2018 年 22 巻 1 号 p. 1-11
Topotactic conversion of layered silicates into zeolites through interlayer condensation is advantageous for the synthesis of zeolites with unusual compositions, structures, and/or morphologies that have not been obtained using conventional hydrothermal methods. Recently, layered silicate RUB-15 was successfully converted to sodalite with relatively few defects through interlayer condensation by refluxing in N-methylformamide (NMF). However, the effect of NMF, an amide molecule, on the interlayer condensation of RUB-15 is not yet fully understood. In this study, RUB-15 was refluxed or heated in one of four amides: NMF, formamide (FA), N,N-dimethylformamide (DMF), and N-ethylformamide (NEF) to understand the effect of amide molecules on the interlayer condensation in terms of both the size of the amide molecules and their interactions with the layered silicate. On the basis of the powder X-ray diffraction patterns and solid-state 29Si MAS NMR spectra of refluxed or heat-treated products, both NMF and DMF are well suited for interlayer condensation of RUB-15, and the most optimal amide is NMF because it produces the fewest defects. FA (smaller than NMF) and NEF (larger than DMF) are less suitable as interlayer organic species for sodalite formation. It was also found that interlayer condensation of layered octosilicate proceeded in the presence of NMF by refluxing, whereas the condensation did not proceed in DMF by refluxing. These results strongly suggest that the matching in size of the amide molecules with respect to the surface structures of the layered silicates and their interactions play major roles in the interlayer condensation.
