Combined temperature-programmed reaction and in situ x-ray scattering studies of size-selected silver clusters under realistic reaction conditions in the epoxidation of propene

Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, USA.
The Journal of Chemical Physics (Impact Factor: 2.95). 09/2009; 131(12):121104-121104-4. DOI: 10.1063/1.3237158


The catalytic activity and dynamical shape changes in size-selected nanoclusters at work are studied under realistic reaction conditions by using a combination of simultaneous temperature-programmed reaction with in situ grazing-incidence small angle x-ray scattering. This approach allows drawing a direct correlation between nanocatalyst size, composition, shape, and its function under realistic reaction conditions for the first time. The approach is illustrated in a chemical industry highly relevant selective partial oxidation of propene on a monodisperse silver nanocatalyst. The shape of the catalyst undergoes rapid change already at room temperature upon the exposure to the reactants, followed by a complex evolution of shape with increasing temperature. Acrolein formation is observed around 50 °C while the formation of the propylene oxide exhibits a sharp onset at 80 °C and is leveling off at 150 °C. At lower temperatures acrolein is produced preferentially to propylene oxide; at temperatures above 100 °C propylene oxide is favored.

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    • "In this field, silver nanoclusters have been widely investigated for their well-known optical properties (Kreibig and Vollmer 1995; Jain and El-Sayed 2010; Lerme et al. 2008 and for their catalytic activity, for example, in alkene oxidation (Bond 1987; Guo et al. 2004). Especially the smaller nanoparticles are of special interest under the latter viewpoint, as they have been proven to be more active and selective than larger particles (Vajda et al. 2009; Lei et al. 2010). Being small objects, nanoclusters have a very high value for ratio between surface and volume ratio (Baletto and Ferrando 2005).The experimental methods for producing free nanoclusters have been reviewed by de Heer (1993). "
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