Scanning Tunnelling Microscopy (STM) was utilised together with the high resolution depth-profiling capabilities of Medium Energy Ion Scattering (MEIS), a technique traditionally associated with single crystal substrates, to probe the mean size and depth dependent composition profile of bimetallic PdAu nanoparticles on planar oxide surfaces as functions of the starting composition and annealing temperature. In order to fit composition profiles to experimental MEIS data, a new analysis tool has been designed that models the particles as flat-topped structures with a hexagonal base which can be divided into a number of shells, each shell corresponding to a particular ion pathlength inside the material. The reliability of this method will be discussed in detail. Fitting results show that the surface layers are always significantly enriched in Au compared to the bulk alloy composition. By comparing MEIS data for clean surfaces data for modified surfaces it was found that Pd generally segregates towards the particle surface on adsorption of acetic acid. The interaction of potassium acetate with Au/Pd{111} alloy surfaces of varying composition has been investigated using Temperature Programmed Desorption (TPD) and Reflection Absorption Infra Red Spectroscopy (RAIRS). At lower coverage, potassium acetate reacts reversibly with the surface to form CO and carbonate. Formation of surface acetate is observed on Pd-rich surfaces only. At higher coverage, acetate is the major surface species formed on all samples examined.

Thesis (M. Tech. Chemistry, Dept. of Chemistry, Faculty of Applied and Computer Sciences)--Vaal University of Technology, 2010. / Membrane separation processes offer a promising alternative to energy-intensive separation processes such as distillation and solvent extraction. NF and RO are among the most investigated membrane processes with a potential use in the chemical industry. Carbon-carbon coupling reactions feature in the top ten most used reactions in the chemical industry. These reactions often use homogeneous palladium, nickel and other precious catalysts which are often difficult to separate from reaction products. This leads to potential product contamination and loss of active catalysts. This not only poses a threat to the environment but is also costly to the chemical industry. The purpose of this study was to investigate the efficiency of the recovery of the metal catalysts by selected membrane processes. Four commercial polymeric NF and RO membranes (NF90, NF270, BW30 and XLE) were selected for the study. Palladium catalysts commonly used in Heck and Suzuki coupling reactions were selected. These are Pd(OAc)2, Pd(OAc)2(PPh3)2, PdCl2 and Pd(PPh3)2Cl2. A range of organic solvents were also selected for the study. All the membranes were characterized for pure water permeability, pure solvent permeability, swelling, surface morphology and chemical structure. The chemical and catalytic properties of the catalysts were determined. Catalytic activity was investigated by performing coupling reactions. These catalysts generally performed well in the Heck coupling reaction with sufficient yields realized. The catalysts showed poor activities in the Suzuki and Sonogashira coupling reactions. These coupling reaction systems were affected by rapid palladium black formation. vi Catalyst retention studies showed the influence of membrane-solute interactions such as steric hindrance and size exclusion. The larger catalyst, Pd(OAc)2(PPh3)2 was rejected better by all the membranes irrespective of the solvent used. The smaller catalyst, Pd(OAc)2 was the most poorly rejected catalyst. This catalyst showed signs of instability in the selected solvents. An interesting finding from this study is that of higher rejections in water compared to other solvents for a particular catalyst. In this regard, the influence of solventsolute effects was evident. Generally, higher rejections were observed in solvents with higher polarity. This has been explained by the concept of solvation. It has been shown that solvents with different polarity solvate solutes differently, therefore leading to a different effective solute diameter in each solvent. Catalyst separation using NF90 membrane was attempted for the Heck coupling reaction system. The reaction-separation procedure was repeated for two filtration cycles with rapid activity decline evident. This was regarded as very poor showing of the catalyst separation efficiency of the membrane. Other authors in similar studies using SRNF membranes have reported reaction-separation processes of up to seven cycles. This observation shows the inferiority of polymeric membranes in organic solvent applications such as catalyst separation.

Este trabalho teve como objetivo investigar eletrocatalisadores de baixo custo à base de carbeto de tungstênio, carbono e ferro submetidos a diferentes processos de nitretação quanto à atividade catalítica para reação de redução do oxigênio (RRO) nos eletrólitos ácido e alcalino. Os catalisadores foram divididos em três séries distintas, a primeira compreendendo aqueles onde houve variação da carga de carbeto de tungstênio em relação ao suporte de carbono, que foram impregnados com o complexo Fe2+(2,4,6-Tris(2-piridil)-1,3,5-Triazina)2, [Fe(TPTZ)2]2+ e tratados em duas temperaturas diferentes, 700 e 800 oC em atmosfera de nitrogênio. Na segunda série foi mantida constante a carga de carbeto de tungstênio (30% de W/C, m/m) sendo que esta mescla foi preparada usando carbonos dopados previamente com três fontes distintas de nitrogênio (HNO3, NH3 e HNO3/NH3); isto foi seguido pela incorporação do complexo Fe[TPTZ]2+ e pelos mesmos tratamentos térmicos acima mencionados. Na terceira série, os eletrocatalisadores foram preparados com três tipos de carbonos (Vulcan, Ketjenblack e Monarch), aos quais foi incorporado o complexo Fe[TPTZ]2+, seguido pelo tratamento térmico a 800 °C em atmosfera de nitrogênio e então por dopagem com amônia a 950 °C. As três séries de eletrocatalisadores sintetizados neste trabalho foram cuidadosamente caracterizadas por espectroscopia infra-vermelho e UV-Visível, difratometria de raio-x, microscopia eletrônica de transmissão, energia dispersiva de raios-x, espectroscipia Raman, espectroscopia fotoeletrônica de raios-x. As investigações eletroquímicas foram realizadas por voltametria cíclica (VC) e pelo levantamento de curvas de polarização de estado estacionário para a RRO, usando a técnica de eletrodo de disco/anel rotatório, com materiais catalíticos formando filmes finos depositados no eletrodo de disco. Nas três séries de catalisadores foram desenvolvidos materiais com bom desempenho para a RRO. Nos estudos da primeira série de catalisadores, notou-se que o material mais ativo foi aquele formado por WC-FeNx/C com 30 % de W/C e 5% de Fe pirolisado a 800 °C. Na segunda série foi observado que os desempenhos dos catalisadores variaram de acordo com o tipo de protocolo de nitretação, presença de ferro e temperatura de tratamento térmico. Em eletrólito alcalino, os eletrocatalisadores apresentaram maiores desempenhos, que resultaram bastante próximos em relação ao do catalisador de Pt dispersa em carbono usado como referência. Na terceira série de eletrocatalisadores investigados, verificou-se que o melhor desempenho obtido foi com o catalisador com carbono Monarch com amônia, cuja atividade catalítica resultou superior à dos demais, devido ao maior número de estruturas ativas FeNx e N/C formadas pelo tratamento com amônia. Os resultados nos meios ácido e alcalino para a primeira e segunda séries de eletrocatalisadores sugerem a ocorrência de um mecanismo indireto (2e- + 2e-), ou seja, em meio ácido (alcalino) primeiro o O2 reduz para H2O2 (HO2 ) e depois de H2O2 (HO2 ) para H2O. Os sítios predominantemente envolvidos na catálise da reação são WC e FeNx em meio ácido e WC e N/C em meio alcalino. Finalmente, para a terceira série de eletrocatalisadores o mecanismo reacional em meio ácido envolve um mecanismo direto de 4e-, com participação importante dos sítios ativos de Fe-N2. / This work aims to investigate low cost electrocatalysts based on tungsten carbide, carbon and iron submitted to different nitriding processes for the catalytic activity for the oxygen reduction reaction (ORR) in acid and alkaline electrolytes. The catalysts were divided into three distinct series, the first one comprising those with different tungsten carbide loads with respect to the carbon support, which were impregnated with the Fe2+ (2,4,6-Tris (2-pyridyl) - 1,3,5-triazine)2, [Fe (TPTZ)]2+, complex and treated at two different temperatures, 700 and 800 oC in nitrogen atmosphere. In the second series, the tungsten carbide load (30% W/C, m/m) was kept constant but this mixture was prepared using previously doped carbons using three different sources of nitrogen (HNO3, NH3 and HNO3/NH3); this was followed by the incorporation of the Fe[TPTZ]2+ complex and by the same heat treatments as mentioned above. In the third series, the electrocatalysts were prepared with three carbon types (Vulcan, Ketjenblack and Monarch), to which the Fe[TPTZ]2+ complex was added, followed by heat treatment at 800 °C under nitrogen and then by nitriding using a flow of ammonia at 950 °C. The three series of electrocatalysts synthesized in this work were carefully characterized by infra-red and UV-Visible spectroscopy, x-ray diffraction, transmission electron microscopy, x-ray energy dispersive, Raman spectroscopy, x-ray photoelectron spectroscopy. The electrochemical investigations were performed by cyclic voltammetry (CV) and by measurements of steady-state polarization curves for ORR using rotating ring-disc electrode technique, with catalytic materials forming thin films deposited on the disc. In the three catalyst series, materials with good performance for the ORR were developed. In the studies of the first series of catalysts, it was seen that the most active material was that formed by WC-FeNx/C with 30%W/C and 5% Fe pyrolyzed at 800 ° C. In the second series it was observed that the performances of the catalysts varied according to the type of nitriding protocol, presence of iron and temperature of heat treatment. The electrocatalysts showed higher performances in alkaline electrolyte, which were very close to that of a reference Pt/C catalyst. In the third series of electrocatalysts, the best performance was obtained with the Monarch carbon catalyst heat-treated with ammonia, whose catalytic activity was higher than all others, due to the greater number of FeNx and N/C active structures formed by the treatment with ammonia. The results in acidic and alkaline conditions for the first and second series of electrocatalysts suggest the occurrence of an indirect ORR mechanism (2e- + 2e-), that is, in acid (alkaline) media first O2 is reduced to H2O2 (HO2) followed by the reduction of H2O2 (HO2). The active sites predominantly involved in the reaction electrocatalysis are WC and FeNx in acid media and WC e N/C in alcaline media. Finally, for the third series of electrocatalysts, the acidic reaction involves a direct 4e- mechanism, having important participation of the Fe-N2 active sites.

Orientadores: Antonio José Gomez Cobo, César Augusto Moraes de Abreu / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-16T13:01:21Z (GMT). No. of bitstreams: 1 Freire_EleonoraMariaPereiradeLuna_D.pdf: 2485469 bytes, checksum: 5c15bdbbb73bd51d623eb4811e9d2248 (MD5) Previous issue date: 2005 / Resumo: Os catalisadores à base de paládio apresentam particular interesse para o tratamento de gases de exaustão automotiva, notadamente no caso da combustão do etanol. O presente trabalho tem o objetivo de estudar as propriedades físico- químicas de catalisadores Pd - Fe e Pd - Co suportados em alumina modificada pelo óxido de cério. Para tanto, catalisadores modelo foram preparados através do método de impregnação por via úmida, empregando-se sais precursores à base de nitrato dos metais, e os suportes Al2O3, CeO2 e CeO2/Al2O3. Os catalisadores obtidos tiveram seus teores metálicos determinados por meio de espectrofotometria de absorção atômica, tendo sido caracterizados através de adsorção de nitrogênio (método B.E.T), espectroscopia no infravermelho, difração de raio-X, redução à temperatura programada. Os sistemas preparados foram avaliados pela reação catalítica de oxidação do etanol em fase gasosa em um microreator tubular de leito fixo, operando a pressão atmosférica e a temperatura de 3500 C. Os catalisadores preparados apresentam frações mássicas em torno de 2 % para o Pd, e de 1% para os aditivos Fe ou Co. A adição de Pd, Pd-Fe e Pd-Co aos suportes Al2O3 e CeO2/Al2O3 não levou a modificações, nos volumes dos poros e nas áreas superficiais específicas. Esses resultados mostram que a adição dos metais pouco influenciam nas características texturais. Enquanto para os bimetálicos suportados em céria, há a hipótese da existência de microporos apesar de ter ocorrido diminuições relativas das áreas superficiais específicas os volumes dos poros permanecem constantes. Na reação de oxidação do etanol, os resultados das análises cromatográficas levam a concluir que a introdução dos aditivos cobalto e ferro ao paládio provoca redução de eficiência na conversão do etanol para os sistemas CeO2 e CeO2/Al2O3. A adição do cobalto ao paládio na alumina aumenta a conversão e apresenta alto rendimento para a oxidação do etanol e o catalisador paládio suportado em céria apresenta conversão menor do que o Pd-Co sobre alumina porém rendimentos semelhantes / Abstract: Palladium based catalysts have been, applied at the treatment of the automotive gas exhaustion, particularly in the case of ethanol combustion. In this context, the actual work has the aim to study the physical and chemical properties of the Pd, Pd-Fe and Pd-Co catalysts supported in alumina, ceria and alumina modified by the cerium oxide. The wet impregnation method was used to develop the model catalysts. Precursor salts metal nitrates as well as the supports Al2O3, CeO2 and CeO2/Al2O3, were used for this purpose. The catalysts were characterised by the methods of BET-N2, infrared spectroscopy (I.R), X- ray diffraction (XRD) and reduction at programmed temperature (TPR). The contents of the metal impregnated in the catalysts was quantified by atomic absorption spectrophotometry (A.A.S.). A fixed-bed tubular microreactor was used to evaluate the performance of the catalysts in the oxidation of ethanol in gas phase, at the atmospheric pressure and temperature of 350o C. The mass fractions observed for the palladium catalysts and those that had Fe and Co as additive, were around 2% and 1%, respectively. The addition of the Pd, Pd-Fe and Pd-Co to the alumina support and alumina modified by cerium oxide does not prove modification into they capacity of the porous and surface areas. This results prove that the addition of metals has no power to the textural characteristics. Whereas the supported bimetallic system in ceria has the theory of the existence of micropores despite of a relative decrease of specific surface areas, the capacity of porous remains stable. The ethanol oxidation reaction, and the results of the cromatographicas analysis conclude that the introduction of cobalt and iron into the palladium decreases the efficacy of ethanol conversion into the CeO2 and CeO2/Al2O3 systems. The addition of cobalt into the palladium in alumina increases the conversion and introduces high performance for the ethanol oxidation and the palladium catalyst supported by cerium shows minor , conversion than to the cobalt-palladium upom alumina, but with the same results / Doutorado / Sistemas de Processos Quimicos e Informatica / Doutor em Engenharia Química

The catalytic decomposition of the methane (DCM) can be recognized as a promising reaction for the production of COx-free hydrogen. At the same time the production of hydrogen formation occurs structured carbonaceous material, carbon nanotubes (NTC), which have intrinsic characteristics, such as flexibility, high thermal and electrical conductivity, high chemical and mechanical stability. This study aimed to the synthesis of catalytic materials for DCM reaction involving two distinct synthesis routes, metal-chitosan complexation preparation support (Al2O3) followed by anchoring (CeO2) and subsequently the active phase Ni or Fe, and replica method for the synthesis support (Al2O3) followed by the docking Ni or Fe. The catalytic activity of the catalysts synthesized were studied varying the temperature of reduction and reaction by checking the effect of conversion into nanostructured carbonaceous material as well as assessing the quality the NTC formed. The results showed that the nickel-containing species had higher methane conversions when compared with the iron catalysts. The variation of reaction conditions yielded different levels of carbon (1.83 to 13.71%), and more favorable at lower temperatures. The presence of nickel catalysts CeO2 inhibit carbon formation on the metal particle due to the redox properties of cerium become promising for hydrogen production. The catalytic activity of the catalysts synthesized by the replica method showed a similar tendency to catalysts synthesized by metal complexation - chitosan, wherein the nickel catalyst results presented satifastórios with carbon contents in the range from 0 to 31%. / Conselho Nacional de Desenvolvimento Científico e Tecnológico / A decomposição catalítica do metano (DCM) pode ser reconhecida com uma reação promissora para a produção de hidrogênio livre de COx. Paralelamente à produção de hidrogênio, ocorre a formação de materiais carbonáceos estruturados, os nanotubos de carbono (NTC), que possuem características intrínsecas, tais como, flexibilidade, elevada condutividade térmica e elétrica, alta estabilidade química e mecânica. Este trabalho teve como objetivo a síntese de materiais catalíticos para a reação de DCM envolvendo duas rotas de síntese distintas, complexação metal-quitosana para preparação do suporte (Al2O3) seguido da ancoragem (CeO2) e posteriormente as fases ativas Ni ou Fe, e o método da réplica para a síntese do suporte (Al2O3) seguido da ancoragem de Ni ou Fe. A atividade catalítica dos catalisadores sintetizados foi estudada variando a temperatura de redução e reacional, verificando o efeito da conversão em materiais carbonáceos nanoestruturados, bem como avaliando a qualidade dos NTC formados. Os resultados mostraram que as espécies contendo níquel obtiveram maiores conversões do metano quando comparados com os catalisadores de ferro. A variação das condições reacionais proporcionou diferentes teores em carbono (1,83 a 13,71%), sendo mais favorável em baixas temperaturas. A presença de CeO2 nos catalisadores de níquel inibiu a formação de carbono sobre a partícula metálica devido às propriedades redox do cério, tornando-se promissores para produção de hidrogênio. A atividade catalítica dos catalisadores sintetizados pelo método da réplica apresentou tendência similar aos catalisadores sintetizados via complexação metal – quitosana, no qual o catalisador de níquel apresentou resultados satifastórios com teores de carbono na faixa de 0 a 31%.

Currently, the oil of easy exploration has become increasingly scarce, and it may promote an increase in the prices of its derivatives and/or a possible shortage of raw materials, chemical products of great importance for the chemical industry. In addition, the reduction of dependence on non-renewable resources, such as the ones on petroleum-based, are firmly linked in the yearning of contemporary society, being the concept of "green" chemistry closely associated with the search for products and/or chemical processes that are linked to the use of clean technologies and sustainable development. Thus, many efforts have been employed in the search for new sources as chemical raw materials and energy through sources like carbohydrates from lignocellulosic biomass. In this context, the aim of this study was to implement and evaluate catalytic systems Sn base (IV) (dibutyltin dilaurate (IV) (DBTDL), Butylstannoic acid (BTA), di-n-butyl-oxo-stannane (DBTO) and tin oxide (SnO2)), in the conversion of carbohydrates such as fructose and glucose and chemical products with high added value (5-hidroximetilfurfal and lactic acid, for example), as compared to conventional systems without using catalyst reactions with the catalyst and sulfuric acid. The activity in terms of conversion, yield and selectivity of these catalytic complexes were evaluated in reactions performed at temperatures of 150 to 190 ° C, in water, at various reaction times. At 150 ° C, the use of catalysts led to low yields and conversions, however, the 190 ° C catalysts BTA, DBTO and DBTDL performed well in the fructose degradation reactions, with complete conversion within 30 min of reaction. The three systems were selective principally to lactic acid: BTA showed lower selectivity (33%) whereas the selectivity to DBTO and DBTDL catalyst was 55% at 30 min. The DBTO was also evaluated at times of 5, 10 and 15 min. The conversion was greater than 90% at 5 and 10 min, and the total in 15 min, with selectivity to lactic acid of 58% already at 15 min. For glucose degradation reactions, the metal complex DBTO was also active in isomerizing glucose to fructose and convert it into products such as 5-hydroxymethylfurfural and lactic acid, but with lower yields when compared with the results obtained with fructose. / Atualmente, o petróleo de fácil exploração vem ficando cada vez mais escasso, podendo promover um aumento nos preços de seus derivados e/ou uma possível escassez das matérias-primas, insumos químicos de grande importância para a indústria química. Além disso, a redução da dependência de recursos não renováveis, como os a base de petróleo, estão firmemente atrelados no anseio da sociedade contemporânea, sendo o conceito de química “verde”, intimamente associado à busca por produtos e/ou processos químicos que estejam vinculados ao uso de tecnologias limpas e ao desenvolvimento sustentável. Com isso, muitos esforços têm sido empregados na busca de novas fontes como insumos químicos e energia através de fontes como carboidratos da biomassa lignocelulósica. Neste contexto, o objetivo deste trabalho foi o de aplicar e avaliar sistemas catalíticos a base de Sn(IV) (Dibutildilaurato de estanho (IV) (DBTDL), Ácido butilestanóico (BTA), Óxido de dibutil estanho (DBTO) e Óxido de estanho (SnO2)), na conversão de carboidratos como frutose e glicose em insumos químicos com alto valor agregado (5-hidroximetilfurfal e ácido lático, por exemplo), comparativamente a sistemas tradicionais como reações sem uso de catalisador e com o catalisador ácido sulfúrico. A atividade em termos de conversão, rendimento e seletividade desses complexos catalíticos foram avaliadas em reações realizadas nas temperaturas de 150 e 190 ºC, em água, em diversos tempos de reação. A 150 ºC, o emprego dos catalisadores conduziram a baixos rendimentos e conversões, porém, a 190 ºC os catalisadores BTA, DBTO e DBTDL apresentaram bom desempenho nas reações de degradação da frutose, havendo conversão total em 30 min de reação. Os três sistemas foram seletivos, principalmente, a ácido lático: o BTA apresentou menor seletividade (33 %) enquanto que a seletividade para os catalisadores DBTO e DBTDL foi de 55 % em 30 min. O DBTO também foi avaliado em tempos de 5, 10 e 15 min. A conversão foi superior a 90 % em 5 e 10 min e total em 15 min, com seletividade a ácido lático de 58 % já em 15 min. Para as reações de degradação da glicose, o complexo metálico DBTO também foi ativo em isomerizar a glicose à frutose, e convertê-la em produtos como o 5-hidroximetilfurfural e ácido lático, porém com menores rendimentos quando se compara com os resultados obtidos com a frutose.

Este trabalho teve como objetivo investigar eletrocatalisadores de baixo custo à base de carbeto de tungstênio, carbono e ferro submetidos a diferentes processos de nitretação quanto à atividade catalítica para reação de redução do oxigênio (RRO) nos eletrólitos ácido e alcalino. Os catalisadores foram divididos em três séries distintas, a primeira compreendendo aqueles onde houve variação da carga de carbeto de tungstênio em relação ao suporte de carbono, que foram impregnados com o complexo Fe2+(2,4,6-Tris(2-piridil)-1,3,5-Triazina)2, [Fe(TPTZ)2]2+ e tratados em duas temperaturas diferentes, 700 e 800 oC em atmosfera de nitrogênio. Na segunda série foi mantida constante a carga de carbeto de tungstênio (30% de W/C, m/m) sendo que esta mescla foi preparada usando carbonos dopados previamente com três fontes distintas de nitrogênio (HNO3, NH3 e HNO3/NH3); isto foi seguido pela incorporação do complexo Fe[TPTZ]2+ e pelos mesmos tratamentos térmicos acima mencionados. Na terceira série, os eletrocatalisadores foram preparados com três tipos de carbonos (Vulcan, Ketjenblack e Monarch), aos quais foi incorporado o complexo Fe[TPTZ]2+, seguido pelo tratamento térmico a 800 °C em atmosfera de nitrogênio e então por dopagem com amônia a 950 °C. As três séries de eletrocatalisadores sintetizados neste trabalho foram cuidadosamente caracterizadas por espectroscopia infra-vermelho e UV-Visível, difratometria de raio-x, microscopia eletrônica de transmissão, energia dispersiva de raios-x, espectroscipia Raman, espectroscopia fotoeletrônica de raios-x. As investigações eletroquímicas foram realizadas por voltametria cíclica (VC) e pelo levantamento de curvas de polarização de estado estacionário para a RRO, usando a técnica de eletrodo de disco/anel rotatório, com materiais catalíticos formando filmes finos depositados no eletrodo de disco. Nas três séries de catalisadores foram desenvolvidos materiais com bom desempenho para a RRO. Nos estudos da primeira série de catalisadores, notou-se que o material mais ativo foi aquele formado por WC-FeNx/C com 30 % de W/C e 5% de Fe pirolisado a 800 °C. Na segunda série foi observado que os desempenhos dos catalisadores variaram de acordo com o tipo de protocolo de nitretação, presença de ferro e temperatura de tratamento térmico. Em eletrólito alcalino, os eletrocatalisadores apresentaram maiores desempenhos, que resultaram bastante próximos em relação ao do catalisador de Pt dispersa em carbono usado como referência. Na terceira série de eletrocatalisadores investigados, verificou-se que o melhor desempenho obtido foi com o catalisador com carbono Monarch com amônia, cuja atividade catalítica resultou superior à dos demais, devido ao maior número de estruturas ativas FeNx e N/C formadas pelo tratamento com amônia. Os resultados nos meios ácido e alcalino para a primeira e segunda séries de eletrocatalisadores sugerem a ocorrência de um mecanismo indireto (2e- + 2e-), ou seja, em meio ácido (alcalino) primeiro o O2 reduz para H2O2 (HO2 ) e depois de H2O2 (HO2 ) para H2O. Os sítios predominantemente envolvidos na catálise da reação são WC e FeNx em meio ácido e WC e N/C em meio alcalino. Finalmente, para a terceira série de eletrocatalisadores o mecanismo reacional em meio ácido envolve um mecanismo direto de 4e-, com participação importante dos sítios ativos de Fe-N2. / This work aims to investigate low cost electrocatalysts based on tungsten carbide, carbon and iron submitted to different nitriding processes for the catalytic activity for the oxygen reduction reaction (ORR) in acid and alkaline electrolytes. The catalysts were divided into three distinct series, the first one comprising those with different tungsten carbide loads with respect to the carbon support, which were impregnated with the Fe2+ (2,4,6-Tris (2-pyridyl) - 1,3,5-triazine)2, [Fe (TPTZ)]2+, complex and treated at two different temperatures, 700 and 800 oC in nitrogen atmosphere. In the second series, the tungsten carbide load (30% W/C, m/m) was kept constant but this mixture was prepared using previously doped carbons using three different sources of nitrogen (HNO3, NH3 and HNO3/NH3); this was followed by the incorporation of the Fe[TPTZ]2+ complex and by the same heat treatments as mentioned above. In the third series, the electrocatalysts were prepared with three carbon types (Vulcan, Ketjenblack and Monarch), to which the Fe[TPTZ]2+ complex was added, followed by heat treatment at 800 °C under nitrogen and then by nitriding using a flow of ammonia at 950 °C. The three series of electrocatalysts synthesized in this work were carefully characterized by infra-red and UV-Visible spectroscopy, x-ray diffraction, transmission electron microscopy, x-ray energy dispersive, Raman spectroscopy, x-ray photoelectron spectroscopy. The electrochemical investigations were performed by cyclic voltammetry (CV) and by measurements of steady-state polarization curves for ORR using rotating ring-disc electrode technique, with catalytic materials forming thin films deposited on the disc. In the three catalyst series, materials with good performance for the ORR were developed. In the studies of the first series of catalysts, it was seen that the most active material was that formed by WC-FeNx/C with 30%W/C and 5% Fe pyrolyzed at 800 ° C. In the second series it was observed that the performances of the catalysts varied according to the type of nitriding protocol, presence of iron and temperature of heat treatment. The electrocatalysts showed higher performances in alkaline electrolyte, which were very close to that of a reference Pt/C catalyst. In the third series of electrocatalysts, the best performance was obtained with the Monarch carbon catalyst heat-treated with ammonia, whose catalytic activity was higher than all others, due to the greater number of FeNx and N/C active structures formed by the treatment with ammonia. The results in acidic and alkaline conditions for the first and second series of electrocatalysts suggest the occurrence of an indirect ORR mechanism (2e- + 2e-), that is, in acid (alkaline) media first O2 is reduced to H2O2 (HO2) followed by the reduction of H2O2 (HO2). The active sites predominantly involved in the reaction electrocatalysis are WC and FeNx in acid media and WC e N/C in alcaline media. Finally, for the third series of electrocatalysts, the acidic reaction involves a direct 4e- mechanism, having important participation of the Fe-N2 active sites.

A set of five new C3-symmetric phosphites were synthesized and tested in palladium-catalyzed asymmetric Suzuki coupling. The observed reactivity and selectivity were dependent upon several factors. One of the phosphites was able to achieve some of the highest levels of enantioselectivity in asymmetric Suzuki couplings with specific substrates. Different hypotheses have been made for understanding the ligand effects and reaction selectivities, and those hypotheses were tested via various methods including DOSY NMR experiments, X-ray crystallography, and correlation of catalyst selectivity with Tolman cone angles. Although only modest enantioselectivities were observed in most reactions, the ability to synthesis these phosphites in only three steps on gram scales and to readily tune their properties by simple modification of the binaphthyl 2´-substituents makes them promising candidates for determining structure-selectivity relationships in asymmetric transition metal catalysis, in which phosphites have been previously shown to be successful. A series of novel chiral oxazoline-based carbodicarbene ligands was targeted for synthesis. Unfortunately, the chosen synthetic route could not be completed due to unwanted reactivity of the oxazoline ring. However, a new and efficient route for Pd-catalyzed direct amination of aryl halides with oxazoline amine was developed and optimized during these studies. Chiral binaphthyl based Pd(II) ADC complexes with different substituent groups have been synthesized and tested in asymmetric Suzuki coupling reactions. Although only low enantioselectivities were observed in Suzuki coupling, this represents a new class of chiral metal-ADC catalysts that could be tested in further catalytic.

Catalysis is a key area of chemistry. Through catalysis it is possible to achieve better synthetic routes, exploit molecules normally considered to be inactive and also attain novel chemical transformations. The development of new catalysts is crucial to furthering chemistry as a field. Computational chemistry, arising from applying the equations of quantum and classical mechanics to solving chemical problems, offers an essential route to investigating the underlying atomistic detail of catalysis. In this thesis calculations have been applied towards studying a number of different catalytic processes. The processing of renewable chemical sources via homogeneous reactions, specifically cardanol from cashew nuts, is discussed. All routes examined for monoreduction of a diene model by [Ru(H)(iPrOH)(Cl)(C₆H₆)] and [Ru(H)(iPrOH)(C₆H₆)]⁺ are energetically costly and would allow for total reduction of the diene if they were operating. While this accounts for the need of high temperatures, further work is required to elucidate the true mechanism of this small but surprisingly complex system. Gold-mediated protodecarboxylation was examined in tandem with experiment to find the subtle steric and electronic effects that dictate CO₂ extrusion from gold N-heterocyclic carbene activated benzene-derived carboxylic acids. The origin of a switch in the rate limiting step from decarboxylation to protodeauration with less activated substrates was also clearly demonstrated. Studies of gold systems are closed with examinations of 1,2-difluorobenzene C–H activation and CO₂ insertion by [Au(IPr)(OH)]. Calculations highlight that the proposed mechanism for oxazole-derived substrates cannot be extended to 1,2-difluorobenzene and instead a digold complex offers more congruent predicted kinetics. The lens of quantum chemistry was turned upon palladium-mediated methoxycarbonylation reactions. An extensive study was undertaken to attempt to understand the bidentate diphosphine ligand dependency on forming either methylpropanoate (MePro) or copolymers. Mechanisms currently suggested in literature are shown to be incongruous with the formation of MePro by Pd(OAc)₂ and bulky diphosphines. A possible alternative route is proposed in this thesis. Four mechanisms for methoxycarbonylation with Pd(2-PyPPh₂)ₙ are detailed. The most accessible route is found to be congruent with experimental reports of selectivity, acid dependency and slight steric modifications. A modification of 2-PyPPh₂ to 2-(4-NMe₂-6-Me)PyPPh₂ is shown to improve both selectivity and turnover, the latter by four orders of magnitude (highest transition state from 22.9 kcal/mol to 16.7 kcal/mol ∆G), and this new second generation in silico designed ligand is studied for its applicability to wider substrate scope and different solvents. The final chapter of this thesis is a mixed quantum mechanics and molecular mechanics (QM/MM) examination of an enzymatic reaction, discussing the need for certain conditions and the role of particular amino acid residues in an S[sub]N2 hydrolysis reaction.