FTIR investigation of the interaction at 77 K of diatomic molecular probeson MCM-22 zeolite

Three different Si(OH)AI sites have been singled out in MCM-22, absorbing a t 3628, 3618 and 3585 cm(-1) tentatively assigned to hydroxyls located in s upercages, 10-membered ring channels and six-membered rings, respectively. FTIR study of the adsorption of CO and N-2 at the nominal temperature of 77 K allowed the measurement of their acidity, which appears close to that me asured for H-ZSM-5 by means of the same technique, and it is not modified b y dealumination. Lewis sites are present in small amounts in vacuum-activat ed samples. After dealumination, no Lewis sites are present, being extrafra mework Al3+ species coordinatively saturated by OH groups. (C) 1999 Elsevie r Science B.V. All rights reserved.