<p>In recent decades, alternatives to traditional coal and
fossil fuels were utilized to reduce carbon emissions. Among these
alternatives, natural gas is a cleaner fuel and is abundant globally. Shale
gas, a form of natural gas that also contains light alkanes (C2-C4), is
presently being employed to produce olefins, which can be upgraded to higher
molecular weight hydrocarbons. This thesis describes efforts to develop new
catalytic materials and characterizations for the conversion of shale gas to
fuels.</p>
<p>In the first half, silica supported Pt-Cr alloys containing
varying compositions of Pt and Pt<sub>3</sub>Cr were used for propane
dehydrogenation at 550°C. Although a change in selective performance was
observed on catalysts with varying promoter compositions, the average
nano-particle structures determined by <i>in situ</i>, synchrotron x-ray
absorption spectroscopy (XAS) and x-ray diffraction (XRD) were identical.
Further, this work presents a method for the characterization of the catalytic
surface by these methods to understand its relationship with olefin selectivity.
From this, we can gain an atomically precise control of new alloys
compositions with tunable surface structures.</p>
<p>Once formed by dehydrogenation, the intermediate olefins are
converted to fuel-range hydrocarbons. In the second half, previously unknown
single site, main group Zn<sup>2+</sup> and Ga<sup>3+</sup> catalysts are shown
to be effective for oligomerization and the resulting products follow a Schutlz
Flory distribution. Mechanistic studies suggest these catalysts form metal
hydride and metal alkyl reaction intermediates and are active for olefin
insertion and b-H elimination elementary steps,
typical for the homogeneous, Cossee-Arlman oligomerization mechanism. Evidence
of metal hydride and metal alkyl species were observed by XAS, Fourier
transform infrared spectroscopy (FTIR), and H<sub>2</sub>/D<sub>2</sub> isotope
exchange. Understanding the reaction intermediates and elementary steps is
critical for identifying novel oligomerization catalysts with tunable product
selectivity for targeted applications. </p>
<p> Through
controlled synthesis and atomic level <i>in situ </i>characterizations, new
catalysts compositions can be developed with high control over the resulting
performance. An atomically precise control of the catalyst structure and
understanding how it evolves under reaction conditions can help shed light on
the fundamental principles required for rational catalyst design. </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/12455987 |
| Date | 16 June 2020 |
| Creators | Nicole J Libretto (8953583) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/ADVANCED_CHARACTERIZATIONS_FOR_THE_IDENTIFICATION_OF_CATALYST_STRUCTURES_AND_REACTION_INTERMEDIATES/12455987 |
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