Abstract
Zeolites with large cavities that are accessible via wide pore windows are desirable but very rare. They have been dominantly used as catalysts in industry. Here we report a novel porous germanosilicate SCM-25, the zeolite structure containing ordered meso-cavities (29.9 × 7.6 × 6.0 Å3) interconnected by 10- and 12-ring channels. SCM-25 was synthesized as nanosized crystals by using a simple organic structure-directing agent (OSDA). Three-dimensional (3D) electron diffraction shows that SCM-25 crystallizes in the orthorhombic space group Cmmm with a = 14.62 Å, b = 51.82 Å, c = 13.11 Å, which is one of the zeolites with the largest unit cell dimensions. We demonstrate that 3D electron diffraction is a powerful technique for determining the complex structure of SCM-25, including the disorders and distributions of framework atoms silicon and germanium. SCM-25 has a high surface area (510 m2/g) and high thermal stability (700 °C). Furthermore, we propose a potential postsynthetic strategy for the preparation of zeolites with ordered meso-cavities by applying the ADOR (assembly–disassembly–organization–reassembly) approach.
Highlights
Zeolites are technologically important crystalline microporous materials that have wide applications in catalysis, adsorption/ separation, and ion-exchange.[1]
We demonstrate that 3D electron diffraction is a powerful technique for determining the complex structure of SCM-25, including the disorders and distributions of framework atoms silicon and germanium
Pores defined by 8, 10, and 12 TO4 tetrahedra are considered as small pores (8-ring), medium pores (10-ring), and large pores (12-ring), respectively. Those with large cavities have been widely applied in many industrial chemical processes and dominate the synthetic zeolite market.[6−8] Some examples are LTA (8 × 8 × 8-ring, sphere-like cavity of 10.8 Å in the largest dimension), CHA (8 × 8 × 8-ring, ellipse-like cavity of 9.9 Å), MWW (10 × 10-ring, ellipse-like cavity of 19.0 Å), and FAU (12 × 12 × 12-ring, sphere-like cavity of 13.0 Å). This is because their pore architectures allow both molecular diffusion and shapeselective catalysis/adsorption.[7−11] zeolites with large cavities interconnected by well-defined pore windows or channels are of great interest.[5,12−15] studies on these excellent zeolites have shown that their maximum capacities in many applications could still be optimized by increasing the size of pores and/or cavities.[16−18]
Summary
Zeolites are technologically important crystalline microporous materials that have wide applications in catalysis, adsorption/ separation, and ion-exchange.[1]. Those with large cavities have been widely applied in many industrial chemical processes and dominate the synthetic zeolite market.[6−8] Some examples are LTA (8 × 8 × 8-ring, sphere-like cavity of 10.8 Å in the largest dimension), CHA (8 × 8 × 8-ring, ellipse-like cavity of 9.9 Å), MWW (10 × 10-ring, ellipse-like cavity of 19.0 Å), and FAU (12 × 12 × 12-ring, sphere-like cavity of 13.0 Å) This is because their pore architectures allow both molecular diffusion and shapeselective catalysis/adsorption.[7−11] zeolites with large cavities interconnected by well-defined pore windows or channels are of great interest.[5,12−15] studies on these excellent zeolites have shown that their maximum capacities in many applications could still be optimized by increasing the size of pores and/or cavities.[16−18]. A potential postsynthesis strategy for preparing zeolites with meso-cavities is proposed based on the structural relationship between SCM-25 and ITQ-21
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