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New zeolites more effective at removal of CO2 from gas mixtures

Researchers from South Korea, the UK and Sweden have identified and prepared a new family of zeolites—crystalline aluminosilicates with frameworks that contain windows and cavities the size of small molecules—that can separate out carbon dioxide more effectively from fuel gases than those previously known. A paper on their work is published in Nature.

Existing zeolites have widespread use in industrial processes that involve gas separation and catalytic conversion. Although many millions of novel structures are both hypothetically possible and energetically feasible, not enough is known about their formation mechanism to prepare them on demand. New materials are discovered via exploratory synthesis as microcrystalline powders and their structures solved by time-consuming, non-routine approaches.

In the new research, the researchers from POSTECH in South Korea, the University of Portsmouth and the University of St. Andrews in the UK, and Stockholm University combined structure solution and prediction with targeted synthesis to prepare the family of novel, highly complex zeolites, which have attractive properties as adsorbents.

The first step in the process was the structure solution of a zeolite, prepared decades ago but the complex structure of which had defied solution. The new method implicitly predicted the existence of a new family of zeolites with close structural relationships.

Using these structures as targets and modifying the syntheses to include organic and inorganic templating agents, the higher family members were realized. As well as being the most complex zeolite structures known, with exquisite structural architectures, they also show rapid and selective uptake of carbon dioxide, the first step in carbon capture and storage strategies.

Here we present an approach that combines structure solution with structure prediction, and inspires the targeted synthesis of new super-complex zeolites. We used electron diffraction to identify a family of related structures and to discover the structural ‘coding’ within them. This allowed us to determine the complex, and previously unknown, structure of zeolite ZSM-25, which has the largest unit-cell volume of all known zeolites (91,554 cubic ångströms) and demonstrates selective CO2 adsorption. By extending our method, we were able to predict other members of a family of increasingly complex, but structurally related, zeolites and to synthesize two more-complex zeolites in the family, PST-20 and PST-25, with much larger cell volumes (166,988 and 275,178 cubic ångströms, respectively) and similar selective adsorption properties. Members of this family have the same symmetry, but an expanding unit cell, and are related by hitherto unrecognized structural principles; we call these family members embedded isoreticular zeolite structures.

—Guo et al.

More generally, this work presents for the first time a combined solution, prediction and synthesis approach to novel zeolite and related structures that encourage future advances in design and preparation of functional materials.

The project is the supported by the Swedish Research Council (VR) and the Swedish Governmental Agency for Innovation Systems (VINNOVA) through Berzelii Center EXSELENT on Porous Materials, the Knut and Alice Wallenberg Foundation through the project grant 3DEM-NATUR, and the Röntgen-Ångström Cluster through the project grant MATsynCELL.

Resources

  • Peng Guo, Jiho Shin, Alex G. Greenaway, Jung Gi Min, Jie Su, Hyun June Choi, Leifeng Liu, Paul A. Cox, Suk Bong Hong, Paul A. Wright & Xiaodong Zou (2015) “A zeolite family with expanding structural complexity and embedded isoreticular structures” Nature doi: 10.1038/nature14575

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