Diss. (sammanfattning). Uppsala : Sveriges lantbruksuniv. / Härtill 4 uppsatser.

Made available in DSpace on 2014-06-11T19:23:29Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-04-19Bitstream added on 2014-06-13T18:50:39Z : No. of bitstreams: 1 antoniassi_bs_me_bauru.pdf: 1977733 bytes, checksum: 9dd271c973d63a540d0f517fcfe56409 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O grande desafio a ser vencido para a utilização de células a combustível de oxidação direta de álcoois (DAFC) refere-se ao desenvolvimento de eletrocatalisadores que favoreçam a oxidação direta do combustível a CO2 e que sejam menos susceptíveis ao envenenamento por intermediários/produtos de reação. Fases intermetálicas ordenadas de Pt têm sido propostas como materiais eletrocatalisadores para estas reações pelo fato de poderem aliar a excelente capacidade de adsorção do orgânico pelos sítios de platina e minimizarem a ação de bloqueadores superficiais. Não menos importante, essa classe de materiais apresenta uma estabilidade físico-química acentuadamente superior a materiais obtidos por deposição de íons metálicos e, desta forma, é mais apropriada para ser empregada diretamente em sistemas reais. Baseado em estudos anteriores a respeito dos materiais obtidos por deposição de íons metálicos sobre a superfície de platina e também estudos preliminares de oxidação de orgânicos em fases intermetálicas ordenadas de PtBi, este trabalho apresenta os resultados obtidos através do estudo da eletrocatálise das reações de oxidação do ácido fórmico e do metanol sobre as fases intermetálicas PtMn, PtMo, PtPb, PtSb e PtSn, em meio ácido... / The great challenge to be won for the use of direct oxidation of alcohols fuel cells (DAFC) refers to the electrocatalytic development that favor the direct oxidation of the fuel CO2 and that are less susceptible to the poisoning by intermediates/products of reaction. Ordered intermetallic phases of Pt have been proposed as electrocatalytic materials for these reactions for the fact of they could ally the excellent capacity of adsorption of the organic for the platinum sites and they minimize the action of blocking superficial. No less important, that class of materials presents a physicochemical stability strongly to materials obtained by deposition of metallic íons and, this way, it is more appropriate to be used directly in real systems. Based on previous studies regarding the materials obtained by deposition of metallic íons on the platinum surface and also preliminary studies of oxidation of organic in ordered intermetallic phases of PtBi, this work presents the results obtained through the study of the electrocatalysis of the reactions of oxidation of the formic acid and of the methanol on the intermetallic phases PtMn, PtMo, PtPb, PtSb and PtSn, in acid middle... (Complete abstract, click eletronic address below)

Ce travail de thèse s'inscrit dans le cadre de la valorisation du CO2 par voie électrochimique. Il est consacré en grande partie à l'élaboration et l'étude physico-chimique d'électrodes à diffusion de gaz (GDE), dans le but de mieux comprendre les mécanismes et les paramètres déterminants pour l'électrocatalyse de la réduction du CO2 avec ce type d'électrodes poreuses. Cette étude est articulée autour de deux axes principaux, le premier concerne des catalyseurs métalliques et le second se focalise sur des catalyseurs moléculaires.Le premier axe est relatif à la préparation, la caractérisation et l'étude électrochimique de catalyseurs de Cu, Co, In, Zn, Bi, Fe et Pb supportés sur poudre de carbone poreux. La mise en œuvre de ces catalyseurs sous forme de GDE a été étudiée, ainsi que leur activité électrocatalytique vis-à-vis la réduction du CO2. En milieu aqueux, les GDE contenant de l'indium ont permis d'obtenir les meilleurs rendements faradiques pour l'électroréduction du CO2 en acide formique. Par comparaison avec une plaque métallique d'indium, les GDE-In/C montrent des performances catalytiques améliorées et une meilleure résistance aux impuretés de l'électrolyte. Nous avons montré, qu'en phase aqueuse, l'apport de CO2 gaz en continu à travers une GDE entraînait une amélioration de l'activité du catalyseur supporté. Ceci met en évidence l'intérêt d'utiliser des métaux sous forme de particules dispersées au sein d'une GDE plutôt que des électrodes métalliques massives.Le second axe de cette étude a fait appel à trois complexes dimère de ruthénium de formule générale [Ru(L)(CH3CN)(CO)2]2(PF6)2. L'étude des propriétés redox de ces précurseurs de catalyseurs contenant des ligands L (bipyridine) diversement substitués a permis de mettre en évidence la formation de polymères à liaisons Ru-Ru par électroréduction. Le ligand portant une fonction pyrrole permet, au préalable, la formation d'un film de polypyrrole conférant au catalyseur une meilleure stabilité et de meilleures performances catalytiques. Différentes stratégies d'immobilisation de ces complexes sur carbone poreux ont été utilisées pour obtenir des GDE modifiées. Cette étude a permis de mieux comprendre l'interaction entre le catalyseur moléculaire et le support lors de la réduction du CO2. Nous avons ainsi montré que l'activité électrocatalytique du catalyseur supporté sur GDE était maintenue en milieu aqueux.Parallèlement à ce travail fondamental, un pilote de laboratoire a été développé pour effectuer la réduction électrocatalytique du CO2 en phase gaz, afin de s'affranchir de limitations rencontrées en milieu aqueux, telles que la solubilité du CO2 et la séparation des produits de la réaction. Cette étude en cours de développement a permis d'identifier certains verrous, notamment la nature de la membrane échangeuse d'ions ainsi que la nature et la proportion du polymère électrolytique entrant dans la formulation de la couche catalytique. Ce travail apporte des connaissances fondamentales et des réponses concrètes qui permettront probablement qu'un tel procédé de valorisation du CO2 puisse constituer un jour un procédé viable à l'échelle industrielle. / This thesis concerns the valorization of CO2 by electrochemical means. It is largely devoted to the preparation and physico-chemical study of gas diffusion electrodes (GDE) in order to better understand the mechanisms and key parameters for electrocatalytic reduction of CO2 using this type of porous electrode. This study revolves around two main axes, the first is related to metal catalysts and the second is focused on molecular catalysts.The first axis deals with the preparation, characterization and electrochemical properties of Cu, Co, In, Zn, Bi, Pb and Fe catalysts supported on porous carbon powder. Their implementation to form GDE and their electrocatalytic activity toward CO2 reduction were studied. In aqueous medium, the GDE containing indium allowed obtaining the highest Faraday yields for electroreduction of CO2 to formic acid. In comparison with a metallic indium foil, the GDE-In/C showed improved catalytic performance and improved resistance to the electrolyte's impurities. We demonstrated that in the aqueous phase, a continuous flow of CO2 through a GDE resulted in an improved reactivity of the supported catalyst. This highlights the advantage of using dispersed metal particles on GDE rather than metal foil electrodes.The second axis of this study focuses on three dimeric ruthenium complexes with the general formula [Ru(L)(CH3CN)(CO)2]2(PF6)2. The study of the redox properties of these catalyst precursors containing variously substituted L (bipyridine) ligands, allowed the formation of polymer bonds of Ru-Ru by electroreduction to be demonstrated. The ligand with a pyrrole functional group allows for the prior formation of a polypyrrole film, conferring improved catalyst stability and enhancing the catalytic performance. Different ways of immobilizing the complex on porous carbon have been used to obtain modified GDE. This study provided insight into the interaction between the molecular catalyst and the catalyst carrier during the CO2 reduction. We have demonstrated that the electrocatalytic activity of the catalyst deposited on the GDE is maintained in an aqueous medium.Alongside this fundamental work, a laboratory pilot was developed to perform the electrocatalytic reduction of CO2 in the gas phase, in order to overcome limitations encountered in an aqueous medium, such as CO2 solubility and reaction products separation. This under development study has not only identified obstacles, including the nature of the ion exchange membrane, but has also identified the nature and proportion of the polymer electrolyte used in the formulation of the catalyst layer. This work has provided fundamental knowledge and concrete answers which probably allow one day that such a process as CO2 valorization may be viable on an industrial scale.

Orientador: Rodnei Bertazzoli / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-17T18:27:14Z (GMT). No. of bitstreams: 1 Ferreira_LeticiaHenn_D.pdf: 8093576 bytes, checksum: 15187c5b0528b3661b423da0a21ff079 (MD5) Previous issue date: 2011 / Resumo: Com a necessidade de mitigação dos gases do efeito estufa, principalmente CO2 torna-se imprescindível o desenvolvimento de novas tecnologias que contribuam para uma menor emissão e, preferencialmente, para a conversão do CO2 a outros produtos. Este é o enfoque deste trabalho: estudar a viabilidade do processo de redução eletroquímica do CO2 para a sua transformação em metanol, etanol e ácido fórmico. Para isto, foram utilizados eletrodos de difusão gasosa (EDG), cuja permeabilidade foi maximizada através de planejamento experimental. Os eletrodos foram catalisados com Cu, Zn, CuO e ZnO, através da decomposição térmica do sal do metal. A caracterização eletroquímica foi feita por voltametria e a microestrutural, por difratometria de raios X e microscopia eletrônica de transmissão. Os eletrodos foram avaliados nas densidades de corrente catódica 50, 70, 100 e 150 mA cm-2 e nas temperaturas 20, 40 e 60 °C, com exceção do catalisado com zinco, estudado somente a 20 °C. Os produtos gerados foram monitorados por técnicas cromatográficas: cromatografia líquida de alta eficiência, para a quantificação do ácido fórmico, e cromatografia gasosa, com prévia extração dos alcoóis pela técnica de SPME (micro extração em fase sólida), para as quantificações do metanol e etanol. O uso dos EDGs catalisados com os metais Cu e Zn, nas condições do estudo, mostraram melhor desempenho para geração de acido fórmico, sendo a temperatura de 20 °C a mais adequada. Obteve-se uma eficiência máxima de 25% para a geração de acido fórmico no caso do EDG/Cu e 94% no caso do EDG/Zn. Os eletrodos catalisados com metais oxidados EDG/CuO e EDG/ZnO no entanto, mostraram maior seletividade para a geração de alcoóis como metanol e etanol, obtendo-se uma maior eficiência na temperatura de 40 °C, especificamente 39% de metanol e 46% de etanol com EDG/CuO e 34% de metanol, 70% de etanol e 24% de ácido fórmico com EDG/ZnO. Os catalisadores de óxidos foram importantes para a obtenção de metanol e etanol, assim como o aumento da temperatura aumentou a seletividade para o etanol / Abstract: With the need for mitigation of greenhouse gases, especially CO2, it is essential to establish novel technologies towards low carbon emission industrial processes and preferably, for the conversion of CO2 to useful products. This is the focus of this work: to study the feasibility of the process of electrochemical reduction of CO2 to its conversion to methanol, ethanol and formic acid. For this, gas diffusion electrodes (GDE) were used, whose permeability was maximized through the experimental design. The electrodes were catalyzed with Cu, Zn, CuO and ZnO by thermal decomposition of metal salts. The electrochemical characterization was carried out by voltammetric experiments and microstructure was examined by X-ray diffraction and transmission electron microscopy. The electrodes were evaluated in electrolysis at cathodic current densities of 50, 70, 100 and 150 mA cm-2 and at temperatures of 20, 40 and 60 ?C, except for the electrode catalyzed with zinc, studied only at 20 ?C. The products were monitored by chromatographic techniques: high performance liquid chromatography to quantify formic acid concentration and gas chromatography preceded by the extraction of the alcohols by the SPME (solid phase micro extraction) technique for the quantification of methanol and ethanol. By using GDEs catalyzed with copper and zinc under the experimental conditions of the study, better performance for the generation of formic acid was achieved. The electrodes catalyzed with CuO and ZnO, showed greater selectivity for the generation of alcohols such as methanol and ethanol. Greater current efficiency was obtained at 40 ?C, specifically 39% for methanol and 46% for ethanol with GDE/CuO. On the other hand, using GDE/ZnO, current efficiency for conversion to methanol was 34%, 70% for ethanol and 24% for formic. The oxide catalysts (CuO and ZnO) were more appropriate for the conversion of CO2 to alcohols and increasing temperatures increased selectivity for ethanol / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica

Orientador: Yoshiyuki Hase / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-13T00:04:59Z (GMT). No. of bitstreams: 1 Sousa_Marcelode_M.pdf: 719258 bytes, checksum: c3faa35c86e3b8438789d2e27f5c2c51 (MD5) Previous issue date: 2008 / Resumo: Um novo método de correção de anarmonicidade está sendo proposto no atual trabalho em termos do campo de força. O objetivo deste método é simplificar a reprodução dos campos de força harmônicos, das freqüências harmônicas e da distribuição de energia potencial pela aplicação dos coeficientes de correção de anarmonicidade ao campo de força da análise de coordenadas normais. A simplificação proposta consiste em se agrupar os coeficientes segundo suas similaridades numéricas, reproduzindo resultados tão semelhantes quanto aos dos coeficientes não agrupados. Os coeficientes de correção de anarmonicidade agrupados e não agrupados foram calculados para o trans-ácido fórmico e aplicados aos campos de força do cis- e dímero da mesma molécula. Os resultados obtidos para as freqüências harmônicas para as espécies de trans-, cis- e dímero do ácido fórmico pelo método proposto foram muito similares àqueles obtidos método de Dennison / Abstract: A new anharmonicity correction method is proposed in this work. The aim of this method is to simplify the reprodution of the harmonic force fields, the harmonic frequencies and potential energy distribution by application of the anharmonicity correction coefficients to the normal coordinate analysis force field. The simplification proposed consists in grouping the coefficients according of their numerical similarities, producing results similar to those obtained without grouping. The grouping and non grouping anharmonicity correction coefficients were calculated for trans-formic acid and applied to the force fields of the cis- and dimer of this molecule. The results obtained for the harmonic frequencies for the trans-, cis- and dimer species by the proposed method are very close to those obtained Dennison method / Mestrado / Físico-Química / Mestre em Química

PtBi/C e PdBi/C foram preparados em diferentes razões atômicas (100:0, 90:10, 80:20, 70:30, 60:40 e 50:50) pelo método de redução via borohidreto de sódio (com adição total da solução de borohidreto em uma única etapa) utilizando H2PtCl6.6H2O, Pd(NO3)2, (BiNO3)3.5H2O como fonte de metais, Vulcan® (XC72-Cabot) como suporte de carbono e com uma carga metálica correspondente a 20% em massa. Os eletrocatalisadores obtidos foram caracterizados por difração de raios-X (DRX), microscopia eletrônica de transmissão (MET) e voltametria cíclica (VC). A atividade dos diferentes materiais preparados para a oxidação eletroquímica do ácido fórmico foi realizada em eletrólito ácido e alcalino utilizando-se as técnicas de voltametria cíclica, e cronoamperometria. Para estes estudos foi utilizado a técnica do eletrodo de camada fina porosa. A caracterização eletroquímica permitiu comparar o desempenho eletroquímico da platina e paládio, além de avaliar o benefício da presença do bismuto nas razões atômicas propostas. Os difratogramas de raio-X (DRX) confirmaram para todos os compostos de PtBi/C e PdBi/C a formação da estrutura cúbica de face centrada (cfc) característicos da rede cristalina da platina e do Paládio respectivamente. Outros picos encontrados foram associados a presença de fases de óxido de bismuto em ambos os compostos, PtBi/C e PdBi/C. A microscopia eletrônica de transmissão (MET) indicou que a presença de maiores teores de bismuto não acarretaram em aumento do tamanho médio da partícula. Os resultados eletroquímicos em meio alcalino indicaram que ainda é necessário uma otimização da concentração de ácido fórmico para que possamos observar melhores resultados quanto à adição de bismuto na platina ou paládio, no entanto os estudos em meio ácido mostraram o efeito benéfico da adição de bismuto tanto para platina quanto para o paládio. / PtBi/C and PdBi/C were prepared with different atomic ratios (100:0, 90:10, 80:20, 70:30, 60:40 and 50:50) by sodium borohydride reduction method (with total addition of the borohydride solution in just one step) using H2PtCl6.6H2O, Pd(NO3)2, (BiNO3)3.5H2O as source of metals, Vulcan® (XC72-Cabot) as carbon support and a metallic charge correspondent to 20% mass. The obtained electrocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and cyclic voltammetry (CV). The activity of the different materials used for the formic acid electrochemical oxidation was performed in acid and alkaline electrolyte through cyclic voltammetry and chronoamperometry, using the porous thin-film electrode technique. The electrochemical characterization allowed for the comparison between the platinum and palladium electrochemical performance, as well as the evaluation of the benefit of having bismuth in the proposed atomic ratios. The X-ray diffraction (XRD) diffractograms confirmed, for every PtBi/C and PdBi/C compounds, the formation of the face-centered cubic structure (fcc) distinctive to platinum and palladiums crystalline net, respectively. Other peaks were found associated to the presence of bismuth oxide phases in both compounds, PtBi/C and PdBi/C. The transmission electron microscopy (TEM) indicated that a higher bismuth presence did not result in a larger particle size. The electrochemical results in alkaline medium indicated that an optimization on formic acid concentration is still necessary so that better results concerning bismuth addition to platinum or palladium could be observed, although the studies done in acid medium presented the beneficial effect of bismuth addition to both platinum and palladium.

A auto-organização é uma das principais características de sistemas naturais. Os fenômenos auto-organizados podem emergir em sistemas suficientemente afastados do equilíbrio termodinâmico. A não-linearidade intrínseca aos sistemas eletroquímicos, permite inúmeros exemplos de comportamento complexo, sendo, grande parte, em eletrocatálise. Apesar do considerável progresso no entendimento dos aspectos mecanísticos da eletro-oxidação oscilatória de moléculas orgânicas pequenas, aparentemente não existe nenhum estudo sistemático do impacto de modificadores superficiais na dinâmica oscilatória. Nesta tese de doutorado, a eletro-oxidação oscilatória do ácido fórmico em bimetálicos de platina, com estanho ou bismuto, é comparada com aquela obtida em platina policristalina. A modificação da superfície afeta drasticamente a dinâmica oscilatória. As oscilações auto-organizadas de potencial foram usadas como sonda para a atividade eletrocatalítica dos eletrodos bimetálicos de platina. Em intermetálicos ordenados de platina e estanho, a velocidade de envenenamento diminui significativamente, o que retarda a desativação da superfície e promove oscilações de longa duração, sem precedentes, com estabilização de mais de 2200 ciclos. Isto corresponde a 30-40 vezes mais estável com relação ao eletrodo de platina. A presença de estanho na superfície do eletrodo tem grande impacto na produção de CO2, como observado em experimentos, modelagem e simulações numéricas, com aumento na velocidade das etapas produtoras de CO2. Com as informações adicionais obtidas em regime oscilatório, frente os experimentos em estado estacionário, foi possível estimar o efeito catalítico dos modificadores como estanho ou bismuto em eletrodos de platina, bem como, alguns aspectos mecanísticos da eletro-oxidação de formaldeído, ácido fórmico, metanol e etanol. / The self-organization is one of the most important features of nature. The self-organization phenomenon can emerge in sufficiently far from thermodynamic equilibrium systems. The non-linearity laws of the electrochemistry systems, allows several examples of complex behavior, most of them in electrocatalysis. Despite the considerable progress in understanding of the mechanistic aspects of the oscillatory electro-oxidation of C1 molecules, there is a apparently no systematic studies concerning the impact of surfaces modifiers on the oscillations dynamics. In this doctoral thesis the electro-oxidation of formic acid on platinum bimetallic electrodes, with tin and bismuth, was compared to that observed on polycrystalline platinum electrodes. Overall, the obtained results were very reproducible, robust and allowed a detailed analysis on the correlation between the catalytic activity and the oscillation dynamics. The modified surfaces promote drastic effect on the oscillatory dynamics. The self-organized oscillations were used as a probe to the electrocatalytic activity of bimetallic electrodes. In ordered intermetallic electrodes of the platinum and tin, the rate of surface poisoning significantly decrease, which slow the surface deactivation and promotes long-lasting oscillations, unprecedented stabilization of more than 2200 oscillatory cycles. This corresponds to 30-40 fold stabilization with respect to the behavior of platinum electrodes. The adsorbed tin affects the reaction pathways that produce CO2, as observed in experiments, modeling and numerical simulations. Further information obtained in oscillatory regime permitted the estimative of the catalytic effect of the surface modifiers, such as tin and bismuth, and some mechanistic aspects of the electro-oxidation of formaldehyde, formic acid, methanol and ethanol.

Avec les récents changements climatiques et la mutation de plusieurs secteurs industriels, une meilleure gestion des rejets de dioxyde de carbone (CO2) est fortement envisagée. De plus en plus d'intérêt est porté sur la valorisation de CO2 au lieu de son stockage simple. Ainsi, ce projet de thèse s'est focalisé sur l'utilisation de polyoxométallates (POMs) et plus particulièrement ceux substitués par des métaux de transition (TMS-POMs), pour la valorisation de CO2 via son électroréduction. Cette approche permet par la même occasion d'assurer une meilleure gestion de l'énergie électrique. Différentes structures de TMS-POMs ont été préparés, donnant des POM mono et polysubstitués aux métaux de transition simples, ainsi qu'un POM fonctionnalisé par un complexe organométallique actif pour l'électroréduction de CO2. Une approche synthétique originale a permis d'obtenir ce dernier complexe, ouvrant la voie à de nouveaux complexes actifs pour l'électroréduction de CO2. Les propriétés électrochimiques, ainsi que leurs aptitudes à catalyser l'électroréduction de CO2 ont été évaluées en différents milieux réactionnels. Une vue globale sur l'application potentielle de cette classe de complexe a ainsi été adopté, montrant notamment la capacité de ces complexes de mener la réduction à 4 électrons et 4 protons de CO2 en formaldéhyde. / With the recent climate change issues and the recent industrial evolutions, a better management of carbon dioxide (CO2) releases is highly demanded. More and more research is focused on CO2 industrial uses rather than its mere storage. Thus, this PhD project deals with the use of polyoxometalates (POMs), especially transition metals substituted ones (TMS-POMs), for CO2 conversion through its électroréduction. This approach allows both a better electrical power and CO2 release management. Different TMS-POMs structures were prepared, yielding mono and polysubstituted POM with simple transition metal and also functionalized ones with active organometallic complex for CO2 électroréduction. An original synthetic approach allowed us to achieve this late functionalization, opening the way for new catalysts for CO2 conversion. Theirs electrochemical properties, as well as their ability to catalyze CO2 électroréduction were investigated in different reaction media. An overview on the potential application of this complex class has been adopted. Noticeably, it highlighted the ability of these complexes to carry out the 4-electrons and 4-protons reduction of CO2 to formaldehyde.

Abstract Lignocellulosic biomass, such as wood or agricultural residues, is a resource widely available for use in chemical production. In a lignocellulosic feedstock biorefinery, the major parts of biomass, cellulose, hemicellulose and lignin, are converted to valuable chemicals, materials and energy. Furfural production is one option for the use of the pentose sugars available in hemicellulose, and the process could be integrated with the pulp or cellulosic ethanol industry. In the past, furfural production catalysed by organic acids has been in industrial use, but no detailed studies about the kinetics exist. However, the use of organic acid would prevent the waste problems linked to the mineral acids widely used in the furfural industry. In this thesis, furfural formation in formic acid media was studied. The major part of this work concerns the kinetics of xylose dehydration into furfural and further furfural degradation. Based on the results of this thesis and a literature review, adequate prediction of furfural yield in the conditions used can be achieved using a simple kinetic model, including three reactions: 1) Xylose dehydration into furfural, 2) Furfural degradation, and 3) Xylose degradation to products other than furfural. Moreover, it was shown that the overall order of the furfural degradation reaction, usually modelled as a first order reaction, changes with acidity (H+-concentration). Suggestions for a possible reaction mechanism have been made based on the results. In the last part of this thesis, furfural formation in the presence of kraft lignin (Indulin AT) was considered. Sulphuric acid was used as a baseline for formic acid. It was shown that the lignin has an acid-neutralising capacity, but the higher pH did not explain all the changes in the xylose conversion and the furfural yield. Thus, it is highly likely the lignin inhibits the formation of furfural. Altogether, the effects were smaller in formic acid than in sulphuric acid. This thesis confirms the fact that formic acid is an effective catalyst for furfural production. The focus of the thesis was on the reaction kinetics, and the results can be used in conceptual process design. Moreover, the results emphasise the importance of including acidity explicitly in the kinetic model and monitoring acidity changes when real process streams are used. / Tiivistelmä Lignoselluloosaa, kuten puita tai maanviljelyn jäännösmateriaaleja, on laajasti saatavilla kemiallisen tuotannon raaka-aineeksi. Biojalostamossa lignoselluloosan pääjakeet, selluloosa, hemiselluloosa ja ligniini, muutetaan arvokkaiksi kemikaaleiksi, materiaaleiksi ja energiaksi. Furfuraalin tuotanto on yksi vaihtoehto hemiselluloosan sisältämien pentoosien hyödyntämiseksi. Furfuraaliprosessi voidaan yhdistää sellun tai bioetanolin tuotantoon, ja orgaanisia happoja käyttämällä voitaisiin välttää mineraalihappoihin liittyvät jäteongelmat furfuraalin tuotannossa. Tämän väitöskirjan aiheena on muurahaishappokatalysoitu furfuraalin muodostuminen ksyloosista. Pääpaino on reaktiokinetiikassa, ja työssä on kehitetty kineettinen malli ksyloosin dehydraatiolle furfuraaliksi ja sitä seuraaville furfuraalin sivureaktioille. Tehdyn tutkimuksen ja kirjallisuusselvityksen perusteella yksinkertainen kolmen reaktion malli antaa riittävän tarkan ennustuksen furfuraalisaannoista käytetyissä olosuhteissa. Reaktiot ovat 1) ksyloosin dehydraatio sekä 2) furfuraalin ja 3) ksyloosin reaktiot sivutuotteiksi. Lisäksi huomattiin, että reaktion, jossa syntyy furfuraalin häviämistuotteita, reaktioaste on riippuvainen happamuudesta (H+-konsentraatio). Työssä onkin ehdotettu mahdollisia reaktiomekanismeja furfuraalin sivureaktioille. Työn viimeisessä osassa tutkittiin ligniinin vaikutusta furfuraalin muodos¬tu¬miseen. Vertailukohtana muurahaishapolle käytettiin rikkihappoa. Tutkimuksessa selvisi, että käytetty ligniini, Indulin AT, huononsi furfuraalisaantoa. Suurin osa vaikutuksesta johtui ligniinin neutralointikapasiteetista, jolloin reaktioliuoksen happamuus laski, mutta mahdollisia sivureaktioita ei voitu sulkea pois. Kaiken kaikkiaan vaikutukset olivat pienempiä muurahaishapolla kuin rikkihapolla. Tämä väitöskirjatutkimus osoitti, että muurahaishappo katalysoi furfuraalin tuotantoa tehokkaasti. Tutkimuksessa muodostettiin reaktiokineettinen malli, jota voidaan käyttää käsitteellisessä prosessisuunnittelussa. Tulosten perusteella on tärkeää huomioida reaktioliuoksen happamuus kinetiikassa ja tarkkailla happamuuden muutoksia käytettäessä prosessisivuvirtoja.

Les recherches présentées dans ce manuscrit s’articulent autour de deux parties distinctes. La première partie concerne une étude mécanistique de la réaction de décomposition de l’acide formique (AF) photocatalysé par le Tetra-n-ButylAmmonium DecaTungstate (TBADT) et explore la réactivité de ce photocatalyseur envers l’AF. La deuxième partie de ces travaux se focalise sur l’étude de la réactivité radicalaire d’anions phosphorés et de leurs analogues chalcogénés. Dans un premier temps, nous nous sommes intéressés à exploiter la réactivité de phosphures-borane et des anions d’oxydes de phosphine pour la formation de liaisons C-P par photo-induction dans le visible. Dans un second temps, nous avons exploré la réactivité radicalaire et ionique des phosphures-borane chalcogénés, par une étude de leur structure et de leur réactivité. Ces propriétés ont été mises en application dans le cadre de réactions de photo-polymérisation radicalaire et de réduction de composés électrophiles. / This dissertation is organized in two distinct parts. The first one is a mechanistic investigation of the photocatalyzed reaction of decomposition of formic acid (AF) under mild conditions using Tetra-n-ButylAmmonium DecaTungstate (TBADT). The second part of this work revolve around the use and study of the radical reactivity of phosphorous anions and their chalcogenated analogues. Firstly, we used the radical reactivity of phosphido-borane and phosphine oxide anions for the formation of C-P bonds. In a last part, we explored the radical and ionic reactivity of chalcogenated phosphido-borane, by studying their structure and reactivity. These properties has been applied to radical photo-polymerization reactions and for the reduction of electrophiles.