A new simple preparation of platinum-nickel alloy nanoparticles and their characterization as an electrocatalyst for methanol oxidation

Pt-Ni alloy nanoparticles were produced by casting 2 or 10 mM H₂PtCl₆ solutions on a Ni column. The apparent particle size for the resultant Pt-Ni alloys increased with the concentration of the H₂PtCl₆ solution, while the content of Pt in the alloy decreased. The potential sweeps of 5 cycles in an H₂SO₄ aqueous solution for Pt-Ni (2 mM)/Ni and Pt-Ni (10 mM)/Ni electrodes led to electrochemical behavior similar to a polycrystalline Pt electrode, suggesting the formation of a few thin Pt layers on each Pt-Ni alloy surface. In electrochemical measurements, both Pt-Ni/Ni electrodes showed more negative onset potential of methanol oxidation and slower degradation of oxidation current of methanol than the polycrystalline Pt electrode. X-ray photoelectron spectroscopy of both Pt-Ni/Ni electrodes showed the shift of Pt4f peaks to a higher binding energy, suggesting that the increase in the d vacancy in the balance band 5d orbital of Pt contributed to the improved electrocatalytic activity and durability of the Pt-Ni/Ni electrodes.     

Studies on Redispersion and Stability of Platinum in Pt/MgO System during Oxygen Treatment at High Temperatures

Transmission Electron Microscopy and X-ray Diffraction showed that high temperature oxygen treatment results in redispersion of Pt/MgO system. Two catalysts in this study were prepared by impregnation using H₂PtCl₆ or Pt(C₅H₇O₂)₂ as the precursors and two MgO supports of different purity. Pt/MgO system indicated a high stability in oxygen at temperature ranging from 550 to 700°C.     

改性H-ZSM-34上氯甲烷催化转化制低碳烯烃

比较了几种典型的沸石分子筛在氯甲烷转化制乙烯、丙烯和丁烯等低碳烯烃反应中的催化性能, 发现H-ZSM-34具有较佳的催化活性和选择性. 经乙二胺四乙酸二钠(Na₂H₂EDTA)水溶液处理, 并经离子交换及焙烧后, H-ZSM-34上氯甲烷转化制低碳烯烃的催化性能显著改善. 当Na₂H₂EDTA浓度为0.1 mol/L, 反应温度为673 K, CH₃Cl分压9.2 kPa时, C₂-C₄烯烃选择性和收率分别达82%和61%. 研究还发现, Ce修饰H-ZSM-34催化剂同样可改善氯甲烷制低碳烯烃的选择性和收率. 表征结果表明, Na₂H₂EDTA处理和Ce修饰均降低了H-ZSM-34的酸性. 酸性的降低可抑制低碳烯烃的氢转移反应, 继而避免了其进一步转化为低碳烷烃.     

Pulsed electrodeposition of Pt nanoclusters on carbon nanotubes modified carbon materials using diffusion restricting viscous electrolytes

A simple method for achieving high dispersion and small platinum nanoparticles down to only 2 or 3 nm on structured carbon supports (carbon nanotubes-modified PAN-based carbon fiber and carbon nanotubes-modified graphite foil) is presented. Pulsed electrodeposition of Pt nanoparticles was performed at increased viscosity of the H₂PtCl₆ containing electrolyte by addition of glycerol. The catalyst nanoparticle size can be controlled by varying the amount of glycerol added into the aqueous H₂PtCl₆ solution, and adjusting the number of the potential pulses. The shape and size of the Pt nanoparticles was characterized by scanning electron microscopy and transmission electron microscopy. The electrocatalytic properties of Pt nanoparticles with respect to O₂ and H₂O reduction were investigated by means of cyclic voltammetry, and the improved catalytic activity of the Pt nanoparticles/carbon nanotubes surfaces could be proved.     

Synthesis of hollow and nanoporous gold/platinum alloy nanoparticles and their electrocatalytic activity for formic acid oxidation

In this work, hollow Au/Pt alloy nanoparticles (NPs) with porous surfaces were synthesized in a two-step procedure. In the first step, tri-component Ag/Au/Pt alloy NPs were synthesized through the galvanic replacement reaction between Ag NPs and aqueous solutions containing a mixture of HAuCl₄ and H₂PtCl₄. In the second step, the Ag component was selectively dealloyed with nitric acid (HNO₃), resulting in hollow di-component Au/Pt alloy NPs with a porous surface morphology. The atomic ratio of Au to Pt in the NPs was easily tunable by controlling the molar ratio of the precursor solution (HAuCl₄ and H₂PtCl₆). Hollow, porous Au/Pt alloy NPs showed enhanced catalytic activity toward formic acid electrooxidation compared to the analogous pure Pt NPs. This improved activity can be attributable to the suppression of CO poisoning via the “ensemble” effect.     

Influences of the H2PtCl6 Solution's pH on the Photocatalytic Activities of Platinum-Loaded TiO2 Nanotubes

By using H₂PtCl₆ and titanate nanotubes as precursor, platinum-loaded TiO₂ nanotubes (Pt/TiO₂NTs) are prepared at different pH by deposition-precipitation method. The prepared materials are characterized with powder x-ray diffraction (XRD) and x-ray photoelectron spectra (XPS). Their photocatalytic performance is evaluated by the degradation rates of methyl orange solution under UV-vis light irradiation. Obtained results indicate that the pH of H₂PtCl₆ solution has obvious influence on the catalytic performance of Pt/TiO₂NTs.     

Darstellung,spektroskopische Charakterisierung und Kristallstrukturen von [(C5H5N)2CH2][PtCl5(SCN)] und cis-[(C5H5N)2CH2][PtCl4(SCN)2]

Preparation, Spectroscopic Characterization, and Crystal Structures of [(C₅H₅N)₂CH₂][PtCl₅(SCN)] and cis -[(C₅H₅N)₂CH₂][PtCl₄(SCN)₂] By treatment of [PtCl₆]^2– with SCN^– in aqueous solution a mixture of chlorothiocyanatoplatinates(IV) is formed, from which [PtCl₅(SCN)]^2– and cis-[PtCl₄(SCN)₂]^2– have been separated by ion exchange chromatography on diethylaminoethyl cellulose. X-Ray structure determinations on single crystals of [(C₅H₅N)₂CH₂][PtCl₅(SCN)] ( 1 ) (tetragonal, space group P 4₃, a = 7.687(1), c = 29.698(4), Z = 4) and cis-[(C₅H₅N)₂CH₂][PtCl₄(SCN)₂] ( 2 ) (monoclinic, space group P 2₁/n, a = 11.2467(9), b = 15.0445(10), c = 11.3179(13), β = 92.840(9)°, Z = 4) show, that the thiocyanate groups are coordinated via S atoms with average Pt–S distances of 2.339 Å and Pt–S–C angles of 104.7° up to 107.1°. Using the molecular parameters of the X-ray determinations the low temperature (10 K) IR and Raman spectra have been assigned by normal coordinate analyses. The valence force constants of the S–Pt–Cl˙ axes are f_d(PtS) = 1.81 ( 1 ) and 1.87 ( 2 ), f_d(PtCl ^× ) = 1.77 ( 1 ) and 1.81 ( 2 ), of the Cl–Pt–Cl axes are f_d(PtCl) = 1.93 ( 1 ) and 1.90 mdyn/Å ( 2 ). The ¹⁹⁵Pt NMR spectra from dichlormethane solutions exhibit each one sharp signal at 3975.6 ( 1 ) and 3231.6 ppm ( 2 ), respectively.     

Shape‐controlled synthesis of Pt nanocrystals: an evolution of the tetrahedral shape

Platinum nanocrystals with sizes smaller than 10 nm are obtained by H₂‐reduction of aqueous K₂PtCl₆ in the presence of different concentrations of poly (N‐vinyl‐2‐pyrrolidone; PVP:M_w ≈ 360 000) at pH = 2.5–7.0. Tetrahedral Pt nanocrystals (3–10 nm) are produced with high selectivity (73–83% by number) at moderate PVP:K₂PtCl₆ ratios. The co‐existing round/spheroidal crystallites are found to be smaller than the tetrahedrally shaped ones in the systems of varying K₂PtCl₆:PVP ratios. Careful examinations of the particle size and shape evolution of the crystallites at different stages of the crystal growth with transmission electron microscopy (TEM) and ultraviolet–visible absorption spectroscopy (UV–vis) suggest that the tetradedrally shaped Pt crystallites share the same type of nuclei with the round ones at the early stage of the crystal formation. Evolution of the tetrahedral shape happens in the later slow crystal growth. Copyright © 2006 John Wiley & Sons, Ltd.     

Catalysis of hydrosilylation: Part XXIV. H2PtCl6 in cyclohexanone as hydrosilylation catalyst—what is the active species in this catalytic system?

A cyclohexanone solution of H₂PtCl₆ was examined to find the catalytic species responsible for the hydrosilylation of the olefinic C=C bond. Similarly to other H₂PtCl₆–solvent systems (e.g. Speier's and Karstedt's catalysts), the real catalyst appeared to be colloidal platinum formed in situ by stepwise reduction [Pt(IV)→Pt(O)] and dechlorination of the platinum precursor. The role of cyclohexanone seems to be to form sufficiently stable platinum complexes to avoid rapid platinum precipitation and aggregation. The studies of H₂PtCl₆–solvent systems are of practical importance since these compounds are widely used catalyst precursors for hydrosilylation on an industrial scale.     

XPS Studies of PtCl4 and H2PtCl6·6H20 doped polyacetylene

The PtCl₄ and H₂PtCl₆-6H₂O doped polyacetylene were studied by X-ray photoelection spectroscopy and transmission electron microscopy. We found that both Pt 4f and Cl 2p peaks could be resolved into two components both with a splitting of ca. 1.5 eV. The higher binding energy components of Pt 4f peak is attributed to Pt⁴⁺ and the lower binding energy one to Pt²⁺ species. From quantitative analysis of the results of decomposition of both Pt 4f and Cl 2p peaks it was found that an atomic ratio of chlorine to platinum for Pt²⁺ species is (Cl) / (Pt) = 2 and that for Pt⁴⁺ species is (Cl) / (Pt) = 6 for both PtCl₄ and H₂PtCl₆·6H₂O doped polyacetylene. The C 1s peaks could be decomposed into two components separated by ca. 1 eV. The intensity of the higher binding energy component increased with increasing dopant concentration. These indicate that the platinum salt doping proceeds through charge transfer from polyacetylene chain to platinum atom resulting in a partial reduction from Pt⁴⁺ to Pt²⁺ state. The existence of PtCl₂ cluster on the surface of the doped polyacetylene film was supported by transmission electron microscopy and electron diffraction observations. These results indicate that a random distribution of the dopant along the macromolecular chain, and the charge per carbon atom in the metallic region of doped polyacetylene has been estimated to be 0.2 |e|. From these results the mechanism of the PtCl₃ and H₂PtCl₆·6H₂O doping process in polyacetylene is clarified as follows: Thus the dopant anion in polyacetylene is PtCl,^2? for both PtCl₄ and H₂PtCl₆·6H₂O doping.     

Spontaneous deposition of Pt‐nanoparticles on HOPG surfaces

Pt nanoparticles were spontaneously generated by immersion of a highly ordered pyrolytic graphite substrate in a 1 mM H₂PtCl₆ + 0.05 M H₂SO₄ plating solution using different immersion times, modifying both size and density of the deposits. Atomic force microscopy images show Pt particles distributed preferentially on surface defects of the electrode, increasing their size and density with deposition time. Scanning electronic microscopy/energy‐dispersive X‐ray spectroscopy images confirmed the formation of Pt deposits after 2 h immersion, forming irregular agglomerates with different sizes distributed over the surface. The open circuit potential studies showed potentials close to the corresponding PtCl₆^2?/Pt and PtCl₄^2?/Pt couples, which would indicate that some of these processes took place at the interface. The voltammetric response of the supported Pt nanoparticles showed an increase in current density towards the hydrogen evolution reaction being more pronounced for deposits formed after an immersion time of 2 h. In this case, the voltammetric behavior was similar to polycrystalline Pt. Copyright © 2015 John Wiley & Sons, Ltd.     

Cost-effective electrodeposition of platinum nanoparticles with ionic liquid droplet confined onto electrode surface as micro-media

We report here for the first time on the use of a droplet of water-immiscible ionic liquid (IL) containing metallic precursor confined onto electrode surface as new micro-media for cost-effective electrodeposition of platinum nanoparticles. 1-n-Butyl-3-methylimidazolium hexafluorophosphate (BmimPF₆), a typical water-immiscible IL, is found to be able to form a stable droplet onto electrode surface in which the metallic precursor (i.e., chloroplatinic acid hexahydrate (H₂PtCl₆)) for electrodeposition of Pt nanoparticles can be stably dissolved when the prepared electrode is used in aqueous solutions. The electrodeposition of Pt nanoparticles is carried out in the aqueous solution of 0.1 M KPF₆ with the H₂PtCl₆-containing IL droplet-confined glassy carbon electrode as working electrode at −1.5 V vs. Ag/AgCl. The Pt nanoparticles electrodeposited from the IL droplet micro-medium are characterized to have a uniform morphology and to possess an excellent electrocatalytic activity toward the oxidation of methanol. Compared with the existing methods for the electrodeposition of metals with ILs as the solvents, the method demonstrated here requires a less amount of ILs and metallic precursors and is thus anticipated to provide a new and cost-effective approach to the deposition of metallic nanoparticles onto conducting substrate.     

The effect of electrochemically treated glassy carbon on the activity of supported Pt catalyst in methanol oxidation

Effect of electrochemical oxidation of glassy carbon on deposition of platinum particles and electrocatalytic activity of platinum supported on oxidized glassy carbon (Pt/GC_OX) were studied for methanol oxidation in H₂SO₄ solution. Platinum was potentiostatically deposited from H₂SO₄ + H₂PtCl₆ solution. Glassy carbon was anodically polarised in 0.5 M H₂SO₄ at 2.25 V vs. saturated calomel electrode (SCE) during 35 s. Electrochemical treatment of GC support, affecting not significantly the real Pt surface area, leads to a better distribution of platinum on the substrate and has remarkable effect on the activity. The activity of the Pt/GC_OX electrode for methanol oxidation is larger than polycrystalline Pt and for more than one order of magnitude larger than Pt/GC electrode. This increase in activity indicates the pronounced role of organic residues of GC support on the properties of Pt particles deposited on glassy carbon.     

Adsorption of PtCl62- anions on the surface of carbon black?

Summary Adsorption of PtCl₆^2- anions on surface of carbon black was studied. It was found that the absence of surface oxygen groups led to a higher Pt loading amount, and the Pt loading amount would decrease as using a higher H₂PtCl₆ impregnating solution concentration. The π sites in the basal planes of carbon black surface act as the chemical adsorption sites, playing a more important role than surface oxygen groups in PtCl₆^2- adsorption. Adsorption of large amounts of H₃O⁺ in the π sites would lead to a decrease of chemical adsorption capacity.     

Synthese und Charakterisierung von Aquapentachloroplatinaten(IV) – Struktur von [K(18-Krone-6)][PtCl5(H2O)]

Synthesis and Characterization of Aquapentachloroplatinates(IV) – Structure of [K(18-crown-6)][PtCl₅(H₂O)] The crown ether complex of the aquapentachloroplatinic acid of the composition [H₁₃O₆][PtCl₅(H₄O₂)] · 2(18-cr-6) ( 2 ) reacts with K₂CO₃ and [NⁿBu₄]OH in aqueous solution to give [K(18-cr-6)][PtCl₅(H₂O)] ( 5 a ) and [NⁿBu₄][PtCl₅(H₂O)] · ¹/₂ (18-cr-6) · H₂O ( 5 b ), respectively. Both compounds were characterized by microanalysis, vibrational (IR, Raman) and NMR (¹H, ¹³C, ¹⁹⁵Pt) spectroscopy. The X-ray structure analysis of 5 a (orthorhombic, pnma; a = 16,550(4), b = 18,044(3), c = 7,415(1) Å; Z = 4; R1 = 0,0183; wR2 = 0,0414) reveals that the crystal is threaded by chains built up of [PtCl₅(H₂O)]^? and [K(18-cr-6)]⁺ units. There are tight K …? Cl contacts (d(K? Cl1)) = 3,0881(9) Å and O_W? H? O_cr hydrogen bridges (d(O1 …? O2) = 2,806(3) Å) between these units. The coordination polyhedron [PtCl₅O] has approximately C_4v symmetry.     

Microstructure and hydrogen production activity of Pt–TiO2 prepared by precipitation–photodeposition

A series of Pt–TiO₂ photocatalysts were prepared by a facile precipitation–photoreduction method under different pH conditions, using H₂PtCl₆ as platinum precursor. The microstructure and chemical state of Pt loaded on the surface of TiO₂ were analyzed by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). It was revealed that the size and distribution of Pt nanoparticles on TiO₂ surface is closely related to the initial pH of H₂PtCl₆ solution. The optimal pH value for forming highly dispersed Pt nanoparticles is 12. The photocatalytic activities of the prepared samples were investigated in terms of hydrogen production. The results indicated that the Pt–TiO₂ sample prepared by precipitation–photodeposition method shows much higher activity than that prepared by traditional photodeposition method.     

Pt/CNTs催化剂的制备及其催化臭氧化活性研究

以碳纳米管(CNTs)为催化剂载体, 以H₂PtCl₆•6H₂O为贵金属活性组分前驱物, 采用等体积浸渍法制备了Pt/CNTs催化剂. 以草酸为目标污染物, 考察了所制备催化剂的催化活性, 并采用SEM, XRD和XPS等分析方法对催化剂进行表征. 对活性组分Pt的负载量、氢还原温度和热处理方式进行了研究, 确定了适宜的制备条件为Pt负载量1.0%、氢还原温度350 ℃. 研究表明, 在本实验条件下, 单独臭氧氧化、碳纳米管载体催化臭氧化和Pt/CNTs催化臭氧化分别能去除溶液中3.0%, 72.9%和97.9%的草酸. Pt的负载明显地提高碳纳米管催化臭氧化的效果. XRD分析显示催化剂的活性组分Pt以单质Pt⁰的形式存在; 与氢还原过程相比, 在空气气氛中焙烧制备的Pt/CNTs催化剂表面Pt的结晶度过高, 而且XPS结果表明此催化剂表面的Pt有化学吸附氧存在, 导致催化活性降低.     

Carbon-supported platinum-decorated nickel nanoparticles for enhanced methanol oxidation in acid media

Carbon-supported platinum-decorated nickel nanoparticles (denoted as Pt-Ni/C) with intimate contact of Pt and Ni are prepared by a galvanic displacement reaction between Ni/C nanoparticles and PtCl₆²⁻ in aqueous solution. It demonstrates a higher mass activity and stability to methanol oxidation reaction than conventional Pt/C and PtRu/C catalysts by a rotating disk electrode in acid solution, which could be attributed to the modified electronic structure of the Pt-Ni/C nanoparticles.     

Asymmetric Hydrogenation of Ethyl Pyruvate using Layered Double Hydroxides–Supported Nano Noble Metal Catalysts

Layered double hydroxide (LDH)–supported nano noble metal heterogeneous catalysts are synthesized by ion exchange of K₂PtCl₆, Na₂PdCl₄ and impregnation of RhCl₃ ^.3H₂O followed by reduction with H₂. The LDH–Rh, Pt, and Pd catalysts are tested in the enantioselective hydrogenation of ethyl pyruvate to ethyl lactate with very good yields and enantiomeric excess's (e.e.'s) of up to 72% were obtained with Pt. The catalyst was recovered and reused for several cycles with consistent activity.     

New process for loading highly active platinum on carbon black surface for application in polymer electrolyte fuel cell

The deposition of platinum on various carbon blacks was carried out by forming active functional groups on the surface of the carbon support, and exchanging these active groups with different platinum complexes. Using H₂PtCl₆ solution, an impregnation rather than an exchange takes place. However, using divalent platinum complexes [Pt(NH₃)₄]²⁺, a fast exchange takes place which leads to extremely small platinum particles highly dispersed on the surface of carbon black. A comparison of the catalytic activities of platinum supported on various carbon blacks was also carried out. The performances of Pefc (Polymer Electrolyte Fuel Cell) based on the process of the ion exchange are reported.