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Gold catalysts prepared by ion exchange for use in ethylene glycol oxidation: An exploratory study
Heterogeneous catalysis using supported gold nanocrystallites has attracted increasing attention over the last two decades for its applicability to a wide range of reactions, offering activity under ambient conditions, as well as high selectivities towards particular products. This study focuses on...
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| Format: | Thesis |
| Language: | English |
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Department of Chemical Engineering
2014
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| _version_ | 1867613443147694080 |
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| access_status_str | Open Access |
| author | Case, Jennifer Margaret |
| author2 | Van Steen, Eric |
| author_browse | Case, Jennifer Margaret Van Steen, Eric |
| author_facet | Van Steen, Eric Case, Jennifer Margaret |
| author_sort | Case, Jennifer Margaret |
| collection | Thesis |
| description | Heterogeneous catalysis using supported gold nanocrystallites has attracted increasing attention over the last two decades for its applicability to a wide range of reactions, offering activity under ambient conditions, as well as high selectivities towards particular products. This study focuses on a relatively uncommon method of gold catalyst preparation, ion exchange, which involves the suspension of the support in a solution containing cationic or anionic gold complex precursors at a fixed pH, followed by separation of the solid catalyst from this solution, drying and calcination. Theoretically, ion exchange preparation offers the possibility of highly dispersed gold crystallites, which are desirable in gold catalysis. A series of catalysts was prepared using both anionic and cationic exchange, with [AuCl4]- and [Au(NH3)4]3+ respectively as gold precursors, with such solution concentrations that maximum loadings in the region of 3 to 4 wt-% Au could be obtained. Activated carbon and γ-alumina were used as supports. Catalysts were prepared at different pHs theorised to influence electrostatic adsorption differentially. Calcination was conducted at 300ºC in hydrogen. Gold loading was established using Atomic Absorption Spectroscopy (AAS) and Thermogravimetric Analysis (TGA). Loading to full capacity was noted in a number of instances with the carbon supported catalysts. Most of the gold uptake took place in the first two hours of aging. In many but not in all cases higher loadings were noted at pHs further away from the iso-electric point (IEP), in the region where the support is oppositely charged to the complexed gold ion, thus confirming the electrostatic adsorption theory for ion exchange. The size of gold crystallites was determined using Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD) and oxygen chemisorption. TEM results were used to calculate average crystallite sizes as well as to give an indication of size distributions. Measurable XRD gold peaks were only visible for supported carbon catalysts, and the crystallite sizes estimated using this technique were notably lower than average crystallite sizes from TEM for these catalysts. The carbon supports showed a large uptake of oxygen in the chemisorption process, and thus this technique was only used as a method for crystallite size determination for alumina supported catalysts. These crystallite sizes showed general iii agreement with the average sizes derived from TEM. In summary, the carbon supported catalysts had average crystallite sizes greater than 10 nm with wide size distributions, while the alumina catalysts had average crystallite sizes nearly all under 10 nm and narrow size distributions. Ethylene glycol oxidation under atmospheric pressure was employed as a test reaction, using 0.05 M ethylene glycol at a temperature of 60 ºC and at a pH of 11. Only the alumina supported catalysts displayed activity under these conditions, with initial reaction rates in the range of 2 to 15 mmol EG / g Au . min which are comparable to those reported in the literature. Across the range of crystallite sizes represented in these catalysts there was no evidence of dependency of activity on crystallite size. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/5362 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:36:13.705Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2014 |
| publishDateRange | 2014 |
| publishDateSort | 2014 |
| publisher | Department of Chemical Engineering |
| publisherStr | Department of Chemical Engineering |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/5362 Gold catalysts prepared by ion exchange for use in ethylene glycol oxidation: An exploratory study Case, Jennifer Margaret Van Steen, Eric Chemical Engineering Heterogeneous catalysis using supported gold nanocrystallites has attracted increasing attention over the last two decades for its applicability to a wide range of reactions, offering activity under ambient conditions, as well as high selectivities towards particular products. This study focuses on a relatively uncommon method of gold catalyst preparation, ion exchange, which involves the suspension of the support in a solution containing cationic or anionic gold complex precursors at a fixed pH, followed by separation of the solid catalyst from this solution, drying and calcination. Theoretically, ion exchange preparation offers the possibility of highly dispersed gold crystallites, which are desirable in gold catalysis. A series of catalysts was prepared using both anionic and cationic exchange, with [AuCl4]- and [Au(NH3)4]3+ respectively as gold precursors, with such solution concentrations that maximum loadings in the region of 3 to 4 wt-% Au could be obtained. Activated carbon and γ-alumina were used as supports. Catalysts were prepared at different pHs theorised to influence electrostatic adsorption differentially. Calcination was conducted at 300ºC in hydrogen. Gold loading was established using Atomic Absorption Spectroscopy (AAS) and Thermogravimetric Analysis (TGA). Loading to full capacity was noted in a number of instances with the carbon supported catalysts. Most of the gold uptake took place in the first two hours of aging. In many but not in all cases higher loadings were noted at pHs further away from the iso-electric point (IEP), in the region where the support is oppositely charged to the complexed gold ion, thus confirming the electrostatic adsorption theory for ion exchange. The size of gold crystallites was determined using Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD) and oxygen chemisorption. TEM results were used to calculate average crystallite sizes as well as to give an indication of size distributions. Measurable XRD gold peaks were only visible for supported carbon catalysts, and the crystallite sizes estimated using this technique were notably lower than average crystallite sizes from TEM for these catalysts. The carbon supports showed a large uptake of oxygen in the chemisorption process, and thus this technique was only used as a method for crystallite size determination for alumina supported catalysts. These crystallite sizes showed general iii agreement with the average sizes derived from TEM. In summary, the carbon supported catalysts had average crystallite sizes greater than 10 nm with wide size distributions, while the alumina catalysts had average crystallite sizes nearly all under 10 nm and narrow size distributions. Ethylene glycol oxidation under atmospheric pressure was employed as a test reaction, using 0.05 M ethylene glycol at a temperature of 60 ºC and at a pH of 11. Only the alumina supported catalysts displayed activity under these conditions, with initial reaction rates in the range of 2 to 15 mmol EG / g Au . min which are comparable to those reported in the literature. Across the range of crystallite sizes represented in these catalysts there was no evidence of dependency of activity on crystallite size. 2014-07-31T11:13:06Z 2014-07-31T11:13:06Z 2009 Thesis http://hdl.handle.net/11427/5362 eng application/pdf Department of Chemical Engineering Faculty of Engineering and the Built Environment University of Cape Town |
| spellingShingle | Chemical Engineering Case, Jennifer Margaret Gold catalysts prepared by ion exchange for use in ethylene glycol oxidation: An exploratory study |
| title | Gold catalysts prepared by ion exchange for use in ethylene glycol oxidation: An exploratory study |
| title_full | Gold catalysts prepared by ion exchange for use in ethylene glycol oxidation: An exploratory study |
| title_fullStr | Gold catalysts prepared by ion exchange for use in ethylene glycol oxidation: An exploratory study |
| title_full_unstemmed | Gold catalysts prepared by ion exchange for use in ethylene glycol oxidation: An exploratory study |
| title_short | Gold catalysts prepared by ion exchange for use in ethylene glycol oxidation: An exploratory study |
| title_sort | gold catalysts prepared by ion exchange for use in ethylene glycol oxidation an exploratory study |
| topic | Chemical Engineering |
| url | http://hdl.handle.net/11427/5362 |
| work_keys_str_mv | AT casejennifermargaret goldcatalystspreparedbyionexchangeforuseinethyleneglycoloxidationanexploratorystudy |