Hydrogen is a vital component in several different chemical reactions as well as a potential fuel source for the future. The water gas shift (WGS) reaction converts CO and water to hydrogen and CO2. The objective of this work is to first, characterize the potential benefits of the addition of lanthanum oxide (lanthana) to the iron-chromium-copper (Fe-Cr-Cu) oxide catalysts industrially used in high temperature water gas shift processes, and second, analyze these catalysts using in-situ UV-Visible spectroscopy. The benefits of each component in the catalyst are discussed as well as potential benefits from the addition of lanthana. Lanthana is a rare earth oxide that dramatically increases the surface area of the iron based WGS catalysts, and small concentrations of other rare earth oxides (i.e. cerium) have been shown to increase the rate of desorption of CO2 from iron surfaces (Hu Yanping 2002). Lanthana has similar chemical properties to other rare earth oxides tested and has not been previously tested as an additive to the WGS catalyst. Therefore catalysts with 0, 1, 2, 5, 10, and 20 wt% lanthana were made via a co-precipitation method in order to measure changes in activity, physical stability, and thermal stability. Catalyst characterization techniques utilized include electron dispersive X-ray spectroscopy (EDX), temperature programmed reduction (TPR) with hydrogen, and nitrogen physisorption (BET). The kinetic analysis was performed utilizing both mass spectroscopy (MS) and gas chromatography (GC). The addition of 1 wt% lanthana to the Fe-Cr-Cu catalysts increases WGS reaction rates of the catalyst at 425°C and 350°C, however the 0% La catalyst has the highest rates at 375°C and 400°C. The 0% La catalyst shows significant drop off in rate at 425°C, suggesting that the lanthana provides a small thermal stabilizing, i.e. the addition of lanthana prevents catalyst sintering at higher temperatures. Traditionally, chromia acts as the sole thermal stabilizer in these catalysts. The addition of large amounts of lanthana inhibits the chromia stabilizing effect, however small additions of lanthana appear to have an additional catalyst promotional effect without interfering with the chromia thermal stabilization. The increased WGS reaction rates at higher temperatures could allow for greater throughput of reactants in industrial settings. Higher concentrations of lanthana decrease the activity due to what is believed to be disruption of the chromia stabilizing effect as well as reduced amount of the active phase of catalyst. In-situ UV-Visible analysis shows that the oxidation state of the iron in the catalyst has a direct correlation to the UV-Visible light absorbance of the surface of the iron catalyst. Extent of reduction is traditionally measured with a synchrotron which is significantly more expensive than UV-Vis spectroscopy. This study uses the more economical UV-Vis spectrometer to determine similar information. The lanthana doped catalysts show an over-reduction of iron during WGS conditions (i.e. rapid reduction of Fe2O3 to Fe3O4 and FeO).

The structural and functional roles of lanthana in unsupported iron-based catalysts for the high-temperature water-gas shift reaction and Fischer-Tropsch synthesis were investigated. The performance of the catalysts with varying lanthana contents was based on their activity, selectivity, and stability. With regard to the former reaction, extent of reduction of the iron in Fe2O3/Cr2O3/CuO/La2O3 water-gas shift catalysts is a key parameter that was characterized using UV-visible spectroscopy. Minor addition of lanthana (<0.5 wt%) produces more active and stable catalysts apparently because it stabilizes the iron-chromium spinel, increases the surface area of the reduced catalysts, enhances the reduction of hematite to the magnetite active phase, and facilitates the adsorption of CO on the surface of the catalyst modeled by an adsorptive Langmuir-Hinshelwood mechanism. Statistical 95% confidence contour plots of the adsorption equilibrium constants show that water adsorbs more strongly than CO, which inhibits the reaction rate. A calibration curve that correlates the oxidation state of surface iron domains to normalized absorbance of visible light was successfully generated and applied to the water-gas shift catalysts. UV-visible studies indicated higher extent of reduction for surface Fe domains for the catalysts promoted with 1 wt% of lanthana and showed potential to be a more convenient technique for surface chemistry studies than X-ray absorption near edge spectroscopy (XANES). Lanthana addition to iron-based Fischer-Tropsch catalysts enhances the olefin-to-paraffin ratio, but decreases their activity, stability, and selectivity to liquid hydrocarbons. Adding lanthana at the expense of potassium reduces the water-gas shift selectivity and enhances the activity and stability of the catalysts. Finally, a model that simulates heat and mass transfer limitations on the particle scale for the Fischer-Tropsch reaction applicable at lab-scale suggests optimal operating and design conditions of 256°C, 30 bar, and 80 mirons are recommended for higher selectivity to liquid hydrocarbons. The model considers pressure drop, deactivation, pore diffusion, film heat transfer, and internal heat transfer when solving for the optimal conditions, and maps them as functions of design variables. This model can be up-scaled to provide guidance for optimal design of commercial-size reactors.

O uso do hidrogênio, como vetor energético, representa uma opção promissora a fim de se reduzir a dependência dos combustíveis fósseis e controlar a emissão de poluentes na atmosfera. Atualmente, uma das rotas mais propícias para produção de hidrogênio envolve a reação de reforma a vapor de álcoois utilizando-se catalisadores de níquel suportados em alumina. O níquel é amplamente utilizado em catálise devido ao baixo custo e à elevada atividade para ruptura da ligação C-C. A alumina, por sua vez, promove maior dispersão do metal ativo devido aos valores elevados de área superficial das estruturas cristalinas de transição, sobretudo da fase gama, característica esta diretamente relacionada às condições de síntese. A incorporação de lantânia, como aditivo, tem sido considerada por moderar a acidez da superfície do suporte e minimizar a deposição de carbono no catalisador durante a reação de reforma. Tendo em vista que a atividade dos catalisadores na reação de reforma é função das características físicas e químicas desses materiais, avaliou-se, no presente trabalho, a rota de síntese por coprecipitação de hidróxidos em associação ao uso de surfactante e tratamento solvotérmico. A rota de mistura de pós de óxido de níquel com alumina, ambos preparados por precipitação individual, foi adotada para comparação dos resultados obtidos por coprecipitação. Nas condições otimizadas do processo, estudou-se o efeito da adição de óxido de lantânio nas propriedades dos materiais sintetizados. Verificou-se que o método de coprecipitação permitiu a obtenção de óxidos mistos com elevada área superficial (na faixa de 170 a 260 m2g-1), ao passo que a mistura de óxidos conduziu à formação de pós constituídos por fases distintas de alumina e óxido de níquel, com menor área superficial (na faixa de 60 a 180 m2.g-1). Após avaliação do comportamento de redução do óxido de níquel contido nesses materiais, as propriedades dos pós obtidos foram correlacionadas com o desempenho na produção de hidrogênio pela reforma do etanol. De acordo com os resultados, o catalisador preparado por coprecipitação apresentou menor atividade na produção de hidrogênio, comparativamente aos materiais obtidos por coprecipitação em associação com tratamento solvotérmico e mistura de óxidos. Em contraste, verificou-se uma menor quantidade de carbono acumulado sobre o catalisador preparado por coprecipitação, indicativo da elevada estabilidade catalítica deste material durante a reação de reforma. / Hydrogen use as an energy vector represents a promising option in order to reduce the dependence on fossil fuels and to control the emission of pollutants into the atmosphere. Nowadays, one of the most important routes for hydrogen production includes steam reforming reactions of alcohols over alumina-supported nickel catalysts. Nickel is largely applied in catalysis because of its low cost and high activity for C-C bond rupture. Alumina, in turn, promotes appropriate dispersion of the active metal due to the high surface area values of its transition crystalline structures, especially gamma phase. These characteristics are related to synthesis conditions. Incorporation of lanthana as an additive has been considered to control alumina surface acidity and to inhibit catalyst deactivation by carbon deposition during reforming reaction. Considering that catalyst activity is a function of materials physical and chemical properties, it was evaluated in this work powder synthesis route by coprecipitation in association with surfactant templating method and solvothermal treatment. Mechanical milling of nickel oxide and alumina powders, which were individually prepared by chemical precipitation, was adopted for comparison purposes. Under optimized preparation conditions, the effect of lanthanum oxide addition on the materials properties was studied. It was verified that coprecipitation allowed the production of high surface area mixed oxides (170-260 m2g-1). Mechanical mixture led to the formation of materials constituted by alumina and nickel oxide phases, with low surface area (60-180 m2.g-1). After evaluation of nickel oxide reduction behavior, in hydrogen atmosphere, a correlation between properties and performance in hydrogen production by ethanol steam reforming was established. According to the results, the catalyst prepared by coprecipitation was less active for hydrogen generation compared to the ones obtained by coprecipitation followed by solvothermal treatment and mechanical milling methods. In contrast, the lowest amount of carbon deposits was found on the catalyst prepared by coprecipitation, which is an indicative of the high catalytic stability during reforming reaction.

O uso do hidrogênio, como vetor energético, representa uma opção promissora a fim de se reduzir a dependência dos combustíveis fósseis e controlar a emissão de poluentes na atmosfera. Atualmente, uma das rotas mais propícias para produção de hidrogênio envolve a reação de reforma a vapor de álcoois utilizando-se catalisadores de níquel suportados em alumina. O níquel é amplamente utilizado em catálise devido ao baixo custo e à elevada atividade para ruptura da ligação C-C. A alumina, por sua vez, promove maior dispersão do metal ativo devido aos valores elevados de área superficial das estruturas cristalinas de transição, sobretudo da fase gama, característica esta diretamente relacionada às condições de síntese. A incorporação de lantânia, como aditivo, tem sido considerada por moderar a acidez da superfície do suporte e minimizar a deposição de carbono no catalisador durante a reação de reforma. Tendo em vista que a atividade dos catalisadores na reação de reforma é função das características físicas e químicas desses materiais, avaliou-se, no presente trabalho, a rota de síntese por coprecipitação de hidróxidos em associação ao uso de surfactante e tratamento solvotérmico. A rota de mistura de pós de óxido de níquel com alumina, ambos preparados por precipitação individual, foi adotada para comparação dos resultados obtidos por coprecipitação. Nas condições otimizadas do processo, estudou-se o efeito da adição de óxido de lantânio nas propriedades dos materiais sintetizados. Verificou-se que o método de coprecipitação permitiu a obtenção de óxidos mistos com elevada área superficial (na faixa de 170 a 260 m2g-1), ao passo que a mistura de óxidos conduziu à formação de pós constituídos por fases distintas de alumina e óxido de níquel, com menor área superficial (na faixa de 60 a 180 m2.g-1). Após avaliação do comportamento de redução do óxido de níquel contido nesses materiais, as propriedades dos pós obtidos foram correlacionadas com o desempenho na produção de hidrogênio pela reforma do etanol. De acordo com os resultados, o catalisador preparado por coprecipitação apresentou menor atividade na produção de hidrogênio, comparativamente aos materiais obtidos por coprecipitação em associação com tratamento solvotérmico e mistura de óxidos. Em contraste, verificou-se uma menor quantidade de carbono acumulado sobre o catalisador preparado por coprecipitação, indicativo da elevada estabilidade catalítica deste material durante a reação de reforma. / Hydrogen use as an energy vector represents a promising option in order to reduce the dependence on fossil fuels and to control the emission of pollutants into the atmosphere. Nowadays, one of the most important routes for hydrogen production includes steam reforming reactions of alcohols over alumina-supported nickel catalysts. Nickel is largely applied in catalysis because of its low cost and high activity for C-C bond rupture. Alumina, in turn, promotes appropriate dispersion of the active metal due to the high surface area values of its transition crystalline structures, especially gamma phase. These characteristics are related to synthesis conditions. Incorporation of lanthana as an additive has been considered to control alumina surface acidity and to inhibit catalyst deactivation by carbon deposition during reforming reaction. Considering that catalyst activity is a function of materials physical and chemical properties, it was evaluated in this work powder synthesis route by coprecipitation in association with surfactant templating method and solvothermal treatment. Mechanical milling of nickel oxide and alumina powders, which were individually prepared by chemical precipitation, was adopted for comparison purposes. Under optimized preparation conditions, the effect of lanthanum oxide addition on the materials properties was studied. It was verified that coprecipitation allowed the production of high surface area mixed oxides (170-260 m2g-1). Mechanical mixture led to the formation of materials constituted by alumina and nickel oxide phases, with low surface area (60-180 m2.g-1). After evaluation of nickel oxide reduction behavior, in hydrogen atmosphere, a correlation between properties and performance in hydrogen production by ethanol steam reforming was established. According to the results, the catalyst prepared by coprecipitation was less active for hydrogen generation compared to the ones obtained by coprecipitation followed by solvothermal treatment and mechanical milling methods. In contrast, the lowest amount of carbon deposits was found on the catalyst prepared by coprecipitation, which is an indicative of the high catalytic stability during reforming reaction.