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

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.

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

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.