The physical state of Ga species in Ga-containing mordenite zeolites

Abstract

A thorough characterization of mordenite zeolites containing framework Ga and Al atoms over the entire compositional range 0 <= Ga/(Ga + Al) <= 1 prepared under wholly inorganic conditions has been done by using powder X-ray diffraction, elemental analysis, N-2 adsorption, scanning and transmission electron microscopies, multinuclear MAS NMR, X-ray photoelectron spectroscopy, and X-ray absorption fine structure. Unlike the case of their as-made Na+ form, calcination of the NH4+-exchanged form of Ga-substituted mordenite materials at elevated temperatures leads to it severe extraction of framework Ga atoms from the tetrahedral positions. Most of the extraframework Ga species were found to remain tetrahedrally coordinated within mordenite micropores in a highly dispersed manner and to become octahedrally coordinated under dehydrating conditions. (C) 2008 Elsevier Inc. All rights reserved.