Abstract The work in this thesis concentrates on finding more active and durable catalysts for the demanding environmental application of the oxidation of sulfur-containing volatile organic compounds (S-VOCs). This application is challenging due to the high purification levels required and the catalyst deactivating nature of sulfur. In this thesis, dimethyldisulfide (DMDS) was used as the model molecule to represent S-VOCs since it is often present in odorous emissions and it is more difficult to treat than most of the other S-VOCs. It was found that the addition of a very small amount of Pt (0.3%) especially improves the selectivity of copper oxide based catalysts towards complete oxidation products ((carbon dioixide (CO2), water (H2O) and sulfur dioxide (SO2)) in DMDS oxidation. Catalyst characterization by transmission electron microscopy, temperature programmed reduction and X-ray photoelectron spectroscopy analyses suggests that this promoting effect is most likely due to the close interaction between Cu and Pt species on the bimetallic PtCu/γ-Al2O3 catalyst. The drawback of using the Al2O3 support is that it is not resistant towards sulfur poisoning. The deactivation of the self-made catalysts was studied with the help of an accelerated ageing procedure that was developed based on the information from the industrially aged volatile organic compound (VOC) catalysts. Industrial deactivation was caused by the sintering of the support and active metals and by the formation of metal sulfates with the support. After accelerated ageing, the silica doped alumina (Al2O3)0.8(SiO2)0.2 supported catalyst, showed remarkably promising results in terms of stability towards sulfur poisoning and the activity in DMDS oxidation was very close to that of the most active PtCu/Al2O3. The addition of less than 20% of SiO2 on the Al2O3 support led to a catalyst that is more selective and resistant to sulfur poisoning. / Tiivistelmä Väitöskirjassa tuotetaan uutta tietoa rikkipitoisten orgaanisten yhdisteiden (S-VOC) hapetukseen soveltuvien uusien katalyyttisten materiaalien synteesistä ja karakterisoinnista. S-VOC-yhdisteiden käsittely on vaativa katalyyttisen polton sovellus, koska näiden päästöjen käsittely edellyttää korkeaa puhdistustehoa, ja lisäksi yhdisteiden sisältämä rikki on katalyyttimyrkky. Tässä väitöskirjassa valittiin S-VOC-yhdisteitä edustavaksi malliaineeksi dimetyylisulfidi (DMDS), koska se on usein mukana käsiteltävissä S-VOC-päästöissä ja sen käsittely on vaativampaa kuin useiden muiden S-VOC-yhdisteiden käsittely. Tutkimustulosten mukaan hyvin pieni Pt-lisäys (0.3 %) parantaa erityisesti kuparioksidikatalyyttien selektiivisyyttä DMDS:n kokonaishapetustuotteiksi (CO2, H2O, SO2). Katalyyttien karakterisoinnin (läpäisyelektronimikroskopia, lämpötilaohjattu pelkistysreaktio, röntgensädefotoelektronispektroskopia) perusteella voidaan esittää parannuksen syyksi kuparin ja platinan läheinen kontakti bimetallisen PtCu/γ-Al2O3-katalyytin pinnalla. Al2O3-tukiaineen heikkoutena on sen deaktivoitumisherkkyys rikkiyhdisteiden läsnä ollessa. Väitöskirjatyössä valmistettujen katalyyttien deaktivitumista tutkittiin laboratoriomittakaavassa nopeutettujen ikäytyskokeiden avulla, jotka kehitettiin teollisessa käytössä deaktivoituneen katalyytin karakterisointien avulla saadun tiedon perusteella. Teollisessa käytössä olleen katalyytin deaktivoitumisen syyksi havaittiin tukiaineen ja aktiivisten metallien sintrautuminen sekä metallisulfidien muodostuminen tukiaineen kanssa. Nopeutettujen ikäytyskokeiden tulosten perusteella havaittiin, että piidioksidin lisäys alumiinioksiditukiaineeseen paransi tukiaineen rikin kestoa merkittävästi. Tutkimuksissa havaittiin myös, että piidioksidilla muokatun katalyytin aktiivisuus oli hyvin lähellä vastaavaa PtCu/γ-Al2O3-katalyytin aktiivisuutta. DMDS:n hapetuksessa selektiivisempi ja stabiilimpi katalyytti voidaan aikaansaada alle 20 %:n SiO2-lisäyksellä Al2O3-tukiaineeseen.

[pt] O aumento do interesse em materiais nanoestruturados, nos anos recentes, tem incentivado o desenvolvimento de materiais compósitos de matriz metálica reforçados com nanotubos de carbono. No presente estudo foi produzido um material nano compósito de matriz de cobre contendo nanotubos de carbono (CNT 2% peso), a partir de síntese por métodos químicos. O procedimento começa pela dissociação do nitrato de cobre na presença de CNT e um tensoactivo aniônico a 250°C e sua posterior redução in-situ com atmosfera de Hidrogênio sobre pressão de 1 atm. a 350°C. A análise por difração de Raios X confirmou a formação de CuO puro no momento da dissociação, assim como de cobre metálico após a redução. A presença dos CNT foi detectada nas duas etapas por essa técnica. Análises por Microscopia Eletrônica de Transmissão (MET)mostram que o tamanho médio de partícula do óxido e de 30nm em quanto que para o material reduzido está na faixa de 150-300nm, apresentando-se boa dispersão dos nanotubos. O material reduzido foi compactado, em forma de pastilhas, por pressão uniaxial a frio sob 25MPa e, posteriormente, por pressão isostática a 150MPa. O material compactado foi sinterizado em atmosfera de Argônio a 650°C por 15 min. Análise por Microscopia Eletrônica de Varredura (MEV) assim como TEM do material sinterizado, mostrou uma distribuição heterogênea de tamanho de grão na faixa de 100nm a 4 μm. Medidas de resistividade elétrica mostram que o compósito apresenta uma resistividade sensivelmente menor a baixa temperatura (2x10(-6) ? .cm) a 83°K que o cobre sem nanotubos (5.9x10(-6) ? .cm). / [en] The increasing interest in nanostructure materials in recent years has provided incentive to develop nanostructure composite materials with metal matrix, reinforced with carbon nanotubes. In the present work, copper matrix nano composite with carbon nanotubos (2% wt) was produced by chemical synthesis method. The procedure begins by the copper nitrate dissociation containing SWCNT and anionic tensoactive agent at 250°C, followed by in-situ reduction at 350°C, under hydrogen atmosphere at pressure of 1atm. CuO and Cu formation was confirmed by X ray diffraction at the moment of dissociation and reduction respectively. CNTs presence was detected at both steps by this characterization method. Transmission Electron Microscopy analysis, estimate particles grain size of 30nm for CuO powder while Cu powder particles were observed to be in the 100-300nm range, showing good dispersion of CNT. Bulk nano-composite pellets of the reduced material were obtained by pre-compactation under uniaxial pressure of 17 MPa followed by issostatic pressure of 150MPa. Sinterizing of the compacted material was carry out at 650°C under Argon atmosphere by 15 min. Scanning Electron Microscopy and Transmission Electron Microscopy analysis of the sinterized material showed an heterogeneous grain size distribution in the 100nm to 4 ìm range. Electric resistivity measures show that the nanocomposite material has lower resistivity at low temperature (2x10(-6) ? .cm) at 83°K than the copper without carbon nanotubes (5.9x10(-6) ? .cm).

The increasing production of natural gas liquids attracts both academia and industry to develop on-purpose techniques converting those light alkanes to value-added chemicals. Dehydroaromatization is an alternative path for light alkane conversion to produce aromatics but still lacks active and stable catalysts. This work aims at the development of efficient dehydroaromatization catalysts by tuning the metal/acid bifunctionality of the Pt/HZSM-5 catalyst. Additionally, through co-processing light alkane with ammonia during the dehydroaromatization process, this study also proposes a new reaction system that could directly link the C-N bond for nitrile synthesis. The results suggested that the activity, selectivity, and stability of the monometallic Pt/HZSM-5 catalyst are highly dependent upon the Pt loading, the limit loading of 100 ppm is required to maintain sufficient metal functionality. To further minimize the Pt loading, the chemical properties of the Pt species were tuned by a second metal such as Zn or Cu. Consequently, the activity and stability of the catalyst are enhanced by orders of magnitude and the maximized metal functionality was achieved at Pt loading of 10 ppm. Characterizations show that Pt can be atomically dispersed as a hybrid [Pt1-Zn6] cluster in the Pt-Zn@HZSM-5 or forming single atom alloy type [Pt1-Cu4] ensembles in the Pt-Cu@HZSM-5. Specifically, the initial turnover frequencies of propane and ethane to BTX are up to 178.8 and 128.7 s-1 over the Pt-Cu@HZSM-5, up to 3-4 orders of magnitude higher than the state-of-the-art Pt-based catalyst. Furthermore, the deactivated catalyst can be continuously regenerated, demonstrating excellent stability of such a catalyst under hash oxidation conditions for coke burn-off. A new catalytic system named ammodehydrogenation (ADeH) for ethane selective conversion to acetonitrile, ethylene, and hydrogen over a bifunctional catalyst is proposed. Ethane ADeH over the Pt/HZSM-5 catalyst is active at low temperatures and atmospheric pressure for CH3CN production. The Pt/HZSM-5 shows high coke-resistibility during the ethane ADeH due to the strong interaction of NH3 with the acid sites of the catalyst. The catalyst can be further optimized by adding Co, the Pt-Co/HZSM-5 catalyst on ethane ADeH indicating that an appropriate balance between the metal and acid functionalities is critical for ethane ADeH.

[pt] Os materiais nanoestruturados têm sido estudados ao longo das últimas décadas, por apresentarem propriedades particulares, promissoras propriedades térmicas, mecânicas e catalíticas, que muitas vezes não estão presentes no material não manométrico. Alguns avanços recentes têm mostrado que estas propriedades podem ser reforçadas pela inclusão de materiais com propriedades diferentes na sua estrutura, formando assim nanocompósitos. Por exemplo, as ligas de CuNi são muito dúcteis, mas a presença de nanopartículas de Al2O3 depositadas na matriz pode melhorar consideravelmente a dureza do material. Tal nanocompósito pode ser obtido, por exemplo, através de decomposição térmica nitratos, seguido por redução seletiva com hidrogênio. Nesse contexto, o presente trabalho tem como foco a síntese de ligas de CuNi e CuNi com adição de nanoparticulas de Al2O3, baseados na redução seletiva de CuO e de NiO com H2, e óxidos coformados com o óxido de alumínio por meio da decomposição térmica de seus nitratos metálicos. Cálculos termodinâmicos mostraram que a redução de Cu e Ni pode ser realizada a temperaturas relativamente baixas (400 mais ou menos 5 Graus C), e também que o processo se desenvolve seletivamente (apenas os óxidos de Ni e de Cu reagem nas condições impostas), resultando em compósitos de CuNi/Al2O3, que consiste na formação de uma liga CuNi contendo 1 por cento de Al2O3 como finas nanopartículas distribuídas homogeneamente. Precursores e amostras reduzidas foram caracterizados por difração de raios x (DRX) para determinar a natureza das fases individuais presentes (óxidos e ligas), microscopia electrónica de varredura (MEV) como uma primeira aproximação da morfologia das partículas e microscopia eletrônica de transmissão (MET). Os resultados obtidos indicam que a via química proposta resultou satisfatória para a elaboração das ligas CuNi contendo nanopartículas de Al2O3 homogeneamente distribuídas. Os resultados obtidos também indicam que, para as condições experimentais impostas tanto a decomposição dos nitratos como as reações de redução alcançaram conversões de 100 por cento. / [en] Materials containing nanostructured particles have been studied over the last decades in order to take advantage of their promising thermal, mechanical and catalytic properties. Some recent progress has shown that these properties can be further enhanced by the inclusion of materials with different properties in their structure, thereby forming nanocomposites. For instance, Ni-Cu alloys are highly ductile, but the presence of Al2O3 nanoparticles deposited inside the alloy matrix can considerably improve the material s hardness. Such a nanocomposite can be obtained, for example, through nitrate solutions thermal decomposition followed by selective reduction with hydrogen. In this context, the present work focuses on the synthesis of CuNi alloys and CuNi/Al2O3 composites based on the selective reduction of copper and nickel oxides with pure H2, co-formed with aluminum oxide through thermal decomposition of aqueous solutions of their metal nitrates. Thermodynamic computations showed that the Cu and Ni reduction can be accomplished at relatively low temperatures (400 plus or minus 5 C degrees), and also that the process develops selectively (only the oxides of Ni and Cu react at the imposed conditions), resulting in Cu-Ni-Al2O3 composites, consisting in a Cu-Ni alloy crystals containing 1 percent of Al2O3 as fine homogeneously distributed nanoparticles. Both the original (co-formed) and reduced oxide samples were characterized using x ray diffraction (XRD) for determining the nature of the individual phases present (oxides and alloys) and scanning electron microscopy (SEM) as a first approach to the investigation of the morphology of the particles. The results indicate that the proposed chemical route resulted in composite materials containing CuNi alloy and Al2O3 particles of controllable composition and homogeneously distributed among the samples. The achieved results also suggest that for the imposed experimental conditions both the nitrate decomposition as well as the reduction reactions could be conducted to 100 percent conversion.

[pt] Esta tese investigou a síntese de metanol via hidrogenação do CO2 empregando dois conjuntos de catalisadores. O primeiro é composto pelos tradicionais catalisadores de Cu/ZnO/Al e o segundo aborda os catalisadores de In2O3 e ZrO2. Com relação ao Cu/ZnO/Al, foram preparados quatro amostras via coprecipitação. Os resultados mostraram que há um teor ótimo (3,8 por cento at.) de Al para a qual se observa uma maior taxa de formação de metanol. Os catalisadores foram caracterizados por fisissorção de N2, titulação com N2O,espectroscopia de absorção atômica, ICP, DRX, XPS, TPD-(CO2,NH3 e H2O), TPSR-CO2/H2, TEM/HRTEM/EDS. Uma correlação entre a taxa de formação de metanol e a quantidade de vacâncias de oxigênio superficiais do catalisador foi observada. Foi verificado que o Al atua como um promotor na geração de vacâncias de oxigênio. Com relação aos sistemas de In2O3, foi realizado um screening e selecionado nove catalisadores. Esses sólidos foram caracterizados pelas seguintes técnicas: DRX, TPD-NH3, TPD-CO2, TPR-H2 e TPSR-CO2/H2. Foi realizado um estudo em dinâmica molecular clássica investigando os efeitos da dopagem do In2O3 e da interação entre o In2O3 e o ZrO2 e relacionando os resultados com a performance dos catalisadores. O melhor desempenho catalítico foi obtido para o inédito catalisador de 0,6Pt-In2O3+6ZnZrO2, sendo esse desempenho associado à presença de vacâncias. Além disso, pelos cálculos teóricos de dinâmica molecular foi verificado que tanto a mistura física quanto a dopagem do In2O3 podem promovem a mobilidade de oxigênio da rede dos óxidos, o que facilita a formação de vacâncias de oxigênio. Sendo assim, os dois conjuntos de catalisadores estudados mostram que as vacâncias de oxigênio têm papel central na formação do metanol a partir da hidrogenação do CO2. As informações geradas neste trabalho contribuirão para o desenvolvimento de catalisadores promissores para a futura exploração industrial da geração de metanol a partir de CO2. / [en] This thesis investigated methanol synthesis via CO2 hydrogenation using two sets of catalysts. The first set consists of the traditional Cu/ZnO/Al catalysts and the second set involves In2O3 and ZrO2 catalysts. Concerning Cu/ZnO/Al, four samples were prepared via coprecipitation. The results showed that there is an optimum Al content (3.8 percent at.) for which a higher methanol formation rate is observed. The catalysts were characterized by N2 physisorption, titration with N2O, atomic absorption spectroscopy, ICP, XRD, XPS (CO2,NH3 and H2O)-TPD, CO2/H2-TPSR, TEM/HRTEM/EDS. A correlation was observed between the rate of methanol formation and the amount of surface oxygen vacancies on the catalyst. It was found that Al acts as a promoter in the generation of oxygen vacancies. Regarding the In2O3 systems, a screening was carried out and nine catalysts were selected. These solids were characterized using the following techniques: XRD, NH3- TPD, CO2-TPD, TPR-H2 and CO2/H2-TPSR. A classical molecular dynamics study was carried out investigating the effects of doping In2O3 and the interaction between In2O3 and ZrO2 and relating the results to the performance of the catalysts. The best catalytic performance was obtained for the new 0,6Pt-In2O3+6ZnZrO2 catalyst, and this performance was associated with the presence of vacancies. In addition, molecular dynamics calculations showed that both the physical mixture and the doping of In2O3 can promote the mobility of oxygen in the oxide lattice, facilitating the formation of oxygen vacancies. Thus, the two sets of catalysts studied show that oxygen vacancies play a central role in the formation of methanol from the hydrogenation of CO2. The information generated in this work will contribute to the development of promising catalysts for the future industrial exploitation of methanol generation from CO2.