Structural, compositional and acidic characteristics of nanosized amorphous or partially crystalline ZSM-5 zeolite-based materials
✍ Scribed by Kostas S. Triantafyllidis; Lori Nalbandian; Pantelis N. Trikalitis; Athanasios K. Ladavos; Thomas Mavromoustakos; Christakis P. Nicolaides
- Publisher
- Elsevier Science
- Year
- 2004
- Tongue
- English
- Weight
- 534 KB
- Volume
- 75
- Category
- Article
- ISSN
- 1387-1811
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✦ Synopsis
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, NH 3 -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 P30 nm) 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 2h-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 conventional silica-alumina.