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1.
采用密度泛函理论对噻吩分子在Ni(100),Cu(100)和Co(100)表面的吸附构型进行了GGA/PBE水平上的计算,通过比较吸附能及各结构参数,预测了各金属的脱硫活性.结果表明:噻吩在Ni表面发生了作用力较强的化学吸附,噻吩的S—C键有解离趋势;在Cu表面发生的是作用力较弱的物理吸附,噻吩分子构型并未发生较大变化;而噻吩在Co表面的吸附作用最强,噻吩的S—C键已经发生解离,和Co原子之间的距离已经达到甚至短于Co—S键的键长.这说明,金属的吸附脱硫活性为CoNiCu,与实验研究结果一致.此3种金属最稳定的分子吸附位均为hol45位. 相似文献
2.
Atomic oxygen chemisorption has been studied for the fourfold hollow site of the Ni(100) surface and for the threefold hollow site of the Ni(111) surface. To model the Ni(100) surface, 10 different clusters in the range Ni5 to Ni41 were used, and for the Ni(111) surface, 11 different clusters in the range Ni13 to Ni43 were used. A detailed analysis of the orbital occupations of the cluster with and without oxygen for the different clusters shows that there are three different possible bonding mechanisms. In two of these, the basic feature is that a1 electrons of the cluster are kicked out by the oxygen 2pz orbital and moved to holes in the 2px, y orbitals. A picture where the oxygen electrons fit into the electronic structure of the cluster is emphasized. The third mechanism, which is applicable for only one cluster, can be described as the formation of two covalent bonds of E symmetry. The final best estimate of the oxygen chemisorption energy for the Ni(100) surface is about 130 kcal/mol, and for the Ni(111) surface, about 115 kcal/mol. In particular for the Ni(111) surface, an excited oxygen state with radical character is identified, which might be a catalytically important species. The excitation energy to reach this state should be on the order of 10 kcal/mol for the Ni(111) surface. 相似文献
3.
Xiang Feng Jia Shuai Qin Yu Ze Xin Wang Yongshan Ma 《Surface and interface analysis : SIA》2008,40(10):1350-1355
Both adsorption and dissociation of the diatomic molecular NO on Pd (100) and (111) surfaces are studied using the extended London‐Eyring‐Polyani‐Sato (LEPS) method constructed by means of 5‐MP (the 5‐parameter Morse potential). All critical characteristics of the system that we obtain, such as adsorption geometry, binding energy, eigenvalues for vibration, are in good agreement with the experimental results. On Pd (100) surface, NO prefers to adsorb in fourfold hollow site (H) uprightly at low coverage. With increase in the coverage NO gradually tilts in fourfold hollow and bridge sites. For NO? Pd (111) system, two adsorption states are found at low coverage, of which one adsorption state is the B(tilt) state that the centroid of NO projects at bridge site, another (H? B? H state) that NO almost parallels to the (111) surface with the vibration frequency of 610 cm?1, but the frequency is near to that of the atoms, which is easy to be ignored in experiments. At high coverage, two transitional states (BH and HT) are found. NO is difficult to dissociate on Pd (100) and (111) surfaces. Especially for NO? Pd (111) system, the three‐well‐potential dissociation mode is initially put forward to show the remarkable dissociation process with two dissociation transitional states of NO on Pd (111). Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
4.
采用密度泛函理论与周期性平板模型相结合的方法,对CO在Pt(111)表面top,fcc,hcp和bridge 4个吸附位和Pt-M(111)(M=Ni,Mg)表面h-top,M-top,Pt(M)Pt-bridge,Pt(M)M-bridge,Pt(Pt)M-bridge,M(Pt)M-bridge,Pt1M2-hcp... 相似文献
5.
The adsorption energy of a CO2 molecule on various sites of the (100) face of NACl is determined (i) by considering the molecule in the electrostatic field created by the substrate, and (ii) by treating the cluster (CO2Cl2)2? in the field created by the rest of the substrate. The electrostatic and polarization contributions are obtained by means of the SCF method. The dispersion-repulsion term is successively estimated by means of the hard-sphere model and an adapted potential model. Whatever the model used, the calculated adsorption energy is in the range 6–10 kcal/mole; this is in acceptable agreement with experiment. However, only the cluster model gives the correct splitting of the ν2 frequency of CO2. 相似文献
6.
Kanai Y Cicero G Selloni A Car R Galli G 《The journal of physical chemistry. B》2005,109(28):13656-13662
Biotin is a promising candidate for functionalization of semiconducting surfaces, given its strong, unmatched affinity to specific proteins such as streptavidin and avidin. Using density functional theory, we have carried out a theoretical investigation of the structural and electronic properties of biotin chemisorbed on a biocompatible substrate; in particular we have considered the clean and hydroxylated Si-SiC(001) surfaces. Our calculations show that, upon chemisorption, biotin retains the electronic properties responsible for its strong affinity to proteins. While the electronic states of the hydroxylated surface undergo negligible changes in the presence of the molecule, those of the clean surface are considerably affected. 相似文献
7.
8.
F. Mollaamin M. T. Baei M. Monajjemi R. Zhiani B. Honarparvar 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2008,82(13):2354-2361
In this study, hydrogen adsorption on the surface of vanadium at various positions (top, bridge, and central sites) was studied,
and the binding energies of hydrogen species adsorbed on vanadium were calculated using density functional theory (DFT) within
the generalized gradient approximation (GGA). The potential of the adsorption of hydrogen on vanadium was examined as a function
of both surface coverage and adsorption site. Our results were in excellent agreement with the experimental values reported
in the literature. The relative stabilities of hydrogen chemisorption were independent of both the transition metal surface
and surface coverage. That is, hydrogen exhibited insignificant selectivity with respect to positions on the metal surface.
Our data on H2/V surface chemisorption revealed that the stablest model for hydrogen adsorption was that on the vertical bridge site. The
adsorption energy for this model was lower than for the other sites. However, adsorption on bridge-hydrogen vacancies was
strong. 相似文献
9.
Mendoza SM Whelan CM Jalkanen JP Zerbetto F Gatti FG Kay ER Leigh DA Lubomska M Rudolf P 《The Journal of chemical physics》2005,123(24):244708
Thin films of fumaramide [2]rotaxane, a mechanically interlocked molecule composed of a macrocycle and a thread in a "bead and thread" configuration, were prepared by vapor deposition on both Ag(111) and Au(111) substrates. X-ray photoelectron spectroscopy (XPS) and high-resolution electron-energy-loss spectroscopy were used to characterize monolayer and bulklike multilayer films. XPS determination of the relative amounts of carbon, nitrogen, and oxygen indicates that the molecule adsorbs intact. On both metal surfaces, molecules in the first adsorbed layer show an additional component in the C 1s XPS line attributed to chemisorption via amide groups. Molecular-dynamics simulation indicates that the molecule orients two of its eight phenyl rings, one from the macrocycle and one from the thread, in a parallel bonding geometry with respect to the metal surfaces, leaving three amide groups very close to the substrate. In the case of fumaramide [2]rotaxane adsorption on Au(111), the presence of certain out-of-plane phenyl ring and Au-O vibrational modes points to such bonding and a preferential molecular orientation. The theoretical and experimental results imply that the three-dimensional intermolecular configuration permits chemisorption at low coverage to be driven by interactions between the three amide functions of fumaramide [2]rotaxane and the Ag(111) or Au(111) surface. 相似文献
10.
Jo o B.L. Martins Vicent Moliner Juan Andr s Elson Longo Carlton A. Taft 《Journal of Molecular Structure》1995,330(1-3):347-351
The adsorption of water molecule and hydroxyl ions on the (10-10) and (0001) ZnO surfaces has been studied for (ZnO)4, (ZnO)5 and (ZnO)6 cluster models. Different representations for the atomic basis sets and the effective core potential (ECP) approximations have been employed and the effects of cluster size, conformation and basis sets are analyzed and discussed. 相似文献
11.
Fernando Ruette Eduardo V. Ludeta Antonio HernÎandez 《International journal of quantum chemistry》1986,29(5):1351-1364
We have used the MINDO/SR molecular orbital method in order to model the migration of hydrogen atoms over a Ni(100) surface. The present calculations indicate the existence of two different states for adsorbed hydrogen, a result which is in agreement with experimental thermal desorption data and LEED . A detailed analysis of the electronic factors involved in this process is presented. 相似文献
12.
We propose a model of the dissociative adsorption of hydrogen on nickel single-crystal face. In this model, we treat the Ni(100) surface as a strongly correlated energetically heterogeneous surface, because the density functional theory (DFT) studies indicate that hydrogen atoms may adsorb either on hollow sites (energetically more favorable, binding energy 48 kJ/mol H) or bridge sites with the binding energy less by 11 kJ/mol H. The essential assumption of the proposed model is that the dissociation of the hydrogen molecule is possible only over the topmost Ni atom, and the resulting H atoms may adsorb either on two free hollow sites (but the adjacent bridge sites must be free) or two bridge sites (the adjacent hollow sites must be free). If the above condition is not fulfilled, then the dissociation and adsorption are impossible. The second assumption is that the rate (probability) of the associative desorption is limited by the rate of diffusion of H atoms on the surface. This is because the two H atoms desorb, giving an H2 molecule, only when they meet on two adjacent hollow-bridge sites. Our model recovers very well the behavior of the experimental equilibrium adsorption isotherms as well as kinetic isotherms. As a result, we stated that hydrogen atoms are not completely free on the surface, but they cannot also be considered localized at room and elevated temperatures. Additionally, while analyzing the kinetic adsorption isotherms, we stated that the rate-limiting step during the dissociative adsorption of H2 is the disintegration of the activated complex and the subsequent adsorption of hydrogen atoms. 相似文献
13.
The application of a radiotracer method to in situ studies of the adsorption of thiourea labelled with either C-14 or S-35 nuclides on smooth n-type and p-type Si (100) electrodes and on rough p-Si electrodes is described. The adsorption takes place over the whole potential range studied, i.e. −0.5 to 1.2 V. It was found that during the interaction of thiourea with the silicon surface, two different products are formed. The dependence of the surface concentration of the adsorbates on the electrode potential and on the bulk concentration of thiourea was determined. Two different species are proposed to be present on the electrode surface as a result of surface processes: physically adsorbed thiourea molecules and sulphur atoms which are chemically bonded to the surface. Different activities of smooth and rough silicon electrodes towards the adsorption of thiourea were demonstrated. 相似文献
14.
By means of density functional theory (B3LYP/6-31G*) coupled with effective cluster models, we predict that the well-known cycloaddition reactions of carbenes and nitrenes to alkenes in organic chemistry can be employed as a new type of surface reaction to organically functionalize the Si (100) and Ge (100) surfaces at low temperature. The well-established abundance of carbenes and nitrenes addition chemistry in organic chemistry provides versatile flexibility of functionalizing the surfaces of Si (100) and Ge (100), which can potentially impart new organic functionalities to the semiconductors surface for novel applications in a diversity of fields. Our predictions strongly advance the concept of using organic reactions to modify the solid surface in a controlled manner and quite intriguing chemistry can lie in the material featuring the analogous bonding motif. In further perspective, implications for other theoretical work, regarding disilenes, digermenes, silenes, and germenes that all feature the bonding motif similar to alkenes, are also discussed. 相似文献
15.
The adsorption losses of chromium(III) or (VI) on the walls of Pyrex, flint glass and polyethylene beakers have been investigated. Chromium(III) or (VI) solutions were stored in beakers at different hydrogen ion concentrations, and losses due to adsorption were measured at various contact times by counting the γ-ray activity from chromium-51 radiotracer. At pH 6.95, chromium(III) solutions showed the greatest instability, particularly in polyethylene beakers, where losses up to 25% were observed at the end of the 15-day contact period. Chromium(VI) showed a completely different pattern; losses less than 1% were observed at the end of 15 days on all the three types of containers. 相似文献
16.
The adsorption behavior of ethylene on Ni(100) at a variety of temperatures has been studied using temperature programmed desorption, and X-ray and UV photoemission. The adsorption of ethylene at 98 K results in molecular adsorption with a saturation C/Ni ratio of 0.76. Heating this surface to any temperature between 213 and 683 K reduces the C/Ni ratio to 0.5. Exposure to ethylene at 300 K leads to decomposition producing surface carbide, adsorbed hydrogen atoms and an adsorbed CxH2x species. A comparison with other work on Ni(111) indicates that ethylene adsorption processes are structure sensitive. 相似文献
17.
An ab initio-based kinetic Monte Carlo algorithm was developed to simulate the direct decomposition of NO over Pt and different PtAu alloy surfaces. The algorithm was used to test the influence of the composition and the specific atomic surface structure of the alloy on the simulated activity and selectivity to form N2. The apparent activation barrier found for the simulation of lean NO decomposition over Pt(100) was 7.4 kcal/mol, which is lower than the experimental value of 11 kcal/mol that was determined over supported Pt nanoparticles. Differences are likely due to differences in the surface structure between the ideal (100) surface and supported Pt particles. The apparent reaction orders for lean NO decomposition over the Pt(100) substrate were calculated to be 0.9 and -0.5 for NO and O2, respectively. Oxygen acts to poison Pt. Simulations on the different Pt-Au(100) surface alloys indicate that the turnover frequency goes through a maximum as the Au composition in the surface is increased, and the maximum occurs near 44% Au. Turnover frequencies, however, are dictated by the actual arrangements of Pt and Au atoms in the surface rather than by their overall composition. Surfaces with similar compositions but different alloy arrangements can lead to very different activities. Surfaces composed of 50% Pt and 50% Au (Pt4 and Au4 surface ensembles) showed very little enhancement in the activity over that which was found over pure Pt. The Pt-Pt bridge sites required for NO adsorption and decomposition were still effectively poisoned by atomic oxygen. The well-dispersed Pt(50%)Au(50%) alloy, on the other hand, increased the TOF over that found for pure Pt by a factor of 2. The most active surface alloy was one in which the Pt was arranged into "+" ensembles surrounded by Au atoms. The overall composition of this surface is Pt(56.2%)Au(43.8%). The unique "+" ensembles maintain Pt bridge sites for NO to adsorb on but limit O2 as well as NO activation by eliminating next-nearest neighbor Pt-bridge sites. The repulsive interactions between two adatoms prevent them from sharing the same metal atoms. The decrease in the oxygen coverage leads to a greater number of vacant sites available for NO adsorption. This increases the NO coupling reaction and hence N2 formation. The inhibition of the rate of N2 formation by O2 is therefore suppressed. The coverage of atomic oxygen decreases from 53% on the Pt(100) surface down to 19% on the "+" ensemble surface. This increases the rate of N2 formation by a factor of 4.3 over that on pure Pt. The reaction kinetics over the "+" ensemble Pt(56.2%)Au(43.8%) surface indicate apparent reaction orders in NO and oxygen of 0.7 and 0.0, respectively. This suggests that oxygen does not poison the PtAu "+" alloy ensemble. The activity and selectivity of the PtAu ensembles significantly decrease for alloys that go beyond 60% Au. Higher coverages of Au shut down sites for NO adsorption and, in addition, weaken the NO and O bond strengths, which subsequently promotes desorption as well as NO oxidation. The computational approach identified herein can be used to more rapidly test different metal compositions and their explicit atomic arrangements for improved catalytic performance. This can be done "in silico" and thus provides a method that may aid high-throughput experimental efforts in the design of new materials. The synthesis and stability of the metal complexes suggested herein still ultimately need to be tested. 相似文献
18.
The adsorption and decomposition of NO have been investigated by using density functional theory method at the generalized gradient approximation level. We have performed calculations on adsorption energies and structures of NO on Ni(211) and Pd(211) surfaces with full-geometry optimization and compared them with the experimental data. The most favorite adsorption on both surfaces occurs at the bridge site parallel to step edge (sb), while the energy difference from the second favorite site of a threefold hollow site near step edge is less than 0.1 eV. Decomposition pathways have been investigated with transition state search. The decomposition pathway, where NO leans toward the step, is most probable for both surfaces. The overall activation energy for decomposition is 0.39 and 1.26 eV for Ni(211) and Pd(211), respectively. The present results clearly show that the NO molecules on Pd(211) are less activated than those on Ni(211). We have studied also reorganization of NO on Pd(211) at higher coverages up to 1/3 ML (monolayer) [three NO molecules in a (3 x 1) unit cell]. The site occupation is not in a sequential manner as the NO coverage is increased, and a reorganization of NO adsorbates occurs (the NO molecule at sb becomes tilting up at higher coverage), which can interpret the experimental data of Yates and co-workers very well. 相似文献
19.
Theoretical studies of CO adsorption on a two-layer Ag(100) film and on a two-layer Ag film on a MgO(100) support are reported. Ab initio calculations are carried at the configuration interaction level of theory using embedding methods to treat the metal-adsorbate region and the extended ionic solid. The metal overlayer is considered in two different structures: where Ag-Ag distances are equal to the value in the bulk solid, and for a slightly expanded lattice in which the Ag-Ag distances are equal to the O-O distance on the MgO(100) surface. The calculated adsorption energy of Ag(100) on MgO(100) is 0.58 eV per Ag interfacial atom; the Ag-O distance is 2.28 A. A small transfer of electrons from MgO to Ag occurs on deposition of the silver overlayer. CO adsorption at an atop Ag site is found to be the most stable for adsorption on the two-layer Ag film and also for adsorption on Ag deposited on the oxide; CO adsorption energies range from 0.12 to 0.19 eV. The CO adsorption energy is reduced for the Ag/MgO system compared to adsorption on the unsupported metal film thereby providing evidence for a direct electronic effect of the oxide support at the metal overlayer surface. Expansion of the Ag-Ag distance in the two-layer system also reduces the adsorption energy. 相似文献