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Kinetic modeling of gas-phase phenol hydrodeoxygenation over Ag/TiO2 catalyst via TGA-FTIR based microreactor / Andrew Ng Kay Lup

Bio-oil produced from biomass pyrolysis is a potential source for liquid fuel. However, bio-oil has high oxygen content due to its complex mixture of oxygen-containing compounds which results in deleterious properties such as lower heating value, corrosion and chemical instability of liquid fuel. Ph...

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Main Author: Andrew Ng , Kay Lup
Format: Thesis
Published: 2019
Subjects:
TP Chemical technology
Online Access:http://studentsrepo.um.edu.my/10080/1/Andrew_Ng_Kay_Lup.pdf
http://studentsrepo.um.edu.my/10080/2/Andrew_Ng_Kay_Lup_%E2%80%93_Thesis.pdf
http://studentsrepo.um.edu.my/10080/
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record_format eprints
institution Universiti Malaya
building UM Library
collection Institutional Repository
continent Asia
country Malaysia
content_provider Universiti Malaya
content_source UM Student Repository
url_provider http://studentsrepo.um.edu.my/
topic TP Chemical technology
spellingShingle TP Chemical technology
Andrew Ng , Kay Lup
Kinetic modeling of gas-phase phenol hydrodeoxygenation over Ag/TiO2 catalyst via TGA-FTIR based microreactor / Andrew Ng Kay Lup
description Bio-oil produced from biomass pyrolysis is a potential source for liquid fuel. However, bio-oil has high oxygen content due to its complex mixture of oxygen-containing compounds which results in deleterious properties such as lower heating value, corrosion and chemical instability of liquid fuel. Phenolics are some of the major O-containing constituents commonly found in lignocellulosic biomass derived bio-oil. Thus, phenolic hydrodeoxygenation (HDO) is a process required for bio-oil upgrading into high quality liquid fuel. In this study, gas-phase hydrodeoxygenation of phenol over Ag/TiO2 catalyst at atmospheric pressure was conducted as a model compound approach in investigating the reaction mechanism and kinetics of oxygen removal from phenolics. Physicochemical properties of Ag/TiO2 catalyst were investigated to explore its potential as hydrodeoxygenation catalyst. The results showed that the metal-support interaction of Ag/TiO2 enabled hydrogen spillover phenomenon and synergistic interaction of acid and metal sites which are fundamental in catalyzing adsorption and activation of phenolics and hydrogen during hydrodeoxygenation. Reduction study of Ag/TiO2 by hydrogen also showed that Ag2O undergoes single-step reduction to form Ag which can be described using unimolecular decay model. Sample encapsulation technique was also proposed in this study to lengthen the release of vaporized phenol sample in microreactor. The delayed volatiles release phenomenon was enhanced by using metal capsule with higher material hardness and smaller surface area for sample evaporation. By using cylindrical tin capsule, significant release of vaporized phenol was extended up to 454—554 K which is above its boiling point. This finding is useful in enabling better catalyst activation and kinetic study of catalytic solid-gas reaction over a larger temperature range but at a fixed reactant amount. FTIR and GC-MS analyses showed the conversion of phenol into benzene as major product over Ag/TiO2 catalyst at atmospheric pressure condition. The proposed kinetic model for the phenol HDO network over Ag/TiO2 confirmed the occurrence of phenol hydrogenolysis and hydrogenation; cyclohexanol dehydration and hydrogenation of benzene and cyclohexene. The reaction rates increase with the following order: r1 (phenol hydrogenolysis) < r2 (phenol hydrogenation) < r5 (benzene hydrogenation) < r3 (cyclohexanol dehydration) < r4 (cyclohexene hydrogenation). Both phenol hydrogenolysis and hydrogenation steps are the respective rate-limiting steps for DDO (direct deoxygenation) and HYD (hydrogenation-dehydration) pathways of phenol hydrodeoxygenation over Ag/TiO2. Application of transition state theory has also indicated formation of more orderly activated complexes in the elementary reaction steps as indicated by the negative entropy change of activation. The proposed kinetic model was able to describe quantitative and qualitative observations in this work with a reasonable agreement and would be a useful tool for kinetic and mechanistic understanding of surface reactions of phenol HDO over supported transition metal catalysts. Successive hydrodeoxygenation runs (4 h) showed no significant degradation in catalytic and physicochemical properties of Ag/TiO2 catalyst. The accumulation of oxidized Ag metal species and coke deposits on Ag/TiO2 catalyst after each HDO run can be removed via H2-activation and calcination in air at 553 K with at least 98.9% removal efficiency.
format Thesis
author Andrew Ng , Kay Lup
author_facet Andrew Ng , Kay Lup
author_sort Andrew Ng , Kay Lup
title Kinetic modeling of gas-phase phenol hydrodeoxygenation over Ag/TiO2 catalyst via TGA-FTIR based microreactor / Andrew Ng Kay Lup
title_short Kinetic modeling of gas-phase phenol hydrodeoxygenation over Ag/TiO2 catalyst via TGA-FTIR based microreactor / Andrew Ng Kay Lup
title_full Kinetic modeling of gas-phase phenol hydrodeoxygenation over Ag/TiO2 catalyst via TGA-FTIR based microreactor / Andrew Ng Kay Lup
title_fullStr Kinetic modeling of gas-phase phenol hydrodeoxygenation over Ag/TiO2 catalyst via TGA-FTIR based microreactor / Andrew Ng Kay Lup
title_full_unstemmed Kinetic modeling of gas-phase phenol hydrodeoxygenation over Ag/TiO2 catalyst via TGA-FTIR based microreactor / Andrew Ng Kay Lup
title_sort kinetic modeling of gas-phase phenol hydrodeoxygenation over ag/tio2 catalyst via tga-ftir based microreactor / andrew ng kay lup
publishDate 2019
url http://studentsrepo.um.edu.my/10080/1/Andrew_Ng_Kay_Lup.pdf
http://studentsrepo.um.edu.my/10080/2/Andrew_Ng_Kay_Lup_%E2%80%93_Thesis.pdf
http://studentsrepo.um.edu.my/10080/
_version_ 1738506326662709248
spelling my.um.stud.100802022-01-03T18:46:35Z Kinetic modeling of gas-phase phenol hydrodeoxygenation over Ag/TiO2 catalyst via TGA-FTIR based microreactor / Andrew Ng Kay Lup Andrew Ng , Kay Lup TP Chemical technology Bio-oil produced from biomass pyrolysis is a potential source for liquid fuel. However, bio-oil has high oxygen content due to its complex mixture of oxygen-containing compounds which results in deleterious properties such as lower heating value, corrosion and chemical instability of liquid fuel. Phenolics are some of the major O-containing constituents commonly found in lignocellulosic biomass derived bio-oil. Thus, phenolic hydrodeoxygenation (HDO) is a process required for bio-oil upgrading into high quality liquid fuel. In this study, gas-phase hydrodeoxygenation of phenol over Ag/TiO2 catalyst at atmospheric pressure was conducted as a model compound approach in investigating the reaction mechanism and kinetics of oxygen removal from phenolics. Physicochemical properties of Ag/TiO2 catalyst were investigated to explore its potential as hydrodeoxygenation catalyst. The results showed that the metal-support interaction of Ag/TiO2 enabled hydrogen spillover phenomenon and synergistic interaction of acid and metal sites which are fundamental in catalyzing adsorption and activation of phenolics and hydrogen during hydrodeoxygenation. Reduction study of Ag/TiO2 by hydrogen also showed that Ag2O undergoes single-step reduction to form Ag which can be described using unimolecular decay model. Sample encapsulation technique was also proposed in this study to lengthen the release of vaporized phenol sample in microreactor. The delayed volatiles release phenomenon was enhanced by using metal capsule with higher material hardness and smaller surface area for sample evaporation. By using cylindrical tin capsule, significant release of vaporized phenol was extended up to 454—554 K which is above its boiling point. This finding is useful in enabling better catalyst activation and kinetic study of catalytic solid-gas reaction over a larger temperature range but at a fixed reactant amount. FTIR and GC-MS analyses showed the conversion of phenol into benzene as major product over Ag/TiO2 catalyst at atmospheric pressure condition. The proposed kinetic model for the phenol HDO network over Ag/TiO2 confirmed the occurrence of phenol hydrogenolysis and hydrogenation; cyclohexanol dehydration and hydrogenation of benzene and cyclohexene. The reaction rates increase with the following order: r1 (phenol hydrogenolysis) < r2 (phenol hydrogenation) < r5 (benzene hydrogenation) < r3 (cyclohexanol dehydration) < r4 (cyclohexene hydrogenation). Both phenol hydrogenolysis and hydrogenation steps are the respective rate-limiting steps for DDO (direct deoxygenation) and HYD (hydrogenation-dehydration) pathways of phenol hydrodeoxygenation over Ag/TiO2. Application of transition state theory has also indicated formation of more orderly activated complexes in the elementary reaction steps as indicated by the negative entropy change of activation. The proposed kinetic model was able to describe quantitative and qualitative observations in this work with a reasonable agreement and would be a useful tool for kinetic and mechanistic understanding of surface reactions of phenol HDO over supported transition metal catalysts. Successive hydrodeoxygenation runs (4 h) showed no significant degradation in catalytic and physicochemical properties of Ag/TiO2 catalyst. The accumulation of oxidized Ag metal species and coke deposits on Ag/TiO2 catalyst after each HDO run can be removed via H2-activation and calcination in air at 553 K with at least 98.9% removal efficiency. 2019-03 Thesis NonPeerReviewed application/pdf http://studentsrepo.um.edu.my/10080/1/Andrew_Ng_Kay_Lup.pdf application/pdf http://studentsrepo.um.edu.my/10080/2/Andrew_Ng_Kay_Lup_%E2%80%93_Thesis.pdf Andrew Ng , Kay Lup (2019) Kinetic modeling of gas-phase phenol hydrodeoxygenation over Ag/TiO2 catalyst via TGA-FTIR based microreactor / Andrew Ng Kay Lup. PhD thesis, Universiti Malaya. http://studentsrepo.um.edu.my/10080/
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