Change in the catalytic reactivity of Pt nanocubes in the presence of different surface-capping agents

Polyvinylpyrrolidone (PVP; MW 55,000)-capped and tetradecyltrimethylammonium bromide (TTAB; MW 336)-capped Pt nanoparticles were synthesized with the same cubic shape and similar particle size (8.1 vs. 8.6 nm, respectively). These Pt nanocubes were used as catalysts for reactions of H+, C2H4, C6H6, and O2NC6H4OH on the Pt surface. With increasing molecular size of the reactants (H+ < C2H4 < C6H6), the ratio of the catalytic activity of TTAB- to PVP-capped nanocubes shows a dramatic increase because TTAB with short alkyl chains provides a larger number of clean Pt atom ensembles for larger reactants. However, similar activity between the two types of nanocubes was measured for a solution-phase reaction (O2NC6H4OH) where the surface-capping agents are able to spread out into solvent media, exposing bare Pt atoms. In this case, the influence of the alkyl length of the surface-capping agent was minimized. (C) 2009 Elsevier B.V. All rights reserved.