Abstract
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, N2 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 25°C 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 ≥30nm) and/or high external surface area. The first Bragg peaks were observed in the XRD patterns of the samples synthesized at 90°C and their position on the 2θ-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 (Brønsted acid sites), as compared to those found in a con-ventional silica-alumina.
Original language | English |
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Pages (from-to) | 89-100 |
Number of pages | 12 |
Journal | Microporous and Mesoporous Materials |
Volume | 75 |
Issue number | 1-2 |
DOIs | |
State | Published - 12 Oct 2004 |
Externally published | Yes |
Keywords
- Acidity
- Framework aluminum
- Nanosized zeolites
- Partially crystalline ZSM-5
- Porosity
ASJC Scopus subject areas
- General Chemistry
- General Materials Science
- Condensed Matter Physics
- Mechanics of Materials