The work presented in this thesis addresses the synthesis of nanomorphic zeolites with controlled thickness and their catalytic application. Zeolites are a family of crystalline aluminosilicates exhibiting ordered micropores. Due to their micropores at the molecular scale and their acidity, they have been widely used in catalysis and separation. Conventional zeolites synthesized with the use of small organic ammonium ions or alkali metals as structure-directing agents (SDAs) typically have micrometer-sized crystals. The limited diffusion of molecules in the crystals often induces an overload on the crystal surface and fast deactivation. To solve this problem, decreasing the diffusion length has been intensively investigated by the synthesis of zeolite as nanomorphic structures. Among the large number of approaches tried, use of an organic surfactant that is functionalized with a zeolite structure-directing group as SDA is one of the most promising strategies. In this thesis, MFI zeolites were synthesized using a small amount of $C_{18} H_{37}-N^{+}(CH^3)_{2} -C_{6}H_{12} -N^{+} (CH_{3})_{2}-C_{6}H_{13}(Br^{-})_{2}$ surfactant $(C_{18-6-6})$ in the absence and presence of $Na^{+}$. In the presence of $Na^{+}$, 2.5 nm thick MFI nanosheets were generated followed by the progressive growth of the nanosheets with the consumption of amorphous aluminosilicate. Under $Na^{+}$-free conditions, the product consisted of 2.5 nm thick nanosheet and amorphous product. It was clearly elucidated that C18-6-6 acted as a SDA for the 2.5 nm zeolite nanosheets, and $Na^{+}$ was involved in the structure direction of the MFI to grow the nanosheets. The structure direction of $C_{18-6-6}$ and $Na^{+}$ was systematically balanced to control the thickness of the MFI zeolites in the range of 2.5 to 20 nm. In addition, the properties of the zeolites were characterized and compared in the conversion of methanol to hydrocarbons. Thicker crystals exhibited higher hydrocarbon yields and shorter lifetimes. These results are explained by the hydrocarbon-pool mechanism and the diffusion in crystals.
계면활성제 $C_{18} H_{37}-N^{+}(CH^3)_{2} -C_{6}H_{12} -N^{+} (CH_{3})_{2}-C_{6}H_{13}(Br^{-})_{2} (C_{18-6-6})$는 2.5 나노미터 두께의 MFI 제올라이트에 대한 구조 유도체로 잘 알려져 있다. 본 학위논문에서는 MFI 제올라이트의 합성에서 $C_{18-6-6}$ 계면활성제를 제한된 양만 사용하여 소듐 이온의 존재 여부에 따라 구조유도 방식이 어떻게 달라지는지 연구하였다. X선 회절 패턴과 전자현미경 사진을 통해 각 합성에서의 시간에 따른 변화를 분석하였다. 그 결과, $C_{18-6-6}$ 계면활성제가 소듐 이온보다 먼저 구조 유도체로 작용하여 2.5 나노미터 두께의 MFI 제올라이트를 소량만 형성하고, 소듐 이온은 나머지 부분을 먼저 형성된 제올라이트를 성장시키는 방향으로 구조유도 작용을 한다는 것을 밝혀냈다. 이 결과를 이용하여 소듐 이온이 존재하는 조건에서 $C_{18-6-6}$ 계면활성제의 양에 따라 MFI 제올라이트의 최종 두께를 20 나노미터까지 체계적으로 변화시킬 수 있었다. 또한, 두께가 조절된 MFI 제올라이트를 메탄올 탄화수소화 반응에 사용하여 제올라이트 결정의 두께가 반응성에 주는 영향에 대해 고찰하였다.
