Electronic properties of Cu clusters and islands and their reaction with O2 on SnO2(110) surfaces

The deposition of Cu on SnO₂(110) surfaces, and its oxidation to Cu_xO, have been studied by low-energy electron diffraction (LEED) and angle-integrated photoemission using synchrotron radiation photoemission spectroscopy (SRPES). With the growth of copper on SnO₂(110), which was found to follow the Volmer-Weber (“islanding”) growth mode, a small amount of metal-phase Sn segregates to the surface, and even when the copper thickness reaches several tens of Å, Sn metal still is seen at the surface. But when this surface is annealed at 800 K in 5 × 10^?6 mbar O₂ for 20 min, the Sn atoms are totally converted to SnO₂. Simultaneously, the deposited Cu atoms become oxidized. The surface charges up both during LEED and SRPES data acquisition. The clean SnO₂(110) surface shows a 1 × 1 structure. With Cu deposition, the substrate LEED pattern gradually becomes weaker. With even more copper deposited, a Cu(111)-1 × 1-oriented particle structure appears, indicating coalescence of the Cu islands to 3-dimensional Cu(111) epitaxy. After subsequent heating to 500 K, the substrate signal appears again, and we see the SnO₂ 1 × 1 pattern. In conclusion, Cu atoms quite easily form clusters on the SnO₂(110) surface already after a slight heat treatment. The results show that this system is quite active towards O₂ gas exposure, and that the surface conductivity changes during O₂ exposure.     

水在HfO2(111)和(110)表面的吸附与解离

运用广义梯度近似密度泛函理论方法(GGA-PW91)结合周期平板模型, 研究水分子在二氧化铪(111)和(110)表面不同吸附位置在不同覆盖度下的吸附行为. 通过比较不同吸附位的吸附能和几何构型参数发现:(111)和(110)表面铪原子(top 位)是活性吸附位. 水分子与表面的吸附能值随覆盖度的变化影响较小. 在(111)和(110)表面, 水分子都倾向以氧端与表面铪原子相互作用. 同时也计算了羟基、氧和氢在表面的吸附, Mulliken 电荷布居, 态密度及部分频率. 结果表明, 在两种表面羟基以氧端与表面铪相互作用, 氧原子与表面铪和氧原子同时成键, 而氢原子直接与表面氧原子相互作用形成羟基. 通过过渡态搜索, 水分子在(111)和(110)表面发生解离, 反应能垒分别为9.7和17.3 kJ·mol^-1, 且放热为59.9和47.6 kJ·mol^-1.     

Radical electrophilicities in solvent

A series of Ti-doped SnO₂(110) surfaces with different oxygen vacancies have been investigated by means of first principles DFT calculations combined with a slab model. Three kinds of defective SnO₂(110) surfaces are considered, including the formations of bridging oxygen (O _b ) vacancy, in-plane oxygen (O _i ) vacancy, and the coexistence of O _b and O _i vacancies. Our results indicate that Ti dopant prefers the fivefold-coordinated Sn site on the top layer for the surface with O _b or O _i vacancy, while the replacement of sublayer Sn atom becomes the most energetically favorable structure if the O _b and O _i vacancies are presented simultaneously. Based on analyzing the band structure of the most stable configuration, the presence of Ti leads to the variation of the band gap state, which is different for three defective SnO₂(110) surfaces. For the surface with O _b or O _i vacancy, the component of the defect state is modified, and the reaction activity of the corresponding surface is enhanced. Hence, the sensing performance of SnO₂ may be improved after introducing Ti dopant. However, for the third kind of reduced surface with the coexistence of O _b and O _i vacancies, the sublayer doping has little influence on the defect state, and only in this case, the Ti doping state partly appears in the band gap of SnO₂(110) surface.     

CO\begin{document}$ _{2} $\end{document} Reduction on Metal-Doped SnO\begin{document}$ _{2} $\end{document}(110) Surface Catalysts: Manipulating the Product by Changing the Ratio of Sn:O

The electrocatalytic carbon dioxide reduction reaction (CO₂RR) producing HCOOH and CO is one of the most promising approaches for storing renewable electricity as chemical energy in fuels. SnO₂ is a good catalyst for CO₂-to-HCOOH or CO₂-to-CO conversion, with different crystal planes participating the catalytic process. Among them, (110) surface SnO₂ is very stable and easy to synthesisze. By changing the ratio of Sn: O for SnO₂(110), we have two typical SnO₂ thin films: fully oxidized (stoichiometric) and partially reduced. In this work, we are concerned with different metals (Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au)-doped SnO₂(110) with different activity and selectivity for CO₂RR. All these changes are manipulated by adjusting the ratio of Sn: O in (110) surface. The results show that stochiometric and reduced Cu/Ag doped SnO₂(110) have different selectivity for CO₂RR. More specifically, stochiometric Cu/Ag-doped SnO₂(110) tends to generate CO(g). Meanwhile, the reduced surface tends to generate HCOOH(g). Moreover, we also considered the competitive hydrogen evolution reaction (HER). The catalysts SnO₂(110) doped by Ru, Rh, Pd, Os, Ir, and Pt have high activity for HER, and others are good catalysts for CO₂RR.     

Acetonitrile adsorption and decomposition on the SnO2 (110) surface: a first-principles computation

The adsorption and decomposition of acetonitrile on the SnO₂ (110) surface were investigated by means of first-principles computations. It is found that acetonitrile could be relatively easier decomposed into CH₃ and CN fragments on the SnO₂ (110) surface than on TiO₂ (110), which agrees with the experimental results. The higher activity of the SnO₂ (110) surface than the TiO₂ (110) surface can be attributed to its higher work function and closer molecular orbital energies.     

Neue molekulare Indium‐Zinn‐Sauerstoff‐ und Indium‐Zinn‐Natrium‐Sauerstoff‐Chlor‐Cluster

Abstract. The five‐membered heteroelement cluster THF · Cl₂In(O^tBu)₃Sn reacts with the sodium stannate [Na(O^tBu)₃Sn]₂ to produce either the new oxo‐centered alkoxo cluster ClInO[Sn(O^tBu)₂]₃ ( 1 ) (in low yield) or the heteroleptic alkoxo cluster Sn(O^tBu)₃InCl₃Na[Sn(O^tBu)₂]₂ ( 2 ). X‐ray diffraction analyses reveal that in compound 1 the polycyclic entity is made of three tin atoms which together with a central oxygen atom form a trigonal, almost planar triangle, perpendicular to which a further indium atom is connected through the oxygen atom. The metal atoms thus are arranged in a Sn₃In pyramid, the edges of which are all saturated by bridging tert‐butoxy groups. The indium atom has a further chloride ligand. Compound 2 has two trigonal bipyramids as building blocks which are fused together at a six coordinate indium atom. One of the bipyramids is of the type SnO₃In with tert‐butyl groups on the oxygen atoms, while the other has the composition InCl₃Na with chlorine atoms connecting the two metals. The sodium atom in 2 has further contacts to two plus one alkoxide groups which are part of a[Sn(O^tBu)₂]₂ dimer disposing of a Sn₂O₂ central cycle. The hetero element cluster in 2 thus combines three closed entities and its skeleton SnO₃InCl₃NaO₂Sn₂O₂ consists of three different metallic and two different non‐metallic elements.     

氧化锡表面的原子簇模型计算

Cluster models of SnO2(110) face and oxygen vacancies and oxygen adsorption on its surface have been calculated by EHMO method. The results show that a tin atom with a coordination number of four is the adsorption center, because the total energy of cluster model becomes lower when an oxygen atom adsorpts on the tin atom with a coordination number of four. The tin atom with this coordination number gains and loses electrons more easily than tin atoms with a coordination number of five. All tin atoms in the cluster of SnO2(110) face are Sn4+.     

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.     

Die Kristallstruktur des Trimethylzinn-methansulfinats, (CH3)3Sn02SCH3

The Crystal Structure of Trimethyltin Methanesulfinate, (CH₃)₃SnO₂SCH₃ Trimethyltin methanesulfinate, (CH₃)₃SnO₂SCH₃ crystallizes orthorhombie in the space group A2₁22. The lattice constants are: a = 7.98 ± 0.01, b = 12.59 ± 0.02 and c = 17.83 ± 0.02 Å Within the crystal structure the Sn atoms are linked together via bridging RSO₂ groups to form a helical chain along [l00]. Each Sn atom is surrounded by three C and two 0 atoms in a trigonal bipyramidal arrangement. The Sn? C distances are in the range from 2.09 to 2.18 Å the Sn? 0 distance amounts to 2.23 Å.     

Adsorption and migration growth of the Ce,O, and F adatoms on the CeO2 (111) surface: A density functional theory study

In order to investigate the microscopic behavior of the crystal surface growth of the fluorinated cerium dioxide polishing powder, the adsorption and migration of the Ce, O, and F atoms on the CeO₂ (111) surface were studied by using density functional theory with Hubbard correction +U. The adsorption energies of three single atoms at five high-symmetry sites and the migration activation energies along the migration pathway on the CeO₂ (111) surface were calculated. Results show that the most stable adsorption sites of the Ce, O, and F atoms were the O_h, Ce_bri, and Ce_t sites, respectively. The Ce atom migrated from the O_h to the O_t site. The O atom migrated from the Ce_bri to the O_bri site. The F atom migrated from the Ce_t to the O_h site. The migration activation energies of the Ce, O, and F atoms along the migration pathways were 1.526, 0.597, and 0.263 eV, respectively. The F adatom does not change the spatial configuration of the Ce and the O atoms. When the O vacancy occurs on the CeO₂ (111) surface, the F adatom can make up for the O vacancy defect.     

Oxygen Atom Adsorption and Diffusion on Pd Low-index Surfaces and （311） Stepped Surface

Introduction Atom adsorption on transition metal surfaces has attracted special attention as a base for understanding the fundamental processes of oxidative catalysis. Particularly interesting is the adsorption and diffusion of oxygen on well-defined metal surfaces. An oxygen covered palladium surface, for example, plays a central role in several important reactions such as oxidation of carbon monoxide and ammonia. In particular, the (100), (111), (110) surfaces and the interactions with oxyge…     

用分子轨道理论研究NO气体在TiO2表面吸附

根据一氧化氮(NO)气体在二氧化钛(TiO₂)表面吸附和脱附的实验结果, 揭示了气体脱附量的变化规律. 利用MOPAC 和GAUSSIAN分子轨道理论计算了在TiO₂(110)表面上吸附NO分子的原子簇模型, 电荷分布以及原子簇的能级, 推断了NO在TiO₂(110)表面吸附的稳定性.     

Theoretical study on the stability and electronic property of Ag2SnO3

Bulk crystal properties of Ag₂SnO₃ were investigated with the advantage of density functional theory. The whole structure has layered feature: hexagonal metallic planes formed by Ag atoms and distorted octahedrons of SnO₆ clusters are configured alternatively along c axis of hexagonal cell. The cohesive energy is about ?2.792 eV/atom, which is less than SnO₂. The Debye temperature of Ag₂SnO₃ is about 231.6 K, and the bulk and shear moduli are 62.13 and 20.63 GPa, respectively. Band structure and DOS show the compound has a small pseudo-band gap value of 1.0 eV and so may be a semiconductor. When checking the PDOS intensity at the Fermi surface of Ag atoms, a weak metallic character can be seen. The distortion mechanism becomes less effective to reduce the total orbital energy both in SnO₂ and in Ag₂SnO₃ and as a result the bond lengths of Sn–O are intended to be isotropy.     

氯原子在Ag低指数面上的吸附位和吸附态

应用原子和表面簇合物相互作用的5参数Morse势方法(简称5-MP)对Cl-Ag低指数表面体系进行了研究, 并获得了全部的临界点特性, 如吸附位、吸附几何、结合能、正则振动等. 计算结果表明: 在Ag(100)面上, Cl原子吸附在四重洞位; 在Ag(111)面上, Cl吸附在三重洞位; 尽管第一与第二周期原子在(110)面上的稳定吸附态大都为赝式三重位和长桥位, 但在Ag(110)面上, 四重洞位是氯原子的稳定吸附态. 理论分析结果和实验推测结果符合得很好. 理论结果给出Cl原子在Ag表面的吸附结合能和表面簇合物的粗糙度有关, 结合能从小到大的顺序为(111)＜(100)＜(110).     

Investigation of the Pore Texture of SnO2-CeO2 Composite Oxides

Gas adsorption techniques have been used to study the pore texture changes occurring in composite SnO₂-CeO₂ materials of varying Sn: Ce atom ratios on calcination at temperatures up to 1273K. The data show that the uncalcined materials are largely microporous in nature, but changes in specific surface area, pore sizes and pore volume occur at an early stage in the calcination process with the formation of mesopores. However, significant changes occur at calcination temperatures>673 K at which point the mesopores are substantially reduced, and at 873 K and above the mean pore size increases greatly finally giving non-porous solids after calcination at 1273 K.     

EPR study of the mechanism of interaction of NO and NO2 molecules with zeolite surfaces

The adsorption of the paramagnetic molecules of NO and NO₂ by zeolites in the alkali and alkaline earth cationic forms has been studied by EPR and reflectance spectroscopic methods. The change in the EPR spectra of adsorbed nitric oxide with increase in the degree of covering of the surface of the alkali cationic form of the zeolites, and also the nature of the change in the spectra when oxygen is adsorbed on zeolites on which NO has previously been adsorbed, indicate the existence of two types of adsorption center. At low degrees of covering of the surface, on the order of 10¹⁸ g^–1, as can be judged from the EPR spectra, the adsorbed NO molecule is strongly polarized and the unpaired electron is almost completely localized on the oxygen atom. At high degrees of covering, for an appreciable proportion of the NO molecules, the bond with the surface is weaker. In this case, the EPR spectra show a hyperfine structure (HFS) with a constant which changes with change in the cation in the order Li⁺ Na⁺ K⁺. The replacement of the singly charged Na⁺ by the doubly charged Ca²⁺ produces a marked change in the adsorption properties of the zeolite. The adsorption of NO on CaA leads not only to polarization of the adsorbed molecule but also to transfer of the electron from the nitrogen atom to the atoms of the adsorbent; this is recorded in the EPR spectrum in the form of an F-center. On further adsorption, the NO molecules are adsorbed both on the nitrogen atom and on the oxygen atom of the first molecule; thus, NO₂ and N₂O are formed.     

First‐principles calculations of oxygen adsorption on the Ti3Al (0001) surface

Adsorption energies and density of states for O atoms adsorption on the Ti₃Al (0001) surface have been calculated using first‐principles calculations based on density functional theory. It is found that the order of O atom adsorption on the Ti₃Al (0001) surface is associated with the adsorption energy as well as the distance of O atoms because of the interaction. The adsorption energy mainly depends on the bond number and bond strength between O and Ti atoms, and the adsorption site with rich‐Ti surface (H_I and HCP_Al) is first priority. The adsorption energy decreases with the increase of the oxygen coverage because of the characteristics of the valence d‐orbitals of transition metals surface. Furthermore, the density of states indicates that the hybridization peak of O and Ti atoms is mainly from the contribution of Ti 3d‐ and O 2p‐orbitals, and the hybridization peak of O and Al atoms from the contribution of Al 2p‐ and O 2p‐orbitals. Copyright © 2016 John Wiley & Sons, Ltd.     

甲硫醇在Cu(111)表面的解离吸附: 密度泛函理论研究

采用基于密度泛函理论的第一性原理方法和平板模型研究了CH₃SH分子在Cu(111)表面的吸附反应.系统地计算了S原子在不同位置以不同方式吸附的一系列构型, 第一次得到未解离的CH₃SH分子在Cu(111)表面顶位上的稳定吸附构型,该构型吸附属于弱的化学吸附, 吸附能为0.39 eV. 计算同时发现在热力学上解离结构比未解离结构更加稳定. 解离的CH₃S吸附在桥位和中空位之间, 吸附能为0.75-0.77 eV. 计算分析了未解离吸附到解离吸附的两条反应路径, 最小能量路径的能垒为0.57 eV. 计算结果还表明S―H键断裂后的H原子并不是以H₂分子的形式从表面解吸附而是以与表面成键的形式存在. 通过比较S原子在独立的CH₃SH分子和吸附状态下的局域态密度, 发现S―H键断裂后S原子和表面的键合强于未断裂时S原子和表面的键合.     

H2分子在LaFeO3表面吸附的第一性原理研究

基于密度泛函理论的第一性原理方法,通过计算表面能确定LaFeO₃(010)表面为最稳定的吸附表面,研究了H₂分子在LaFeO₃(010)表面的吸附性质。LaFeO₃(010)表面存在LaO和FeO₂两种终止表面,但吸附主要发生在FeO₂终止表面,由于LaFeO₃(010)表面弛豫的影响,使得凹凸不平的表面层增加了表面原子与H原子的接触面积,表面晶胞的纵向体积增加约2.5%,有利于H原子向晶体内扩散。研究发现,H₂分子在LaFeO₃(010)表面主要存在3种化学吸附方式:第一种吸附发生在O-O桥位,2个H原子分别吸附在2个O原子上,形成2个-OH基,这是最佳吸附位置,此时H原子与表面O原子的作用主要是H1s与O2p轨道杂化作用的结果,H-O之间为典型的共价键。H₂分子的解离能垒为1.542 eV,说明表面需要一定的热条件,H₂分子才会发生解离吸附;第二种吸附发生在Fe-O桥位,1个H原子吸附在O原子上形成1个-OH基,另一个H原子吸附在Fe原子上形成金属键;第三种吸附发生在O顶位,2个H原子吸附在同一个O原子上,形成H₂O分子,此时H₂O分子与表面形成物理吸附,H₂O分子逃离表面后容易形成氧空位。此外,H₂分子在LaFeO₃(010)表面还可以发生物理吸附。     

Cyclische Diazastannylene. XV [1]. Charakterisierung einer instabilen Zwischenstufe: 1,3-Di-tert-butyl-2,2-dimethyl-4-tert-butylammonium-1,3,2,4λ3-diazasilastannatetidin

Cyclic Diazastannylenes. XV. Characterization of an Unstable Intermediate: 1,3-Di-tert-butyl-2,2-dimethyl-4-tert-butyl-ammonium-1,3,2,4λ³-diazasilastannatetidine The primary step in the reaction of 1, 3-di-tert-butyl-2,2-dimethyl-1,3,2,4λ²-diazasilastannetidine ( 1 ) with tert-butylamine is the formation of the Lewis-acid-base adduct 5 . In 5 the electrophilic tin atom of 1 is coordinated by the nucleophilic nitrogen atom of the tert-butylamine. 5 crystallizes below ?110°C in a triclinic cell with dimensions (conventional cell see Table 2): a = 1034(4), b = 1492(5), c = 654(3) pm, α= 89.9(3), β = 96.8(3), γ = 91.6(3)°, Z = 2. Above ?110°C the triclinic phase of 5 can be transformed to a monoclinic one (space group P2₁/m) with cell dimensions a = 1048(3), b = 1513(4), c = 654(2) pm, β = 96.9(3)°, Z = 2. An X-ray structural investigation of the latter phase reveals the adduct 5 to have C_S(m)-point symmetry. Important molecular dimensions are the rather long donor bond Sn→N of 242(3) pm, the Sn? N distances within the ring of 211(2) pm and the trigonal pyramidal coordination of the tin atom with mean N? Sn? N angles of 82.3°. The nitrogen atoms of the ring are pyramidal disturbing the planarity of the ring by a bending of 12°. This geometry is due to intramolecular N? H contacts (～290 pm) of the amino-hydrogen atoms with the nitrogen atoms of the ring. Some conclusions for the reaction path can be drawn from the structure of 5 .