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The molecular sieve UTD-1 is investigated using scanning and transmission electron microscopies (TEM), solid-state NMR spectroscopy, electron (ED) and X-ray diffraction (XRD), adsorption studies, and catalytic test reactions. The results confirm that UTD-1 is the first high-silica zeolite to contain a one-dimensional, extra-large 14-ring pore system. TEM and ED show that UTD-1 is faulted along the (002) planes. Simulations of XRD patterns of faulted structures using DIFFaX indicate that the XRD pattern of a framework containing the so-called double crankshaft chains is in better agreement with the experimental pattern than a framework with the narsarsukite chains previously reported. Thermal/hydrothermal stability studies show that UTD-1 has similar stability to other medium- and large-pore, high-silica zeolites. The ratio of isomerization to disproportionation, and the distribution of trimethylbenzene isomers in the m-xylene isomerization test reaction from UTD-1 are similar to those obtained from other large-pore zeolites (zeolites Y or L). However, UTD-1 shows a p-/o-xylene ratio of products below one.

Table 10. Anisotropic displacement parameters Ulj [107 pm 2 ] for la. The anisotropic displacement factor exponent takes the form:-2 it 2 [h 2 a* 2 U 1 1 + ... + 2 h k a* b* U 12 ].

A model for the structure of the zeolite SSZ-31 is presented. The model is obtained by combining information from adsorption capacity measurements, transmission electron microscopy, and high-resolution X-ray diffraction. SSZ-31 is a one-dimensional large-pore zeolite with a framework density of 18.7 tetrahedral(T)-atoms per nm-3 and a bulk density of 1.87 g cm-3. The pore apertures are elliptical with major and minor axes of approximately 8.6 Å × 5.7 Å. SSZ-31 is an extreme example of a complex and highly faulted zeolite. The structure can be described as an intergrowth of four different but structurally related polymorphs.