What CAN It Be?

Elucidating Cerium Solution Chemistry

Image courtesy of Argonne National Laboratory
The newly-proposed structure of ceric ammonium nitrate, with an oxygen bridge, may explain why this popular industrial reagent is so versatile.

The Science

Ceric ammonium nitrate (CAN) is used to manufacture everyday chemicals and was known to have a simple structure that was thought to persist when in solution. Recently, scientists revealed that CAN changes its chemical form when it is dissolved. It immediately assembles into a complex structure, in which an oxygen bridges two cerium ions. This novel solution structure allows CAN to involve two of its electrons during reactions, not just one as previously thought. The discoveries raise pertinent questions regarding the behavior of cerium in chemical industries while providing insights into possible new opportunities for its use.

The Impact

This study shatters long-held assumptions about a vital feedstock that underpins swathes of applied chemistry. The findings will impact diverse applications where ceric ammonium nitrate (CAN) is used in the chemical industry ranging from rare-earth separations to chemical manufacturing.

Summary

Ceric ammonium nitrate (CAN) is produced directly from rare-earth hydrometallurgical processes via crystallization out of solution as a simple salt. From there, it is used in myriad industries, especially as an oxidizing agent for the manufacture of organic chemicals. The majority of these applications employ CAN in solution. Text books on the rare earths will often have a chapter dedicated to CAN, where it is said that the structure in solution is the same as the solid. Thus, this ubiquitous salt is thought to consist of a sole cerium ion in solution that acts as a simple one-electron oxidant. However, researchers at Argonne National Laboratory are challenging this perception. Using synchrotron x-rays and Raman spectroscopy, this group has found that CAN immediately assembles to form a complex composed of two cerium ions linked through a single oxo-bridge, even in acidic solutions. This revelation suggests CAN chemistry may be more complicated than currently believed and helps to explain why it is such a versatile reagent, de-mystifying longstanding questions regarding its peculiar behavior in extractive separations. The discovery of the oxo-bridged dinuclear complex of CAN is expected to have far-reaching effects on the chemical industry due to the wide array of applied uses.

Contact

Ross J. Ellis
Argonne National Laboratory
rellis@anl.gov

Funding

This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences under contract number DE-AC02-06CH11357.

Publications

T. J. Demars, M. K. Bera, S. Seifert, M. R. Antonio, and R. J. Ellis, “Revisiting the solution structure of ceric ammonium nitrate.” Angewandte Chemie International Edition 54, 7534-7538 (2015). [DOI: 10.1002/anie.201502336]

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