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Neste trabalho os diferentes sistemas eletrocatalíticos PtIn/C, PtRu/C, PtRuIn/C e suas diferentes proporções mássicas foram sintetizados pelo método de redução por Borohidreto de Sódio, a fim de serem utilizados como ânodo na célula a combustível alcalina de metanol direto (DMFC). Os materiais obtidos foram caracterizados pelas técnicas de EDX, DRX e MET. O método de redução aplicado na síntese se mostrou efetivo, uma vez que as partículas apresentaram boa dispersão no suporte de carbono Vulcan XC72, de acordo com as analises de EDX e MET. Os resultados obtidos por DRX evidenciaram em todos os difratogramas apresentados a estrutura CFC da platina e um relativo deslocamento do pico equivalente ao plano (220) para valores maiores e menores que 2θ. O tamanho médio do cristalito e os parâmetros de rede calculados indicaram a inserção de átomos de Índio e Rutênio à estrutura da Platina, supondo a formação de ligas. A oxidação eletroquímica do metanol foi estudada por voltametria cíclica, cronoamperometria e curvas de polarização. Os experimentos eletroquímicos demonstraram que nos eletrocatalisadores binários com maior composição de Índio e Rutênio a eficiência catalítica frente a oxidação do combustível foi melhor e para os ternários, o eletrocatalisador que possuía maior composição de Rutênio se mostrou mais eficiente. Nos experimentos práticos em células a combustível, as curvas de polarização mostraram divergências de resultados com os obtidos por voltametria cíclica e cronoamperometria, justificadas por problemas de prensagem e descolamento de MEA\'s em sistemas que apresentaram maior quantidade de cocatalisador como Índio e Rutênio. / In this work the different electrocatalytic systems PtIn/C, PtRu/C, PtRuIn/C and their different mass proportions were synthesized by the sodium borohydride reduction method, in order to be used as an anode in the alkaline direct methanol fuel cell (DMFC). The obtained materials were characterized by EDX, DRX and MET techniques. The reduction method applied in the synthesis was effective, since the particles showed good dispersion in the carbon support Vulcan XC72, according to the EDX and MET analyzes. The results obtained by XRD showed in all the diffractograms presented the CFC structure of platinum and a relative displacement of the equivalent peak to the plane (220) for values greater than and less than 2θ. The mean crystallite size and the calculated net parameters indicated the insertion of Indium and Ruthenium atoms to the Platinum structure, assuming the formation of alloys. The electrochemical oxidation of methanol was studied by cyclic voltammetry, chronoamperometry and polarization curves. The electrochemical experiments showed that in the binary electrocatalysts with higher composition of Indium and Ruthenium, the catalytic efficiency against the oxidation of the fuel demonstrated a better result. Meanwhile the ternary, the electrocatalyst with the higher Ruthenium composition was more efficient. In terms of the practical experiments in fuel cells, the polarization curves showed divergences of results with those obtained by cyclic voltammetry and chronoamperometry, which can be justified by issues of pressing and detachment of MEA\'s in systems that presented higher amounts of cocatalysts such as Indium and Ruthenium.

Orientador: Hebe de las Mercedes Villullas / Banca: Elisabete Inácio Santiago / Banca: Margarida Juri Saeki / Resumo: Nesse trabalho foi realizado um estudo da atividade de catalisadores de PdRu suportados em carbono para a reação de oxidação de metanol em meio alcalino, fazendo-se uma comparação com materiais similares baseados em Pt (PtRu/C). Os catalisadores foram sintetizados pelo método do poliol modificado, com composições nominais Pd:Ru e Pt:Ru de 1:1. Os estudos foram realizados de modo comparativo utilizando os materiais como preparados e tratados termicamente em 200 ºC e 400 ºC em atmosfera de argônio. Os estudos por difratometria de raios X mostraram incorporação de Ru na rede do Pd que, pela sua vez, aumentou com o tratamento térmico. Diferentemente, a incorporação de Ru na rede da Pt foi observada somente após tratamento a 400 ºC. As microscopias eletrônicas de transmissão mostraram tamanho médio de partículas próximo dos 3 nm para os materiais a base de Pd e 2 nm para os materiais a base de Pt. As medidas de espectroscopia de absorção de raios X (XAS) mostraram que para todos os materiais a adição de Ru aumenta a vacância da banda 4d do Pd ou 5d da Pt. A oxidação de metanol nos catalisadores de PdRu mostrou uma relação com a vacância da banda 4d do Pd, onde o material com a banda mais vazia foi o que mostrou a maior densidade de corrente. Os espectros na região do infravermelho mostraram que tanto para os materiais de Pd quanto para os de Pt os produtos majoritários são formiato, carbonato e dióxido de carbono, em proporção que varia com o potencial. Os dados indicam que os desempenhos dependem principalmente das propriedades eletrônicas, que pela sua vez determinariam a frequência de "turnover". Os catalisadores de Pt mostraram comportamentos similares, com correntes de oxidação um pouco maiores. As diferenças de desempenho, no entanto, não são muito marcantes e permitiriam substituir Pt por Pd. / Abstract: In this work, we present a study of the activity of carbon-supported PdRu catalysts for the methanol oxidation reaction in alkaline medium, as well as the comparison with similar materials based on Pt (PtRu/C). The catalysts were synthesized by a modified poliol method with nominal atomic composition Pd:Ru and Pt: Ru of 1:1. The studies were carried out in a comparative fashion for the as-prepared materials and those thermally treated at 200 ° C and 400 ° C in an argon atmosphere. X-ray diffraction (XDR) showed incorporation of Ru into the Pd lattice, which increased with heat treatment. In contrast, Ru incorporation in Pt network was observed only after treatment at 400 °C. Transmission electronic microscopy showed average particle sizes near 3 nm for Pd and near 2 nm for Pt-based materials. Measurements of X-ray absorption spectroscopy (XAS) showed that for all materials the addition of Ru increases the vacancy of the Pd 4d band or Pt 5d band. Methanol oxidation on PdRu catalysts showed a relation with the Pd 4d band vacancy, at the time that the material with the highest vacancy was the one that showed the largest current density. The infrared spectra showed that, for both Pd and Pt materials, formate and CO32- / CO2 are the main products, while their relative amounts change with applied potential. Data indicate that methanol oxidation activity depends mainly on the electronic properties, which determine the turnover frequency. Pt catalysts showed similar behavior, with slightly higher current densities. The differences in performances, however, are not very large and, thus, substitution of Pt by Pd would be feasible. / Mestre

A sociedade moderna depende integralmente da produção e consumo de energia em seu dia a dia desde cozinhar, ter energia elétrica, transporte, e para processos industriais. O aumento da demanda de energia elevou também os níveis de poluição, o que produz efeitos diretos na saúde do homem. Desta forma, o homem tem que pesquisar novas formas de energia, que em condições ideais, deve ser gerada de forma limpa. Uma alternativa para que se possa enfrentar este problema é a conversão eletroquímica de energia, a qual pode ser realizada de forma eficiente e limpa através das células a combustível. Existe um interesse muito grande em células que oxidam metanol como combustível, para a aplicação em veículos e equipamentos portáteis. No entanto, para se implementar estas células, é necessário um grande progresso na caracterização dos fenômenos eletródicos associados a esta reação, tanto em nível fundamental quanto tecnológico. No presente trabalho foram desenvolvidos catalisadores de PtW, PtOs, PtRuW, PtWOs, suportados em carbono de alta área superficial, para a oxidação de metanol. Os catalisadores foram preparados através da redução por ácido fórmico e através do método de Bonnëmann. As composições dos materiais foram determinadas por EDX. O tamanho médio das partículas foi obtido por TEM, e foi comparado ao tamanho médio dos cristalitos à partir dos difratogramas de raios X. Os estudos eletroquímicos foram realizados através de voltametrias cíclicas e curvas corrente potencial de estado estacionário utilizando-se a técnica do eletrodo de camada fina porosa. Foram feitas também medidas de EXAFS nos catalisadores mais promissores. Os catalisadores possuem atividade na faixa de potencial de interesse, e foram feitos alguns testes em células a combustível. / Modern society integrally depends on the production and consumption of energy for its activities like cooking, lighting and transportation and also for industrial processes. The increase in the demand for energy increases the levels of pollution, which has a direct negative effect in human health. Thus, it is imperative to search for new power sources which, under ideal conditions, do not pollute the environment. One of the alternatives to attack this problem is the electrochemical energy conversion of chemical energy into electricity which can be carried out in an efficient and clean way with fuel cells. Presently, there is a great interest in fuel cells that oxidize methanol directly, for application in vehicles, portable devices and distributed generation. To make these cells a reality it is still necessary much progress in the understanding of the electrodic phenomena associated to the oxidation of methanol, and in the development of suitable electrocatalysts, at both the fundamental and the technological levels. In this work, PtW; PtOs, PtRuW and PtWOs eletrocatalysts, supported on high surface area carbon, for the direct oxidation of methanol were developed. The catalysts were prepared by reduction with formic acid of the corresponding precursors and by Bonnëmann´s method. Their composition was determined by XRD. The average particle size was determined from TEM, and the results compared to crystallite sizes determined from x-ray diffractograms. The electrochemical studies were carried out with cyclic voltammetry and steady state polarization curves using the thin porous coating electrode technique. Some catalysts were also studied by the EXAFS technique. The catalysts prepared show activity in the potential region of interest, and some of then were tested in single fuel cells.

Tese de doutoramento. Engenharia Química e Biológica. Faculdade de Engenharia. Universidade do Porto. 2009

<p>The main objectives of the thesis work were: (1), to study the oxidation of methanol and formic acid on platinum electrodes by employing conventional and advanced electrochemical methods, and (2), to develop membrane electrode assemblies based on polybenzimidazole membranes that can be used in fuel cells up to 200 °C.</p><p>D.c. voltammetry and a.c. voltammetry studies of methanol and formic acid on polycrystalline platinum in sulphuric acid electrolyte were performed to determine the mechanism and kinetics of the oxidation reactions.</p><p>A combined potential step and fast cyclic voltammetry experiment was employed to investigate the time dependence primarily of methanol oxidation on platinum. Charge measurements clearly demonstrated the existence of a parallel path at low potentials and short times without formation of adsorbed CO. Furthermore, experimental results showed that only the serial path, via adsorbed CO, exists during continuous cycling, with the first step being diffusion controlled dissociative adsorption of methanol directly from the bulk electrolyte. The saturation charge of adsorbed CO derived from methanol was found to be significantly lower than CO derived from formic acid or dissolved CO. This was attributed to the site requirements of the dehydrogenation steps, and possibly different compositions of linear, bridged or multiply bonded CO. The coverage of adsorbed CO from formic acid decreased significantly at potentials just outside of the hydrogen region (0.35 V vs. RHE), while it did not start to decrease significantly until about 0.6 V vs. RHE for methanol. Adsorbed CO from dissolved CO rapidly oxidized at potentials above about 0.75 V due to formation of platinum oxide.</p><p>Data from a.c. voltammograms from 0.5 Hz up to 30 kHz were assembled into electrochemical impedance spectra (EIS) and analyzed using equivalent circuits. The main advantages of collecting EIS spectra from a.c. voltammetry experiments are the ability to directly correlate the impedance spectra with features in the corresponding d.c. voltammograms, and the ability to investigate conditions with partially covered surfaces that are inaccessible in steady-state measurements.</p><p>A variety of spectral types were observed, and for methanol these showed only a single adsorption relaxation aside from the double-layer/charge-transfer relaxation, though some structure in the phase of the latter relaxation hints at another process. The charge-transfer resistance showed Tafel behaviour for potentials in the rising part of the oxidation peak consistent with a one-electron process in the rate-determining step. The rate limiting step was proposed to be the electrochemical reaction between adsorbed CO and OH at the edge of islands of OH, with competition between OH and CO adsorption for the released reaction sites. Only a single adsorption relaxation in methanol oxidation was observed, implying that only one single coverage is required to describe the state of the surface and the kinetics. It was assumed that this single coverage is that of OH, and all the surface not covered with OH is covered with CO so that the coverage of CO is not an independent variable. Inductive behaviour and negative relaxation times in the methanol oxidation were attributed to nucleation and growth behaviour. Linear voltammetry reversal and sweep-hold experiments also indicated nucleation-growth-collision behaviour in distinct potential regions, both in the forward and reverse potential scan for methanol oxidation on platinum.</p><p>In both methanol oxidation and formic acid oxidation, a negative differential resistance (NDR) was observed in the potential regions that possess a negative d.c. polarization slope, and was attributed to the formation of surface oxide which inhibited the oxidation of methanol or formic acid.</p><p>EIS spectra for formic acid clearly showed the presence of an additional low frequency relaxation at potentials where we expect adsorbed dissociated water or platinum oxide to be present, implying that more than one single coverage is required to describe the state of the surface and the kinetics. Two potential regions with hidden negative differential resistance (HNDR) behaviour were identified in the positive-going sweep, one prior to platinum oxide formation, assumed to involve adsorbed dissociated water, and one just negative of the main oxidation peak, assumed to involve platinum oxide. Oscillatory behaviour was found in the formic acid oxidation on platinum by adding a large external resistance to the working electrode circuit, which means that there is no longer true potentiostatic control at the interface. By revealing the system time constants, impedance measurements can be used to assist in explaining the origin of the oscillations. In the case of formic acid, these measurements showed that the oscillations do not arise from the chemical mechanism alone, but that the potential plays an essential role.</p><p>Preparation and optimization of gas-diffusion electrodes for high temperature polymer electrolyte fuel cells based on phosphoric acid doped polybenzimidazole (PBI) membranes was performed. This fuel cell allows for operating temperatures up to 200 °C with increased tolerance towards catalytic poisons, typical carbon monoxide. In this work we employed pure hydrogen and oxygen as the fuel cell feeds, and determined the optimum morphology of the support layer, and subsequently optimized the catalytic layer with respect to platinum content in the Pt/C catalyst and PBI loading. A smooth and compact support layer with small crevices and large islands was found to be beneficial with our spraying technique in respect to adhesion to the carbon backing and to the catalyst layer. We found that a high platinum content catalyst gave a significantly thinner catalyst layer (decreased porosity) on both anode and cathode with superior performance. The PBI loading was found to be crucial for the performance of the electrodes, and a relatively high loading gave the best performing electrodes.</p>

The main objectives of the thesis work were: (1), to study the oxidation of methanol and formic acid on platinum electrodes by employing conventional and advanced electrochemical methods, and (2), to develop membrane electrode assemblies based on polybenzimidazole membranes that can be used in fuel cells up to 200 °C. D.c. voltammetry and a.c. voltammetry studies of methanol and formic acid on polycrystalline platinum in sulphuric acid electrolyte were performed to determine the mechanism and kinetics of the oxidation reactions. A combined potential step and fast cyclic voltammetry experiment was employed to investigate the time dependence primarily of methanol oxidation on platinum. Charge measurements clearly demonstrated the existence of a parallel path at low potentials and short times without formation of adsorbed CO. Furthermore, experimental results showed that only the serial path, via adsorbed CO, exists during continuous cycling, with the first step being diffusion controlled dissociative adsorption of methanol directly from the bulk electrolyte. The saturation charge of adsorbed CO derived from methanol was found to be significantly lower than CO derived from formic acid or dissolved CO. This was attributed to the site requirements of the dehydrogenation steps, and possibly different compositions of linear, bridged or multiply bonded CO. The coverage of adsorbed CO from formic acid decreased significantly at potentials just outside of the hydrogen region (0.35 V vs. RHE), while it did not start to decrease significantly until about 0.6 V vs. RHE for methanol. Adsorbed CO from dissolved CO rapidly oxidized at potentials above about 0.75 V due to formation of platinum oxide. Data from a.c. voltammograms from 0.5 Hz up to 30 kHz were assembled into electrochemical impedance spectra (EIS) and analyzed using equivalent circuits. The main advantages of collecting EIS spectra from a.c. voltammetry experiments are the ability to directly correlate the impedance spectra with features in the corresponding d.c. voltammograms, and the ability to investigate conditions with partially covered surfaces that are inaccessible in steady-state measurements. A variety of spectral types were observed, and for methanol these showed only a single adsorption relaxation aside from the double-layer/charge-transfer relaxation, though some structure in the phase of the latter relaxation hints at another process. The charge-transfer resistance showed Tafel behaviour for potentials in the rising part of the oxidation peak consistent with a one-electron process in the rate-determining step. The rate limiting step was proposed to be the electrochemical reaction between adsorbed CO and OH at the edge of islands of OH, with competition between OH and CO adsorption for the released reaction sites. Only a single adsorption relaxation in methanol oxidation was observed, implying that only one single coverage is required to describe the state of the surface and the kinetics. It was assumed that this single coverage is that of OH, and all the surface not covered with OH is covered with CO so that the coverage of CO is not an independent variable. Inductive behaviour and negative relaxation times in the methanol oxidation were attributed to nucleation and growth behaviour. Linear voltammetry reversal and sweep-hold experiments also indicated nucleation-growth-collision behaviour in distinct potential regions, both in the forward and reverse potential scan for methanol oxidation on platinum. In both methanol oxidation and formic acid oxidation, a negative differential resistance (NDR) was observed in the potential regions that possess a negative d.c. polarization slope, and was attributed to the formation of surface oxide which inhibited the oxidation of methanol or formic acid. EIS spectra for formic acid clearly showed the presence of an additional low frequency relaxation at potentials where we expect adsorbed dissociated water or platinum oxide to be present, implying that more than one single coverage is required to describe the state of the surface and the kinetics. Two potential regions with hidden negative differential resistance (HNDR) behaviour were identified in the positive-going sweep, one prior to platinum oxide formation, assumed to involve adsorbed dissociated water, and one just negative of the main oxidation peak, assumed to involve platinum oxide. Oscillatory behaviour was found in the formic acid oxidation on platinum by adding a large external resistance to the working electrode circuit, which means that there is no longer true potentiostatic control at the interface. By revealing the system time constants, impedance measurements can be used to assist in explaining the origin of the oscillations. In the case of formic acid, these measurements showed that the oscillations do not arise from the chemical mechanism alone, but that the potential plays an essential role. Preparation and optimization of gas-diffusion electrodes for high temperature polymer electrolyte fuel cells based on phosphoric acid doped polybenzimidazole (PBI) membranes was performed. This fuel cell allows for operating temperatures up to 200 °C with increased tolerance towards catalytic poisons, typical carbon monoxide. In this work we employed pure hydrogen and oxygen as the fuel cell feeds, and determined the optimum morphology of the support layer, and subsequently optimized the catalytic layer with respect to platinum content in the Pt/C catalyst and PBI loading. A smooth and compact support layer with small crevices and large islands was found to be beneficial with our spraying technique in respect to adhesion to the carbon backing and to the catalyst layer. We found that a high platinum content catalyst gave a significantly thinner catalyst layer (decreased porosity) on both anode and cathode with superior performance. The PBI loading was found to be crucial for the performance of the electrodes, and a relatively high loading gave the best performing electrodes.

Det nya svaveldirektivet för hur mycket svavel fartygen i Östersjön och Nordsjön får släppa ut börjar gälla 2015. Detta har stor betydelse bland annat för färjerederierna som trafikerar inom SECA i Östersjön och Nordsjön. Idag finns det ingen självklar lösning på hur färjerederierna ska uppfylla det nya svaveldirektivet, så hur har de tänkt klara det? Hur såg färjerederiernas resonemang ut innan de valde vilken teknisk lösning de skulle använda sig av? För att få svar på frågeställningen används en kvalitativ metod. Rådata som varit till grund för slutsatsen har samlats in från sju olika talespersoner för färjerederier i Norden. Dessa talespersoner har varit insatta i fartygens drift och har goda kunskaper om fartygen och deras framdrift. I slutsatsen har vi sammanfattat resultaten av olika tekniska lösningar som rederierna har diskuterat under intervjuerna. Slutsatsen av undersökningen är att de flesta av färjerederierna kommer gå över helt till MGO eller WRD för att klara de nya svaveldirektivet år 2015, tills något bättre alternativ finns. De inblandade rederierna och deras talespersoner har tilldelats fingerade namn. / The new sulphur directive, concerning the quantity of sulphur that vessels in the Baltic Sea and North Sea are allowed to discharge in form of exhaust gases, takes effect in 2015. This has a great impact on the shipping companies traveling the Baltic- and North Sea SECA. Today there are no obvious solutions on how the ferry companies will be able to follow the new sulphur regulations, so how are they supposed to cope? In what way did they discuss matters before deciding upon which technical solution to choose? To answer the questions a qualitative method was used. Data, that has been the basis of this paper, has been collected from spokespersons from seven ferry companies in Scandinavia. These spokespersons have been familiar with the machinery on board and have significant knowledge of their vessels. In the conclusion we have summarized the results of different technical solutions that the shipping companies have discussed during the interviews. The conclusion of this paper is that most of the ferry companies will use MGO or WRD to cope with the new sulphur regulations until a better alternative is introduced. In order to maintain anonymity, the names of participating shipping companies and interviewees have been changed.

Orientador: Hebe de las Mercedes Villullas / Banca: Cecílio Sadao Fugivara / Banca: Marcelo Linardi / Resumo: Nanopartículas de Pt-Ru, com composição atômica nominal 50:50, foram preparadas utilizando-se microelmulsões de AOT (dietilhexilsulfosuccinato de sódio)/n-heptano/água e suportadas sobre carbono de alta área superficial (20% Pt-Ru/C em massa). Os precursores metálicos, dissolvidos na fase aquosa, foram reduzidos pela adição de NaBH4 sólido e, posteriormente, o carbono foi adicionado à mistura para a ancoragem das partículas. O material foi filtrado, lavado e seco a 75 °C. Os catalisadores suportados obtidos foram caracterizados por difração de raios X, espectroscopia de raios X por energia dispersiva, microscopia eletrônica de transmissão, termogravimetria e calorimetria exploratória diferencial. Os resultados das análises comprovaram os valores nominais de composição e mostraram que as nanopartículas estão uniformemente dispersas sobre o carbono e que o tamanho médio de cristalito variou de ~2,6 a 3,4 nm, dependendo da razão molar w = [água]/[surfactante]. Verificou-se ainda que o parâmetro de rede dos catalisadores preparados é menor, comparado ao da Pt suportada sobre carbono, indicando a formação de liga e que fração de Ru na liga aumentou com o tamanho de partícula. O tratamento térmico, em todos os casos, promoveu um aumento do tamanho de partícula e do grau de liga. Experimentos de oxidação de CO mostraram que os catalisadores preparados com diferentes valores de w apresentam diferenças significativas na estrutura e composição da superfície. A oxidação de metanol foi estudada por voltametria cíclica e cronoamperometria. O melhor desempenho eletrocatalítico foi observado para catalisadores preparados por microemulsão com w = 8. / Abstract: Pt-Ru nanoparticles, with nominal atomic composition 50:50, were prepared in AOT/nheptane/water microemulsions and supported on high surface area carbon (20% Pt-Ru/C weight). The metallic precursors, dissolved in the aqueous phase, were reduced by NaBH4 added as a solid. The carbon was directly incorporated into the mixture for the anchorage of the particles. The material was then filtered, washed, and dried at 75 °C. The supported catalysts obtained have been characterized by X-ray diffraction (DRX), energy dispersive Xray analysis (EDX), transmission electron microscopy (TEM), thermogravimetry (TGA) and differential scanning calorimetry (DSC). The results of these analyses confirmed the nominal chemical composition and showed an uniform dispersion of the particles on the carbon support. The average crystallite size was found to vary from ~2.6 to 3.4 nm, depending on the water to surfactant molar ratio w = [water]/[surfactant]. The lattice parameter of the prepared catalysts was found to be smaller than that for carbon supported Pt, indicating formation of a solid solution phase. The fraction of the alloyed Ru increased with particle size. In all cases, the heat treatment promoted an increase in the particle size and in the amount of alloying. CO stripping measurements showed that the surface properties of the prepared Pt-Ru/C catalysts are significantly different, depending on w values used in the synthesis. The methanol oxidation reaction was studied by cyclic voltammetry and chronoamperometry. The best performance was observed for catalysts prepared by microemulsions with w = 8. / Mestre

Orientador: Leinig Antonio Perazolli / Banca: Elias de Souza Monteiro Filho / Banca: Arnaldo Sarti / Banca: Eduardo Bessa Azevedo / Banca: Marcelo Henrique Armoa / Resumo: Este trabalho permitiu avaliar as propriedades fotocatalíticas de oxidação e redução de pós fotocatalisadores fixados na forma de filmes espessos e porosos de TiO2 em multicamadas modificados estruturalmente com nióbio, tântalo e tungstênio obtidos pelo do método Pechini e pela modificação superficial pela deposição de Pt metálica via sputtering. A modificação estrutural do TiO2 com estes metais visou substituir o Ti4+ por Nb5+, Ta5+ e W6+ o que promoveu além do aumento no tempo de recombinação do par elétron/lacuna e a geração de níveis doadores de elétrons na estrutura cristalina e pela modificação superficial dos filmes com Pt metálica depositados por sputtering que atuou na condução dos elétrons fotogerados. Os pós e filmes foram caracterizados utilizando-se as técnicas DRX, Rietveld, área de superfície SBET, Fotoluminescência, UV-Vis, MEV/EDS e XPS para verificação das fases presentes nos filmes além, de sua morfologia, características e interações superficiais. Foram realizados três ensaios fotoquímicos em meio aquoso no qual dois foram de oxidação (descoloração do corante rodamina B e degradação do hormônio 17α-etinilestradiol) e um de redução (formação de metanol a partir da redução do CO2). Para avaliar a ocorrência da oxidação, amostras de rodamina B e do 17α-etinilestradiol foram coletadas em tempos pré-estabelecidos durante as reações que foram analisadas por espectroscopia na região do UV-Vis e cromatografia líquida de alta eficiência respectivamente e para o ens... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This present work assessed the oxidative and reductive photocatalytic properties of powders fixed in the form of thick and porous TiO2 films in multilayers modified with niobium, tantalum and tungsten obtained by the Pechini method and the surface modification by the metallic Pt deposition through sputtering. The structural modification of TiO2 with these metals aimed at replacing Ti4+ by Nb5+, Ta5+ and W6+, which promoted, besides the increase in the electron-hole pair recombination time, the generation of electron donor levels in the crystalline structure and the surface modification of the films with metallic Pt deposited by sputtering that acted in the conduction of photogenerated electrons. The powders and films were characterized using the techniques XRD, Rietveld, SBET surface area, PL, UV-Vis, SEM/EDS and XPS to verify the phases present in the films beyond their morphology, characteristics and surface interactions. Three photochemical assays were performed in aqueous medium in which two oxidations (discoloration of rhodamine B dye and degradation of 17α-ethynylestradiol hormone) and one reduction (methanol formation from CO2) were performed. To assess the oxidation occurrence, samples were collected at pre-established times and analyzed by spectrophotometry in the UV-Vis region and by HPLC respectively. For the CO2 reduction test, samples were withdrawn and analyzed by GC to quntify the formation of methanol. The best result achieved by the surface modification with ... (Complete abstract click electronic access below) / Doutor