A STUDY OF STRUCTURAL PROPERTIES AND PERFORMANCE OF Ni-Co-Mg-Al-Ox CATALYST FOR CARBON DIOXIDE REFORMING OF METHANE
Date
2018-03-22
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ORCID
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Thesis
Degree Level
Doctoral
Abstract
Previous work from our group has established Ni-Co-Mg-Al-Ox catalyst to be an active and stable catalyst for CO2 reforming of Methane, also known as dry reforming of Methane (DRM). Additionally, bimetallic Ni-Co showed better performance compared to individual monometallic catalysts of Ni or Co. Further studies revealed that Ni and Co showed different extent and kinetics of reduction. The relationship between the bulk structure and reducibility of active metals (Ni and Co) has not yet been studied. The individual interaction of the active metals with the component of the support is yet to be examined. Likewise, exploration of other feed source for DRM or dry reforming of higher hydrocarbon on Ni-Co-Mg-Al-Ox catalyst has not been studied. The primary aim of this research work is to study the effects of Mg/Al ratio (support) on the bulk structure, basicity, metal support interaction, metal site formation and site performance of Ni-Co-Mg-Al-Ox catalyst for CO2 reforming of CH4 (DRM).
The research plan for this project is divided into two parts. Part one focuses on understanding the relationship between bulk structure, site formation and catalytic performance of monometallic (Ni or Co) and bimetallic Ni-Co-Mg-Al-Ox for DRM, as the Mg/Al ratio in the support changes. The second part focuses on the exploration of DRM using simulated coal gas feed and CO2 reforming of C2H6 (shale gas contains appreciable amount of C2H6).
For part one, the effects of Mg/Al ratio on the bulk structure, site formation and performance of Ni-Co-Mg-Al-Ox for dry reforming were studied. High Mg/Al ratio showed NiCoO2 + MgO-solid phase + spinel structure, compared to the lower ratio that showed a complete spinel structure. This additional MgO phase improved the basicity and the easy of reduction of the active metals, leading to better activity and stability of catalyst to DRM reaction. With respect to the monometallic catalysts, supported Ni and Co showed similar structure, but different metal reducibility and site performance for DRM. The Al-Ox supported Co catalyst showed no reducibility and activity, appreciable amounts of both properties was found in the corresponding Ni catalyst. Introduction of MgO into the support improved metal reduction and basicity of support, making the performance of the catalysts better. These observations were related to the different interaction and distribution of the metals within the support system.
For part two, DRM was studied using simulated coal feed gas at higher temperature (900 oC) using larger catalyst loading. Better activity, stability and product selectivity were observed in bimetallic Ni-Co with higher Mg/Al ratio compared to the lower ratio and monometallic Ni catalyst. Also, appreciable amount of activity was found using the coal gas feed, even though the amount of CO2 and CH4 were small compared to other components of the feed. The difference in the activity of catalysts using both feed was related to the difference in the composition of CH4 and CO2 in both feeds. For CO2 reforming of Ethane (CRE), two main points were addressed in this study; C2H6 dissociation study and CO2 reforming of C2H6. Results showed that the catalyst support, catalyst in oxide form and reduced catalysts can activate CO2 reforming of C2H6, unlike DRM that needs reduced catalyst for the reaction to proceed. Additionally, higher Mg/Al ratio catalysts showed preference for CRE over C2H6 dissociation, while lower Mg/Al ratio catalysts showed preference for C2H6 dissociation over CRE.
In conclusion, variation of the composition of Mg/Al ratio in the support led to changes in the bulk structure, basicity, metal support interaction, active metal distribution, reducibility and performance of monometallic (Ni, Co) and bimetallic (Ni-Co) catalysts for DRM. Higher Mg/Al ratio improved the basicity of support leading to easy activation of CO2, which helped in the conversion of deposited carbon to CO. The presence of sufficient active site helped (synergistically with support) in the activation of the CH4, leading to better catalytic performance.
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Keywords
CO2 reforming of CH4, CO2 reforming of ethane, Basicity, Mono-metallic catalysts, Bimetallic catalysts
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Chemical and Biological Engineering
Program
Chemical Engineering