NMR Evidence for Specific Germanium Siting in IM-12 Zeolite

• Published in: Chemistry of materials Vol. 26; no. 19; pp. 5556 - 5565
• Main Authors: Kasian, Nataliia, Tuel, Alain, Verheyen, Elke, Kirschhock, Christine E. A., Taulelle, Francis, Martens, Johan A.
• Format: Journal Article
• Language: English
• Published: American Chemical Society 14.10.2014
• Subjects: Catalysis; Chemical Sciences; Environment and Society; Environmental Sciences
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/cm502525w

Ge-rich ITQ-13 and ITQ-22 zeolites were degermanated by acid leaching of as-madestill containing organic templateand calcined forms. These two zeolites could be almost completely degermanated without modifying the framework structure. This behavior is different from IM-12 zeolite, which undergoes framework transformation from UTL to OKO type upon degermanation. All three zeolite types contain double four-ring (D4R) units populated by germanium atoms. The UTL to OKO transformation involves the elimination of Germanate 4 rings (Ge 4R) from double four-ring (D4R) units connecting the layers. The differences of Si and Ge atom siting in D4R units in the three zeolites were probed using 19F MAS NMR after post synthetic incorporation of fluoride and 1H–29Si CP/MAS NMR. In IM-12, NMR suggests that Ge atoms are all located in one of the faces of D4R units and form 4Rs that connect Si-rich layers together. In the degermanation process, the 4 Ge atoms of the Ge 4Rs are dislodged simultaneously, in excellent agreement with earlier EXAFS data. In ITQ-13 and ITQ-22 zeolites, Ge distributions are more complex, leading a progressive degermanation of the framework and to the presence of Si–O–Si bridges that prevents the structure from collapsing upon Ge extraction. Data suggest that IM-12 is unique in the family of Ge-containing zeolites.