Opportunities for selective catalysis within discrete portions of zeolites: The case for SSZ-57LP

Abstract

We describe a new zeolite catalyst where we develop only a portion of the structure for strong acid sites. This is achieved using zeolite SSZ-57 in boron lattice substitution (weak acid sites) and then replacing the boron sites in the large pore segments of this novel zeolite, while the intermediate pores (with MEL topology) remain unchanged. We can achieve the creation of such a novel catalyst system due to the inherent structure of SSZ-57 (repeat domains of MEL topology, periodically interrupted by a short segment of large pores) because the re-insertion of aluminum for boron requires that the pores be large to effect substitution. In this work, we describe the preparation and characterization of the novel material designated as SSZ-57LP. We use three model compound reactions to demonstrate the unique behavior for this novel large pore (but short path) zeolite and contrast it with intermediate pore zeolite Al-ZSM-11 (MEL topology) and the Al-SSZ-57 where the strong acid sites are in both intermediate and large pore regions (from direct zeolite synthesis with aluminum in the gel). The reactions studied are the Constraint Index probing reactant selectivity for cracking n-hexane and 3-methylpentane, the hydroisomerization of n-hexane where the formation of dimethylbutanes is examined for large pore space within a zeolite, and then finally, the isomerization and disproportionation of 1,3-diethylbenzene, again as a probe for large enough transition state selectivity within a given zeolite.

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