Synthesis and characterization of new pyrazolyl and ferrocenyl-pyrazolyl Ru(II) and Ru(0) complexes as catalyst precursors for the hydroformylation of 1 - Octene
- Authors: Sekati, Kagiso M.J.
- Date: 2018
- Subjects: Pyrazoles , Ruthenium compounds - Synthesis , Ruthenium catalysts , Catalysis
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/279311 , uj:29993
- Description: M.Sc. (Chemistry) , Abstract: A series of pyrazolyl and ferrocenyl-pyrazolyl ligands were synthesized. These ligands were reacted with ruthenium dimeric metal complex [RuCl2(Cy)]2 (where Cy = p – cymene) and a ruthenium carbonyl dimer [(ղ4-Ph4C4C=O)(CO)2Ru]2 to produce a series of monometallic and heterobimetallic Ru(II) arene complexes, as well as monometallic and heterobimetallic Ru(0) carbonyl complexes respectively. All the complexes were characterized by various spectroscopic and analytical techniques including 1H NMR and 13C NMR spectroscopy, FT-IR spectroscopy, mass spectrometry, elemental analysis (CHN) and single-crystal X-ray diffraction (complex C1). These techniques revealed that the proposed structures were indeed what had been formed. The techniques were also able to show that the various complexes were chemically different and displayed different chemical traits (such as functional groups). All the complexes, including the ferrocenyl-pyrazolyl ligands were tested as catalyst precursors in the hydroformylation of 1-octene. The Ru(II) and Ru(0) complexes were all active hydroformylation catalyst precursors and converted 1-octene to mainly aldehydes and alcohols, with minimal amounts of internal alkenes and octane produced. Branched and linear aldehydes as well as alcohol products were produced as a result of hydroformylation, followed by hydrogenation, while internal octenes and octane were produced via isomerization and hydrogenation reactions respectively. Of the various catalysts, Ru(II) complexes C1 and C2 displayed better hydroformylation/hydrogenation activity than their Ru(0) analogues, with C2 being the better of the two. On the contrary, catalyst precursors C4 – C6 possessed a higher degree of isomerization. The Ru(0) complexes showed no hydrogenation activity throughout the reactions conduted. Collectively, Ru(II) catalysts C1 – C3 favoured a regioselectivity for branched aldehydes compared to the Ru(0) catalysts C4 – C6. The substituents (tBu and Ph) on the pyrazolyl ring of the monometallic complexes have an influence on the regioselectivity of the catalyst. The tBu substituent favoured the formation of branched aldehydes in a minority of instances whereas the phenyl group resulted in an exclusive preference of linear aldehydes produced. Branched aldehydes were more favoured with the Ru(II) heterobimetallic catalyst precursor whilst the Ru(0) analogue yielded linear aldehydes...
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- Authors: Sekati, Kagiso M.J.
- Date: 2018
- Subjects: Pyrazoles , Ruthenium compounds - Synthesis , Ruthenium catalysts , Catalysis
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/279311 , uj:29993
- Description: M.Sc. (Chemistry) , Abstract: A series of pyrazolyl and ferrocenyl-pyrazolyl ligands were synthesized. These ligands were reacted with ruthenium dimeric metal complex [RuCl2(Cy)]2 (where Cy = p – cymene) and a ruthenium carbonyl dimer [(ղ4-Ph4C4C=O)(CO)2Ru]2 to produce a series of monometallic and heterobimetallic Ru(II) arene complexes, as well as monometallic and heterobimetallic Ru(0) carbonyl complexes respectively. All the complexes were characterized by various spectroscopic and analytical techniques including 1H NMR and 13C NMR spectroscopy, FT-IR spectroscopy, mass spectrometry, elemental analysis (CHN) and single-crystal X-ray diffraction (complex C1). These techniques revealed that the proposed structures were indeed what had been formed. The techniques were also able to show that the various complexes were chemically different and displayed different chemical traits (such as functional groups). All the complexes, including the ferrocenyl-pyrazolyl ligands were tested as catalyst precursors in the hydroformylation of 1-octene. The Ru(II) and Ru(0) complexes were all active hydroformylation catalyst precursors and converted 1-octene to mainly aldehydes and alcohols, with minimal amounts of internal alkenes and octane produced. Branched and linear aldehydes as well as alcohol products were produced as a result of hydroformylation, followed by hydrogenation, while internal octenes and octane were produced via isomerization and hydrogenation reactions respectively. Of the various catalysts, Ru(II) complexes C1 and C2 displayed better hydroformylation/hydrogenation activity than their Ru(0) analogues, with C2 being the better of the two. On the contrary, catalyst precursors C4 – C6 possessed a higher degree of isomerization. The Ru(0) complexes showed no hydrogenation activity throughout the reactions conduted. Collectively, Ru(II) catalysts C1 – C3 favoured a regioselectivity for branched aldehydes compared to the Ru(0) catalysts C4 – C6. The substituents (tBu and Ph) on the pyrazolyl ring of the monometallic complexes have an influence on the regioselectivity of the catalyst. The tBu substituent favoured the formation of branched aldehydes in a minority of instances whereas the phenyl group resulted in an exclusive preference of linear aldehydes produced. Branched aldehydes were more favoured with the Ru(II) heterobimetallic catalyst precursor whilst the Ru(0) analogue yielded linear aldehydes...
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Fischer-Tropsch reaction over alumina-supported cobalt catalyst : activation using H2 and CO
- Khangale, Phathutshedzo Rodney
- Authors: Khangale, Phathutshedzo Rodney
- Date: 2016
- Subjects: Fischer-Tropsch process , Catalysis , Cobalt catalysts
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/212944 , uj:21058
- Description: Abstract: The catalytic activity for Fischer-Tropsch (FT) reaction over cobalt-based catalysts mainly depends on two parameters, namely the reducibility of cobalt precursors and cobalt dispersion. Therefore, a perfect catalyst would comprise of an optimal combination of these two parameters. Cobalt precursor’s reduction is usually performed in the presence of H2 and is usually limited by metal-support interactions which, in some cases, lead to the formation of metal-support compounds that are not reducible under a practical reduction temperature range. The water vapour that is formed during cobalt-based reduction by H2 has been reported to promote the formation of these metal-support compounds in some cases. An investigation on a reduction process that does not produce water would potentially offer opportunities for better cobalt-based catalyst reduction. Therefore, the aim of this project was to investigate the effect of activating Co/Al2O3 FT catalyst using H2 or CO on the catalyst structure and performance for FT reactions. The catalyst was prepared by impregnation of the support (Al2O3) with a cobalt nitrate (Co(NO3)2•6H2O) solution and calcined in air at 500°C for 10 hours to decompose and transform the cobalt nitrate to cobalt oxide. XRD analysis was performed to determine the structure of the catalyst prepared. BET analysis was performed to determine the surface area and porosity of the catalyst. Temperature programmed reduction (TPR) was performed on calcined Co/Al2O3 catalyst using a H2 and CO containing gas mixture respectively to study the reduction behaviour of the catalyst. The catalyst morphology was studied using scanning electron microscopy (SEM) analysis. The catalyst was tested for FT reaction in a fixed bed reactor and the outlet gas products were analysed using a Dani master gas chromatograph (GC) equipped with thermal conductivity detector (TCD) and flame ionisation detector (FID). It was found that CO activates the Co/Al2O3 catalyst at a lower temperature than H2 and is accompanied by carbon deposition on the catalyst surface. The main forms of cobalt species in catalyst samples reduced by CO or H2 at 300 oC were CoO. Co0 and CoO were the major cobalt phases for the catalyst samples respectively reduced by CO and H2 at 350 oC. The highest catalytic activity for FT reaction with the highest rate of C5+ hydrocarbons formation were measured on CO-activated catalyst samples. The deposited carbon on COreduced samples is believed to be a precursor for possible cobalt carbide formation during FT reaction that led to high methane selectivity. , M.Tech. (Chemical Engineering)
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- Authors: Khangale, Phathutshedzo Rodney
- Date: 2016
- Subjects: Fischer-Tropsch process , Catalysis , Cobalt catalysts
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/212944 , uj:21058
- Description: Abstract: The catalytic activity for Fischer-Tropsch (FT) reaction over cobalt-based catalysts mainly depends on two parameters, namely the reducibility of cobalt precursors and cobalt dispersion. Therefore, a perfect catalyst would comprise of an optimal combination of these two parameters. Cobalt precursor’s reduction is usually performed in the presence of H2 and is usually limited by metal-support interactions which, in some cases, lead to the formation of metal-support compounds that are not reducible under a practical reduction temperature range. The water vapour that is formed during cobalt-based reduction by H2 has been reported to promote the formation of these metal-support compounds in some cases. An investigation on a reduction process that does not produce water would potentially offer opportunities for better cobalt-based catalyst reduction. Therefore, the aim of this project was to investigate the effect of activating Co/Al2O3 FT catalyst using H2 or CO on the catalyst structure and performance for FT reactions. The catalyst was prepared by impregnation of the support (Al2O3) with a cobalt nitrate (Co(NO3)2•6H2O) solution and calcined in air at 500°C for 10 hours to decompose and transform the cobalt nitrate to cobalt oxide. XRD analysis was performed to determine the structure of the catalyst prepared. BET analysis was performed to determine the surface area and porosity of the catalyst. Temperature programmed reduction (TPR) was performed on calcined Co/Al2O3 catalyst using a H2 and CO containing gas mixture respectively to study the reduction behaviour of the catalyst. The catalyst morphology was studied using scanning electron microscopy (SEM) analysis. The catalyst was tested for FT reaction in a fixed bed reactor and the outlet gas products were analysed using a Dani master gas chromatograph (GC) equipped with thermal conductivity detector (TCD) and flame ionisation detector (FID). It was found that CO activates the Co/Al2O3 catalyst at a lower temperature than H2 and is accompanied by carbon deposition on the catalyst surface. The main forms of cobalt species in catalyst samples reduced by CO or H2 at 300 oC were CoO. Co0 and CoO were the major cobalt phases for the catalyst samples respectively reduced by CO and H2 at 350 oC. The highest catalytic activity for FT reaction with the highest rate of C5+ hydrocarbons formation were measured on CO-activated catalyst samples. The deposited carbon on COreduced samples is believed to be a precursor for possible cobalt carbide formation during FT reaction that led to high methane selectivity. , M.Tech. (Chemical Engineering)
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Rhodium(I) Vaska-type phosphite complexes as model homogeneous catalysts.
- Authors: Kirsten, Leo
- Date: 2008-05-14T10:48:45Z
- Subjects: Rhodium compounds synthesis , Rhodium compounds , Catalysis , Chemical kinetics , Ligands , Phosphates , Complex compounds
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/390594 , uj:7257 , http://hdl.handle.net/10210/390
- Description: Please refer to full text to view abstract , Prof. A. Roodt
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- Authors: Kirsten, Leo
- Date: 2008-05-14T10:48:45Z
- Subjects: Rhodium compounds synthesis , Rhodium compounds , Catalysis , Chemical kinetics , Ligands , Phosphates , Complex compounds
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/390594 , uj:7257 , http://hdl.handle.net/10210/390
- Description: Please refer to full text to view abstract , Prof. A. Roodt
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Application of monometallic and bimetallic dendrimer encapsulated nanoparticles (DENs) and their catalytic evaluation on reduction of 4-nitrophenol
- Authors: Patala, Rapelang
- Date: 2016
- Subjects: Dendrimers , Dendrimers - Synthesis , Catalysis , Inorganic compounds - Analysis , Nanostructured materials
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/226086 , uj:22850
- Description: M.Sc. (Chemistry) , Abstract: The compound 4-nitrophenol found in wastewater streams is mainly the result of industrial and agricultural production. Having adverse health effects associated with it, 4-nitrophenol should be removed from the environment or converted to less hazardous forms as efficiently as possible. Feasible techniques to get rid of this chemical compound are of great research interest. The synthesized nanoparticles encapsulated inside dendrimers (DENs) will be evaluated for catalytic activity against the reaction of 4-nitrophenol reduction. Transition metal nanoparticles find their application in catalysis; this makes them to be of great technological importance. They can be synthesized by evaporation, condensation and chemical or electrochemical reduction of metal salts in the presence of stabilizers. Dendrimers were used as templates for the synthesis of both monometallic and bimetallic nanoparticles which were evaluated as catalysts for the reduction of 4-nitrophenol. We also focused on comprehensive kinetic analysis of 4-nitrophenol reduction using dendrimer encapsulated metal nanoparticles (DENs). The adsorption rates and reaction rates were found and evaluated, and it could be concluded that bimetallic catalysts were more catalytically active than monometallic ones. Different ratios of bimetallic (AuPd) nanoparticles were also supported on different mesoporous metal oxides (MMOs) and their catalytic activity evaluated on reduction of 4-nitrophenol. The results were interpreted in the light of Langmuir Hinshelwood model. The AuPd bimetallic nanoparticles supported on MMOs showed synergistic effect. With the use of power rate law it was shown that 4-nitrophenol reduction follows first order kinetics.
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- Authors: Patala, Rapelang
- Date: 2016
- Subjects: Dendrimers , Dendrimers - Synthesis , Catalysis , Inorganic compounds - Analysis , Nanostructured materials
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/226086 , uj:22850
- Description: M.Sc. (Chemistry) , Abstract: The compound 4-nitrophenol found in wastewater streams is mainly the result of industrial and agricultural production. Having adverse health effects associated with it, 4-nitrophenol should be removed from the environment or converted to less hazardous forms as efficiently as possible. Feasible techniques to get rid of this chemical compound are of great research interest. The synthesized nanoparticles encapsulated inside dendrimers (DENs) will be evaluated for catalytic activity against the reaction of 4-nitrophenol reduction. Transition metal nanoparticles find their application in catalysis; this makes them to be of great technological importance. They can be synthesized by evaporation, condensation and chemical or electrochemical reduction of metal salts in the presence of stabilizers. Dendrimers were used as templates for the synthesis of both monometallic and bimetallic nanoparticles which were evaluated as catalysts for the reduction of 4-nitrophenol. We also focused on comprehensive kinetic analysis of 4-nitrophenol reduction using dendrimer encapsulated metal nanoparticles (DENs). The adsorption rates and reaction rates were found and evaluated, and it could be concluded that bimetallic catalysts were more catalytically active than monometallic ones. Different ratios of bimetallic (AuPd) nanoparticles were also supported on different mesoporous metal oxides (MMOs) and their catalytic activity evaluated on reduction of 4-nitrophenol. The results were interpreted in the light of Langmuir Hinshelwood model. The AuPd bimetallic nanoparticles supported on MMOs showed synergistic effect. With the use of power rate law it was shown that 4-nitrophenol reduction follows first order kinetics.
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Methanol amination using natural clinoptilolite
- Authors: Levin, Lance Robin
- Date: 2012-09-10
- Subjects: Catalysis , Methanol , Clinoptilolite
- Type: Thesis
- Identifier: uj:9846 , http://hdl.handle.net/10210/7249
- Description: M.Tech. , Clinoptilolite possesses acid and base properties, and is hydrothermally stable at high temperatures. It can be reactivated by simple oxidation, and is highly selective due to its unique-shape selectivity. It is also not harmful to the environment and it has shown benefits to soil as well (Mumpton,1977). An initial study of the reactions of methanol amination was done using both natural local and synthetic clinoptilolites. Characterization of each was done before and after modification using XRD, TPD and BET analysis. The BET analysis showed an increase in the surface area and pore diameter of both the natural and synthetic types after acid treatment and calcination. Most interesting of all was the large increase in surface area, where the natural type increased from 16 to 36.7 m 2/g after acid treatment and the synthetic type increased almost 13 times, from 2 to 27.7 m2/g after acid treatment. This effect had a strong influence on the selectivity of methylamines by allowing a larger surface area to be in contact with the feed reagents. The XRD of the treated and untreated natural and synthetic clinoptilolite were compared and discussed. The catalytic properties of zeolites depend on the treatment of clinoptilolite, and the characteristic peaks of natural and the acid treated form can be identified in the XRD plots.The TPD analyses showed that there were two acid sites associated with the clinoptilolite; one weak and one strong. The synthetic clinoptilolite weak acid site also showed a much lower ammonia uptake, than the natural clinoptilolite weak acid site. Clinoptilolite was shown to be successful as a catalyst for the production of dimethylamine with high selectivity. This was attributed to a transition state shape selectivity associated with the clinoptilolite channels. The natural clinoptilolite displayed good selectivities at 400°C and a 5:1 ratio of methanol to ammonia, and gave a high conversion of > 90% ammonia to amines. The synthetic clinoptilolite gave better conversions and lower TMA selectivity than the natural clinoptilolite over a large range of feed ratios and temperatures. This included conversions of over 90% for most ratios (at 400 and 450°C). The natural clinoptilolite gave better results than those obtained using the amorphous clinoptilolite, which is currently used in industry. For example, low TMA selectivity was observed when a ratio of 5:1 or greater (methanol to ammonia) was used. The TMA selectivity is still far lower than the thermodynamic equilibrium selectivities obtained without a catalyst (62%). The catalyst lifetime has been shown to deteriorate with time.
- Full Text:
- Authors: Levin, Lance Robin
- Date: 2012-09-10
- Subjects: Catalysis , Methanol , Clinoptilolite
- Type: Thesis
- Identifier: uj:9846 , http://hdl.handle.net/10210/7249
- Description: M.Tech. , Clinoptilolite possesses acid and base properties, and is hydrothermally stable at high temperatures. It can be reactivated by simple oxidation, and is highly selective due to its unique-shape selectivity. It is also not harmful to the environment and it has shown benefits to soil as well (Mumpton,1977). An initial study of the reactions of methanol amination was done using both natural local and synthetic clinoptilolites. Characterization of each was done before and after modification using XRD, TPD and BET analysis. The BET analysis showed an increase in the surface area and pore diameter of both the natural and synthetic types after acid treatment and calcination. Most interesting of all was the large increase in surface area, where the natural type increased from 16 to 36.7 m 2/g after acid treatment and the synthetic type increased almost 13 times, from 2 to 27.7 m2/g after acid treatment. This effect had a strong influence on the selectivity of methylamines by allowing a larger surface area to be in contact with the feed reagents. The XRD of the treated and untreated natural and synthetic clinoptilolite were compared and discussed. The catalytic properties of zeolites depend on the treatment of clinoptilolite, and the characteristic peaks of natural and the acid treated form can be identified in the XRD plots.The TPD analyses showed that there were two acid sites associated with the clinoptilolite; one weak and one strong. The synthetic clinoptilolite weak acid site also showed a much lower ammonia uptake, than the natural clinoptilolite weak acid site. Clinoptilolite was shown to be successful as a catalyst for the production of dimethylamine with high selectivity. This was attributed to a transition state shape selectivity associated with the clinoptilolite channels. The natural clinoptilolite displayed good selectivities at 400°C and a 5:1 ratio of methanol to ammonia, and gave a high conversion of > 90% ammonia to amines. The synthetic clinoptilolite gave better conversions and lower TMA selectivity than the natural clinoptilolite over a large range of feed ratios and temperatures. This included conversions of over 90% for most ratios (at 400 and 450°C). The natural clinoptilolite gave better results than those obtained using the amorphous clinoptilolite, which is currently used in industry. For example, low TMA selectivity was observed when a ratio of 5:1 or greater (methanol to ammonia) was used. The TMA selectivity is still far lower than the thermodynamic equilibrium selectivities obtained without a catalyst (62%). The catalyst lifetime has been shown to deteriorate with time.
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Synthesis and application of monodisperse silver and gold nanoparticles as catalysts for kinetic investigations of model reactions
- Authors: Ilunga, Ali Kabeya
- Date: 2015
- Subjects: Electrocatalysis , Nanoparticles , Gold , Catalysis
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/82587 , uj:18976
- Description: Abstract:A hyperbranched polymers, dendrimers, synthesized for the first time by Tomalia and available in market in the form of poly-amidoamine (PAMAM) and poly-propylene imine (PPI) dendrimers are used as templates in the synthesis of metal nanoparticles to prevent agglomeration. Here, we study the synthesis of generation five amino-terminated poly(amidoamine) dendrimer encapsulated silver and gold nanoparticles. To avoid the intra-dendrimer stabilization, a spectrophotometric titration of the silver and gold ions into the dendrimer was performed. The results lead to the determination of the loading capacity of the dendrimers. The influence of temperature was evaluated by performing the titration at different temperatures. The colloidal metal nanoparticles were purified by dialyzing overnight against de-ionized water. The synthesis process of the silver and gold nanoparticles was monitored using UV-vis spectroscopy. The interaction of metal ions and tertiary amine group was assessed using a FTIR spectroscopy. TEM and EDX analysis were performed to obtain the distribution and average size of the metal nanoparticles, and to evaluate the purity of colloidal metal nanoparticles, respectively. The concentration of the metal nanoparticles in solution was determined by AAS. The specific surface area of silver and gold nanoparticles were estimated by self-assembled monolayer approach using the UV-photometric analysis to quantify the absorbed and unabsorbed organothiol. The catalytic activities of silver and gold nanoparticles were evaluated using the oxidation reaction of two different dyes, methylene blue and morin, as benchmark reactions. Hydrogen peroxide was used as an oxidizing agent and its stability during the catalytic process was assured by maintaining the pH constant using carbonate buffer. The Langmuir-Hinshelwood mechanism was applied to evaluate the catalytic performance of encapsulated silver and gold nanoparticles. This mechanism requires the adsorption of the reactants onto the catalyst surface prior to the start of the reaction. The catalytic process and the kinetic data set recorded were performed using UV-vis spectroscopy. The stability of the encapsulated metal nanoparticles during the reaction was evaluated by a three cycle runs using a dialysis bag. , M.Sc. (Chemistry)
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- Authors: Ilunga, Ali Kabeya
- Date: 2015
- Subjects: Electrocatalysis , Nanoparticles , Gold , Catalysis
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/82587 , uj:18976
- Description: Abstract:A hyperbranched polymers, dendrimers, synthesized for the first time by Tomalia and available in market in the form of poly-amidoamine (PAMAM) and poly-propylene imine (PPI) dendrimers are used as templates in the synthesis of metal nanoparticles to prevent agglomeration. Here, we study the synthesis of generation five amino-terminated poly(amidoamine) dendrimer encapsulated silver and gold nanoparticles. To avoid the intra-dendrimer stabilization, a spectrophotometric titration of the silver and gold ions into the dendrimer was performed. The results lead to the determination of the loading capacity of the dendrimers. The influence of temperature was evaluated by performing the titration at different temperatures. The colloidal metal nanoparticles were purified by dialyzing overnight against de-ionized water. The synthesis process of the silver and gold nanoparticles was monitored using UV-vis spectroscopy. The interaction of metal ions and tertiary amine group was assessed using a FTIR spectroscopy. TEM and EDX analysis were performed to obtain the distribution and average size of the metal nanoparticles, and to evaluate the purity of colloidal metal nanoparticles, respectively. The concentration of the metal nanoparticles in solution was determined by AAS. The specific surface area of silver and gold nanoparticles were estimated by self-assembled monolayer approach using the UV-photometric analysis to quantify the absorbed and unabsorbed organothiol. The catalytic activities of silver and gold nanoparticles were evaluated using the oxidation reaction of two different dyes, methylene blue and morin, as benchmark reactions. Hydrogen peroxide was used as an oxidizing agent and its stability during the catalytic process was assured by maintaining the pH constant using carbonate buffer. The Langmuir-Hinshelwood mechanism was applied to evaluate the catalytic performance of encapsulated silver and gold nanoparticles. This mechanism requires the adsorption of the reactants onto the catalyst surface prior to the start of the reaction. The catalytic process and the kinetic data set recorded were performed using UV-vis spectroscopy. The stability of the encapsulated metal nanoparticles during the reaction was evaluated by a three cycle runs using a dialysis bag. , M.Sc. (Chemistry)
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A structural study of palladium complexes containing hemilabile ligands
- Authors: Thompson, Catharine
- Date: 2012-09-06
- Subjects: Palladium compounds , Chemical reactions , Ligands , Catalysis , Catalysts
- Type: Thesis
- Identifier: uj:9678 , http://hdl.handle.net/10210/7092
- Description: D.Phil. , Palladium chemistry has advanced dramatically in the last few years, with a huge number of wide-ranging studies, particularly with respect to the application of palladium complexes as catalysts, having been performed. The discovery of the phenomenon of hemilability (the ability of a ligand to be bidentately coordinated but with one donor atom more weakly bound and thus able to decoordinate in the presence of a catalytic substrate) has further assisted the growth, since it has allowed a greater understanding of the mechanisms of catalytic-reactions. However, the focus of much of this work has been on ligands containing phosphorus and oxygen as potential donor atoms, with little attention being turned to ligands with other donor atoms. The current study concentrates on a series of palladium complexes containing potentially hemilabile thioether, selenoether and telluroether carboxylate ligands with the oxygen as the strongly coordinating atom. Each complex was completed by the palladium coordinating to a phenyl ligand trans to the oxygen of the hemilabile ligand and either one or two triphenylphosphine ligands, depending on whether or not the -hemilabile ligand was monodentately or bidentately coordinated. These complexes are of interest as possible catalysts for the oligomerisation of ethene, and had been previously synthesised and characterised by NMR spectroscopy, mass spectrometry and catalytic studies. In the current work the crystal and molecular structures of the various complexes were determined. Since a number of pairs of complexes containing the monodentate and bidentate forms of the ligands were identified the hemilability of the ligands was confirmed.
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- Authors: Thompson, Catharine
- Date: 2012-09-06
- Subjects: Palladium compounds , Chemical reactions , Ligands , Catalysis , Catalysts
- Type: Thesis
- Identifier: uj:9678 , http://hdl.handle.net/10210/7092
- Description: D.Phil. , Palladium chemistry has advanced dramatically in the last few years, with a huge number of wide-ranging studies, particularly with respect to the application of palladium complexes as catalysts, having been performed. The discovery of the phenomenon of hemilability (the ability of a ligand to be bidentately coordinated but with one donor atom more weakly bound and thus able to decoordinate in the presence of a catalytic substrate) has further assisted the growth, since it has allowed a greater understanding of the mechanisms of catalytic-reactions. However, the focus of much of this work has been on ligands containing phosphorus and oxygen as potential donor atoms, with little attention being turned to ligands with other donor atoms. The current study concentrates on a series of palladium complexes containing potentially hemilabile thioether, selenoether and telluroether carboxylate ligands with the oxygen as the strongly coordinating atom. Each complex was completed by the palladium coordinating to a phenyl ligand trans to the oxygen of the hemilabile ligand and either one or two triphenylphosphine ligands, depending on whether or not the -hemilabile ligand was monodentately or bidentately coordinated. These complexes are of interest as possible catalysts for the oligomerisation of ethene, and had been previously synthesised and characterised by NMR spectroscopy, mass spectrometry and catalytic studies. In the current work the crystal and molecular structures of the various complexes were determined. Since a number of pairs of complexes containing the monodentate and bidentate forms of the ligands were identified the hemilability of the ligands was confirmed.
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Siklopentadienielyster(II)verbindings in sintese en homogene katalise
- Authors: Cronje, Stephanie
- Date: 2014-02-11
- Subjects: Transition metals , Transition metal compounds , Catalysis
- Type: Thesis
- Identifier: uj:3876 , http://hdl.handle.net/10210/9243
- Description: Ph.D. (Chemistry) , Please refer to full text to view abstract
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- Authors: Cronje, Stephanie
- Date: 2014-02-11
- Subjects: Transition metals , Transition metal compounds , Catalysis
- Type: Thesis
- Identifier: uj:3876 , http://hdl.handle.net/10210/9243
- Description: Ph.D. (Chemistry) , Please refer to full text to view abstract
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Functionalised porphyrazines and their use in catalysis
- Authors: Tshivhase, Mmboneni Gifty
- Date: 2012-08-16
- Subjects: Catalysis , Porphyrins , Phthalocyanines , Palladium compounds , Heck reaction , Imidazoles , Ligands
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/367536 , uj:2573 , http://hdl.handle.net/10210/6024
- Description: D.Phil. , Porphyrazines like porphyrins and phthalocyanines have unique physical, chemical and spectral properties. This allows them to have many impressive applications. They are less studied than phthalocyanines because of the absence of convenient methods for their synthesis. However, recent studies, including this one, have made these compounds more accessible. The palladium-imidazolium salt systems have proved to be one of the most successful catalysts for the Heck and Suzuki coupling reactions. Substituents on nitrogen atoms of imidazolium significantly influence the catalytic activities of the corresponding palladiumimidazolium salt systems in the Heck and Suzuki coupling. The synthesis of the imidazolium salts is discussed in this study. The synthesis of the imidazoles started from diamines. A new route for the synthesis of 4,5-diaminophthalonitrile is discussed here and so far it is the most convenient and less tedious route with higher yields. The catalytic activities on different substrates have also been extensively investigated and gave impressive results, on the Heck and Suzuki reaction. The catalysis study was first performed using the dicyanoimidazolium salts and then with the imidazolium salts of the porphyrazines. The results indicate that both these systems are active ligands for Suzuki and Heck reactions. Two complexes, [1’,1’’-dibutyl-3’,3’’-(4,5-(1,2-dicyanobenzene))diimidazolium dibromide] and [2,3-benzo(2’,3’-(3’’,3’’’-dibutyldiimidazolium-2’,2’’-diylidene)palladium(II)- dibromide)-7,8,12,13,17,18-hexapropyl,porphyrazine] were synthesised successfully in good yields and used for Suzuki and Heck catalysis reactions. Catalyst recovery in homogeneous catalysis is always a major problem; this led this study to make use of porphyrazines in biphasic catalysis because of their high extinction coefficient which comes from their very intense colour. The reactions were performed in a combination of water with toluene and also water with ionic liquid. Both this systems gave results which proved that it is possible to separate the catalyst and the products once the reaction is complete. Two aminoporphyrazines and phthalonitriles were also synthesised in multistep synthesis. The synthesis involved a lot of protection and deprotection steps. These compounds are starting materials to aminophosphine ligands which have a wide variety of catalysis applications.
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- Authors: Tshivhase, Mmboneni Gifty
- Date: 2012-08-16
- Subjects: Catalysis , Porphyrins , Phthalocyanines , Palladium compounds , Heck reaction , Imidazoles , Ligands
- Type: Thesis
- Identifier: http://ujcontent.uj.ac.za8080/10210/367536 , uj:2573 , http://hdl.handle.net/10210/6024
- Description: D.Phil. , Porphyrazines like porphyrins and phthalocyanines have unique physical, chemical and spectral properties. This allows them to have many impressive applications. They are less studied than phthalocyanines because of the absence of convenient methods for their synthesis. However, recent studies, including this one, have made these compounds more accessible. The palladium-imidazolium salt systems have proved to be one of the most successful catalysts for the Heck and Suzuki coupling reactions. Substituents on nitrogen atoms of imidazolium significantly influence the catalytic activities of the corresponding palladiumimidazolium salt systems in the Heck and Suzuki coupling. The synthesis of the imidazolium salts is discussed in this study. The synthesis of the imidazoles started from diamines. A new route for the synthesis of 4,5-diaminophthalonitrile is discussed here and so far it is the most convenient and less tedious route with higher yields. The catalytic activities on different substrates have also been extensively investigated and gave impressive results, on the Heck and Suzuki reaction. The catalysis study was first performed using the dicyanoimidazolium salts and then with the imidazolium salts of the porphyrazines. The results indicate that both these systems are active ligands for Suzuki and Heck reactions. Two complexes, [1’,1’’-dibutyl-3’,3’’-(4,5-(1,2-dicyanobenzene))diimidazolium dibromide] and [2,3-benzo(2’,3’-(3’’,3’’’-dibutyldiimidazolium-2’,2’’-diylidene)palladium(II)- dibromide)-7,8,12,13,17,18-hexapropyl,porphyrazine] were synthesised successfully in good yields and used for Suzuki and Heck catalysis reactions. Catalyst recovery in homogeneous catalysis is always a major problem; this led this study to make use of porphyrazines in biphasic catalysis because of their high extinction coefficient which comes from their very intense colour. The reactions were performed in a combination of water with toluene and also water with ionic liquid. Both this systems gave results which proved that it is possible to separate the catalyst and the products once the reaction is complete. Two aminoporphyrazines and phthalonitriles were also synthesised in multistep synthesis. The synthesis involved a lot of protection and deprotection steps. These compounds are starting materials to aminophosphine ligands which have a wide variety of catalysis applications.
- Full Text:
DoM chemistry and phosphines: synthesis and catalystic aspects
- Mokhadinyana, Molise Stephen
- Authors: Mokhadinyana, Molise Stephen
- Date: 2008-06-11T06:31:34Z
- Subjects: Phosphine , Ligands , Catalysis , Organometallic compounds' synthesis
- Type: Thesis
- Identifier: uj:2601 , http://hdl.handle.net/10210/604
- Description: The main objective of the research described in this dissertation was the preparation of a range of bulky and electron-rich phosphine ligands using the DoM methodology developed in our labs for this purpose. These ligands would be employed in the Suzuki cross-coupling reaction of deactivated aryl bromides and aryl chlorides. Initially, a range of phosphinic amides was synthesised and tested for DoM reactivity. TMSCl, MeI and O2 were successfully used as electrophiles, incorporating TMS, Me and OH groups in the ortho-position of these phosphinic amide systems. This development was encouraging and provided a route to incorporate a phosphine on the ortho-position of these phosphinic amide systems by using Ph2PCl and Cy2PCl as electrophiles to incorporate Ph2P and Cy2P, respectively. The route was versatile and a range of electrophiles was used to prepare phosphine ligands with varying electronic and steric properties. These electrophiles (of the R2PCl variety) were often specifically prepared from PCl3 and the corresponding Grignard reagent. Phosphine ligands synthesised in this research project using our DoM (directed ortho metallation) methodology were tested in Suzuki cross-coupling reactions of deactivated aryl bromides and some aryl chlorides and showed excellent reactivity, with the advantage that the ligands of this study are oxidatively and hydrolytically stable. Efforts were also made to modifying the phosphinic amide-functionalised phosphine ligands to generate their water-soluble derivatives. One way of achieving this was by the hydrolysis of the phosphinic amide moiety to the phosphinic acid analogue. Salts of these phosphinic acid derivatives have promising activities as water-soluble substrates. This route was successful only iii with less electron-rich systems providing an opening for more research in this regard. In an alternative synthetic route to polar water-soluble phosphines it was envisioned that phosphonate-derivatised phosphines would offer access to water-soluble phosphine ligands by using milder hydrolysis conditions. These phosphonate systems were also tested for DoM reactivity and showed promising reactivity. Phosphonates have not previously being employed as DoM groups, and this alone expands the application and potential scope of P-based DoM groups. , Prof. D.B.G. Williams
- Full Text:
- Authors: Mokhadinyana, Molise Stephen
- Date: 2008-06-11T06:31:34Z
- Subjects: Phosphine , Ligands , Catalysis , Organometallic compounds' synthesis
- Type: Thesis
- Identifier: uj:2601 , http://hdl.handle.net/10210/604
- Description: The main objective of the research described in this dissertation was the preparation of a range of bulky and electron-rich phosphine ligands using the DoM methodology developed in our labs for this purpose. These ligands would be employed in the Suzuki cross-coupling reaction of deactivated aryl bromides and aryl chlorides. Initially, a range of phosphinic amides was synthesised and tested for DoM reactivity. TMSCl, MeI and O2 were successfully used as electrophiles, incorporating TMS, Me and OH groups in the ortho-position of these phosphinic amide systems. This development was encouraging and provided a route to incorporate a phosphine on the ortho-position of these phosphinic amide systems by using Ph2PCl and Cy2PCl as electrophiles to incorporate Ph2P and Cy2P, respectively. The route was versatile and a range of electrophiles was used to prepare phosphine ligands with varying electronic and steric properties. These electrophiles (of the R2PCl variety) were often specifically prepared from PCl3 and the corresponding Grignard reagent. Phosphine ligands synthesised in this research project using our DoM (directed ortho metallation) methodology were tested in Suzuki cross-coupling reactions of deactivated aryl bromides and some aryl chlorides and showed excellent reactivity, with the advantage that the ligands of this study are oxidatively and hydrolytically stable. Efforts were also made to modifying the phosphinic amide-functionalised phosphine ligands to generate their water-soluble derivatives. One way of achieving this was by the hydrolysis of the phosphinic amide moiety to the phosphinic acid analogue. Salts of these phosphinic acid derivatives have promising activities as water-soluble substrates. This route was successful only iii with less electron-rich systems providing an opening for more research in this regard. In an alternative synthetic route to polar water-soluble phosphines it was envisioned that phosphonate-derivatised phosphines would offer access to water-soluble phosphine ligands by using milder hydrolysis conditions. These phosphonate systems were also tested for DoM reactivity and showed promising reactivity. Phosphonates have not previously being employed as DoM groups, and this alone expands the application and potential scope of P-based DoM groups. , Prof. D.B.G. Williams
- Full Text:
Metals at your service
- Authors: Darkwa, James
- Date: 2008-11-03T07:12:38Z
- Subjects: Metals , Metals as catalysts , Catalysis , Chemistry
- Type: Inaugural
- Identifier: uj:14897 , http://hdl.handle.net/10210/1447
- Description: Inaugural lecture--Dept. of Chemistry, University of Johannesburg, 4 October 2006
- Full Text:
- Authors: Darkwa, James
- Date: 2008-11-03T07:12:38Z
- Subjects: Metals , Metals as catalysts , Catalysis , Chemistry
- Type: Inaugural
- Identifier: uj:14897 , http://hdl.handle.net/10210/1447
- Description: Inaugural lecture--Dept. of Chemistry, University of Johannesburg, 4 October 2006
- Full Text:
The influence of ligands and co-catalysts on selected catalytic transformations
- Authors: Bredenkamp, Tyler
- Date: 2011-11-21
- Subjects: Ligands , Catalysis , Phosphine , Organometallic compounds
- Type: Thesis
- Identifier: uj:1718 , http://hdl.handle.net/10210/4060
- Description: M.Sc. , There were two main objectives of the research presented m this dissertation. Firstly, the synthesis of bulky electron withdrawing phosphine-alkene ligands for classic ligand testing in the Suzuki cross-coupling reaction was performed. Previously, a range of electron deficient phosphine-alkenes was prepared from 2- ( diphenylphosphino )benzaldehyde, using both Wittig and Knoevenagel chemistry. These were tested for catalysis and gave high yields for the Suzuki reaction. In the present instance, 2-( di-otolylphosphino) benzaldehyde was synthesised making use of Grignard technology from acetyl protected 2-bromobenzaldehyde and chloro(di-o-tolyl)phosphine (itself prepared from PCh. And the appropriate o-tolyl Grignard reagent. This material served as a building block for the generation of P-alkene ligands which were synthesised making use of Wittig, Knoevenagel and transesterification chemistry. These o-tolyl analogues of the P-alkene ligands prepared in the previous study were used in ligand testing experiments in the Pd-catalysed Suzuki cross-coupling reaction. The results of the catalysis showed an enhanced activity with these ligands over the previous cases The second part of this dissertation involved determining the role (influence on activity) of the non coordinating counterion in the catalyst system in the methoxycarbonylation reaction. To this end discrete Pd complexes were synthesised and used directly in the methoxycarbonylation reaction. There have been a few reports on the role of the non-coordinating counterions of the catalyst systems in the methoxycarbonylation reaction. The catalyst is typically a palladium compound in the presence of a Bmnsted acid co-catalyst. Changes to the Bmnsted co-catalyst cause two variables to change, namely the acidity of the acid and the nature of the counterion that the acid provides. The work presented in this dissertation shows the results of only one variable being changed (that of the counterion) and as such allowed the specific role of the counterion in the outcome of the reaction to be determined. Previous work done in our laboratories made use of the Lewis acid Al(OTf)3 to co-catalyse the methoxycarbonylation reaction with rates and high yields being observed. In the present instance discrete Pd complexes were synthesised from Pd(OAc)2 using p-TsOH, MsOH and TfOH as the acids containing the weakly coordinating counterions. These Bnmsted acids have the ability to displace the OAc- anion from the Pd and as such formed the discrete L2PdX2complexes (L = PPh3; X = Mso-, p-Tso-, TfO} Synthesis of these discrete complexes was impeded by a lack of knowledge of the specific conditions under which to prepare the complexes and many avenues were pursued before successful isolation of these complexes was achieved. These discrete catalysts were used in the methoxycarbonylation reaction co-catalysed by Al(OT£)3. Here, the Al(OTt)3 forms the basis of a constant acid cocatalyst allowing only the counterion to be changed with the view to determining its role in these reactions. It was found that the counterion appears to play no role at all (Aco-, p-Tso-, Mso-, TfO-) in the outcomes of these reactions under the conditions employed. A comparative study is also detailed herewithin of the effects of both ex situ and in situ catalyst generation on the activity in the methoxycarbonylation reaction, which provides some insightful results.
- Full Text:
- Authors: Bredenkamp, Tyler
- Date: 2011-11-21
- Subjects: Ligands , Catalysis , Phosphine , Organometallic compounds
- Type: Thesis
- Identifier: uj:1718 , http://hdl.handle.net/10210/4060
- Description: M.Sc. , There were two main objectives of the research presented m this dissertation. Firstly, the synthesis of bulky electron withdrawing phosphine-alkene ligands for classic ligand testing in the Suzuki cross-coupling reaction was performed. Previously, a range of electron deficient phosphine-alkenes was prepared from 2- ( diphenylphosphino )benzaldehyde, using both Wittig and Knoevenagel chemistry. These were tested for catalysis and gave high yields for the Suzuki reaction. In the present instance, 2-( di-otolylphosphino) benzaldehyde was synthesised making use of Grignard technology from acetyl protected 2-bromobenzaldehyde and chloro(di-o-tolyl)phosphine (itself prepared from PCh. And the appropriate o-tolyl Grignard reagent. This material served as a building block for the generation of P-alkene ligands which were synthesised making use of Wittig, Knoevenagel and transesterification chemistry. These o-tolyl analogues of the P-alkene ligands prepared in the previous study were used in ligand testing experiments in the Pd-catalysed Suzuki cross-coupling reaction. The results of the catalysis showed an enhanced activity with these ligands over the previous cases The second part of this dissertation involved determining the role (influence on activity) of the non coordinating counterion in the catalyst system in the methoxycarbonylation reaction. To this end discrete Pd complexes were synthesised and used directly in the methoxycarbonylation reaction. There have been a few reports on the role of the non-coordinating counterions of the catalyst systems in the methoxycarbonylation reaction. The catalyst is typically a palladium compound in the presence of a Bmnsted acid co-catalyst. Changes to the Bmnsted co-catalyst cause two variables to change, namely the acidity of the acid and the nature of the counterion that the acid provides. The work presented in this dissertation shows the results of only one variable being changed (that of the counterion) and as such allowed the specific role of the counterion in the outcome of the reaction to be determined. Previous work done in our laboratories made use of the Lewis acid Al(OTf)3 to co-catalyse the methoxycarbonylation reaction with rates and high yields being observed. In the present instance discrete Pd complexes were synthesised from Pd(OAc)2 using p-TsOH, MsOH and TfOH as the acids containing the weakly coordinating counterions. These Bnmsted acids have the ability to displace the OAc- anion from the Pd and as such formed the discrete L2PdX2complexes (L = PPh3; X = Mso-, p-Tso-, TfO} Synthesis of these discrete complexes was impeded by a lack of knowledge of the specific conditions under which to prepare the complexes and many avenues were pursued before successful isolation of these complexes was achieved. These discrete catalysts were used in the methoxycarbonylation reaction co-catalysed by Al(OT£)3. Here, the Al(OTt)3 forms the basis of a constant acid cocatalyst allowing only the counterion to be changed with the view to determining its role in these reactions. It was found that the counterion appears to play no role at all (Aco-, p-Tso-, Mso-, TfO-) in the outcomes of these reactions under the conditions employed. A comparative study is also detailed herewithin of the effects of both ex situ and in situ catalyst generation on the activity in the methoxycarbonylation reaction, which provides some insightful results.
- Full Text:
Bifunctional phosphines : synthesis and evaluation in catalysis
- Authors: Shaw, Megan Lorraine
- Date: 2012-09-10
- Subjects: Phosphorus compounds - Synthesis , Catalysis , Ligands , Transition metal catalysts
- Type: Thesis
- Identifier: uj:9860 , http://hdl.handle.net/10210/7261
- Description: M.Sc. , This study focused on the synthesis and evaluation of phosphine ligands with multiple functional ities. Polar ligands suitable for use in homogeneous catalysis in aqueous/organic systems were synthesised, as were ligands incorporating a boron atom in an intramolecular Lewis acid-Lewis base interaction with the phosphorus atom. A malonate moiety was readily incorporated into a phosphorus starting material, and derivatives were obtained by reduction of the ester groups. The polar diol products were reacted with 1,4-butanesultone which made them water soluble and thus ideal for biphasic catalysis. Wittig chemistry was employed to introduce alkenes of varying electronic nature into a phosphorus-containing aldehyde starting material. The catalysed hydroboration reaction making use of diboron reagents was used to introduce a boron functionality into the resulting a, n-unsaturated ester phosphine I igands. All of the ligands produced were tested in transition metal-catalysed reactions, namely the Heck reaction, the Suzuki reaction, the Stille reaction, the carboxymethylation reaction and the hydroformylation reaction. The polar and water soluble ligands all showed comparable or improved yields to the standard benchmark triphenylphosphine ligand in organic, biphasic and ionic liquid media. The electronic nature of the alkene ligands largely dictated the activities observed in the Heck, Suzuki and Stille reactions. The electron rich ligands showed improved activities in the Heck reaction, while the electron poor ligands showed improved activities in the Suzuki reaction. In contrast, the Stille reaction seemed to be more affected by the steric demands of the ligands rather than by electronic considerations. It was also found that the boron containing ligands showed an enhanced activity in comparison to the boron free unsaturated and saturated ester ligands. This enhancement was directly ascribable to the Lewis acidic boron atom. This study allowed the synthesis of a range of functionally varying phosphine ligands which where shown to influence transition metal-catalysed reactions based specifically on the functionality present.
- Full Text:
- Authors: Shaw, Megan Lorraine
- Date: 2012-09-10
- Subjects: Phosphorus compounds - Synthesis , Catalysis , Ligands , Transition metal catalysts
- Type: Thesis
- Identifier: uj:9860 , http://hdl.handle.net/10210/7261
- Description: M.Sc. , This study focused on the synthesis and evaluation of phosphine ligands with multiple functional ities. Polar ligands suitable for use in homogeneous catalysis in aqueous/organic systems were synthesised, as were ligands incorporating a boron atom in an intramolecular Lewis acid-Lewis base interaction with the phosphorus atom. A malonate moiety was readily incorporated into a phosphorus starting material, and derivatives were obtained by reduction of the ester groups. The polar diol products were reacted with 1,4-butanesultone which made them water soluble and thus ideal for biphasic catalysis. Wittig chemistry was employed to introduce alkenes of varying electronic nature into a phosphorus-containing aldehyde starting material. The catalysed hydroboration reaction making use of diboron reagents was used to introduce a boron functionality into the resulting a, n-unsaturated ester phosphine I igands. All of the ligands produced were tested in transition metal-catalysed reactions, namely the Heck reaction, the Suzuki reaction, the Stille reaction, the carboxymethylation reaction and the hydroformylation reaction. The polar and water soluble ligands all showed comparable or improved yields to the standard benchmark triphenylphosphine ligand in organic, biphasic and ionic liquid media. The electronic nature of the alkene ligands largely dictated the activities observed in the Heck, Suzuki and Stille reactions. The electron rich ligands showed improved activities in the Heck reaction, while the electron poor ligands showed improved activities in the Suzuki reaction. In contrast, the Stille reaction seemed to be more affected by the steric demands of the ligands rather than by electronic considerations. It was also found that the boron containing ligands showed an enhanced activity in comparison to the boron free unsaturated and saturated ester ligands. This enhancement was directly ascribable to the Lewis acidic boron atom. This study allowed the synthesis of a range of functionally varying phosphine ligands which where shown to influence transition metal-catalysed reactions based specifically on the functionality present.
- Full Text:
Ligand synthesis and Pd-catalysed C-C bond-forming reactions
- Authors: Hughes, Tanya
- Date: 2012-08-17
- Subjects: Ligands , Catalysis , Catalysts - Synthesis , Phosphine
- Type: Thesis
- Identifier: uj:2667 , http://hdl.handle.net/10210/6110
- Description: Ph.D. , The focus of this study was placed on developing stable recyclable catalyst systems that are both active and selective in Pd-catalysed reactions such as the Suzuki-Miyaura cross-coupling reaction, and the methoxycarbonylation reaction. The aim was therefore to prepare ligands with improved efficiencies as catalyst precursors, which are stable towards oxidation and/or hydrolysis, that are soluble in aqueous media and that can be recycled a number of times without significant loss in activity. This study initially focused on the preparation of functionalised phosphine ligands to be loaded onto the peripheries of different generations of PAMAM and PPI dendrimers. These functionalised ligands were then to be used in the Pd catalysed Suzuki-Miyaura cross-coupling of phenylboronic acid and aryl halides, as well as the Pd catalysed carbonylation of phenylacetylene. It was thought that loading of these ligands onto the dendrimers would result in a soluble support for subsequent catalyst systems to allow catalyst recycling. This would then potentially bridge the gap between heterogeneous and homogeneous catalysis. There has been a lot of progress made over the last decade or so in the preparation and use of dendritic phosphines and the positive effects seen are summarised in the first chapter. Water-soluble and thus environmentally friendly ligands have also gained widespread interest as these ligands offer economical and environmental advantages for many reactions. One of the aims of this study was therefore to prepare ligands that show greater solubility in aqueous solvents that can be successfully recycled and that show retention of activity upon reuse. Initially covalent loading of the prepared phosphine ligands onto the peripheries of the dendrimers were attempted. However based on all the problems experienced with the covalent bonding, as discussed in Chapter 2 of this document, a simple acid base titration allowed loading of the prepared phosphine ligands onto the peripheries of the dendrimers via electrostatic interactions, to afford a stable phosphine ligand-dendrimer salt. Electrostatic interactions contribute much more to the solubility enhancement of poorly soluble compounds, thus the formation of the non-covalent phosphine-dendrimer salts was expected to result in greater potential for catalysis in biphasic systems as well as catalyst recycling. Only low generation dendrimers were utilised as previous reports indicated that an increase of the dendrimer generation leads to observation of negative dendritic effects due to the increased bulk that inhibits the approach of the catalytic metal centre.
- Full Text:
- Authors: Hughes, Tanya
- Date: 2012-08-17
- Subjects: Ligands , Catalysis , Catalysts - Synthesis , Phosphine
- Type: Thesis
- Identifier: uj:2667 , http://hdl.handle.net/10210/6110
- Description: Ph.D. , The focus of this study was placed on developing stable recyclable catalyst systems that are both active and selective in Pd-catalysed reactions such as the Suzuki-Miyaura cross-coupling reaction, and the methoxycarbonylation reaction. The aim was therefore to prepare ligands with improved efficiencies as catalyst precursors, which are stable towards oxidation and/or hydrolysis, that are soluble in aqueous media and that can be recycled a number of times without significant loss in activity. This study initially focused on the preparation of functionalised phosphine ligands to be loaded onto the peripheries of different generations of PAMAM and PPI dendrimers. These functionalised ligands were then to be used in the Pd catalysed Suzuki-Miyaura cross-coupling of phenylboronic acid and aryl halides, as well as the Pd catalysed carbonylation of phenylacetylene. It was thought that loading of these ligands onto the dendrimers would result in a soluble support for subsequent catalyst systems to allow catalyst recycling. This would then potentially bridge the gap between heterogeneous and homogeneous catalysis. There has been a lot of progress made over the last decade or so in the preparation and use of dendritic phosphines and the positive effects seen are summarised in the first chapter. Water-soluble and thus environmentally friendly ligands have also gained widespread interest as these ligands offer economical and environmental advantages for many reactions. One of the aims of this study was therefore to prepare ligands that show greater solubility in aqueous solvents that can be successfully recycled and that show retention of activity upon reuse. Initially covalent loading of the prepared phosphine ligands onto the peripheries of the dendrimers were attempted. However based on all the problems experienced with the covalent bonding, as discussed in Chapter 2 of this document, a simple acid base titration allowed loading of the prepared phosphine ligands onto the peripheries of the dendrimers via electrostatic interactions, to afford a stable phosphine ligand-dendrimer salt. Electrostatic interactions contribute much more to the solubility enhancement of poorly soluble compounds, thus the formation of the non-covalent phosphine-dendrimer salts was expected to result in greater potential for catalysis in biphasic systems as well as catalyst recycling. Only low generation dendrimers were utilised as previous reports indicated that an increase of the dendrimer generation leads to observation of negative dendritic effects due to the increased bulk that inhibits the approach of the catalytic metal centre.
- Full Text:
Functional silver nanoparticle catalysed [3+] cycloaddition reaction : greener route to substituted-1,2,3-triazolines
- Hemmaragala, Nanjyndaswamy Marishetty, Abrahamse, Heidi, George, Blassan Placktal Adimuriyil, Gannimani, Ramesh, Govender, Patrick
- Authors: Hemmaragala, Nanjyndaswamy Marishetty , Abrahamse, Heidi , George, Blassan Placktal Adimuriyil , Gannimani, Ramesh , Govender, Patrick
- Date: 2016
- Subjects: Fuctionalized silver nanoparticles , Protorhuslongifolia , Catalysis
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/215143 , uj:21369 , Citation: Hemmaragala, N.M. et al. 2016. Functional silver nanoparticle catalysed [3+] cycloaddition reaction : greener route to substituted-1,2,3-triazolines.
- Description: Abstract: Abstract: Please refer to full text to view abstract
- Full Text: false
- Authors: Hemmaragala, Nanjyndaswamy Marishetty , Abrahamse, Heidi , George, Blassan Placktal Adimuriyil , Gannimani, Ramesh , Govender, Patrick
- Date: 2016
- Subjects: Fuctionalized silver nanoparticles , Protorhuslongifolia , Catalysis
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/215143 , uj:21369 , Citation: Hemmaragala, N.M. et al. 2016. Functional silver nanoparticle catalysed [3+] cycloaddition reaction : greener route to substituted-1,2,3-triazolines.
- Description: Abstract: Abstract: Please refer to full text to view abstract
- Full Text: false
Carbon dioxide conversion via modified Fischer Tropsch Synthesis (FTS) over cobalt-based catalyst
- Authors: Bopape, Abegail Tebogo
- Date: 2017
- Subjects: Fischer-Tropsch process , Catalysis , Cobalt catalysts , Carbon dioxide , Atomic emission spectroscopy
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/242783 , uj:25053
- Description: Abstract: Human population is drastically increasing; in turn, it increases human activities that contribute to CO2 emissions, resulting in global warming. Effective CO2 mechanisms that can mitigate CO2 emissions to the environment are in high demand. One among the other approaches would be to develop processes that can utilize CO2 as feedstock to produce useful products. In this study CO2 is used as feedstock for hydrocarbons production via modified FTS over a cobalt-based (Co/γ-Al2O3) catalyst in a fixed bed reactor. The catalyst was prepared by precipitation-deposition method and characterized by using atomic absorption spectroscopy (AAS), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and temperature programmed reduction (TPR) analysis. The feed to the reactor consisted of CO2/H2/N2 with a H2 to CO2 ratio of 3:1. The project aimed at evaluating the effect of operating temperature, pressure and mixing cobalt-based catalyst with methanol synthesis catalyst (Cu/ZnO/ZrO2) on CO2 conversion and product selectivity during CO2 hydrogenation. The effect of operating temperature was studied in a range of 200-250 ⁰C in two ways: i) step-up experiment where the temperature was increased from 200-250 ⁰C in steps of 10 ⁰C and ii) step-down where the reverse temperature variation was used. The effect of operating pressure was studied over a pressure range from atmospheric to 20 bar at an operating temperature of 220 ⁰C while the other operating parameters were kept unchanged. The effect of methanol synthesis catalyst (Cu/ZnO/ZrO2) on CO2 hydrogenation over the Co/γ-Al2O3 catalyst was studied by physically mixing the two catalysts in equal proportions. CO2 conversions were found to increase with the increase in operating temperature and went through a maximum at 230 ⁰C and started decreasing due to catalyst deactivation. The methane selectivity decreased while the CO selectivity increased as the operating temperature was increased suggesting that high temperatures favoured the RWGS reaction. CO2 conversions were higher at high operating pressures with no clear trend on methane selectivity. CO was only detected at atmospheric pressure suggesting that at high pressures CO is readily hydrogenated to hydrocarbons. When the methanol synthesis catalyst was mixed with the Co/γ-Al2O3 catalyst the CO2 conversion was observed to increase with the increase in operating temperature up to 300 ⁰C above which rapid decline in catalyst activity was observed. The presence of Cu/ZnO/ZrO2 shifted the deactivation temperature of the Co/γ-Al2O3 catalyst to higher temperature, i.e. above 300 ⁰C compared to 230 ⁰C... , M.Tech. (Chemical Engineering)
- Full Text:
- Authors: Bopape, Abegail Tebogo
- Date: 2017
- Subjects: Fischer-Tropsch process , Catalysis , Cobalt catalysts , Carbon dioxide , Atomic emission spectroscopy
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/242783 , uj:25053
- Description: Abstract: Human population is drastically increasing; in turn, it increases human activities that contribute to CO2 emissions, resulting in global warming. Effective CO2 mechanisms that can mitigate CO2 emissions to the environment are in high demand. One among the other approaches would be to develop processes that can utilize CO2 as feedstock to produce useful products. In this study CO2 is used as feedstock for hydrocarbons production via modified FTS over a cobalt-based (Co/γ-Al2O3) catalyst in a fixed bed reactor. The catalyst was prepared by precipitation-deposition method and characterized by using atomic absorption spectroscopy (AAS), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and temperature programmed reduction (TPR) analysis. The feed to the reactor consisted of CO2/H2/N2 with a H2 to CO2 ratio of 3:1. The project aimed at evaluating the effect of operating temperature, pressure and mixing cobalt-based catalyst with methanol synthesis catalyst (Cu/ZnO/ZrO2) on CO2 conversion and product selectivity during CO2 hydrogenation. The effect of operating temperature was studied in a range of 200-250 ⁰C in two ways: i) step-up experiment where the temperature was increased from 200-250 ⁰C in steps of 10 ⁰C and ii) step-down where the reverse temperature variation was used. The effect of operating pressure was studied over a pressure range from atmospheric to 20 bar at an operating temperature of 220 ⁰C while the other operating parameters were kept unchanged. The effect of methanol synthesis catalyst (Cu/ZnO/ZrO2) on CO2 hydrogenation over the Co/γ-Al2O3 catalyst was studied by physically mixing the two catalysts in equal proportions. CO2 conversions were found to increase with the increase in operating temperature and went through a maximum at 230 ⁰C and started decreasing due to catalyst deactivation. The methane selectivity decreased while the CO selectivity increased as the operating temperature was increased suggesting that high temperatures favoured the RWGS reaction. CO2 conversions were higher at high operating pressures with no clear trend on methane selectivity. CO was only detected at atmospheric pressure suggesting that at high pressures CO is readily hydrogenated to hydrocarbons. When the methanol synthesis catalyst was mixed with the Co/γ-Al2O3 catalyst the CO2 conversion was observed to increase with the increase in operating temperature up to 300 ⁰C above which rapid decline in catalyst activity was observed. The presence of Cu/ZnO/ZrO2 shifted the deactivation temperature of the Co/γ-Al2O3 catalyst to higher temperature, i.e. above 300 ⁰C compared to 230 ⁰C... , M.Tech. (Chemical Engineering)
- Full Text:
Iodine mediated preparation of beta-acetoxysulfides and stereoselective synthesis of (E)-1,3-diphenyl-1-butene dimers
- Authors: Marakalala, Mokgethwa B.
- Date: 2018
- Subjects: Sulfur compounds , Catalysis , Chromatographic analysis , Stereochemistry
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/279618 , uj:30031
- Description: Abstract: -Hydroxysulfides comprise a significant segment of sulfur-containing natural products. Owing to their biological importance, their presence in a number of natural products in addition to their use as key intermediates in the synthesis of pharmaceuticals and substrates for the preparation of allylic alcohols, benzoxathiepines, benzodiazepines, thioketones, -substituted unsaturated enones, and -hydroxysulfoxides [15b], a number of methodologies have been reported for the synthesis of β-hydroxysulfides. Regioselective epoxide ring opening and 1,2-difunctionalization of alkenes are the commonly employed routes in the synthesis of such compounds. However, most of the reported methods suffer from one or more limitations including the use of transition metals, poor regioselectivity, long reaction times, limited substrate scope, the need for expensive and toxic reagents as well as the need for the preparation of an epoxide precursor and the formation of undesirable side products via rearrangement of epoxides and the oxidation of thiols, especially in the thiolysis of epoxides. In addressing some of these issues, we herein report in the current study a transition metal-free iodine catalysed preparation of acetate masked -hydroxysulfides (-acetoxysulfides) in the presence of a disulfide and a diacetoxyiodobenzene. The scope and limitations of the methodology are investigated in detail. In demonstrating the importance of (-acetoxysulfides) in organic synthesis, the methodology was fine tuned to provide styrene dimers that incorporate a sulfur heteroatom via a head-to-tail dimerization. The importance of sulfur in the synthesis of advanced materials, the scarcity of methodologies for the incorporation of sulfur to styrene monomers, as well as the attractiveness of the head-to-tail dimerization which generates an allylic chiral centre that is reported to be present in a number of biologically important organic molecules, makes the current method attractive in organic synthesis and thus, the results from the investigation of the scope and limitations of the reaction are reported along with full experimental details. , M.Sc. (Chemistry)
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- Authors: Marakalala, Mokgethwa B.
- Date: 2018
- Subjects: Sulfur compounds , Catalysis , Chromatographic analysis , Stereochemistry
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/279618 , uj:30031
- Description: Abstract: -Hydroxysulfides comprise a significant segment of sulfur-containing natural products. Owing to their biological importance, their presence in a number of natural products in addition to their use as key intermediates in the synthesis of pharmaceuticals and substrates for the preparation of allylic alcohols, benzoxathiepines, benzodiazepines, thioketones, -substituted unsaturated enones, and -hydroxysulfoxides [15b], a number of methodologies have been reported for the synthesis of β-hydroxysulfides. Regioselective epoxide ring opening and 1,2-difunctionalization of alkenes are the commonly employed routes in the synthesis of such compounds. However, most of the reported methods suffer from one or more limitations including the use of transition metals, poor regioselectivity, long reaction times, limited substrate scope, the need for expensive and toxic reagents as well as the need for the preparation of an epoxide precursor and the formation of undesirable side products via rearrangement of epoxides and the oxidation of thiols, especially in the thiolysis of epoxides. In addressing some of these issues, we herein report in the current study a transition metal-free iodine catalysed preparation of acetate masked -hydroxysulfides (-acetoxysulfides) in the presence of a disulfide and a diacetoxyiodobenzene. The scope and limitations of the methodology are investigated in detail. In demonstrating the importance of (-acetoxysulfides) in organic synthesis, the methodology was fine tuned to provide styrene dimers that incorporate a sulfur heteroatom via a head-to-tail dimerization. The importance of sulfur in the synthesis of advanced materials, the scarcity of methodologies for the incorporation of sulfur to styrene monomers, as well as the attractiveness of the head-to-tail dimerization which generates an allylic chiral centre that is reported to be present in a number of biologically important organic molecules, makes the current method attractive in organic synthesis and thus, the results from the investigation of the scope and limitations of the reaction are reported along with full experimental details. , M.Sc. (Chemistry)
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Sterically hindered and unsymmetrical phosphines: synthetic and catalytic aspects
- Authors: Evans, Stephen John
- Date: 2008-05-15T13:27:40Z
- Subjects: Phosphine , Phosphorus compounds synthesis , Catalysis , Chemical reaction
- Type: Thesis
- Identifier: uj:1697 , http://hdl.handle.net/10210/402
- Description: The design of catalysts for transition metal-mediated reactions is an active field in chemistry in the 21st century. It has been well recognised that ligands employed in these processes have a significant impact on the outcome of the reactions. The design and application of ligands in homogeneous catalysis reactions were the overarching aims of this project. Two areas were explored in this project, on the ligand synthesis side: 1. The use of directed ortho metallation (DoM) technology to synthesise unsymmetrical phosphines. 2. The synthesis of sterically hindered phosphines and their application to transition metal-mediated reactions. For the first sub-project, a range of N,N-dialkyl-diphenylphosphinic amides was synthesised in near quantitative yields. Deprotonation with s-BuLi and quenching the anion formed in the reaction with a range of electrophiles resulted in the desired ortho-substituted products in good yields. Differentiation of the second aromatic ring was possible, if the isolated mono-substituted products were used in further DoM reactions as starting materials. This methodology provided a range of highly substituted unsymmetrical phosphinic amides. Incorporation of other directing groups can change the selectivity of subsequent DoM reactions providing efficient routes to 2,2’ and 2,6-disubstituted products. Hydrolysis of the phosphinic amide moiety to the phosphinic acid with aqueous HCl, chlorination (SOCl2) and reaction of the acid chloride with a range of Grignard reagents provided an efficient method for the conversion of the phosphinic amide into a P-chirogenic but racemic phosphine oxide. Known methodology can convert this phosphine oxide into a phosphine that can be applied to transition metal catalysed reactions. This methodology provides an effective method for the synthesis of highly functionalised unsymmetrical phosphines. The approach facilitated substantial modifications to the ligand, which allows for efficient tailoring thereof for the metal-mediated reaction in which it is to be used. In the second sub-project, the DoM reaction was again employed but with (diaryl or dialkyl) phosphines as electrophilic quenches, resulting in the isolation of sterically hindered phosphines. Comparison between the ligands was made using the palladium-catalysed Suzuki reactions (catalytic approaches), Vaska type complexes (electronic effects) and phosphine selenium coupling constants (stereo-electronic effects). It was concluded that steric bulk and electronic characteristics affect the activity of catalysts formed from the ligands of this study, in line with the literature. The ligands were successfully applied to the palladium-catalysed Suzuki reaction using strongly deactivated aryl bromides and also some activated aryl chlorides as substrates at low (0.1% Pd) catalyst loadings. Significant improvements in catalytic activity were observed as the project progressed, using a structure-activity study as a guide. , Prof. D.B.G. Williams
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- Authors: Evans, Stephen John
- Date: 2008-05-15T13:27:40Z
- Subjects: Phosphine , Phosphorus compounds synthesis , Catalysis , Chemical reaction
- Type: Thesis
- Identifier: uj:1697 , http://hdl.handle.net/10210/402
- Description: The design of catalysts for transition metal-mediated reactions is an active field in chemistry in the 21st century. It has been well recognised that ligands employed in these processes have a significant impact on the outcome of the reactions. The design and application of ligands in homogeneous catalysis reactions were the overarching aims of this project. Two areas were explored in this project, on the ligand synthesis side: 1. The use of directed ortho metallation (DoM) technology to synthesise unsymmetrical phosphines. 2. The synthesis of sterically hindered phosphines and their application to transition metal-mediated reactions. For the first sub-project, a range of N,N-dialkyl-diphenylphosphinic amides was synthesised in near quantitative yields. Deprotonation with s-BuLi and quenching the anion formed in the reaction with a range of electrophiles resulted in the desired ortho-substituted products in good yields. Differentiation of the second aromatic ring was possible, if the isolated mono-substituted products were used in further DoM reactions as starting materials. This methodology provided a range of highly substituted unsymmetrical phosphinic amides. Incorporation of other directing groups can change the selectivity of subsequent DoM reactions providing efficient routes to 2,2’ and 2,6-disubstituted products. Hydrolysis of the phosphinic amide moiety to the phosphinic acid with aqueous HCl, chlorination (SOCl2) and reaction of the acid chloride with a range of Grignard reagents provided an efficient method for the conversion of the phosphinic amide into a P-chirogenic but racemic phosphine oxide. Known methodology can convert this phosphine oxide into a phosphine that can be applied to transition metal catalysed reactions. This methodology provides an effective method for the synthesis of highly functionalised unsymmetrical phosphines. The approach facilitated substantial modifications to the ligand, which allows for efficient tailoring thereof for the metal-mediated reaction in which it is to be used. In the second sub-project, the DoM reaction was again employed but with (diaryl or dialkyl) phosphines as electrophilic quenches, resulting in the isolation of sterically hindered phosphines. Comparison between the ligands was made using the palladium-catalysed Suzuki reactions (catalytic approaches), Vaska type complexes (electronic effects) and phosphine selenium coupling constants (stereo-electronic effects). It was concluded that steric bulk and electronic characteristics affect the activity of catalysts formed from the ligands of this study, in line with the literature. The ligands were successfully applied to the palladium-catalysed Suzuki reaction using strongly deactivated aryl bromides and also some activated aryl chlorides as substrates at low (0.1% Pd) catalyst loadings. Significant improvements in catalytic activity were observed as the project progressed, using a structure-activity study as a guide. , Prof. D.B.G. Williams
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Coordination chemistry of functionalized triazole lanthanide complexes and their catalytic application
- Authors: Makhoba, Sizwe
- Date: 2017
- Subjects: Coordination compounds , Rare earth metals , Triazoles , Catalysis
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/292792 , uj:31824
- Description: Abstract: Please refer to full text to view abstract. , M.Sc. (Chemistry)
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- Authors: Makhoba, Sizwe
- Date: 2017
- Subjects: Coordination compounds , Rare earth metals , Triazoles , Catalysis
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/292792 , uj:31824
- Description: Abstract: Please refer to full text to view abstract. , M.Sc. (Chemistry)
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The evaluation of dendrimer encapsulated ruthenium nanoparticles, immobilised on silica, as catalysts in various catalytic reactions and the effect of ionic liquids on the catalytic activity
- Authors: Antonels, Nathan Charles
- Date: 2015-04-22
- Subjects: Dendrimers , Catalysis , Nanostructured materials , Nanoparticles
- Type: Thesis
- Identifier: uj:13555 , http://hdl.handle.net/10210/13696
- Description: Ph.D. (Chemistry) , This study discusses the preparation of various sized dendrimer encapsulated ruthenium nanoparticles (RuDEN) with the use of the generation 4 (G4), generation 5 (G5) and generation 6 (G6) hydroxyl-terminated poly(amidoamine) (PAMAM-OH) dendrimers as templating agents. The size of the nanoparticles ranges from 1.1-2.2 nm. The RuDENs were used as nanoparticle solutions in catalytic reactions or immobilised on amorphous silica 60 and silica 100 and subsequently referred to as RuSil catalysts. These catalysts were evaluated in the reduction of 4-nitrophenol, toluene hydrogenation, citral hydrogenation, cinnamaldehyde hydrogenation and styrene oxidation...
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- Authors: Antonels, Nathan Charles
- Date: 2015-04-22
- Subjects: Dendrimers , Catalysis , Nanostructured materials , Nanoparticles
- Type: Thesis
- Identifier: uj:13555 , http://hdl.handle.net/10210/13696
- Description: Ph.D. (Chemistry) , This study discusses the preparation of various sized dendrimer encapsulated ruthenium nanoparticles (RuDEN) with the use of the generation 4 (G4), generation 5 (G5) and generation 6 (G6) hydroxyl-terminated poly(amidoamine) (PAMAM-OH) dendrimers as templating agents. The size of the nanoparticles ranges from 1.1-2.2 nm. The RuDENs were used as nanoparticle solutions in catalytic reactions or immobilised on amorphous silica 60 and silica 100 and subsequently referred to as RuSil catalysts. These catalysts were evaluated in the reduction of 4-nitrophenol, toluene hydrogenation, citral hydrogenation, cinnamaldehyde hydrogenation and styrene oxidation...
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