| 초록 |
Niobium silicalite-1 (NbS-1) molecular sieves with MFI structure were prepared using the hydrothermal synthesis method. X-ray diffraction, scanning and transmission electron microscopies, Fourier transform infrared spectroscopy, ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy, 29Si magic-angle spinning nuclear magnetic resonance spectroscopy, ammonia temperature-programmed desorption (NH3-TPD), physical adsorption of nitrogen and elemental analysis were then performed to evaluate their physico-chemical properties and to provide evidences for the incorporation of Nb5+ into the zeolite framework. The unit cell volume of niobium silicalite-1 increased linearly with increasing niobium content, suggesting isomorphous substitution of Si4+ by Nb5+ in the lattice framework. The framework infrared spectrum showed a characteristic absorption band at 963 cm-1, probably due to Si−O−Nb linkages. In the UV-vis spectrum, the absorption assigned to the presence of Nb5+ in the zeolite framework was observed at around 200 nm. NH3-TPD studies revealed weak acidity in niobium silicalite-1 due possibly to [Nb···(OH)–Si] sites in the framework. |
