Structural, compositional and acidic characteristics of nanosized amorphous or partially crystalline ZSM-5 zeolite-based materials

Partially crystalline and X-ray amorphous ZSM-5 zeolite-based aluminosilicates have been synthesized and thoroughly characterized by chemical analysis, XRD, FT-IR, solid state MAS NMR, N-2 adsorption, TEM, NH3-TPD and isopropanol dehydration as the catalytic test reaction. The X-ray amorphous and low-crystallinity samples were hydrothermally synthesized at temperatures as low as 25degreesC and consisted of nanosized well-formed particles of almost spherical shape and with dimensions of about 20-30 nm. These samples exhibited very low microporosity and remarkably high meso/macropore volume (pore diameters greater than or equal to30 nm) and/or high external surface area. The first Bragg peaks were observed in the XRD, patterns of the samples synthesized at 90 degreesC and their position on the 2theta-axis was the same as those of a reference highly crystalline ZSM-5 zeolite sample. The particle/crystal size and microporosity of the partially crystalline materials increased with increasing hydrothermal synthesis temperature and % relative XRD crystallinity. Incorporation of aluminum in the ZSM-5 zeolitic framework was significantly enhanced at higher relative crystallinities. i.e. >60%. The X-ray amorphous aluminosilicates possessed tetrahedral aluminum atoms which were more zeolitic in character and induced a higher number of acidic framework hydroxyls (Bronsted acid sites), as compared to those found in a conventional silica-alumina. (C) 2004 Elsevier Inc. All rights reserved.