2-氯噻吩在 Rh(111) 表面吸附的密度泛函理论研究

 采用密度泛函理论探讨了 2-氯噻吩分子在 Rh(111) 表面上吸附行为. 结果表明, 平行的 hol 位及 bridge 位上的吸附最稳定. 吸附后, 2-氯噻吩键长发生明显变化, 分子平面被扭曲, 分子中 C–H(Cl, S) 相对于金属表面倾斜上翘. 垂直吸附模式不如平行吸附模式稳定, 但吸附后噻吩环未发生变形. hol 及 bridge 吸附模式下 2-氯噻吩的芳香性已遭破坏, 噻吩环上的碳原子呈现准 sp3 杂化. 在平行的 hol 位吸附后, 2-氯噻吩环累计得到 0.77 个电子, 而 Rh(111) 表面累计失去 1.19 个电子.     

噻吩在M(111)(M=Pd,Pt,Au)表面的吸附(英文)

采用密度泛函理论(DFT),选取DMol3程序模块,对噻吩在M(111)(M=Pd,Pt,Au)表面上的吸附行为进行了探讨.通过对噻吩在不同底物金属上的吸附能、吸附构型、Mulliken电荷布居、差分电荷密度以及态密度的分析发现,噻吩在Pd(111)面上的吸附能最大,Pt(111)面次之,Au(111)面最小.吸附后,噻吩在Au(111)面上的构型几乎保持不变,最终通过S端倾斜吸附于top位;噻吩在Pd(111)及Pt(111)面上发生了折叠与变形,环中氢原子向上翘起,最终通过环平面平行吸附于hollow位.此外,噻吩环吸附后芳香性遭到了破坏,环中碳原子发生sp3杂化,同时电子逐渐由噻吩向M(111)面发生转移,M(111)面上的部分电子也反馈给了噻吩环中的空轨道,这种协同作用最终导致了噻吩分子稳定吸附于M(111)面.     

噻吩在M(111)(M=Pd,Pt, Au)表面的吸附

采用密度泛函理论(DFT), 选取DMol³程序模块, 对噻吩在M(111) (M=Pd, Pt, Au)表面上的吸附行为进行了探讨. 通过对噻吩在不同底物金属上的吸附能、吸附构型、Mulliken 电荷布居、差分电荷密度以及态密度的分析发现, 噻吩在Pd(111)面上的吸附能最大, Pt(111)面次之, Au(111)面最小. 吸附后, 噻吩在Au(111)面上的构型几乎保持不变, 最终通过S端倾斜吸附于top 位; 噻吩在Pd(111)及Pt(111)面上发生了折叠与变形, 环中氢原子向上翘起, 最终通过环平面平行吸附于hollow 位. 此外, 噻吩环吸附后芳香性遭到了破坏, 环中碳原子发生sp³杂化, 同时电子逐渐由噻吩向M(111)面发生转移, M(111)面上的部分电子也反馈给了噻吩环中的空轨道, 这种协同作用最终导致了噻吩分子稳定吸附于M(111)面.     

A DFT Study of Thiophene Adsorption on the Rh（111） Surfaces

Thiophene adsorption on the Rh(111) surfaces has been investigated by density functional theory.The results show that the adsorption at the hollow and bridge sites is the most stable.The molecular plane of the thiophene ring is distorted,the C=C bond is stretched to 1.448  and the C-C bond is shortened to 1.390.The C-H bonds tilt 22～42oaway from the surface.The calculated adsorption geometries are in reasonable agreement with population analysis and density of states.The thiophene molecule obtains 0.74 electrons,reflecting the interaction between the lone pair of sulfur and the d-orbitals of metal.The reaction paths and transition states for desulfurization of the molecule have been investigated.The bridge adsorption structure of thiophene leads to a thiol via an activated reaction with an energetic barrier of 0.30 eV.This second step is slightly difficult,and dissociation into a C4H4 fragment and a sulfur atom is possible,with an energetic barrier of 0.40 eV.     

苯在Rh(111)表面化学吸附的DV-Xα研究

The chemisorption of benzene on the Rh(111) surface is calculated using DVX_a method. The electronic structure, the ground states valence levels, Mulliken overlap populations, and the density of states (LDOS and TDOS) of the adsorption system C_6H_6/Rh_6(111) are obtained. The results of DV-X_a calculations indicate that the adsorbed benzene structure is unpertured from its stable gas-phase structure, is π-bonded to the Rh surface with ring plane parallel to the metal plane, and has a C_(3ν)(σ_d) bonding symmetry. We also discuss the charge transfer between adsorbate and substrate. The π electrons of benzene transfer to the empty d orbitals of Rh, so is resonance stability decreases and is easy to be hydrogenated. The results of TDOS are in agreement with UPS, supporting the LEED structural analysis. From figure 3, it can be found that the two peaks at 5—6 eV and 7—9 eV under Fermi level (E_F) move to left by about 0.5 eV in the process of adsorption, which are mainly contributed by the 2π and 1π orbiatls of benzene respectively and are widened, and the peaks at 2 eV and 4 eV over Fermi level also move to left, which are contributed by the empty d orbitals of Rh.     

Adsorption, vibration, and diffusion of O atoms on Rh low-index and (711) stepped defective surfaces

The adsorption, vibration, and diffusion of O atoms on Rh(100), Rh(111), Rh(110), and Rh(711) surfaces were studied using the 5-parameter Morse potential (5-MP) of interaction between an adatom and a metal surface cluster. Our theoretical calculations provide information about adsorption sites, adsorption geometry, binding energy, and eigenvibration. Our results agreed very well with experimental results. Four major results follow. First, the theoretical calculation showed that on the Rh(100) surface the 4-fold hollow site is the only adsorption site. Second, on the O-Rh(111) system, the 3-fold hollow site is the stable adsorption site. Third, on the Rh(110) surface at low coverage, the O atom is adsorbed preferably on the pseudo-3-fold site, while with increasing coverage, the O atom is adsorbed not only on the pseudo-3-fold site but also on the long bridge site. Last, as for the Rh(711) stepped surface, the 3-fold site on the (111) step is metastable, whereas the 4-fold sites on the (100) terrace are stable, which enables the O atoms to diffuse easily from the 3-fold to the 4-fold site at low coverage. Therefore, the O atoms are adsorbed preferrably on the stable 4-fold sites of the (100) terrace and then later as coverage increases on the metastable 3-fold site of the (110) step.     

吡啶与Rh(111)面相互作用的EHMO研究

吡啶作为加氢脱氮的模型化合物,与过渡金属Pt(111),Ni(100),Pd(110,111),Mo(110),Rh(111)面的吸附作用已有大量的实验研究,所采用的技术基本上是LEED,TDS,XPS,HREELS等,然而吡啶与Rh(111)面作用的理论研究尚未见报道.本文用EHMO法研究了吡啶与Rh(111)面的吸附作用,得到了最优吸附构型、结合能、集居数以及电荷分布和转移等,为新的脱氮催化剂开发提供了理论依据. 计算采用EHMO法,其中非对角矩阵元采用MWH近似:     

周期性密度泛函理论研究氯气在CuCl(111)表面上的吸附与解离

运用广义梯度密度泛函理论(Generalized Gradient Approximation，GGA)的PBE(Perdew-Burke-Ernzerh)方法结合周期性平板模型，研究了氯气分子和氯原子在CuCl(111)表面上的吸附。通过对不同吸附位和不同单层覆盖度下的吸附能和几何构型参数的计算和比较发现：氯气分子在CuCl(111)表面的吸附为解离吸附；单层覆盖度为0.50时的吸附构型为稳定的吸附构型；氯气分子平行吸附在CuCl(111)表面时最稳定，吸附能最大，达364.5 kJ·mol^-1；伸缩振动频率的计算结果表明，吸附后的氯气分子的伸缩振动频率与自由氯气分子的伸缩振动频率相比，都发生了红移；布居分析结果表明整个吸附体系发生了由Cu原子向氯气分子的电荷转移。氯原子吸附的计算结果显示氯原子以穴位稳定的吸附在CuCl(111)表面。     

Adsorption properties and vibrational spectra of propyne adsorbed on Rh(111). Comparison with other (111) metal surfaces

We have studied the adsorption properties of propyne on the Rh(111) surface by means of the generalized gradient approach of density functional theory using periodic slab models. The simulation of the vibrational spectra has permitted us to corroborate and complete the experimental band assignment and to confirm the adsorption site preference. Propyne prefers to sit on a 3-fold hollow site, with the C[triple bond]C axis parallel to a Rh-Rh bond and the molecular plane tilted away from the surface normal. The comparison between the adsorption behaviour of propyne on Rh(111) and on other (111) metal surfaces allows one to provide an explanation for the different reactivity observed experimentally.     

贵金属原子在CeO2(111)表面吸附的密度泛函理论研究

利用密度泛函理论系统研究了贵金属原子(Au、Pd、Pt和Rh)在CeO₂(111)表面的吸附行为。结果表明,Au吸附在氧顶位最稳定,Pd、Pt倾向吸附于氧桥位,而Rh在洞位最稳定。当金属原子吸附在氧顶位时,吸附强度依次为Pt > Rh > Pd > Au。Pd、Pt与Rh吸附后在Ce 4f、O 2p电子峰间出现掺杂峰;Au未出现掺杂电子峰,其d电子峰与表面O 2p峰在-4～-1 eV重叠。态密度分析表明,Au吸附在氧顶位、Pd与Pt吸附在桥位、Rh吸附在洞位时,金属与CeO₂(111)表面氧原子作用较强,这与Bader电荷分析结果相一致。     

NO在Rh(100),Rh(111)面上吸附与直接分解的密度泛函理论研究

本文应用第一性原理的密度泛函(DFT)方法,使用DMol³计算程序,对NO在Rh(100)和Rh(111)面上的吸附与分解进行量化计算,力图解决NO在Rh(100)和Rh(111)面上的优选吸附位、直接分解的过渡态和活化能等重要问题.     

甲氧基在Rh(111)表面吸附的密度泛函研究

采用密度泛函理论(DFT)的B3LYP方法,以原子簇Rh13(9,4)为模拟表面,在6-31G(d,p)与Lanl2dz基组水平上,对甲氧基在Rh(111)表面的四种吸附位置(fcc、hcp、top、bridge)的吸附模型进行了几何优化、能量计算、Mulliken电荷布局分析以及前线轨道的计算。结果表明,当甲氧基通过氧与金属表面相互作用时,在bridge位的吸附能最大,吸附体系最稳定,在top位转移的电子数最多;吸附于Rh(111)面的过程中C—O键被活化,C—O键的振动频率发生红移。     

Au/Pd(111)双金属表面催化噻吩加氢脱硫的反应机理

采用密度泛函理论(DFT)计算了Pd(111)表面含有N(N=1-4)个Au原子数目时的表面形成能,选取最优构型进一步研究了噻吩在Au/Pd(111)双金属表面的吸附模式及加氢脱硫反应过程.结果表明:当Pd(111)表面含有1个Au原子时,其形成能最低.在Au/Pd(111)双金属表面噻吩初始吸附于Pd-Hcp-30°位时,其构型最稳定.在各加氢脱硫过程中,反应总体均放出热量.对于直接脱硫机理,其所需活化能较低,但脱硫产物较难控制;对于间接脱硫机理,反应最有可能按照顺式加氢方式进行,C―S键断裂开环时所需活化能最高,是反应的限速步骤.此外,与单一Au(111)面及Pd(111)面相比,Au/Pd(111)双金属表面限速步骤的反应能垒最低,表明AuPd双金属催化剂比Au、Pd单金属催化剂更有利于噻吩加氢脱硫反应的进行.     

Au/Pd(111)双金属表面催化噻吩加氢脱硫的反应机理

采用密度泛函理论（DFT）计算了Pd（111）表面含有N（N=1-4）个Au原子数目时的表面形成能,选取最优构型进一步研究了噻吩在Au/Pd（111）双金属表面的吸附模式及加氢脱硫反应过程. 结果表明：当Pd（111）表面含有1个Au原子时,其形成能最低. 在Au/Pd（111）双金属表面噻吩初始吸附于Pd-Hcp-30°位时,其构型最稳定. 在各加氢脱硫过程中,反应总体均放出热量. 对于直接脱硫机理,其所需活化能较低,但脱硫产物较难控制;对于间接脱硫机理,反应最有可能按照顺式加氢方式进行,C―S键断裂开环时所需活化能最高,是反应的限速步骤. 此外,与单一Au（111）面及Pd（111）面相比,Au/Pd（111）双金属表面限速步骤的反应能垒最低,表明AuPd双金属催化剂比Au、Pd单金属催化剂更有利于噻吩加氢脱硫反应的进行.     

Computational study of the adsorption and dissociation of phenol on Pt and Rh surfaces

The adsorption of phenol on flat and stepped Pt and Rh surfaces and the dissociation of hydrogen from the hydroxyl group of phenol on Pt(111) and Rh(111) were studied by density functional calculations. On both Pt(111) and Rh(111), phenol adsorbs with the aromatic ring parallel to the surface and the hydroxyl group tilted away from the surface. Furthermore, adsorption on stepped surfaces was concluded to be unfavourable compared to the (111) surfaces due to the repulsion of the hydroxyl group from the step edges. Transition state calculations revealed that the reaction barriers, associated with the dissociation of phenol into phenoxy, are almost identical on Pt and Rh. Furthermore, the oxygen in the dissociated phenol is strongly attracted by Rh(111), while it is repelled by Pt(111).     

Ab initio thermodynamics examination of sulfur species present on Rh, Ni, and binary Rh-Ni surfaces under steam reforming reaction conditions

The stable form of adsorbed sulfur species and their coverage were investigated on Rh, Ni, and Rh-Ni binary metal surfaces using density functional theory calculations and the ab initio thermodynamics framework. S adsorption, SO(x) (x = 1-4) adsorption, and metal sulfide formation were examined on Rh(111) and Ni(111) pure metals. Both Rh and Ni metals showed a preference for S surface adsorption rather than SO(x) adsorption under steam reforming conditions. The transition temperature from a clean surface (<(1)/(9) ML) to S adsorption was identified on Rh(111), Ni(111), Rh(1)Ni(2)(111), and Rh(2)Ni(1)(111) metals at various P(H(2))/P(H(2)S) ratios. Bimetallic Rh-Ni metals transition to a clean surface at lower temperatures than does the pure Rh metal. Whereas Rh is covered with (1)/(3) ML of sulfur under the reforming conditions of 4-100 ppm S and 800 °C, Rh(1)Ni(2) is covered with (1)/(9) ML of sulfur at the lower end of this range (4-33 ppm S). The possibility of sulfate formation on Rh catalysts was examined by considering higher oxygen pressures, a Rh(221) stepped surface, and the interface between a Rh(4) cluster and CeO(2)(111) surface. SO(x) surface species are stable only at high oxygen pressure or low temperatures outside those relevant to the steam reforming of hydrocarbons.     

CO和H2分子在Cu(111)面的吸附和溶剂化效应

采用广义梯度近似(GGA)密度泛函理论(DFT)的PW91方法结合周期性模型, 在DNP基组下, 利用Dmol3模块研究了CO和H2在真空和液体石蜡环境下在Cu(111)表面上不同位置的吸附. 计算结果表明, 溶剂化效应对H2和CO的吸附结构参数和吸附能的影响非常显著. 在液体石蜡环境下, H2平行吸附在Cu(111)表面是解离吸附, 而CO 和H2在两种环境下的垂直吸附都是非解离吸附. 相比真空环境吸附, 在液体石蜡环境中, Cu(111)吸附CO时, 溶剂化效应能够提高CO吸附的稳定性, 同时有利于CO的活化. 在真空中, H2只能以垂直方式或接近垂直方式吸附在Cu(111)表面. 当Cu(111)顶位垂直吸附H2, 相比真空环境吸附, 溶剂化效应能够提高H2吸附的稳定性, 但对H2的活化没有明显影响. Cu(111)表面的桥位或三重穴位(hcp和fcc)垂直吸附H2时, 溶剂化效应能明显提高H2的活化程度, 但降低H2的吸附稳定性; 在液体石蜡中, 当H2平行Cu(111)表面吸附时, 溶剂化效应使H—H键断裂, 一个H原子吸附在fcc位, 另一个吸附在hcp位.     

DFT Study of Thiophene Adsorption on the Pd（111） and Pt（111） Surfaces

Thiophene adsorption on the(111) surfaces of Pd and Pt have been investigated by density functional theory.The results indicate that the adsorption at the hollow sites is the most stable.To our interest,the molecular plane of thiophene ring is distorted with C=C bond being elongated to 1.450  and C-C bond being shortened to 1.347 ,and the C-H bonds tilt 13.91～44.05o away from this plane.Furthermore,analysis on population and density of states verified the calculated adsorption geometries.Finally,charge analysis suggests that thiophene molecule is an electron acceptor,reflecting the interaction between the lone pair of sulfur and the d-orbitals of metal.     

噻吩在γ-Mo_2N(100)表面上加氢脱硫反应的密度泛函理论研究

利用密度泛函理论研究了γ-Mo2N(100)表面上的噻吩加氢脱硫(HDS)过程.噻吩在γ-Mo2N(100)表面上不同作用形式的结构优化结果显示,η5-Mo2N吸附构型最稳定,具有最大的吸附能(-0.56 eV),此时噻吩通过S原子与Mo2原子相连平行表面吸附在四重空位(hcp位).H原子和噻吩在hcp位发生稳定共吸附,hcp位是噻吩HDS的活性位点.噻吩在γ-Mo2N(100)表面进行直接脱硫反应,HDS过程分为S原子脱除和C4产物加氢饱和两部分.过渡态搜索确定了HDS最可能的反应机理及中间产物,首个H原子的反应需要最大的活化能(1.69 eV),是噻吩加氢脱硫的控速步骤.伴随H原子的不断加入,噻吩在γ-Mo2N(100)表面上优先生成―SH和丁二烯,随后―SH加氢生成H2S,丁二烯加氢饱和生成2-丁烯和丁烷.由于较弱的吸附,H2S、2-丁烯和丁烷很容易在γ-Mo2N(100)表面脱附成为产物.     

甲醇在Pt-Fe(111)/C表面吸附的理论研究

采用密度泛函理论和周期平板模型相结合的方法, 对CH3OH分子在Pt-Fe(111)/C表面top, fcc, hcp和bridge位的吸附模型进行了构型优化、能量计算, 结果表明bridge位是较有利的吸附位. 掺杂后费米能级的位置发生了右移, 价带和导带均增宽, 极利于电子-空穴的迁移, 这对提高催化活性是非常有利的. 考察抗中毒性发现: CO在Pt(111)/C面上的吸附能比甲醇吸附能要高, CO在Pt-Fe(111)/C的吸附能比甲醇吸附能要低, 可说明CO在Pt(111)/C面上有中毒效应, 而Pt-Fe(111)/C的抗CO中毒能力增强, 是催化氧化甲醇良好的催化剂.