Synthesis of an IWW-type germanosilicate zeolite using 5-azonia-spiro[4,4]nonane as a structure directing agent

Abstract

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 °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 °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.