Transition-metal catalysis nanoparticles

Polymeric materials containing finefy-divided metal or metal-oxide nanoparticles show unusual properties that could make them e edally useful in many technological applications. Transition metal catalysis is certainly a field that can benefit to a great extent by the introduction of these novel materials. The search for thetic methods to obtain nanoparticles that are stabilized within a polymer matrix, the characterization of these materials, and their application in catalytic reactions are receiving increased attention. 

Binary systems of ruthenium sulfide or selenide nanoparticles (RujcSy, RujcSey) are considered as the state-of-the-art ORR electrocatalysts in the class of non-Chevrel amorphous transition metal chalcogenides. Notably, in contrast to pyrite-type MS2 varieties (typically RUS2) utilized in industrial catalysis as effective cathodes for the molecular oxygen reduction in acid medium, these Ru-based cluster materials exhibit a fairly robust activity even in high methanol content environments of fuel cells. 

Late transition metal or 3d-transition metal irons, such as cobalt, nickel, and copper, are important for catalysis, magnetism, and optics. Reduction of 3d-transition metal ions to zero-valent metals is quite difficult because of their lower redox potentials than those of noble metal ions. A production of bimetallic nanoparticles between 3d-transi-tion metal and noble metal, however, is not so difficult. In 1993, we successfully established a new preparation method of PVP-protected CuPd bimetallic nanoparticles [71-73]. In this method, bimetallic hydroxide colloid forms in the first step by adjusting the pH value with a sodium hydroxide solution before the reduction process, which is designed to overcome the problems caused by the difference in redox potentials. Then, the bimetallic species... 

In materials chemistry, nanoparticles of noble metals are an original family of compounds. Well-defined in terms of their size, structure and composition, zero-valent transition-metal colloids provide considerable current interest in a variety of applications. Here, the main interest is their application in catalysis. Zerovalent nanocatalysts can be generated in various media (aqueous, organic, or mixture) from two strategic approaches according to the nature of the precursor, namely (i) mild chemical reduction of transition-metal salt solutions and (ii) metal atom... 

Two classes of catalysts account for most contemporary research. The first class includes transition-metal nanoparticles (e.g., Pd, Pt), their oxides (e.g., RUO2), and bimetallic materials (e.g., Pt/Ni, Pt/Ru) [104,132-134]. The second class, usually referred to as molecular catalysts, includes all transition-metal complexes, such as metalloporphyrins, in which the metal centers can assume multiple oxidation states [ 135 -137]. Previous studies have not only yielded a wealth of information about the preparation and catalytic properties of these materials, but they have also revealed shortcomings where further research is needed. Here we summarize the main barriers to progress in the field of metal-particle-based catalysis and discuss how dendrimer-encapsulated metal nanoparticles might provide a means for addressing some of the problems. 

In heterogeneous catalysis, transition metal nanoparticles are supported on different substrates and are utilized as catalysts for different reactions [57], such as hydrogenations and enantioselective synthesis of organic compounds [58], oxidations and epoxidations [59], and reduction and decomposition [57],... 

It seems to be possible that most transition metal oxides can be made in porous crystals with different morphologies using various mesoporous silicas as templates. It is expected that these materials have potential in applications such as catalysis, fuel cell, gas sensors and Li-batteries. Their physical properties would fall in between nanoparticles and bulk specimens, although our knowledge about these properties is still very limited. 

Transition metal nanoparticles have attracted great attention due to their unique size-dependent properties and applications in diverse areas, including magnetic storage materials, catalysis, sensors and drug delivery. Depositions of various Pt-containing alloys are summarized in Table 2. Particularly, chemically synthesized transition metal alloy... 

Catalysis with Transition Metal Nanoparticles in Colloidal Solution Heterogeneous or Homogeneous ... 

Narayanan R, El-Sayed MA (2005) Catalysis with transition metal nanoparticles in colloidal solution nanoparticle shape dependence and stability. J Phys Chem B 109 12663... 

Ott LS, Finke RG (2007) Transition-metal nanocluster stabilization for catalysis a critical review of ranking methods and putative stabilizers. Coord Chem Rev 251 1075 Yang J, Lee JY, Too H-P (2006) Size effect in thiol and amine binding to small Pt nanoparticles. Anal Chim Acta 571 206... 

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