含锰钢表面氢原子/氢分子吸附行为的第一性原理研究

采用基于密度泛函理论的第一性原理方法研究了氢原子和氢分子在纯铁表面和锰原子掺杂表面的吸附与解离行为.研究结果表明,氢原子可在纯铁(001)表面稳定吸附,吸附能按照顶位,桥位和心位依次增强;而溶质原子锰降低了氢原子距离表面的位置并强化了氢原子的吸附行为.氢分子在纯铁表面的吸附解离行为取决于氢分子距离模型表面的初始距离和初始空间构型.氢分子平行于纯铁(001)表面时,距离心位1.2?发生解离,而桥位、顶位均不会发生解离;氢分子垂直放置时,距离桥位0.6?、顶位1.0?发生解离,心位不会发生解离.氢分子平行于锰掺杂纯铁(001)表面时,距离桥位0.6?、顶位0.7?、心位1.2?发生解离;氢分子垂直放置时,距离桥位、心位0.8?发生解离,而顶位放置氢分子不发生解离.归纳可知,锰溶质原子掺杂会增加铁基体表面氢原子和氢分子的吸附作用并促进氢分子发生分解.     

氢在Ni(511)台阶面的吸附与解离研究

应用EAM模型研究了氢在Ni(511)面的吸附和解离.首先计算了单个氢原子在Ni(511)面上的吸附能、吸附键长及吸附高度,发现氢在Ni(511)面上有三种相对稳定的吸附位,即台阶棱上的二重桥位B、台阶面上的三重洞位H3′以及平台面上的四重洞位H1和H2.与Ni(001)低指数面相比,明显的增加了台阶棱上的二重桥位B以及台阶面上的三重洞位H3′,并且H1位的吸附性也有所增强,说明台阶的存在影响了氢在Ni(511)表面的吸附性,使台阶附近的吸附位增多且吸附性增强;然后计算了氢分子在台阶表面上解离吸附时的活化势垒、吸附能、氢镍之间键长及氢氢之间的距离,计算结果表明台阶底部更易于使氢分子解离,台阶附近是氢吸附和解离的活性部位.     

H2O在SrTiO3-(001)TiO2表面上吸附和解离的密度泛函理论研究

利用密度泛函理论研究了0.25单层(ML),0.5ML,0.75ML和1ML吸附率下H2O在SrTiO3-(001)TiO2表面上的吸附行为.比较了不同吸附率下分子吸附和解离吸附的稳定性,利用微动弹性带(nudged elastic band)方法计算了H2O的解离势垒.结果表明:在低吸附率(0.25ML和0.5ML)时,H2O表现为解离吸附;在0.75ML吸附率下,分子吸附和解离吸附同时存在;而在全吸附(吸附率为1ML)时,分子吸附更稳定.基于对H2O分子与表面之间以及H2O分子之间的电荷转移和相互作用的分析,讨论了吸附率对H2O吸附和解离的影响.     

水分子在Yn (n=2-8)团簇表面的分子吸附与解离吸附

运用密度泛函理论,对H2O在Yn (n=2-8) 团簇表面的分子吸附与解离吸附两种模式进行了结构优化,电子性质分析。结果表明：分子吸附中H2O倾向于O端吸附于Y-Y原子桥位,而解离吸附中H2O解离的H, O原子倾向于吸附于Yn团簇的面位。两种吸附模式都导致了（解离吸附n=4, 5除外）主团簇Y原子平均键长增大。分子吸附和解离吸附的吸附强度和化学活性都随尺寸增加而增大。解离吸附中体系的稳定性明显高于分子吸附,且与体系的电子壳层效应密切相关。     

水分子在Yn (n=2-8)团簇表面的分子吸附与解离吸附

运用密度泛函理论,对H2O在Yn (n=2-8) 团簇表面的分子吸附与解离吸附两种模式进行了结构优化,电子性质分析。结果表明：分子吸附中H2O倾向于O端吸附于Y-Y原子桥位,而解离吸附中H2O解离的H, O原子倾向于吸附于Yn团簇的面位。两种吸附模式都导致了（解离吸附n=4, 5除外）主团簇Y原子平均键长增大。分子吸附和解离吸附的吸附强度和化学活性都随尺寸增加而增大。解离吸附中体系的稳定性明显高于分子吸附,且与体系的电子壳层效应密切相关。     

氢分子在Mg2Ni(010)面的吸附与分解

本文采用基于密度泛函理论(DFT)的第一原理赝势平面波(PW-PP)方法,对氢分子在Mg2Ni(010)面的吸附与分解进行了研究,发现氢分子以Horl的方式吸附在表面层Ni原子的顶位时吸附能最高,为0.6769 eV,这表明氢分子最可能以Horl的方式吸附在表面层Ni原子的顶位,此时氢分子跟表面的距离(rd)和氢分子的键长(rH)分别为1.6286 A和0.9174 (A).在分子吸附的基础上计算了氢分子沿着选取的反应路径分解时的反应势垒,发现要使氢分子分解需要0.2778 eV的活化能,而氢分子分解时的吸附能为0.8390 eV,分解后两个氢原子的距离为3.1712(A).在分子吸附和分解吸附时氢原子跟正下方的Ni原子都有较强的相互作用,氢原子所得到的电子主要来自氢分子正下方的Ni原子.     

H2在Al12X (X=Al, Ni, Cu)团簇表面解离吸附的第一性原理研究

以Ni和Cu原子中心替换的二十面体Al12X(X=Ni、Cu)团簇为基体、采用密度泛函理论系统计算研究了H原子及H2分子在团簇表面的吸附,并对比了纯Al13团簇对H及H2的吸附,结果表明：相对于纯Al13中H原子的桥位吸附、掺杂团簇Al12X(X=Ni、Cu)中H原子均吸附于团簇顶位;无论是吸附H原子还是H2分子,Al12Ni的几何结构均发生大的畸变;相较H2在纯Al13团簇表面的解离吸附,H2在掺杂团簇Al12X(X=Ni、Cu)表面的解离反应过程中反应能均增大、势垒均降低,这表明掺杂团簇Al12X(X=Ni、Cu)相较纯Al13团簇更有利于H2解离吸附的发生。     

氢分子在Mg2Ni(010)面的吸附与分解

本文采用基于密度泛函理论(DFT)的第一原理赝势平面波(PW-PP)方法,对氢分子在Mg2Ni(010)面的吸附与分解进行了研究,我们发现氢分子以Hor1的方式吸附在表面层Ni原子的顶位时吸附能最高,为0.6769eV,这表明氢分子最可能以Hor1的方式吸附在表面层Ni原子的顶位,此时氢分子跟表面的距离( )和氢分子的键长( )分别为1.6286Å和0.9174Å. 在分子吸附的基础上计算了氢分子沿着选取的反应路径分解时的反应势垒,发现要使氢分子分解需要0.2778eV的活化能,而氢分子分解时的吸附能为0.8390eV,分解后两个氢原子的距离为3.1712Å. 在分子吸附和分解吸附时氢原子跟正下方的Ni原子都有较强的相互作用,氢原子所得到的电子主要来自氢分子正下方的Ni原子.     

致密气在α-SiO_2(010)面吸附的第一性原理研究

致密气在砂岩储层中的赋存状态一直是人们研究的热点.为了论证致密气在石英砂岩表面吸附性的强弱,基于密度泛函理论的第一性原理方法,以CH_4分子为主要研究对象,研究了CH_4、C_2H_6、CO_2、N_2分子在α-SiO_2(010)面的吸附性质.结果表明:CH_4、C_2H_6、CO_2、N_2分子在α-SiO_2(010)面的吸附能力从小到大依次为CO_2N_2CH_4C_2H_6,其中CH_4分子在B12位的吸附能最低,为-0.5379 eV,几何结构变化最小,吸附最稳定,是一种物理吸附;烃类气体的吸附性比非烃类的吸附性强;不同高对称位的吸附能变化范围很小,气体在α-SiO_2(010)面的流动性很强;在B12位吸附后,CH_4分子的s态、p态电子密度整体向低能量区域偏移约3.2 eV,而α-SiO_2(010)表面硅原子的电子态密度曲线几乎不变.     

氢分子在Na2Al6团簇上的吸附和解离性能

氢的物理和化学吸附是氢存储的基本形式,而H₂分子的解离能垒是决定可逆储氢动力学性能的重要因素.纳米团簇是研究材料储氢性能的重要物质层次,研究氢与Na-Al团簇的相互作用性质能够了解纳米尺度的Na-Al氢化物的储氢性能.本文利用密度泛函理论,计算研究了H₂分子在较小的合金团簇Na₂Al₆上的吸附与解离性能.结果表明H₂分子在Na₂Al₆团簇上是弱的物理吸附,但很容易发生解离.氢分子的解离能垒很低,解离可以在环境温度下发生,纳米结构的Na₂Al₆团簇具有良好的化学储氢性能.     

Enhancement of H2 adsorption on a boron-doped carbon system for hydrogen storage

We study the adsorption of the molecular hydrogen on boron-doped polypyrrole ((–C₄BH₃)_n) using first-principles density functional calculations. We find that the binding energy of H₂ molecules is slightly reduced to 0.39 eV/H₂ from 0.51 eV/H₂ as the number of adsorbed H₂ molecules increases. This is in sharp contrast to the case of boron-doped fullerenes where the binding energy is drastically reduced as the number of adsorbed H₂ molecules increases. We find that the enhancement of H₂ adsorption is due to a local charge transfer by H₂ adsorption in the B-doped polypyrrole as opposed to a delocalized charge transfer in the B-doped fullerenes. Our finding shows that B-doped carbon systems could be utilized for room temperature hydrogen storage.     

Enhancement of sonochemical degradation of phenol using hydrogen atom scavengers

Sonochemical degradation of phenol was found to be enhanced in the presence of the volatile hydrogen atom scavengers CCl4 and perfluorohexane. The non-volatile hydrogen atom scavenger iodate did not enhance phenol degradation. The first order rate constant for aqueous phenol degradation in separate experiments using different sonochemical probes increased in the presence of 150 microM CCl4 from 0.014 to 0.031 min(-1) (probe 1) and from 0.022 to 0.061 min(-1) (probe 2). In the presence of <1.5 microM C6H14, the first order rate constant increased from 0.014 to 0.032 min(-1) (probe 1). Hydroquinone was the major observed reaction intermediate both in the presence and absence of hydrogen atom scavengers. Hydroquinone yields were substantially higher in the presence of hydrogen atom scavengers, suggesting that hydroxyl radical pathways for phenol degradation were enhanced by the hydrogen atom scavengers. These additives may be useful in improving pollutant degradation efficiency or improving synthetic processes that rely on hydroxyl radical as a key intermediate.     

Hydrogen storage in novel organometallic buckyballs

Transition metal (TM) atoms bound to fullerenes are proposed as adsorbents for high density, room temperature, ambient pressure storage of hydrogen. C60 or C48B12 disperses TMs by charge transfer interactions to produce stable organometallic buckyballs (OBBs). A particular scandium OBB can bind as many as 11 hydrogen atoms per TM, ten of which are in the form of dihydrogen that can be adsorbed and desorbed reversibly. In this case, the calculated binding energy is about 0.3 eV/H(2), which is ideal for use on board vehicles. The theoretical maximum retrievable H2 storage density is approximately 9 wt %.     

A bonding evolution theory study on the catalytic Noyori hydrogenation reaction

ABSTRACT

The electronic rearrangements involved in Noyori hydrogenation reactions with double bonds (ethene and formaldehyde) are analysed using the bonding evolution theory. The study and analysis of the changes on the electron localisation function topology along a given reaction path reveals fluxes of electron density, allowing to unambiguously identify the main chemical events happening along the chemical reactions. This analysis shows that the first hydrogen transfer (with hydride character) occurs before the transition state (TS), while the second hydrogen transfer (with proton character) takes places after having reached the TS. The lower energy barrier found for formaldehyde over ethene is explained by two reasons. First, the hydride transfer is favoured for the C?=?O bond over C?=?C due to the electrophilic character of the carbon atom. Second, a negatively charged CH₃–X (X?=?CH₂, O) hidden intermediate is formed in the proximities of the TS region. The oxygen atom is able to stabilise this negatively charged species more effectively than the CH₂ group due to its higher electronegativity and the presence of V(O) lone pairs. The obtained analysis explains and rationalises catalyst chemoselectivity (C?=?O vs. C?=?C). Finally, a curly arrow representation diagram accounting for the electronic rearrangements is proposed on the basis of BET results.     

Effect of boron-doping on the hydrogen evolution from a-Si:H films

We have found that the hydrogen evolution from boron-doped a-Si:H films prepared by the glow-discharge decomposition of silane-diborane mixtures, differs appreciably from that of undoped or phosphorus-doped material. Firstly, the peaks in the hydrogen evolution rate are shifted to lower temperature by as much as 160°C and, secondly, the peak position is almost independent of the film thickness. Differences in the hydrogen content are also observed. These findings indicate the presence of strong microstructural inhomogeneities in boron-doped films. Implications of this property are consistent with recent transport data.     

H2S在Fe(100)面吸附的第一性原理研究

基于密度泛函理论第一性原理, 在广义梯度近似下, 研究了表面覆盖度为0.25 ML (monolayer)时硫化氢分子在Fe(100)面吸附的结构和电子性质, 并与单个硫原子吸附结果进行了对比. 结果表明: 硫化氢分子吸附在B2位吸附能最小为-1.23 eV, 最稳定, B1位吸附能最大为-0.01 eV, 最不稳定; 并对硫化氢分子在B1位和B2位吸附后的电子态密度进行了分析, 也表明了吸附在B2位稳定, 且吸附在B2位后硫化氢分子几何结构变化不大; 将硫化氢中硫原子吸附与单个硫原子吸附的电子性质进行了比较, 发现前者吸附作用非常微弱; 同时对吸附后的Fe(100)面进行了对比, 单个硫原子吸附的Fe(100)面电子态密度出现了一系列峰值且离散分布, 生成了硫化亚铁, 表明在硫化氢环境下, 主要是硫化氢析出的硫原子发生了吸附. 关键词： 第一性原理 Fe(100)表面 吸附能 硫化氢     

Adsorption Mechanism of Hydrogen on Boron-Doped Fullerenes

The C35BH-H2 complex and two other possible isomers, C34BCaH-H2 and C34BCbH-H2, are investigated using the local-spin-density approximation （LSDA） method. The results indicate that a single hydrogen molecule could be strongly adsorbed on two isomers, C34BCaH and C34BCbH, with binding energies of 0.42 and 0.47eV, respectively, and that these calculated binding energies are suitable for reversible hydrogen adsorption/desorption near room temperature. However, it is difficult for the H2 molecule to be firmly adsorbed on C35BH. We analyze the interaction between C34BCxH （x= a, b） and the H2 molecule using dipole moments and molecular orbitals. The charge analysis showed there was a partial charge （about 0.32e） transfer from 1-12 to the doped fullerenes. These calculation results should broaden our understanding of the mechanisms of hydrogen storage using borondoped fullerenes.     

富勒烯有机溶液光致荧光研究

本文研究了C60、C70有机溶液的荧光效应,发现它们的Pyridine溶液在可见和紫外激光激发下有强而且宽的荧光峰,两种分子的吸收谱和荧光谱具有特殊的互补性,其混合物可以实现红绿蓝三色光致发光,体现了富勒烯在白光有机光致发光材料开发方面的潜在价值。     

First-principles study of palladium atom adsorption on the boron- or nitrogen-doped carbon nanotubes

We have performed first-principles calculation to investigate the adsorption of a single palladium atom on the surface of the pristine and boron- or nitrogen-doped carbon nanotubes (CNTs). The results show that for the adsorption of a single palladium atom on the pristine CNT surface, the most stable site is Bridge1 site above the axial carbon–carbon bond. Either boron- or nitrogen-doped CNTs can assist palladium surface adsorption, but the detailed mechanisms are different. The enhanced palladium adsorption on boron-doped CNT is attributed to the palladium d orbital strongly hybridized with both boron p orbital and carbon p orbital. The enhancement in palladium adsorption on nitrogen-doped CNT results from activating the nitrogen-neighboring carbon atoms due to the large electron affinity of nitrogen. Furthermore, the axial bond is preferred over the zigzag bond for a palladium atom adsorbed on the surface of all three types of CNTs. The most energetically favorable site for a palladium atom adsorbed on three types of CNTs is above the axial boron–carbon bond in boron-doped CNT. The enhancement in palladium adsorption is more significant for the boron-doped CNT than it is for nitrogen-doped CNT with a similar configuration. So we conclude that accordingly, the preferred adsorption site is determined by the competition between the electron affinity of doped and adsorbed atoms and preferred degree of the axial bond over the zigzag bond.     

Ni(111)表面一氧化碳和氢共吸附的密度泛函理论研究

本文用密度泛函理论(DFT)的总能计算研究了一氧化碳和氢原子在Ni(111)表面上p(2×2)共吸附系统的原子结构和电子态，结果表明CO和H原子分别被吸附于两个对角p(1×1)元胞的hcp和fcc位置.以氢分子和CO分子作为能量参考点，总吸附能为2.81 eV，相应的共吸附表面功函数φ为6.28 eV.计算得到的C—O，C—Ni和H—Ni的键长分别是1.19?, 1.96?和 1.71?，并且CO分子以C原子处于hcp的谷位与金属衬底原子结合.衬底Ni(111)的最外两层的晶面间距在吸附后的相对变化分别是 关键词： Fisher-Tropsch反应 催化作用 Ni(111) p(2×2)/(CO+H) 共吸附