合金纳米颗粒的动力学行为及其对小分子气体的吸附

发布时间：2018-04-27 00:10

  本文选题：恒温分子动力学 + 团簇　； 参考：《新疆大学》2017年硕士论文

【摘要】：本文基于恒温分子动力学和第一性原理的密度泛函理论(Density Functional Theory,DFT)计算了如下三部分内容:(1)不同尺寸不同组分的Au-Pd,Au-Ag和Au-Pt双金属团簇的退火行为。(2)纯金属团簇(Au_(13)和Pt_(13))及混合金属团簇(Au_(12)Pt和Pt_(12)Au)的几何结构和电子特性。(3)Rh_n(n=6、7)团簇的基态结构特征,以及在Rh_n(n=6、7)团簇上吸附小分子(H_2、O_2、N_2、NO、CO、NO_2、CO_2、N_2O)体系的基态结构和电子特性。得出的主要结论如下:(1)双金属Au-Pd和Au-Pt团簇在发生退火行为时,其Au原子会发生偏析行为:当Au原子比重少于Pd或Pt原子时,Au原子倾向于占据表面;当两者比重接近时,Au原子则绝大部分占据团簇表面。在双金属Au-Ag团簇中,会发生Ag原子的偏析,其偏析行为与Au-Pd(Au-Pt)团簇中的Au原子类似。在Au-Pt双金属团簇中,随着Au原子比重的增大,其δ-CV曲线将由无序变为有序。(2)基于第一性原理的DFT计算了纯金属团簇(Au_(13)和Pt_(13))及混合金属团簇(Au_(12)Pt和Pt_(12)Au)的几何结构和电子特性。得到的结果表明:找到了Pt_(13)团簇新的基态候选者,13个原子的纯金属团簇存在明显的低能同分异构现象(特别是Au_(13)团簇),但是通过掺杂Au(Pt)元素可抑制原团簇的同分异构现象;在计算垂直电离能(Vertical Ionization Potential,VIP)和垂直电子亲和势(Vertical Electron Affinities,VEA)时发现,Au_(13)团簇的VIP和VEA的值与实验值及其相近(存在相对论的情况下),掺杂对VIP和VEA的影响较小,但是掺杂可以改变团簇费米能处d电子的分布,团簇费米能处的d电子分布情况可能与其催化活性相关。(3)采用第一性原理的DFT计算研究了Rh_n(n=6、7)团簇的基态结构特性以及Rh_n(n=6、7)团簇吸附小分子气体(H_2、O_2、N_2、NO、CO、NO_2、CO_2,N_2O)基态几何结构和电子结构特性。计算结果表明:Rh6团簇的基态结构的对称性为Oh且不存在低能同分异构体;Rh7团簇基态结构存在竞争性。在Rh6团簇上发生物理吸附的气体有O_2、N_2、NO、CO和CO_2;在Rh7团簇A结构上发生物理吸附的气体有O_2、N_2、CO、CO_2、NO;在Rh7团簇B结构上发生物理吸附的气体有H_2、O_2、N_2、CO、CO_2、NO、NO_2。这八种气体在三个结构上均能发生化学反应的是N_2O。就发生物理吸附的气体而言,Ead(NO)Ead(O_2)≈Ead(NO_2)≈Ead(CO)Ead(N_2)≈Ead(CO_2)Ead(H_2)。在与八种气体的相互作用中,存在电荷转移。电荷转移的多少,与气体分子中是否含有O元素相关,气体中存在O元素,则能得到更多的电子。就发生物理吸附的气体而言,电荷转移情况:q(CO_2)≈q(O_2)q(NO_2)q(NO)≈q(CO)q(N_2)q(H_2)。
[Abstract]:Based on the isothermal molecular dynamics and first-principles density functional theory (Density Functional Theoryn DFT), the annealing behavior of Au-PdU Au-Ag and Au-Pt bimetallic clusters with different sizes and different sizes are calculated as follows: Au-PdU Au-Ag and Au-Pt bimetallic clusters. The geometric structure and electronic properties of the mixed metal cluster (AuSch 12Pt and PtSZ 12Au.) the ground state structure characteristics of the mixed metal cluster, And the ground state structure and electronic properties of the adsorbed small molecule S / H _ 2O _ 2N _ T _ 2N _ T _ 2NOT _ 2N _ 2C _ 2C _ 2T _ 2C _ 2C _ 2C _ 2T _ 2C _ 2C _ 2C _ 2C _ 2C _ 2T _ 2O _ 2N _ 2C _ 2C _ 2N _ 2O _ The main conclusions are as follows: (1) the au atoms of bimetallic Au-Pd and Au-Pt clusters tend to segregate when annealing occurs: the au atoms tend to occupy the surface when the specific gravity of au atoms is less than PD or Pt atoms; When the specific gravity of the two atoms is close, the au atoms occupy most of the surface of the cluster. The segregation of Ag atoms occurs in bimetallic Au-Ag clusters, and the segregation behavior is similar to that of au atoms in Au-PdO Au-Pt) clusters. In Au-Pt bimetallic clusters, with the increase of au atom specific gravity, the 未 -CV curve will change from disorder to order.) based on the first-principle DFT, the geometric structure and electronic properties of pure metal clusters (AuStuc 13) and PTS (13) and mixed metal clusters (Austi 12Pt and PTV 12Au2) have been calculated. The results show that a new ground state candidate has been found. The pure metal clusters of 13 atoms have obvious low energy isomerism (especially AuStue 13) clusters, but the homogeneity phenomenon of the original clusters can be restrained by doping the Autopt13 elements. In the calculation of Vertical Ionization potential VIPs and Vertical Electron affinities (VEAA), it is found that the VIP and VEA values of these clusters are similar to those of the experimental ones (where relativistic is present, the influence of doping on VIP and VEA is relatively small. But doping can change the distribution of d electrons at the Fermi energy of clusters. The distribution of d electrons at Fermi energy in the cluster may be related to its catalytic activity. (3) the ground state structure and electronic structure characteristics of the main structure and electronic structure of the Rh / S / S / C / S / S / C / S / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C / C clusters are studied, and the ground state structure and electronic structure characteristics of the clusters are studied by first-principle DFT calculations than by using the first principle DFT method. The results show that the symmetry of the ground state structure of the 1: Rh6 cluster is Oh and there is no competitive ground state structure of the low energy isomer Rh7 cluster. The gas of physical adsorption on Rh6 cluster is O _ 2O _ 2S _ 2NOCO and CO _ 2s _ 2; the gas of physical adsorption on Rh7 cluster A is O _ 2N _ 2C _ 2C _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O _ 2no _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O _ 2O It is N _ 2O _ 2 that can react on all three structures of these eight gases. As far as the gas for physical adsorption is concerned, Eadnou No2) 鈮，

本文编号：1808291