ABSTRACT
The interacting induced-dipoles polarization model, implemented in our program POLAR, is used for the calculation of the effective polarizability of the zeolitic bridged OH group, which is much higher than that of the free silanol group. A high polarizability is also calculated for the bridged OH group with a Si4+, in absence of Lewis-acid promotion of silanol by Al3+. The crystal polarizability is estimated from the Clausius-Mossotti relationship. Siliceous zeolites are low-permittivity isolators. The interaction of a weak base with the zeolitic OH can be considered as a local bond. Only when cations are located in the zeolite micropore next to tetrahedra that contain trivalent cations are large electrostatic fields generated. They are short ranged, and the positive cation charges are compensated for by corresponding negative lattice charges.
