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.