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 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

Calcined dehydrated AlP04-5 has been studied by X-ray powder diffraction, 31P MAS, and 27Al MAS and double-rotation (DOR) NMR. The results indicate that three crystallographically different sites can be distinguished in the structure of dehydrated AlP04-5 in the ratio 1:l:l. The observed splitting of the N M R spectra is correlated to the line width of the XRD peaks between 219 = 19O and 28 = 23'. Simulations of 27Al DOR (4.7,9.4, and 1 1.7 T) and MAS spectra (7.0 and 9.4 T ) yield theisotropicchemical shifts (6i,),quadrupolar coupling constants (CQ), and the asymmetry parameters ( T ) of the different sites in dry AFI. The interaction of water, methanol, ammonia, and acetonitrile with AlP04-5 and AlPO4-11 is studied by XRD and 27Al DOR and MAS NMR. Both water and ammonia are able to coordinate to part of the framework aluminum, leading to five-and/or six-coordinated aluminum. The relative amounts of five-and six-coordinated aluminum depend on the crystal structure and the interacting sorbate. Whereas water in AlPO4-11 is interacting with one specific aluminum site (Alz), the interaction of water with AlP04-5 occurs randomly. This leads to a broadening of the tetrahedral signals at higher water loading (above 10-12 wt %). At low MAS frequencies some dipolar broadening occurs, whereas at high spinning frequencies or 850-1000 Hz DOR the broadening is caused by site distribution. Methanol and acetonitrile do not interact with framework atoms. These molecules are too big to coordinate to framework aluminum in AFI and AEL type molecular sieves. The broadening of the spectral features observed after methanol adsorption is apparently due to an increase in chemical shift dispersion brought about by nonspecific interactions of methanol with the framework, thereby causing a larger spread in AI-0-P angles.

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Highly crystalline samples of the chabazite-related aluminophosphate AlPO4-18 (AEI) have been prepared and characterized by adsorption measurements as well as by *7Al double rotation (DOR) N M R studies. Whereas the heat curves and isotherms of n-paraffins on AEI show the common feature for adsorption on nonpolar molecular sieves with a given pore dimension, methanol gives an unusual heat curve with a deep minimum for a loading >4 molecules per cavity. This corresponds to the extended low-pressure hysteresis loop of the isotherm which is absent in SAPO-34. In accordance with the structure determination and Rietveld refinement of the as-synthesized AEI, three crystallographically inequivalent A1 positions including one pentacoordinated A1 could be detected and assigned by 27Al DOR NMR. Calcination as well as the adsorption of polar molecules results in a structure change. While water and ammonia generate octahedrally coordinated Al, methanol gives only AIV as has been found for the template-containing sample. The methanol adsorption has been studied in more detail. It has been found that the formation of the A P requires more than one methanol molecule per All site. This process occurs for a loading between one and four molecules per cavity; it is isobaric and compares to a hydration process. Two additional molecules can be accommodated in the AEI cavity which seems to be related to the second step of the methanol isotherm and the extended low-pressure hysteresis loop which is absent in the isotherm of water. This is accompanied by another reversible structure change resulting in four N M R lines for the six different A1 positions in the double 6-ring, the secondary building unit of the AEI. IntroductionAluminophosphate molecular sieves represent a new family of microporous adsorbents of broad structural diversity1 which includes now 23 accepted structure types with 14 novel structures.2 One of these new structures is the small-pore molecular sieve AlP04-18 (AEI), which recently has been characterized by synchrotron-based X-ray powder diffraction and Rietveld refinement as a chabazite-related three-dimensional 8-ring channel system. After calcination structural changes occur.3 In the assynthesized form, it contains pentacoordinated A1 caused by the presence of the tetraethylammonium hydroxide in its cavities. Therefore, some unusual adsorption properties, especially regarding polar molecules, can be expected as has been shown for other structures of this family such as VFI, AFI, AEL, ERI, and others using NMR or adsorption techniques.&lS Very little, however, is known about the adsorption properties of AEI as only a few related studies have been carried out so far.I6In the present contribution the adsorption behavior of the pure aluminophosphate AEI has been investigated using adsorption calorimetry. To explain the unusual adsorption properties of this molecular sieve with regard to polar molecules, the27Al DOR (double rotation) NMR technique has been applied to samples with different loadings. For the first time ...

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