(398bj) Supported, Homogeneously Alloyed Bimetallic Nanoparticles By Electrostatic Adsorption

Supported,
Homogeneously Alloyed Bimetallic Nanoparticles by Electrostatic Adsorption

Andrew P. Wong, Qiuli Liu, and John R. Regalbuto

Department
of Chemical Engineering, University of South Carolina

ABSTRACT

Bimetallic catalysts are often important
for chemical reactions due to their enhanced performance over monometallic
catalysts [1].  Incorporating a secondary metal into a system can benefit
the catalytic system through ensemble, bifunctional, and electronic
effects.  The most prevalent method for synthesizing supported catalysts
is dry impregnation (DI), also known as incipient wetness, in which a solution
containing a specific amount of metal precursor is added to just fill the pore
volume of the support [2].  While the procedure is simple and the metal
loading is precisely known, limitations of DI preparations often include larger
particle sizes and less intimate metal-support interactions.  Moreover,
bimetal catalysts produced through DI often exhibit a poor degree of alloying between
the metals.

Our goal was to demonstrate a
simple, effective method to synthesize highly dispersed, well alloyed
bimetallic nanoparticles using strong electrostatic adsorption (SEA). SEA is
achieved by charging the support by controlling the pH of the solution.  A
metal precursor that is oppositely charged can then be adsorbed onto the
surface of the charged support.  Using a simultaneous adsorption of either
two cationic or anionic precursors allows excellent bimetallic
interactions.  The combinations of multiple bimetallic systems (Cu, Co,
Ni, Pd, and Pt) prepared by SEA were compared to equivalent DI catalysts. 
Particle sizes and the degree of alloying were determined through electron
micrographs, elemental mapping of nanoparticles, and powder XRD.

Results from XRD show the
bimetallic catalysts produced by SEA were highly dispersed (<2 nm), while
the DI catalysts exhibited large XRD peaks (>5nm).  Initial elemental
maps and STEM images indicate the SEA catalysts had a higher degree of alloying
compared to the DI catalyst, and particle agglomeration was avoided for the SEA
catalyst.  A complete comparison of the bimetal systems prepared by DI and
SEA will be discussed.

References

[1] Sankar, M., et al. (2012).
"Designing bimetallic catalysts for a green and sustainable future." Chemical
Society Reviews 41(24): 8099-8139.

[2] Cho, H.-R. and J. R.
Regalbuto (2015). "The rational synthesis of Pt-Pd bimetallic catalysts by
electrostatic adsorption." Catalysis today 246: 143-153.