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6
Chapter 1: The Role of Zeolites in Heterogeneous Catalysis
1.1. Heterogeneous Cataylsis
Heterogeneous catalysis is a field that utilizes solid materials to
simplify the separation process. A wide variety of solid supports are
available for this purpose from specialized nanoparticles to amorphous silica
surfaces. Zeolites are of particular interest in this field due to their uniform
microporous structures and unique internal topologies that make them ideal
candidates for a broad array of catalytic applications.
1.2. Zeolites and Zeotypes
Zeolites are a class of minerals discovered in the mid-1700s by
Swedish mineralogist Axel Fredrik Cronstedt. Upon observation of large
quantities of steam generated from the heating of a rock called stilbite,
Cronstedt designated the material “zeolithos” from the Greek for “boiling
stone.” Vast natural deposits of zeolites are often found in regions with
volcanic activity where volcanic ash (predominately composed of silicon and
aluminum oxides) deposited in lakes can react with alkaline water under
pressure and elevated temperatures.1 To a lesser extent, zeolites can form
in arid regions with alkaline soil and rich salt deposits.
Zeolites are aluminosilicates with well-defined crystalline structures.
The microporous structures are series of interconnected channels, pores,
Object Description
| Title | Modification of methanol-to-olefin hydrocarbon pool species by oxygenates on acidic zeolites |
| Author | Hayman, Miranda Jeanette |
| Author email | mirandah@usc.edu; mirandahayman@gmail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Chemistry |
| School | College of Letters, Arts and Sciences |
| Date defended/completed | 2011-02-11 |
| Date submitted | 2011 |
| Restricted until | Unrestricted |
| Date published | 2011-04-26 |
| Advisor (committee chair) | Haw, James F. |
| Advisor (committee member) |
Flood, Thomas C. Jessen, Kristian |
| Abstract | The mechanism of methanol-to-olefin (MTO) catalysis employs organic reaction centers, both aromatic and olefinic, to generate olefins on acid zeolites. Generally, propene is the favored MTO olefin on most zeolite catalysts, but ethylene is a more desirable olefin due to its prevalence in consumer plastics. Much research has been conducted to alter the MTO product selectivities to favor ethylene. This focus of this dissertation is selective modification of the olefinic reaction centers, converting them into aromatic reaction centers known to be responsible for the majority of ethylene production.; Formaldehyde reactivity was studied on HSAPO-34, and found to react with propene through a Prins reaction to form butadiene, which readily cyclized to aromatic species. Evidence of formaldehyde formation was observed from methanol oxidation on the stainless-steel surface of the reactor tubing. This reaction was then studied in HZSM-5 where olefinic reaction centers dominate the hydrocarbon pool. The olefinic reaction centers were converted to aromatic species, and a significant increase in ethylene selectivity was observed. Other oxygenated species, such as acetaldehyde, were also studied in conjunction with methanol on HZSM-5 and an improvement in ethylene selectivity was noted. The consequence of the increased ethylene selectivity however was an increase in the rate of deactivation due to the accelerated formation of aromatic species. |
| Keyword | MTO; methanol-to-olefins; zeolite; heterogeneous catalysis; hydrocarbon pool; HZSM-5 |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m3780 |
| Contributing entity | University of Southern California |
| Rights | Hayman, Miranda Jeanette |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | cisadmin@lib.usc.edu |
| Filename | etd-Hayman-4358 |
| Archival file | uscthesesreloadpub_Volume23/etd-Hayman-4358.pdf |
Description
| Title | Page 17 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 6 Chapter 1: The Role of Zeolites in Heterogeneous Catalysis 1.1. Heterogeneous Cataylsis Heterogeneous catalysis is a field that utilizes solid materials to simplify the separation process. A wide variety of solid supports are available for this purpose from specialized nanoparticles to amorphous silica surfaces. Zeolites are of particular interest in this field due to their uniform microporous structures and unique internal topologies that make them ideal candidates for a broad array of catalytic applications. 1.2. Zeolites and Zeotypes Zeolites are a class of minerals discovered in the mid-1700s by Swedish mineralogist Axel Fredrik Cronstedt. Upon observation of large quantities of steam generated from the heating of a rock called stilbite, Cronstedt designated the material “zeolithos” from the Greek for “boiling stone.” Vast natural deposits of zeolites are often found in regions with volcanic activity where volcanic ash (predominately composed of silicon and aluminum oxides) deposited in lakes can react with alkaline water under pressure and elevated temperatures.1 To a lesser extent, zeolites can form in arid regions with alkaline soil and rich salt deposits. Zeolites are aluminosilicates with well-defined crystalline structures. The microporous structures are series of interconnected channels, pores, |
