Carbonylation of cyclohexene with carbon dioxide (CO2) using transition metals as heterogeneous and homogeneous catalysts
- Authors: Sekaleli, Bafokeng Thabelo
- Date: 2024-10-11
- Subjects: Carbonylation , Carbon dioxide , Catalysts , Transition metals , Cyclohexene
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/464565 , vital:76522
- Description: From a green chemistry perspective, carbon dioxide (CO2) emerges as an appealing C1 synthon, given its abundance in the atmosphere and cost-effectiveness. Many essential chemicals for daily life are derived from fossilized carbon sources like coal, petroleum, and natural gas. However, the by-product of these processes, CO2, poses environmental risks when excessively emitted as a greenhouse gas. Achieving a balance between carbon emissions and removal is crucial to address environmental concerns surrounding CO2. Utilizing CO2 as a C1 source in organic synthesis holds promise for mitigating this balance in the long term. Combining CO2 with other underutilized fine chemicals, such as alkanes, alkenes, and alkynes, to produce more valuable platform chemicals presents an economically viable strategy due to carbon dioxide’s abundance, low cost, and recyclability. Despite its simplicity, CO2's high thermodynamic stability and low kinetic reactivity, owing to its highly oxidized state, pose challenges to its use as a feedstock. Overcoming these hurdles requires catalysts to enhance CO2 reactivity. Our work focuses on developing and employing catalytic systems capable of activating CO2 as a C1 synthon in reactions with cyclohexene and a reducing agent to yield carboxylic acids or esters. In one approach, we have developed heterogeneous catalyst systems comprising transition metals (Au, Fe, Ni, Ru) supported on metal oxide (TiO2). Characterization techniques such as TEM, EDX, UV-Vis, BET, and XRD were used to study the properties of these materials. The catalysts were evaluated in a reaction involving cyclohexene, CO2, and H2O. In another approach, we explored the use of cyclo-tris(tetracarbonylruthenium) [Ru3(CO)12] as a homogeneous catalyst in a reaction involving cyclohexene, methanol, and CO2 in the presence of an ionic liquid, 1-Butyl-3-methylimidazolium chloride ([BMIM]+Cl-). 1H NMR and ATR-FT-IR were utilized to characterize [BMIM]+Cl-. The reaction product was characterised utilizing GC-MS. Upon seeing that Ru3(CO)12 changes color from orange to black when exposed to heat, an investigation was undertaken on the kind of transformations that the catalyst undergoes. This investigation was carried out with the hopes of finding the structures that could be resulting from Ru3(CO)12 during the reaction and their significance to it. The orange and black Ru complexes were characterized utilizing DSC, TGA, ATR-FT-IR and PXRD. , Thesis (MSc) -- Faculty of Science, Chemistry, 2024
- Full Text:
- Date Issued: 2024-10-11
- Authors: Sekaleli, Bafokeng Thabelo
- Date: 2024-10-11
- Subjects: Carbonylation , Carbon dioxide , Catalysts , Transition metals , Cyclohexene
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/464565 , vital:76522
- Description: From a green chemistry perspective, carbon dioxide (CO2) emerges as an appealing C1 synthon, given its abundance in the atmosphere and cost-effectiveness. Many essential chemicals for daily life are derived from fossilized carbon sources like coal, petroleum, and natural gas. However, the by-product of these processes, CO2, poses environmental risks when excessively emitted as a greenhouse gas. Achieving a balance between carbon emissions and removal is crucial to address environmental concerns surrounding CO2. Utilizing CO2 as a C1 source in organic synthesis holds promise for mitigating this balance in the long term. Combining CO2 with other underutilized fine chemicals, such as alkanes, alkenes, and alkynes, to produce more valuable platform chemicals presents an economically viable strategy due to carbon dioxide’s abundance, low cost, and recyclability. Despite its simplicity, CO2's high thermodynamic stability and low kinetic reactivity, owing to its highly oxidized state, pose challenges to its use as a feedstock. Overcoming these hurdles requires catalysts to enhance CO2 reactivity. Our work focuses on developing and employing catalytic systems capable of activating CO2 as a C1 synthon in reactions with cyclohexene and a reducing agent to yield carboxylic acids or esters. In one approach, we have developed heterogeneous catalyst systems comprising transition metals (Au, Fe, Ni, Ru) supported on metal oxide (TiO2). Characterization techniques such as TEM, EDX, UV-Vis, BET, and XRD were used to study the properties of these materials. The catalysts were evaluated in a reaction involving cyclohexene, CO2, and H2O. In another approach, we explored the use of cyclo-tris(tetracarbonylruthenium) [Ru3(CO)12] as a homogeneous catalyst in a reaction involving cyclohexene, methanol, and CO2 in the presence of an ionic liquid, 1-Butyl-3-methylimidazolium chloride ([BMIM]+Cl-). 1H NMR and ATR-FT-IR were utilized to characterize [BMIM]+Cl-. The reaction product was characterised utilizing GC-MS. Upon seeing that Ru3(CO)12 changes color from orange to black when exposed to heat, an investigation was undertaken on the kind of transformations that the catalyst undergoes. This investigation was carried out with the hopes of finding the structures that could be resulting from Ru3(CO)12 during the reaction and their significance to it. The orange and black Ru complexes were characterized utilizing DSC, TGA, ATR-FT-IR and PXRD. , Thesis (MSc) -- Faculty of Science, Chemistry, 2024
- Full Text:
- Date Issued: 2024-10-11
Mobilising indigenous technologies of making oshikundu and uumboloto to motivate and enable sense making of the topic carbon dioxide by grade 8 rural school learners
- Nandjedi, Fredinard Nghinaounditala
- Authors: Nandjedi, Fredinard Nghinaounditala
- Date: 2022-10-14
- Subjects: Science Study and teaching (Secondary) Social aspects Namibia , Culturally relevant pedagogy Namibia , Ethnoscience Namibia , Carbon dioxide
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/405357 , vital:70164
- Description: Poor performance in Science has been noted in most rural schools and this has become a concern to education planners and implementers. Part of the failure is said to be caused by inadequate school resources, under-preparedness of teachers to teach Science, poor command of the Language of Learning and Teaching, negative attitudes that are accompanied by lack of insights into the value of Science, low self-efficacy, and poor-quality environments for learning Science. In this regard, literature has revealed that many Science teachers in Namibia do not consider learners’ local indigenous knowledge (IK) also known as indigenous technology to mediate learning. Yet, it is a requirement of the Namibian Science curriculum. I assume that this could be due in part to the fact that the Science curriculum is not explicit on how IK should be integrated into Science teaching. It is against this backdrop that this study sought to explore the opportunities IK integration into Science may offer in mediating learning and sense-making on the topic of carbon dioxide (CO2). Learners’ indigenous technological practices of making oshikundu and uumboloto were used as vehicles of learning. This qualitative case study is underpinned by the interpretive and indigenous research paradigms. Within the indigenous research paradigm, I focused on the Ubuntu perspective. This study was conducted at a rural under-resourced school in the Ohangwena region in Namibia. Thirty Grade 8 learners, one science teacher and two expert community members were involved as participants. Data were gathered using focus group interviews (sharing circles), group activities, participatory observations, and journal reflections. Data interpretation and analysis were done using Vygotsky’s sociocultural theory and Ogunniyi’s contiguity argumentative theory. A thematic approach to data analysis was adopted. That is, an inductive approach was employed whereby sub-themes were identified, and thereafter common sub-themes were combined into themes. The findings of this study revealed that the process of making oshikundu and uumboloto can be used to enable learners to make sense of the topic of CO2 and other related concepts. Furthermore, the study revealed that hands-on practical activities done with easily accessible resources which are related to learners’ indigenous technologies help learners learn Science easily. The study thus recommends that educators should use oshikundu and/or uumboloto to mediate learning of topics such as CO2. Science teachers should always try to tap into learners’ socio-cultural backgrounds in their lessons to enhance better understanding of Science concepts. , Thesis (MEd) -- Faculty of Education, Education, 2022
- Full Text:
- Date Issued: 2022-10-14
- Authors: Nandjedi, Fredinard Nghinaounditala
- Date: 2022-10-14
- Subjects: Science Study and teaching (Secondary) Social aspects Namibia , Culturally relevant pedagogy Namibia , Ethnoscience Namibia , Carbon dioxide
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/405357 , vital:70164
- Description: Poor performance in Science has been noted in most rural schools and this has become a concern to education planners and implementers. Part of the failure is said to be caused by inadequate school resources, under-preparedness of teachers to teach Science, poor command of the Language of Learning and Teaching, negative attitudes that are accompanied by lack of insights into the value of Science, low self-efficacy, and poor-quality environments for learning Science. In this regard, literature has revealed that many Science teachers in Namibia do not consider learners’ local indigenous knowledge (IK) also known as indigenous technology to mediate learning. Yet, it is a requirement of the Namibian Science curriculum. I assume that this could be due in part to the fact that the Science curriculum is not explicit on how IK should be integrated into Science teaching. It is against this backdrop that this study sought to explore the opportunities IK integration into Science may offer in mediating learning and sense-making on the topic of carbon dioxide (CO2). Learners’ indigenous technological practices of making oshikundu and uumboloto were used as vehicles of learning. This qualitative case study is underpinned by the interpretive and indigenous research paradigms. Within the indigenous research paradigm, I focused on the Ubuntu perspective. This study was conducted at a rural under-resourced school in the Ohangwena region in Namibia. Thirty Grade 8 learners, one science teacher and two expert community members were involved as participants. Data were gathered using focus group interviews (sharing circles), group activities, participatory observations, and journal reflections. Data interpretation and analysis were done using Vygotsky’s sociocultural theory and Ogunniyi’s contiguity argumentative theory. A thematic approach to data analysis was adopted. That is, an inductive approach was employed whereby sub-themes were identified, and thereafter common sub-themes were combined into themes. The findings of this study revealed that the process of making oshikundu and uumboloto can be used to enable learners to make sense of the topic of CO2 and other related concepts. Furthermore, the study revealed that hands-on practical activities done with easily accessible resources which are related to learners’ indigenous technologies help learners learn Science easily. The study thus recommends that educators should use oshikundu and/or uumboloto to mediate learning of topics such as CO2. Science teachers should always try to tap into learners’ socio-cultural backgrounds in their lessons to enhance better understanding of Science concepts. , Thesis (MEd) -- Faculty of Education, Education, 2022
- Full Text:
- Date Issued: 2022-10-14
The effects of elevated CO2 on feeding guild responses of biological control agents of Pontederia crassipes Mart. (Pontederiaceae)
- Authors: Paper, Matthew Keenan
- Date: 2022-04-06
- Subjects: Carbon dioxide , Pontederia crassipes , Biological pest control agents , Invasive plants Biological control , Pontederiaceae Climatic factors
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/455338 , vital:75422
- Description: Elevated CO2 (eCO2) and rising global temperatures have the potential to alter plant-insect interactions with important implications for plant community structure and function. Previous studies on plant-insect interactions have shown that eCO2 will affect insect feeding guilds differently, impacting negatively, positively or having very little effect. The implications of this on the global invasive plant biological control programme is largely unknown. This study investigates the response of one of the world’s most invasive aquatic plants, Pontederia ( = Eichhornia) crassipes Mart. (Pontederiaceae), to predicted eCO2 conditions of 800 ppm and how this may affect the feeding response of two biological control agents representing different feeding guilds; the leaf chewing Cornops aquaticum Brüner (Orthoptera: Acrididae) and the phloem-feeding Megamelus scutellaris Berg (Hemiptera: Delphacidae). A factorial eCO2 x feeding impact study was conducted at the Rhodes University Elevated CO2 Facility in the Eastern Cape Province of South Africa over 13 weeks in the growing season of 2019. The effect of insect herbivory by C. aquaticum and M. scutellaris at two atmospheric CO2 concentrations, representing current and future predicted concentrations (400 ppm and 800 ppm) on P. crassipes was examined through both biomass and ecophysiological measures. Assimilation rates, C:N ratio, total dry weight and relative growth rate of P. crassipes were unaffected by eCO2 conditions, and plants experienced no CO2 fertilization in eutrophic water conditions representative of South African waterways. Effects of eCO2 on insect herbivory varied depending on the feeding guild. Pontederia crassipes showed compensatory growth responses when exposed to C. aquaticum herbivory regardless of CO2 treatment, but chewing herbivory damage remained constant, and the agent maintained efficacy. Pontederia crassipes showed down-regulation of photosynthesis when exposed to M. scutellaris due to eCO2-related feeding responses by M. scutellaris increasing substantially through a significant (30%) increase in adult population density under eCO2 conditions. These results indicate that the plant-insect interactions that underpin biological control programmes for P. crassipes should remain successful under future CO2 conditions. Phloem-feeding insect damage (M. scutellaris) was significantly greater than chewing damage in this study, suggesting that invasive plant biological control programmes will need to shift focus away from the charismatic chewing insect herbivores and onto the often-neglected phloem-feeding biological control agents due to their overwhelmingly positive response to eCO2. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Date Issued: 2022-04-06
- Authors: Paper, Matthew Keenan
- Date: 2022-04-06
- Subjects: Carbon dioxide , Pontederia crassipes , Biological pest control agents , Invasive plants Biological control , Pontederiaceae Climatic factors
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/455338 , vital:75422
- Description: Elevated CO2 (eCO2) and rising global temperatures have the potential to alter plant-insect interactions with important implications for plant community structure and function. Previous studies on plant-insect interactions have shown that eCO2 will affect insect feeding guilds differently, impacting negatively, positively or having very little effect. The implications of this on the global invasive plant biological control programme is largely unknown. This study investigates the response of one of the world’s most invasive aquatic plants, Pontederia ( = Eichhornia) crassipes Mart. (Pontederiaceae), to predicted eCO2 conditions of 800 ppm and how this may affect the feeding response of two biological control agents representing different feeding guilds; the leaf chewing Cornops aquaticum Brüner (Orthoptera: Acrididae) and the phloem-feeding Megamelus scutellaris Berg (Hemiptera: Delphacidae). A factorial eCO2 x feeding impact study was conducted at the Rhodes University Elevated CO2 Facility in the Eastern Cape Province of South Africa over 13 weeks in the growing season of 2019. The effect of insect herbivory by C. aquaticum and M. scutellaris at two atmospheric CO2 concentrations, representing current and future predicted concentrations (400 ppm and 800 ppm) on P. crassipes was examined through both biomass and ecophysiological measures. Assimilation rates, C:N ratio, total dry weight and relative growth rate of P. crassipes were unaffected by eCO2 conditions, and plants experienced no CO2 fertilization in eutrophic water conditions representative of South African waterways. Effects of eCO2 on insect herbivory varied depending on the feeding guild. Pontederia crassipes showed compensatory growth responses when exposed to C. aquaticum herbivory regardless of CO2 treatment, but chewing herbivory damage remained constant, and the agent maintained efficacy. Pontederia crassipes showed down-regulation of photosynthesis when exposed to M. scutellaris due to eCO2-related feeding responses by M. scutellaris increasing substantially through a significant (30%) increase in adult population density under eCO2 conditions. These results indicate that the plant-insect interactions that underpin biological control programmes for P. crassipes should remain successful under future CO2 conditions. Phloem-feeding insect damage (M. scutellaris) was significantly greater than chewing damage in this study, suggesting that invasive plant biological control programmes will need to shift focus away from the charismatic chewing insect herbivores and onto the often-neglected phloem-feeding biological control agents due to their overwhelmingly positive response to eCO2. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Date Issued: 2022-04-06
Accelerated carbon dioxide deliming of cattle hides and sheepskins
- Authors: Flowers, Karl Bernard
- Date: 2002
- Subjects: Tanning , Hides and skins , Carbon dioxide
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3918 , http://hdl.handle.net/10962/d1003977 , Tanning , Hides and skins , Carbon dioxide
- Description: To avoid environmental pressure from water authorities, specifically regarding nitrogen and sulfate limits in tannery wastewater, modifications to existing deliming processes have been made. Conventional ammonium salt deliming methods contribute to Total Kjeldahl Nitrogen values in the region of 0.5 – 1.0g/L (33-67% of total TKN). Sulfate levels are increased with the use of organic deliming and ammonium sulfate deliming to the extent of 0.9g/L (27% of total sulfate). To understand the dynamics and kinetics of carbon dioxide equilibrium, the movement of carbon dioxide into deliming water, through carbonic acid, bicarbonate and ultimately into carbonates at liming or early deliming pH was studied. It was shown in this study that effective lime removal, at optimum conditions, resulted in fully delimed pelts at highly comparable quality and times compared to conventional ammonium salt deliming
- Full Text:
- Date Issued: 2002
- Authors: Flowers, Karl Bernard
- Date: 2002
- Subjects: Tanning , Hides and skins , Carbon dioxide
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3918 , http://hdl.handle.net/10962/d1003977 , Tanning , Hides and skins , Carbon dioxide
- Description: To avoid environmental pressure from water authorities, specifically regarding nitrogen and sulfate limits in tannery wastewater, modifications to existing deliming processes have been made. Conventional ammonium salt deliming methods contribute to Total Kjeldahl Nitrogen values in the region of 0.5 – 1.0g/L (33-67% of total TKN). Sulfate levels are increased with the use of organic deliming and ammonium sulfate deliming to the extent of 0.9g/L (27% of total sulfate). To understand the dynamics and kinetics of carbon dioxide equilibrium, the movement of carbon dioxide into deliming water, through carbonic acid, bicarbonate and ultimately into carbonates at liming or early deliming pH was studied. It was shown in this study that effective lime removal, at optimum conditions, resulted in fully delimed pelts at highly comparable quality and times compared to conventional ammonium salt deliming
- Full Text:
- Date Issued: 2002
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