O2在具有氧和镁缺陷MgO(001)表面的吸附

在密度泛函理论的框架下，采用嵌入点电荷簇模型研究了O2在具有氧缺陷和镁缺陷MgO(001)表面上的吸附.用电荷自洽的方法确定了点电荷的值.计算结果表明，O2倾向吸附在具有氧缺陷的MgO(001)表面上.通过和我们近期研究过的O2在低配位的边、角上吸附结果相比较，发现具有氧缺陷的MgO(001)表面更加有利于O2的吸附和解离. Mülliken电荷分析表明，电荷由底物向吸附的O2反键轨道上转移是导致O2键强削弱的主要原因.势能曲线表明，O2在具有氧缺陷的MgO(001)表面上发生解离所需要克服的能垒比在角阳离子端发生解离所需克服的能垒有大幅度降低.     

NO双分子和二聚体与Cu2作用的理论计算

采用密度泛函理论(DFT)中的B3LYP方法，在Lanl2DZ基组下，对NO双分子和二聚体与铜原子簇相互作用的结构进行了研究. 结果表明，NO可以在铜表面相邻的两个铜原子上形成稳定的双分子吸附和二聚体吸附，而在双分子吸附形式中NO以氮原子吸附在铜上的构型最稳定，且顶点吸附的稳定性不如非顶点吸附形式.在二聚体吸附形式中， N－N键被加强，而N－O键被削弱的程度大于双分子吸附形式，说明二聚体的形成有利于NO在金属铜表面的直接分解.同时电荷布居分析表明，单重态的二聚体与铜作用时，铜原子上的平均电荷达到0.66 e,说明在这种吸附形式中铜被离子化的倾向较大，而且这种吸附形式最有利于NO的分解.这些结果说明NO经二聚体形式在铜表面直接催化分解是可行的.     

NiO(001)面吸附NO电子结构的理论研究

用嵌入点电荷的簇为模型,采用B3LYP方法研究了NO在NiO(001)面上不同吸附位置和不同吸附方式的电子结构,并计算了振动频率。结果表明在完整表面上最稳定的吸附方式是N端歪斜吸附在Ni位,这与实验结果相符;而在缺陷表面上,NO以直线方式吸附在角位上最为稳定。振动频率计算表明,NO吸附后NO振动频率红移约50cm-1。我们根据价轨道电子密度图解释了NO吸附后振动频率红移的原因,这个解释完全不同于传统认为的3d对2π的反馈键理论。     

MgO缺陷和不规则表面吸附Cl2的电子结构研究

采用从头算程序对MgO表面 3种不同配位位置吸附Cl2 的构型进行优化 ,并用扩展休克尔紧束缚 (EHT)晶体轨道方法对MgO的缺陷和不规则表面吸附Cl2的可能构型进行能带计算 ,讨论了吸附前后能带组成和成键性质的变化。研究表明 :MgO表面吸附Cl2 将更趋向于吸附在O原子上而非Mg原子上 ,而且在 3种配位中MgO表面三配位氧最有利于吸附Cl2 ;吸附时 ,电子从O原子转移到Cl2 分子的反键轨道 ,但是各种吸附构型的MgO表面对Cl2 的吸附作用均比较微弱 ,是典型的物理吸附。     

MgO缺陷和不规则表面吸附CO的能带和电子结构研究

采用从头算程序优化MgO表面三种不同配位位置吸附CO构型,并用扩展休克尔紧束缚(EHT)晶体轨道方法对MgO的缺陷和不规则表面吸附CO的可能构型进行能带计算,讨论了能带结构及组成,不同构型吸附前后能带和成键性质的变化,以及吸附前后的电荷转移和吸附键的变化规律。研究结果发现,CO的C端更有利于在MgO固体表面的吸附,具有氧缺陷结构的MgO更有利于吸附分解CO。     

NO双分子在Cu2O(111)面吸附与解离的理论研究

采用广义梯度密度泛函理论结合周期平板模型方法, 在DNP基组下, 研究了NO双分子在三重态和单重态两种电子组态下在Cu2O(111)完整表面的吸附情况. 考虑了Cu+(NO)(NO)、Cu+(NO)(ON)及Cu+(ON)(ON)这三种构型, 计算了它们的吸附能和Mulliken电荷, 分析并预测了吸附后可能产生的物种. 结果表明, 当两个NO分子都以O端吸附在Cu2O(111)表面时即Cu+(ON)(ON)构型, N—N键长很短, 只有124.4 pm, 吸附的两个NO分子形成了二聚体形式, 这种吸附构型有利于进一步离解产生N2或N2O并形成Cu-O表面物种.     

NOx/CO2/H2O在BaO(001)表面吸附的理论研究

采用密度泛函理论(DFT)研究了NOx/CO2/H2O在BaO(001)表面不同覆盖度下的吸附情况.计算表明NO以N端吸附在表面氧位,形成NO22-吸附物种;CO2以C端吸附在表面氧位,形成表面CO32-;而H2O在表面发生解离吸附,导致BaO表面的羟基化.NO2有两种主要的吸附模式:以N端吸附在表面氧位,或以O端吸附表面Ba位.各物种在表面的吸附顺序为:NO≈H2O相似文献   

乙炔在Ge(001)表面吸附的反应路径

采用第一性原理方法研究了乙炔分子在Ge(001)表面的吸附反应.通过系统考察0.5和1.0ML覆盖度时形成di-σ和end-bridge构型的反应路径,研究在表面形成di-σ和paired-end-bridge构型的反应几率.除了表面反应以外,本文还涉及了亚表层Ge原子参与的吸附反应,乙炔在亚表层原子上吸附形成的亚稳态结构sub-di-σ,是形成end-bridge结构的第二条途径,此反应机理对于表面吸附结构的形成起重要的作用.与乙炔分子不同的是,表面以下原子参与时乙烯分子的吸附反应为吸热反应.综合热力学和动力学的分析表明,paired-end-bridge构型是乙炔分子吸附的主要构型,此结论解释了乙炔分子在Ge(001)表面吸附构型的实验结果.对于乙烯和乙炔两分子在Ge(001)表面吸附的分析比较揭示了导致两者之间差异的原因.     

CO在某些过渡金属表面吸附活化的DFT研究

采用DFT方法对CO在M(100)(M= Cu、Ag、Au、Pd、Pt)表面上的吸附行为进行了系统的比较性研究.结果表明,CO分子在这些过渡金属单晶表面上发生的是非解离性吸附,吸附后C－O键长都变长了,均不同程度地削弱了C－O键,继而活化了CO分子；从表面结合能、重叠集居数、轨道电子数变化等方面分析了成键强弱顺序,发现CO的吸附强度随Pd(100)、Pt (100)、Cu (100)、Ag(100)、Au(100)顺序依次减弱,并且将CO与过渡金属间的结合能(BE)、过渡金属的d电子转移数分别与水煤气变换反应活性数据进行了关联,在定性上比较好地解释了金属铜的催化活性优于其它金属的原因.     

MoP(001)表面苯胺C―N键断裂机理

油品脱氮可以减少燃烧过程中氮氧化物的排放,并且减弱催化剂的中毒现象,过渡金属磷化物因具有高催化活性和优异的稳定性而成为最具应用前景的新型加氢脱氮(HDN)催化剂。本工作基于周期性平板模型,通过密度泛函理论(DFT)计算研究了苯胺在磷化钼(MoP)(001)表面的吸附以及C―N断键机理。结果表明在MoP(001)表面,苯胺吸附以平躺吸附构型为主,有较大的吸附能,C―C键和C―N键均被吸附活化;苯胺C―N键的直接断裂路径主要起始于与共吸附H_2发生反应,产物为苯和氨,吸附的环己胺的C―N键断裂主要路径是环己胺与共吸附的H发生反应脱去氨基,生成产物为环己烯和氨。     

Conversion of N2O to N2 on MgO （001） Surface with Vacancy： A DFT Study

The adsorption and decomposition of NzO at regular and defect sites of MgO (001) surface have been studied using cluster models embedded in a large array of point charges (PCs) by DFT/B3LYP method. The results indicate that the MgO (001)surface with oxygen vacancies exhibits high catalytic reactivity toward N2O adsorptive-decomposition. It is different from the regular MgO surface or the surface with magnesium vacancies.Much elongation of O—N bond of N2O after adsorption at oxy-gen vacancy site with O end down shows that O—N bond has been broken with concurrent production of N2, leaving a regu-lar site instead of the original oxygen vacancy site (F center ).The MgO (001) surface with magnesium vacancies hardly ex-hibits catalytic reactivity. It can be concluded that N2O dissoci-ation likely occurs at oxygen vacancy sites of MgO (001) sur-face, which is consistent with the generally accepted viewpoint in the experiments. The potential energy surface (PES) reflects that the dissociation process of N2O does not virtually need to surmount a given energy barrier.     

Density functional embedded cluster study of Cu(4), Ag(4) and Au(4) species interacting with oxygen vacancies on the MgO(001) surface

Cu(4), Ag(4), and Au(4) species adsorbed on an MgO(001) surface that exhibits neutral (F(s)) and charged (F(s) (+)) oxygen vacancies have been studied using a density functional approach and advanced embedding models. The gas-phase rhombic-planar structure of the coinage metal tetramers is only moderately affected by adsorption. In the most stable surface configuration, the plane of the tetramers is oriented perpendicular to the MgO(001) surface; one metal atom is attached to an oxygen vacancy and another one is bound to a nearby surface oxygen anion. A very similar structural motif was recently found on defect-free MgO(001), where two O(2-) ions serve as adsorption sites. Following the trend of the interactions with the regular MgO(001) surface, Au(4) and Cu(4) bind substantially stronger to F(s) and F(s) (+) sites than Ag(4). This stronger adsorption interaction at oxygen vacancies, in particular at F(s), is partly due to a notable accumulation of electron density on the adsorbates. We also examined the propensity of small supported metal species to aggregate to adsorbed di-, tri- and tetramers. Furthermore, we demonstrated that core-level ionization potentials offer the possibility for detecting experimentally supported metal tetramers and characterizing them structurally with the help of calculated data.     

Mechanism for NO2 charging on metal supported MgO

NO2 adsorbed on MgO(100) supported by Ag or Pt is explored by density functional theory calculations. NO2 is weakly adsorbed on MgO(100), with a bond involving minor oxide to adsorbate charge transfer. However, if MgO is supported, then the adsorption energy is considerably enhanced and NO2 is adsorbed as a nitrite (N). Analysis reveals that the NO2 excess charge originates from the oxide side of the oxide/metal interface and that the electron abstraction increases the oxide/metal adhesion. The proposed mechanism is general and should apply for oxidizing surface species.     

O2在MgO(001)完整和缺陷表面上的吸附

在密度泛函理论的框架下， 采用嵌入点电荷簇模型研究了O2在MgO(001)完整和缺陷表面上的吸附.用电荷自洽的方法确定了点电荷的值.计算结果表明， O2倾向吸附在低配位的角Mg2＋端.并且发现， 当O2为平躺吸附时，键长有较大的拉伸，将有利于O2的解离.同时，分别计算了使用裸簇和嵌入表观±2.0 e点电荷簇模型时的吸附能，并与采用电荷自洽方法的计算值进行了比较.结果表明，电荷自洽方法更能有效反映簇周围的环境，得到的计算结果能够较好地与实验值吻合.最后，分别计算了不同吸附情况下O2的振动频率.     

Methanol adsorption on the beta-Ga2O3 surface with oxygen vacancies: theoretical and experimental approach

Methanol adsorption on beta-Ga2O3 surface has been studied by Fourier transform infrared spectroscopy (FTIR) and by means of density functional theory (DFT) cluster model calculations. Adsorption sites of tetrahedral and octahedral gallium ions with different numbers of oxygen vacancies have been compared. The electronic properties of the adsorbed molecules have been monitored by computing adsorption energies, optimized geometry parameters, overlap populations, atomic charges, and vibrational frequencies. The gallia-methanol interaction has different behaviors according to the local surface chemical composition. The calculations show that methanol can react in three different ways with the gallia surface giving rise to a nondissociative adsorption, a dissociative adsorption, and an oxidative decomposition. The surface without oxygen vacancies is very reactive and produces the methanol molecule decomposition. The molecule is nondissociatively adsorbed by means of a hydrogen bond between the alcoholic hydrogen atom and a surface oxygen atom and a bond between the alcoholic oxygen atom and a surface gallium atom. Two neighbor oxygen vacancies on tetrahedral gallium sites produce the dissociation of the methanol molecule and the formation of a bridge bond between two surface gallium atoms and the methoxy group.     

DFT Study of Metal Atoms Adsorbed at Low-coordinated Sites of MgO （001） Surface

1 INTRODUCTION The interfaces between metals and oxide play a vital role in many industrial applications: hetero- geneous catalysis, microelectronics, thermal barriers, corrosion protection, metal processing and so on[1]. In catalysis, the choice of metal and oxide support is critical in order to obtain a desired reactivity and selectivity[2]. This is due in part to the inherent reac- tivity of the two components. Also the size and shape of the metal particle, which depend on the choice…     

Cu/MgO催化剂上NO-TPO和CO-NO反应性能

采用TPD技术考察了Cu/MgO催化剂表面NO的脱附和分解。载体MgO表面有两类NO吸附中心,为MgO表面碱中心。负载Cu后,由于Cu覆盖了MgO表面碱中心,使Cu/MgO(>1%)催化剂表面只有吸附在Cu上的NO。热脱附过程伴有明显的分解,产物为N~2,N~2O和O~2。CO-NO反应低温有利于N~2O生成,而高温有利于N~2生成,反应活性与NO-TPD峰温有较好的对应关系。NO在催化剂表面解离(NO~a→N~a+O~a)是CO-NO反应的速控步。     

Experimental and theoretical studies on the reaction of H(2) with NiO: role of O vacancies and mechanism for oxide reduction.

Reduction of an oxide in hydrogen is a method frequently employed in the preparation of active catalysts and electronic devices. Synchrotron-based time-resolved X-ray diffraction (XRD), X-ray absorption fine structure (NEXAFS/EXAFS), photoemission, and first-principles density-functional (DF) slab calculations were used to study the reaction of H(2) with nickel oxide. In experiments with a NiO(100) crystal and NiO powders, oxide reduction is observed at atmospheric pressures and elevated temperatures (250-350 degrees C), but only after an induction period. The results of in situ time-resolved XRD and NEXAFS/EXAFS show a direct NiO-->Ni transformation without accumulation of any intermediate phase. During the induction period, surface defect sites are created that provide a high efficiency for the dissociation of H(2). A perfect NiO(100) surface, the most common face of nickel oxide, exhibits a negligible reactivity toward H(2). The presence of O vacancies leads to an increase in the adsorption energy of H(2) and substantially lowers the energy barrier associated with the cleavage of the H-H bond. At the same time, adsorbed hydrogen can induce the migration of O vacancies from the bulk to the surface of the oxide. A correlation is observed between the concentration of vacancies in the NiO lattice and the rate of oxide reduction. These results illustrate the complex role played by O vacancies in the mechanism for reduction of an oxide. The kinetic models frequently used to explain the existence of an induction time during the reduction process can be important, but a more relevant aspect is the initial production of active sites for the rapid dissociation of H(2).     

Effect of Hydrogen on O2 Adsorption and Dissociation on a TiO2 Anatase (001) Surface

The effect of hydrogen on the adsorption and dissociation of the oxygen molecule on a TiO₂ anatase (001) surface is studied by first‐principles calculations coupled with the nudged elastic band (NEB) method. Hydrogen adatoms on the surface can increase the absolute value of the adsorption energy of the oxygen molecule. A single H adatom on an anatase (001) surface can lower dramatically the dissociation barrier of the oxygen molecule. The adsorption energy of an O₂ molecule is high enough to break the O?O bond. The system energy is lowered after dissociation. If two H adatoms are together on the surface, an oxygen molecule can be also strongly adsorbed, and the adsorption energy is high enough to break the O?O bond. However, the system energy increases after dissociation. Because dissociation of the oxygen molecule on a hydrogenated anatase (001) surface is more efficient, and the oxygen adatoms on the anatase surface can be used to oxidize other adsorbed toxic small gas molecules, hydrogenated anatase is a promising catalyst candidate.