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In a catalytic bed made up of magnesium oxide not missing any oxygen atoms, (upper left) the excess charge (blue) is much less than in a bed with missing oxygen atoms (upper right). The excess charge, in the form of extra electrons, helps weaken the bands in O2 and CO molecules (bottom left). |
The cluster's structure, which they can control by adding or subtracting atoms, is a major factor. This could lead to new, tailor-made catalysts that lower manufacturing costs for everything from fertilizers to plastics.
"Designing catalysts atom by atom will be more efficient, selective, and specific to certain reactions and should lead to significant savings in manufacturing. Understanding the principles that govern nanocatalysis is key," says Uzi Landmand, director of the school's Center for Computational Material.
Gold for example, is not a catalyst in bulk form. But when in clusters of eight atoms, it takes on a specific structure that speeds some reactions or lets them take place at lower temperatures and pressures. Researchers set up an experiment in which carbon monoxide and oxygen combine into carbon dioxide using magnesium oxide as the catalytic bed and clusters of eight gold atoms as the catalyst. The reactions only took place when some of the magnesium oxide was missing oxygen atoms.
The Georgia Tech team showed that the electronic structure of the gold cluster let it anchor to the site of the missing oxygen on the magnesium-oxide bed. The structure also let the gold match up with oxygen and carbon monoxide, transferring charge to them. This weakens the bonds holding the oxygen and carbon monoxide molecules together. Once the bonds are weak enough, the molecules break apart and react with each other, producing carbon dioxide.