Spying On Oscillating Reactions

Many chemical reactions that occur on solids exhibit spontaneous oscillatory behavior, a phenomenon that is not well understood. In such systems, the transformation of reactants to products varies with time, even though reaction conditions are held constant. For reactions of gases on nanoparticle catalysts, scientists have proposed that these oscillations are tied to periodic changes in the catalyst surface. But until now, they had not observed such oscillations directly under reaction conditions. Researchers in Europe have done just that for the case of CO oxidation on platinum nanoparticles, a key reaction in automobile emissions cleanup (Nat. Mater. 2014, DOI: 10.1038/nmat4033). Patricia Kooyman of Delft University of Technology in the Netherlands, Stig Helveg of Danish catalyst manufacturer Haldor Topsøe, and coworkers used a specially designed miniature reactor to follow simultaneous changes in catalyst surface structure and gas product composition at elevated temperatures and pressures representative of automotive exhaust catalysis. By combining results from transmission electron microscopy, mass spectrometry, and computational modeling, the team showed that the oscillatory CO oxidation reaction is synchronized with periodic reversible faceting of the Pt nanoparticles. They found that during periods of highest CO conversion, the particles adopt highly faceted structures.