Au-Pd nanoparticles

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]. 

As Table 1 shows, sequential reduction can be used to selectively prepare either well-mixed or core/shell DENs [27-31]. In a typical synthesis, such as the preparation of [Au](Pd) nanoparticles [21], l PdCLi is added to a solution of G6-Q116(Au5s) seeds and stirred to produce G6-Q116[Au55](Pd2+)95. H2 is then bubbled through the solution (10-fold excess of ascorbic acid was also explored as the reductant) to produce G6 - Q116 [ Au55 ] (Pd)95. 

Mejia-Rosales SJ, Fernandez-Navarro C, Perez-Tijerina E, Montejano-Carrizalles JM, Jose-Yacaman M (2006) Two-stage melting of Au-Pd nanoparticles. J Phys Chem B 110 12884... 

Other one-phase preparations of bimetallic nanoparticles include NOct4(BHEt3) (Oct = octyl, Et = ethyl) reduction of platinum and ruthenium chlorides to give Pt/Ru(l/1) nanoparticles by Bonnemann et al. [102-104], sono-chemical reduction of gold and palladium ions to provide Au/Pd nanoparticles by Mizukoshi et al. [105,106], and NaBH4 reduction of PtCl - and PdCl - dendrimer complexes to give dendrimer-stabilized Pd/Pt nanoparticles by Crooks et al. [107]. 

In a different study [40], argon-saturated aqueous solutions of NaAuCT and PdCh or K2PtCl4 were reduced simultaneously by ultrasound irradiation to prepare noble metal alloy nanoparticles. The Au-Pd nanoparticles exhibited mono-dispersive distribution (8 nm), and consisted of a gold core and a palladium shell. Au-Pt alloy nanoparticles could not be produced from NaAuCl4 and K2PtCl4 aqueous solutions by either simultaneous or successive reduction. 

M. Sankar et al.. Controlling the Duality of the Mechanism in Liquid-Phase Oxidation of Ben l Alcohol Catalysed by Supported Au-Pd Nanoparticles, Chem. -Eur.J., 2011, 17(23), 6524-6532. 

Bimetallic Au/Pd nanoparticle synthesis reported by Wu etal. [401] involved mixing of microemulsion A (AOT/isooctane/aqueous solution of Pd(II)chloride and hydrogen tetrachloroaurate) and microemulsion B (AOT/isooctane/aqueous solution of hydrazine) to obtain within Ih particles of Pd, Au or Au/Pd(l 1) in the size range of -4.5-6, -3.5-4.5 and -2.5-3 nm respectively. 

An alternative, safer and more environmentally friendly method to produce H2O2 in low concentrations involves direct oxidation of to using O. This method creates less waste, can be carried out in a benign solvent such as water (eliminating extraction/separation steps) and is obviously more atom efficient than the AO process. It is also feasible on a smaller scale, allowing for the possibility of in situ production of when required [139-141]. This process can be catalysed by supported Pd, Au or Au-Pd nanoparticles. 

In theory, a composite material composed of the Au/Pd nanoparticles supported on the Ti-grafted MCF catalyst should be an active and selective... 

Not only Fe species in ZSM-5 but also supported Au-Pd nanoparticles have been found to catalyze the methane oxidation to methanol with hydrogen peroxide [75]. However, they perform less active and selective than the iron species. Moreover, these catalytic systems also differ in their reaction mechanism. In contrast to the oxidation of methane over Fe-ZSM-5, methyl radicals are involved in methanol formation over supported Au-Pd nanoparticles. 

Also nanoalloys, i.e., clusters with two (or more) different elements, have been the focus of some research. As a first example we mention the combined experimental and theoretical study of Mejia-Rosales et a/." on bimetallic Au/Pd nanoparticles with stoichiometries 1 3, 1 1, and 3 1. In their theoretical calculations, they used molecular-dynamics simulations in combination with a simplified description of the interatomic interactions that, in turn, were approximated through simple funetions of the interatomic distances. They found that the structures of the nanoalloys were less regular than those of the pure elements, so that the surfaces of the former contain many types of defects. A possible consequence of this is that such nanosystems possess a much higher catalytic activity than those of the pure elements. 

SankarM, NowickaE, TiruvalamR, etal. Controlhng the duality ofthe mechanism in liquid-phase oxidation of benzyl alcohol catalysed by supported Au—Pd nanoparticles. Chem Eur J. 2011 17 6524-6532. 

Su R, Tiruvalam R, Logsdail AJ et al (2014) Designer titania-supported Au-Pd nanoparticles for efficient photocatalytic hydrogen production. ACS Nano 8 3490-3497... 

---