The high temperature synthesis of CsAlSiO<inf>4</inf>-ANA, a new polymorph in the system Cs<inf>2</inf>OAl<inf>2</inf>O<inf>3</inf>SiO<inf>2</inf>. I. The end member of ANA type of zeolite framework

Abstract

High temperature phase transformations of Cs+ exchanged zeolites were investigated. Above 1000°C, CsX, CsY (FAU), and Cs, ZK-4 (LTA) frameworks recrystallized in a pollucite phase. A Cs+ loaded mordenite recrystallized at 1300°C in the orthorhombic CsAlSi5O12 phase. A Cs+ exchanged zeolite A at 960°C recrystallized in a mixture of two polymorphic CsAlSiO4 phases having different (Al,Si)O4 frameworks. The unstable orthorhombic CsAlSiO4ABW phase has a topotactic transition at 1150°C into an ordered low CsAlSiO4-ANA framework. Further calcination produces, at 1200°C, transformation of the low CsAlSiO4-ANA phase to the more stable high CsAlSiO4-ANA polymorph having cubic (a0 = 13.6595 (5) A ̊) symmetry and an ordered SiAl distribution. The crystal structure of high CsAlSiO4ANA, a new polymorph in the system Cs2OAl2O3SiO2, was determined using X-ray Rietveld analyses and 29Si MAS NMR spectroscopy. © 1991.