The Diesel Oxidation Catalyst (DOC) is a key component in the exhaust after-treatment system of diesel engines. In this study two aspects of a DOC were investigated: catalyst distribution and reactant species interactions. In the first part, the effect of an axial Pt distribution along a DOC was investigated by comparing a standard sample, with a homogeneous Pt distribution along the length, with a zoned sample, where the Pt was non-homogeneously distributed along the length. Temperature-programmed oxidation (TPO) and spatially-resolved gas-phase concentration measurement experiments were used to compare the CO, C3H6 and NO oxidation performance of the standard and zoned catalysts. Both catalyst types had the same total amount of Pt but different distributions. The zoned catalyst, with more Pt located in the upstream portion, showed better performance than the standard catalyst, especially at high total flow rate and when a mixture of the reactants were used. The superior performance of the zoned sample is due to a larger, localized exotherm in the upstream region, where more Pt is located, and a decrease in the self-poisoning effect downstream, where reaction light-off occurs. In addition, catalyst durability against thermal degradation was tested by exposing the whole catalyst (homogeneous aging) and part of the catalyst (heterogeneous aging) to high temperatures. In general, the zoned catalyst showed better performance than the standard catalyst after thermal aging, especially after heterogeneous aging. The reason for the superior performance of the zoned catalyst, especially after heterogeneous aging, is that the back of the catalyst, which is exposed to higher temperature, contains less Pt than the front; therefore, most of the Pt particles in the zoned catalyst were not affected by thermal aging. However, after homogeneous aging, the performance of the standard catalyst was better than the zoned catalyst at higher flow rate and temperature most likely due to the different sintering rates in the zoned sample compared to the standard one. In the second part of this research, the interactions between CO, C3H6, H2, and NO were tested over a commercial Pt/Al2O3 monolith sample by studying these reactions during ignition and extinction (warm-up and cool-down). Results showed that CO, C3H6, and NO inhibit their own oxidation and each other’s oxidation due to the self-poisoning effect and competitive adsorption over active sites. In the case of a CO + C3H6 mixture, interesting CO and C3H6 oxidation trends were observed during the extinction phase. As the C3H6 concentration increased in the mixture, the catalytic activity of CO oxidation during the extinction phase decreased until it was actually poorer than that during the ignition phase. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed different C3H6 oxidation intermediates during the extinction phase on the catalyst surface, thus blocking active sites and lowering catalyst activity.

The racemic (±)-2,4-di-tert-butyl-6-(((2-(dimethylamino)cyclohexyl)(methyl) amino)methyl)phenol ((±)-(NNMeOtBu)H), (±)-2,4-di-tert-butyl-6-((2-(dimethylamino) cyclohexylamino)methyl)phenol ((±)-(NNHOtBu)H), and (±)-2-(((2-(dimethylamino) cyclohexyl)(methyl)amino) methyl)phenol ((±)-(NNMeOH)H) are chiral ancillary NNO proligands, which synthesis was adapted from a published procedure. Reaction of (±)-(NNMeOtBu)H ((±)-2), (±)-(NNMeOH)H ((±)-3) and (±)-(NNHOtBu)H ((±)-1) with ZnEt2 successfully yielded the corresponding zinc ethyl complexes (±)-5, (±)-6 and (±)-7 respectively; the enantiomerically pure (R,R)-5 was synthesized from (R,R)-2. NMR spectroscopy experiments and X-ray crystallography allowed identification of two stereoisomers for (±)-5, which were observed in solution and in the solid state. The two stereoisomers, 5-α and 5-β, are in equilibrium in solution, with 5-β being thermodynamically favored. The zinc ethyl complexes were found to be unreactive towards weakly acidic alcohols (methanol, ethanol, isopropanol). However, the zinc chloride complex (±)-(NNMeOtBu)ZnCl ((±)-8) and the zinc phenoxide (NNMeOtBu)ZnOPh ((±)-9 and (R,R)-9) could be isolated and characterized. Comparison of the reactivity of both (±)-5 and the reported L₁ZnEt (L₁ = 2,4-di-tert-butyl-6- {[(2'-dimethylaminoethyl) methylamino]methyl}phenolate) in presence of pyridine led to the proposal of a dissociative mechanism explaining the fundamental difference between the two zinc ethyl species. Polymerization of rac-lactide catalyzed by 9 showed that the complex, in its racemic or enantiomerically pure version, has a slow activity and is not stereoselective.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23910号 / 工博第4997号 / 新制||工||1780(附属図書館) / 京都大学大学院工学研究科材料化学専攻 / (主査)教授 中尾 佳亮, 教授 松原 誠二郎, 教授 杉野目 道紀 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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.

This dissertation research resulted in the development of a Fe based catalyst with Co as a co catalyst, and Ru and ZnO as promoters. The role of Cu and K as promoters and the effect of SiO2 as an alternate support to gamma- Al2O3 were also investigated. A series of Fe-based catalysts for Fischer-Tropsch (F-T) synthesis were prepared. The different promoters were incorporated into the catalyst by impregnation The catalysts were characterized by several methods. The catalytic performance of these materials for F-T synthesis were investigated in a newly designed fixed bed reactor system in the gas phase. It should be noted that the three phase slurry bubble reactors systems are commercially preferred. The reaction conditions were varied for benchmarking the Fe-Zn-K/ gamma- Al2O3 catalyst and for the bimetallic Fe-Co-Zn/ gamma- Al2O3 catalyst and to identify optimal process parameters for further catalyst designs. The H2:CO ratio used in this study was 2. The newly designed catalysts showed significantly high activity towards CO conversion (>70 %), along with low selectivity towards CO2 (5 -15 %) and methane (ND - 3 %). The data show that varying the process conditions, it is possible to achieve narrow distribution of the liquid products. The results employing Fe-Zn-K catalysts showed that an increase in pressure increased the mean carbon chain length. In contrast, an increase in temperature resulted in a decline in the average carbon chain length. Increasing the feed flow rate, or in other words decreasing the residence time of the reactants and the intermediates, resulted in a decrease in the average carbon number in the product hydrocarbons. The evaluation of the effect of process conditions on the performance of Fe-Co-Zn catalysts revealed that the effect of pressure on the carbon chain length was reversed. Increasing the pressure from 250 to 350 psig decreased the carbon chain length. The increase in temperature, however, resulted in a decrease in the carbon chain length as observed in the Fe-Zn-K catalysts. Fe catalysts groups containing different proportions of Co were prepared. It was determined that an Fe:Co ratio of 4:1 is sufficient to obtain high CO conversions with a high selectivity towards liquid hydrocarbons. The hydrocarbon distribution on the other hand remained almost unchanged due to a change in the Co content. The use of silica, as opposed to alumina as the catalyst support, enhanced the CO conversion and the selectivity of the process towards liquid hydrocarbons. The methane and CO2 selectivities on both the supports remained unchanged. However, a significant difference in the liquid hydrocarbon distribution was observed. Addition of K to the catalyst resulted in a change in the liquid hydrocarbon distribution in that a slight increase in the heavier hydrocarbons was observed. A series of Fe4Co1Zn0.04 based catalysts for Fischer-Tropsch (F-T) synthesis, in which the different amounts of Ru are incorporated by the impregnation were also studied. The results showed the incorporation of Ru suppressed the CH4 formation at the cost of increasing the CO2 selectivity.

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.

Chiral phosphoric acids are bifunctional catalysts that have the ability to activate electrophiles and nucleophiles through hydrogen bonding, and they have been successful in catalysing highly enantioselective additions of a wide range of nucleophiles to imines. In most literature reports it is not frequently revealed how these catalysts impart enantioselectivity. Thus, the vast majority of time required for reaction development is expended on the optimisation of the catalyst features. The research described here explores the ability of relating computational derived catalyst parameters to enantioselectivity as a means to assess the catalyst features important for enantioinduction. The proposed features are evaluated computationally and summarised into simple qualitative models to understand and predict outcomes of similar reactions. In Chapter 1, I provide an overview of the progress and challenges in the development of chiral phosphoric acid mediated reactions. I highlight leading computational studies that have enabled a greater understanding of how the catalyst imparts reactivity and selectivity. In general, the studies focus on the most effective catalyst and do not do a detailed investigation into the effects of changing the substituents at the 3,3’ positions. Implicating steric effects from reasonably large groups as a key component in imparting enantioselectivity. However, it is clear that they have a more subtle effect. A large group is required but if it is too large poor or unusual results are obtained, making the correct choice of reaction conditions challenging. In Chapter 2, I develop a quantitative assessment of the substituents at the 3,3’ positions. I show in Chapters 3 and 4 that I can use rotation barriers in combination with a novel steric parameter, AREA(θ), to correlate enantioselectivity. By exploiting this finding, the catalyst features important for enantioselectivity can be identified, and this is validated by QM/MM hybrid calculations. Summarising these detailed calculations into a single qualitative model, guides optimal catalyst choice for all seventy-seven literature reactions reporting over 1000 transformations. These mechanistic studies have guided the design of a new catalyst with increased versatility, which is discussed in Chapter 5. Chapter 6 details my study into the effect of the hydroxyl group on the mechanism of transfer hydrogenation of imines derived from ortho-hydroxyacetophenone. I show, using detailed DFT and ONIOM calculations, that transition states of these reactions involve hydrogen bonding from both the hydroxyl group on the imine and the nucleophile’s proton to the phosphate catalyst. In Chapter 7, computational analysis is used to provide insight into the origins of enantioselectivity in chiral phosphoric acid catalysed Friedel-Crafts and Mannich reactions proceeding through monoactivation mechanisms. The final chapter contains an in-depth look into the stereoelectronic effects altering enantioselectivity in the silver-phosphate mediated spirocyclisation reaction involving aromatic ynones. In this study I show that enantioselectivity is governed by the non-covalent interactions between the aromatic group of the ynone and the 3,3’ substituent. I was able to propose synthetic modifications to the substrate used in this reaction, resulting in an improvement in enantioselectivity.

High performance catalyst supports and packing materials are playing an increasing role in many reactions and separations. The dispersion in packed bed reactors and separation columns can be reduced by the development of new packing structures having open and connected pore geometries. The application of new materials in High Performance Liquid Chromatography (HPLC) with sub 5 micron particle sizes are growing. These small particles offer better performance and improved bed and column efficiencies. Recently developed, twinned Alumina Nanosheets (TAN) are 2D/3D nanomaterials that offer promising open geometries for use as column packings and catalysts supports. They have a small particle size (4 um in length, 1 um in width and 0.1 um in thickness) and excellent flow-through capabilities. TANs have recently been used to successfully produce high throughput dynamic membranes. However, their resistance to compaction is unknown and thought to be limited. A technique was developed to reinforce the TAN nanomaterial. Two binder materials were tested as reinforcing agents; SiO2 and AlH6O12P3. The binder-reinforced TANs were then packed into columns. Eleven columns having a 4 cm initial packing length were assembled. Tracer injection studies were performed to investigate the flow behavior and dispersion in these columns. SEM images were also taken to characterize the particles before and after compaction. The best results were obtained using a binding solution containing 7.5 (wt%) SiO2. The binder SiO2 offered a better resistance to compaction than the AlH6O12P3. The Peclet (Pe) number for the columns ranged from 22 to 648. When the content of SiO2 increased from 0 to 7.5 (wt%), the columns showed an increase in the Pe number. When SiO2 increased from 7.5 to 20 (wt%), the columns showed a decrease in the Pe number. However, AlH6O12P3 did not present any relation between the binder content and the Pe number. The results of this work demonstrate that reinforced TANs, are a new type of material that offers a packing with an open pore structure and improved channel connectivity. The new reinforced material offers considerable potential in many applications such as catalysis and separations over conventional materials. If they are used as packing materials in HPLC columns or packed bed reactors, they can contribute to a higher separation efficiency or an enhanced conversion rate or productivity, bringing more advantages and benefits than ordinary packing materials.

Signal Amplification by Reversible Exchange, or SABRE, is a type of PHIP (ParaHydrogen Induced Polarization) pioneered by Duckett, Green, and co-workers where an organometallic catalyst is used to co-locate parahydrogen (pH2) and a molecular substrate to be hyperpolarized. Like traditional PHIP, SABRE is of interest because it is cost-effective, potentially continuous, scalable, and rapid (achieving polarization enhancement in seconds). However unlike traditional PHIP, SABRE does not require permanent alteration of the substrate to hyperpolarize it. In addition to achieving 1H polarizations of several percent, SABRE in microTesla fields has enabled the creation of ~10% polarization for heteronuclear (15N) spins. I will discuss on a series of novel catalysts that I developed in my Ph.D program. Firstly of all, a heterogeneous SABRE ("HET-SABRE") catalyst where catalytic moieties were tethered to solid supports. Although NMR enhancements were modest (5), this initial work showed the feasibility of the approach. Next, two types of nanoscale catalysts were created to explore SABRE at the interface between heterogeneous and homogeneous conditions. Nanoparticle and polymer comb variants were synthesized by covalently tethering Ir-based catalysts to support materials comprised of TiO2/PMAA (poly methacrylic acid) and PVP (polyvinyl pyridine), respectively, and characterized by AAS, NMR, and DLS. Following pH2 delivery to mixtures containing one type of "nano-SABRE" catalyst, a target substrate, and ethanol, up to ~(-)40-fold and ~(-)7-fold 1H NMR signal enhancements were observed for pyridine using the nanoparticle and polymer comb catalysts, respectively, following transfer to high field (9.4 T). These enhancements appear to result from intact particles and not from any catalyst molecules leaching from their supports. Unlike the case with homogeneous SABRE catalysts, high-field (in situ) SABRE effects were generally not observed with the nanoscale catalysts. The potential for separation and reuse of such catalyst particles is also demonstrated. Besides the effort on green chemistry of SABRE catalyst, I have been investigating the preparation of different variants of the "standard" SABRE catalyst--[IrCl(COD)(IMes)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; COD=cyclooctadiene)]--for performing SABRE in otherwise "pure" aqueous environments. Because of the poor aqueous solubility of SABRE catalysts, previous promising efforts have used co-solvents to achieve SABRE in aqueous/organic mixtures. However, I have found that the chemical changes that accompany this catalyst's activation also endow it with water solubility. Complete removal of the organic solvent following activation and subsequent re-constitution of the activated structure in deuterated water allowed up to ~(-)33-fold 1H signal enhancements to be obtained for nicotinamide. Additionally, I have investigated chemical alteration of the structure of the pre-activated catalyst to endow greater water solubility. PEGylation of the aromatic carbine moiety provided much greater aqueous solubility, but while SABRE-active in organic solutions, the catalyst lost activity in >50% water (an effect under ongoing study). As an alternative approach, synthesis of a di-Ir complex precursor where the COD rings have been replaced by CODDA (1,2-dihydroxy-3,7-cyclooctadiene) permits creation of a water-soluble catalyst [IrCl(CODDA)IMes] that enables aqueous SABRE in a single step without need for any organic co-solvent; the potential utility of the catalyst is demonstrated with the ~(-)32-fold enhancement of 1H signals of pyridine in water with only 1 atm of pH2. Taken together, these results support the utility of rational design for improving SABRE and HET-SABRE for applications varying from fundamental studies of catalysis to biomedical imaging. In the following, I also investigate different aspects of how catalyst structure can affect resulting SABRE enhancements, including the interplay of catalyst structure and temperature for optimal SABRE, as well as the confounding effects on catalyst activation. Results from the "standard" Ir SABRE catalyst (1)--[IrCl(COD)(IMes)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; COD=cyclooctadiene)]--are compared with those obtained with variants respectively created by synthetically replacing the -Cl moiety with 4-amino-pyridine (4AP, 2), (diphenylphosphino)ethylamine (DPPA, 3), triphenyl phosphine (TPP, 4), and tribenzyl phosphine (TBP, 5); a sixth variant (6) was serendipitously created by an alternate synthetic route for (1) that appears to result in a polymorph according to x-ray crystallography. Studies of activation rate found that (4) and (5) activated the fastest under pH2 exposure (~20 s, an order of magnitude faster than (1)); activation rate was inversely correlated with SABRE enhancement, with peak 1H polarization enhancement ( ranging from only ~(-)44 for (4) to nearly ~(-)1900 for (1) (or PH~6%) for pyridine at 9.4 T, and ~(-)240 for nicotinamide. Although (1) gave the overall highest  values as expected, other catalysts gave rise to better SABRE performance in other temperature regimes: Optimal temperatures varied significantly, e.g. ~273 K for (2) to ~310-320 K for (1); the optimal temperature for (6) was considerably lower (<273 K) than that for (1), despite the apparent structural similarity. Taken together, these results show that full optimization of SABRE enhancement for a given experiment (with respect to substrate, target nucleus, etc.) may require systematic variation of parameters including catalyst ligand choice and temperature (to modulate binding affinities and off rates with respect to relevant spin-spin couplings), in addition to pH2 partial pressure, flow rate, and magnetic field. Finally, some research on an ssNMR will be represented, to show the potential application of ssNMR on the coating detection.

ABSTRACT This thesis presents the results from research conducted on Fischer-Tropsch synthesis (FTS) in supercritical CO2 from syngas (H2:CO =1:1) typically produced from coal gasification and using a Fe-Zn-K catalyst. Experiments were conducted with syngas alone at different pressures (200 psi - 1050 psi) and temperatures (275, 350 and 375 oC). Experiments were also conducted with a syngas pressure of 200 psi and at different partial pressures of an inert diluent (N2) such that the total pressure varied from 200 psi to 1050 psi. Finally, experiments were conducted with CO2 as a diluent and at a syngas pressure of 200 psi. The CO2 partial pressure was increased from 0 psi to 1400 psi (non critical to supercritical conditions). The data show an enhancement in the hydrocarbon selectivity and reduction in the parasitic loss of carbon efficiency due to CO2 formation along with significant improvement in the conversion rates. The experiments were conducted in a unique reactor setup that can conduct gas phase or supercritical phase FT synthesis in both batch or flow modes. The use of the supercritical CO2 (ScCO2) inhibited both CH4 and CO2 selectivities while enhancing the rates of synthesis. In addition, the use of supercritical CO2 is expected to prolong the life of the catalyst presumably by removing the heat of reaction from the catalyst's surface and solubilizing the waxes that tend to deposit on the surface. Although not within the scope of this thesis, the products from such a reactor system can be easily separated without the need of an additional unit process simply by tuning the pressure and temperature. The product spectrum and the selectivities for the different products are presented for each set of experiments. The effects of process parameters such as temperature, pressure, N2 partial pressure, and CO2 partial pressure on the product spectrum are also discussed. The clear increase in CO conversion at H2:CO ratio of 1:1 in supercritical phase as compared to gas phase reaction, the decrease in CO2 and CH4 selectivity, and an overall shift in the product distribution towards higher hydrocarbons have been demonstrated. Thus the use of supercritical CO2 has the potential through the FT process to convert coal to liquid fuels using Fe based catalysts, especially since the reactions can be conducted in a two phase regime without losing the benefits of the 3-phase slurry reactor systems