Pd nanoparticle

F1 NMR of chemisorbed hydrogen can also be used for the study of alloys. For example, in mixed Pt-Pd nanoparticles in NaY zeolite comparaison of the results of hydrogen chemisorption and F1 NMR with the formation energy of the alloy indicates that the alloy with platinum concentration of 40% has the most stable metal-metal bonds. The highest stability of the particles and a lowest reactivity of the metal surface are due to a strong alloying effect. 

The longtime stabihty of surfactant-coated Pd nanoparticles in w/o microemulsions has been investigated. It has been proven that under suitable conditions, the use of the functionalized surfactant Pd(AOT)2 allows very stable nanosize Pd particles to be obtained and to finely control their average size [229],... 

Ni/Pd nanoparticles and similar sized Pd nanoparticles for the following Sonogashira coupling reactions using equal amount of palladium in the reaction mixtures. As expected, the Ni/Pd... 

Pt/Pd bimetallic nanoparticles can be prepared by refluxing the alcohol/water (1 1, v/v) solution of palla-dium(II) chloride and hexachloroplatinic(IV) acid in the presence of poly(A-vinyl-2-pyrrolidone) (PVP) at ca. 95 °C for Ih [15,16,48]. The resulting Pd/Pt nanoparticles have a Pt-core/Pd-shell structure with a narrow size distribution and the dispersion is stable against aggregation for several years. The core/shell structure was confirmed by the technique of EAXFS. Composition of Pt/Pd nanoparticles can be controlled by the initially feed amount of two different metal ions, i.e., in this case one... 

Our first attempt of a successive reduction method was utilized to PVP-protected Au/Pd bimetallic nanoparticles [125]. An alcohol reduction of Pd ions in the presence of Au nanoparticles did not provide the bimetallic nanoparticles but the mixtures of distinct Au and Pd monometallic nanoparticles, while an alcohol reduction of Au ions in the presence of Pd nanoparticles can provide AuPd bimetallic nanoparticles. Unexpectedly, these bimetallic nanoparticles did not have a core/shell structure, which was obtained from a simultaneous reduction of the corresponding two metal ions. This difference in the structure may be derived from the redox potentials of Pd and Au ions. When Au ions are added in the solution of enough small Pd nanoparticles, some Pd atoms on the particles reduce the Au ions to Au atoms. The oxidized Pd ions are then reduced again by an alcohol to deposit on the particles. This process may form with the particles a cluster-in-cluster structure, and does not produce Pd-core/ Au-shell bimetallic nanoparticles. On the other hand, the formation of PVP-protected Pd-core/Ni-shell bimetallic nanoparticles proceeded by a successive alcohol reduction [126]. 

Michaelis and Henglein [131] prepared Pd-core/Ag-shell bimetallic nanoparticles by the successive reduction of Ag ions on the surface of Pd nanoparticles (mean radius 4.6 nm) with formaldehyde. The core/shell nanoparticles, however, became larger and deviated from spherical with an increase in the shell thickness. The Pd/Ag bimetallic nanoparticles had a surface plasmon absorption band close to 380 nm when more than 10-atomic layer of Ag are deposited. When the shell thickness is less than 10-atomic layer, the absorption band is located at shorter wavelengths and the band disappears below about three-atomic layer. 

Damle et al. observed that the reduction of the Pd(II) ions in the stearic acid-Ag nanocomposite film leads to the formation of a mixture of individual Ag and Pd nanoparticles as well as particles in the Ag-core/Pd-shell structure. Thermal treatment of the stearic acid-(Ag/Pd) nanocomposite film at 100 °C, however, resulted in the formation of an AgPd alloy [142]. 

Figure 10. Absorption spectrum of the Pd nanoparticles before (0) and after deposition of various amounts of silver, m number of monolayers of silver. (Reprinted from Ref [131], 1994, with permission from American Chemical Society.)...

Figure 11. X-ray diffraction patterns of PVP-protected metal nanoparticles (a) PVP-protected CuPd (Cu Pd = 2 1) bimetallic nanoparticles (b) PVP-protected Pd nanoparticles (c) PVP-protected Cu dispersion (d) physical mixture of (b) and (c) (Cu Pd = 2 1). (Reprinted from Ref [71], 1993, with permission from The Chemical Society of Japan.)...

We investigated on structure of CuPd (2 1) bimetallic nanoparticles by XRD [71]. Since the XRD peaks of the PVP-protected CuPd nanoparticles appeared between the corresponding diffraction lines of Cu and Pd nanoparticles, as shown in Figru e 11, the bimetallic alloy phase was clearly formd to be formed in CuPd (2 1) bimetallic nanoparticles. We also characterized Ag-core/Rh-shell bimetallic nanoparticles, which formed during simple physical mixing of the corresponding monometallic ones, by XRD coupled with TEM [148]. 

On the other hand, the XPS data near the Fermi level provide us the valuable information about the band structures of nanoparticles. XPS spectra near the Fermi level of the PVP-protected Pd nanoparticles, Pd-core/ Ni-shell (Ni/Pd = 15/561, 38/561) bimetallic nanoparticles, and bulk Ni powder were investigated by Teranishi et al. [126]. The XPS spectra of the nanoparticles become close to the spectral profile of bulk Ni, as the amount of the deposited Ni increases. The change of the XPS spectrum near the Fermi level, i.e., the density of states, may be related to the variation of the band or molecular orbit structure. Therefore, the band structures of the Pd/Ni nanoparticles at Ni/Pd >38/561 are close to that of the bulk Ni, which greatly influence the magnetic property of the Pd/Ni nanoparticles. 

This means that the improvement of catalytic activity of Pd nanoparticles by involving the Pt core is completely attributed to the electronic effect of the core Pt upon shell Pd. Such clear conclusion can be obtained in this bimetallic system only because the Pt-core/Pd-shell structure can be precisely analyzed by EXAFS and Pd atoms are catalytically active while Pt atoms are inactive. 

Size Controlled Pd Nanoparticles Anchored to Carbon Fiber Fabrics Novel Structured Catalyst Effective for Selective Hydrogenation... 

Figure 3. Transmission electron microphotographs and histograms of the particle size distribution for Pd nanoparticles synthesized at Wo 3 (a) and 7 (b) [23] and isolated via the proposed method.

Figure 5. TEM image of the carbon-supported Pd nanoparticles prepared via a typical synthetic procedure.

Figure 4. High-resolution transmission electron microphoto-graph of an isolated Pd nanoparticle.

A Case History Enantioselective Allylic Alkylation Catalysed by Pd Nanoparticles... 

The catalysts were prepared by deposition of Pd nanoparticles on the CFl, CF2, CF3, and CF4 resins respectively, shown in Figure 5, by chemical reduction of Pd(II) precursors such as Pd(OAc)2 and PdCl2(NCR)2 (R = Ph, Me), following the CIR procedure, or by deposition from Pd-solvated atoms obtained via MVS. 

Zhang J, Mo Y, Vukmirovic MB, Klie R, Sasaki K, Adzic RR. 2004. Platinum monolayer electrocatalysts for O2 reduction Pt monolayer on Pd(lll) and on carbon-supported Pd nanoparticles. J Phys Chem B 108 10955-10964. 

Additional experiments were carried out to study the behavior of Pd nanoparticles coated with Pt or with Pt plus M, which more closely reflects the morphology of actual catalyst particles. Figure 9.18a displays the polarization curves for the ORR on commercial carbon-supported Pt nanoparticles (Pt/C), Pd nanoparticles (Pd/C), a monolayer of Pt on Pd/C (PtMu/Pd/C), and mixed (Pto.gIro.a/ML/Pd/C and... 

Schalow T, Brandt B, Starr DE, Laurin M, Shaikhutdinov SK, Schauermann S, Libuda J, Freund HJ. 2007. Particle size dependent adsorption and reaction kinetics on reduced and partially oxidized Pd nanoparticles. Phys Chem Chem Phys 9 1347-1361. 

Bimetallic Au/Pd nanoparticles were prepared by ultrasound irradiation of a mixture solution of NaAuCl4-H20/PdCl2 2NaCl-3H20 by which the Au and Pd ions were reduced to the metallic state. The Mossbauer spectra of AuPd-SDS particles, with SDS (sodium dodecyl sulfate) representing the surfactant of the system, consist of two components, one for the pure Au core and the other for the alloy layer at the interface of Au core and Pd shell [435]. 

Figure 9.13 (a) SEM BSE image and (b) STEM HAADF image of Pd nanoparticles on a carbon support. The clarity of the images illustrates the advantage of the HAADF and BSE approach. (Reproduced from Ref. 36). 

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