In/Au(111)和Ir/Au(111)面上巴豆醛选择加氢的机理研究及比较

基于巴豆醛在M/Au(111)合金表面(M=In,Ir)垂直吸附的最稳定吸附结构,采用密度泛函理论对其不完全加氢的反应机理进行探究。从不同加氢机理下各基元反应的活化能、反应热计算以及构型变化分析中可知,巴豆醛在M/Au(111)面上均优先对距离合金表面较近的CO进行加氢,且以C为活性中心优先进行加氢为最优机理,其中第1步加氢反应的活化能较高,是该机理的控速步骤。反应物巴豆醛的O原子与合金的掺杂原子M形成较强的化学吸附,提高了M/Au(111)面对CO加氢的选择性。巴豆醛按最优机理加氢的基元反应中在In/Au(111)面上最高反应能垒为0.969 e V,比在Ir/Au(111)面的最高反应能垒1.332 e V低,因此认为In/Au合金对其不完全加氢有更好的催化活性。     

肉桂醛在M13(M=Au,Pt)团簇表面加氢反应机理分析

采用密度泛函理论系统地研究了肉桂醛在正二十面体M₁₃(M=Au,Pt)团簇上的选择性加氢反应机理(C=O,C=C以及1,4共轭加成机理)。在稳定吸附构型的基础上,通过Complete LST/QST方法探索肉桂醛选择性加氢反应中各基元反应的过渡态,得到各反应的活化能和反应热。计算结果表明:肉桂醛在Au₁₃团簇最可能发生1,4共轭加成得到烯醇,但烯醇很不稳定,会发生异构生成苯丙醛,反应总体放出热量;肉桂醛在Pt₁₃团簇最可能发生C=O加成得到肉桂醇,肉桂醇进一步加氢得到饱和醇,反应总体吸收热量。     

Pt/Au(111)表面合金电化学稳定性的第一性原理研究

利用密度泛函理论(DFT)对Pt/Au (111)表面合金的电化学稳定性进行了初步研究。形成能计算结果表明,Au与Pt不易在块体中形成合金,但能在Pt (111)面形成表面合金。溶解电位计算结果进一步表明,Pt/Au (111)面上Pt原子的溶解电位与其第一近邻Au原子数有很好的线性关系,而Au对第二近邻及更远近邻的Pt溶解电位的影响可忽略。这些结果意味着可建立表面配位环境与表面原子溶解电位间的标度关系,为揭示表面合金的"结构-电化学稳定性"构型关系奠定了基础。     

4种吡嗪类缓蚀剂及其在Cu(111)面吸附行为的密度泛函理论研究

为了探究吡嗪类缓蚀剂对铜的缓蚀机理,对比研究4种缓蚀剂的吸附性能。采用基于密度泛函理论（DFT）的量子化学方法,研究了4种吡嗪类缓蚀剂分子的反应活性及其在Cu（111）面的吸附行为,结果表明：4种缓蚀剂分子的前线轨道均分布在吡嗪环上,且吡嗪环上的N原子为分子的反应活性中心;4种吡嗪类缓蚀剂分子均能与Cu原子发生化学吸附形成共价键,且吸附强度排序为2-氨基吡嗪（AP）> 2-氨基-5-溴吡嗪（ABP）> 2-甲基吡嗪（MP）> 吡嗪（PY）;另外,缓蚀剂分子也可以通过静电相互作用与金属表面发生物理吸附。     

双相等离子体Au/TiO2纳米复合材料抗菌研究

具有独特的表面等离子体共振（SPR）的金属纳米晶体是一种良好的宽带隙半导体可见光敏化材料。本研究通过溶剂热和煅烧合成了0.3％摩尔比的金修饰氧化钛（Au/TiO2）纳米复合材料。利用X射线晶体衍射（XRD）,X射线光电子能谱（XPS）,透射电子显微镜（TEM）和紫外-可见（UV-vis）等方法对合成的Au/TiO2纳米复合材料进行表征。结果表明,由于强的表面等离子体共振效应,Au纳米颗粒可以显著提高TiO2的可见光吸收性能。随着煅烧温度的升高,可见光吸收峰从?550 nm红移到670 nm,这便于更好地利用太阳光谱。Au/TiO2纳米复合材料对大肠杆菌（E. coli）的抗菌活性显示,在450 ℃下煅烧后形成的金修饰的锐钛矿相和金红石相的混晶相,具有最好的光催化抗菌活性。     

荷正电聚砜/Al_2O_3复合纳滤膜的制备及其分离Au(Ⅲ)

采用含浸法制备聚砜/Al2O3复合荷正电纳滤膜。探讨各种主要工艺条件对膜分离性能的影响。通过测定膜流动电位及其对不同无机盐阳离子截留率,分析制膜条件对膜电性能的影响。利用扫描电镜(SEM)分析膜表面及截面形貌,利用傅里叶红外光谱仪(FTIR)分析表面活性层结构及成膜机理。对硫脲浸金液中Au(Ⅲ)进行富集分离研究,Au(Ⅲ)的截留率可达88%～95%,为膜法分离贵金属提供了新的思路。     

大颗粒SiO_2载体负载Ir/FeO_x催化剂的巴豆醛加氢性能

选择粒径(1~3)mm的Si O2为载体,采用浸渍法制备Ir/Fe Ox/Si O2催化剂,考察Fe含量对催化剂气相巴豆醛选择加氢反应性能的影响,采用X射线粉末衍射、拉曼光谱及光电子能谱等对催化剂进行表征。结果表明,随着Fe添加量的增加,反应1 h时巴豆醛转化率和反应10 h时巴豆醇选择性呈现先提高后下降趋势,n(Fe)∶n(Ir)=1.0时,反应1 h时巴豆醛转化率最高(达67%);n(Fe)∶n(Ir)=0.3时,反应1 h时巴豆醛转化率和反应10 h时巴豆醇选择性分别达88%和95%,反应过程中催化剂表面积炭是导致巴豆醛转化率降低的主要原因。对于同种催化剂,反应后电子结合能往低结合能方向偏移可能是导致选择性提高的原因。     

Pt/WC催化剂甲醇脱氢反应机理的研究

采用密度泛函理论(DFT)和周期平板模型,研究了甲醇在PtML/WC(0001)催化剂表面上的脱氢反应机理。通过对甲醇分解过程中反应物、中间体及产物的结构优化和对可能基元反应的过渡态搜索,得到了各吸附物种在最稳定吸附构型下的吸附能和各基元反应的活化能垒。通过对三条可能反应路径的比较,即甲醇分子中O—H键断裂生成甲氧基(CH_3O~*)和氢(H~*)、C—H键断裂生成羟甲基(CH_2OH~*)和氢(H~*)、C—O键断裂生成甲基(CH_3~*)和羟基(OH~*),发现O—H键的断裂所需活化能最低。因此,在PtML/WC(0001)表面上,甲醇分子中的O—H键断裂生成CH_3O~*为整个反应的速控步骤。     

Au(Ⅲ)离子在黑曲霉菌上的吸附热力学和动力学特性

以黑曲霉菌作为生物吸附剂,研究其对Au(Ⅲ)离子的吸附特性,考察了pH值、吸附时间、温度和初始Au(Ⅲ)离子浓度等因素对吸附过程的影响。结果表明,Au(Ⅲ)离子在黑曲霉菌上的吸附过程对溶液pH值具有一定的依赖性,最佳pH值为2.0～3.0。升温能明显加快吸附进程,20℃下吸附过程分为2个阶段进行,分别对应于Au(Ⅲ)离子还原前和还原后的吸附,24 h后吸附趋于平衡,而30、40、60℃下吸附过程均无明显分段现象,并分别于12、6、1 h后趋于吸附平衡。Au(Ⅲ)离子初始浓度<233.32 mg·L^-1时,吸附量几乎不随温度的变化而变化,初始浓度>367.94 mg·L^-1时,升温明显促进了吸附的进行。Au(Ⅲ)离子在黑曲霉菌上的吸附等温线可用Langmuir方程很好地模拟,20、30、40、50℃时其饱和吸附量分别为185.19、202.02、235.85、277.78 mg·g^-1。热力学参数Gibbs自由能变(ΔG⁰)、吸附焓变(ΔH⁰)和吸附熵变(ΔS⁰)的计算结果表明,Au(Ⅲ)离子在黑曲霉菌上的吸附过程是一个自发的吸热和熵增过程。吸附动力学可用准二级速率方程描述,吸附活化能为55.71 kJ·mol^-1。傅里叶变换红外光谱分析的结果进一步揭示了菌体表面的酰氨基、羧基和羟基是参与吸附的主要功能基团。     

Zn(Al)O复合氧化物负载Au催化剂催化氧化甘油制备1,3-二羟基丙酮

以尿素为沉淀剂,采用均匀沉积沉淀法制备了Zn(Al)O复合氧化物负载Au催化剂,并用于无碱条件下催化氧化甘油制备1,3-二羟基丙酮（DHA）反应,值得注意的是随着载体中Zn/Al摩尔比的不同,负载Au催化剂的催化活性和产物DHA的选择性呈现明显差距。结合X射线衍射（XRD）、X射线光电子能谱（XPS）、透射电镜（TEM）、CO吸附傅里叶变换红外光谱（CO吸附FTIR）等表征手段,发现载体Zn(Al)O复合氧化物中Zn/Al摩尔比会影响表面氧物种的含量并进一步会影响催化剂的催化活性和选择性。当Zn/Al摩尔比为7∶1、反应温度为80℃、氧气压力为10bar、反应2h时获得最佳的甘油转化率（58.5%）和DHA的选择性（95.3%）。同时,还考察了反应温度、反应时间、反应压力及载体的焙烧温度对催化性能的影响,并发现反应条件对催化剂的催化活性和选择性均有不同程度的影响。此外,以Au/Zn(Al)O-7∶1催化剂为基准考察了催化剂的稳定性,并通过表征手段分析了催化剂失活的主要原因。     

The adsorption of methyl nitrite on the Au(111) surface

The interaction of the methyl nitrite molecule (CH₃ONO) with the gold(111) surface has been studied by means of density functional calculations. The perfect Au(111) surface has been represented by a rather large cluster model, Au₂₂, that was in turn used to extract information about the preferred adsorption geometry of the CH₃ONO species. Vibrational frequencies and adsorption energy are also reported. The calculated adsorption energies are 31.2 kJ/mol with respect to gas phase cis-conformer and 35.1 kJ/mol with respect to trans-methyl nitrite, very close to the experimental adsorption energy of 33.5 kJ/mol. From the analysis of vibrational frequencies of gas phase and adsorbed species it is concluded that only the cis-conformer is present at the Au(111) surface.     

Reaction of Au(111) with Sulfur and Oxygen: Scanning Tunneling Microscopic Study

The reaction of sulfur and oxygen with the gold surface is important in many technological applications, including heterogeneous catalysis, corrosion, and chemical sensors. We have studied reactions on Au(111) using scanning tunneling microscopy (STM) in order to better understand the surface structure and the origin of gold’s catalytic activity. We find that the Au(111) surface dynamically restructures during deposition of sulfur and oxygen and that these changes in structure promote the reactivity of Au with respect to SO₂ and O₂ dissociation. Specifically, the Au(111) herringbone reconstruction lifts when either S or O is deposited on the surface. We attribute this structural change to the reduction of tensile surface stress via charge redistribution by these electronegative adsorbates. This lifting of the reconstruction was accompanied by the release of gold atoms from the herringbone structure. At high coverage, clusters of gold sulfides or gold oxides form by abstraction of gold atoms from regular terrace sites of the surface. Concomitant with the restructuring is the release of gold atoms from the herringbone structure to produce a higher density of low-coordinated Au sites by forming serrated step edges or small gold islands. These undercoordinated Au atoms may play an essential role in the enhancement of catalytic activity of gold in reactions such as oxygen dissociation or SO₂ decomposition. Our results further elucidate the interaction between sulfur and oxygen and the Au(111) surface and indicate that the reactivity of Au nanoclusters on reducible metal oxides is probably related to the facile release of Au from the edges of these small islands. Our results provide insight into the sintering mechanism which leads to deactivation of Au nanoclusters and into the fundamental limitation in the edge definition in soft lithography using thiol-based self-assembled monolayers (SAMs) on Au. Furthermore, the enhanced reactivity of Au after release of undercoordinated atoms from the surface indicate a relatively insignificant role of an oxide support for high reactivity.     

Pd deposition onto Au(111) from nitrate solution

The initial stages of palladium deposition onto Au(111) from 0.1 M HNO₃ + 0.2 mM Pd(NO₃)₂ have been studied by cyclic voltammetry and in situ scanning tunnelling microscopy. It is demonstrated that nucleation starts exclusively at surface defects such as monoatomic high steps, which is at variance with recently published work. From this and our previous work it thus appears that surface defects are the preferred nucleation sites indeed for nitrate, sulphate and chloride containing solutions.     

Ethylene dimerization over a model Sn/Pt(111) catalyst

The dimerization reaction of ethylene was studied over Pt(111) and (3×3)R30°-Sn/ Pt(111) model catalysts at moderate pressures (20–100 Torr). The catalyst surfaces were prepared and characterized in a UHV surface analysis system and moderate pressure catalytic reactions were conducted with an attached batch reactor. The overall catalytic activity of the (3×3)R30°-Sn/Pt(111) surface alloy for C₄ products was slightly higher than that at Pt(111). In addition to the dimerization reaction, hydrogenolysis of ethylene to propane and methane was also observed, with the (3×3)R30°-Sn/Pt(111) surface alloy less active than Pt(111). Among the C₄ products, butenes andn-butane were the major components. Carbon buildup was observed to be significant above 500 K with the (3×3)R30°-Sn/Pt(111) surface alloy much more resistant than Pt(111). The dimerization of ethylene was not eliminated by the presence of surface carbonaceous deposits and even at significant surface coverages of carbon the model catalysts exhibited significant activities. The results are discussed in terms of the surface chemistry of ethylene and the previously reported catalytic reactions of acetylene trimerization andn-butane hydrogenolysis at these surfaces.     

Influences of H on the Adsorption of a Single Ag Atom on Si(111)-7 × 7 Surface

The adsorption of a single Ag atom on both clear Si(111)-7 × 7 and 19 hydrogen terminated Si(111)-7 × 7 (hereafter referred as 19H-Si(111)-7 × 7) surfaces has been investigated using first-principles calculations. The results indicated that the pre-adsorbed H on Si surface altered the surface electronic properties of Si and influenced the adsorption properties of Ag atom on the H terminated Si surface (e.g., adsorption site and bonding properties). Difference charge density data indicated that covalent bond is formed between adsorbed Ag and H atoms on 19H-Si(111)-7 × 7 surface, which increases the adsorption energy of Ag atom on Si surface.     

Synergistic Effect in the Dehydrogenation of Cyclohexene on C/W(111) Surfaces Modified by Submonolayer Coverage Pt

The dehydrogenation and decomposition of cyclohexene on the Pt-modified C/W(111) surfaces have been studied by temperature-programmed desorption (TPD), Auger electron spectroscopy (AES) and high-resolution electron energy loss spectroscopy (HREELS). The objective of the current study is to investigate how the surface reactivity of tungsten carbide is modified by the presence of submonolayer Pt. Similar to that observed on Pt(111), Pt(100) and C/W(111) surfaces, the characteristic reaction pathway on Pt/C/W(111) is the selective dehydrogenation of cyclohexene to benzene. At a Pt coverage of 0.52 monolayer, the selectivity to the gas-phase benzene product is 86±7%, which is slightly higher than that on Pt(111) (75%) and on C/W(111) (67±7%). More importantly, the desorption of benzene on Pt/C/W(111) is a reaction-limited process that occurs at 290 K, which is much lower than the benzene desorption temperature of 400 K from Pt(111).     

A combined experimental and theoretical study of the generation of palladium clusters on Au(111) with a scanning tunnelling microscope

Palladium clusters have been deposited on the surface of a Au(111) electrode with the tip of a scanning tunnelling microscope. The distance over which the tip was moved towards the surface has a decisive influence on the properties of the clusters: the larger this distance, the larger the generated clusters, and the more stable they are. These findings are supported by computer simulations, which further suggest that the larger clusters contain a sizable amount of gold, which enhances their stability. Dissolution of the clusters occurs from the edges rather than layer by layer.