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

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

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.

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 Dmol^3 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-[Al]MOR, Cu-[Al]MOR and Ag-[Al]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.