Supported nanoparticles, properties

Supported nanoparticles, properties, 73 Surface chemistry, supported metal nanoclusters, 66... 

The mass activity MA (in A g ) of the Pt catalyst is, of course, the product of the specific activity js (in A m ) and the specitic surface area 5mass (in ni g ) MA = js mass- Because S ass is inversely proportional to the particle diameter dpt, the use of supported Pt nanoparticles is effective for increasing MA, if js is a constant independent of dpt- However, even at pure Pt, conflicting results on the values of js and P(H202) have been reported, suggesting the presence of differences in electrochemical properties between bulk and supported nanoparticles. For example, Bregoli [1978]... 

To determine the phase properties of the calcined bimetallic nanoparticles, a detailed x-ray diffraction (XRD) study was carried out. The XRD data of AuPt/C showed that the diffraction patterns for the carbon-supported nanoparticles show a series of broad Bragg peaks, a picture typical for materials of limited structural coherence. Nevertheless, the peaks are defined well enough to allow a definitive phase identification and structural characterization. The diffraction patterns of Au/C and Pt/C could be unambiguously indexed into an fcc-type cubic lattice occurring with bulk gold and platinum. We estimated the corresponding lattice parameters by carefully determining... 

Nanoparticles, which often show enhanced catalytic abilities [32, 33] unusual optical properties [34], and novel quantum size effects [35], have been widely used in fields such as catalysis [36, 37], sensing [38], optoelectronics [39], and microelectronics [40]. Nanoparticle catalysis is industrially and experimentally important because a large variety of C-C coupling [41] and alcohol oxidation [32] can be effectively catalyzed by nanoparticles. In this part, we will present a brief review on recent advances in supported nanoparticle heterogeneous catalysts on various mesoporous materials. Heterogeneous nanoparticle catalysts have several... 

Supported nanoparticles (1-1.5 nm) based on Ru4Pt2 entities have been obtained by using a Ru4Pt2(CO)i8 precursor on carbon black and fullerene soot [63]. XANES analysis showed differences between the interaction of nanoparticles with both carbon black and fullerene supports. In particular, a change in the electronic properties of the nanoparticles on fullerene is proposed this change was related to a strong interaction between the nanoparticle and a surface-atom, probably via the formation of a Ru-carbide phase. 

Infrared spectroscopy of adsorbed CO is a useful characterization tool for dendrimer-templated supported nanoparticles, because it directly probes particle surface features. In these experiments, which are performed in a standard infrared spectrometer using an in-situ transmission or DRIFTS cell, a sample of supported DENs is first treated to remove the organic dendrimer. Samples are often reduced under H2 at elevated temperature, flushed with He, and cooled to room temperature. Dosing with CO followed by flushing to remove the gas-phase CO allows for the spectrum of surface-bound CO to be collected and evaluated. Because adsorbed CO stretching frequencies are sensitive to surface geometric and electronic effects, it is potentially possible to evaluate the relative effects of each on nanoparticle properties. 

Nanoparticles, see Supported nanoparticles Nanophase ceramics adhesion of osteoblasts to ceramic surfaces, 152-153 bending properties, 158 enhancing osteoblast and osteoclast functions, 153-155... 

Sinfelt has greatly contributed to the catalyses of bimetallic nanoparticles [18]. His group has thoroughly studied inorganic oxide-supported bimetallic nanoparticles for catalyses and analyzed their microstructures by an EXAFS technique [19-22]. Nuzzo and co-workers have also studied the structural characterization of carbon-supported Pt/Ru bimetallic nanoparticles by using physical techniques, such as EXAFS, XANES, STEM, and EDX [23-25]. These supported bimetallic nanoparticles have already been used as effective catalysts for the hydrogenation of olefins and carbon-skeleton rearrangement of hydrocarbons. The alloy structure can be carefully examined to understand their catalytic properties. Catalysis of supported nanoparticles has been studied for many years and is practically important but is not considered further here. 

When the catalytic properties of supported clusters are measured by standard electrochemical methods such as cyclic voltammetry or oxidation transient measurement, only the average properties of the entire distribution of active particles on the electrode surface can be measured. A range of properties of supported nanoparticles, e.g., their geometric structure, their electronic and magnetic properties, as well as their catalytic activity, depends on the size of the particles. Geometric as well as electronic effects have been used to explain particle-size effects in electrocatalysis. 

Specific Physical Properties of Free and Supported Nanoparticles... 

Heterogeneous catalysis also directly probes the surface properties of supported nanoparticles, and has been employed for dendrimer templated PtAu [37], PdAu [79], and PtCu [36] nanoparticles. Figure 4.17 shows CO oxidation for Pti Aui / Si02 catalysts compared with monometallic catalysts. Similar to the homogeneous catalysis studies, all three metal systems show synergism in catalytic activity CO oxidation catalysis, with the bimetalHc catalysts being more active than any of the corresponding monometallic catalysts. 

Most of the examples of metal MOFs and metaloxides MOFs discussed up to now have been synthesized in order to obtain novel kinds of supported nanoparticles with potentially advantageous properties for applications in catalysis. The catalytic properties of the composite materials Pd MOF-5 and Cu MOF-5 were among the first to be tested. The Pd MOF-5 composite that was obtained by the gas phase loading/photolysis synthetic protocol (35.6 wt% Pd) showed moderate activity in catalysis of hydrogenation of cyclooctene [59], The Pd MOF-5 (1 wt%) synthesized by the incipient wemess technique from [PdCacac) ] was tested as catalyst in hydrogenation of styrene, 1-octene and c/x-cyclooctene, and exhibited a shghtly higher catalytic activity than Pd supported on activated carbon (Pd/Norit A Fig. 23) [51]. 

Supported nanoparticles are the main catalysts used in current fuel cell devices. The combined DFT, single crystal, polycrystalline, and electrochemical experiments demonstrated that WC and Pt/WC have catalytic properties that are promising for use as anode DMFC electrocatalysts. These fundamental results still left questions unanswered as to how these materials could be incorporated into a realistic device. These questions led to studies of WC and Pt/WC nanoparticles in a fuel cell test station [23]. The WC nanoparticles were obtained from Japan New Metals Company. The Pt/WC nanoparticles were prepared with a 10 wt% Pt loading using incipient... 

The support being the electronic pathway for the TPB must have good electronic conductivity to provide a pathway for electrons to reach the platinum nanoparticles. It is also beneficial for the support to be cheap, environmentally friendly, have high surface area, and be able to withstand the operating conditions of a fuel cell. The support surface properties are also of great importance when considering the interaction and dispersion between the support and the metal catalyst (Antolini, 2009). 

Simulations of physical properties of realistic Pt/support nanoparticle systems can provide interaction parameters that are used by molecular-level simulations of self-organization in CL inks. Coarse-grained MD studies presented in the section Mesoscale Model of Self-Organization in Catalyst Layer Inks provide vital insights on structure formation. Information on agglomerate formation, pore space morphology, ionomer structure and distribution, and wettability of pores serves as input for parameterizations of structure-dependent physical properties, discussed in the section Effective Catalyst Layer Properties From Percolation Theory. CGMD studies can be applied to study the impact of modifications in chemical properties of materials and ink composition on physical properties and stability of CLs. 

The continued development of new single-source molecular precursors should lead to increasingly complex mixed-element oxides with novel properties. Continued work with grafting methods will provide access to novel surface structures that may prove useful for catalytic apphcations. Use of molecular precursors for the generation of metal nanoparticles supported on various oxide supports is another area that shows promise. We expect that the thermolytic molecular precursor methods outlined here will contribute significantly to the development of new generations of advanced materials with tailored properties, and that it will continue to provide access to catalytic materials with improved performance. 

Size reduction of metal particles results in several changes of the physico-chemical properties. The primary change is observed in the electronic properties of the metal particles which can be characterized by ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS, respectively) as well as Auger-electron spectroscopy (AES) measurements. Furthermore, morphology of the metal nanoparticles is highly sensitive to the environment, such as ion-metal interaction (e.g. metal-support interaction)... 

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