Nanoparticles catalytic behavior

Before investigating the effect of size, shape, and structure on catalytic behavior, that is, TOFs, a set of five requirements concerning the metal particles has to be met. Besides a monodisperse size distribution, the nanoparticles should be fully reduced, unpoisoned, unperturbed by... 

Okitsu K, Yue A, Tanabe S, Matsumoto H (2000) Sonochemical preparation and catalytic behavior of highly dispersed palladium nanoparticles on alumina. Chem Mater 12 3006-3011... 

Okitsu K, Murakami M, Tanabe S, Matsumoto H (2000) Catalytic behavior of Au core/Pd shell bimetallic nanoparticles on silica prepared by sonochemical and sol-gel processes. Chem Lett 29 1336-1337... 

Various metallic nanoparticles have been prepared in the case of PS-P2(4) VP reverse micelles, as illustrated by the works of Moller et al. [ 109-111 ] and Antonietti and coworkers [112]. Very recently, Bronstein et al. reported on the synthesis of bimetallic colloids formed in PS-P4VP micelles and their catalytic behavior for the selective hydrogenation of dehydrolinalool [113]. 

Another specific feature of the catalytic behavior of the structures under study consists in that the chemical nature of a metal becomes a factor less important for catalysis as the surface nanoparticles density increases. This is well seen in Figure 15.14, which shows the results obtained in measurements of the activity of copper- and nickel-based catalysts in the reaction of carbon tetrachloride addition to olefins. Presented in this figure are the activities of catalysts prepared by laser electrodispersion and the conventional deposition techniques. Two important features are worth noting. First, the activity... 

Considered in this chapter are specific features of the catalytic behavior of metallic nanostructures of new type, produced by laser electrodispersion of metals. This method makes it possible to obtain Cu, Ni, or Pd nanoparticles whose sizes are specific to each particular metal, with the relative particle size scatter being exceedingly narrow, <10%. An important distinctive... 

Ceria/noble metal (such as Ru, Rh, and Pd) catalysts are composed of noble metal species such as nanoparticles and clusters dispersed on the ceria supports. The catalysts show typical strong metal-support interactions (SMSI) (Bernal et al., 1999), that is, the catalysts exhibit a number of features for SMSI effects including (1) reducible supports (2) "high temperature" reduction treatments (3) heavily disturbed chemical properties and significant changes in catalytic behavior of the dispersed metal phase (4) reversible for recovering the conventional behavior of the supported metal phase. In these cases, the reducibility of ceria NPs is greatly enhanced by the noble metal species and the catalytic activities of the noble metals are enhanced by ceria NPs. 

Sharma RK, Sharma P, Maitra A (2003) Size-dependent catalytic behavior of platinum nanoparticles on the hexacyanoferrate(lll)/thiosulfate redox reaction. J Colloid Interface Sci 265 134... 

From not only the scientific but the technological point of view, bimetallic nanoparticles composed of two different metal elements are of greater interest and importance than monometallic nanoparticles [7,8]. Scientists have especially focused on bimetallic nanoparticles as catalysts because of their novel catalytic behaviors affected by the second metal element added. This effect of the second metal element can often be explained in terms of an ensemble and/or a ligand effect in catalyses. Such effects appear in bimetallic catalysts composed of both zerovalent metal atoms and another metal ions [9,10]. In this case, however, metal ions do not construct nanoparticles but are located close to them to exhibit an ensemble effect. This chapter covers the bimetallic nanoparticles composed of only zerovalent metals in homogeneous systems the supported or heterogeneous systems of metal nanoparticles are not covered. 

On the other hand, bimetallic nanoparticles are very important as catalysts because of their high surface-to-volume ratios [29] and their novel catalytic behavior induced by the second metal element. The addition of a second metal can drastically change the catalytic properties of catalysts, even when the second metal is inactive... 

The combined information obtained by the different characterization methods applied allows the conclusion that deposits of ruthenium oxide at BDD, ranging from approximately one hundredth of a monolayer, maintain the physicochemical properties of RUO2, which proves the very limited degree of chemical interaction with the support. The deposits are most probably organized in nanoparticles growing around nucleation sites. When particles and clusters of particles reach a size of 50-60 nm, their charge-storage and catalytic behavior closely resembles that of thick oxide films. 

Bulk nanostructured materials are soUds with nanosized microstructure. Their basic units are usually nanoparticles. Several properties of nanoparticles are useful for applications in electrochemical sensors [67], However, their catalytic behavior is one of the most important. The high ratio of surface atoms with free valences to the total atoms has led to the catalytic activity of nanostructured SEs being used in electrochemical reactions. The catalytic properties of nanoparticles could decrease the overpotential of electrochemical reactions and even provide reversibility of redox reactions, which are irreversible at the bulk metal SE [68], Multilayers of conductive nanoparticles assembled on electrode surfaces produce a high porous surface with a controlled microenviromnent. These structures could be thought of as assemblies of nanoelectrodes with controllable areas. 

Along with monometalUc Pd nanoparticles, we studied the synthesis and properties of PdAu, PdPt, and PdZn bimetallic nanoparticles prepared at a molar ratio of 4/1 in PS-b-P4VP micelles and their catalytic behavior in DHL hydrogenation [44]. Because the amount of Pd in all the bimetallic nanoparticles is much higher than that of the second metal, Pd mainly determines the catalytic properties. 

To address these issues, we studied the catalytic behavior of Pt nanoparticles formed in several nanostructured polymeric systems in the selective oxidation of L-sorbose to 2-keto-L-gulonic acid (Table 3.5) [89]. Commercial Pt/7-Al203 (3% Pt, Degussa AG) was used for comparison. The reaction has been conducted in alkaU media (NaHCOs), yet gradual alkaline loading (NaHCOs) provides the highest selectivity, while one-shot results in the highest TOP. 

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