二元铜族团簇负离子催化CO氧化反应机理

用密度泛函理论B3LYP方法研究了二元铜族团簇负离子AuAg^-, AuCu^-和AgCu^-催化CO氧化反应的详细机理. 计算结果表明: CO在混合团簇中的吸附位顺序为Cu>Au>Ag; O₂也优先吸附到Cu上, 其次为Ag, 最难的为Au; 另外, O₂分子较CO分子易于吸附到混合团簇上. CO氧化反应有三条反应通道, 在热力学和动力学上均容易进行. AuAg-团簇催化CO氧化反应的最优反应通道为CO插入AuAgO₂^-中的Ag―O键形成中间体[Au―AgC(O―O)O]^-, 然后直接分解形成CO₂和AuAgO^-, 或另一个CO分子进攻中间体[Au―AgC(O―O)O]^-形成两分子的CO₂和AuAg^-. 而AuCu^-和AgCu^-催化CO氧化反应的最优反应通道为CO和O₂共吸附到团簇上,然后形成四元环中间体,最后四元环中间体分解形成产物或另一个CO分子进攻四元环中间体从而形成产物. 第二个CO分子的协同效应不明显. AuAg^-和AuCu^-对CO氧化反应催化活性强于Au₂^-团簇, 因此, Ag和Cu掺杂可以提高金团簇的催化活性, 与之前实验研究结果一致.     

Aun(n=2-9)团簇与乙醇分子相互作用的第一性原理研究

利用密度泛函理论研究了Au_n(n=2-9)团簇吸附一个乙醇分子的结构和电子性质. 研究结果表明: Au_n(n=2-9)团簇的最稳定构型为二维平面结构, Au6团簇最稳定; 吸附过程是通过金团簇上一个特定的金原子与乙醇分子中氧原子相互作用完成, 形成了20种稳定构型; 金原子的配位数对吸附作用影响明显; 作为吸附主体的金团簇和被吸附的乙醇分子在吸附前后构型无明显变化, 它们之间为弱相互作用.     

从头计算方法比较研究B2Au4, Al2Au4和BAlAu4的几何和电子结构

Au/H 相似性的研究是现代化学中的一个热门话题. 我们从理论上报道Au/H 相似的新成员: 共价化合物B₂Au₄, 离子化合物Al₂Au₄和BAlAu₄. 采用密度泛函和波函数理论方法对比研究了缺电子体系B₂Au₄、Al₂Au₄和BAlAu₄的几何和电子结构. 详细讨论了它们基态结构的轨道、适应性自然密度划分(AdNDP)和电子局域函数(ELF)分析. 计算结果表明稍微扭曲变形的C₂B₂Au₄是基态结构, 在这个共价化合物中含有两个B―Au―B三中心二电子(3c-2e)键. 然而C_3v Al⁺(AlAu₄)^-和C_3v Al⁺(BAu₄)^-被研究证明是含有三个X―Au―Al 三中心二电子键的类盐化合物(在Al₂Au₄中X=Al, BAlAu₄中X=B). Al₂Au₄和BAlAu₄是至今为止首例报道的在离子缺电子体系中含有金桥键的化合物. 同时计算了B₂Au₄^-、Al₂Au₄^- 和BAlAu₄^- 阴离子基态结构的绝热剥离能和垂直剥离能, 为实验表征提供依据. 文中报道的金桥键为共价键和离子键相结合的缺电子体系提供了一个有趣的键合模式, 有助于设计含有高度分散金原子的新材料和催化剂.     

CeO2(110)负载Au纳米颗粒催化CO+NOx反应的DFT+U研究

通过在位库伦校正的密度泛函理论（DFT+U）方法计算,我们研究了CO和NO_x分子在Au负载CeO₂（110）表面的吸附. 结果表明,CO在Au纳米颗粒的顶位有很强的吸附能,大约为1.2 eV,而NO在Au纳米颗粒上或者Au与CeO₂载体界面处都是弱吸附. 然而,当NO_x在界面处形成N₂O₂二聚体之后,通过断裂末端的N-O键能够有效地被降解. 纵观整个反应过程,第一步CO+N₂O₂的反应遵循了Langmuir-Hinshelwood机理,活化能只有0.4 eV,通过形成ONNOCO的中间物种最终产生N₂O和CO₂. 不同的是,第二步消除N₂O反应遵循了Eley-Rideal碰撞机理,需要相当高的能垒,约为1.8 eV. 通过进一步分析表明,稀土Ce元素独特的电子特性能够使电子从Au上转移并且局域到载体表面的Ce阳离子上,并且有助于形成带负电的N₂O₂分子. 而且Au纳米颗粒有很强的结构流动性,能够促进吸附的CO分子靠近界面处的N₂O₂并与之反应.     

TinO2和TinO2-(n=1-10)团簇的几何结构、电子和磁性质

基于密度泛函理论(DFT)的B3LYP方法, 研究了Ti_nO₂和Ti_nO₂^- (n=1-10)团簇的几何结构、电子结构以及磁性. 结果表明, 两个氧以分离的原子状态吸附在金属团簇的表面, 呈现出以一个钛原子为中心的O-Ti-O 的相邻吸附形式. 中性团簇和阴离子团簇的能量最低结构相似. 稳定性分析表明Ti_nO₂具有很高的稳定性, 特别是TiO₂和Ti₇O₂. 此外, 详细讨论了团簇的电离势、电子亲和能、电子解离能和能隙. 基于最低能量结构, 讨论了团簇的磁性, 发现电荷从Ti 原子向O原子转移, 并且电荷转移主要发生在Ti_nO₂的Ti-3d、Ti-4s和O-2p轨道. 磁性团簇中反铁磁序占据主导, 磁矩主要来源Ti-3d电子的贡献, 而两个氧原子的贡献非常小.     

Au/α-Fe2O3 催化剂存贮失活环境因素及机理分析

 采用沉积沉淀法制备了 CO 低温氧化催化剂 Au/α-Fe₂O₃, 通过 X 射线衍射、X 射线光电子能谱、N₂ 吸附-脱附、傅里叶变换红外光谱、H₂ 程序升温还原和 CO₂ 程序升温脱附等手段对催化剂进行了表征, 探讨了在室温大气气氛下光线照射以及表面吸附等环境因素所导致的催化剂存贮失活及其作用机理. 结果表明, 经 110 ^oC 干燥的 Au/α-Fe₂O₃催化剂表面同时存在 Au³⁺和 Au^δ+ (0 ≤ δ ≤ 1) 物种, 且前者催化 CO 氧化的活性更高; 在室温大气气氛下, 紫外线照射会引起 Au³⁺的还原和 Au 颗粒的生长, 导致催化剂的不可逆失活. 此外, 空气中的 H₂O 和 CO₂ 可同时吸附在 α-Fe₂O₃的表面, 形成表面碳酸盐物种, 会引起催化剂的可逆失活.     

CO在M55（M=Cu,Ag,Au）团簇上吸附的密度泛函研究

在全电子相对论BVP86/DNP水平下对CO在Au55,Ag55和Cu55团簇上的吸附进行了比较研究,并考察了电荷对吸附的影响.计算结果表明,CO在Au55团簇上吸附能最大,其次为Cu55团簇,最弱的为Ag55团簇.团簇电荷对C—O键活化和CO与团簇表面原子成键影响较小.金团簇的电荷对吸附能影响较大,而银和铜团簇的电荷对吸附能影响较小.CO吸附到团簇上导致团簇上电子向CO转移.C—O键活化强度与吸附位置密切相关,其中孔位吸附导致C—O键活化程度最大,最弱的为顶位吸附.CO在金团簇上吸附具有较好选择性,而在银和铜团簇上吸附无选择性.     

Pt原子在γ-Al2O3(001)表面的吸附及迁移

采用密度泛函理论(DFT)中广义梯度近似(GGA)方法, 对Pt原子与γ-Al₂O₃(001)面的相互作用及迁移性能进行了研究. 分析了各种可能吸附位及吸附构型的松弛和变形现象, 吸附能和迁移能垒的计算结果表明: Pt团簇能够稳定吸附在该表面. Pt原子在表面O位的吸附能明显较高, 这主要是由Pt向基底O原子转移了电子所致. 电荷布居分析表明, Pt原子显电正性, Pt和Al原子之间存在排斥作用, 导致与Al原子产生较弱相互作用. 计算的平均吸附能大小依赖于Pt团簇的大小和形状, 总体趋势是随着Pt原子数增多, 吸附能降低. Pt原子在γ-Al₂O₃(001)表面迁移过程所需克服的迁移能垒最高值为0.51 eV. 随着吸附的Pt原子数增多,更倾向于形成Pt团簇. 因此, Pt原子在γ-Al₂O₃(001)表面的吸附演变不可能形成光滑、均匀平铺的吸附构型, 而在一定条件下容易出现团聚.     

非血红素铁(III)活化氧分子反应的自旋轨道耦合和零场分裂

采用密度泛函理论对原儿茶酚3,4-双加氧酶(3,4-PCD)活化O₂分子的反应机理进行了探讨. 初始复合物, 六重态⁶1的超快形成主要归因于电子交换诱导系间穿越(EISC), Fe d_z:O₂ π^*(z)是主要的交换通道, 在Fe―O键长为0.2487 nm处, 交换重叠积分S_ij=ád_z α|π^*(z) β>=0.3758. 从六重态⁶1 形成四重态中间体⁴1, 有两种效应共存, 即电子交换耦合作用和自旋轨道耦合(SOC)作用, 且相互竞争. 计算结果表明, 自旋轨道耦合(SOC)作用起主导因素(SOC=353.16 cm^-1). 至于O―O键的解离主要取决于儿茶酚(PCA)最高占据分子轨道(HOMO)的电子转移, 非血红素酶的铁中心仅承担PCA向O₂电子转移的缓冲作用.²²     

B2Au20/-/2-: 硼金团簇中的硼-硼多重键

采用密度泛函和波函数理论方法对B₂Au^20/-/2-的几何结构和电子结构进行研究. 计算结果表明阴离子B₂Au^2- ([Au-B B-Au]^-) (C_2h, ²A_u)和B₂Au^22- ([Au-B≡B-Au]^2-) (C_2h, ¹A_g)的基态结构均为线性结构, 即以含有多重键的BB单元(B B或B≡B)为中心, 两端各连接一个Au原子, 但两端的B－Au键不在同一直线上, 结构稍有变形; 而中性分子B₂Au₂ ([Au-B＝B-Au]) (D_∞h, ³Σ_g^-)的基态结构是以B＝B为中心, 两端各与一个Au原子相连的完美的线性结构. C_2h B₂Au^2-的单电子垂直剥离能和对称性伸缩振动频率的计算结果为实验表征提供依据.另外, 计算发现无机盐B₂Au₂Li₂结构中仍包含B≡B, 此结果一方面为其实验合成提供了可能性, 另一方面表明含有B≡B的B₂Au₂^2-结构极为稳定, 可作为结构单元存在于凝聚相中.     

Theoretical study of oxygen adsorption on pure Au(n+1)+ and doped MAu(n)+ cationic gold clusters for M = Ti, Fe and n = 3-7

A comparative study of the adsorption of an O2 molecule on pure Au(n+1)+ and doped MAu(n)+ cationic gold clusters for n = 3-7 and M = Ti, Fe is presented. The simultaneous adsorption of two oxygen atoms also was studied. This work was performed by means of first principles calculations based on norm-conserving pseudo-potentials and numerical basis sets. For pure Au4 +, Au6+, and Au7+ clusters, the O2 molecule is adsorbed preferably on top of low coordinated Au atoms, with an adsorption energy smaller than 0.5 eV. Instead, for Au5+ and Au8+, bridge adsorption sites are preferred with adsorption energies of 0.56 and 0.69 eV, respectively. The ground-state geometry of Au(n)+ is almost unperturbed after O2 adsorption. The electronic charge flows towards O2 when the molecule is adsorbed in bridge positions and towards the gold cluster when O2 is adsorbed on top of Au atoms, and both the adsorption energy and the O-O bond length of adsorbed oxygen increase when the amount of electronic charge on O2 increases. On the other hand, we studied the adsorption of an O2 molecule on doped MAu(n)+ clusters, leading to the formation of (MAu(n)O2+) ad complexes with different equilibrium configurations. The highest adsorption energy was obtained when both atoms of O2 bind on top of the M impurity, and it is larger for Ti doped clusters than for Fe doped clusters, showing an odd-even effect trend with size n, which is opposite for Ti as compared to Fe complexes. For those adsorption configurations of (MAu(n)O2+) ad involving only Au sites, the adsorption energy is similar to or smaller than that for similar configurations of Au(n)+1O2 + complexes. However, the highest adsorption energy of (MAu(n)O2+) ad is higher than that for (Au(n)+1O2+) ad by a factor of approximately 4.0 (1.2) for M = Ti (M = Fe). The trends with size n are rationalized in terms of O-O and O-M bond distances, as well as charge transfer between oxygen and cluster substrates. The spin multiplicity of those (MAu(n)O2+) ad complexes with the highest O2 adsorption energy is a maximum (minimum) for M = Fe (Ti), corresponding to parallel (anti-parallel) spin coupling of MAu(n)+ clusters and O2 molecules. Finally, we obtained the minimum energy equilibrium structure of complexes (Au(n)O2+) dis and (MAu(n)O2+) dis containing two separated O atoms bonded at different sites of Au(n)+ and MAu(n)+ clusters, respectively. For (MAu(n)O2 (+)) dis, the equilibrium configuration with the highest adsorption energy is stable against separation in MAu(n)+ and O2 fragments, respectively. Instead, for (Au(n)O2+) dis, only the complex n = 6 is stable against separation in Au(n)+ and O2 fragments. The maximum separation energy of (MAu(n)O2+) dis is higher than the O2 adsorption energy of (MAu(n)O2+) ad complexes by factors of approximately 1.6 (2.5), 1.6 (1.7), 1.5 (2.4), 1.5 (1.3), and 1.6 (1.8) for M = Ti (Fe) complexes in the range n = 3-7, respectively.     

Adsorption of molecular hydrogen and hydrogen sulfide on Au clusters

The authors present theoretical results describing the adsorption of H2 and H2S molecules on small neutral and cationic gold clusters (Au(n)((0/+1)), n=1-8) using density functional theory with the generalized gradient approximation. Lowest energy structures of the gold clusters along with their isomers are considered in the optimization process for molecular adsorption. The adsorption energies of H2S molecule on the cationic clusters are generally greater than those on the corresponding neutral clusters. These are also greater than the H2 adsorption energies on the corresponding cationic and neutral clusters. The adsorption energies for cationic clusters decrease with increasing cluster size. This fact is reflected in the elongations of the Au-S and Au-H bonds indicating weak adsorption as the cluster grows. In most cases, the geometry of the lowest energy gold cluster remains planar even after the adsorption. In addition, the adsorbed molecule gets adjusted such that its center of mass lies on the plane of the gold cluster. Study of the orbital charge density of the gold adsorbed H2S molecule reveals that conduction is possible through molecular orbitals other than the lowest unoccupied molecular orbital level. The dissociation of the cationic Au(n)SH2+ cluster into Au(n)S+ and H2 is preferred over the dissociation into Au(m)SH2+ and Au(n-m), where n=2-8 and m=1-(n-1). H2S adsorbed clusters with odd number of gold atoms are more stable than neighboring even n clusters.     

Adsorption of O2 on tubelike Au24 and Au24- clusters

The nondissociative adsorptions of O(2) on the neutral and anionic Au(24) have been studied using the density functional theory (DFT) in the generalized gradient approximation. Their geometrical structures are optimized by using a combination of the relativistic effective core potential and all-electron potential with scalar relativistic corrections. It is found that the adsorptions of O(2) on the tubelike Au(24) and Au(24) (-) are more stable than it on their space-filled counterparts. Mulliken population analysis shows that the O(2) adsorbed on the tubelike Au(24) and Au(24) (-) got more electrons than on the amorphous ones, which may be a reason why the O(2) can be adsorbed more easily on the former rather than on the latter. Compared with the previous DFT studies of O(2) adsorbed on small Au(n) (n< or =10) clusters, we have shown that the O(2) can also be adsorbed on the neutral even Au(24) with an adsorption energy compatible with that on the small neutral odd gold clusters, but the adsorption energy of O(2) on the anionic Au(24) (-) is lower than that on the small anionic Au(n) with even n. In all the optimized geometrical structures of the O(2)-adsorbed Au(24) and Au(24) (-) clusters, including both tubelike and amorphous ones, we found that O(2) prefers its two O atoms to be attached to two near gold atoms with the least coordination number rather than only one O atom to be attached to one gold atom.     

A study of the reactions of molecular hydrogen with small gold clusters

This work presents a study of reactions between neutral and negatively charged Au(n) clusters (n=2,3) and molecular hydrogen. The binding energies of the first and second hydrogen molecule to the gold clusters were determined using density functional theory (DFT), second order perturbation theory (MP2) and coupled cluster (CCSD(T)) methods. It is found that molecular hydrogen easily binds to neutral Au(2) and Au(3) clusters with binding energies of 0.55 eV and 0.71 eV, respectively. The barriers to H(2) dissociation on these clusters with respect to Au(n)H(2) complexes are 1.10 eV and 0.59 eV for n=2 and 3. Although negatively charged Au(n) (-) clusters do not bind molecular hydrogen, H(2) dissociation can occur with energy barriers of 0.93 eV for Au(2) (-) and 1.39 eV for Au(3) (-). The energies of the Au(2)H(2) (-) and Au(3)H(2) (-) complexes with dissociated hydrogen molecules are lower than the energies of Au(2) (-)+H(2) and Au(3) (-)+H(2) by 0.49 eV and 0.96 eV, respectively. There is satisfactory agreement between the DFT and CCSD(T) results for binding energies, but the agreement is not as good for barrier heights.     

单个金或银原子掺杂的氧化钒团簇上的甲烷活化反应

运用密度泛函理论系统研究了甲烷在MV_3O_y~q (M=Au/Ag,y=6–8,q=0或±1)团簇上的吸附和活化。研究得到了吸附体系的微观几何构型、吸附能、电荷分布等性质,找到了5个可以明显活化甲烷分子的含Au团簇。在这些体系中,Au均吸附在基底团簇V_3O_y~q的O位置,而CH_4均在Au原子上被活化。团簇电荷对活化能力有明显影响,阳离子团簇的活化能力最强,中性体系次之,阴离子团簇的活化能力很弱。测试计算表明引入D3色散矫正对于体系结构和能量的计算结果影响不大。本文作为单原子催化剂上甲烷吸附和活化反应的团簇模型研究,为进一步研究单原子催化剂上甲烷的活化机理提供了基础,也为合理设计低温下甲烷转化的单原子催化剂提供了有益的线索。     

Theoretical study of nitric oxide adsorption on Au clusters

The adsorption properties of NO molecule on anionic, cationic, and neutral Au(n) clusters (n=1-6) are studied using the density functional theory with the generalized gradient approximation, and with the hybrid functional. For anionic and cationic clusters, the charge transfer between the Au clusters and NO molecule and the corresponding weakening and elongation of the N-O bond are essential factors of the adsorption. The neutral Au clusters have also remarkable adsorption ability to NO molecule. The adsorption energies of NO on the cationic clusters are generally greater than those on the neutral and anionic clusters.     

Density functional study of the interaction between small Au clusters, Au(n) (n=1-7) and the rutile TiO(2) surface. I. Adsorption on the stoichiometric surface

This is the first paper in a series of four dealing with the adsorption site, electronic structure, and chemistry of small Au clusters, Au(n) (n=1-7), supported on stoichiometric, partially reduced, or partially hydroxylated rutile TiO(2)(110) surfaces. Analysis of the electronic structure reveals that the main contribution to the binding energy is the overlap between the highest occupied molecular orbitals of Au clusters and the Kohn-Sham orbitals localized on the bridging and the in-plane oxygen of the rutile TiO(2)(110) surface. The structure of adsorbed Au(n) differs from that in the gas phase mostly because the cluster wants to maximize this orbital overlap and to increase the number of Au-O bonds. For example, the equilibrium structures of Au(5) and Au(7) are planar in the gas phase, while the adsorbed Au(5) has a distorted two-dimensional structure and the adsorbed Au(7) is three-dimensional. The dissociation of an adsorbed cluster into two adsorbed fragments is endothermic, for all clusters, by at least 0.8 eV. This does not mean that the gas-phase clusters hitting the surface with kinetic energy greater than 0.8 eV will fragment. To place enough energy in the reaction coordinate for fragmentation, the impact kinetic energy needs to be substantially higher than 0.8 eV. We have also calculated the interaction energy between all pairs of Au clusters. These interactions are small except when a Au monomer is coadsorbed with a Au(n) with odd n. In this case the interaction energy is of the order of 0.7 eV and the two clusters interact through the support even when they are fairly far apart. This happens because the adsorption of a Au(n) cluster places electrons in the states of the bottom of the conduction band and these electrons help the Au monomer to bind to the five-coordinated Ti atoms on the surface.     

Adsorption of O2 and oxidation of CO at Au nanoparticles supported by TiO2(110)

Density functional theory calculations are performed for the adsorption of O2, coadsorption of CO, and the CO+O2 reaction at the interfacial perimeter of nanoparticles supported by rutile TiO2(110). Both stoichiometric and reduced TiO2 surfaces are considered, with various relative arrangements of the supported Au particles with respect to the substrate vacancies. Rather stable binding configurations are found for the O2 adsorbed either at the trough Ti atoms or leaning against the Au particles. The presence of a supported Au particle strongly stabilizes the adsorption of O2. A sizable electronic charge transfer from the Au to the O2 is found together with a concomitant electronic polarization of the support meaning that the substrate is mediating the charge transfer. The O2 attains two different charge states, with either one or two surplus electrons depending on the precise O2 adsorption site at or in front of the Au particle. From the least charged state, the O2 can react with CO adsorbed at the edge sites of the Au particles leading to the formation of CO2 with very low (approximately 0.15 eV) energy barriers.     

Adsorption energies of molecular oxygen on Au clusters

The adsorption properties of O(2) molecules on anionic, cationic, and neutral Au(n) clusters (n=1-6) are studied using the density functional theory (DFT) with the generalized gradient approximation (GGA), and with the hybrid functional. The results show that the GGA calculations with the PW91 functional systemically overestimate the adsorption energy by 0.2-0.4 eV than the DFT ones with the hybrid functional, resulting in the failure of GGA with the PW91 functional for predicting the adsorption behavior of molecular oxygen on Au clusters. Our DFT calculations with the hybrid functional give the same adsorption behavior of molecular oxygen on Au cluster anions and cations as the experimental measurements. For the neutral Au clusters, the hybrid DFT predicts that only Au(3) and Au(5) clusters can adsorb one O(2) molecule.