Control of Al for B framework substitution in zeolite Beta by counterions

Al insertion into boron Beta zeolite is quantitatively controlled by a three-step procedure. First, a mixed Na+/NH4+ counterion series balancing the charge of tetrahedral framework boron is prepared by ion exchange. Subsequent calcination converts NH4+ to H+ which is accompanied by the transformation of boron to trigonal coordination. Secondly, the calcined Na+/H+ samples are deboronated in water which allows a preferential extraction of boron at protonated sites. The sites which are balanced by sodium cations are protected against deboronation due to the low reactivity of tetrahedral boron. Finally, aluminum insertion into the vacated framework sites is achieved by ethanol solutions of Al(NO3)3. The ratio of Na+/NH4+ counterions determines the extent of Al substitution for boron. Each step is quantitatively analyzed using solid state NMR. The extent of Al–B exchange can be tuned in a large range.

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► Quantitative control of B/Al exchange in the framework of zeolite Beta is achieved by adjusting the counterion composition.
► A large variation of Al in the zeolite is achieved by Al insertion in alcoholic solutions.
► Multinuclear solid state NMR is employed to verify each step in the modification procedure.