CRYSTALLOGRAPHY OF MICRO-AND MESOPOROUS
FRAMEWORK STRUCTURES Hartmut Fuess, C. Kirschhock, C. Pophal, Fachbereich Materialwissenschaft Technische Hochschule Petersenstr. 20, 64287 Darmstadt
Whereas the crystal structures of microporous zeolitic materials have extensively been studied by X-ray, neutron and synchrotron radiation only a limited amount of knowledge on the structure of mesoporous materials is yet available. High resolution powder data of Direct Methods or Patterson techniques and the refinement of structural details like the localization of organic molecules in the voids and channels. Their position could be compared to molecular mechanics calculations [1].
Mesoporous materials like MCM-41 and similar structures based on AlPO4 and other oxides consist of large pores (ca. 4 nm) and walls of approximately 0.8nm - 1.2nm. X-ray powder patterns reveal the periodicity of the pores but show features of amorphous organisation with the walls. Wide-angle scattering and subsequent Fourier synthesis produce radial distribution functions which allow the calculation of a model of the arrangement of the neighbours. The structure of mesoporous materials will be presented and compared to zeolite structures.
[1] H. Klein, C. Kirschhock, H. Fuess J. Chem. Phys., 98, 12345-12360 (1994)