I&EC 112 |
| Zeolites are of significant practical importance, due to their use in technologically important processes such as catalysis, adsorption and separation. Many researchers have been working on the design and tailor-made synthesis of zeolites with unique pore topologies and functionalities for specific applications, which still remains a formidable challenge. In recent years, a series of novel zeolites containing double four membered rings (D4MR) such as ITQ-7, ITQ-17 and ITQ-21 have been synthesis by introducing germanium into the synthesis mixture. While, the structure directing effects of Ge towards D4MR containing structures are well known, little is known about the underlying chemistry. In this work, plane wave Density Functional Theory (DFT) calculations are used to characterize and rationalize the site preferences, energies and structural changes occurring when Ge is gradually substituted into the ITQ-17 framework. Our calculations show that the site preference and energy is strongly dictated by the intrinsic flexibility of a given T-O-T linkage (where T = Si or Ge), which is dictated by the overall lattice structure, coupled with its ability to relax to geometries preferred by Ge. These calculations are extended to incorporate the effect of fluoride anions, which is often present during synthesis. DFT calculations on small molecular fragments are used to explore observed geometric variations in Ge-substituted zeolites and corroborate our findings. Finally, the insight gained from this work is used to develop generalized methods for screening other potential framework substituents. |
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Computational Material Design in Chemical Industries, Sponsored by Novel Chemistry with Industrial Applications Sub-Division
1:30 PM-5:00 PM, Monday, 11 September 2006 Moscone Center -- Room 252/254, Oral
Division of Industrial & Engineering Chemistry |