The structural and electronic properties of the acidic site in zeolites is of extreme importance in determining the sorption and transport of organic molecules in these cage-like structures. We present results of Kohn-Sham density functional theory calculations that serve to elucidate these structural and electronic features. In our calculations, the core electrons are represented via pseudopotentials, and the local density approximation for the exchange-correlation energy is used. We have investigated the structure of the acidic site upon aluminum substitution at each of the twelve distinct tetrahedral sites. Unlike previous studies, full structural relaxation is allowed using Hellman-Feynman forces. We find that the T12 site is the most energetically stable site for aluminum substitution. Details of the local structure of the aluminum site and the charge compensating proton will be presented. Furthermore, the electron density distribution in the vicinity of the acid site (which serves to characterize the acidity) will be discussed. The acidic site is found to be fairly soft.
|Number of pages||1|
|Journal||American Chemical Society, Division of Petroleum Chemistry, Preprints|
|State||Published - Mar 1992|
|Event||Symposium on Molecular Modeling of Petroleum Processes and Catalysis - San Francisco, CA, USA|
Duration: 5 Apr 1992 → 10 Apr 1992