Comet supercomputer for demonstrating methane storage applications

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Figure shows methylidene phenals (MPh), a molecular maquette of porous carbon surfaces such as ZTC. The central atom (X1 = C, B or N) is the place of the heteroatom substitution and the methane bond. Illustration by Professor Nick Stadie, Montana State University

Porous carbon is an established class of materials with considerable potential for a wide range of applications – from water treatment and gas separation to energy storage and thermal insulation. There is a class of freshmen too, especially if they have already been part of an international research team whose work could have implications for the technology needed to make low-carbon or carbon-free chemical fuels for vehicles.

Ryan Rowsey, a freshman chemistry student at UC San Diego, received a bachelor’s degree from Montana State University, Bozeman (MSU) and worked with an international team of researchers, the comet at the San Diego Supercomputer Center (SDSC) at UC San Diego to complete a detailed study of a specific subset of porous carbon called Zeolite-Templated Carbon (ZTC) as a gas storage material.

“The computational chemistry skills and tools I learned from doing this job have been invaluable to my growth as a researcher, and now that I am starting graduate school I feel like I am prepared with unique skills,” said Rowsey.

The work Rowsey was referring to is the research team’s use of computer models of ZTC structural units (referred to as maquettes – small models of surface sites of interest) to assess the binding energy of methane gas as a function of chemical composition. Led by Nicholas Stadie, Assistant Professor of Physical Chemistry and Materials Science at MSU, and Robert Szilagyi, Associate Professor of Chemistry and Biochemistry at MSU, the team’s study results were recently presented in the Journal of Physical Chemistry A.

“From an extensive series of calculations, we clearly identified the preference for methane over nitrogen-substituted adsorption sites,” said Szilagyi. “The theoretically estimated binding energies and the experimentally measured values ​​of the heat of adsorption agree well and confirm the use of computational chemistry as a tool to develop new porous carbon materials for methane storage applications – a key technology for bridging the gap to low-carbon or low-carbon free chemical fuels for vehicles.”

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This animation shows how an incoming methane molecule (adsorbate) and a carbon surface model (adsorbent) mutually change the electron density. The methane molecule “lander” touches the carbon “moon surface” and “swirls” “dust” (ie electron density, shown in pink and green). Photo credit: Robert K. Szilagyi, Montana State University

Why it matters

Computer-aided streamlined design of new materials offers an efficient way to develop or optimize new or existing energy storage and conversion technologies. Rather than a traditional trial-and-error approach, computer modeling of chemical processes speeds time-to-market, minimizes chemical waste, and maximizes the use of human resources and brainpower.

In particular, the storage and conversion of methane into energy or chemical raw materials without greenhouse gas emissions is a long overdue goal of the petrochemical industry. Computer model-based material design enables the simulation of every step of methane storage or conversion at the atomic level, providing a clear understanding of potential inhibition steps and insights into reducing harmful emissions and toxic chemical waste.

Presentation of nitrogen doping of carbon materials

While the experimental results used in the calculations were obtained in Stadie’s laboratory, Stadie and Szilagyi next showed that experimentalists can use simulation results to guide their strategies in the synthesis of nitrogen-doped carbon materials for methane storage and release. The calculation results clearly documented the benefits of concentrating on nitrogen doping of carbon materials in methane storage. In addition, Szilagyi said, this work serves as a chemical accuracy map for simplified but realistic models of porous carbon surfaces for many other problems.

“We were really surprised by the clear and consistent preference for methane over nitrogen-substituted porous carbon models over both the unsubstituted and boron-substituted models,” said Szilagyi.

“This may not seem like a huge effect to many, but it was exactly the size we were expecting,” added Stadie. “This effect has very important effects on methane storage at ambient temperature.”

How supercomputing helped

While the team had access to a humble lab workstation cluster and MSU’s Hyalite high-performance computing system, they could access it comet enabled the quick completion of particularly intensive computer experiments that would otherwise have been very demanding. The team was able to perform calculations of the potential energy surface mapping in which each grid point was calculated on the corresponding theoretical level without any reductions or simplifications.

“The additional computational resources allowed us to do a more thorough study, including computer control and blank simulations, which are mandatory for experimental work but are often left out in theoretical studies,” said Szilagyi.

“The experimental physicists’ approach to computational chemistry has great potential to improve theoretical models so that they interact directly with observations from our laboratory,” continued Stadie. “The successful combination of theory and experiment increases the effect of calculations in the rationalization of experiments and the generation of experimentally verifiable hypotheses.”

What’s next?

The approach developed in the first two years of this work has direct implications for the ongoing experimental research directions in the stadium laboratory, from assisting in screening synthesis conditions to down-selecting gas adsorption studies and predicting new technological applications beyond gas storage. The research team has already started evaluating other molecular substitutions, examining larger molecular models with oxygen-containing functional groups, considering other adsorbates, and extending computational methods to larger, periodic systems, to name a few.

In addition to Rowsey and MSU PhD student Erin Taylor, Stadie and Szilagyi worked with Stephan Irle of the Oak Ridge National Laboratory, a scientist in computational soft materials. Further collaborators were Prof. Hirotomo Nishihara from Tohoku University in Japan and the scientists Tamas Szabo (Hungary), Eva Scholtzova (Slovakia), Amrita Jain (Poland) and Monica Michalska (Czech Republic).

“If you consider that I’m going to UC San Diego, I might even be able to work in a while Expanse (the new supercomputer at SDSC) in my new research, ”said Rowsey.

This research was supported by the Office of Energy Efficiency and Renewable Energy (EERE) of the US Department of Energy within the hydrogen and fuel cell technology and vehicle technology departments (Grant No. DE-EE0008815). The analysis of the theoretical results was supported by the Fossil Energy and Carbon Management Program of the US Department of Energy, the Advanced Coal Processing Program, the C4WARD project. Additional support came from the American Chemical Society Petroleum Research Fund and the MSU Undergraduate Scholars Program. Calculation comet was supported through XSEDE, supported by the National Science Foundation (Grant # ACI-1548562). Additional calculations were performed using the Hyalite HPC system operated and supported by the University Information Technology Research Cyberinfrastructure at Montana State University.


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