Controlling the microstructure of MFI zeolites with Mg(OH)2 nanocrystals to improve their catalytic performances

Abstract

Control of the microstructure and morphology of molecular sieve crystals will significantly affect their catalytic performances. In this paper, titanium silicalite-1 (TS-1) and silicalite-1 (S-1) crystals were synthesized under hydrothermal conditions in the presence of Mg(OH)₂ nanocrystals (NCs). XRD, TEM, FT-IR, and N₂ adsorption were used to characterize the structure of TS-1 and S-1 crystals. The introduction of Mg(OH)₂ NCs endow the as-synthesized TS-1 and S-1 with a much more rugged surface and some voids and slits via attachment onto the surface or entrapment inside TS-1 and S-1 crystals. The crystallinity behavior, microstructure and morphology of TS-1 and S-1 also are effectively affected and modified by the presence of Mg(OH)₂ NCs. The obtained TS-1 and S-1 crystals were examined as catalysts for the cyclohexanone ammoximation and vapor phase Beckmann rearrangement of cyclohexanone oxime, respectively. The highest catalytic performances of the two reactions had been obtained when the Mg(OH)₂ additive amount was 10 wt%. The catalytic performance was improved when the appropriate amount of Mg(OH)₂ NCs was introduced into the MFI zeolite synthesis solution.