Higher oxygenates synthesis by catalytic conversion of synthesis gas are the potential approaches to replace fossil fuels and produce chemicals for pharmaceutical manufacture, detergents and polymer industry. Cobalt-based catalysts are the most promising catalysts to replace noble metal catalysts for producing ethanol, acetaldehyde and higher oxygenates via CO hydrogenation. The formation of higher oxygenates requires active sites that can adsorb CO non-dissociatively and insert to the alkyl intermediate. The hydrogenation of the CO-inserted intermediates yields C2 and C2+ oxygenates. The main focus of this study is to investigate the active site for non-dissociative CO adsorption, and the modification of the catalysts to enhance the production rate for higher oxygenates.
The effect of different structural promoters are investigated on copper-cobalt catalysts. Three cobaltcopper catalysts singly promoted with La, Zr, or Al were studied for catalytic conversion of syngas to higher alcohols. CO hydrogenation was carried out, and catalyst activity and selectivity to higher alcohols are the greatest on La promoted catalyst. La promoted catalyst differs from the other two in the first 10 h of time-on-stream, with the product distribution shifted to favor oxygenates formation. These results suggest changes on La promoted catalyst during the reaction. The DRIFTS study of CO adsorption behavior on La promoted copper-cobalt catalyst observed that CO linearly adsorbed on Co2C site. A cobalt carbide phase was formed in the reaction, and Co2C is able to adsorb CO associatively and insert to the intermediates. X-ray absorption techniques detected the existence of cobalt carbide in the lanthanum promoted cobalt-copper catalysts. A further reaction study on a promoter-free bulk Co2C catalyst also detected higher oxygenates as products.
To improve the selectivity to ethanol and higher oxygenates and provide a stable catalyst for CO hydrogenation, a novel method using metal organic framework as precursors was performed to synthesize a series of potassium-promoted cobalt catalysts for higher oxygenates synthesis. The MOF-mediated synthesis method provide the catalyst with superior resistance to sintering and deactivation. The potassium promoters suppresses the formation of methane and higher hydrocarbons, while cobalt carbide is formed from the metallic cobalt and the carbon in the catalyst. As a result, the potassium-promoted catalyst synthesized by MOF-mediated method gives high yields to ethanol and higher oxygenates.
CO hydrogenation was also carried out using real biomass-derived syngas. The low CO composition and high CO/H2 ratio in the biomass-derived syngas require special catalysts to carry out Fischer-Tropsch reaction and produce liquid fuels. By using K-promoted iron catalysts and ruthenium catalysts, along with the addition of steam into the syngas feedstock, a high yield of liquid hydrocarbons were achieved in the reaction. This study shed light on using biomass-derived syngas for the production of higher oxygenates.
| Identifer | oai:union.ndltd.org:LSU/oai:etd.lsu.edu:etd-10272016-154101 |
| Date | 16 November 2016 |
| Creators | Wang, Zi |
| Contributors | Spivey, James, Sprunger, Phillip, Dooley, Kerry, Xu, Ye, Flake, John |
| Publisher | LSU |
| Source Sets | Louisiana State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lsu.edu/docs/available/etd-10272016-154101/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached herein a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to LSU or its agents the non-exclusive license to archive and make accessible, under the conditions specified below and in appropriate University policies, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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