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

Abstract

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 (Δ ν 1/2) and frequency shift (Δ ν) 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 Δ ν 1/2–Δ ν 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.