For the first time, shape-controlled Pt 3 Sn, PtSn, and PtSn 2 intermetallic nanocrystals were synthesized in octadecene (ODE) by a versatile hot-injection method with 1,2-hexadecanediol (HDD) as the reducing agent. Transmission electron microscopy (TEM) measurements reveal that the metal composition has an influence on the particle morphology: with the increase in the Sn content, the Pt/Sn nanoparticles obtained by the hot-injection synthesis show flower-like, irregular faceted, cubic/tetrahedral, hexagonal, and spherical/nanowire structures. A facile phase-transfer preparative procedure for the synthesis of Pt/Sn core/shell nanoparticles was also developed, in which ligand-free Pt nanoparticles were used as precursors. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements confirm a Pt-core/Snshell structure. The surface characteristic of the Pt/Sn core/shell nanoparticles was also investigated by IR spectroscopy of CO adsorption experiments (i.e., with a highly surface sensitive technique). These experiments reveal a few Pt atoms to be left on the surface as adsorption sites for CO. However, the intensity of the corresponding infrared (IR) bands is almost negligible. Furthermore, Pt/Sn random-alloy nanoparticles with different metal compositions and particle sizes were synthesized in this work by heating-up methods. Energy dispersive X-ray (EDX) and XRD analyses show different alloying extent of Sn with Pt.

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PtSn bimetallic nanoparticles with different particle sizes (1-9 nm), metal compositions (Sn content of 10-80 mol %), and organic capping agents (e.g., amine, thiol, carboxylic acid and polymer) were synthesized by colloidal chemistry methods. Transmission electron microscopy (TEM) measurements show that, depending on the particle size, the as-prepared bimetallic nanocrystals have quasi-spherical or faceted shapes. Energy-dispersive X-ray (EDX) analyses indicate that for all samples the signals of both Pt and Sn can be detected from single nanoparticles, confirming that the products are actually bimetallic but not only a physical mixture of pure Pt and Sn metal nanoparticles. X-ray diffraction (XRD) measurements were also conducted on the bimetallic particle systems. When compared with the diffraction patterns of monometallic Pt nanoparticles, the bimetallic samples show distinct shifts of the Bragg reflections to lower degrees, which gives clear proof of the alloying of Pt with Sn. However, a quantitative analysis of the lattice parameter shifts indicates that only part of the Sn atoms are incorporated into the alloy nanocrystals. This is consistent with X-ray photoelectron spectroscopy (XPS) measurements that reveal the segregation of Sn at the surfaces of the nanocrystals. Moreover, short PtSn bimetallic nanowires were synthesized by a seed-mediated growth method with amine-capped bimetallic particles as precursors. The resulting nanowires have an average width of 2.3 nm and lengths ranging from 5 to 20 nm.

In contrast to conventional methods, colloidally prepared heterogeneous supported metal catalysts are excellent systems to study the catalytic properties as a function of metal loading, monodispersity, particle shape, or the type of support without changing the other parameters, as will be demonstrated herein. Colloidal, ligand‐capped Pt nanoparticles deposited on oxide supports are investigated for CO adsorption and oxidation. Dodecylamine and different alkanethiols are used as ligands. IR spectroscopic experiments reveal that small molecules, such as CO, can pass through the ligand shell and can adsorb on the particle surface, even if the ligand shell is not removed by a special pretreatment. The ability to penetrate the shell was found to depend on the type of ligand used which renders ligand‐capped nanoparticles potentially interesting for reaction and selectivity control. In the case of CO oxidation, high activity is detected only at temperatures at which a partial loss of ligands has already occurred, resulting in a rather similar catalytic behavior independent on the type of ligand. However, there are no indications for poisoning of the catalysts by decomposition of the ligand shell. Simple purification procedures of the Pt nanoparticles are sufficient to avoid further poisoning effects. Depositing nanoparticles with the same size in different amounts on a support enabled a detailed study of the influence of metal loading on the activity. The activity per gram metal increases with the metal loading. Local autothermal heating is responsible for this effect, which is also detected for a reference system consisting of Pt nanoparticles prepared without a ligand shell.

The catalytic performance of ligand‐capped monometallic Pt and bimetallic PtSn nanoparticles supported on SiO2 toward the selective hydrogenation of acetylene to ethylene in ethylene‐rich streams was investigated. To evaluate the effect of organic ligands on the hydrogenation performance, dodecylamine (DDA)‐capped monometallic and bimetallic nanoparticles were compared with ligand‐free nanoparticles. Both ligands and Sn promote the selectivity of the catalysts. The most selective catalyst was found to be the DDA‐capped PtSn catalyst, with a nominal metal atom ratio of 1:1. An increase in Pt content resulted in a decrease in the selectivity, whereas an increase in Sn content caused a decrease in the activity.