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Molecular Mimic of Solid Catalyst

Metal-organics: Synthetic compound possesses key yet uncommon nanoparticle feature

by Mitch Jacoby
February 13, 2012 | A version of this story appeared in Volume 90, Issue 7

Credit: Science
The triangular arrangement of MoS2 units in MoS2 nanoparticles (left) is mimicked by the arrangement of atoms in this pentapyridyl compound (right).
The triangular arrangement of MoS2 units in this compound with multiple pyridine rings matches the structure of catalytically active sites in MoS2 particles. Mo is green; S is yellow; F is light blue; O is red; N is blue; C is gray.
Credit: Science
The triangular arrangement of MoS2 units in MoS2 nanoparticles (left) is mimicked by the arrangement of atoms in this pentapyridyl compound (right).

New ways to synthesize catalytic materials for energy conversion and storage may be possible with a synthetic molecular complex that mimics the shape and reactivity of catalytically active sites in molybdenum disulfide nanoparticles.

MoS2 is well-known and thoroughly studied, because of its extensive use in the petroleum industry as a hydrodesulfurization (sulfur removal) catalyst. Several years ago, researchers in Denmark predicted and showed experimentally that MoS nanoparticles can also serve as effective catalysts for the hydrogen evolution reaction, a key step in light-driven hydrogen production from water.

Those results pointed to a low-cost alternative to the precious platinum group metals typically used for the hydrogen evolution reaction. Other studies have indicated that the nanocrystal bulk is mostly inactive and that the catalyst’s active sites are the relatively few triangular MoS2 units along the particle edges.

Now, a team from the University of California, Berkeley, which includes Hemamala I. Karunadasa, Christopher J. Chang, Jeffrey R. Long, and coworkers, has prepared a synthetic Mo(IV)-disulfide pentapyridyl complex that features the same type of uncommon triangular MoS2 units found along the nanocrystal edges (Science, DOI: 10.1126/science.1215868).

On the basis of electrochemical measurements and gas chromatographic analysis of acidic organic and aqueous solutions containing the complex, including a sample of unpurified California seawater, the team concludes that the new compound serves as an effective hydrogen evolution catalyst.

“These molecules, which possess the essential geometric and electronic structures of MoS2’s active sites, appear remarkably robust,” says University of Washington, Seattle, chemistry professor Daniel R. Gamelin. He adds that the compounds may open new routes to preparing highly active hydrogen evolution catalysts and provide insights into their inner workings.


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