Theoretically predicted innovative palladium stripe dopingcobalt(111) surface with excellent catalytic performance for carbonmonoxide oxidative coupling to dimethyl oxalate

Pd-based catalysts are extensively employed to catalyze CO oxidative coupling to generate DMO,while the expensive price and high usage of Pd hinder its massive application in industrial production.Designing Pd-based catalysts with high efficiency and low Pd usage as well as expounding the catalytic mechanisms are significant for the reaction.In this study,we theoretically predict that Pd stripe doping Co(111)surface exhibits excellent performance than pure Pd(111),Pd monolayer supporting on Co(111)and Pd single atom doping Co(111)surface,and clearly expound the catalytic mechanisms through the density functional theory(DFT)calculation and micro-reaction kinetic model analysis.It is obtained that the favorable reaction pathway is COOCH_(3)-COOCH_(3)coupling pathway over these four catalysts,while the rate-controlling step is COOCH_(3)+CO+OCH_(3)→2COOCH_(3)on Pd stripe doping Co(111)surface,which is different from the case(2COOCH_(3)→DMO)on pure Pd(111),Pd monolayer supporting on Co(111)and Pd single atom doping Co(111)surface.This study can contribute a certain reference value for developing Pd-based catalysts with high efficiency and low Pd usage for CO oxidative coupling to DMO.

Frictional contact analysis of a rigid solid with periodic surface sliding on the thermoelectric material

Understanding and characterizing rough contact and wavy surfaces are essential for developing effective strategies to mitigate wear,optimize lubrication,and enhance the overall performance and durability of mechanical systems.The sliding friction contact problem between a thermoelectric(TE)half-plane and a rigid solid with a periodic wavy surface is the focus of this investigation.To simplify the problem,we utilize mixed boundary conditions,leading to a set of singular integral equations(SIEs)with the Hilbert kernels.The analytical solutions for the energy flux and electric current density are obtained by the variable transform method in the context of the electric and temperature field.The contact problem for the elastic field is transformed into the second-kind SIE and solved by the Jacobi polynomials.Notably,the smoothness of the wavy contact surface ensures that there are no singularities in the surface contact stress,and ensures that it remains free at the contact edge.Based on the plane strain theory of elasticity,the analysis primarily examines the correlation between the applied load and the effective contact area.The distribution of the normal stress on the surface with or without TE loads is discussed in detail for various friction coefficients.Furthermore,the obtained results indicate that the in-plane stress decreases behind the trailing edge,while it increases ahead of the trailing edge when subjected to TE loads.

DFT Investigation of the Adsorption/dissociation Mechanisms of Methyl Nitrite on the Pd(111) Surface

The adsorption behavior of methyl nitrite （MN） on the closed-packed Pd（111） sur- face has been investigated in detail by using density functional theory （DFT）. MN binds to the surface in two alternative forms, using the nitrogen atom attached to the surface. An overall net charge transfer from the substrate to the cis-MN molecule is also confirmed. In addition, the reaction mechanism for the dissociation of MN on the Pd（111） surface has been identified and compared with the methanol decomposition via O-H scission. The results demonstrate that MN is a more active reactant than methanol for the oxidative addition to the Pd catalyst. The possible reason has been analyzed from the adsorption behaviors and reaction barriers, that is, MN is chemically absorbed on the Pd（111） surface; the CHaO-NO bond scission, leading to the formation of adsorbed methoxy species, is much more favorable than that of the O-H bond scission and has a large exothermic behavior.

Formation and local electronic structure of Ge clusters on Si（111）-7×7 surfaces

We report the formation and local electronic structure of Ge clusters on the Si（111）-7×7 surface studied by using variable temperature scanning tunnelling microscopy （VT-STM） and low-temperature scanning tunnelling spectroscopy （STS）. Atom-resolved STM images reveal that the Ce atoms are prone to forming clusters with 1.0 nm in diameter for coverage up to 0.12 ML. Such Ce clusters preferentially nucleate at the centre of the faulted-half unit cells, leading to the ＇dark sites＇ of Si centre adatoms from the surrounding three unfaulted-half unit cells in filled-state images. Biasdependent STM images show the charge transfer from the neighbouring Si adatoms to Ce clusters. Low-temperature STS of the Ce clusters reveals that there is a band gap on the Ce cluster and the large voltage threshold is about 0.9 V.

The STM Images of Pt (111) (<img src="http://latex.codecogs.com/gif.latex?\sqrt{3}\times&space;\sqrt{3}"title="\sqrt{3}\times \sqrt{3}"/>)R30&deg;/CO Surface by DFT Calculations

In this work we have performed total-energy calculations of the chemisorption properties and STM images of Pt (111) ( × )R30°/CO Surface;STM Image;ChemisorptionR30°/CO surface by using the density functional theory (DFT) and the projector-augmented wave (PAW) method. The calculations show that carbon monoxide molecule (CO) adsorbs on FCC site in the Pt (111) ( × )R30°/ surface is energetically favored by the GGA-PBE XC-functional, this is in agreement with most of the theoretical calculations which is using different XC-functional at the most. However, these results strongly conflicted with the existing experiments. Actually the calculated work function for the FCC adsorption is quite different from the experiments while the atop one is in good agreement with experiments. We speculate that the atop adsorption for (CO is favorable for the adsorption case at the most. Furthermore, we have calculated the scanning tunneling microscopy (STM) images for both adsorption geometries and suggest that there should be existed remarkable differences in the STM images. The present work provides a faithful criterion accounting for the local surface geometry in Pt (111) ( × )R30°/CO surface from surface work functions and STM images instead of totalenergy calculations.

Adsorption of HCN on Ni/Pt(111)Bimetallic Surfaces Investigated with Density Functional Theory Method

We applied periodic density-functional theory to investigate the adsorption of HCN on x Ni@Pt（111） bimetallic surfaces（x = 1~4）. The results have been compared with those obtained on pure Ni（111） and Pt（111） surfaces. For all bimetallic surfaces,HCN is preferentially tilted with the CN bond parallel to the surface,and adsorption energies increase with an increasing number of layer Ni atoms on the surface. The adsorption energies of HCN on all bimetallic surfaces are larger than that on the Pt（111） surface,whereas the adsorption energies of HCN on 3Ni@Pt（111） and 4Ni@Pt（111） are larger than that on the Ni（111） surface,indicating that the introduction of Ni to the Pt catalyst could increase the activity of bimetallic catalyst in the hydrogenation reaction for nitriles. Larger adsorption energy of HCN leads to a longer C–N bond length and a smaller CN vibrational frequency. The analysis of Bader charge and vibrational frequencies showed obvious weakening of the adsorbed C–N bond and an indication of sp2 hybridization of both carbon and nitrogen atoms.

A Periodic Density Functional Study on Adsorption Properties of Methoxy on Au(111) Surface

Adsorption of CH3O at four sites （top, bridge, hcp, fcc） on Au（111） surface has been investigated by density functional theory method at the generalized gradient approximation level. We have performed calculations on adsorption energies, structures, Mulliken charges and vibrational frequencies of CH3O on Au（111） surface with full-geometry optimization. The predicted results are compared with the available experimental observation. The calculated CH3O adsorption structure and stretching vibrational frequencies agree well with experimental ones, and precise determinations of adsorption sites are carded out. The most favorite adsorption on Au（111） occurs at the bridge site, and O-C axis is tilted to the surface. However, on hollow sites （hcp, fcc） the species is adsorbed in an upright geometry （pseudo-C3v local symmetry）.

First-principles Study on Geometric and Electronic Structures of Si（111）-√7× √3-In Surface Reconstruction

In order to determine the structures of Si（111）-√7 √3-In surfaces and to understand their electronic properties, we construct six models of both hexagonal and rectangular types and perform first-principles calculations. Their scanning tunneling microscopic images and work functions are simulated and compared with experimental results. In this way, the hex-H3＇ and rect-T1 models are identified as the experimental configurations for the hexagonal and rectangular types, respectively. The structural evolution mechanism of the In/Si（lll） surface with indium coverage around 1.0 monolayer is discussed. The 4×1 and -√7× √3 phases are suggested to have two different types of evolution mechanisms, consistent with experimental results.

近化学计量比的HgCdTe薄膜表面处理方法

本文采用X射线光电子能谱检测技术分别对溴-甲醇(Br_(2):Me)、溴-氢溴酸(Br_(2):HBr)和溴-氢溴酸-乙二醇(Br_(2):HBr:Eg)3种体系的腐蚀液处理后的HgCdTe表面状态进行了研究,结果表明这3种溴基腐蚀液均会造成HgCdTe表面富碲(Te^(0)),且富碲程度为(Br_(2):HBr:Eg)<(Br_(2):HBr)<(Br_(2):Me)。为了获得接近化学计量比的表面,一般采取先氧化富碲为TeO_(2)后腐蚀的方式去除表面富碲,然而,湿法腐蚀去除表面富碲的方法存在各种缺点。等离子体氧化具有氧化性强,工艺稳定,安全环保等优点,因此本文通过氧等离子体氧化Br_(2):HBr:Eg处理后的HgCdTe表面,进一步研究了盐酸、乳酸和氢氧化铵溶液腐蚀去除HgCdTe表面氧化物的情况,结果表明低浓度的盐酸能够较彻底地去除HgCdTe表面氧化物且不引入碳等其他污染物。在此接近化学计量比的表面制备的CdTe钝化膜与HgCdTe界面孔洞大小及数量显著减小,说明CdTe/HgCdTe界面的缺陷密度更低。

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.

Theoretical Study on the Adsorption and Decomposition of Methanol over the Pt-Mo(111)/C Surface

The density functional theory（DFT） and self-consistent periodic calculation were used to investigate the methanol adsorption on the Pt-Mo（111）/C surface.The adsorption energies,equilibrium geometries and vibration frequencies of CH3OH on nine types of sites on the Pt-Mo（111）/C surface were predicted and the favorite adsorption site for methanol is the top-Pt site.Both sites of valence and conduction bands of doped system have been broadened,which are favorable for electrons to transfer to the cavity.The possible decomposition pathway was investigated with transition state searching and the calculation results indicate that the O-H bond is first broken,and then the methanol decomposes into methoxy.The activation barrier of O-H bond breaking with Pt-Mo catalyst is only 104.8 kJ mol-1,showing that carbon supported Pt-Mo alloys have promoted the decomposition of methanol.Comparing with the adsorption energies of CH3OH on the Pt（111）/C surface and that of CO,the adsorption energies of CO are higher,and Pt（111）/C is liable to be oxidized and loses the activity,which suggests that the catalyst Pt-Mo（111）/C is in favor of decomposing methanol and has better anti-poisoning ability than Pt（111）/C.

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.

Adsorption behavior of Fe atoms on a naphthalocyanine monolayer on Ag(111) surface

Adsorption behavior of Fe atoms on a metal-free naphthalocyanine（H2Nc） monolayer on Ag（111） surface at room temperature has been investigated using scanning tunneling microscopy combined with density functional theory（DFT）based calculations. We found that the Fe atoms were adsorbed on the centers of H2Nc molecules and formed Fe–H2Nc complexes at low coverage. DFT calculations show that Fe sited in the center of the molecule is the most stable configuration, in good agreement with the experimental observations. After an Fe–H2Nc complex monolayer was formed, the extra Fe atoms self-assembled to Fe clusters of uniform size and adsorbed dispersively at the interstitial positions of Fe–H2Nc complex monolayer. Therefore, the H2Nc monolayer grown on Ag（111） could be a good template to grow dispersed magnetic metal atoms and clusters at room temperature for further investigation of their magnetism-related properties.

A Density Functional Theory Study on the Adsorption of CN on Ni(111) Surface

The interaction of cyanide (CN) with different sites on Ni(111) surface is studied by using density functional theory (DFT). Ni19 cluster is used to simulate the surface. The present calculations show that the end-on bonded (through C atom) configuration is much more preferable than the side-on bonded CN or other configurations on the same adsorption site. For all adsorption modes, adsorption energies at the top, bridge, and three-fold sites on Ni(111) are comparable, with the bridge site of the end-on bonded CN (through C atom) more favorable than other adsorption sites. CN vibrational frequencies are red-shifted at all cases, except that the end-on CN bonded (through C atom) on the top site is blue-shifted. The bonding of CN on the Ni(111) surface is large- ly ionic.

Acetonitrile(CH_3CN)and methyl isocyanide(CH_3NC) adsorption on Pt(111)surface:a DFT study

The adsorption of CH3CN and CH3NC on the Pt（lll） surface at the 1/4 monolayer （ML） coverage has been car-ried out at the level of density functional theory for understanding hydrogenation processes of nitriles. The most favored ad-sorption structure for CH3 CN is the C--N bond almost parallel to the surface with the C-N bond interaction with adjacent surface Pt atoms. For CH3NC, the most stable configuration is the CH3 NC locates at the face center cubic （fcc） site with the C-atom bonded to three Pt atoms. In addition, the HCN and HNC adsorption has been computed, and the adsorption pattern is nearly similar to the CH3CN and CH3NC, respectively. The adsorbed molecules rehybridize on the surface, be-coming non-linear with a bent C-C-N or C-N-C angle. Furthermore, the binding mechanism of these molecules on the Pt（111） surface is also analyzed.

Thermoelectric Transport by Surface States in Bi2Se3-Based Topological Insulator Thin Films

We develop a tractable theoretical model to investigate the thermoelectric （TE） transport properties of surface states in topological insulator thin films （TITFs） of Bi2Sea at room temperature. The hybridization between top and bottom surface states in the TITF plays a significant role. With the increasing hybridization-induced surface gap, the electrical conductivity and electron thermal conductivity decrease while the Seebeck coefficient increases. This is due to the metal-semiconductor transition induced by the surface-state hybridization. Based on these TE transport coefficients, the TE figure-of-merit ZT is evaluated. It is shown that ZT can be greatly improved by the surface-state hybridization. Our theoretical results are pertinent to the exploration of the TE transport properties of surface states in TITFs and to the potential application of Bi2Sea-based TITFs as high-performance TE materials and devices.

小型TE_(111)无泡隔膜腔氢脉泽的实验研究

研究了圆柱形TE111模式无泡谐振腔,根据脉泽振荡条件验证了新模式的可行性,对该谐振腔进行了模式分析、结构设计及腔频灵敏度计算,并对这种氢脉泽进行了感应辐射信号的观察和正反馈振荡实验。

窄带隙IV-VI族半导体PbTe(111)的表面氧化及氧的热脱附机理

利用X射线光电子能谱(XPS)、扫描隧道显微镜(STM)以及低能电子衍射(LEED),对PbTe(111)薄膜的表面氧化及氧的热脱附机理进行了研究.结果表明:PbTe(111)薄膜经500VAr+轰击加上250℃高温退火循环处理,可得到呈(1×1)周期性排列的清洁表面.将此清洁表面暴露于大气两天后,表面被氧化形成了PbO2、PbO和TeO2,氧化层的厚度大于2个单原子层(ML),与清洁PbTe(111)表面相比,被氧化的PbTe(111)表面的Te3d5/2与Pb4f7/2芯态谱峰的面积比明显减小,表明被氧化的PbTe(111)表面是富Pb的.在热脱附处理过程中,PbO2和TeO2的芯态峰消失,且O1s芯态峰的强度迅速减弱,表明加热处理不仅使PbO2和TeO2发生了分解,同时也使氧发生了脱附,但PbO即使在350℃退火仍吸附于PbTe(111)表面.

TE_(111)双模圆柱腔椭圆函数滤波器的耦合设计

滤波器是邻频频道合成器的关键部件之一 ,而耦合问题又是滤波器设计的关键。文中论述了TE111双模圆柱腔椭圆函数滤波器中 ,简并腔模及腔间与端面的耦合设计。文中巧妙地使用调谐螺钉和耦合螺钉 ,解决了TE111双模圆柱腔椭圆函数滤波器中 ,简并腔模及腔间与端面的耦合设计问题 ,最后给出了该方法设计出的产品的实测数据。

单原子Ge助剂修饰Cu(111)晶面上CO_(2)加氢制甲醇的机理研究

针对CO_(2)热催化转化制甲醇过程中CO_(2)吸附、活化较困难及副产物较多的问题,提出采用单原子Ge助剂修饰Cu(111)晶面的解决思路,通过密度泛函理论(DFT)计算研究了CO_(2)在Ge-Cu(111)晶面上加氢合成甲醇的反应机理。结果表明,单原子Ge助剂的电子调控增加了与其相邻的Cu原子的电子云密度,使CO_(2)分子在含Ge活性界面上的吸附能力显著增强:CO_(2)在GeCu(111)晶面上的吸附能约为Cu(111)晶面的1.5倍,约为Pd改性Cu(111)晶面的2.4倍,进而使逆水煤气变换(RWGS)反应路径速控步骤的活化能降低了近20 kJ·moL^(-1),同时衍生出3条生成甲醇的RWGS新路径;此外,Ge-Cu(111)晶面上甲酸盐路径由于速控步骤活化能大幅上升而被禁阻,进而CO及烃类等副产物选择性大幅降低,Ge-Cu(111)晶面上CO_(2)加氢制甲醇选择性升高。