QUANTUM-CHEMICAL STUDIES OF ZEOLITE PROTON CATALYZED-REACTIONS

Theoretical chemistry applied to zeolite acid catalysis is becoming an important tool in the understanding of the adsorption and interaction of guest molecules with the zeolitic lattice. Especially the understa nding of the mechanisms by which zeolite catalyzed chemical reactions proceed becomes possible. It is shown here that the old interpretation of carbonium and carbenium ions as intermediates for zeolite catalyze d reactions has to be replaced by a new approach in terms of positivel y charged transition states that are strongly stabilized by the zeolit ic lattice. The large deprotonation energy of the acidic zeolite is ov ercome by stabilization of the intermediate or transition state positi ve charge by the negative charge left in the lattice. The zeolitic sit es responsible for the adsorption and/or reaction of guest molecules a re the Bronsted-acid and Lewis-base sites. We also show that different transition states are responsible for different kinds of reactions, s uch as cracking, dehydrogenation, etc.