Unraveling the Perplexing Structure of the Zeolite SSZ-57

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Science  26 Aug 2011:
Vol. 333, Issue 6046, pp. 1134-1137
DOI: 10.1126/science.1207466

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Previous high-resolution x-ray powder diffraction and transmission electron microscopy studies of the zeolite SSZ-57 could not fully elucidate the structural basis for its puzzling adsorption behavior, which appears to be intermediate between that of a medium- (10-ring) and a large-pore (12-ring) zeolite. Now by applying advanced crystallographic techniques (structure solution in four-dimensional space and interpretation of three-dimensional diffuse scattering by Monte Carlo simulation) and crystal chemistry considerations to high-quality single-crystal x-ray diffraction data collected on a microcrystal (about 2 micrometers by 2 micrometers by 8 micrometers), we have been able to derive a comprehensive description of its silicate framework structure. The framework is related to that of ZSM-11 but is commensurately modulated along the c axis (P4¯m2, a = b = 20.091 Å, c = 110.056 Å) to yield a structure with a 12-ring:10-ring ratio of 1:15. Disorder of the 12-rings results in a three-dimensional 10-ring channel system with large isolated pockets. The structure helps to clarify the material’s catalytic activity.

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