Synthesis of an IWW-type germanosilicate zeolite using 5-azonia-spiro[4,4] nonane as a structure directing agent
Kirschhock, Christine E. A.
Faculty of Sciences. Physics
New journal of chemistry. - Montrouge
, p. 4319-4324
University of Antwerp
An IWW-type zeolite with a Si/Ge ratio of 4.9 is obtained using 5-azonia-spiro[4,4] nonane as a template in fluoride-free medium under hydrothermal conditions at 175 degrees C. In an otherwise identical synthesis, using related 5-azonia-spiro[4,5] decane as a structure directing agent, a mixture of IWW and NON zeolite types was formed. In the absence of GeO2 from the reactant mixture, pure NON formed. The IWW zeolite was characterized by XRD, SEM, and HRTEM. The IWW zeolite displayed a unique morphology and could be calcined at 600 degrees C without the loss of crystallinity. The Si/Ge ratio of the IWW zeolite was increased by postsynthesis modification. Part of germanium could be eliminated from the as-synthesized IWW zeolite by acid leaching using 6 M HCl solution. Also the calcined material could be degermanated. Here the presence of a silicon source in the acidic leaching solution minimized structural damage. In this way the Si/Ge ratio of the IWW zeolite was increased from 4.9 up to 10.