C2H4在Ru(1010)表面吸附与分解的研究

用X射线电子能谱(XPS)、热脱附谱(TDS)和紫外光电子能谱(UPS)方法研究了乙烯(C_{2H4)在Ru(1010)表面的吸附,在低温下(200K以下)乙稀(C2Ｈ4})可以在Ru(1010)表面上以分子状态稳定吸附,在200K以上乙烯(C₂H ₄)则发生了脱氢分解反应.TDS结果表明乙烯(C₂H₄)分 解后的主要产物为乙炔(C< 关键词： 乙烯 钌(1010)表面 吸附与分解     

C2H2,C2H4与K在Ru(1010)表面上共吸附的UPS研究

利用紫外光电子谱(UPS)对乙烯(C₂H₄)和乙炔(C₂H₂)气体在Ru(1010)表面的吸附及与K的共吸附进行了研究,实验结果表明:当衬底温度超过200K,乙烯即发生脱氢反应后,σ_CH和σ_CC能级均向高结合能方向移动.在室温下,σ_CH和σ_CC能级位置与乙炔在Ru(1010)表面的吸附时的分子能级完全一致.乙烯发生脱氢反应后的主要产 关键词： 乙烯 乙炔 钾 Ru(1010)表面     

C2H4在Ru(10(1-)0)表面吸附与分解的研究

用X射线电子能谱(XPS)、热脱附谱(TDS)和紫外光电子能谱(UPS)方法研究了乙烯(C2H4)在Ru(10(1-)0)表面的吸附,在低温下(200K以下)乙稀(C2H4)可以在Ru(10(1-)0)表面上以分子状态稳定吸附,在200K以上乙烯(C2H4)则发生了脱氢分解反应.TDS结果表明乙烯(C2H4)分解后的主要产物为乙炔(C2H2).乙烯(C2H4)分解后C的1s能级向低结合能方向移动了0.3eV,而价态σCC和σCH轨道能级向高结合能方向分别移动了0.5和1.1eV.     

乙烯在Ru（1010）表面价带电子特性研究

在200K以下乙烯(C2H4)可以在Ru（1010）表面上以分子状态稳定吸附,200K以上乙烯发生了脱氢分解反应生成乙炔(C2H2)。乙烯分解生成乙炔后,σCC和σCH分子轨道能级向高结合能方向分别移动了0．5和1.1eV。偏振角分辨紫光电子谱（ARUPS)结果表明：在RM（1010）表面上,乙烯和脱氨反应后生成的乙炔分子的C—C键轴都不平行于表面,而是沿表面(0001)晶向倾斜。     

乙烯在Ru( )表面价带电子特性研究

在200K以下乙烯（C2H4）可以在Ru（1010^-）表面上以分子状态稳定吸附,200K以上乙烯发生了脱氢分解反应生成乙炔（C2H2）。乙烯分解生成乙炔后,σCC和σCH 分子轨道能级向高结合 能方向分别移动了0.5和1.1eV。偏振角分辨紫外光电子谱（ARUPS）结果表明：在Ru(10106-)表面上,乙烯和脱氢反应后生成的乙炔分子在C－C键轴都不平行 于表面,而是沿表面&lt;0001&gt;晶向倾斜。     

C_2H_2,C_2H_4与K在Ru(100)表面上共吸附的UPS研究

利用紫外光电子谱 (UPS)对乙烯 (C2 H4)和乙炔 (C2 H2 )气体在Ru(10 10 )表面的吸附及与K的共吸附进行了研究 ,实验结果表明 :当衬底温度超过 2 0 0K ,乙烯即发生脱氢反应后 ,σCH 和σCC 能级均向高结合能方向移动 .在室温下 ,σCH和σCC 能级位置与乙炔在Ru(10 10 )表面的吸附时的分子能级完全一致 .乙烯发生脱氢反应后的主要产物为乙炔 .衬底温度从 12 0K升到室温 ,Ru(10 10 )表面上乙炔的σCH 和σCC 能级均未发现变化 .室温下乙炔仍然可以在Ru(10 10 )表面以分子状态稳定吸附 .在有K的Ru(10 10 )表面上 ,室温时σCC谱峰几乎消失 .碱金属K的存在促进了乙炔的分解 .     

C2H2,C2H4与K在Ru（1010）表面上共吸附的UPS研究

利用紫外光电子谱(UPS)对乙烯(C2H4)和乙烯(C2H2)气体在Ru(1010)表面的吸附及与K的共吸附进行了研究,实验结果表明：当衬底温度超过200K,乙烯即发生脱氢反应后,σCH和σCC能级均高结合方向移动．在室温下、σCH和σCC能级位置与乙炔在Ru(1010)表面的吸附时的分子能级完全一致．乙烯发生脱氢反应后的主要产物为乙炔。衬底温度从120K升到室温,Ru(1010)表面上乙炔的σCH和σCC能级均未发现变化．室温下乙炔仍然可以在Ru(1010)表面以分子状态稳定吸附．在有K的Ru(1010）表面上．室温时σCH谱峰几乎消失．碱金属K的存在促进了乙炔的分解．     

Ru(0001) 表面BaO吸附层的原子结构和氮分子的吸附性质

采用密度泛函理论研究了Ru(0001) /BaO表面的原子层结构和氮分子的吸附性质. 研究结果表明, 在低覆盖度下氧化钡倾向于以相同的构型形成Ru(0001) 表面原子层. 在此构型中, 氧原子位于表面p(1× 1) 结构的hcp谷位, 而钡原子则位于同一p(1× 1) 结构的顶位附近. 钌氧键键长等于0.209 nm, 比EXAFS的实验值大0.018 nm. 在Ru(0001) /BaO表面氮分子倾向吸附于钡原子附近. 相应位置的氮分子吸附能位于0.70到0.87 eV之间, 大于氧原子附近的氮分子吸附能. 钡原子附近的钌原子对氮分子具有更强的活化性能. 相应位置的氮分子拉伸振动频率等于1946 cm^{- 1}, 比氧原子附近的最大分子振动频率小约130 cm^-1. Ru(0001) /BaO表面氮分子键强度介于清洁Ru(0001) 和Ru(0001) /Ba表面之间. Ru(0001)/BaO表面不同位置的氮分子吸附性质差异是由钡和氧原子化学性质不同造成的. 表面钡原子的作用能够减少吸附氮分子的σ^*轨道电子密度, 增加π^*轨道电子密度, 从而增强氮分子和钌原子间的轨道杂化作用, 弱化氮分子键.     

TiO2分子在GaN(0001)表面吸附的理论研究

采用基于密度泛函理论的平面波超软赝势法,计算了TiO₂分子在GaN(0001)表面的吸附成键过程、吸附能量和吸附位置. 计算结果表明不同初始位置的TiO₂分子吸附后,Ti在fcc或hcp位置,两个O原子分别与表面两个Ga原子成键,Ga-O化学键表现出共价键特征,化学结合能达到7.932-7.943eV,O-O连线与GaN[1120]方向平行,与实验观测(100)[001] TiO₂//(0001)[1120]GaN一致. 通过动力学过程计算分析,TiO₂分子吸附过程经历了物理吸附、化学吸附与稳定态形成的过程,稳定吸附结构和优化结果一致. 关键词： GaN(0001)表面 2分子')" href="#">TiO₂分子 密度泛函理论 吸附     

NO在清洁和Cs覆盖的Ru(100)表面上吸附的热脱附谱

用热脱附谱等方法研究了NO分别在清洁和Cs覆盖的Ru(1010)表面上的吸附.结果表明:存在两种NO分子吸附态(a1,a2),脱附温度分别处于325℃和550℃附近.Cs的存在增加了Ru(1010)表面上a2态的吸附位置,提高了该态的脱附温度.Cs在Ru(1010)表面上的存在同时促进了吸附NO分子的分解.NO在Ru(1010)表面上分解后形成吸附O原子和N原子.N原子复合以N2在约500℃附近脱附,同时Cs的存在也促进了N2O的形成.在Cs覆盖的Ru(1010)表面上,N2O的脱附温度约在425℃.     

Thermal evolution of acetylene and ethylene on Pd(111)

The thermal evolution of acetylene and ethylene and their deuterated counterparts on a palladium (111) surface has been studied by high-resolution electron energy loss spectroscopy in the temperature range 150–500 K. Analysis of the vibrational spectra indicates that chemisorbed acetylene evolves at 300 K in the presence of surface hydrogen to mainly ethylidyne, CCH₃, and a small amount of residual acetylene. Spectra obtained with and without preadsorbed hydrogen provide evidence for a 〉C CH₂ intermediate in the reaction. Chemisorbed ethylene also evolves to ethylidyne after heating from 150 to 300 K but much of the ethylene desorbs. The high temperature (400–500 K) behavior of C₂H₂ and C₂H₄ involves formation of a CH species. Although a small amount of the CH species may be formed from the dehydrogenation of ethylidyne, it is found that carbon-carbon bond scission of acetylene near 400 K is the dominant mechanism in CH formation.     

BaxOy小团簇修饰Ru(0001)表面的结构稳定性和氮分子吸附性质

为了说明钡助剂的存在形式, 本文采用第一性原理方法研究了Ba_xO_y小团簇修饰Ru(0001)表面的结构稳定性和氮分子吸附性质. 基于总能的热力学分析发现, 在实验条件下(500 K, P_H2O/P_H2<10^-3), Ba₂O团簇比BaO₂, BaO, Ba和O等团簇(原子)更加稳定. 这证实含有金属性钡原子的团簇也是氧化钡助剂可能的工作状态. 表面电荷差分密度说明Ba₂O团簇的氧和钡原子与衬底的作用不同. 不过Ba₂O团簇氧和钡原子附近的氮分子吸附行为相似, Ba₂O团簇增强了氮分子和衬底的相互作用. Ba₂O团簇氧和钡原子附近的氮分子吸附能分别为0.78 和0.88 eV, 均大于清洁表面的0.67 eV. 氮分子间距和氮分子的拉伸振动频率都表明Ba₂O团簇在一定程度上活化了吸附氮分子. Ba₂O团簇氧和钡原子附近的N–N键长分别为0.117和0.116 nm, 大于清洁表面的0.114 nm. 氧和钡原子附近氮分子的拉伸振动频率分别为 1888 和1985 cm^-1, 小于清洁表面的2193 cm^-1. 电荷差分密度的计算结果说明, 削弱作用主要来自于Ba₂O团簇中钡离子和氮分子间的静电作用. 两者间的静电作用增加了氮分子π 反键轨道的占据数, 促进了氮分子极化, 从而削弱氮分子键.     

Characterization of methylidyne on Pt(1 1 1) with infrared spectroscopy

Methylidyne (CH) was prepared on Pt(1 1 1) by three methods: thermal decomposition of diiodomethane (CH₂I₂), ethylene decomposition at temperatures above 450 K, and surface carbon hydrogenation. Methylidyne and its precursors are characterized by reflection absorption infrared spectroscopy (RAIRS). The C-I bond of diiodomethane breaks upon adsorption to produce methylene (CH₂), which decomposes to methylidyne at temperatures above 130 K. Above 200 K, methylidyne is the only hydrocarbon species observed with RAIRS, although reaction channels for the formation of methane (CH₄) and ethylene (C₂H₄) are indicated by temperature programmed desorption (TPD). As is well known from numerous previous studies, ethylene decomposes to ethylidyne (CCH₃) upon exposure to Pt(1 1 1) at 410 K. Upon annealing to 450 K, ethylidyne dissociates through two reaction pathways, dehydrogenation to ethynyl (CCH) and C-C bond scission to methylidyne. Ethylene dehydrogenation on the surface at 750 K and under low ethylene exposures produces surface carbon that can be hydrogenated to methylidyne with C-H and C-D stretch frequencies of 2956 and 2206 cm⁻¹, respectively. Hydrogen co-adsorption on the surface causes these frequencies to shift to higher values. Methylidyne is stable on Pt(1 1 1) to temperatures up to 500 K.     

CH3OH在ZnO(0001)表面的光催化解离

本文利用266 nm波长的激光及程序升温脱附的方法研究了甲醇在ZnO(0001)表面的光催化反应. TPD结果显示部分的CH₃OH以分子的形式吸附在ZnO(0001)表面,而另外一部分在表面发生了解离. 实验过程中探测到H₂,CH₃^·,H₂O,CO,CH₂O,CO₂和CH₃OH这些热反应产物. 紫外激光照射实验结果表明光照可以促进CH₃OH/CH₃O^·解离形成CH₂O,在程序升温或光照的过程中它又可以转变为HCOO^-. CH₂OH_Zn与OH_ad反应在Zn位点上形成H₂O分子. 升温或光照都能促进CH₃O^·转变为CH₃^·. 该研究对CH₃OH在ZnO(0001)表面的光催化反应机理提供了一个新的见解.     

LEED,AES and thermal desorption studies of chemisorbed Hydrogen and hydrocarbons (C2H2, C2H4, C6H6, C6H12) on the (111) and stepped [6(111) × (100)] iridium crystal surfaces; comparison with platinum

The adsorption of hydrogen, ethylene, acetylene, cyclohexane and benzene was studied on both the (111) and stepped [6(111) × (100)] crystal surfaces of iridium. The techniques used were low energy electron diffraction, Auger electron spectroscopy, and thermal desorption mass spectrometry. At 30°C, acetylene, ethylene and benzene are adsorbed with a sticking probability near unity. The sticking probability of cyclohexane is less than 0.1 on both surfaces. Heating the (111) surface above 800°C, in the presence of the hydrocarbons, results in the formation of an ordered carbonaceous overlayer with a diffraction pattern corresponding to a (9 × 9) surface structure. No indication for ordering of the carbonaceous residue was found on the stepped iridium surface in these experimental conditions. The hydrocarbon molecules form only poorly ordered surface structures on both iridium surfaces when the adsorption is carried out at 30°C. Benzene is the only gas that can be desorbed from the surfaces in large amounts by heating. Ethylene remains largely on the surface, only a few percent is removed by heating while acetylene and cyclohexane cannot be desorbed at all. When adsorption is carried out at 30°C and the crystal is subsequently flashed to high temperature, hydrogen is liberated from the surface. The hydrogen desorption spectra from the iridium surfaces exposed to C₂H₄, C₂H₂, or C₆H₆ exhibit two hydrogen desorption peaks, one around 200°C and the second around 350°C. The temperatures where these peaks appear vary slightly with the type of hydrocarbon. The relative intensities of these two peaks depend strongly on the surface used. Arguments are presented that decomposition of the hydrocarbon molecules (C-H bond breaking nd possibly also C-C bond breaking) occurs easier on the stepped iridium surface than on the (111) surface. Hydrogen is desorbed at a higher temperature from an iridium surface possessing a high density of surface imperfections than from a perfect iridium (111) surface. The results are compared with those obtained previously on similar crystal surfaces of platinum. It appears that C-H bond breaking occurs more easily on iridium than on platinum.     

Temperature programmed desorption study of acetylene on a clean,H-covered,and O-covered Pt(111) surface

The reactions of acetylene on a clean, a H-covered and an O-covered Pt(111) surface were studied by temperature programmed desorption for various coverages of acetylene, and acetylene to H or O ratios. The desorption products were quantitatively determined. On a clean surface, acetylene decomposes to hydrogen and surface carbon. A small amount of self-hydrogenation to ethylene also occurs during decomposition. On a H-covered surface, hydrogenation to CH₄, C₂H₆, and ethylene, and decomposition to hydrogen and surface carbon occur simultaneously. The reactions on these two surfaces can be explained by the presence of two sites. One site is a bare surface Pt atom on which decomposition is the primary reaction pathway. The other site is a Pt atom with adsorbed H on which hydrogenation is the primary reaction pathway. On the O-covered surface, the decomposition reaction takes place together with an oxidation reaction which yields CO, CO₂, and water. The oxidation reaction probably proceeds via an intermediate that has a stoichiometry of CH. Results on the O-covered surface are consistent with the model that oxygen absorbs in islands, and the oxidation reaction takes place at the perimeter of the islands. These results are compared with those of ethylene reaction on the same Pt surfaces.     

Adsorption of ethylene on the Pt(100) surface

Clean Pt(100) surfaces with bulk-like 1×1 structure, or the stable, reconstructed 5×20 structure and held at 200 or 330 K were exposed to ethylene. Ultraviolet photoemission spectroscopy identified the nature of the adsorbed species which depends on the structure and temperature of the clean surface and the amount adsorbed. It is ethylene on the 5 × 20 structure at 200 K, a vinyl radical on the same surface at 300 K up to half a monolayer, the remainder being added as acetylene; it is acetylene on the 1 × 1 surface at 330 K and a mixture of acetylene, vinyl and ethylene on the 1 × 1 surface at 200 K. Whatever the nature of the adsorbate, the surface coverage θ increased with exposure ? as $\text{(1 ? θ = C?}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>3</mtext>}}\text{)}$. By contrast, on a surface covered with any C₂ hydrocarbon acetylene adsorbs with Langmuir kinetics. The kinetics are explained in terms of the relationship between the attraction an approaching molecule experiences from the bare surface and its Van der Waals repulsion from preadsorbed molecules.     

Low temperature formation of benzene from acetylene on a Pd(111) surface

Experiments with UPS, metastable noble gas deexcitation spectroscopy (MDS) and thermal desorption demonstrated that C₂H₂ adsorbed on Pd(111) at 140 K undergoes cyclotrimerisation to C₆H₆ after higher (? 100 L) exposures. If the surface is intermediately warmed up to 300 K, the low temperature state of adsorbed acetylene transforms irreversibly into another species which is unreactive. The surface species formed by reaction was identified by comparison with the electron spectroscopic data of C₆H₆ adsorbed from the gas phase as well as with those of free C₆H₆. The molecules are only weaky held on the surface and start to desorb already at about 150 K.