by Shusuke Ito
I joined the Sun research group at the University of Michigan, led by Professor Sun, as a visiting scholar to collaborate on research into thermodynamics in zeolites.
Motivation
Zeolite is a representative polymorphic material with over 260 polymorphs and often plays a central role in several industrial processes. To direct the crystallization of a targeted zeolite, a template molecule and/or inorganic cation that occupies the pores defined by a specific zeolite topology is commonly used. Although many computer-assisted algorithms are poised to optimize experimental conditions to control the final phase, a significant gap remains between simulations and real-world systems.
During my study abroad, I visited the research group led by Professor Sun at the University of Michigan. He possesses valuable expertise in thermodynamics, which he uses to elucidate the synthesis of various inorganic materials and to optimize experimental conditions. I plan to apply their methods to the zeolite systems.
Figure 1. Crystal structures of AEI-type, CHA-type, and ERI-type zeolites. They are often composed of aluminosilicate frameworks.
Achievements
Modeling
To consider the thermodynamics of zeolites during the synthesis, it is required to obtain plausible atomistic models of as-synthesized zeolites. During zeolite synthesis, inorganic or organic molecular cations act as templates, filling and stabilizing the pores, cages, or channels. At the same time, these cation species are recognized as charge compensators countering the negative charge induced by the Al atom, to which the Si atom is substituted. Based on this prior knowledge, I built the computational workflow to generate the plausible atomistic model of as-synthesized zeolites. By running this workflow, I obtained ~50,000 as-synthesized zeolites and performed atomistic simulations to calculate the energetic data.
Figure 2. The schematic illustration of the as-synthesized zeolite, with template cation species filling the pore of the zeolite and countering the negative charge coming from the insertion of Al3+ substituting Si4+.
Thermodynamics
I derived a thermodynamic framework to describe zeolite synthesis. By combining this thermodynamic framework and accumulated data from the modeling workflow, I constructed the first phase diagram of zeolites. The key feature of this theoretical approach is that it bridges the gap between experimental conditions and computationally derived phase diagrams, which represent concentrations of several species and energetic data.
I chose choline as a molecular cation and organic template, and Na+, K+, Cs+, and Rb+ as inorganic templates. In addition, I consider the SOD-, AEI-, LEV-, CHA-, and ERI-type zeolites.
I plan to conduct experiments to validate this approach for polymorph selection in zeolites.
Figure 3. An example of a computationally derived phase diagram of zeolite. Black dashed lines in the M to μ diagram designate the concentration of several species, which are experimental conditions. And the black dashed lines in the diagram at the bottom indicate the energetic value (μ) derived from the M to μ diagram. The values and ticks are omitted because they have not yet been published.
Life in Ann Arbor
My apartment is located in the downtown area of Ann Arbor. I enjoy walking around and appreciating the beautiful townscape and historic buildings. I sometimes hang out with members of the Sun research group and enjoy Thanksgiving, Christmas, New Year’s, etc., in Ann Arbor.
I had a truly memorable time with the group members. I’m deeply grateful for their generous support, not only in research but also as wonderful friends.
I am confident that this experience will have a lasting impact on my future life and career.
Acknowledgment
I would like to express my sincere gratitude to Friends of UTokyo, Inc. for their generous support, which made my research visit to the University of Michigan possible.
