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.

Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2013-04-22T14:27:39Z No. of bitstreams: 1 Ana Paula Monteiro.pdf: 956595 bytes, checksum: 5e950a1fe60917822320be861db1043f (MD5) / Made available in DSpace on 2013-04-22T14:27:39Z (GMT). No. of bitstreams: 1 Ana Paula Monteiro.pdf: 956595 bytes, checksum: 5e950a1fe60917822320be861db1043f (MD5) Previous issue date: 2005 / O estireno é uma das substâncias químicas básicas mais importantes para produção de valiosos artigos como poliestireno, acrilonitrila-butadieno-estireno e estireno-butadieno-estireno. É produzido comercialmente pela desidrogenação do etilbenzeno com excesso de vapor d’água a temperaturas altas de 600-700ºC. Este processo é termodinamicamente limitado e consome energia. O uso de um oxidante, tal como oxigênio, permite superar as limitações termodinâmicas e por conseguinte operar a temperaturas mais baixas com reação exotérmica. Porém, há uma perda significantiva de seletividade a estireno, assim se buscou outro oxidante por muito tempo. O uso de gás carbônico surge como um potencial oxidante, além da conveniência do uso do gás causador do efeito estufa. Na busca de um catalisador alternativo para esta reação, neste trabalho estudou-se o efeito do método de preparação nas propriedades de óxido de ferro. As amostras foram preparadas incorporando óxido de ferro em lantânia, nióbia, titânia, magnésia e zircônia através de dois métodos: a impregnação de nitrato férrico e a deposição de nanoparticulas de óxido de ferro previamente preparadas. Os sólidos foram calcinados a 600ºC por 4 h e caracterizados por análise química, termogravimetria, análise térmica diferencial, difração de raios X, área de superfície específica e medidas de porosidade e redução a temperatura-programada. Os catalisadores foram avaliados na desidrogenação do etilbenzeno na presença de dióxido de carbono, usando um microreator que opera a 1 atm e a 600ºC e uma relação molar gás carbônico/etilbenzeno de 10. Depois dos testes, as amostras foram caracterizadas por difração de raios X e área de superfície específica. Observou-se que a concentração do óxido de ferro incorporado depende do tipo do suporte e do método de preparação. A hematita foi observada nos catalisadores novos. Durante a desidrogenação do etilbenzeno, os suportes não se alteraram, mas a hematita se transformou em magnetita. Os suportes e os catalisadores são sólidos macroporosos com pequena contribuição de mesoporos. A área específica mudou devido à adição de óxido de ferro e foi influenciada pelo método de preparação. A incorporação das nanoparticulas conduziu a um aumento da área superficial específica, indiferentemente do tipo do suporte, fato que foi atribuído ao tamanho pequeno das partículas. As áreas específicas não se alteraram durante a reação. Os sólidos mostraram diferentes resistência contra redução que se deve ao suporte e ao método de incorporação do óxido de ferro. A impregnação de nitrato férrico produziu sólidos menos redutíveis. Os suportes foram cataliticamente ativos na desidrogenação do etilbenzeno na presença de gás carbônico e também eram seletivos a estireno. A adição de compostos de ferro melhorou estas propriedades e a deposição de nanoparticulas melhoraram ainda mais. O óxido ferro suportado em magnésia, preparado pela deposição de nanoparticulas, foi o mais ativo (2,8 x 10-3 mol.g-1.h-1) e catalisador seletivo a estireno (96%) na desidrogenação do etilbenzeno na presença de gás carbônico. A atividade e a seletividade foram mais altos do que um catalisador comercial à base de óxido de ferro, cromo e potássio (a=1,2 x 10-3 mol. g-1. h-1 e S=90%) , sendo o catalisador promissor na reação. / Salvador

Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2013-04-23T13:14:32Z No. of bitstreams: 1 Raphael Holt.pdf: 5449117 bytes, checksum: 052b88f3a4242aebdef5fdf978a8b5ce (MD5) / Made available in DSpace on 2013-04-23T13:14:32Z (GMT). No. of bitstreams: 1 Raphael Holt.pdf: 5449117 bytes, checksum: 052b88f3a4242aebdef5fdf978a8b5ce (MD5) Previous issue date: 2008 / A principal rota utilizada industrialmente para a produção de estireno é a desidrogenação catalítica do etilbenzeno, responsável por mais de 90% da produção mundial de estireno. O processo industrial é operado na faixa de temperatura de 550-700 oC, em excesso de vapor d’água aquecido, sobre catalisadores de óxido de ferro promovidos com potássio e cromo, que são tóxicos e possuem vida útil limitada a 2 anos. Neste contexto, existe a demanda por catalisadores que sejam ativos e seletivos nessa reação e que apresentem elevada vida útil, além de não serem tóxicos. Na busca de sistemas alternativos, neste trabalho foram desenvolvidos catalisadores de vanádio e magnésio suportados em carvão ativado obtido pela pirólise do copolímero estireno-divinilbenzeno, em atmosfera não oxidativa. Os catalisadores foram caracterizados pela medida da área superficial específica e de porosidade, difração de raios X, termogravimetria, análise térmica diferencial, espectrofotometria de absorção atômica, microscopia eletrônica de varredura acoplada ao sistema de quantificação por energia dispersiva. Os catalisadores foram avaliados na desidrogenação do etilbenzeno em ausência de vapor d’água, a 530 oC e 1 atm, para a produção de estireno. Verificou-se a presença de trióxido de vanádio e de aglomerados de vanádio e magnésio de diferentes tamanhos, nos sólidos. Os materiais apresentaram isotermas de adsorção e dessorção de nitrogênio do Tipo II ou IV, que são típicas de sólidos meso e macroporos com microporos associados, e uma histerese do Tipo H I, característica de materiais com poros cilíndricos. Estes sólidos apresentaram áreas superficiais específicas entre 378 e 611 m2/g. Os catalisadores com vanádio e magnésio apresentaram menor perda da área superficial específica que o carvão ativado, durante a desidrogenação do etilbenzeno. A adição de magnésio e vanádio provocou um aumento da atividade catalítica do carvão ativado e da seletividade ao estireno. Todos catalisadores foram mais ativos que uma amostra de catalisador comercial. O catalisador contendo 5 % de vanádio foi o mais promissor. Esta amostra conduziu, em ausência de vapor d’água, 35% de conversão do etilbenzeno, que é cerca de três vezes o valor obtido com uma amostra de catalisador comercial em presença de vapor d’água. Isto foi atribuído à ação catalítica do vanádio e à presença de grupos oxigenados na superfície do carvão que possuem atividade na desidrogenação do etilbenzeno. / Salvador

Doctor of Philosophy / Department of Chemical Engineering / Mary E. Rezac / Membrane reactor is a device that simultaneously carrying out reaction and membrane-based separation. The advantageous transport properties of the membranes can be employed to selectively remove undesired products or by-products from the reaction mixture, to break the thermodynamic barrier, and to selectively supply the reactant. In this work, membrane reactor technology has been exploited with robust H₂ selective polymeric membranes in the process of hydrogenation and dehydrogenation. A state-of-the-art 3-phase catalytic membrane contactor is utilized in the processes of soybean hydrogenation and bio-oil hydro-deoxygenation, where the membrane functions as phase contactor, H₂supplier, and catalytic support. Intrinsically skinned asymmetric Polyetherimide (PEI) membranes demonstrated predominant H₂permeance and selectivity. By using the PEI membrane in the membrane contactor, soybean oil is partially hydrogenated efficiently at relatively mild reaction conditions compared with a conventional slurry reactor. In the hydroprocessing of bio-oil using the same system, the membrane successfully removed water, an undesired component from bio-oil by pervaporation. The more industrially feasible membrane-assisted reactor is studied in the alkane dehydrogenation process. Viable polymeric materials and their stability in elevated temperatures and organic environment are examined. The blend polymeric material of Matrimid® 5218 and Polybenzimidazole (PBI) remained H₂permeable and stable with the presence of hydrocarbons, and displayed consistent selectivity of H2/hydrocarbon, which indicated the feasibility of using the material to fabricate thermally stable membrane for separation. The impact of membrane-assisted reactor is evaluated using finite parameter process simulation in the model reaction of the dehydrogenation of methylcyclohexane (MCH). By combining tested catalyst performance, measured transport properties of the material and hypothetical membrane configuration, by using a membrane assisted packed-bed reactor, the thermodynamic barrier of the reaction is predicted to be broken by the removal of H₂. The overall dehydrogenation conversion can be increased by up to 20% beyond equilibrium. The predicted results are justified by preliminary experimental validation using intrinsically skinned asymmetric Matrimid/PBI blend membrane. The conversions at varied temperatures partially exceeded equilibrium, indicating successful removal of H₂by the blend membrane as well as decent thermal stability of the membrane at elevated temperatures with the presence of hydrocarbons. The successful outcome of membrane contactor and membrane-assisted reactor using robust polymeric membranes shows the effectiveness and efficiency of membrane reactors in varied application. The future work should be focusing on two direction, to further develop durable and efficient membranes with desired properties; and to improve the reactor system with better catalytic performance, more precise control in order to harvest preferable product and greater yield.

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: Teresa Massako Kakuta Ravagnani / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-17T16:55:35Z (GMT). No. of bitstreams: 1 Possani_Germano_M.pdf: 3312667 bytes, checksum: 30058f7ade4b339ee579a28950283ff8 (MD5) Previous issue date: 2011 / Resumo: Dentre os termoplásticos mais utilizados atualmente na indústria, pode-se mencionar o estireno, principal responsável pela produção de plásticos e borrachas. No processo de fabricação de estireno, a principal rota química é por meio da desidrogenação de etilbenzeno, com o hidrogênio como subproduto. A conversão de etilbenzeno nesta reação é em torno de 50,0 %, devido ao equilíbrio termodinâmico. Para deslocar esse equilíbrio e aumentar a produtividade de estireno,foram desenvolvidas novas configurações de reatores, tal como os reatores com membrana. eatores equipados com membranas de paládio fornecem uma seletividade maisalta ao estireno uando comparados com reatores equipados apenas com membranas porosas. Para explorar o otencial desse tipo de reator, modelagens matemáticas foram desenvolvidas a fim de determinar os parâmetros cruciais que regem esses processos. O objetivo deste trabalho foi modelar e simular um reator de leito fixo catalítico, envolto por uma membrana inerte permseletiva ao hidrogênio com transferência de calor e massa, sendo composta por uma camada de aço inoxidável de 1,6 mm de espessura, a qual serviu de suporte para a deposição de um filme de 20 µm de paládio. Para essa modelagem foram utilizados os métodos de Runge-Kutta-Gill para o cálculo das variáveis no sentido axial, tanto no retentato quanto no permeado, considerando no retentato um leito fixo catalítico descrito pelo modelo Pseudo-homogêneo, e para os cálculos das equações não lineares das frações molares das espécies e do fluxo mássico de hidrogênio na direção radial do reator foi utilizado o método de Newton-Raphson. Foram analisados os perfis de temperatura, pressão e concentração dos componentes da reação axialmente, considerando a transferência de massa e energia através da membrana, além dos valores para a conversão do etilbenzeno e produtividade em relação ao estireno. Como resultados das simulações foram obtidos valores para a conversão e produtividade de 50,3 % e 35,2 %, respectivamente, para o reator na condição de reator de leito fixo catalítico convencional, e 71,2 % e 60,2 %, para o reator na condição de reator de leito fixo catalítico envolto por uma membrana permseletiva ao hidrogênio, sendo estes valores 41,6 % maiores para a conversão do etilbenzeno e 71,0 % maiores para a produtividade em relação ao estireno. Concluiu-se que com a implementação da membrana no reator em estudo, considerando também a troca térmica na membrana, esta é uma boa opção como nova alternativa para o processo de fabricação do estireno / Abstract: Among the most widely used thermoplastics in the industry, styrene can be mentioned, the main responsible for the production of plastics and rubbers. In the manufacturing process of styrene, the principal chemical route is by means of dehydrogenation of ethylbenzene, with hydrogen as a byproduct. The conversion of ethylbenzene in this reaction is around 50,0 % due to thermodynamic equilibrium. To overcome this equilibrium and increase the productivity of styrene, new reactor configurations were developed such as membrane reactors. Membrane reactors equipped with a palladium membrane provide a higher selectivity compared with reactors that are equipped only with a porous membrane. To explore the potential of this type of reactor, mathematical models were developed to determine the crucial parameters governing these processes. The aim of this study was to model and simulate a fixed bed catalytic reactor, surrounded by a permselective to hydrogen inert membrane with heat and mass transfer, composed by a layer of stainless steel of 1,6 mm thickness, which served as support for deposition of a 20 µm film of palladium. For this modeling the Runge-Kutta-Gill method was used to calculate the variables in the axial direction, both in tube side and in permeate side, considering in tube side a catalytic fixed bed described by Pseudo-homogeneous model, and for the calculations of nonlinear equations of the mole fractions of species and the mass flow of hydrogen in the radial direction it was used the method of Newton-Raphson. Profiles of temperature, pressure and concentration of reaction components on axial toward were analyzed considering the heat and mass transfer across the membrane, besides the values for ethylbenzene conversion, selectivity and productivity in relation to styrene. As the simulation results, values were obtained for the conversion and productivity of 50,3 % and 35,2 %, respectively, putting the reactor on condition of conventional catalytic fixed bed reactor, and 71,2 % and 60,2 % for the reactor on condition of catalytic fixed bed reactor surrounded by a permselective membrane to hydrogen, then , the obtained values were 41,6 % higher for the conversion of ethylbenzene and 71,0 % higher for the productivity of styrene. It was concluded that with the implementation of a membrane in reactor under study, also considering the heat transfer in the membrane, this technology is a good option as new alternative to the styrene manufacturing process / Mestrado / Sistemas de Processos Quimicos e Informatica / Mestre em Engenharia Química

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

<div>As shale gas exploitation has been developed, production of shale gas in the US has rapidly increased during the last decade. This has motivated the development of techniques to covert shale gas components (mainly C₁ to C₃) to liquid fuels by catalytic conversion. The main goal of the dissertation is to study the geometric and electronic structures of the metal catalysts, which are crucial for understanding the structure-property relationship.</div><div><br></div><div><div>The fi?rst project studies bimetallic Pt-Bi catalyst for non-oxidative coupling of methane. In a recent publication published in ACS catalysis, Pt-Bi/ZSM-5 catalyst</div><div>has been shown to stably convert methane into C2 for 8 hours under non-oxidative conditions. In this thesis, structure of the Pt-Bi/ZSM-5 was shown with HAADF</div><div>imaging, synchrotron XAS and XRD. A new surface cubic Pt₃Bi phase on Pt nanoparticles with Pt-Bi bond distance of 2.80 A was formed. Formation of noble metal intermetallic alloys such as Pt₃M may be the clue for non-oxidative conversion of methane.</div></div><div><br></div><div><div>The second and third project highlight strong metal-support interaction catalysts for propane dehydrogenation. Chemisorption showed partial coverage of the SMSI oxides</div><div>on the surface of the nanoparticles. In situ X-ray absorption near edge (XANES), resonant inelastic X-ray scattering (RIXS), X-ray photoelectron spectroscopy (XPS)</div><div>have shown that little electronic effect on the metal nanoparticles. The catalyst activity per mol of metal decreased due to the partial coverage of the SMSI oxides on the surface of the catalysts. The catalysts, however, had higher selectivity due to smaller ensembles inhibiting hydrogenolysis.</div></div><div><br></div><div><div>In the fourth project Pt-P catalyst was investigated to understand the promoting effect of P.Pt-P catalysts had much higher selectivity for propane dehydrogenation</div><div>(>95%). These give two types of catalysts, a PtP₂-rich surface on Pt core and full PtP₂ ordered structure, which were con?rmed by scanning transmission electron microscopy (STEM), and in situ methods of EXAFS, synchrotron XRD, XPS, and Resonant Inelastic X-ray Spectroscopy (RIXS). The PtP₂ structure has isolated Pt</div><div>atoms separated by P₂atoms. In addition XANES, XPS and RIXS indicate a strong electronic modi?cation in the energy of the valence orbitals.</div></div><div><br></div><div><div>It can be concluded from the Pt-Bi catalyst that intermetallic alloys might be selective for NOCM. Therefore, promoters with higher reduction temperature, such as Mn and Cr, should be used to have stable catalysts at high temperature. Moreover, both Pt-Bi and Pt/CeO₂suggest that selective catalysts for propane dehydrogenation and NOCM may have some correlation. Further studies would be conducted to understand the correlation between the two reactions.</div></div>

Abstract: Isobutylene is a high demand chemical that contributes to the production of fuel, plastic, and rubbers. It is produced industrially by different processes, as a byproduct of steam cracking of naphtha or a fluidized catalytic cracking or by isobutane dehydrogenation. Catalytic dehydrogenation of isobutane is in increasing importance because of the growing demand for isobutylene and the better economic advantage compared to other isobutylene production processes. Isobutane dehydrogenation is an endothermic reaction and to achieve good yields; it is preferred to work at higher temperatures. At these temperatures, carbon deposition leads to catalyst deactivation, which requires the catalyst to be regenerated on a frequent basis. Most of the current processes to produce isobutylene use either expensive platinum-based metal or toxic chromium-based catalysis. Hence, there is a demand to search for alternative catalysts that are a relatively cheap and non-toxic. To achieve this goal, Zirconia-supported Iron catalysts were prepared. To study the effect of active phase distribution, different iron loadings were tested for impregnation (3% to 10%) and co-precipitation (10%-20%). The catalysts show promising results that can achieve an isobutylene selectivity and yield of 91% and 31%, respectively, with isobutane conversion of 35%.

<p>The recent surge in shale gas production led to increases in alkane resources across the United States. One promising approach to convert the alkanes to higher value products is through dehydrogenation and oligomerization processes. This conversion to alkenes, if done in small modular units near the shale wells further aids in the ease of transportation and distribution of the final products. However, having highly selective processes is a major hindrance to improve the economic feasibility of the modular processes. Theoretical studies are of great significance to analyze detailed reaction mechanisms and identify the reaction pathways that leads to unselective product formations. These studies further enable the search for selective catalysts for any given chemistry based on descriptor analysis. Therefore, in this work Density Function Theory and Ab-initio Molecular Dynamics methods are used in conjunction with microkinetic modeling analyses to investigate the complex reaction networks involved in the shale gas conversion. Specifically, the work focuses on propane dehydrogenation (PDH) on alloy surfaces along with ethylene oligomerization on zeolite catalysts.</p><p> A major part of thesis is focused on finding selective and stable alloy catalysts for PDH chemistry. The initial work focused on understanding the selectivity, activity, and stability differences between 1:1 intermetallic alloys (PdIn) and the pure metal surfaces. This combined experimental and computational study shed light on the important role of step surfaces in understanding the activity trends across alloys. Through a detailed microkinetic analysis and simplified rate expression analysis, a novel selectivity descriptor in terms of effective barriers for propane C-H bond breaking and propyne C-C bond breaking was derived for propylene formation. This newly proposed descriptor showed greater fidelity for predicting the trends in experimental selectivities for a small set of Pd alloys than the previously proposed selectivity descriptors. Building upon these insights, a high throughput screening framework using graph-theory algorithms and python-based databasing has been developed to identify trends across a larger set of alloy combinations. The framework helped us identify a novel set of alloys that have not been explored until now for this chemistry. These alloy combinations were then experimentally tested and shown to have high selectivities for propylene formation and along with stabilities close to benchmark Pt-Sn catalysts. Detailed transition state analysis on terraces shows that the undesired C-C bond breaking pathways involves larger surface atom ensembles (4-5 atoms) while the C-H bond breaking involves smaller surface atom ensembles (1-2 atoms). This led to the conclusion that the site-isolation of active metal atoms is important to increase the selectivities for propylene formation. More importantly the combination of detailed mechanistic and screening studies using graph-theory methods shows a generalized framework towards finding new catalysts spaces for complex chemistries.</p><p>The work on ethylene oligomerization on the other hand is focused on understanding the role of mobility of active Ni species in the zeolites towards isomerization and deactivation reaction mechanisms. For this specific project, we have used state-of-the-art AIMD methods, including potential of mean force calculations, for accurate estimation of free energies for the reaction intermediates and transition states. The thermodynamic and kinetic analyses show that the reaction pathways involving mobile intermediates have the highest rates towards butene formations even under pressures lower than 1 bar. Further the isomerization step is found to be feasible on Ni-ethyl complex in agreement with experiments. Finally, the mobile complexes were shown to dimerize through alkyl bridged complexes and the generated complex has higher barriers for C-C bond formation than the isolated complex indicating that these are likely pathways for catalyst deactivation. This mechanistic understanding paves the way for fine-tuning the reaction conditions as well as ways in which the active site can be speciated inside the zeolitic frameworks to increase the selectivity towards 1-butene and reduce deactivation.</p>