On the Face of It

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Science  31 Mar 2006:
Vol. 311, Issue 5769, pp. 1837
DOI: 10.1126/science.311.5769.1837a

Varying the size of a nanometer-scale metal cluster can alter its catalytic activity. This phenomenon is usually attributed either to geometrical effects (such as the distribution of defect atoms or step sites) or to electronic effects (such as the scaling of metallic character with particle size) but has rarely been quantified for very small catalyst particles. Wilson et al. have systematically measured the size-dependent activity of cuboctahedral Pd clusters toward the catalysis of allyl alcohol hydrogenation. Clusters of precise size were synthesized using dendrimer templates and ranged in diameter from 1.3 to 1.9 nm (or ∼50 to ∼250 atoms). For clusters larger than 1.5 nm, the observed increase in reaction rate with increasing diameter was best fit by positing preferential reaction on facial sites, thus suggesting a geometrical origin for the activity change. For smaller clusters, reactivity did not correlate with physical properties such as the number of defect atoms or surface area, and activity changes were therefore attributed to electronic effects. — PDS

J. Am. Chem. Soc. 128, 10.1021/ja058217m (2006).

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