UHV Studies of Methanol Decomposition on Mono‐ and Bimetallic CoPd Nanoparticles Supported on Thin Alumina Films

Bimetallic nanoparticles often turn out to be superior to the corresponding monometallic systems with respect to their catalytic properties. To study such effects for the methanol decomposition reaction, model catalysts were prepared by physical vapor deposition of Pd and Co under ultrahigh‐vacuum (UHV) conditions. Monometallic Pd and Co particles as well as CoPd core–shell particles were generated on an epitaxial alumina film grown on NiAl(110). The interaction with methanol is examined by temperature‐programmed desorption of methanol and carbon monoxide and by X‐ray photoelectron spectroscopy. The decomposition of methanol proceeds in two reaction pathways independent of the particle composition: complete dehydrogenation towards carbon monoxide and hydrogen, and C? O bond scission yielding carbon deposits. Pd is the most active material studied here. The relative importance of the two channels varies for the different particle systems: on Pd dehydrogenation is preferred, whereas the C? O bond cleavage is more pronounced on Co. The bimetallic clusters show a moderate performance for both pathways. Carbon deposition poisons the model catalysts by blocking the adsorption sites for methoxide, which is the first intermediate product during methanol decomposition. In particular on Co, large amounts of carbon deposits can also be caused by dissociation of the final product of the dehydrogenation pathway, carbon monoxide. A comparison with the results of methanol decomposition on Co, Pd, and CoPd catalysts in continuous‐flow reactors demonstrates that the findings of the present UHV study are relevant for catalytic performance under high‐pressure conditions.     

硫化钴改性石墨炔构建S型异质结高效光催化产氢

石墨炔(GDY,g-CnH2n-2)作为一种新型的由sp和sp2杂化的碳原子构成的二维碳材料,因其独特的纳米级孔隙、二维层状共轭骨架结构及半导体性质等特性,使之在能源、电化学、光催化、光学、电子学等诸多领域具有显著优势.它作为一种具有良好的层状结构的新型碳材料,其可调节的电子结构弥补了石墨烯无明显带隙的缺点,有望在光催...     

Autoreduction of Pd-Co and Pt-Co cyanogels: exploration of cyanometalate coordination chemistry at elevated temperatures

Cyanogels are coordination polymers made from the reaction of a chlorometalate and a cyanometalate in aqueous solution, which undergo a sol-gel transition to form stable gels. At temperatures above 240 degrees C, the cyanide ligand acts as a reducing agent and reduces the metal centers to lower oxidation states. To understand the mechanism of the autoreduction, the thermal reduction of the Pd-Co cyanogel system formed by the reaction of PdCl4(2-) and Co(CN)6(3-) was studied in an inert atmosphere. It was found that the reduction proceeds through two polymeric cyanide-containing intermediates, CoPd(CN)4 and Pd(CN)2, that form upon reduction of Co(3+) to Co(2+) and involves a significant rearrangement of the coordination structure. The two intermediates upon further heating reduce to metallic products, which by solid-state diffusion form a single Pd/Co alloy product. CoPd(CN)4 was found to have a hydrated form Co(H2O)2Pd(CN)4 x 4 H2O with a layered structure crystallizing in an orthorhombic Pnma space group. The Pt-Co cyanogel was found to autoreduce via a similar route. CoPt(CN)4 was confirmed as an intermediate. Understanding of the mechanism of the cyanogel autoreduction is an important step toward better understanding of opportunities that cyanogels offer in materials chemistry, as well as an expansion of the knowledge of coordination chemistry at elevated temperatures in general.     

Cooperative Effect of Two Metals: CoPd(OAc)4‐Catalyzed CH Amination and Aziridination

The first Co/Pd‐cocatalyzed intramolecular C?H amination and aziridination reactions were developed. Sulfamate esters were converted to oxathiazinanes by using CoPd(OAc)₄ as catalyst and PhI(OAc)₂ as oxidant. The mutual presence of both Co and Pd is crucial for the catalytic activity. This combination of two metals with simple acetate ligands provides an economical alternative to the Rh‐catalyzed insertion of nitrenoids into C?H bonds.     

Synthesis of Co4S3/Co9S8 nanosheets and their Fe/Cr dual heteroatom co-doped components for the promoted OER properties

Journal of Solid State Electrochemistry - Co4S3/Co9S8 nanosheets, Co-based sulfides with mixed crystalline phase, were first successfully prepared via solvothermal approach combined with ultrasonic...     

CoPd Nanoalloys with Metal–Organic Framework as Template for Both N-Doped Carbon and Cobalt Precursor: Efficient and Robust Catalysts for Hydrogenation Reactions

In this work, a series of metal–organic framework (MOF)-derived CoPd nanoalloys have been prepared. The nanocatalysts exhibited excellent activities in the hydrogenation of nitroarenes and alkenes in green solvent (ethanol/water) under mild conditions (H₂ balloon, room temperature). Using ZIF-67 as template for both carbon matrix and cobalt precursor coating with a mesoporous SiO₂ layer, the catalyst CoPd/NC@SiO₂ was smoothly constructed. Catalytic results revealed a synergistic effect between Co and Pd components in the hydrogenation process due to the enhanced electron density. The mesoporous SiO₂ shell effectively prevented the sintering of hollow carbon and metal NPs at high temperature, furnishing the well-dispersed nanoalloy catalysts and better catalytic performance. Moreover, the catalyst was durable and showed negligible activity decay in recycling and scale-up experiments, providing a mild and highly efficient way to access amines and arenes.     

Metal/metal sulfide functionalized single-walled carbon nanotubes: FTO-free counter electrodes for dye sensitized solar cells

The use of single-walled carbon nanotubes (CNT) thin films to replace conventional fluorine-doped tin oxide (FTO) and both FTO and platinum (Pt) as the counter electrode in dye sensitized solar cells (DSSC) requires surface modification due to high sheet resistance and charge transfer resistance. In this paper, we report a simple, solution-based method of preparing FTO-free counter electrodes based on metal (Pt) or metal sulfide (Co(8.4)S(8), Ni(3)S(2)) nanoparticles/CNT composite films to improve device performance. Based on electrochemical studies, the relative catalytic activity of the composite films was Pt > Co(8.4)S(8) > Ni(3)S(2). We achieved a maximum efficiency of 3.76% for the device with an FTO-free counter electrode (Pt/CNT). The device with an FTO- and Pt-free (CoS/CNT) counter electrode gives 3.13% efficiency.     

Contributions to the Chemistry of Silicon—Sulphur Compounds. 66. Synthesis,crystal and molecular structure of bis(tri-tert-butoxysilanethiolato)(acetonitrile)cobalt(II)[(t-C4H9O)3SiS]2Co(NCCH3)

The title compound [(t-C₄H₉O)₃SiS]₂Co(NCCH₃)] 1 was obtained by reaction of anhydrous cobalt(II) chloride with tri-tert-butoxysilanethiol and triethylamine in acetonitrile as a solvent. The compound crystallizes as deep-blue orthorhombic plates with a = 17.779(4), b = 45.363(9), c = 9.096(2) Å, space group Fdd2 and Z = 8. The structure was solved by Patterson synthesis and refined to the R value of 0.0343. The crystal consists of mononuclear complexes in which the cobalt atom is five-fold coordinated to two sulphurs, two oxygens and one nitrogen in a distorted trigonal bipyramidal arrangement. The relevant bond distances and angles are: Co? S, 2.2680(7); Co? N, 2.065(4); Co? O1, 2.283(2); S? Si, 2.0666(8) Å; S? Co? S′, 119.14(4); N? Co? S, 120.43(2); O1? Co? O1′, 178.81(10)°.     

Fe/Co和Ni/Co镍黄铁矿型析氢反应电催化剂

作为析氢反应的电催化剂,富金属的过渡金属硫化物因能克服富硫金属催化剂所存在的如导电性有限和缺乏必要的纳米结构等不足,近年来受到越来越多的关注.本文介绍了具有镍黄铁矿型结构的三元富金属硫化物复合材料FexCo9-xS8和NiyCo9-yS8(x=y=0-4.5)的合成、表征及其电催化研究.首先,研究了二元钴化合物Co9S...     

负载硫化钴纳米颗粒的N、S共掺杂石墨烯氧还原电催化剂的制备及性能

采用D-氨基葡萄糖作为Co分散剂和碳源,硫脲作为氮源和硫源,以NaCl为模板制备负载硫化钴纳米颗粒的N、S共掺杂三维石墨烯氧还原电催化剂(CoS/N/S/rGO)。CoS/N/S/rGO具有良好的氧还原反应(ORR)活性,起始电位和半波电位分别为960和815 mV,性能与商业Pt/C相当。此外,CoS/N/S/rGO表现出明显的4电子转移特性和超低的过氧化氢产率。与基于Pt/C的锌-空气电池相比,基于CoS/N/S/rGO的锌-空气电池在6 mol·L~(-1) KOH和0.2 mol~(-1) Zn(CH_3COO)_2碱性电解质中显示出更高的恒电流放电性能以及更好的稳定性。     

Narrow pore-diameter polypyrrole nanotubes

Bulk quantities of electrically conducting nanotubes of polypyrrole having narrow pore diameter (6 nm) can be synthesized rapidly by chemical oxidative polymerization of pyrrole in the presence of stoichiometric amounts of V2O5 nanofibers. The V2O5 nanofibers act as templates for polymerization and yield, as the initial product, polypyrrole nanotubes with pores filled with V2O5. The V2O5 dissolves readily in aq. 1.0 M HCl, yielding hollow polypyrrole nanotubes having conductivity of approximately 2 S/cm. As-synthesized polypyrrole nanotubes spontaneously reduce noble metal ions to the corresponding metal nanoparticles at room temperature without any capping or dispersing agents. For example, 3-5 nm size nanoparticles of Ag, Au, and Pd, etc., deposit readily on the surface of the tubes which then migrate spontaneously to the pore, and, in the case of Ag, coalesce in the core, yielding 4-8 nm diameter coaxial cables of Ag surrounded by a 20-30 nm thick polypyrrole fiber sheath.     

混合金属簇(PhC≡CPh)(PhCH=CPh)Co_3Ru(CO)_9和(PPh_3)Fe_2Co(CO)_7(NO)S的合成与表征

对于羰基混合金属簇的合成,利用配体的交换反应,制备含有不同配体的羰基混合金属簇。配体取代后的羰基金属簇的性质发生了变化,如可逆氧化还原性质,催化活性与选择性等。由于过渡金属原子的性质各不相同,配位取代反应也有很大差异,所以研究配体取代反应,制备含有不同配体的羰基过渡金属簇成为金属簇化学的重要组成部分。     

New low-temperature preparations of some simple and mixed co and ni dispersed sulfides and their chemical behavior in reducing atmosphere

A series of simple (CoS(2), Co(9)S(8), NiS(2), NiS, Ni(3)S(2)) and mixed sulfides (NiCo(2)S(4), Ni(0.33)Co(0.67)S(2), Ni(3)Co(6)S(8), CuCo(2)S(4), Cu(0.33)Co(0.67)S(2)) was prepared using low-temperature procedures. To obtain the mixed sulfides, the mixtures of the solutions of the corresponding salts were precipitated by Na(2)S and then heated in a sulfiding atmosphere at 300 degrees C. It has been found that the product phase composition depends on the sulfiding atmosphere. Using a H(2)S/Ar mixture leads to pyrite type sulfides, whereas treatment in H(2)S/H(2) flow allowed the preparation of Ni-Co and Cu-Co thiospinels. The as prepared highly dispersed single-phase materials were characterized by X-ray powder diffraction, scanning electron microscopy, temperature-programmed reduction (TPR), elemental analysis, and BET surface area measurements.     

Synthesis and characterization of highly magnetized nanocrystalline Co(30)Fe(70) alloy by chemical reduction

Co(30)Fe(70) nanoparticles with mean particle size of about 8 nm were successfully synthesized by the chemical reduction of cobalt chloride and iron chloride with borohydride as a reducing agent in aqueous solution. The composition and size of the Co(30)Fe(70) nanoparticles were optimized by controlling the molar ratio of starting materials, reaction time, and dropping rate of aqueous reducing agent. As alloy powders prepared by chemical reduction tend to be amorphous in the as-synthesized state, the as-precipitated Co(30)Fe(70) nanoparticles were heat-treated to achieve crystallinity at the different temperatures for 1 h. The Co(30)Fe(70) nanocrystallite by chemical reduction shows excellent soft magnetic behavior, such as high permeability, negligible coercivity, and high saturation magnetization like that of Co(30)Fe(70) bulk.     

Enhanced catalytic activity of ternary NiCoPd nanocatalyst dispersed on carbon nanotubes toward methanol oxidation reaction in alkaline media

Ternary NiCoPd nanocatalyst dispersed on multi-walled carbon nanotubes (CNTs), NiCoPd/CNTs, was synthesized using a simple and green sonochemical method. The as-prepared NiCoPd/CNT hybrids were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma-atomic emission spectrometry (ICP-AES). The electrochemical measurements revealed that the ternary NiCoPd/CNTs exhibited an enhanced electrocatalytic activity for the methanol oxidation reaction (MOR), much superior to those of the binary NiPd/CNT and CoPd/CNT, as well as monometallic Pd/CNT counterparts, which likely resulted from the synergistic function of the dopant metals of Ni and Co.     

Mixed iron cobalt carbonyl sulphides

Two new mixed iron cobalt carbonyl sulphide clusters HFe₂(CO)₉S and Fe₂Co(CO)₈(NO)S have been prepared and characterized. The hydride complex undergoes acidic dissociation in polar solvents and the resulting anion was isolated as (Et₄N)[Fe₂Co(CO)₉S]. An efficient high pressure synthesis has been found for H₂Fe₃(CO)₉S.     

Electrochemical preparation and structural characterization of Co thin films and their anomalous IR properties

Nanometer scale cobalt thin films of different structures and thicknesses supported on glassy carbon were prepared by electrochemical deposition under cyclic voltammetric conditions (denoted nm-Co/GC(n)). The thickness of Co thin films was altered systematically by varying the number (n) of potential cycling within a defined potential range in electrodeposition. Electrochemical in situ scanning tunneling microscopy (STM) and ex situ scanning electron microscopy (SEM) were employed to characterize the surface structure of Co thin films. It has been illustrated that the Co thin films were uniformly composed of Co nanoparticles, whose structure and size varied with increasing n. The structure of nanoparticles inside the Co thin films underwent a transition from bearded nanoparticles to multiform nanoparticles and finally to hexagonal nanosheets, accompanying with an increase of average size. In situ FTIR reflection spectroscopic studies employing CO adsorption as probe reaction revealed that the Co thin films all exhibited anomalous IR properties; that is, along with their different nanostructures they presented abnormal IR effects, Fano-like IR effects, and surface-enhanced IR absorption effects. CO adsorbed on Co thin films dominated by bearded nanoparticles yielded abnormal IR absorption bands; that is, the direction of the bands is inverted completely, with enhanced intensity in comparison with those of CO adsorbed on a bulk Co electrode. The enhancement of abnormal IR absorption has reached a maximal value of 26.2 on the nm-Co/GC(2) electrode. Fano-like IR features, which describe the bipolar IR bands with their positive-going peak on the low wavenumbers side, were observed in cases of CO adsorbed on Co thin films composed mainly of multiform nanoparticles, typically on the nm-Co/GC(8) electrode. IR features were finally changed into surface-enhanced IR absorption as CO adsorbed on the nm-Co/GC(30) electrode, on which the Co thin film is dominated by Co hexagonal nanosheets.     

Hydrothermal fabrication and characterization of polycrystalline linneite (Co(3)S(4)) nanotubes based on the Kirkendall effect

In this study, polycrystalline linneite (Co(3)S(4)) nanotubes constructed with nanoparticles have been firstly fabricated using 1D Co(CO(3))(0.35)Cl(0.20)(OH)(1.10) nanowires as the sacrificial templates under hydrothermal conditions. The samples are characterized by means of XRD and TEM. The formation mechanism of the Co(3)S(4) nanotubes can be explained by the nanoscale Kirkendall effect, which results from the difference in diffusion rates between cobalt source and hydrogen sulfide. This simple synthetic route is expected to prepare other nanomaterials with the tubular structures.     

Synthesis and molecular structures of mononitrosyl (N2S2)M(NO) complexes (M = Fe, Co)

A series of tetragonally distorted square pyramids of formula N2S2M(NO) (M = Fe, Co) is prepared and characterized by nu(NO) IR and EPR spectroscopies, magnetism and electrochemical properties, as well as solid-state crystal structure determinations. While the nu(NO) IR frequencies and the angleM-N-O angles indicate differences in the electronic environment of NO consistent with the Enemark-Feltham notation of [Fe(NO)]7 and [Co(NO)]8, the reduction potentials, assigned to [Fe(NO)]7 + e- <==> [Fe(NO)]8 and [Co(NO)]8 + e- <==> [Co(NO)]9 respectively, are very similar, and in cases identical, for most members of the series. Coupled with the potential for the M(NO) units to breathe out of and into the N2S2 core plane are unique S-M-N-O torsional arrangements and concomitant pi-bonding interactions which may account for the unusual coherence of reduction potentials within the series.     

Photoinduced Fe-Cp bond cleavage and insertion reactions of strained silicon- and sulphur-bridged [1]ferrocenophanes in the presence of transition-metal carbonyls

The photochemical reactions of the moderately strained sila[1]ferrocenophane [Fe(eta-C(5)H(4))(2)SiPh(2)] (1) and the highly strained thia[1]ferrocenophane [Fe(eta-C(5)H(4))(2)S] (8) with transition-metal carbonyls ([Fe(CO)(5)], [Fe(2)(CO)(9)] and [Co(2)(CO)(8)]) have been studied. The use of metal carbonyls has allowed the products of photochemically induced Fe-cyclopentadienyl (Cp) bond cleavage reactions in the [1]ferrocenophanes to be trapped as stable, characterisable products. During the course of these studies the synthesis of 8 from [Fe(eta-C(5)H(4)Li)(2)TMEDA] (TMEDA=N,N,N',N'-tetramethylethylenediamine) and S(SO(2)Ph)(2) has been significantly improved by a change of reaction solvent and temperature. Photochemical reaction of 1 with excess [Fe(CO)(5)] in THF gave the dinuclear complex [Fe(2)(CO)(2)(mu-CO)(2)(eta-C(5)H(4))(2)SiPh(2)] (9). The analogous photolytic reaction of 8 with [Fe(CO)(5)] in THF gave cyclic dimer [Fe(eta-C(5)H(4))(2)S](2) (10) and [Fe(2)(CO)(2)(mu-CO)(2)(eta-C(5)H(4))(2)S] (11), with the former being the major product. Photolysis of 1 with [Co(2)(CO)(8)] afforded the remarkable tetrametallic dimer [(CO)(2)Co(eta-C(5)H(4))SiPh(2)(eta-C(5)H(4))Fe(CO)(2)](2) (13). The corresponding photochemical reaction of 8 with [Co(2)(CO)(8)] gave a trimetallic insertion product in high conversion, [Co(CO)(4)(CO)(2)Fe(eta-C(5)H(4))S(eta-C(5)H(4))Co(CO)(2)] (14). These reactivity studies show that UV light promotes Fe-Cp bond cleavage reactions of both of the [1]ferrocenophanes 1 and 8. We have found that, whereas the less strained sila[1]ferrocenophane 1 requires photoactivation for Fe-Cp bond insertions to occur, the highly strained thia[1]ferrocenophane 8 undergoes both irradiative and non-irradiative insertions, although the latter occur at a slower rate. Our results suggest that such photoinduced bond cleavage reactions may be general and applicable to other related strained organometallic rings with pi-hydrocarbon ligands.