Oxidation of methanol on Pt(Mo) electrodes obtained using galvanic displacement method

The electrocatalytic Pt-Mo system was obtained by formation of platinum particles on the Mo surface under its contact with PtC₆²⁻ (PtCl₄²⁻) under the open circuit conditions. Cyclic voltammograms of the obtained Pt(Mo) electrodes feature well pronounced peaks of hydrogen adsorption and desorption on Pt particles. Nonuniform platinum distribution across the electrode surface was found. Pt(Mo) electrodes showed a higher specific activity in the reaction of methanol oxidation in the potential range of 0.35–0.45 V (RHE) as compared to Pt/Pt.     

A general and high-yield galvanic displacement approach to Au-M (M = Au, Pd, and Pt) core-shell nanostructures with porous shells and enhanced electrocatalytic performances

In this work, we utilize the galvanic displacement synthesis and make it a general and efficient method for the preparation of Au-M (M = Au, Pd, and Pt) core-shell nanostructures with porous shells, which consist of multilayer nanoparticles. The method is generally applicable to the preparation of Au-Au, Au-Pd, and Au-Pt core-shell nanostructures with typical porous shells. Moreover, the Au-Au isomeric core-shell nanostructure is reported for the first time. The lower oxidation states of Au(I), Pd(II), and Pt(II) are supposed to contribute to the formation of porous core-shell nanostructures instead of yolk-shell nanostructures. The electrocatalytic ethanol oxidation and oxygen reduction reaction (ORR) performance of porous Au-Pd core-shell nanostructures are assessed as a typical example for the investigation of the advantages of the obtained core-shell nanostructures. As expected, the Au-Pd core-shell nanostructure indeed exhibits a significantly reduced overpotential (the peak potential is shifted in the positive direction by 44?mV and 32?mV), a much improved CO tolerance (I(f)/I(b) is 3.6 and 1.63 times higher), and an enhanced catalytic stability in comparison with Pd nanoparticles and Pt/C catalysts. Thus, porous Au-M (M = Au, Pd, and Pt) core-shell nanostructures may provide many opportunities in the fields of organic catalysis, direct alcohol fuel cells, surface-enhanced Raman scattering, and so forth.     

Nanoporous Pt@Au(x)Cu(100-x) by hydrogen evolution assisted electrodeposition of Au(x)Cu(100-x) and galvanic replacement of Cu with Pt: electrocatalytic properties

Electrodeposition of high-surface-area nanoporous Au-Cu foams under conditions of hydrogen codeposition is studied. The honeycomb-like Au(x)Cu(100-x) foams with 0 ≤ x ≤ 100 are electrodeposited by controlling the amount of corresponding ions in the solution. The amount of metal ions in deposited films follows that in used electrolytes. Compared to monometallic foams, the Au(x)Cu(100-x) structures are characterized by smaller ligament or particle sizes (less than 10 nm) and improved stability. The addition of even a small amount of Cu to the Au matrix is found to dramatically improve the stability of the structure in air environment or an acidic medium. Pt@Au(x)Cu(100-x) structures are formed by the galvanic displacement of Cu from Au(x)Cu(100-x) templates. During the displacement of Cu by Pt, Au serves as a buffer, decreasing mechanical stresses and preventing the detachment of the foam from the substrate. The surface ratio of Pt to Au atoms is controlled by adjusting the amount of Cu in the template. Pt@Au(x)Cu(100-x) electrodes are investigated as novel electrocatalysts for methanol oxidation in alkaline media. The Au-enriched surfaces show higher catalytic activity toward methanol oxidation, while the electrodes with a higher amount of Pt are more stable.     

Three-dimensional porous Au nanocoral structure decorated with Pt submonolayer via galvanic displacement of copper adatoms for electrooxidation of formic acid

Three-dimensional (3D) porous Au nanocoral network (GNN) structure was fabricated on glassy carbon (GC) electrode by one-step, template-free electrodeposition and decorated with ultrathin Pt film by combining the underpotential deposition (UPD) of copper adatoms and the galvanic displacement (GD) between PtCl₆^2- and Cu. The thickness of Pt atomic layers can be controlled precisely by repeating the UPD–GD process. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) were employed to characterize the morphology of GNN and Pt_n/GNN (n, the cycles of repeating the UPD–GD process). Cyclic voltammometric and chronoamperometric tests indicate that all Pt_n/GNN samples effectively support the direct oxidation of formic acid and show higher electrocatalytic performance than the commercial Pt/C catalyst (Pt, 20 wt %, Johnson Matthey Co.), where Pt₁/GNN completely eliminates the indirect oxidation of formic acid, exhibiting the best electrocatalytic activity and stability among all Pt_n/GNN samples due to the optimal coverage and distribution of Pt atoms on GNN.     

A new promising Pt(Mo2C) catalyst for hydrogen evolution reaction prepared by galvanic displacement reaction

Journal of Solid State Electrochemistry - A new method for the synthesis of Pt(Mo2C) catalysts using the redox reaction between Mo2C and solution containing potassium tetracholoplatinate (II) is...     

Novel cyclometallated Pd(II) and Pt(II) complexes with indole derivatives and their use as catalysts in Heck reaction

Several palladacycle and platinacycle complexes have been prepared from easily available or naturally occurring indole derivatives, such as gramine and related compounds. Dimeric complexes were obtained with Pd(OAc)₂, while Pt(DMSO)₂Cl₂ mainly afforded monomeric structures. A notable feature of these reactions was the formation of new M-C bonds between Pd or Pt and C-2 and C-3 of the indole ring. With ligands like 2-(2′-pyridyl)-1H-indoles, N-N metallacycles were generated instead: in fact new C-M bonds with the C-3 position could only form if N-substituted indoles were used. The reactivity of Pd dimeric complexes with PPh₃, sym-collidine and DMAP was explored to obtain monomeric complexes. Three such compounds were prepared, one of which was characterized by X-ray diffraction. Metathetical reactions were carried out to effect a ligand exchange replacing OAc with halide ions, with the aim to synthesize μ-Cl and μ-Br bridged structures. Turning to the synthesis of hetaryl complexes, functionalization of the C-2 position on the indole ring was achieved. These complexes were prepared by substitution reactions starting from gramine and/or its alkylammonium salts.     

Cu UPD at Pt(100) and stepped faces Pt(610), Pt(410) of platinum single crystal electrodes

The processes of adsorption/desorption of copper adatoms on the basal Pt(100) face and stepped Pt(610), Pt(410) surfaces have been studied in perchloric acid solution by cyclic voltammetry. It has been shown that the positions of the Cu stripping peaks are determined by perfection of the adlayer. The “island” model is suggested to describe electrochemical behavior of the Pt(hkl)+Cu_ad system. Obtained results are important for target modification of shape-controlled nanoparticles that are used in electrocatalysis.     

Modification effect of Cu upon Pt In Pt?Cu?Al2O3 catalysts

In Pt–Cu–Al₂O₃ catalysts Cu might display either Electronic Ligand Effect or Ensemble Effect, depending on the preparation method of catalysts. For catalysts with Pt added before Cu, the latter exhibits an Electronic Ligand Effect. However, for catalysts with Cu added before Pt or with co-added Pt and Cu, Cu mainly demonstrates an Ensemble Effect.

---

Pt–Cu/Al₂O₃ , . Pt Cu, , .

     

Anodic Stripping Determination of Pt (IV) Based on the Anodic Oxidation of Cu from the Intermetallic Phase of Cu3Pt

It is shown that platinum can be determined by anodic stripping voltammetry at the peak of selective electrooxidation of copper from intermetallic phase with platinum of Cu₃Pt composition. The composition of intermetallic copper-platinum phase formed on the electrode during pre-electrolysis was calculated on the amount of potential displacement (ΔЕ) of copper electrooxidation.     

Peculiarities of the Pt(Cu)/C catalyst formation by galvanic displacement of copper in H<Subscript>2</Subscript>PtCl<Subscript>4</Subscript> solutions

Specific features of the formation of a Pt(Cu) catalyst by the galvanic displacement of electroplated copper (carbon support) in a PtCl₄²⁻ solution are considered. The composition, the structure, and electrochemical properties of Pt(Cu) deposits in different stages of displacement are studied by a complex of methods (SEM, TEM, XPS, voltammetry, etc.). The gradual formation of a stable “core(Pt, Cu)-shell(Pt)” structure with the average atomic ratio Pt : Cu ≈ 3 : 1 is observed. The results for PtCl₄²⁻ are compared with the analogous results for PtCl₆²⁻ published earlier. Particularly, the reasons for the differences in the steady state potentials established on the Pt(Cu)_st/C electrode in the presence of PtCl₄²⁻ and PtCl₆²⁻ are discussed.     

Study of the charge displacement at constant potential during CO adsorption on Pt(110) and Pt(111) electrodes in contact with a perchloric acid solution

A new electrochemical approach has been made, employing the current—time transient responses when a CO adlayer is formed at a platinum electrode at various controlled potentials where CO oxidation does not take place. The case of Pt(110) is compared with those of Pt(111) and Pt(111) disordered after ten cycles of oxygen adsorption—desorption. In order to avoid interference with anion-specific adsorption, the study was carried out in a perchloric acid solution. There is good agreement between the charge measured by voltammetry in the absence of CO and the charges measured during the current—time transients. This is indicative that the latter charges are produced by the displacement of the species at the interface as a result of CO adlayer formations. The sign of the current transient has been found to depend on the potential at which CO adsorption is carried out. This dependence may be related to the nature of species which are present in the interfacial region, providing new complementary information that voltammetry cannot yield.     

Cycloisomerization of dienes with carbophilic lewis acids: mimicking terpene biosynthesis with Pt(II) catalysts

[reaction: see text]. Dicationic Pt(II) complexes containing triphosphine pincer ligands are excellent catalysts for the cycloisomerization of 1,6- and 1,7-dienes into bicyclopropane carbocycles. In analogy to the biosynthetic route to these monoterpene-like compounds, carbocation intermediates are proposed and supported by trapping experiments. Reactivation of the trapped intermediates indicates that cation generation by C-C bond formation is both rapid and reversible.     

Ordering of Cu(II) ions in supported copper-titanium oxide catalysts

Two types of ESR spectrum (A and B) of exchange-coupled Cu²⁺ ions have been found for Cu-Ti-O catalysts at 77 K and 300 K. In associates A and B, the Cu²⁺ ions form a system with orbital ordering. The difference between the spectra is due to the difference between the ground states of adjacent Cu²⁺ ions in the associates: the ground states are $d_{x^2 } $ and $d_{y^2 } $ for A type associates and $d_{x^2 - y^2 } $ and $d_{z^2 - x^2 } $ for B type associates. The copper associates lie on the surface of the TiO₂ (anatase) support microparticles.     

Cu、Ni、Ru、Pt对费托合成Fe催化剂的助剂作用研究

考察了Cu、Ni、Ru、Pt对费托合成Fe催化剂的助剂作用。XRD结果表明,加入Cu、Ni助剂对催化剂有一定的分散作用,而Ru、Pt影响不大。XPS结果表明,所有添加的助剂在催化剂表面均有一定程度的富集,且4种过渡金属助剂与Fe存在不同程度的电荷相互作用。H₂-TPR表明,Cu、Pt、Ru在催化剂还原过程中首先还原为金属态,进而能够明显促进催化剂的还原。CO-TPD表明,加入Cu、Pt、Ni助剂对CO的吸附活化有明显的促进作用。用固定床反应器对催化剂的费托反应性能进行了评价,反应结果表明,加入Ru、Ni、Pt、Cu会依次提高催化剂的反应活性,Pt、Cu、Ru、Ni助剂会依次使催化剂的CH₄选择性增加,并降低C₅₊的选择性。     

Pt(Cu)/C Electrocatalysts with Low Platinum Content

The structure characteristics and the electrochemical behavior of Pt(Cu)/C electrocatalysts synthesized by consecutive deposition of copper and platinum on carbon-support microparticles is studied. The stability and catalytic activity of Pt(Cu)/C materials in reactions of oxygen electroreduction and methanol electrooxidation are assessed and compared with analogous characteristics of a commercial Pt/C material. It is shown that combining the method of galvanic displacement of Cu by Pt with the additional chemical deposition of Pt favors optimization of the structure and functional characteristics of Pt(Cu)/C electrocatalysts. The effect of thermal treatment on the characteristics and properties of electrocatalysts is studied and the optimal conditions of such pretreatment are revealed.     

Mechanistic studies on the formation of Pt(II) hydroformylation catalysts in imidazolium-based ionic liquids

The kinetics of the formation of the active species cis-[Pt^II(PPh₃)₂Cl(SnCl₃)] and cis-[Pt^II(PPh₃)₂(SnCl₃)₂] from the hydroformylation catalyst precursor cis-[Pt^II(PPh₃)₂Cl₂] in the presence of SnCl₂, was studied in two different imidazolium-based ionic liquids. A large range of different chlorostannate melts consisting of 1-butyl-3-methyl-imidazolium cations and [Sn_xCl_y]^{(−y + 2x)} anions with varying molar fraction of SnCl₂, were prepared and characterized by ¹H and ¹¹⁹Sn NMR. The observed chemical shifts point to major changes in the composition of the anionic species within the melt. The second ionic liquid employed, viz., 1-butyl-3-methyl-imidazolium-bis(trifluormethylsulfonyl)amide was prepared in a colorless quality that enabled its application in kinetic studies. The concentration and temperature dependence of the substitution of Cl⁻ by [SnCl₃]⁻ to yield cis-[Pt^II(PPh₃)₂Cl(SnCl₃)], could be studied in detail. Theoretical (DFT) calculations were employed to model the reaction progress and to resolve the role of the ionic liquid in the activation of the catalyst. The available results are presented and a plausible mechanism for the formation of the catalytically active species is suggested.     

Ratiometric displacement approach to Cu(II) sensing by fluorescence

A chelation-enhanced fluorescence method for the detection of paramagnetic copper(II) ions is developed. Two dyes with unequal metal ion binding constants are used, each giving strong fluorescence enhancement in the presence of a diamagnetic reporter ion such as cadmium(II). Upon presentation of copper(II) to a 1:1:1 mixture of the two dyes and cadmium(II), the Cd(II) is displaced from one dye to the other, resulting in quenching of one dye by the Cu(II) and enhancement of the weaker binding dye by complexation of the Cd(II). Although several criteria must be met, this method holds promise for analysis of a wide range of analytes.     

The EPR spectrum and structure of Cu(CO)3

Cu(CO)₃ is formed when Cu atoms and CO are allowed to react on adamantane at 77 K in a rotating cryostat. This carbonyl has most of the unpaired spin in a 4p_z orbital on Cu and is a trigonal planar π radical.     

一氧化氮在Cu_3Pt(111)表面的吸附行为

运用密度泛函理论中广义梯度近似(GGA)的PW91方法,结合周期性平板模型,探讨了NO分子在Cu3Pt(111)表面上不同吸附位的吸附行为.结果表明:NO分子以N端朝下方式吸附在top-Pt以及hcp1和fcc2位(分别为表面Cu2Pt和Cu3簇)的吸附模式最稳定,吸附能分别为101.8、124.5和118.1kJ·mol-1.对于hcp1和fcc2位的吸附,NO中的N原子分别与底物的Cu2Pt和Cu3簇成键.吸附前后的电荷布居、态密度和振动频率的分析结果表明,净电子从底物合金表面转移到NO,N—O键伸长,频率发生红移.合金Cu3Pt和纯贵金属Pt对NO的吸附性质相似.