Zeodirect - Spatial Control of Zeolite Synthesis

Zeolites are crucial for numerous industries, such as refinery and upgrading of fossil or renewable resources, catalysis and separation, but also in newly emerging fields like water purification and desalination, (nuclear) waste management and as solar thermal collectors. Zeolites are sophisticated inorganic solids produced on industrial scale via the hydrothermal gel method. For investigating the mechanism of zeolite formation however gels are rather inconvenient. To overcome this problem zeolite synthesis from solution has been developed. The crystallisation of Silicalite-1 zeolite from clear solution is a well-known model system for investigating the growth mechanism. A consistent model for zeolite formation is however not yet formulated. In particular the early stages of formation remain elusive. The goal of this project is to establish new methods to observe and control the formation of synthetic zeolites. Chemical microreactors will be equipped with electrode structures to generate electric fields. The hypothesis is that the emerging zeolite crystals react differently in each stage of the growth process. Most interesting are long ranged electrostatic or hydrodynamic forces leading to collective behavior. Acoustic methods for manipulating the zeolite particles in solution will applied as well. The combination with optical and X-ray scattering will lead to a better understanding of the whole synthesis process and pave the way for zeolites tailored for specific applications. These methods will be advantageous to all kinds of phase transitions in liquids.

The research project ZeoDirect is an international collaborative research effort between the Institute for Microelectronics and Microsensors (IME) at JKU Linz with the Centre for Surface Chemistry and Catalysis (COK-KAT) at KU Leuven. Understanding the basic principles of zeolite formation is essential for creating novel and stable materials for versatile applications such as molecular sieving, catalysis, energy storage, and selective removal of contaminants. The project focused on synthesizing zeolites using hydrated silica ionic liquids (HSILs) and engineering novel methods for measuring physical parameters of the complex synthesis liquids. The team developed a novel method for electrochemical analysis called 'moving electrode electrochemical impedance spectroscopy' (MEEIS) that can be used for accurate and stable conductivity measurements of chemically aggressive substances and for monitoring the associated phase transformation processes. This approach complements existing methods for monitoring zeolite formation from the early stages of nucleation to the crystallisation of micrometer-sized crystalline particles. Combining conductivity with nuclear magnetic resonance (NMR), dynamic light scattering (DLS), and small-angle-X-Ray-scattering (SAXS) measurements lead to advanced models for predicting the nanostructure from the basic synthesis ingredients. Simulations on the molecular level were also pursued to link experimentally measured parameters with atomistic processes. In addition, the team made an intriguing observation of Marangoni flows driven by the partial evaporation of zeolite synthesis liquids. Careful experimental observation resulted in the development of a numerical model that simulated the phenomenon. The team also developed a setup that combined electrical impedance measurements with a dual quartz crystal microbalance. Overall, the project made significant progress in two different research fields, engineering of sensors and measurement devices, as well as fundamental material chemistry.