O titanato de estrôncio (SrTiO3) é um óxido de estrutura perovskita e tem sido intensamente estudado para uso em diversas aplicações, entre elas, como suporte catalítico. Entretanto, sua utilização especificamente na reação de deslocamento gás-água ainda é pouco explorada. Esta reação é de interesse para a produção de hidrogênio livre de CO, necessário para aplicações como o abastecimento de células de combustível. Este trabalho de tese teve como objetivo o estudo dos compostos SrTi1-xCuxO3, CuO/SrTiO3 e NiO/SrTiO3 como catalisadores para a reação de deslocamento gás-água, uma vez que, dentre os metais de baixo custo, Cu e Ni são altamente ativos para esta reação. As amostras SrTi1-xCuxO3 foram sintetizadas pelo método dos precursores poliméricos com calcinação em N2 e O2, possibilitando a obtenção de partículas de maior área superficial em comparação com a calcinação convencional em atmosfera ambiente. Para as amostras CuO/SrTiO3 e NiO/SrTiO3, o suporte SrTiO3, foi sintetizado pelo método de sol-precipitação e a impregnação com cobre e níquel foi realizada por via úmida. As técnicas de absorção e difração de raios-X in situ em condições de reação mostraram a estabilidade da estrutura e do estado de oxidação após o tratamento de redução. Imagens de microscopia eletrônica de varredura (MEV) e de transmissão (TEM) em conjunto com a espectroscopia de raios-X de energia dispersiva (EDX) foram utilizadas a fim de estabelecer uma relação entre a atividade catalítica e o teor a dispersão de fase ativa sobre o suporte. Todas as composições estudadas se mostraram ativas entre 250 e 350°C, entretanto, a composição NiO/SrTiO3 com 10% de Ni apresentou o melhor resultado, com uma conversão de CO a 350°C, próxima ao equilíbrio e estável por um período mínimo de10 h. / Strontium titanate (SrTiO3) is an oxide of perovskite structure and has been extensively studied for use in several applications, including as catalytic support. However, its use specifically in the water-gas shift reaction is still little explored. This reaction is of interest for the production of CO-free hydrogen, required for applications such as in fuel cell. This work aimed to study SrTi1-xCuxO3, CuO/SrTiO3 and NiO/SrTiO3 compounds to be applied as catalysts for the water-gas shift reaction, since, among the low-cost metals, Cu and Ni are highly active for this reaction. The SrTi1-xCuxO3 samples were synthesized by the polymeric precursor method with the samples submitted to a N2 and O2 calcination, making possible to obtain particles with a larger surface area compared to conventional calcination in ambient atmosphere. For the CuO/SrTiO3 and NiO/SrTiO3 samples, the SrTiO3 support was synthesized by the sol-precipitation method and the impregnation with copper and nickel on the support was performed by a wet method. The in situ X-ray absorption and diffraction techniques under reaction conditions showed the stability of the structure and the oxidation state after the reduction treatment. Scanning electron microscopy (SEM) and transmission (TEM) images in conjunction with energy dispersive X-ray spectroscopy (EDX) were used in order to establish a relationship between the catalytic activity and the content and dispersion of the active phase on the support. All the compositions studied were active at 250 to 350 °C, however, the NiO/SrTiO3 sample with 10% of Ni presented the best result, with a CO conversion at 350 °C, close to equilibrium and stable for a minimum of 10 h.

Doctor of Philosophy / Department of Chemical Engineering / Bin Liu / Efficient and selective catalysis lies at the heart of many chemical reactions, enabling the synthesis of chemicals and fuels with enormous societal and technological impact. A fundamental understanding of intrinsic catalyst properties for effective manipulation of the reactivity and selectivity of industrial catalysts is essential to select proper catalysts to catalyze the reactions we want and hinder the reactions we do not want. The progress in density functional theory (DFT) makes it possible to describe interfacial catalytic reactions and predict catalytic activities from one catalyst to another. In this study, water-gas shift reaction (WGSR) was used as a model reaction. First-principles based micro-kinetic modeling has been performed to deeply understand interactions between competing reaction mechanisms, and the relationship with various factors such as catalyst materials, structures, promoters, and interactions between intermediates (e.g., CO self-interaction) that govern the observed catalytic behaviors. Overall, in this thesis, all relevant reaction mechanisms in the model reaction on well-defined active sites were developed with first-principles calculations. With the established mechanism, the promotional effect of K adatom on Ni(111) on WGSR compared to the competing methanation was understood. Moreover, the WGSR kinetic trend, with the hydrogen production rate decreasing with increasing Ni particle diameters (due to the decreasing fractions of low-coordinated surface Ni site), was reproduced conveniently from micro-kinetic modeling techniques. Empirical correlations such as Brønsted-Evans-Polanyi (BEP) relationship for O-H, and C-O bond formation or cleavage on Ni(111), Ni(100), and Ni(211) were incorporated to accelerate computational analysis and generate trends on other transition metals (e.g., Cu, Au, Pt). To improve the numerical quality of micro-kinetic modeling, later interactions of main surface reaction intermediates were proven to be critical and incorporated successfully into the kinetic models. Finally, evidence of support playing a role in the enhancement of catalyst activity and the impact on future modeling will be discussed. DFT will be a powerful tool for understanding and even predicting catalyst performance and is shaping our approach to catalysis research. Such molecular-level information obtained from computational methods will undoubtedly guide the design of new catalyst materials with high precision.

In this research project, adsorption is considered in conjunction with the reverse water gas shift reaction in order to convert CO2 to CO for synthetic fuel production. If the CO2 for this process can be captured from high emitting industries it can be a very good alternative for reduced fossil fuel consumption and GHG emission mitigation. CO as an active gas could be used in Fischer-Tropsch process to produce conventional fuels. Literature review and process simulation were carried out in order to determine the best operating conditions for reverse water gas shift (RWGS) reaction. Increasing CO2 conversion to CO requires CO2/CO separation downstream of the reactor and recycling unreacted CO2 and H2 back into the reactor. Adsorption as a viable and cost effective process for gas separation was chosen for the CO2/CO separation. This was started by a series of adsorbent screening experiments to select the best adsorbent for the application. Screening study was performed by comparing pure gas isotherms for CO2 and CO at different temperatures and pressures. Then experimental isotherm data were modeled by the Temperature-Dependent Toth isotherm model which provided satisfactory fits for these isotherms. Henry law’s constant, isosteric heat of adsorption and binary mixture prediction were determined as well as selectivity for each adsorbent. Finally, the expected working capacity was calculated in order to find the best candidate in terms of adsorption and desorption. Zeolite NaY was selected as the best candidate for CO2/CO separation in adsorption process for this project. In the last step breakthrough experiments were performed to evaluate operating condition and adsorption capacity for real multi component mixture of CO2, CO, H2 in both cases of saturated with water and dry gas basis. In multi components experiments zeolite NaY has shown very good performance to separate CO2/CO at low adsorption pressure and ambient temperature. Also desorption experiment was carried out in order to evaluate the working capacity of the adsorbent for using in industrial scale and eventually temperature swing adsorption (TSA) process worked very well for the regeneration step. Integrated adsorption system downstream of RWGS reactor can enhance the conversion of CO2 to CO in this process significantly resulting to provide synthetic gas for synthetic fuel production as well as GHG emission mitigation.

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京都大学 / 新制・課程博士 / 博士(工学) / 甲第24106号 / 工博第5028号 / 新制||工||1785(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 江口 浩一, 教授 安部 武志, 教授 阿部 竜 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

The conversion of biomass to biouel has received considerable attention as a sustainable way to produce energy. As worldwide fossil fuels become depleted these efforts grow in importance. The overall strategy is to transform the parent biomass feedstock to increase C-C bonds while reducing oxygen in the final products. A catalytic approach is often used to achieve good yields of transportation grade liquid hydrocarbons from biomass. Development of novel catalyst systems to aid in the thermochemical conversion of biomass to biouel is the focus of this thesis. Gasification of biomass produces synthesis gas (CO and H2). Synthesis gas can be converted to liquid hydrocarbons using Fischer-Tropsch (FT) synthesis. Mo/ZSM-5 FT catalysts with a potassium (K) promoter are introduced to enhance liquid hydrocarbon production and CO conversion of synthesis gas. Liquid products and CO conversion were determined using GC-MS analysis with respect to changes in K loading from 0-2%. The highest liquid product selectivity (21.7%) was found with 1.0% K loading while largest CO conversion (63%) was found with 1.2% K loading. This catalyst work was extended by introducing Ni and Co into the Mo/ZSM-5 catalysts. A copper based water gas shift catalyst (WGS) was also used in concert with the FT catalyst to improve product selectivity. This WGS catalyst promotes the in-situ production of H2 while decreasing water content. The FT+WGS catalyst were used to convert both 1:1 CO: H2 syngas and bio-syngas at 280 °C and 350 °C. The liquid hydrocarbon selectivity was significantly changed and the CO conversion was remarkably increased compared to the reactions without the dual catalyst at both temperatures. In the fourth chapter, FT+WGS catalysts were studied for upgrading bio-oil model compounds. Guaiacol and furfural were used as the model compounds and upgrading reactions were done under H2, syngas and bio-syngas at 200, 250 and 300 °C. Significant conversion of both guaiacol (85%) and furfural (100%) occurred with syngas at 300 °C. Products upgraded from syngas had a higher combined heat of combustion than the products with pure H2. This suggests the incorporation of some C from CO with model compound upgrading reactions with syngas.

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An investigation was undertaken to determine the feasibility of increasing the hydrogen production rate by coupling the water gas shift (WGS) process to the hybrid sulphur process (HyS). This investigation also involved the technical and economical analysis of the water gas shift and the H2 separation by means of Pressure swing adsorption (PSA) process. A technical analysis of the water gas shift reaction was determined under the operating conditions selected on the basis of some information available in the literature. The high temperature system (HTS) and low temperature system (LTS) reactors were assumed to be operated at temperatures of 350ºC and 200ºC, respectively. The operating pressure for both reactors was assumed to be 30 atmospheres. The H2 production rate of the partial oxidation (POX) and the WGS processes was 242T/D, which is approximately two times the amount produced by the HyS process alone. The PSA was used for the purification process leading to a hydrogen product with a purity of 99.99%. From the total H2 produced by the POX and the WGS processes only 90 percent of H2 is recovered in the PSA. The unrecovered H2 leaves the PSA as a purge gas together with CO2 and traces of CH4, CO, and saturated H2O. The estimated capital cost of the WGS plant with PSA is about US$50 million. The production cost is highly dependent on the cost of all of the required raw materials and utilities involved. The production cost obtained was US $1.41/kg H2 based on the input cost of synthesis gas as produced by the POX process. In this case the production cost of synthesis gas based on US $6/GJ for natural gas and US $0/Ton for oxygen was estimated to be US $0.154/kg. By increasing the oxygen and natural gas cost, the corresponding increase in synthesis gas has resulted in an increase in H2 production cost of US $1.84/kg. / Thesis (M.Sc. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2006.

Chemical reactions can have a staggering amount of molecular complexity. Reaction mechanisms have been proposed with over one hundred elementary reaction steps that occur in the same system simultaneously. While several methods exist to simplify and make sense of the pathways and kinetics via which these reactions proceed, e.g., reaction graphs, sensitivity or flux analysis, microkinetic analysis, and comparison of energy landscapes, etc., these methods all have limitations and are often not able to capture a comprehensive picture of the kinetics of system. It has been found useful to view these mechanisms as a network, i.e., a reaction graph. These graphs enable the visualization of the pathways of the reaction and can provide an analytical tool for pathway and kinetic analysis. However, many of the specific graph-theoretic approaches in the literature are not the most suitable for kinetic analysis of complex mechanisms; as they are simply not based on rules that are rigorous enough to fully enumerate all the pathways or provide quantitative analysis of the reaction rates. Our Reaction Route (RR) Graph approach is different in that it depicts the mechanism by a graph that is consistent with all physical and chemical laws associated with reaction networks, particularly being consistent with mass and energy conservation, i.e., Kirchoff’s Flux Law (KFL) and Kirchoff’s Potential Law (KPL). Because of their adherence to these laws, RR Graphs are able to provide an accurate graph-theoretical tool not only for depicting all reactions routes as walks (hence the name RR Graph) but also for pruning mechanisms and allowing a simplified but accurate quantitative description of reaction rates. This adherence to KFL and KPL does mean that the construction and implementation of these graphs can be prohibitively difficult for large mechanisms. For large reaction systems,especially nonlinear mechanisms, it is not realistic to generate these graphs by hand. And although there exists an analytical solution to find a determinant matrix for the RR Graph of a mechanism, the process involves an exhaustive search for a solution which experiences a combinatorial explosion as the number of steps gets very large. This leads to the idea of developing an algorithm for a computer program that can determine how to generate these graphs automatically. Unfortunately, the same combinatorial explosion is present such that for a moderately sized twenty step mechanism, it could take an average computational processor over a decade to find a solution. We have determined, however, that this brute force combinatorial approach can be avoided if heuristics could be developed to bridge gaps in our knowledge of how these graphs are constructed. Thus, developing a better analytical approach and/or a tighter set of heuristics for a computer algorithm are the overarching goals of this work. To make progress toward developing such heuristics, a set of microkinetic mechanisms were analyzed with the notion that the realization of the RR Graphs would highlight a better approach to their construction and usage. In particular, a very large linear reaction system, a smaller linear system and two non-linear reaction systems were analyzed to develop insights into how each graph is manually constructed and analyzed. Furthermore, kinetic analysis was done for these mechanisms and compared to experimental data and other analytical tools to prove not only the validity of the RR Graphs, but also how they are a significant improvement over more commonly used approaches for mechanistic and kinetic analysis. Based on the lessons learned through a consideration of these examples, a set of heuristics are established and enumerated with the ultimate goal of developing an intuitive algorithm that can help automate drawing and kinetic analysis via RR Graphs of complex mechanisms.