Pt/Cu(001)-p(2×2)-O表面吸附结构的总能计算

采用密度泛函理论(DFT)研究了氧吸附后Pt/Cu(001)表面合金的原子结构和表面性质. 计算结果表明, 在Pt/Cu(001)-p(2×2)-O表面最稳定结构中, 衬底表面原子层不发生再构, 氧原子吸附于4重对称的Pt原子谷位, 每个氧原子吸附能约为2.303 eV. 吸附结构的Cu—O和Pt—O键键长分别为0.202和0.298 nm, 氧原子的吸附高度ZCu—O约为0.092 nm. 吸附前后Pt/Cu(001)-1ML(monolayer)表面合金的表面功函数分别为4.678和5.355 eV. 吸附表面氧原子和衬底的结合主要来自氧原子2p轨道和衬底金属原子d轨道的杂化作用, 氧原子吸附形成的表面电子态主要位于费米能级以下约-2.7 eV 处.     

Pt/Cu（001）-p（2×2）-O表面吸附结构的总能计算

采用密度泛函理论（DFT）研究了氧吸附后Pt/Cu（001）表面合金的原子结构和表面性质.计算结果表明,在Pt/Cu（001）-p（2×2）-O表面最稳定结构中,衬底表面原子层不发生再构,氧原子吸附于4重对称的Pt原子谷位,每个氧原子吸附能约为2.303 eV.吸附结构的Cu—O和Pt—O键键长分别为0.202和0.298 nm,氧原子的吸附高度ZCu—O约为0.092 nm.吸附前后Pt/Cu（001）-1ML（monolayer）表面合金的表面功函数分别为4.678和5.355 eV.吸附表面氧原子和衬底的结合主要来自氧原子2p轨道和衬底金属原子d轨道的杂化作用,氧原子吸附形成的表面电子态主要位于费米能级以下约-2.7 eV处.     

吸附O的Cu(110)c(2×1)表面原子结构和电子态

采用第一性原理的密度泛函理论方法计算了清洁Cu(110)表面和吸附O原子的Cu(110) c(2×1)表面的原子结构, 结构弛豫和电子结构, 得到了各种表面结构参数. 分别计算了O原子在Cu(110)表面三个可能吸附位置吸附后的能量, 并给出了能量最低的吸附位置上各层原子的弛豫特性和态密度. 结果表明O吸附后的Cu(110)表面有附加列(added-row)再构的特性, O原子吸附在最表层铜原子上方, 与衬底Cu原子的垂直距离为0.016 nm, 以氧分子为能量基准的吸附能为－1.94 eV; 同时由于Cu 3d- O 2p态的杂化作用使得低于费米能级5.5~6.0 eV的范围内出现了局域的表面态. 计算得到清洁的和氧吸附的Cu(110)表面的功函数分别为4.51 eV和4.68 eV. 电子态密度的结果表明：在Cu(110) c(2×1) 表面O吸附的结构下, 吸附O原子和金属衬底之间的结合主要是由于最表层Cu原子3d态和O原子2p态的相互作用.     

N_2O在Cu/t-ZrO_2(101)表面的吸附与解离

运用广义梯度密度泛函理论结合周期性平板模型方法研究了N2O在完整及负载Cu的四方相ZrO2(101)表面的吸附与解离.结果表明,N2O在完整ZrO2(101)表面的吸附均为物理吸附,Cu在其完整表面的次表层第一氧位为最稳定吸附位,且覆盖度为0.25ML时的吸附最为稳定,吸附能为155.8kJ/mol;N2O分子中O端弱物理吸附于Cu/ZrO2(101)表面,其N端及平行吸附方式得到的稳定吸附能分别为121.6和66.8kJ/mol.频率及电荷布居计算表明,吸附后对称和反对称伸缩振动频率均发生红移,电子由Cu负载底物表面转移给N2O分子.对N2O分子的解离考虑了N端垂直吸附和平行吸附两种解离反应过程,发现平行吸附过程的解离更易发生.     

CO在CeO2(111)表面的吸附与氧化

采用密度泛函理论计算了CO在CeO2(111)表面的吸附与氧化反应行为. 结果表明, O2在洁净的CeO2(111)表面为弱物理吸附, 而在氧空位表面是强化学吸附, 且O2分子活化程度较大, O—O键长为0.143 nm. CO在CeO2(111)表面吸附行为的研究表明, CO在洁净表面及氧空位表面上为物理吸附, 吸附能均小于0.42 eV; 当表面氧空位吸附O2后, CO可吸附生成二齿碳酸盐中间体或直接生成CO2, 与原位红外光谱结果相一致. 表面碳酸盐物种脱附生成CO2的能垒仅为0.28 eV. 计算结果表明, 当CeO2表面存在氧空位时, Hubbard参数U对CO吸附能有一定的影响. CeO2载体在氧化反应中可能的催化作用为, 在氧气氛下, CeO2表面氧空位吸附O2分子, 形成活性氧物种, 参与CO催化氧化反应.     

Al修饰C_2N对甲醛降解的吸附增强机理及潜在催化活性的密度泛函理论研究（英文）

羰基化合物,特别是甲醛,是室内最常见的对人体有害的空气污染物之一.如何对甲醛进行有效的控制已成为当前研究热点.在本工作中,我们使用密度泛函理论化学计算方法研究了甲醛分子在C_2N和Al修饰C_2N上的吸附性能.结果表明,纯C_2N对甲醛分子的吸附能力较弱,吸附能仅为–0.583 eV,C_2N经Al原子修饰改性后,吸附能为–2.585 eV,超过了改性前的4倍,有效增强了体系对甲醛分子的吸附能力.为了研究甲醛分子在Al修饰C_2N上的吸附增强机理,我们对局部态密度(PDOS)、Mulliken电荷分布及电子密度分布进行了计算.结果表明,Al原子修饰改变了附近的电子分布,从而改变了修饰Al原子的化学和物理行为,使其起到了连接甲醛分子和C_2N层的桥梁作用,从而加强了吸附能力.此外,为了研究产生对甲醛活化有效的羟基自由基(·OH)和超氧(O_2~(·–))自由基的可能,我们还计算了C_2N结构对H_2O分子和O_2分子的吸附.结果表明,Al修饰的C_2N对H_2O分子和O_2分子同样有很强的吸附能力.对于H_2O分子,在纯C_2N结构中的吸附能为–0.743 eV,在Al原子修饰后的结构中,其吸附能高达–3.177 eV,并且此时H_2O分子能够自发解离成一个羟基和一个H原子,其中羟基与修饰的Al原子相连,这为羟基自由基的生成提供了良好的条件.而对于O_2分子,在纯C_2N结构中的吸附能仅为–0.206 eV,在Al原子修饰后其吸附能高达–2.767 eV,约为修饰前的13倍,这使得化学吸附的O_2分子也具有更高的获得额外电子和高电位被激活为超氧自由基的潜能,这也为超氧自由基的生成提供了良好基础.上述研究表明,Al修饰C_2N是一种有前途的材料,可用于甲醛分子的吸附及催化降解.     

氧化铜表面臭氧分解路径及表面氧物种生成机理研究

基于密度泛函理论（DFT）计算研究了O3在完整和具有氧空位的CuO(111)表面吸附的吸附位、吸附结构、吸附能和电子转移情况,比较了O3在完整表面和具有氧空位的表面分解的路径和能垒,分析了氧空位和表面吸附氧的生成机理。结果表明,在完整CuO表面,O3分子通过化学吸附或物理吸附表面结合,吸附能最高为-1.22eV（构型bri(2)）。O3在具有氧空位的CuO表面均为化学吸附,吸附能最高为-2.95eV（构型ovbri(3)）,显著高于完整表面的吸附能。O3吸附后,Cu吸附位的电荷密度减小,O3中的O原子附近的电荷密度显著增强,电荷从CuO表面转移到O3,并形成Cu-O离子键。O3分解后形成了超氧物种,提高了表面的氧化活性。在完整表面,以构型bri(2)为起始构型的路径反应能垒最低,为0.52eV;O2*在完整表面的脱附所需要的最低能量为0.42eV,形成氧空位的O2*脱附能为2.06eV。在具有氧空位的表面,O3分解的反应能垒为0.30eV（构型ovbri(1)）和0.12eV（构型ovbri(3)）,均低于完整表面的反应能垒;分解形成的O2*的最低脱附能也低于完整表面,为0.27eV。可见,氧空位的形成提高了吸附能,降低了反应能垒,使O3分子更容易吸附在CuO表面,并加快了O3的催化分解。     

甲醛在CeO2(111)表面吸附的密度泛函理论研究

采用基于第一性原理的密度泛函理论和周期平板模型, 研究了甲醛在以桥氧为端面的CeO2(111)稳定表面上的吸附行为. 通过对不同覆盖度, 不同吸附位的甲醛吸附构型、吸附能及电子态密度的分析发现, 甲醛在CeO2(111)表面存在化学吸附与物理吸附两种情况. 化学吸附结构中甲醛的碳、氧原子分别与表面的氧、铈原子发生相互作用, 形成CH2O2物种; 吸附能随着覆盖度的增加而减小. 与自由甲醛分子相比, 物理吸附的甲醛构型变化不大, 其吸附能较小. 利用CNEB(climbing nudged elastic band)方法计算了甲醛在CeO2(111)表面的初步解离反应活化能(约1.71 eV), 远高于甲醛脱附能垒, 这与甲醛在清洁CeO2(111)表面程序升温脱附实验中产物主要为甲醛的结果相一致.     

NH3在V2O5/AC催化剂表面的吸附与氧化

 将V2O5担载在活性焦(AC)上制得V2O5/AC催化剂,通过吸附脱附实验、程序升温脱附实验与原位质谱结合,对200 ℃下NH3在V2O5/AC催化剂表面的吸附和氧化行为进行了研究. 结果表明, AC具有吸附NH3和将NH3转化为NO的能力,这种能力可能源于两种活性位; 担载V2O5后,催化剂对NH3的吸附能力显著增强,并产生了新的NH3氧化产物N2, 但NH3氧化为NO的能力减弱; SO2在催化剂表面的吸附进一步增大了V2O5/AC对NH3的吸附量,这可能是因为硫铵盐的生成消除了催化剂将NH3氧化转化为NO和N2的能力. 当催化剂表面吸附的NH3接近饱和,即表面接近酸碱平衡后NH3才能被氧化为N2. NH3的几个氧化反应都主要依赖气相的O2, 催化剂自身的化合氧作用很小.     

V2O5/ACF催化剂低温下选择性催化还原NO的机理

将V2O5担载在活性炭纤维(ACF)上制得V2O5/ACF催化剂,并采用暂态响应实验和NH3吸附氧化实验等考察了影响V2O5/ACF催化剂上选择性催化还原(SCR)反应的关键因素.结果表明,NH3在催化剂表面的吸附是必要的,而且该吸附是一个快速过程;气相O2的存在有利于形成催化剂中所需的活性氧化态物种.NH3吸附.脱附与原位质谱相结合的实验表明,V2O5/ACF催化剂具有吸附NH3和将NH3氧化为N2H2的能力,N2H2为NH3氧化的一种中间体.     

Dissociative double photoionization of N2 using synchrotron radiation: appearance energy of the N2+ dication

Photoionization cross sections for the production of the doubly charged ion N2+ from N2 have been measured by means of synchrotron radiation in the photon energy range from 50 to 110 eV. The appearance energy for N2+ has been determined as 55.2+/-0.2 eV, i.e., about 1.3 eV higher than the spectroscopic dissociation limit leading to the charge asymmetric dissociation channel N2+(2P)+N(4S) at 53.9 eV. The onset of a second threshold at 59.9+/-0.2 eV is detected and the energy dependence of photoion intensities near the threshold regions is interpreted in terms of the Wannier theory. The production of the N2+ dication is discussed in terms of direct and indirect mechanisms for dissociative charge asymmetric photoionization and by comparison with the potential energy curves of the intermediate N(2)2+ dication. Experimental evidences for the opening of the Coulomb explosion channel N2++N+ at high photon energies are provided by measuring the kinetic energy release spectra of N2+ fragments at selected photon energies.     

Anisotropy of the angular distribution of fragment ions in dissociative double photoionization of N2O molecules in the 30-50 eV energy range

The double photoionization of N2O molecules by linearly polarized light in the 30-50 eV energy range has been studied by coupling ion imaging technique and electron-ion-ion coincidence. For the two possible dissociative processes, leading to N++NO+ and O++N2+, angular distributions of ionic fragments have been measured, finding an evident anisotropy. This indicates that the molecules ionize when their axis is parallel to the light polarization vector and the fragments are separating in a time shorter than the dication rotational period. The analysis of results provides, in addition to the total kinetic energy of ionic fragments, crucial information about the double photoionization dynamics.     

Electron scattering on OH-(H2O)n clusters (n = 0-4)

The cross sections for electron scattering on OH-(H2O)n for n = 0-4 were measured from threshold to approximately 50 eV. All detachment cross sections were found to follow the classical prediction given earlier [Phys. Rev. Lett. 74, 892 (1995)] with a threshold energy for electron-impact detachment that increased upon sequential hydration, yielding values in the range from 4.5 eV +/- 0.2 eV for OH- to 12.10 eV +/- 0.5 eV for OH-(H2O)4. For n > or = 1, we found that approximately 80% of the total reaction events lead to electron detachment plus total dissociation of the clusters into the constituent molecules of OH and H2O. Finally, we observed resonances in the cross sections for OH-(H2O)3 and for OH-(H2O)4. The resonances were located at approximately 15 eV and were ascribed to the formation of dianions in excited states.     

Energetics of the manganese oxide cluster cations Mn(N)O+ (N = 2-5): role of oxygen in the binding of manganese atoms

The photodissociation of manganese oxide cluster cations Mn(N)O+ (N = 2-5), into Mn(N-1)O+ (one-atom loss) and Mn(N-2)O+ (two-atom), was investigated in the photon-energy range of 1.08-2.76 eV. The bond-dissociation energies D0(Mn(N-1)O+...Mn) for N = 3, 4, and 5 were determined to be 1.84+/-0.03, 0.99+/-0.05, and 1.25+/-0.14 eV, respectively, from the threshold energies for the one- and two-atom losses. As Mn2O+ did not dissociate even at the highest photon energy used, the bond dissociation energy of Mn2O+, D0(Mn+...MnO), was obtained from a density-functional-theory calculation to be 3.04 eV. The present findings imply that the core ion Mn2O+ is bound weakly with the rest of the manganese atoms in Mn(N)O+.     

High resolution electron attachment to CO₂ clusters

Electron attachment to CO? clusters performed at high energy resolution (0.1 eV) is studied for the first time in the extended electron energy range from threshold (0 eV) to about 10 eV. Dissociative electron attachment (DEA) to single molecules yields O(-) as the only fragment ion arising from the well known (2)Π(u) shape resonance (ion yield centered at 4.4 eV) and a core excited resonance (at 8.2 eV). On proceeding to CO? clusters, non-dissociated complexes of the form (CO?)(n)(-) including the monomer CO?(-) are generated as well as solvated fragment ions of the form (CO?)(n)O(-). The non-decomposed complexes appear already within a resonant feature near threshold (0 eV) and also within a broad contribution between 1 and 4 eV which is composed of two resonances observed for example for (CO?)(4)(-) at 2.2 eV and 3.1 eV (peak maxima). While the complexes observed around 3.1 eV are generated via the (2)Π(u) resonance as precursor with subsequent intracluster relaxation, the contribution around 2.2 eV can be associated with a resonant scattering feature, recently discovered in single CO? in the selective excitation of the higher energy member of the well known Fermi dyad [M. Allan, Phys. Rev. Lett., 2001, 87, 0332012]. Formation of (CO?)(n)(-) in the threshold region involves vibrational Feshbach resonances (VFRs) as previously discovered via an ultrahigh resolution (1 meV) laser photoelectron attachment method [E. Leber, S. Barsotti, I. I. Fabrikant, J. M. Weber, M.-W. Ruf and H. Hotop, Eur. Phys. J. D, 2000, 12, 125]. The complexes (CO?)(n)O(-) clearly arise from DEA at an individual molecule within the cluster involving both the (2)Π(u) and the core excited resonance.     

Tungsten and nitrogen co‐doped TiO2 nanobelts with significant visible light photoactivity

Tungsten and nitrogen co‐doped TiO₂ nanobelts (W/N‐TNBs) have been successfully synthesized via 1‐step hydrothermal method. The structure, morphology, and composition of prepared samples were characterized by X‐ray diffraction, scanning electron microscopy, and X‐ray photoelectron spectroscopy, respectively. The prominent phase of all as‐prepared samples is anatase crystal. For samples with N doping, new energy states can be introduced on top of O 2p states which reduced the band gap by 1.1 eV. The reduced band gap leads to efficient visible light activity. The 3%‐W/N‐TNBs were found to exhibit the highest activity. The photocatalytic performance of 3%‐W/N‐TNBs under visible light is about 4.8 times than that of pure TiO₂ nanobelts, which emphasizes the synergistic effect of W and N co‐doping for effectively inhibiting the recombination of photogenerated electrons and holes. In addition, our results testify the different redox potentials of the photoelectrons at different final states.     

Selected ion flow tube study of the reactions between gas phase cations and CHCl2F, CHClF2, and CH2ClF

The branching ratios and rate coefficients have been measured at 298 K for the reactions between CHCl2F, CHClF2, and CH2ClF and the following cations (with recombination energies in the range 6.3-21.6 eV); H3O+, SFx+ (x = 1-5), CFy+ (y = 1-3), NO+, NO2+, O2+, Xe+, N2O+, O+, CO2+, Kr+, CO+, N+, N2+, Ar+, F+, and Ne+. The majority of the reactions proceed at the calculated collisional rate, but the reagent ions SF3+, NO+, NO2+, and SF2+ do not react. Surprisingly, although all of the observed product channels are calculated to be endothermic, H3O+ does react with CHCl2F. On thermochemical grounds, Xe+ appears to react with these molecules only when it is in its higher-energy 2P1/2 spin-orbit state. In general, most of the reactions form products by dissociative charge transfer, but some of the reactions of CH2ClF with the lower-energy cations produce the parent cation in significant abundance. The branching ratios produced in this study and by threshold photoelectron-photoion coincidence spectroscopy agree reasonably well over the energy range 11-22 eV. In about one-fifth of the large number of reactions studied, the branching ratios are in excellent agreement and appreciable energy resonance between an excited state and the ground state of the ionized neutral exists, suggesting that these reactions proceed exclusively by a long-range charge-transfer mechanism. Upper limits for the enthalpy of formation at 298 K of SF4Cl (-637 kJ mol-1), SClF (-28 kJ mol-1), and SHF (-7 kJ mol-1) are determined.     

具有Lindqvist结构的[Mo6O19]2-化合物及其二钨取代物的电子性质和稳定性的理论研究

采用密度泛函理论研究了具有Lindqvist结构的[Mo6O19]2-及其两个钨原子取代化合物的电子性质和稳定性, 计算得到的几何数据和实验值符合得很好. 从Mulliken电荷分布、键能大小以及轨道性质的分析可以得出结论, 当两个钨原子在邻位取代钼原子时所得到的取代产物([4,5-W2Mo4O19]2-)比当两个钨原子在对位取代钼原子时所得到的产物([4,6-W2Mo4O19]2-)更稳定, 而[4,5-W2Mo4O19]2-的反应活性比[4,6-W2Mo4O19]2-的大.     

O2 induced Cu surface segregation in Au-Cu alloys studied by angle resolved XPS and DFT modelling

Surface segregation effects on polycrystalline Au-Cu alloys (Au(0.80)Cu(0.20), Au(0.85)Cu(0.15) and Au(0.90)Cu(0.10)) were studied at room temperature by angle resolved XPS (ARXPS) and density functional theory (DFT) before and after exposure to O(2). Au surface enrichment was found as predicted from calculations showing that this process is energetically favourable, with a segregation energy for Au in a Cu matrix of -0.37 eV atom(-1). Surface enrichment with Cu was observed after exposure to O(2) due to its dissociative adsorption, in agreement with DFT calculations that predicted an energy gain of -1.80 eV atom(-1) for the transfer of Cu atoms to a surface containing adsorbed oxygen atoms, thus leading to an inversion in surface population.     

Ultralow energy ion beam surface modification of low density polyethylene

Ultralow energy Ar+ and O+ ion beam irradiation of low density polyethylene has been carried out under controlled dose and monoenergetic conditions. XPS of Ar+-treated surfaces exposed to ambient atmosphere show that the bombardment of 50 eV Ar+ ions at a total dose of 10(16) cm(-2) gives rise to very reactive surfaces with oxygen incorporation at about 50% of the species present in the upper surface layer. Using pure O+ beam irradiation, comparatively low O incorporation is achieved without exposure to atmosphere (approximately 13% O in the upper surface). However, if the surface is activated by Ar+ pretreatment, then large oxygen contents can be achieved under subsequent O+ irradiation (up to 48% O). The results show that for very low energy (20 eV) oxygen ions there is a dose threshold of about 5 x 10(15) cm(-2) before surface oxygen incorporation is observed. It appears that, for both Ar+ and O+ ions in this regime, the degree of surface modification is only very weakly dependent on the ion energy. The results suggest that in the nonequilibrium plasma treatment of polymers, where the ion flux is typically 10(18) m(-2) s(-1), low energy ions (<50 eV) may be responsible for surface chemical modification.