Date of Award
12-2024
Document Type
Dissertation
Department
Chemical and Biomolecular Engineering
Committee Chair/Advisor
Dr. Ming Yang
Committee Member
Dr. David Bruce
Committee Member
Dr. Ana C. Alba-Rubio
Committee Member
Dr. Thompson O. Mefford
Abstract
Carbon dioxide (CO₂) emissions, primarily from fossil fuel use in energy and chemical production, are the leading driver of global warming. The chemical industry is the third-largest source of these emissions, so reducing its carbon footprint—and ultimately achieving “CO₂ emissions-free” chemical manufacturing—is critical to combating global warming. Thermal catalysis is the workhorse of industrial chemical manufacturing, generating CO₂ emissions from two main sources: the actual chemical transformations of fossil feedstocks and burning of fossil fuels to provide the process heat. Therefore, developing and implementing technologies to mitigate the carbon emissions associated with these emissions sources is essential for decarbonizing the chemical industry and mitigating climate change. Viable catalytic technologies that convert CO₂ into valuable products would provide a techno-economic pathway to tackle post-process CO2 emissions. Further, replacing fossil fuel combustion with electricity-driven alternative heating techniques for industrial thermal reactors would eliminate CO₂ emissions accruing from process heat generation.
Thermal catalytic hydrogenation of carbon dioxide to carbon monoxide, known as reverse water-gas-shift (RWGS) reaction, is one of the most investigated promising strategies for CO2 valorization, offering an alternative source for syngas (a mixture of CO and H2), a versatile precursor for many industrial chemicals and fuels. However, given that CO2 is highly thermodynamically stable, the RWGS reaction is strongly endothermic, requiring temperatures above 600 °C. To potentially reduce industrial costs, operating RWGS reaction at low temperatures — ~ 400 °C is desirable. Unfortunately, this desirable low-temperature window favors an exothermic side reaction leading to methane formation over the endothermic RWGS reaction. Although atomically dispersed supported metal catalysts, where the atomically dispersed supported metal is the entire or the center of the actual catalytic active site, would favor CO selectivity during RWGS reaction, the overall CO2 hydrogenation reaction rate becomes inherently compromised. This is because of linear scaling relationship and the competition by the critical RWGS elementary reaction steps for the single catalytic site (metal-support interface) in traditional metal oxide-based catalysts. In this dissertation, a novel dual-site catalyst design strategy leveraging catalytically active support to decouple the often-competing RWGS critical reaction steps is reported. Through a unique bifunctional mechanism, the dual-site single-atom catalysts (Pt/α-MoC) render record-high RWGS reaction rates and invariant ~ 100 % CO selectivity at low temperatures, surpassing traditional metal-oxide-based catalysts. More significantly, as a potential generalizable caution for the design of high-loading supported metal catalysts, this work uncovers that arbitrary increase in the supported metal density, even when stable, can unexpectedly compromise the per-weight reactivity of catalysts, especially when the support itself is also catalytically active.
As an emerging advancement in chemical reaction engineering, magnetic induction heating (MIH) is a scalable alternative to the standard furnace-based heating, driving thermal reactions by enabling self-heating of ferromagnetic nanoparticles (FNPs) under a high-frequency alternating magnetic field. Pioneering studies focused on optimizing FNPs for improved heating efficiency, viewed MIH as simply an alternative heating approach for thermal reactions, assuming MIH-driven reactions to be equivalent to standard thermal reactions. Contrastingly, considering that MIH derives from the continuous, periodic regulation of unpaired electron spins — the same domain within which catalysis can be triggered, this dissertation demonstrates that when FNPs serve as both magnetic heating susceptor and catalyst, MIH may alter thermal catalytic reaction pathways beyond the well-known efficient and fast heating. Comparing catalytic CO oxidation reaction over a carefully designed ferromagnetic Pt/Fe3O4 nanocatalyst in both MIH and standard thermal (furnace-heating) modes, under consistent temperature profiles and excluding heat and mass transfer artefacts, the MIH mode boosted reactivity over 25-fold. More importantly, the MIH-triggered thermal catalytic reaction exhibited lower apparent activation energy and unique reaction rate orders compared to the standard thermal mode, suggesting that their reaction pathways were dramatically different. These preliminary findings indicate that through rational catalyst design, MIH can bring more than just heat to directly touch the core of thermal catalytic reactions, potentially paving the way to launch MIH-assisted thermal catalysis as a distinct category of chemical reaction.
Recommended Citation
Chukwu, Ewa, "Regulating Cox Conversion Through Catalyst Design and Reaction Energy Input" (2024). All Dissertations. 3775.
https://open.clemson.edu/all_dissertations/3775
Author ORCID Identifier
0000-0003-2873-7832
