PARTITIONING OF ALUMINUM ATOMS IN CRYSTALLOGRAPHICALLY NONEQUIVALENT TETRAHEDRAL SITES OF THE ZEOLITE OFFRETITE BY SI-29 MAS NMR

For the zeolite offretite, a formula is proposed which includes the fr amework Si/Al ratio (R), the partitioning ratio of Al over two crystal lographically non-equivalent tetrahedral sites (r) and intensities of the observed peaks in the Si-29 MAS NMR spectrum. By this formula, the framework Si/Al ratio of offretite can be estimated from the Si-29 MA S NMR spectrum. Combined with chemical analysis of the Si/Al ratio, Al partitioning in two kinds of T sites can also be deduced. It is concl uded that the T-B sites are favored by Al atoms in parent offretites a nd Al atoms at T-B sites can more easily be substituted isomorphously by Si when treated with (NH4)(2)SiF6. The formula proposed here is bas ed only on experiments and may be used to testify some statistical mod els of Al distributions in offretites.