Monometallic catalytic material

In heterogeneous catalysis by metal, the activity and product-selectivity depend on the nature of metal particles (e.g., their size and morphology). Besides monometallic catalysts, the nanoscale preparation of bimetallic materials with controlled composition is attractive and crucial in industrial applications, since such materials show advanced performance in catalytic processes. Many reports suggest that the variation in the catalyst preparation method can yield highly dispersed metal/ alloy clusters and particles by the surface-mediated reactions [7-11]. The problem associated with conventional catalyst preparation is of reproducibility in the preparative process and activity of the catalyst materials. Moreover, the catalytic performances also depend on the chemical and spatial nature of the support due to the metal-support interaction and geometrical constraint at the interface of support and metal particles [7-9]. 

An alternate bimetallic pathway was also suggested, but not favored, by Heck and Breslow (also shown in Scheme 1). The acyl intermediate could react with HCo(CO)4 to undergo intermolecular hydride transfer, followed by reductive elimination of aldehyde to produce the Co-Co bonded dimer Co2(CO)s. A common starting material for HCo(CO)4-catalyzed hydroformylation, Co2(CO)g is well-known to react with H2 under catalysis reaction conditions to form two equivalents of HCo(CO)4. The bimetallic hydride transfer mechanism is operational for stoichiometric hydroformylation with HCo(CO)4 and has been proposed to be a possibility for slower catalytic hydroformylation reactions with internal alkenes.The monometallic pathway involving reaction of the acyl intermediate with H2, however, has been... 

Nanoscale materials such as multimetallic nanoparticles, particularly when alloyed, are of great importance due to their diverse range of electrical, optical, and catalytic properties. Bimetallic nanoparticles often exhibit enhanced catalytic reaction rates and better selectivity compared to the monometallic compounds. Such mixed nanoparticles were successfully synthesized by irradiating a solution containing a mixture of two (and even more) metal ions and precursors. Different bimetallic systems were studied, such as Ag/Pd, Au/Pd and Ag/Au nanoparticles. However, depending on the experimental conditions, both situations of alloyed or, more often, core-shell nanoparticles can be obtained. 

Intense research in the field of metal nanoparticles by chemists, physicists, and materials scientists is motivated by the search for new materials that hold novel physical (electronic, magnetic, optical) and chemical (catalytic) properties. Recently, the research on monometallic nanoparticles has been carried out in order to further miniaturize electronic devices [26-28] as well as to elucidate the fundamental question of how electronic properties of molecular aggregates evolve into novel properties with increasing size in this intermediate region between a molecule and a bulk [3,29-33]. Possible future applications include the areas of ultrafast communication and a large quantity of data storage [3,31,32,34]. 

From the above examples, it is clearly evident that supported bimetallic nanoalloy catalysts have much more interesting catalytic properties compared to their monometallic catalysts. However, to exploit the catalytic properties of these nanoalloy catalysts, it is important to tune the structural properties appropriately. Example-1 demonstrates the synthesis strategies utilized to control the size, composition and nanostructure of supported Au-Pd catalysts. This in-tum has a dramatic effect on the catalytic activity and stability of these materials for the direct synthesis of H2O2 from H2 and O2. The catalyst with Au-Pd particles between 2-10 nm and a homogeneous random alloy structure is found to... 

Citrate-derived monometallic Pt and bimetallic Pt tAujo. colloidal particles have been prepared and adsorbed onto graphitic supports their adsorptive and catalytic properties are considered as is the wider applicability of this preparative route to heterogeneous catalysts. It appears that P Au,(x,.j dispersed bimetallic particles have properties which are very close to those of bulk materials and therefore that colloidal preparative routes to mono- and bi-metallic catalysts are very promising. However, the cleanliness of surfaces needs to be considered as does the extent of surface emiclunent caused by the method of preparation. 

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