Nanoparticle size and composition often have a critical role in chemical reactions. 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 [1]. This typically creates larger particles or causes a poor degree of alloying for bimetallic catalysts.<br/><br/>Our goal was to demonstrate simple, effective methods in synthesizing highly dispersed, well alloyed bimetallic nanoparticles and in improving nanoparticle size control through modified DI methods. These catalysts were synthesized using strong electrostatic adsorption (SEA) and charged-enhanced dry impregnation (CEDI). SEA and CEDI are 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. CEDI was used to synthesize Pt supported on silica. Careful selection of the Pt counter-ion and the addition of other salts were used to control nanoparticle sizes. Particle sizes and the degree of alloying were determined through electron micrographs, elemental mapping of nanoparticles, and powder XRD.<br/><br/>Results from XRD show the bimetallic catalysts produced by SEA were highly dispersed (&lt;2 nm), while the DI catalysts exhibited large XRD peaks (&gt;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. CEDI catalysts showed high dispersion (&lt;2 nm) nanoparticles using a hydroxide counter-ion Pt precursor. The introduction of halides had a direct effect on Pt particle size, thus demonstrating a control over the average particle size. A comparison of the DI and SEA bimetal systems and further developments of CEDI will be discussed.

Electrostatic adsorption for synthesis and size control of supported metal catalysts

253rd National Meeting (2017)

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