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A study of molybdenum carbide catalysts supported on carbon derived from petroleum coke for hydrotreating Wang, Haiyan
Abstract
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 < 0.44. Extending these results to petcoke, the transition of Mo species and the corresponding changes to the activated petroleum coke (APC) morphology that occur during CHR were determined. A maximum mesoporosity of 37% was achieved for a sample reduced to 750 ℃. The activity of the Mo₂C/APC catalysts for the HDO of 4-MP was > 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.
Item Metadata
Title |
A study of molybdenum carbide catalysts supported on carbon derived from petroleum coke for hydrotreating
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
2018
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Description |
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 < 0.44.
Extending these results to petcoke, the transition of Mo species and the corresponding changes to the activated petroleum coke (APC) morphology that occur during CHR were determined. A maximum mesoporosity of 37% was achieved for a sample reduced to 750 ℃. The activity of the Mo₂C/APC catalysts for the HDO of 4-MP was > 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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Genre | |
Type | |
Language |
eng
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Date Available |
2018-11-09
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Provider |
Vancouver : University of British Columbia Library
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Rights |
Attribution-NonCommercial-NoDerivatives 4.0 International
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DOI |
10.14288/1.0373612
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
2019-02
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Campus | |
Scholarly Level |
Graduate
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Rights URI | |
Aggregated Source Repository |
DSpace
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Attribution-NonCommercial-NoDerivatives 4.0 International