INFRARED-SPECTROSCOPY, THERMOPROGRAMMED DESORPTION, AND NUCLEAR-MAGNETIC-RESONANCE STUDY OF THE ACIDITY, STRUCTURE, AND STABILITY OF ZEOLITE MCM-22

Zeolite MCM-22 has been studied by infrared (i.r.) spectroscopy, therm oprogrammed desorption (t.p.d.) of NH3, and Al-27 n.m.r. with magic an gle spinning (MAS). It has been found that zeolites MCM-22 and ZSM-5 b oth have framework i.r, bands at about 1,245 and 550 cm(-1), and zeoli tes MCM-22 and Y both have two pore opening i.r, bands at about 380 an d 317 cm(-1). In MCM-22 there are two kinds of bridged hydroxyls (3,62 0 and 3,575 cm(-1)) and two kinds of internal silanols (3,500 and 3,70 0 cm(-1)). The latter two i.r. frequencies are similar to those in zeo lites ZSM-5 and Y, respectively. Al-27 n.m.r. reveals two kinds of fra mework tetrahedral Al. The spectroscopic similarities and the dual app earance of the relevant i.r, bands/n.m.r, peaks seem to indicate that MCM-22 probably has two distinct pore systems containing 10- and 12-me mber rings, which is in accordance with our recently published results of catalytic tests, Quantitative results on Bronsted and Lewis acidit y are reported from the i.r, study of pyridine adsorption and from t.p .d. of NH3. The Bronsted sites are strongly acidic and accessible for pyridine. MCM-22 is very sensitive to the calcination conditions, bein g more dealuminated on heating in air than in a vacuum or N-2. The dea lumination occurs even during grinding in a mortar with a concomitant decrease in the acidity of the final sample.