Catalytic nanopartide

Finally, a very interesting approach has been suggested by the same group to apply an ionic liquid to the preparation of Ru nanopartides of defined size on a meso-porous silica support [279]. The authors made use of the ionic liquid [TGA] [lactate] to customize particles obtained by reduction of dissolved RuQs on the silica support. However, prior to catalysis, the ionic liquid film was removed thermally by heating to 220 °C for 3 h. In this way a quite active catalyst for the hydrogenation of benzene to cyclohexane (TOFs up to 83 h at 10 bar H2 pressure) was obtained. Such an approach obviously combines successfully features of SILP catalysis (see Section 5.6 for details) with the use of catalytic nanopartides. 

Bimetallic nanoparticles, either as alloys or as core-shell structures, exhibit unique electronic, optical and catalytic properties compared to pure metallic nanopartides [24]. Cu-Ag alloy nanoparticles were obtained through the simultaneous reduction of copper and silver ions again in aqueous starch matrix. The optical properties of these alloy nanopartides vary with their composition, which is seen from the digital photographs in Fig. 8. The formation of alloy was confirmed by single SP maxima which varied depending on the composition of the alloy. 

Catalytically active gold from nanopartides to ultrathin films. Accounts of Chemical Research, 39, 739—746. 

Jacinto, M.J., Kiyohara, P.K., Masunaga, S.H., Jardim, R.F. and Rossi, L.M. (2008) Recoverable rhodium nanopartides synthesis, characterization and catalytic performance in hydrogenation reactions. Applied Catalysis A General, 338 (1-2), 52-57. 

Hmbach, L.K., Wick, P., Manser, P., Grass, R.N., Bruinink, A., and Stark, W.J. (2007) Exposure of engineered nanopartides to human lung epithelial cells influence of chemical composition and catalytic activity on oxidative stress. Environmental Science and Technology,... 

There are many published examples in which the coupling of two different materials leads to an increase in the photocatalytic activity. Many of them concern coupling and junctions between different nanopartides, considering also different topologies, like coupled and capped systems [72]. Tentative explanations based on possible heterojunction band profiles are given. However, in-depth analysis of the hetero junction band alignment, the physical structure of the junction, the role of (possible) interfadal traps and of spedfic catalytic properties of the material is still lacking. Some recently published models and concepts based on (nano)junction between different materials are briefly reviewed here. 

Reaction of the sandwich-type POM [(Fc(0H2)2)j(A-a-PW9034)2 9 with a colloidal suspension of silica/alumina nanopartides ((Si/A102)Cl) resulted in the production of a novel supported POM catalyst [146-148]. In this case, about 58 POM molecules per cationic silica/alumina nanoparticle were electrostatically stabilized on the surface. The aerobic oxidation of 2-chloroethyl ethyl sulfide (mustard simulant) to the corresponding harmless sulfoxide proceeded efficiently in the presence of the heterogeneous catalyst and the catalytic activity of the heterogeneous catalyst was much higher than that of the parent POM. In addition, this catalytic activity was much enhanced when binary cupric triflate and nitrate [Cu(OTf)2/Cu(N03)2 = 1.5] were also present [148],... 

Size affects the stmcture of nanopartides of materials such as CdS and CdSe, and also their properties such as the melting point and the electronic absorption spectra. In Figures 1.4 and 1.5, we show such size effects graphically. It should be noted that even metals show nonmetallic band gaps when the diameter of the nanocrystals is in the 1-2 nm range. Hg dusters show a nonmetallic band gap which shrinks with increase in cluster size. It appears that around 300 atoms are necessary to dose the gap. It is also noteworthy that metal partides of 1-2 nm diameter also exhibit unexpected catalytic activity, as exemplified by nanocatalysis by gold particles. 

The discovery of MSP materials led immediately to the development of many experimental methods for the deposition of materials, especially catalysts, into the mesopores. We have deposited Mo oxide, and Co/Mo oxides into MCM-41 as well as into the pores of Al-MCM-41 [103]. We have also anchored Fe203 into the mesopores of titania [104]. A large variety of nanopartides has been introduced into many MSP materials. This work, however, has not been published. In addition to the characterization studies of the composite catalyst-mesoporous product, catalytic studies have also been conducted. 

Spherical and uniform Pt nanopartides, 3.5-4.0 nm supported on carbon, were prepared by microwave irradiation [177]. The products exhibited very high electro-catalytic activity in the room-temperature oxidation of liquid methanol. The preparation method was similar to that of Komarneni [175], namely, a polyol reduction. 

By designing semiconductor-metal composite nanopartides it is possible to improve the catalytic properties of photocatalysts (Figure 19.12). Contact of metal... 

The photochemical properties of various nanoassemblies discussed in this chapter highlight the ways in which the metal and semiconductor nanopartides interact with light. Furthermore, one can fine tune these responses by subjecting nano-stmctures to an externally applied electrochemical bias. The ability to functionalize these nanopartides with photoactive molecules has opened new avenues to utilize these nanoassemblies in light energy conversion and catalytic applications. By suitably modulating the fluorescence of the surface bound fluorophore these... 

Electrode surfaces can be modified with metal nanopartides and such surfaces have found numerous applications in the field of bioelectrochemistry, particularly in biosensors [7, 155]. Gold nanopartides are often utilized in such studies since they are known to retain the activity of the biomolecule with electrochemical activity intact as well [15]. It has also been observed that these nanopartides can act as conduction centers fadlitating the transfer of electrons. In addition, they provide large catalytic surface areas. 

The high dispersity inside the nano-honeycomb matrix and the high surface area of the nanopartides leads to very good electrocatalytic activity. The electrocatalytic activities of nanosized platinum particles for methanol, formic add and formaldehyde electrooxidation have been recently reported [215]. The sensitivity of the catalyst particles has been interpreted in terms of a catalyst ensemble effect but the detailed microscopic behaviour is incomplete. Martin and co-workers [216] have demonstrated the incorporation of catalytic metal nanopartides such as Pt, Ru and Pt/Ru into carbon nanotubes and further used them in the electrocatalysis of oxygen reduction, methanol electrooxidation and gas phase catalysis of hydrocarbons. A related work on the incorporation of platinum nanopartides in carbon nanotubes has recently been reported to show promising electrocatalytic activity for oxygen reduction [217]. 

Presently, the scientific community is making every effort to study irmovative catalytic materials that combine morphological features suited to a fast counterdiffusion of PO, surface properties designed to favor the desorption of PO and limited side-reactions deriving from acid or base-catalyzed reactions - especially those leading to heavy product accumulation - as well as to stabilizing metal nanopartides. 

Chen et al. [19] have reported very active, stable platinum nanopartide catalysts prepared by alcohol reduction of PtCls using poly(N-isopropylacrylamide) previously grafted on PS microspheres as stabilizing polymer. The observed catalytic activity in the hydrogenation of allyl alcohol was more than five times higher than with Pt/C. Moreover, it was possible to recycle the resin-based catalysts for at least six cycles, whereas Pt/C was not recyclable at all. When comparing the catalytic activity of free and heterogeneous colloidal platinum particles, only a small decrease in the reaction rate was observed. 

Catalytic hydrogenation reactions have to date been explored using nanopartides of palladium, platinum, ruthenium, iridium and rhodium. 

Dupont and coworkers obtained Pt nanopartides (2-2.5 nm) in [BMIM][Pp6] by reducing dissolved Pt2(dba)3 with H2 (4 atm) at 75 °C [274]. The formed nanopartides catalyzed the hydrogenation of both alkenes and arenes under the same, relatively mild conditions. However, the ionic hquid suspension gave a less active catalytic system (lower TOF) compared to the same partides under solventless conditions or in acetone. The generated Pt(0) nanopartides were found to be quite stable and could be re-used, as solid, or re-dispersed in [BMIM][PF6] several times with little loss of catalytic activity. 

Ru nanopartides have also been prepared in ionic liquids and used for catalytic hydrogenation reactions. Dupont s group described the reduction of RuCh with hydrogen in different ionic liquids with the [BMIM] cation [275]. The Ru nanopartides were characterized by TEM and XRD and were 2.0-2.5 nm in diameter with a narrow size distribution. The authors demonstrated that the partides dispersed in the ionic liquid were less prone to oxidation compared to isolated nanopartides. 

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