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Synthesis and 129Xe NMR Characterization of LTA Zeolite with Controlled Mesoporosity

2009년 8월 10일 16시 53분 49초
금29B4구 이곳을 클릭하시면 발표코드에 대한 설명을 보실 수 있습니다.
금 14시 : 30분
재료화학 - Recent Progresses in Materials Chemistry
저자 및
조강희, 유룡
KAIST 화학과, Korea
A series of mesoporous LTA zeolite samples was hydrothermally synthesized by using various amounts of 3-(trimethoxysilyl)propyl hexadecyl dimethylammonium chloride as the mesopore-generating agent. The LTA zeolite exhibited a fairly narrow distribution of mesopore diameter, as indicated by N2 adsorption isotherms. The pore diameter at the maximum of distribution shifted gradually from 6 to 10 nm with increasing the amount of the organosilane surfactant. The mesopore diameters were somewhat larger than the values that could be expected from the size of the surfactant molecules. Successive analyses of the pore diameters as synthesized, after solvent washing, and also after calcination in air revealed that the large mesopores were templated by surfactant micelles which were expanded by the excessive surfactants. The mesopores were disordered and 3-dimensionally interconnected as shown in transmission electron micrographs taken after generation of Pt nanowires. Molecular diffusion into the LTA zeolite was characterized by 129Xe NMR spectroscopy after xenon was put in contact for 12 h under 1 atm at 297 K. In the case of the most highly mesoporous zeolite, the 129Xe NMR spectrum clearly showed six peaks corresponding to xenon atoms located in the zeolite micropores. On the other hand, the solely microporous LTA zeolite showed no conspicuous 129Xe NMR signals. This 129Xe NMR experiment provided direct evidence for rapid transport of xenon into the zeolitic micropores via mesopores. The adsorption analysis revealed that the xenon diffusion into the mesoporous LTA zeolite occurred 200 times more rapidly than diffusion into solely microporous zeolite.