Strategy for Synthesizing Nano-sized Zeolites using Germanium Oxide
This invention establishes an approach to prepare nano-sized zeolites using germanium oxide (GeO2) as a component of the overall synthesis composition. Zeolites are nanoporous crystalline materials that exhibit internal diffusion limitations to guest molecules, which often compromises their performance as catalysts and sorbents. Different strategies have been used to reduce mass transport limitations, including the synthesis of nano-sized crystals (with sizes <100 nm), 2-dimentional nanosheets, and hierarchical materials with interconnected mesopores and micropores. These strategies often involve multi-step synthesis procedures and/or require the use of expensive organic molecules. In this invention, we propose a simplistic and generalizable strategy to reduce the size of conventional zeolites of different crystal structures via the addition of GeO2 to synthesis gels (for example, using molar ratios of Si/Ge ≥ 10). We have demonstrated that the presence of germanium reduces the crystal size of zeolite ZSM-11 (MEL framework) by a 8-fold (i.e. from 400 to 50 nm). Similar outcomes were observed for zeolite ZSM-5 (MFI framework) where the addition of germanium resulted in an increased population of nanoparticles (<50 nm). Moreover, we demonstrated that GeO2 added to syntheses of mordenite (MOR framework) alters crystal morphology from large particles (> 5 µm) to intergrown layers (with layer thickness < 200 nm). As the synthesis conditions of these three zeolite frameworks are different, this highlights the generalizability of this strategy for diverse synthesis conditions and zeolite crystal structures. The insertion of Ge in zeolite frameworks can stabilize smaller rings (<5 member ring); however, our findings reveal that most of the Ge added to these syntheses is not incorporated in the final crystalline product (for example, Si/Ge >25), thus a majority of Ge can be recovered and reused, which can be commercially beneficial for the preparation of nano-sized zeolite crystals. In certain cases, such as ZSM-11, GeO2 leads to higher product yields. Analysis of nano-sized H-ZSM-11 and H-ZSM-5 catalysts prepared from GeO2-containing syntheses also reveal enhanced catalyst lifetime in the methanol to hydrocarbons reaction compared to samples prepared by conventional synthesis methods.
63/352,021, (Provisional, Pre-Conversion)
Professor, Chemical & Biomolecular Engineering