ABSTRACT
Pt nanoparticles through chemical reduction of K2PtCl4 by H2 in the presence of sodium polyacrylate [39]. After this pioneer work, various Pt nanocrystals with different shapes have been obtained by using different Pt precursors, capping agents, reducing agents, and solvents. A detailed summary of the most significant methodologies to prepare shape-controlled Pt nanoparticles will be reported in the following section of this chapter. From a catalytic point of view, the effect of the shape/surface structure of the Pt nanoparticles on catalytic activity and selectivity has been intensively investigated by the El-Sayed and Somorjai groups [40-51]. Thus, El-Sayed and coworkers have reported the influence of the shape/surface structure of Pt nanoparticles on reactions such as propylene hydrogenation, electron-transfer, and Suzuki reactions, pointing out the importance of controlling the shape of the nanoparticles [40-48]. Using a similar approach, Somorjai and coworkers have also shown the importance of the shape/surface structure by considering the ethylene and benzene hydrogenations and carbon monoxide adsorption and oxidation as surface reaction probes [49-51]. More recently, Rodriguez-Reinoso et al. have also studied the influence of the shape/surface structure of Pt nanoparticles on the selective hydrogenation of crotonaldehyde and cinnamaldehyde [52]. Also, Zaera and coworkers have recently reported how catalytic selectivity for the promotion of carboncarbon double-bond cis-trans isomerization reaction in olefins may be modified by modifying the shape of the Pt nanoparticle catalysts [53]. Besides, Baiker and coworkers have recently investigated the structure sensitivity of enantioselective hydrogenations on chirally modified Pt nanoparticles [54]. The results obtained revealed that the process is shape-selective and that both the reaction rate and the enantioselectivity increased with the increase in the Pt(111) to Pt(100) ratio. In addition, in a more recent contribution, Baiker and coworkers have also studied the influence of the crystallographic faces of the Pt nanoparticles on the diastereoselective hydrogenation of cinchonidine [55]. Finally, in a very recent paper, Somorjai and coworkers have synthesized sub-10 nm Pt nanocubes and nanopolyhedra with tunable size [56]. These size-and shape-controlled Pt nanoparticles were loaded into MCF-17 mesoporous silica for catalytic studies. Ethylene and pyrrole hydrogenations were used as catalytic probes. These and some other examples clearly illustrate the importance of shape control to the efficient utilization of Pt nanoparticles in catalysis.
