Chemical and Biological Engineering ETDs

Jonathan Paiz

Publication Date

2-14-2014

Abstract

This study used PdZn as a model system to investigate phase transformations and its influence on reactivity. Aerosol synthesis was used to study the oxide precursors of the PdZn system, spin coating was used to synthesize model PdZn nanoparticles for phase transformations studies and preliminary work with CO oxidation coupled with methanol steam reforming (MSR) was used to gain insight into in-situ surface reactivity of PdZn for MSR. Multiple characterization techniques including XRD, Raman Spectroscopy, XPS, EDX along with TEM and STEM were used to gain valuable insight into the nature of the samples used in these studies. Investigations into the Pd:Zn aerosol derived oxides demonstrated the existence of 2 mixed oxides, a previously undocumented (Pd,Zn)O and a greater characterized bulk (Zn,Pd)O. TEM and SEM were used to show to distinct phases of different morphologies and EDX showed the differences in Pd and Zn ratios for each phase. XRD was used to demonstrate the change in unit cell volume of PdO and Raman was used to show incorporation of Pd into the ZnO lattice. The model system synthesized via spin coating demonstrated a simple platform for the study of complex multimetallic catalysts. The use of the silica as a TEM support combined with aberration corrected HRSTEM, EDX, XPS and Raman allowed for a very detailed look into PdZn nanoparticle formation from (Pd,Zn)O → α-Pd → β1-PdZn → Pd2Zn and back to α-Pd. This study provided insight into the role of reduction temperature, showing that nanoparticles of the desired tetragonal PdZn phase can be formed at relatively low temperatures on suitable supports along with phase transformations leading to changes in activity. CO oxidation studies of 1wt% Pd/ZnO gave insight into the dynamic nature of the PdZn system at various reduction temperatures. The preliminary results suggest that the number of active sites decrease on Pd/ZnO with increase in reduction temperature while MSR activity remains constant, this implies that lager particles show higher turn over frequency for MSR.

Keywords

PdZn, Catalysis

Document Type

Dissertation

Language

English

Degree Name

Chemical Engineering

Level of Degree

Doctoral

Department Name

Chemical and Biological Engineering

First Committee Member (Chair)

Atanassov, Plamen

Second Committee Member

Brearley, Adrian

Third Committee Member

Ward, Tim

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