原位DRIFTS研究CH4部分氧化和CO2重整的耦合

8%Ru-5?/γ-Al2O3催化剂对于甲烷的低温活化具有较好的催化活性,在500℃下甲烷、二氧化碳和氧气的耦合反应中,吸热反应二氧化碳重整和放热反应甲烷部分氧化进行耦合强化,使得耦合反应中的甲烷转化率为38.8%。用原位漫反射傅里叶红外光谱法对钌系催化剂耦合甲烷部分氧化和二氧化碳重整反应体系机理进行研究。CO在8%Ru-5?/γ-Al2O3上吸附,表明CO在催化剂表面上波数为2 167 cm-1(2 118 cm-1)和2031 cm-1(2 034 cm-1)处形成孪生态Ru(CO)2和Ce(CO)2吸附物种,而且高温下CO吸附物种很容易从催化剂表面脱附出来。原位漫反射红外实验结果表明甲烷部分氧化反应时催化剂表面上有吸附物种碳酸根、甲酰基(甲酸盐)和一氧化碳的形成,其中表面的甲酰基和甲酸盐物种是甲烷部分氧化反应的主要活性中间物,这些中间活性中间体由甲烷吸附态CHx和催化剂表面的氧吸附态结合而形成的,随后这种中间物种再分解为CO产物;甲烷和二氧化碳重整反应时没有新的吸附物种产生,由此提出重整反应的机理是吸附态的甲烷和二氧化碳在催化剂活性中心上进行活化解离而生成合成气;甲烷、二氧化碳和氧气耦合反应过程中出现新的羟基物种(桥式羟基Ru-(OH)2),耦合反应机理复杂可能是由部分氧化和重整两类反应机理的复合,其中桥式羟基Ru-(OH)2参与了反应的进行。     

Adsorption d'hydrogène entre 300 et 873 K sur un catalyseur Pt/MgO

Hydrogen adsorption on MgO-supported platinum was studied by thermal desorption and infrared spectroscopy at 300 and 800 K. For both temperatures, reversibly and irreversibly adsorbed species have been detected. At 300 K, reversible adsorption leads to the appearance of infrared bands at 2120 and 2060 cm^?1, attributed to terminal Pt-H species. Irreversibly adsorbed hydrogen has been detected by thermal desorption, whereas no infrared band was detected in the spectral range 4000–4750 cm^?1 for Pt/MgO sample. For hydrogen adsorption at 800 K, reversibly adsorbed hydrogen gave the same picture as for the 300 K adsorption. An additional form of irreversibly adsorbed hydrogen has been evidenced both by thermal desorption and infrared spectroscopy. This form corresponds to hydrogen strongly adsorbed on platinum and gives an infrared band at 950 cm^?1 which is characteristic of an hydrogen atom in interaction with more than one platinum atom (multicentered) species.     

IR spectroscopy of CH2CBrF adsorbed on TiO2 and quantum-mechanical studies

The adsorption at room temperature of 1-bromo-1-fluoroethene (CH₂CBrF) on TiO₂ has been investigated by Fourier-transform infrared spectroscopy after a preventive assignment of the fundamentals in the gas-phase, carried out for the first time. The spectrum resulting from the adsorption has been compared with the gas-phase one and the most important differences consist in a red-shift of the CH₂ stretching vibration and in the presence of two distinct absorptions for both the C=C and C–F stretching modes. Basing on the observed features it has been inferred that there is the formation of an H-bond between the CH₂ group and a surface Lewis basic site and that the adsorption can occur through the double C=C bond or the F atom. Two proposed adsorbate-substrate structures have been investigated by periodic quantum-mechanical calculations at DFT/B3LYP level considering the rutile (110) surface. In the case of the adsorption by the F atom, also the formation of the H-bond has been considered. The interaction energy resulting from the adsorption through the double C = C bond is smaller than that arising from the interaction by means the F atom and the H-bond. The shifts due to the adsorption of the calculated vibrational frequencies well reproduce the experimental data.     

Contaminant Flow and Transport Simulation in Cracked Porous Media Using Locally Conservative Schemes

The purpose of this paper is to analyze some features of contaminant flow passing through cracked porous medium, such as the influence of fracture network on the advection and diffusion of contaminant species, the impact of adsorption on the overall transport of contaminant wastes. In order to precisely describe the whole process, we firstly build the mathematical model to simulate this problem numerically. Taking into consideration of the characteristics of contaminant flow, we employ two partial differential equations to formulate the whole problem. One is flow equation; the other is reactive transport equation. The first equation is used to describe the total flow of contaminant wastes, which is based on Darcy law. The second one will characterize the adsorption, diffusion and convection behavior of contaminant species, which describes most features of contaminant flow we are interested in. After the construction of numerical model, we apply locally conservative and compatible algorithms to solve this mathematical model. Specifically, we apply Mixed Finite Element (MFE) method to the flow equation and Discontinuous Galerkin (DG) method for the transport equation. MFE has a good convergence rate and numerical accuracy for Darcy velocity. DG is more flexible and can be used to deal with irregular meshes, as well as little numerical diffusion. With these two numerical means, we investigate the sensitivity analysis of different features of contaminant flow in our model, such as diffusion, permeability and fracture density. In particular, we study $K_d$ values which represent the distribution of contaminant wastes between the solid and liquid phases. We also make comparisons of two different schemes and discuss the advantages of both methods.     

Adsorption of small molecules on a (2 × 1) PdZn surface alloy on Pd(1 1 1)

The adsorption of methanol, formaldehyde, methoxy, carbon monoxide and water on a (2 × 1) PdZn surface alloy on Pd(1 1 1) has been studied using DFT calculations. The most stable adsorption structures of all species have been investigated with respect to the structure and the electronic properties. It was found that methanol is only weakly bound to the surface. The adsorption energy only increases with higher methanol coverage, where chain structures with hydrogen bonds between the methanol molecules are formed. The highest adsorption energy was found for the formate species followed by the methoxy species. The formaldehyde species shows quite some electronic interaction with the surface, however the stable η₂ formaldehyde has only an adsorption energy of about 0.49 eV. The calculated IR spectra of the different species fit quite well to the experimental values available in the literature.     

Partial structures and compressibilities of ions in fused potassium bromide

Treating the coulomb interaction between ion species as a perturbation on the Waisman-Lebowitz solution for direct correlation function within the hard core region, the total direct correlation function in K-space has been formulated, which gives a direct method of evaluating the partial structure factors between different ion species of the fused salts through the use of Pearson-Rushbrooke equations. The partial structure factors so obtained have been applied to evaluate the partial radial distribution functions of ion pairs. In addition, many other important associated functions such as the static correlations of total number, mass and charge densities have been computed by particular linear combination of partial structure factors. The charge neutrality relate the partial structure factors to the isothermal compressibility for the wavevectorK → 0 and hence the evaluation of the compressibilities of ions in fused KBr is possible, which agrees well with the observed value. As such the present method is very useful in investigating the structure of molten salts since only the parametersσ _ij , the distances of closest approach between ions andɛ, the effective dielectric constant (which can be estimated from the literature) are enough for this work.     

硫在Fe(111)面吸附的密度泛函研究

采用基于密度泛函理论的第一性原理方法,系统研究了不同覆盖度下硫在Fe（111）表面的吸附构型和吸附特性,计算并分析了硫在Fe（111）表面的吸附能、电荷密度、分波态密度、电荷布局、电子局域化函数等数据. 研究结果表明：S在Fe（111）面的H位吸附最稳定,并且吸附能随着覆盖度的增加而增加. 另外,电子态密度、电子局域化函数和布局分析表明Fe、S之间呈较弱的共价键,这种作用力主要是Fe的3d轨道和S的2p轨道杂化所贡献,而随着覆盖度的增加,Fe、S之间的作用力逐渐减弱,这可能是由于S原子之间的排斥力减弱了Fe、S之间的作用. S在Fe（111）、Fe（110）和Fe（100）这三个晶面上吸附情况的对比分析发现,S与Fe（111）表面的相互作用最强,Fe（100）面次之,而Fe（110）面最弱.     

Vibration of small molecules on Pt(1 1 1) surface

The adsorption of methanol and other small molecules onto transition metal surfaces is an important issue in electrochemistry, fuel cells, etc. Despite the overwhelming interest there are still unresolved issues beginning from the geometry of the adsorbed species to the correct assignments of different vibrational modes of the adsorbed molecules on the surface.In order to understand the adsorption processes, we have performed density functional theory (DFT) calculations for small molecules (methanol, formaldehyde, formic acid) on Pt(1 1 1) surfaces. We investigated the nature of the metal-ligand bonding in these adsorption processes using electron density difference and PDOS (partial density of states) methods. Ab initio vibration spectra have been calculated for these systems.     

Synthesis and structural characterization of mixed aluminum-gallium-offretites

A new synthesis procedure is reported for the preparation of mixed Al,Ga-offretites over the entire solid solution range 0 ≤ Ga/(Ga + Al) ≤ 1. The resulting materials are characterized by X-ray powder diffraction, adsorption microcalorimetry and multinuclear solid state NMR. The ²⁹Si MAS-NMR data are consistent with statistical occupancy of the T₁ and T₂ sites by aluminum and gallium, and also show no positive evidence for preferential siting effects between both framework metals. Isotropic chemical shifts and nuclear electric quadrupolar coupling constants for ²⁷Al and ⁷¹Ga have been obtained from a field-dependent analysis of the center of gravity in the MAS-NMR spectra. H-Al, Ga-offretites produced by ammonium exchange and subsequent calcination reveal evidence of partial demetallation of the framework with formation of extra-lattice metal species.     

太阳能固体吸附-喷射制冷联合循环系统研究

本文提出了一种新型太阳能固体吸附-喷射制冷联合循环系统,并建立了相应的物理模型.通过对系统运行原理和热力参数的分析与计算,认为该系统为解决太阳能固体吸附制冷系统的不连续性问题提供了一种行之有效的方法.同时,由于对吸附热的有效回收,系统的COP有一定的提高.     

特定和非特定溶剂化对BPTI在金表面吸附的分子动力学模拟

采用分子动力学方法研究了三种水溶剂环境(即介电常数模型、部分溶剂化模型和全溶剂化模型)中牛胰蛋白酶抑制剂(BPTI)在金表面上的吸附效应. 结果表明BPTI在介电常数模型中会发生快而强的吸附作用并导致蛋白质结构发生大的结构偏差、明显的沿金表面的平铺展开、二级结构的快速消失、更多的原子出现在与金表面强相互作用的区域. 与介电常数模型相比,部分溶剂化模型中蛋白质与金表面间的显含水分子削弱了金的吸附作用,使得吸附速度和结构的变化程度减弱,但金吸附导致的蛋白质紧密水化层的损失仍然使得它的结构发生明显的变化. 蛋白质在全溶剂化的体系中吸附速度和程度是最慢最弱的,结构变化最小并能发生一定程度的旋转来寻找合适的吸附     

A quantum-mechanical study of the vinyl fluoride adsorbed on the rutile TiO2(1 1 0) surface

The adsorption of vinyl fluoride on the rutile TiO₂(1 1 0) surface has been simulated, on the basis of a recently proposed experimental model, using hybrid-exchange density functional theory. Different surface coverages have been considered and the lateral interaction between adsorbed vinyl fluoride molecules has been quantified through a simple model of nearest and next nearest neighbouring molecules. The vibrational frequencies of the adsorbed molecule have been calculated and are found to be in excellent agreement with those observed providing support for the proposed adsorption model. The effect of the adsorption on the electronic structure of the molecule and the surface have been characterised by computing electrostatic potential maps and the local density of states.     

The acid-base properties of the surface of native zinc oxide layers: An XPS study of adsorption of 1,2-diaminoethane

The acid-base properties of native zinc oxide surfaces have been studied using X-ray photoelectron spectroscopy (XPS). The native layers of zinc oxide have been obtained by ageing mechanically polished pure zinc disks in a glass dryer for 1 month. Such a treatment lead to the formation of an unstable oxide layer and dehydroxylation has been observed during storage in vacuum. By following adsorption in ultrahigh vacuum of 1,2-diaminoethane (DAE) several types of active sites have been evidenced. Zinc cations react with the probe molecule following a Lewis acid/base interaction, while the hydroxyl and the carbonate-like species react following a Brønsted acid/base reaction. Although initial interaction via the Brønsted-like mechanisms is favoured, it has been shown that the resulting complexes are not stable. Under vacuum conditions, the adsorbed DAE molecules either partly desorb or modify their interaction mode with the surface to form additional Lewis-like bonded stable complexes. In addition, a cleaning effect of the molecule has been observed which lead to partial removal of the carbonate-like contamination.     

Chemisorption of silyl radicals onto Pd(1 0 0) surface: A computational DFT study

We have investigated the adsorption of silane and silyl radicals onto a Pd(1 0 0) surface. The solid metal has been modelled by a 24-atom-2-layer Pd cluster. Density Functional Theory calculations have been performed for the different species approaching the surface, adopting the hybrid B3LYP functional. It is found that all species, in the hollow position, dissociate up to SiH, which is then stable in this position. Dissociated hydrogen atoms are chemisorbed onto the surface in distinct bridge positions. Dissociation mechanism is studied through computation of selected sections of the potential energy surface.     

甲基和羟基在Ir(111)表面吸附的密度泛函理论研究

在超原胞近似和slab模型基础上,采用周期性密度泛函理论,在0.11覆盖度（ML）下,对甲基与羟基在Ir(111)表面的吸附进行了研究,得到了甲基和羟基在Ir(111)表面不同吸附位置的吸附能和吸附构型,计算了它们的振动频率,同时分析了甲基和羟基共吸附于Ir(111)表面的情况。结果表明,甲基和羟基在Ir(111)表面的最稳定吸附位置都是top位,甲基是碳端向下吸附,羟基是通过氧端向下倾斜吸附。通过频率分析发现吸附后CH3中C-H键的对称伸缩振动、反对称伸缩振动以及剪切振动频率均发生了红移,而羟基中的O-H键的振动频率发生蓝移现象。通过计算对比发现甲醇分解为甲基和羟基过程是一个放热反应,从热力学角度来说该反应是可行的。     

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。     

The adsorption of CO on Pt(111) studied by infrared-reflection-adsorption spectroscopy

The adsorption of CO on Pt(111) between 85K and 300K has been studied by infrared-reflection-absorption spectroscopy together with TPD and LEED. The intensity of the absorption band due to the CO stretch of the linear species shows a maximum at the formation of the (√3 × √3)R30° LEED pattern followed by a minimum at the c(4×2) structure during the adsorption of CO at low temperatures (150K). The absorption band due to the C-O stretch of the bridging species appears only after the formation of the (√3 × √3)R30° pattern and reaches maximum intensity at the c(4×2) structure. Adsorption of CO to higher coverages (corresponding to the compression structures) broadens and shifts this absorption band. At higher temperatures (150K) a third peak is observed at 40cm⁻¹ below the peak due to the bridging species and is attributed to adsorption in the three-fold sites. At 300K both peaks in this region are very broad. The intensity data differs from that measured with EELS (ref.1) and favors a “faultline” structure of the type proposed by Avery (ref.2). Together with the additional information from bandwidths it is possible to distinguish between the various structural models. The results obtained here may also be important in explaining data from other systems such as CO/Cu.     

LCAO studies of hydrogen chemisorption on nickel: I. Tight-binding calculations for adsorption on periodic surfaces

The model we have used to study hydrogen chemisorption on nickel surfaces is a tightbinding Extended Hückel method applied to finite (periodic) crystals up to about 250 atoms, the non-orthogonal basis set comprising five 3d orbitals, one 4s orbital and three 4p orbitals per atom. After calculating the band structure of fcc nickel, we have examined, by this model, the effect of the (100), (110) and (111) surfaces on the local density of states and the charge distribution. The results agree closely with moment calculations of the density of states in semi-infinite crystals and with experimental (XPS, UPS and INS) spectra. Extensive studies have been made of the influence of adsorption on the (partial) densities of states in order to illuminate the nature of the chemisorption bond. Particularly, we have concluded that both the 3d electrons and the conduction electrons take part in this bond. Equilibrium positions for adsorption on various sites have been determined and the adsorption energy has been computed and compared with experimental data. We find that the stability of adsorption decreases in the order (110) > (100) > (111) and Atop > Bridge > Centred.     

Adsorption of cyclic hydrocarbons on Pt and the interaction of the adsorbed species with hydrogen

The adsorption of six-membered hydrocarbon cycles and cyclopentane and the interaction of hydrogen with the adsorbed layer on polycrystalline Pt-foil have been studied. The work function change (Δφ) was followed by a Kelvin probe and the C/Pt peak ratio was determined by Auger electron spectroscopy. Combining these two techniques made it possible to distinguish between chemisorption via σ-bonds and π-complex formation. Benzene and toluene adsorbed first as π-complex while cyclohexane showed initially a partial aromatization and a π-complex-like bonding to the surface. Excess hydrocarbon or addition of hydrogen transformed the π-complex into σ-bonded species. Cyclopentane adsorbed via σ-bonds and showed no significant hydrogen effect.