The Catalyst Review April 2020 - 18

MOVERS & SHAKERS
John R. (JR) Regalbuto, PhD

Professor of Chemical Engineering, University of South Carolina
John R. (JR) Regalbuto did his undergraduate studies at Texas A&M and went on to the University of Notre Dame, where
he received his PhD in Chemical Engineering. Following 25 years at the University of Illinois at Chicago, including three
years (2006-2009) as a rotator directing the Catalysis and Biocatalysis Program in the Engineering Directorate of the
National Science Foundation, JR joined the Department of Chemical Engineering at the University of South Carolina in
2011 as the Smartstate (endowed) Chair of the Center of Catalysis for Renewable Fuels. At UofSC, he is directing his
passion for rational catalyst synthesis toward the optimization of supported metal catalysts for biomass conversion. Prof. Regalbuto
currently directs the NSF-sponsored Industry/University Cooperative Research Center led by UofSC, the Center for Rational Catalyst
Synthesis (CeRCaS). He can be reached at regalbuj@cec.sc.edu.

The Catalyst Review asked Professor Regalbuto to share his insights on the synthesis of supported,
bimetallic, "single atom alloy" nanoparticles.
Isolating a single atom in a matrix of a second metal can lead to the formation of a heterogeneous catalyst which can mimic
a homogeneous catalyst, if the second metal matrix is inert, or to a true bimetallic catalyst if the single atom is affected
electronically or sterically by the second metal, or if the second metal adds a second function. Model, low area "single atom
alloy" catalysts have been synthesized by depositing metal atoms on the single crystal surface of a second metal. A limited
number of high surface area catalysts, featuring supported nanoparticles with single atoms diluted in a matrix of a second
metal, have been prepared by galvanic displacement of surface atoms of the metal matrix by individual atoms of the active
metal. Galvanic displacement cannot be employed in a general fashion, however, and there is a need for a more general
method for the synthesis of high surface area, single-atom alloyed nanoparticles.
At UofSC, a colleague and I may have an answer or two to this synthesis challenge. My answer is to employ a variation
of the method of "strong electrostatic adsorption" (SEA) which was used a few years ago (Wong et al., Science 2017) to
synthesize ten different sets of homogeneously alloyed ~1 nm bimetallic nanoparticles supported on a high surface area
silica support. Using spot EDXS analysis, these workers confirmed a 1:1 atomic ratio of the nanoparticles. We call this method
of preparation "simultaneous SEA" or co-SEA, and the synthesis of nanoparticles at a 1:1 atomic ratio was achieved by
controlling the concentration of the metal solutions at about a 1:1 atomic ratio.
So here is the latest, greatest potential application of co-SEA: if we employ a 1:35 ratio of metal precursors in solution, and
presuming the precursors are well mixed, and the adsorbed precursors remain well mixed, and the resulting nanoparticles
are about 1 nm average size (and so contain about 35 atoms) we hypothesize that each nanoparticle will contain one atom
of the desired metal. There may be a little leeway here, for if we place two atoms per nanoparticle, they may still end up
effectively isolated. Given this manner of synthesis, by the way, I am more inclined to call the resulting particles "dilute limit
alloys" as opposed to "single atom alloys."
I would be remiss not to mention the possibility offered by the bimetallic synthesis method being developed by my UofSC
colleague, Prof. John Monnier. Prof. Monnier can control the deposition of a shell metal onto a supported nanoparticle core
metal by the process of electroless deposition (ED). In the same way that co-SEA can be employed with a high ratio of metal
precursors, ED can be employed with just a smidgeon of deposited shell metal, and the assumption will be that the metal
does not all deposit onto one nanoparticle, but that individual atoms disperse evenly onto the core metal nanoparticles (see
https://regalbutocatalusc.net/research/).
Let the best method prevail. SEA might be better for some systems, ED for others. Between the two methods, we hope to
offer the field of catalysis a simple, scalable, generalizable way to synthesize "dilute limit alloy" catalysts within the next
several years.

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The Catalyst Review

April 2020

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The Catalyst Review April 2020

Table of Contents for the Digital Edition of The Catalyst Review April 2020