The study of heterogeneity of OH groups in zeolites by comparing the half-width of IR band of hydroxyls interacting with adsorbed molecules

We propose a method of the studies of heterogeneity of OH groups in zeolites by comparing the half-width of the band of OH groups interacting with adsorbed molecules with that of homogenous acidic hydroxyls. We determined a correlation between half-width (Delta nu (1/2)) and frequency shift (Delta nu) for homogenous OH groups in phenol, acetic acid, trifluoroacetic acid, and on SiO(2) surface as well as in NaHX zeolite (Si/Al = 1.0) interacting with various electrodonor molecules (n-hexane, benzene, toluene, p-xylene, ethene, propene, butene-1, acetonitrile and diethyl ether). The application of our correlation to the problem of heterogeneity of OH groups in zeolites was tested for homogenous OH groups in NaHA and dealuminated H-beta zeolite and heterogeneous OH groups in H-mordenite and H-beta. We used the Delta nu (1/2)-Delta nu correlation to study the problem of heterogeneity of OH groups in H-ZSM-5 zeolites in which some previous studies suggested heterogeneity and some others homogeneity of OH groups. We also studied the problem of heterogeneity of P-OH groups in cloverite. (C) 2001 Elsevier Science B.V. All rights reserved.