This Dissertation investigates the kinetics of CO2 methanation over nickel and cobalt catalysts. Methanation was studied for both Ni/γ-Al2O3 and Co/ZrO2 catalysts, which were synthesised using an incipient wetness impregnation technique and subsequently characterised using analyses based on gas adsorption, XRD, TPR and thermogravimetry. Separately a CO hydrogenation reaction, the Fischer-Tropsch process, was modelled numerically to examine the influence of mass transfer in practical, commercial pellets of catalyst. The kinetics of methanation was investigated for Ni/γ-Al2O3 over a wide range of reactant partial pressures using a gradientless, spinning-basket reactor operated in batch mode and in a laboratory-scale, continuous fixed-bed reactor. Langmuir-Hinshelwood kinetic models were developed to represent the observed kinetics in each reactor: these models were then compared. For the batch reactor, a rate expression based the dissociation of a chemisorbed CO intermediate being the rate-limiting step was found to be consistent with the experimental results. However, results from the fixed-bed suggested that the hydrogenation of an adsorbed C atom determined the rate of reaction. These differences in the kinetics on Ni/γ-Al2O3 between the fixed-bed and batch reactors suggest that a Langmuir approach using a single, rate-determining step may not be representative across all conversions. The rate over the Co/ZrO2 catalyst was characterised in the fixed-bed reactor over a range of reactant partial pressures at temperatures between 433 K and 503 K. The rate was observed to be dependent on hydrogen partial pressure and temperature, with the rate increasing with both. Previous research has reported a wide range of values of the apparent activation energy, with a study suggesting it was sensitive to pressure. Accordingly, the apparent activation energy was investigated for pressure sensitivity over a range of pressures between 5 and 15 barg: it was found to be constant. The values determined (~88-91±8 kJ/mol) were notably consistent with those reported for CO hydrogenation on cobalt. Kinetic schemes based on Langmuir-Hinshelwood and power law equations were evaluated, with the results best described by a reaction scheme based on the carbide pathway, with a rate-determining step of CH hydrogenation. A reaction-diffusion model of the Fischer-Tropsch process in a 2-D hollow cylinder was developed and analysed across a range of Thiele moduli and the extents of error in both effectiveness factor and selectivity were quantified relative to one-dimensional sphere and slab analogues. The errors between 2-D and 1-D analogues were found to be most significant between Thiele moduli of ~0.25 and ~3. Hollow cylinder effectiveness factors were bounded by those of sphere and slab above and below Thiele moduli of ~0.75 and ~1.15 respectively for the conditions examined, with the effectiveness factors exceeding those of both sphere and slab models between these moduli. A comparison of the hollow cylindrical pellets against spheres of equivalent volume demonstrated that hollow cylinders provided improved fixed-bed performance, with improved effectiveness factors and selectivities due to the lowered diffusion lengths of the hollow cylindrical geometry.

Submitted to School of Chemical and Metallurgical Engineering, Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, South Africa in Fulfillment of the Award of the Degree of MSc (ENG) in Chemical Engineering 25 October 2016 / The motivation behind this study is the need to manage and reduce wastes, in particular waste tyre and biomass, while in turn recovering energy from these carbonaceous materials. These wastes were gasified to produce synthetic gas which served as a feed to the Fischer-Tropsch Synthesis process to produce hydrocarbons. The formed hydrocarbons can be used as fuels for different purpose like transportation, domestic and industrial heating systems. Cobalt supported on zeolite catalysts are used because of their high acidic sites present in the zeolite that can break the Anderson-Schultz-Flory polymerization kinetics and also because cobalt-based catalysts are preferred for low temperature Fischer-Tropsch (LTFT) synthesis process due to their negligible water and carbon dioxide formation as well as stability and life span. In this research, a bi-functional Co/H-ZSM-5 catalyst was synthesized, characterized and evaluated for direct production of hydrocarbons at different process conditions. The bi-functional catalyst was prepared by incipient wetness impregnation method of an aqueous cobalt solution as the source of cobalt metal onto an H-ZSM-5 zeolite support, thereafter dried at 120 °C and calcined at 400 °C to obtain the finished Co/H-ZSM-5 catalyst. Physicochemical analyses performed included, Nitrogen Physisorption at 77 K to determine the surface area, pore volume and size of the synthesized catalyst. Also the N2 adsorption was used to determine the adsorptive properties of the catalyst. X-ray diffraction at 2θ region between 10 to 90 ° by using Co-Kα radiation (λ=1.79026 Å) was used to determine the material crystallinity, structure and composition. For the morphology and elemental composition of the catalyst, a Scanning Electron Microscopy coupled with an Energy Dispersive X-ray Spectroscopy was used. Thermal stability of the catalyst was checked using a Thermal Gravimetric Analyzer to determine how the catalyst degraded with time when temperature was increased uniformly. Reducibility of the catalyst was determined by using Temperature Programmed Reduction equipment in a hydrogen environment from room temperature to 900 °C. Transmission Electron Microscopy was used to check the catalyst morphology, and the dispersion of the metal-oxide particles within the catalyst support. The bi-functional zeolite supported catalyst was found to possess a surface area of 292 m2/g, pore volume of 0.18 cm3/g and pore size of 2.83 nm. The catalyst morphology was found to be irregular and aggregated-circular shape with a particle size of about 2.5 ± 0.5 μm. The embedded cobalt-oxide particles were obtained to be about 8 ± 3 nm located closer to the surface of the support and were reduced to metallic cobalt of 25% composition, at 330 °C in a hydrogen rich environment with an expected hydrogen consumption of 133 %. The process conditions under study involved flow rate, pressure and temperature and synthetic gas of different H2/CO ratio. The Synthetic gas mixture was purchased from Afrox and prepared in a way to mimic or simulate the syngas mixture expected from gasification of the waste tyre and biomass. However the study mainly focused on Hydrogen, Carbon Monoxide and Carbon dioxide as the dominant constituents of a waste tyre produced syngas. The bi-functional, Co/H-ZSM-5 performance evaluation was compared to commercial Co/SiO2 catalyst under similar conditions. The performance evaluation and comparison was made based on conversion and selectivity at different conditions. The process conditions considered were a flow rate of 1200, 2400 and 3600 GHSV (ml/gcat.hr), a pressure of 2, 8 and 15 bar, Low Temperature Fischer-Tropsch (LTFT) process at 220 and 250 °C was used, with a syngas composition that included H2/CO ratio of 1.5, 2.5 and 2.5 with 5 % of CO2 present in the reactant feed. The combination of 2 bar, 1200 GHSV and temperature of 220 °C and 1.5 of ratio was considered as low process conditions. While the combination of 15 bar, 1200 GHSV, 250 °C and ratio of 2.5 was considered as high process condition. Three pre-calibrated GCs (two online and one offline) were used to analyze the reaction products and the feed and the integrated peak-data analyses was captured by the use of a Data Apex Chromatograph software package known as Clarity ® (v. 2.5). The captured and analyzed data was used to calculate conversion and selectivity according to the methods reported in literature. With regard to the effect of process conditions, at low process conditions, the bi-functional catalyst, Co/H-ZSM-5, resulted in a 3 % CO conversion, while the commercial Co/SiO2 catalyst, resulted in 15 % of CO conversion. However the bi-functional catalyst was more selective to gasoline range products and 16 % selectivity to C5 hydrocarbons was obtained and 79 % to C6+, as compared to selectivities of 4 and 75 % for C5 and C6+ respectively, for Co/SiO2 catalyst. Also Co/SiO2 was found to be more selective to Olefins, the undesired products, with a selectivity of about 91 % to C6+ hydrocarbons as compared to a selectivity of 87 % for C6+ hydrocarbon obtained by using the bi-functional Co/H-ZSM-5 catalyst. Methane production was high for the Co/SiO2 catalyzed reaction, (about 13 % selectivity) with some quantity of water produced, as compared to 3 % methane selectivity for Co/H-ZSM-5 catalyst with no water produced during the reaction. At low process condition, both catalysts were less prone to middle distillates hydrocarbon production. At high process conditions, a CO conversion of about 54 and 68 % was obtained by Co/H-ZSM-5 and Co/SiO2 catalyst respectively. At these conditions the H-ZSM-5 supported catalyst was observed to produce more methane, about 53 % selectivity while for Co/SiO2 catalyst it was obtained to be 35 % selective to methane, with 66 and 7 % of C6+ olefin and paraffin selectivity respectively. Co/H-ZSM-5 offered 9 % selectivity to C6+ per olefin and paraffin hydrocarbons. The commercial catalyst showed an orderly manner of distributing products at these conditions while the bi-functional catalyst randomly distributed the formed products with a high selectivity to middle olefin distillates. In terms of CO2 co-feeding in the reactant feed, both CO and CO2 were hydrogenated to hydrocarbons. A CO conversion of about 73 % was obtained by Co/H-ZSM-5 catalyzed reaction while for Co/SiO2 catalyzed reaction a conversion of 70 % was obtained. About 63 and 75 % of CO2 conversion was obtained by H-ZSM-5 and SiO2 supported catalyst. These results were obtained at high process conditions. No change in paraffin selectivity was observed when comparing a state in which CO2 was present and absent, however olefin selectivity is significantly affected by the presence of CO2. Thus, an increase in olefin selectivity is observed with Co/SiO2, achieving 76 % of C6+ Olefin from 66 % and Co/H-ZSM-5 increasing middle olefin distillated from 25 to about 30 % of selectivity. Based on the performance evaluation the bi-functional catalyst was proven to yield higher hydrocarbons from a simulated waste-tyre synthetic gas with no requirement of downstream hydrocracking, since the bi-functional catalyst cut-off higher hydrocarbons due to its acidic sites. While the metallic sites of the catalyst, catalyzes the reaction of synthetic gas to hydrocarbons. This type of catalyst with both metallic sites and acidic sites is a hybrid-catalyst commonly known as bi-functional catalyst (Kang et al., 2014). At low process conditions the bi-functional Co/H-ZSM-5 catalyst is found to be more preferred while at higher process conditions the commercial catalyst was found to be more preferred, however in the presence of CO2 co-feeding, either catalyst can be used, but if water elimination is required the bi-functional catalyst is more suitable for the process. / MT2017

In this thesis, a range of TiO2-based photocatalysts and cobalt-based Fischer-Tropsch (FT) catalysts were developed and synthesised via the one-step Flame Spray Pyrolysis(FSP). The work starts with the demonstration of bare TiO2 nanoparticles synthesis with controlled characteristics such as specific surface areas, crystallite sizes and anatase content. A comparative study was carried out by benchmarking with commercial Degussa P25 TiO2. The FSP TiO2 was shown to be more efficient in mineralising pollutants requiring direct charge transfer such as the saccharides, while P25 was better for mineralising alcoholic and aromatic compounds. Both catalysts were equally as active in mineralising carboxylic acids. Upon identifying the optimal synthesis of bare TiO2, an in situ co-precipitation of highly dispersed Pt on TiO2 was carried out in the flame. Deposition of Pt resulted in enhanced photocatalytic performance as a result of efficient charge trappings. It is highlighted here the inter-relationship between Pt oxidation states and the TiO2photocatalysis of carboxylic acid, alcohol and aromatic compounds. Depending on the mineralisation path adopted by the model organic compounds, they were shown to have direct influence on the Pt oxidation states. These oxidation states in turn affect the mineralisation rates of the organic compounds. Substitutional-doping of TiO2 with Fe(III) with tunable bandgap was also possible by FSP synthesis. The high temperature synthesis coupled with rapid quenching resulted in 5 times higher solubility limit (Fe/Ti = 0.05) than that previously reported in the literature. Under visible light irradiation, FSP-made Fe-TiO2 improved the photocatalytic mineralisation of oxalic acid by more than 6 times, with respect to P25 and FSP TiO2. Furthermore, the photocatalyst was reusable over a number of repetitions with minimal leaching or loss in activity. The last part of the work concerns the development of bare and Ru-doped Co-ZrO2 catalysts, where cobalt was finely dispersed within the zirconia matrix. Doping of Ru enhanced significantly the reducibility of cobalt, reducing even the embedded cobalt beneath the zirconia surface. It also increased the extent of CO-chemisorption and as such, enhanced the FT activity. This is the first time, catalysts of such type is synthesised and tested for FT reaction.

The main objectives of the present Ph.D. thesis are comprehensive studies on activity, selectivity and stability of iron catalysts supported on carbon nanotubes (CNTs) for Fischer-Tropsch (FT) reactions. In order to prepare iron catalyst supported on CNTs, it was necessary to study CNT synthesis in bulk scale. Therefore, a part of this research was devoted to the production and characterization of CNTs. High purity, aligned films of multi-walled carbon nanotubes were grown on quartz substrates by feeding a solution of ferrocene in toluene, in a carrier gas of Ar/H2, into a horizontal chemical vapour deposition (CVD) reactor. Results for CNTs synthesized using a wide range of toluene concentrations indicated that, for carbon concentrations higher than ~9.6 mol/m3, catalyst deactivation occurs due to encapsulation of iron metal particles.<p> As the first step of catalyst development for FT reactions a fixed bed micro-reactor system was built and the effects of acid treatment on the activity, product selectivity and stability of iron Fischer-Tropsch catalysts supported on carbon nanotubes were studied. The results of Raman analysis showed that the acid treatment increased the number of functional groups as anchoring sites for metal particles. Fe catalysts supported on CNTs which were pre-treated with nitric acid at 110°C were more stable and active compared to the un-treated catalysts. In order to study the effects of catalytic metal site position on FT reactions, a method was developed to control the position of the deposited metal clusters on either the inner or outer surfaces of the CNTs. According to the results of the FT experiments, the catalyst with catalytic metal sites inside the pores exhibited higher selectivity (C₅⁺ = 36 wt%) to heavier hydrocarbons compared to one with sites on the outer surfaces (C₅⁺ = 24 wt%) . In addition, deposition of catalytic sites on the interior surfaces of the nanotubes resulted in a more stable catalyst.<p> The effects of pore diameter and structure of iron catalysts supported on CNTs on Fischer-Tropsch reaction rates and selectivities were also studied. In order to examine the effects of pore diameter, two types of CNTs with similar surface areas and different average pore sizes (12 and 63 nm) were prepared. It was found that the deposition of metal particles on the CNT with narrow pore size (in the range of larger than 10-15 nm) resulted in more active and selective catalyst due to higher degree of reduction and higher metal dispersion.<p> Promotion of the iron catalyst supported on CNTs with Molybdinium in the range of 0.5-1 wt % resulted in a more stable catalyst. Mo improves the stability of the iron catalyst by preventing the metal site agglomeration. Promotion of the iron catalysts with potassium increased the activity of FT and water-gas-shift reactions and the average molecular weight of the hydrocarbon products. Promotion of the iron catalyst supported on CNTs with 0.5% Cu and 1wt% K resulted in an active (5.6 mg HC/g-Fe.h), stable and selective catalyst (C₅⁺ selectivity of 76%) which exhibited higher activity and better selectivity compared to the similar catalysts reported in the literature. Kinetic studies were conducted to evaluate reaction rate parameters using the developed potassium and copper promoted catalyst. It was found that the CO₂ inhibition is not significant for FT reactions. On the other hand, water effects and presence of vacant sites should be considered in the kinetic models. A first-order reaction model verified that the iron catalyst supported on CNTs is more active than precipitated and commercial catalysts. The results of the present Ph.D. thesis research provide a map for designing catalysts using carbon nanotubes as a support. The key messages of the present thesis are as follows:<p> 1- If the interaction of the metal site and support is strong, which poses negative effects on the catalytic performance, carbon nanotubes can be one solution.<p> 2- Acid pre-treatments are required prior to impregnating nanotubes with metal salt solution. Also, the strong acid treatment should be used for deposition of catalytic sites inside the pores of nanotubes.<p> 3- The structure and pore size of nanotubes have significant influence on the stability, activity and selectivity of the target catalyst.<p> 4- The position of the catalytic sites has to be selected based on the type of reaction. In the case of Fischer-Tropsch reactions, the deposition of catalytic sites inside the pores of nanotubes results in higher activity, longer life span.<p> The outcome of this Ph.D. thesis has been published/submitted in the form of 13 journal papers, one patent, one technical report and presented at 11 conferences.

This research project is part of a larger Canadian endeavour to evaluate feasibility of using new nanocatalyst formulations for Fischer-Tropsch synthesis (FTS) to convert fossil-derived or renewable gaseous fuels into green diesel. The green diesel is a clean fuel (with no aromatics and sulfur compounds) suitable for the commonly used transportation system. The catalyst investigated is cobalt metal supported on carbon nanotubes (CNTs). The physical properties of CNTs have improved the common cobalt catalyst currently used in industry. Carbon nanotubes have high surface area, a very stable for FTS activity and, contrary to other common supports, do not interact with the catalyst active phase to produce undesirable compounds. Moreover, CNTs differ from graphite in their purity and by their cylindrical form, which increases the metal dispersion and allows confinement of the particles inside the tubes. Thus, carbon nanotubes as a new type of carbon material have shown interesting properties, favoring catalytic activity for FTS cobalt catalyst. Their surface area can be modified from 170 to 214 m^2/g through acid treatment. The CNT support lowers the amount of Ru promoter needed to increase the catalyst activity up to 80 % CO conversion and potassium promoter increases the selectivity for á-olefins. The olefin to paraffin (O/P) ratio for Co/CNT and CoK/CNT are 0.76 and 0.90, respectively. Moreover, the Co-Fe bimetallic catalysts supported on CNT have proved to be much more attractive in terms of alcohol formation, up to 26.3 % for the Co10Fe4/CNT. The structural characteristics of CNTs have shown to be suitable for use as catalytic support materials for FTS using microemulsion preparation method as applied to produce nanoparticle catalysts. Microemulsion technique results show uniform nanoparticle that are easy to reduce. In addition, the confinement of the particles inside the CNT has improved the lifetime of the catalyst by decreasing the rate of sintering. The deactivation rate at high FTS activity is linear (XCO = -0.13 t(hr) + 75) and at low FTS activity is related to a power law expression of order 11.4 for the cobalt particles outside the tubes and 30.2 for the cobalt particles inside the tube. The optimized catalyst studied was the CoRuK/CNT catalyst. The best kinetic model to describe the CoRuK/CNT catalyst is: 18.5 x 10 ^-5 PH2^0.39/ (1 + 7.2 10 ^-2 PCO^0.72 PH2^0.1)^2.

The main objectives of the present Ph.D. thesis are comprehensive studies on activity, selectivity and stability of iron catalysts supported on carbon nanotubes (CNTs) for Fischer-Tropsch (FT) reactions. In order to prepare iron catalyst supported on CNTs, it was necessary to study CNT synthesis in bulk scale. Therefore, a part of this research was devoted to the production and characterization of CNTs. High purity, aligned films of multi-walled carbon nanotubes were grown on quartz substrates by feeding a solution of ferrocene in toluene, in a carrier gas of Ar/H2, into a horizontal chemical vapour deposition (CVD) reactor. Results for CNTs synthesized using a wide range of toluene concentrations indicated that, for carbon concentrations higher than ~9.6 mol/m3, catalyst deactivation occurs due to encapsulation of iron metal particles.<p> As the first step of catalyst development for FT reactions a fixed bed micro-reactor system was built and the effects of acid treatment on the activity, product selectivity and stability of iron Fischer-Tropsch catalysts supported on carbon nanotubes were studied. The results of Raman analysis showed that the acid treatment increased the number of functional groups as anchoring sites for metal particles. Fe catalysts supported on CNTs which were pre-treated with nitric acid at 110°C were more stable and active compared to the un-treated catalysts. In order to study the effects of catalytic metal site position on FT reactions, a method was developed to control the position of the deposited metal clusters on either the inner or outer surfaces of the CNTs. According to the results of the FT experiments, the catalyst with catalytic metal sites inside the pores exhibited higher selectivity (C₅⁺ = 36 wt%) to heavier hydrocarbons compared to one with sites on the outer surfaces (C₅⁺ = 24 wt%) . In addition, deposition of catalytic sites on the interior surfaces of the nanotubes resulted in a more stable catalyst.<p> The effects of pore diameter and structure of iron catalysts supported on CNTs on Fischer-Tropsch reaction rates and selectivities were also studied. In order to examine the effects of pore diameter, two types of CNTs with similar surface areas and different average pore sizes (12 and 63 nm) were prepared. It was found that the deposition of metal particles on the CNT with narrow pore size (in the range of larger than 10-15 nm) resulted in more active and selective catalyst due to higher degree of reduction and higher metal dispersion.<p> Promotion of the iron catalyst supported on CNTs with Molybdinium in the range of 0.5-1 wt % resulted in a more stable catalyst. Mo improves the stability of the iron catalyst by preventing the metal site agglomeration. Promotion of the iron catalysts with potassium increased the activity of FT and water-gas-shift reactions and the average molecular weight of the hydrocarbon products. Promotion of the iron catalyst supported on CNTs with 0.5% Cu and 1wt% K resulted in an active (5.6 mg HC/g-Fe.h), stable and selective catalyst (C₅⁺ selectivity of 76%) which exhibited higher activity and better selectivity compared to the similar catalysts reported in the literature. Kinetic studies were conducted to evaluate reaction rate parameters using the developed potassium and copper promoted catalyst. It was found that the CO₂ inhibition is not significant for FT reactions. On the other hand, water effects and presence of vacant sites should be considered in the kinetic models. A first-order reaction model verified that the iron catalyst supported on CNTs is more active than precipitated and commercial catalysts. The results of the present Ph.D. thesis research provide a map for designing catalysts using carbon nanotubes as a support. The key messages of the present thesis are as follows:<p> 1- If the interaction of the metal site and support is strong, which poses negative effects on the catalytic performance, carbon nanotubes can be one solution.<p> 2- Acid pre-treatments are required prior to impregnating nanotubes with metal salt solution. Also, the strong acid treatment should be used for deposition of catalytic sites inside the pores of nanotubes.<p> 3- The structure and pore size of nanotubes have significant influence on the stability, activity and selectivity of the target catalyst.<p> 4- The position of the catalytic sites has to be selected based on the type of reaction. In the case of Fischer-Tropsch reactions, the deposition of catalytic sites inside the pores of nanotubes results in higher activity, longer life span.<p> The outcome of this Ph.D. thesis has been published/submitted in the form of 13 journal papers, one patent, one technical report and presented at 11 conferences.

This research project is part of a larger Canadian endeavour to evaluate feasibility of using new nanocatalyst formulations for Fischer-Tropsch synthesis (FTS) to convert fossil-derived or renewable gaseous fuels into green diesel. The green diesel is a clean fuel (with no aromatics and sulfur compounds) suitable for the commonly used transportation system. The catalyst investigated is cobalt metal supported on carbon nanotubes (CNTs). The physical properties of CNTs have improved the common cobalt catalyst currently used in industry. Carbon nanotubes have high surface area, a very stable for FTS activity and, contrary to other common supports, do not interact with the catalyst active phase to produce undesirable compounds. Moreover, CNTs differ from graphite in their purity and by their cylindrical form, which increases the metal dispersion and allows confinement of the particles inside the tubes. Thus, carbon nanotubes as a new type of carbon material have shown interesting properties, favoring catalytic activity for FTS cobalt catalyst. Their surface area can be modified from 170 to 214 m^2/g through acid treatment. The CNT support lowers the amount of Ru promoter needed to increase the catalyst activity up to 80 % CO conversion and potassium promoter increases the selectivity for á-olefins. The olefin to paraffin (O/P) ratio for Co/CNT and CoK/CNT are 0.76 and 0.90, respectively. Moreover, the Co-Fe bimetallic catalysts supported on CNT have proved to be much more attractive in terms of alcohol formation, up to 26.3 % for the Co10Fe4/CNT. The structural characteristics of CNTs have shown to be suitable for use as catalytic support materials for FTS using microemulsion preparation method as applied to produce nanoparticle catalysts. Microemulsion technique results show uniform nanoparticle that are easy to reduce. In addition, the confinement of the particles inside the CNT has improved the lifetime of the catalyst by decreasing the rate of sintering. The deactivation rate at high FTS activity is linear (XCO = -0.13 t(hr) + 75) and at low FTS activity is related to a power law expression of order 11.4 for the cobalt particles outside the tubes and 30.2 for the cobalt particles inside the tube. The optimized catalyst studied was the CoRuK/CNT catalyst. The best kinetic model to describe the CoRuK/CNT catalyst is: 18.5 x 10 ^-5 PH2^0.39/ (1 + 7.2 10 ^-2 PCO^0.72 PH2^0.1)^2.

No description available.

Higher alcohols synthesized via CO hydrogenation reactions have been a topic of intense study both in industry and academia for over thirty years. A variety of transition metals and promoters have been used in catalysts for this reaction. MoS₂, in particular, is popular due to its low cost, resistance to sulfur poisoning, and ability to selectively produce higher alcohols over hydrocarbons. The bulk material has a rich history in hydrodesulfurization reactions (HDS), and as such, a great deal is known about the material's structure and reactivity. However, even with this deep body of knowledge about the bulk catalyst, no one has yet been able to implement an industrially viable variation of the catalyst to make higher alcohols. Supported MoS₂ has also been studied for the same purpose. Generally, supports are employed to improve catalyst productivity per gram of Mo by dispersing the metal and increasing the amount of catalytically active surface area. However, product selectivity may also be influenced by chemical properties of the supports. Specifically, gamma alumina has been shown to raise hydrocarbon formation due to intrinsic surface acidity. The effects of basic supports are reported on the CO hydrogenation reaction are reported. K promoted Mo is supported on two basic materials - commercial sepiolite (Si₁₂Mg₈O₃₀(OH)₄) and hydrotalcite-derived Mg/Al mixed metal oxides (MMO). The catalysts are reacted with syngas, and the resultant product selectivities are compared at isoconversions. Activated carbon supported Mo and bulk MoS₂ are also used as controls. It is shown that MMO provides a unique promotional effect by suppressing methanol formation and favoring higher alcohols. The specific role of MMO in the reaction is investigated by combining it in three different ways with Mo. 1) MMO is impregnated with Mo in the classic fashion. 2) Bare MMO or MMO/K is placed as a secondary bed downstream of the principle catalyst (K promoted Mo supported on MMO). 3) Bare MMO or MMO/K is mixed with the principle catalyst to make a homogeneous bed. It is shown that MMO by itself is somewhat inert in the reaction while MMO/K has some higher alcohol forming activity. More importantly however, it is shown that the MMO:Mo ratio has far greater effects on selectivity than the morphology of MoS₂. There is evidence however that MoS₂ morphology can affect activity. It is hypothesized that a greater degree of stacking in MoS₂ domains leads to reduced activity. The existence of coupling and homologation pathways are investigated by feeding methanol or ethanol into the syngas as it enters the catalyst bed. By comparing changes in the productivity of different higher alcohols with the liquid feed, it is shown that an MMO supported catalyst is much more reactive with methanol and somewhat more reactive with ethanol than its bulk MoS₂ counterpart. It is shown that for both the bulk and supported catalysts, the addition of a Cx alcohol results in the largest increase in Cx+1 products, suggesting that alcohol homologation is in fact the most favored route to higher alcohols by these materials.

In this thesis, a range of TiO2-based photocatalysts and cobalt-based Fischer-Tropsch (FT) catalysts were developed and synthesised via the one-step Flame Spray Pyrolysis(FSP). The work starts with the demonstration of bare TiO2 nanoparticles synthesis with controlled characteristics such as specific surface areas, crystallite sizes and anatase content. A comparative study was carried out by benchmarking with commercial Degussa P25 TiO2. The FSP TiO2 was shown to be more efficient in mineralising pollutants requiring direct charge transfer such as the saccharides, while P25 was better for mineralising alcoholic and aromatic compounds. Both catalysts were equally as active in mineralising carboxylic acids. Upon identifying the optimal synthesis of bare TiO2, an in situ co-precipitation of highly dispersed Pt on TiO2 was carried out in the flame. Deposition of Pt resulted in enhanced photocatalytic performance as a result of efficient charge trappings. It is highlighted here the inter-relationship between Pt oxidation states and the TiO2photocatalysis of carboxylic acid, alcohol and aromatic compounds. Depending on the mineralisation path adopted by the model organic compounds, they were shown to have direct influence on the Pt oxidation states. These oxidation states in turn affect the mineralisation rates of the organic compounds. Substitutional-doping of TiO2 with Fe(III) with tunable bandgap was also possible by FSP synthesis. The high temperature synthesis coupled with rapid quenching resulted in 5 times higher solubility limit (Fe/Ti = 0.05) than that previously reported in the literature. Under visible light irradiation, FSP-made Fe-TiO2 improved the photocatalytic mineralisation of oxalic acid by more than 6 times, with respect to P25 and FSP TiO2. Furthermore, the photocatalyst was reusable over a number of repetitions with minimal leaching or loss in activity. The last part of the work concerns the development of bare and Ru-doped Co-ZrO2 catalysts, where cobalt was finely dispersed within the zirconia matrix. Doping of Ru enhanced significantly the reducibility of cobalt, reducing even the embedded cobalt beneath the zirconia surface. It also increased the extent of CO-chemisorption and as such, enhanced the FT activity. This is the first time, catalysts of such type is synthesised and tested for FT reaction.