(41g) Nanoparticle Synthesis Via Electrostatic Adsorption Using Incipient Wetness Impregnation

  Nanoparticle Synthesis via
Electrostatic Adsorption using Incipient Wetness Impregnation

Sonia Eskandari and John
R.Regalbuto

The University of
South Carolina (USA)

Department of
Chemical Engineering, 541 Main Street, Columbia, SC 29208 (USA)

Incipient wetness impregnation is commonly
used for supported metal catalyst synthesis given its simplicity.  The
disadvantage, however, is that most often the metal precursors do not interact
with the support surface and form large agglomerates during the drying process,
leading to poor metal utilization.  In Strong Electrostatic Adsorption
(SEA) [1], coulombic metal precursor-support interactions are induced between a
protonated, positively charged surface and an anionic metal precursor complex
such as platinum hexachloride, [PtCl₆]^2-, or a
deprotonated, negatively charged surface and a cationic metal precursor such as
platinum tetraammine, [(NH₃)₄Pt]²⁺.  The
strong interaction of the precursors give high dispersion of the metal after
drying and reduction [1].  SEA is normally employed with excess liquid
solution, such that an additional filtering step is required vis-à-vis
incipient wetness impregnation.

In this talk we demonstrate the extension
of electrostatic adsorption, which gives small particle sizes, to the incipient
wetness procedure; we call this method “Charge-Enhanced Dry Impregnation (CEDI)
[2].  This is done by intensely acidifying or basifying the small
quantities of solution needed for incipient wetness, to achieve a strong charge
on the support surface.  We extend our preliminary studies of CEDI [2,3]
to a wider variety of  noble (Pt, Pd) and base (Co, Ni, Cu) metals. 
We employed tetra- and hexaammine precursors over a high surface area silica
support (Aerosil 300, 280 m²/g).  Using precursors with OH^-
counterions, such as (NH₃)₄Pt(OH)₂, small
particle size was immediately achieved, and when precursors with chloride
counterions such as (NH₃)₄PtCl₂were used,
particles were much larger.  However, particle size could be reduced
without much loss of metal by an appropriate washing step.  We further
demonstrate that the residual counterions can be used to control the particle
size. 

References

[1] J.R. Regalbuto,
Strong Electrostatic Adsorption of Metals onto Catalyst Supports, in Catalyst
Preparation:  Science and Engineering, J.R. Regalbuto, ed., Taylor and
Francis/CRC Press, 2007.

[2] X.R. Zhu, H.R.
Cho, M. Pasupong, J.R. Regalbuto, ACS Catal. 3 (2013) 625–630.

[3] D,Souza, L., Barnes, S., and Regalbuto,
J.R., Catalysts 2016, 6, 72.