A presente pesquisa avaliou diferentes razões de recirculação do meio líquido com a finalidade de identificar a melhor condição de mistura para uma produção elevada e contínua de hidrogênio em um reator anaeróbio de leito fixo com fluxo ascendente alimentado com um meio contendo sacarose como fonte de carbono e uréia como fonte de nitrogênio. Foi utilizado polietileno de baixa densidade como meio suporte para imobilização da biomassa. O experimento foi iniciado com ensaios hidrodinâmicos (pulso, utilizando dextran blue como traçador) que determinaram as seguintes razões de recirculação em relação à vazão de alimentação utilizadas: R = 0,25, 0,5, 1,0 e 2,0. O experimento foi realizado em duas etapas, nas quais foram operados dois reatores idênticos simultaneamente, testando-se duas razões de recirculação diferentes. A DQO da água residuária foi de 2000 mg/L. O tempo de detenção hidráulica teórico foi de 2 horas e a temperatura foi mantida em 25 graus Celsius. A remoção de sacarose apresentou valores médios de 67%, 79%, 71% e 70% para R = 0,25, 0,5, 1,0 e 2,0, respectivamente. Os valores médios de rendimento de hidrogênio foram 1,14 mol \'H IND.2\'/mol sac, 1,43 mol \'H IND.2\'/mol sac, 1,34 mol \'H IND.2\'/mol sac e 0,86 mol \'H IND.2\'/.mol sac e de produção volumétrica de hidrogênio foram 74,34 mL \'H IND.2\'/(h.L), 124,78 mL \'H IND.2\'/(h.L), 96,57 mL \'H IND.2\'/(h.L) e 73,49 mL \'H IND.2\'/(h.L) para as vazões de recirculação de 0,25, 0,5, 1,0 e 2,0, respectivamente. O biogás produzido foi composto de \'H IND.2\', e \'CO IND.2\', com valores percentuais médios para \'H IND.2\', de 50%, 56%, 56% e 46% para R = 0,25, 0,5, 1,0 e 2,0, respectivamente. Não houve presença de metano em nenhuma fase de operação. Os principais produtos intermediários produzidos durante a produção de \'H IND.2\', foram ácido acético, ácido butírico e etanol, de forma similar para todas as fases de recirculação. Analisando todos os parâmetros de operação, foi possível notar que a melhor vazão de recirculação obtida foi de R = 0,5. Ajustando os dados obtidos a uma função polinomial, porém, chegou-se a um ponto de ótimo em R = 0,6. Durante os experimentos observou-se uma queda na produção do biogás, provavelmente por atuação de microrganismos consumidores deste. / The present research evaluated different recirculation rates of the liquid medium for the purpose of identify the best mixture condition for a high and continuous hydrogen production in an anaerobic upflow fixed-bed reactor fed with a medium containing sucrose as carbon source and urea as nitrogen source. Low density polyethylene was used as medium for biomass immobilization. The experiment began with hydrodynamic tests (pulse, using dextran blue as tracer) which led to the following recirculation rates related with the feed flow rate used in this work: R = 0,25, 0,5, 1,0 and 2,0. The experiment was conducted in two stages, where two identical reactors were operated simultaneously, by testing two different recirculation rates. COD from wastewater was 2000 mg/L. The theoretical hydraulic retention time was 2 hours and the temperature was maintained at 25 Celsius degrees. The average values of sucrose consumption were 67%, 79%, 71% and 70% for R = 0,25, 0,5, 1,0 and 2,0, respectively. The average values of hydrogen yield were 1,14 mol \'H IND.2\'/mol sac, 1,43 mol \'H IND.2\'/mol sac, 1,34 mol \'H IND.2\'/mol sac and 0,86 mol \'H IND.2\'/mol sac and of hydrogen production rate were 74.34 mL \'H IND.2\'/(h.L), 124.78 mL \'H IND.2\'/(h.L), 96.57 mL \'H IND.2\'/(h.L) and 73.49 mL \'H IND.2\'/(h.L) for recirculation rates of 0.25, 0.5, 1.0 and 2.0, respectively. The biogas produced was composed by \'H IND.2\', and \'CO IND.2\', with average values for \'H IND.2\', of 50%, 56%, 56% and 46% for R = 0,25, 0,5, 1,0 and 2,0, respectively. Methane was not detected. The main intermediate products produced during the hydrogen production were acetic acid, butyric acid and ethanol, similar in all stages of recirculation. Analyzing all operating parameters, it was identified that the better recirculation rate obtained during the experiments was R = 0.5. Adjusting all data obtained with a polynomial function, it was found an optimal recirculation rate of R = 0.6. During the experiments there was a drop in biogas production, probably by the activity of microrganisms consumers of this biogas.

As necessidades de energia global são, na sua maioria, dependentes de combustíveis fósseis. Hidrogênio é uma energia limpa alternativa a esses combustíveis fósseis. Bactérias fototróficas produzem hidrogênio a partir de compostos orgânicos por meio de processo anaeróbio dependente de luz. Assim, este trabalho visou avaliar o efeito das concentrações iniciais de ácido acético e biomassa, e a influência da intensidade luminosa, na produção de hidrogênio por bactéria fototrófica púrpura não-sulfurosa. Foram utilizados reatores em batelada de 2000 mL, com volume útil de 1000 mL e headspace de 1000 mL preenchido com hélio. Nos reatores foi adicionado ácido acético e glutamato de sódio (0,8 mmol/L) como fontes de carbono e nitrogênio, respectivamente, e cultura de bactéria fototrófica púrpura não-sulfurosa previamente purificada. O aumento da concentração inicial de ácido acético de 10 mmol/L para 17 mmol/L não promoveu mudanças significativas tanto no crescimento celular, quanto, na produção de hidrogênio (8,3 mL \'H IND.2\'/g massa seca.h e 8,8 mL \'H IND.2\'/g massa seca.h, respectivamente), para intensidade luminosa de 9000 - 10.000 lux. Nessa mesma intensidade luminosa, o aumento da concentração de biomassa inicial de 0,02 g/L para 0,04 g/L favoreceu o aumento da produção de hidrogênio de 8,8 mL \'H IND.2\'/g massa seca.h para 10,6 mL \'H IND.2\'/g massa seca.h, respectivamente. A produção de hidrogênio diminuiu acentuadamente de 10,6 mL \'H IND.2\'/g massa seca.h para 1,0 mL \'H IND.2\'/g massa seca.h com a diminuição da intensidade luminosa de 9000 - 10.000 lux para 4000 - 5000 lux. Na ausência de luz não ocorreu crescimento e produção de hidrogênio. A cultura manteve-se predominantemente avermelhada e as análise microscópicas mostraram a predominância de bacilos curvos, gram-negativos, aglomerados em formações de roseta; características típicas de alguns gêneros de bactérias fototróficas púrpuras não-sulfurosas. Todos os ensaios foram realizados à temperatura de 30 \'+ OU -\' 1 grau Celsius. A análise da estrutura da comunidade microbiana foi realizada por reação de polimerização em cadeia (PCR) de fragmentos de gene RNAr 16S, seguida de eletroforese em gel de gradiente desnaturante (DGGE), e revelou que não houve variações relevantes na estrutura das populações microbianas em função das diferentes condições de cultivo. / The global energy requirements are mostly dependent on fossil fuels. Hydrogen is a clean energy alternative to these fuels. Phototrophic bacteria produce hydrogen from organic compounds by an anaerobic light-dependent electron transfer process. Therefore, this study aimed at to evaluate the effect of the initial concentrations of acetic acid and biomass, and the influence of the light intensity on hydrogen production by purple non-sulfur phototrophic bacteria. The experiments were performed in batch operation, in reactors of 2000 mL, with culture volume of 1000 mL and headspace of 1000 mL, filled with helium. Acetic acid and sodium glutamate (0.8 mmol/L) were used as sources of carbon and nitrogen, respectively, and culture of purple non-sulfur phototrophic bacteria previously purifided. The increase of the initial acetic acid concentration from 10 mmol/L to 17 mmol/L did not promote significant changes in the cell growth and in the hydrogen production (8.3 mL \'H IND.2\'/g dry weight.h and 8.8 mL \'H IND.2\'/g dry weight.h, respectively), under a light intensity of 9000 - 10,000 lux. In this same light intensity, the increase of the initial biomass concentration from 0.02 g/L to 0.04 g/L resulted in an increase in the hydrogen production from 8.8 mL \'H IND.2\'/g dry weight.h to 10.6 mL \'H IND.2\'/g dry weight.h, respectively. The hydrogen production suddenly decreased from 10.6 mL \'H IND.2\'/g dry weigh.h to 1.0 mL \'H IND.2\'/g dry weight.h with the reduction of the light intensity from 9000 - 10,000 lux to 4000 - 5000 lux. Hydrogen production was not observed in absence of light. The culture remained predominantly purple and the microscopic analysis showed the predominance of rod-shaped cells, gram-negative, accumulated in formation of rosettes; typical characteristics of some types of purple non-sulfur phototrophic bacteria. The analysis of the structure of the microbial community was carried out by reaction of polymerization in chain (PCR) of the RNAr 16S, followed of denaturing gradient gel electrophoresis (DGGE), and reveled that the structure of the microbial populations did not change significantly in function of the different conditions of culture.

Modelos matemáticos oferecem grandes benefícios para a compreensão dos mecanismos envolvidos nos processos de tratamento de águas residuárias uma vez que fornecem interpretações e possibilitam previsões de desempenho, comparações de alternativas de tratamento, otimização de futuras plantas ou o aprimoramento das existentes, podendo subsidiar a elaboração de projetos em escala real. Em virtude disto, nesta pesquisa visou-se o desenvolvimento de um modelo bioquímico-matemático para descrever o processo de degradação da glicose em um reator anaeróbio de leito fixo com fluxo ascendente, com a resultante produção biológica de hidrogênio por meio do processo de fermentação. O desenvolvimento do modelo foi baseado em estudos sobre a cinética bioquímica e as características hidrodinâmicas do sistema. Os parâmetros de ajuste do modelo aos dados experimentais foram as constantes de velocidade das reações bioquímicas envolvidas na produção de hidrogênio. A calibração foi realizada manualmente buscando minimizar o desvio global. Para a determinação dos parâmetros foi utilizada a técnica de geração de números aleatórios com distribuição de freqüência uniforme e em seguida, o método de inversão de matrizes. O modelo matemático se revelou bastante adequado para a previsão do perfil de concentrações ao longo do reator, e possibilitou a representação das rotas de utilização da matéria orgânica. A reação de oxidação do ácido propiônico pelas bactérias acidogênicas produtoras de hidrogênio constitui a principal via de produção de \'H IND.2\' no sistema. / Mathematical models bring benefits to the understanding of mechanisms involved on wastewater treatment processes because they provide interpretations and make possible performance predictions, evaluation of design alternatives, optimization of future plants or the improvement to existing systems. Therefore, in this work a mathematical model to describe the glucose degradation process, with hydrogen production through the fermentation, in an upflow anaerobic packed-bed reactor is developed. The model equations were based on studies of biochemical kinetics and hydrodynamics features of the system. The parameters considered were the rates of the biochemical reactions involved in the hydrogen production. The calibration was made through the minimization of the global deviation. The parameters determination was obtained with the use of a technique of generation of aleatory numbers, and after that, the method of matrices inversion for the solution of the system of linear equations. The mathematical model developed showed to be adequate for the concentrations prediction along the reactor, and it made possible the representation of the routes of organic material utilization. The oxidation reaction of propionic acid is the main hydrogen production route in the reactor.

Magister Scientiae - MSc / In this study SBA-15 mesoporous silica template was synthesized and used as a sacrificial template in the preparation of ordered mesoporous carbon material. A chemical vapour deposition (CVD) technique using LPG or alternatively sucrose, pyrolyzed upon a mesoporous Si matrix were used to produce nanostructured ordered mesoporous carbon (OMC) with graphitic character after removing the Si template. The sucrose method was found to be a suitable route for preparing OMC. The OMC was used as a conductive three dimensional porous support for depositing catalytic nanophase Pt metal. Deposition of Pt nanoparticles on OMC was accomplished using a CVD method with Pt(acac)2 as a precursor. The synthesized nano-composite materials were characterized by several techniques such as, HRTEM, HRSEM, EDS, XRD, BET, TGA, FT-IR and CV. / South Africa

Hydrogen, nature’s simple and the most abundant element has been in the limelight for the past few decades from the stand point of the so-called hydrogen economy. With a high calorific value (142 MJ/kg) that is three times as large as the liquid hydrocarbons, hydrogen has emerged as a promising and environmentally friendly source of energy for the future generations. However, on-board hydrogen storage is one of the bottlenecks for its widespread usage for mobile applications. Storing hydrogen in liquid or compressed form is extremely difficult because of its low density. One of the best alternatives is to store hydrogen in a chemical form. Despite extensive work in this area, none of the materials seem to satisfy the essential criteria of reversible hydrogen storage with high gravimetric content. With regard to chemical hydrogen storage, apart from metal hydrides, ammonia borane (H3N•BH3, AB) is a promising prospect with a very high gravimetric storage of 19.6 wt% of hydrogen. Objectives 1) Develop cost-effective and active first-row transition metal based catalysts for the generation of hydrogen from AB in protic solvents 2) Study the dehydrogenation of AB in fluorinated alcohols and acids in order to realize compounds that are suitable for regeneration. 3) Study the interaction of Cu2+ with AB in non-aqueous medium using 11B NMR spectroscopy and powder XRD techniques. 4) Generation of highly pure hydrogen from ammonia borane in the solid state under mild conditions in the presence of late first row transition metal salts. 5) Synthesis of highly monodisperse ultrasmall colloidal Mg nanoparticles using the Solvated Metal Atom Dispersion (SMAD) method and digestive ripening technique; study the effect of size on the desorption temperature of MgH2. 6) Synthesize Cu/ZnO and Cu/MgO nanocomposites from the individual metal nanoparticles using co-digestive ripening technique and establish the structure of the composites using TEM, EF-TEM, and powder XRD techniques. Significant results Hydrogen generation from AB in protic solvents was realized using first-row transition metal catalysts. Initial studies were carried out using Cu nanocatalyst synthesized by the solvated metal atom dispersion method (SMAD). The activity order was found to be Cu2O > Cu@Cu2O > Cu. In addition, the late first-row transition metal ions, Co2+, Ni2+, and Cu2+ ions were also found to be highly active towards AB hydrolysis. These ions assisted AB hydrolysis via in-situ formation of metal atoms/clusters. Cu2+ assisted the hydrolysis of AB via the in-situ generation of both H+ and Cu clusters. At higher concentrations of AB, hydrolysis resulted in the evolution of NH3 in addition to H2 whereas, methanolysis afforded pure H2. In the case of methanolysis, for catalyst/AB = 0.2, three equiv of H2 were liberated in 2.5, 4.2, and 1.5 min when Co-Co2B, Ni-Ni3B, and Co-Ni-B nanopowders were used as catalysts, respectively. Dehydrogenation of ammonia borane (AB) was carried out in 2,2,2-trifluoroethanol and trifluoroacetic acid in order to realize compounds that are suitable for regeneration. The final byproduct obtained after the catalytic dehydrogenation of AB in 2,2,2-trifluoroethanol was NH4+B(OCH2CF3)4–. The FTIR data showed that the B-O bond in NH4+B(OCH2CF3)4 is slightly weaker compared to that in boric acid. Dehydrogenation of AB in trifluoroacetic acid in a controlled manner resulted in the formation of [CF3COO]–[BH2NH3]+ as the final by-product. Ammonia-borane was regenerated from [CF3COO]–[BH2NH3]+ by its reaction with LiAlH4, which served as the hydride source. Dehydrogenation of AB in non-aqueous medium and in the solid state were studied in hydrogen storage point of view. Cu2+ was found to activate the B–H bond in amine boranes in non-aqueous medium even at room temperature. As a result of the B–H bond cleavage in AB, [H3N•BH2]Cl species is formed. This compound reacts with unreacted AB via 3 separate pathways one involving hydrogen evolution, a second involving formation of a stable diammoniate of diborane cation [(NH3)2BH2]Cl without hydrogen evolution, and the third involving the formation of [H2NBH2]n and BNHx polymers accompanied by the generation of H2. Mechanisms of these pathways have been elaborated using 11B NMR spectroscopy and powder X-ray diffraction methods. These studies demonstrate that Cu(II) salts can be used as effective initiators for the dehydrogenation of amine boranes. Copper-induced hydrogen generation from AB in the solid state was also studied: for Cu2+/AB = 0.05, two equiv of H2 were liberated in 6.5 h at 333 K, which is equal to 9 wt% of the system. The 11B MAS NMR studies showed that the reaction proceeds through the intermediacy of [NH4]+[BCl4]– which eliminates the formation of borazine impurity, thereby affording pure H2. The cost effectiveness of CuCl2 makes this reaction scheme extremely attractive for real time applications. In the context of hydrogen storage in metal hydrides, highly monodisperse colloidal Mg nanoparticles with a size regime of 2–4 nm were synthesized by using the SMAD method followed by digestive ripening technique. The Mg-HDA nanopowder was fully hydrided at 33 bar and 391 K. Onset of hydrogen desorption from MgH2 nanoparticles was observed at a remarkably low temperature, 388 K compared to > 623 K in the case of bulk MgH2. The present study is a step towards realizing hydrogen storage materials that could operate close to ambient conditions. Colloids of Cu and Zn nanoparticles stabilized by 2-butanone have been prepared by the SMAD method. The as-prepared colloids which are polydisperse in nature have been transformed into highly monodisperse colloids by the digestive ripening process in the presence of hexadecylamine. Using this process, copper nanoparticles of 2.1 ± 0.3 nm and zinc nanoparticles of 3.91 ± 0.3 nm diameters have been obtained. Co-digestive ripening of Cu, Zn and Cu, Mg colloids resulted in the formation of Cu/ZnO and Cu/MgO nanocomposites, respectively. The structures of these nanocomposites were established using UV-visible spectroscopy, TEM, EF-TEM, and powder XRD techniques.

Alternative energy research into hydrogen production via water electrolysis addresses environmental and sustainability concerns associated with fossil fuel use. Renewable-powered electrolyzers are foreseen to produce hydrogen if energy and cost requirements are achieved. Electrocatalysts reduce the energy requirements of operating electrolyzers by lowering the reaction kinetics at the electrodes. Platinum group metals (PGMs) tend to be utilized as electrocatalysts but are not readily available and are expensive. Ni1-xMox alloys, as low-cost and earth-abundant transition metal nanoparticles (NPs), are emerging as promising electrocatalyst candidates to replace expensive PGM catalysts in alkaline media. Pure-phase cubic and hexagonal Ni1-xMox alloy NPs with increasing Mo content (0–11.4%) were synthesized as electrocatalysts for the hydrogen evolution reaction (HER). In general, an increase in HER activity was observed with increasing Mo content. The cubic alloys were found to exhibit significantly higher HER activity in comparison to the hexagonal alloys, attributed to the higher Mo content in the cubic alloys. However, the compositions with similar Mo content still favored the cubic phase for higher activity. To produce a current density of -10 mA/cm2, the cubic and hexagonal alloy NPs require over-potentials ranging from -62 to -177 mV and -162 to -242 mV, respectively. The cubic alloys exhibited over-potentials that rival commercial Pt-based electrocatalysts (-68 to -129 mV at -10 mA/cm2). The cubic Ni0.934Mo0.066 alloy NPs showed the highest alkaline HER activity of the electrocatalysts studied and therefore a patent application was submitted. Bulk Ni–Mo phases have been known as electrocatalysts for the HER for decades, while recently transition metal phosphides (TMPs) have emerged as stable and efficient PGM alternatives. Specifically, Ni2P has demonstrated good HER activity and improved stability for both alkaline and acidic media. However, Ni2P electrocatalysts are a compromise between earth-abundance, performance (lower than Ni–Mo and PGMs) and stability. For the first time Ni–Mo–P electrocatalysts were synthesized with varying atomic ratios of Mo as electrocatalysts for alkaline HER. Specific phases, compositions and morphologies were studied to understand the intrinsic properties of TMPs leading to high HER activity. The Ni1.87Mo0.13P and Ni10.83Mo1.17P5 NPs were shown to be stable for 10 h at –10 mA cm-2 with over-potentials of –96 and –82 mV in alkaline media, respectively. The Ni1.87Mo0.13P and Ni10.83Mo1.17P5 NPs exhibited an improved performance over the synthesized Ni2P sample (–126 mV at –10 mA cm-2), likely a result of the overall phosphorous content and hetero-structured morphologies. A strong correlation between phase dependence and the influence of Mo on HER activity needs to be further investigated. Furthermore, understanding the intrinsic properties of electrocatalysts leading to high water splitting performance and stability can apply electrocatalysts in other research applications, such as photoelectrochemical (PEC) water splitting, water remediation and sustainable chemical processing applications. Contributions to photocatalytic water remediation and electrochemical chlorinated generation to halogenate pyridone-based molecules are reported. Electrochemical techniques were developed and reported herein to aid in understanding electrochemical performance, chemical mechanisms and the stability of electrocatalysts at the electrode-electrolyte interfaces.

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