Abstract
Vanadium-containing zeolite beta (V-Beta) with molar atomic composition of V/Al/Si = 0.013/1/23 was synthesized by direct hydrothermal method. The synthesized V-Beta exhibits a unique structure that was characterized by ICP-mass, XRD, TEM, STEM/EDS, i.r., u.v.-vis, 29Si and 27Al MAS n.m.r., and EPR spectroscopies. The structure of V-Beta is isomorphous with H-form zeolite beta (H-Beta) of the same Si/Al ratio and is like H-Beta in cubic shape, but the average size is significantly larger. The incorporated vanadium also shows remarkable effect on 29Si and 27Al MAS n.m.r. spectra that seems to increase the framework Si/Al ratio and the T-O-T angle of the zeolite Beta. A typical EPR spectrum of vanadyl ions (VO[su2+]) was clearly presented by the synthesized V-Beta after calcination, and an additional superhyperfine structure due to interaction with 27Al appeared after dehydration. The spectroscopic results indicate that isolated V(IV) ions are atomically dispersed at cation or vacant acid sites near Al. The infrared spectrum of pyridine adsorption shows an enhanced Lewis acidity for the vanadium-containing zeolite beta.
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