As a means to produce high pressure hydrogen in order to reduce compression penalty, we propose to reform liquid fuel (e.g., bio-ethanol) in supercritical water (pressure above 221 bar and temperature greater than 374°C). Catalytic ethanol reforming in supercritical water for hydrogen production has been carried out in a high pressure packed bed reactor made of Inconel-625. Since Inconel-625 contains mainly nickel, it is expected that the reactor itself can be active toward ethanol reforming. Therefore, a series of tests were first performed in the empty reactor, whose results are a benchmark when studying reforming in the presence of a catalyst. Ethanol reforming in the empty reactor was studied in the temperature range of 450 to 600°C and showed coking/plugging problem at 575°C and above. The ethanol conversion with the empty reactor could be as high as 25% at 550°C and residence time of about one minute. The main reaction products with the empty reactor were H2, CO and CH4. A catalyst screening study was performed to investigate the performance of nickel and cobalt as active metals, supported on γ-Al2O3, α-Al2O3, ZrO2 and YSZ for temperatures between 475°C and 550°C. The presence of the catalyst did increase the activity of ethanol reforming, especially at higher temperatures. All experiments in the catalyst screening study were carried out with non-reduced catalysts. Nickel catalysts were found more active than cobalt, likely because of higher reducibility. Indeed, the higher amount of oxygen in Co3O4 compared to NiO requires more hydrogen to fully reduce the metal oxides. Both Ni/γ-Al2O3 and Co/γ-Al2O3 showed little activity below 500°C, and led to failed experiments due to coking/plugging at temperatures of 525°C and above. The strong acid sites on γ-Al2O3 are responsible for high selectivity toward ethylene, a known coke precursor. The support α-Al2O3 in combination with Ni was active, but yielded lower H2 selectivity and higher CH4 selectivity than the zirconia-based catalysts. The Co/α-Al2O3 shows low activity. The ZrO2-based catalysts were active and yielded high H2 selectivity, but were found very fragile. Finally, the YSZ support was strong and yielded good conversion. Below 550°C the activity of Ni/YSZ is higher than that of Co/YSZ, but at 550°C both catalysts yield nearly complete conversion. The advantage of Co/YSZ is then higher H2 selectivity and lower CH4 selectivity compared to Ni/YSZ. Therefore, Co/YSZ was selected for a more detailed study. The effect of temperature, flowrate, residence time, catalyst weight, Co loading, concentration, and pretreatment with H2 were considered. Two methods for catalyst reduction were applied: ex-situ reduction where the catalyst is reduced in a different reactor and in-situ reduction where the catalyst is reduced in the SCW reactor prior to ethanol reforming. At 550°C, Co/YSZ converts all ethanol for residence times as low as 2 s, even with non-reduced catalyst. At 500°C the activity of the in-situ and ex-situ reduced catalysts were similar and greater than for the non-reduced catalyst. At 475°C the ex-situ reduced catalyst showed low activity, comparable to that of the non-reduced catalyst, but the in-situ reduced catalyst yielded much higher conversion. The better performance of the in-situ reduced catalyst was attributed to active metal sites on the reactor’s wall after pre-treatment in H2. The low activity of the ex-situ reduced catalyst is due to the fact that, when exposed to supercritical water for less than 30 minutes, it re-oxidized to CoO. The temperature of 475°C is then too low to generate sufficient hydrogen that will start reducing the catalyst. Finally, analysis of reaction pathways for ethanol reforming over Co/YSZ showed that the reaction proceeds mostly via ethanol dehydrogenation to form acetaldehyde, the latter species reacting with lattice oxygen on the catalyst to produce acetone and CO2. Acetone is then reformed by water into CO and H2. Finally, H2 and CO react via the methanation reaction to form CH4. Over Co/YSZ it was found that the water-gas shift reaction is fast (CO selectivity most of the time is less than 0.5%), but the methanation reaction is kinetically controlled. Stopping the methanation reaction before equilibrium allowed for H2 selectivity higher than what is expected at equilibrium (likewise, CH4 selectivity is smaller than equilibrium value). For well-controlled reaction Co/YSZ is a promising catalyst that can be highly selective toward hydrogen during ethanol reforming in supercritical water.

Heterogeneous Ziegler-Natta catalysts are responsible for most of the industrial production of polyethylene and polypropylene. A unique feature of these catalysts is the presence of more than one active site type, leading to the production of polyolefins with broad distributions of molecular weight (MWD), chemical composition (CCD) and stereoregularity. These distributions influence strongly the mechanical and rheological properties of polyolefins and are ultimately responsible for their performance and final applications. The inherent complexity of multiple-site-type heterogeneous Ziegler-Natta catalysts, where mass and heat transfer limitations are combined with a rather complex chemistry of site activation in the presence of internal and external donors, plus other phenomena such as comonomer rate enhancement, hydrogen effects, and poisoning, makes the fundamental study of these systems a very challenging proposition. In this research project, new mathematical models for the steady-state and dynamic simulation of propylene polymerization with Ziegler-Natta heterogeneous catalysts have been developed. Two different modeling techniques were compared (population balances/method of moments and Monte Carlo simulation) and a new mechanistic step (site transformation by electron donors) were simulated for the first time. Finally, polypropylene tacticity sequence length distributions were also simulated. The model techniques showed a good agreement in terms of polymer properties such as molecular weights and tacticity distribution. Furthermore, the Monte Carlo simulation technique allowed us to have the full molecular weight and tacticity distributions. As a result, the 13C NMR analytical technique was simulated and predicted.

As a means to produce high pressure hydrogen in order to reduce compression penalty, we propose to reform liquid fuel (e.g., bio-ethanol) in supercritical water (pressure above 221 bar and temperature greater than 374°C). Catalytic ethanol reforming in supercritical water for hydrogen production has been carried out in a high pressure packed bed reactor made of Inconel-625. Since Inconel-625 contains mainly nickel, it is expected that the reactor itself can be active toward ethanol reforming. Therefore, a series of tests were first performed in the empty reactor, whose results are a benchmark when studying reforming in the presence of a catalyst. Ethanol reforming in the empty reactor was studied in the temperature range of 450 to 600°C and showed coking/plugging problem at 575°C and above. The ethanol conversion with the empty reactor could be as high as 25% at 550°C and residence time of about one minute. The main reaction products with the empty reactor were H2, CO and CH4. A catalyst screening study was performed to investigate the performance of nickel and cobalt as active metals, supported on γ-Al2O3, α-Al2O3, ZrO2 and YSZ for temperatures between 475°C and 550°C. The presence of the catalyst did increase the activity of ethanol reforming, especially at higher temperatures. All experiments in the catalyst screening study were carried out with non-reduced catalysts. Nickel catalysts were found more active than cobalt, likely because of higher reducibility. Indeed, the higher amount of oxygen in Co3O4 compared to NiO requires more hydrogen to fully reduce the metal oxides. Both Ni/γ-Al2O3 and Co/γ-Al2O3 showed little activity below 500°C, and led to failed experiments due to coking/plugging at temperatures of 525°C and above. The strong acid sites on γ-Al2O3 are responsible for high selectivity toward ethylene, a known coke precursor. The support α-Al2O3 in combination with Ni was active, but yielded lower H2 selectivity and higher CH4 selectivity than the zirconia-based catalysts. The Co/α-Al2O3 shows low activity. The ZrO2-based catalysts were active and yielded high H2 selectivity, but were found very fragile. Finally, the YSZ support was strong and yielded good conversion. Below 550°C the activity of Ni/YSZ is higher than that of Co/YSZ, but at 550°C both catalysts yield nearly complete conversion. The advantage of Co/YSZ is then higher H2 selectivity and lower CH4 selectivity compared to Ni/YSZ. Therefore, Co/YSZ was selected for a more detailed study. The effect of temperature, flowrate, residence time, catalyst weight, Co loading, concentration, and pretreatment with H2 were considered. Two methods for catalyst reduction were applied: ex-situ reduction where the catalyst is reduced in a different reactor and in-situ reduction where the catalyst is reduced in the SCW reactor prior to ethanol reforming. At 550°C, Co/YSZ converts all ethanol for residence times as low as 2 s, even with non-reduced catalyst. At 500°C the activity of the in-situ and ex-situ reduced catalysts were similar and greater than for the non-reduced catalyst. At 475°C the ex-situ reduced catalyst showed low activity, comparable to that of the non-reduced catalyst, but the in-situ reduced catalyst yielded much higher conversion. The better performance of the in-situ reduced catalyst was attributed to active metal sites on the reactor’s wall after pre-treatment in H2. The low activity of the ex-situ reduced catalyst is due to the fact that, when exposed to supercritical water for less than 30 minutes, it re-oxidized to CoO. The temperature of 475°C is then too low to generate sufficient hydrogen that will start reducing the catalyst. Finally, analysis of reaction pathways for ethanol reforming over Co/YSZ showed that the reaction proceeds mostly via ethanol dehydrogenation to form acetaldehyde, the latter species reacting with lattice oxygen on the catalyst to produce acetone and CO2. Acetone is then reformed by water into CO and H2. Finally, H2 and CO react via the methanation reaction to form CH4. Over Co/YSZ it was found that the water-gas shift reaction is fast (CO selectivity most of the time is less than 0.5%), but the methanation reaction is kinetically controlled. Stopping the methanation reaction before equilibrium allowed for H2 selectivity higher than what is expected at equilibrium (likewise, CH4 selectivity is smaller than equilibrium value). For well-controlled reaction Co/YSZ is a promising catalyst that can be highly selective toward hydrogen during ethanol reforming in supercritical water.

Partial oxidation of CH4, CO2 reforming of CH4, and oxidative CO2 reforming of CH4 to produce synthesis gas at 700°C over supported Ni catalysts have been studied. A Ni/Mg-Al catalyst was prepared by the solid phase crystallization (spc-) method starting from a hydrotalcite-type (HT) anionic precursor. From XRD analysis, only Ni0.5Mg2.5Al catalyst consists of the layered hydrotalcite-type structure; not Ni0.5Ca2.5Al and Ni/Al2O3 catalysts. By TPR test, the Ni0.5Mg2.5Al-HT catalyst requires a high reduction temperature than the Ni0.5Ca2.5Al catalyst. It implies that the Ni0.5Mg2.5Al-HT which has a layered structure shows the stronger interaction strength between the molecules. It might increase the resistance of coke formation on the surface of the catalyst. For the reaction tests, the Ni0.5Ca2.5Al showed the highest initial activity for synthesis gas production for all reactions; but, its activity was decreased quickly due to coke formation except during the partial oxidation of CH4. The Ni0.5Mg2.5Al-HT showed a relatively higher reactivity compared to the equilibrium level than Ni/Al2O3 catalyst; and it shows very stable reactivity than other catalysts. By TPO test, the Ni0.5Mg2.5Al-HT has the lower amount of coke formed during the reaction than the Ni0.5Ca2.5Al catalyst. It confirms that the Ni0.5Mg2.5Al-HT catalyst has stronger resistance to coke formation; and it leads to provide stable reactivity in any reforming conditions at high temperature. Therefore, the Ni0.5Mg2.5Al-HT catalyst was the most promising catalyst in terms of activity and stability for partial oxidation, CO2 reforming, and oxidative CO2 reforming of CH4. The Ni0.5Mg2.5Al-HT catalyst was used to investigate the CO2 reforming of CH4 kinetics. With increasing CH4 partial pressures at constant CO2 partial pressure, the rates of CH4 consumption were increased. However, with increasing CO2 partial pressure at constant CH4 partial pressure, CH4 consumption rates was increased at lower CO2 partial pressure, but turned to independent at higher CO2 partial pressure. When the partial pressure of H2 was increased, the CO formation rate was decreased; it confirmed that the reverse water-gas shift (RWGS) reaction was occurring during the CO2 reforming of CH4 reaction. In addition, the reaction kinetic expression was proposed when the CH4 dissociation step was considered as a rate-limiting step.

Production of hydrogen is primarily achieved via catalytic steam reforming, partial oxidation,and auto-thermal reforming of natural gas. Although these processes are mature technologies, they are somewhat complex and CO is formed as a by-product, therefore requiring a separation process if a pure or hydrogen-rich stream is needed. As an alternative method, supported metal catalysts can be used to catalytically decompose hydrocarbons to produce hydrogen. The process is known as catalytic cracking of hydrocarbons. Methane, the hydrocarbon containing the highest percentage of hydrogen, can be used in such a process to produce a hydrogen-rich stream. The decomposition of methane occurs on the surface of the active metal to produce hydrogen and filamentous carbon. As a result, only hydrogen is produced as a gaseous product, which eliminates the need of further separation processes to separate CO2 or CO. Nickel is commonly used in research as a catalyst for methane cracking in the 500-700C temperature range. To conduct methane catalytic cracking in a continuous manner, regeneration of the deactivated catalyst is required and circulation of the catalysts between cracking and regeneration cycles must be achieved. Different reactor designs have been successfully used in cyclic operation, such as a set of parallel fixed-bed reactors alternating between cracking and regeneration, but catalyst agglomeration due to carbon deposition may lead to blockage of the reactor and elevated pressure drop through the fixed bed. Also poor heat transfer in the fixed bed may lead to elevated temperature during the regeneration step when carbon is burned in air, which may cause catalyst sintering. A fluidized bed reactor appears as a viable option for methane catalytic cracking, since it would permit cyclic operation by moving the catalyst between a cracker and a regenerator. In addition, there is the possibility of using fine catalyst particles, which improves catalyst effectiveness. The aims of this project were 1) to develop and characterize a suitable nickel-based catalyst and 2) to develop a model for thermal catalytic decomposition of methane in a fluidized bed.

C3H6 oxidation over a Pt/Al2O3 catalyst with or without NOx present was investigated. In particular, its reaction mechanism was studied using diffuse reflectance infrared spectroscopy (DRIFTS), a reactor system designed for monolith-supported catalysts and a micro-reactor system designed for powder catalysts referred to as CATLAB. These experiments reveal that C3H6 oxidation is inhibited by the presence of NO, NO oxidation is inhibited by the presence of CeH6, and that adsorbed NOx can react with gas phase C3H6. DRIFTS and CATLAB results confirm the reaction between C3H6 and nitrates, which are formed during NOx adsorption, with linear nitrites observed as reaction products. Therefore, a reaction route is proposed for C3H6 oxidation in the presence of NOx, namely, nitrates acting as oxidants. Using NO2 instead of NO, or using a high NOx/C3H6 ratio, which is beneficial for nitrate formation, favors this reaction pathway. Data also showed that Pt is required for this reaction, which suggests the nitrates in proximity to the Pt particles are affected/relevant. Reaction kinetics studies of C3H6 oxidation over Pt/Al2O3 and Pt/SiO2 catalysts were performed in CATLAB using a temperature-programmed oxidation method with different oxidants: O2, NO2 and nitrates. The reaction kinetics of these possible reactions were compared in order to determine which reaction is more important. NOx adsorption does not occur on the SiO2 surface so the reaction between C3H6 and NO2 could be isolated and the effect of nitrates could be observed as well when compared to the results from Pt/Al2O3. The Pt dispersions were determined using H2 chemisorption and were 1.3 and 1.6% for Pt/Al2O3 and Pt/SiO2, respectively. C3H6 oxidation starts at a lower temperature with O2 than with NO2 but the activation energy was lower with NO2. This gives indication that hydrocarbons must be activated first for NO2 to be favored in hydrocarbon oxidation. When the experiment was done with C3H6 and nitrates, the reaction did not occur until NOx started to desorb from the catalyst at higher temperatures, when nitrates become unstable and decompose. Therefore, O2 was added to the system and the reaction began at even lower temperature than with just C3H6 and O2. This proved that hydrocarbons need to be activated in order for surface nitrates to affect C3H6 oxidation and this reaction also resulted in a lower activation energy than with just C3H6 and O2. Nitrate consumption was also observed as less NOx desorbed from the catalyst at the later stage of the temperature ramp compared to the amount desorbed when the catalyst was not exposed to C3H6.

Zone-coated diesel oxidation catalysts (DOCs) can be used to obtain overall improved performance in oxidation reaction extents. However, why this occurs and under what conditions an impact is expected are unknown. In order to demonstrate why these catalysts work better than their standard counterparts and how significant the improved performance is, the CO oxidation performance over a series of Pt−Pd/Al2O3 catalysts, each with a different distribution of precious metal down the length, while maintaining equivalent totals of precious metal, was modeled. Simulations with different flow rates, ramp rates, steady-state temperatures at the end of the ramp rate, different total precious metal loadings, and CO inlet values were compared. At conversions less than 50%, the most significant differences were noted when the temperature was ramped to just at the CO oxidation light-off point (a typical measure of 50% conversion/oxidation), with catalysts containing more precious metal at the downstream portions leading to better light-off conversion performance. However, in terms of cumulative emissions over a long period of time, a “front-loaded” design proved best. These results are readily explained by decreased CO poisoning and the propagation of the heat derived from the exotherm from the front to the rear of the catalyst. Also, although the trends were the same, regardless of change in the parameter, the impact of different distributions was more apparent under conditions where a catalyst would be challenged, i.e., at low temperature ramp rates, higher CO inlet concentrations, and lower amounts of total catalyst used. At higher ramp rates, the input heat from the entering gas stream played an increasingly important role, relative to conduction associated with the exotherm, dampening the effects of the catalyst distribution. Therefore, although catalysts that are zone-coated with precious metals, or any active sites, could prove better in terms of performance than homogeneously distributed active site catalysts, this improvement is only significant under certain reaction conditions. In a mixture of three reactants, CO, C3H6 and NO oxidation, it was found that a loading a larger amount of active sites in the catalyst middle, maintained better CO and C3H6 oxidation but not NO oxidation, which required the whole catalyst length. A faster light-off conversion was also related to higher amount of precious metal at the catalyst outlet. The CO conversion performance for a variety of distributed precious metal designs was evaluated as a function of exposure time to sulphur and the spatial accumulation profile of sulphur along the monolith length was predicted. The results illustrate that the sulphur accumulates near the catalyst inlet and decreases toward the outlet, resulting in shifting the reaction zones further toward the catalyst outlet. With sulfation, light-off temperatures (T50) increased and the time for back to front reaction propagation also increased. A back loaded catalyst resulted in the best light-off conversion compared to the other catalyst designs and a middle loaded catalyst maintained a higher overall conversion if sulphur poisoning takes place. These catalyst designs were also tested under thermal aging conditions by using a second order sintering model integrated with the CO oxidation reaction model. The spatial normalized dispersion profiles along the monolith showed that the catalyst outlet experienced significant damage relative to the inlet due to sintering. A front loaded catalyst design had the highest catalytic activity due its resistance to sintering.

Sol-gel (solution-gelation) method was used to prepare Ni-Ti and Ni-Ti-Al catalysts for reforming of methane with carbon dioxide. This method, after optimizing the parameters such as hydrolysis and acid/alkoxide ratio, is able to make a Ni-Ti catalyst with a surface area as high as 426m2/g when calcined at 473K; but calcination at higher temperature lead to dramatic decrease in surface area. XRD, XPS, TEM and SEM were used to understand this change. Using a packed bed reactor, the catalysts were evaluated with the reforming reaction. It was found that the activity of the Ni-Ti catalyst increases with the Ni loading in the range of 1-10wt%. The reduction temperature has strong effect on activity of the reduced catalyst. Up to 973K, the activity increases with the reduction temperature; but after 973K, the activity decreases and become 0 when the temperature is over 1023K. The Ni-Ti catalyst also deactivated as 15% after 4h of time on stream. The XRD analysis shows that Ti3O5 formed in the catalyst after higher-temperature reduction as well as after the reaction for a period of time. The formation of Ti3O5 may render the catalyst to loss its activity. However, further study is expected to understand the mechanism. TG/DTA analysis shows that both Ni-Ti and Ni-Ti-Al catalysts had carbon deposition; but the latter maintained higher activity in a longer period of time.

Boron-doped carbon nanotubes are predicted to behave as semiconductors over a large range of diameters and chiralities and might thus constitute a suitable class of material for nanoelectronics technology. Boron-doped CNTs were reported as by-products when BC2N nanotubes were prepared by an arc-discharge method. The potential doping of CNTs with different kinds of atoms might provide a mechanism for controlling their electronic properties. We have synthesized boron-doped carbon nanotubes (CNTs) directly on copper catalyst by decomposition of B(OCH3)3 in chemical vapor deposition method. The results were characterized and analyzed by scanning electron microscopy (SEM), Raman, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), solid-state NMR and TGA.

Hydrogenation and dehydrogenation on Pd- and Pt- catalysts are encountered in many industrial hydrocarbon processes. The present work considers the development of catalysts and their kinetic modeling along a general and rigorous approach. The first part deals with the kinetics of selective hydrogenation, more particularly of the C3 cut of a thermal cracking unit for olefins production. The kinetics of the gas phase selective hydrogenation of methyl-acetylene (MA) and propadiene (PD) over a Pd/γ-alumina catalyst were investigated in a fixed bed tubular reactor at temperatures 60 - 80 oC and a pressure of 20 bara. Hougen-Watson type kinetic equations were derived. The formation of higher oligomers slowly deactivated the catalyst. The effect of the deactivating agent on the rates of the main reactions as well as on the deactivating agent formation itself was expressed in terms of a deactivation function multiplying the corresponding rates at zero deactivation. Then, the kinetic model was plugged into the reactor model to simulate an industrial adiabatic reactor. In the second part the production of hydrogen from hydrocarbons was investigated. In both cyclohexane and decalin dehydrogenations, conversions higher than 98% could be obtained over Pt/γ-alumina catalyst at temperature of 320 and 340 oC, respectively, with no apparent deactivation for 30 h and with co-feed of H2 in the feed. Except for H2 and trace amounts of side cracking products, less than 0.01%, benzene was the only dehydrogenated product in cyclohexane dehydrogenation. In the case of decalin dehydrogenation, partially dehydrogenated product, tetralin, was also formed with selectivity lower than 5%, depending on operating conditions. A rigorous Hougen-Watson type kinetic model was derived, which accounted for both the dehydrogenation of cis- and trans- decalin in the feed and also the isomerization of the two isomers. Jet A is the logic fuel in the battlefields. The dehydrogenation of Jet A can produce H2 for military fuel cell application. Although the H2 production is lower than that of steam/autothermal reforming, it eliminates the needs of high temperature and product separation operation.