乙炔高温裂解的从头算动力学模拟

本文采用了从头算动力学结合量化计算来研究乙炔的热裂解,发现了一条通过连续乙烯基卡宾加成生成苯环的机理,并和与这条路径相竞争的路径进行了对比. 此外,还得到了乙烯基卡宾的寿命.     

Stability of the ground state vinylidene anion H2CC-

A technique to measure very low collisionless decay rates of ionic species has been applied at a new electrostatic storage ring to obtain the rate for spontaneous rearrangement of the vinylidene anion to neutral acetylene. The measurement yields a rate of k(0) = (0.009+/-0.006) s(-1), corresponding to a natural lifetime of the vinylidene anion of tau(0) approximately 110 s.     

Angle-resolved photoelectron measurements on the first two orbitals of acetylene using synchrotron radiation

The angle-resolved photoelectron spectrum of acetylene has been measured using synchrotron radiation over a range of photon energies from 12 to 28 eV.     

Ultraviolet photoemission studies of acetylene and ethylene adsorptions on the Pt(111) surface: Correlations with LEED studies

The chemisorption of acetylene and ethylene on platinum (111) surfaces for T ≥ 300 K has been studied with ultraviolet photoelectron spectroscopy (UPS) at 21.2 eV. An activated metastable-stable acetylene transition observed recently in low-energy electron diffraction (LEED) intensity-energy profiles has been seen with the UPS spectra. The upperlying electronic levels of the metastable acetylene state are related to a shifted gas-phase acetylene spectrum. The stable acetylene state appears to involve a stronger molecule-surface interaction and probable rehybridization, consistent with the LEED analysis showing the molecule to be situated in a triangular position at covalent Pt-C distances. Ethylene is founf to dehydrogenate at room temperature to the stable acetylene species on Pt(111) surfaces.     

Structural, reactive and kinetic properties of acetylene on clean Mo(100)

Acetylene adsorbs onto Mo(100) at 80 K via precursor state kinetics, saturating the chemisorbed overlayer at a coverage of 1.0. Further exposure to acetylene adsorbs multilayers, which are desorbed by heating to 100 K. Two surface species are identified using angle-resolved ultraviolet photoelectron spectroscopy after adsorbing acetylene at 80 K. One species is undistorted chemisorbed acetylene, the other is an acetylenic species which is rehybridized to approximately sp² and is adsorbed with its C-C axis oriented at 45° with respect to the surface normal. On heating this surface to above 110 K, all the chemisorbed acetylene converts into the rehybridized species. This is stable up to a surface temperature of 180 K, following which it starts to decompose. Thermal decomposition is complete by 300 K. Only hydrogen is detected in thermal desorption spectroscopy, and the spectra are characteristic of hydrogen desorption from a carbided surface.     

The interaction of acetylene with Ni(111), chemisorbed oxygen on Ni(111), and NiO(111); the formation of CH species on chemically modified Ni(111) surfaces

Ultraviolet photoelectron spectroscopy, temperature programmed thermal desorption and low-energy electron diffraction have been used to study the interaction of acetylene with a clean Ni(111) surface, with a Ni(111) surface having co-adsorbed oxygen and with an epitaxially grown NiO(111) surface produced by room temperature oxidation ofNi(111). The adsorption of a (2 × 2) overiayer of π-bonded acetylene or oxygen on the Ni(111) surface markedly alters the subsequent interaction and reaction of the surface with incident acetylene. We find that in the presence of either a (2 × 2) overiayer of oxygen or π-bonded acetylene, a new more strongly bound hydrocarbon phase forms at room temperature. We identify this new phase from its ionization levels as a CH species, and for saturation coverages we find approximately twice as many of these species as the number of π-bonded acetylene molecules in the (2 × 2) structure. Preadsorption of oxygen limits the adsorption of π-bonded acetylene but does not affect the subsequent formation of this CH species. Exposure of acetylene to NiO at room temperature produces only CH species. Based upon these results we propose idealized models for the bonding geometry of π-bonded acetylene and CH species on the Ni(111) surface. The conditions for the formation of CH species and the significance of CH species to surface reactions on Ni are also discussed.     

Photoelectron diffraction imaging for C2H2 and C2H4 chemisorbed on Si(100) reveals a new bonding configuration

A new adsorption site for adsorbed acetylene on Si(100) is observed by photoelectron imaging based on the holographic principle. The diffraction effects in the carbon 1s angle-resolved photoemission are inverted (including the small-cone method) to obtain an image of the atom's neighboring carbon. The chemisorbed acetylene molecule is bonded to four silicon surface atoms. In contrast to the C2H2 case, the image for adsorbed C2H4 shows it bonded to two Si surface atoms.     

Photoelectron diffraction study of a catalytically active overlayer: C2H2 on Pd{111}

A quantitative structure determination of a newly discovered (2×2) adsorption phase of acetylene chemisorbed on Pd{111} has been performed by scanned-energy mode photoelectron diffraction: this phase corresponds to the threshold coverage for the catalytic conversion of acetylene to benzene. The carbon atoms in the C₂H₂ molecule are located almost over bridge sites with a C–C bond length of 1.34+0.10 Å, the centre of the molecule being positioned almost over a hollow site. Of the two hollow sites the hcp site (directly above a second layer Pd atom) is favoured, particularly by a subset of the data most sensitive to this aspect of the structure, but the full analysis indicates that the fcc site (above a third layer Pd atom) cannot formally be excluded. The adsorption site adopted by acetylene in the higher coverage phase on Pd{111} is essentially identical. This is the dominant structure in the coverage regime which is catalytically active for the conversion of acetylene to benzene. The implications of these findings for acetylene coupling reactions over Pd{111} are discussed.     

In situ surface characterization of the intermetallic compound PdGa – A highly selective hydrogenation catalyst

The structurally well-defined intermetallic compound PdGa – a highly selective catalyst for the semi-hydrogenation of acetylene – was characterized by Fourier transform infrared spectroscopy (FTIR) in situ X-ray photoelectron spectroscopy and in situ prompt gamma activation analysis. A strong modification of the electronic states in PdGa compared to elemental Pd was revealed as well as the complete isolation of the Pd atoms on the surface of PdGa. In situ investigations proved the high stability of the surface, thus excluding segregation phenomena (common for alloys) or sub-surface chemistry involving C and/or H atoms (known for elemental Pd). By suppressing the sub-surface chemistry, the electronic modification as well as the site isolation lead to the high selectivity and long-term stability of PdGa in the semi-hydrogenation of acetylene.     

Study of the combined carbonization of poly(vinylidene fluoride) by X-Ray photoelectron spectroscopy

The surface composition of two samples synthesized by the combined carbonization of poly(vinylidene fluoride) (PVDF) films is studied by X-ray photoelectron spectroscopy. One of them is successively exposed only to chemical and radiation impacts, and the treatment of the other includes chemical, heat, and radiation exposure. The chemical preparation of both samples is the same. It is shown that the magnitude and direction of the gradient of the residual fluorine concentration in the surface layer of PVDF carbonization products can be controlled. Since dehydrofluorination decreases the surface electrical resistance of the material, a combination of chemical, heat, and radiation treatments can be used to create a predetermined sequence of heterolayers with different fluorine concentration on a flexible and transparent polymer base and, therefore, with different conductivities.     

Simultaneous treatment of polymer surface by EUV radiation and ionized nitrogen

In this paper chemical modification of a poly(vinylidene fluoride) surface by extreme ultraviolet (EUV) irradiation in a presence of ionized nitrogen was demonstrated for the first time. Nitrogen gas, injected into an interaction region, was ionized and excited by the EUV radiation from a laser-plasma source. The ionization degree and excited states of nitrogen were investigated using EUV spectrometry and the corresponding spectra are presented. Chemical modification of polymer after combined EUV and ionized nitrogen treatment was investigated using X-ray photoelectron spectroscopy. A?significant contribution of nitrogen atoms in near-surface layer of the polymer after the treatment was demonstrated.     

Electronic, chemical and structural characterization of CNTs grown by acetylene decomposition over MgO supported Fe-Co bimetallic catalysts

The electronic and chemical structure of carbon nanotubes synthesized by decomposition of acetylene over Fe-Co bimetallic catalysts in different growth conditions, were analyzed by valence band photoelectron spectroscopy and scanning electron microscopy. A clear relationship between the bonding features and the growth condition allowed us to determine the key parameters in terms of temperature, growth time and catalyst content. Furthermore, the analysis allowed a determination of the byproducts.     

Pd/C催化剂在乙炔选择加氢反应中的催化性能：载体效应

Pd/C catalysts were prepared by deposited Pd nanoparticles (NPs) on different carbon supports including activated carbon (AC), graphite oxide (GO), and reduced graphite oxide (rGO) using sol-immobilization method. Through transmission electron microscopy, powder X-ray di raction, and X-ray photoelectron spectroscopy, the role of the carbon supports for the catalytic performances of Pd/C catalysts was examined in selective hydrogenation of acetylene. The results indicate that Pd/AC exhibited higher activity and selectivity than Pd/GO and Pd/rGO in the gas phase selective hydrogenation of acetylene. Thermal and chemical treatment of AC supports also have some effect on the catalytic performance of Pd/AC catalysts. The differences in the activity and selectivity of various Pd/C catalysts were partly attributed to the metal-support interaction.     

绿色助溶剂三乙二醇在乙炔电化学氧化过程中的作用机制

建立在常温、常压条件下准确定量测定溶解乙炔含量的紫外-可见分光光度法,并对乙炔在丙酮、三乙二醇、N,N-二甲基甲酰胺和二甲基亚砜中的溶解特性进行系统考察;采用循环伏安法研究助溶剂丙酮、三乙二醇、N,N-二甲基甲酰胺和二甲基亚砜对乙炔电化学氧化过程的影响以及绿色溶剂TEG对该过程影响的作用机制。实验结果表明在常温、常压条件下,溶解乙炔的含量可采用紫外-可见分光光度法通过紫红色的乙炔铜进行准确测定,N,N-二甲基甲酰胺溶解乙炔的能力最强;在乙炔电化学氧化过程中,水分子和三乙二醇之间强烈的氢键作用是提高乙炔在Na₂SO₄溶液中溶解度的决定性因素;在含体积分数为9%TEG的0.5 mol·L-1 Na₂SO₄溶液中,乙炔电化学氧化过程的表观活化能为13.20 kJ·mol-1,属于受吸附控制的不可逆过程。该研究以期寻找一种乙炔的良好溶剂,为乙炔电化学氧化过程的研究、乙炔传感器(尤其是乙炔的电化学传感器)、绿色化学以及乙炔化工等的发展提供理论依据和实验指导。     

不同氮掺杂浓度碳纳米管的制备及其成键特性分析

采用化学气相沉积法,以吡啶为氮源,乙炔为碳源,制备出了不同氮掺杂含量的碳纳米管.使用透射电子显微镜(TEM)和X射线荧光光谱(XPS)对样品的形貌和成键特性进行了观察和分析.TEM测试发现随着掺杂量的增大,氮掺杂碳纳米管的竹节长度从120 nm减小为40 nm左右,同时管身变得更加弯曲,管壁变得粗糙.XPS测试发现氮元素在碳纳米管中以“吡啶”、“吡咯”和“石墨”三种C—N键合方式存在.结合三种价键的形成原因,分析了氮掺杂浓度对键合形式的影响,并根据价键的存在形式解释了碳纳米管形貌变化的原因. 关键词： 碳纳米管 氮掺杂 XPS     

C2H4在Ru(1010)表面吸附与分解的研究

用X射线电子能谱(XPS)、热脱附谱(TDS)和紫外光电子能谱(UPS)方法研究了乙烯(C_{2H4)在Ru(1010)表面的吸附,在低温下(200K以下)乙稀(C2Ｈ4})可以在Ru(1010)表面上以分子状态稳定吸附,在200K以上乙烯(C₂H ₄)则发生了脱氢分解反应.TDS结果表明乙烯(C₂H₄)分 解后的主要产物为乙炔(C< 关键词： 乙烯 钌(1010)表面 吸附与分解     

Improving the hydrophilicity of poly(vinylidene fluoride) porous membranes by electron beam initiated surface grafting of AA/SSS binary monomers

Poly(vinylidene fluoride) (PVDF) membranes were pre-irradiated by electron beam in vacuum, and then the hydrophilic sulfonate groups were introduced by the single step grafting method with binary monomer solution of acrylic acid (AA) and sodium 4-styrenesulfonate (SSS). The effect of binary monomer ratio and pH of reaction solution on the degree of grafting was investigated. The surface chemical change was characterized by Fourier transform infrared attenuated total reflection spectroscopy (FT-IR-ATR) and X-ray photoelectron spectroscopy (XPS). Morphological changes on the membrane surface were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface hydrophilicity of the modified membrane was characterized through water contact angle measurement. It was found that the water contact angle of the membrane surface decreased significantly when compared with the original one, indicating the improvement of the surface hydrophilicity.     

Efficient micromachining of poly(vinylidene fluoride) using a laser-plasma EUV source

In this paper an efficient micromachining of poly(vinylidene fluoride) (PVDF) by direct photo-etching with a laser-plasma EUV (extreme ultraviolet) source was demonstrated for the first time. Mass spectroscopy was employed to investigate the ablation products and revealed emission of numerous molecular species of C-containing fragments of the polymer chain. Chemical surface changes after irradiation were investigated using X-ray photoelectron spectroscopy (XPS). The XPS spectra obtained for PVDF samples, irradiated with low and high EUV fluence, indicate significant differences between chemical structures in near-surface layers. It was shown that irradiation with low fluence results in defluorination and thus carbon enrichment of the polymer in near-surface layer. In contrary, irradiation with high fluence leads to intense material ablation and hardly modifies the chemical structure of the remaining material.     

Influence of the substrate structure on the bonding of chemisorbed acetylene to transition metal surfaces

The electronic spectrum of acetylene adsorbed on various transition metals has been measured by ultraviolet photoemission spectroscopy in various laboratories. At low temperatures (T < 150 K), all measurements concur in finding an electron spectrum that differs only moderately from the gas phase spectrum of acetylene. At room temperature, the electron spectrum of acetylene is reported to be similar to the low-temperature form on Ir(100) and Pt(100), but acetylene is reported to form an olefinic surface complex on Pd(111) and Pt(111) surfaces. In order to examine whether the surface structure of the substrate is responsible for the difference, we have measured the electronic spectrum of acetylene adsorbed on the Pd(100) and Ru(0001) surfaces. At 120 K, the spectrum of adsorbed acetylene is again a distorted gas phase spectrum on both surfaces. At 330 K, we find the acetylenic form (with a splitting of 2.5 eV of the σ-orbitals) on Pd(100) and an olefinic form on the basal plane of Ru. We conclude that the olefinic complex is proper to the threefold symmetry of the (111) and (0001) surfaces and the gas-like form is favored on the (100) surfaces of the fcc crystals.     

The polymorphism of poly(vinylidene fluoride) V. The effect of hydrostatic pressure on the melting behavior of copolymers of vinylidene fluoride

The high-pressure melting behavior of samples of vinylidene fluoride copolymerized with vinyl fluoride, trifluoroethylene, or tetrafluoroethylene indicate that the copolymers have a lower entropy of melting than the poly(vinylidene fluoride) homopolymers in the same phase. As the comonomer size increases, the entropy of melting decreases. High-pressure crystallization of copolymers of 91-9 mole% vinylidene fluoride-trifluoroethylene and 93-7 mole% vinylidene fluoride-tetrafluoroethylene results in a high-melting form of phase I (planar zig-zag).