%0 Journal Article
%T Catalytic Mechanism of Pd Adsorption on S-Terminated GaAs(001)-(2 ¡Á 6) Surface
%A Deng-feng Li
%A Zhi-cheng Guo
%A Bo-Lin Li
%A Ming Luo
%J Advances in Condensed Matter Physics
%D 2013
%I Hindawi Publishing Corporation
%R 10.1155/2013/130868
%X Structural and electronic properties of Pd adsorption on clean and S-terminated GaAs(001)-(2 ¡Á 6) surfaces are studied using first-principle simulations. Our calculations show that the Pd atom prefers to occupy the HH3 site. The Pd atom is lower than the S atom with 0.15£¿£¿. The density of states analysis confirms that S¨CGa bond plays an important role in Heck reaction. We also find that the Pd catalysis activity for Pd adsorption on clean GaAs(001)-(2 ¡Á 6) surface is weak while it is enhanced when the Pd atom is adsorbed on the S-terminated GaAs(001)-(2 ¡Á 6) surface, which is in good agreement with the experiments. 1. Introduction Transition metals such as palladium (Pd) and platinum (Pt) are very important catalysts in the field of synthetic chemistry since they have favorable catalysis properties in Heck reaction [1¨C3]. Heck reaction plays an important role in drug discovery and pharmaceutical industries. However, the homogeneous Pd catalysis has some disadvantages, such as low reusability, difficulty of separating the catalyst from the products or solvents after reaction. Recently, heterogeneous catalyst has been extensively investigated in order to reduce the waste of noble metal and develop the high yield of Heck reaction. For Pd adsorption on the sulfur-terminated GaAs(001) surface, experimental results show that the Pd catalyst is reusable [4¨C8]. Arisawa et al. prepare it with Pd(PPh3)4 [5]. They find that Pd is adsorbed on the S-terminated GaAs surface by X-ray photoelectron spectroscopy (XPS) and Pd can be reused at least 3 times. Takamiya et al. find that Ga¨CS bond fixes Pd on S-terminated GaAs(001)-( ) surface [6, 7], which plays an important role in Heck reaction. It effectively enhances the activity of the Heck reaction more than homogeneous Pd catalyst and could be recycled at least 10 times. In their further study [8], using a new Pd source of Pd(OAc)2 and another technique of heated washing, they obtain a higher catalysis activity and stability for Heck reaction than the sophisticated method of deposition organometallic Pd(PPh3)4 on S-terminated GaAs(001)-( ) surface. Recently, Konishi et al. report that S-GaAs( ) surface structure is preserved after deposition Pd(CH3COO)2 on its surface using reflection high-energy electron diffraction (RHEED) and scanning tunneling microscopy (STM) [9]. However, the detailed structure and micromechanism are unknown. Earlier theoretical study is focused on the system of Pd adsorption on S-terminated GaAs(001)-( ) surface [10], which is different from the experiments [7, 9, 11]. In this paper, in order
%U http://www.hindawi.com/journals/acmp/2013/130868/