Date of Award

2018

Document Type

Open Access Dissertation

Department

Chemical Engineering

Sub-Department

College of Engineering and Computing

First Advisor

John R. Regalbuto

Abstract

Supported catalysts are used extensively in a variety of heterogeneously catalyzed reactions for industrial processes. Techniques for preparing supported noble metal catalysts are typically chosen to achieve high metal dispersions in order to obtain high activity for a given metal loading. Enhancing the catalytic performance of heterogeneous catalysts can be done by increasing active site count as well as modification of the physico-chemical characteristics of the catalyst material. For supported metal nanoparticles this can be achieved by decreasing particle size, thus increasing dispersion or metal utilization on the surface of the particles, while modification of metal properties can be attained by addition of a secondary metal that has a strong interaction to the primary metal, beneficial for a given reaction. In this dissertation, the first two chapters cover preparation methods to control metal particles size and the third chapter goes over evaluations of monometallic and bimetallic catalyst.

In the preparation of supported metal catalysts, the methods of Strong Electrostatic Adsorption (SEA), and its incipient wetness analog, Charge Enhanced Dry Impregnation (CEDI), can yield supported metal nanoparticles with high dispersion and narrow size distribution. Catalysts prepared by SEA and CEDI therefore are desirable as seeds for addition of secondary metal using Electroless Deposition (ED), as the prepared bimetallic catalysts should be of similar dispersion as the base catalyst. CEDI and ED methods were used to demonstrate the preparation of monometallic and bimetallic catalysts containing noble and base metals which were then characterized and evaluated for hydrogenation reactions. The first system used Pt, Pd, Co, Ni as the single metal, prepared by CEDI on silica support. In the second system Ag-Ir bimetallic catalysts prepared by ED method were characterized with hydrogenation reactions, FTIR and H2 temperature program desorption (H2-TPD).

In the first work, it was demonstrated that sintering of metal nanoparticles can be induced by the presence of residual balancing ions such as Cl-. We further show how particle size can be drastically reduced by the removal of residual ions. X- ray diffraction (XRD) was used to analyze the particle size.

In the second work, Pt(NH3)4(OH)2 as a model metal precursor has been studied to investigate the effect of different anions such as Cl-, Br-, NO3-, and C6H5O7-3- on the size and polydispersity. Chloride, and bromide had largest impact on sintering and growth of Pt particles along with wide size distribution, confirmed by XRD and STEM images.

In the third work, Ag-Ir bimetallic catalysts at different coverages of Ag were studied. A direct method of reaction and two indirect methods including H2-TPD and FTIR experiments were done to evaluate the unusual H2-uptake of these catalysts. Two different hydrogenation reactions were used to evaluate catalytic properties of the Ir@Ag catalysts, the hydrogenation of propylene (C3H6) and hydrogenolysis of methyl cyclopentane (MCP). In situ transmission Fourier transform infrared spectroscopy (FTIR) of CO adsorption indicates that the Ag is randomly deposited on all types of Ir surface sites during the ED process.

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