THE TEXTURE AND ELECTRON-ACCEPTOR, ACID-BASE, AND CATALYTIC PROPERTIES OF MODIFIED ZSM-5 TYPE ZEOLITES .2. A STUDY OF PYRIDINE ADSORPTION BY IR SPECTROSCOPY AND THERMODESORPTION

IR spectroscopic and TPD measurements of pyridine adsorption were made on a series of ZSM-5 type zeolites prepared by direct synthesis (SiO2 /Al2O3 = 28, 34, 44, 56, 81, and 168) and calcined at 500 and 800-degr ees-C. It is shown that the total quantity of pyridine sorbed reaches 5 - 7 molecules per unit cell (u.c.) and does not depend on either the SiO2/Al2O3 ratio or the temperature of precalcination. At the same ti me, the amount of strongly adsorbed pyridine (T(des) = 250 - 600-degre es-C) is independent of the calcination temperature but falls from 2.0 to 0.3 molecules per u.c. as the SiO2/Al2O3 ratio rises. The increase in zeolite calcination temperature results in a growing contribution of Lewis sites. Modification of the outer zeolitic surface by tetraeth oxysilane treatment does not noticeably change the total quantity of p yridine sorbed or the number of strongly adsorbed molecules.