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1.
采用密度泛函理论和slab模型,研究NH3在Ni单原子层覆盖的Pt(111)和WC(001)表面上的物理与化学行为,计算了Ni单原子覆盖表面的电子结构以及NH3的吸附与分解.表面覆盖的单原子层中,Ni原子的性质与Ni(111)面上的Ni原子明显不同.与Ni(111)相比,Ni/Pt(111)和Ni/WC(001)表面上Ni原子dz2轨道上的电子更多地转移到了其它位置,该轨道上电荷密度降低有利于NH3吸附.在Ni/Pt(111)和Ni/WC(001)面上NH3吸附能均大于Ni(111),NH3分子第一个N-H键断裂的活化能则明显比Ni(111)面上低,有利于NH3的分解,吸附能增大使NH3在Ni/Pt(111)和Ni/WC(001)面上更倾向于分解,而不是脱附.N2分子的生成是NH3分解的速控步骤,该反应能垒较高,说明N2分子只有在较高温度下才能生成.WC与Pt性质相似,但Ni/Pt(111)和Ni/WC(001)的电子结构还是有差异的,与Ni(111)表面相比,NH3在Ni/Pt(111)表面上分解速控步骤的能垒降低,而在Ni/WC(001)上却升高.要获得活性好且便宜的催化剂,需要对Ni/WC(001)表面做进一步改进,降低N2分子生成步骤的活化能.  相似文献   

2.
电催化CO2还原反应可以产生HCOOH和CO,目前该反应是将可再生电力转化为化学能存储在燃料中的最有前景的方法之一. SnO2作为将CO2转换为HCOOH和CO的良好催化剂,其反应发生的晶面可以是不同的. 其中(110)面的SnO2非常稳定,易于合成. 通过改变SnO2(110)的Sn:O原子比例,得到了两种典型的SnO2薄膜:完全氧化型(符合化学计量)和部分还原型. 本文研究了不同金属(Fe、Co、Ni、Cu、Ru、Rh、Pd、Ag、Os、Ir、Pt和Au)掺杂的SnO2(110),发现在CO2还原反应中这些材料的催化活性和选择性是不同的. 所有这些变化都可以通过调控(110)表面中Sn:O原子的比例来控制. 结果表明,化学计量型和部分还原型Cu/Ag掺杂的SnO2(110)对CO2还原反应具有不同的选择性. 具体而言,化学计量型的Cu/Ag掺杂的SnO2(110)倾向于产生CO(g),而部分还原型的表面倾向于产生HCOOH(g). 此外,本文还考虑了CO2还原的竞争析氢反应. 其中Ru、Rh、Pd、Os、Ir和Pt掺杂的SnO2(110)催化剂对析氢反应具有较高的活性,其他催化剂对CO2还原反应具有良好的催化作用.  相似文献   

3.
利用XPS和RPES技术研究了CeO2-x(111)薄膜表面上的氧空位对Ag纳米颗粒的生长和电子结构的影响. XPS结果表明,室温下,Ag纳米颗粒在部分还原的CeO2-x(111)薄膜上呈三维岛状生长, 并且岛密度比完全氧化的CeO2(111)薄膜表面上的大, 说明氧空位可以作为Ag纳米粒子生长的中心. Ag3d5/2芯能级的结合能随着Ag颗粒尺寸的减小而增大, 主要来源于终态效应的贡献. Ag和CeO2-x  相似文献   

4.
采用基于第一性原理的密度泛函理论结合周期模型方法对甲醇在Pt(100)完整表面的吸附与解离进行了研究. 通过比较不同吸附位置的吸附能与构型参数发现,表面top吸附位为最稳定吸附位,甲醇分子通过氧原子吸附于Pt(100)表面. 同时计算了甲醇分子在top吸附位可能的解离路径,发现在解离过程中OH键首先断裂的路径为最低能量路径. 分解生成的若干产物其吸附稳定性排序为CH3O>CH2OH>CH3>CH2O.  相似文献   

5.
Pt单原子在低温CO氧化反应中具有很高的催化活性. 利用扫描隧道显微术与密度泛函理论,研究了Pt单原子在还原性TiO2(110)表面的吸附行为及其与CO和O2分子的相互作用. 研究发现在80 K低温下,TiO2表面的氧空位缺陷是Pt单原子的最优吸附位. 将CO和O2分子分别通入Pt单原子吸附后的TiO2表面,研究相应的吸附构型. 实验表明在低覆盖度下,单个Pt原子会俘获一个CO分子,CO分子同时与表面次近邻的五配位Ti原子(Ti5c)成键,进而形成非对称的Pt-CO 复合物构型. 将样品从80 K升温到100 K后,TiO2表面的CO分子会迁移到Pt-CO处形成Pt-(CO)2的复合结构. 对于O2分子,单个Pt原子同样会吸附一个O2分子,O2分子也会与最近邻或次近邻的Ti5c原子成键形成两种Pt-O2构型. 这些结果在单分子尺度上揭示了CO和O2与Pt单原子的相互作用,呈现了CO与O2反应中的初始状态.  相似文献   

6.
吴鸣成 《物理学报》1988,37(11):1785-1793
本文用X射线光电子能谱(XPS),紫外光电子能谱(UPS),电子能量损失谱(EELS)和低能电子衍射(LEED)研究了O与预覆盖K的Ag(110)表面相互作用及其性质。在低覆盖度K下,发现有两种O的吸附态,经鉴别为溶解到表面下的O2-和表面上吸附的Ox-增加K的覆盖度,出现分子状态的吸附物O2δ-,它与表面下存在的K相联系。XPS和UPS均清楚地显示出对应于三种不同吸附态的光电子发射峰。Ag(110)表面预覆盖K后的粘滞系数大大增加。K和O的共吸附引起它们彼此向Ag(110)表面下的溶解。LEED实验结果表明,清洁Ag(110)表面覆盖单层K原子后衍射图形从(1×1)变到(1×2),再吸附O后表面吸附层结构变为(2×1)。另外,结合UPS和EELS测量初步考察了O/K/Ag(110)共吸附系统的电子结构。本文还提出了一个共吸附模型来解释这些现象。 关键词:  相似文献   

7.
对氧化钇(Y2O3)部分稳定氧化锆(ZrO2)样品在室温下进行了Ni离子注入(140kev,5×1015-2×1017ios/cm2)和热退火处理.应用电学测量,Rutherford背散射技术(RBS),X射线光电子能谱(XPS)和喇曼光谱方法研究了Ni离子注入多晶ZrO2的表面电性能,注入层结构及其热退火的影响。  相似文献   

8.
并五苯分子在Ag(110)表面成膜过程中的结构研究   总被引:4,自引:1,他引:3       下载免费PDF全文
采用低能电子衍射原位研究了并五苯分子(C22H14)在Ag(110)单晶表面的生长,观察了在初期沉积过程及随后基底变温过程中分子层结构的形成和变化.室温下并五苯分子在Ag(110)基底表面具有高的迁移性,从开始无序的亚单层膜结构逐渐形成有序的单层膜结构.实验和理论分析表明:并五苯分子平铺在Ag(110)表面,形成了与基底构成有关的有序结构,存在沿基底晶向成镜面对称的两种畴界取向,在基底温度从室温升高到接近并五苯升华温度的过程中,基底上的有序分子层结构保持稳定不变 关键词: 并五苯 低能电子衍射图案 分子层结构 Ag(110)  相似文献   

9.
本文利用程序升温脱附技术研究了氧空位浓度对甲基基团和CO在R-TiO2(110)表面吸附的影响. 结果表明,随着氧空位浓度的变化,吸附在桥氧位的甲基基团和吸附在五配位Ti4+位点上的CO分子的脱附温度呈现了不同的趋势,揭示了表面缺陷可能对R-TiO2(110)不同位点上的物质吸附具有重要影响.  相似文献   

10.
本文采用第一性原理密度泛函理论计算研究了MgH2(110)表面吸附单原子Pd后的氢脱附反应. 计算发现,在吸附一个Pd单原子后,MgH2(110)表面氢脱附反应的能垒可以从1.802 eV显著地降低到1.154 eV,表明Pd单原子对于氢脱附具有很强的催化效应. 并且,Pd单原子催化还可以将氢脱附的温度从573 K显著地降低到了367 K,从而使MgH2(110)表面的氢脱附反应更加容易和快速地发生. 此外,通过MgH2(110)表面氢溢出机制的反向过程来讨论了氢脱附反应的微观过程. 该研究表明Pd/MgH2薄膜在未来的实验中可作为良好的储氢材料.  相似文献   

11.
The interaction of methanol with clean and oxygen-covered Pt(111) surfaces has been examined with high resolution electron loss spectroscopy (EELS) and thermal desorption spectroscopy (TDS). On the clean Pt(111) surface, methanol dehydrogenated above 140 K to form adsorbed carbon monoxide and hydrogen. On a Pt(111)-p(2 × 2)O surface, methanol formed a methoxy species (CH3O) and adsorbed water. The methoxy species was unstable above 170 K and decomposed to form adsorbed CO and hydrogen. Above room temperature, hydrogen and carbon monoxide desorbed near 360 and 470 K, respectively. The instability of methanol and methoxy groups on the Pt surface is in agreement with the dehydrogenation reaction observed on W, Ru, Pd and Ni surfaces at low pressures. This is in contrast with the higher stability of methoxy groups on silver and copper surfaces, where decomposition to formaldehyde and hydrogen occurs. The hypothesis is proposed that metals with low heats of adsorption of CO and H2 (Ag, Cu) may selectively form formaldehyde via the methoxy intermediate, whereas other metals with high CO and H2 chemisorption heats rapidly dehydrogenate methoxy species below room temperature.  相似文献   

12.
The present paper is aimed mainly to investigate theoretically the diffusion of Ag, Cu, Au and Pt adatoms on the (1 × 1) unreconstructed geometry for Ag, Cu and Pt (110), and reconstructed geometries ((1 × 2), (1 × 3) and (1 × 4)) for Pt and Au (110) surfaces. We consider the single adatom diffusion when additional atoms are deposited in adjacent row. For this study, we have used the molecular statics simulations combined with the embedded atom method. For several systems, we have calculated the activation barriers for hopping mechanism. For the diffusion on the unreconstructed surfaces, the trends for the activation barriers are the same for all considered systems except for Cu/Ag (110) system, where the activation barrier do not change. Further, our results indicate that additional atoms lead to a small decreasing of activation barriers for diffusion on reconstructed surfaces for some systems, while for other systems; the activation barrier remains practically unchanged.  相似文献   

13.
The decomposition pathways of methanol and water on Pt-modified W(110) bimetallic surfaces have been investigated using density functional theory (DFT), temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS). The reaction of methanol on submonolayer and monolayer Pt-modified W(110) surfaces is compared to that on clean Pt(111) and W(110). Similar to clean W(110), the Pt/W(110) bimetallic surfaces remain active toward the dissociation of methanol, although the reaction pathway leading to the production of CH4 is reduced on the bimetallic surfaces. The Pt/W(110) surfaces are also active toward the decomposition of water. These results are compared with previous studies of the reactions of H2 and ethylene on Pt/W(110) bimetallic surfaces to reveal the different Pt-modification effects for the dissociation of oxygen-containing molecules.  相似文献   

14.
The chemisorption of NO on clean and Na-dosed Ag(110) has been studied by LEED, Auger spectroscopy, and thermal desorption. On the clean surface, non-dissociative adsorption into the α-state occurs at 300 K with an initial sticking probability of ~0.1, and the surface is saturated at a coverage of about 125. Desorption occurs without decomposition, and is characterised by an enthalpy of Ed ~104 kJ mol?1 — comparable with that for NO desorption from transition metals. Surface defects do not seem to play a significant role in the chemistry of NO on clean Ag, and the presence of surface Na inhibits the adsorption of αNO. However, in the presence of both surface and subsurface Na, both the strength and the extent of NO adsorption are markedly increased and a new state (β1NO) with Ed ~121 kJ mol?1 appears. Adsorption into this state occurs with destruction of the Ag(110)-(1 × 2)Na ordered phase. Desorption of β1NO occurs with significant decomposition, N2 and N2O are observed as geseous products, and the system's behaviour towards NO resembles that of a transition metal. Incorporation of subsurface oxygen in addition to subsurface Na increases the desorption enthalpy (β2NO), maximum coverage, and surface reactivity of NO still further: only about half the adsorbed layer desorbs without decomposition. The bonding of NO to Ag is discussed, and comparisons are made with the properties of α and βNO on Pt(110).  相似文献   

15.
Angular dependent electron spin resonance measurements were taken for paramagnetic molecules adsorbed on metallic single crystal surfaces in UHV. For the hydrated Cu(NO3)2 complex on a Cu[111] surface an angular dependent ESR signal is recorded. The plane ofthe molecule is found to lie preferentially out of the surface plane. Experiments on chemisorbed molecular O2 on Ag[110] at 25 K and NO on Pt[111] at 110 K show no sharp ESR signal characteristic for well localized moments. If one assumes that NO on Pt (respectively Pd) carries an unpaired spin, one can estimate a lower limit for the spin flip rate of π?1>2×109s?.  相似文献   

16.
H.P. Bonzel 《Surface science》1982,121(1):L531-L534
It is known that the Pt(110) surface exhibits in its stable state a 1 × 2 reconstruction. It seems therefore not appropriate to compare theoretical surface diffusion coefficients calculated for the regular, non-reconstructed Pt(110) surface with the experimental data obtained by field ion microscopy. In particular, the process of cross-channel diffusion by atom exchange which is observed on the regular (110) surface by molecular dynamics simulations may have no relationship to the experimental findings of cross-channel adatom diffusion on reconstructed Pt(110) and Ir(110) surfaces. An alternate mechanism for easy cross-channel adatom diffusion on reconstructed (110)?1 × 2 surfaces of Pt and Ir is proposed.  相似文献   

17.
利用同步辐射高分辨光电子能谱研究了金团簇在部分还原TiO2-(1×1)表面的生长和稳定性.价带谱实验结果观察到非常少量金团簇的沉积导致了Ti3+的3d峰完全消失,表明金团簇成核在TiO2-(1×1)表面的氧缺陷位.Au4f芯电子光电子能谱实验结果证明了TiO2-(1×1)表面氧缺陷位向金团簇转移电荷.还对比研究了化学剂量比和部分还原的TiO2-(1×1)表面上金团簇的热稳定性.当金团簇尺寸相近时部分还原的TiO2-(1×1)表面上金团簇要比化学剂量比的TiO2-(1×1)面上金团簇稳定;在相同的表面上尺寸大的金团簇要比尺寸小的金团簇稳定.  相似文献   

18.
Reported are studies by LEED and Auger spectroscopy of silver layers electrodeposited on well-characterized Pt(111) surfaces from aqueous solution. Prior to electrodeposition. the Pt(111) surface was treated with I2 vapor to form the Pt(111) (7 × 7)R19.1°-I superlattice which protected the Pt and Ag surfaces from attack by the electrolyte and residual gases. Electrodeposition of silver occurred in four distinct ranges of electrode potential. Ordered layers having (3 × 3) and (18 × 18) (coincidence lattice) LEED patterns were formed at all coverages from the onset of deposition to the highest coverages studied, about twenty equivalent atomic layers. Formation of ordered Ag layers has therefore been demonstrated, at least for deposits of limited thickness. Auger spectra revealed that for deposits of a few atomic layers. The iodine layer remained attached to the surface during multiple cycles of electrodeposition and dissolution of silver from iodine-free solution. Each peak of the voltammetric current-potential scan produced a change in the LEED pattern.  相似文献   

19.
The adsorption and reaction of the isomers nitromethane (CH3NO2) and methyl nitrite (CH3ONO) on two ordered Sn/Pt(111) surface alloys were studied using TPD, AES, and LEED. Even though the Sn–O bond is stronger than the Pt–O bond and Sn is more easily oxidized than Pt, alloying with Sn reduces the reactivity of the Pt(111) surface for both of these oxygen-containing molecules. This is because of kinetic limitations due to a weaker chemisorption bond and an increased activation energy for dissociation for these molecules on the alloys compared to Pt(111). Nitromethane only weakly adsorbs on the Sn/Pt(111) surface alloys, shows no thermal reaction during TPD, and undergoes completely reversible adsorption under UHV conditions. Methyl nitrite is a much more reactive molecule due to the weak CH3O–NO bond, and most of the chemisorbed methyl nitrite decomposes below 240 K on the alloy surfaces to produce NO and a methoxy species. Surface methoxy is a stable intermediate until 300 K on the alloys, and then it dehydrogenates to evolve gas phase formaldehyde with high selectivity against complete dehydrogenation to form CO on both alloy surfaces.  相似文献   

20.
The surface chemistry of NO and NO2 on clean and oxygen-precovered Pt(1 1 0)-(1 × 2) surfaces were investigated by means of high resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS) and thermal desorption spectroscopy (TDS). At room temperature, NO molecularly adsorbs on Pt(1 1 0), forming linear NO(a) and bridged NO(a). Coverage-dependent repulsive interactions within NO(a) drive the reversible transformation between linear and bridged NO(a). Some NO(a) decomposes upon heating, producing both N2 and N2O. For NO adsorption on the oxygen-precovered surface, repulsive interactions exist between precovered oxygen adatoms and NO(a), resulting in more NO(a) desorbing from the surface in the form of linear NO(a). Bridged NO(a) experiences stronger repulsive interactions with precovered oxygen than linear NO(a). The desorption activation energy of bridged NO(a) from oxygen-precovered Pt(1 1 0) is lower than that from clean Pt(1 1 0), but the desorption activation energy of linear NO(a) is not affected by the precovered oxygen. NO2 decomposes on Pt(1 1 0)-(1 × 2) surface at room temperature. The resulted NO(a) (both linear NO(a) and bridged NO(a)) and O(a) repulsively interact each other. Comparing with NO/Pt(1 1 0), more NO(a) desorbs from NO2/Pt(1 1 0) as linear NO(a), and both linear NO(a) and bridged NO(a) exhibit lower desorption activation energies. The reaction pathways of NO(a) on Pt(1 1 0), desorption or decomposition, are affected by their repulsive interactions with coexisting oxygen adatoms.  相似文献   

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