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Gill, Christopher Stephen. "Novel hybrid organic/inorganic single-sited catalysts and supports for fine chemical and pharmaceutical intermediate synthesis." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28218.
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Thesis (M. S.)--Chemical Engineering, Georgia Institute of Technology, 2009.Committee Chair: Jones, Christopher; Committee Member: Agrawal, Pradeep; Committee Member: Teja, Amyn; Committee Member: Weck, Marcus; Committee Member: Zhang, John.
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Johnston, Eric. "New Tools for Green Catalysis : Studies on a Biomimetic Hybrid Catalyst and a Novel Nanopalladium Catalyst." Doctoral thesis, Stockholms universitet, Institutionen för organisk kemi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-65079.
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The first part of this thesis describes an improved synthetic route to hybrid (hydroquinone-Schiff base)cobalt catalysts. Preparation of the 5-(2,5-hydroxyphenyl)salicylaldehyde building block was improved by altering the protective groups of the hydroquinone (HQ) starting material. Both protection and deprotection could be carried out under mild conditions, resulting in high yields. By optimizing the reaction conditions of the Suzuki cross-coupling, an efficient and inexpensive synthetic route with a good overall yield was developed. The second part describes the use of the hybrid catalyst as an electron transfer mediator (ETM) in the palladium-catalyzed aerobic carbocyclization of enallenes. By covalently linking the HQ to the cobalt Schiff-base complex the reaction proceeded at lower temperatures with a five-fold increase of the reaction rate compared to the previously reported system. The third part describes the application of the hybrid catalyst in the biomimetic aerobic oxidation of secondary alcohols. Due to the efficiency of the intramolecular electron transfer, the hybrid catalyst allowed for a lower catalytic loading and milder reaction conditions compared to the previous separate-component system. Benzylic alcohols as well as aliphatic alcohols were oxidized to the corresponding ketones in excellent yield and selectivity using this methodology. The fourth part describes the synthesis and characterization of highly dispersed palladium nanoparticles supported on aminopropyl-modified siliceous mesocellular foam. The Pd nanocatalyst showed excellent activity for the aerobic oxidation of a wide variety of alcohols under air atmosphere. Moreover, the catalyst can be recycled several times without any decrease in activity or leaching of the metal into solution. Finally, the fifth part describes the application of the Pd nanocatalyst in transfer hydrogenations and Suzuki coupling reactions. The catalyst was found to be highly efficient for both transformations, resulting in chemoselective reduction of various alkenes as well as coupling of a variety of aryl halides with various boronic acids in excellent yields. Performing the latter reaction under microwave irradiation significantly increased the reaction rate, compared to conventional heating. However, no significant increase in reaction rate was observed for the transfer hydrogenations, under microwave heating.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Submitted. Paper 5: Manuscript.
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Guo, Chris. "Alkane Oxidation Catalysis by Homogeneous and Heterogeneous Catalyst." Thesis, The University of Sydney, 2005. http://hdl.handle.net/2123/622.
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Abstract Cobalt-based complexes are widely used in industry and organic synthesis as catalysts for the oxidation of hydrocarbons. The Co/Mn/Br (known as "CAB system") catalyst system is effective for the oxidation of toluene. The Co/Mn/Br/Zr catalyst system is powerful for the oxidation of p-xylene, but not for the oxidation of toluene. [Co3O(OAc)5(OH)(py)3][PF6] (Co 3+ trimer 5) is more effective than [Co3O(OAc)6(py)3][PF6] (Co 3+ trimer 6) as a catalyst in the CAB catalyst system. Higher temperatures favour the oxidation of toluene. Zr 4+ does not enhance the oxidation of toluene. Zr 4+ could inhibit the oxidation of toluene in the combination of Co/Br/Zr, Co/Mn/Zr or Co/Zr. NHPI enhances the formation of benzyl alcohol, but the formation of other by-products is a problem for industrial processes. Complex(es) between cobalt, manganese and zirconium might be formed during the catalytic reaction. However, attempts at the preparation of complexes consisting of Co/Zr or Mn/Zr or Co3ZrP or Co8Zr4 clusters failed. The oxidation of cyclohexane to cyclohexanone and cyclohexanol is of great industrial significance. For the homogeneous catalysis at 50 o C and 3 bar N2 pressure, the activity order is: Mn(OAc)3 �2H2O > Mn12O12 cluster > Co 3+ trimer 6 > [Co3O(OAc)3(OH)2(py)5][PF6]2 (Co 3+ trimer 3) > Co 3+ trimer 5 > Co(OAc)2 �4H2O > [Co2(OAc)3(OH)2(py)4][PF6]-asym (Co dimerasym) > [Co2(OAc)3(OH)2(py)4][PF6]-sym (Co dimersym); whereas [Mn2CoO(OAc)6(py)3]�HOAc (Mn2Co complex) and zirconium(IV) acetate hydroxide showed almost no activity under these conditions. But at 120 o C and 3 bar N2 pressure, the activity order is changed to: Co dimerasym > Co(OAc)2 �4H2O > Co trimer 3 and Mn(OAc)3 �2H2O > Co 3+ trimer 6 > Mn2Co complex > Co 3+ trimer 5 > Co dimersym > Mn12O12 cluster. The molar ratio of the products was close to cyclohexanol/cyclohexanone=2/1. Mn(II) acetate and zirconium(IV) acetate hydroxide showed almost no activity under these conditions. Among those cobalt dimers and trimers, only the cobalt dimerasym survived after the stability tests, this means that [Co2(OAc)3(OH)2(py)4][PF6]-asym might be the active form for cobalt(II) acetate in the CAB system. Metal-substituted (silico)aluminophosphate-5 molecular sieves (MeAPO-5 and MeSAPO-5) are important heterogeneous catalysts for the oxidation of cyclohexane. The preparation of MeAPO-5 and MeSAPO-5 and their catalytic activities were studied. Pure MeAPO-5 and MeSAPO-5 are obtained and characterised. Four new pairs of bimetal-substituted MeAPO-5 and MeSAPO-5(CoZr, MnZr, CrZr and MnCo) were prepared successfully. Two novel trimetal-subtituted MeAPO-5 and MeSAPO-5 (MnCoZr) are reported here. Improved methods for the preparation of four monometal-substituted MeAPO-5 (Cr, Co, Mn and Zr) and for CoCe(S)APO-5 and CrCe(S)APO-5 are reported. Novel combinational mixing conditions for the formation of gel mixtures for Me(S)APO-5 syntheses have been developed. For the oxidation of cyclohexane by TBHP catalysed by MeAPO-5 and MeSAPO-5 materials, CrZrSAPO-5 is the only active MeSAPO-5 catalyst among those materials tested under conditions of refluxing in cyclohexane. Of the MeAPO-5 materials tested, whereas CrCeSAPO-5 has very little activity, CrZrAPO-5 and CrCeAPO-5 are very active catalysts under conditions of refluxing in cyclohexane. MnCoAPO-5, MnZrAPO-5 and CrAPO-5 are also active. When Cr is in the catalyst system, the product distribution is always cyclohexanone/cyclohexanol equals 2-3)/1, compared with 1/2 for other catalysts. For MeAPO-5, the activity at 150 o C and 10 bar N2 pressure is: CrZrAPO-5 > CrCeAPO-5 > CoZrAPO-5. For MeAPO-5 and MeSAPO-5, at 150 o C and 13 bar N2 pressure, the selectivity towards cyclohexanone is: CrZrAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5 > MnCoAPO-5 > MnZrAPO-5; and the selectivity towards cyclohexanol is: MnZrAPO-5 > CrZrAPO-5 > MnCoAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5. Overall the selectivity towards the oxidation of cyclohexane is: CrZrAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5 > MnCoAPO-5 > MnZrAPO-5. The amount of water in the system can affect the performance of CrCeAPO-5, but has almost no effect on CrZrAPO-5. Metal leaching is another concern in potential industrial applications of MeAPO-5 and MeSAPO-5 catalysts. The heterogeneous catalysts prepared in the present work showed very little metal leaching. This feature, coupled with the good selectivities and effectivities, makes them potentially very useful.
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Guo, Chris. "Alkane Oxidation Catalysis by Homogeneous and Heterogeneous Catalyst." University of Sydney. Chemistry, 2005. http://hdl.handle.net/2123/622.
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Abstract Cobalt-based complexes are widely used in industry and organic synthesis as catalysts for the oxidation of hydrocarbons. The Co/Mn/Br (known as "CAB system") catalyst system is effective for the oxidation of toluene. The Co/Mn/Br/Zr catalyst system is powerful for the oxidation of p-xylene, but not for the oxidation of toluene. [Co3O(OAc)5(OH)(py)3][PF6] (Co 3+ trimer 5) is more effective than [Co3O(OAc)6(py)3][PF6] (Co 3+ trimer 6) as a catalyst in the CAB catalyst system. Higher temperatures favour the oxidation of toluene. Zr 4+ does not enhance the oxidation of toluene. Zr 4+ could inhibit the oxidation of toluene in the combination of Co/Br/Zr, Co/Mn/Zr or Co/Zr. NHPI enhances the formation of benzyl alcohol, but the formation of other by-products is a problem for industrial processes. Complex(es) between cobalt, manganese and zirconium might be formed during the catalytic reaction. However, attempts at the preparation of complexes consisting of Co/Zr or Mn/Zr or Co3ZrP or Co8Zr4 clusters failed. The oxidation of cyclohexane to cyclohexanone and cyclohexanol is of great industrial significance. For the homogeneous catalysis at 50 o C and 3 bar N2 pressure, the activity order is: Mn(OAc)3 �2H2O > Mn12O12 cluster > Co 3+ trimer 6 > [Co3O(OAc)3(OH)2(py)5][PF6]2 (Co 3+ trimer 3) > Co 3+ trimer 5 > Co(OAc)2 �4H2O > [Co2(OAc)3(OH)2(py)4][PF6]-asym (Co dimerasym) > [Co2(OAc)3(OH)2(py)4][PF6]-sym (Co dimersym); whereas [Mn2CoO(OAc)6(py)3]�HOAc (Mn2Co complex) and zirconium(IV) acetate hydroxide showed almost no activity under these conditions. But at 120 o C and 3 bar N2 pressure, the activity order is changed to: Co dimerasym > Co(OAc)2 �4H2O > Co trimer 3 and Mn(OAc)3 �2H2O > Co 3+ trimer 6 > Mn2Co complex > Co 3+ trimer 5 > Co dimersym > Mn12O12 cluster. The molar ratio of the products was close to cyclohexanol/cyclohexanone=2/1. Mn(II) acetate and zirconium(IV) acetate hydroxide showed almost no activity under these conditions. Among those cobalt dimers and trimers, only the cobalt dimerasym survived after the stability tests, this means that [Co2(OAc)3(OH)2(py)4][PF6]-asym might be the active form for cobalt(II) acetate in the CAB system. Metal-substituted (silico)aluminophosphate-5 molecular sieves (MeAPO-5 and MeSAPO-5) are important heterogeneous catalysts for the oxidation of cyclohexane. The preparation of MeAPO-5 and MeSAPO-5 and their catalytic activities were studied. Pure MeAPO-5 and MeSAPO-5 are obtained and characterised. Four new pairs of bimetal-substituted MeAPO-5 and MeSAPO-5(CoZr, MnZr, CrZr and MnCo) were prepared successfully. Two novel trimetal-subtituted MeAPO-5 and MeSAPO-5 (MnCoZr) are reported here. Improved methods for the preparation of four monometal-substituted MeAPO-5 (Cr, Co, Mn and Zr) and for CoCe(S)APO-5 and CrCe(S)APO-5 are reported. Novel combinational mixing conditions for the formation of gel mixtures for Me(S)APO-5 syntheses have been developed. For the oxidation of cyclohexane by TBHP catalysed by MeAPO-5 and MeSAPO-5 materials, CrZrSAPO-5 is the only active MeSAPO-5 catalyst among those materials tested under conditions of refluxing in cyclohexane. Of the MeAPO-5 materials tested, whereas CrCeSAPO-5 has very little activity, CrZrAPO-5 and CrCeAPO-5 are very active catalysts under conditions of refluxing in cyclohexane. MnCoAPO-5, MnZrAPO-5 and CrAPO-5 are also active. When Cr is in the catalyst system, the product distribution is always cyclohexanone/cyclohexanol equals 2-3)/1, compared with 1/2 for other catalysts. For MeAPO-5, the activity at 150 o C and 10 bar N2 pressure is: CrZrAPO-5 > CrCeAPO-5 > CoZrAPO-5. For MeAPO-5 and MeSAPO-5, at 150 o C and 13 bar N2 pressure, the selectivity towards cyclohexanone is: CrZrAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5 > MnCoAPO-5 > MnZrAPO-5; and the selectivity towards cyclohexanol is: MnZrAPO-5 > CrZrAPO-5 > MnCoAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5. Overall the selectivity towards the oxidation of cyclohexane is: CrZrAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5 > MnCoAPO-5 > MnZrAPO-5. The amount of water in the system can affect the performance of CrCeAPO-5, but has almost no effect on CrZrAPO-5. Metal leaching is another concern in potential industrial applications of MeAPO-5 and MeSAPO-5 catalysts. The heterogeneous catalysts prepared in the present work showed very little metal leaching. This feature, coupled with the good selectivities and effectivities, makes them potentially very useful.
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Baumgart, Jerry William. "Characterization of a CoMo/Al[subscript]2O[subscript]3 catalyst exposed to a coke inducing environment." Thesis, Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/11714.
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Ford, David Dearborn. "The Role of Catalyst-Catalyst Interactions in Asymmetric Catalysis with (salen)Co(III) Complexes and H-Bond Donors." Thesis, Harvard University, 2013. http://dissertations.umi.com/gsas.harvard:11154.
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In asymmetric catalysis, interactions between multiple molecules of catalyst can be important for achieving high catalyst activity and stereoselectivity. In Chapter 1 of this thesis, we introduce catalyst-catalyst interactions in the context of the classic Kagan nonlinear effect (NLE) experiment, and present examples of the strengths and drawbacks of the NLE experiment. For the remainder of the thesis, we explore catalyst-catalyst interactions in the context of two different reactions. First, in Chapter 2, we apply a combination of reaction kinetics and computational chemistry to a reaction that is well known to require the cooperative action of two molecules of catalyst: the (salen)Co(III)-catalyzed hydrolytic kinetic resolution (HKR) of terminal epoxides. In our investigation, we demonstrate that stereoselectivity in the HKR is achieved through catalyst-catalyst interactions and provide a model for how high selectivity and broad substrate scope are achieved in this reaction. In Chapter 3, we focus our attention on the thiourea-catalyzed enantioselective alkylation of alpha-chloroethers with silyl ketene acetal nucleophiles, a reaction that was not known to require the cooperative action of two molecules of catalyst at the outset of our investigation. By using a wide range of physical organic chemistry tools, we established that the resting state of the optimal thiourea catalyst is dimeric under typical reaction conditions, and that two molecules of catalyst work cooperatively to activate the alpha-chloroether electrophile. The implications of this mechanism for catalyst design are discussed.Chemistry and Chemical Biology
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Nguyen, Joseph Vu. "Design, synthesis, and optimization of recoverable and recyclable silica-immobilized atom transfer radical polymerization catalysts." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6860.
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Despite the growing interest in heterogeneous polymerization catalysis, the majority of the polymerization catalysts used industrially are single-use entities that are left in the polymer product. Recoverable and recyclable polymerization catalysts have not reached the industrial utility of single-use catalysts because the catalyst and product separation have not become economical. The successful development of recyclable transition metal polymerization catalysts must take a rational design approach, hence academic and industrial researchers need to further expand the fundamental science and engineering of recyclable polymerization catalysis to gain an understanding of critical parameters that allow for the design of economically viable, recoverable solid polymerization catalysts.
Unfortunately, the rapid development of Atom Transfer Radical Polymerization over the past 10 years has not resulted in its wide spread industrial practice. Numerous reports regarding the immobilization of transition metal ATRP catalysts, in attempts to increase its applicability, have extended the fundamentals of recyclable polymerization catalysis. However, for industrial viability, more research is required in the area of how the catalyst complex immobilization methodology and support structure affect the catalyst polymerization performance, regeneration, and recyclability. A comprehensive rational catalyst design approach of silica-immobilized ATRP catalyst was undertaken to answer these questions and are discussed here.
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Meyer, Simon [Verfasser]. "Carbide Materials as Catalysts and Catalyst Supports for Applications in Water Electrolysis and in Heterogeneous Catalysis / Simon Meyer." München : Verlag Dr. Hut, 2014. http://d-nb.info/1058284967/34.
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Craig, Kim Meyer. "New concepts in catalyst design: homogeneous organometallic catalysts with tunable architectures." Thesis, University of Auckland, 2010. http://hdl.handle.net/2292/6114.
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This theses describes the development of homogeneous catalysts containing receptor elements which are capable of participating in reversible bonding interactions with groups bearing complementary functionality. This approach is amenable to combinatorial chemistry, and could facilitate catalyst development processes which are conventionally expensive and time-intensive. To date, the implication of reversible supra molecular interactions in anthropogenic organometallic catalysis are not widely understood.
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Mansor, N. B. "Development of catalysts and catalyst supports for polymer electrolyte fuel cells." Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1460064/.
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Polymer Electrolyte Membrane fuel cells (PEMFC) are clean and efficient electrochemical energy converters that can be adapted to a wide range of domestic and automotive applications. However, large-scale commercialisation is hindered by issues of cost and durability relating to the catalyst layer. This work aims to address the need for cheaper and durable catalysts through the development of novel catalyst and catalyst support. The initial aim of this work is to investigate the potential application of Pd-based alloy catalyst in PEMFC. Pd is about 42% cheaper than Pt and 50 times more abundant on earth. Previous studies have shown that there is a correlation between electronic structure and catalytic activity of Pd binary alloys, and therefore it is possible to design a highly efficient Pd-based alloy catalyst. In this work, Pd-based catalyst was synthesised and characterized electrochemically in ex-situ and in-situ configurations to determine their activity and durability. It was found that Pd-based catalyst could potentially replace Pt as a low-cost anode catalyst. The second part of this work investigated the potential application of graphitic carbon nitride materials as catalyst support. Carbon black is the most widely used catalyst support for state-of-the-art PEMFCs even though it is known to undergo carbon corrosion during operation. Graphitic carbon nitride could offer enhanced durability and activity due to their graphitic structure and intrinsic catalytic properties. In addition, graphitic carbon nitride is low-cost, fairly simple to synthesise and highly tunable. In this work, various graphitic carbon nitride materials were prepared and characterised using accelerated carbon corrosion protocol. They were found to be more electrochemically stable compared to conventional carbon black. Superior methanol oxidation activity is also observed for graphitic carbon nitride supported Pt catalysts on the basis of the catalyst electrochemical surface area. However further work is needed to optimise the deposition and utilisation of metal catalyst on graphitic carbon nitride materials.
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Paliga, James Francis. "Developing Earth-abundant metal-catalysts for hydrofunctionalisation." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31115.
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The iron-catalysed hydromagnesiation of styrene derivatives has been developed further from previous publications, expanding the electrophile scope to enable the regioselective formation of new carbon-carbon and carbon-heteroatom bonds (Scheme A1). A commercially available pre-catalyst and ligand were used to give an operationally simple procedure that did not require prior synthesis of a catalyst. This work also investigated the hydromagnesiation of dienes, using a screen of ligands commonly used in transition metal catalysis. An investigation into the magnesium-catalysed hydroboration of olefins was also carried out. Although mostly unsuccessful, it was demonstrated that in the presence of a magnesium catalyst, a small amount of vinyl boronic ester could be formed from an alkyne (Scheme A2). Simple magnesium salts were also investigated for the reduction of carbonyls. Lastly, this work explored the titanium-catalysed hydrosilylation of olefins, using a novel activation method developed within the group (Scheme A3). The results were compared to those published previously using traditional organometallic activation methods and attempts at identifying conditions to improve chemoselectivity were carried out.
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Sherborne, Grant John. "Catalyst deactivation in copper-catalysed C-N cross-coupling reactions." Thesis, University of Leeds, 2017. http://etheses.whiterose.ac.uk/17595/.
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This thesis details research into the mechanism of the copper-catalysed cross-coupling reaction, with a focus on the N-arylation of secondary amines and amides (Ullmann-Goldberg reaction). Issues limiting the application of the Ullmann-Goldberg reaction on industrial scale are uncovered and understood from a mechanistic point of view, to provide a platform for more efficient copper catalysts. In situ kinetic monitoring using 1H NMR spectroscopy is used to understand the role of each key component in the N-arylation of piperidine using a copper catalyst in a fully homogeneous system. Key roles of the amine and catalyst are observed, whilst product inhibition was found to significantly inhibit the reaction. Solvent effects are evaluated by repeating the in situ kinetic investigation in d7-DMF and d3-MeCN. The kinetic findings indicate deviation of the mechanism from the accepted literature mechanism, with a rate-limiting amine coordination proposed. Kinetic studies are also used to show the key role that the solubility of inorganic bases such as Cs2CO3 and K3PO4 play in rate-determining equilibria between copper species. Slow catalyst turnover was observed for up to 14 hours at lowered catalyst loadings, before a dramatic increase in the rate of reaction. A link between particle size, solubility and the deprotonation of the cyclic amide substrate are made, with the results having important implications on the use of inorganic bases in cross-coupling reactions. Inhibition of the reaction from inorganic side products and precipitation of copper from solution is combined with findings of a novel interaction between copper and cesium cation to give evidence for a non-innocent role of the cesium cation in copper-catalysed N-arylation. Heterogeneous catalysis is explored, where it is shown that copper precipitated from the reaction is capable of catalysis, introducing a question of a pseudo-heterogeneous mechanism and phase equilibria. A multi-edge XAFS (X-ray absorption fine structure) study is combined with laboratory experiments to uncover the activation, deactivation and reactivation pathways of an immobilised iridium transfer hydrogenation catalyst. The key role of an Ir-Cl bond is shown, where initial ligand exchange activates the catalyst, followed by further, slow ligand exchange, leading to deactivation of the catalyst.
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Yang, Fangfang. "Targeted supported laccase based hybrid catalyst for continuous flow catalysis." Electronic Thesis or Diss., Ecole centrale de Marseille, 2021. http://www.theses.fr/2021ECDM0009.
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Les catalyseurs hétérogènes sont aujourd’hui'hui largement développés afin d'obtenir une meilleure stabilité, une meilleure réutilisation ainsi qu'une meilleure localisation. Dans cette optique, nous avons d'abord préparé des catalyseurs hétérogènes à base d'enzymes par l'immobilisation d’une laccase d'origine fongique contenant seulement deux lysines de surface spatialement proches (K40, K71) ainsi que deux de ses variants contenant une lysine unique -une située à proximité du site d'oxydation du substrat (K157) et une à l'opposé de ce site d'oxydation (K71)- dans des mousses de silice de type Si(HIPE) à porosités contrôlées. L'immobilisation a été réalisée par liaison covalente entre l'enzyme et la mousse activée à faible teneur en glutaraldéhyde. En testant la décoloration de colorants dans un réacteur à flux continu, nous montrons que l'activité du catalyseur hétérogène est comparable à son homologue homogène. Son activité opérationnelle reste aussi élevée que 60 % après douze cycles de décoloration consécutifs et un an de stockage. Plus important encore, en comparant les activités sur différents substrats pour des catalyseurs orientés différemment, nous montrons une discrimination double pour l'ABTS par rapport à l'ascorbate. Par ailleurs, les métalloenzymes artificielles peuvent utiliser les avantages des catalyseurs métalliques et enzymatiques pour réaliser une oxydation aérobie de manière durable. Nous avons donc immobilisé un complexe Pd(II) à base de biquinoline et une laccase dans des monolithes de silice pour l'oxydation de l'alcool veratrylique. Afin de contrôler la réactivité, trois méthodes d'immobilisation ont été utilisées pour la construction de ces catalyseurs hybrides hétérogènes. Les catalyseurs hybrides immobilisés présentent une activité améliorée par rapport au complexe de Pd immobilisé seul pour chaque méthode testée, attestant de la synergie entre le Pd et la laccase. En modulant l'orientation de l'enzyme vers le complexe de Pd(II) et la mousse de silice, nous montrons que l'activité de l'hybride de Pd(II)/UNIK157 est en moyenne deux fois plus importante que celle de Pd(II)/UNIK71. Une bonne stabilité et réutilisation est observée quel que soit l'orientation de l'enzyme. Cette étude donne un aperçu de l'utilisation de supports solides qui au-delà de permettre la stabilité et la réutilisation deviennent des partenaires synergiques dans le processus catalytiqueHeterogeneous catalysts are now widely developed to obtain improved stability, reusability, and localization. In this view, we first prepared the enzyme-based heterogeneous catalysts by the immobilization of a fungal laccase containing only two spatially close surface lysines (K40, K71) and its variants containing a unique lysine -one located in the vicinity of the substrate oxidation site (K157) and one at the opposite side of this oxidation site (K71)- into Si(HIPE) type silica foams bearing controlled porosities. Immobilization was achieved by a covalent bond forming reaction between the enzyme and the low glutaraldehyde activated foam. Testing dye decolorization in a continuous flow reactor, we show that the activity of the heterogeneous catalyst is comparable to its homogeneous counterpart. Its operational activity remains as high as 60 % after twelve consecutive decolorization cycles and one-year storage. More importantly, comparing activities on different substrates for differentially oriented catalysts, we show a two-fold discrimination for ABTS relative to ascorbate. In addition, artificial metalloenzymes can use the advantages of both metallic and enzymatic catalysts to perform aerobic oxidation in a sustainable fashion. We thus co-immobilized a biquinoline-based-Pd(II) complex and laccase into silica monoliths for veratryl alcohol oxidation. To address the control of reactivity, three methods of immobilization were used for the construction of the heterogeneous hybrid catalysts. The immobilized hybrid catalysts show an improved activity compared to the immobilized Pd complex alone for each tested method, attesting for the synergy between Pd and laccase. By tuning enzyme orientation towards Pd(II) complex and silica foam, we show that the activity of the Pd(II)/UNIK157 hybrid exhibits an averaged two-fold increase compared to Pd(II)/UNIK71. A good stability and reusability is observed for both enzyme orientations. This study provides insights into the use of solid supports that beyond allowing stability and reusability becomes synergistic partners in the catalytic process
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Blaney, Katie Bethan. "Characterising catalyst preparation : from adsorbed precursor complex to catalyst particle." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/72952/.
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Catalyst performance can be enhanced by the high dispersion of precious metals onto supports. The deposition of metal particles and the structural arrangement they adopt once impregnated on a support is therefore of interest in determining the necessary conditions required for maximum catalyst efficiency. The details of the relationship between precursor and the final catalyst structure have not been extensively investigated; therefore it is the aim of this project to examine this relationship using techniques such as EXAFS, XRD and TEM. A selection of Pt and Pd precursors has been deposited onto both Al2O3 and SiO2 supports and the resulting materials examined using these characterisation methods. Bimetallic combinations of these precursors have also been prepared and characterised. The EXAFS showed that the ligand stays intact during adsorption onto the support and that it is lost during heating. The type of support used had an effect on the dispersion of both the monometallic and bimetallic catalysts and also on the type of bimetallic particle formed. Al2O3 supported bimetallic particles consisted of a Pt rich core with a Pd outer shell whilst SiO2 supported bimetallic particles were made up of a mixture of monometallic Pt and Pd particles and bimetallic Pt/Pd particles.
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Swaminathan, Sneha. "Metal Oxide Nanofibers as Filters, Catalyst and Catalyst Support Structures." University of Akron / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=akron1279564885.
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Mantri, K. "Mcm-41 as an adsorbent, catalyst and/or catalyst support." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2001. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2335.
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Casabán, Julián José. "Greener catalyst preparation." Thesis, Queen's University Belfast, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.600637.
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Heterogeneous catalysts which consist of metal (nano)particles dispersed on a support material are conventionally prepared in multi-step procedures. Commonly, the metal precursor is in the form of a soluble metal nitrate salt and several calcination, dissolution, precipitation and reduction steps are required to form the active metal catalyst. This processing releases significant NOx and is also wasteful in terms of the number of process steps required to produce the catalyst. The main objective of this work was to examine alternative more direct catalyst preparation methods. Two more direct deposition methods were proposed, which may be performed electrochemically or electrolessly. Specifically, a base metal in elemental form could be oxidized (stripped) into solution and then deposited onto a support material in the same vessel. In this way, the ionized form of the metal is generated only transiently and no nitrate is consumed. Depending on the metal, the support, and the conditions applied, the oxidation and deposition steps may be induced electrochemically or may even occur spontaneously under appropriate conditions. In order to facilitate the overall process, the characteristics of such a system could be tuned through the preparation parameters but also by adding ligands to the solution which would ideally be recyclable, acting as shuttles to provide the solubilised metal in the form of a complex of a desired stability. The stability of the complex is sufficiently low that the ligands can be released back into solution upon metal deposition. The development of such a system was investigated for copper using aqueous ligand solutions. Stripping and electrodeposition processes were investigated using ethylenediamine. The recyclability of the ligand was successfully proved when Cu-graphite materials were synthesised by stripping-electrodeposition processes combined in the same vessel. Alternatively, in the presence of oxide supports, stripping and electroless deposition were combined in the same vessel using aqueous ammonia solutions and active water gas shift Cu-AI20 3 catalysts were prepared by this new ligand-assisted route from Cu metal and Cu ores. These new copper-alumina materials showed enhanced catalytic activity in comparison with standard impregnated catalysts and greater stability when compared against commercial WGS catalysts. Active water gas shift Cu/Al20 3 catalysts were also prepared by solvent-free mechanochemistry using a ball mill. Similar catalytic activity was observed using a Cu/Ab03 catalyst prepared by ball milling (from CuO as the copper source), compared with a conventionally prepared Cu/Ab03 catalyst (wet impregnation)
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Hammond, Max Leonard. "Imine catalyst stability." Thesis, University of Warwick, 2006. http://wrap.warwick.ac.uk/1172/.
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Chapter 1 presents a review of the background and current research regarding Schiff-base olefin polymerization catalysts, with special reference to the salicylaldimine species. An attempt is made to review trends within the current literature. Chapter 2 describes the synthesis and polymerization properties of tetradentate ligands with a bibenzyl backbone at titanium and zirconium centres, prepared with the intent of sterically hindering a 1,2-Migratory Insertion into the ligand imine functionality. A custom-built polymerization reactor was used to determine the stability of the catalytic systems. Steric protection is moderately successful in enhancing the stability of these systems. Chapter 3 reports the synthesis and detailed polymerization behaviour of a series of group 4 catalysts based on salicyloxazoline ligands, which should be resistant to 1,2-Migratory Insertion. Comparisons are made between polymerization under different conditions, including using High-Throughput methodology to screen catalysts under a range of differing conditions rapidly. Such systems are extremely active for polymerization of ethene, but demonstrate limited stability at elevated temperature. Chapter 4 presents our investigations into the polymerization behaviour of salicyloxazoline catalysts containing a para-methoxy substituent on the phenoxy donor unit. This substituent significantly enhances the stability of the catalysts at elevated temperature. Chapter 5 explores the nature of the active species in polymerizations with group 4 salicyloxazoline species. Alkyl cations of such species are generated from metal alkyl species with borate activators, and also from metal chloride species with MAO. We conclude that the primary deactivation mechanism is loss of ligand to aluminium co-catalyst, and that the methoxy substituent prevents this. A computational approach (DFT) is also applied, to examine the catalytic pathways which may be available to various stereoisomers of the catalyst. Chapter 6 details the experimental procedures used during this work.
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Patrick, Ardhe, and Sebastian Karlsson. "The crypto catalyst." Thesis, Linnéuniversitetet, Institutionen för marknadsföring (MF), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-75548.
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In a scope where continuous innovations are seen each day, the cyberspace can be seen as the tech-entrepreneurs’ playground for delivering new solutions to customers. Digital start-ups who interact through the cyberspace operate with little to no restriction despite having limiting resource. In 2008 a man named Satoshi Nakamoto developed a new technology called blockchain. The new breed of firms providing blockchain solutions have been painted to live in a borderless world with little technical restrictions. Exploring the effects that blockchain brings to their internationalisation has brought our attention to study the early internationalisation of blockchain born globals and their business ecosystem. The deductive and qualitative approach gave the results from four different companies that were involved in blockchain technology. By using previous theory on internationalisation and a deductive approach a conceptual synthesis was developed. The synthesis was later applied in the case-companies to observe the results. The findings have shown that the firms implementing blockchain in the core offering has resulted in an accelerated internationalisation. The major factors contributing to this quick internationalisations is the spread of knowledge between buyers and sellers, trough the cyberspace. However, the authors were unable to find a relationship between the accelerated internationalisation and to the extent in which a firm has implemented blockchain in its core offering. The finding has given the authors prominent answers to the research question and has highlighted the complexity of the subject. The, authors conclude the thesis by displaying the importance of cyberspace in the business ecosystem; how it attracts customers and the importance of the company’s business model. Blockchain technology proved to have effects on the process of internationalisation due to superior technological performance, but also its hype.
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Widyaningrum, Rosalia Nugraheni. "Mesoporous silica-supported catalysts to enhance hydrogen production during cellulose pyrolysis." Thesis, The University of Sydney, 2011. https://hdl.handle.net/2123/28917.
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Pyrolysis of biomass has been studied worldwide as a potential path to produce hydrogen from renewable sources. Major problem in a non-catalytic biomass pyrolysis is tar formation, which causes complication in the utilization of product gas. Elimination of tar requires a high temperature, and it leads to low energy efficiency since tar itself contains high potential energy.
The utilization of metal catalysts is considered an effective method to reduce tar content and subsequently increase the hydrogen production. Nickel catalyst has been previously investigated for its tar cracking activity and identified as one of the best catalysts, but it has a drawback when used at high temperature because sintering of metal particle and carbon deposition occur. To address this challenge, a suitable catalyst support and promoter are required to minimize sintering and enhance the activity of nickel catalyst.
This project approached the issue by studying the potential catalyst supports and the effect of promoter in the catalytic activity of nickel catalyst. Three catalyst supports: mesoporous silica SBA-15 (Santa Barbara Amorphous), MCF (Mesocellular Foam), and commercial y-Alz03 were investigated, and palladium was chosen as a promoter. Mesoporous silica SBA-15 and MCF were synthesized using sol-gel method with Pluronic P123 as a structure directing agent, tetraethyl orthosilicate (TEOS) as a silica source, and 1,3,5-trimethylbenzene as a swelling agent for MCF synthesis. Nickel and palladium were deposited into the supports by wet impregnation techniques. The catalysts were characterized using N2 adsorption-desorption (BET and BJH methods), xray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray fluorescence (XRF). The activity of the catalyst was tested in cellulose pyrolysis using thermogravimetric analyzer coupled to a mass spectroscopy (TGA-MS).
This work studied the role of nickel catalysts in the pyrolysis of cellulose, the role of catalyst supports, and the effect of Pd promoter in increasing the catalytic activity to enhance hydrogen production. The results of this study suggest that mesoporous silica MCF was a good catalyst support because the MCF-supported Ni catalyst gave the highest H2 yield. The H2 yield was 73.5 mL/ g cellulose, which was 1.7 times H2 yield from SBA-15-supported Ni-catalyst, and 3.3 times H2 yield produced by y-Alz03-supported Ni-catalyst. The addition of 0.5 wt% Pd promoter also increased the H2 yield by 14%.
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Markovits, Iulius [Verfasser]. "Ionic Liquids in Oxidation Catalysis: from Solvent to Catalyst / Iulius Markovits." München : Verlag Dr. Hut, 2017. http://d-nb.info/1126297577/34.
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Venable, Margaret Hamm. "Syntheses, structures and support interactions of potential metal oxide catalyst precursors." Thesis, Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/26940.
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Otor, Hope O. "Catalyst Development and Control of Catalyst Deactivation for Carbon Dioxide Conversion." University of Toledo / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1596134702392137.
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Gomes, Umesh Prasad. "Catalyst-assisted and catalyst-free growth of III-V semiconductor nanowires." Doctoral thesis, Scuola Normale Superiore, 2017. http://hdl.handle.net/11384/85884.
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The aim of this thesis is to understand the dynamics of the nucleation and growth of III-V semiconductor nanowires and associated heterostructures grown by chemical beam epitaxy. These nanowires represent well-controlled and high quality materials suitable for both fundamental physics and applications in optical and electronic devices.
The first part of the thesis investigates growth recipes to obtain Au-catalyzed InAs NWs with controlled morphology. Good control of NW length and diameter distributions has been achieved by a systematic study of two different Au deposition techniques: Au thin film deposition and colloidal dispersion.
Triggered by the issues of Au contamination and CMOS compatibility, the second part of the thesis is dedicated to the investigation of the nucleation and growth mechanisms of Au-free InAs NWs on Si (111) substrates. A thorough analysis of the silicon substrate preparation is conducted and an optimized silicon surface for the nucleation of Au-free nanowires is identified. We show that the silicon surface can be modified by in situ and ex situ parameters allowing us to control the density of NWs. Growth conditions were established for growing InAs NWs either by catalyst-free or self-catalyzed mechanisms on Si (111). The catalyst-free growth proceeds in the vapor-solid growth mechanism without the use of any catalyst particle while the self-catalyzed growth proceeds in the vapor-liquid-solid mechanism involving a liquid In droplet. Growth models are proposed in order to interpret the experimental findings.
The third part of the thesis concerns the growth of axial and radial (core-shell) heterostructured NWs. Nanowire heterostructures combining either highly lattice mismatched materials (GaAs and InAs) or almost lattice matched materials (InAs and GaSb) are investigated. GaAs/InAs and InAs/GaAs axial heterostructures are grown by Au-catalyzed method. Here, it is demonstrated that the catalyst composition, rather than other growth parameters, as postulated so far, controls the growth mode and the resulting NW morphology. We have also explored the growth of core-shell InAs/GaSb heterostructures by catalyst-free mechanism. The morphology and structural properties of InAs/GaSb core-shell heterostructures are optimized to fabricate Esaki tunnel diodes exploiting their broken-gap band alignment.
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Kröger, V. (Virpi). "Poisoning of automotive exhaust gas catalyst components:the role of phosphorus in the poisoning phenomena." Doctoral thesis, University of Oulu, 2007. http://urn.fi/urn:isbn:9789514286087.
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Abstract
The aim of this thesis project was to gain new knowledge on the effect of phosphorus on the catalytic activity and characteristics of automotive exhaust gas catalyst components. The simultaneous roles of phosphorus and calcium were also studied.
The first test series of powdery catalyst samples contained Rh and oxide (Test series 1) and the second, Pt and oxide or ZSM-5 (Test series 2). The catalysts were analyzed when fresh and after two ageing and phosphorus poisoning procedures developed in this work. The procedures consisted of adding poison via impregnation in an aqueous solution (for Test series 1) and in the gaseous phase under hydrothermal conditions (for Test series 2). The poison compounds formed and the changes in the washcoat were studied by using physisorption analyses, SEM, TEM, XRD, and FTIR-ATR. The poison content of the samples was determined by ICP-OES and XRF. Laboratory-scale activity measurements were done to investigate the catalytic activity. Thermodynamic calculations were used to obtain information about ageing conditions and phosphorus compounds formed during ageing.
Phosphorus decreased the catalytic activity and the characteristic surface areas of the catalysts. Addition of calcium to a phosphorus-poisoned catalyst was found to have even a regenerating effect on the catalysts' activity. The poisoning methods developed in this study resulted in the same phosphorus compounds as can be found in vehicle-aged catalysts. Phosphorus was identified as cerium, zirconium, aluminium, and titanium phosphates. Phosphorus was detected in zeolites, but phosphorus-containing compounds were not observed. Phosphorus poisoning takes place in the gas phase at high operating temperatures and with high oxygen and water contents. It was also shown that the role of phosphorus poisoning was more pronounced than the role of hydrothermal ageing alone. Phosphorus poisoning mainly affects the oxide components used in this study, not the noble metals.
The results can be utilized in the development of catalytic materials and catalyst compositions that can better tolerate phosphorus poisoning under hydrothermal conditions. The results can also be applied in evaluating the effects of phosphorus on different catalyst compositions and in estimating the age of commercial catalysts.
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Coffin, Aaron. "Efforts at Expanding the Scope of Peptides as Enantioselective Organic Catalysts." Thesis, Boston College, 2008. http://hdl.handle.net/2345/968.
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The development of peptides as catalysts for preparing optically active molecules is an ongoing investigation. Efforts at expanding the use of peptides are explored in two ways: investigating novel reactions in which peptides can act as asymmetric catalysts and through expanding the substrate scope of peptides in performing kinetic resolutions. Attempts at furthering the reaction scope of acylsulfonamide-containing peptides to act as BrØnsted acids through promoting the attack of 7-methyl oct-6-ene-1-tosylaziridine (9) by an internal π-nucleophile are discussed herein. Also reported is the use of pentameric peptides containing a π(-methyl)histidine residue in the kinetic resolution of the primary alcohol 4-hydroxymethyl cyclopent-2-enone (76) and the secondary aliphatic alcohol 2- pentanol. Moderate selectivities were observed in the kinetic resolution of 4-hydroxymethyl cyclopent-2-enone (76) and promising results were obtained in the initial screening of catalysts for the resolution of 2-pentanolThesis (MS) — Boston College, 2008
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
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Malm, Christian [Verfasser]. "Catalyst Substrate Interaction of Organo Phosphate Brønsted Acid Catalysts with Imines / Christian Malm." Mainz : Universitätsbibliothek der Johannes Gutenberg-Universität Mainz, 2020. http://d-nb.info/1223379434/34.
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Zhang, Zhiwei. "Oxygen reduction on lithiated nickel oxide as a catalyst and catalyst support." Case Western Reserve University School of Graduate Studies / OhioLINK, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=case1057093196.
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Day, Craig. "Efficient New Routes to Leading Ruthenium Catalysts, and Studies of Bimolecular Loss of Alkylidene." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/38675.
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Olefin metathesis is an exceptionally versatile and general methodology for the catalytic assembly of carbon-carbon bonds. Ruthenium metathesis catalysts have been widely embraced in academia, and are starting to see industrial uptake. However, the challenges of reliability, catalyst productivity, and catalyst cost have limited implementation even in value-added technology areas such as pharmaceutical manufacturing. Key to the broader adoption of metathesis methodologies is improved understanding of catalyst decomposition. Many studies have focused on phenomenological relationships that relate catalyst activity to substrate structure, and on the synthesis of new catalysts that offer improved activity. Until recently, however, relatively little attention was paid to catalyst decomposition. The first part of this thesis explores a largely overlooked decomposition pathway for “second-generation” olefin metathesis catalysts bearing an N-heterocyclic carbenes (NHC) ligand, with a particular focus on identifying the Ru decomposition products. Efforts directed at the deliberate synthesis of these products led to the discovery of a succinct, high-yielding route to the second-generation catalysts.
Multiple reports, including a series of detailed mechanistic studies from our group, have documented the negative impact of phosphine ligands in Ru-catalyzed olefin metathesis. Phosphine-free derivatives are now becoming widely adopted, particularly in pharma, as recognition of these limitations has grown. Decomposition of the phosphine-free catalysts, however, was little explored at the outset of this work. The only documented pathway for intrinsic decomposition (i.e. in the absence of an external agent) was -hydride elimination of the metallacyclobutane (MCB) ring as propene. An alternative mechanism, well established for group 3-7 and first-generation ruthenium metathesis catalysts, is bimolecular coupling (BMC) of the four-coordinate methylidene intermediate. However, this pathway was widely viewed as irrelevant to decomposition of second-generation Ru catalysts. This thesis work complements parallel studies from the Fogg group, which set out to examine the relevance and extent of BMC for this important class of catalysts. First, -hydride elimination was quantified, to assess the importance of the accepted pathway. Even at low catalyst concentrations (2 mM Ru), less than 50% decomposition was shown to arise from -hydride elimination. Parallel studies by Gwen Bailey demonstrated ca. 80% BMC for the fast-initiating catalyst RuCl2H2IMes(=CHPh)(py)2 GIII. Second, the ruthenium products of decomposition were isolated and characterized. Importantly, and in contrast to inferences drawn from the serendipitous isolation of crystalline byproducts (which commonly show a cyclometallated NHC ligand), these complexes show an intact H2IMes group. This rules out NHC activation as central to catalyst decomposition, suggesting that catalyst redesign should not focus on NHC cyclometallation as a core problem. Building on historical observations, precautions against bimolecular coupling are proposed to guide catalyst choice, redesign, and experimental setup.
The second part of this thesis work focused on the need for more efficient routes to second-generation Ru metathesis catalysts, and indeed a general lack of convenient, well-behaved precursors to RuCl2(H2IMes). This challenge was met by building on early studies in which metathesis catalysts were generated in situ by thermal or photochemical activation of RuCl2(p-cymene)(PCy3) in the presence of diazoesters. Such piano-stool complexes (including the IMes analogue) have also been applied more broadly as catalysts, inorganic drugs, sensors, and supramolecular building blocks. However, RuCl2(p-cymene)(H2IMes), which should in principle offer access to the RuCl2(H2IMes) building block, has been described as too unstable for practical use. The basis of the instability of RuCl2(p-cymene)(H2IMes) toward loss of the p-cymene ring was examined. Key factors included control over reaction stoichiometry (i.e. limiting the proportion of the free NHC), limiting exposure to light, and maintaining low concentrations to inhibit bimolecular displacement of the p-cymene ring. A near-quantitative route to RuCl2(p-cymene)(H2IMes) was achieved using appropriate dilutions and rates of reagent addition, and taking precautions against photodecomposition. This approach was used to develop atom-economical syntheses of the Hoveyda catalyst, RuCl2(H2IMes)(=CHAr) (Ar = 2-isopropoxybenzylidene) and RuCl2(H2IMes)(PPh3)(=CHPh), a fast-initiating analogue of GII. Related p-cymene complexes bearing bulky, inflexible imidazolidene or other donors may likewise be accessible.
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Aydilek, Emre, and Ali Eroglu. "Ulvsunda as Urban Catalyst." Thesis, KTH, Stadsbyggnad, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-144870.
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Bohannon, Cermetrius Lynell. "The Urban Catalyst Concept." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/9954.
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Urban catalysts are new redevelopment strategies comprised of a series of projects that drive and guide urban development. Redevelopment efforts in the past, such as urban renewal and large-scale redevelopment projects, have often jeopardized the vitality of downtowns. The difference between the urban catalyst and these redevelopment strategies is that catalytic redevelopment is a holistic approach, not a clean-slate approach, to revitalizing the urban fabric. Many cities have considered urban catalysts as a means for revitalization. Among the most noted catalytic projects are sports stadiums and arenas: however not all catalytic projects have to be designed at such a grand scale, nor do all cities possess a threshold of support to successfully sustain such developments.
This thesis design project examines the significance of the urban catalyst as a means of urban revitalization. The urban catalyst theory says design can be linked to place through the study of contextual factors in urban design. These factors include: morphological, social, functional, perceptual, visual, and temporal. For the urban catalyst to respond to its setting it also must possess a strong sense of place and authenticity.
Each component of my research supports my position that each city has unique attributes that can serve as basic models or seeds for urban redevelopment. These components are used as a basis for developing a design framework that is applied to two sites in Memphis, Tennessee.
This position is tested through the contextual analysis and design of two projects that are of major significance to Downtown Memphis, Tennessee. The first demonstrates the role that Court Square plays as a critical social and spatial element in the revitalization of the center city. The second is the revitalization of the South Side Neighborhood, an area full of history and character.Master of Landscape Architecture
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Ralphs, Kathryn Louise. "Catalyst synthesis by mechanochemistry." Thesis, Queen's University Belfast, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709699.
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Irman, Svraka, and Österdahl Wetterhag Linus. "Model Based Catalyst Control." Thesis, Linköpings universitet, Fordonssystem, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-158634.
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A one dimensional discretized model of a two brick three way catalyst (TWC) system was developed and implemented in MATLAB, Simulink and TargetLink in collaboration with Volvo Cars and Linköpings Universitet - ISY. The purpose of this thesis was to increase system understanding and create a model based TWC control for further development at Volvo Cars. A total of 50 states were modelled, including emission concentrations (O2, CO, C3H6, C3H8, H2, NOx, CO2, H2O), temperature and oxygen buffer level (OBL). A model based control structure was implemented in the form of five separate PID-controllers enabling possibilities to control the OBL of each separate slice of each brick individually and through simple reference handling. The control structures includes anti-windup, feedforward control and feedback safety for model reset during sensor indication of leakage. Specific equipment and software used included MATLAB, Simulink, TargetLink, Volvo SULEV30 TWC and testing rigs. Overall increase in system understanding was achieved in comparison with contemporary TWC modelling and control, as well as sufficient system performance in regard to estimate emissions, simulation duration and pedagogical value. Concluding thoughts of the thesis revolve the complexity of the actual TWC modelling, parameter estimation as well as control. The model presented in this thesis has great potential of describing TWC systems but with great effort during parameter estimation. With ECU performance available in temporary vehicle production year 2019, a complex model may be combined with a simple control strategy whilst a simple model may be combined with a complex control strategy.
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Bjoerkert, U. Stefan. "High temperature COâ†2 permselective planar membranes." Thesis, University of Warwick, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340092.
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Kim, Kyungduk. "Novel Nanocatalyst for the Selective Hydrogenation of Bio-Oil Model Compounds." Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/16353.
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This thesis focuses on the understanding the effect of various factors, such as physical structures of metal particles, chemical composition of supports and metal-support interactions, on the catalytic performance of Pd or Pt nanocatalysts for hydrodeoxygenation (HDO) of bio-oil model compounds. The first part of the thesis addressed the alternative catalyst synthesis strategy based on emerging double-flame spray pyrolysis method (FSP), which was able to tune the catalytic properties of nanocatalysts without changing their precursors and chemical compositions during the synthesis. A series of Pd catalysts on the silica-alumina supports, SiO2- , and Al2O3 supports have been synthesized with the tunable surface properties within micro-seconds. The characterization results showed that various flow rates of precursors and gases used for the synthesis of catalysts influenced the formation of the catalyst structures and further change the surface acidity of catalysts due to the correlation between acidity and structure, but, the flow rates did not influence the electronic properties of Pd particles. Therefore, the higher conversion but the similar chemoselectivity have been reached in the hydrogenation of the bio-oil model ketone compound-acetophenone The second part is to identify the dominant effects from size of metal catalysts (under uniform shape and face) or the support acidity in the hydrodeoxygenation of the bio-oil model compounds of acetophenone, benzaldehyde, and butyrophenone. The uniform cubic Pd particles with different size (8, 13, and 21 nm) have been synthesized and loaded on the most popular supports (SiO2-, Al2O3-, and silica-alumina) with various functional groups and acidity. The results showed different acidities on the supports (Brønsted acidic site for Silica-alumina, Lewis acidic site for Al2O3-, and non/weak silanol OH group for SiO2- support) could not influence the chemoselectivity of the reaction but effected the conversion obviously. The particle size has more significant influence than the acidity. The smallest (8nm) Pd particle catalysts regardless of kinds of supports revealed the highest conversion for the hydrogenation the bio-oil model compounds. The third part focused on the influence of various types of catalysts with different acidities, chemical composition, and metal-support interaction on enantioselective hydrogenation of several model compounds in two reaction systems: 1). Pt-cinchrona modified system, and 2). Pd-(S) proline modified system. The result indicated acidic supports promoted the both conversion and enantioselectivity. Specially, Pd/SA made by double-FSP method, which has the highest Brønsted acid sites, showed 100 % conversion of isopherone on 60 min with 99% ee values.
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Patterson, Veronica A. "The effects of carbon deposition on catalyst deactivation in high temperature Fischer-Tropsch catalysts." Thesis, University of St Andrews, 2012. http://hdl.handle.net/10023/3086.
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In this work, carbonaceous deposits on spent HTFT catalysts were investigated. This research was required in order to better understand the observed loss in productivity observed in the industrial reactors, with the aim of improving the economy of the HTFT process. A host of complementary techniques were employed to systematically determine the composition of a typical catalyst recovered from a reactor. Spent HTFT catalysts are comprised of magnetite and a mixture of iron carbides as well as adsorbed hydrocarbon products (soft carbon) and hard carbon. Reaction initiates at the particle surface and along the promoter-rich grain boundaries toward the core of the grains. A partially reacted particle would therefore have a core-shell structure, with magnetite representing the unreacted region of the catalyst. The reacted region consists of a porous carbonaceous matrix with soft carbon and carbide crystallites nestled in this matrix. The hard carbonaceous species is a mixture of polymeric carbon and polycyclic aromatic hydrocarbons. The particle structure is linked to the sample preparation method and an alternative method yielding catalyst particle with uniformly distributed promoter elements could be beneficial. Investigating carbonaceous species is a complex process, and development of a fresh methodology would aid in the quest for insight into the nature of carbonaceous species in various systems. A new approach which entails a combination of the traditional techniques combined with MALDI-TOF MS enabled a deeper investigation. Additional aspects such as the molecular weight distributions along with known information about crystallinity and morphology of the catalyst provide a comprehensive study of carbonaceous material. Polymeric carbon and very large polycyclic aromatic hydrocarbons constitute hard carbon and can be observed with minimal sample preparation procedures. The evolution of the HTFT catalysts was investigated as a function of time-on-stream. This enabled us to study the effects of increasing amounts of hard carbon on the activity and the chemical and physical properties of the catalysts. The catalyst activity was found to decrease with increasing hard carbon content, although the effect of carbon deposition cannot be distinguished from phase transformation (oxidation) which occurs simultaneously. A method to quantify the amount of hard carbon, which progressively builds up on the catalyst, was demonstrated. This required a great deal of method development, which provides a platform for future investigations of these catalysts. Importantly, it allows predictions of the amounts of carbon that will be deposited after a certain reaction time. This allows more efficient regulation of catalyst replacement. The production of fine carbon-rich particles in the industrial reactor poses a major problem in the process. Carbon deposition leads to an increase in particle diameter with time on-stream. Permissible levels of hard carbon were identified, beyond which the mechanical strength of the catalyst particles deteriorate. This leads to break-up of the particles and therefore fines formation. The surface area and pore volume generally increase with progressive deposition of hard carbon, while the bulk density of the catalyst material exhibits a linear decrease with carbon build-up. A mechanism is proposed for hard carbon formation which apparently occurs through the dissociative adsorption of CO to form a carbon monolayer. This is followed by polymerisation of the carbon atoms. Meta-stable interstitial carbides are formed at the iron-carbon interface. Owing to a carbon concentration gradient between the top of the surface and the bottom of the metal or carbide particle, carbon diffusion across the crystal (carbide decomposition) and grows as a PAH molecule lifting the iron carbide away from the particle. As this corrosion process is intrinsic to iron-based catalysts, a catalyst that contains sulphur is proposed for future development.
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Fiske, Thomas Haukli. "Correlation of Catalyst Morphology with Attrition Resistance and Catalytic Activity of Fischer-Tropsch Catalysts." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for kjemisk prosessteknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-22778.
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Three alumina based support materials for the Fischer-Tropsch synthesis (FTS) catalyst has been prepared and investigated. The three support materials were prepared in order to obtain different mechanical strengths, henceforth denoted weak, medium and strong support. Magnesium modified γ-alumina support material calcined at 950°C and 1050°C were prepared as the medium and strong support respectively, whereas the unmodified alumina was used as the weak support. The modified support materials were both prepared by the incipient wetness impregnation method to obtain 10 wt .% Mg. Several batches were prepared to gain enough material for the planned experiments.Each of the support materials were subject to one crushing process in order to try to alter the particle morphology. The chosen method was determined based on the results from the specialization project. In this project, one method gave a larger change in morphology than other methods. Therefore a ball mill was the method of choice. Unprocessed samples and samples subjected to the ball mill for the three different materials were tested for attrition in an attrition rig, and characterized in terms of morphology using a particle analyzer. The different fractions were also analyzed with respect to particle morphology using an environmental scanning electron microscope (ESEM). FTS catalysts with 12 wt. % Co and 0,5 wt. % Re were prepared from the weak and the medium support materials, both unprocessed and milled fractions, using the incipient wetness impregnation. These four catalyst samples were tested for dispersion using a chemisorption experiment, and for activity and selectivity using a dedicated setup. Results from the particle analyzer showed that the morphology had not been altered as much as expected. Most change in shape occurred for the medium strength support material, but the observed alteration was much less than observed for the same experiment in the specialization project. For the weaker and stronger support, only a slight change was observed, and for the strong support material this change was in the direction of rounder particles. This is probably due to the excellent mechanical strength of the strong support, which leads to grinding of the kinks and corners of the particles and not the breakage of whole particles to smaller and more uneven fragments. With such relative small differences in morphology between the unprocessed and the milled materials, correlations of morphology with other parameters are difficult to obtain. The same correlation as from the specialization project, with rounder particles having a higher attrition resistance, was observed. A slight degree of correlation was also found between particle morphology and dispersion, where more uneven particles gave a slightly higher value of cobalt dispersion.
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Jones, Rebecca S. "Carbon Dioxide as a Benign Solvent for Homogeneous Catalyst Recovery and Recycle." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/11641.
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We have successfully investigated the use of CO2 as a miscibility switch to create an environment in which we can run a homogeneously catalyzed reaction while maintaining a heterogeneous separation. We explored the use of this technique with fluorous biphasic systems, a fluorous solid support, and aqueous biphasic systems.
In the case of the fluorous systems, CO2 was added to induce solubility of the fluorous catalyst. When the reaction was completed, CO2 was vented and the system returned to a biphasic state, making the separation easy.
For the aqueous biphasic systems, the organic phase is chosen such that it is fully miscible with water at ambient conditions. Examples include acetonitrile, THF, and dioxane. The addition of CO2 reduces the polarity of the solvent and causes a phase split. The recovery of the water-soluble catalyst is once again heterogeneous.
The application to aqueous biphasic systems is the most exciting studied. Aqueous biphasic systems are used industrially in the hydroformylation of propylene. With our technique, these systems can be extended to more hydrophobic substrates. We have shown a rate increase of 65 fold and 99% product recovery at modest pressures for the hydroformylation of 1-octene.
These aqueous biphasic systems also show much promise in the arena of enzyme catalyzed reactions. We can create an environment in which the enzyme kinetics will no longer be mass transfer limited.
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Mikus, Malte Sebastian. "Mechanistic Studies, Catalyst Development, and Reaction Design in Olefin Metathesis:." Thesis, Boston College, 2019. http://hdl.handle.net/2345/bc-ir:108382.
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Thesis advisor: Amir H. HoveydaChapter 1. Exploring Ligand Effects in Ruthenium Dithiolate Carbene Complexes. Ruthenium dithiolate metathesis catalysts discovered in the Hoveyda group have been a valuable addition to the field of olefin metathesis. While the catalyst shows unique selectivity and reactivity, quantifying and mapping key interactions in the catalyst framework to elucidate and explain causes is difficult. We, therefore, decided to use the neutral chelating or monodentate ligand, controlling initiation, as a structural probe. By altering its properties and observing changes in the catalyst, we sought to deepen our understanding of these complexes. We established a trans influence series with over 20 catalysts and correlated the impact on catalyst initiation. Further, we show that in the case of strongly σ-donating and π-accepting ligands such as phosphites and isonitriles, the complex exhibits fluxional behavior. The catalysts ground state is elevated to such a degree that thiolate Ruthenium bonds become labile and rapidly exchange. While Ruthenium dithiolate catalysts were readily applied to metathesis polymerization, their use in the synthesis of small molecules was initially less forthcoming. Specifically, reactions involving terminal olefins lead to rapid catalyst deactivation and only low conversion. We were able to determine that the potential energy stored in the trans-influence between the thiolate ligand and the NHC can be released in a sulfur shift to reactive Ruthenium methylidene species. Since methylidenes are formed by reaction with terminal olefins, use of an excess of internal olefins can prevent their formation. Chapter 2. Harnessing Catalyst Fluxionality in Olefin Metathesis. Depending on its use, material requirements can vary significantly. Materials that can easily be adapted to a given application, for example by varying tensile strength, melting point or solubility, are desirable. Controlling the polymers tacticity (the adjacent stereocenters in a polymer chain) is a straight forward way to achieve just that. Ru dithiolate catalysts should give highly syndiotactic polymers due to their single stereocenter undergoing inversion during every metathesis step. The fluxional nature of the catalyst allows for control of polymer tacticity from 50% (atactic) to ≥95% syndiotacticity by changing monomer concentration. We determined the factors which are responsible for fluxionality and synthesized complexes that give either high or low levels of tacticity over a broader range of monomer concentration. Chapter 3. Harnessing Catalyst Fluxionality in Olefin Metathesis. The importance of fluorine-containing molecules is hard to understate, keeping in mind the surge of new methodologies for their synthesis and the medical breakthroughs they enable. However, efficient and practical syntheses of stereodefined alkenyl fluorides are rare. In this context, we have developed enantioselective boryl allylic substitution of allylic fluorides, which yield enantioenriched γ-alkenyl fluoride substituted allyl boronate esters. The reaction is catalyzed by Cu-based catalysts that are prepared in-situ and delivered as products with high yield and enantioselectivity. Mechanistic inquiry shows the reaction is not a concerted allylic substitution. An intermediate Cu alkyl complex is formed after the Cu boron addition is made to the double bond, which only slowly undergoes β-fluorine elimination in the presence of a Lewis acid
Thesis (PhD) — Boston College, 2019
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
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Richardson, John Michael. "Distinguishing between surface and solution catalysis for palladium catalyzed C-C coupling reactions: use of selective poisons." Diss., Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22704.
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This work focuses on understanding the heterogeneous/homogeneous nature of the catalytic species for a variety of immobilized metal precatalysts used for C-C coupling reactions. These precatalysts include: (i) tethered organometallic palladium pincer complexes, (ii) an encapsulated small molecule palladium complex in a polymer matrix, (iii) mercapto-modified mesoporous silica metalated with palladium acetate, and (iv) amino-functionalized mesoporous silicas metalated with Ni(II). As part of this investigation, the use of metal scavengers as selective poisons of homogeneous catalysis is introduced and investigated as a test for distinguishing heterogeneous from homogeneous catalysis. The premise of this test is that insoluble materials functionalized with metal binding sites can be used to selectively remove soluble metal, but will not interfere with catalysis from immobilized metal. In this way the test can definitely distinguish between surface and solution catalysis of immobilized metal precatalysts.
This work investigates three different C-C coupling reactions catalyzed by the immobilized metal precatalysts mentioned above. These reactions include the Heck, Suzuki, and Kumada reactions. In all cases it is found that catalysis is solely from leached metal. Three different metal scavenging materials are presented as selective poisons that can be used to determine solution vs. surface catalysis. These selective poisons include poly(vinylpyridine), QuadrapureTM TU, and thiol-functionalized mesoporous silica. The results are contrasted against the current understanding of this field of research and subtleties of tests for distinguishing homogeneous from heterogeneous catalysis are presented and discussed.
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Wang, Xia. "Artificial Photosynthesis : Carbon dioxide photoreduction and catalyst heterogenization within solid materials." Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLET025/document.
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Dans le contexte du réchauffement climatique et de l’usage abusif de combustibles fossiles, la recherche de sources d’énergie propres et durables est l’un des défis les plus importants de notre époque. Récemment, le stockage d’énergie solaire par la réduction de CO2 a fait l’objet d’un nouvel intérêt. Bien que la réduction de CO2 en carburants liquides ou gazeux soit une question à la fois fascinante et fondamentale, sa mise en œuvre dans les dispositifs technologiques reste très difficile à cause de la grande stabilité de CO2 et du caractère endergonique de sa transformation. On outre, les réactions impliquent multiples électrons et protons et ainsi demandent des catalyseurs efficaces et stables pour diminuer les barrières cinétiques importantes.Cette comprend deux parties. Après une introduction, la première partie décrit des études sur des catalyseurs homogènes en combinaison avec un photosensibilisateur, soit séparément soit connecté par liaison covalente. Grâce à la possibilité de les modifier par synthèse et à leur facile caractérisation, les photosystèmes moléculaires homogènes sont plus modulables et peuvent permettre un meilleur contrôle de la sélectivité des réactions et l’étude des mécanismes réactionnels.Cependant, les catalyseurs moléculaires ne peuvent être facilement transposés pour des applications à plus large échelle dans un contexte industriel. En effet, les catalyseurs homogènes sont moins stables et plus difficilement recyclables que les catalyseurs hétérogènes. Dans ce contexte, l’intégration de catalyseurs moléculaires au sein d’un support solide a l’avantage de maintenir leur activité catalytique tout en permettant une séparation et un recyclage plus faciles. La deuxième partie de cette thèse porte donc sur l’immobilisation de catalyseurs moléculaires dans les matériaux. Le but ultime de cette thèse est d’incorporer à la fois le catalyseur et le photosensibilisateur dans le support solideIn the context of global warming and the necessary substitution of renewable energies (solar and wind energy) for fossil fuels, efficient energy-storage technologies need to be urgently developed. Recently, energy storage via the reduction of CO2 has seen renewed interest. Although reduction of CO2 into energy-dense liquid or gaseous fuels is a fascinating fundamental issue, its practical implementation in technological devices is highly challenging due to the high stability of CO2 and thus the endergonic nature of its transformation. Furthermore, the reactions involve multiple electrons and protons and thus require efficient catalysts to mediate these transformations.The objective of this thesis is to investigate different strategies for the storage of solar energy in chemical compounds, through visible-light-driven CO2 reduction. This thesis comprises of two main parts. After an introduction, the first part describes the investigation of homogeneous catalysts in combination with a photosensitizer, either separately or connected covalently. Due to the easily-tunable synthesis and facile characterization of molecular catalysts, homogeneous photosystems are more controllable and can give deep insight into product selectivity and mechanistic issues.With regards to future applicability, however, homogeneous catalysis often suffers from additional costs associated with solvents, product isolation and catalyst recovery, amongst other factors. The integration of molecular catalysts into solid platforms offers the possibility to maintain the advantageous properties of homogeneous catalysts while moving towards practical system designs afforded by heterogeneous catalysis. The second part of this thesis is therefore the immobilization of molecular catalysts within solid materials, namely MOFs and PMO. The ultimate goal of this thesis is to incorporate both catalyst and photosensitizer into the solid support
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Todd, Richard. "Catalyst and monomer design : targeting polymer properties via organic catalysed ring opening polymerisation." Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/62045/.
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The work undertaken in this thesis focuses on the synthesis of biodegradable materials with desirable properties via the organic catalysed ring opening polymerisation (ROP) of cyclic monomers. Influence over the resulting polymer properties is obtained either through the careful design of catalyst or monomer. Chapter 1 reviews organic catalysts that have been developed for ring opening polymerisation, focussing on particular advantages and disadvantages of each and providing an overview of compatible types of cyclic monomers. (-)-Sparteine in conjunction with a co-catalyst is capable of synthesising isotactic PLA with very few stereoerrors, but its sudden commercial unavailability has led to a need for a replacement. Chapter 2 therefore focuses on the synthesis of benzyl bispidine, a (-)-sparteine analogue, demonstrating its almost identical behaviour as a ring opening polymerisation catalyst to produce polymers with optimal properties from lactide. Post-polymerisation provides access to functionalities not compatible with ROP, and allowing careful tailoring of polymer properties. Whilst a range of cyclic carbonate monomers have been designed to provide this ability after ROP, poly(carbonate)s with only low glass transition have been obtained. Chapter 3 describes the synthesis of 9-vinyl-2,4,8,10-tetraoxaspiro[5.5]undecan-3-one (VDC), a sterically bulky, vinyl functional cyclic carbonate and its subsequent ROP and thiol-ene functionalisation to yield functional poly(carbonate)s with improved thermal properties. In Chapter 4, work is undertaken to tailor the glass transition temperature of functional poly(carbonate)s. Copolymers of VDC with the allyl functional cyclic carbonate allyl 5-methyl-2-oxo-1,3-dioxane-5-carboxylate (MAC) are synthesised to demonstrate the ability to produce poly(carbonate)s with a predetermined glass transition temperature after post-polymerisation functionalisation depending on the initial monomer feed ratio. In Chapter 5 the results from the previous chapters are discussed, with the experimental data obtained for these chapters provided in Chapter 6.
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Elliott, Paul. "Mixing and crystallisation conditions in supported nickel catalyst preparation and their influence on catalyst." Thesis, University of Birmingham, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633086.
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The results are reported of an investigation into the influence of preparative conditions on catalyst performance, using silica-supported nickel as a model system. Nickel(Il)dimethylglyoximate was precipitated from aqueous solution in the presence of silica in a stirred mixing vessel. After filtration, washing and drying, reduction with hydrogen produced a catalyst of metallic nickel supported on silica. Catalysts thus prepared were characterised according to nickel crystallite size, specific metal surface area, reducibility, and specific catalytic activity. Varying the precipitation conditions enabled the relationship between preparative parameters and catalytic performance to be examined. The crystal size distribution of the Nickel(Il)dimethylglyoximate catalyst precursor was dependent upon a variety of precipitation parameters, but the properties and performance of the final catalyst were found to be independent of the preparation conditions. The reduction of nickel(H)dimethylgloximate by heating in hydrogen is accompanied by a sublimation process. This vapour-phase redistribution of the material prior to reduction is believed to be responsible both for the exceptionally high surface areas (>200m 2 /gNi) observed for catalysts prepared by this route, and for the discovered lack of correlation between catalytic activity and preparation conditions.
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Alaje, Taiwo Olubunmi. "Nitrogen doped highly ordered mesoporous carbon as catalyst and catalyst support for oxygen reduction." Thesis, University of Newcastle upon Tyne, 2016. http://hdl.handle.net/10443/3473.
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Fuels such as hydrogen, produced from renewable resources and efficiently utilized in environment friendly fuel cells are crucial to long term energy security. However, the lack of cost-effective catalysts, with a performance similar to that of platinum, is a major obstacle to the development of the fuel cell technology. This work researched cheap and environmental friendly oxygen reduction catalysts, based on carbon, which can replace platinum for oxygen reduction reaction (ORR) in the cathode of alkaline and microbial fuel cells. Nitrogen doped mesoporous carbon was prepared by pyrolyzing 1,2-diaminobenzene in a template of highly ordered mesoporous silica (KIT-6) at 700, 800 and 900 oC. Manganese oxides are active catalysts for ORR and as they are an earth abundant metal with widespread availability, this offsets a key drawback of the platinum group metals (PGM). A simple chemical deposition method (using KMnO4) and physical deposition followed by heat treatment (using Mn(NO3)2) was used to prepare amorphous and crystalline manganese oxides which were separately deposited on ordered mesoporous nitrogen doped carbon (OMNC) and on ordered mesoporous carbon (OMC) without nitrogen doping respectively. The catalysts were characterized by Transmission Electron Microscopy (TEM), X-ray powder diffraction (XRD), Raman Spectroscopy, X-Ray Photoelectron Spectroscopy (XPS) and nitrogen adsorption-desorption. Cyclic voltammetry and linear sweep voltammetry (LSV) with a rotating-ring disk electrode (RRDE) were used for electrochemical characterisation of the iv oxygen reduction reaction (ORR). They were also tested as cathode catalysts in a microbial fuel cell. The best catalysts in alkaline media (0.1 M KOH) were amorphous manganese oxide on OMNC and OMC. They had onset potentials of 1.04 V and 1.05 V (RHE); half-wave potentials of 0.83 V and 0.82 V (RHE) respectively. This behaviour may be because the amorphous oxide maintained the ordered pore structure of the catalysts by depositing a thin coating of nanoparticle catalysts within them, thus causing a fast three phase reaction and excellent catalyst utilization. In the microbial fuel cell, the best catalysts were the amorphous MnO2 on OMC and on nitrogen doped carbon pyrolyzed at 900oC with equal power densities of.
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Ivaldi, Chiara. "Hybrid catalysts based on N-heterocyclic carbene anchored on hierarchical zeolites." Doctoral thesis, Università del Piemonte Orientale, 2021. http://hdl.handle.net/11579/127848.
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With the aim of preparing Class II hybrid, based on strong chemical bonds between the organic and inorganic building units, hierarchical inorganic zeotypes, which retain the bulky microporous structure but possess an additional mesoporous network improving mass transport to internal active sites, represent a viable alternative to microporous and mesoporous materials to host organic functionalities, rendering a new and promising class of organic-inorganic hybrid catalysts to perform cascade and tandem reactions. The high mechanical and thermal stability of hierarchical materials, as well as their resistance to structural changes in the presence of organic reactants and solvents, ensure flexibility in the grafting methodologies and in a wide range of applications. Moreover, the possibility of tuning their textural hydrophobic/hydrophilic and acidic properties, together with the speciation of the active sites, allow to maximise conversion and selectivity towards the desired products. In light of the foregoing, the Ph.D. research activity was initially focused on the optimization of different synthetic strategies to prepare hierarchical zeotype catalysts. Subsequently, optimised hierarchical materials were selected and used as inorganic support to covalently anchor different organic functionalities. The as-obtained hierarchical porous organic-inorganic hybrid catalysts were deeply characterized, using a multi technique approach and their catalytic activity was evaluated in industrially-relevant reactions. Alongside, in order to get a deeper insight in the nature of organic-inorganic interface in hybrid materials, the influence of silicodactyly (i.e. number of hydrolysable alkoxy groups used by the organosilane to grab the inorganic surface) and silicopodality (i.e. number of alkyl chains through which the organosilane is anchored to the surface) in the design of a Class II hybrid catalyst was investigated through a combined experimental and computational approach.
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Lummiss, Justin Alexander MacDonald. "Olefin Metathesis: Life, Death, and Sustainability." Thesis, Université d'Ottawa / University of Ottawa, 2015. http://hdl.handle.net/10393/32277.
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Over the past 15 years, ruthenium-catalyzed olefin metathesis has emerged as a cornerstone synthetic methodology in academia. Applications in fine-chemicals and pharmaceutical manufacturing, however, are just beginning to come on stream. Industrial uptake has been impeded by economic constraints associated with catalyst costs. These are due both to direct costs (exacerbated by intellectual property issues), and to further pressure exerted by the low turnover numbers attainable, and the need for extensive purification to remove ruthenium residues. From another perspective, however, these difficulties can be seen as arising from our rudimentary understanding of the fundamental organometallic chemistry of the Ru=CHR bond.
In particular, we know little about the nature and reaction pathways of the Ru-methylidene unit present in the active species that propagates metathesis, and in the catalyst resting state. We know slightly more about the ruthenacyclobutane species, but still too little to guide us as to their non-metathetical reaction pathways, their contribution to deactivation relative to the methylidene species, and potential work-arounds. This thesis work was aimed at improving our understanding of the reactivity, speciation, and decomposition of key ruthenium intermediates in olefin metathesis. A major focus was the behaviour and deactivation of species formed from the second-generation Grubbs catalyst RuCl2(H2IMes)(PCy3)(=CHPh) (S-GII), which dominates ring-closing metathesis. Also studied were derivatives of the corresponding IMes catalyst A-GIIm, containing an unsaturated Nheterocyclic
carbene (NHC) ligand. The methylidene complexes RuCl2(NHC)(PCy3)(=CH2) (GIIm) represent the resting state of
the catalyst during ring-closing and cross-metathesis reactions: that is, the majority Ru species
present during catalysis. Mechanistic studies of these key intermediates have been restricted,
however, by the low yields and purity with which they could be accessed. Initial work therefore
focused on designing a clean, high-yield route to the second-generation Grubbs methylidene
complexes S-GIIm and A-GIIm. These routes were subsequently expanded to develop access to
isotopically-labelled derivatives. Locating a 13C-label at the key alkylidene site, in particular,
offers a powerful means of tracking the fate of the methylidene moiety during catalyst
deactivation. Access to GIIm enabled detailed studies of the behaviour and decomposition of the Grubbs
catalysts. First, the long-standing question of the impact of saturation of the NHC backbone (i.e.
IMes vs. H2IMes) was examined. Dramatic differences in the behaviour of the two complexes
were traced to profound differences in PCy3 lability arising from the diminished π-acidity of the
IMes ligand. Secondly, the vulnerability of GIIm to nucleophiles was examined. This is an
important issue from the perspective of decomposition by adventitious nucleophiles in the
reaction medium during catalysis, but also reflects on substrate scope. For amine additives, the
dominant deactivation pathway was shown to typically involve attack on the resting-state
methylidene complex, not the metallacyclobutane, which has often been regarded as the most
vulnerable intermediate. In addition, the sigma-alkyl intermediate formed by nucleophilic attack
of displaced phosphine at the methylidene carbon was trapped by moving to the first-generation
complex, and using a nitrogen donor (pyridine) that cannot promote decomposition via N–H
activation pathways. Interception of this long-suspected species led to the proposal of “donorinduced”
deactivation as a general decomposition pathway for Grubbs-class catalysts.
Finally, the capacity of phosphine-free catalysts to overcome the shortcomings of the secondgeneration
Grubbs catalysts was demonstrated, in a case study involving application of crossmetathesis
(CM) to the synthesis of a high-value antioxidant. An efficient CM methodology was
developed for the reaction of renewable essential-oil phenylpropenoids with vinyl acrylates. This
work illustrates a new paradigm in sustainable metathesis. Rather than degrading unsaturated
feedstocks via metathesis (a process that can be termed “metathe[LY]sis”), it demonstrates how
metathesis with directly-functionalized olefins can be used to augment structure and function.
From the perspective of organometallic chemistry and catalyst design, key comparisons built
into this thesis are the effect of the NHC ligand (IMes vs. H2IMes) and its trans ancillary ligand
on the efficient entry into catalysis; the susceptibility to nucleophilic attack of the alkylidene
ligand (benzylidene vs. methylidene) vs. the metallacyclobutane; and the effect of replacing a
phosphine ancillary ligand with a non-nucleophilic donor.
From a practical standpoint, Chapter 2 brings new life to metathesis with the high-yield
synthesis of the resting state species, Chapters 3 and 4 examine the deactivation, or death, of the
methylidene complexes, and Chapter 5 establishes a new paradigm for olefin metathesis within
the context of sustainable synthesis.
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Di, Jiexun. "Development of highly active internal steam methane reforming catalysts for intermediate temperature solid oxide fuel cells." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:a36ce531-e7b2-48fb-a59b-dbca6b435643.
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Fuel processing is one of the essential parts for development of intermediate solid oxide fuel cells (IT-SOFC). Natural gas (methane) is considered as the most abundant and cost effective fuel for the production of hydrogen for IT-SOFC. The primary aim of this thesis is to use a novel precursor material—layered double hydroxide (LDH) – for developing a new type of cost effective, highly active and long lasting catalyst which can reform natural gas in IT-SOFC anode environment. Small amount of noble metals Pd, Rh and Pt are used as promoters to enhance the catalyst’s performance as while maintaining the cost relatively low. The research objectives are achieved by a series of studies including catalysts synthesis, characterisation and the catalytic activities. The thesis initially gives a comprehensive review on fuel cell and SOFC technology, steam methane reforming and reforming catalyst to provide better understanding of the research. Experimental studies include the effects of the synthetic conditions of the LDH precursors and thermal treatments on the physical, chemical behaviours and catalytic activities of the catalysts and promotional effects by noble metals. The LDH derived catalysts compositions, promoter quantities and operating conditions are optimised for the best performance in the IT-SOFC anode environment. A new method for the development of precursor sol for easy coating of the anode is developed and studied. The sol preparation is achieved by acid attack. The sol developed is found to produce better coating and has very high catalytic properties after activation. The catalysts developed were tested for their stability and self-activation ability to ensure its use in the commercial cells. The findings of the present study indicate that the catalysts developed show excellent catalytic performance and these catalysts have very high potential for further commercialisation in IT-SOFC.
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KAMYAB, ALI. "Preparation and evaluation of sulfided NiMo/γ-Al2O3 hydrotreating catalysts." Thesis, KTH, Skolan för kemivetenskap (CHE), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-190904.
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Four nickel-molybdenum catalysts were synthesized on gamma alumina with higher surface area and on NiMo catalyst was prepared using gamma alumina with lower surface area. Catalysts with higher-surface-area support were prepared by co-impregnation, sequential impregnation and adding phosphorous. Theses catalysts were calcined at 500 ͦC. Effect of higher calcination temperature was investigated by preparation of one catalyst calcined at 700 ͦC. Catalysts were thoroughly characterized via four characterization techniques. The hydrotreating activity of three catalysts was carried out in a micro reactor at high pressure and three different temperatures with Nynas vacuum middle distillate. Prior to the test, sulfiding was carried out to activate the catalysts. Hydrotreated-oil samples as products were analyzed to evaluate the activity and conversion of the catalyst. Also, the spent catalysts were characterized to evaluate the surface area characteristics and deactivation of catalysts. Addition of phosphorous to NiMo/gamma-Al2O3 improved the interaction between the metals and the support as well as reduced the coke formation as observed in scanning electron microscopy micrographs.
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El, Solh Tarek. "Heterogeneous catalyst for methane reforming." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0007/MQ30748.pdf.
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Buxser, Nathan E. "A catalyst for gradual change." PDF viewer required Home page for entire collection, 2008. http://archives.udmercy.edu:8080/dspace/handle/10429/9.
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