Date of Award

1-1-2013

Document Type

Open Access Dissertation

Department

Chemical Engineering

First Advisor

John R Regalbuto

Abstract

Many catalysts are today prepared by impregnation (also called incipient wetness or dry impregnation) in which nominal amounts of metals are placed into the amount of solution just necessary to fill the pore volume of the support material. While dry impregnation (DI) is simple and the amounts of metals easily controlled, no attention is paid to metal-support or metal-metal interaction. When DI-deposited metal precursors are reduced, the particles tend to be large in size and there is often ppor contact between two metals in a bimetallic system. In this work we demonstrate the application of "strong electrostatic adsorption" (SEA) for the rational synthesis of inorganic metallic catalysts with high metal dispersion and intimate metal1-metal2 interaction of bimetallic catalysts. For monometallic catalysts, we suggested charge-enhanced dry impregnation (CEDI) which can produce highly dispersed single metal catalysts by inducing electrostatic interaction between dissolved precursor and support while using a simple DI method. Two variations will be demonstrated that produce bimetallic catalysts: using simultaneous or co-SEA, two metal precursors are simultaneously placed in solution and electrostatically adsorbed onto a support in a mixed monolayer of precursors. This produces homogeneously alloyed bimetallic particles when the precursor layer is reduced. On the other hand, SEA can be applied in a two step sequence (seq-SEA); the core metal precursor is electrostatically adsorbed onto the support and oxidized, and then the shell metal precursor is selectively adsorbed onto the core metal oxide and not onto the support. A core-shell morphology persists after the reduction step. Pt/Pd bimetallic catalysts supported by oxidized and unoxidized carbon, alumina and silica have been synthesized by co-SEA. Seq-SEA has been used to produce Pd cores/Pt shell (Pd@Pt) on silica and alumina, and Pt cores/Pd shell (Pt@Pd) on alumina. These are compared with DI-prepared catalysts of the same nominal composition. Seq-SEA can also produce well-dispersed uniform Pd@Au catalysts for Benzyl alcohol oxidation. Catalysts synthesized using this method, have 10 times the activity of comparable DI-prepared catalysts, while using 25 times less gold. The materials were characterized by powder XRD, STEM, EDXS nanoparticle mapping, and TPR. Au/Pd/C catalysts were evaluated by benzyl alcohol oxidation reaction at Cardiff University, England.

Rights

© 2013, Hyeran Cho

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