Abstract
The escalating climate crisis, driven by anthropogenic carbon dioxide (CO2) emissions, necessitates the development of advanced Carbon Capture and Utilization (CCU) technologies. A critical distinction within CCU lies between transient carbon cycling, which converts CO2 into fuels, and permanent sequestration, which transforms it into durable, solid materials. This dissertation addresses fundamental catalytic challenges across both pathways to develop economically viable and technologically sound solutions for CO2 valorization. This work seeks to answer two primary research questions: (1) How can the catalyst temperature mismatch and stability limitations in the tandem conversion of CO2 to Liquefied Petroleum Gas (LPG) be overcome to create cost-effective, low-temperature processes? (2) How can the formidable thermodynamic barrier of direct CO2 splitting be circumvented to achieve permanent carbon sequestration in high-value solid materials? Utilizing advanced catalyst synthesis, comprehensive material characterizations, and in situ spectroscopic techniques, this dissertation elucidates critical structure-performance relationships and establishes new design principles for tandem catalysis. First, this study investigates the roles of palladium (Pd) incorporation and acid treatment in the catalytic performance of β-zeolite in low-temperature CO2-to-LPG synthesis. Our research challenges conventional reliance on Pd, demonstrating that Pd-free catalysts can achieve rapid stabilization and exhibit efficient catalytic activity. We demonstrate that judicious acid treatment of the zeolite component, not the incorporation of expensive noble metals like palladium, is the key factor enabling low-temperature activity. This is achieved by stabilizing surface methoxy species, the crucial intermediates for C-C bond formation. Palladium is shown to be not only unnecessary but detrimental, as it diverts these intermediates into parasitic side reactions. Furthermore, we systematically investigate this structure-performance relationship by engineering an inverse Zr0.2Cu catalyst with two distinct ZnO architectures for low-tempearture LPG synthesis: a homogeneously dispersed promoter via co-precipitation (6%ZnO) and a conformal surface overlayer via atomic layer deposition (ALD). We reveal that the spatial arrangement of the ZnO promoter governs long-term stability. A conformal surface promoter is shown to physically obstruct hydrogen transport pathways between catalytic components, leading to rapid deactivation by coking, whereas a bulk-dispersed promoter preserves these pathways and ensures robust performance. Second, this dissertation advances the conversion of CO2 to solid carbon for permanent sequestration. An efficient low-temperature CO2 methanation catalyst (Ni-MgO-SG) is first developed via a sol-gel method that synergistically optimizes metal dispersion, surface area, basicity, and oxygen vacancy concentration, resulting in markedly enhanced activity. Building on this, an innovative two-step tandem thermochemical strategy is designed and validated. This integrated process utilizes a highly active and stable sol-gel prepared Ni87Ce6.5Zr6.5-SG catalyst for the low-temperature CO2 methanation step, which is then coupled with a durable core-shell methane pyrolysis catalyst (Ni@Al2O3). This tandem system achieves nearly 99% overall CO2 conversion and a high carbon yield to carbon nanotubes (CNTs) in a single pass, providing a definitive proof-of-concept for a technologically viable pathway to transform a gaseous pollutant into a durable, high-value solid material. The findings of this research advance the fundamental science of catalyst design for tandem reactions and provide practical solutions for CO2 valorization. The noble-metal-free catalyst design paradigms and insights into promoter architecture offer pathways to more economical and sustainable fuel production. The successful demonstration of the integrated CO2-to-CNTs process establishes a compelling new technology for achieving negative emissions, contributing to the development of a circular carbon economy.
Committee Chair
Xinhua Liang
Committee Members
Feng Jiao; Marcus Foston; Miao Yu; Young-Shin Jun
Degree
Doctor of Philosophy (PhD)
Author's Department
Energy, Environmental & Chemical Engineering
Document Type
Dissertation
Date of Award
12-19-2025
Language
English (en)
DOI
https://doi.org/10.7936/pnc6-mq61
Recommended Citation
Wang, Kaiying, "Transforming CO2 into Value-Added Products: Liquefied Petroleum Gas and Solid Carbon Materials" (2025). McKelvey School of Engineering Theses & Dissertations. 1321.
The definitive version is available at https://doi.org/10.7936/pnc6-mq61