WxC/SBA-16催化剂的制备、表征及催化加氢脱硫性能

以正硅酸乙酯为硅源, 仲钨酸铵为钨源, P123和F127为混合模板剂,采用水热晶化法一步合成了不同钨含量(以n(Si):n(W)表示)的WO3/SBA-16, 然后经甲烷/氢气(V(CH4)/V(H2)=1/4)混和气体程序升温还原碳化(TPC), 制备出了WxC/SBA-16(x=1, 2)催化剂. 采用XRD、N2-吸附/脱附、TEM和FTIR等分析测试技术对样品的结构进行了表征, 并以噻吩作为模型化合物, 对WxC/SBA-16催化剂的加氢脱硫催化活性进行了评价. 结果表明, 在一定钨含量的条件下, WO3/SBA-16和WxC/SBA-16样品仍然保持立方笼状介孔结构, 当n(Si):n(W)为30-10时, 碳化钨的物相为W2C; n(Si):n(W)为7.5时, 碳化钨的物相为W2C和WC. WxC/SBA-16催化剂表现出了良好的加氢脱硫催化性能.     

双核钨簇合物W2Cl4（OR）4（ROH）2结构的EXAFS研究

我们曾用EXAFS和X射线单晶衍射研究了M_3W_2Cl_9类双钨簇合物的结构,发现簇胳[W_2Cl_9]~(3-)的结构很牢固,改变阳离子M~+的性质和大小,都不会改变其结构。W_2Cl_9(RO)_4(R′OH)_2类簇合物与M_3W_2Cl_9类似,具有一个双钨簇胳。Anderson等曾研究R为甲基或乙基的两个簇合物的单晶结构,正四价的两个钨原子间用双键及两个氧桥键相联接。与M_3W_2Cl_9另一不同处是取代基RO及R′OH与钨原子直接相联,其间还形成氢键,故RO或R′OH对簇胳的影响要大于M_3W_2Cl_9中阳离子M~+。本文合成6种具有不同取代基的W_2Cl_4·(RO)_4(ROH)_2化合物,用EXAFS研究其结构,以期了解不同取代基对簇胳结构的影响。     

纳米晶WC-Co-Ni复合材料的制备及其电催化性能

采用喷雾干燥-气固反应法制备了具有介孔结构的纳米晶碳化钨-钴-镍(WC-Co-Ni)复合材料. 通过XRD, SEM, EDS和粒径分析等测试手段对样品的形貌、物相组成、化学成分、粒径分布进行了表征, 采用线性扫描法对WC-Co-Ni复合材料在氢析出反应中的电催化性能进行了评价. 结果表明, WC-Co-Ni复合材料由缺碳六方WC相、立方Co相和立方Ni相组成, 化学成分为W, C, Co和Ni, W与C的原子比接近1∶1; WC-Co-Ni复合材料具有空心球状或层状形貌, 其表面具有介孔结构; 样品颗粒的粒径集中分布在3～30 µm, 该区间内样品分布呈单分散性, 其中位径(d50)为10 µm; 在碱性溶液中, 复合材料对氢析出反应的电催化性能明显强于具有介孔结构的碳化钨样品.     

核壳结构碳化钨/碳化钨铁复合材料的制备与电催化活性

以铁黄为载体,偏钨酸铵为钨源,将直接包覆与原位还原碳化技术相结合制备了碳化钨/碳化钨铁复合材料.经X射线衍射(XRD)分析和透射电子显微镜(TEM)观察,复合材料的主要物相为碳化钨铁(Fe3W3C)、碳化钨(WC)和碳化二钨(W2C),且构成了以Fe3W3C为核、WC和W2C为壳的核壳结构.采用三电极体系循环伏安法测试了复合材料在酸性、中性和碱性体系中对甲醇的电催化氧化活性.结果表明,与颗粒状碳化钨和介孔空心球状碳化钨相比,复合材料的电催化活性有了明显的提高;进一步研究发现,复合材料的电催化活性不仅受到体系性质的影响,还与其物相组成和微结构相关.上述结果说明,通过控制复合材料的物相组成及微结构,以及反应体系的性质可实现对其电催化活性的调控;同时表明,核壳结构是提高碳化钨催化材料活性的有效途径之一.     

[WNCl3 · 0,5 HN3]4; Kristallstruktur und IR-Spektrum

[WNCl₃ · 0.5 HN₃]₄: Crystal Structure and I.R. Spectrum [WNCl₃ · 0.5 HN₃]₄ is formed from tungsten hexachloride and iodine azide in dichloro methane solution yielding dark red and needleshaped crystals. The crystal structure was determined by aid of X-ray diffraction data. The compound crystallises in the triclinic space group P1 with one formula unit per unit cell (R = 0.08, 2 811 independent reflexions). The four metal atoms are arranged in a square, the edges being formed by almost linear W?N? W bridge bonds of alternating length (168 and 210 pm). Two opposite tungsten atoms are coordinated by theαN atom of a HN₃ molecule and by three terminal chloro ligands. The other tungsten atoms achieve coordination number 6 by two terminal and two bridging Cl atoms, linking the tetrameric units to bands along [010]. The i.r. spectrum is reported and assigned.     

合成聚苯胺/碳化钨复合材料及聚合机理探讨

采用在原位聚合苯胺的反应介质中分散碳化钨(WC)的方法制备了掺杂聚苯胺/碳化钨(PANI/WC)复合物,并研究了苯胺在WC表面的聚合机理.通过扫描电镜(SEM)、透射电镜(TEM)、傅立叶红外光谱(FTIR)、拉曼光谱(Raman)和X射线衍射(XRD)对复合物进行了表征.结果表明,苯胺的聚合倾向于在WC颗粒表面进行,形成了PANI包覆WC的复合材料;WC粒子与PANI大分子之间存在强的相互作用,并且复合前后WC的晶型并未发生变化,WC的存在导致红外光谱有明显的蓝移现象,复合后在3446 cm-1处的红外吸收峰变得很弱;在拉曼光谱中,代表醌环C N键的伸缩振动峰红移了9 cm-1,并且强度也有很大程度提高.说明PANI与WC之间有化学键的作用,它们之间的化学键作用发生在C N键的N原子上.聚合反应优先在WC粒子表面进行,生成PANI包覆结构,并提出了PANI/WC复合物的形成机制.     

碳化钨/碳化二钨核壳结构纳米复合材料的制备及电化学性能

以偏钨酸铵为钨源, 铁黄(FeOOH)为载体, 将表面包覆法与原位还原碳化技术相结合, 制备出了具有核壳结构的碳化钨(WC)/碳化二钨(W₂C)纳米复合材料; 应用X射线衍射(XRD)分析、透射电子显微镜(TEM)和X射线能量散射谱(EDS)等手段对不同阶段样品的晶相、形貌、微结构和化学组成等特征进行了表征. 结果表明, 负载体经煅烧后, 载体及包裹层的物相均发生了变化, 形貌也相应地发生了改变; 经盐酸处理及还原碳化后, 样品由WC和W₂C纳米颗粒构成, 并构成了以W₂C为壳, 以WC为核的典型核壳结构; 结合表征结果对核壳结构的形成机理进行了探讨. 采用三电极体系循环伏安法测试了样品在酸性、中性和碱性溶液中对甲醇的电催化氧化活性. 结果表明, 与颗粒状碳化钨和介孔空心球状碳化钨相比, 样品的电催化活性有了明显的提高. 这说明W₂C与WC构成核壳结构纳米复合材料后, 其电化学性能有了明显的提升, 核壳结构纳米复合材料是提高碳化钨催化材料活性的有效途径之一.     

Crystal structure and carbon vacancy hardening of (W0.5Al0.5)C1-x prepared by a solid-state reaction.

Novel solid solutions of aluminum in tungsten carbide (WC) with or without carbon vacancies, which can be expressed by the chemical formula (W(0.5)Al(0.5))C(1-x) (x=0.0-0.5), have been synthesized by the solid-state reaction of W(0.5)Al(0.5) alloy and the proper amount of carbon at around 1673 K in vacuum. The reaction time decreases from 73 to 50 h on increasing the carbon vacancy concentration from 0 to 50 %. The formation of the intended products is certified, by X-ray diffraction, environmental scanning electron microscopy-energy-dispersive X-ray analysis, and inductively coupled plasma-atomic emission spectroscopy, even though the carbon vacancy concentration reaches the astonishing value of 50 %. The as-prepared (W(0.5)Al(0.5))C(1-x) samples have been identified as the hexagonal WC-type structure belonging to the space group P6m2 (Z=1). Moreover, the crystallographic results reveal that the substituting aluminum atoms in the WC are located in the 1a site (the W atom position of the WC structure) and the cell parameters decrease slightly with increasing vacancy concentration. The hardness of the (W(0.5)Al(0.5))C(1-x) system increases up to a maximum 2659 kg mm(-2) at a carbon vacancy concentration of about 35 %, and the density of (W(0.5)Al(0.5))C(1-x) is far lower than that of WC.     

Tungsten carbide nanocrystal promoted Pt/C electrocatalysts for oxygen reduction

Tungsten carbide nanocrystals on carbon (W2C/C) and tungsten carbide nanocrystals and Pt on carbon (Pt-W2C/C) composite electrocatalysts were prepared by the intermittent microwave heating (IMH) method and tested for the electroreduction of oxygen in the acidic media for the first time. The results revealed that the tungsten carbide nanocrystal promoted Pt/C electrocatalyst was very active for ORR with the onset potential of 1.0 V vs SHE at ambient temperature that is over 100 mV more positive compared with that of traditional Pt/C electrocatalyst. The kinetic parameters were determined. The exchange current densities at both high and low overpotential regions are two orders higher for ORR on Pt-W2C/C than that on Pt/C, showing a synergetic effect to improve the activity for ORR. The novel electrocatalysts show a poisoning resistant property toward methanol.     

Effect of Nb,Ti, and W ion implantation on surface properties and cell compatibility of silicon carbide

Silicon carbide is considered as a bio-inert semiconductor material; consequently, it has been proposed for potential applications in human body implantation. In this study, we study the effect of implanting different metal ions on the surface properties of silicon carbide single crystal. The valence states of the elements and the surface roughness of implanted SiC were studied using X-ray photoelectron spectroscopy and atomic force microscope, respectively. Osteoblastic MG-63 cells were utilized to characterize the cytocompatibility of ion implanted SiC. The results show that after Nb ion implantation on the SiC surface, it mainly exists in the form of Nb–C bond, Nb–O bond, and a small amount of metallic niobium. The titanium implanted on SiC primarily forms Ti-C bond and Ti-O bond. The tungsten implanted on SiC mostly presents as metallic tungsten and W–O bond. The roughness of silicon carbide single crystal is improved by ion implantation of all three metal ions. Ion implantation of titanium and niobium can improve the cell compatibility and hydrophilicity of silicon carbide, whereas ion implantation of tungsten reduces the cell compatibility and hydrophilicity of silicon carbide.     

Morphological and chemical characteristics of airborne tungsten particles of Fallon, Nevada.

Morphological and chemical characteristics were determined for airborne tungsten particles in Fallon, Nevada, a town that is distinguishable environmentally by elevated airborne tungsten and cobalt. From samples of airborne dust collected previously at six different places in Fallon, tungsten-rich dust particles were isolated and analyzed with automated electron microprobe and wavelength-dispersive spectrometry. Representative W particles were further analyzed using transmission electron microscopy. Morphologically, Fallon W particles are angular and small, with minimum and maximum sizes of < or = 1 microm and 5.9 microm in diameter, respectively. The number and size of tungsten-rich particles decrease in Fallon with distance from a hard-metal facility located near the center of town. Chemically, Fallon airborne W particles include mixtures of tungsten with cobalt plus other metals such as chromium, iron, and copper. No W-rich particles were identifiable as CaWO4 (scheelite) or MnWO4 (huebnerite). From d-spacings, Fallon particles are most consistent with identification as tungsten carbide. Based on these multiple lines of evidence, airborne W particles in Fallon are anthropogenic in origin, not natural. The hard-metal facility in Fallon processes finely powdered W and W-Co, and further investigation using tracer particles is recommended to definitively identify the source of Fallon's airborne tungsten.     

The crystal and molecular structure of tetracarbonyl(6-p-styryl-2,2′-bipyridyl)tungsten(0). An examination of the affect of a bulky group α to one coordinating nitrogen atom in a bidentate ligand

The crystal and molecular structure of tetracarbonyl(6-p-styryl-2,2′-bipyridyl)tungsten(0) have been determined by single crystal X-ray techniques. Cell dimensions are a 13.735(17), b 8.839(6) and c 17.105(12) Å for the monoclinic unit cell with β 109.06(8)° and Z = 4. The space group was determined as P2₁/n. The structure was solved by conventional Patterson and Fourier methods and refined to a final R-value of 0.055 (1734 unique reflections) by block diagonal least squares. The molecule consists of monomeric units containing one tungsten atom bound to four terminal carbonyl groups and to one 6-p-styryl-2,2′-bipyridyl ligand via its two nitrogen atoms. The presence of the styryl group α to one coordinating nitrogen causes a significant difference in the bond lengths between the central tungsten atom and the nitrogen atoms (WN(1), 2.29(1) Å; WN(2) 2.23(1) Å).     

Geometries and properties of bimetallic phosphido-bridged complex Cp(CO)2W(μ-PPh2)W(CO)5 and Cp(CO)3W(μ-PPh2)W(CO)5

Complete geometry optimizations were carried out by HF and DFT methods to study the molecular structure of binuclear transition-metal compounds (Cp(CO)₃W(μ-PPh₂)W(CO)₅) (I) and (Cp(CO)₂W(μ-PPh₂)W(CO)₅) (II). A comparison of the experimental data and calculated structural parameters demonstrates that the most accurate geometry parameters are predicted by the MPW1PW91/LANL2DZ among the three DFT methods. Topological properties of molecular charge distributions were analyzed with the theory of atoms in molecules. (3, −1) critical points, namely bond critical point, were found between the two tungsten atoms, and between W1 and C10 in complex II, which confirms the existence of the metal–metal bond and a semi-bridging CO between the two tungsten atoms. The result provided a theoretical guidance of detailed study on the binuclear phosphido-bridged complex containing transition metal–metal bond, which could be useful in the further study of the heterobimetallic phosphido-bridged complexes.     

掺氮碳化钨的制备及其电催化性能的研究

碳化钨是一种具有应用前景的电催化剂,本文尝试对碳化钨的非金属位进行氮掺杂,以钨酸钠为钨源,经由中间体氮化钨（WN）,并在一氧化碳气体中进行渗碳后合成掺氮的碳化钨纳米片（WN|WC）. 通过扫描电镜（SEM）和透射电镜（TEM）观测发现,WN|WC纳米片尺寸均匀,碳原子进入WN晶格中形成具有密排六方结构的WC晶相,并和WN的晶格条纹紧密联结而形成异质结构. X射线衍射（XRD）结果显示碳化后的样品中含有WN和WC两种晶型,XPS结果进一步表明WN|WC表面形成了WN和WC的异质结构. 为讨论氮元素掺杂对电催化性能的影响,本文通过微波辅助加热法负载少量铂制备Pt/WN|WC催化剂,并以甲醇氧化为指针反应,纯相碳化钨和商用铂碳材料（Pt/C）等为对比样,评价了Pt/WN|WC催化剂的电化学性能. 电化学测试表明,该催化剂甲醇氧化的电流密度是商业Pt/C的3倍,具有较高的交换电流密度和速率常数,且经过200周的循环伏安扫描后,正扫峰电位（Ep_f）和负扫峰电位（Ep_b）仍保持稳定,结果表明氮的掺杂改变了碳化钨表面的电子状态,形成了WN和WC的异质界面,有利于催化性能的提高.     

Local environment of tungsten in mixed valence tungsten phosphate glasses: An EXAFS study

The local order around tungsten atoms in some phosphotungstate glasses of the K₂OP₂O₅WO_3−x system was studied by EXAFS and X-ray diffusion techniques. From a previous work by EPR and optical spectra, an axially distorted octahedral environment was deduced around tungsten in these glasses. In agreement with this result, EXAFS shows that the structure of the phosphotungstate glasses is built up of distorted WO₆ octahedra joined by corners with PO₄ tetrahedra: long WO distances can be associated with WOP bonds and short WO distances with WOW bonds as was already observed in crystallized phosphotungstates. X-Ray diffusion shows that even for large WO₃ contents, WO₆ octahedra are predominantly joined by corners.     

Preparation of Nano-crystalline Tungsten Carbide Thin Film by Magnetron Sputtering and Their Electrocatalytic Property for PNP Reduction

Nano-crystalline tungsten carbide thin films were deposited on Ni substrates by magnetron sputtering using WC as target material. The crystal structure and morphology of the thin films were characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM） Electrochemical investigations showed that the electrode of the thin film exhibited higher electrocatalytic activity in the reaction of p-nitrophenol （PNP） reduction. FT-IR analysis indicated that p-aminophenol （PAP） was synthesized after two step reduction of PNP on nano-crystalline tungsten carbide thin film electrode.     

Synthese und Kristallstruktur von [WNCl3 · NC–Ph]4 · 3 CH2Cl2

Synthesis and Crystal Structure of [WNCl₃ · NCPh]₄ · 3 CH₂Cl₂ The adduct of tungsten nitride trichloride with benzonitrile, [WNCl₃ · NCPh]₄, is formed by the reaction of N,N,N'-tris(trimethylsilyl)benzamidine and tungsten hexachloride in CCl₄ solution. It forms red crystal needles and was characterized by its IR spectrum and an X-ray crystal structure determination (1983 unique observed reflexions, R = 0.075). Crystal data: a = 1464.8, b = 1902.6, c = 2033.8 pm, β = 102.27°, space group C2/c, Z = 4. In the [WNCl₃ · NCPh]₄ molecule the tungsten atoms were located at the vertices of a square and are linked with one another via linear W?N? W nitrido bridges with alternating short and long bonds having average lengths of 166 and 211 pm. The N atoms of the benzonitrile ligands are in the positions trans to the W?N bonds at distances of 237 pm.     

WC/纳米碳管复合材料制备及其电化学性能

碳化钨具有类铂催化性能和较强的抗中毒能力, 但其催化活性远低于铂等贵金属催化剂. 如何提高其催化活性是碳化钨应用研究所面临的主要难点与热点之一. 为寻找改善碳化钨催化性能的技术方法, 本文将表面修饰与原位还原碳化技术相结合, 成功制备了碳化钨/纳米碳管复合材料, 采用XRD, HRTEM等手段对其形貌和晶相组成进行了表征, 并应用粉末微电极对其电催化性能进行了评价. 实验结果表明, 样品由碳化钨颗粒和纳米碳管组成, 碳化钨为形态不规则纳米颗粒, 均匀地生长于纳米碳管的外表面; 在碱性溶液中, 复合材料对对硝基苯酚的电催化性能明显强于具有介孔结构的纯碳化钨样品. 这说明将碳化钨复合到纳米碳管的外表面是提高碳化钨电催化活性的有效技术方法之一.     

A strategy for the analysis of chiral polyoxotungstates by multinuclear (31P, 183W) NMR spectroscopy applied to the assignment of the 183W NMR spectra of alpha1-[P2W17O61]10- and alpha1-[YbP2W17O61]7-

This paper describes the complete assignment of the 183W NMR spectra of the chiral polyoxometalates alpha1-[P2W17O61]10- and alpha1-[YbP2W17O61]7- in aqueous solution. These spectra display each 17 lines of equal intensity with a relatively narrow chemical shift distribution. The identification of signals is based on selective 31P-183W decoupling and recognition of particular sets of coupling constants for tungsten atoms around the lacunary site. Further assignment is obtained by 183W 2D-COSY NMR experiments. We demonstrate herewith a new way for the unambiguous assignment of 183W NMR spectra of polyoxotungstates without any symmetry elements or tungsten atoms in special positions. This way relies on the correlation of the magnitude of 2J(W-W) coupling constants with the geometry of oxo-bridges in polyoxotungstates. These results open the way to monitor interaction sites of chiral polyoxotungstates with organic ligands.     

A new class of electrocatalysts for hydrogen production from water electrolysis: metal monolayers supported on low-cost transition metal carbides

This work explores the opportunity to substantially reduce the cost of hydrogen evolution reaction (HER) catalysts by supporting monolayer (ML) amounts of precious metals on transition metal carbide substrates. The metal component includes platinum (Pt), palladium (Pd), and gold (Au); the low-cost carbide substrate includes tungsten carbides (WC and W(2)C) and molybdenum carbide (Mo(2)C). As a platform for these studies, single-phase carbide thin films with well-characterized surfaces have been synthesized, allowing for a direct comparison of the intrinsic HER activity of bare and Pt-modified carbide surfaces. It is found that WC and W(2)C are both excellent cathode support materials for ML Pt, exhibiting HER activities that are comparable to bulk Pt while displaying stable HER activity during chronopotentiometric HER measurements. The findings of excellent stability and HER activity of the ML Pt-WC and Pt-W(2)C surfaces may be explained by the similar bulk electronic properties of tungsten carbides to Pt, as is supported by density functional theory calculations. These results are further extended to other metal overlayers (Pd and Au) and supports (Mo(2)C), which demonstrate that the metal ML-supported transition metal carbide surfaces exhibit HER activity that is consistent with the well-known volcano relationship between activity and hydrogen binding energy. This work highlights the potential of using carbide materials to reduce the costs of hydrogen production from water electrolysis by serving as stable, low-cost supports for ML amounts of precious metals.