Metal nanoparticle-decorated titanium dioxide (M@TiO₂) materials are an increasingly popular class of heterogeneous catalyst, useful in both photochemical and thermal systems. Heterogenous catalysts offer the advantage of reusability and ease of catalyst separation, when compared to similar homogeneous systems. M@TiO₂ catalysts also have the benefit of water/air environment stability, strong photoactivity for oxidation and reduction reactions, as well as easy and low cost synthesis of the catalyst. Other heterogeneous catalysts can offer better activity for certain reactions; however, M@TiO₂ materials are extremely versatile in a variety of different reactions and applications, and often are cheaper than other alternatives. In this dissertation, M@TiO₂ catalysts will be evaluated in hydrogen generation, solvent radical chemistry, and organic synthesis utilizing calcium carbide. Firstly, M@TiO₂ were evaluated for photocatalytic hydrogen generation from pure water splitting, and with the presence of sacrificial electron donors (SEDs) such as methanol. Efficient pure water splitting is of great interest for fuel production as it offers a perfect cycle with hydrogen gas burning to reform water as the only product. However, quite often SEDs are utilized to boost hydrogen gas generation due to poor conversion from pure water. It is often assumed that a photocatalyst effective with a SED will also be effective with water splitting. This assumption was tested, by comparing a variety of different M@TiO₂ photocatalysts for both water splitting, and SED-based hydrogen generation. Interestingly, it was found that the trends of hydrogen generation between photocatalysts are not the same in pure water splitting, as when SEDs are present. For example, Pd@TiO₂ shows great activity with a 1% methanol solution; however, no considerable H₂ generation for pure water splitting. This shows that the mechanisms of hydrogen generation with water splitting, and when SEDs are present, are very different and not directly comparable. It was also found that M@TiO₂ materials offer decent hydrogen generation rates, especially when considering the overall cost of the material. M@TiO₂ materials were then tested for their ability to photocatalytically form usable free-radicals from ethers. This was evaluated with scavenging of generated radicals by TEMPO, as well as monitoring the resulting H₂ production during the reduction portion of the system. Overall, it was found that M@TiO₂ photocatalysts are exceptional at forming radicals from ethers. All the ethers tested are able to undergo proton-coupled electron transfer (PCET) with the hole of TiO₂, as seen by the H₂ generation observed. The main considerations are instead for the ether-radical, and if the radical will fragment or primarily undergo other reactions. This led to only some of the ethers being able to form TEMPO-ether adducts. The photogenerated hole of TiO₂ is also strong enough to form benzylic radicals from toluene, highlighting the further versatility of the catalyst. To further explore TiO₂-generated radicals, heterogeneous laser flash photolysis techniques were then developed. Laser flash photolysis of TiO₂ suspensions is an uncommon, and underdeveloped technique in the research field. It was considered if low concentration suspensions of TiO₂ could allow for lowered impact from the absorbance and scattering from the TiO₂ particles. This allowed for monitoring the transient absorbance of a benzylic radical from the reaction between 1,1-diphenylethylene and 1,3-dioxolane solvent radicals formed by the photogenerated hole of TiO₂. The strength of this transient signal also showed dependence on the solvent, with 1,4-dioxane showing lower signal as expected from it's reactivity. This technique, with further development, should prove useful in expanding the kinetic evaluation of radicals generated by TiO₂ suspensions. Finally, Pd@TiO₂ was evaluated as a thermal catalyst for a Sonogashira-like reaction between calcium carbide and bromobenzene in DMSO under low water conditions. This palladium catalyst was effective in catalyzing the reaction; however, the more interesting aspect was in the chemistry of the calcium carbide itself. Calcium carbide is typically used for the in-situ formation of acetylene gas through the addition of water. However, it was found that in DMSO with low amounts of water, the formation of a soluble ethynyl calcium hydroxide intermediate could be selected for. This allowed for a more controlled and effective coupling with bromobenzene in solution. Further expansion on the use of this intermediate may be invaluable in expanding calcium carbide chemistry beyond the formation of acetylene gas.

III-nitride nanowires (NWs) have been recognized as efficient photoelectrochemical (PEC) devices due to their large surface-to-volume ratio, tunable bandgap, and chemical stability. Doping engineering can help to enhance the PEC performance further. Therefore, addressing the effects of Si and Mg doping on the III-nitride NW photoelectrodes is of great interest. In this study, doping levels of NWs were tuned by the dopant effusion cell temperature of the molecular beam epitaxy (MBE) growth. The successful doping of the III-nitride NWs was confirmed using photoluminescence (PL), Raman spectroscopy, and open circuit potential (OCP) measurements. The ionized dopant concentrations of Si-doped InGaN/GaN NWs were systematically quantified by electrochemical impedance studies (EIS). Due to the three dimensional surfaces of NWs, modified Mott-Schottky formulas were induced to improve the accuracy of ionized dopant concentrations. The highest dopant concentration of Si-doped InGaN NWs can reach 2.1x1018 cm-3 at Tsi = 1120 oC. Accordingly, the estimated band edge potentials of the tested NWs straddled the redox potential of water splitting. The PEC performance of these devices was investigated by linear scan voltammetry (LSV), chronoamperometry tests, and gas evolution measurements. The results were consistent with the quantified dopant concentrations. The current density of n-InGaN NWs doped at TSi = 1120 oC was nine times higher than the undoped NWs. Additionally, the doped NWs exhibited stoichiometric hydrogen and oxygen evolution. By doping Mg into InGaN and GaN segments separately, the p-InGaN/p-GaN NWs demonstrated improved PEC performance, compared with undoped-InGaN/p-GaN and n-InGaN/n-GaN NWs. The p-InGaN/p-GaN NWs exhibited a highly stable current density at ~-9.4 mA/cm2 for over ten hours with steady gas evolution rates (~107 μmol/cm2/hr for H2) at near a stoichiometric ratio (H2: O2~ 1.8:1). This study demonstrated that optimizing the doping level and appropriate band engineering of III-nitride NWs is crucial for enhancing their PEC water splitting performance.

Global warming and the energy crisis are two of the greatest challenges on which mankind is currently focused. This has forced governments and other organisations to think how to protect the environment and how to reduce fuel costs. A variety of new and exciting technologies are being investigated to address the energy problem. Alternative energy sources such as solar power, fuel cells, wind power and tidal waves are active areas of commercial and scientific pursuit. A major area of current research is moving towards the hydrogen economy and hydrogen based energy systems. Hydrogen can be produced in many ways, most commonly by steam reforming of hydrocarbon (70% to 85% thermal efficiency) but the downside is that it releases carbon mono oxide (CO)), compared with commercial PEM electrolysers where performance has been reported to be 56 -73% at normal temperature pressure(NTP) with zero carbon emission. Electrochemical production of hydrogen has several advantages: (i) It gives pure hydrogen. (ii) It allows portability (e.g. Solar energy could be used to power the electrochemical cell). (iii) It can be produced on demand. The generation of Hydrogen via electrolysis has been the subject of many studies over the last two hundred years. However, there is still room for further work to improve both the efficiency of the process and methods of storage of the gas. The cleanest method at present is to produce hydrogen by electrolysis, and the main focus of this research is to design and develop such a green energy fuel cell for on-demand application. The aim of the work presented in this thesis was to further investigate the electrolysis method for hydrogen production. An Electrochemical fuel cell contains a minimum of two electrodes: the positively charged electrode called the anode where oxygen bubble will form, and the second negatively charged electrode called the cathode, where hydrogen bubbles will form during a chemical reaction caused by applying electrical current between these electrode. The project was initiated with the objective of finding a low cost solution for on-demand hydrogen generation. To establish a starting point, the first cell (cell-1) design was based on the work of Stephen Barrie Chambers (see chapter 3) to check the performance levels. The fabrication of the cell-1 design resulted in a mixture of hydrogen and oxygen in the same chamber, which means the cell-1 design, has a possible fire and explosion hazard. The device also has the drawback of lower performance of hydrogen production; columbic efficiency is between 40% to 46% at 1 amp to 3 amp current in 30% KOH alkaline solution. However, the advantage of reproducing Stephen’s innovation is that it allowed a quick and deep understanding of hydrogen generation. This thesis presents recent work on the fabrication of low cost electrolysis cells containing continuous flow alkaline (KOH, up to 30%) electrolyte using low cost electrodes (stainless steel 316) and membranes based on ultrahigh molecular weight polyethylene (UHMW PE) to produce hydrogen without the hazard of fire and explosion. In this research an On-Demand Hydrogen Generation cell-3 achieved a 95% hydrogen generation coulombic efficiency, which is about 49% efficiency improvement as compared to the stainless steel electrode, and was 22% better than the nano structured electrode. The typical cell voltage is 2.5 V at current flow ranging from 30 to 120 mA cm-2 in 30% KOH electrolyte. The achievement here of such high efficiencies paves the way for more research in the areas of space management, electrode surface structure and flow control (based on the application requirement). This invention can be used for aeronautic, marine and automotive application as well as in many other areas.

Sodium borohydride (NaBH4) offers a simple and safe technology for storage and on demand production of hydrogen being a promising and a feasible method for fuel cell applications. The objectives of the present study are to emphasize the role of sodium borohydride as a part of future hydrogen energy system, to investigate the kinetics of the catalytic hydrolysis reaction of NaBH4 in a batch and flow system with respect to temperature, concentration, catalyst and flow rate for flow reactor by proposing a kinetic model and finally based on kinetic analysis, to design a prototype reactor to meet the hydrogen requirement for a 100W PEM fuel cell and operate it in steady state conditions. To express hydrolysis reaction by a kinetic model, series of batch experiments was performed in a glass flask (30mL) where the following parameters were systematically changed: the solution temperature varied as 20, 30 and 50&deg / C, the NaBH4 concentration changed as 0.17, 0.23 and 0.3M, NaOH concentration varied as 0.27, 1.32 and 2.85M and catalyst amount was changed as 0.048, 0.07 and 0.1g Pt/C (ETEK&reg / ). In the kinetic model catalyst effect proposed within the rate constant. The kinetic model was purposed as: For flow reactor system, in a differential glass reactor (5mL) concentration, catalyst amount, catalyst type and flow rate was systematically analyzed at a constant temperature. For Pt/C catalyst the purposed model was: Also, for intrazeolite Co(0) nanoclusters, as a result of controlled experiments, the rate expression was found as: Based on these data prototype reactor (recycle) with internal volume of 122cm3 and storage volume of 1336 cm3 was designed, manufactured from Delrin&reg / and operated.

This dissertation presents the preparation and characterization of rhodium(0) nanoparticles supported on hydroxyapatite, and investigation of their catalytic activity in hydrogen generation from the hydrolysis of hydrazine-borane and ammonia-borane. Rh+3 ions were impregnated on hydroxyapatite by ion-exchange / then rhodium(0) nanoparticles supported on hydroxyapatite were formed in-situ during the hydrolysis of hydrazine-borane at room temperature. The rhodium(0) nanoparticles supported on hydroxyapatite were isolated as black powders by centrifugation and characterized by ICP-OES, SEM, TEM, EDX, XRD, XPS, and N2 adsorption-desorption spectroscopy. Rhodium(0) nanoparticles supported on hydroxyapatite have a mean particle size of 2.7&plusmn / 0.7 nm. The catalytic activity of rhodium(0) nanoparticles supported on hydroxyapatite was tested separately in the hydrolysis of hydrazine-borane and ammonia-borane. The hydrolysis of hydrazine-borane was started by adding the precatalysts, Rh+3-exchanged hydroxyapatite into the aqueous solution of hydrazine-borane / whereas, the hydrolysis of ammonia-borane was initiated by adding the catalyst rhodium(0) nanoparticles supported on hydroxyapatite which have been isolated from the first run of hydrolysis of hydrazine-borane. Rhodium(0) nanoparticles supported on hydroxyapatite provide a turnover frequency value of 6700 h-1 in the hydrolysis of hydrazine-borane at room temperature. The reuse experiments reveal that these supported nanoparticles are isolable, bottlable, and redispersible in solution. Furthermore, they retain 62 % of their initial activity at the fifth run in the hydrolysis of hydrazine-borane with release of 3 equivalents hydrogen. Activity of rhodium(0) nanoparticles supported on hydroxyapatite is maintained after the redispersion of the sample and 3 equivalents hydrogen generation from the hydrolysis of ammonia-borane confirms the activity of preformed catalyst. Rhodium(0) nanoparticles supported on hydroxyapatite provide a turnover frequency value of 3990 h-1 in the hydrolysis of ammonia-borane at room temperature.

Orientadores: Ana Flávia Nogueira, Flávio Leandro de Souza / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-27T13:00:11Z (GMT). No. of bitstreams: 1 Carminati_SaulodoAmaral_M.pdf: 3434559 bytes, checksum: 5dc1e86f14ccc0bccd7264ae9b28c11e (MD5) Previous issue date: 2015 / Resumo: O Resumo poderá ser visualizado no texto completo da tese digital / Abstract: The Abstract is available with the full electronic digital document / Mestrado / Quimica Organica / Mestre em Química

No description available.

No description available.

<div>Hydrous hydrazine (N₂H₄·H₂O) is a promising hydrogen carrier for convenient storage and transportation owing to its high hydrogen content (8.0 wt%), low material cost and stable liquid state at ambient temperature. Particularly, generation of only nitrogen as byproduct, in addition to hydrogen, thus obviating the need for on-board collection system for recycling, ability to generate hydrogen at moderate temperatures (20-80 °C) which correspond to the operating temperature of a proton exchange membrane fuel cell (PEMFC), and easy recharging using current infrastructure of liquid fuels make hydrous hydrazine a promising hydrogen source for fuel cell electric vehicles (FCEVs). Since hydrogen can be generated from catalytic hydrazine decomposition, the development of active, selective and cost-effective catalysts, which enhance the complete decomposition (N₂H₄ → N₂+2H₂) and simultaneously suppress the incomplete decomposition (3N₂H₄ → 4NH₃+N₂), remains a significant challenge.</div><div>In this dissertation, CeO₂ powders and various Ni-based catalysts for hydrous hydrazine decomposition were prepared using solution combustion synthesis (SCS) technique and investigated. SCS is a widely employed technique to synthesize nanoscale materials such as oxides, metals, alloys and sulfides, owing to its simplicity, low cost of precursors, energy- and time-efficiency. In addition, product properties can be effectively tailored by adjusting various synthesis parameters which affect the combustion process.</div><div>The first and second parts of this work (Chapters 2 and 3) are devoted to investigating the correlation between the synthesis parameters, combustion characteristics and properties of the resulting powder. A series of CeO₂, which is a widely used material for various catalytic applications and a promising catalyst support for hydrous hydrazine decomposition, and Ni/CeO₂ nanopowders as model catalysts for the target reaction were synthesized using conventional SCS technique. This demonstrated that crystallite size, surface property and concentration of defects in CeO₂ structure which strongly influence the catalytic performance, can be effectively controlled by varying the synthesis parameters such as metal precursor (oxidizer) type, reducing agent (fuel), fuel-to-oxidizer ratio and amount of gas generating agent. The tailored CeO₂ powder exhibited small CeO₂ crystallite size (7.9 nm) and high surface area (88 m²/g), which is the highest value among all prior reported SCS-derived CeO₂ powders. The Ni/CeO₂ catalysts synthesized with 6 wt% Ni loading, hydrous hydrazine fuel and fuel-to-oxidizer ratio of 2 showed 100% selectivity for hydrogen generation and the highest activity (34.0 h^-1 at 50 ºC) among all prior reported catalysts containing Ni alone for hydrous hydrazine decomposition. This superior performance of the Ni/CeO₂ catalyst is attributed to small Ni particle size, large pore size and moderate defect concentration.</div><div>As the next step, SCS technique was used to develop more efficient and cost-effective catalysts for hydrous hydrazine decomposition. In the third part (Chapter 4), noble-metal-free NiCu/CeO₂ catalysts were synthesized and investigated. The characterization results indicated that the addition of Cu to Ni/CeO₂ exhibits a synergistic effect to generate significant amounts of defects in the CeO₂ structure which promotes catalytic activity. The 13 wt% Ni_0.5Cu_0.5/CeO₂ catalysts showed 100% H₂ selectivity and 5.4-fold higher activity (112 h^-1 at 50 ºC) as compared to the 13 wt% Ni/CeO₂ (20.7 h^-1). This performance is also superior to that of most reported non-noble metal catalysts and is even comparable to several noble metal-based catalysts. In the fourth part (Chapter 5), low Pt loading NiPt/CeO₂ catalysts were studied. The modified SCS technique was developed and applied to prepare NiPt/CeO₂ catalysts, that overcomes the typical problem of conventional SCS which leads to deficiency of Pt at catalyst surface due to the diffusion of Pt into bulk CeO₂. The Ni_0.6Pt_0.4/CeO₂ catalysts with 1 wt% Pt loading exhibited high activity (1017 h^-1 at 50 ºC) along with 100% H₂ selectivity owing to the optimum composition of NiPt alloy, high metal dispersion and a large amount of CeO₂ defects. Its activity is higher than most of the reported NiPt-based catalysts which typically contain high Pt loading (3.6-42 wt%).</div><div>Next, the intrinsic kinetics of hydrous hydrazine decomposition over the NiPt/CeO₂ catalysts, which are necessary for efficient design and optimization of the hydrous hydrazine-based hydrogen generator system, were investigated (Chapter 6). From the experimental data obtained at different reaction temperatures, the intrinsic kinetic model based on the Langmuir-Hinshelwood mechanism was established. The developed model</div><div>provides good predictions with the experimental data, especially over a wide range of initial reactant concentration, describing well the variation of reaction order from low to</div><div>high reactant concentration.</div><div>Finally, the conclusions of the dissertation and recommendations for future work are summarized in Chapter 7.</div>

Nuclear-based hydrogen generation is a promising way to supply hydrogen for this large market in the future. This thesis focuses on one of the most promising methods, a thermochemical Cu-Cl cycle, which is currently under development by UOIT, Atomic Energy of Canada Limited (AECL) and the Argonne National Laboratory (ANL). The safety issues of the Cu-Cl cycle are addressed in this thesis. An investigation of major accident scenarios shows that potential tragedies can be avoided with effective risk analysis and safety management programs. As a powerful and systematic tool, fault tree analysis (FTA) is adapted to the particular needs of the Cu-Cl system. This thesis develops a new method that combines FTA with a reliability analysis tool, multi-state system (MSS), to improve the accuracy of FTA and also improve system reliability. / UOIT