氢原子在镍台阶面上吸附、振动和表面扩散行为的理论研究

本文用对势方法研究了氢原子在Ni(510)台阶面上的吸附和振动, 计算结果与实验符合得很好。并考察了氢原子在Ni(997)台阶面上的吸附和扩散, 结果表明,台阶对下台面上扩散的氢原子开成捕获势阱, 对上台面扩散的氢原子形成反射势,这也很好地支持了实验结果。     

氮原子在Ni平坦和缺陷表面上的吸附和振动

 构造了氮－镍相互作用的5－参数Morse势，研究了氮原子在Ni（\r\n100），Ni（110）和Ni（111）平坦表面的吸附和振动，获得了氮原子\r\n在三个低指数表面的吸附位、吸附构型、结合能和本征振动等数据，计\r\n算结果与实验结果非常吻合．同时，与Ni（100）表面对比，系统研究\r\n了氮原子在Ni（510）台阶面的吸附和扩散．计算结果表明，氮原子在\r\n台阶下部形成最稳定的吸附态，台阶对下台面上扩散的氮原子形成捕获\r\n势，对上台面上扩散的氮原子形成反射势．     

Ni(115)台阶面对氢表面微观动力学行为的影响

用５参数Ｍｏｒｓｅ势模拟氢－镍表面体系相互作用势，考察了氢原子在Ｎｉ（１１５）台面上吸附扩散行为。同时构造了氢分子与Ｎｉ（１００）和Ｎｉ（１１５）台阶面 相互作用推广的ＬＥＰＳ势面面，考察了氢分子解离化学吸附的微观动力学性质。     

氢原子在金属锂表面台阶附近吸附和表面扩散行为的ab initio研究

取Li7H和Li9H两个原子簇模拟氢原子与含台阶的金属锂表面的相互作用, 以小基组用ab initip方法计算了体系的吸附和表面扩散势能面(或势能曲线)。结果表明: (1)对Li7H体系, 台阶面附近沿垂直边棱方向存在三种不同的桥位吸附位, 最稳定的吸附位在上台面接近台阶边棱处, 台阶面显著地改变了表面扩散活化能, 台阶边棱处有一个较高的势垒。于是, 迁移原子将会在台阶边棱处受到反射, 并可被捕获于台阶面上及其附近。由势能面确定了最低能量表面扩散途径。(2)对Li9H体系, 在Li7H原子簇基础上增加次表面层两个锂原子后, 表面扩散活化能略有减小, 氢原子在上台面的桥位吸附更趋稳定, 各吸附位相对稳定性及势垒内何位置几无改变, 这些结果显示了台阶面对氢原子的化学吸附和表面扩散发生扰动, 台阶边棱对表面扩散起着重要作用。     

氢原子在金属锂表面台阶附近吸附和表面扩散行为的ab initio研究

取Li_7H和Li_9H两个原子簇模拟氢原子与含台阶的金属锂表面的相互作用,以小基组用abinitio方法计算了体系的吸附和表面扩散势能面(或势能曲线),结果表明:(1)对Li_7H体系,台阶面附近沿垂直于边棱方向存在三种不同的桥位吸附位,最稳定的吸附位在上台面接近台阶边棱处,台阶面显著地改变了表面扩散活化能,台阶边棱处有一个较高的势垒,于是,迁移原子将会在台阶边棱处受到反射,并可被捕获于台阶面上及其附近,由势能面确定了最低能量表面扩散途径,(2)对Li_9H体系,在Li_7H原子簇基础上增加次表面层两个锂原子后,表面扩散活化能略有减小,氢原子在上台面的桥位吸附更趋稳定,各吸附位相对稳定性及势垒几何位置几无改变,这些结果显示了台阶面对氢原子的化学吸附和表面扩散发生扰动,台阶边棱对表面扩散起着重要作用。     

氢原子在钯低指数表面上的吸附和扩散

采用氢－钯相互作用的五参数Ｍｏｒｓｅ势，用对势方法研究了氢原子在Ｐｄ（１００）、Ｐｄ（１１１）和Ｐｄ（１１０）低指数平坦表面上的吸附和扩散，得到氢原子在三个表面上的吸附位、吸附几何、结合能和本征振动等数据，计算结果和实验结果符合得很好。在此基础上，系统地研究了三个系统的吸附扩散势能面结构。     

氢原子在Ni(111)次表面和Ni(211)、(533)台阶面上的吸附与振动

应用原子与表面簇合物相互作用的五参数Morse势(5-MP)方法对氢原子在Ni(111)表面和次表面以及Ni(211), (533)台阶面进行了系统研究, 得到了氢原子在上述各面的吸附位、吸附几何、结合能和本征振动频率. 计算结果表明, 在Ni(111)面上, 氢原子优先吸附在三重位, 随着覆盖度的增加会吸附在次表面八面体位和四面体位. Ni(211), (533)的最优先吸附位都是四重位, 当氢原子的覆盖度增大时占据(111)平台的三重吸附位. 靠近台阶面的吸附位受台阶和平台高度的影响很大. 此外, 我们计算了氢原子在各表面的不同吸附位的扩散势垒, 获得氢原子在各表面的最低能量扩散通道.     

氢原子在Ru(0001)和Ru(1010)面上吸附扩散势能面的结构

本文构造了H-Ru相互作用的五参数Morse势,用经典的对势方法研究了氢原子在Ru(0001)和Ru(1010)面上的吸附和扩散,得到了氢原子在两个表面上的吸附位、吸附几何、结合能及本征振动等数据与实验结果符合得很好;同时研究了两个体系的吸附扩散势能面结构。     

氢原子在Ru(0001)和Ru(100)面上吸附扩散势能面的结构

本文构造了H—Ru相互作用的五参数Morse势,用经典的对势方法研究了氢原子在Ru(0001)和RU(1010)面上的吸附和扩散,得到了氢原子在两个表面上的吸附位、吸附几何、结合能及本征振动等数据与实验结果符合得很好;同时研究了两个体系的吸附扩散势能面结构.     

氢原子在Ni(100), Ni(111)和Ni(110)面上吸附扩散势能面的结构

本文构造了氢-镍相互作用的5参数Morse势, 用经典的对势方法研究氢原子在Ni(100), Ni(111)和Ni(110)面上的吸附和扩散, 得到氢原子在三个表面上的吸附位、吸附几何、结合能及本征振动等数据, 和实验结果符合得很好。同时, 系统地研究了三个体系的吸附扩散势能面结构。     

氢在Ni(511)台阶面的吸附与解离研究

The adsorption and dissociation of hydrogen on stepped surface (511) of nickel are studied with the embedded-atom model (EAM) method. The adsorption energy, the length of the adsorption bond and the adsorption height for a single hydrogen atom are calculated. Three kinds of stable sites are found for hydrogen adsorption. There are the double-fold bridge site B on the step edge, the three-fold hollow site H3′ on the step surface and the four-fold hollow sites H1 and H2 on the terrace surface. Compared with a hydrogen atom adsorbed on low-index (001) surface, there are two other adsorption sites near the step: the two-fold bridge site B on the step edge and the three-fold hollow site H3′ on the step surface. At the same time, the absorbability of the hydrogen atom at the site H1 is intensified. The results show that hydrogen adsorption on Ni (511) is affected by the existence of the step. The active barriers, adsorption energy and corresponding bond length for dissociation of a hydrogen molecule on the stepped surface are presented. The results show that the dissociation is easier at the bottom of the step. It is shown that the steps are the active sites for hydrogen adsorption and dissociation.     

Adsorption of carbon monoxide on Pd (210) and (510) surfaces

Adsorption of carbon monoxide on Pd (210) and (510) stepped surfaces has been investigated by the extended London‐Eyring‐Polyani‐Sato method constructed using a five‐parameter Morse potential. Pd (210) and (510) stepped surfaces consist of terrace with (100) structure and step with (110) character. These results show that there exist common characteristics of CO adsorption on these two surfaces. At low coverage, CO adsorbs in twofold bridge site of the (100) terrace. The critical characteristics inherit that of CO molecule adsorbed in twofold bridge site of (100) original surface. When the coverage is increased, the top site of (110) step is occupied. The critical characteristics resemble that of CO molecule adsorbed in top site of (110) original surface. A number of new sites are exposed on the boundary regions, for example, the fivefold hollow site (H) of these two surfaces. There are stable adsorption sites at high coverage. Because of the different length of the (100) terrace, the (210) and (510) stepped surfaces have some different characteristics. First, CO is tilted adsorption on bridge site of terrace of (210), but perpendicular on terrace of (510) surface. Second, the bridge site (B₁) where one Pd atom at the top of the step and the other at the bottom of the step is a stable adsorption site on (210), but the same type of site on Pd (510) surface is not. Copyright © 2012 John Wiley & Sons, Ltd.     

Study of Hydrogen Adsorption on Pt/WO3-ZrO2 through Pt Sites

The rate determining step and the energy barrier involved in hydrogen adsorption on Pt/WO_3- ZrO_2 were studied based on the assumption that the hydrogen adsorption occurs only through Pt sites. The rate of hydrogen adsorption on Pt/WO_3-ZrO_2 was measured in the adsorption temperature range of 323-573 K and an initial hydrogen pressure of 50 Torr.The rates of hydrogen uptake were very high for the initial few minutes and the adsorption continued for more than 5 h below 523 K.The hydrogen uptake far exceeded the H/Pt ratio of unity for all adsorption temperatures,indicating that the adsorption of hydrogen involved the dissociative adsorption of hydrogen on Pt sites to form hydrogen atoms,the spillover of hydrogen atoms onto the surface of the WO_3-ZrO2 catalyst,the diffusion of spiltover hydrogen atom over the surface of the WO_3-ZrO_2 catalyst,and the formation of protonic acid site originated from hydrogen atom by releasing an electron in which the electron may react with a second hydrogen atom to form a hydride near the Lewis acid site.The rate determining step was the spillover with the activation energy of 12.3 kJ/mol.The rate of hydrogen adsorption cannot be expressed by the rate equation based on the assumption that the rate determining step is the surface diffusion.The activity of Pt/WO_3-ZrO_2 was examined on n-heptane isomerization in which the increase of hydrogen partial pressure provided positive-effect on the conversion of n-heptane and negative-effect on the selectivity towards iso-heptane.     

Adsorption, vibration, and diffusion of O atoms on Rh low-index and (711) stepped defective surfaces

The adsorption, vibration, and diffusion of O atoms on Rh(100), Rh(111), Rh(110), and Rh(711) surfaces were studied using the 5-parameter Morse potential (5-MP) of interaction between an adatom and a metal surface cluster. Our theoretical calculations provide information about adsorption sites, adsorption geometry, binding energy, and eigenvibration. Our results agreed very well with experimental results. Four major results follow. First, the theoretical calculation showed that on the Rh(100) surface the 4-fold hollow site is the only adsorption site. Second, on the O-Rh(111) system, the 3-fold hollow site is the stable adsorption site. Third, on the Rh(110) surface at low coverage, the O atom is adsorbed preferably on the pseudo-3-fold site, while with increasing coverage, the O atom is adsorbed not only on the pseudo-3-fold site but also on the long bridge site. Last, as for the Rh(711) stepped surface, the 3-fold site on the (111) step is metastable, whereas the 4-fold sites on the (100) terrace are stable, which enables the O atoms to diffuse easily from the 3-fold to the 4-fold site at low coverage. Therefore, the O atoms are adsorbed preferrably on the stable 4-fold sites of the (100) terrace and then later as coverage increases on the metastable 3-fold site of the (110) step.     

TPD and FT-IRAS investigation of ethylene oxide (EtO) adsorption on a Au(211) stepped surface

Adsorption of ethylene oxide, CH(2)CH(2)O (EtO), on a Au(211) stepped surface was studied by temperature programmed desorption (TPD) and Fourier transform infrared reflection-absorption spectroscopy (FT-IRAS). Ethylene oxide was completely reversibly adsorbed, and desorbed molecularly during TPD following adsorption on Au(211) at 85 K. EtO TPD peaks appeared at 115 K from the multilayer film and 140 and 170 K from the monolayer. Desorption at 140 K was attributed to EtO desorption from terrace sites, and that at 170 K to EtO desorption from step sites. Desorption activation energies and corresponding adsorption energies were estimated to be 8.4 and 10.3 kcal mol(-1), respectively. The EtO ring (C(2)O) deformation band appeared in IRAS at 865 cm(-1) for EtO in multilayer films and when adsorbed in the monolayer at terrace sites. The stronger chemisorption bonding of EtO at Au step sites slightly weakens the bonding within the molecule and causes a small red-shift of this band to 850 cm(-1) for adsorption at step sites. EtO presumably binds via the oxygen atom to the surface, and observation of the EtO-ring absorption band in IRAS establishes that the molecular ring plane of EtO adsorbed at step and terrace sites is nearly upright with respect to the crystal surface plane.