Addressing the Challenge of Manufacturing Highly Siliceous Zeolites

The discovery of new and useful zeolite structures and/or compositions is critical for advancing the field of zeolite science and for the commercialization of new zeolite materials. While many interesting and important research advances have been made in this area, the proposed synthesis approaches can often be costly (expensive organic or inorganic reagents, long synthesis times, lengthy post-synthesis processes) or present additional health and safety challenges (fluoride-containing syntheses) that impede the commercial viability of these technologies. Research efforts that reveal synthesis routes of these newly reported zeolite structures (or compositions) using conventional synthesis methods and raw materials are important for progressing toward commercial reality. As one example, the manufacture of highly siliceous or pure-silica zeolites remain a challenge today. This talk will present results from our laboratory showing a feasible and reproducible approach to the production of highly crystalline and nearly pure-silica chabazite (CHA) zeolites. Under conditions very similar to those that normally form SSZ-24 (AFI), we report a narrow window using seeded, hydroxide-mediated gels that avoids the fluoride-mediated or dry-gel conditions typically used to form this composition. The materials exhibit excellent stability under severe hydrothermal calcination conditions (800-900^oC), and we also show results suggesting their utility in the kinetic separation of propylene and propane.