Hydration of AlPO4-11 studied with x-ray powder diffraction and aluminum-27 and phosphorus-31 NMR

Mart P. J. Peeters, Jan W. de Haan, Leo J. M. van de Ven, Jan H. C. van Hooff
1993 The Journal of Physical Chemistry  
The influence of water adsorption in AlP04-11 has been studied with X-ray powder diffraction and 27AI and 3IP NMR. With X-ray powder diffraction, a change of the crystal symmetry from ZMA2 to PNA2, is observed upon water adsorption, resulting in a diminished unit-cell volume and more elliptical pores. N M R was used to study the hydration on an atomic scale. With 27Al double rotation (DOR) and magic angle spinning (MAS) NMR, the quadrupole coupling constants (CQ) and asymmetry parameters (7) of
more » ... the different A1 sites in dry and wet AlPO4-11 were determined and correlated with the symmetry of the A1 site obtained from literature data. In contrast with earlier 27Al DOR measurements,' spectral simulations of 27Al MAS and DOR N M R spectra measured at 7.0 T prove the preferential hydration of one tetrahedral aluminum site in Alp@-1 1 (five crystallographically different sites), transforming this site reversibly into octahedrally coordinated aluminum.* From the observed correlation between the XRD data and CQ, it was concluded that the A12 site becomes preferentially octahedrally coordinated. On the basis of 27Al DORand 31P MAS NMRmeasurements performed on the partially hydrated samples, it is shown that the transformation upon hydration is a local process, comparable to the symmetry change observed upon adsorption of sorbates in
doi:10.1021/j100122a030 fatcat:qxpb62ciyffzrdodnfhepfpim4