O2在M2-(M=Au,Ag,Cu,Pt)系列团簇上的吸附行为研究

用密度泛函理论(DFT)方法研究了O2在M2-(M=Au,Ag,Cu,Pt)系列团簇上的吸附行为,首次确定存在2个O原子与同一个Au作用的吸附方式(记为D2),并讨论了该吸附方式对Au2-催化CO氧化的重要作用.结果表明,相对于研究者所关注的O原子与Au作用的D1吸附方式,D2吸附方式的O2分子活化程度更高,更有利于促进CO氧化.相对D1吸附方式,从D2式出发,CO按Eley-Rideal机理插入形成Au2CO3-的势垒更低,稳定性更高,更有利于CO2脱附.Ag体系的计算结果与Au类似,Cu、Pt体系则明显不同.     

Theoretical study of adsorption and dissociation of NH3 on the Ir{110}（1×2） surface

The adsorption and dissociation of NH3 on Ir{110}（1×2） have been investigated using the density- functional calculations at a coverage of 0.25 ML. The adsorption sites, energy, and geometries were obtained for NH3, NH2, and H adsorptions on the surface. The transition state for NH3 dissociation on Ir{110}（1×2） was also identified. It was found that NH3 is adsorbed preferentially at the ridge atop site, while NH2 and H are adsorbed at the ridge bridge site. The activation barrier of NH3 dissociation is 78.4 kJ/mol, which is very close to the NH3 adsorption energy of 90.0 kJ/mol. This indicates that the desorption and dissociation of NH3 on Ir{110}（1×2） are very competitive, which is consistent with the recent experimental results.     

CO 和 O2与 Aumn 簇相互作用的 DFT 研究（I）

在B3LYP/LAN2DZ（＋ECP）对金、6-311＋G*基组对碳和氧水平下,对Aumn （ n＝3～5,m＝0,±1）簇及其CO在簇上发生单分子吸附几何进行全优化和振动分析。获得了与实验结果一致的基态Aumn 簇结构,以及CO在相应各簇上形成吸附配合物AunCOm（n＝3～5, m＝0,±1）的最低能量结构和吸附能。通过对其结构、能量和振动分析,获得了CO与Aumn 簇相互作用的性质和变化规律。结果表明, CO在Au n＋上的吸附能比在相应中性和阴离子簇上大,其值随簇尺寸减小呈减小趋势,CO在组成较大的Aun-簇上的反应活性更高。     

Density functional theory calculation on the C―H bond insertion reaction of dibromocarbene with acetaldehyde

The insertion reaction mechanism of CBr2 with CH3CHO has been studied by using the B3LYPI6-31G（d） method. The geometries of reactions, transition state and products were completely optimized. All the energy of the species was obtained at the CCSD（T）/6-31G（d） level. All the transition state is verified by the vibrational analysis and the internal reaction coordinate （IRC） calculations. The results show that the propionaldehyde （Hp1） is the main product of CH2 insertion with CH3CHO. The calculated results indicated that all the major pathways of the reaction were obtained on the singlet potential energy surface. The singlet CBr2 not only can insert the Cα-H [reaction I（1）]） but also can react with Cβ-H [reaction l1（1）]. The statistical thermodynamics and Eyring transition state theory with Wigner correc-tion are used to study the thermodynamic and kinetic characters of I（1） and I1（1） in temperature range from 100 to 2200 K. The results show that the appropriate reaction temperature rang is 250 to 1750 K and 250 to 1600 K at 1.0 atm for I（1） and I1（1） respectively. The rate constant and equilibrium constant are distinct in the range from 250 to 1000 K so that I（1） more easily occurs, while the reactions are not selected in the temperature range of 1000-1600 K.     

The influence of molar ratios of Ce/Zr on the selective catalytic reduction of NOx with NH3 over Fe2O3-WO3/CexZrl-xO2 （0 〈 x 〈 1） monolith catalyst

A series of CexZrl_xO2 （0 ≤ x ≤ 1） with dif- ferent molar ratios of Ce/Zr were syhthesized via coprecip- itation method, and Fe2O3-WO3/CexZrl-xO2 monolithic catalysts were prepared, for selective catalytic reduction of nitrogen oxides by ammonia （NH3-SCR）. The structural properties and redox behavior of the catalysts were com- prehensively characterized by N2 physisorption, X-ray diffraction （XRD）, X-ray photoelectron spectra （XPS）, H2-temperature programmed reduction （H2-TPR） and activity measurement for NH3-SCR. The results showed that the NH3-SCR activities of the catalysts were gradually enhanced by increasing the molar ratios of Ce/Zr, especially the low- temperature catalytic activity and the reaction temperature window. Fe2O3-WO3/Ceo.68Zro.3202 monolithic catalyst presented the best NH3-SCR activity among the investigated catalysts, more than 90 % NOx could be removed in the temperature range of 247-454 ℃ on the catalyst under the gas hourly space velocities of 30,000 h- 1. And it always held more than 99 % N2 selectivity and less than 20 ppm （1 ppm =10-6 L/L ） N20 generation concentration between 200 and 500 ℃, the catalyst also displayed its strong resistance of H20 and SO2. Good textural and structural properties, more surface Fe, Ce and active oxygen were together contributed to the excellent NH3-SCR performance of Fe2O3-WO3/ Ce0.68Zr0.32O2 catalyst.     

Theoretical study on the lithium bond interaction of furan homologues C4H4Y （Y=O,S） with LiCH3 via DFT and MP2

The optimizations geometries and interaction energy corrected by BSSE of the complexes between C4H4Y （Y=O, S） and CHiLi have been calculated at the B3LYP/6-311＋＋G^＊＊ and MP2/6-311＋＋G^＊＊ levels. Three complexes were obtained. Abnormally, the calculations showed that all the C10--Li14 bond lengths increased obviously but the blue-shift of C10-Li14 stretching frequency occurred after formed complexes. The calculated binding energy with basis set super-position error （BSSE） and zero-point vibrational energy corrections of complexes I-III is -45.757, -35.700 and -39.107 kJ·mol^-1, respectively. The analyses on the combining interaction with the atom-in-molecules theory （AIM） also showed that a relatively strong lithium bond interaction presented in furan homologues C4H4Y-LiCH3 systems. Natural bond orbital theory （NBO） analysis has been performed, and the results revealed that the complex I is formed with n-σ type lithium bond interaction between C4H40 and LiCH3, complex II is formed with TT-s type lithium bond interaction between C4H4O and LiCH3, and complex III is formed with TT-s and n-s type lithium bond interactions between C4H4S and LiCH3, respectively.     

CO吸附在Pd/Pt(111)双金属表面的密度泛函理论研究

采用密度泛函理论研究了CO在Pd/Pt(111)双金属表面的吸附性质.分别考虑了Pd原子全部取代表层Pt原子以及部分取代表层和次表层Pt原子的情况,分析了CO吸附在双金属不同表面的吸附能、C-O和C-Pt键长及振动频率.结果表明无论是在表层或者次表层加入Pd原子,相比CO吸附在干净Pt(111)表面情况,CO在双金属表面的吸附能几乎没有变化,而键长、频率也未见明显改变.这些吸附特性说明Pt催化剂的抗CO中毒性质主要依赖于最外层的Pt原子,临近的Pd原子可能会对其产生影响,但是未见明显变化.     

Cu(111)面上原子扩散势垒的密度泛函理论研究

用密度泛函理论(DFT)结合平板周期模型方法,对Cu在Cu(111)表面fcc洞位、hcp洞位的吸附模型进行了几何优化,并用从fcc洞位到hcp洞位过渡态计算的方法,研究了Cu在Cu(111)表面的扩散势垒.通过对不同基底层数、不同表面弛豫层数、不同覆盖率的比较,得到基底层数为4层、表面弛豫1层、覆盖率为1/4ML(monolayer)时,Cu在Cu(111)表面的扩散势垒和实验结果吻合得较好.在此基础上,计算了Fe、Ni、Co等磁性原子在Cu(111)表面的扩散势垒.     

硅苯-Cr(CO)_3配合物与H_2O的加成反应的计算研究

采用密度泛函理论方法,研究了硅苯-Cr(CO)_3配合物(R)与H_2O的1,2-及1,4-加成反应的微观机理和势能剖面,考察了H_2O分子数目、Si原子上的2,4,6-三甲基苯基(Mes)取代基及四氢呋喃溶剂对反应势能剖面的影响.结果表明,R可分别与H_2O的单聚体、二聚体及三聚体发生加成反应.R与H_2O二聚体的加成反应在动力学上比其与H_2O单聚体及三聚体的相应反应有利.Cr(CO)_3与硅苯形成配合物对硅苯与H_2O的加成反应的动力学性质影响较小,但在热力学上对反应非常不利,特别是对1,4-加成反应的影响更为显著.当Cr(CO)_3与硅苯形成配合物后,实验观察到的完全的位置选择性主要由热力学因素控制.Si原子上具有较大体积的Mes取代基对反应不利.四氢呋喃溶剂在热力学和动力学上均不利于R与H_2O的加成反应.     

HCOOH在电极Pd(110)表面电吸附的密度泛函研究

采用密度泛函理论和周期平板模型相结合方法,对HCOOH分子在Pd(110)表面bridge,bidentate和unidentate三种形态吸附位进行吸附结构、Mulliken布居和振动频率等性质的计算;计算结果表明HCOOH在金属态表面bidentate为最稳定的吸附位,电极表面unidentate为最稳吸附位;HCOOH在电极表面的吸附远大于金属态表面的吸附能,表明电化学反应比普通化学反应容易进行.电极表面吸附的结构和频率分析显示,吸附过程中O—H、C—H键均伸长,v(O—H)键和v(C—H)振动频率均发生明显红移,表明H原子在吸附过程中容易断裂,脱离HCOOH分子.Mulliken电荷布居分析表明在电吸附过程中电子由HCOOH分子向Pd(110)表面进行转移,有利于电催化反应进行.     

Structure of self-assembled monolayer of NPAN on Au(111) electrode

Recently, much attention has been paid to the self-assembled monolayers (SAMs) or Langmuir-Blodgett films (LB films) of molecules bearing azobenzene group on the surface. Azobenzene derivatives are attractive ow-ing to their interesting photoresoponsive behavior[1—5]. Azobenzene and its derivatives take both trans (E) and cis (Z) structures with respect to the azo linkage and normally exist in the more stable trans form[6]. Being irradiated with appropriate light, organic molecules and po…     

HREELS study on coadsorption of oxygen and cyclohexanone on the Pt(111) surface

The coadsorption of cyclohexanone and oxygen on Pt(111) has been investigated by HREE-LS and TDS. At 205 K the presence of oxygen induces an “extra” red-shift of the C = O stretching of coadsorbed cyclohexanone. Heating this coadsorbed surface from 205 to 250 K leads to further dehydrogenation to form intermediate species and to complete disappearance of the C = O stretching band. Above 300 K, the molecule rings of dehydrogenation species cleave to form hydrocarbon fragments and CO molecules which directly desorb into the vacuum or react with preadsorbed oxygen to produrn CO₂ which leave the surface immediately. TDS results provide further evidence that the preadsorbed oxygen promotes the decomposition of cyclohexanone.     

密度泛函方法研究HFe（CO）_5~＋中H~＋的电离反应

用密度泛函方法（ＤＦＴ）的ＬＤＡ和ＮＬ／ＬＤＡ优化分子片试剂ＨＦｅ（ＣＯ）５＋和Ｍｎ（ＣＯ）５－的几何结构，并计算了Ｆｅ（ＣＯ）５的ＮＬ／ＬＤＡ质子亲合能，其值为７５１．６ｋＪ·ｍｏｌ－１，介于文献报道的ＨＣＮ和ＮＨ３的质子亲合能之间，解释了Ｆｅ（ＣＯ）５容易从Ｈ２ＣＮ＋中得到质子而难以由ＮＨ４＋夺得质子的实验事实。ＨＦｅ（ＣＯ）５＋电离Ｈ＋后其几何结构由Ｃ４ｖ对称性变为Ｄ３ｈ对称性，与等电子体ＨＭｎ（ＣＯ）５电离Ｈ＋后几何构型的弛豫相类似。ＮＬ／ＬＤＡ计算的分子片Ｆｅ（ＣＯ）５的弛豫能为－５９．７８ｋＪ·ｍｏｌ－１。计算结果还表明，ＨＦｅ（ＣＯ）５＋电离Ｈ＋后Ｆｅ→ＣＯ反馈π键得到加强，使得ＦｅＣ键缩短，ＣＯ键增长；同时，Ｆｅ原子上的电子电荷减少，而Ｃ和Ｏ原子上的电子电荷增加。Ｍｕｌｉｋｅｎ布居分析同样表明，在ＨＦｅ（ＣＯ）５＋电离Ｈ＋后，Ｆｅ和Ｃ之间的Ｍｕｌｉｋｅｎ键级增加，Ｃ和Ｏ原子之间的键级减少     

C3H7/NH2/Fe+体系反应活性的密度泛函研究

采用B3LYP密度泛函理论对C3H7/NH2／Fe^＋体系生成乙烯和丙烯的反应路径进行了研究。在B3LYP／6-31＋G＊＊水平上，优化了4重态势能面上的极小值和过渡态的几何构型，计算了它们的能量和频率等参数，得到了该反应的势能面以及反应基元过程的详细信息。     

Density functional theory study on the insertion reaction mechanism of dibromocarbene with formaldehyde

The insertion reaction mechanism of CBr2 with CH3CH2O has been studied by using the B3LYP/6-311G(d) and CCSD(T)/6-311G(d) at single point. The geometries of reactions,transition state and products were completely optimized. All the transition state is verified by the vibrational analysis and the internal re-action coordinate (IRC) calculations. The results show that reaction (1) is the dominant reaction path,which proceeds via two steps: i) two reactants form an intermediate (IM1),which is an exothermal re-action of 8.62 kJ·mol?1 without energy barrier; ii) P1 is obtained via the TS1 and the H-shift,in which the energy barrier is 44.53 kJ·mol?1. The statistical thermodynamics and Eyring transition state theory with Wigner correction are used to study the thermodynamic and kinetic characters of this reaction in temperature range from 100 to 2200 K. The results show that the appropriate reaction temperature ranges from 200 to 1900 K at 1.0 atm,in which the reaction has a bigger spontaneity capability,equi-librium constant (K) and higher rate constant (k).     

一氧化碳在外延薄膜Pd(111)表面的催化氧化

在外延薄膜Pd(111)表面上暴露覆盖系数θ≈0.45一氧化碳后,仍能吸附氧并发生一氧化碳催化氧化反应,这与在由溅射、退火方法制备的体材料钯表面上观察到的结果不同,其原因可能归结于两者微观形貌的差别。