Algorithm finds 300 crystals to store methane

NORTHWESTERN (US) — A new algorithm automatically generates and tests porous crystals to quickly find the most promising structure for natural gas storage out of millions of possibilities.

Using the new computational method researchers were able to identify more than 300 different crystals—called metal-organic frameworks (MOFs)—that are predicted to be better than any known material for methane (natural gas) storage.

They then synthesized one of the promising materials and found it beat the U.S. Department of Energy (DOE) natural gas storage target by 10 percent.



There already are 13 million vehicles on the road worldwide today that run on natural gas—including many buses in the U.S.—and the number is expected to increase sharply due to recent discoveries of natural gas reserves.

In addition to gas storage and vehicles that burn cleaner fuel, MOFs may lead to better drug-delivery, chemical sensors, carbon capture materials, and catalysts.

“When our understanding of materials synthesis approaches the point where we are able to make almost any material, the question arises: Which materials should we synthesize?” says Randall Q. Snurr, professor of chemical and biological engineering at Northwestern University.

“This paper presents a powerful method for answering this question for metal-organic frameworks, a new class of highly versatile materials.”

Christopher E. Wilmer, a graduate student in Snurr’s lab, developed the new algorithm. Wilmer is first author of the paper published online in the journal Nature Chemistry.

“Currently, researchers choose to create new materials based on their imagining how the atomic structures might look,” Wilmer says. “The algorithm greatly accelerates this process by carrying out such ‘thought experiments’ on supercomputers.”

Researchers were able to determine which of the millions of possible MOFs from a given library of 102 chemical building block components were the most promising candidates for natural-gas storage.

In just 72 hours, the researchers generated more than 137,000 hypothetical MOF structures. This number is much larger than the total number of MOFs reported to date by all researchers combined (approximately 10,000 MOFs).

They then winnowed that number down to the 300 most promising candidates for high-pressure, room-temperature methane storage.

In synthesizing the natural-gas storage MOF that beat the DOE storage target by 10 percent, the research team showed experimentally that the material’s actual performance agreed with the predicted properties.

The new algorithm combines the chemical “intuition” that chemists use to imagine novel MOFs with sophisticated molecular simulations to evaluate MOFs for their efficacy in different applications. The algorithm could help remove the bottleneck in the discovery process, the researchers say.

The Defense Threat Reduction Agency and the U.S. Department of Energy, Office of Science, Basic Energy Sciences, supported the research.

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