### MD模拟研究MFI沸石晶体双模板剂择优生长机理

1. 复旦大学化学系 上海市分子催化与新材料重点实验室 上海 200433
• 投稿日期:2012-03-04 发布日期:2012-05-29
• 通讯作者: 龙英才 E-mail:yclong@fudan.edu.cn
• 基金资助:
项目受国家基础研究发展计划(No. 2003CB615801)和国家自然科学基金(Nos. 20073010, 20025310)资助.

### Growth Mechanism Study on b-axis Oriented MFI Zeolite with MD Simulation

Yu Hui, Guo Juan, Wang Jing, Long Yingcai

1. Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Department of Chemistry, Fudan University, Shanghai 200433
• Received:2012-03-04 Published:2012-05-29
• Supported by:
Project supported by the Basic Research Program of China (No. 2003CB615801) and the National Natural Science Foundation of China (Nos. 20073010, 20025310).

Co-templating role in the growth of b-axis oriented siliceous MFI type zeolite crystals was studied by molecular dynamic (MD) simulation. A siliceous supercell consisting of 2×2×2 unit cell is adopted as the inner part of the simulated structure for the zeolite. The crystal structures, adopted as simulated growing part of the zeolite, are four cleavage surface models along a or b axis individually, which cleaved from a supercell consisting of 1×1×2 unit cell and the Si-O hanging bonds are saturated by H atoms. The dynamic behaviors of two templates (n-propylamine and hexamethylene tetramine) in the cages of channel intersections and the opening channel windows were investigated with NVT MD simulations in 450 K for 5×105 fs each run, using pcff forcefields. The simulations were performed by Discover module from Accelrys Material Studio. The interaction energies between the templates and the zeolite, and the average values of coordinates imaging the trajectories of the templates in times of whole MD simulation, are used as two indicators for investigating the dynamic adsorption sites and the size match with the channel wall for the templates. The results indicate: (1) hexamethylene tetramine (HMTA) molecule is hold at the opening window of the channel along a axis (site I) and extruded out of the opening window of channel along b axis (site III) to nearby crystal-growing site (site IV); (2) mean-squared-displacement (MSD) analysis reveals that strong interaction exists between n-propylamine molecule and the zeolite because of the fact that N-atom is sticking to the adsorption site while other atoms of the molecule are rotating and moving with freedom. On the other hand, all atoms of HMTA molecule are almost frozen in the constrained space of the channel cage. As an evidently deduction, n-propylamine molecules play a major directing role in the formation and the growth of the zeolite crystals, while HMTA molecules promote the growth of the crystal surface along a axis and impede the growth of the crystal surface along b axis.