Zinc oxide makes CO2 active

From sluggish stabs become reactive hooks

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From a chemical point of view, carbon dioxide - the most important greenhouse gas - is a rather reactionary molecule. Accordingly, it is difficult to move CO2 molecules from the atmosphere to participate in reactions. But now scientists have discovered a trick on how they can activate the CO2.

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A systematic study of the interaction of zinc oxide with various small molecules surprised researchers of the Ruhr-Universität Bochum: It showed that zinc oxide can activate CO2 even at relatively low temperatures. On the surface, the stubby, reactive carbon dioxide forms the strongly bent carbonate ion, which is chemically significantly more active. The researchers report on their findings in the journal Angewandte Chemie.

Contradiction with the previously adopted mechanism

The experimental results obtained by a combination of different techniques for the interaction of CO2 with ZnO were initially incomprehensible to the researchers and only to be interpreted by close collaboration with their colleagues in theoretical chemistry. These allowed the reactions to run in the computer and thus enabled their detailed investigation. "Of particular interest is the way in which the activation of carbon dioxide takes place, " explains Christof Wöll, spokesman for the Collaborative Research Center Metal-Substrate Interactions in Heterogeneous Catalysis. "This is not a reaction to defects, that is, gaps in the crystal lattice - the reaction mechanism that is currently most likely to be held by experts in the field - but an attachment to perfect, undisturbed areas of a zinc oxide surface." This particular orientation became hitherto regarded as rather reactionary and not considered as a candidate for interesting chemical processes.

Key fits exactly in the lock

The theoretical calculations show that the activation on this surface is due to a key-lock principle: the angled CO2 fits exactly into the surface structure of the special zinc oxide surface; therefore activation of this gas phase linear molecule is possible even at relatively low temperatures. "It is essential that the surface is not densely covered with these carbonates, but that there is enough space to adsorb another molecule between two carbonates, " explains Prof. Wöll. This opens up a new opportunity to chemically produce activated carbon from reaction with other molecules that can either be used elsewhere or stored at low cost. display

Application of painting to sunscreen

Zinc oxide is a comparatively cheap material that is used in a variety of ways. The applications range from painting (zinc white) to sun protection. In chemistry, this oxide is mainly used as a catalyst in addition to tire production.

(Ruhr-University Bochum, 10.07.2007 - NPO)