SAPO‐34 Framework Contraction on Adsorption of Ammonia: A Neutron Scattering Study

Neutron scattering data was recorded from SAPO‐34 using the OSIRIS instrument before and after repeated ammonia adsorption at pressures up to 8 bar. Coherent scattering from the zeolite framework provides the neutron powder diffraction pattern and gave evidence for anisotropic contraction on ammonia...

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Bibliographic Details
Published in:Chemphyschem 2019-07, Vol.20 (13), p.1747-1751
Main Author: Silverwood, Ian P.
Format: Article
Language:English
Subjects:
Adsorption
Ammonia
anisotropic contraction
Coherent scattering
Crystal lattices
Diffraction patterns
diffusion
neutron diffraction
Neutron scattering
Neutrons
Zeolites
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Summary:Neutron scattering data was recorded from SAPO‐34 using the OSIRIS instrument before and after repeated ammonia adsorption at pressures up to 8 bar. Coherent scattering from the zeolite framework provides the neutron powder diffraction pattern and gave evidence for anisotropic contraction on ammonia dosing. Incoherent quasielastic scattering from the hydrogen of the ammonia showed that mobile ammonia was present in the framework. The quasielastic data was fitted to a model where the ammonia was confined within the chabazite cage in the c direction of the crystal lattice, with diffusion solely occurring through the perpendicular 8‐membered rings. The calculated diffusion constant reached a maximum of 6.3×10−8 m2 s−1 at 5 bar. Strong relationship: Zeolites show interesting deformation characteristics when gas molecules condense in their framework. The strong interaction with ammonia causes the unit cell to shrink, in contrast to the previously seen expansion with weakly adsorbed species.
ISSN:1439-4235
1439-7641
DOI:10.1002/cphc.201900230