物理化学学报 >> 2009, Vol. 25 >> Issue (10): 2123-2129.doi: 10.3866/PKU.WHXB20091040

研究论文 上一篇    下一篇

Cu-[M’]MOR和Ag-[M’]MOR (M’=B, Al, Ga, Fe)的酸性

刘洁翔, 魏贤, 张晓光, 韩恩山   

  1. 河北工业大学化工学院, 天津 300130|南开大学化学学院, 天津 300071
  • 收稿日期:2009-04-13 修回日期:2009-07-03 发布日期:2009-09-29
  • 通讯作者: 刘洁翔, 张晓光 E-mail:jxliu@hebut.edu.cn; xgzhang@nankai.edu.cn

Acidities of Cu-[M’]MORand Ag-[M’]MOR (M’=B, Al, Ga, Fe)

LIU Jie-Xiang, WEI Xian, ZHANG Xiao-Guang, HAN En-Shan   

  1. School of Chemical Engineering, Hebei University of Technology, Tianjin 300130, P. R. China|College of Chemistry, Nankai University, Tianjin 300071, P. R. China
  • Received:2009-04-13 Revised:2009-07-03 Published:2009-09-29
  • Contact: LIU Jie-Xiang, ZHANG Xiao-Guang E-mail:jxliu@hebut.edu.cn; xgzhang@nankai.edu.cn

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摘要：

采用Dmol3程序中基于密度泛函理论(DFT)的广义梯度方法(GGA)和BLYP方法以及DND基组, 研究了丝光沸石H-[M']MOR、Cu-[M']MOR和Ag-[M']MOR(M'=B, Al, Ga, Fe)结构及其对NH3分子的吸附, 获得了吸附平衡构型和吸附能. NH3分子在H-[M']MOR中的吸附主要是通过NH3分子中氮原子上的孤对电子与质子酸位作用, NH3分子在H-[Al]MOR、H-[Ga]MOR和H-[Fe]MOR上发生化学吸附, 而在H-[B]MOR上发生物理吸附, 这与文献结果相符. NH3分子与Cu-[M']MOR 和Ag-[M']MOR分子筛之间主要通过氮上的孤对电子和平衡离子(Cu+和Ag+)的s空轨道间配位作用而发生化学吸附. 吸附能数据表明, 在H-[M']MOR、Cu-[M']MOR 和Ag-[M']MOR中, A1原子进入骨架导致H-[A1]MOR、Cu-[A1]MOR和Ag-[A1]MOR的酸强度最强; 对于同一种原子取代的丝光沸石, 其酸强度次序为: Cu-[M']MOR > Ag-[M']MOR > H-[M']MOR. 此外, 还对吸附前后的沸石中平衡离子(H+、Cu+和Ag+)及NH3分子的Mulliken电荷集居数作了研究和分析.

关键词: 丝光沸石, 杂原子, 平衡离子, 酸性, 密度泛函理论

Abstract:

NH3 adsorption in Mordenties H-[M']MOR, Cu-[M']MOR, and Ag-[M']MOR (M'=B, Al, Ga, Fe) was investigated using density functional theory (DFT) with the generalized gradient approximation (GGA) and the Becke exchange plus Lee-Yang-Parr correlation (BLYP) method as well as the DND basis set in the Dmol3 module. Equilibrium configurations and adsorption energies of NH3 in H-[M']MOR, Cu-[M']MOR, and Ag'[M']MOR were obtained and discussed. NH3 was adsorbed in H-[M']MOR by the interaction between the lone electron pair of nitrogen and the proton acidic site. NH3 was adsorbed in H-[Al]MOR, H-[Ga]MOR, and H-[Fe]MOR by chemical adsorption and in H-[B]MOR by physical adsorption which agreed well with results from the literature. NH3 was adsorbed in Cu-[M']MOR (or Ag-[M']MOR) through the chemical adsorption between the lone electron pair of nitrogen and the s empty orbital of the Cu+ (or Ag+) cation. Calculated adsorption energies showed that the acidities of H-[A1]MOR, Cu-[A1]MOR and Ag-[A1]MOR were the strongest among all the H-[M']MOR, Cu-[M']MOR and Ag-[M']MOR, respectively. The acidity decreased as follows: Cu-[M']MOR>Ag-[M']MOR>H-[M']MOR for the same atom substitution. In addition, Mulliken populations of counterpoise ions (H+, Cu+, and Ag+) and the NH3 molecule were also investigated and analyzed before and after adsorption.

Key words: Mordenite, Heteroatom, Counterpoise ion, Acidity, Density functional theory