Zn and Cu doped Si-, C-, BP- and AlP-nanocages and nanotubes as catalysts for processes of CO 2 reduction reaction

Adsorption of HCOOH on Rh(111) and its reaction with preadsorbed oxygen

When Catalysts Breathe

Probing *CO intermediate and Water Structure during electrochemical CO2 reduction reaction by operando spectroscopyElectrochemical CO2 or CO (Cox) reduction reactions have been widely investigated to produce value-added chemicals. To understand the catalytic activities and modulate the selectivity for the target products, operando investigation of the catalyst surface is crucial. Particularly, operando attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR–SEIRAS) can reveal the correlation between *CO intermediate species and COxRR activity or interfacial water structure and catalytic activity. Here, we first investigate the influence of cations on the *CO adsorption configuration and product distribution of the CO2RR. The cations shift the preference of the *CO intermediate on the Cu surface and affect the product distribution. Time−resolved SEIRAS scans show how the kinetically dominant species converts to a more stable species. In addition, vibrational spectroscopy can provide information on the water structure near the catalyst surface by the modulation of O-H stretching modes. The water structure can be deconvoluted into strongly and weakly bounded hydrogen bonds in addition to the free water structure near the surfaces, and each structure can have different activity between CO2RR and hydrogen evolution reaction (HER). As a model system, we will compare the interfacial water structures near the Ag catalysts coated by various ionomer polymers and discuss the CO2RR to CO production activity. These efforts with operando ATR-SEIRAS can be utilized as the platform analytic technique.

High demand of energy, environmental problems, and energy crisis have brought great attentions in renewable and environment-friendly energy resources(1). Among various candidate energy sources, electrochemistry based energy storage and harvesting devices such as rechargeable batteries, supercapacitors, utilized regenerative fuel cells(URFCs), and solar cells have received great interests (1, 2). Particularly, URFCs which include fuel cells and water electrolyzers are getting a big spotlight in the renewable energy fields due to their high efficiency and clean properties(3, 4). The key technology for URFCs is to develop the cost-effective, durable, and high catalytic active catalysts for oxygen reduction(ORR) and evolution reactions(OER) in order to decrease the overpotential and improve efficiency of cells (5). Ideal bifunctional ORR and OER catalysts are Pt, RuO, and IrO for URFCs(6-8). However, precious metal-based catalysts are inadequate in terms of price competitiveness and limited durability to commercialize the URFCs(9). Recently, modification of cobalt oxides nanostructures with various dopants have reported to reduce the overpotential with high OER and ORR performances (10). Furthermore, nitrogen-doped graphene oxide is used to further enhance the electronic conductivity with durable mechanical property, because nitrogen sites can function as electrochemical active sites(11). In this work, several short-length N-doped carbon nanofibers(N-CNF) are introduced to maximize electrochemical active sites of catalysts. The shortened N-CNF catalysts are synthesized by the hydrothermal method. The physicochemical properties of the N-CNF-supported cobalt oxides nanostructures are investigated by various tools such as X-ray diffraction, scanning electron microscope, Brunauer Emmett Teller, and transmission electron microscope. To analyze electrochemical activities, rotating ring disk electrode system is used with an Hg/HgO, a platinum wire, and a 0.1M KOH solution for reference, counter, and electrolyte respectively. The electrochemical characteristics are measured by linear sweep voltammetry at a scan rate of 5 mVs-1 for OER (1.2V–1.7V) and ORR (0.2V–1.2V). To analyze the long-term stability for OER and ORR, the accelerated degradation tests are performed at a scan rate of 200 mVs-1. References Wang H-F, Tang C, Zhang Q. Template growth of nitrogen-doped mesoporous graphene on metal oxides and its use as a metal-free bifunctional electrocatalyst for oxygen reduction and evolution reactions. Catalysis Today. 2017. Kushwaha HS, Halder A, Thomas P, Vaish R. CaCu3Ti4O12: A Bifunctional Perovskite Electrocatalyst for Oxygen Evolution and Reduction Reaction in Alkaline Medium. Electrochimica Acta. 2017;252(Supplement C):532-40. Bau VM, Bo XJ, Guo LP. Nitrogen-doped cobalt nanoparticles/nitrogen-doped plate-like ordered mesoporous carbons composites as noble-metal free electrocatalysts for oxygen reduction reaction. J Energy Chem. 2017;26(1):63-71. Zhang X, Ding P, Sun Y, Li X, Li H, Guo J. CoMoS3.13 nanosheets grafted on B, N co-doped graphene nanotubes as bifunctional catalyst for efficient water electrolysis. Journal of Alloys and Compounds. 2018;731(Supplement C):403-10. Yang J, Fujigaya T, Nakashima N. Decorating unoxidized-carbon nanotubes with homogeneous Ni-Co spinel nanocrystals show superior performance for oxygen evolution/reduction reactions. Scientific Reports. 2017;7. Song W, Ren Z, Chen SY, Meng Y, Biswas S, Nandi P, et al. Ni- and Mn-Promoted Mesoporous Co3O4: A Stable Bifunctional Catalyst with Surface-Structure-Dependent Activity for Oxygen Reduction Reaction and Oxygen Evolution Reaction. ACS Applied Materials and Interfaces. 2016;8(32):20802-13. Elumeeva K, Masa J, Tietz F, Yang F, Xia W, Muhler M, et al. A Simple Approach towards High-Performance Perovskite-Based Bifunctional Oxygen Electrocatalysts. ChemElectroChem. 2016;3(1):138-43. Lee DU, Park MG, Park HW, Seo MH, Ismayilov V, Ahmed R, et al. Highly active Co-doped LaMnO3 perovskite oxide and N-doped carbon nanotube hybrid bi-functional catalyst for rechargeable zinc-air batteries. Electrochem Commun. 2015;60:38-41. Zhao BT, Zhang L, Zhen DX, Yoo S, Ding Y, Chen DC, et al. A tailored double perovskite nanofiber catalyst enables ultrafast oxygen evolution. Nat Commun. 2017;8. So IS, Kim NI, Cho SH, Kim YR, Yoo J, Seo Y, et al. Enhancement of Bifunctional Activity of the Hybrid Catalyst of Hollow-Net Structure Co3O4 and Carbon Nanotubes. J Electrochem Soc. 2016;163(11):F3041-F50. Kim NI, Afzal RA, Choi SR, Lee SW, Ahn D, Bhattacharjee S, et al. Highly active and durable nitrogen doped-reduced graphene oxide/double perovskite bifunctional hybrid catalysts. Journal of Materials Chemistry A. 2017;5(25):13019-31.

Rapidly increasing levels of atmospheric carbon dioxide and their damaging impact on the global climate system raise doubts about the sustainability of the fossil resource based energy system. Meanwhile, raising living standards and increasing global population lead to an ever growing need for energy. Renewable energy sources are believed to present a solution to these problems with the sheer abundance of solar energy showing particular promise to fulfill the world's energy needs. However, for large scale application of solar energy to be possible, the problem of its storage has to be addressed. The insufficient flexibility of present-day storage technologies has led to the quest for producing solar fuels, centering on hydrogen as a fuel in a prospective hydrogen economy. Nevertheless, the gaseous state, low volumetric energy density and explosive nature of hydrogen makes it a challenging fuel for practical applications. Using solar energy to produce carbon-based liquid fuels solves these challenges, closes the anthropogenic carbon cycle and allows for the continued utilization of existing infrastructures. A promising method for the production of such fuels consists in the photoelectrochemical and electrochemical conversion of carbon dioxide. In this thesis, both methods are investigated using molecular homogeneous catalysts and heterogeneous systems. The photoelectrochemical reduction of carbon dioxide on TiO2-protected Cu2O photocathodes was investigated using a rhenium bipyridyl catalyst in solution. Important charge transport limitations were encountered, which could be overcome by the addition of protic additives to the electrolyte. Improving on this result, the molecular catalyst was covalently immobilized on the TiO2 surface of the photocathode by modifying the bipyridyl ligand with a phosphonate binding group. A nanostructure of TiO2 was needed to support sufficient catalyst to sustain the photocurrent generated by the Cu2O photoelectrode. The complete device showed photocurrents exceeding 2.5 mA cm-2 and large faradaic efficiency for the production of CO. Moving toward heterogeneous catalysis, the promotion of the CO2 to CO conversion reaction on silver surfaces by imidazolium cations was investigated. Replacing the imidazolium C2 proton with a phenyl substituent led to an enhancement of the co-catalytic effect. Replacing the C4 and C5 protons with methyl groups, however, suppressed the catalysis-promoting effect of the imidazolium salt for different C2 substituents and led to new insights into the role of imidazolium. The unassisted solar-driven splitting of CO2 into CO and O2 was demonstrated using water as electron source. This was achieved by the use of a porous gold cathode and an IrO2 anode, driven by three methylammonium lead iodide perovskite solar cells in series. Extended operation over 18 h was shown, achieving a solar to CO efficiency exceeding 6.5 %. Atomic layer deposition (ALD) modification of CuO nanowire cathodes with SnO2 was investigated, leading to striking impacts on the catalytic selectivity of this system. In an aqueous electrolyte, bare CuO led to the production of a wide spectrum of products, which was modified to the production of CO with high selectivity upon ALD modification. By exploiting the oxygen evolving activity of SnO2-coated CuO, a low cost bifunctional system was constructed, achieving sustained solar-driven production of CO with up to 13.4% efficiency.

The existing natural gas transportation pipelines can withstand a hydrogen content of 0 to 50%, but further research is still needed on the pathways of NO and CO production under moderate or intense low oxygen dilution (MILD) combustion within this range of hydrogen blending. In this paper, we present a computational fluid dynamics (CFD) simulation of hydrogen-doped jet flame combustion in a jet in a hot coflow (JHC) burner. We conducted an in-depth study of the mechanisms by which NO and CO are produced at different locations within hydrogen-doped flames. Additionally, we established a chemical reaction network (CRN) model specifically for the JHC burner and calculated the detailed influence of hydrogen content on the mechanisms of NO and CO formation. The findings indicate that an increase in hydrogen content leads to an expansion of the main NO production region and a contraction of the main NO consumption region within the jet flame. This phenomenon is accompanied by a decline in the sub-reaction rates associated with both the prompt route and NO-reburning pathway via CHi=0–3 radicals, alongside an increase in N2O and thermal NO production rates. Consequently, this results in an overall enhancement of NO production and a reduction in NO consumption. In the context of MILD combustion, CO production primarily arises from the reduction of CO2 through the reaction CH2(S) + CO2 ⇔ CO + CH2O, the introduction of hydrogen into the system exerts an inhibitory effect on this reduction reaction while simultaneously enhancing the CO oxidation reaction, OH + CO ⇔ H + CO2, this dual influence ultimately results in a reduction of CO production.

Ferrite is a porous material, which is a common catalyst in many chemical processes. α-Fe2O3(d=5μm) was used to oxidize CO in novel, and CO could be oidized to CO2. Commercial α-Fe2O3 (d < 45μm, RdH) was used in this study to evaluate the efficiencies of simultaneous reducing NO and oxidizing CO by packed bed reactor. There were four reaction parameters in this study： reaction temperature、NO influent、CO influent and α-Fe2O3 dosage. Possible reaction steps were investigated by reacted Fe2O3XRD spectrum. The NO removal efficiency was low in the initial, but NO removal efficiency increased when the reduced iron site by CO increased on the ferrite’s surface. NO and CO removal efficiencies would achieve steady states until operating for awhile. CO reacted efficiency was linearly correlated with reaction temperature. Reaction temperature from 623 K increased to 773 K, CO reacted efficiency from 19% increased to 55%. NO removal efficiency was linearly correlated with reaction temperature only in 623~673 K. The ratio of CO removal molar rate and NO removal molar rate (RNO/RCO) remained constant in 648~773 K, RCO was the major parameter of NO removal efficiency. NO removal efficiency were over 95% in NO influents 240~720 ppmv, and CO reacted efficiency increased to 73% from 55%. NO influent over 720 ppmv, NO removal efficiency decreased but CO reacted efficiency didn’t change. The ratio of CO conversion and NO conversion (XCO/XNO) was linearly correlated with NO influent. NO removal efficiency was only 4.45% in CO influent 955 ppmv, it was assumed the reduced iron site by CO was not sufficient to provide NO reducing in low CO influent environment. NO efficiency increased to 95% when CO influent increased to 1910 ppmv or above. RCO was higher in higher CO influent, but RNO remained stable. It could be considered the increasing reduced iron by CO oxidized didn’t participate NO reduction reaction, the reduced iron must have another reaction steps in the system. XCO was 27.67% and XNO was 58.61% at α-Fe2O3 dosage 0.5g, there were no sufficient sites for rteactions in this dosage obviosly. The dosage increased from 2g to 3g, XCO remained 53% ~55%, XNO both were 96%. α-Fe2O3 dosage over 2g was excess in the system, the efficiencies could not be increased when dosage increased. XRD (X-Ray Diffraction) was conducted to analyze the crystal structure and oxidation state of the reacted Fe2O3. It is considered carbon monoxide reduced Fe3+ ion of Fe2O3 to Fe2+, nitric oxide oxidized Fe2+ back to Fe3+ ion, Fe2O3 is a catalyst in the reaction. But the molar rate of carbon monoxide and nitric oxide were not equal, carbon monoxide also consumed a part of Fe2+ to Fe0.

Motivated by the population growth, climate change and limited fossil fuel resources, renewable alternatives for fuels and chemicals production are becoming more and more important. Biomass, especially residual lignocellulosic biomass shows a significant potential as feedstock for bioenergy, due to its high carbon content and short-term availability. Among the thermochemical conversion technologies, fast pyrolysis for biomass liquefaction can be considered already well stablished, as several commercial plants are spread worldwide. However, fast pyrolysis bio-oil, the main product of fast pyrolysis, currently shows limited bioenergy application as boiler fuel for heat production. It can be explained by its chemical composition and properties, as fast pyrolysis bio-oil is an acidic multi-component product, with low energetic density due to its high content of water and oxygenated compounds. Moreover, wood is the only feedstock currently used commercially. In order to expand the feedstock range and application viability, an additional upgrading treatment may be required in order to improve the fast pyrolysis properties, meeting existing fuel standards. In order to do so, catalytic hydrotreatment is considered a promising upgrading treatment, as it is a well-known technology currently applied in petroleum refineries for heteroatoms removal from crude oil. However, due to the differences in chemical composition, the hydrotreatment conditions applied to crude oil cannot be simply applied to fast pyrolysis bio oil. Although research in this field has been carried out for a few decades, there are still open questions to enable hydrotreatment to produce fuel oils from residual biomass in stable processes. By developing a robust fast pyrolysis bio-oil hydrotreatment process, small biorefineries units could be installed near to feedstock sourcing or even be installed in biorefinery units already stablished, such as a sugarcane biorefinery, in which high volumes of residual biomass are generated. Also, co-processing of crude oil and fast pyrolysis bio-oil in petroleum refineries may be a feasible option. In view of the importance of the hydrotreatment for expansion of the range of chemicals obtained by thermochemical conversion of residual biomass, the presented work investigated the hydrotreatment of fast pyrolysis bio-oil applying nickel-based catalysts. In a systematic evaluation nickel-based catalysts with different metal loading, supports and promoters have been studied. Overall, six nickel-based catalyst were screened and compared to ruthenium supported in activated carbon. The hydrotreatment conditions in terms of reaction time, temperature and pressure were optimized and fast pyrolysis bio-oils derived from beech wood and residual biomass (sugarcane bagasse) were hydrotreated. Additionally, the heavy phase separated from beech wood bio-oil, characterized by its high content of lignin-derived compounds, was hydrotreated. The effect of deactivation by sulphur on the hydrotreatment was investigated by use of model substances in a continuously operated trickle bed reactor, since with this reactor the deactivation can be observed depending on time (in contrast to batch experiments). Finally, a 2 step upgrading approach of a previously upgraded fast pyrolysis bio-oil was proposed and verified. Initially two high loaded nickel-based catalysts (monometallic nickel and nickel chromium) were evaluated in comparison to Ru/C by batch hydrotreatment of beech wood bio-oil at 80 bar, 4 h, 175 °C and 225 °C. Both nickel-based catalysts revealed similar hydrodeoxygenation activities for the conditions applied and the nickel catalysts showed the higher hydrogenation activity compared to Ru/C. The nickel-chromium catalyst demonstrated the highest activity for conversion of organic acids, ketones and sugars, attributed to the strength of the acid sites promoted by chromium oxide. When applied in a second hydrotreatment step of a previously upgraded oil, the oxygen content of the oil was reduced by 64.8 % in comparison to the original feedstock while the water concentration was reduced by 90 %. Nearly 96 % of the organic acids were converted and the higher heating value was increased by 90.1 %. Despite nickel-chromium demonstrated the best activity in the one step hydrotreatment reactions and contributed significantly in the 2-step upgrading, the oxygen content of 25.3 wt.% dry basis in the upgraded oil was still considered high. Thus, the upgrading conditions were further optimized, aiming to achieve higher hydrodeoxygenation performance. The conditions of batch hydrotreatment were optimized with nickel-chromium catalyst considering two pressures (80 and 100 bar), four temperatures (175 °C, 225 °C, 275 °C and 325 °C), for both the complete beech wood fast pyrolysis bio-oil, as well as for the heavy phase after spontaneous separation induced by intentional ageing of the bio-oil. At higher temperatures, increased hydrodeoxygenation levels were reached, while at higher pressure larger hydrogen consumption was observed with no significant influence on hydrodeoxygenation. The best conditions among all tested was obtained by hydrotreating the beech wood bio-oil at 325 °C and 80 bar; in this case, 43 % of hydrodeoxygenation was reached. Although improved hydrodeoxygenation activity observed with nickel-chromium at optimized conditions, the results motivated the synthesis and evaluation of new nickel-based catalysts, targeting higher deoxygenation levels. In the next part of this study, four nickel-based catalyst were synthesized by wet impregnation and evaluated for the hydrotreatment of beech wood fast pyrolysis bio-oil. The catalysts were supported in silica and zirconia and the influence of copper as promoter was studied. Among them, nickel-silica was the most active for hydrodeoxygenation, reducing the oxygen content of the upgraded beech wood fast pyrolysis bio-oil by more than 50 %. The highest degree of water removal as well as low gas and char production were also considered good properties attributed to this catalyst. The investigation on repeated cycles of hydrotreatment with the same catalyst showed a remaining activity even after the fourth reuse, in which 43 % of oxygen was removed. Thus, based on the results obtained with Ni/SiO2, this catalyst was selected together with nickel-chromium catalyst to be used for hydrotreatment of fast pyrolysis bio-oil from residual biomass, as until this point the study had considered only wood-based fast pyrolysis bio oil. Based on the studies so far, the integration of hydrotreatment into a thermochemical conversion route of residues in a sugarcane refinery was proposed. For that, the study encompassed sugarcane bagasse characterization, fast pyrolysis and hydrotreatment of the so derived bio-oils with nickel-chromium and nickel-silica catalyst. The detailed investigation of the bagasse and the fast pyrolysis bio-oil compositions allowed the correlation of the biomass building blocks with the monomers obtained. The hydrotreatment showed that nickel-chromium showed highest activity for organic acids conversion, as previously observed with beech wood bio-oil, whereas nickel-silica revealed more active for conversion of aromatics. Hydrodeoxygenation of 43.3 % was obtained with nickel-silica. Although both catalysts demonstrated to be active at the conditions evaluated, the high viscosities of the upgraded oils in comparison to those obtained from fast pyrolysis showed that polymerization took place and must be further investigated in detail, as it is one of the limiting factors for further application of fast pyrolysis bio-oil hydrotreatment. Overall, this studied showed to be very promising and future studies are planned. In the final part of the thesis, both high loaded nickel-based catalysts studied in the first chapters were selected for a detailed investigation in a continuous operated tricked bed hydrotreatment reactor, due to the similar nickel concentration, nickel particle size and support. The selection of both catalysts aimed to investigate the influence of sulfur on long term catalyst deactivation and the role of chromium in catalyst deactivation. Both catalysts were active for conversion of model substances over more than 48 h of reaction time. By the presence of sulfur, the selectivity of both catalysts changed, mainly towards alkene formation, while the activity remained in the same range. Formation of Ni3S2 was observed for both catalysts, but the highest intensity in the diffraction peak of metallic nickel in the nickel-chromium catalyst might be an indication of higher resistance to sulfur poisoning in comparison to Ni catalyst. In general, the catalysts were active for the conditions tested, although the hydrogenation activity was compromised by sulfur poisoning. Overall, all the catalysts tested in this study were active for hydrotreatment of fast pyrolysis bio-oils. If only stabilization of reactive compounds such as aldehydes and furfurals is required, all of them could be considered suitable candidates. In terms of hydrodeoxygenation activity, Ni/SiO2 showed the highest performance, while nickel-chromium showed to be the most active for conversion of organic acids and superior hydrogenation capacity than Ni/SiO2.

Achieving CO2 reduction with H2O on metal photocatalysts and understanding the corresponding mechanisms at the molecular level are challenging. Herein, we report that quantum-sized Au nanoparticles can photocatalytically reduce CO2 to CO with the help of H2O by electron-hole pairs mainly originating from interband transitions. Notably, the Au photocatalyst shows a CO production rate of 4.73 mmol g−1 h−1 (~100% selectivity), ~2.5 times the rate during CO2 reduction with H2 under the same experimental conditions, under low-intensity irradiation at 420 nm. Theoretical and experimental studies reveal that the increased activity is induced by surface Au–O species formed from H2O decomposition, which synchronously optimizes the rate-determining steps in the CO2 reduction and H2O oxidation reactions, lowers the energy barriers for the *CO desorption and *OOH formation, and facilitates CO and O2 production. Our findings provide an in-depth mechanistic understanding for designing active metal photocatalysts for efficient CO2 reduction with H2O.

Silver-based catalysts have been exten sively investigated as the platinum substituted catalysts due to their high catalytic efficiency,low cost and long-term durability.In this study,the surfactant-free silver nanoparticles supported on graphene quantum dots were synthesized through a facile approach without addition of any other protecting ligands and reducing agents.The"surface-clean" silver nanoparticles had remarkable electrocatalytic performance towards oxygen reduction reaction(ORR) with the most efficient four-electron transfer process.Compared with commercial Pt/C catalyst,the hybrid nanoparticles showed comparable catalytic performance for ORR but much higher tolerance to methanol.Such silver nanoparticles supported on graphene quantum dots may have promising applications in alkaline fuel cells as an efficient Pt-free catalyst with high catalytic performance and low cost.

The electrocatalytic CO 2 reduction reaction (CO 2 RR) holds great promise for converting CO 2 into value‐added fuels and mitigating global carbon emissions. Electrocatalysts play a pivotal role in enhancing reaction efficiency, reducing overpotential, and improving product selectivity, making them the core of CO 2 RR research. This review systematically summarizes recent advances in CO 2 RR electrocatalysts, focusing on the structure‐performance relationships and optimization strategies. Noble metal catalysts exhibit excellent catalytic activity and stability, but their high cost limits large‐scale applications; nanostructuring and element doping have been developed to improve their efficiency and reduce usage. Transition metal complex catalysts show great potential due to their low cost and high performance, with optimization approaches including coordination structure design, nanostructure engineering, and bimetallic alloying to regulate active sites and electron transfer. Carbon‐based materials, including modified carbon, biomass‐derived carbon, and MOF‐derived carbon, have emerged as cost‐effective alternatives, with heteroatom doping and defect engineering being key to enhancing their catalytic activity. By integrating the latest research on catalyst design, modification, and mechanism exploration, this review aims to provide comprehensive insights for developing high‐efficiency, low‐cost CO 2 RR electrocatalysts, promoting their practical application in carbon neutrality and sustainable energy conversion.

This project studies the conversion of CO2 into fuels and chemicals in a dielectric barrier discharge (DBD) reactor. CO2, H2 and CH4 have been used as reactants, and special attention has been paid on understanding the plasma-catalytic synergy when a catalyst is placed in a plasma discharge. CO2 and CH4 are major greenhouse gases, responsible for the global greenhouse effect and climate change. The overall aim of this project is to initiate CO2 hydrogenation and biogas reforming at ambient temperature and atmospheric pressure by using plasma-catalysis. In this project, non-thermal plasma has been generated in a DBD reactor with and without a packed-bed of catalyst, enabling the CO2 conversion to be investigated under three conditions: Plasma alone, thermal catalysis and plasma-catalysis. Transitional metal catalysts such as Cu, Co, Mn, and Ni supported on Al2O3 and SiO2 have been screened, and their performance in the CO2 hydrogenation and biogas reforming have been compared under the three conditions. The synergy between non-thermal plasma and catalysts has been clearly identified. The effects of a catalyst’s properties and operational parameters on the reactions have also been studied. The project starts by the investigation of CO2 hydrogenation with H2. Results showed that reverse water-gas shift reaction and CO2 methanation were dominant in the plasma CO2 hydrogenation process. Compared to plasma CO2 hydrogenation without a catalyst, the combination of plasma with Cu/Al2O3, Mn/Al2O3 and Cu-Mn/Al2O3 catalysts enhanced the conversion of CO2 by 6.7% to 36%. The Mn/Al2O3 catalyst showed the best catalytic activity, as it increased the CO yield by 114% and the energy efficiency of CO production by 116%. The Ni/Al2O3 was even better than the Mn/Al2O3 catalyst, while its presence in the DBD reactor has clearly demonstrated a plasma-catalytic synergy at low temperatures. In addition, the introduction of argon in the reaction has enhanced the conversion of CO2, the yield of CO and CH4 and the energy efficiency of the plasma process. The formation of metastable argon (Ar*) in the plasma has created new reaction-routes which made a significant contribution to the enhanced CO2 conversion and CH4 yield. Biogas reforming has also been initiated at ambient temperatures by non-thermal plasma. The combination of plasma with the Co/Al2O3, Cu/Al2O3, Mn/Al2O3 and Ni/Al2O3 catalysts significantly enhanced CH4 conversion and showed a plasma-catalytic synergy for CH4 conversion and overall energy efficiency of the process. The best CH4 conversion of 19.6% and syngas production have been achieved over the Ni/Al2O3 catalyst at a discharge power of 7.5 W and a gas flow rate of 50 ml min-1. Moreover, the addition of K-promoter into the catalyst has further improved the performance of the Ni/Al2O3 catalyst. A conclusion of the findings of this project and outlook for further work is presented in Chapter seven, where it is concluded that non-thermal plasma has initiated the CO2 hydrogenation and biogas reforming at lower temperatures, comparing with thermal catalytic processes. The combination of plasma and catalyst has further improved the performance of the hydrogenation processes, in terms of conversion, yield, and energy efficiency, while significant synergy between DBD plasma and catalysts has been observed. By upgrading the catalyst and adjusting the operational parameters (e.g. molar ratio of feed gas, preparation method of catalyst, composition of catalyst, and promoters), the plasma-catalytic CO2 hydrogenation and biogas reforming processes can be further optimised.

Antibody-drug conjugates (ADC) constitute a groundbreaking advancement in the field of targeted therapy. In the widely utilized cysteine conjugation, the cytotoxic payload is attached to reduced interchain disulfides which involves a reduction of the native monoclonal antibody (mAb). This reaction needs to be thoroughly understood and controlled as it influences the critical quality attributes (CQAs) of the final ADC product, such as the drug-to-antibody ratio (DAR) and the drug load distribution (DLD). However, existing methodologies lack a mechanistic description of the relationship between process parameters and CQAs. In this context, kinetic modeling provides comprehensive reaction understanding, facilitating the model-based optimization of reduction reaction parameters and potentially reduces the experimental effort needed to develop a robust process. With this study, we introduce an integrated modeling framework consisting of a reduction kinetic model for the species formed during the mAb reduction reaction in combination with a regression model to quantify the number of conjugated drugs by DAR and DLD. The species formed during reduction will be measured by analytical capillary gel electrophoresis (CGE), and the DAR and DLD will be derived from reversed-phase (RP) chromatography. First, we present the development of a reduction kinetic model to describe the impact of reducing agent excess and reaction temperature on the kinetic, by careful investigation of different reaction networks and sets of kinetic rates. Second, we introduce a cross-analytical approach based on multiple linear regression (MLR), wherein CGE data is converted into the RP-derived DAR/DLD. By coupling this with the newly developed reduction kinetic model, an integrated model encompassing the two consecutive reaction steps, reduction and conjugation, is created to predict the final DAR/DLD from initial reduction reaction conditions. The integrated model is finally utilized for an in silico screening to analyze the effect of the reduction conditions, TCEP excess, temperature and reaction time, directly on the final ADC product.

The electrochemical reduction of CO2 is a promising approach for achieving a closed carbon cycle. An increase in the current density is essential for the practical implementation of this technology. As CO2 electrolysis technology for CO production is approaching industrial practicality, there is now an increasing demand for electrolysis technologies that convert the produced CO into higher-valued multicarbon (C2+) products under high-current-density conditions. Herein, we report a substantial enhancement of the partial current density for the reduction of CO to C2+ products over Cu nanoparticles supported on gas diffusion electrodes in 1 M KOH, achieving a record value of 1.6 A cm−2 for C2+ formation at a total current density of 3 A cm−2. This high-current-density CO electrolysis was enabled by the extremely large triple-phase interface area in our electrode, which maximized CO transport. Notably, the partial current density for acetate reached 519 mA cm−2 at −1.74 V vs. Ag/AgCl, with a Faradaic efficiency of 26.0%. The selectivity for acetate in the CO reduction reaction was several times higher than that in the CO2 reduction reaction over the wide total current density range from 0.2 to 3 A cm−2. The coupling between adsorbed reduced species and gaseous CO is expected to form an intermediate for acetate. Under high CO partial pressures, the formation of this intermediate is favored in CO reduction reactions over CO2 reduction reactions. In addition, high-current-density electrolysis increases the surface pH at the electrode, promoting the insertion of OH− into the adsorbed precursor, thereby facilitating acetate formation, as suggested by the analysis of the simulated surface pH.

Pt/C catalysts supported on carbon (5 wt.% Pt) synthesized by photo-deposition and impregnation methods were electrochemi- cally evaluated in the oxygen reduction reaction. Platinum nanoparticles were prepared by photo-irradiation of Pt precursors (H2PtCl6 and C10H14O4Pt) with UV-irradiation (365 nm) at room temperature. The photo-reduction of H2PtCl6 to metallic platinum (Pt4+→Pt2+→Pt0) was faster than C10H14O4Pt (Pt2+→Pt0) at the same operation conditions. The Pt/C samples were characterized by XRD, EDS, H2 chemisorption, TEM, cyclic and linear voltammetry techniques. XRD and TEM/EDS studies showed that Pt particles synthesized with C10H14O4Pt by the photo-deposition method were smaller with a higher dispersion on carbon than those prepared with H2PtCl6. A similar behavior was found when the impregnation method is used. The platinum particle size was smaller with C10H14O4Pt as compared to H2PtCl6 precursor. The Pt/C catalyst synthesized with C10H14O4Pt by the photo-deposition method displayed a catalytic activity in the oxy- gen reduction reaction comparable to a commercial 10 wt. % Pt/C, ETEK catalyst.