American Chemical Society, ACS Catalysis, 9(4), p. 3105-3111, 2014
DOI: 10.1021/cs5008014
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The structure−property relationship of palla-dium (Pd) catalysts in Suzuki−Miyaura cross-coupling reactions was investigated using Pd nanocrystals of uniform size and shape. Superior catalytic reactivity was observed for Pd nanoparticles with high-index {730} surface facets compared to low-index {100} facets. Although the nanocrystal morphologies were maintained during the reaction, the presence of Pd clusters, identified by high-resolution trans-mission electron microscopy (TEM), indicates a leaching mechanism. The nature of the surface facets on the nanoparticles was observed to influence the rate of Pd leaching during the Suzuki coupling reaction. The enhanced reactivity observed for the high-index facet catalysts stems from the greater number of leachable atoms of low abstraction energy available on high-index planes. KEYWORDS: palladium nanocrystals, shape control nanoparticles, Suzuki coupling, leaching ■ INTRODUCTION Noble metal nanocrystals (NCs) with high-index surface facets have attracted much interest due to their potential for enhanced catalytic performance. 1 High index facets are denoted by a set of Miller indices {hkl}, where one index is greater than 1. Unlike low-index planes characterized by {111} and {100} facets, which are relatively smooth, the surface atomic structure of high-index facets is characterized by a high-density of step, terrace, and kink sites. 2 Such surfaces are well-known to improve catalytic rates for many reactions. 3 The physical origins of structure sensitivity are complex and generally ascribed to electronic and geometrical effects that influence adsorption energies and reaction pathways. 4 Chemisorption of reaction species can be preferential on step and kink sites due to their lower co-ordination numbers (6−7) or allow more energeti-cally favorable transition states compared to close-packed surfaces. 5