Development highly efficient catalysts

Development of highly efficient catalysts

11:42 PM, 12th February 2012
Development of highly efficient catalysts
Metal cluster built up like a Russian matryoshka.

MUNICH, GERMANY: Thomas Faessler, Professor, Technische Universitaet Muenchen (TUM) explained his molecule as pack of one atom in a cage within an atom framework. With their large surfaces these structures can serve as highly efficient catalysts. Professor Faessler’s work group was the first to generate spatial structures built up in three layers as isolated metal clusters in bronze alloys. In the laboratory the substance is an unimpressive, fine, grayish-black powder, yet the structure models are in colour and in various nested shapes. These powders, with their large surfaces, are interesting as an interim step for catalysts that transfer hydrogen, for instance. Similar structures made of silicon could be used in solar cells to capture light from the sun more effectively.

Most people view metals as uniform materials with a rather unspectacular structure. The metal compounds from Faessler’s institute are quite the opposite. His desk is piled high with various multicoloured cage models with yellow spheres representing copper atoms and blue ones for tin. The analogy to the carbon spheres that caused a sensation as Buckyballs cannot be overlooked. Here, too, there are geometric structures made up of triangles, pentagons and hexagons. However, they are not made of carbon, heavier metals such as tin and lead can also form such isolated cage structures.

The new bronzes from the Faessler laboratory are different. The Saskia Stegmaier, PhD candidate, TUM melted a particularly pure form of copper wire and tin granulate under special conditions – protected from air and moisture in an argon atmosphere. The bronze produced in this manner was then sealed into an alkali metal such as potassium in an ampoule made of tantalum. The melting point of tantalum is 3,000 degrees Celsius, making it particularly well suited as a vessel for other metals in contact with each other. When bronze is heated, together with potassium or sodium, to 600 to 800 degrees Celsius, the alkali metals act like scissors that cut up the alloy grid and then edge their way between the pieces, thereby stabilizing the isolated atomic clusters. On their own, these clusters cannot organize themselves into dense, uniformly structured layers to form crystals.

“Our clusters are small units. They are piles of atoms that are not connected to their neighbours. That makes them ideal for catalytic applications because they are consistent in size, they are much better at steering chemical reactions than classical catalysts,” explained Faessler. However, Stegmaier’s and Faessler’s reaction vessel contained more surprises. Aside from the clusters, the scientists noticed a fibre like material whose ends could be bent a little. In the meantime the yield of the fibres has been improved by using sodium as scissors to cut up the bronze. This time the result was not spheres, but multilayered rods. In the middle is a string of tin atoms, surrounded by a layer of copper atoms, and around that yet another tube of tin atoms. Just as the hollow Matryoshka molecules are reminiscent of Buckyballs, the new fibres with their tubes are akin to carbon nanotubes. Analogously, such fibres could one day be used as molecular wires with various electrical properties.

© TUM News

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