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Breaking molecular traffic jams with finned nanoporous materials

Aug. 11, 2020 - Thousands of chemical processes used by the energy industry and for other applications rely on the high speed of catalytic reactions, but molecules frequently are hindered by molecular traffic jams that slow them down. Researchers at the University of Minnesota are part of an international team that has invented an entirely new class of porous catalysts using unique fins to speed up the chemistry by allowing molecules to skip the lines that limit the reaction. The discovery has immediate relevance to industry for a host of applications, including the production of fuels, chemicals for plastics and polymers, and reactions that make molecules for food, medicine and personal care products. The research was published in Nature Materials, the leading journal of materials science.

The breakthrough focused on reducing barriers for molecules accessing the interior pores of catalysts, called zeolites— aluminosilicates with pores smaller than a nanometer. Zeolites are widely used in commercial processes as solid catalysts for the production of gasoline and value-added chemicals and other products.

Researchers at the University of Houston, led by Jeffrey Rimer, Abraham E. Dukler Professor of chemical and biomolecular engineering, developed a way to induce larger catalyst particles to behave like nanoparticles—that is, to allow molecules to enter, spark a reaction and exit quickly, by growing protrusions, or fins, on the surfaces of catalyst particles. By adding nanoscale fins that protrude from the external surface of large particles, the roughened exterior of the particle significantly increased in surface area, granting molecules increased access and reducing the transport limitations that frequently plague conventional zeolite materials.

“Our new synthesis approach capitalizes on work we have been doing in our group for many years, focused on controlling zeolite crystallization in ways that enable the growth of fins,” Rimer said. “This new class of materials bypasses the need to directly synthesize nanoparticles, creating a new paradigm in zeolite catalyst design.”

Rimer worked with a team of international experts in materials synthesis, characterization and modeling to demonstrate the capability of finned zeolites to improve the performance of this unique family of solid catalysts. By comparing finned zeolites with conventional catalytic materials, they showed that zeolites with fins lasted almost eight times longer. Rimer said the incorporation of fins leads to shorter internal diffusion pathways and ensures molecules efficiently reach the reaction sites while reducing the propensity of carbon-based species to become immobilized. That build up ultimately deactivates the catalyst.

Additional work at the University of Minnesota by the research group of Paul Dauenhauer, professor of chemical engineering and materials science, and by Michael Tsapatsis, professor of chemical and biomolecular engineering at Johns Hopkins University, confirmed the enhanced mass transport properties of finned zeolites. Using a new method to track molecule diffusion by infrared light, the UMN researchers demonstrated that the fins enhanced molecule transport between 100 and 1,000 times faster than conventional particles.

“The addition of fins allows molecules to get inside the channels of zeolites where the chemistry happens, but it also lets molecules quickly get out of the particle, which lets them operate for a much longer period of time,” Dauenhauer said.

Researchers had expected the fins would perform better than a standard-sized zeolite catalyst, he said. “But we found it was not just a 10 percent or 20 percent improvement. It was a tripling of efficiency. The magnitude of the improvement was a real surprise to us.”

This work was supported by and is part of a larger mission of the U.S. Department of Energy, with additional support provided by various international funding agencies.

To read the full research paper entitled “Finned zeolite catalysts,” visit: https://www.nature.com/articles/s41563-020-0753-1

Excerpt from news release written by Rhonda Zurn, College of Science of Engineering.

Related Link: https://cse.umn.edu/college/news/breaking-molecular-traffic-jams-finned-nanoporous-materials

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