京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19740号 / 工博第4195号 / 新制||工||1647(附属図書館) / 32776 / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 田中 庸裕, 教授 阿部 竜, 教授 陰山 洋 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

A study of how Svensk Plaståervinning i Motala AB (SPÅ) can use intermodal transports to work towards their goal of CO2 reduction. The study shows a quantitaive reduction in CO2 emissions compared to road transports. / <p>Examensarbetet är utfört vid Institutionen för teknik och naturvetenskap (ITN) vid Tekniska fakulteten, Linköpings universitet</p>

<p>Current industrial practice in the steel Industry involves the use of natural gas with high methane content as a primary energy source. Natural combustion produces greenhouse gases, and with the continued focus on managing and reducing harmful emissions from industrial processes, there is a need for research into alternative sources of energy. Among several alternatives that have been studied is hydrogen: a non-carbon-based fuel. This work uses a coupled computational fluid dynamics (CFD)-finite element analysis (FEA) combustion model to investigate hydrogen utilization as a fuel in a reheat furnace and how it impacts the quality of the steel produced by understanding the three dimensional (3D) flow behavior, furnace temperature profile, thermal stress distribution, heat flux, formation of iron oxides, emission gases and mode of heat transfer onto the steel slabs. The modeling process integrates the five different zones of a pusher type reheating furnace (top and bottom) and modeled using Ansys Fluent 2020R1 and Ansys Workbench 2022R1. Changes in these parameters are determined by comparison to a baseline case that uses methane as fuel and maintaining the same heat input in terms of chemical energy into the furnace. Global mechanism was used for hydrogen and two step mechanism was used for methane combustion. Results revealed a 2.6% increase in average temperature to 1478K across the furnace for hydrogen which resulted in 6.45% increase in maximum heat flux into the slabs. Similar flue gas flow patterns were seen for both cases and heat transfer mode from the combustion gases to the slabs was primarily by radiation (~97%) for both methane and hydrogen. 11.5% increase in iron oxide formation on the slab was recorded for the hydrogen case, however, the bulk of the iron oxide formed was more of wüstites which are the easiest form of iron oxide to descale. However, elevated nitrogen oxide (NOx) levels were recorded for hydrogen combustion which led to further study into NOx mitigation techniques. Application of the staged combustion method using hydrogen fuel showed potentials for NOx reduction. The use of regenerative burners further conserved exergy losses in hydrogen fuel application. Insignificant deviation from base case thermal stress distribution and zero carbon emission from the hydrogen case indicates the usability of hydrogen as an alternative fuel in reheating furnace operations. </p>

A major contribution to global warming is CO2 emitted from the combustion of fossil fuels. Electrochemical processes can help to mitigate the elevated CO2 emissions through either the conversion of CO2 into value-added chemicals or the replacement of fossil fuels with clean fuels such as hydrogen produced from water oxidation. The present dissertation focuses on the mechanistic aspects of electrochemical processes. Electrochemical water oxidation is hindered by the low efficiency of oxygen evolution reaction (OER) at the anode whereas electrochemical reduction of CO2 (ERCO2) is hampered by high overpotentials and poor product selectivity. In this dissertation, we studied the catalytic activity of transition metal-based catalysts, including FeNi spinels, metal-oxide/copper, and d metal cyclam complexes, for both OER and ERCO2 using the density functional theory (DFT) computational approach.We report a combined effort of fabricating FeNi oxide catalysts and identifying the active component of the catalyst for OER. Our collaborators at the University of California, Santa Cruze fabricated a series of FeNi spinels-based materials including Ni(OH)Fe2O4(Cl), Ni(OH)Fe2O4, Fe(OH)Fe2O4(Cl), Fe(OH)Fe2O4, Ni(OH)O(Cl), Ni(OH)O and some show exceptional activity for OER. Combined experimental characterization and computational mechanistic study based on the computational hydrogen electrode (CHE) model revealed that Ni(OH)Fe2O4(Cl) is the active ensemble for exceptional OER performance. We also investigated CO2 reduction to C1 products at the metal-oxide/copper interfaces ((MO)4/Cu(100), M = Fe, Co and Ni) based on the CHE model. The effect of tuning metal-oxide/copper interfaces on product selectivity and limiting potential was clearly demonstrated. This study showed that the catalyst/electrode interface and solvent can be regulated to optimize product selectivity and lower the limiting potential for ERCO2. Applied potential affects the stability of species on the surface of the electrode. The proton-coupled electron transfer (PCET) equilibrium assumed in the CHE model does not capture the change in free energy under the influence of the applied potential. In contrast, the constant electrode potential (CEP) model captures changes in free energy due to applied potential, we applied the CEP model to ERCO2 and OER on (MO)4/Cu(100) and compared the results with those from the CHE model. The results demonstrate that the CHE and the CEP models predict different limiting potentials and product selectivity for ERCO2, but they predict similar limiting potentials for OER. The results demonstrate the importance of accounting for the applied potential effect in the study of more complex multi-step electrochemical processes. We also studied transition metal-based homogeneous catalysts for ERCO2. We examined the performance of transition metal(M) - cyclam(L) complexes as molecular catalysts for the reduction of CO2 to HCOO- and CO, focusing on the effect of changing the metal ions in cyclam on product selectivity (either HCOO- or CO), limiting potential and competitive hydrogen evolution reaction. Our results show that among the complexes, [LNi]2+ and [LPd]2+ can catalyze CO2 reduction to CO, and [LMo]2+ and [LW]3+ can reduce CO2 to HCOO-. Notably, [LMo]2+, [LW]3+, [LW]2+ and [LCo]2+ have a limiting potential less negative than -1.6 V and are based on earth-abundant elements, making them attractive for practical application. In summary, the dissertation demonstrates high-performance catalysts can be designed from earth-abundant transition metals for electrochemical processes that would alleviate the high CO2 level in the environment. On the other hand, completely reversing the increasing trend of CO2 level in the atmosphere requires a collective human effort.

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Yes / This article explores the electro-chemical Carbon dioxide Reduction Cell (eCO2RC), delving into fundamental principles, methods, applications, and the latest approaches for converting CO2 emissions into valuable products. Product outcomes depend on electron exchange and electrode surface attributes used in the CO2 reduction. The study focuses on C1 and C2 products, emphasizing the necessity for selective materials and catalysts to enhance product recovery while minimizing energy consumption. Converting eCO2 into valuable products is seen as a crucial method for transforming waste into value, addressing the challenge of mitigating global warming through gas emission reduction. / The authors would like to thank Qatar National Research Fund (QNRF) for its support, through Grant # NPRP NPRP13S-0202-200228, and Qatar Shell Research Technology Center (QSRTC) as a co-founder.

In the pursuit of renewable and sustainable energy sources, this century presents humanity with an imperative driven by the crisis of conventional energy shortages and environmental pollution. Clean electrochemical energy storage and conversion technologies play a pivotal role in shaping the future landscape of power generation and energy utilization. However, the judicious design of the catalysts capable of efficiently and robustly driving electrochemical conversion remains a pressing challenge. In my dissertation, I addressed the critical challenges related to enhancing energy conversion efficiency in zinc-air batteries (ZABs) and electrocatalytic carbon dioxide reduction (CO2RR). These innovations show promise in utilizing renewable electricity to generate power and actively contribute to decarbonization efforts. The core focus of my dissertation revolves around the strategy of interface engineering for materials design and characterization. It is coupled with an in-depth mechanistic investigation of structure-property relationship at the interface level. The construction of a strong metal-support oxide interaction (SMMOI) has been demonstrated in the PdNiMnO porous film and has shown promising results. This interaction significantly enhances the activity of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) through electronic perturbation of Pd, reducing the reliance on precious metals and substantially improving the ZAB performance. On the other hand, my dissertation expands the decarbonization concept of electrocatalytic CO2RR towards value-added chemical production such as CO and formate. By designing bio-inspired tin oxide (SnOx) porous films through multiscale approaches of morphology engineering, surface chemistry, and phase transformation, the CO2RR Faradaic efficiency can be significantly improved. This is achieved by establishing a triple-phase interface and preserving the active phase through controlled pulsed electrochemical potentials during reactions. This innovative approach effectively addresses limitations associated with CO2 capture on the electrode and CO2 solubility issues in the electrolyte. The interface engineering strategies outlined in this dissertation illuminate the path toward next-generation catalyst designs that are highly efficient and tailored for sustainable and renewable energy applications.

2024 / On a global scale, Fe–S clusters (among other essential redox cofactors, such as hemes, flavins, or amino acid residues) drive the core metabolic reactions of life by transporting electrons through a suite of redox-active enzymes—the oxidoreductase superfamily (Fuchs, 2011). On a per-active-site basis, these enzymes are the most efficient catalysts for several chemical reactions crucial for renewable energy (storage and usage); thus, understanding their inner workings is paramount for developing alternative, green technologies (Reda et al., 2008; Wang et al., 2014). Therefore, this dissertation examines the mechanistic principles of one class of enzyme catalyst bearing Fe–S clusters, the 2-oxoacid:ferredoxin oxidoreductase (OFOR) enzyme superfamily. Although OFORs are considered reversible enzymes, they appear to have an inherent bias toward either the reductive or oxidative chemistry, often believed to reflect the native function of the enzyme (Li et al., 2016). However, revealing the factors that influence an enzyme’s directionality has been difficult. Therefore, by examining a series of unique OFOR enzymes and mutants, this dissertation addresses the following questions: Given the diversity of OFOR enzymes (i.e., cofactor content, number of subunits, and domain modularity), what factors control catalytic bias of CO2 fixation or evolution? What role does the OFOR’s partner protein, ferredoxin, play in biasing reaction directionality? The electrochemical study of the structurally unique PFOR enzymes from C. tepidum, M. marinus, and M. acetivorans will provide critical information regarding the significance of the domain and structure composition of an OFOR enzyme. It will further reveal whether the native function of the enzyme influences the resting-state reduction potentials of the [4Fe–4S] clusters in the ET chain. Detailed site-directed mutagenesis studies of the Ct PFOR will provide a foundation for understanding the relationship between cluster potentials and ET/catalytic rates of the OFOR family and give insight into the role the protein matrix plays in tuning cluster potentials. Furthermore, electrocatalytic studies of the Ct PFOR/Fd system will provide an example of how the identity of a partner protein could direct or support enzyme catalysis and elucidate factors that contribute to successful intermolecular-ET. Understanding how Fd characteristics influence catalysis applies to many other biological systems, including the chemistry of hydrogenases or nitrogenases. Finally, the study of the Fe proteins from the nitrogenase provides insight into the thermodynamic driving force that initiates nitrogen fixation in the catalytic component of the nitrogenase, further improving our understanding of how the nitrogenase accomplishes its chemistry. / 2027-02-07T00:00:00Z

Excessive CO2 emissions can negatively impact society and our planet. Reduction of CO2 is one potential avenue for its abatement. One of the most significant challenges to reducing CO2 is its extremely stable linear form. Experimentally, Cu/TiO2 has shown promise for CO2 photocatalytic reduction. Dispersed atomic catalysts can achieve high catalytic efficiency on a per atom basis. Active sites also typically having lower coordination number, and therefore may be more reactive. Using density functional theory and experimental techniques, we have investigated the role of surface oxygen vacancies (Ov) and photoexcited electrons on supported single atom catalysts and CO2 reduction. Cu atoms with Ov have shown to aid in the process of bent, anionic CO2 formation. In the first step involving CO2 dissociation (CO2* --> CO* + O*), a single Cu atom in Ov lowered the activation barrier to 0.10 - 0.19 eV, which could enable fast reduction of CO2 even at room temperature, in agreement with experimental findings. A photoexcited electron model was shown to readily promote Cu binding to the surface vacancy, and CO2 adsorption and direct dissociation. Finally, we briefly compare our results to calculations of supported single Pt atoms to determine how metals besides Cu may behave as photocatalysts for CO2 reduction, and we found a single Pt with Ov can promote CO2 dissociation. Our results show that tailoring TiO2 surfaces with defects in conjunction with atomic catalysts may lead to useful catalysts in the photoreduction of CO2.

The risk for climate change is a growing concern for theglobal society. According to what is known as the Kyoto Protocol,developed countries have committed themselves to reduce theirgreenhouse gas (GHG) emissions. The purpose of this thesis hasbeen to analyse opportunities for CO2 reductions in Swedish pulpand paper mills. The pulp and paper industry accounts forsignificant shares of the Swedish utilisationof both electricityand, in particular, biomass fuels. In this thesis, it has been agoal to focus not only on the technical potential of alternativesfor CO2 reductions in the energy systems of pulp and paper mills,but also on analysing the costeffectiveness of the studiedmeasures. Moreover, the analysis has covered questions concerningthe capacity and willingness among the actors involved with thepulp and paper mills’energy systems to realise CO2reduction potentials. A broad techno-economical evaluation of available technologiesfor increased power production as well as more efficient energyutilisation is carried out. Furthermore, a more indepth analysisof pulp mill-based biomass energy with CO2 removal and permanentsequestration (BECS) is presented. An evaluation is made of thepotential for pulp and paper production with a negative CO2balance through the implementation of BECS. In recent yearsoutside suppliers, mainly energy service companies (ESCOs), havebegun to operate energy facilities in some Swedish pulp and papermills. Based on interviews with managers from pulp and papercompanies and ESCOs, the main driving forces behind theincreasing co-operation as well as the opportunities and riskswith energy related co-operation are presented. Furthermore, the technical possibility of carbon-negativitythrough the implementation of BECS is discussed in relation tocarbon management on both corporate and global levels. The extentto which CO2-reducing measures in pulp and paper mills arerealised will have an impact on Sweden’s capacity to reachCO2 reduction targets. Whether or not technologies for CO2capture and sequestration are developed and implemented inSwedish pulp mills has a very large impact on the size ofSweden’s long-term CO2 reduction potential. Moreover, thedevelopment of business and competence focus in pulp and papercompanies and ESCOs suggests that cooperation will become ofincreasing importance for future sustainable industrial energymanagement. <b>Keywords:</b>CO2 reduction, pulp and paper industry, energysystem, biomass, CO2 capture and sequestration, black liquor,gasification, power production, outsourcing, sustainable energymanagement