SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF MIXED ALUMINUM-GALLIUM-OFFRETITES

A new synthesis procedure is reported for the preparation of mixed Al, Ga-offretites over the entire solid solution range 0 less than or equa l to Ga/(Ga + Al) less than or equal to 1. The resulting materials are characterized by X-ray powder diffraction, adsorption microcalorimetr y and multinuclear solid state NMR. The Si-29 MAS-NMR data are consist ent with statistical occupancy of the T-1 and T-2 sites by aluminum an d gallium, and also show no positive evidence for preferential siting effects between both framework metals. Isotropic chemical shifts and n uclear electric quadrupolar coupling constants for Al-27 and Ga-71 hav e been obtained from a field-dependent analysis of the center of gravi ty in the MAS-NMR spectra, H-Al,Ga-offretites produced by ammonium exc hange and subsequent calcination reveal evidence of partial demetallat ion of the framework with formation of extra-lattice metal species. (C ) 1997 Elsevier Science B.V.