Synthesis of aluminosilicate and gallosilicate zeolites via a charge density mismatch approach and their characterization.
Aluminosilicate and gallosilicate zeolite syntheses via a charge density mismatch (CDM) approach are compared at intermediate-silica compositions (Si/Me = 5-16, where Me is Al or Ga). With a variation of the crystallization temperature and of the type and/or concentration of alkali metal ions added as a crystallization structure-directing agent (SDA) to tetraethylammonium-tetramethylammonium, tetraethylammonium-hexamethonium, and strontium-choline mixed-SDA systems, we were able to obtain 11 different zeolite structures. However, only 5 out of a total 40 pairs of aluminosilicate and gallosilicate synthesis runs at otherwise identical chemical compositions were found to give the same zeolite product with no detectable impurities, suggesting that the structure-directing ability of Ga is quite different from that of Al even in intermediate-silica synthesis conditions. The CDM approach to offretite synthesis led to hexagonal plate-like crystals with aspect ratios lower than 0.3, and UZM-22 exhibited no significant preference of Al substitution for particular tetrahedral sites, especially for site T1, unlike its framework type material ZSM-18. More interestingly, the EU-1 zeolite obtained from an aluminosilicate synthesis mixture containing Li(+) as an inorganic crystallization SDA in the tetraethylammonium-hexamethonium double-organic additive system has been characterized to locate about half of its Li(+) ions in the framework, while the Li distribution over the 10 topologically different tetrahedral sites is nonrandom in nature.
Department of Chemical Engineering and School of Environmental Science and Engineering, POSTECH, Pohang 790-784, Korea.
Min Bum
MB
Park
Sung June
SJ
Cho
Suk Bong
SB
Hong
D000538:Aluminum Silicates / Q000138:chemical synthesis*; D060326:Chemistry Techniques, Synthetic / Q000379:methods*; D004583:Electrons; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D013816:Thermodynamics; D017641:Zeolites / Q000138:chemical synthesis* / Q000737:chemistry*
D000538:Aluminum Silicates; D017641:Zeolites; C049037:aluminosilicate