Synthesis, modification, and characterization of NH4 zeolites and their relationships to their hydrogen forms
Final Report Abstract
The aim of this project was to characterize ammonium bearing zeolites at ambient and hightemperature conditions to get detailed information on its deammoniation behavior. It could be shown by X-ray diffraction, Raman spectroscopy, and electron microprobe analysis that a natural merlinoite from Chile contains ammonium and thus represents a new mineral species merlinoite-NH4. Investigations on ammonium exchanged zeolite A revealed that it is not stable upon deammoniation. Powder samples decompose already below 100 °C under vacuum conditions, and above 110 °C in air. Single crystals of NH4-exchanged zeolite A show a progressive dealumination after ion exchange when they are kept at ambient conditions for 16 days. Al is determined in the origin of the unit cell (space group Fm-3c) with an electron density of about 20 e/Å3. It is coordinated by water molecules in a distance of 1.90 Å. Partially exchanged powder samples with composition K9.6(NH4)2.4Al11.7Si12.3O48 remain stable up to about 900 °C. The stability decreases upon further exchange. All X-ray fluorescence and electron microprobe analyses of zeolite A (as synthesized and cation exchanged) yielded a Si/Al ratio greater than 1. This is supported by the results of the crystal-structure refinement which yielded almost ideal Si-O distances but Al-O distances being slightly too short and thus indicating mixed occupancy with Si on the Al position. It could be shown that the decrease of the intensities in X-ray diffraction experiments of Ba and Sr exchanged zeolite A can be entirely related to the higher absorption effect of Ba (and Sr) and thus is not caused by a loss of crystallinity as proposed before. Ammonium replaces K in the natural zeolite willhendersonite without significant changes in the crystal structure.
Publications
- „Synthesis, modification, and characterization of zeolite A and some cation-exchanged forms“. 17th International Zeolite Conference, Moscow (2013)
L. Wang, I. Spiess, H. Lührs, W.H. Baur, R.X. Fischer
- „Crystalchemical characterization of ammonium exchanged zeolites.“ Jahrestagung der Deutschen Mineralogischen Gesellschaft (2014)
I. Spieß, L. Wang, H. Hölzen, J. Birkenstock, W. H. Baur, R. X. Fischer
- „Synthesis, modification, and characterization of zeolite A and some cation-exchanged forms”. Jahrestagung der Deutschen Mineralogischen Gesellschaft (2014)
L.Wang, I. Spiess, H. Lührs, W.H. Baur, R.X. Fischer
- Crystallographic characterization and thermal decomposition behavior of ammonium exchanged zeolites. Jahrestagung der Deutschen Kristallographischen Gesellschaft (DGK) 2016
I. Spiess, M. Fischer, L. Wang, J. Birkenstock, W. H. Baur, R. X. Fischer
