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Synthesis of Ultrathin MFI Zeolite with a Single-Unit-Cell Thickness

2009년 8월 10일 17시 25분 49초
금29B10구 이곳을 클릭하시면 발표코드에 대한 설명을 보실 수 있습니다.
금 16시 : 40분
재료화학 - Recent Progresses in Materials Chemistry
저자 및
나경수, 김정남, 유룡
KAIST 화학과, Korea
Zeolites are microporous crystalline aluminosilicates, which have been widely used as catalysts in petrochemistry and fine-chemical synthesis. Strong acid sites in the uniform micropores (diameter < 1 nm) enables size- and shape-selective catalyses. Despite the advantages, the sole presence of microporosity often imposes a diffusion limitation. Reactions involving larger molecules than micropores cannot be hosted by zeolites. In the diffusion-controlled regime, only the outer rim of zeolite crystals (typically synthesized in micrometer length scale) participates in catalytic reactions, leading to cokes formation and a loss of catalytic activity. Syntheses of zeolite nanocrystals, exfoliation of layered zeolites, and mesopore generation via templating strategies or demetallation processes were demonstrated as a means of reducing zeolite thickness and thereby achieving a minimal diffusion path length. In this presentation, we present a zeolite synthesis strategy using bifunctional surfactants that can direct structures in meso- and micro-length scales simultaneously. This led to direct crystallization of MFI zeolite nanosheets, in which the framework thickness corresponded to only a single unit cell dimension along b-axis (2.0 nm). Due to the large amount of acid sites on the external surface, the zeolites were highly active for catalytic conversion of large organic molecules. Furthermore, as compared with bulk zeolite crystals, the zeolite nanosheets exhibited a dramatic increase of catalyst lifetime in methanol-to-gasoline (MTG) conversion.