An Experimental and Theoretical Investigation of the Inversion of Pd@Pt Core@Shell Dendrimer-Encapsulated Nanoparticles

Abstract

Bimetallic PdPt dendrimer-encapsulated nanoparticles (DENs) having sizes of about 2 nm were synthesized by a homogeneous route that involved (1) formation of a Pd core, (2) deposition of a Cu shell onto the Pd core in the presence of H2 gas, and (3) galvanic exchange of Pt for the Cu shell. Under these conditions, a Pd@Pt core@shell DEN is anticipated, but detailed characterization by in-situ extended X-ray absorption fine structure (EXAFS) spectroscopy and other analytical methods indicate that the metals invert to yield a Pt-rich core with primarily Pd in the shell. The experimental findings correlate well with density functional theoretical (DFT) calculations. Theory suggests that the increased disorder associated with <~2 nm diameter nanoparticles, along with the relatively large number of edge and corner sites, drives the structural rearrangement. This type of rearrangement is not observed on larger nanoparticles or in bulk metals.

Bimetallic core–shell Ag@Pt nanoparticle-decorated MWNT electrodes for amperometric H2 sensors and direct methanol fuel cells

“…Several approaches to the synthesis various bimetallic NPs have been reported, including the chemical reduction method, electrochemical deposition, ethylene glycol-assisted polyol process, photochemical or radiolytic routes, and the galvanic replacement reaction (GRR) [4][5][6][7]. Among them, the GRR method can be used to prepare a wide variety of bimetallic nanostructures such as spherical nanoshells, cubic nanoboxes, nanocages, nanotubes, and nanodendrites [7][8][9][10].…”

Correlating Structure and Function of Metal Nanoparticles for Catalysis

“…[8] 57 Fig. 1 illustrates the synthetic routes to form random alloy [9,7,58 10-12], core-shell [13][14][15][16], and alloy-core@shell DENs [17]. Random 59 alloy DENs are prepared by a co-complexation method, where two 60 types of metal cations are reduced simultaneously to form an alloy par-61 ticle.…”

Structural evolution of bimetallic Pd-Ru catalysts in oxidative and reductive applications

“…However, core-shell structure inversion may occur even during catalyst synthesis due to the rearrangement of high-energy corner and edge atoms on ultra-small particles (<2 nm) [16]. To verify whether Pd atoms are present on the surface of the as-synthesized Pd(c)Ru(s) nanoparticles, a selective chemical probe surface reaction was used.…”

“…The traditional preparation methods that support impregnation with metal precursor solutions followed by calcination do not allow the production of well-defined uniform nanoparticles, so their structural evolution studies are complicated by the wide polydispersity of the original nanoparticles. At present, the steadily increasing number of colloidal chemistry techniques to prepare structure-and size-controlled metal nanoparticles [12][13][14][15] enable experimental studies of the bimetallic nanoparticle rearrangement, including structure inversion during synthesis or after thermal activation and/or catalysis [16][17][18]. The structural changes depend on the Scheme 1.…”