- Title
- Functionalized three dimensional mesoporous catalytic materials for CO₂ conversion
- Creator
- Ismaili, Arsh Aminmahamad
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2025
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Global warming and climate change are the most serious issues concerning the planet, which have been seriously aggravated by high levels of carbon dioxide (CO₂) emitted into the atmosphere by human activities. Prior to the Industrial Revolution, the levels of CO₂ concentration hovered around 280 parts per million (ppm), which increased drastically to 420 ppm today. The increased burning of fossil fuels due to the rise in energy demand, deforestation and rapid urbanisation are the primary causes for the increase in CO₂ levels in the atmosphere. As CO₂ is an extremely strong greenhouse gas that traps heat, which is reflected to the earth, the earth's surface temperature increases quite rapidly, causing global warming. This increased temperature has resulted in more severe weather extremes, increasing glacier meltwater flow rates and rising sea levels, all of which have significant effects on natural ecosystems and biodiversity. Therefore, it is highly critical to capture the CO₂ molecules and convert them to value-added products for a sustainable future. Technologies such as CO₂ conversion capture and storage (CCS) are the first steps towards reducing global warming. Capturing CO₂ from energy generation plants and the industrial sector and storing it underground in geological reservoirs is considered one of the effective ways to reduce CO₂ emissions. On the other hand, converting the adsorbed CO₂ into fuels or chemicals through catalytic converters, known as CO₂ conversion, is highly critical for the circular carbon economy. Through this catalytic process, depending on local energy cost, CO₂ can be converted into value-added products such as C1 compounds (e.g., methane and methanol) or higher carbon compounds (e.g., ethylene and propylene). Among the C1 products, methane, in particular, is desirable due to its high energy density and versatility and is considered an excellent storage medium for hydrogen. As the global energy demand increases, the value of methane is projected to grow significantly, making the carbon capture and utilization (CCU) process a potential solution for global warming. Various catalytic processes such as thermo-catalytic, photo-catalytic, and electro-catalytic processes have been considered to effectively convert CO₂ into methane. Apart from their advantages, catalysts play a crucial role in influencing reaction efficiency and product yield in all catalytic approaches. Moreover, cost of catalysts, catalyst stability, durability and reusability are the key factors that should be considered before selecting these catalysts. Although various catalysts have been employed in the lab scale for the CO₂ conversion process, they failed to demonstrate at an industrial scale due to technical challenges such as high energy requirements for the reaction and environmental and safety concerns. In this thesis, we aim to address some of these challenges by developing a novel metal functionalized 3-dimensional (3D) mesoporous catalytic support and optimize their performance and explore the potential in the thermocatalytic process. This thesis offers an overview of the current scenario of CO₂ as a real problem to the world and the areas where solutions are still needed. Later, it provides a comprehensive literature review on converting CO₂ to C1 products using mesoporous catalytic materials. This review covers the genuine need for CO₂ conversion to value-added products and their reaction mechanism and further provides a deeper understanding of the pathways that can mitigate the environmental damage caused by CO₂ emissions. In addition, it highlights the potential of different mesoporous catalytic systems, which include metal-functionalized mesoporous silica (1D/2D and 3D) with the single and bi-metal catalytic systems, mesoporous metal oxides, mesoporous carbon and their functionalized counterparts, mesoporous phosphides/sulfides and mesoporous carbon nitrides and their functionalized counterparts for CO₂ conversion to C1 products. The importance of mesoporous silica as support and the strategies to overcome the limitations of CO₂ conversion to CH4 are reviewed in detail. Moreover, we demonstrate the development of nickel-functionalized 3D mesoporous silica SBA-1 with a unique cage-type and open window pore morphology and its influence on CO₂ methanation. The pristine SBA-1 exhibits a high specific surface area (1315 m² g⁻¹) and improved mass transfer kinetics due to the unique pore structure. For the first time, SBA-1 has been functionalized with nickel (5–25 wt%) via the wet impregnation method for CO₂ methanation. Nickel functionalization led to a decrease in the surface area (453 -1089 m2 g-1), and a shift in low-angle XRD peaks towards the high angle indicates blockage of pores and agglomeration of metal species compared to pristine SBA-1. FTIR displays strong metal-oxygen vibration peaks, and TPR analysis confirms the presence of nickel species through the reducibility occurring around 350 to 400 °C. Among the prepared catalysts, 20Ni/SBA-1 demonstrates optimal performance, with uniform metal dispersion within the pores and on the surface of SBA-1. Catalytic activity was evaluated for CO₂ methanation under various conditions, including temperature (250, 300, 350 and 400 °C), gas hourly space velocity (GHSV), and CO₂ concentration to optimize conversion, selectivity, and stability. Among the catalysts studied, the 20Ni/SBA-1 catalyst shows excellent CO₂ conversion (80.1%) and CH4 selectivity (96.9%), maintaining stability over five consecutive 24-hour cycles. These findings highlight the potential of 3D mesoporous silica SBA-1 as support and can be extended for further development and application in CO₂ reduction processes. Furthermore, we demonstrate the development of a novel approach to incorporate nickel into the framework of 3D-ordered mesoporous silica MCM-48 to circumvent the issues of wet impregnation that lead to metal agglomeration. The resulting nickel-substituted MCM-48 with interconnected pore channels preserves the Ia3d symmetry while exhibiting comparable surface area (905 – 1033 m2 g-1), increased pore width (>3.0 nm) and volume (> 0.6 g cm-3) to that of the bare MCM-48 (1261 m2 g-1). The low-angle PXRD peaks moving towards the lower angle demonstrate an increase in pore width as Ni2+ owing to its larger atomic radius (75 pm) affecting unit cell length as well as pore diameter, confirming the substitution of nickel in the MCM-48 matrix. Characterization studies, including TEM and XPS, confirm the successful incorporation of nickel into the MCM-48 framework, whereas the elemental mapping confirms that the metal dispersion improves significantly with higher nickel, resulting in enhanced catalytic activity. Temperature-programmed reduction analysis further confirms the strong interaction between nickel and the silica matrix. The catalytic activity of Ni-MCM-48 for converting CO₂ to CH4 under different experimental conditions such as temperature, GHSV, the concentration of reactants, and durability of the catalyst have been explored. The optimised Ni-MCM-48 catalyst shows high catalytic activity with 68.1% CO₂ conversion and 90.6% CH4 selectivity at the GHSV of 30,000 mL h-1g-1catalyst. Moreover, the catalyst exhibits excellent stability over multiple reaction cycles (5 cycles each for 24 h), which is attributed to the strong Ni-O-Si bonds within the MCM-48 framework. This approach highlights the potential of direct metal substitution in MCM-48, which has a 3D porous structure for CO₂ conversion and other catalytic applications, as the unique structure offers not only a great platform for highly dispersed metal incorporation and high stability but also helps to enhance the mass transfer. Overall, this thesis highlights the potential of 3D mesoporous silica materials as a catalytic support for CO₂ methanation. It demonstrated how the catalysts with 3D porous structure influence both the catalytic preparation and the final performance of the CO₂ methanation. An attempt is made to understand the structure-property-performance relationship of the catalyst with 3D mesoporous structure and high specific surface area and the mechanism of the formation of C1 product from CO₂ molecules through the thermocatalytic pathway. The catalysts with 3D structures functionalised with Ni atoms show much better performance than the support with the unidimensional porous system. Although the prepared catalysts show excellent performance and stability for CO₂ methanation, the addition of single metal or bimetal atoms in these supports is expected to further improve the performance. Therefore, in the future, much focus should be devoted to the fabrication and characterisation of these catalytic nanostructures for CO₂ methanation. It is also believed that integrating both carbon capture and conversion systems is going to be an efficient and sustainable system and will help speed up the commercialisation process. Therefore, much focus should be devoted to developing integrated CO₂ capture and conversion systems in the future.
- Subject
- CO₂ methanation; three dimensional mesoporous silica; catalysis; SBA-1; direct metal substitution; nickel-functionalized catalysts; MCM-48
- Identifier
- http://hdl.handle.net/1959.13/1520182
- Identifier
- uon:57444
- Rights
- Copyright 2025 Arsh Aminmahamad Ismaili
- Language
- eng
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