Application of the Statistical Rate Theory of interfacial transport to investigate the kinetics of mixed-gas adsorption onto the energetically homogeneous and strongly heterogeneous surfaces

Kinetics of mixed-gas adsorption by using the Statistical Rate Theory is studied. Applying the adsorption lattice model two cases are investigated: when adsorption occurs like on the homogeneous surface and when energetic heterogeneity of adsorption system can be described by the rectangular adsorption energy distribution function. The model of calculations offers possibility of theoretical prediction of the rate of adsorption/desorption of mixture components by using the single-gas equilibrium and kinetic data. Possible changes of adsorbate concentration near the adsorbing surface are also taken into account. The obtained theoretical expressions were verified using real adsorption systems.     

Application of the statistical rate theory of interfacial transport to investigate the kinetics of divalent metal ion adsorption onto the energetically heterogeneous surfaces of oxides and activated carbons

Divalent metal cation adsorption from solution onto oxides or activated carbons can be described by the Surface Complexation Model (SCM). We assumed that the adsorbent surface is strongly energetically heterogeneous and derived the adsorption isotherm using rectangular distribution of adsorption energy and condensation approximation for the local isotherm equation. Assuming additionally that the bulk concentration of divalent metal ion is low and does not change considerably during the adsorption process and next applying the Statistical Rate Theory of Interfacial Transport (SRT) we derived the Elovich equation—the experimental formula describing adsorption kinetics.     

Molecular adsorption at a well defined gas-solid interphase: Statistical Rate Theory approach

The objective of Statistical Rate Theory is to derive explicitly the coverage dependence of the expression for the rate of adsorption. The other parameters in the rate expression can then be viewed as material properties of a gas-solid surface combination, since they have no coverage dependence. After these properties have been tabulated, they can be used with Statistical Rate Theory to predict the rate of adsorption in independent circumstances. This hypothesis is examined by considering CO adsorbing on Ni(1,1,1). The properties of this well defined gas-solid surface are first established from the EELS spectrum, ellipsometric isotherms, and an ultraviolet photoemission spectroscopic study of the desorption rate. These studies were conducted in different laboratories. After these material properties are measured, they are used with Statistical Rate Theory to predict the rate of CO adsorption on Ni(1,1,1) and the result is compared with a set of measurements. Close agreement was found throughout the experimental period. It had been previously reported that Absolute Rate Theory could not describe these results unless both the pre-exponential factor and the activation energy were allowed to depend on coverage.     

Tetrathia- and tetraselenafulvalene adsorbed on Ag(110): A theoretical study

We have studied the adsorption properties of the π-donor molecule TXF, where X stands for the chalcogens sulfur and selenium [TTF = tetrathiafulvalene, TSF = tetraselenafulvalene], respectively, on the (110) surface of silver by means of periodic plane-waves based DFT (Density Functional Theory) calculations using slab models. We have determined and characterized the stable adsorption sites and have evaluated the charge transfer from TXF molecules into the surface. The simulation of the vibrational spectra for TXF and the fully deuterated TXF species has permitted to identify the fingerprints of both molecules on this surface.     

Density functional theory study of the water adsorption at Bi(111) electrode surface

The adsorption of a water molecule on a basal Bi(111) electrode surface, crystallising in the rhombohedral system, has been studied in the framework of cluster model. The quantum chemical calculations were performed at the Density Functional Theory (DFT) level and the electrical double layer effects were analysed by using an external electric field. In contrast to computational predictions reported previously for other metal surfaces, crystallising in the face-centred cubic or hexagonal close-packed systems, a hollow site for Bi(111) was found to be energetically the most preferable; the water adsorption energy amounts to ? 28 kJ mol^? 1. In a wide range of surface charge densities the water molecule is bound preferentially through the O atom in orientation perpendicular to the surface plane. The Bi(111) hydrophilic properties are compared with those for other metals. Some adsorption characteristics of a hydrogen atom and a hydroxyl group at Bi(111) are reported as well, which give evidence in favour of the non-dissociative adsorption of water molecules.     

Adsorption of molecular gases on porous materials in the SAFT-VR approximation

A simple molecular thermodynamic approach is applied to the study of the adsorption of gases of chain molecules on solid surfaces. We use a model based on the Statistical Associating Fluid Theory for Variable Range (SAFT-VR) potentials [A. Gil-Villegas, A. Galindo, P.J. Whitehead, S.J. Mills, G. Jackson, A.N. Burgess, J. Chem. Phys. 106 (1997) 4168] that we extend by including quasi-two-dimensional approximation to describe the adsorption properties of these types of real gas [A. Martínez, M. Castro, C. McCabe, A. Gil-Villegas, J. Chem. Phys. 126 (2007) 074707]. The model is applied to ethane, ethylene, propane, and carbon dioxide adsorbed on activated carbon and silica gel, which are porous media of significant industrial interest. We show that the adsorption isotherms obtained by means of the present SAFT-VR modeling are in fair agreement with the experimental results provided in the literature.     

On the ways of generalization of adsorption kinetic equations for the case of energetically heterogeneous surfaces

In this work, we present three different ways of incorporation of the effects of surface energetic heterogeneity in the Statistical Rate Theory kinetic equation. These ways are critically discussed and finally, we come to the conclusion that the most consistent method is based on the assumption that the adsorbing surface should not be considered as composed from independent subsystems but it should be treated as one physical entity. As an illustration, we show the numerical analysis of the experimental data concerning the adsorption of CO₂ on scandia. The estimated best-fit parameters are physically correct and consistent with the results of calorimetric measurements.     

Effect of side by side interactions on the thermodynamic properties of adsorbed CO molecules on the Ni(111) surface: a cluster model study

The effect of electrostatic interactions on vibrational frequencies and thermodynamic properties of CO adsorbate on the Ni(111) surface is calculated by taking the first and second nearest-neighbour interactions into account. In order to obtain reasonable results, the cluster model of various surface adsorption sites with CO adsorbate is partially optimized, using Density Functional Theory and also the MP2 method for the hcp site. Comparison between DFT and MP2 results shows that DFT results are more reliable for this system. The stretching and bending frequencies of CO adsorbate are calculated using both Partial Hessian Analysis and Cluster–Adsorbate Coupling methods. Stretching and bending frequencies are both shifted by the side by side interactions. The coupling of surface phonons and adsorbate vibrations reduces the side effects. The largest side effects on the vibrational internal energy, isochoric heat capacity, entropy and total Helmholtz free energy of adsorbed CO molecule calculated using the CAC method are found for 0.5 ML coverage. The results of the CAC method are better, but the PHA method can be used as a simple upper bound estimation. The adsorptive phase acts as an intelligent material in such a way that it changes its configuration in order to reduce the side effects.     

First-principles molecular dynamics simulations of uranyl ion interaction at the water/rutile TiO2(110) interface

The effects of temperature and solvation on uranyl ion adsorption at the water/rutile TiO₂(110) interface are investigated by Density Functional Theory (DFT) in both static and Born–Oppenheimer molecular dynamics approaches. According to experimental observations, uranyl ion can form two surface complexes in a pH range from 1.5 to 4.5. Based on these observations, the structures of the complexes at 293 K are first calculated in agreement with vacuum static calculations. Then, an increase in temperature (293 to 425 K) induces the reinforcement of uranyl ion adsorption due to the release of water molecules from the solvation shell of uranyl ion. Finally, temperature can modify the nature of the surface species.     

CH_4/H_2O/CO_2在β-SiO_2(100)面吸附的第一性原理研究

多孔介质中的吸附直接影响页岩气赋存、运移.基于密度泛函理论从量子力学角度研究CH_4/H_2O/CO_2在页岩储层主体矿物成分SiO_2上的吸附构型和吸附特性,计算并分析了吸附能与态密度等特征.研究表明:CH_4、H_2O和CO_2在β-SiO_2(100)面的吸附能分布在-0.2 eV～-0.1eV区间内,为物理吸附;最小吸附能大小依次为:CH_4 H_2O CO_2,即,CO_2的吸附能力最强,H_2O次之,CH_4最弱;各吸附质处于吸附能最大与最小时的键长键角变化均小于1%,最大吸附能对应的吸附质键长键角变化率均大于吸附能最小时的,吸附质的物理结构变化微弱表明其所受作用力微弱;基底处于最稳定吸附位时态密度基本重合,表明各吸附质与β-SiO_2表面相互作用相似且差异较小;CH_4、H_2O、CO_2的态密度均出现不同程度偏移,且CO_2在能量更低的区域具有态密度分布,更易优先吸附.     

基于DFT的间羟基苯甲酸分子表面增强拉曼光谱研究

本文研究了间羟基苯甲酸(m-hydroxybenzoic acid,MHBA)的常规拉曼散射(normal Raman scattering,NRS)光谱及其吸附在Ag纳米颗粒上的表面增强拉曼散射(surface-enhanced Raman scattering,SERS)光谱。采用密度泛函理论(density functional theory,DFT),在B3LYP/6-31+G**(C、H、O)/LANL2DZ(Ag)水平上,对MHBA分子进行了几何结构优化,在此基础上计算了MHBA分子的NRS光谱以及其吸附在Ag纳米颗粒上两种不同吸附构型下的SERS光谱,并和实验值进行比较。结果表明,间羟基苯甲酸分子通过羧基与羟基共同吸附构型的计算结果比该分子通过羧基吸附构型的计算结果更符合实验值。最后,利用GaussView可视化软件对其振动模式进行了全面归属。     

Biomass-derived oxygenate reforming on Pt(111): A demonstration of surface science using d-glucose and its model surrogate glycolaldehyde

Molecules derived from cellulosic biomass, such as glucose, represent an important renewable feedstock for the production of hydrogen and hydrocarbon-based fuels and chemicals. Development of efficient catalysts for their reformation into useful products is needed; however, this requires a detailed understanding of their adsorption and reaction on catalytically active transition metal surfaces. In this paper we demonstrate that the standard surface science techniques routinely used to characterize the reaction of small molecules on metals are also amenable for use in studying the adsorption and reaction of complex biomass-derivatives on single crystal metal surfaces. In particular, Temperature Programmed Desorption (TPD) and High Resolution Electron Energy Loss Spectroscopy (HREELS) combined with Density Functional Theory (DFT) calculations were used to elucidate the adsorption configuration of d-glucose and glycolaldehye on Pt(111). Both molecules were found to adsorb in an η₁ aldehyde configuration partially validating the use of simple, functionally-equivalent model compounds for surface studies of cellulosic oxygenates.     

葡萄糖分子的表面增强拉曼光谱研究

本文以密度泛函理论(density functional theory, 简称DFT)采用B3LYP混合泛函和6-31++G(d, p)基函数组计算的葡萄糖的分子振动光谱为根据, 首次对葡萄糖分子的常规拉曼光谱(NRS)进行了详细的指认, 并对葡萄糖分子的振动模式进行了归属。在以4-巯基吡啶为桥联剂分子修饰的银镜衬底上, 观测到葡萄糖分子的表面增强拉曼散射(SERS), 并对葡萄糖分子在银表面的吸附状态进行了分析。     

The adsorption of a substituted benzene,the ethynyl-trifluoro-toluene on Si(100)-2 × 1

The adsorption of 3-ethynyl-trifluoro-toluene (ETFT) on Si(100)-2 × 1 surface in ultra high vacuum is studied in the low coverage regime, through a joint experimental and theoretical approach. The STM images of both filled and empty states revealed few distinct adsorption configurations. On the basis of Density Functional Theory (DFT) calculations the STM images were simulated and three main adsorption configurations were identified, with a predominance of di-sigma bonded species that leave the benzene ring unreacted. A discussion of the reactivity of the reconstructed silicon surface towards benzene derivatives is proposed by comparing the adsorption of ETFT close related molecules, like styrene and phenylacetylene.     

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.     

硫原子在镍基合金825(001)面吸附的第一性原理研究

元素硫在镍基合金表面吸附产生严重的电化学腐蚀,为从原子尺度研究硫腐蚀机理,采用第一性原理方法,构建并优化了镍基合金825的晶胞结构模型,计算分析了S原子在镍基合金825耐蚀性较差面(001)晶面的吸附及电子转移情况.结果表明:Ni原子占据顶角, Cr原子和Fe原子对称占据面心是镍基合金825稳定的晶胞结构;原子S在镍基合金825(001)面上最稳定的吸附位为四重穴位,吸附能为-6.51 eV; S吸附前后的态密度(DOS)和二维电荷差分密度图(DCD)对比发现,镍基合金825中Fe与S之间电荷偏移明显,形成离子键,易生成腐蚀产物Fe_xS_y. S的吸附对镍基合金825中Cr原子的电子分布影响不大,且合金中Cr和Ni抑制了合金中Fe与S之间的相互作用,从而提高了合金耐蚀性.     

A Density Functional Theory study on gold cyanide interactions: The fundamentals of ore cleaning

We have employed Density Functional Theory calculations to study the adsorption of CN, CN^? and KCN on Au(111) and Au(211) surfaces and compare the obtained results to CO. The adsorption of CN, CN^?, and KCN are exothermic with respect to the gas-phase moieties, and the adsorption energy increases at steps. Our results show that the binding mechanism of CN^? is different from that of CO. The projected LDOS indicates that the bond between the flat surface and CN shows very small overlap between metal and CN states. This overlap increases provided that extra charge is present or low-coordinated Au atoms are available. Charge transfer is analyzed via the Bader method and the Electron Localization Function. Both suggest that Au–CN bonding resembles that in the gas-phase [Au(CN)₂]^?, which has been identified as covalent. The present study justifies the mechanism described in the literature involving a first CN^? adsorption, electron transfer to form AuCN, and second adsorption of a CN^? to form the soluble species and dissolve gold atoms from low grade ores.     

The effect of the topography of heterogeneous surfaces on the adsorption energy distribution,evaluated by the asymptotically correct,condensation approximation

In our previous paper [1], we used the well-known CA(Condensation Approximation) method, to evaluate the adsorption energy distribution from experimental isotherms, assuming that adsorption sites of different adsorption energies are distributed on adsorbent surface completely at randon.This note is an extension of our theory, using the ACCA, (Asymptotically Correct Condensation Approximation), which, in the hitherto investigation, was used only to adsorption on surfaces, with the patchwise topographical distribution of adsorption sites.     

Millimeter-wave band microwave signal spectrum measurement on the basis of the Hilbert transform of Josephson junction function response

Theory and the canonical algorithm for the Hilbert-spectroscopy of microwave signals based on of the AC Josephson effect are propoused. The spectrum analyzer microwave unit using the Josephson junction as a measuring sensor is described.     

CO2 adsorption on calcium oxide: An atomic-scale simulation study

We present a detailed study of CO₂ adsorption on CaO, by means of atomic-scale simulations relying on Density Functional Theory. Combining ab initio thermodynamics of the CO₂ gas phase and a thorough analysis of its interaction with the oxide, we build an orientation-sensitive adsorption model, which demonstrates that low coverage by the gas is expected in a wide range of working conditions, including the domain of stability of CaCO₃ calcite. Investigation of the interactions between the adsorbed molecules reinforces this conclusion. Our work thus provides a strong hint that calcite nucleation should occur by a localised mechanism, discarding the possibility of collective surface transformation.