Date of Award

12-15-2014

Document Type

Open Access Dissertation

Department

Chemical Engineering

First Advisor

Michael D. Amiridis

Abstract

The performance of supported metal catalysts largely depends on the structure and composition of the metal particles and the nature of the support. In order to achieve better control over these parameters, synthetic route based on the use of templating agents has been proposed. Among the different templating agents, poly(amidoamine) (PAMAM) dendrimers have attracted a lot of recent attention as nanoparticle stabilizers. In this thesis, Au/G4OH nanocomposites were synthesized in aqueous solutions and used as precursors for the preparation of SiO2-supported Au nanoparticles. Elemental analysis, UV-Vis, and STEM measurements were used to estimate the extent of the Au-dendrimer interactions and to illustrate how the solution pH affect the number of Au atoms complexed with each dendrimer molecule, as well as the final size of the SiO2-supported gold particles. At pH=7, Au5/G4OH nanocomposites with sizes of Au particles below 2 nm can be formed and used as precursors for the preparation of solid materials. We show that such nanocomposites can be deposited intact on the surface of SiO2 and yield highly dispersed and nearly uniform Au nanoparticles with dimensions on the order of 1.6 nm.

One of the simplest, least expensive methods of catalyst preparation is the wet impregnation, where an oxide support is contacted for a certain time with a liquid solution containing the metal precursor. In certain circumstances when the impregnation conditions are controlled it is possible to end up with uniform and highly dispersed metal particles. One of these examples is the "Strong Electrostatic Adsorption" (SEA). In this thesis, the extension of SEA is made to an important noble metal, silver. Evaluation of the uptake of Ag diammine (Ag(NH3)2+) over supports with low and mid-point of zero charge (PZC) (Nb2O5, SiO2, Al2O3 and ZrO2) was performed and this knowledge was used to prepare highly dispersed monometallic Ag nanoparticles. Temperature-programmed reduction (TPR) was used to determine the reduction temperature of the final Ag/SiO2 (low-PZC) and Ag/Al2O3 (mid-PZC) catalytic materials. Finally, STEM and XRD measurements were also used to image and determine the size of the resulting supported metal nanoparticles, respectively.

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