Platinum Metal Particles Research Articles

An optimised cell for in situ XAS of gas diffusion electrocatalyst electrodes

The quality of in situ XAS of electrochemical systems is highly sensitive to electrode disturbances, such as gas evolution and gas consumption at an electrolyte / catalyst interface. A novel in situ spectro‐electrochemical X‐ray absorption spectroscopy cell is presented as a new tool for the characterisation of gas evolving and consuming electrocatalysts at high overpotentials. By utilising a thin, porous membrane with efficient electrolyte and gas circulating loops, an improved three phase interface that enabled efficient gas supply and minimised the interference from bubble formation. X‐ray absorption spectroscopy measurements were conducted in fluorescence mode with three experiments selected to demonstrate the cell’s performance. The first two reactions; an in‐situ study of a highly active amorphous iridium oxide catalyst during the oxygen evolution reaction and an in‐situ study of copper oxide during the carbon dioxide reduction reaction are used to exemplify the XAS data quality achieved under operational conditions. Thirdly, a detailed XAS investigation of a highly dispersed platinum catalyst during the oxygen reduction reaction is presented, along with comparative data in nitrogen. These measurements show the retention of oxygen on the surface of the platinum metal particles down to 0.48 V (vs. RHE), well below the platinum oxide reduction peak.

Platinum complexation with glutamate amino acid: Computational study

In this research work, complex formation of platinum (Pt) metal particle with the glutamate (Glu) amino acid was investigated by performing density functional theory (DFT) calculations. Such application could be very much important regarding the importance of developing metal based biosensors for biological media. To achieve the purpose of this work, two spin numbers of 0 and 1 were considered for Pt for locating separately towards neutral and anionic forms of Glu for Pt / Glu complexes formations. The obtained results of optimization and QTAIM analyses indicated various configurations for different spin numbers of Pt metal particle towards each of neutral and anionic forms of Glu. Existence of covalent bond was observed for most cases in addition to existence of weak van der Waals interactions for the complexes.

Hydrothermal Synthesis of Platinum–Chromium Oxidation Catalysts on Metal Supports

Catalysts containing highly dispersed platinum metal particles in a matrix of chromium oxides with different degrees of oxidation on metallic supports were obtained using the hydrothermal decomposition reactions of [Pt(NH3)4]CrO4 and [Cr(NH3)5Cl][PtCl4] complexes. The Kh18N10T and Kh20N80 alloys as chips or metal rubber blocks were used as the metal supports. The properties of the catalysts were studied in model reactions of the complete oxidation of propane and n-hexane.

Decoration of Carbon Nanomaterial Powders with Dispersed Platinum Metal Particles

Carbon nanomaterials (fullerite, detonation nanodiamonds, Taunit, fullerenol, fullerene-containing black) were decorated with platinum group metal nanoparticles in situ in one step by low-temperature combustion (~250–270°С) of a powdered mixture of platinum metal acetylacetonate [Pt-M(асас)n, Pt-М = Pt(II), Pd(II), Rh(III), Ir(III), acac = CH3COCHCOCH3, n is the oxidation state of Pt-М] with carbon nanomaterials in air. As shown by thermal analysis, the process is based on thermal oxidative degradation of the organometallic complex, catalyzed by carbon nanomaterials, with oxidation (combustion) of the organic moiety and release of the metal into the condensed phase. The thermal process in an open system occurs in the glowing mode (210–250°С); the size of the nanoparticles formed is 7–30 nm. Under the conditions restricting the air access to the reaction mixture and free outflow of gaseous products formed by oxidation of acac ligands, the nanoparticle size decreases to 3–10 nm. The particle size depends on the metal amount in the initial powder mixture and on the support morphology.

Selective Hydrogenation of Cinnamaldehyde Over Platinum Nanosheets Intercalated Between Graphite Layers.

Platinum nanosheets between graphite layers were prepared by a thermal treatment of the mixture of platinum chloride (IV) and graphite powder under 0.3 MPa of chlorine at 723 K for 7 days, followed by the reduction under 40 kPa of hydrogen at 573 K for 1 h. Two-dimensional platinum metal nanosheets of 1-3 nm thickness and of 100-200 nm width were intercalated between graphite layers (Pt-GIC). The platinum nanosheets had a number of hexagonal holes and edges with angle of 120°. Liquid phase hydrogenation of cinnamaldehyde (CAL) was studied over Pt-GIC which was compared with that over platinum metal particles supported on graphite layers (Pt/Gmix). The conversion of cinnamaldehyde over Pt-GIC was lower than that over Pt/Gmix; however, the selectivity to cinnamyl alcohol (COL) was higher than that over Pt/Gmix. For similar CAL conversion of around 25% (in 60 min over Pt-GIC and 15 min over Pt/Gmix), the COL selectivities over 5 and 10 wt% Pt-GIC (56 and 54%) were higher than those over 5 and 10 wt% Pt/Gmix (33 and 19%).

Ammonium hydroxide addition and its influence on the catalytic activities of Pt-based catalysts for methane oxidation

A series of binary chromium-platinum catalysts were prepared and the catalytic activity was tested in methane oxidation. The effects of aqueous ammonium hydroxide addition into binary catalyst chromium-platinum catalysts were investigated. All the catalysts were prepared by impregnation method. The reactant gases were consisted of methane-oxygen-argon. The reaction was conducted at an atmospheric pressure and the temperature was ranged from 573 to 773 K. The products were analyzed using thermal conductivity detector. Under this experiment conditions, the only products were carbon dioxide and water. The catalysts were characterized using carbon monoxide chemisorptions and x-ray photoelectron spectrometer. The catalytic activity results showed that the catalyst with the addition of aqueous ammonium hydroxide has smaller platinum metal particle size and its catalytic activity is the highest compared to the other catalysts. X-ray photoelectron spectrometer recorded higher intensities and clear peaks on high pH catalysts indicating a change of interaction between chromium and platinum on alumina. However, active state of chromium was not observed on catalyst surface.

Microwave-assisted conversion of lignin into aromatic compounds

Low-power (≤10 W) microwave radiation considerably reduces the initial temperature in the catalytic hydrocracking of lignin as compared to conventional thermal heating. The microwave-assisted catalytic transformation of lignin at 260-290°C under atmospheric pressure afforded in high yield C6-C10 aromatic and aliphatic hydrocarbons in addition to methoxyphenols and alkylated methoxyphenols. A correlation has been found between the activity of the catalyst (1% Pt/C) and the size of platinum metal particles.

Size effect in the oxidation–reduction processes of platinum particles supported onto silicon dioxide

The interaction of the Pt/SiO2 model catalysts as thin films on the surface of tantalum supports with a mixture of NO + O2 (1: 1) was studied by X-ray photoelectron spectroscopy. The pressure of the reaction mixture was varied from 6 to 64 mbar, and the temperature was varied from room temperature to 500°C. Two types of the catalysts, in which the Pt/Si atomic ratios were ~0.1 and ~0.3 (0.1-Pt/SiO2 and 0.3-Pt/SiO2, respectively) according to the XPS data, were studied. In 0.1-Pt/SiO2, the particles of platinum predominantly had a size from 1 to 2.5 nm; a wide Pt particle size distribution in a range from 1 to 15 nm with a maximum at ~4 nm was characteristic of 0.3-Pt/SiO2. The interaction of all of the samples with NO + O2 at room temperature led to the dissolution of oxygen atoms in the bulk of platinum metal particles. As the reaction temperature was increased, PtO x platinum oxide particles were formed: from small Pt particles in 0.1-Pt/SiO2 at 300°C and from larger particles in 0.3-Pt/SiO2 at 400–500°C. It was established that the reactivity of platinum oxide particles toward hydrogen also depended on the particle size. The small particles of platinum oxide were converted into platinum metal under the action of hydrogen (16 mbar) at 300°C. The coarse particles of PtO x in the samples of 0.3-Pt/SiO2 were reduced much more easily starting with room temperature.

Hydrogen Storage in Pristine and d10-Block Metal-Anchored Activated Carbon Made from Local Wastes

Activated carbon has been synthesized from local palm shell, cardboard and plastics municipal waste in the Kingdom of Saudi Arabia. It exhibits a surface area of 930 m2/g and total pore volume of 0.42 cm3/g. This pristine activated carbon has been further anchored with nickel, palladium and platinum metal particles by ultrasound-assisted impregnation. Deposition of nanosized Pt particles as small as 3 nm has been achieved, while for Ni and Pd their size reaches 100 nm. The solid-gas hydrogenation properties of the pristine and metal-anchored activated carbon have been determined. The pristine material exhibits a reversible hydrogen storage capacity of 2.3 wt% at 77 K and 3 MPa which is higher than for the doped ones. In these materials, the spillover effect due to metal doping is of minor importance in enhancing the hydrogen uptake compared with the counter-effect of the additional mass of the metal particles and pore blocking on the carbon surface.

Preparation of polymeric modifier-attached graphene-supported bimetallic Pt–Pd nanocomposites, and their electrochemical properties as electro-catalysts

Graphene-supported bimetallic nanocomposites were synthesized by a modified sodium borohydride reduction method. Poly(diallyldimethylammonium chloride) (PDDA) was used as modifier for good dispersion and higher metal alloy content. The micro-structure and dispersive properties of the electro-catalysts were determined by X-ray diffraction, Fourier-transform-infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. The electrochemical properties of the Pt–Pd electro-catalysts were studied by cyclic voltammetry. This analysis confirmed that functional groups on the graphene oxide (GO) sheet were chemically bonded to the PDDA layer. The average particle diameter of Pt–Pd1 to 0.5–PDDA–reduced graphene oxide (RGO) was found to be 2.4 ± 0.4 nm which is the smallest platinum metal particle size among Pt–Pd–PDDA–RGO electro-catalysts. The electrochemically active surface area was studied and the activity was found to be enhanced by use of the polymeric modifier.

Highly Dispersed Platinum Nanoparticles on TiO2 Prepared by Using the Microwave‐Assisted Deposition Method: An Efficient Photocatalyst for the Formation of H2 and N2 from Aqueous NH3

A simple and practical technique to synthesize nanosized platinum particles loaded on TiO(2) (Pt-TiO(2)) by using a microwave (Mw)-assisted deposition method has been exploited in the development of a highly efficient photocatalyst for the formation of H(2) and N(2) gases from harmful nitrogen-containing chemical wastes, for example, aqueous ammonia (NH(3)). Upon Mw irradiation, a platinum precursor can be deposited quickly on the TiO(2) surface from an aqueous solution of platinum and subsequent reduction with H(2) affords the nanosized platinum metal particles with a narrow size distribution (Mw-Pt-TiO(2)). Characterization by CO adsorption, platinum L(III)-edge X-ray absorption fine structure analysis, and TEM analysis revealed that the size of the metal nanoparticles strongly depended on the preparation methods. Smaller platinum nanoparticles were obtained by the Mw heating method than those obtained by conventional preparation techniques, such as photoassisted deposition (PAD), impregnation (Imp), and equilibrium adsorption (EA) deposition by conventional convective heating. The H(2) and N(2) formation rates increased with increasing dispersity of platinum. Pt-TiO(2) prepared by the Mw heating method exhibited a specifically high H(2) formation activity in the photocatalytic decomposition of aqueous NH(3) in a nearly stoichiometric 3:1 (H(2)/N(2)) molar ratio under inert conditions. The present Mw heating method is applicable to a variety of anatase-type TiO(2) species possessing different specific surface areas to provide small and highly dispersed platinum nanoparticles with a narrow size distribution.

Structural Characterization and Catalytic Activity of Pt Dendrimer Encapsulated Nanoparticles Supported Over Al<SUB>2</SUB>O<SUB>3</SUB> for SCR of NO<SUB><I>x</I></SUB>

Pt/Al2O3 and Pt-Mg/Al2O3 nano composites were successfully prepared by dendrimer templated synthesis route. The obtained dendritic nanoparticles were dispersed in alumina support and they were evaluated for SCR of NOx using methane as reductant. Thermal analysis results of uncalcined samples revealed that the oxygen can accelerate the rate of dendrimer shell decomposition. X-ray diffractograms of 500 degrees C calcined samples disclosed the amorphous nature of materials, whereas 1000 degrees C air calcined samples showed enhanced crystallinity as well as diffraction pattern corresponding to Pt and PtO. HRTEM images of Pt40-G4OH dendritic nanoparticles showed uniform particulate distribution with average particle size of 2.4 nm. The STEM results of 0.5 Pt/Al2O3 sample calcined at 500 degrees C exhibited a wide range of particles between 2 and 20 nm. This indicates the huge segregation of platinum metal particles during impregnation and subsequent calcination. Among the synthesized materials 0.5 wt% Pt/Al2O3 sample showed excellent conversion and selectivity for SCR of NOx.

Synthesis of Nano-Sized Platinum Metal Particles on Ti-Containing Mesoporous Silica Using Microwave-Assisted Deposition Method

Using microwave-assisted deposition method the uniform and nano-sized platinum metal particles were prepared on the tetrahedrally coordinated Ti-oxide moieties isolated within the framework of mesoporous silica supports. The present nano-sized metal catalyst exhibited a higher activity for hydrogenation of nitrobenzene than the catalyst prepared by a conventional impregnation method.

Catalytic properties of platinum-promoted acid cesium salts of molybdophosphoric and molybdovanadophosphoric heteropoly acids in the gas-phase oxidation of benzene to phenol with an O2 + H2 mixture

Acid salts CsxH3 + n − xPMo12 − nVnO40 (n = 0, 1, 2, or 3; x = 2.5 or 3.5) with coprecipitated or supported platinum were studied using thermogravimetry, IR spectroscopy, and temperature-programmed reduction. The thermal region of the full stability of these salts is limited by the decomposition temperature of the corresponding acid H3PMo12O40 (∼400°C) or H3 + nPMo12 − nVnO40 (∼300–350°C). The degree of reduction of heteropoly anions with hydrogen is regulated by temperature. Deeply reduced heteropoly anions (at 300°C) are slowly oxidized with oxygen with structure and composition regeneration. The states of molybdenum and vanadium on the surface of samples with coprecipitated platinum Pt0.1-Cs2.5H0.5PMo12O40 (1) and Pt0.1-Cs2.5H2.5PMo10V2O40 (2), which were studied using XPS, correspond to reduced or reoxidized heteropoly anions in the bulk. Platinum metal particles of ∼5 nm in size were observed in high-resolution TEM images obtained after the reduction and storage of sample 1 in air. A heteropoly compound forms two texture levels: spherical nanoparticles of 10–20 nm in size are collected in closely packed globules of 100–300 nm in size. Detailed texture studies, which were performed using nitrogen adsorption isotherms, demonstrated texture mobility under the ambient conditions. The cesium salts of the heteropoly acids were tested in the gas-phase oxidation of benzene to phenol with an O2 + H2 mixture at 180°. The effect of platinum concentration on the specific catalytic activity in the presence of deeply reduced heteropoly anions was monitored. The samples containing the salt Cs2.5H0.5PMo12O40 exhibited the highest activity in the formation of phenol. The introduction of vanadium into the heteropoly anion impaired the catalytic performance of both deeply and slightly reduced samples.

Synthesis of heterogeneous catalysts with well shaped platinum particles to control reaction selectivity

Colloidal and sol-gel procedures have been used to prepare heterogeneous catalysts consisting of platinum metal particles with narrow size distributions and well defined shapes dispersed on high-surface-area silica supports. The overall procedure was developed in three stages. First, tetrahedral and cubic colloidal metal particles were prepared in solution by using a procedure derived from that reported by El-Sayed and coworkers [Ahmadi TS, Wang ZL, Green TC, Henglein A, El-Sayed MA (1996) Science 272:1924-1926]. This method allowed size and shape to be controlled independently. Next, the colloidal particles were dispersed onto high-surface-area solids. Three approaches were attempted: (i) in situ reduction of the colloidal mixture in the presence of the support, (ii) in situ sol-gel synthesis of the support in the presence of the colloidal particles, and (iii) direct impregnation of the particles onto the support. Finally, the resulting catalysts were activated and tested for the promotion of carbon-carbon double-bond cis-trans isomerization reactions in olefins. Our results indicate that the selectivity of the reaction may be controlled by using supported catalysts with appropriate metal particle shapes.

Interaction of platinum and molybdophosphoric heteropoly acid under conditions of catalyst preparation for benzene oxidation to phenol with an O2-H2 gas mixture

The transformations of platinum and a heteropoly acid (HPA) in binary systems prepared from H2PtCl6 or H2PtCl4 and H3PMo12O40 were studied using IR and UV-VIS spectroscopy, elemental analysis, XPS, EXAFS, TPR, and HREM. The calcination of platinum chloride with the HPA to 450°C resulted in the formation of a platinum salt of the HPA along with decomposition products (mixture I). The reduction of calcined samples containing Pt: HPA = 1: 1 with hydrogen at 300°C (mixture II) followed by exposure to air resulted in the regeneration of the HPA structure. The resulting solid samples of Pt 1−n 0 Pt n II ClmOxHy) (H3+p PMo 12−p VI Mo p V O40) (III) contained platinum and molybdenum in both oxidized and reduced states. The following association species were isolated from mixtures I and II by dissolving in water: [Pt n II PMo12O40] (I s) (n = 0.3−0.8) and [Pt n 0 PMo 12 red O40] (II s) (n ≈ 1). Under exposure to air, the solutions of I s were stable (pH ∼2), whereas Ptmet was released from II s. After the drying of I s, the solid association species (Pt n II ClmOxHy). (H3PMo12O40), where n = 0.3−0.8, m = 0.2−1, and x = 3−0, (I solid) were obtained. The I solid/SiO2 supported samples were prepared by impregnating SiO2 with a solution of I s and drying at 100°C. Platinum metal particles of size ∼20 A and a mixed-valence association species of platinum with the HPA were observed after the reduction of I solid/SiO2 with hydrogen at 100–250°C. These samples were active in the gas-phase oxidation of benzene to phenol at 180°C with the use of an O2-H2-N2 mixture.

Effects of Sub-100 nm Platinum Metal Particle on the Acoustic Attenuation Properties of Silicone Rubber Lens for Medical Array Probe

The acoustic attenuation properties of room temperature vulcanization (RTV) silicone rubber lenses with platinum (Pt) metal particle sizes ranging from 10 to 94 nm were investigated for the acoustic lens application for a medical ultrasound array probe. Pt particle size did not change their sound velocities, 858–861 m/s, but changed their acoustic attenuation property noticeably. RTV silicone rubber doped with the largest Pt particle, 94 nm, showed the largest attenuation, 2.24 dB/mmMHz, whereas, RTV silicone rubber doped with the smallest Pt particle, 10 nm, showed the smallest attenuation, 0.84 dB/mmMHz, with an acoustic impedance of 1.31 MRayls. The fine particle size with the application of a high-density dopant to RTV silicone rubber is important for realizing a low-acoustic-attenuation silicone lens for a probe for high-frequencies of higher than 5 MHz.

Preparation of Platinum−Nafion−Carbon Black Nanocomposites via a Supercritical Fluid Route as Electrocatalysts for Proton Exchange Membrane Fuel Cells

Novel platinum−Nafion−carbon black nanocomposites were synthesized using supercritical deposition. The method consists of preparation of a Nafion-carbon black composite followed by impregnation of a platinum precursor (PtMe2COD) into the composite via adsorption from a solution of supercritical carbon dioxide. Subsequently, the impregnated composite is subjected to thermal treatment resulting in a platinum−Nafion−carbon black composite. The platinum−Nafion−carbon black composite was characterized by hydrogen chemisorption, and the average size of the platinum metal particles was found to be around 2.6 nm. A preliminary cyclic voltammetry test demonstrated that the composite displayed promising electroactivity as an electrocatalyst for proton exchange membrane fuel cells. To investigate the effects of the impregnation under supercritical conditions at high pressures and subsequent thermal reduction at elevated temperatures on the Nafion structure, composite films of platinum−Nafion 112 were prepared by the same supercritical deposition method. The infrared spectra of the films indicated that the structure of Nafion 112 did not change significantly during processing.

Radiolytic preparation of nanosized Pt particles in sodium zeolite A

Nanosized platinum metal particles in zeolite NaA have been prepared by four different methods, namely, (I) γ-radiolysis of zeolite A sample exchanged with [Pt(NH3)4]2+, (II) γ-radiolysis of precursor gel containing Pt2+ ions followed by hydrothermal crystallisation to form zeolite A, (III) hydrogen reduction of Pt2+ ions containing precursor gel followed by hydrothermal crystallisation and (IV) impregnation of zeolite A with H2PtCl6 solution followed by reduction at 200 °C in hydrogen flow. The size of Pt metal particles has been evaluated from X-ray line broadening and TEM and is found to be in the range of 5–15 nm for samples II, III and IV. Based on catalytic activity of these samples for hydrogenation of ethylene and cyclohexene, it is inferred that for sample I, Pt metal particles are confined to the pores of zeolite A. Unlike this, the Pt metal particles are randomly distributed in the zeolite matrix for samples II and III. For sample IV, the Pt metal particles are present over the surface of zeolite A.

Structure and Reduction Behavior of Platinum Chloride Intercalated in Graphite Layers

Platinum chloride-graphite intercalation compounds (PtCl4-GICs) were synthesized from platinum chloride (PtCl4) and graphite under pressurized chlorine atmosphere. The analysis of XRD patterns showed that platinum chloride was inserted into graphite layers and the PtCI4-GICs with a stage 3 structure were formed. The curve-fitting analysis of Pt LIII-edge EXAFS showed that the distance of the Pt-Cl-Pt bond of 5 wt% PtCl4-GIC was 0.06 A longer than that of the PtCl4 bulk, indicating that PtCl4 had a distorted structure in graphite layers. PtCl4 samples were reduced in hydrogen atmosphere to produce platinum metal particles in graphite layers. EXAFS analysis showed that the coordination numbers of Pt-Pt metal bond for PtCl4-GIC samples reduced at various temperatures were lower than those of the mixture of PtCl4 and graphite (PtCl4-Gmix) samples reduced in the same manners.