外吸附CO过渡金属团簇Pd5(CO)n(n=1 to 6)的几何结构、电子性质、前线轨道和磁性的密度泛函计算研究

本文采用密度泛函理论中的广义梯度近似对过渡金属团簇Pd5(CO)n(n=1 to 6)的几何结构、电子性质、前线轨道和磁性进行计算研究，由结构优化可知：当CO分子的C原子吸附在面桥位时形成的单重态Pd5CO结构热力学最稳定，和Zanti等人（Eur. J. Inorg. Chem. 2009, 3904）得到的结论一致。Pd5(CO)2和Pd5(CO)3最稳定结构中，第二个和第三个CO分子都吸附在边桥位，而第一个CO分子吸附在面桥位。但是对于最稳定的Pd5(CO)n(n=4,5,6), 所有的CO分子都位于边桥位。从吸附能的角度看，Pd5(CO)2应该是最容易得到的吸附产物。由能隙可知：Pd5(CO)n(n=1 to 6)的动力学稳定性相比较Pd5有所增加，但是并不会随着CO分子数目的增加而呈现递增或者递减的规律，其中Pd5(CO)3具有最好的动力学稳定性。CO在Pd5上发生非解离性化学吸附，CO健的强度变化逐渐变小。CO对HOMO和LUMO贡献很小，使得HOMO和LOMO的成分发生一定的改变。由VIP和VEA计算可知：随着CO数目的增加，Pd5(CO)n(n=1 to 6)的失电子能力逐渐降低，而得电子能力逐渐增强。Pd5具有2μB的磁矩，但是Pd5(CO)n(n=1 to 6)的磁性完全淬灭。     

外吸附CO过渡金属团簇Pd5(CO)n(n=1～6)的几何结构、电子性质、前线轨道和磁性的密度泛函计算研究

本文采用密度泛函理论中的广义梯度近似对过渡金属团簇Pd5(CO)n(n=1～6)的几何结构、电子性质、前线轨道和磁性进行计算研究,由结构优化可知:当CO分子的C原子吸附在面桥位时形成的单重态Pd5 CO结构热力学最稳定,和Zanti等人(Eur.J.Inorg.Chem.2009,3904)得到的结论一致.Pd5(CO)2和Pd5 (CO)2最稳定结构中,第二个和第三个CO分子都吸附在边桥位,而第一个CO分子吸附在面桥位.但是对于最稳定的Pd5 (CO)n(n=4,5,6),所有的CO分子都位于边桥位,从吸附能的角度看,Pd5(CO)2应该是最容易得到的吸附产物.由能隙可知:Pd5 (CO)n(n=1～6)的动力学稳定性相比较Pd5有所增加,但是并不会随着CO分子数目的增加而呈现递增或者递减的规律,其中Pd5 (CO)3具有最好的动力学稳定性.CO在Pd5上发生非解离性化学吸附,CO健的强度变化逐渐变小.CO对HOMO和LUMO贡献很小,使得HOMO和LOMO的成分发生一定的改变.由VIP和VEA计算可知:随着CO数目的增加,Pd5(CO)n(n=1～6)的失电子能力逐渐降低,而得电子能力逐渐增强.Pd5具有2μB的磁矩,但是Pd5 (CO)n(n=1～6)的磁性完全淬灭.     

基于密度泛函理论研究掺杂Pd石墨烯吸附O2及CO

基于第一性原理的密度泛函理论研究了单个O₂和CO气体分子吸附于本征石墨烯和掺杂钯(Pd)的石墨烯的体系, 通过石墨烯掺Pd前后气体分子的吸附能、电荷转移及能带和态密度的计算, 发现掺Pd后气体分子吸附能和电荷转移显著增大, 这是由于Pd的掺杂, 在本征石墨烯能带中引入了杂质能级, 增强了石墨烯和吸附气体分子间的相互作用; 氧化性气体O₂和还原性气体CO吸附对石墨烯体系能带结构和态密度的影响明显不同, 本征石墨烯吸附O₂后, 费米能级附近态密度变大, 掺Pd后在一定程度变小; 吸附还原性的CO后, 石墨烯费米能级附近态密度几乎没有改变, 表明掺杂Pd不会影响石墨烯对CO的气体灵敏度, 但由于CO对石墨烯的吸附能增大, 可以提高石墨烯对还原性气体的气敏响应速度.     

HCOOH在Pd-Fe(111)(nPd∶nFe=1∶1)表面吸附的密度泛函理论研究简

采用密度泛函理论与周期性平板模型相结合的方法,对HCOOH在Pd(111)表面top,fcc,hcp,bridge四个吸附位和Pd-Fe(111)表面Pd-top,Fe-top,PdPd-bridge,PdFe-bridge,FeFe-bridge,Pd2Fehcp,PdFe2-hcp,Pd2Fe-fcc,PdFe2-fcc等9个吸附位的13种吸附模型进行了能量计算、构型优化,得到了HCOOH较有利的吸附位;并对清洁表面进行能带分析.结果表明:掺杂Fe后,Pd催化剂对HCOOH催化活性增强;HCOOH在Pd(111)表面的最稳定吸附位fcc的吸附能是-41.8kJ·mol-1,在Pd-Fe(111)表面的最稳定吸附位Pd2Fe-hcp的吸附能是-126.5kJ·mol-1,而且HCOOH在金属表面属于化学吸附.     

Pd与CeO2(111)面的相互作用的第一性原理研究

采用基于广义梯度近似的投影缀加平面波(projector augmented wave) 赝势和具有三维周期性边界条件的超晶胞模型，用第一性原理计算方法，计算并分析了Pd在CeO₂(111)面上不同覆盖度时的吸附能，价键结构和局域电子结构. 考虑了单层Pd和1/4单层Pd两种覆盖度吸附的情况. 结果表明：1)在单层吸附时，Pd的最佳吸附位置是O的顶位偏向Ce的桥位；在1/4单层吸附时，Pd最易在O的桥位偏向次层O的顶位吸附.2) 单层覆盖度吸附时，吸附原子Pd之间的作用较强；1/4单 关键词： 三元催化剂 Pd 2')" href="#">CeO₂ 吸附 密度泛函理论     

HCOOH在Pd-Fe(111)(nPd:nFe=1:1)表面吸附的密度泛函理论研究

采用密度泛函理论与周期性平板模型相结合的方法,对HCOOH在Pd(111)表面top, fcc, hcp, bridge 四个吸附位和Pd-Fe(111)表面Pd-top, Fe-top, PdPd-bridge, PdFe-bridge, FeFe-bridge, Pd2Fe-hcp, PdFe2-hcp, Pd2Fe –fcc, PdFe2-fcc等9个吸附位的13种吸附模型进行了能量计算、构型优化,得到了HCOOH较有利的吸附位;并对清洁表面进行能带分析。结果表明：掺杂Fe后,Pd催化剂对HCOOH催化活性增强;HCOOH在Pd(111)表面的最稳定吸附位fcc的吸附能是-41.8kJ•mol-1,在Pd-Fe(111)表面的最稳定吸附位Pd2Fe-hcp的吸附能是-126.5 kJ•mol-1,而且HCOOH在金属表面属于化学吸附。     

用Xα-DV方法研究CO,NO在Ⅷ族过渡金属表面的化学吸附(Ⅱ)——NO分子在Pd(111)表面的化学吸附

本文用X_α-DV方法计算了NO在Pd(111)表面化学吸附问题。得到了它的电子结构,包括分子丛轨道能量本征值谱、态密度、电荷转移等等结果。在计算中特别考虑了NO之间的相互作用,所得总态密度与实验UPS十分相符,从而支持了LEED所示的几何结构,决定了NO的吸附高度为1.27?,并得知吸附于Pd表面的NO分子之间的相互作用十分重要。从理论上探讨了NO分子在Pd表面吸附时的活化作用。计算了NO分子各个轨道上的占有数,发现其电荷转移情况与CO在过渡金属表面吸附的情况相似。另外,还发现NO的吸附对Pd的价电子能带无重大影响。 关键词：     

用X_α-DV方法研究CO,NO在Ⅷ族过渡金属表面的化学吸附(Ⅱ)——NO分子在Pd(111)表面的化学吸附

本文用X_α-DV方法计算了NO在Pd(111)表面化学吸附问题。得到了它的电子结构,包括分子丛轨道能量本征值谱、态密度、电荷转移等等结果。在计算中特别考虑了NO之间的相互作用,所得总态密度与实验UPS十分相符,从而支持了LEED所示的几何结构,决定了NO的吸附高度为1.27A,并得知吸附于Pd表面的NO分子之间的相互作用十分重要。从理论上探讨了NO分子在Pd表面吸附时的活化作用。计算了NO分子各个轨道上的占有数,发现其电荷转移情况与CO在过渡金属表面吸附的情况相似。另外,还发现NO的吸附对Pd的价电子能带无重大影响。     

CO在Pd掺杂Rh(111)表面吸附的理论研究

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Rh(111)表面top、fcc、hcp、bridge四个吸附位和Rh-Pd(111)表面Rh-top、Pd-top、Rh Rh-bridge、Rh Pd-bridge、Pd Pd-bridge、Rh2Pdhcp、Rh Pd2-hcp、Rh2Pd-fcc、Rh Pd2-fcc九个吸附位的13种吸附模型进行了构型优化、能量计算,得到了CO较有利的吸附位;并对最佳吸附位进行总态密度分析.结果表明:CO在Rh(111)和Rh-Pd(111)表面的最稳定吸附位分别为Rh-hcp和Rh-top位,其吸附能的大小顺序为Ph(111)Rh-Pt(111);CO与金属表面成键,属于化学吸附.     

钴原子及其团簇在Rh(111)和Pd(111)表面的扫描隧道显微学研究

利用扫描隧道显微镜和扫描隧道谱(STM/STS)及单原子操纵,系统研究了单个钴原子(Co) 及其团簇在Rh (111)和Pd (111)两种表面的吸附和自旋电子输运性质. 发现单个Co原子在Rh (111)上有两种不同的稳定吸附位,分别对应于hcp和fcc空位, 他们的高度明显不同,在针尖的操纵下单个Co原子可以在两种吸附位之间相互转化. 在这两种吸附位的单个Co原子的STS谱的费米面附近都存在很显著的峰形结构, 经分析认为Rh (111)表面单个Co原子处于混价区,因此这一峰结构是d轨道共振 和近藤共振共同作用的结果.对于Rh (111)表面上的Co原子二聚体和三聚体, 其费米面附近没有观测到显著的峰,这可能是由于原子间磁交换相互作用 和原子间轨道杂化引起的体系态密度改变所共同导致.与Rh (111)表面不同, 在Pd (111)表面吸附的单个Co原子则表现出均一的高度.并且对于Pd (111)表面所有 单个Co原子及其二聚体和三聚体,在其STS谱的费米面附近均未探测到显著的电子结构, 表明Co原子吸附于Pd (111)表面具有与Rh (111)表面上不同的原子-衬底相互作用与自旋电子输运性质.     

A theoretical study of Zn adsorption and desorption on a Pd(111) substrate

The adsorption and structure of Zn on a Pd(111) surface has been investigated using density functional theory (DFT). It could be shown that Zn prefers adsorption sites with a maximum amount of Pd neighbours on the Pd(111) surface. Zn does form a stable PdZn surface alloy on Pd(111) which shows a (2 × 1) structure. The surface energy of this surface alloy decreases with increasing numbers of PdZn layers. Furthermore the adsorption of Zn on the PdZn surface alloy was investigated. The electronic structure of the Zn layers approaches the bulk Zn state only after a thickness of 4 additional Zn layers. A clear charge transfer between Pd and Zn has been found and the electronic structure of the Zn suggests an anisotropic binding of the Zn, with higher binding energy within a Zn layer and lower binding energy between two Zn layers. This is also reflected in the different desorption energies of different Zn layers found in experiments.     

Molecular beam study of CO chemisorption on alumina-supported Pd particles

The adsorption of carbon monoxide on small alumina-supported Pd particles and on a Pd(111) single crystal has been studied with a molecular beam techniques. The measured sticking coefficient shows that CO adsorbs on palladium surface according to precursor states. It is noted that a temperature dependent diffusion of gas molecules on the support influences the sticking probability of CO.     

Effect of the electronic structure of a substrate on the photoinduced behavior of adsorbed NO and CO molecules

Photoprocesses in systems produced by adsorption of NO and CO molecules on the Pt(111) and Ni(111) surfaces, as well as on the (111) surface of Pt-Ge alloy, is studied by the IR absorption spectroscopy, resonant multiphoton ionization, and UV photoelectron spectroscopy methods. The energy of photons varies between 2.3 and 6.4 eV. The character of the processes depends on the type of the metallic substrate. On the Pt(111) surface, NO molecules dissociate or are desorbed, depending on the degree of coverage. On the Ni(111) surface, the molecules only dissociate. Conversely, NO molecules adsorbed on the (111) surface of the Pt-Ge alloy are only desorbed from the surface. In the CO/Pt(111) and CO/Pt(111)-Ge systems, CO molecules adsorbed on on-top adsorption sites are desorbed under the action of the photons, while those occupying bridging adsorption sites change their properties insignificantly. A model of photoinduced processes is suggested. According to this model, the lifetime of a state excited by charge transfer between the valence band of the metal and the 2π-antibonding molecular orbital plays a decisive part in the occurrence of one or the other of these processes.     

Adsorption of carbon monoxide on silver/palladium alloys

The adsorption of carbon monoxide on epitaxial (100) and (111) planes of Ag/Pd alloys with definite surface compositions has been studied by means of LEED, Auger electron spectroscopy and work function measurements. The formation of ordered adsorbed structures is prevented by even small amounts of silver in the surfaces. The maximum variation of the work function with CO adsorption bears no simple relationship to the surface composition. From measured adsorption isotherms the isosteric heats of adsorption have been evaluated. For CO adsorption on pure Pd planes the adsorption energies E_ad are either constant or decrease slowly up to high coverages, whereas a continuous decrease was observed with the alloys indicating the energetical heterogeneity. The results are discussed on the basis of our knowledge about the nature of the CO chemisorption and about the electronic structure of Ag/Pd alloys.     

Formation, stability and CO adsorption properties of PdAg/Pd(1 1 1) surface alloys

The formation, stability and CO adsorption properties of PdAg/Pd(1 1 1) surface alloys were investigated by X-ray photoelectron spectroscopy (XPS) and by adsorption of CO probe molecules, which was characterized by temperature-programmed desorption (TPD) and high resolution electron energy loss spectroscopy (HREELS). The PdAg/Pd(1 1 1) surface alloys were prepared by annealing (partly) Ag film covered Pd(1 1 1) surfaces, where the Ag films were deposited at room temperature. Surface alloy formation leads to a modification of the electronic properties, evidenced by core-level shifts (CLSs) of both the Pd(3d) and Ag(3d) signal, with the extent of the CLSs depending on both initial Ag coverage and annealing temperature. The role of Ag pre-coverage and annealing temperature on surface alloy formation is elucidated. For a monolayer Ag covered Pd(1 1 1) surface, surface alloy formation starts at ∼450 K, and the resulting surface alloy is stable upon annealing at temperatures between 600 and 800 K. CO TPD and HREELS measurements demonstrate that at 120 K CO is exclusively adsorbed on Pd surface atoms/Pd sites of the bimetallic surfaces, and that the CO adsorption behavior is dominated by geometric ensemble effects, with adsorption on threefold hollow Pd₃ sites being more stable than on Pd₂ bridge sites and finally Pd₁ a-top sites.     

Adsorption of hydrogen on palladium single crystal surfaces

The adsorption of hydrogen on clean Pd(110) and Pd(111) surfaces as well as on a Pd(111) surface with regular step arrays was studied by means of LEED, thermal desorption spectroscopy and contact potential measurements. Absorption in the bulk plays an important role but could be separated from the surface processes. With Pd(110) an ordered 1 × 2 structure and with Pd(111) a 1 × 1 structure was formed. Maximum work function increases of 0.36, 0.18 and 0.23 eV were determined with Pd(110), Pd(111) and the stepped surface, respectively, this quantity being influenced only by adsorbed hydrogen under the chosen conditions. The adsorption isotherms derived from contact potential data revealed that at low coverages θ ∞ √p_H2, indicating atomic adsorption. Initial heats of H₂ adsorption of 24.4 kcal/mole for Pd(110) and of 20.8 kcal/mole for Pd(111) were derived, in both cases E_ad being constant up to at least half the saturation coverage. With the stepped surface the adsorption energies coincide with those for Pd(111) at medium coverages, but increase with decreasing coverage by about 3 kcal/mole. D₂ is adsorbed on Pd(110) with an initial adsorption energy of 22.8 kcal/mole.     

The adsorption and reaction of CO and O2 on PdAu alloy wires

Temperature programmed desorption (TPD) of CO and O₂ on PdAu alloy wires has been studied. The heat of adsorption, sticking coefficient and maximum coverage of CO were recorded for Pd, 83 Pd 17 Au, 60 Pd 40 Au. For Pd and Pd-rich alloys the heat of adsorption remained fairly constant but the maximum coverage fell markedly from 0.42 for Pd to less than 0.05 for bulk palladium atom fraction X_B^pd ? 0.83. The heat of adsorption, sticking coefficient and maximum coverage of O₂ were investigated for pure Pd. A very limited adsorption was recorded on 83 Pd 17 Au and none on the more Au-rich alloys. The adsorption data are used to discuss the CO + O₂ reaction. Activation energy and frequency factor are estimated on Pd, for the TPD conditions used here. Earlier rate constants (0.2 Torr, 150°C) for CO + O₂ on PdAu as a function of Au content correlates with the maximum coverage of chemisorbed CO, which in turn is correlated with the probability of finding a Pd_9±1 ensemble in the surface. Modern results on the d-band structure of the PdAu alloys suggest that the Pd₉ ensemble, i.e. a surface Pd atom without an Au atom in its coordination shell, would tend to optimise both the donor and acceptor actions of the Pd atoms involved in chemisorbing CO.     

Angular resolved studies of the photoemission bands from carbon monoxide adsorbed on palladium single crystals,and the assignment of these bands

The photoemission from CO adsorbed on a Pd(111) surface has been studied as a function of electron exit angle and of photon incidence angle; some studies have also been made using Pd(100) and Pd(110). The variations of intensity of the two photoemission bands support the sequence of levels 1π > 5θ ? 4θ for adsorbed CO. The adsorption on some other metals is discussed briefly.