Zinc air batteries have great promise as a new age energy storage device due to their environmental benignity, high energy density in terms of both mass and volume, and low cost Zinc air batteries get their high energy density by using oxygen from the air as the active material. This means that all the mass and volume that are normally required for active material in a battery are replaced by a thin gas diffusion electrode which allows for oxygen from the air to diffuse into the cell. Although this seems ideal, there are many technical challenges associated with the cell being open to the atmosphere. Some of these issues include electrolyte and electrode drying out, poor reaction kinetics involving sluggish reaction, the need for bifunctional catalysts to charge and discharge, and durability of the gas diffusion electrode itself. The bifuntional catalysts used in these systems are often platinum or other precious metals since these are commonly known to have the highest performance, however the inherent cost of these materials limits the feasibility of zinc air systems. Thus, there is a need to limit or remove the necessity for platinum carbon catalysts. There are many types of non precious metal catalysts which can be used in place of platinum, however their performance is often not as high, and the durability of these catalysts is also weak. Similar limitations on feasibility are invoked by the poor durability of the gas diffusion electrodes. Carbon corrosion occurs at the harsh caustic conditions present at the gas diffusion electrodes, and this corrosion causes catalyst dissolution. Moreover, many issues with zinc electrode fabrication limit durability and usable anode surface area within these systems. There is a need for a stable, porous, high surface area anode with good structural integrity. These issues are addressed in this work by three studies which each focuses on solving some of the issues pertaining to a crucial component of zinc air batteries, those being the gas diffusion electrode, the zinc electrode, and the bifunctional catalyst necessary for oxygen reduction reactions (ORR) and oxygen evolution reactions (OER). The first study addresses the need for improvements to the zinc anode electrode. A new process is proposed for the production of porous zinc electrodes in which the porosity can be easily controlled. This process involves the mixing of atomized zinc powder with a filler compound such as ammonium chloride. The mixture is then pressed into a pellet and heat treated to a temperature which simultaneously sublimes/decomposes the filler compound, and anneals the zinc structure to improve structural integrity. The resultant porous anode showed significantly charge and discharge potentials over the solid plate anode, while allowing for increased control of porosity over other porous electrodes due to the ability to adjust pore size based on the filler compound particle size. The discharge potentials observed from these porous anodes were 20% greater than zinc plate anodes at 100mA, but up to 200% greater at elevated currents of 200mA. Similarly the charging potentials were 53.8% lower at 100mA, and 55.5% lower at 200mA., suggesting greatly improved performance by the porous anode. The second study addresses the need for more durable gas diffusion electrodes. In this study, the bifunctional catalyst was bound directly to a stainless steel current collector via polymer binding in an attempt to remove the possibility of carbon corrosion and catalyst dissolution. The new gas diffusion electrode was successful in eliminating carbon corrosion, wherein, the durability of cells which incorporate this type of electrode was significantly increased. The durability of cell was increased to a point where little to no degradation occurred over 1000 cycles of full cell testing, showing great promise for future use and commercial viability. The final study addresses the need for durable and high performance non precious metal catalysts. The effects of catalyst morphology were studied wherein various morphologies of spinel type cobalt oxide were synthesized and compared. Cobalt oxide nanosheets were successfully synthesized and compared to nanoparticles of comparable size. The cobalt oxide nanosheets showed better charge and discharge potentials as well as durability of the nanoparticles. Impedance analyses showed reduced charge transfer and cell component resistances associated with the nanosheet morphology. Cobalt oxide nanosheets were further compared against platinum carbon. Cobalt oxide nanosheets showed significantly better durability as well as lower charging potentials and higher discharge potentials over 75 cycles. After 75 cycles the platinum carbon had lost 55.7% of its discharge potential wherein cobalt oxide nanosheets lost none of its discharge potential. Three issues pertaining to three major cell components a zinc air were addressed with promising solutions proposed for each. This work provides a basis for advanced zinc electrode fabrication in which further improvements can be incorporated to address other issues pertaining to zinc electrode use. This work set up a basis for electrode design which focuses on non carbon supported catalysts, eliminating the issue of carbon corrosion and associated catalyst dissolution. Finally, the results from the morphology study elucidate the benefits of controlled morphology for bifunctional catalysts, showing how morphology can be adjusted to improve performance by improving cell and charge transfer resistances.

Zinc air batteries are among the most promising energy storage devices due to their high energy density, low cost and environmental friendliness. The low mass and cost of zinc air batteries is a result of traditional active materials replacement with a thin gas diffusion layer which allows the battery to use the oxygen directly from the air. Despite the environmental and electronic advantages offered by this system, challenges related to drying the electrolyte and catalyst, determining a high activity bifictional catalyst, and ensuring durability of the gas diffusion layer need to be optimized during the fabrication of rechargeable zinc-air batteries. To date, platinum on carbon (Pt/C) provides the best electrochemical catalytic activity in acidic and alkaline electrolytes. However, the difficult acquisition and high cost of this catalyst mandates investigation into a new composition or synthesis of a bifunctional catalyst. A number of non-precious metal catalyst have been introduced for zinc-air batteries. Nevertheless, their catalytic activities and durability are still too low for commercial rechargeable zinc-air batteries. Thus, it is very important to synthesize a highly active bifunctional catalyst with good durability for long term charge and discharge use. In this study, it is proposed that a manganese-based perovskite oxide nanoparticle combined with nitrogen doped carbon nanotubes willshow promising electrochemical activity with remarkable cycle stability as a bifunctional catalyst for zinc-air batteries. In the first part of this work, nano-sized LaMnO3 and LaMn0.9Co0.1O3 were prepared to research the effectiveness of Co doping into LaMnO3 and its effect on electrochemical catalytic activities. To prepare LaMnO3 and LaMn0.9Co0.1O3, a hydrothermal reaction method was applied to synthesize nanoparticles which can increase the activity of perovskite type oxides. The result shows that while perovskite oxides replacing 10 wt. % of Mn doped with Co metal did not iv change its crystalline structure, the oxygen evolution reaction (OER) performance was increased by 600%. In the second part, a core-corona structured bifunctional catalyst (CCBC) was synthesized by combining LaMn0.9Co0.1O3 nanoparticles with nitrogen doped carbon nanotubes (NCNT). NCNT was chosen because of its large surface area and high catalytic activity for ORR. SEM and TEM analysis show that metal oxide nanoparticles were surrounded with nanotubes. Based on the electrochemical performances, ORR and OER activity is attributed to NCNT and the metal oxide core, respectively, complementing the activities of each other. Furthermore, its unique morphology introduces synergetic activity especially for OER. Electrochemical test results show that the onset potential was enhanced from -0.2 V (in LaMnO3 and LaMn0.9Co0.1O3) to -0.09 V (in CCBC) and the half wave potential was improved from -0.38 V to -0.19 V. In the third part, a single cell zinc-air battery test was performed using CCBC as the bifunctional catalyst for the air electrode. These results were compared with battery performance against a high-performance and expensive Pt/C based air catalyst. The results show that the battery containing catalytic CCBC consumes less energy during charge/discharge. The single cell long-term durability performance was compared, further proving that CCBC provides a more suitable catalyst for zinc-air battery than Pt/C.

Doctor of Philosophy / Department of Chemical Engineering / Keith L. Hohn / The present work describes the conversion of bio-derived methyl ethyl ketone (MEK) into different useful chemicals. The first part discusses the direct conversion of MEK to butene over supported copper catalysts (Cu-Al₂O₃, Cu-zeolite Y sodium (Cu-ZYNa) and Cu-zeolite Y hydrogen (Cu-ZYH)) in a fixed bed reactor. In this reaction, MEK is hydrogenated to 2-butanol over metal sites, and further dehydrated on acid sites to produce butene. Experimental results showed that the selectivity of butene was the highest over Cu-ZYNa, and it was improved by finding the optimum reaction temperature, hydrogen pressure and the percentage of copper loaded on ZYNa. The highest selectivity of butene (97.9%) was obtained at 270 °C and 20 wt% Cu-ZYNa. Over Cu-Al₂O₃, the selectivity of butenes was less than Cu-ZYNa since subsequent hydrogenation of butene occurred to produce butane. It was also observed that with increasing H₂/MEK molar ratio, butane selectivity increased. However, when this ratio was decreased, hydrogenation of butene was reduced, but dimerization to C₈ alkenes and alkane began to be favored. The main products over 20% Cu-Al₂O₃ were butene and butane, and the maximum selectivity of butene (87%) was achieved at an H₂/MEK molar ratio of five. The lowest selectivity of butene was obtained using Cu-ZYH, reaching ~40%. It was found that the amount of acidity in Cu-ZYH is much higher than in Cu-ZYNa (from (NH₃-TPD) measurements). This could have caused the selectivity of butene to decrease as a result of dimerization, oligomerization and cracking reactions. The second part describes the conversion of MEK to higher ketones in one step using a multifunctional catalyst having both aldol condensation (aldolization and dehydration) and hydrogenation properties. 15% Cu supported zirconia (ZrO₂) was investigated in the catalytic gas phase reaction of MEK in a fixed bed reactor. The results showed that the main product was 5-methyl-3-heptanone in addition to 5-methyl-3-heptanol and 2-butanol with side products including other heavy products (C₁₂ and up). The effects of temperature and the molar ratio of reactants (H₂/MEK) on overall product selectivity were studied. It was found that with increasing temperature, the selectivity to C₈ ketone increased, while selectivity to 2-butanol decreased. The hydrogen pressure plays significant role on the selectivity of products. It was observed that with increasing the H₂/MEK molar ratio, 2-butanol selectivity increased due to hydrogenation reaction while decreasing this ratio leads to increasing aldol condensation products. In addition, it was noted that both conversion and selectivity to the main product increased using a low loading percentage of copper, 1% Cu-ZrO₂. The highest selectivity of 5-methyl-3-heptanone (~63%) was obtained at temperatures around 180 °C and a molar ratio of H₂/MEK of 2. Other metals (Ni, Pd and Pt) supported on ZrO₂ also produced 5-methyl 3-heptanone as the main product with slight differences in selectivity, suggesting that a hydrogenation catalyst is important for making the C₈ ketone, but the exact identity of the metal is less important. The third part discusses the conversion of C₈ ketones to C₈ alkenes and C₈ alkane over a catalyst consisting of a transition metal (Cu or Pt) loaded on alumina (Al₂O₃). These bifunctional catalysts provide both hydrogenation and dehydration functionalities. The main products over 20% Cu-Al₂O₃ were a mixture of 5-methyl-3-heptene, 5-methyl-2-heptene and 3-methyl heptane. However, using 1% Pt-Al₂O₃ the major product was 3-methyl heptane with a selectivity reaching over 97% and a conversion of 99.9 %. Both temperature and the hydrogen pressure play an important role on the conversion of C₈ ketone as well as the selectivity of products (C₈ alkenes and C₈ alkane). Over 20% Cu-Al₂O₃, it was observed that increasing the reaction temperature led to an increase in the selectivity to C₈ alkane as a result of hydrogenation of the C₈ alkene. Also, it was observed that with an increase in H₂/C₈ ketone molar ratio, C₈ alkane selectivity increased. However, when this ratio was decreased, the further hydrogenation of C₈ alkene to C₈ alkane was reduced. The highest selectivity of C₈ alkene (81.7%) was obtained at 220 °C and a H₂/C₈ ketone molar ratio of 2. In addition, an experiment was carried out using a low loading percentage of copper, and it was noted that both conversion and selectivity to the main products decreased over 1% Cu-Al₂O₃. Over 1% Pt-Al₂O₃, C₈ alkane was the major product with different temperatures indicating that further hydrogenation of C₈ alkene was promoted on 1% Pt-Al₂O₃. At low temperature, for both Cu-Al₂O₃ and Pt-Al₂O₃, significant amounts of C₈ alcohols are formed because subsequent reactions do not proceed at a fast enough rate. Also using 1% Pt-Al₂O₃, the main product selectivity is still C₈ alkane with all H₂/C₈ ketone ratios.

Increasing prices of crude oil derived transportation fuels ascended the researches on seeking alternative fuels, in last decades. Moreover, the increasing rate of global warming, because of high greenhouse gas emissions initiated new research for environment-friendly clean alternative fuels. Due to its low NOx emission, good burning characteristics and high cetane number, dimethyl ether (DME) attracted major attention as a transportation fuel alternative. Two possible pathways have been proposed for DME production. One of these pathways is DME synthesis through conventional methanol dehydration. More recently, direct DME synthesis in a single step has attracted significant attention of researchers and fuel producers. Catalysts having two active sites are required for direct DME synthesis from synthesis gas. The aim of this work was to synthesize novel bifunctional direct DME synthesis catalysts and test their activity in a high pressure fixed bed flow reactor. Bifunctional mesoporous catalysts were synthesized by using one-pot hydrothermal synthesis, impregnation and physical mixing methods. These materials were characterized by XRD, EDS, SEM, N2 physisorption and diffuse reflectance FT-IR (DRIFTS) techniques. Characterization results of the catalysts synthesized by one-pot hydrothermal synthesis procedures in basic and acidic routes showed that pH value of the synthesis solution was highly effective on the final physical structure and chemical nature of the catalysts. Increase in the pH value promoted the incorporation of Cu, Zn and Al into the mesoporous MCM-41 structure. Also, effects of Na2CO3 addition on the catalyst structure during the hydrothermal synthesis procedure were investigated. The characterization results showed that metals were incorporated into the catalyst structure successfully. However, surface area results showed that loaded metals blocked the pores of MCM-41 and decreased the surface area of the catalysts. Effects of zirconium (Zr) metal with different weight ratios were also investigated. Results showed that Zr loading increased the surface area of the catalyst. A high pressure fixed bed flow reactor was built and the catalyst testing experiments were performed between the temperature range of 200-400&deg / C, at 50 bars. The activity results of the catalyst synthesized by impregnation method showed that no DME was formed over this catalyst / however it showed promising results for production of methanol and ethanol. Selectivity values of these alcohols were between 0.35 and 0.2. Formation of methane and CO2 indicated the occurrence of reverse dry reforming reaction. Incorporation of Zr into the catalyst structure at neutral synthesis condition caused significant activity enhancement, giving CO conversion values of about 40% at 400&deg / C. Product distribution obtained with this catalyst indicated the formation of DME, ethanol, methanol as well as CH4 and CO2. Highest DME selectivity (60%) was observed with the catalyst prepared by physical mixing of commercial methanol reforming catalyst with silicotungstic acid incorporated methanol dehydration catalyst having W/Si ratio of 0.4.

No processo de hidrocraqueamento para a produção de lubrificantes ocorre a formação de uma corrente rica em compostos parafínicos que possuem alto ponto de fluidez, apesar dos mesmos apresentarem excelentes desempenhos em termos de estabilidade térmica e oxidativa. A transformação das n-parafinas obtidas nestas correntes em isoparafinas e compostos naftênicos, os quais possuem menores pontos de fluidez, se faz necessária a fim de enquadrar esta propriedade. Uma das rotas catalíticas mais importantes neste sentido é a hidroisodesparafinação ou HIDW (hydroisodewaxing) que consiste na conversão de n-parafinas nas respectivas isoparafinas, onde são empregados catalisadores bifuncionais zeolíticos com a ocorrência de seletividade de forma. No caso dos catalisadores industriais, se faz necessária a dispersão da fase metálica e da zeólita em uma matriz amorfa para viabilizar sua conformação e melhorar a resistência mecânica do catalisador final. Neste cenário, o objetivo deste trabalho foi preparar e analisar o desempenho de uma série de catalisadores à base de zeólita beta inseridos numa matriz de alumina, variando-se o teor de zeólita e o tipo de precursor de Pt utilizado. Os catalisadores foram avaliados na reação de hidroisomerização de um composto modelo, no caso, n-hexadecano. Os testes realizados para avaliação da atividade e seletividade foram conduzidos em um reator de fluxo contínuo em alta pressão e fase líquida em unidade de laboratório. Os catalisadores foram testados em condições operacionais que proporcionassem uma ampla faixa de conversões do n-C16. Verificou-se que as atividades dos catalisadores foram proporcionais ao teor de zeólita no catalisador, indicando que a função ácida, neste catalisador bifuncional, é a etapa limitante do processo. Quanto à natureza do precursor de Pt, o catalisador preparado com ácido cloroplatínico foi sensivelmente mais ativo que os preparados com o complexo aminplatina. No entanto, para todos os catalisadores, a distribuição de produtos em função da conversão foi similar, independente do teor de zeólita e da natureza do precursor de platina. Foi também determinado o ponto de fluidez de uma série de produtos de reação, obtendo-se valores entre 17,5 C (n-hexadecano) e - 41 C (produto com 98% de conversão). Obteve-se uma boa correlação entre o ponto de fluidez e a composição dos produtos, considerando-se a presença de isômeros mono, di e tri-substituídos e compostos de menor peso molecular que C16 / The residual oil of hydrocracking process is a useful stream for the production of lubricants. This product is rich in paraffinic compounds which have a high pour point despite having the excellent performances in terms of thermal and oxidation stability. The conversion of the heavy n-paraffins or long alkyl chains into isoparaffins and naphthenic compounds, which have lower pour points, is necessary in order to lower the pour point to adequate values for lubricants formulation. One of the most important catalytic routes in this direction is hydroisodewaxing or HIDW, which consists in the conversion of n-paraffins in the respective isoparaffins with minimum formation of cracked products. For this objective, zeolitic bifunctional catalysts are employed, using zeolites presenting shape selectivity properties in order to avoid n-paraffin cracking. In the case of industrial catalysts, it is necessary to disperse the metallic phase and the zeolite in an amorphous matrix for obtaining adequate shape and mechanical strength. In this work, we studied the performance of a series of catalysts prepared with beta zeolite embedded in a alumina based matrix and varying the content of zeolite and the type of platinum precursor. The catalyst performance was evaluated in the hydroisomerization of a model compound, in this case, n-hexadecane, using a continuous flow reactor at high pressure and liquid phase in laboratory unit. Operating conditions were selected in order to provide a broad range of n-C16 conversions. Catalyst activities were proportional to the zeolite content in the support indicating that the acid function is the limiting one in these catalysts. Moreover,a catalyst prepared with chloroplatinic acid was more active than the one prepared with amine-platinum complex, for the same zeolite content. In despite of the different conversions, all catalysts presented similar isomerized and cracked product distributions as function of the overall n-C16 conversion. Pour points of a series of reaction products were measured and values between 17.5 C (n-hexadecane) and -41 C (98 % conversion) were obtained. A good correlation with pour point and product composition was obtained, taking in account the concentrations of mono, di and tri-branched isoparaffins and cracked products

No processo de hidrocraqueamento para a produção de lubrificantes ocorre a formação de uma corrente rica em compostos parafínicos que possuem alto ponto de fluidez, apesar dos mesmos apresentarem excelentes desempenhos em termos de estabilidade térmica e oxidativa. A transformação das n-parafinas obtidas nestas correntes em isoparafinas e compostos naftênicos, os quais possuem menores pontos de fluidez, se faz necessária a fim de enquadrar esta propriedade. Uma das rotas catalíticas mais importantes neste sentido é a hidroisodesparafinação ou HIDW (hydroisodewaxing) que consiste na conversão de n-parafinas nas respectivas isoparafinas, onde são empregados catalisadores bifuncionais zeolíticos com a ocorrência de seletividade de forma. No caso dos catalisadores industriais, se faz necessária a dispersão da fase metálica e da zeólita em uma matriz amorfa para viabilizar sua conformação e melhorar a resistência mecânica do catalisador final. Neste cenário, o objetivo deste trabalho foi preparar e analisar o desempenho de uma série de catalisadores à base de zeólita beta inseridos numa matriz de alumina, variando-se o teor de zeólita e o tipo de precursor de Pt utilizado. Os catalisadores foram avaliados na reação de hidroisomerização de um composto modelo, no caso, n-hexadecano. Os testes realizados para avaliação da atividade e seletividade foram conduzidos em um reator de fluxo contínuo em alta pressão e fase líquida em unidade de laboratório. Os catalisadores foram testados em condições operacionais que proporcionassem uma ampla faixa de conversões do n-C16. Verificou-se que as atividades dos catalisadores foram proporcionais ao teor de zeólita no catalisador, indicando que a função ácida, neste catalisador bifuncional, é a etapa limitante do processo. Quanto à natureza do precursor de Pt, o catalisador preparado com ácido cloroplatínico foi sensivelmente mais ativo que os preparados com o complexo aminplatina. No entanto, para todos os catalisadores, a distribuição de produtos em função da conversão foi similar, independente do teor de zeólita e da natureza do precursor de platina. Foi também determinado o ponto de fluidez de uma série de produtos de reação, obtendo-se valores entre 17,5 C (n-hexadecano) e - 41 C (produto com 98% de conversão). Obteve-se uma boa correlação entre o ponto de fluidez e a composição dos produtos, considerando-se a presença de isômeros mono, di e tri-substituídos e compostos de menor peso molecular que C16 / The residual oil of hydrocracking process is a useful stream for the production of lubricants. This product is rich in paraffinic compounds which have a high pour point despite having the excellent performances in terms of thermal and oxidation stability. The conversion of the heavy n-paraffins or long alkyl chains into isoparaffins and naphthenic compounds, which have lower pour points, is necessary in order to lower the pour point to adequate values for lubricants formulation. One of the most important catalytic routes in this direction is hydroisodewaxing or HIDW, which consists in the conversion of n-paraffins in the respective isoparaffins with minimum formation of cracked products. For this objective, zeolitic bifunctional catalysts are employed, using zeolites presenting shape selectivity properties in order to avoid n-paraffin cracking. In the case of industrial catalysts, it is necessary to disperse the metallic phase and the zeolite in an amorphous matrix for obtaining adequate shape and mechanical strength. In this work, we studied the performance of a series of catalysts prepared with beta zeolite embedded in a alumina based matrix and varying the content of zeolite and the type of platinum precursor. The catalyst performance was evaluated in the hydroisomerization of a model compound, in this case, n-hexadecane, using a continuous flow reactor at high pressure and liquid phase in laboratory unit. Operating conditions were selected in order to provide a broad range of n-C16 conversions. Catalyst activities were proportional to the zeolite content in the support indicating that the acid function is the limiting one in these catalysts. Moreover,a catalyst prepared with chloroplatinic acid was more active than the one prepared with amine-platinum complex, for the same zeolite content. In despite of the different conversions, all catalysts presented similar isomerized and cracked product distributions as function of the overall n-C16 conversion. Pour points of a series of reaction products were measured and values between 17.5 C (n-hexadecane) and -41 C (98 % conversion) were obtained. A good correlation with pour point and product composition was obtained, taking in account the concentrations of mono, di and tri-branched isoparaffins and cracked products

Orientador: Heloise de Oliveira Pastore / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-07T11:21:16Z (GMT). No. of bitstreams: 1 Albuquerque_Angela_D.pdf: 3045566 bytes, checksum: 280ada8d591e09adc89304ad0847ca95 (MD5) Previous issue date: 2006 / Resumo: A síntese da peneira molecular vanadoaluminossilicato com estrutura MWW, [V,Al]-MCM-22, foi realizada por tratamento hidrotérmico estático. Os materiais recém sintetizados, calcinados e trocados com íons H, Na ou K foram caracterizados por diversas técnicas analíticas e espectroscópicas. Foi preparado também um material por troca iônica do [Al]-MCM-22 com íons vanadila, o VO-[Al]-MCM-22. Todos os materiais apresentaram estrutura cristalina semelhante à observada para o [Al]-MCM-22. A presença de sítios redox (pares V/ V) foi monitorada por espectroscopia no UV -Vis com refletância difusa e por espectroscopia de infravermelho com transformada de Fourier (FTlR) com adsorção de CO a 100 K. As características ácidas foram monitoradas por FTlR com adsorção de NH3 e por dessorção termoprogramada (TPD) de NH3. Em testes catalíticos na reação de desidrogenação oxidativa do propano, os vanadoaluminossilicatos apresentaram maiores valores de conversão em relação aos aluminossilicatos, com valores de seletividade semelhantes. A troca iônica com íons alcalinos pode promover modulação na acidez dos catalisadores, tomando-os mais seletivos, por diminuir a seletividade para produtos de craqueamento. / Abstract: The synthesis of the vanadoaluminosilicate molecular sieve with MWW structure, [V,AI]-MCM-22, has been performed by static hydrothermal synthesis. As-synthesized, calcined, and H, Na or K ion-exchanged materiaIs were characterized by various analytical and spectroscopical techniques. It has also been prepared a material by ion-exchanging [AI]-MCM-22 with vanadyl ions, VO-[AI]-MCM-22. AlI the materiaIs presented a crystalIine structure similar to that observed for [AI]-MCM-22. The presence of redox sites (V/ V couples) was monitored by diffuse reflectance UV-vis spectroscopy and by Fourier transform infrared spectroscopy (FTlR) with CO adsorption at 100 K. Acid characteristics were monitored by FTlR with NH3 adsorption and by thermoprogrammed NH3 desorption (TPD). When tested in the oxidative dehydrogenation of propane catalytic reaction, vanadoaluminosilicates presented higher conversion values when compared to aluminosilicates, with similar selectivity data. Ion-exchange with alkaline ions may promote modulation in the acidity of the catalysts, making them more selective by decreasing their selectivity to products of cracking reactions. / Doutorado / Quimica Inorganica / Doutor em Quimica

<p>  </p> <p>Cyclar process was previously developed to convert propane and butane into aromatics using gallium-promoted ZSM-5 zeolites (Ga/ZSM-5). However, it has two major limitations. Firstly, light gases (methane and ethane) limit the yield of higher molecular weight hydrocarbons for propane conversion. Secondly, ethane is unreactive on Ga/ZSM-5 catalysts. Relative rates and selectivity for propane conversion on two components, gallium (Ga/Al2O3) and acid ZSM-5 (H-ZSM-5) were investigated, and the results suggest that light gas was produced by propane monomolecular cracking on ZSM-5 due to the imbalance of alkane dehydrogenation and olefin conversion rates on two catalytic functions. A PtZn alloy catalyst, which has >99% propene selectivity and 30 times higher rate than Ga, was used for the dehydrogenation function. The bifunctional PtZn/SiO2+ZSM-5 catalyst has high yields of aromatics with low methane selectivity (<5%) at ~70% propane conversion. The results suggest methane can be minimized by utilizing the PtZn alloy and lowering the monomolecular cracking rate by ZSM-5. In addition, PtZn alloy increases aromatics selectivity. Aromatics formation pathway was investigated by studying the rate and selectivity of a model intermediate (cyclohexene) on ZSM-5, PtZn/SiO2 and Ga/Al2O3. Benzene is formed at similar rates on Ga/Al2O3 and ZSM-5 but cracking of cyclohexene on the latter is two orders of magnitude higher than the benzene formation rate, indicating cracking of cyclic hydrocarbons leads to low aromatization rate on Ga/ZSM-5. The benzene formation rate on the PtZn/SiO2 is 200 times higher than that on ZSM-5, suggesting aromatics are formed by the metal pathway on PtZn/SiO2+ZSM-5. </p> <p>Unlike Ga/ZSM-5 catalysts, PtZn/SiO2+ZSM-5 catalysts also convert propane to aromatics at low temperature (350 ℃). The temperature effect on propane dehydroaromatization pathways on the PtZn/SiO2+ZSM-5 bifunctional catalysts was investigated to develop strategies for propane conversion to valuable liquid hydrocarbons. At high temperature (550 ℃), high dehydrogenation rates and lower monomolecular cracking rates are required to minimize methane formation, leading to primarily propene and BTX (benzene, toluene, and xylenes). By recycling propene in the propane conversion range of 30-45%, >80% BTX yields is likely achievable at full recycle. At mid temperature (400-450 ℃), the product has high selectivity to gasoline-blending hydrocarbons (butanes, C5+ hydrocarbons, toluene, and xylenes) at 15-25% propane conversions because dehydrogenation rates are moderately high, and oligomerization is more favored than cracking. At low temperature (350℃), ~25% propane conversion is achieved and has high selectivity (~60%) to butanes, but the propane conversion rates are likely too low to be practical. While methane formation by monomolecular cracking limits liquid yields at high reaction temperature, at mid and low temperatures, hydrogen co-produced at high propane conversions saturates light olefins to make undesired ethane, which becomes major yield-loss reaction on the PtZn/SiO2+ZSM-5. </p> <p>Finally, PtZn/SiO2+ZSM-5 catalysts can convert ethane to C3+ and aromatics but the methane selectivity increases rapidly at high ethane conversion. The roles of two catalytic function (Pt-Zn alloy and ZSM-5) in the dehydroaromatization pathways of ethane and propane will be further studied and their product distribution will be compared to have better understandings on the differences in the dominant yield-loss reaction and dehydroaromatization pathways. </p>

<p>The expanded production of shale gas has increased the desire for developing methods for converting light alkanes, especially propane and ethane, into aromatic species (i.e., benzene, toluene, and xylene). A multi-step process for conversion of light alkanes to aromatics may be developed, where the first stage converts light alkanes into olefins and hydrogen, and the second stage converts olefins to aromatics. However, to determine the viability of this process, better understanding of the performance of olefin aromatization in the presence of equimolar hydrogen is necessary. </p> <p><br></p> <p>Previous studies on the conversion of olefins to aromatics with bifunctional ZSM-5 catalysts have concluded that benzene, toluene, and xylenes (BTX) yields are significantly higher than for ZSM-5 alone. These results were attributed to the presence of a dehydrogenation function of Ga or Zn leading to higher rates of aromatics formation. In this study, a highly active, bifunctional PtZn/SiO2 (1.3 wt% Pt, 2.6 wt% Zn) with H-ZSM-5 (Si/Al = 40) catalyst is investigated for propene aromatization at 723 K and 823 K. At low to moderate propene conversions, in addition to BTX, light alkanes and olefins are produced. Many of these may also be converted to aromatics at higher propene conversion while others are not, for example, light alkanes. When compared at equivalent space velocity and propylene conversion, the bifunctional catalyst has a much higher selectivity to aromatics than ZSM-5; however, when compared at equivalent conversion of all reactive intermediates, the bifunctional catalyst exhibits very similar BTX selectivity. At 723 K, for both ZSM-5 and the bifunctional catalyst, the primary non-reactive by-products are propane and butane. At 823 K, both ZSM-5 and the bifunctional catalyst convert propane and butane to aromatics increasing the aromatic yields, and the by-products are methane and ethane.</p> <p><br></p> <p>Additionally, previous studies have investigated the H-ZSM-5 and Ga/H-ZSM-5 in the absence of H2, which is necessary to understand in order to develop a process for the conversion of light alkanes to aromatics. Herein, proton-form ZSM-5 and Ga modified H-ZSM-5 are compared for propylene aromatization in the presence and absence of equimolar hydrogen at 1.9 kPa and 50 kPa partial pressures. At 1.9 kPa, the presence of H2 is shown to have no impact on the product distribution on H-ZSM-5 or Ga/H-ZSM-5. At 50 kPa, H2 is shown to have no significant impact on H-ZSM-5 and has no impact on Ga/H-ZSM-5 at conversions <80%. Additionally, the addition of Ga to H-ZSM-5 is shown to have no impact on the product distribution in the presence or absence of H2, contrary to previous reports. The disagreement with previous literature stems from previous literature comparing H-ZSM-5 and Ga/H-ZSM-5 at equivalent space velocity rather than equivalent propylene conversion despite previous studies showing that the presence of Ga increases the conversion at equivalent space velocity for olefin aromatization. </p>

Un des principaux défis lors de l'élaboration des catalyseurs adéquats pour le procédé de déparaffinage catalytique (hydroisomérisation) est de maximiser le rendement en isomères et l'activité du catalyseur, tout en maintenant une faible sélectivité en produits de craquage. En effet, des catalyseurs avec sélectivité de forme à base de zéolithes à taille de pore intermédiaire, par exemple Pt/ZSM-22, sont sélectives en isomères, tandis que les zéolithes à large pore sont plus actifs, mais moins sélectif. L'objectif principal de cette thèse était, alors, d’étudier et de développer un catalyseur à la fois actif et sélectif en isomères. Deux études parallèles ont été realisées: la première basée sur l'impact de la proximité entre les sites actifs sur la réaction (Part I), et la seconde, portant sur le développement d'un catalyseur d'hydroisomérisation de haute performance en utilisant des nanocristaux de zéolithe BEA comme support acide (Part II). La participation de l’épandage d’hydrogène (Hsp) sur le mécanisme de la réaction d'hydroisomérisation a été démontrée. En effet, lorsque les sites actifs sont proches, les espèces Hsp diffusent au voisinage des sites acides provocant l'hydrogénation directe des ions carbénium. Un mécanisme de réaction a, alors, été proposé utilisant ce phénomène comme une alternative au mécanisme classique proposé par Weisz, où la réaction d'hydrogénation a lieu uniquement sur les sites métalliques. Ce phénomène justifie l'activité et la sélectivité plus élevées observées sur les catalyseurs, où les sites actifs sont proches. Sur la deuxième partie de ce manuscrit, des nanocristaux de zéolithe BEA ont été utilisés pour développer un catalyseur d’hy / One of the main challenges when developing adequate catalysts for the catalytic dewaxing process (hydroisomerization) is to maximize the isomerization products yield and the catalyst activity, while maintaining a low selectivity towards light cracking products. Indeed, shape selective catalysts based on medium pore zeolites, e.g. Pt/ZSM-22, were proven to produce high yields of isomerization products, whereas larger pore zeolites were more active but less selective. The main objective of this thesis was, then, to study and develop a catalyst with both high activity and selectivity towards the production of isomerization products. For that two parallel studies were made: the first based on the impact of the proximity between the active sites on the reaction (Part I); and the second, focused on the development of a high performance hydroisomerization catalyst using BEA zeolite nanocrystals as an acid support (Part II). The participation of the spilt-over hydrogen (Hsp) species on the hydroisomerization reaction mechanism played a major role on the study performed on the first part of this manuscript. Indeed, when the active sites were near enough the Hsp species were able to diffuse into the vicinity of the acid sites promoting the direct hydrogenation of the carbenium ions. Due to this fact, a reaction mechanism was proposed using this reaction as an alternative to the classical mechanism proposed by Weisz, where the hydrogenation reaction takes place on the metallic sites. This phenomenon justified the higher activity and selectivity observed on the catalysts where the active sites were sideby side. On the second part of this manuscript nanocrystals of BEA zeolite were