Synthesis of titanium, niobium, and tantalum silicalite-1 by microwave heating of the mixed oxide xerogel precursors

摘要

Titanium (TS-1), niobium (NbS-1), and tantalum silicalite-1 (TaS-1) with MFI structure werernsynthesized by microwave heating of the TPAOH impregnated xerogels, which in turn werernprepared from respective alkoxide precursors by sol-gel process. Under the microwavernirradiation, highly crystalline products were obtained in 30 min to 2 h with yields over 90%.rnCharacterization of the transition metal containing molecular sieves by XRD, SEM, FT-IRrnand UV-Vis spectroscopy established that the materials obtained by microwave heating of thernmixed oxide gels are composed of well isolated metals with Si-O-Ti(Nb,Ta) bonds essentiallyrndemonstrating identical chemical properties to ones prepared by conventional means usingrnliquid gels of mixed alkoxides. Particle size and surface morphology, however, were affectedrnby synthesis methods. These catalysts showed high catalytic performances in Beckmannrnrearrangement of cyclohexanone oxime to caprolactam.