Liquid organic chemical hydride is a promising candidate for hydrogen storage and transport. Methylcyclohexane (MCH) to toluene (TOL) cycle has been considered as one of the feasible hydrogen carrier systems, but selective dehydrogenation of MCH to TOL has only been achieved using the noble Pt-based catalysts. The aim of this study is to develop non-noble, cost-effective metal catalysts that can show excellent catalytic performance, mainly maintaining high TOL selectivity achievable by Pt based catalysts. Mono-metallic Ni based catalyst is a well-known dehydrogenation catalyst, but the major drawback with Ni is its hydrogenolysis activity to cleave C-C bonds, which leads to inferior selectivity towards dehydrogenation of MCH to TOL. This study elucidate addition of the second metal to Ni based catalyst to improve the TOL selectivity. Herein, ubiquitous bi-metallic nanoparticles catalysts were investigated including (Ni–M, M: Ag, Zn, Sn or In) based catalysts. Among the catalysts investigated, the high TOL selectivity (> 99%) at low conversions was achieved effectively using the supported NiZn catalyst under flow of excess H2. In this work, a combined study of experimental and computational approaches was conducted to determine the main role of Zn over Ni based catalyst in promoting the TOL selectivity. A kinetic study using mono- and bimetallic Ni based catalysts was conducted to elucidate reaction mechanism and site requirement for MCH dehydrogenation reaction. The impact of different reaction conditions (feed compositions, temperature, space velocity and stability) and catalyst properties were evaluated. This study elucidates a distinctive mechanism of MCH dehydrogenation to TOL reaction over the Ni-based catalysts. Distinctive from Pt catalyst, a nearly positive half order with respect to H2 pressure was obtained for mono- and bi-metallic Ni based catalysts. This kinetic data was consistent with rate determining step as (somewhat paradoxically) hydrogenation of strongly chemisorbed intermediate originating from TOL. DFT calculation indicated that Zn metal prefers to occupy the step sites of Ni where unselective C–C bond breaking was considered to preferentially occur, explaining suppression of hydrogenolysis activity. Additionally, it confirmed that the H-deficient species at methyl position group (C6H5CH2) was stable on the surface, making its hydrogenation being rate determining step, consistent with positive order in H2 pressure on TOL formation rate. This may explain the conclusive role by H2 in facilitating desorption of the H-deficient surface species that was produced through further dehydrogenation of TOL.

Hydrogen storage for stationary and mobile applications is an expanding research topic. Using liquid organic hydrides for hydrogen storage is one of the most promising alternatives as it provides simple and safe handling. Liquid organic hydrides are largely compatible with current transport infrastructure, whereas alternatives such as liquid and gaseous hydrogen and metal hydrides would require a completely new infrastructure. An attractive storage system is the so-called MTH system (Methylcyclohexane, Toluene and Hydrogen). The dehydrogenation of methylcyclohexane is a highly endothermic reaction. To improve the reaction kinetics, this research was to develop a structured catalyst with a conductive metal support (Fecralloy) which could hold an adherent catalytic washcoat (γ - Al2O3). The active phase was impregnated onto this support and the developed catalyst was tested for the dehydrogenation of methylcyclohexane. The catalyst preparation involved three key steps which were support oxidation, loading of an adherent washcoat and finally impregnation of the active phase. The oxidation and washcoat stages required significant optimisation. The optimum oxidation conditions were found to be 950 °C for 10 h. The washcoating procedure was optimised by modifying a one-step hybrid washcoating method suggested in patent literature. Characterization techniques including SEM, XRD and EDX were used to study each step of catalyst preparation. In addition the technique of STEM was used to study platinum dispersion on the catalytic washcoat. Finally the catalytic activity of the developed catalyst was compared with an in-house pelleted catalyst based on the material used to prepare the structured catalyst and commercially available platinum on γ - Al2O3. Three key factors: activity, selectivity and stability were evaluated. The activity and selectivity were studied at varied operating conditions of T = 340 °C - 400 °C, W/F = 7345 - 14690 g s/mol, H2/MCH molar ratio = 0 - 9 and P = 1.013 bar. The dehydrogenation reaction of methylcyclohexane was found to be very selective to toluene (above 99%). Compounds, which are considered coke precursors, were identified, to attempt to explain the mechanism of catalyst deactivation. By-product distribution was monitored and possible reaction pathways were postulated. To gauge the stability of the catalyst, long term life tests were also performed on the structured catalyst at 400 °C and W/F = 14690 g s/mol for approximately 400 h. The stability study investigated the different types of deactivation mechanisms. The catalyst evaluation study helped identify the effect of the alloy support, the alumina washcoat and platinum dispersion on the selectivity of the catalyst.

This thesis describes the theoretical results of mercury-sensitized photochemical reactions of isopropyl benzene and methylcyclohexane. The reactions are carried out and the results are analyzed.

The focus of the present work is on the empirical characterization and modeling of ignition trends of ternary blends of three distinct hydrocarbon classes, namely a methyl ester (C9H18O2), a linear alkane (n-C9H20), and a cycloalkane (MCH). Numerous surrogate biofuel formulations have been proposed in the literature, yet specific blending of these species has not been studied. Moreover, the effects of blending biofuel compounds with conventional hydrocarbons are not widely studied and a further point is the lack of studies paying specific attention to the effects of fuel variation within a given blended biofuel. To this end, a statistical Design of Experiments L9 array, comprised of 4 parameters (%MO, %MCH, pressure, and equivalence ratio) with 3 levels of variation, constructed in order to systematically study the effects of relative fuel concentrations within the ternary blend enabled variations in fuel concentration for methyl octanoate and MCH of 10% - 30% and 20% - 40%, respectively. Variation in pressure of 1 atm, 5 atm, and 10 atm and in equivalence ratio of 0.5, 1.0, and 2.0 were used, respectively. The fuel-volume percentage of n-nonane varied from 30% - 70%. In total, 10 ternary blends were studied. Ignition delay times for the ternary blends and for the three constituents were obtained by monitoring excited-state OH or CH transitions, A2Epsilon+ -> X2Pi or A2Delta -> X2Pi, respectively, behind reflected shock waves using a heated shock tube facility. Dilute conditions of 99% Ar (vol.) were maintained in all shock tube experiments with the exception of a separate series of n-nonane and MCH experiments under stoichiometric conditions which used 4% oxygen (corresponding to ~ 95% Ar dilution). Temperatures behind reflected shock waves were varied over the range 1243 < T (K) < 1672. From over 450 shock tube experiments, empirical ignition delay time correlations were constructed for all three pure fuels and a master correlation equation for the blended fuels. Ignition experiments conducted on the pure fuels at 1.5 atm indicated the following ignition delay time order, from shortest to longest: methyl octanoate < n-nonane < MCH. With increased pressure to 10 atm (nominal) the order remained, in general, consistent. Under fuel-lean conditions, ignition trends between methyl octanoate and n-nonane exhibited overlap at temperatures below 1350 K, below which the trends diverged with methyl octanoate having shorter ignition delay times. Similar behavior was observed under fuel-rich conditions, yet with the overlap occurring above 1450 K. Stoichiometric ignition trends did not display overlapping behavior under either 1.5 atm or 10 atm pressure. Laminar flame speed measurements were performed at 1 atm and an initial temperature of 443 K on the pure fuel constituents. Additional flame speed measurements of MCH were conducted at 403 K to compare with literature values and were shown to agree strongly with experiments conducted in a constant-volume apparatus. The experiments conducted herein, for the first time, measure laminar flame speeds methyl octanoate. A detailed chemical kinetics mechanism was compiled from three independent, well-validated models for the constituent fuels, where the sub-mechanisms for methyl octanoate and MCH were extracted for integration into a base n-nonane model. The compiled mechanism in the present study (4785 reactions and 1082 species) enables modeling of oxidation processes of the ternary fuel blends of interest. Calculations were performed using the compiled model relative to the base models to assess the impact of utilizing different base chemistry sets. In general, results were reproduced well relative to base models for both n-nonane and MCH, however results for methyl octanoate from both the compiled model and the base model are in disagreement with the results measured herein. Ignition delay times of the fuel blends are well-predicted for several conditions, specifically for blends at lean/high-pressure and stoichiometric/high-pressure conditions, however are not accurately modeled at fuel-rich, high-pressure conditions.

No description available.

Le craquage du méthylcyclohexane (MCH) à 450 °C et la conversion de l'éthanol (EtOH) en hydrocarbures à 350 °C sous 30 bar sont effectués sur zéolithes HZSM-5 (de taille de cristallite micrométrique et nanométrique) hiérarchisées. Ces deux réactions modèles mais complexes conduisent à la formation du coke, qui est toxique en MCH et potentiellement actif en EtOH. La toxicité (Tox) et la réactivité du coke dépendent fortement des propriétés texturales des catalyseurs. Dans ce travail, il est démontré que quelle que soit la réaction, le coke dans le cas des zéolithes taille micrométriques est « lourd », il est principalement constitué d'alkylphénanthrènes et alkylpyrènes et est localisé dans les micropores. Dans les zéolithes de taille nanométriques et hiérarchisées (méso-microporeux), le coke est plutôt « léger », formé majoritairement d'alkylbenzènes et alkylnaphtalènes ; ce coke qualifié de léger, est localisé en surface externe. Le coke situé dans les canaux et intersection de la zéolithe HZSM-5 est plus toxique (Tox ≥ 1) que celui situé en surface externe (Tox < 1). La diminution du chemin de diffusion offre également un avantage certain lors de la régénération des catalyseurs en abaissant les températures d'élimination totale de ces cokes. Les effets des propriétés texturales sur les performances catalytiques et la désactivation sont nettement plus marqués dans le cas de EtOH (réaction plus sensible) que MCH. / The Methylcyclohexane (MCH) cracking at 450 °C and the ethanol (EtOH) conversion into hydrocarbons at 350 °C under 30 bar are performed over Hierarchical HZSM-5 zeolites (with micro- and nanometer crystal size). These two model but complex reactions lead to the formation of coke which is toxic with MCH and active with EtOH. The toxicity (Tox) and the reactivity of coke depend strongly on the catalysts textural properties. In this work, it's shown that whatever the reaction, coke in the case of micrometric zeolites is "heavy" and consists mainly of alkylphenanthrenes and alkylpyrenes located into the micropores. In nano-sized and hierarchical (meso-microporous) zeolites, coke is rather "light" and consisting mostly of alkyl benzenes and naphthalenes located on the external surface. The coke located into the channels and at the channels intersections of HZSM-5 zeolite is more toxic (Tox ≥ 1) than that located on the external surface (Tox <1). The decrease in the diffusion path also offers a clear advantage in the catalysts regeneration by lowering the temperature of total coke removal. The effect of textural properties on the catalytic performances and the deactivation are more pronounced in the case of EtOH (more sensitive reaction) than MCH.

Hydrogen is currently considered by many as the “fuel of the future”. It is particularly favoured as a replacement for fossil fuels due to its clean-burning properties; the waste product of combustion being water. While hydrogen is relatively easy to produce, there is currently a lack of practical storage methods for molecular H2, and this is greatly hindering the use of hydrogen as a fuel. Gases are normally stored in vessels under only moderate pressures and in liquid form where possible, which yields the highest energy density. However, to store reasonable quantities of hydrogen in similar volume containers, cryogenic temperatures or extreme pressure are required. Many potential hydrogen storage technologies are currently under investigation, including adsorption on metal hydrides, nanotubes and glass microspheres, and the chemical breakdown of compounds containing hydrogen to release H2. Recent studies have sparked interest in hydrates as a potential hydrogen storage material. The molecular storage of hydrogen in clathrate hydrates could offer significant benefits with regard to ease of formation/regeneration, cost and safety, as compared to other storage materials currently under investigation. Here, we present new experimental hydrate stability data for sII forming hydrogen–water (up to pressures of 180 MPa) and hydrogen–water–tetrahydrofuran systems, the structure-H forming hydrogen–water–methyclycohexane system, and semi-clathrate forming hydrogen–water–tetra-n-butyl ammonium bromide/tetra–n-butyl ammonium fluoride systems.

Submitted by Alison Vanceto (alison-vanceto@hotmail.com) on 2017-02-09T10:54:21Z No. of bitstreams: 1 DissHRAD.pdf: 15161052 bytes, checksum: e10c4924acc9cc8afc5ecbec12ee85aa (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-03-20T17:16:45Z (GMT) No. of bitstreams: 1 DissHRAD.pdf: 15161052 bytes, checksum: e10c4924acc9cc8afc5ecbec12ee85aa (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-03-20T17:16:55Z (GMT) No. of bitstreams: 1 DissHRAD.pdf: 15161052 bytes, checksum: e10c4924acc9cc8afc5ecbec12ee85aa (MD5) / Made available in DSpace on 2017-03-20T17:24:11Z (GMT). No. of bitstreams: 1 DissHRAD.pdf: 15161052 bytes, checksum: e10c4924acc9cc8afc5ecbec12ee85aa (MD5) Previous issue date: 2015-03-13 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Nowadays, the Brazilian petroleum is extracted from very deep fields and possesses a high naphthenic hydrocarbons composition, which imposes new challenges to refineries and specially to the catalytic cracking process. In that process, the catalyst must act maximizing the production of the highly demanded gasoline, diesel and light olefins from heavy fractions. Taking into consideration the above discussed context, this work aimed to evaluate the effect of basic or acid treatments applied on ZSM-5 zeolites (Si/Al=12 or 23) in the activity to cyclohexane or methylcyclohexane transformation. XRD and 27Al-NMR showed that the dealuminated zeolites presented an increase in their crystallinity due to the extra-framework aluminum lixiviation. On the other hand, in the desilicated zeolites occurred a decrease in their crystallinity as a consequence of the extra-framework aluminum generation. MEV images do not evidence any morphological change that could have been produced by the acid or basic treatments, however, the desilicated ZSM-5 zeolites treated under harder conditions presented significant textural modifications. As expected, the chemical ICP analyses showed a decrease in the Si/Al ratio in the desilicated zeolites and an increase of that ratio for those dealuminated ones, being the last variation more significative in the external surface of the zeolite crystals, as was evidenced by XPS analyses. Data from NH3-TPD showed that the acid treatment resulted in a higher ratio of strong acid sites, which suffered more deactivation during reaction. N2 fisisorption analyses of the ZSM-5 zeolites, showed that the desilication done at higher temperature was more efficient to mesopore generation. In the cyclohexane and methylcyclohexane transformation, the dealuminated zeolites were less active due to their lower aluminum content, nevertheless were more stable and presented a small increase to light olefins selectivity. The desilicated ZSM-5 zeolites presented higher activity and higher yield to light olefins that were supported by their lower Si/Al ratio and mainly by the presence of mesoporosity that enhanced the reagents and products internal diffusivity. / A produção nacional de petróleo, extraído de jazidas cada vez mais profundas, possui um elevado teor de hidrocarbonetos naftênicos, o que impõe novos desafios às refinarias brasileiras e, em particular, ao processo de craqueamento catalítico. Nesse processo, o catalisador deve maximizar a transformação das frações pesadas em produtos de alta demanda como gasolina, diesel e olefinas leves. Nesse contexto, esta dissertação objetivou avaliar o efeito de tratamentos de lixiviação ácida ou básica em zeólitas ZSM-5 (Si/Al=12 ou 23), na atividade para a transformação de cicloexano ou metilcicloexano. Dados de DRX e 27Al-RMN mostraram que as zeólitas desaluminizadas apresentaram um aumento da sua cristalinidade devido à remoção de átomos de alumínio extra-rede, por outro lado, nas zeólitas dessilicalizadas ocorreu uma redução da cristalinidade devido à geração de alumínio extra rede. As micrografias de MEV não evidenciaram modificação morfológica devido aos tratamentos, entretanto nas amostras dessilicalizadas sob condições mais severas, houve significativa mudança das propriedades texturais. Como esperado, as análises químicas por ICP mostraram uma redução na razão Si/Al para as amostras dessilicalizadas e um aumento dessa razão para as zeólitas desaluminizadas, sendo essa variação mais significativa na superfície externa dos cristais, como mostraram resultados de XPS. As análises de DTP-NH3 mostraram que o tratamento ácido resultou numa maior proporção de sítios ácidos fortes, os quais sofreram maior desativação durante a reação. Dados de fisissorção de N2 das zeólitas mostraram que a dessilicalização em temperatura mais elevada foi mais eficiente na geração de mesoporos. Na transformação do cicloexano e do metilcicloexano, as zeólitas desaluminizadas apresentaram menor conversão como resultado da diminuição do teor de alumínio, entretanto tiveram maior estabilidade e apresentaram um ligeiro aumento na seletividade a olefinas leves. As amostras dessilicalizadas apresentaram maiores conversões e rendimentos a olefinas leves, que se justificaram em função da diminuição da razão Si/Al, mas principalmente, como resultado da presença de mesoporosidade, que melhorou a difusão interna de reagentes e produtos.