SSZ-45: A High-Silica Zeolite with Small Pore Openings, Large Cavities, and Unusual Adsorption Properties

Separations of small molecules such as CO2 and N2 or CH4 and CO2 are key to many industrial processes, but it is not always easy to find a molecular sieve that can discriminate between these molecules and withstand the harsh conditions often required. The high-silica zeolite SSZ-45, which was synthesized using N-cyclopentyldiazabicyclooctane as the structure directing agent (SDA), was found to exhibit excellent thermal stability and rather unusual adsorption properties under pressure. That is, it has potential in the area of small molecule separations. Of particular interest, therefore, was the structural basis for its peculiar adsorption behavior. The relatively complex silicate framework structure of SSZ-45 was determined from a combination of synchrotron powder diffraction and rotation electron diffraction data. Once the framework was known, it was possible to locate the organic SDA in the cavities and to better understand its contribution to the formation of the zeolite. Here we describe the synthesis of SSZ-45, the analysis of its structure, and the subsequent investigation of its small molecule separation properties.