>Magister Scientiae - MSc / Transition metals are a group of metals which are light in weight and have high hydrogen solubility. Their interaction with hydrogen is exorthermic and this phenomenon makes them “ideal” candidates for various applications of hydrogen storage systems. This explains why the phenomenon of hydrogen storage in Pd is used as a model for hydrogen storage systems because of the nature of absorption associated with it (like a sponge even at low temperatures). The hydrogenation process can be conducted at either room or high temperatures in a furnace under low pressure-low hydrogen gas concentration-short hydrogenation time (LP-LC-ST) and in intelligent gravimetric analyser under high pressurehigh hydrogen gas concentration-long hydrogenation time conditions. Most of the research on hydrogen storage sytems is based on gravimetric analysis of absorbed and desorbed hydrogen concentration. In this work, a comparison study of the hydrogen content in pure Pd, Pd-Pt coated systems, Pd-Pt alloys, commercially pure Ti and Ti-6Al-4V alloy determined by gravimetric methods and elastic recoil detection analysis (which is based on the detection of recoiled hydrogen after interaction with He+ ions) technique was investigated. The changes in the structural properties and the hydrogen content of the materials when exposed to a hydrogen gas environment for different durations at various system temperatures and pressures will be reported. These changes have an effect on the microstructure of CP-Ti and Ti-6Al-4V alloy and structural properties of all the hydrogenated materials. The results obtained from optical microscopy, scanning electron microscopy, x-ray diffraction, intelligent gravimetric analyser, digital balance, elastic recoil detection analysis and Vickers hardness test, show the following: it is found that hydrogenation of Pd at elevated temperatures (550 ˚C and 650 ˚C) does not yield hydrides under LP-LC-ST conditions. However, at room temperature the absorption of hydrogen occurred faster at the beginning of the process. Furthermore, the absorption of hydrogen increased with pressure where optimum absorption (0.67 wt. % hydrogen concentration) occurred under a system pressure of 2000 mbar. After pressure release, the remaining hydrogen content in the Pd sample was 0.6 wt. %. The Pd-Pt coated system provide hydrogen mobility at 550 and 650 ˚C where hydrides were formed under LP-LC-ST conditions. In addition to the decrease of hydrogen solubility in Pd-Pt alloys with an increase in Pt content, the probability of the alloys to achieve full saturation also decreases with an increase in Pt content under HP-HC-LT conditions. CP-Ti and Ti-6Al-4V alloy absorb substantial amount of hydrogen in the first hour of room temperature hydrogenation under LP-LC-ST conditions but hydrides were not formed. Therefore, under LP-LC-ST conditions at room temperature, Pd is able to store hydrogen in the form of hydrides whereas Ti and Ti-6Al-4V alloy could not. The 550 ˚C is the optimum temperature for hydrogenation of CP-Ti under LP-LC-ST conditions. The Ti- 6Al-4V alloy absorb optimum hydrogen at 650 ˚C under LP-LC-ST conditions. Consequently, the change of microhardness of CP-Ti and Ti-6Al-4V alloy was found to depend on hydrogenation temperature.

O desenvolvimento industrial e urbano tem causado aumento mundial das emissões de poluentes atmosféricos. Nas áreas metropolitanas o problema da deterioração da qualidade do ar tem se constituído numa das mais graves ameaças à qualidade de vida dos seus habitantes e os veículos automotores contribuem diretamente com o aumento do material particulado (MP). Neste trabalho foram descritas as etapas metodológicas para validar a Tibouchina granulosa como biomonitor ambiental. Assim, foram abordados a caracterização das folhas, categorização do MP, protocolo de remoção de MP e determinação dos EGPs (Pd, Pt e Rh) na deposição seca das folhas. Para tanto foram realizadas quatro coletas anuais (2011-2014) de folhas, entre os meses de agosto e setembro, em pontos específicos. Os resultados da caracterização mostraram que as folhas permanecem residentes nos ramos por até 6 meses e ocorre o desenvolvimento duas novas folhas por nó a cada mês, indicando que o biomonitoramento pode ser realizado com distribuição temporal e espacial. Os caracteres anatômicos foliares mais relevantes são os tricomas, sendo caracterizados quatro tipos (glandular, adpresso-escabro, base ramificada e estrigoso) que adsorvem o MP. No protocolo de remoção da deposição seca, o número de MP variou de acordo com os diferentes reagentes analíticos utilizados, sendo os mais significativos o ALCONOX&reg e a água régia, que apresentaram valores de remoção na faixa de 99-98% e de 94-99%. As estimativas das incertezas analíticas dos EGPs apresentam valores de uCPt=5% (Pt), uCPd=12% (Pd) e uCRh=5% (Rh) e as incertezas de amostragem, os valores de 57% para o Pd, 24% para a Pt e 27% para o Rh. Portanto, a incerteza expandida foi da Pt U=48%, Pd U=86% e Rh U=9%, a incerteza do Rh apresentou valor mais baixo por ser o elemento minoritário. A elevada sensibilidade do método para determinação dos EGPs apresentou limite de detecção de 0,1 pg g-1 para o Pd, 1,3 pg g-1 para Pt e 0,3 pg g-1 para o Rh e acompanhada boa reprodutibilidade. As concentrações dos EGPs encontradas na deposição seca nos vários pontos de coletas indicaram a clara diferença de acúmulo destes elementos entre o ponto de referência e os locais impactados, sugerindo que a liberação dos EGPS pelos catalisadores veiculares pode ser considerada alta. A evidência da presença dos EGPs na deposição seca foi confirmada por meio da análise da distribuição, que mostrou claramente a similaridade com o material de referência certificado Used Auto Catalystc-2557. As distribuições espaciais dos EGPs foram semelhantes para a Coleta 2, indicando os hot points da RMSP. As concentrações do EGPs foram ordenadas em Pt>Pd>Rh e foram mais baixas no ponto de coleta para controle das amostragens em comparação com os outros locais amostrados. Pode ser concluído que as folhas de T. granulosa foram validadas como biomonitor passivo dos EGPs constituintes de catalisadores veiculares. / Industrial and urban development has caused worldwide increase in emissions air pollutants. In metropolitan areas, the problem of deterioration air quality has been one the most serious threats to quality life its inhabitants, motor vehicles contribute directly increase pollutants. This work describes the methodological steps to validate Tibouchina granulosa as environmental biomonitor, which involved the characterization the leaves, PM categorization, PM removal protocol and determination PGEs in dry deposition, for which four annual collections (2011-2014) were performed between August and September of each year. The of results leaf characters showed that leaves in the branches remain for up to 6 months and the development two new leaf occurs every month. The most relevant foliar characters anatomical are trichomes, being characterized five types. The highest particle concentrations adsorbed to stray trichomes and star-based trichomes. In dry deposition removal protocol, MP number varied according to different analytical reagents used, the most significant being ALCONOX&reg and aqua regia, which presented range removal values of 99-98% and 94-99%, respectively. The estimates analytical uncertainties PGEs show de uCPt=5% (Pt), uCPd=12% (Pd) e uCRh=5% (Rh) and sampling uncertainties values were 57% (Pd), 24% (Pt) and 27% (Rh). Therefore, the expanded uncertainty was Pt u=48%, Pd u=86% e Rh u=9%, in case Rh the uncertainties should be reevaluated by presenting minority values. The high sensitivity of the method for determination of PGEs showed a detection limit of 0.1 pg g-1 for Pd, 1.3 pg g-1 for Pt and 0.3 pg g-1 for Rh and good reproducibility of the results. The concentrations PGEs found in dry deposition in various collection points indicated the clear difference accumulation these elements between reference point and impacted sites, suggesting that release PGEs by the vehicle catalysts can be considered high. Confirming this evidence, through the ternary graphs, which clearly showed similar distributions in the environmental samples and equality with MRC (Used Auto Catalysts). The spatial distributions of Pt, Pd and Rh are similar for Collection 2. Concentrations of the PGEs were ordered in Pt>Pd>Rh and were lower at the collection points for control samplings compared to other sites sampled. In view of the above, it can be concluded that the leaves of T. granulosa can be used as environmental biomonitor of vehicular emissions of PGEs constituent of vehicular catalysts.

O desenvolvimento industrial e urbano tem causado aumento mundial das emissões de poluentes atmosféricos. Nas áreas metropolitanas o problema da deterioração da qualidade do ar tem se constituído numa das mais graves ameaças à qualidade de vida dos seus habitantes e os veículos automotores contribuem diretamente com o aumento do material particulado (MP). Neste trabalho foram descritas as etapas metodológicas para validar a Tibouchina granulosa como biomonitor ambiental. Assim, foram abordados a caracterização das folhas, categorização do MP, protocolo de remoção de MP e determinação dos EGPs (Pd, Pt e Rh) na deposição seca das folhas. Para tanto foram realizadas quatro coletas anuais (2011-2014) de folhas, entre os meses de agosto e setembro, em pontos específicos. Os resultados da caracterização mostraram que as folhas permanecem residentes nos ramos por até 6 meses e ocorre o desenvolvimento duas novas folhas por nó a cada mês, indicando que o biomonitoramento pode ser realizado com distribuição temporal e espacial. Os caracteres anatômicos foliares mais relevantes são os tricomas, sendo caracterizados quatro tipos (glandular, adpresso-escabro, base ramificada e estrigoso) que adsorvem o MP. No protocolo de remoção da deposição seca, o número de MP variou de acordo com os diferentes reagentes analíticos utilizados, sendo os mais significativos o ALCONOX&reg e a água régia, que apresentaram valores de remoção na faixa de 99-98% e de 94-99%. As estimativas das incertezas analíticas dos EGPs apresentam valores de uCPt=5% (Pt), uCPd=12% (Pd) e uCRh=5% (Rh) e as incertezas de amostragem, os valores de 57% para o Pd, 24% para a Pt e 27% para o Rh. Portanto, a incerteza expandida foi da Pt U=48%, Pd U=86% e Rh U=9%, a incerteza do Rh apresentou valor mais baixo por ser o elemento minoritário. A elevada sensibilidade do método para determinação dos EGPs apresentou limite de detecção de 0,1 pg g-1 para o Pd, 1,3 pg g-1 para Pt e 0,3 pg g-1 para o Rh e acompanhada boa reprodutibilidade. As concentrações dos EGPs encontradas na deposição seca nos vários pontos de coletas indicaram a clara diferença de acúmulo destes elementos entre o ponto de referência e os locais impactados, sugerindo que a liberação dos EGPS pelos catalisadores veiculares pode ser considerada alta. A evidência da presença dos EGPs na deposição seca foi confirmada por meio da análise da distribuição, que mostrou claramente a similaridade com o material de referência certificado Used Auto Catalystc-2557. As distribuições espaciais dos EGPs foram semelhantes para a Coleta 2, indicando os hot points da RMSP. As concentrações do EGPs foram ordenadas em Pt>Pd>Rh e foram mais baixas no ponto de coleta para controle das amostragens em comparação com os outros locais amostrados. Pode ser concluído que as folhas de T. granulosa foram validadas como biomonitor passivo dos EGPs constituintes de catalisadores veiculares. / Industrial and urban development has caused worldwide increase in emissions air pollutants. In metropolitan areas, the problem of deterioration air quality has been one the most serious threats to quality life its inhabitants, motor vehicles contribute directly increase pollutants. This work describes the methodological steps to validate Tibouchina granulosa as environmental biomonitor, which involved the characterization the leaves, PM categorization, PM removal protocol and determination PGEs in dry deposition, for which four annual collections (2011-2014) were performed between August and September of each year. The of results leaf characters showed that leaves in the branches remain for up to 6 months and the development two new leaf occurs every month. The most relevant foliar characters anatomical are trichomes, being characterized five types. The highest particle concentrations adsorbed to stray trichomes and star-based trichomes. In dry deposition removal protocol, MP number varied according to different analytical reagents used, the most significant being ALCONOX&reg and aqua regia, which presented range removal values of 99-98% and 94-99%, respectively. The estimates analytical uncertainties PGEs show de uCPt=5% (Pt), uCPd=12% (Pd) e uCRh=5% (Rh) and sampling uncertainties values were 57% (Pd), 24% (Pt) and 27% (Rh). Therefore, the expanded uncertainty was Pt u=48%, Pd u=86% e Rh u=9%, in case Rh the uncertainties should be reevaluated by presenting minority values. The high sensitivity of the method for determination of PGEs showed a detection limit of 0.1 pg g-1 for Pd, 1.3 pg g-1 for Pt and 0.3 pg g-1 for Rh and good reproducibility of the results. The concentrations PGEs found in dry deposition in various collection points indicated the clear difference accumulation these elements between reference point and impacted sites, suggesting that release PGEs by the vehicle catalysts can be considered high. Confirming this evidence, through the ternary graphs, which clearly showed similar distributions in the environmental samples and equality with MRC (Used Auto Catalysts). The spatial distributions of Pt, Pd and Rh are similar for Collection 2. Concentrations of the PGEs were ordered in Pt>Pd>Rh and were lower at the collection points for control samplings compared to other sites sampled. In view of the above, it can be concluded that the leaves of T. granulosa can be used as environmental biomonitor of vehicular emissions of PGEs constituent of vehicular catalysts.

Multi-metallic aerogels have emerged as a promising unsupported, high surface area-based metal material for different applications in heterogeneous catalysis and electrochemistry. The fabrication of these multi-metallic aerogels is based on a complex gelation process which is characterized by controlled aggregation of metallic nanoparticles to form a macroscopic network structure in aqueous solution. However, achieving structural homogeneity of the multi-metallic aerogels in terms of diameter of the nanochains and chemical composition at the nano- as well as at the macro-scale is still a great challenge. In this paper, we show the characterization of two Pd-Pt aerogels prepared by the two-step gelation method. The structural homogeneity and chemical distribution of both metals (Pd and Pt) inside the aerogels were analyzed using high-resolution (scanning) transmission microscopy (HR(S)TEM), energy-dispersive X-ray spectroscopy (EDX), extended X-ray absorption fine structure (EXAFS) spectroscopy, and cyclic voltammetry. Based on the microscopic and spectroscopic results, the Pd-Pt aerogels show the presence of Pd/Pt-rich domains inside the long-range framework. It is evident that the initial monometallic features dominate over alloying during the gelation process. Although the same synthetic approach for Pd-Pt aerogels with different atomic ratios was used, we observed that the sizes of these monometallic domains strongly varied between the Pd-rich and Pt-rich aerogels. For instance, the Pd-rich aerogels showed larger clusters with a size range from few nanometers up to several tens of nanometers, while the dimension of the clusters of the Pt-rich aerogels varies from the sub-nanometers to a few nanometers. The presence of the metal clusters strongly influenced the electrochemical robustness of these Pd-Pt aerogels. Electrochemical durability investigations revealed that the aerogels with a high content of Pd are less stable due to the gradual dissolution of the less noble metal in particular inside the Pd-rich domains. A better chemical and structural homogeneity might improve the life-time of the Pd-Pt aerogels under electrochemical conditions. In this work, we provide a better understanding about the structure and chemical distribution of the bimetallic aerogel framework prepared by the two step gelation process.

Multi-metallic aerogels have emerged as a promising unsupported, high surface area-based metal material for different applications in heterogeneous catalysis and electrochemistry. The fabrication of these multi-metallic aerogels is based on a complex gelation process which is characterized by controlled aggregation of metallic nanoparticles to form a macroscopic network structure in aqueous solution. However, achieving structural homogeneity of the multi-metallic aerogels in terms of diameter of the nanochains and chemical composition at the nano- as well as at the macro-scale is still a great challenge. In this paper, we show the characterization of two Pd-Pt aerogels prepared by the two-step gelation method. The structural homogeneity and chemical distribution of both metals (Pd and Pt) inside the aerogels were analyzed using high-resolution (scanning) transmission microscopy (HR(S)TEM), energy-dispersive X-ray spectroscopy (EDX), extended X-ray absorption fine structure (EXAFS) spectroscopy, and cyclic voltammetry. Based on the microscopic and spectroscopic results, the Pd-Pt aerogels show the presence of Pd/Pt-rich domains inside the long-range framework. It is evident that the initial monometallic features dominate over alloying during the gelation process. Although the same synthetic approach for Pd-Pt aerogels with different atomic ratios was used, we observed that the sizes of these monometallic domains strongly varied between the Pd-rich and Pt-rich aerogels. For instance, the Pd-rich aerogels showed larger clusters with a size range from few nanometers up to several tens of nanometers, while the dimension of the clusters of the Pt-rich aerogels varies from the sub-nanometers to a few nanometers. The presence of the metal clusters strongly influenced the electrochemical robustness of these Pd-Pt aerogels. Electrochemical durability investigations revealed that the aerogels with a high content of Pd are less stable due to the gradual dissolution of the less noble metal in particular inside the Pd-rich domains. A better chemical and structural homogeneity might improve the life-time of the Pd-Pt aerogels under electrochemical conditions. In this work, we provide a better understanding about the structure and chemical distribution of the bimetallic aerogel framework prepared by the two step gelation process.

Multi-metallic aerogels have recently emerged as a novel and promising class of unsupported electrocatalyst materials due to their high catalytic activity and improved durability for various electrochemical reactions. Aerogels can be prepared by a spontaneous one-step gelation process, where the chemical co-reduction of metal precursors and the prompt formation of the nanochain-consisting hydrogels, as a preliminary stage for the preparation of aerogels take place. However, detailed knowledge about the homogeneity and chemical distribution of these three-dimensional Pd-Pt aerogels at the nano-scale as well as at the macro-scale is still unclear to date. Therefore, we used a combination of spectroscopic and microscopic techniques to obtain a better insight into the structure and elemental distribution of the various Pd-rich Pd-Pt aerogels prepared by the spontaneous one-step gelation process. Synchrotron-based extended X-ray absorption fine structure (EXAFS) spectroscopy and high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) in combination with energy-dispersive X-ray spectroscopy (EDX) were employed in this work to uncover the structural architecture and chemical composition of the various Pd-rich Pd-Pt aerogels over a broad length range. The Pd80Pt20, Pd60Pt40 and Pd50Pt50 aerogels showed heterogeneity in the chemical distribution of the Pt and Pd atoms inside the macroscopic nanochain-network. Features of monometallic clusters were not detected by EXAFS or STEM-EDX, indicating alloyed nanoparticles. However, the local chemical composition of the Pd-Pt alloys strongly varied along the nanochains and thus within a single aerogel. To determine the electrochemically active surface area (ECSA) of the Pd-Pt aerogels for applications in electrocatalysis, we used the electrochemical CO stripping method. Due to high porosity and extended network structure, the resulting values of the ECSA for the Pd-Pt aerogels were higher than that for a commercially available unsupported Pt black catalyst. We show that the Pd-Pt aerogels possess a high utilization of catalytically active centers for electrocatalytic applications based on the nanostructured bimetallic framework. Knowledge about the homogeneity and chemical distribution of the bimetallic aerogels can help to further optimize their preparation by the spontaneous one-step gelation process and to tune their electrocatalytic reactivity.

Multi-metallic aerogels have recently emerged as a novel and promising class of unsupported electrocatalyst materials due to their high catalytic activity and improved durability for various electrochemical reactions. Aerogels can be prepared by a spontaneous one-step gelation process, where the chemical co-reduction of metal precursors and the prompt formation of the nanochain-consisting hydrogels, as a preliminary stage for the preparation of aerogels take place. However, detailed knowledge about the homogeneity and chemical distribution of these three-dimensional Pd-Pt aerogels at the nano-scale as well as at the macro-scale is still unclear to date. Therefore, we used a combination of spectroscopic and microscopic techniques to obtain a better insight into the structure and elemental distribution of the various Pd-rich Pd-Pt aerogels prepared by the spontaneous one-step gelation process. Synchrotron-based extended X-ray absorption fine structure (EXAFS) spectroscopy and high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) in combination with energy-dispersive X-ray spectroscopy (EDX) were employed in this work to uncover the structural architecture and chemical composition of the various Pd-rich Pd-Pt aerogels over a broad length range. The Pd80Pt20, Pd60Pt40 and Pd50Pt50 aerogels showed heterogeneity in the chemical distribution of the Pt and Pd atoms inside the macroscopic nanochain-network. Features of monometallic clusters were not detected by EXAFS or STEM-EDX, indicating alloyed nanoparticles. However, the local chemical composition of the Pd-Pt alloys strongly varied along the nanochains and thus within a single aerogel. To determine the electrochemically active surface area (ECSA) of the Pd-Pt aerogels for applications in electrocatalysis, we used the electrochemical CO stripping method. Due to high porosity and extended network structure, the resulting values of the ECSA for the Pd-Pt aerogels were higher than that for a commercially available unsupported Pt black catalyst. We show that the Pd-Pt aerogels possess a high utilization of catalytically active centers for electrocatalytic applications based on the nanostructured bimetallic framework. Knowledge about the homogeneity and chemical distribution of the bimetallic aerogels can help to further optimize their preparation by the spontaneous one-step gelation process and to tune their electrocatalytic reactivity.

About 8 tons of dry undigested solid waste is generated by the MixAlco process for every 40 tons of food residue waste fed into the process. This MixAlco process produces liquid fuels and the sludge generated can be further converted into synthesis gas using the process of pyrolysis. The hydrogen component of the product synthesis gas may be separated by pressure swing adsorption and used in the hydrogenation of ketones into fuels and chemicals. The synthesis gas may also be catalytically converted into liquid fuels via the Fischer-Tropsch synthesis process. The auger-type pyrolyzer was operated at a temperature between 630-770 degrees C and at feed rates in the range of 280-374 g/minute. The response surface statistical method was used to obtain the highest syngas composition of 43.9 +/- 3.36 v % H2/33.3 +/- 3.29 v % CO at 740 degrees C. The CH4 concentration was 20.3 +/- 2.99 v %. For every ton of sludge pyrolyzed, 5,990 g H2 (719.3 MJ), 65,000 g CO (660 MJ) and 21,170 g CH4 (1055.4 MJ) were projected to be produced at optimum condition. At all temperatures, the sum of the energies of the products was greater than the electrical energy needed to sustain the process, making it energy neutral. To generate internal H2 for the MixAlco process, a method was developed to efficiently separate H2 using pressure swing adsorption (PSA) from the synthesis gas, with activated carbon and molecular sieve 5A as adsorbents. The H2 can be used to hydrogenate ketones generated from the MixAlco process to more liquid fuels. Breakthrough curves, cycle mass balances and cycle bed productivities (CBP) were used to determine the maximum hydrogen CBP using different adsorbent amounts at a synthesis gas feed rate of 10 standard lpm and pressure of 118 atm. A 99.9 % H2 purity was obtained. After a maximum CBP of 66 % was obtained further increases in % recovery led to a decrease in CBP. The synthesis gas can also be catalytically converted into liquid fuels by the Fischer-Tropsch synthesis (FTS) process. A Co-SiO2/Mo-Pd-Pt-ZSM-5 catalyst with a metal-metal-acid functionality was synthesized with the aim of increasing the selectivity of JP-8 (C10-C17) fuel range. The specific surface areas of the two catalysts were characterized using the BET technique. The electron probe microanalyzer (with WDS and EDS capabilities) was then used to confirm the presence of the applied metals Co, Mo, Pd and Pt on the respective supports. In addition to the gasoline (C4-C12) also produced, the synthesis gas H2:CO ratio was also adjusted to 1.90 for optimum cobalt performance in an enhanced FTS process. At 10 atm (150 psig) and 250 degrees C, the conventional FTS catalyst Co-SiO2 produced fuels rich in hydrocarbons within the gasoline carbon number range. At the same conditions the Co-SiO2-Mo-Pd-Pt/HZSM-5 catalyst increased the selectivity of JP-8. When Co-SiO2/Mo-Pd-Pt-HZSM-5 was used at 13.6 atm (200 psig) and 250 degrees C, a further increase in the selectivity of JP-8 and to some extent diesel was observed. The relative amounts of olefins and n-paraffins decreased with the products distribution shifting more towards the production of isomers.

No description available.