Cheng, Yu-Chieh and Veser, Götz
(2017)
Isomorphous Fe Substituted ZSM-5 for Methane Dehydroaromatization.
Master's Thesis, University of Pittsburgh.
(Unpublished)
Abstract
Shale gas has become an abundant source of natural gas in recent years; methane is one of its major chemical components. Meanwhile, benzene, which is applied into the manufacturing of complex chemicals, is an important chemical intermediate in petrochemical industry. Direct methane dehydroaromatization (DHA) under non-oxidative condition is an alternative approach to convert methane into benzene. The reaction mechanism is generally considered a synergistic result of metal sites and Bronsted acid sites of HZSM-5. Here, methane is activated by metal site while zeolite provides the shape-selective environment and the diffusion channel for reactive molecules. Among different bi-functional catalysts, Mo/HZSM-5 is the most studied catalyst for this reaction due to its strong catalytic performance. However, coke formation driven by thermodynamics will ultimately lead to catalyst deactivation. This problem is exacerbated by the fact that the catalyst regeneration for Mo/ZSM-5 is relatively lengthy and uneconomical due to its loss of activity after burn-off.
Recent reports suggested that atomically dispersed iron on silica can have high conversion of methane to higher hydrocarbon and can potentially suppress coke formation. Our group previously found that highly dispersed iron on ZSM-5, H-(Fe)ZSM-5, also shows high benzene selectivity and reduced coke formation. However, severe coke formation still result from secondary reactions of product on Bronsted acid site of ZSM-5.
The purpose of this research is to study how catalytic performance and coke formation are influenced by the catalyst structure of H-(Fe)ZSM-5 and how this structure can be affected by the ZSM-5 synthesis. Specifically, the impact of hydrothermal time, hydrolysis time and template ratio in ZSM-5 synthesis were investigated since these parameters can have influence on both crystallinity and particle size. It is found that both of these structural parameters can have significant influence on catalytic performance. In addition, we found that passivation of external Bronsted acid sites can improve catalyst stability by reducing coke formation but simultaneously also decreases the reactivity. Overall, we developed a well-defined catalyst with high selectivity (~86%) in DHA by optimizing only synthetic parameters without applying any post-treatment.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
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| Date: |
13 June 2017 |
| Date Type: |
Publication |
| Defense Date: |
28 March 2017 |
| Approval Date: |
13 June 2017 |
| Submission Date: |
6 April 2017 |
| Access Restriction: |
3 year -- Restrict access to University of Pittsburgh for a period of 3 years. |
| Number of Pages: |
87 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Chemical and Petroleum Engineering |
| Degree: |
MS - Master of Science |
| Thesis Type: |
Master's Thesis |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
Isomorphous substitution
ZSM-5
Methane dehydroaromatization |
| Date Deposited: |
13 Jun 2017 14:31 |
| Last Modified: |
22 Apr 2024 12:30 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/31392 |
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