Abstract
Hexagonal mesoporous silicate (HMS) molecular sieve containing zirconium species (Zr-HMS) has been synthesized using a neutral template of hexadecylamine with ethanol and water. A disordered channel structure with a uniform diameter of 44.1 A was confirmed by powder X-ray diffraction after calcination. From N2 adsorption/desorption measurement, it is found that Zr-HMS has a very high surface area of about 910 m2/g (BET) and a mesopore with a size of 21 A (BJH). According to the X-ray absorption spectroscopy at the Zr K-edge, it is confirmed that Zr atoms are coordinated by six oxygen neighbors with a distance of 2.13 A, which is shorter than the (Zr—O) bond distance found in ZrO2 or ZrOCl2·8H2O. The 29Si MAS-NMR spectrum for Zr-HMS shows two additional peaks around −94.6 and −107.2 ppm due to the Q3Zr and Q4Zr components, respectively, besides three peaks at −91.1, −101.5, and −111.3 ppm due to the silicate network. The relation between the pore and crystal structures and the local environment around Zr is discussed in detail.
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