Structural changes of synthetic paulingite (Na,H-ECR-18) upon dehydration and CO2 adsorption
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The structure of dehydrated calcined ECR-18, synthetic paulingite, topology type PAU, unit cell composition Na132H28Si512Al160O1344, has been determined by Rietveld refinement against synchrotron X-ray powder diffraction data. Upon dehydration the symmetry of Na,H-ECR-18 changes from Im3m to I 43m, with a corresponding decrease of cubic unit cell a parameter from 34.89412(1) A to 33.3488(3) A. This occurs as the framework distorts to afford closer coordination of Na+ cations by framework O atoms in 8-ring window sites of the seven cage types present. Na+ cations in 8R sites block the access of N2 molecules to the internal pore space at 77 K but CO2 adsorption at 308 K is observed, and is postulated to occur via a 'trapdoor' mechanism. In situ PXRD during CO2 adsorption at pressures up to 10 bar show reversible broadening of diffraction peaks that is attributed to local crystallographic strain.
Greenaway , A G , Shin , J , Cox , P A , Shiko , E , Thompson , S P , Brandani , S , Hong , S B & Wright , P A 2015 , ' Structural changes of synthetic paulingite (Na,H-ECR-18) upon dehydration and CO 2 adsorption ' Zeitschrift fur Kristallographie , vol 230 , no. 4 , pp. 223-231 . DOI: 10.1515/zkri-2014-1824
Zeitschrift fur Kristallographie
(c) 2014, Paul A. Wright et al., published by De Gruyter. This article is distributed under the terms of the Creative Commons Attribution 3.0 Public License. (CC BY 3.0)
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