Ni-ZSM-5 and Cu-ZSM-5 Synthesized Directly from Aqueous Fluoride Gels

Abstract

Ni-ZSM-5 and Cu-ZSM-5 have been synthesized in a slightly acidic fluoride medium. A low water H-ZSM-5 formula was used to synthesize the metal-substituted systems using bis(tetraethylammonium) tetrachloronickelate(II) [N(CH2CH3)4]2[NiCl4] and bis(tetraethylammonium) tetrachlorocuprate(II) [N(CH2CH3)4]2[CuCl4] as the tetrahedrally coordinated metal species. X-ray diffraction analysis established the presence of highly crystalline and thermally stable material. Unit cell dimensions increased with increasing levels of metal substitution. X-ray fluorescence (XRF) bulk analysis showed increasing levels of metals in the material and corresponding decreases in the moles of silica. The maximum levels of substitution achieved were Ni 3.93 and Cu 4.38 (in wt %). Analysis by scanning electron microscopy (SEM) showed a crystal morphology similar to that of H-ZSM-5 but with smaller crystals having an increasing aspect ratio in the substituted materials. There was evidence of twinned crystals and the appearance of raised faces in all substituted samples. Thermogravimetric and derivative thermogravimetric analysis showed anomalous losses, which could be explained by Jahn-Teller distortions. Fourier transform infrared analysis of the materials showed an increasing level of distortion in significant regions of the spectra. Analysis of the filtrate, from EDTA-exchanged material, by atomic absorbance spectroscopy (AAS) showed that there were tetrahedrally coordinated M2+ species in the material and relatively small amounts were removed by ion exchange.