442852 Catalyst Synthesis of Ruthenium Hexaamine on Silica By Strong Electrostatic Adsorption at High Surface Loadings

Monday, November 9, 2015
Exhibit Hall 1 (Salt Palace Convention Center)
Eric Bringley, Department of Chemical Engineering, University of South Carolina, Columbia, SC, Jadid Samad, University of South Carolina and John R. Regalbuto, Chemical Engineering, University of South Carolina, Columbia, SC

Strong Electrostatic Adsorption (SEA) is a catalyst synthesis method that takes advantage of the Coulombic force between two charged species, to adsorb metals onto oxide and carbon supports. Oxide supports, such as Silica, contain terminal hydroxyl groups in aqueous solution that can be protonated or deprotonated by adjusting the pH, creating a charged surface for the ionic metal complex to adsorb. SEA has been shown to produce ultra-small metal nanoparticles (approximately 1nm) creating more active sites per gram of precious metal. SEA is commonly performed on thin slurries because it is hypothesized that metal adsorption capacity will be inhibited by higher counter ion concentrations present in thick slurries. This retardation of adsorption is also predicted by the Revised Physical Adsorption Model (RPA). The most widely used method of catalyst synthesis is Dry Impregnation (DI) which is performed with enough liquid containing metal precursor complex to wet the support. Although it is simple method to perform with no loss of metal, metal-support interactions are often uncontrolled and produce a wide distribution of particle size. An effective synthesis strategy that combines the advantages of dry impregnation (thick slurry) and SEA (small metal particles) has been introduced. Nevertheless, a systematic study showing how metal ion adsorption capacity via SEA varies with slurry thickness as well as ionic strength is still lacking. In this study, we have studied SEA of cationic Ruthenium complex on two different Silica samples at different slurry thicknesses. At high concentration and pH, cationic Ruthenium hexaammine precursor complex underwent side reactions as seen from the UV-Vis analysis. This prevented control of chemical species in the system particularly for thicker slurries. Consequently, we attribute differences between experimental results and RPA model at different slurry thicknesses to a combined effect of this uncontrolled side reaction as well as the ions that resulted from them.

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