from first principles PP-I-1

PP-III-46On Different Polarization Ability of Different Ion Exchanged BivalentCations in Different ZeolitesKazansky V.B., Subbotina I.R.N.D. Zelinsky Institute of Organic Chemistry RAS, Moscow, Russiasubbot@ioc.ac.ruIt is generally belived that chemical activation at different molecules adsorbed by cationexchanged zeolites results from their polarization by cations. In the present study this wasexamined by IR spectra of molecular hydrogen, methane, ethane and propane adsorbed bybivalent cations in ZSM-5, mordenite and Y zeolites. The obtained results indicated thatpolarization of those molecules by the same cations in these zeolites is different. It is thestrongest in ZSM-5 and the weakest in Y zeolite, while polarization of adsorbed molecules bybivalent ions in mordenite is intermediate.In was suggested that this is connected with different state at exchanged bivalent cations inthese zeolites [1]. In ZSM-5 where the negatively charged [AlO 4 ] tetrahedra are stronglydistantly separated from each other only one half of them is neutralized by bivalent cationsresulting in superacidic adsorption Lewis sites while the second part of negatively charged[AlO 4 ] tetrahedra is free. In Y zeolite each positively charged bivalent cation interacts withtwo neighboring negatively charged [AlO 4 ] tetrahedra that results in a better neutralization oftheir positive charges. Mordenite represents an intermediate case with weaker compensationof positive charges of bivalent cations than in Y zeolite. Such superacidic Lewis sitesdissociatively adsorb light alkanes. In [2] this conclusion was supported by quantum chemicalcalculations.[1] V.B. Kazansky, A.I. Serykh, Microporous and Mesopous Materrials, 2004, v. 70, P. 151-157[2] G. M. Zhidomirov, A. A. Shubin, V. B. Kazansky and R. A. Van Santen, International Journal ofQuantum Chemistry, 2004, Volume 100, Issue 4, pages 489–494199