Electrosorption of hydrogen into palladium-gold alloys

Hydrogen electrosorption into Pd-Au alloys has been studied in acidic solutions (1 M H₂SO₄) using cyclic voltammetry. Pd-Au electrodes with limited volume were prepared by electrochemical co-deposition. It was found that the maximum H/(Pd+Au) ratios decrease monotonically with increasing gold content and reach zero at ca. 70 at% Au. Similarly to the case of Pd limited volume electrodes, two peaks in the hydrogen region, corresponding to two types of sorbed hydrogen, are observed on voltammograms for Pd-rich alloys. The hydrogen capacity, H/(Pd+Au), measured electrochemically, depends on the sweep rate in the cyclic voltammetry experiments, which suggests that two different mechanisms for hydrogen desorption from the Pd-Au alloy are possible. After a strong decrease of Pd concentration at the electrode surface, caused by long cyclic polarization to sufficiently anodic potentials, the amount of absorbed hydrogen is still significant for alloys initially rich in Pd. The results obtained from CO adsorption experiments suggest that only Pd atoms are active in the hydrogen absorption/desorption process. Electronic Publication     

炭载体的表面处理对Pd/C催化剂电催化活性的影响

采用处理与未处理的活性炭制备Pd/c催化剂,运用循环伏安法(CV)和计时电流法检测两种Pd/C催化剂对甲酸的电催化氧化活性和稳定性.通过透射电镜(TEM)对催化剂进行了表征.结果表明,用硝酸处理的活性炭所制备的Pd/C催化剂中Pd粒子的分散更均匀,对甲酸的电催化氧化活性和稳定性都有不同程度的提高.     

Oxygen reduction reaction on carbon-supported palladium nanocubes in alkaline media

Carbon-supported Pd nanocubes with the size of 30, 10 and 7 nm were prepared and their electrocatalytic activity towards the oxygen reduction reaction (ORR) in alkaline solution was studied. For comparison carbon-supported spherical Pd nanoparticles and commercial Pd/C catalyst were used. The catalysts were characterised by transmission electron microscopy, electro-oxidation of carbon monoxide and cyclic voltammetry and the ORR activity was evaluated using the rotating disk electrode method. The ORR on all studied Pd/C catalysts proceeded via four-electron pathway where the rate-limiting step was the transfer of the first electron to O₂ molecule. The specific activity of Pd nanocubes was more than two times higher than that of spherical Pd nanoparticles and increased with increasing the particle size.     

Direct growth of highly catalytic palladium nanoplates array onto gold substrate by a template-free electrochemical route

A novel palladium nanoplates array (Pd NPA) directly grown on gold substrate by a facile electrochemical approach is developed without any template. Different from general electrodeposition utilizing constant potential or current, cyclic potential scan is used, which corresponds to cyclic deposition/dissolution of Pd on substrate. The formation mechanism is proposed for the evolution of Pd NPA which resulted from the selective growth of Pd nanocrystals under the regulation of potential and surfactant. The Pd NPA electrode shows extraordinary electro-catalytic activity towards the oxidation of methanol. This approach provides a facile route for the synthesis of highly catalytic Pd NPA with an excellent electrical contact to a substrate, which is important for the overall device performance.     

Preparation and characterization of Pd/PPy-SDS/foam-Ni and Pd/PPy-CTAB/foam-Ni electrodes with high electroactive surface area

Surfactant-doped electrodes, palladium/polymeric pyrrole-sodium dodecyl sulfate/foam-nickel (Pd/PPy-SDS/foam-Ni) electrode and palladium/polymeric pyrrole-cetyl trimethyl ammonium bromide/foam-nickel (Pd/PPy-CTAB/foam-Ni) electrode, were prepared by electrochemical deposition method. The characteristics of the prepared electrodes were investigated. Based on the results of scanning electron microscope, X-ray diffraction, inductively coupled plasma-atomic emission spectrometry, and cyclic voltammetry tests, both of the two surfactants could improve the electrodes' electrocatalytic activity. Results also indicate that Pd/PPy-SDS/foam-Ni electrode has higher catalytic potential capability than Pd/PPy-CTAB/foam-Ni electrode.     

Pd/TiO2/C复合催化剂的制备及其在碱性溶液中对乙醇氧化的电催化性能

钛酸四丁酯前驱体水热合成制备纳米TiO₂颗粒,在TiO₂和Vulcan XC-72活性炭复合载体上液相还原负载Pd纳米颗粒,制得Pd/TiO₂/C复合催化剂. 通过透射电镜（TEM）和X射线衍射（XRD）测试表明其具有面心立方结构,Pd金属粒子（粒径约3 ~ 4 nm）均匀分散在锐钛矿型的纳米TiO₂和活性炭的复合载体上. 循环伏安和计时电流曲线测试表明,与相同Pd载量的Pd/C相比,20% Pd载量的Pd/TiO₂/C颗粒在常温常压下对乙醇的电催化氧化有很高活性和稳定性. 这主要归功于纳米TiO₂改变了Pd表面的电子特性,且增大了其比表面积.     

Thermodynamic and kinetic control over the reduction mechanism of the Pd(3)(dppm)(3)(CO)(I)(+) cluster

The reduction mechanism of the title cluster has been investigated by means of cyclic voltammetry (CV), rotating disk electrode (RDE) voltammetry, and coulometry. The 2-electron reduction proceeds via two routes simultaneously. The first one involves two 1-electron reduction steps, followed by an iodide elimination to form the neutral Pd(3)(dppm)(3)(CO)(0) cluster (EEC mechanism). The second one is a 1-electron reduction process, followed by an iodide elimination, then by a second 1-electron step (ECE mechanism) to generate the same final product. Control over these two competitive mechanisms can be achieved by changing temperature, solvent polarity, iodide concentration, or sweep rate. The reoxidation of the Pd(3)(dppm)(3)(CO)(0) cluster in the presence of iodide proceeds via a pure ECE pathway. The overall results were interpreted with a six-member square scheme, and the cyclic and RDE voltammograms were simulated, in order to extract the reaction rate and equilibrium constants for iodide exchange for all three Pd(3)(dppm)(3)(CO)(I)(n)() (n = +1, 0, -1) adducts.     

Mixed-metal (platinum, palladium), mixed-pyrimidine (uracil, cytosine) self-assembling metallacalix[n]arenes: dynamic combinatorial chemistry with nucleobases and metal species

Reactions between the mononuclear mixed-nucleobase complex [Pt(en)(UH-N1)(CH2-N3)]+ (1; en: ethylenediamine; UH-N1: uracil monoanion bonded through the N1 atom; CH2-N3: neutral cytosine bonded through the N3 atom) and [Pd(II)(en)] or [Pd(II)(2,2'-bpy)] (2,2'-bpy: 2,2'-bipyridine) lead to libraries of compounds of different stoichiometries and different connectivities. In these compounds, the palladium entity binds to or cross-links either the N3 sites of uracil and/or the N1 sites of cytosine, following deprotonation of these positions to give uracil dianions (U) and cytosine monoanions (CH). Cyclic species, which can be considered as metallacalix[n]arenes, have been detected in several cases, with n being 4 and 8. The complexity of the compounds formed not only results from the possibility of the two different nucleobases in building block 1 engaging in different connectivities with the Pd entities, but also from the potential for the formation of oligomers of different sizes and different conformations; in the case of cyclic tetranuclear Pt(2)Pd(2) species, this can, in principle, lead to the various arrangements (cone, partial cone, 1,2-alternate, 1,3-alternate) known from calix[4]arene chemistry. A further complication arises from the fact that, depending on the mutual orientation of the exocyclic groups of the two nucleobases (O2 and O4 of uracil, O2 and N4 of cytosine), these sites can be engaged in additional chelation of [Pd(II)(en)] and [Pd(II)(2,2'-bpy)]. Thus, penta-, hexa-, and octanuclear complexes, Pt(2)Pd(3), Pt(2)Pd(4), and Pt(2)Pd(6), derived from cyclic Pt(2)Pd(2) tetramers have been isolated and characterized.     

Cyclic trimer versus head-tail dimer in metal-nucleobase complexes: importance of relative orientation (syn, anti) of the metal entities and relevance as a metallaazacrown compound

The formation and crystal structure analysis of a cyclic trinuclear Pd complex with bridging 1-methylcytosinato model nucleobases is reported: [[(tmeda)Pd(1-MeC(-)-N3,N4)]3] (ClO4)3.5.5H2O (tmeda = N,N,N',N'-tetramethylethylenediamine; 1-MeC- = 1-methylcytosine deprotonated at exocyclic amino group) is obtained, among others, from the hydroxo-bridged dinuclear species [[(tmeda)Pd(OH)]2](ClO4)2, which likewise has been characterized by X-ray crystallography, and 1-MeC (1-MeC = neutral 1-methylcytosine) in aqueous solution. The usual head-tail dimer (HT1) appears not to be formed presumably because of the steric bulk of the tmeda ligand, which prevents a close approach of two tmeda ligands. There is also no evidence for formation of an alternative head-tail dimer structure (HT2) which, in principle, would not lead to any steric clash of ligands, but would require an orientation of the metal at N4 that is almost perpendicular to the nucleobase plane. In the Pd3 compound, the bridging metals are approximately in an anti arrangement, thereby leading to Pd...Pd separations within the Pd3 triangle close to 5.2 angstroms. This arrangement is reflected in the 1H NMR spectrum by a strongly deshielded H5 resonance of the nucleobase, occurring at 6.56 ppm (D2O). The overall structure of the Pd3 is that of a double cone, with ClO4- counterions approaching the cavities from either side. The trinuclear structure is also maintained in Me2SO-d6. In this solvent, Pd3 acts as a fluoride anion receptor, with F- binding to the N4H protons, as evident from large downfield shifts of these protons. The compound is compared with cyclic adeninato complexes of hexacoordinated metal ions, and a conceptional analogy with [12]metallacrown-3 species is outlined.     

Enantioselective Pd-catalyzed hydrogenation of enesulfonamides

Asymmetric hydrogenation of cyclic enesulfonamides affords chiral cyclic sulfonamides using Pd(OCOCF(3))(2)/diphosphine complexes as catalysts with up to 98% ee.     

Palladium-catalyzed approach to stereodefined ten-membered cycles from 1,5-bisallenes

A three-component Pd(0)-catalyzed reaction of 1,5-bisallenes with organic halides in the presence of primary amines was observed to afford stereodefined not readily available ten-membered cyclic compounds highly chemo- and regioselectively. A mechanism involving two π-allylic palladium intermediates was proposed to account for the observed regio- and stereoselectivity.     

Pd/Mm(富铈稀土)薄膜电极在KOH溶液中的电化学行为

利用磁控溅射法制备了Pd/Mm(Mischmetal)混合稀土薄膜,采用X射线衍射、AFM及循环伏安和交流阻抗谱等电化学测试技术研究了Pd/Mm稀土薄膜的晶体结构、表面形貌及其在KOH溶液中的电化学行为.结果表明,Pd/Mm薄膜表面的Pd层由纳米级的孤岛状颗粒构成,颗粒大小为100～200 nm.循环伏安法研究表明,氢的电化学氧化和还原均通过表面Pd金属层进行.Pd/Mm稀土薄膜电极的交流阻抗图由两个容抗弧组成,低频区的容抗弧对应氢在电极中的固态扩散过程,而高频段的容抗弧对应氢在电极表面的电化学还原过程,其中氢在薄膜电极内部的扩散是速率控制步骤.     

Formation of Au/Pd–Sn trimetallic particles onto vitreous carbon

The sequential deposition process of Pd and Sn on Au microcrystals, previously electrodeposited onto vitreous carbon (VC) was investigated in sulphuric acid solution by cyclic voltammetry and Auger electron spectroscopy (AES). Scanning electron microscopy was used to characterize Au deposits. The results reveal that the deposition of Pd and Sn is selective on the Au microcrystals, uniformly distributed on the VC surface, due to the strong interaction energy between the three metals. From the cyclic voltammetric and AES measurements in the VC/Au/Pd/Sn system, the existence of a Sn core–shell structure with Pd can be inferred. Similar voltammetric results were obtained for the VC/Au/Sn/Pd system, where in this case, the Pd adsorbed layer screened the Sn deposits on the VC/Au interface. However, the AES spectrum shows that Sn is still present on the surface, indicating that probably, the Sn deposits have diffused to the surface, or they are not completely covered by Pd. The VC/Au/Pd/Sn modified substrate appears as an interesting electrocatalyst material for the reduction of nitrate ions. Copyright © 2013 John Wiley & Sons, Ltd.     

单晶硅表面贵金属晶粒层的制备

将预处理过的单晶硅p-Si(100)浸入含贵金属盐的HF溶液, 制备了Ag, Au, Pd和Pt的晶粒层. 用原子力显微镜(AFM)、开路电位(OCP)、循环伏安(CV)和交流阻抗(A. C. Impedance)方法对晶粒层性能进行了考察. 形貌显示, 在浸镀20 s后, Ag和Pd晶粒层基本上覆盖了硅基底, Ag颗粒致密, Pd颗粒之间仍有空隙且晶粒较Ag大. Au晶粒层部分覆盖了基底, 而Pt只有极少数的晶粒. 60 s后, Ag, Pd和Au晶粒层都完全覆盖了基底, 而Pt晶粒仍然较少, 但晶粒有所长大. 循环伏安显示, Pd的溶出峰电流比Ag, Au, Pt高1个数量级. 交流阻抗测量表明, Pd晶粒层阻抗最小. 结果表明, Ag, Pd和Au都能用浸入沉积的方法在单晶硅上短时间内制备出晶粒层, 而Pt不能, 选用哪种晶粒层, 需要根据后续工序和实际需要而定.     

Synthesis,Characterization, and Theoretical Investigation of Two‐Coordinate Palladium(0) and Platinum(0) Complexes Utilizing π‐Accepting Carbenes

An elegant general synthesis route for the preparation of two coordinate palladium(0) and platinum(0) complexes was developed by reacting commercially available tetrakis(triphenylphosphine)palladium/platinum with π‐accepting cyclic alkyl(amino) carbenes (cAACs). The complexes are characterized by NMR spectroscopy, mass spectrometry, and single‐crystal X‐ray diffraction. The palladium complexes exhibit sharp color changes (crystallochromism) from dark maroon to bright green if the C‐Pd‐C bond angle is sharpened by approximately 6°, which is chemically feasible by elimination of one lattice THF solvent molecule. The analogous dark orange‐colored platinum complexes are more rigid and thus do not show this phenomenon. Additionally, [(cAAC)₂Pd/Pt] complexes can be quasi‐reversibly oxidized to their corresponding [(cAAC)₂Pd/Pt]⁺ cations, as evidenced by cyclic voltammetry measurements. The bonding and stability are studied by theoretical calculations.     

Pd在p型单晶硅(100)表面自催化化学沉积

研究了Pd在氢终止的p型单晶硅(100)表面的自催化化学沉积(AED). 在室温下将刻蚀过的硅片浸入常规的HF-PdCl2-HCl溶液制备了Pd膜. 将沉积了Pd的基底作为工作电极, 用循环伏安法(CV)、原子力显微镜(AFM)和X射线光电子能谱(XPS)研究了Pd膜的阳极溶出行为和形貌. 结果表明, Pd的生长遵循Volmer-Weber (VW)生长模式, Pd膜给出了很好的支持.     

Electrochemical Reduction of Palladium-containing Heteronuclear Complexes

Reduction of a series of palladium-containing complexes with MnPd, Fe2Pd, and Fe3Pd skeletons was studied by classical polarography, cyclic voltammetry, and controlled-potential electrolysis in acetonitrile. The electrochemical behavior of these complexes was compared to that of relared platinum complexes.     

Preparation of Pd/MgO-reduced graphene oxide hybrid catalyst and enhanced activity for methanol electrooxidation

Magnesium oxide modified reduced graphene oxide supported Pd nanocatalyst (Pd/MgO-RGO) was facilely prepared by a chemical approach. The as-prepared material was characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray diffraction. The electrocatalytic behavior of Pd/MgO-RGO for methanol oxidation was studied using cyclic voltammetric and chronoamperometric methods. The results indicated that Pd/MgO-RGO nanocatalyst exhibits higher electrocatalytic activity and better stability than Pd/RGO.     

Palladium-catalyzed C-N bond formation via direct C-H bond functionalization. Recent developments in heterocyclic synthesis

The formation of carbon-nitrogen bonds by reaction between a nitrogen atom and an unactivated carbon-hydrogen bond is a highly atom-economical process that attracted the attention of the chemists in the last two decades. The widely useful amination and hydroamination reactions, which furnish acyclic or cyclic products, give access to various nitrogen-containing basic and fine chemicals. This review highlights recent progress in the development of palladium-catalyzed reactions that occur by direct functionalization of simple carbon-hydrogen bonds to give heterocyclic products. Pd(0)- and Pd(II)-catalyzed reactions are described separately, emphasizing the different behavior of the metal in these two oxidation states.     

High catalytic activity of nanostructured Pd thin films electrochemically deposited on polycrystalline Pt and Au substrates towards electro-oxidation of methanol

Nanostructured Pd thin films are directly formed on polycrystalline Pt and Au substrates in the absence of hard and soft templates by using a cyclic potential sweep technique, which is confirmed by both SEM observation and their unusual cyclic voltammetric characteristics in H₂SO₄ solution. Interestingly, the bimetallic electrodes obtained after the deposition of ultrathin Pd films onto Pt and Au substrates display much higher catalytic activity towards the electro-oxidation of methanol than the bulk Pt electrode. Besides, it is found that the foreign metal substrate has great influence on the electro-catalytic behavior of the Pd films.