Pt-nanoparticle catalyzed

Scheme 3 Pt-nanoparticle catalyzed reaction of polybutadiene with various chlorosUanes...

Figure 6. Thermogravimetric analysis (TGA) of free 55 K PVP and 7.1 nm Pt-PVP nanoparticles in oxygen. Oxidative decomposition of free PVP begins at 573K, while significant weight loss due to the catalyzed oxidation of PVP on PVP-protected Pt nanoparticles occurs at 473 K. It appears that PVP layer is not a complete monolayer or the entanglement of PVP chains causes a porous polymer layer enabling oxygen diffusion to the nanoparticle surface [17]. (Reprinted from Ref [17], 2006, with permission from Springer.)...

Figure 12. Cyclic voltammograms of direct methanol oxidation catalyzed by the porous Pt nanoparticle membrane and as-made Pt nanoparticles. The reaction solution was made of an aqueous mixture containing O.IMHCIO4 and 0.125 M methanol. (Reprinted with permission from Ref [31], 2005, Wiley-VCH.)...

As can be seen from Table 3.5 ( 4), Pt nanoparticles formed in HPS are more selective in L-sorbose oxidation than the catalysts based on block copolymers but still the selectivity is not sufficient We believe that low selectivity may be attributed to saturation of the nanoparticle surface with H2 during reduction, which alters the sorption-desorption equilibria of the L-sorbose, oxygen and 2-keto-L-gulonic acid [89]. As was demonstrated in Ref [96], L-sorbose oxidation can be catalyzed not only with Pt(o) but also in the presence of Pt ions. This prompted us to investigate the catalytic properties of HPS-Pt without Pt ion reduction. 

However, it was observed that the surface of these nanoparticles was contaminated by residual Ag ions. When these different shapes of nanoparlicles catalyzed ethylene hydrogenation, which is a surface-insensitive reaction, no difference in the activity was expected for the various shaped nanoparticles. However, the cubes had a turnover frequency of 8.6 s", whereas the turnover frequency of the octahedra was 0.02 s" [22]. The Ag residing on the Pt nanoparticles hindered the catalytic reaction. The catalytic reaction on Pt octahedra with the greatest residual Ag ion concentration showed the poorest activity. Although beautifully shaped nanocrystals were obtained, the effect of the surface crystalline structure on catalytic activity could not be observed because of surface contamination. 

Recently, Pt DENs were used as an electrophilic catalyst in an intramolecular addition of phenols to alkynes (intramolecular hydroalkoxylation), as shown in Fig. 4.13b [100], The Pt DENs were supported on a mesoporous silica material known as SBA-15 (Fig. 4.13a). Since the as-synthesized SBA-15 consists of micrometer-sized particles, the supported Pt DENs can be easily separated from the reaction solution by centrifugation. This reaction has only been catalyzed by homogeneous catalysts (e.g., PtCy before this report. The use of the supported Pt DENs to catalyze this reaction was the first demonstration that a heterogeneous catalyst could also catalyze this conversion. It was also found that adding an oxidation agent, PhICF, would dramatically increase the benzofuran yield from 10 to 98 %, as shown in Fig. 4.13b. The authors proposed that PhICl2 could render the surface of the Pt nanoparticles more electrophilic, which is required for the Pt DENs to be active for the hydroalkoxylation reaction. 

Another electro-oxidation example catalyzed by bimetallic nanoparticles was reported by D Souza and Sam-path [206]. They prepared Pd-core/Pt-shell bimetallic nanoparticles in a single step in the form of sols, gels, and monoliths, using organically modified silicates, and demonstrated electrocatalysis of ascorbic acid oxidation. Steady-state response of Pd/Pt bimetallic nanoparticles-modified glassy-carbon electrode for ascorbic acid oxidation was rather fast, of the order of a few tens of seconds, and the linearity was observed between the electric current and the concentration of ascorbic acid. 

Formation of single-walled carbon nanotubes (SWNTs) was found to be catalyzed by metal nanoparticles [207]. Wang et al. [114] investigated bimetallic catalysts such as FeRu and FePt in the size range of 0.5-3 nm for the efficient growth of SWNTs on flat surfaces. When compared with single-component catalysts such as Fe, Ru, and Pt of similar size, bimetallic catalysts Fe/Ru and Fe/Pt produced at least 200% more SWNTs [114]. 

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