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 further demonstrate that residual balancing ions such as Cl- from (NH3)4PtCl2 can be used to control the particle size, and we also show how the residual ions can be removed to drastically reduce particle size. XRD patterns confirm that ultrasmall nanoparticles are produced via CEDI of the Pt tetraammine hydroxide complex, while residual chloride from the chloride complex causes particle growth.

Nanoparticle synthesis via electrostatic adsorption using incipient wetness impregnation

254th National Meeting (2017)

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