Catalysis by Gold Clusters

Choudhary TV, Goodman DW. 2002. Oxidation catalysis by supported gold nano-clusters. Top... 

The oxidation of CO is the simplest reaction and has been the most intensively studied since Langmuir first presented a theory of adsorption and catalysis for this reaction [13]. Supported Au NPs such as Au/Ti02, Au/Fe203 and Au/Co304 are extraordinarily active in CO oxidation, even at 200 K, and are much more active than the other noble metals catalysts at temperatures below 400 K [14—16]. Gold clusters composed of several atoms can promote the reaction between CO and 02 to form C02 at as low as 40 K [17]. Most recently, Lahr and Ceyer [18] have extended the temperature range at which the activity for CO oxidation is observed to as low as 70 K by using an Au/Ni surface alloy. 

It is well established that ultrasmall metal clusters on supports have catalytic properties distinct from those properties of large bulk-like particles, as illustrated by the selective oxidation of propylene to propylene oxide by gold, alkene and arene hydrogenation catalysis,and CO oxidation. In these examples, the catalytic properties improve as the clusters become smaller. On the other hand, a reduction in size of the metal cluster can lead to less desirable catalytic properties as seen for ammonia synthesis on iron. Various explanations have been offered to account for the unique properties of nanoscaled metal catalysts, however, much remains to be understood. Clearly, experimental and theoretical studies will be required to develop an in-depth under-... 

L. Pignolet, in Catalysis by Di- and Polynuclear Metal Cluster Complexes Catalysis by Mixed-Metal Clusters Containing Gold Phosphine Groupings, (Eds, R. D, Adams, F, A, Cotton), Wiley-VCH, New-York, 1998, pp. 95. 

Comparison between the behavior of 35-nm and 3-nm platinum particles confirms the observations with gold clusters. Unfortunately, molecule-like Pt clusters have not yet been investigated. Assuming that the metal —> non-metal transition occurs over a size range similar to that for gold it is obvious that catalysis by a particle > M55 must be different from that by a cluster consisting of only a dozen or even fewer atoms. 

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