The Fischer-Tropsch process in South Africa, used for producing chemicals from synthesis gas, which is mostly derived from the gasification of coal, gives a large amount of medium chain length alkanes (C4-C8), which have little commercial value. Internationally, industry has recently placed more focus on the conversion of alkanes to value-added products. Two important routes to achieving this are dehydrogenation and oxidative dehydrogenation. The latter is an economically feasible route, in which there is growing interest by the international research community, and was investigated in this study. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2007.

Non-oxidative dehydrogenation of hydrocarbons is an attractive alternative route for the production of CO- and CO2-free hydrogen. It will satisfy a major requirement for successful utilization of polymer electrolyte membrane (PEM) fuel cells (< 10 ppm CO) and sequestering carbon as a potentially valuable by-product, carbon nanotubes (CNTs). Due to the deposition of carbon on the surface of catalyst particles during the reaction, catalyst performance, life-time, and purification of the generated carbon product, are significant issues to solve in order to make the process practically feasible. The scope of this thesis includes: the development of novel Fe, Ni, and Fe-Ni catalysts supported on a Mg(Al)O support to achieve improved catalytic performance with easily-purified CNTs; evaluation of catalysts for ethane/methane dehydrogenation at moderate reaction temperatures; and study of activation and deactivation mechanisms by a variety of characterization techniques including TEM, HRTEM, XRD, Mössbauer spectroscopy, and x-ray absorption fine structure (XAFS) spectroscopy. The Mg(Al)O support was prepared by calcination of synthetic MgAl-hydrotalcite with a Mg to Al ratio of 5. The catalysts were prepared either by conventional incipient wetness method or by a novel nanoparticle impregnation method, where the monodisperse catalyst nanoparticles were prepared in advance by thermal decomposition of a metal-organic complex in an organic-phase solution and then dispersed onto the Mg(Al)O support. Dehydrogenation of undiluted methane was conducted in a fix-bed plug-flow reactor. Before reaction, the catalysts were activated by reduction in hydrogen. Fe-based catalysts exhibit a higher hydrogen yield at temperature above 600ºC compared with monometallic Ni catalyst. FeNi-9 nm/Mg(Al)O, Fe-10 nm/Mg(Al)O and Fe-5 nm/ Mg(Al)O nanoparticle catalysts show much improved performance and longer life-times compared with the corresponding FeNi IW/Mg(Al)O and Fe IW/Mg(Al)O catalysts prepared by incipient wetness. 10 nm is the optimum particle size for methane dehydrogenation. Addition of Ni to Fe forming a bimetallic FeNi alloy catalyst enhances the catalytic performance at the temperatures below 650ºC. Metallic Fe, Ni, FeNi alloy and Fe-Ni-C alloy, unstable iron carbide are all catalytically active components. Catalysts deactivation is due to the carbon encapsulation. The carbon products are in the form of stack-cone CNTs (SCNTs) and multi-walled CNTs (MWNTs), depending on the reaction temperature and catalyst composition. The growth of CNTs follows a tip growth mechanism and the purity of cleaned CNTs is more than 99.5%.

The availability of kinetic data for the oxidative dehydrogenation (ODH) of n-butane from Téllez et al. (1999a and 1999b) and Assabumrungrat et al. (2002) presented an opportunity to submit a chemical process of industrial significance to Attainable Region (AR) analysis. The process thermodynamics for the ODH of n-butane and 1-butene have been reviewed. The addition of oxygen in less than the stoichiometric ratios was found to be essential to prevent deep oxidation of hydrocarbon products {Milne et al. (2004 and 2006c)}. The AR concept has been used to determine the maximum product yields from the ODH of n-butane and 1-butene under two control régimes, one where the partial pressure of oxygen along the length of the reactor was maintained at a constant level and the second where the oxygen partial pressure was allowed to wane. Theoretical maxima under the first régime were associated with very large and impractical residence times. The Recursive Convex Control policy {Seodigeng (2006)} and the second régime were applied to confirm these maxima {Milne et al. (2008)}. Lower and more practical residence times ensued. A differential side-stream reactor was the preferred reactor configuration as was postulated by Feinberg (2000a). Abstract A.D. Milne Page 4 of 430 The maximum yield of hydrocarbon product, the associated residence time and the required reactor configuration as functions of oxygen partial pressure were investigated for the series combinations of an inert porous membrane reactor and a fixed-bed reactor. The range of oxygen partial pressures was from 85 kPa to 0.25 kPa. The geometric profile for hydrocarbon reactant and product influences the residence times for the series reactors. The concept of a residence time ratio is introduced to identify the operating circumstances under which it becomes advantageous to select an inert membrane reactor in preference to a continuously stirred tank reactor and vice versa from the perspective of minimising the overall residence time for a reaction {Milne et al. (2006b)}. A two-dimensional graphical analytical technique is advocated to examine and balance the interplay between feed conditions, required product yields and residence times in the design of a reactor {Milne et al. (2006a)}.. A simple graphical technique is demonstrated to identify the point in a reaction at which the selectivity of the feed relative to a product is a maximum {Milne et al. (2006a)}. Literature Cited Assabumrungrat, S. Rienchalanusarn, T. Praserthdam, P. and Goto, S. (2002) Theoretical study of the application of porous membrane reactor to Abstract A.D. Milne Page 5 of 430 oxidative dehydrogenation of n-butane, Chemical Engineering Journal, vol. 85, pp. 69-79. Feinberg, M. (2000a) Optimal reactor design from a geometric viewpoint – Part II. Critical side stream reactors, Chemical Engineering Science, vol. 55, pp. 2455-2479. Milne, D., Glasser, D., Hildebrandt, D., Hausberger, B., (2004), Application of the Attainable Region Concept to the Oxidative Dehydrogenation of 1- Butene in Inert Porous Membrane Reactors, Industrial and. Engineering Chemistry Research, vol. 43, pp. 1827-1831 with corrections subsequently published in Industrial and Engineering Chemistry Research, vol. 43, p. 7208. Milne, D., Glasser, D., Hildebrandt, D., Hausberger, B., (2006a), Graphical Technique for Assessing a Reactor’s Characteristics, Chemical Engineering Progress, vol. 102, no. 3, pp. 46-51. Milne, D., Glasser, D., Hildebrandt, D., Hausberger, B., (2006b), Reactor Selection : Plug Flow or Continuously Stirred Tank?, Chemical Engineering Progress. vol. 102, no. 4, pp. 34-37. Milne, D., Glasser, D., Hildebrandt, D., Hausberger, B., (2006c), The Oxidative Dehydrogenation of n-Butane in a Fixed Bed Reactor and in an Inert Porous Membrane Reactor - Maximising the Production of Butenes and Butadiene, Industrial and Engineering Chemistry Research vol. 45, pp. 2661-2671. Abstract A.D. Milne Page 6 of 430 Milne, D., Seodigeng, T., Glasser, D., Hildebrandt, D., Hausberger, B., (2008), The Application of the Recursive Convex Control (RCC) policy to the Oxidative Dehydrogenation of n-Butane and 1-Butene, Industrial and Engineering Chemistry Research, (submitted for publication). Seodigeng, T.G. (2006), Numerical Formulations for Attainable Region Analysis, Ph.D. thesis, University of the Witwatersrand, Johannesburg, South Africa. Téllez, C. Menéndez, M. Santamaría, J. (1999a) Kinetic study of the oxidative dehydrogenation of butane on V/MgO catalysts, Journal of Catalysis, vol. 183, pp. 210-221. Téllez, C. Menéndez, M. Santamaría, J. (1999b) Simulation of an inert membrane reactor for the oxidative dehydrogenation of butane, Chemical Engineering Science, vol. 54, pp. 2917-2925. __________________________________

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Na reação de desidrogenação oxidativa de propano (ODHP), propano reage com oxigênio da superfície de metais de transição para produzir propeno e água, em temperaturas de 300-700C. Porém, o propeno pode facilmente oxidar, formando CO e CO2. Assim, busca-se catalisadores que promovam a seletividade do propeno. Compostos tipo hidrotalcitas estão sendo apontados como catalisadores de grande potencial para a reação. Portanto, o principal objetivo desse trabalho foi sintetizar precursores tipo hidrotalcitas (contendo íons Ni2+, Mg2+ e Al3+ e tereftalato, heptamolibdato e decavanadato como ânions de compensação) para serem testados na reação de desidrogenação oxidativa de propano. Esses precursores foram sintetizados com uma razão Al/(Al+Ni+Mg)=0,5, variando a razão de Ni/Mg. Além disso, realizou-se a troca iônica do tereftalato (TA) por heptamolibdato (Mo7O24) e decavanadato (V10O28). Esses compostos foram calcinados, obtendo-se assim, óxidos mistos de NiMgAl, NiMgAlMo e NiMgAlV que foram testados como catalisadores na reação de ODHP. Para a determinação das propriedades dos catalisadores foram usadas as técnicas de caracterização: DRX, TGA, volumetria de N2, TPR, Raman e FTIR e ICP. Os resultados indicaram que os materiais tipo hidrotalcita foram obtidos com sucesso. No caso dos precursores preparados por troca iônica a cristalinidade foi menor que os da série NiMgAl-TA. Estes mesmos precursores quando calcinados apresentaram áreas muito altas. Nas três séries, os precursores calcinados são constituídos por óxidos mistos como NiO, NiMoO4, Ni2V2O7 cristalinos e espécies de alumínio e magnésio não detectados na DRX. No teste catalítico de ODHP, observou-se que com o aumento da conversão diminuía a seletividade de propeno, para os óxidos mistos que não continham molibdênio. Os catalisadores da série molibdênio foram os que obtiveram melhor desempenho com altas seletividades, mesmo em altas conversões e a série de cujo precursor foi o tereftalato foi a que exibiu maiores conversões, mas com seletividades menores que da série de Mo / In the reaction of oxidative dehydrogenation of propane (ODHP), propane reacts with oxygen in the transition metal surface to produce propylene and water at temperatures of 300-700 C. However, the propylene can easily oxidize, forming CO and CO2. Thus, catalysts that promote the selectivity of propylene are being searched. Hydrotalcites type compounds are identified as potential major catalysts for the reaction. Therefore, the main objective of this work was to synthesize precursors hydrotalcites type (containing Ni2+, Mg 2+ and Al 3+ ions and terephthalate, heptamolybdate and decavanadate as compensation anions) to test in the reaction of oxidative dehydrogenation of propane.These precursors were synthesized with Al/(Ni+Mg+Al) = 0.5 for different ratios of Ni/Mg. In addition, there was the ion exchange terephthalate (TA) by heptamolybdate (Mo7O24) and decavanadate (V10O28). These compounds were calcined, to obtain NiMgAl, NiMgAlMo and NiMgAlV mixed oxides and tested as catalysts in the ODHP reaction.For determining the properties of the catalysts the following characterization techniques were used: XRD, TGA, N2 volumetry, TPR, ICP, FTIR and Raman spectroscopy. The results indicated that the hydrotalcite-like materials were successfully obtained. In the case of the precursors prepared by ion exchange crystallinity was lower than those of NiMgAl-TA series. These same precursors when calcined had very high areas. In three series, the calcined precursors are comprised by mixed oxides such as crystalline NiO, NiMoO4, Ni2V2O7 and Al an Mg species not detected by XRD. In ODHP catalytic test, it was observed that with increasing conversion the propylene selectivity decreased to the mixed oxides containing no molybdenum. The catalysts of molybdenum series were those who performed better with high selectivity even at high conversions and the terephthalate precursor series shows the highest conversions, but with lower selectivity than Mo series

In this research, oxidative dehydrogenation of ethane to ethylene was studied over Cr-O and Cr-V-O mixed oxide catalysts through steady-state and dynamic experiments. The catalysts were prepared by the complexation method. By XRD, presence of Cr2O3 phase in Cr-O / and the small Cr2O3 and V2O4 phases of Cr-V-O were revealed. In H2-TPR, both catalysts showed reduction behaviour. From XPS the likely presence of Cr+6 on fresh Cr-O was found. On Cr-V-O, the possible reduction of V+5 and Cr+6 forms of the fresh sample to V+4, V+3 and Cr+3 states by TPR was discovered through XPS. With an O2/C2H6 feed ratio of 0.17, Cr-O exhibited the highest total conversion value of about 0.20 at 447&deg / C with an ethylene selectivity of 0.82. Maximum ethylene selectivity with Cr-O was obtained as 0.91 at 250&deg / C. An ethylene selectivity of 0.93 was reached with the Cr-V-O at 400&deg / C. In the experiments performed by using CO2 as the mild oxidant, a yield value of 0.15 was achieved at 449&deg / C on Cr-O catalyst. In dynamic experiments performed over Cr-O, with C2H6 pulses injected into O2-He flow, the possible occurrence of two reaction sites for the formation of CO2 and H2O was detected. By Gaussian fits to H2O curves, the presence of at least three production ways was thought to be probable. Different from Cr-O, no CO2 formation was observed on Cr-V-O during pulsing C2H6 to O2-He flow. In the runs performed by O2 pulses into C2H6-He flow over Cr-V-O, formation of CO rather than C2H4 was favored.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Na reação de desidrogenação oxidativa de propano (ODHP), propano reage com oxigênio da superfície de metais de transição para produzir propeno e água, em temperaturas de 300-700C. Porém, o propeno pode facilmente oxidar, formando CO e CO2. Assim, busca-se catalisadores que promovam a seletividade do propeno. Compostos tipo hidrotalcitas estão sendo apontados como catalisadores de grande potencial para a reação. Portanto, o principal objetivo desse trabalho foi sintetizar precursores tipo hidrotalcitas (contendo íons Ni2+, Mg2+ e Al3+ e tereftalato, heptamolibdato e decavanadato como ânions de compensação) para serem testados na reação de desidrogenação oxidativa de propano. Esses precursores foram sintetizados com uma razão Al/(Al+Ni+Mg)=0,5, variando a razão de Ni/Mg. Além disso, realizou-se a troca iônica do tereftalato (TA) por heptamolibdato (Mo7O24) e decavanadato (V10O28). Esses compostos foram calcinados, obtendo-se assim, óxidos mistos de NiMgAl, NiMgAlMo e NiMgAlV que foram testados como catalisadores na reação de ODHP. Para a determinação das propriedades dos catalisadores foram usadas as técnicas de caracterização: DRX, TGA, volumetria de N2, TPR, Raman e FTIR e ICP. Os resultados indicaram que os materiais tipo hidrotalcita foram obtidos com sucesso. No caso dos precursores preparados por troca iônica a cristalinidade foi menor que os da série NiMgAl-TA. Estes mesmos precursores quando calcinados apresentaram áreas muito altas. Nas três séries, os precursores calcinados são constituídos por óxidos mistos como NiO, NiMoO4, Ni2V2O7 cristalinos e espécies de alumínio e magnésio não detectados na DRX. No teste catalítico de ODHP, observou-se que com o aumento da conversão diminuía a seletividade de propeno, para os óxidos mistos que não continham molibdênio. Os catalisadores da série molibdênio foram os que obtiveram melhor desempenho com altas seletividades, mesmo em altas conversões e a série de cujo precursor foi o tereftalato foi a que exibiu maiores conversões, mas com seletividades menores que da série de Mo / In the reaction of oxidative dehydrogenation of propane (ODHP), propane reacts with oxygen in the transition metal surface to produce propylene and water at temperatures of 300-700 C. However, the propylene can easily oxidize, forming CO and CO2. Thus, catalysts that promote the selectivity of propylene are being searched. Hydrotalcites type compounds are identified as potential major catalysts for the reaction. Therefore, the main objective of this work was to synthesize precursors hydrotalcites type (containing Ni2+, Mg 2+ and Al 3+ ions and terephthalate, heptamolybdate and decavanadate as compensation anions) to test in the reaction of oxidative dehydrogenation of propane.These precursors were synthesized with Al/(Ni+Mg+Al) = 0.5 for different ratios of Ni/Mg. In addition, there was the ion exchange terephthalate (TA) by heptamolybdate (Mo7O24) and decavanadate (V10O28). These compounds were calcined, to obtain NiMgAl, NiMgAlMo and NiMgAlV mixed oxides and tested as catalysts in the ODHP reaction.For determining the properties of the catalysts the following characterization techniques were used: XRD, TGA, N2 volumetry, TPR, ICP, FTIR and Raman spectroscopy. The results indicated that the hydrotalcite-like materials were successfully obtained. In the case of the precursors prepared by ion exchange crystallinity was lower than those of NiMgAl-TA series. These same precursors when calcined had very high areas. In three series, the calcined precursors are comprised by mixed oxides such as crystalline NiO, NiMoO4, Ni2V2O7 and Al an Mg species not detected by XRD. In ODHP catalytic test, it was observed that with increasing conversion the propylene selectivity decreased to the mixed oxides containing no molybdenum. The catalysts of molybdenum series were those who performed better with high selectivity even at high conversions and the terephthalate precursor series shows the highest conversions, but with lower selectivity than Mo series

Orientador: Heloise de Oliveira Pastore / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-07T11:21:16Z (GMT). No. of bitstreams: 1 Albuquerque_Angela_D.pdf: 3045566 bytes, checksum: 280ada8d591e09adc89304ad0847ca95 (MD5) Previous issue date: 2006 / Resumo: A síntese da peneira molecular vanadoaluminossilicato com estrutura MWW, [V,Al]-MCM-22, foi realizada por tratamento hidrotérmico estático. Os materiais recém sintetizados, calcinados e trocados com íons H, Na ou K foram caracterizados por diversas técnicas analíticas e espectroscópicas. Foi preparado também um material por troca iônica do [Al]-MCM-22 com íons vanadila, o VO-[Al]-MCM-22. Todos os materiais apresentaram estrutura cristalina semelhante à observada para o [Al]-MCM-22. A presença de sítios redox (pares V/ V) foi monitorada por espectroscopia no UV -Vis com refletância difusa e por espectroscopia de infravermelho com transformada de Fourier (FTlR) com adsorção de CO a 100 K. As características ácidas foram monitoradas por FTlR com adsorção de NH3 e por dessorção termoprogramada (TPD) de NH3. Em testes catalíticos na reação de desidrogenação oxidativa do propano, os vanadoaluminossilicatos apresentaram maiores valores de conversão em relação aos aluminossilicatos, com valores de seletividade semelhantes. A troca iônica com íons alcalinos pode promover modulação na acidez dos catalisadores, tomando-os mais seletivos, por diminuir a seletividade para produtos de craqueamento. / Abstract: The synthesis of the vanadoaluminosilicate molecular sieve with MWW structure, [V,AI]-MCM-22, has been performed by static hydrothermal synthesis. As-synthesized, calcined, and H, Na or K ion-exchanged materiaIs were characterized by various analytical and spectroscopical techniques. It has also been prepared a material by ion-exchanging [AI]-MCM-22 with vanadyl ions, VO-[AI]-MCM-22. AlI the materiaIs presented a crystalIine structure similar to that observed for [AI]-MCM-22. The presence of redox sites (V/ V couples) was monitored by diffuse reflectance UV-vis spectroscopy and by Fourier transform infrared spectroscopy (FTlR) with CO adsorption at 100 K. Acid characteristics were monitored by FTlR with NH3 adsorption and by thermoprogrammed NH3 desorption (TPD). When tested in the oxidative dehydrogenation of propane catalytic reaction, vanadoaluminosilicates presented higher conversion values when compared to aluminosilicates, with similar selectivity data. Ion-exchange with alkaline ions may promote modulation in the acidity of the catalysts, making them more selective by decreasing their selectivity to products of cracking reactions. / Doutorado / Quimica Inorganica / Doutor em Quimica

Carbon nanotubes (CNT) have gained interest for wide use as both support and catalyst due to the ease of uniquely tunable surface chemistry. Increasingly severe greenhouse effects have attracted attention to novel materials and technologies capable of capturing carbon dioxide (CO2). In this context, we develop a CNT based solid state amine for the CO2 capture. CNT are functionalized under various methods as a support for polymeric amines. Polyethyleneimine are physically adsorbed on CNT and are further characterized and studied for reversible CO2 capture. We obtain a high CO2 capture capacity (6.78 mmol∙g-1) for linear polyethyleneimine (LPEI) and 6.18 mmol∙g-1 for branched polyethyleneimine (BPEI). Based on the study of pore structure, we also demonstrate that in a steam post-combustion environment, supported polymeric amines on CNT show higher stability than traditional metal oxides. Besides the increased stability of the support in steam, we also improve the stability of amines under steam conditions by developing a covalent modification method. The CO2 capture capacity of the covalent bonded materials under steam conditions improved by 14% compared to dry conditions. In addition, the loading, chemical properties of PEI, and the surface chemistry of CNT remained stable under steam conditions compared to physically adsorbed PEI on CNT. These results suggest that covalent bonded PEI on CNT can be more suitable for CO2 capture in post-combustion processes. A different CNT application is as a catalyst for oxidative dehydrogenation (ODH) of ethane, and herein we develop a new processing technique for tuning the surface chemistry of the CNT-based catalyst. A one-step, gas-phase hydrogen (H2) surface modification is used to reduce carboxylic groups to phenolic groups on carbon nanotube (CNT) materials. This technique is greener and more facile for large-scale industrial catalysts than what has previously been reported. This method uses fundamental principles of CNT surface chemistry to efficiently reduce the unselective oxidation sites and enhances the active sites used for alkane oxidative dehydrogenation. The resulting catalyst improves the ethylene selectivity and yield by at most 81% and 28% respectively compared to the non-modified catalyst. A clear linear correlation between the functional groups and catalytic activity reveals the effect of specific oxygen species on performance. As the catalyst surface area increases, pretreatments generate more selective active sites instead of over-oxidation sites, providing a guideline for catalyst optimization. We suggest that the gas-phase H2 method is general for reducing carbon catalysts to increase selective oxidation sites for gas phase reactions.

The Investigation of Nickel-Based Catalysts for the Oxidative Dehydrogenation of Ethane Justin Lane ParkDepartment of Chemistry & Biochemistry, BYU Doctor of Philosophy Chemistry The advancement of creating ethylene from ethane via oxidative dehydrogenation (ODH) rather than the traditional direct dehydrogenation is right on the cusp of commercialization. The oxidative pathway provides a novel route that reduces the operating temperature of this reaction by 400-500°C. A variety of metals including Mo, V, and Ni that have redox properties suitable for the partial oxidation of small chain alkanes have been investigated. Currently, a MoVNbTe oxide is the most promising catalyst but it suffers from a long and difficult preparation method and the combination of four expensive metals. Nickel based catalysts have also shown great promise but are limited by the reactivity of the oxygen species on the surface of the catalyst. In this manuscript, the details for improving the activity of the nickel and altering the activation mechanism are outlined.Bulk CeNiNb oxide catalysts were shown to almost double the rate of ethylene yields at temperatures as low as 300°C. This is partially related to the improved rate of oxygen adsorption and transfer to the active oxygens on the nickel oxide via the ceria additive. However, with further characterization of these materials, it was shown that there is likely an interaction between the Ce and Nb, forming a Ce-O- Nb linkage that is also selective towards ethylene. This facilitates a higher activity of the catalyst by creating two redox active sites. The improved rates of ethylene formation observed with these catalysts led to the initial development of a commercially viable nickel based catalyst. The support interactions of NiO with a novel silica doped alumina support show higher yields than previously reported studies of NiO on alumina for ODH. These initial metal support interactions show that the addition of the niobium and ceria to this catalyst should give ethylene yields that are satisfactory for the commercialization of this catalyst.

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