PKU-9: An Aluminogermanate with a New Three-Dimensional Zeolite Framework Constructed from CGS Layers and Spiro-5 Units

摘要

Zeolites have been extensively studied over many years as a result of their use in industrial applications for catalysis, ion exchange, adsorption, and separation. The synthesis of new frameworks with large pores and low framework densities (FDs) is always a great challenge. Because of the correlation between FD and the smallest rings in tetrahedral networks, it has been suggested that small rings, i.e., 3- and 4-rings, are essential for the formation of a framework with low FD. Zeolite frameworks with 4-rings are common, but those with 3-rings are relatively rare because of the inner tension arising from this small circuit. Silicon seldom forms 3-rings with oxygen atoms alone because of the short Si-O bond length (～1.61 A) and large Si-O-Si angle (～145°); ZSM-18(MEI) is the only known aluminosilicate zeolite containing 3-rings. On the other hand, incorporation of low-valent cations such as Be~(2+), Zn~(2+), and even Li~+ in one of the tetrahedra in a 3-ring can provide the flexibility necessary to stabilize the 3-rings in the zeolite frameworks, which indeed led to the discovery of the frameworks with very low FD, such as OBW (13.1 TV1000 A~3) and OSO (13.4 T/1000 A~3).