在不同构型分子筛催化剂中吸附和扩散的分子模拟

基于巨正则蒙特卡洛和分子动力学，对NH₃-SCR反应体系中吸附质分子（NO与NH₃）在不同拓扑结构沸石分子筛（LTL、FER、LEV、BEA、MOR、FAU、CHA和MFI）上的吸附和扩散特性进行系统研究。结果表明，对于全硅分子筛而言，其分子筛的拓扑结构影响NO与NH3在分子筛上的吸附，综合吸附量及吸附作用能发现，MFI和LEV分子筛对NO具有较优的吸附特性；MFI和BEA分子筛对NH₃ 具有较优的吸附特性。研究了Si与Al物质的量比对BEA分子筛吸附性能影响，结果表明，随着Si与Al物质的量比降低，分子筛自由体积逐渐增加，进而有助于分子筛催化剂对NO和NH₃的吸附。采用分子动力学模拟计算NO与NH₃在不同构型全硅分子筛上的扩散系数，发现具有三维直通道且孔径较大的分子筛催化剂有利于NO和NH₃在其孔道内部的扩散，MFI虽然具备三维孔道结构，但由于存在Z型交叉通道，一定程度阻碍了反应物分子的扩散。

Molecular simulations of adsorption and diffusion of NO and NH3 over zeolite catalysts with various structure configurations

The adsorption and diffusion of NO and NH₃ as the reactant of NH3-SCR reaction system over various kinds of zeolite catalysts (LTL,FER,LEV,BEA,MOR,FAU,CHA,MFI) were investigated by employing molecule simulation methods of Monte Carlo and Molecular Dynamics.The results indicated that the zeolitic topology greatly influenced the adsorption of NO and NH₃ molecules according to the simulation results of adsorption amount and adsorption energy.Accordingly,it was found that MFI and LEV were efficient for NO adsorption,and MFI and BEA were efficient for NH3 adsorption.The effects of Si/ Al molar ratio on the adsorption of NO and NH₃ over BEA zeolite were also studied.The study showed that the free volume of zeolite catalysts gradually increased along with the decrease of Si/Al molar ratios,which facilitated the adsorption of NO and NH₃.The molecular dynamics was further employed for the calculations of diffusion coefficient of NO and NH₃ on all-silicon zeolites with different topological structure.It was found that 3 dimensional straight channel and large pore size contributed to better diffusions of NO and NH₃ molecules.Although MFI zeolite also possessed three dimensional pore structures,it hindered the diffusion of reactant molecules to some extent due to the presence of Z type cross channel.