Thermal and electrochemically assisted Pd-Cl bond cleavage in the d9-d9 Pd2dppm2Cl2 complex by Pd3 dppm3COn+ clusters (n = 2, 1, 0)

A new aspect of reactivity of the cluster [Pd3(dppm)3(micro3-CO)]n+, ([Pd3]n+, n = 2, 1, 0) with the low-valent metal-metal-bonded Pd2(dppm)2Cl2 dimer (Pd2Cl2) was observed using electrochemical techniques. The direct reaction between [Pd3]2+ and Pd2Cl2 in THF at room temperature leads to the known [Pd3(dppm)3(micro3-CO)(Cl)]+ ([Pd3(Cl)]+) adduct and the monocationic species Pd2(dppm)2Cl+ (very likely as Pd2(dppm)2(Cl)(THF)+, [Pd2Cl]+) as unambiguously demonstrated by UV-vis and 31P NMR spectroscopy. In this case, [Pd3]2+ acts as a strong Lewis acid toward the labile Cl- ion, which weakly dissociates from Pd2Cl2 (i.e., dissociative mechanism). Host-guest interactions between [Pd3]2+ and Pd2Cl2 seem unlikely on the basis of computer modeling because of the strong screening of the Pd-Cl fragment by the Ph-dppm groups in Pd2Cl2. The electrogenerated clusters [Pd3]+ and [Pd3]0 also react with Pd2Cl2 to unexpectedly form the same oxidized adduct, [Pd3(Cl)]+, despite the known very low affinity of [Pd3]+ and [Pd3]0 toward Cl- ions. The reduced biproduct in this case is the highly reactive zerovalent species "Pd2(dppm)2" or "Pd(dppm)" as demonstrated by quenching with CDCl3 (forming the well-known complex Pd(dppm)Cl2) or in presence of dppm (forming the known Pd2(dppm)3 d10-d10 dimer). To bring these halide-electron exchange reactions to completion for [Pd3]+ and [Pd3]0, 0.5 and 1.0 equiv of Pd2Cl2 are necessary, respectively, accounting perfectly for the number of exchanged electrons. The presence of a partial dissociation of Pd2Cl2 into the Cl- ion and the monocation [Pd2Cl]+, which is easier to reduce than Pd2Cl2, is suggested to explain the overall electrochemical results. It is possible to regulate the nature of the species formed from Pd2Cl2 by changing the state of charge of the title cluster.     

钯前驱体对汽车尾气处理Pd/Ce_(0.67)Zr_(0.33)O_2催化剂催化性能的影响(英文)

分别以Pd(NO3)2,Pd(NH3)4(NO3)2和H2Pd Cl4为钯前驱体制备了Pd/Ce0.67Zr0.33O2(CZ)催化剂.以硝酸钯为钯前驱体制得的Pd/CZ(NO)催化剂具有较高的储氧量,存在较多的小的钯簇,其钯与载体间相互作用较强,因此在三种新鲜催化剂中对HC和CO的消除表现出了最好的催化活性.以硝酸四氨钯为钯前驱体制得的Pd/CZ(NH)催化剂具有较高的钯分散度,存在较多的大的钯簇,同时存在金属态和氧化态的钯,从而对NO和NO2的消除表现出了较好的催化活性.以氯钯酸为钯前驱体制得的Pd/CZ(Cl)催化剂由于钯分散度较小,钯与载体间作用较弱,存在的CeOCl抑制了氧空穴的生成,因此对各种反应物的催化活性都较低.但Pd/CZ(Cl)催化剂表现出了较好的热稳定性,这是由于老化处理消除了残余的氯物种并且促进了钯与载体间的作用.     

石墨烯的制备及石墨烯载Pd催化剂对甲酸的电催化氧化

以纳米石墨为原料,用两种方法分别制得石墨烯GN-1和GN-2。结果表明,用两种方法制备的石墨烯比表面积比纳米石墨都有显著增加。两种方法制备的石墨烯GN-1和GN-2形貌不同,孔径分布也有很大的差异。分别以两种方法制备的石墨烯为载体制备了Pd催化剂Pd/GN-1和Pd/GN-2。Pd/GN-1和Pd/GN-2催化剂的电化学比表面积分别为34.66和71.25 m2/g。这两种催化剂对甲酸的电催化氧化活性都较纳米石墨作载体制备的催化剂Pd/G有显著的提高,甲酸在Pd/GN-1和Pd/GN-2催化剂上的氧化峰电流密度分别为66.0和95.8 mA/cm2。两种催化剂对甲酸的氧化都有很好的稳定性。     

Tetrapalladium complex with bridging germylene ligands. Structural change of the planar Pd4Ge3 core

A complex with a planar hexagonal Pd(4)Ge(3) core, [Pd{Pd(dmpe)}(3)(μ(3)-GePh(2))(3)], was synthesized and characterized by X-ray and NMR measurements as well as by DFT calculations. 4-tert-Butylbenzenethiol converted the Pd(4) complex into a hexapalladium complex, [{Pd(3)(μ-GePh(2))(2)(μ-H)(μ(3)-GePh(2)(SC(6)H(4)(t)Bu-4))}(2)(μ-dmpe)], composed of two Pd(3)Ge(3) units bridged by a dmpe ligand. The addition of CuI or AgI to the Pd(4) complex yielded [Pd(μ-MI){Pd(dmpe)}(3)(μ(3)-GePh(2))(3) ] (M = Cu, Ag), in which Cu or Ag bridges a Pd-Pd bond of the Pd(4)Ge(3) core. The CuI adducts in solution undergo a pivot motion of the CuI on the surface of the Pd(4)Ge(3) plane on the NMR time scale.     

Efficient and convenient heterogeneous palladium-catalyzed regioselective deuteration at the benzylic position

The Pd/C-catalyzed efficient and regioselective hydrogen-deuterium (H-D) exchange reaction on the benzylic site proceeded in D2O in the presence of a small amount of H2 gas. The use of the Pd/C-ethylenediamine complex [Pd/C(en)] as a catalyst instead of Pd/C led to the efficient deuterium incorporation into the benzylic site of O-benzyl protective groups without hydrogenolysis. These H-D exchange reactions provide a post synthetic and D(2)-gas-free deuterium-labeling method on a wide variety of benzylic sites using D2O as the deuterium source and heterogeneous Pd/C or Pd/C(en) as a reusable heterogeneous palladium catalyst under mild and neutral conditions.     

Electrooxidation of 2-propanol on Pt, Pd and Au in alkaline medium

Pd and Au are investigated as electrocatalysts for 2-propanol oxidation and compared with the conventional catalyst of Pt in alkaline medium. The current density for 2-propanol oxidation on Pd electrode is much higher than that on Pt electrode. The onset potential for 2-propanol oxidation on Pd electrode is more negative compared with that on Pt electrode. The results show that Pd is a good electrocatalyst for 2-propanol oxidation and the activity for the electrooxidation of 2-propanol is higher than Pt and Au in alkaline medium. Pd has higher electrocatalytic activity and better stability for the electrooxidation of 2-propanol. The present study shows a promising choice of Pd as effective electrocatalyst for 2-propanol electrooxidation in alkaline medium.     

Catalytic Hydrodechlorination of 1,2,4,5‐Tetrachlorobenzene over Various Supports Loaded Palladium Catalysts

Water pollution by polychlorinated aromatic hydrocarbons has always been a global issue. In this work, we reported a synthesis of supported palladium catalysts Pd/C, Pd/CeO₂, Pd/SBA‐15, Pd/ZrO₂,Pd/SiO₂, and Pd/Al₂O₃ as well as their catalytic activities on hydrodechlorination (HDC) of 1,2,4,5‐tetrachlorobenzene (TeCB). These Pd catalysts were characterized by Brunauer‐Emmett‐Teller (BET) specific surface area, Transmission electron microscopy (TEM), X‐ray diffraction (XRD), energy Dispersive X‐ray Fluorescence (EDXRF), CO‐chemisorption, and H2‐temperature programmed reduction (H2‐TPR) analysis. Pd/C, Pd/CeO₂ and Pd/SBA‐15 catalysts showed relatively high catalytic activities. The catalytic activities were associated with dispersion of Pd, metal surface area, and reaction temperature, etc.     

Highly chemoselective hydrogenation method using novel finely dispersed palladium catalyst on silk-fibroin: its preparation and activity

A palladium-fibroin complex (Pd/Fib) was prepared by soaking silk-fibroin in MeOH solution of Pd(OAc)₂ for 2 days (under Ar atmosphere)—4 days (under air). Pd(OAc)₂ was gradually absorbed by fibroin and the rapid reduction of fibroin conjugated Pd(OAc)₂ proceeded with MeOH as a reductant at room temperature to be the Pd(0) complex. Pd/Fib catalyzed chemoselective hydrogenation of acetylenes, olefins and azides in the presence of aromatic ketones and aldehydes, halides, N-Cbz protective groups and benzyl esters which are readily hydrogenated using Pd/C or Pd/C(en) as a catalyst.     

笼形聚偕胺肟树脂的研究──Pd(Ⅱ)在碱式树脂上的吸附动力学

研究了碱式笼形聚偕胺树脂（BCAO）吸附Pd（Ⅱ）的行为．溶液pH值对吸附容量有重要的影响．在一定条件下,BCAO在中性溶液中吸附Pd（Ⅱ）的量是酸性溶液中的一倍以上,但提高溶液的酸性有利于从稀溶液中回收钯．Pd（Ⅱ）在盐酸溶液中显H_2PdCI_4结构．吸附结果生成AO－Pd络合物．当溶液被碱中和至近中性时,Pd（Ⅱ）以Pd~(2+)和[Pd（OH）_2CI_2]2-的形式存在,吸附过程中先后生成AO－Pd,AO-Pd_2和AO_2－Pd_3先等不同组成的给合物．由于AO与Pd（Ⅲ）之间较大的电位差,部分Pd（Ⅱ）被还原成Pd（0）,并汇聚在BCAO表面上．     

Preparation of microporous polymer-encapsulated Pd nanoparticles and their catalytic performance for hydrogenation and oxidation

Palladium nanoparticles (Pd NPs) encapsulated by conjugated microporous polymers (CMPs) were prepared by the Pd-catalyzed polymerization followed by a thermal treatment with N₂ or H₂. The Pd catalysts were embedded in the porous network during polymerization and used as a precursor for the generation of Pd NPs in CMP. Although no Pd NPs were formed in the as-synthesized Pd/CMPs, Pd NPs with 1.6–3.5 nm size were formed after the thermal treatment. The obtained Pd/CMP-N₂ and -H₂ catalysts were highly selective in the hydrogenation of 4-nitrostyrene to 4-ethylnitrobenzene, whereas Pd NPs supported on carbon (Ketjen black) gave a fully reduced product, 4-ethylaniline. Substituents in CMP framework could change the catalytic activity of Pd NPs; hydroxy-substituted CMP encapsulated Pd NPs showed higher catalytic activity than Pd/CMP-H₂ for benzyl alcohol oxidation.     

Sb对Pd基催化剂用于常压直接合成H2O2的促进效应

H2O2作为一种高效绿色氧化剂, 广泛应用于造纸、纺织、水处理等工业领域. 目前蒽醌法是工业上生产 H2O2的主要方法, 相比之下, 利用 H2和 O2直接合成 H2O2, 能耗低, 污染小, 适合与下游工艺技术进行耦合. 而缺乏高性能催化剂是制约直接法合成 H2O2工业化的主要原因. 本文通过浸渍法制备了一系列负载型 Pd-Sb/TiO2双金属催化剂, 并用于常压下H2O2直接催化合成反应. 利用透射电子显微镜 (TEM), X 射线光电子能谱 (XPS), H2/O2程序升温脱附 (H2/O2-TPD), X 射线衍射 (XRD), 原位 CO 吸附的傅里叶变换漫反射红外光谱 (CO-DRIFTS) 等手段对催化剂的电子和几何结构进行解析, 深入研究了助剂 Sb 对该体系的促进作用.结果显示, 与单金属 Pd 催化剂相比, 适量金属 Sb 的加入有效提高了催化性能, 抑制了副反应的发生. 当 Pd/Sb 摩尔比为 50/1(Pd50Sb) 时, H2O2的选择性高达 73%; 但是当 Pd/Sb 为 2 时, 催化剂对生成 H2O2几乎没有活性. TEM 和 XRD 证明, Sb 的加入显著促进了 Pd 颗粒在载体 TiO2上的分散. XPS 和 H2-TPD 实验, 发现, Sb 改变了催化剂表面 Pd2+/Pd0的比例, 抑制了金属 Pd 的氧化; 同时, Sb 主要以氧化态存在, 在催化剂表面形成 Sb2O3氧化层, 覆盖表面的 Pd 活性位, 从而抑制了反应中 H2在催化剂表面的活化以及 H2O2加氢副反应的发生. O2-TPD 结果表明, 随着 Sb 的加入, O2的脱附峰明显减弱, 表明 Pd-Sb/TiO2不利于 O2的解离吸附. 此外, 原位 CO-DRIFTS 实验结果表明, Sb 均匀分布在 Pd-Sb 催化剂表面, 致使有利于生成 H2O 的连续 Pd 活性位明显减少, 而有利于合成 H2O2的单个 Pd 原子活性位明显增加.总的来说, Sb 对 Pd 表面起到了显著的修饰作用, 提高了催化剂表面 O2的非解离活化, 从而促进了 H2O2的高选择性合成. 但是过量 Sb 的加入会抑制催化剂对 H2的活化作用, 致使催化剂活性下降, 因此优选 Pd/Sb 的比例对于提高催化剂性能具有重要作用.     

乙醇在碳修饰的二氧化钛纳米管负载的钯电催化剂上的催化氧化

 通过有机物分解碳化处理TiO2 纳米管制得了TiO2C, 并以其为载体制备了Pd/TiO2C电催化剂,考察了该催化剂对碱性介质中乙醇电催化氧化的活性. 结果表明,碳化导电处理的TiO2C纳米管载体能有效改善催化剂中贵金属的分散度和电极结构,从而提高催化剂的电催化活性. 对催化剂活性组分的优化实验表明, Pd/TiO2C质量比为1/1时催化剂的活性最高. 在1 mol/L KOH溶液中Pd载量均为0.3 mg/cm2的条件下, Pd/TiO2C催化剂对乙醇氧化的催化活性是Pd/C催化剂的3.8倍.     

Theoretical investigation into the mechanism of reductive elimination from bimetallic palladium complexes

Reductive elimination of C-Cl and C-C bonds from binuclear organopalladium complexes containing Pd-Pd bonds with overall formal oxidation state +III are explored by density functional theory for dichloromethane and acetonitrile solvent environments. An X-ray crystallographically authenticated neutral complex, [(L-C,N)ClPd(μ-O(2)CMe)](2) (L = benzo[h]quinolinyl) (I), is examined for C-Cl coupling, and the proposed cation, [(L-C,N)PhPd(1)(μ-O(2)CMe)(2)Pd(2)(L-C,N)](+) (II), examined for C-C coupling together with (L-C,N)PhPd(1)(μ-O(2)CMe)(2)Pd(2)Cl(L-C,N) (III) as a neutral analogue of II. In both polar and nonpolar solvents, reaction from III via chloride dissociation from Pd(2) to form II is predicted to be favored. Cation II undergoes Ph-C coupling at Pd(1) with concomitant Pd(1)-Pd(2) lengthening and shortening of the Pd(1)-O bond trans to the carbon atom of L; natural bond orbital analysis indicates that reductive coupling from II involves depopulation of the d(x(2)-y(2)) orbital of Pd(1) and population of the d(z(2)) orbitals of Pd(1) and Pd(2) as the Pd-Pd bond lengthens. Calculations for the symmetrical dichloro complex I indicate that a similar dissociative pathway for C-Cl coupling is competitive with a direct (nondissociative) pathway in acetonitrile, but the direct pathway is favored in dichloromethane. In contrast to the dissociative mechanism, direct coupling for I involves population of the d(x(2)-y(2)) orbital of Pd(1) with Pd(1)-O(1) lengthening, significantly less population occurs for the d(z(2)) orbital of Pd(1) than for the dissociative pathway, and d(z(2)) at Pd(2) is only marginally populated resulting in an intermediate that is formally a Pd(1)(I)-Pd(2)(III) species, (L-Cl-N,Cl)Pd(1)(μ-O(2)CMe)Pd(2)Cl(O(2)CMe)(L-C,N) that releases chloride from Pd(2) with loss of Pd(I)-Pd(III) bonding to form a Pd(II) species. A similar process is formulated for the less competitive direct pathway for C-C coupling from III, in this case involving decreased population of the d(z(2)) orbital of Pd(2) and strengthening of the Pd(I)-Pd(III) interaction in the analogous intermediate with η(2)-coordination at Pd(1) by L-Ph-N, C(1)-C(2).     

l‐Arginine‐Triggered Self‐Assembly of CeO2 Nanosheaths on Palladium Nanoparticles in Water

Pd@CeO₂ core–shell nanostructures with a tunable Pd core size, shape, and nanostructure as well as a tunable CeO₂ sheath thickness were obtained by a biomolecule‐assisted method. The synthetic process is simple and green, as it involves only the heating of a mixture of Ce(NO₃)₃, l ‐arginine, and preformed Pd seeds in water without additives. Importantly, the synthesis is free of thiol groups and halide ions, thus providing a possible solution to the problem of secondary pollution by Pd nanoparticles in the sheath‐coating process. The Pd/CeO₂ nanostructures can be composited well with γ‐Al₂O₃ to create a heterogeneous catalyst. In subsequent tests of catalytic NO reduction by CO, Pd@CeO₂/Al₂O₃ samples based on Pd cubes (6, 10, and 18 nm), Pd octahedra (6 nm), and Pd cuboctahedra (9 nm) as well as a simply loaded Pd cube (6 nm)–CeO₂/Al₂O₃ sample were used as catalysts to investigate the effects of the Pd core size and shape and the hybrid nanostructure on the catalytic performance.     

High-nuclearity close-packed palladium-nickel carbonyl phosphine clusters: heteropalladium

[Pd(16)Ni(4)(CO)(22)(PPh(3))(4)](2)(-) (1) and [Pd(33)Ni(9)(CO)(41)(PPh(3))(6)](4)(-) (2) were obtained as the two major products from the reduction of PdCl(2)(PPh(3))(2) with [Ni(6)(CO)(12)](2)(-). Their crystal structures as [PPh(4)](+) salts were unambiguously determined from CCD X-ray crystallographic analyses; the resulting stoichiometries were ascertained from elemental analyses. Infrared, multinuclear (1)H, (31)P[(1)H] NMR, UV-vis, CV, variable-temperature magnetic susceptibility, and ESI FT/ICR mass spectrometric measurements were performed. The Pd(16)Ni(4) core of 1 ideally conforms to a ccp nu(3) tetrahedron of pseudo-T(d)() (4 3m) symmetry. Its geometry normal to each tetrahedral Pd(7)Ni(3) face (i.e., along each of the four 3-fold axes) may be viewed as a four-layer stacking of 20 metal atoms in a ccp [a(Ni(1)) b(Pd(3)) c(Pd(6)) a(Pd(7)Ni(3))] sequence. A comparative analysis of the different ligand connectivities about the analogous metal-core geometries in 1 and the previously reported [Os(20)(CO)(40)](2)(-) has stereochemical implications pertaining to the different possible modes of carbon monoxide attachment to ccp metal(111) surfaces. The unique geometry of the Pd(33)Ni(9) core of 2, which has pseudo-D(3)(h)() (6 2m) symmetry, consists of five equilateral triangular layers that are stacked in a hcp [a(Pd(7)Ni(3)) b(Pd(6)) a(Pd(7)Ni(3)) b(Pd(6)) a(Pd(7)Ni(3))] sequence. Variable-temperature magnetic susceptibility measurements indicated both 1 and 2 to be diamagnetic over the entire temperature range from 5.0 to 300 K. Neutral Pd(12)(CO)(12)(PPh(3))(6) (3) and [Pd(29)(CO)(28)(PPh(3))(7)](2)(-) (4) as the [PPh(4)](+) salt were obtained as minor decomposition products from protonation reactions of 1 and 2, respectively, with acetic acid. Compound 3 of pseudo-D(3)(d)() (3 2/m) symmetry represents the second highly deformed hexacapped octahedral member of the previously established homopalladium family of clusters containing uncapped, monocapped, bicapped, and tetracapped Pd(6) octahedra. The unprecedented centered 28-atom polyhedron for the Pd(29) core of 4 of pseudo-C(3)(v)() (3m) symmetry may be described as a four-layer stacking of 29 metal atoms in a mixed hcp/ccp [a(Pd(1)) b(Pd(3)) a(Pd(10)) c(Pd(15))] sequence.     

In-situ UV-visible study of Pd nanocluster formation in solution

The formation of Pd nanoclusters in solution is studied. This system has two types of light-absorbing species: Pd ions which absorb light via electronic transitions and Pd clusters and aggregates which absorb light via valence-conduction transitions and also scatter light due to their nanometric dimensions. Here we monitor these dynamic changes using UV-visible spectroscopy. The reduction and clustering concentration profiles are extracted from the raw data using a combination of net analyte signal (NAS) and principal component analysis (PCA) methods. PdCl2, Pd(OAc)2 and Pd(NO3)2 are used as Pd2+ precursors and various tetra-n-octylammonium carboxylates are applied as reducing and stabilising agents. This in situ approach enables the quantification of both the reduction of the Pd2+ ions and the growth of the Pd clusters. Kinetic models that account for ion reduction, cluster growth and aggregation are presented and the influence of the counteranions and the reducing agents on these processes is discussed.     

改进的罗丹明类钯离子荧光分子探针

用罗丹明B与水合肼反应生成的中间体与溴丙炔反应合成了荧光增强型Pd2+检测用探针RPd5。 与Pd2+结合后,RPd5的吸收及荧光强度明显增强,其荧光强度增强约40倍,并使检测时间缩短至约16 min。 探针RPd5对Pd2+的响应灵敏,最低检出限为2.31×10-6 mol/L,可以在较宽pH值范围内特别是近中性pH值环境下有效检测Pd2+。 RPd5可以实现对Pd2+以比色及荧光2种途径的可视化识别,并可应用于土壤、池塘水等实际样品中痕量Pd2+的检测。 RPd5还可制成试纸用于纯净水中Pd2+检测。     

Di- and tetranuclear palladium complexes incorporating phospha- and diphosphaferrocenes as ligands

Monophosphaferrocenes and 4 react with [Pd(COD)Cl2] (COD = cyclooctadiene) to afford cis- [Pd(1 or 4)2Cl2] complexes that slowly decompose in solution to give dimeric complexes 3 and 6 of general formula [[Pd(1 or 4)Cl]2]. In these dimers, which incorporate a Pd-Pd bond, phosphaferrocenes act as four electron donors through the phosphorus-atom lone pair (mu2-bonded) and through one orbital of appropriate symmetry at iron. These dimers can also be more conventionally prepared from the reaction of cis- [Pd(1 or 4) Cl2] complexes with [Pd(dba)2] (dba = dibenzylidene acetone). The reaction of octaethyldiphosphaferrocene (7) with [Pd(COD)Cl2] yields a dinuclear complex [Pd2(7)2Cl4] (8) in which the two ligands 7 are coordinated in a trans fashion through the phosphorus-atom lone pairs. Decomposition of 8 in solution yields a dimeric dicationic complex of general formula [[Pd2(7)2Cl]2]2+[FeCl4]2- (9a) incorporating four palladium atoms. In each ligand. one phospholyl ring behaves as a two-electron donor through the phosphorus-atom lone pair whereas the second binds two palladium centers in a mu2-fashion. A plausible mechanism that explains the formation of dimers 3, 6, and 9a involves the preliminary oxidation of the mono- or diphosphaferrocene ligand. Parallel experiments aimed at confirming this hypothesis have shown that complex 9a can be synthesized from the reaction of FeCl2 with complex 8. Also presented is another synthetic approach to the synthesis of the tetranuclear complex 9b (counterion is GaCl4-) from the reaction of the palladium(0) complex [Pd(7)2] (10) with [Pd(COD)Cl2] the presence of GaCl3 as chloride abstractor.     

Searching for precursors to metal-metal bonded dipalladium species: a study of Pd2(4+) complexes

Reactions of Pd3(OAc)6 with lithium salts of mononegative bidentate N,N-ligands, L, of various types, such as formamidinates, benzamidinates, triazinates, and guanidinates, were investigated in a search for ways to obtain Pd2(4+) compounds that could serve as precursors to paddlewheel complexes with a metal-metal bond and a Pd2(5+) core. It was found that the reactions are complex and that either square planar mononuclear or dinuclear species may be formed depending on the reaction conditions or the method of isolation. For Pd2L4 compounds, alpha and beta isomers were sometimes obtainable. In the alpha isomer, all N,N-ligands serve as bridges, whereas in the beta isomer, two ligands bridge the Pd2(4+) unit and each of the other two chelate to a metal atom. Electrochemistry shows that the paddlewheel compounds Pd2(TolNC(H)NTol)4, Pd2(PhNC(Ph)NPh)4, and Pd2(PhNC(Ph)NPh)3(OAc) and the orthometalated complex cis-Pd2[eta2-C6H4NC(Ph)N(H)Ph]2(mu-OAc)2 have reversible oxidation waves between 0.70 and 0.92 V vs Ag/AgCl, which makes them good candidates for chemical oxidation.     

Pd/C催化剂用于CO2电化学还原生成CO:Pd载量的影响

CO₂电化学还原反应可以将CO₂转化为燃料并同时实现再生能源的有效存储. 目前纳米结构的多相催化剂已经广泛应用于此反应,其中碳负载钯纳米粒子（Pd/C）表现出优异的CO₂电化学还原性能. 本工作研究了钯载量对于Pd/C催化剂结构以及其催化CO₂还原生成CO反应活性和选择性的影响. 不同载量的Pd/C催化剂通过液相还原方法制备,钯纳米粒子均匀地分散在碳载体上,载量并没有明显改变对纳米粒子的粒径. 在优选的电解质（0.1 mol·L^-1 KHCO₃）中,CO法拉第效率与载量呈现火山型曲线关系,-0.89 V时载量为20wt%的Pd/C催化剂达到最高的CO法拉第效率(91.2%). 生成CO的几何电流密度随着钯载量的增加而增加,但CO转换频率具有相反的趋势,载量为2.5wt%的Pd/C催化剂具有最高的转换频率. 这种载量对CO₂电化学还原反应活性和选择性的影响主要由活性位的数量、反应动力学、中间物种的稳定性以及反应物、中间物种和产物的传质过程等共同决定.