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

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, N2 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 a 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.