nm and 2.68±0.61nm, respectively. The fcc lattice parameters of the PtIrCo-alloy (0.389nm at 600°C and 0.386nm at 900°C) were smaller than that of the Pt fcc lattice (0.392nm) and the lattice parameters reduced proportionally to the heat-treatment temperatures. After 50 electrochemical cycles, PtIrCo/CA catalysts display improved MOR specific activity (∼2.5 X Pt/C), mass activity (∼3 X Pt/C) at 0.7V vs. SHE, higher CO-tolerance, and better electrochemical stability than Pt/C, but less CO-tolerance and stability than PtRu/C. Regarding ORR, the PtIrCo/CA catalysts demonstrate enhanced ORR specific activity (∼5.5 X Pt/C) and mass activity (∼6.3 X Pt/C) at 0.7V vs. SHE along with superior methanol-tolerance in comparison to Pt/C. The structural changes associated with PtIrCo/CA fcc-lattice parameter with respect to Pt-lattice have contributed to better MOR and ORR activities. Faster surface diffusion associated with weak adsorption of hydroxide species and higher selective adsorption of oxygen in comparison to methanol onto PtIrCo-alloy surface could have contributed to their better CO-tolerant MOR and methanol-resistant ORR activity compared to Pt-catalyst.

The preparation of self-humidifying Nafion/various Pt-containing SiO2 composite membranes and their application in PEMFC

Various Pt-containing silica nanoparticles were successfully synthesized and adopted in the fabrication of Nafion/silica and Nafion/Pt-containing silica composite membranes. X-ray diffraction and X-ray photoelectron spectroscopy analyses for Pt-containing silica nanoparticle were conducted to identify the phase and oxidation state of Pt incorporated onto silica nanoparticles. Transmission electron micrograph analysis shows 2–3nm of Pt nanoparticles on the surface of silica nanoparticle. Water uptakes of Nafion/Pt-containing silicas and Nafion/silica composite membranes were measured. All these composite membranes show higher water uptakes than that of casting Nafion membrane. In addition, S-Pt/SiO2 and Pt-S/SiO2 composite membranes show a little higher water uptake than that of Nafion/Pt/SiO2 composite membrane due to hydrophilic sulfonic group. The cell test using various MEAs shows that under zero humidity, Nafion/S-Pt/SiO2 composite membrane shows 0.45A/cm2 at 0.6V and even comparable to that of casting Nafion membrane under 100% humidity. It is seen that the cell performance was rather decreased with the increase of Pt-containing silica content due to water flooding and/or electron loss due to the electrical conduction transfer network formed by too much Pt within the membrane. Finally, in case of sulfonation, the order of sulfonation seems to be critical.

Selective ring opening of decalin with Pt–Ir/Al2O3 catalyst prepared by catalytic reduction

The reaction of selective ring opening using alumina supported Pt–Ir catalysts with and without Mg addition was studied. The catalysts were prepared by the method of catalytic reduction, having 1wt% of Pt whereas the Ir content varied in the range 0.1–0.6wt%. Electron diffraction showed that the method of preparation leads to catalysts with strong interaction between Pt and Ir being observed the presence of a solid phase of Pt–Ir. In the catalysts without Mg no changes in the hydrogenolysis activity was observed as the Ir content increases. However, a decrease both in acidity and dehydrogenating activity was observed. In the Mg containing catalysts, the addition of Ir increases the acidity, the dehydrogenating and hydrogenolytic activity. For the isomerization reaction of n-pentane it was found that the addition of Ir improves the stability of the catalysts and formation of isomers of C5 in both series of catalysts (with and without Mg). The conversion of decalin by ring opening depends on the content of Ir for both studied series.

Reply to “Comment on ‘CO Oxidation on Pt-Group Metals from Ultrahigh Vacuum to Near Atmospheric Pressures. 2. Palladium and Platinum’”

First of all, it is essential to clarify the terms “reactive phase” and “most reactive phase” since the central point of all the arguments in the Comment is the relative reactivity of various phases. The most reactive phase would clearly be that phase upon which the impinging CO and O2 molecules achieve a reaction probability of unity or near unity. The classical molecular beam work by Ertl and co-workers1-3 has demonstrated that under optimum conditions, a reaction probability of near-unity is obtainable on metallic Pt and Pd surfaces. In contrast, a reaction probability even remotely close to the CO/ O2 collision limit has never been achieved on any oxidized phase.2,4-6 These results in themselves constitute a self-proof that an oxide phase is much less reactive than a metallic phase. In the paper to which the Comment is addressed, the Pt and Pd surfaces that exhibited the highest CO2 formation rates (TOFs) were those observed to be metallic, covered with a full layer of chemisorbed oxygen and an undetectable amount of CO at reactant pressures of e10-3 Torr. In other words, the most highly reactive phase of unsupported Pt and Pd catalysts is invariably a metallic surface. If collision-limited reaction rates could be achieved on the most highly reactive surfaces at realistic catalytic pressures, reaction rates or TOFs would reach ∼107 CO2 molecules site-1 s-1.8 Of course, these rates are never reached in reality because of mass transfer limitations, that is, the reaction rate is limited by the availability of reactant molecules in the near surface region. The reaction rate on planar catalysts, such as those used in the studies being discussed, can be enhanced by circulation of the reactants or by reducing the size of the catalyst.7,8 Such efforts invariably lead to enhanced TOFs to some extent (approaching ∼104 CO2 molecules site-1 s-1 with the experimental setup described in ref 8). This is to say, metallic surfaces outside the CO-inhibited regime are capable of reaching extremely high TOFs and the so-called “jump” points shown in Figure 1a of the Comment are manifestations of this behavior. Whether or not this jump behavior is observed depends critically on the CO supply in the near surface region and to a large extent on the experimental reactor configuration. In any case, the explanation of the results observed in Figure 1b of the Comment of van Rijn et al. is rather straightforward. In the mass transfer limited regime (TOF ∼102-103 CO2 molecules site-1 s-1), the number of highly active sites (sites that are capable of achieving TOF ∼107 CO2 molecules site-1 s-1) required to consume the available CO is an extremely small fraction of the total number of surface sites. For example, for a TOF of 102, only ∼0.01-0.001% of active surface sites would be required. SXRD is a technique that determines the structure of the majority surface phases whereas the observed reaction rate can be easily sustained by only a very small fraction of the total surface sites. For a reaction dominated by minority sites, SXRD is not an appropriate technique to “see” the nature of the active site nor can it be expected to correlate the active structure with the reaction kinetics measurements. It is also noteworthy that the kinetic data of Figure 1b in the Comment of van Rijn et al. are questionable particularly in the CO-inhibited regime given that numerous previous studies have shown that the CO2 formation is approximately +1 order with respect to O2 and -1 order with respect to CO.4,9,10 This behavior is clearly not exhibited by the data in Figure 1b. In summary, the most reactive phase of Pt and Pd at low and high pressures is identical and corresponds to the reduced metal. At pressures, for example, 10-5 mbar, collision-limited reaction is not possible due to mass-transfer limitations. Also because of mass-transfer limitations, the most reactive phase can quickly become oxidized at reaction conditions outside the CO-inhibited regime. Within this mass-transfer limited regime, the oxide phases so formed do not contribute significantly to the observed reactivity, but rather the residual activity arises primarily from a very small fraction of reduced or metallic-like sites.

Synthesis of highly active nanostructured PtRu electrocatalyst with three-dimensional mesoporous silica template

Nanostructured PtRu material has been successively synthesized via chemical co-reduction of hexachloroplatinic acid and ruthenium trichloride using three-dimensional (3D) hexagonal mesoporous SBA-12 silica as a solid template, and has been studied as an electrocatalyst toward methanol electro-oxidation. The ordered nanostructure of the PtRu particles has been disclosed by transmission electron micrographs and is characterized by regular pores of ca. 3.0 ± 0.3 nm in diameter separated by walls of ca. 3.0 ± 0.3 nm thick. X-ray diffraction and energy dispersive X-ray spectroscope studies indicate that the PtRu material comprises of complicated phases rather than a single alloy phase of Pt and Ru. The specific electrochemical surface area of the nanostructured powder measured using both CO and underpotential deposited Cu stripping techniques is 74–78 m 2 g –1, higher than that of unsupported precious metal catalysts prepared using standard techniques. The combination of high surface area and periodic nanostructure of the templated PtRu makes it an interesting promising fuel cell electrocatalyst. This has been demonstrated by the high activity of the templated PtRu towards the methanol electrooxidation. Therefore the solid template route based on 3D mesoporous silica with controlled pore size and high pore interconnectivity provides an interesting alternative to produce promising high-surface-area electrode materials.

Pt–Ni/γ-Al2O3 catalyst for the preferential CO oxidation in the hydrogen stream

The preferential CO oxidation (PROX) in the presence of excess hydrogen was studied over Pt–Ni/γ-Al2O3. CO chemisorption, X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy and temperature-programmed reduction were conducted to characterize active catalysts. The co-impregnated Pt–Ni/γ-Al2O3 was superior to Pt/Ni/γ-Al2O3 and Ni/Pt/γ-Al2O3 prepared by a sequential impregnation of each component on alumina support. The PROX activity was affected by the reductive pretreatment condition. The pre-reduction was essential for the low-temperature PROX activity. As the reduction temperature increased above 423 K, the CO2 selectivity decreased and the atomic percent of Ni in the bimetallic phase of Pt–Ni increased. This catalyst exhibited the high CO conversion even in the presence of 2% H2O and 20% CO2 over a wide reaction temperature. The bimetallic phase of Pt–Ni seems to give rise to high catalytic activity for the PROX in H2-rich stream.

Improved pinning effect in PtMn/NiFe system by Cr addition into PtMn

The exchange bias and thermal properties of Pt1−xMnx–Cr∕NiFe films were investigated. Adding Cr into Pt1−xMnx film by inserting thin Cr layers was found to decrease the exchange bias considerably for x>0.5 but lead to a great enhancement of the pinning field along with unvarying coercivity and better thermal stability for x⩽0.5. An optimum pinning field of ∼180 Oe was obtained for Pt0.55Mn0.45–Cr(4%) pinning 150 Å NiFe—almost twice that of pure Pt0.55Mn0.45, and even larger than that of Pt0.5Mn0.5, by 20%. Although possessing a smaller grain size, Pt0.55Mn0.45–Cr(4%) has a higher blocking temperature than either pure Pt0.55Mn0.45 or Pt0.5Mn0.5. Structure characterization revealed that adding Cr promoted the ordering process of Pt1−xMnx (x⩽0.5) greatly, and a perfect ordering phase of Pt(MnCr) was formed. The present results suggest that PtMn–Cr has favorable properties as a pinning layer.

Voltammetric and UHV characterisation of the (1×1) and reconstructed hex-R0.7° phases of Pt{100}

The voltammetry of the clean (1×1) and reconstructed hex-R0.7° phases of Pt{100} prepared in UHV are reported. By comparison with the UHV data, both phases may readily be prepared using a flame-annealing procedure so long as the conditions of sample cooling are precisely controlled. The well-ordered (1×1) phase may be formed by cooling in hydrogen. Back transfer to UHV of the hydrogen-cooled sample gave rise to a p(1×1) LEED pattern. These findings are in accordance with previous investigations [Attard and Price, Surf. Sci. 335 (1995) 63 and erratum; Al-Akl et al., J. Chem. Soc. Faraday Trans. 91 (1995) 3585; Sashikata et al., Langmuir 14 (1998) 2896; Tidswell et al., Phys. Rev. Lett. 71 (1993) 1601]. The voltammetry of the UHV-prepared hex-R0.7° phase can be obtained only after a flame-anneal treatment by cooling rapidly in a flow of inert gas such as argon in which oxygen has been rigorously excluded. In contrast to the hydrogen cooled Pt{100} electrode, subsequent LEED analysis of the argon cooled sample showed a reconstruction pattern similar, though not identical to one reported recently by Zei et al. for a partially deconstructed Pt{100} electrode. On the basis of these results it is suggested that the p(1×1) and hex-R0.7° phases of Pt{100} may be prepared under ambient conditions in an electrochemical cell. Although the potentials at which the reconstructed phase is stable are different from those reported by Zei and co-workers, the data do support their earlier results showing that the reconstructed phase of Pt{100} is stable when in contact with electrolyte solutions.

Templating fabrication of platinum nanoparticles and nanowires using the confined mesoporous channels of FSM-16—their structural characterization and catalytic performances in water gas shift reaction

The robust trigonal prismatic Pt 18 and Pt 15 cluster anions are selectively synthesized via [Pt(CO)Cl 3] − in FSM-16 (4.7 nm) and cis-Pt(CO) 2Cl 2 in FSM-16 (2.8 nm) by the reductive carbonylation of H 2PtCl 6 in the confined mesoporous channels of FSM-16, respectively. The Pt cluster anions extracted from the resulting samples in the THF solution by cation metathesis with [PPN]Cl are identified as [Pt 3(CO) 6] 5 2− in FSM-16 (2.8 nm) and [Pt 3(CO) 6] 6 2− in FSM-16 (4.7 nm) by the FTIR and UV–Vis spectroscopic data. The EXAFS and FTIR studies demonstrated that [Pt 3(CO) 6] 5 2−/FSM-16 (2.8 nm) ( ν CO=2078, 1880 cm −1) and [Pt 3(CO) 6] 6 2−/FSM-16 (4.7 nm) ( ν CO=2056, 1879 cm −1) were transformed by heating at 300–343 K into the partially decarbonylated Pt clusters (Pt–Pt; C.N.=7.6, R=2.73 Å) characteristic of a linear CO band ( ν CO=2015 cm −1). According to the EXAFS and TEM observation, Pt carbonyl clusters are eventually converted above 473 K to naked Pt particles of 11 Å (Pt–Pt C.N.=6.7, R=2.72 Å) in FSM-16 (2.8 nm) and of 15 Å (C.N.=7.9, R=2.74 Å) in FSM-16 (4.7 nm). On the other hand, the platinum nanowires [2 and 4 nm (diameter)×50–500 nm (long)] are prepared using the cylindrical mesoporous channels of FSM-16 (2.8 and 4.7 nm) in the templating reduction of H 2PtCl 6 by the exposure to γ-ray or UV-light ( λ max>254 nm) under the atmosphere of 2-propanol and water. It was demonstrated by the TEM observation and EXAFS characterization that the diameters of Pt nanowires formed in FSM-16 are consistent with those of FSM-16 used (2.8 and 4.7 nm), whereas the average lengths of Pt wires are varied by the function of the Pt loading mass and time exposure to γ-ray and UV-light. The observed electron beam diffraction patterns indicate that the Pt wires consist of a single crystal phase of Pt(110) having a lattice fringe of 2.27 Å. It is of interest to find that the Pt nanowires in FSM-16 (2.8 nm and 4.7 nm) exhibited an unique IR spectrum in CO chemisorption and the remarkable activities per surface Pt atom (TOF) for water gas-shift reaction at 323–393 K by 60–90 times larger than those of Pt nanoparticles in FSM-16 and even conventional metal catalysts.

Electrochemical Epitaxial Growth of a Pt(111) Phase on an Au(111) Electrode

The electrochemical deposition of platinum on an Au(111) single-crystal electrode in acidic solutions containing H2PtCl6 was studied using an electrochemical scanning tunneling microscope (STM) and electrochemical quartz crystal microbalance (EQCM). The STM investigation showed an ordered adlayer of PtCl62- on the electrode surface during the electrochemical deposition of platinum and a Pt(111)-(1×1) structure on the electrode surface after the electrode was rinsed with a Pt complex-free solution. Formations of the Pt(111) bulk phase and surface structure of Pt(111)-(1×1) were confirmed by X-ray diffraction (XRD) and the underpotential deposition of copper and hydrogen, respectively.

Characterisation and O2 titration of CO islands on Pt 100: helium atom scattering and reactive sticking probability measurements

Abstract Thermal energy atom scattering (TEAS) has been used simultaneously with molecular beam adsorption and thermal desorption to probe the lateral distribution of CO on a Pt 100 single-crystal surface. On the initial hex-R phase at 350 K, (1 × 1) island growth occurs at a constant local coverage ( θ (1 × 1) CO ) of 0.4 ML. However, during desorption the surface remains wholly in the (1 × 1) state until ( θ (1 × 1) CO ) ≈ 0.25 ML. Subsequent reconstruction to hex occurs at a constant local coverage of 0.19 ML in the remaining (1 × 1) domains. Hysteresis is not observed for the pre-prepared (1 × 1) surface, on which a random CO distribution is observed during adsorption. The scattering cross-section Σ for a single CO molecule on the hex-R and (1 × 1) surfaces at 350 K has been determined as 71 ± 10 and 130 ± 18A 2 respectively. The behaviour during oxidation of (1 × 1)-CO islands on the initial hex-R surface prepared by either adsorption or desorption is found to be consistent with the TEAS data. The first sticking probabilities for O 2 and CO on the CO ad -freed and O ad -freed (1 × 1) phase of Pt 100 are also reported.