On Metal Segregation of Bimetallic Nanocatalysts Prepared by a One-Pot Method in Microemulsions

Abstract

A comparative study on different bimetallic nanocatalysts prepared from microemulsions using a one-pot method has been carried out. The analysis of experimental observations, complemented by simulation studies, provides detailed insight into the factors affecting nanoparticle architecture: (1) The metal segregation in a bimetallic nanocatalysts is the result of the combination of three main kinetic parameters: the reduction rate of metal precursors (related to reduction standard potentials), the material intermicellar exchange rate (determined by microemulsion composition), and the metal precursors concentration; (2) A minimum difference between the reduction standard potentials of the two metals of 0.20 V is needed to obtain a core-shell structure. For values ∆ε 0 smaller than 0.20 V the obtaining of alloys cannot be avoided, neither by changing the microemulsion nor by increasing metal concentration; (3) As a rule, the higher the film flexibility around the micelles, the higher the degree of mixture in the nanocatalyst; (4) A minimum concentration of metal precursors is required to get a core-shell structure. This minimum concentration depends on the microemulsion flexibility and on the difference in reduction rates.

Synthesis, Structure, Properties, and Applications of Bimetallic Nanoparticles of Noble Metals

“…[ 7a,8a,39 ] Electrochemical arguments have been used to predict the formation of core–shell and alloyed nanoparticles. [ 40 ] The laser‐based synthesis of metallic nanoparticles for catalysis has also been investigated in detail as a model top‐down approach. [ 41 ]…”

Microemulsions as Nanoreactors to Obtain Bimetallic Nanoparticles

“…As a rule, it is observed a tendency from nanoalloy to core-shell structure as difference in reduction potential is increased (see Table 1 in Ref. [44]). Previous simulation studies allow to clearly observe a better separation of the two metals as reduction rate ratio is larger (for a deeper discussion, see Ref.…”

“…It was proposed that if the intermicellar exchange rate can only modify the rate of metals whose reduction is very fast [38], such as Au, only bimetallic nanoparticle including Au could be prepared with different metal distributions as a function of microemulsion composition (intermicellar exchange rate) by a one-pot method (see Table 1 in Ref. [44]). To the best of our knowledge, only Au/Pt, Au/Ag, and Au/Pd have been synthesized in a different intrastructure by different authors.…”

Synthesis of carbon-supported bimetallic palladium–iridium catalysts by microemulsion: characterization and electrocatalytic properties

“…The colloid-based preparation method, namely a reverse "water-in-oil" microemulsion (w/o), was also reported to be effective in the synthesis of alloyed nanoparticles such as Pd-Pt, Pd-Au, Pt-Au, Pd-Ni, C-Ni and Au-Ag [5]. In w/o method, all processes including the chemical reduction of metal ions, nucleation and growth of the metal particles take place within the confined space of aqueous droplets dispersed in a continuous oil phase stabilized by surfactant molecules [6,7].…”

“…According to the molecular dynamic simulations [5,[8][9][10], if the reduction of the metal ions is J Mater Sci (2021) 56:392-414 instantaneous, as when reducing agent is directly added to the micellar system containing metal precursors, the formation of metal particles is governed by the nucleation processes. As a result, the bimetallic particles of uniform size are formed.…”