Heat blunts sharp edges of catalyst effect
Chemical reactions can easily take place on the surface of a catalyst which would otherwise not occur or scarcely occur. Chemists know that the sharp edges of catalysts, in particular, are ideal reaction locations but that sometimes flat terraces are also suitable. However, it was not clear why. Dr. Irene Groot and her colleagues have found out that temperature plays a crucial role in this. The research forms a fundamental insight that can be used in the development of new catalysts. The researchers from the FOM Institute for Plasma Physics Rijnhuizen in Nieuwegein, Leiden University and the University of Amsterdam presented their results in the leading journal Angewandte Chemie.
Catalysts are vitally important in the chemical industry, so a lot of research is carried out into how they work. However, up until now no consensus had been reached about the ideal shape of a piece of catalyst: according to one study the acting substances have a strong preference for sharp edges, whereas other experiments revealed that flat terraces on a catalyst also enable a reaction to take place. In their article, Groot and her colleagues solve the puzzle of reaction locations.
Temperature was found to exert a significant effect: "On the edges of a catalyst particle, slightly more chemical activity is available to facilitate a chemical reaction between slowly moving molecules", explains Prof. Aart Kleyn. "On the flat terraces hardly any reactions take place." At higher temperatures, particles that land on a terrace also gain enough speed to start a chemical reaction.
The researchers used the reaction between hydrogen and platinum as a test case. Amongst other things, this metal is used as a catalyst in fuel cells. However, it is scarce and very expensive. This is one of the reasons why fuel cell cars are prohibitively expensive. The development of new catalysts is a long and complicated process in which both trial and error and fundamental mechanistic insights play a role. This article contributes to our fundamental knowledge.
Contact
Dr. Ludo Juurlink (Faculty of Science, Leiden Institute of Chemistry, Catalysis and Surface Chemistry), +31 (0)71 527 42 21.
Reference
'The Energy Dependence of the Ratio of Step and Terrace Reactivity for H2 Dissociation on Stepped Platinum' Dr. Irene M.N. Groot, Prof. Aart W. Kleyn, Dr. Ludo B.F. Juurlink.