11:33 a.m., May 10, 2010----A team of chemical engineering researchers at the University of Delaware has developed a computational framework for screening potential bimetallic catalysts. The finding was published online in Nature Chemistry on April 25.

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The paper, “Using First Principles to Predict Bimetallic Catalysts for the Ammonia Decomposition Reaction,” was authored by Danielle Hansgen, a fourth-year doctoral candidate, and her advisers, Dion Vlachos, Elizabeth Inez Kelley Professor, and Jingguang Chen, Claire D. LeClaire Professor.

Chen explains that the decomposition reaction is critical to the use of ammonia as a hydrogen storage medium for applications such as fuel cells that require an extremely pure form of hydrogen. Ruthenium has proven to be an effective catalyst for breaking ammonia down into its constituents, nitrogen and hydrogen, but as a rare metal, it is scarce and expensive.

“Ruthenium is the best single element for this reaction,” Chen says, “but since it's not a viable option for large-scale commercialization, we began to look at combinations of two metals that are more abundant to see if we could achieve similar results.”

To narrow the pairs of metals for consideration, the researchers first examined the characteristics that make ruthenium so effective. They developed a chemical descriptor of the bond -- it had to be strong enough to decompose ammonium but weak enough to allow for complete catalysis and leave a clean surface -- and then validated that descriptor using an appropriate bimetallic catalyst.

That pair -- nickel and platinum -- proved to be an effective “guinea pig” for the experimental work, but it is still too expensive for broad use. However, with the descriptor validated, the researchers now have a framework for examining other bimetallic catalysts that use more plentiful elements.

Vlachos points out that the same principles could be applied to search for cheaper catalysts for other reactions, including the selective oxidation of carbon monoxide for hydrogen purification and hydrogenation of hydrocarbons.

Both faculty members give full credit for the work to Hansgen, with Vlachos providing support on the computational and Chen on the experimental side.

The research was carried out under UD's Center for Catalytic Science and Technology.

Article by Diane Kukich
Photo by Kathy F. Atkinson