Lisa M. Knight

Experimental charge density matching approach to zeolite synthesis

Abstract An Experimental Charge Density Matching (ECDM) approach to zeolite synthesis is described. The method features the initial formation of a Charge Density Mismatch (CDM) aluminosilicate reaction mixture characterized by the mismatch between the charge density on the organoammonium structure directing agent (SDA) and the charge density on the potential aluminosilicate network that is expected to form. This amounts to creating an aluminosilicate reaction mixture using a large SDA and a low Si/A1 ratio, but also depends on hydroxide levels and crystallization temperature. The crystallization of a zeolite from such a reaction mixture may be difficult, or even impossible. Crystallization can be induced by the controlled addition of supplemental SDAs that have charge densities that are more suitably matched to that of the desired low ratio aluminosilicate network. Advantages of this approach are greater control over the crystallization process and reliable cooperation of multiple templates. The approach is demonstrated in the TEA-TMA template system, in which the new zeolites UZM-4, UZM-5, and UZM-9 are synthesized.

UZM-13, UZM-17, UZM-19 and UZM-25: synthesis and structure of new layered precursors and a zeolite discovered via combinatorial chemistry techniques

Abstract A combinatorial chemistry investigation screening the abilities of the diethyldimethylammonium (DEDMA), ethyltrimethylammonium (ETMA), and [Me 3 N(CH 2 ) 4 NMe 3 ] 2+ (diquat-4, DQ-4) cations to form zeolites over a range of conditions was carried out. Each of the templates formed a layered precursor; UZM-13, UZM-17, and UZM-19 forming in the DEDMA, ETMA, and DQ-4 systems, respectively. The layered materials are distinct from, but similar to MCM-47 by XRD. The structure of UZM-13 was solved from powder data and was confirmed to contain MCM-47-like aluminosilicate layers. Calcination of these layered materials led to condensation along the b-axis, forming similar 3-dimensional zeolitic species designated UZM-25. However, the UZM-25 derived from the UZM-13 material was superior in crystallinity and had the only XRD pattern that could be indexed. The structure of UZM-25 was determined to be of the CDO structure type, which contains 2-dimensional intersecting 8-ring pores, from both powder and single crystal data.

A novel screening approach utilizing combinatorial methods in the ethyltrimethylammonium template system

Abstract A template screening approach which applies combinatorial methods is used to investigate the structure directing properties of the ethyltrimethylammonium (ETMA) template, both by itself and in combination with other structure directing agents (SDA), in the range Si/Al=2-48. A central theme of the approach is to decouple the elements of zeolite crystallization, namely the silica, alumina and hydroxide sources, from the sources of the additional SDAs that strongly influence crystallization pathways, to more easily elucidate the roles of each in synthesis. This is accomplished by using ETMA aluminosilicate solutions, ETMAOH as the sole hydroxide source and supplemental SDAs (alkali and alkaline earth cations) as salts. The resulting experiment is well integrated with combinatorial methods, yields the new zeolite species UZM-4, UZM-8, UZM-15, UZM-17, and demonstrates the broad potential of a single organic template to make both small and large pore materials.

High Throughput Screening of Complex Hydrides for Hydrogen Storage

The discovery that dopants, such as Ti, cause NaAlH 4 to reversibly desorb H 2 at mild conditions has spurred a great deal of research into complex metal hydrides. However, no complex hydride meets the targets for automotive hydrogen storage. Our approach is to accelerate the rate of discovery of improved hydrides and dopants through the combination of Virtual High Throughput Screening (VHTS) and Combinatorial Synthesis and Screening (CSS). Our CSS methods will allow us to screen thousands of samples in a year. These samples will be prepared by ball milling mixtures of hydrides and dopants similar to the established method of preparing Ti doped NaAlH 4 . VHTS exploits a molecular mechanics method to screen a thousand phases in a month. The combination of combinatorial methods and VHTS will help us discover the most promising complex hydrides for hydrogen storage. We will show the results of our medium throughput CSS and VHTS as applied to the NaAlH 4 –LiAlH 4 – Mg(AlH 4 ) 2 mixed alanate compositions.