Inhomogeneity of Broensted acid sites in H-mordenite

Bronsted acid sites in H-mordenite have been studied using adsorption-desorption of probe molecules (ammonia, benzene, cyclohexane) and monitored by FTIR spectroscopy. Both the second derivative of the spectrum and NH 3 thermodesorption show that the asymmetrical stretch band of bridged OH groups at 3607 cm -1 consists of two components, one at a higher frequency of 3612 cm -1 (lower effective acidity) and another at a lower frequency of 3585 cm -1 (higher effective acidity) with the intensity ratio of 2:1. The low-frequency OH groups are inaccessible to bulky molecules such as benzene and cyclohexane, which suggests that they are located in the small channels