Single parameter synthesis of high silica CHA zeolites from fluoride media

A series of high silica CHA zeolites with a true single parameter variation has been synthesized, where only the Si/AI ratio changes, using N,N,N-1-trimethyladamantammonium hydroxide as the structure directing agent in fluoride media. The materials have been synthesized with high crystallinity, and with a Si/AI ratio ranging from 20 to infinity, i.e. pure SiO2. Powder XRD shows that the unit cell parameters increase with increasing amount of Al incorporated into the framework, while BET and SEM shows that the specific surface area and the particle size is fairly independent of the Si/AI ratio. We also present an explanation for the earlier reported disagreement in Si/AI ratio determined by elemental analysis and Si-29 MAS NMR. (C) 2011 Elsevier Inc. All rights reserved.