锐钛矿型TiO2(101)面本征点缺陷的理论研究

采用平面波超软赝势方法计算了锐钛矿型TiO₂(101)面存在本征空位和间隙点缺陷的几何结构以及缺陷形成能.首先分析了点缺陷对表面结构的影响,发现不同类型缺陷导致缺陷周围原子有不同的位移趋势：O空位的产生导致空位周围的Ti原子向空位外移动,Ti₁和Ti₂空位的产生均使O₁自发地与周围的O原子团聚,O_i原子易被周围的氧原子吸附而成键,而Ti_i2缺陷几乎 关键词： 第一性原理 2')" href="#">TiO₂ 点缺陷 表面结构     

过渡金属Cu、Cr掺杂TiO2表面氧化性气体NO2光学气敏传感特性

采用密度泛函理论（DFT）体系广义梯度近似（GGA）第一性原理平面波超软赝势方法,分析锐钛矿型TiO₂（101）表面吸附NO₂分子光学气敏传感的微观机理.结果表明：Cu和Cr原子易于掺入TiO₂（101）表面,掺杂表面能稳定地吸附NO₂分子且吸附后光学性质发生显著变化.表面吸附NO₂分子后,Cu掺杂TiO₂（101）表面对分子的吸附能最大,吸附后结构更稳定,分子与表面的距离最短.通过分析差分电荷密度和电荷布居数发现,NO₂分子与基底表面间发生电荷转移,转移电子数目：Cu掺杂表面 > Cr掺杂表面 > 无掺杂表面.对比吸收光谱和反射光谱发现,在Cu掺杂表面吸附分子后,光学性质变化最明显,说明表面与吸附分子间氧化还原能力是决定光学气敏传感性能的核心因素.在过渡金属中,Cu与Cr都有4s价电子结构,其4s电子降低了材料表面氧空位的氧化性,增加了其还原性.对于氧化性气体,可以提升表面与分子的氧化还原作用,而Cu的4s电子更加活泼,从而光学气敏传感特性更加明显.因此,Cu掺杂的TiO₂对氧化性气体是一种较好的光学气敏传感材料.     

金属Sc修饰Ti2CO2吸附气体分子的第一性原理研究

基于第一性原理计算研究了Ti₂CO₂和金属Sc修饰的Ti₂CO₂的几何结构和电子性质,分析了不同有害气体(CO, NH₃, NO, SO₂, CH₄, H₂S)在这两种材料表面的吸附过程,讨论了金属修饰对Ti₂CO₂二维过渡金属碳化物(MXene)电子性能和气体吸附性能的影响.计算结果表明, Sc原子位于空心位C原子上方的结构具有较大的结合能,但小于固体Sc的内聚能实验值(3.90 e V), Sc原子可以有效避免成簇.表面Sc金属为气体吸附提供了活性位点.通过分析不同气体的最佳吸附点位、吸附能等参数,分析金属Sc修饰的Ti₂CO₂对这些气体的吸附效果.其中对SO₂的吸附效果更好,吸附能从–0.314 eV提升到–2.043 eV,其他气体的吸附效果均有改善.通过电荷转移、态密度和功函数等参数解释了其吸附...     

单原子Al修饰空位缺陷V2C（MXene）对H2气体表面吸附的第一性原理研究

基于第一性原理计算方法,对含空位缺陷的V₂C(MXene)在不同位点修饰单原子Al的相关性能进行系统研究.研究表明,几何优化后得到含空位缺陷的V₂C稳定结构表面能为-3075.53 J/m²,单原子Al修饰本征V₂C单原子的吸附能为1.5511eV、单原子Al修饰空位缺陷V₂C的吸附能为-2.0763 eV,这表明含空位缺陷的V₂C,由于单原子Al的修饰可以明显改善晶体结构稳定性.进一步从态密度、分波态密度、吸氢能力研究发现,各体系态密度和分波态密度均出现分波越过费米能级的现象,表现出较强的金属性;V₂C吸附H₂气体分子吸附能为-7.5867 eV,而空位缺陷V₂C和单原子Al修饰空位缺陷V₂C两个体系对H₂气体分子的吸附能仅为-0.9851 eV、-2.7130 eV,均未能进一步改善V₂C对H₂气体分...     

Zn吸附到含有氧空位(VO)以及羟基(-OH)的锐钛矿相TiO2(101)表面电子结构的第一性原理计算

基于密度泛函理论的第一性原理平面波超软赝势方法, 计算了Zn吸附到TiO₂(101)清洁表面、含有氧空位(V_O)的缺陷表面以及既含有氧空位(V_O)又含有羟基(-OH)表面的能量、Mulliken重叠布居数以及电子结构, 并找到了Zn在每种表面的最稳定结构(分别为模型(c), 模型(aI)以及模型(aII)). 通过对三种表面稳定结构的分析、对比发现: 首先, Zn原子吸附到清洁TiO₂(101)表面上, 主要与表面氧相互作用, 形成Zn–O共价键; 其次, 当Zn原子吸附到缺陷表面时, 吸附能减小到-1.75 eV, 说明Zn更容易吸附到氧空位上(模型(aI)); 最后, 纵观表面模型的能带结构以及态密度图发现, -OH的引入并没有引进新的杂质能级, Zn吸附此表面, 即Zn-TiO₂-V_O-OH, 使得禁带宽度缩短到最小(1.85 eV), 从而有望提高TiO₂的光催化活性. 关键词： 密度泛函理论 氧空位 羟基 Zn原子     

Ni与钇稳定的氧化锆(111)表面相互作用以及界面活性的第一性原理研究

采用基于密度泛函理论的第一性原理方法, 系统研究了Ni原子在钇稳定的氧化锆(YSZ)(111)和富氧的YSZ(YSZ+O)(111)表面不同位置的吸附, 以及CO和O₂分子在Ni₁(单个镍原子)/YSZ和Ni₁/YSZ+O表面吸附的几何与电子结构特征. 结果表明: 1) 单个Ni原子倾向于吸附在O原子周围, 几乎不吸附在Y原子周围, 且Ni原子在氧空位上吸附最稳定; 2)和YSZ相比, 单个Ni原子在YSZ+O表面易发生氧化现象, Ni原子失去1.06 e电子, 被氧化成了Ni⁺, 吸附能力更强; 3)被氧化的Ni催化活性大幅下降, 大大减弱了表面对O₂和CO等燃料气体的吸附作用.     

Ni(C3H10N2)2NO2(ClO4)晶体的ESR研究

报道了Ni(C₃H₁₀N₂)₂NO₂(ClO₄)晶体在T=1.5K温度和W波段的ESR实验.建立了d⁸离子基态³A₂(F)的零场分裂参量D,E,和g因子与斜方对称晶场势参量间的关系,并应用于Ni(C₃H₁₀N₂)₂NO₂(ClO₄)晶体.计算值与实验数据符合很好,表明所给关系式是合理的.     

CH3NO2在Cu(111)面吸附态的研究

用CNDO/2半经验量化计算方法对CH₃NO₂分子在Cu(111)面四个吸附位上25种吸附态进行了优化计算,得到以CH₃NO₂分子中的-NO₂取向吸附在Cu(111)面的桥位上,且CH₃NO₂分子中的ONO面与Cu-Cu键成60°时为最稳吸附态。计算得到的这一稳定吸附态的吸附取向和吸附体系的态密度结果与我们的实验结果是一致的;从吸附态的轨道成分分析表明, 关键词：     

高氧空位简并锐钛矿TiO2半导体电子寿命的第一性原理研究

为了研究锐钛矿TiO₂晶体中高氧空位浓度对电子寿命的影响,利用基于局域密度泛函理论框架下的广义梯度近似平面波超软赝势方法, 用第一性原理对含高氧空位浓度的锐钛矿TiO₂晶体进行了结构优化处理、能带分布和态密度分布计算, 表明在温度一定和高氧空位浓度的条件下, 锐钛矿TiO₂的电子寿命随氧空位浓度的增大而减小;电子浓度的大小对电子寿命无影响.同时,锐钛矿TiO₂晶体中高氧空位浓度时,发现有莫特相变的现象. 关键词： 高氧空位 2半导体')" href="#">锐钛矿TiO₂半导体 电子寿命 第一性原理     

BH2和AlH2分子的结构及其解析势能函数

运用二次组态相关(QCISD)方法，分别选用6-311++G(3df,3pd)和D95(3df,3pd)基组，对BH₂和AlH₂分子的结构进行了优化计算，得到BH₂分子的稳态结构为C_2v构型，电子态为²A₁、平衡核间距R_BH=0.1187nm、键角∠HBH=128.791°、离解能D_e=3.65eV、基态振动频率ν₁(a₁)=1020.103cm^-1,ν₂(a₁)=2598.144cm^-1,ν₃(b₂)=2759.304cm^-1.AlH₂分子的稳态结构也为C_2v构型，电子态为²A₁、平衡核间距R_AlH=0.1592nm、键角∠HAlH=118.095°、离解能D_e=2.27eV、基态振动频率ν₁(a₁)=780.81cm^-1,ν₂(a₁)=1880.81cm^-1，ν₃(b₂)=1910.46cm^-1.采用多体项展式理论推导了基态BH₂和AlH₂分子的解析势能函数，其等值势能图准确再现了BH₂和AlH₂分子的结构特征及其势阱深度与位置.分析讨论势能面的静态特征时得到BH+H→BH₂反应中存在鞍点，活化能为150.204kJ/mol；AlH+H→AlH₂反应中也存在鞍点，活化能为54.8064kJ/mol. 关键词： 2')" href="#">BH₂ 2')" href="#">AlH₂ Murrell-Sorbie函数 多体项展式理论 解析势能函数     

Heterogeneous reaction mechanism of elemental mercury oxidation by oxygen species over MnO2 catalyst

MnO₂-based catalysts have attracted great attention in the field of elemental mercury (Hg⁰) catalytic oxidation because of their superior catalytic performance and wide temperature window. Quantum chemistry calculations based on density functional theory (DFT) combined with periodic slab models were carried out to investigate the heterogeneous mechanism of Hg⁰ oxidation by oxygen species (gas-phase O₂, chemisorbed oxygen, and lattice oxygen) on MnO₂ surface. The results indicate that Hg⁰ and HgO are chemically adsorbed on MnO₂ surface with the adsorption energies of ?69.50 and ?226.48?kJ/mol, respectively. The adsorption of O₂ on MnO₂ surface belongs to chemisorption. O₂ can decompose on MnO₂ surface with an energy barrier of 97.46?kJ/mol to produce two atomic adsorbed oxygen. The perpendicular adsorbed O₂ and dissociative adsorbed O₂ are more favorable for Hg⁰ catalytic oxidation than lattice oxygen, and perpendicular adsorbed O₂ is the most active oxygen for Hg⁰ oxidation. The reaction pathway of Hg⁰ oxidation by perpendicular adsorbed O₂ includes three reaction steps: Hg⁰?→?Hg(ads)?→?HgO(ads)?→?HgO. The third step (HgO(ads)?→?HgO) is endothermic by 168.17?kJ/mol with an energy barrier of 179.48?kJ/mol, and it is the rate-limiting step of the whole Hg⁰ oxidation reaction.     

Roles of γ-Fe2O3 in fly ash for mercury removal: Results of density functional theory study

First-principle calculations based on density function theory (DFT) are used to clarify the roles of γ-Fe₂O₃ in fly ash for removing mercury from coal-fired flue gases. In this study, the structure of key surface of γ-Fe₂O₃ is modeled and spin-polarized periodic boundary conditions with the partial relaxation of atom positions are employed. Binding energies of Hg on γ-Fe₂O₃ (0 0 1) perfect and defective surfaces are calculated for different adsorption sites and the potential adsorption sites are predicted. Additionally, electronic structure is examined to better understand the binding mechanism. It is found that mercury is preferably adsorbed on the bridge site of γ-Fe₂O₃ (0 0 1) perfect surface, with binding energy of −54.3 kJ/mol. The much stronger binding occurs at oxygen vacancy surface with binding energy of −134.6 kJ/mol. The calculations also show that the formation of hybridized orbital between Hg and Fe atom of γ-Fe₂O₃ (0 0 1) is responsible for the relatively strong interaction of mercury with the solid surface, which suggests that the presently described processes are all noncatalytic in nature. However, this is a reflection more of mercury's amalgamation ability.     

Reaction mechanism of ammonia oxidation over RuO2(1 1 0): A combined theory/experiment approach

Combining state-of-the-art density functional theory (DFT) calculations with high resolution core level shift spectroscopy experiments we explored the reaction mechanism of the ammonia oxidation reaction over RuO₂(1 1 0). The high catalytic activity of RuO₂(1 1 0) is traced to the low activation energies for the successive hydrogen abstractions of ammonia by on-top O (less than 73 kJ/mol) and the low activation barrier for the recombination of adsorbed O and N (77 kJ/mol) to form adsorbed NO. The NO desorption is activated by 121 kJ/mol and represents therefore the rate determining step in the ammonia oxidation reaction over RuO₂ (1 1 0).     

Simultaneous removal of NO and Hg0 from flue gas over MnSmCo/Ti catalyst at low temperature

The MnSmCo/Ti catalyst was designed for the simultaneous removal of NO and Hg⁰ at low temperature. The MnSmCo/Ti catalyst exhibited 80% NO conversion, almost 100% N₂ selectivity and 100% Hg⁰ removal in the absence of HCl within the temperature range of 150–250 °C with a gas hourly space velocity of 100,000 h^?1. The influence of flue gas components on Hg⁰ oxidation was investigated and the NO and O₂ are mainly responsible for Hg⁰ oxidation. Hg balance analysis revealed that the Hg⁰ removal was achieved through chemisorption and catalytic oxidation. Furthermore, the Hg⁰ oxidation mechanism was explored using transient reaction along with temperature-programmed desorption of mercury and X-ray photoelectron spectroscopy. Hg⁰ oxidation proceeds through Mars–Maessen mechanism in which adsorbed Hg⁰ is bound to MnO_x to form weakly bonded HgMnO_x+1 species and follows Langmuir?Hinshelwood mechanism, where adsorbed Hg⁰ reacts with active NO₂ to generate HgO.     

Comprehensive evolution mechanism of SOx formation during pyrite oxidation

Pyrite (FeS₂) oxidation during coal combustion is one of the main sources of harmful SO₂ emission from coal-fired power plants. Density functional theory (DFT) study was performed to uncover the evolution mechanism of SO_x formation during pyrite oxidation. The results show that chemisorption mechanism is responsible for O₂, SO₂ and SO₃ adsorption on FeS₂ surface. The presence of formed oxidation layer (Fe₂O₃) weakens the interaction between O₂ molecule and FeS₂ surface. The adsorbed O₂ molecule easily dissociates into active surface O atom for SO_x formation. The dissociation reaction of O₂ is activated by 77.38?kJ/mol, and exothermic by 138.46?kJ/mol. Compared to the further oxidation of SO₂ into SO₃, SO₂ prefers to desorb from FeS₂ surface. The dominant reaction pathway of SO₂ formation from the oxidation of the outermost FeS₂ surface layer is a three-step process: surface lattice S oxidation, SO₂ desorption and replenishment of S vacancy by activated surface O atom. The elementary reaction of surface lattice S oxidation has an activation energy barrier of 197.96?kJ/mol, and is identified as the rate-limiting step. SO₂ formation from the further oxidation of bulk FeS₂ layer is controlled by a four-step process: bulk lattice S migration, lattice S oxidation, SO₂ desorption and surface O atom deposition. Migration of lattice S from bulk position to the outermost surface shows a high activation energy barrier of 175.83?kJ/mol. The deposition process of surface O atom is a relatively easy step, and is activated by 21.05?kJ/mol.     

The adsorption of hydrogen on iron; A surface orbital modified occupancy — bond energy bond order calculation

A Surface Orbital Modified Occupancy — Bond Energy Bond Order (SOMO-BEBO) model calculation of hydrogen adsorption on iron is presented. This calculation represents a novel approach to the CFSO-BEBO method in that the calculation is correlated in a consistent way with the thermal desorption spectra of the hydrogen-iron system. Heats of molecular adsorption calculated are ?32.88, ?35.68 and ?49.57 kJ/mol for the iron (110), (100), and (111) surfaces, respectively. Heats of dissociative adsorption calculated are ?54.40, ?75.30 and ?87.90 kJ/mol for the three states on the iron (111) surface; ?51.21 and ? 73.62 kJ/mol for the two states on the iron (100) surface; and ?63.78 kJ/mol for the one state on the iron (110) surface. Activation energies for dissociative adsorption were found to be small or zero for the iron (111) surface while non-zero activation energies of 49.27 and 45.05 kJ/mol were calculated for the iron (100) and (110) surfaces, respectively. The FeH single-order bond energy has been calculated to be 298.2 kJ/mol. The radius of the hydrogen surface atom has been estimated to be 1.52 × 10^?10 m consistent with the expected size of an H^? ion. The elimination of certain surface sites for molecular adsorption as a result of the ferromagnetism of iron is suggested by the calculation. The reason for the absence of well defined LEED patterns for hydrogen adsorption on the iron (111) and (100) surfaces [Bozso et al., Appl. Surface Sci. 1 (1977) 103] is explained on the basis of the size of the H^? surface ion. The adsorption of hydrogen on the iron (110) surface is consistent with a relatively stable, small-sized H⁺₂ surface ion giving, therefore, a regular LEED pattern and a positive surface potential upon adsorption of hydrogen on this surface.     

The energetics of mercury adsorption on Cu(100)

We have investigated the adsorption of mercury overlayers on Cu(100) by atom beam scattering, low energy electron diffraction and angle resolved photoemission. From our data we have calculated the isosteric heats in the adsorbed Hg layer on Cu(100) and compared these with results obtained for mercury on Fe(100), W(100) and Ni(100). We observe changes in the isosteric heat of adsorption that can be associated with the ordering of a c(2 × 2) Hg overlayer phase and the transition from a c(2 × 2) overlayer to a c(4 × 4) overlayer. The isosteric heat of adsorption is 0.50 ± 0.07 eV/atom (48 ± 7 kJ/mol) at zero coverage and reaches a maximum of 0.73 ± 0.04 eV/atom (70 ± 4 kJ/mol). From a combination of ABS and LEED, the structures of the two equilibrium ordered phases of Hg on Cu(100) have been identified, as well as the structures of several non-equilibrium phases.     

TiO2表面氧空位对NO分子吸附的作用

采用程序升温热脱附(TPD)实验方法测定了NO在TiO2表面吸附后的脱附谱，利用分子轨道理论研究了TiO2吸附NO的原子簇模型及吸附前后的原子簇能级变化．结果表明，NO在TiO2表面吸附后可在两个峰值温度450和980K脱附出N2．TiO2表面经预覆氧处理后，N2的脱附量降低．吸附时NO中的O能够占据TiO2表面氧空位并与N脱离，而N原子则相互结合成为N2脱附．分子轨道理论计算证明在TiO2(110)表面能够存在氧空位并具备吸附NO的结构条件．     

Interaction of C2N2 with clean and oxygen dosed Cu(111) surface studied by AES,ELS and TDS measurements

The adsorption and surface reaction of cyanogen on clean and oxygen covered Cu(111) have been investigated. From electron energy loss measurements, thermal desorption spectroscopy and electron beam effects in Auger spectroscopy, it is proposed that cyanogen adsorbs dissociatively on Cu(111) at 300 K. The activation energy for the desorption was calculated to be 180 kJ/mol. Cyanogen adsorption onto oxygen predosed Cu(111) is inferred to produce the NCO surface species. This interpretation was aided by data of electron energy loss measurements and from HNCO adsorption onto Cu(111) at 300 K. A reaction began in the co-adsorbed layer above 400 K, yielding CO₂ and N₂.     

Sulfur poisoning of the CO adsorption on Co(0 0 0 1)

CO adsorption on a sulfur covered cobalt surface at 185 K has been studied using XPS, TDS, LEED, and WF measurements. As in the case of CO adsorption on the clean Co(0 0 0 1) surface, CO adsorbs and desorbs molecularly and no dissociation was observed. The saturation coverage of CO decreases linearly from 0.54 ML to 0.27 ML when the S pre-coverage increases to 0.25 ML. The WF increased during CO adsorption, but did not reach the value obtained for CO adsorption on the clean surface. The smaller work function change is explained by the reduced adsorption of CO on the sulfur-precovered surface. A reduction in the activation energy of desorption for CO from 113 kJ/mol to 88 kJ/mol was observed indicating weaker bonding of the CO molecules to the surface. The behavior of the CO/S/Co(0 0 0 1) system was explained by a combination of steric and electronic effects.