CHARACTERIZATION OF INCORPORATED GALLIUM IN BETA-ZEOLITE

Framework and nonframework gallium species in beta zeolites were chara cterized by n.m.r., XPS, and i.r. spectroscopic methods. The isomorpho us substitution of Al+3 by Ga+3 in the framework of beta zeolite gives 1 and 3 ppm downfield shifts of Si(1M) and Si(2M) peaks (M = Ga inste ad of Al) in Si-29 MAS n.m.r. spectra, such shifts have been confirmed by SCF-GIAO theoretical calculation. During heat treatment, the frame work Ga and AI of beta zeolites can change into nonframework species, as were detected by Ga-71- and Al-27-MAS n.m.r., and XPS, and such cha nge shifts the binding energy of Ga-3d XPS from 20.7 to 21.4 eV and gi ves an i.r. band of extraframework hydroxyl groups at 3,685 cm(-1) (Ga OH) or 3,655 cm(-1) (AIOH) with the i.r. band of bridging hydroxyl gro ups at 3,619 cm(-1) (Ga(OH)Si) or 3,607 cm(-1) (Ai(OH)Si). The extrafr amework Ga species probably exist in cation-like state. (C) Elsevier S cience Inc. 1997