Synthesis, characterization, and catalytic properties of [Zr]-ZSM-5

Abstract

Crystalline, microporous, zirconium silicas have been synthesized. XRD and selected area electron diffraction revealed their MFI structure with orthorhombic symmetry. Absence of other crystalline or amorphous phases was also confirmed by electron microscopy. Uniform spherical crystallites of 0.2 μm size were observed by electron microscopy. The samples were substantially free from aluminum (Si/Al > 2000). An increase in unit cell volume from 5294 (Å)3, for pure [Si]-ZSM-5, to 5402 (A)3, for [Zr]-ZSM-5 (Si/Zr = 24), was observed, suggesting isomorphous substitution of Si4+ by Zr4+ in the lattice framework. On calcination of the as-synthesized sample in air, there was a change in crystalline symmetry from orthorhombic to monoclinic. This change in symmetry could, however, be prevented by carrying out the calcination carefully, first in N2 and then in air. Framework i.r. spectra exhibited a band at 963 cm−1, probably due to Si-O-Zr linkages, in addition to other bands characteristic of the MFI structure. [Zr]-ZSM-5 is active in the hydroxylation of benzene to phenol and phenol to dihydroxy benzenes.