Date of Award

4-11-2026

Thesis Type

PhD

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Divisions

Faculty of Engineering

Department

Department of Science and Technology Studies

Institution

Universiti Malaya

Abstract

Carbon capture and utilization (CCU) is increasingly being adopted as a strategy to minimize carbon dioxide (CO₂) emissions. Integrated CO₂ capture and utilization (ICCU) is more attractive as it reduces overall cost and energy consumption by eliminating the need for gas compression and transportation. Advances in ICCU and the development of dual functional materials (DFMs) capable of adsorbing and in situ converting CO₂ have attracted increasing attention in both academia and industry, driven by the need for efficient CO₂ utilization pathways. After a detailed analysis of the literature, zeolites have emerged as prominent materials for use as adsorbents and catalyst supports due to their high surface area, thermal stability, and tunable pore sizes. However, their potential in developing DFMs for integrated carbon capture and the reverse water–gas shift reaction (ICCC–RWGS) remains largely unexplored. Therefore, this study aims to explore the potential of zeolite-based DFMs for ICCC–RWGS. For this purpose, the 13X zeolite were used to synthesize DFMs, with nickel (Ni) as the catalyst and calcium oxide (CaO) as the adsorbent. Optimization of the DFM synthesis conditions identified a zeolite–to–Ni ratio of 6.82, a CaO–to–zeolite ratio of 6.85, and a calcination temperature of 542 °C as the optimal synthesis parameters. Fourier Transform Infrared Spectroscopy (FTIR) confirmed that high CaO content in the optimized Ni/13X–CaO DFM enhanced the intensity of the Ca–O peak. Field Emission Scanning Electron Microscopy (FESEM) revealed that the DFM exhibits a network-like morphology, suggesting interconnections between Ni/13X and CaO, while Energy Dispersive X-ray Spectroscopy (EDX) confirmed the uniform dispersion and high content of Ni and Ca, providing more active sites. The X-ray Diffraction (XRD) pattern displays a high CaO normalized peak area contribution of 71.31% and a small average CaO crystallite size of 26.95 nm. The investigation of the effects of operating parameters showed that CO₂ adsorption and CO yield increased by 12.99% and 8.89%, respectively, with increasing CO₂ concentration. In contrast, increasing H₂ concentration led to decreases of 32.56% and 38.76% in CO₂ adsorption and CO yield, respectively, while increasing reaction temperature caused decreases of 25.77% and 27.15%, respectively. Under the conditions of 20% CO₂/N₂, 10% H₂/N₂, and a reaction temperature of 600 °C, the optimized Ni/13X–CaO DFM achieved its optimal performance, with a CO₂ adsorption capacity of 4.86 mmol/g and CO production of 4.80 mmol/g. The mechanism shows that CO₂ adsorption on CaO sites forms monodentate carbonates, while its interaction with the dissociated hydrogen yields bicarbonates. CO generation via RWGS is evidenced by formate, gaseous CO, and Ni–CO intermediates. Kinetic analysis revealed that CO generation is jointly influenced by gas diffusion and the reaction interface (Ni–CaO), aligning with the proposed mechanism. The RWGS reaction and CO₂ diffusion were determined to be the rate-limiting steps in the 1st and 10th cycles of the ICCC–RWGS process, respectively. In summary, this study demonstrates the potential of Ni/13X–CaO as a DFM for efficient ICCC–RWGS, providing valuable insights for its future industrial application.

Initial

khm

Additional Information

Thesis (PhD) - Faculty of Engineering, Universiti Malaya, 2026.

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