Hexachloroplatinic Acid Solution Research Articles

Negative effect of Ni on PtHY in n-pentane isomerization evidenced by IR and ESR studies

Ni/PtHY with different Ni loadings was prepared by impregnating HY with hexachloroplatinic acid solution and Ni 2+/N, N-dimethylformamide solution. An increase in the Ni loading decreased the crystallinity, specific surface area and meso-micropores of the catalysts. Ni interacted with hydroxyl groups to produce IR absorption bands at 3740–3500 cm −1. Increasing Ni loadings resulted in a decrease in the intensities of the broad bands at 3730-3500 cm −1 and the sharp band at 3740 cm −1 with simultaneous development of new absorbance band at 3700 cm −1 that was attributed to (–OH)Ni. The acidity of the samples did not significantly change with Ni loadings up to 1.0 wt%, which indicated that Ni mostly interacts with non-acidic silanol groups (terminal- and structural-defect OH groups). The presence of Ni decreased the activity of PtHY toward the isomerization of n-pentane because of a decrease in the number of active protonic-acid sites that formed from molecular hydrogen. IR and ESR studies confirmed that Pt facilitated the formation of protonic-acid sites from molecular hydrogen, whereas Ni, even when combined with Pt, didn't exhibit such ability. The absence of protonic-acid sites from molecular hydrogen significantly decreased the yield of iso-pentane and markedly increased the cracking products.

Study of Platinum Deposition on Untreated and Thermally Modified Glassy Carbon

Platinum was deposited from aqueous sulphuric acid solution of hexachloroplatinic acid under potentiostatic conditions upon untreated as well as thermally treated glassy carbon (GC). The influence of thermal treatment of GC on electrochemical platinum deposition was thoroughly investigated in terms of the size, the size distribution and coverage of Pt deposits, using scanning electron microscopy and X-ray photoelectron spectroscopy. A decrease in Pt particle diameter and an increased Pt coverage was observed for various deposition pulse lengths on thermally pre-treated GC. This thermal pre-treatment led to a formation of a microporous layer on the substrate surface, thus influencing particle size distribution and coverage. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) measurements have shown that the chemical composition and surface roughness of GC are not affected by the treatment.

Syntheses of poly(cyclodextrin)-stabilised metal nanoparticles and their quenching abilities of active oxygen species

Metal nanoparticles have been developed to increase the catalytic activity of metals due to the larger surface area of smaller particles. We report the synthesis of novel cyclodextrin-stabilised metal nanoparticles and their application to catalysts for the quenching of active oxygen species. Platinum nanoparticles stabilised by poly(cyclodextrin) (PCyD-Pt) were prepared by UV irradiation of an aqueous solution of hexachloroplatinic(IV) acid in the presence of PCyD. Most PCyD-Pt nanoparticles were distributed in the range of 1–6 nm. PCyD-Pt nanoparticles have higher catalytic activity than a commercial platinum catalyst for quenching of superoxide anion radical. The PγCyD-stabilised Au/Pt bimetallic nanoparticles showed higher catalytic activity than the corresponding monometallic nanoparticles.

EFFECT OF IMPREGNATION PROCEDURE OF Pt/γ-AL<sub>2</sub>O<sub>3</sub> CATALYSTS UPON CATALYTIC OXIDATION OF CO

The oxidation of carbon monoxide by oxygen using two catalysts prepared by two different methods has been investigated. In the first method, catalyst prepared by immersing γ-Al2O3 into the hexa-chloroplatinic acid solution at 80oC for 4 h, resulted Pt/γ-Al2O3 catalyst having platinum highly dispersed on the support. While that of immersing γ-Al2O3 in the hexa-chloroplatinic acid solution at room temperature for 12 h, produced Pt/ γ-Al2O3 catalyst where platinum dispersion was much lower. Catalytic activity test showed that platinum well dispersed on the support enhanced the activity for oxidation of carbon monoxide. The platinum impregnated at room temperature resulted in the poor activity. Keywords: platinum catalyst, alumina, supported material, oxidation

EFFECT OF IMPREGNATION PROCEDURE OF Pt/γ-Al<sub>2</sub>O<sub>3</sub> CATALYSTS UPON CATALYTIC OXIDATION OF CO

The oxidation of carbon monoxide by oxygen using two catalysts prepared by two different methods has been investigated. In the first method, catalyst prepared by immersing γ-Al2O3 into the hexa-chloroplatinic acid solution at 80oC for 4 h, resulted Pt/γ-Al2O3 catalyst having platinum highly dispersed on the support. While that of immersing γ-Al2O3 in the hexa-chloroplatinic acid solution at room temperature for 12 h, produced Pt/ γ-Al2O3 catalyst where platinum dispersion was much lower. Catalytic activity test showed that platinum well dispersed on the support enhanced the activity of oxidation of carbon monoxide. The platinum impregnated at room temperature resulted in the poor activity. Keyword: Catalyst, CO Oxidation, Platinum.

Influence of foreign Fe ions on wet chemical synthesis of Pt nanoparticle thin films at ambient temperature: in situversus direct addition

Novel Pt nanoparticle thin films have been successfully synthesized on glass surfaces via a wet chemical method that comprised reduction of aqueous hexachloroplatinic acid solution by ascorbic acid in the presence of hematite (α-Fe2O3) at room temperature. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), atomic absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), UV-Vis absorption spectroscopy and a scratch testing method have been used to characterize the final and intermediate products of Pt films. It was found that there existed competition between precipitation of nanoparticles and formation of Pt nanoparticle thin films, which is controlled by the source of foreign Fe ions i.e. in situ or direct addition of foreign ions. Besides, the negatively charged glass surface and positively charged hematite surface under the synthesis condition of pH ∼3 assisted heterogeneous nucleation of Pt on glass surfaces. The measured adhesive strength of the film on glass substrate is 106 Mpa and the density of states overlaps the Fermi energy (Ef = 0), indicating the conducting films are strongly bonded on the glass surface. The synthetic protocol outlined here shows a new synthetic route to integrate metal nanoparticles directly on glass substrates.

Electrodeposition of Platinum on Carbon Black for Fuel Cell Application

The electrodeposition of Pt is carried out on carbon black, from a solution of hexachloroplatinic acid, using cyclic voltammetry and pulse deposition. The substrate is previously submitted to an activation process, consisting in the formation of a hydrophilic overlayer. SEM and TEM images show that surface C black particles are totally or partially covered, depending on electrodeposition conditions. Cross section analysis shows that the deposit occurs to a depth of less than 5 µm. Results from single cell testing are shown.

Preparation and Characterization of Nanocrystalline Pt/TCG Counterelectrodes for Dye-Sensitized Solar Cells

Transparent counter electrodes were prepared on transparent conductive glass (TCG) substrates from a hexachloroplatinic acid (H2PtCl6) solution applying the thermal decomposition method in combination with the spin-coating deposition technique. The effect of the precursor concentration and the number of deposited platinum layers on the surface characteristics of the Pt films was examined, and the relation between those surface characteristics and the electrochemical properties of the corresponding modified Pt/TCG electrodes was defined. Four types of counterelectrodes were prepared, differing in the concentration of the H2PtCl6 solution (0.03M and 0.15M) and in the number of Pt layers (one or two Pt layers); their performance as counterelectrodes was evaluated after their incorporation into dye-sensitized solar cells (DSSCs) employing a solid state redox electrolyte. The obtained results show that solar cells using counterelectrodes prepared from the 0.03MH2PtCl6 solution and consisting of two Pt layers (Pt032 electrode) exhibited the best performance characteristics (diffusion coefficient D*I3−=1.58×10−5cm2s−1, conversion efficiency η=2.16%, fill factor ff=62.14%, and short circuit photocurrent Isc=4.71mAcm−2). The electrochemical behavior of the modified counterelectrodes is consistent with the surface characteristics of the Pt film that formed on the conductive glass substrate, which seems to be significantly affected by the adopted method and the adjusted experimental parameters (Pt concentration and number of Pt layers). Specifically, this type of electrodes beside their low roughness (Rq=11.5nm), also presents a high complexity (Df=2.3). As a result, for this kind of solid state DSSCs, the less rough but the more complex the Pt/TCG electrode surface, the higher the efficiency of the corresponding solar cells.

Preparation of carbon supported platinum catalysts: role of π sites on carbon support surface

The role of the π sites in the adsorption of anionic platinum precursor (PtCl 6 2− ) on the carbon surface was studied. A set of carbon supports was prepared by the oxidative treatments of a commercial carbon black in liquid or thermal treatment in a nitrogen gas flow. The supports obtained had similar physical structure, but were different in their surface chemistry, e.g., the types and the amount of the surface functional groups. The Pt/C catalysts were prepared by the impregnation of the supports with an aqueous solution of hexachloroplatinic acid. N2 adsorption, acid-base titration, X-ray photoelectron spectrometry (XPS), ICP, and TEM were used to characterize the supports and the catalysts. It was found that the absence of the surface acidic groups led to a higher platinum loading amount on the supports; and platinum loading amount would decrease when the higher H2PtCl6 impregnating solution concentration was used. The π sites in the basal planes play a more important role than the surface acidic groups in PtCl 6 2− ions adsorption on the carbon surface. Upon impregnation, the delocalized π electrons form coordination bonds with the platinum precursors, and further cause the reduction of Pt(IV) complex to Pt(II) complex, which was strongly chemisorbed on the surface of the supports. PtCl 6 2− ions adsorbing at the surface acidic groups would easily desorb during the washing process. However, when the impregnating solution was used at a higher concentration, a large amount of H3O+ was firstly adsorbed in the π sites, leading to a decrease of the amount of strong PtCl 6 2− ions adsorption on the supports.

Antireflective porous layer formation on multicrystalline silicon by metal particle enhanced HF etching

Antireflection of silicon (Si) surface is one key technology for the manufacture of efficient solar cells. Metal particle enhanced HF etching is applied to produce uniform antireflecting porous layer on multicrystalline Si wafers that cannot be uniformly texturized by anisotropic etching with an alkaline solution. Fine platinum (Pt) particles are deposited on multicrystalline n-Si wafers by electroless displacement reaction in a hexachloroplatinic acid solution containing HF. Both macroporous and luminescent microporous layers are uniformly formed by immersing the Pt-particle-deposited multicrystalline Si wafers in a HF solution. The reflectance of the wafers is reduced from 30% to 6% by the formation of porous layer. The photocurrent density of photoelectrochemical solar cells using porous multicrystalline n-Si has a 25% higher value than non-porous Si cells.

Preparation of tungsten oxide promoted zirconia by different methods

The platinum on tungsten oxide promoted zirconia preparation using different procedures has been studied. Zirconium oxyclhoride, ammonium hydroxide, ammonium metatungstate, and hexachloroplatinic acid solutions were used as raw materials in all cases. Tungsten oxide promoted zirconium hydroxide (obtained using the three first reagents) was calcined at 700 or 800 °C; then, each fraction was impregnated with hexachloroplatinic acid solutions. The solids were characterized by nitrogen adsorption, X-ray diffraction (XRD), NH 3–TPD, temperature-programmed reduction (TPR) and used as catalysts for n-hexane isomerization at 200 °C, WHSV = 4 h −1, 6 kg cm −2 and H 2: n-hexane (molar) = 7. The solids have different properties depending on the preparation procedure: surface area, pore size distribution, X-ray diffraction patterns, TPR profiles and activity for the isomerization reaction. Different WO x domain sizes are also obtained, which modify the TPR profiles and the catalytic activity for n-hexane isomerization.

Ta 2O 5 templated growth of droplet-like platinum particles by potentiodynamic polarization of tantalum in aqueous solution of hexachloroplatinic acid

By potentiodynamic polarization of mechanically polished tantalum in a diluted aqueous solution of hexachloroplatinic acid, droplet-like platinum microparticles were electrodeposited, embedded into the simultaneously formed Ta 2O 5 film. The roughness factor of platinum of 31 was achieved. Within the potential region of both hydrogen and oxygen underpotential deposition, in both acidic and alkaline solutions, the composite Pt/Ta 2O 5 electrode displayed an excellent electrochemical response characteristic of smooth polycrystalline platinum. The preparation method applied in this work presents an easy way to obtain an electrode surface combining the behaviour of smooth polycrystalline platinum with the behaviour of microdisc arrays. Its electrocatalytic effectiveness was demonstrated for an oxygen reduction reaction in alkaline solutions.

Electrochemical response of a composite Pt/TiO 2 layer formed potentiodynamically on titanium surfaces

By potentiodynamic polarization of mechanically polished titanium in a diluted aqueous solution of hexachloroplatinic acid, nearly spherical Pt microparticles were grown, embedded into the simultaneously formed TiO 2 film. The real surface of platinum may be easily controlled by the number of potentiodynamic cycles, and roughness factors exceeding 100 were obtained. Within the potential region of both hydrogen and oxygen underpotential deposition, in both acidic and alkaline solutions, the electrode displayed an excellent electrochemical response characteristic of smooth polycrystalline platinum, unlike to highly dispersed platinum electrodes produced by other methods. The preparation method applied in this work presents an easy way to obtain an electrode surface combining the behaviour of smooth polycrystalline platinum with the behaviour of microdisc arrays. Its high electrocatalytic effectiveness was demonstrated for oxygen reduction and bromide ion adsorption/oxidation.

Preparation and characterisation of Pd and Pt/SiO 2–Al 2O 3 non-permselective membranes

Pd and Pt/SiO 2–Al 2O 3 tubular membranes were prepared with the aim of obtaining uniform pore size and precious metal distribution throughout the cross-section. Membrane permeability was controlled by depositing silica inside the pores of α -Al 2O 3 supports. This was achieved by immersing the support inside colloidal silica solution followed by freeze-drying and calcination. Various techniques were evaluated in order to avoid the formation of a thin SiO 2 layer on the external support surface. Pt and Pd were introduced by impregnation of the SiO 2–Al 2O 3 membrane with hexachloroplatinic acid and palladium nitrate solution, respectively. Freeze-drying provided more uniform metal distribution than conventional drying.

Synthesis of platinum/multi-wall carbon nanotube catalysts

The purpose of this research is to investigate the feasibility of the synthesis of platinum/multi-wall carbon nanotube (Pt/MWNT) catalysts and such catalysts' application in fuel cells. The as-received MWNTs were purified and decorated by pretreatment. Infrared-spectrum indicates the carboxylic (-COOH) and carbonyl (-C=O) groups were introduced on the surface of the MWNTs after pretreatment. These functional groups will act as anchor sites for the Pt deposition. Then the Pt particles in nano scale were deposited on the surface of MWNTs by reduction of a solution of hexachloroplatinic acid. Transmission electron microscopy examination reveals that Pt particles are attached to the surface of MWNTs. If as-received MWNTs are not pretreated in the proper way, the Pt particle aggregates are mostly found on the open end of MWNTs. Occasionally Pt penetrated inside the tube of MWNTs. The relationship between the Pt particle morphology and the conditions of pretreatment and reduction reaction is discussed. After heat treatment, Pt particles recrystallized to form the Pt/MWNT catalysts. The Pt/MWNT catalysts were applied to a single cell and the test result shows a promising future of these catalysts with low Pt loading when applied in proton exchange membrane fuel cells (PEMFCs).

Properties of Carbon-Supported Platinum Catalysts: Role of Carbon Surface Sites

The effect of oxidation treatments of the support on the properties of carbon-supported platinum catalysts has been analyzed. A set of activated carbon carriers has been prepared by oxidative treatments of a commercial carbon in liquid as well as in gas phase. The carbons obtained had largely identical pore structures but differed considerably in their surface chemistry as shown, for example, by their point of zero charge (PZC) values. The catalysts were prepared by equilibrium impregnation of the supports with an aqueous solution of hexachloroplatinic acid. N2 adsorption, TPD, XPS, TPR, and H2 chemisorption were used to characterize the supports and the catalysts. The Pt load of the catalysts was found to depend on the PZC of the supports. However, the Pt dispersion was found to depend on the total surface oxygen content of the supports. These results were rationalized by the assumption that the surface basic groups of the supports are anchoring sites for the strong adsorption of platinum.

Electrochemical deposition of fine Pt particles on n-Si electrodes for efficient photoelectrochemical solar cells

Fine platinum (Pt) particles were deposited electrochemically on n-type silicon (n-Si) electrodes from an aqueous hexachloroplatinic acid(IV) solution by the single potential step (SPS) and double potential step (DPS) methods. The distribution density of the Pt particles on n-Si was 10 8 cm −2 for the SPS method, whereas it increased from 10 9 to 10 10 cm −2 by a shift of the pulse potential at the initial step of the DPS method from −1.0 to −4.0 V versus SCE and remained nearly constant at more negative potentials. The size of the Pt particles enlarged with the charge density passing across the electrode surface at a potential of −0.70 V versus SCE, which was applied throughout for the SPS method and at the second step for the DPS method. Photoelectrochemical (PEC) solar cells equipped with Pt-electrodeposited n-Si electrodes generated open-circuit photovoltages ( V OC) of 0.51–0.61 V, much higher than those for n-Si electrodes coated with continuous Pt layers (ca. 0.2–0.3 V). Solar cell characteristics changed with the pulsed potential and charge density passing across the electrode surface which changed the size and distribution density of the Pt particles. The characteristics were explained well by our previous theory on metal-dot coated n-Si electrodes.

Preparation of porous materials as catalysts for isomerization reactions

The preparation of platinum on tungsten oxide promoted zirconia using different procedures has been studied. Zirconium oxyclhoride, ammonium hydroxide, ammonium metatungstate, and hexachloroplatinic acid solutions were used as raw materials. Tungsten oxide promoted zirconium hydroxide (obtained using the three first reagents) was calcined at different temperatures before platinum incorporation. The solids were characterized by different techniques and used as catalysts for the isomerization of n-hexane at 200 °C. According to the preparation procedure, the solids have different properties: surface area, pore size distribution, X-ray diffraction patterns and activity for the isomerization reaction.

New Developments in Chemical Wet Processes. Electrochemical Deposition of Metal Particles on Si Electrodes for Efficient Photoelectrochemical Solar Cells.

Fine platinum (Pt) particles were electrodeposited on n-type silicon (n-Si) electrodes from an aqueous hexachloroplatinic acid (IV) solution by single potential step and double potential step (DPS) methods. The distribution density of the Pt particles on the electrode increased from 109 to 1010 cm−2 as the pulse potential at the initial step of the DPS method decreased from −1 to −4 V vs. SCE. The size of the Pt particles became larger with increasing the electricity passing across the electrode surface. Photoelectrochemical solar cells equipped with Pt-electrodeposited n-Si electrodes generated open-circuit photovoltage of 0.6 V and provided an energy conversion efficiency of 10%. Solar cell characteristics changed with the size and distribution density of the Pt particles.

Exposure-effect relationship of platinum salt allergy in a catalyst production plant: Conclusions from a 5-year prospective cohort study

Background: There is a high incidence of occupational asthma and rhinitis caused by platinum (Pt) salts in precious-metal refineries. Objective: We sought to assess exposure to Pt salts and the incidence of Pt salt allergy in a catalyst production plant. Methods: A 5-year prospective cohort study was performed in 159 catalyst production workers (94.6% of recruited), 50 craftsmen (92.6% of recruited), and 66 control subjects (76.7% of recruited) at yearly intervals. Subjects were assigned to exposure categories of high levels of Pt (n = 115), persistently low levels of Pt (n = 51), intermittently low levels of Pt (n = 61), or no Pt (n = 48) after the initial survey according to job title and job location. Skin prick test conversion from a negative response to a 4 mm or larger wheal response with a 10–2 mol/L hexachloroplatinic acid solution was chosen as the outcome variable. Results: Exposure assessment of airborne Pt and Pt in the serum of workers demonstrated clear differences between exposure categories. The threshold limit value of 2 μg/m3 for soluble Pt was exceeded in 3 (4%) of 78 measurements. Thirteen subjects assigned to high exposure showed skin test conversion, and new allergic symptoms were associated with exposure. Among the high-exposure category, the incidence rate of skin prick test conversion was 5.9 per 100 person-years for newly employed subjects (n = 79) and 2.1 per 100 person-years for those who had already been employed at the time of the initial survey (n = 36). A predicting factor for skin test conversion in highly exposed subjects was smoking status (relative risk, 3.9; 95% confidence interval, 1.6-9.7) but not atopy or bronchial hyperresponsiveness. Conclusion: Sensitization to Pt salts may develop in workers of catalyst production plants. Both the exposure to Pt salts and the incidence of Pt salt allergy were lower compared with reported data from precious-metal refineries. (J Allergy Clin Immunol 2000;105:364-70.)