| 研究実績の概要 |
In this research project, design and synthesis of zeolites with controlled locations of framework heteroatoms such as Al and Zn have been investigated with an aid of computational calculations. In general, the atomic distribution in zeolites is thought to be controlled kinetically. The results suggest that, however, in many cases the Al atoms in the framework positions of zeolites can be determined thermodynamically where the energetic stability is considered to be a dominant determining factor. It is shown that in the absence of organic structure-directing agents (OSDAs) FAU-type zeolite with spatially biased Si Speciation can be successfully synthesized to yield atomic configuration with lower energy. The crystallographic tetrahedral site (T site)-specific incorporation of Al is successfully demonstrated with IFR-type zeolites synthesized using OSDAs. In this case, the T site-specific Al can be achieved due to the low mobility of OSDAs, providing the specificity of the structure-directing ability. The clear correlation between thermodynamic stability of Al at different T sites and Al occupancy provides evidence that the Al location is primarily governed by the energetic preferences. It can therefore be suggested that zeolites with specific atomic distribution can be achieved as an “equilibrium” product by controlling the energetic pathways of crystallization (e.g., selection of crystallization conditions and appropriate SDAs). In addition to Al, incorporation Zn into the zeolite frameworks has been examined by selecting MOR- and CHA-type zeolites as model examples.
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