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Characterization and Kinetic Evaluation of Ag-Pt Bimetallic Catalysts Prepared by Electroless Deposition

Melanie Schaal, Anna Pickerell, John R. Monnier, and Christopher Williams. Chemical Engineering, University of South Carolina, 2C02, Swearingen Engineering Center, 301 South Main Street; USC, Columbia, SC 29208

Bimetallic catalysts are often used to improve catalyst performance, particularly with respect to enhancing selectivity to the desired products. Such catalysts are typically prepared by either co-impregnation or successive impregnation of both metal salts onto the catalyst support. For either of these preparative methods, it is virtually impossible to ensure formation of only bimetallic particles; rather, formation of separate metallic particles of both metals can and does occur. Thus, it is very difficult to characterize such catalytic systems, and even more difficult to correlate catalyst performance with bimetallic catalyst composition. An alternative approach for the preparation of bimetallic catalysts is the use of electroless deposition (ED) of reducible metal salts onto other metals. ED is a catalytic or auto-catalytic process for the deposition of metallic components by a controlled chemical reaction that is catalyzed by the pre-existing metal (catalysis) or the metal which is being deposited (auto-catalysis). In this work, we report the synthesis, characterization, and evaluation of a series of Ag-Pt bimetallic catalysts prepared by electroless deposition. The rate equation for Ag deposition from the ED solution has been studied and the key parameters have been determined. The resulting catalysts have been characterized using atomic adsorption, molecule selective hydrogen chemisorption, and FT-IR CO adsorption. IR results suggest that the Pt(111) sites are selectively covered by Ag. Additional investigations conducted to ascertain the presence of ensemble and/or electronic effects via FT-IR experiments with CO isotopic gas will be reported. Finally, kinetic studies were conducted using the selective hydrogenation of 3,4-epoxy-1-butene, a multifunctional molecule that can serve as an intermediate for production of specialty chemicals. The addition of a small amount of Ag to Pt-containing catalysts results in a 3-fold increase in activity and a modification of product selectivity. Further silver addition results in the expected poisoning of the catalyst.