Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.
Crude oil derived from Canadian oil sands has a propensity for coke formation during hydrotreatment over NiMoS catalysts, due to the high olefin content of the oil. This dissertation investigates the influence of catalyst acidity and Mo dispersion on the hydrogenation and dimerization of conjugated olefins at low temperature (
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Electrocatalytic hydrogenation-hydrogenolysis (ECH) is a prospective route for valorization of lignin derivatives, mainly for synthesis of organic chemicals. This environmentally benign process enables the integration of biorefinery and renewable electrical energy for clean fuels and chemicals production. Electrochemical water and/or proton reduction facilitates in situ, continuous generation of chemisorbed hydrogen on an electrocatalyst surface. However, most conventional ECH studies were operated at low current densities with low Faradaic efficiencies, owing to diffusion limitations of the organic molecules to the electrode surface. Polar organic electrolyte, which could facilitate the solubility of non-polar organic substrates in aqueous electrolyte, has not been extensively studied for the ECH purposes. This work presents the ECH of lignin model compounds (e.g., guaiacol and phenol) using dispersed metal catalysts (e.g., Pt/C, Ru/C, Pd/C) in diverse aqueous electrolytes under mild conditions (25–60 oC, 1 atm). The stirred slurry electrochemical reactor (SSER) configuration enables ECH operation at high current densities (> |100 mA cm⁻²|) and efficiencies (>50%) due to the improved mass, heat, and electron transfers between the reacting molecules and catalyst particles. Different catholyte-anolyte pair effects were investigated under potentiostatic and galvanostatic conditions whereby the electrocatalyst activity was found to be dependent on electrolyte pH and composition. In the process development, electrocatalytic reduction of bio-oil substrates was conducted using organic solvent-mixed acidic electrolytes for mild depolymerization. Acid-acid and neutral-acid catholyte-anolyte pairs were efficient for ECH of guaiacol and phenol, capable of resulting in high conversions (>90%) and efficiencies (>70%). This electrolyte pair combination enables the synergy of electrocatalyst and electrolyte, which could improve Faradaic efficiency and extend the pH-dependent catalyst options. Polar organic solvents (e.g., isopropanol) improve the reactant solubilization and affect proton stabilization for enhancing dehydration reaction, however they could also hinder substrate reactivity owing to competitive adsorption on the catalyst and suppressed ionic activities in the electrolyte. Electrocatalytic hydrodeoxygenation (HDO) of alkyl guaiacols in the mixed electrolytes could produce cycloalkanes at the low temperatures, suggesting the potential of ECH routes for the synthesis of alkane fuels, besides the value-added chemicals. Finally, challenges and opportunities for future development of electrocatalytic pathways for lignin valorization are discussed.
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Mo₂C catalysts supported on carbon have been investigated for use in hydrotreating reactions that remove S, N and O from oil fractions. The thesis reports on the stability of the catalysts in the presence of different model reactants. The synthesis of mesoporous carbons derived from petroleum coke (petcoke), a by-product of Canadian oilsand upgrading, is described. The impact of the mesoporous carbon as a support of the Mo₂C catalysts is also examined. An activated charcoal (AC) was initially used as the carbon source to prepare Mo₂C/AC and Ni-Mo₂C/AC catalysts by carbothermal hydrogen reduction (CHR). The most active catalyst for 4-methylphenol (4-MP) hydrodeoxygenation (HDO) was obtained at a CHR temperature of 650 ℃. The direct deoxygenation selectivity of this catalyst was > 78%, indicative of high O removal with low H₂ consumption. The effect of a Ni promoter on the synthesis and activity of Ni-Mo₂C/AC catalysts was also assessed. The presence of Ni significantly reduced the CHR temperature required for Mo₂C formation by 100 ℃. However, the Ni accelerated catalyst sulfidation during hydrodesulphurization (HDS) and formed a unique core-shell Mo₂C-MoS₂ structure. Additionally, there was an improved activity in HDS of dibenzothiophene (DBT) in the presence of Ni, provided the Ni:Mo 3x’s higher than that of Mo₂C/AC because of the high surface area (~2000 m²/g) of the Mo₂C/APC catalyst, and the high dispersion of the Mo₂C nanoparticles. Finally, the stability of the Mo₂C/APC catalysts during the HDS, hydrodenitrogenation and HDO of DBT, carbazole and dibenzofuran, respectively, was determined as a function of the Mo₂C average particle size. DFT calculations were combined with experimental data to explain the selectivity change from hydrogenation to DDS observed during the HDS of DBT. Both S and N irreversibly deactivated the catalysts; whereas, the effect of O was reversible.
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A two-step bio-oil upgrading process has been investigated using carbon supported molybdenum carbide catalysts.The waste materials, petcoke (PC) and biochar (BC) were activated to yield the Mo₂C/APC and Mo₂C/ABC catalysts (APC – activated petcoke and ABC – activated biochar). These catalysts presented very high (approximately 85%) direct deoxygenation (DDO) selectivity in the hydrodeoxygenation (HDO) reaction. Furthermore, the Mo₂C/APC catalysts with low Mo loading (1 and 2 wt %) were acid washed in H₂SO₄ and both the Mo₂C/APC catalysts and the acid treated Mo₂C/APC catalysts were active for the esterification of acetic acid and 1-butanol.The hydrodeoxygenation (HDO) of 2-methoxyphenol over Pd, Ru and Mo₂C catalysts supported on activated charcoal (AC) was compared. The overall 2-methoxyphenol consumption rate decreased in the order Pd > Ru > Mo₂C due to Mo₂C’s lower hydrogenation activity. Mo₂C was the most efficient in terms of O-removal with minimal H₂ consumption. To enhance the hydrogenation activity of the Mo₂C catalysts, promotion of a 10 % Mo₂C/carbon catalyst with 1%Cu, 1%Ni and 1%Pd was assessed for the HDO of dibenzofuran (DBF). The addition of Ni and Pd decreased the temperature required for the removal of the oxygen layer from the Mo₂C that is formed during catalyst passivation. This enhanced ability of the promoted catalyst to hydrogenate surface oxide species suggests that the same catalyst could improve the stability of the catalyst during HDO. Finally, the catalysts were assessed in a two-step bio-oil upgrading process that combined esterification and hydrodeoxygenation to improve the bio-oil fuel quality. In the first step, the Mo₂C catalysts were shown to have sufficient acidity so as to catalyse esterification reactions at 180 °C and 10.3 MPa that stabilized the bio-oil. In the 2nd step of the upgrading process, the best Mo₂C catalyst 1Ni-10Mo₂C/ABC achieved 69% HDO with an overall carbon yield of 67% when operated at 350 °C and 15.0 MPa. The Ni-Mo₂C catalysts are proven to be promising catalysts for the proposed two-step bio-oil upgrading.
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Unburned CH₄ from natural gas vehicle (NGVs) exhausts limits the use of natural gas as a vehicle fuel. CH₄ is a potent greenhouse gas with a high C-H bond strength (~435 kJ mol⁻¹) making it difficult to oxidize in catalytic converters. This study is focused on the assessment of the activity and stability of selected catalysts placed in a monolith reactor with the goal of improving NGV emission control. Firstly, the washcoat formulation was investigated with the activity and stability of PdO/AlOOH/Al₂O₃, PdO/Ce/AlOOH/Al₂O₃ and Pt-PdO/Ce/AlOOH/Al₂O₃ monolith catalysts for CH₄ oxidation in the presence of H₂O, CO, CO₂ and SO₂ reported. Secondly, the effect of adding a washcoat overlayer to improve the performance of the monolith catalyst was investigated.The monolith catalysts were prepared using a cordierite (2MgO.2Al₂O₃.5SiO₂) mini-monolith (400 cells per square inch (CPI), 1 cm diameter x 2.5 cm length; ~52 cells) that was washcoated using a Al₂O₃ suspension combined with boehmite (AlOOH), followed by sequential deposition of Ce and Pd(Pt) by wet impregnation. The initial activity of the mini-monolith catalyst was measured by temperature-programmed CH₄ oxidation (TPO) at a GHSV of 36000 h⁻¹. Time-on-stream (TOS) tests were used to quantify the stability of the catalysts at 425 and 550°C using a feed gas with 10 vol % H₂O. The results showed that the composition of the washcoat plays a major role in the stability of the catalysts, with both AlOOH or CeO₂ enhancing the stability of the PdO/Al₂O₃ catalyst in the presence of H₂O. Moreover, a washcoat overlayer applied to the PdO(Pt/CeO₂)/AlOOH/Al₂O₃ monolith catalysts, is shown to enhance CH₄ oxidation activity and stability at low temperature (
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This dissertation investigates the reactions of conjugated olefins that lead to catalyst deactivation and fouling in naphtha hydrotreater reactors using a commercial Ni-Mo-S/γ-Al₂O₃ catalyst. The reactions were performed in a micro-scale fixed bed reactor system operated at 150-250°C, 3-4 MPa H₂, LHSV of 1-8 hr-¹ and a H₂/feed ratio of 392-1200 standard mL/mL. During isoprene hydrogenation, an increase in dimerization activity with temperature was attributed to a higher activation energy of dimerization compared to hydrogenation. Conjugated olefin content was also shown to impact oligomerization as an increase in the conjugated olefin content resulted in a decrease in hydrogenation product yield while the oligomerization activity and gum content increased. By investigating different olefin structures, conjugation was shown to enhance dimerization/oligomerization while steric hindrance limited dimer/oligomer formation by limiting access and reactivity of the double bonds.The addition of cyclohexene to 4-methylstyrene resulted in a significant loss in catalyst hydrogenation activity while the dimerization activity remained almost the same for a period of up to 30 days time-on-stream. The loss in catalyst activity can be attributed to a higher concentration of 4-methylstyrene when the overall conversion was lower, resulting in higher dimerization and gum formation. This in turn resulted in increased catalyst deactivation compared to the case of no cyclohexene in the feed. Reactor fouling was shown to be linked to dimer and gum formation, as the pressure drop across the reactor increased with higher dimerization yield and gum formation. The increase in pressure drop was well described by a decreasing average reactor bed voidage caused by cumulative gum deposition within the catalyst bed.An overall trend of increasing gum yield with increasing dimer yield is reported, suggesting that the dimers are precursors for gum formation. In addition, catalyst deactivation was linked to carbon deposition on the catalyst caused by dimer and gum formation; increased dimer and gum formation were accompanied by an increased carbon deposition and decreased BET surface area of the catalyst. A kinetic model of the hydrogenation and dimerization of 4-methylstyrene over spent commercial Ni-Mo-S/γ-Al₂O₃ showed that hydrogenation has much lower activation energy (24.8 kJ/mol) than dimerization (68.2 kJ/mol).
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To assess the effect of Co particle size on the deactivation of Co catalysts during Fischer-Tropsch (FT) synthesis, a series of Co/Al₂O₃ and Re-Co/Al₂O₃ FT catalysts with varying Co particle size, were tested in a continuous flow, stirred tank reactor operated at 220ºC, 2.1MPa and a H₂/CO = 2/1 synthesis gas for periods up to 190 h time-on-stream (TOS). At the chosen operating conditions, carbon deposition was the main cause of catalyst deactivation and the initial rate of carbon deposition per active Co site increased with increased Co particle size (dC₀=2– 22 nm) when measured at approximately the same CO conversion level.Results showed that catalyst stability was dependent upon the Co particle size, degree-of-reduction (DOR) of the catalyst precursor and the CO conversion. The initial rate of carbon deposition increased with increase in CO conversion, when CO conversion ≤ 40%, for a particular catalyst, whereas at high concentrations of H₂O and CO₂ in the reactor (CO conversions> 60%), the initial rate of carbon deposition decreased with increased CO conversion. Furthermore, Co/Al₂O₃ catalysts with small Co particles (dC₀ = 2 nm and dC₀ = 1 nm) were activated with TOS during the FT synthesis. These catalysts had a low DOR (≤3%) and were reduced further when exposed to the synthesis gas.Comparison between the extent of catalyst deactivation for the Co/Al₂O₃ and Re-Co/Al₂O₃ model catalysts and a commercial Co/P-Al₂O₃ catalyst (Co catalyst on a P modified Al₂O₃ support), showed that the Co/P-Al₂O₃ catalyst was more stable during ~160 TOS due to a reduced carbon deposition rate. However, when the catalyst was operated over a range of process conditions (i.e, temperature, pressure and H₂/CO ratio) for extended operating periods (up to1200 h), the CH₄ selectivity increased at TOS > 400 h and when the catalyst was exposed to high temperature (T≥ 230 ºC) and a PH₂O/PH₂ ratio > 0.5. The change in CH₄ selectivity was shown to be dependent on the high ??₂? in the reactor which resulted in Co oxidation and hence a change in product selectivity.
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Natural gas is a promising alternative fuel for transportation systems because of reduced CO, CO₂, SO₂, and NOx emissions into the environment, and its abundance and low cost compared with gasoline and diesel. A significant obstacle in the use of NG for vehicle fuels is that CH₄ is difficult to oxidize in the presence of CO₂ and H₂O and at the low exhaust gas temperature (500-550°C) of natural gas vehicles (NGV). Although Pd is the most active catalyst for CH₄ oxidation, the presence of H₂O suppresses the catalyst activity. The effect of H₂O on the activity of Pd/Al₂O₃ catalysts with Pd loadings of 0.3, 2.6 and 6.5Pd (wt.%) and corresponding dispersions of 57%, 48%, and 33%, was well described by a kinetic model that accounted for the effect of H₂O. Langmuir adsorption was assumed to determine the amount of H₂O adsorbed on active sites for the catalysts with different Pd dispersions under wet and dry reaction conditions. The estimated kinetic parameters of apparent activation energy, Ea of 60.6±11.5 kJ.mol-¹ and heat of H₂O adsorption, ∆H(H₂O) of -81.5±9.1 kJ.mol-¹ indicate that CH₄ oxidation is independent of Pd dispersion. Using different preparation methods and varying Ce:Pd ratios, it was found that sequential impregnation of the Al₂O₃ support by Ce and Pd, with Ce:Pd ratio of 5, yielded a catalyst that had the least inhibition by H₂O. H₂O adsorption is the dominant mechanism for activity loss, although some sintering of the support may also occur. In a Time-on-Stream (TOS) study with extra H₂O added to the feed gas, the chemical and physical properties of the catalysts showed only small changes before and after use. The less negative effect of H₂O at higher temperature and at lower H₂O concentration was also confirmed by the kinetic study. The kinetic model is consistent with a Langmuir mechanism in which H₂O adsorption suppresses C-H bond activation on the active sites. The kinetic analysis shows that the Ce added to the PdO/Al₂O₃ catalyst suppresses the amount of H₂O adsorbed onto the catalyst, thereby reducing the H₂O inhibition effect in the presence of Ce.
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Natural gas vehicles (NGVs) generate considerably fewer emissions of CO, NOx and CO₂ in comparison to conventional diesel and gasoline vehicles, although these benefits are mitigated by the presence of significant amounts of CH₄ in the exhaust. The relatively low temperature (423–823 K) and high concentrations of CO₂ and H₂O in the NGV exhaust gas make current catalytic converters inefficient for the removal of unburned CH₄. Although Pd is the most active metal for CH₄ oxidation, Pd catalysts deactivate after long time exposure to the NGV exhaust conditions. This thesis develops an understanding of the deactivation mechanisms of Pd supported catalysts following thermal treatments and examines the kinetics of CH₄ oxidation, accounting for the effect of H₂O.Hydrothermal aging (HTA) at high temperatures (673–973 K) is shown to significantly deactivate PdO/SiO₂ catalysts used for CH₄ oxidation. PdO occlusion by the SiO₂ support is responsible for catalyst deactivation at low HTA temperatures (673 K), whereas a combination of PdO sintering and PdO occlusion contributes to significant deactivation at high HTA temperatures (973 K). The stability of PdO catalysts during HTA is dependent upon the support. PdO/α-Al₂O₃ is found to have the highest catalyst stability during HTA at 973 K for up to 65 h and its high stability is attributed to a strong Pd-support interaction. Although PdO crystallites sinter and are occluded by the support during HTA, PdO occlusion only affects PdO/SiO₂ performance significantly. The deactivation of PdO/γ-Al₂O₃ and PdO/SnO₂ during HTA at 973 K is attributed to PdO sintering and a PdO → Pd⁰ transformation. The kinetics of CH₄ oxidation over a PdO/γ-Al₂O₃ catalyst is also reported. A power law model can accurately predict the observed temperature-programmed CH₄ oxidation data profiles measured for PdO/γ-Al₂O₃ at conversions
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The mechanism by which hydroconversion catalysts promote residue conversion and coke suppression is unclear. Several theories are proposed in the literature but these have all been opposed, usually due to their lack of controlled mechanistic studies. A promising catalyst for residue hydroconversion is unsupported MoS₂. This catalyst is effective but expensive and deactivates during the reaction. Model compound studies were needed to elucidate the mechanism of MoS₂ catalysis in hydroconversion reactions, how this relates to residue hydroconversion and hence propose deactivation mechanisms and regeneration methodologies. Model compound screening in a commercially available stirred slurry-phase batch reactor identified diphenylmethane (DPM) as a suitable model reagent. Experiments were conducted at industrially applicable conditions of 445°C, 13.8 MPa H₂ and catalyst loadings of 0 - 1800 ppm Mo (introduced as Mo octoate which formed the MoS₂ active phase in-situ). Slow heat-up rates and wall catalysis, however, made this reactor unsuitable for detailed mechanistic studies. A novel mixed slurry-phase micro-reactor system was designed using externally applied vortex mixing and removable glass-inserts to allow for greater analytical resolution and determination of the thermocatalytic mechanism. Deactivated MoS₂ catalysts, as coke-catalyst agglomerates recovered from residue hydroconversion studies (Rezaei and Smith, 2013), were evaluated using the DPM testing methodology and a deactivation mechanism proposed. It was determined that the unsupported MoS₂ crystallites hydrogenate the DPM feed to cyclohexylmethylbenzene (CHMB) which undergoes thermolysis to short chain hydrocarbon radicals. These short chain radicals stabilise, by radical addition or radical disproportionation, other radicals in the system by a chain stabilisation reaction, itself promoted by catalytic hydrogenation (for instance of olefins formed during disproportionation). Deactivation of unsupported MoS₂ in residue hydroconversion was proposed to be due to the formation of an unreactive, porous carbonaceous structure upon which the otherwise unaltered catalyst particles become supported. The pores physically exclude larger species, such as asphaltenes, from reaching the active sites. Inter-recycle solvent extraction to remove coke precursors was proposed to inhibit deactivation in residue hydroconversion whilst mechanical and chemical size reduction were suggested for breaking the porous structure and re-exposing the MoS₂ crystallites.
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This dissertation addresses the hydrodeoxygenation (HDO) of the model compound 4-methylphenol and pyrolysis oil, over alternative, non-sulfided catalysts. The HDO of 4-methylphenol was studied over unsupported, low surface area MoS₂, MoO₂, MoO₃, and MoP catalysts. The initial turn over frequency (TOF) for the HDO of 4-methylphenol decreased in the order MoP > MoS₂ > MoO₂ > MoO₃. Among the catalysts examined, MoP had the highest hydrogenating selectivity, lowest activation energy, and per site activity (TOF) for the HDO of 4-methylphenol. However, the observed conversion over MoP was limited by its low surface area and CO uptake. Addition of citric acid (CA) improved the properties of unsupported MoP. CA acted as a structural promoter and formed a metal citrate during the catalyst preparation, which increased the surface area and CO uptake of the MoP. High surface area Ni₂P catalysts were prepared similarly and based on initial TOFs, Ni₂P was 6 times more active than MoP for the HDO of 4-methylphenol. The HDO of 4-methylphenol was found to be structure insensitive over both MoP and Ni₂P. However, the Ni₂P catalysts deactivated due to C deposition on the catalyst surface. A kinetic model of the direct deoxygenation and hydrogenation reaction pathways for the HDO reaction over MoP showed the former to have a higher barrier energy (Ea = 106 kJ/mol) than the latter (Ea = 85 kJ/mol).Finally, to validate the use of model compounds to screen catalysts, the HDO of 4-methylphenol was compared to the HDO of pyrolysis oil over sulfide, oxide, and phosphide catalysts. MoP was found to have the highest yield of O-free liquid and the lowest coke yield, followed by Ni₂P, NiMoS/Al₂O₃, MoS₂, and MoO₃ for the HDO of pyrolysis oil. Those catalysts displaying high hydrogenating abilities had a high degree of O free liquid and a low yield of coke (MoP), while those catalysts displaying high isomerization abilities (MoO₃) had a high coke yield. Overall, this thesis identified phosphide catalysts as a new class of catalysts for HDO reactions with strong hydrogenating abilities, and their activity was superior to commercial NiMoS/Al₂O₃ for the HDO of pyrolysis oil.
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The application of slurry-phase hydroconversion to upgrade residue oil derived from the Canadian oilsands (CLVR) is hindered by the cost of the catalyst, in part because the catalyst is used once-through before being discarded as part of the solid product (coke). The goal of the present study was to assess the potential of recycling the slurry-phase catalyst under high residue conversion conditions and to identify the cause of catalyst deactivation during catalyst recycle.Catalyst screening in a batch reactor operated at 415 °C and 5.6 MPa initial H₂ pressure with CLVR as reactant, showed that MoS₂ prepared in reversed micelles was most active for coke suppression and liquid yield among a series of Fe- and Mo-based catalysts. Furthermore, MoS₂ derived from Mo-micelle and Mo-octoate precursors had equivalent coke yields, but were more active for coke suppression than a water-soluble ammonium heptamolybdate precursor, as measured in a semi-batch reactor under more severe hydroconversion conditions (T = 445 °C and H₂ pressure of 13.8 MPa and 900 mL(STP)/min). MoS₂ prepared using Mo-micelle and Mo-octoate precursors over a range of Mo concentrations (0 – 1800 ppm) were recycled in the semi-batch reactor to assess the activity of the recycled catalyst in terms of coke suppresion and selectivity toward different products. The MoS₂ catalyst remained active for up to 4 reaction cycles, depending on the initial concentration of Mo added to the reactor. Characterization of the coke and catalyst recovered after each recycling step showed that the coke associated with the catalyst undergoes significant chemical and morphological changes during recycle and these changes result in deactivation of the catalyst. A conceptual model of the catalyst deactivation mechanism based on the characterization results was developed and ex-situ simulation of catalyst aging validated the proposed deactivation mechanism in the semi-batch slurry-phase upgrading reactor. Finally, a kinetic model of the CLVR hydroconversion reactions was developed that included the consumption and production of coke as an important step in the overall kinetic scheme.
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The selective synthesis of C₂ oxygenates, especially ethanol, from C₁ species such as CH₃OH and synthesis gas (CO/H₂) is of interest as the demand for clean fuels, including biofuels, increases. However, over alkali-promoted Cu-ZnO catalysts the synthesis of C₂ oxygenates occurs with very low selectivity. Previous mechanistic studies suggest that the basic properties and the Cu properties of these catalysts are critical in determining the C₂ oxygenate selectivity. However, the possible synergistic effect of these catalyst properties on the selectivity of C₂ oxygenates is poorly understood. In the present study, Cu-MgO catalysts were investigated since MgO possesses noticeably higher basic properties compared to ZnO. Furthermore to address the knowledge gap in the literature with respect to a synergistic effect between catalyst basic properties and Cu properties on the synthesis of C₂ oxygenates from CH₃OH/CO, MgO, Cu-MgO and Cs (K)-promoted-Cu-MgO catalysts were prepared, characterized and tested at 101kPa and 498-523K. The catalysts had intrinsic basicities of 3.9 – 17.0 μmol CO₂.m⁻², SACu° of 66 C-atom%). The reaction kinetics of CH₃OH was studied. The Cs-Cu-MgO catalyst was noticeably less active for the synthesis of oxygenates, compared to a conventional Cs-Cu-ZnO catalyst, which was caused by lower Cu dispersion and weaker Cu-metal oxide interaction in the Cs-Cu-MgO compared to Cs-Cu-ZnO, as well as poor electronic-conductivity and lack of hydrogenation-activity of MgO compared to ZnO.
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Due to the very low density of H₂, practical storage and recovery of H₂ has beena challenge in utilizing H₂ as an alternative fuel. Organic heteroaromatics haveattracted interest because of their thermal stability and high storage capacity. Inthis study, H₂ storage and recovery from these compounds were investigated. Thekinetics of the hydrogenation/dehydrogenation reactions was studied and DFT calculationswere used to understand the dehydrogenation product distribution.The hydrogenation of N-ethylcarbazole and carbazole at 403-423 K on a supportedRu catalyst was well described by first-order kinetics. The hydrogenation ofN-ethylcarbazole was significantly faster than the hydrogenation of carbazole, and>95 % selectivity to dodecahydro-N-ethylcarbazole and dodecahydrocarbazolewas achieved, respectively.The dehydrogenation kinetics of dodecahydro-N-ethylcarbazole was studied at101 kPa and 423-443 K over a Pd catalyst prepared by wet impregnation and calcinationin air. The reactions followed first-order kinetics with 100 % conversion butonly 69 % recovery of H₂ was achieved at 443 K, due to minimal selectivity to Nethylcarbazole.The complete recovery of H₂ from dodecahydro-N-ethylcarbazolewas achieved at 443 K and 101 kPa using Pd/SiO₂ catalysts prepared by incipientwetness impregnation with calcination in He. The dehydrogenation TOF and selectivityto N-ethylcarbazole were dependent upon the Pd particle size.The effect of the N heteroatom on the dehydrogenation of polyaromatics wasstudied by comparison of dodecahydro-N-ethylcarbazole, dodecahydrocarbazoleand dodecahydrofluorene dehydrogenation over Pd catalysts. The dehydrogenationof dodecahydro-N-ethylcarbazole and dodecahydrocarbazole were structuresensitive. The dehydrogenation rate of dodecahydrocarbazole was slower thandodecahydro-N-ethylcarbazole. Despite catalyst poisoning through the N atomin dodecahydrocarbazole, the N heteroatom was found to favor dehydrogenation,making heteroaromatics better candidates for H₂ storage than aromatics.The structure sensitivity of the reactions and the observed product distributionare explained in view of DFT calculations that showed that the adsorptionof dodecahydro-N-ethylcarbazole on Pd required multiple catalytic sites and theheat of adsorption was dependent upon the surface structure. The effect of theethyl group and the N heteroatom on the dehydrogenation rate of dodecahydro-N-ethylcarbazole was also investigated by comparing the adsorption energies ofdodecahydro-N-ethylcarbazole with dodecahydrocarbazole and dodecahydrofluorene.
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Molecular simulation and experimental methods have been used to assess the catalytic behavior of MoP in the conversion of synthesis gas (CO, CO₂, H₂) to oxygenated hydrocarbons. The potential energy surface of synthesis gas conversion to methane and methanol was investigated on a Mo₆P₃ cluster model of the MoP catalyst. The potential energy surface (PES) for CH₄ formation was determined to be: COad → CHOad → CH₂Oad → CH₂OHad → CH₂.ad+H₂Oad → CH₃.ad+H₂Oad → CH₄+H₂O and for CH₃OH : COad → CHOad → CH₂Oad → CH₂OHad → CH₃OHad. The hydroxymethyl (CH₂OH) species was a common reaction intermediate for both CH₄ and CH₃OH formation and the simulation predicted selective formation of CH₄ rather than CH₃OH from syngas over MoP. The cluster model was modified to investigate the effect of a SiO₂ support and a K promoter. Both SiO₂ and K decreased the activation energy for methanol formation. However, the activation energy for methanol formation remained higher than the activation energy for C-O bond cleavage. The high adsorption energy of methanol and the formation of geminal dicarbonyl species on the K-Mo₆P₃-Si₃O₉ cluster suggested the possibility of the formation of higher oxygenates. The conversion of syngas to alcohols was also investigated on 5, 10, and 15 wt% MoP supported on silica, with 0, 1, and 5 wt% K added as a promoter The major products were acetaldehyde, acetone and ethanol. Low selectivities to methanol (
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Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.
Canadian bitumen is a plentiful source of hydrocarbons. However, to obtain oils which may be sold to consumers, bitumen must be upgraded. Among other processes, bitumen upgrading includes lowering sulphur content and correcting the carbon to hydrogen ratio mostly by carbon rejection, which results in the formation of petroleum coke (PC), a byproduct which must be stored or disposed of. This study's focus was the preparation of a molybdenum disulphide (MoS₂) catalyst for a more facile removal of intercalated sulphur from bitumen, by synthesising nano-sized MoS₂ particles. Simultaneously, this study attempted to use PC as a catalyst support. Carbon-supported MoS₂ catalysts were successfully prepared by two methods using ammonium tetrathiomolybdate: reverse micelles using the water/IGEPAL CO-520/cyclohexane system, and incipient wetness impregnation from ultra pure water. MoS₂ prepared by impregnation was supported on PC, and MoS₂ prepared by reverse micelles was supported on both PC and activated carbon (AC). Catalysts prepared by reverse micelles contained nanosized MoS₂ with low stacking order, and the catalyst prepared by impregnation consisted of long sheets of MoS₂ with a higher stacking order. The catalysts were screened for hydrodesulphurization activity in a novel slurry-phase batch microreactor using dibenzothiophene as a model compound. The overall rate constant for DBT conversion per gram of molybdenum for the MoS₂/PC prepared by impregnation was greater than that for the catalysts prepared by reverse micelles in the temperature range of 350 - 375 °C. MoS₂ supported on AC and PC showed a similar activity toward catalysing the HDS of DBT when the MoS₂ was prepared by reverse micelles; therefore, PC is a good alternative support to AC for MoS₂/C catalysts prepared by this method. The rate constant associated with hydrogenation was an order of magnitude greater for the catalyst prepared by impregnation than that for the catalysts prepared by reverse micelles. It was concluded that the larger stacking order in MoS₂/PC prepared by impregnation provided more sites for hydrogenation, which resulted in an overall larger rate constant than that for the catalysts prepared by reverse micelles, whose MoS₂ stacking orders were minimal due to the small particle size.
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Hydrodesulphurization (HDS) is the major process used to remove S from crude oil feedstocks in order to improve fuel quality and meet environmental regulations. The goal of this study was to determine if petroleum coke (petcoke), derived from Alberta oilsands, could be converted into a useful catalyst support. Hence the HDS activity and selectivity of nickel molybdenum sulfided catalysts supported on activated carbon (NiMoS/AC), petroleum coke (NiMoS/PC) and conventional alumina (NiMo/γ-Al₂O₃) have been compared using dibenzothiophene (DBT) as a model reactant. The reactions were carried out in a novel slurry-phase batch microreactor at different reaction times (30-120 min) and temperatures (588-638 K) and a fixed H2 pressure (4.8 MPa). The results showed that NiMoS/PC had higher activity towards the HDS of DBT when compared with NiMoS/AC, although the catalysts had very similar product selectivities. The highest activity for DBT HDS, corresponding to 90% DBT conversion, occurred at 638 K for the NiMoS/AC catalyst and at 623K for the NiMoS/PC catalyst. The reaction proceeded by two pathways: the direct desulphurization (DDS) reaction route and the hydrogenation (HYD) reaction route. The power law pseudo 1st-order kinetic model was applied to the HDS of DBT. The estimated kinetic parameters showed similar magnitudes for the HYD versus the DDS routes over both catalysts, whereas the DDS pathway had higher apparent activation energy compared to the HYD route for both catalysts.
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Oilsands bitumen upgrading to produce naphtha, among other products, is a feasible approach to increasing the supply of refined oil products. However, naphtha derived from bitumen is relatively unstable as it contains unsaturated hydrocarbons (5 vol% diolefins, 15 wt% aromatics). The unsaturated hydrocarbons tend to polymerize and form carbonaceous deposits on the catalyst during mild hydrotreating (~200 °C), resulting in pressure build-up in the reactor that causes the early shut down of the hydrotreating unit. This dissertation addresses diolefin hydrogenation and dimerization kinetics and gum formation over a commercial Ni-Mo-S hydrotreating catalyst. Two model compounds, styrene and α-methylstyrene (AMS), were selected to represent the diolefin present in the naphtha feed. Styrene reactions were based on orthogonal analysis with temperature (200, 225, 250 °C), diolefin concentration (3.7-7.4 wt%), and catalyst amount (0.5, 1, 2 g) varied. For the AMS reactions, a single variable test was applied by changing the AMS content (4.2-6.3 wt%) or temperature (200, 225 and 250 °C). The styrene and AMS hydrogenation kinetics were developed as 1st-order in reactant and 0-order in H₂, based on a simplified Langmuir-Hinshelwood (L-H) model. Pseudo 1st-order in model compound kinetics was employed for the dimerization reaction. The results revealed that the rate of hydrogenating or dimerizing styrene was faster than AMS due to steric hindrance effects. The activation energy for styrene and AMS hydrogenation was 45.3 and 87.7 kJ/mol, respectively. The activation energy for styrene dimerization was 99.6 kJ/mol. Additionally, the relationship between dimer content and gum formation at the end of the reaction indicated that higher dimer concentration increased gum content in styrene reactions. However, this relationship was not observed in AMS reactions because of steric hindrance effects. Finally, competitive reactions between olefins and diolefins were also examined. Cyclohexene hydrogenation to cyclohexane was initially suppressed by AMS hydrogenation to cumene. With longer reaction time (510 mins), the cyclohexane concentration exceeded cumene, suggesting that competitive hydrogenation occurred between the cyclohexene and AMS. Adding cyclohexene to the AMS significantly reduced the dimer content in the product possibly due to competitive adsorption on the acidic sites.
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Selective ring opening of naphthenic rings is the optimum process for reducing the cyclo-paraffin and aromatic content of gas oils in order to improve its quality and consequently its value. The aim of this study was to examine the reaction rates of ring opening of a model multi-ring compound, namely decalin, using a bifunctional catalyst. Three catalysts, Pd/H-Y-30, Ir/H-Beta-300 and Ir/H-Beta-25, were tested to examine the activity and yield of ring opened products at the same reaction conditions. The reaction was performed in a continuously-stirred, batch reactor at 350°C and 3 MPa H₂ pressure. The results showed that Ir/H-Beta-25 had the highest activity and yield of ring opened products. By comparing the Ir/H-Beta-25 catalyst and the Ir/H-Beta-350 catalyst, it was concluded that higher activity was achieved with higher acidity, confirming the important role of catalyst acidity in selective ring opening.The effect of reaction conditions, namely temperature (275-350°C) and pressure (3-6 MPa), on the activity and product selectivity was also investigated. Results showed that as the temperature increased, the initial catalyst activity increased. Although the effect of pressure was minimal at 275°C, as the temperature increased, the effect of pressure became more significant and higher conversions were achieved at higher pressures. The concentration of ring opened products increased as the conversion increased for all temperatures and pressures. The ring opened product concentrations increased with increased temperature at 3 MPa. At 275°C, higher ring opened product concentrations were obtained at higher conversions as the pressure increased.Based on the experimental results, a Langmuir Hinshelwood (L-H) kinetic model for the ring opening of decalin was developed. The kinetic model assumed a bifunctional catalytic process in which hydrogenation/dehydrogenation reactions occurred on metal sites, whereas isomerization, ring-opening and cracking occurred on acid sites. The model parameters were estimated by minimizing the difference between measured experimental data and model predictions by the sum of least-squares method. The model was able to estimate the experimental results well, with a R₂ of 0.8. Activation energies estimated from the model parameters showed that ring opening had the lowest activation energy (135.4 kJ/mol), whereas cracking had the highest (229.7 kJ/mol).
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