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The effect of hydrothermal and acid dealumination on the structural, acid and catalytic properties of Mordenite
Although there have been a number of studies of the effect of hydrothermal and acid dealumination on the properties of Mordenite, there is a lack of clarity on many issues related to the changes which these treatments cause to the structure, acidity and catalytic activity of Mordenite. Both methods...
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| Format: | Thesis |
| Language: | English |
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Department of Chemical Engineering
2016
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| _version_ | 1867613316322426880 |
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| access_status_str | Open Access |
| author | O'Donovan,Anthony William |
| author2 | O'Connor, Cyril T |
| author_browse | O'Connor, Cyril T O'Donovan,Anthony William |
| author_facet | O'Connor, Cyril T O'Donovan,Anthony William |
| author_sort | O'Donovan,Anthony William |
| collection | Thesis |
| description | Although there have been a number of studies of the effect of hydrothermal and acid dealumination on the properties of Mordenite, there is a lack of clarity on many issues related to the changes which these treatments cause to the structure, acidity and catalytic activity of Mordenite. Both methods remove aluminium from the framework thus creating extra framework aluminium species. Although there are some reports that these species, particularly when created by mild steaming, increase the acidity and catalytic activity of the dealuminated sample, it has also been reported that these species have either a negative or no effect on thecatalyst's acidity and activity [Mirodatos and Barthomeuf, 1981; Chen eta/., 1992; Meyerseta/., 1988; Bamwenda eta/., 1994; Brunner eta/., 1994]. These conflicting reports are understandable when one considers that the dealumination conditions in the various studies are usually not equivalent to each other and consequently the resultant catalysts may differ. The use of Mordenite from different sources to compare acidity in one case and structure in another may also lead to different and conflicting results. This has affected the interpretation of observed trends in the structure, acidity and catalytic behaviour of dealuminated Mordenite. A systematic study of the effect of acid washing of sodium Mordenite and hydrogen exchanged Mordenite, both before and after steaming, has been carried out. The bulk removal of aluminium was monitored by elemental analysis of samples. The study investigated the effect of different conditions of acid washing, steaming and steaming followed by acid washing on the solid state properties of Mordenite by use of solid state ²⁷AI and ²⁹Si nuclear magnetic resonance, x-ray diffraction and infrared techniques. The effect of these changes on the number, type and strength of acid sites in Mordenite was then investigated by ammonia temperature programmed desorption, Fourier-Transform infrared analysis of pyridine adsorption and proton nuclear magnetic resonance studies. The changes caused by dealumination to the catalytic activity and shape selective properties of Mordenite as determined by studies of isobutane cracking, cyclohexanol dehydration and isopropylation of naphthalene, were then explained in terms of the acidic and structural properties of the dealuminated Mordenite samples. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/21502 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:34:10.861Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2016 |
| publishDateRange | 2016 |
| publishDateSort | 2016 |
| 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:11427/21502 The effect of hydrothermal and acid dealumination on the structural, acid and catalytic properties of Mordenite O'Donovan,Anthony William O'Connor, Cyril T Chemical Engineering Although there have been a number of studies of the effect of hydrothermal and acid dealumination on the properties of Mordenite, there is a lack of clarity on many issues related to the changes which these treatments cause to the structure, acidity and catalytic activity of Mordenite. Both methods remove aluminium from the framework thus creating extra framework aluminium species. Although there are some reports that these species, particularly when created by mild steaming, increase the acidity and catalytic activity of the dealuminated sample, it has also been reported that these species have either a negative or no effect on thecatalyst's acidity and activity [Mirodatos and Barthomeuf, 1981; Chen eta/., 1992; Meyerseta/., 1988; Bamwenda eta/., 1994; Brunner eta/., 1994]. These conflicting reports are understandable when one considers that the dealumination conditions in the various studies are usually not equivalent to each other and consequently the resultant catalysts may differ. The use of Mordenite from different sources to compare acidity in one case and structure in another may also lead to different and conflicting results. This has affected the interpretation of observed trends in the structure, acidity and catalytic behaviour of dealuminated Mordenite. A systematic study of the effect of acid washing of sodium Mordenite and hydrogen exchanged Mordenite, both before and after steaming, has been carried out. The bulk removal of aluminium was monitored by elemental analysis of samples. The study investigated the effect of different conditions of acid washing, steaming and steaming followed by acid washing on the solid state properties of Mordenite by use of solid state ²⁷AI and ²⁹Si nuclear magnetic resonance, x-ray diffraction and infrared techniques. The effect of these changes on the number, type and strength of acid sites in Mordenite was then investigated by ammonia temperature programmed desorption, Fourier-Transform infrared analysis of pyridine adsorption and proton nuclear magnetic resonance studies. The changes caused by dealumination to the catalytic activity and shape selective properties of Mordenite as determined by studies of isobutane cracking, cyclohexanol dehydration and isopropylation of naphthalene, were then explained in terms of the acidic and structural properties of the dealuminated Mordenite samples. 2016-08-24T12:55:20Z 2016-08-24T12:55:20Z 1995 Doctoral Thesis Doctoral PhD http://hdl.handle.net/11427/21502 eng application/pdf Department of Chemical Engineering Faculty of Engineering and the Built Environment University of Cape Town |
| spellingShingle | Chemical Engineering O'Donovan,Anthony William The effect of hydrothermal and acid dealumination on the structural, acid and catalytic properties of Mordenite |
| thesis_degree_str | Doctoral |
| title | The effect of hydrothermal and acid dealumination on the structural, acid and catalytic properties of Mordenite |
| title_full | The effect of hydrothermal and acid dealumination on the structural, acid and catalytic properties of Mordenite |
| title_fullStr | The effect of hydrothermal and acid dealumination on the structural, acid and catalytic properties of Mordenite |
| title_full_unstemmed | The effect of hydrothermal and acid dealumination on the structural, acid and catalytic properties of Mordenite |
| title_short | The effect of hydrothermal and acid dealumination on the structural, acid and catalytic properties of Mordenite |
| title_sort | effect of hydrothermal and acid dealumination on the structural acid and catalytic properties of mordenite |
| topic | Chemical Engineering |
| url | http://hdl.handle.net/11427/21502 |
| work_keys_str_mv | AT odonovananthonywilliam theeffectofhydrothermalandaciddealuminationonthestructuralacidandcatalyticpropertiesofmordenite AT odonovananthonywilliam effectofhydrothermalandaciddealuminationonthestructuralacidandcatalyticpropertiesofmordenite |