The transition to zero-carbon fertilizers challenges conventional ammonia production via the Haber-Bosch process. Electrochemical ammonia synthesis offers a sustainable alternative using only water, electricity, and nitrogen from waste streams such as nitrate and NOx. This dissertation employs a polymer electrolyte membrane (PEM) electrolyzer and addresses key cost and efficiency drivers through catalyst design, mechanistic analysis, and cell-level engineering.

Ru/C catalysts were optimized with polyvinylpyrrolidone (PVP), reducing Ru loading from 40 to 10 wt.% while enhancing NH₃ faradaic efficiency, electrochemical surface area, hydrogen binding, and wettability. Earth-abundant MoS₂ catalysts were phase-engineered to steer proton-electron transfer pathways for selective NO reduction. A CO-mediated poisoning strategy was developed to suppress the competing hydrogen evolution reaction, improving NH₃ selectivity.

Proof-of-concept C–N coupling for urea synthesis from bicarbonate and nitrate was demonstrated using gas-diffusion electrodes. Finally, a novel operando ATR-IR cell was designed to probe reaction mechanisms under realistic conditions, bridging the gap between batch-cell studies and PEM electrolyzer operation. ... Read more

Current society is challenged with climate change and aims to adapt and improve to mitigate climate change. This is an extremely challenging transition that requires a paradigm shift from our current fossil fuel driven world to a primarily renewable electricity based one. Increasing the electricity generation alone would not be sufficient, as balance between supply and demand is required. Solar and wind power are intrinsically intermittent with strong diurnal and seasonal variations. 

Therefore, the need arises for electricity storage to compensate for intermittence. Within this thesis we focus on the combined system that can handle both situations, the Ni-Fe alkaline battery and electrolyser. Previously the Ni-Fe battery suffered from limited round-trip efficiency due to hydrogen and oxygen generation. However, when utilized within an integrated electrolysis application, the gas production is intentionally applied for long-term energy storage.
So, within chapter 4, we aimed at improving the Ni electrode by reducing the amount of required nickel, while also improving both electrolyser and battery properties. Depending on the amount of copper substitution, a significant improved electrochemical activity can be obtained. In addition, the Cu doped nickel hydroxide showed stability for over 1000 cycles with the amount of dopant reduced to Ni_0.95Cu_0.05(OH)₂. Overall, this would thus result in requiring 40% less nickel for the same observed capacity.
 
In addition to decarbonizing the electricity production, it is mandatory to replace current industrial processes that require fossil fuel and feedstock with renewable energy and feedstock based alternative processes. Within this Thesis we focused on the oxidation of ammonia to nitrite and nitrate. These products are mainly applied within the synthetic fertilizer production. Ammonia oxidation to nitrites and nitrates is currently performed in the Ostwald process with Pt/Rh gauze. As the ammonia electrooxidation is feasible in ammonia fuel cells, electrochemical oxidation could have potential for replacement of this thermal Ostwald process.
Therefore, in chapter 2, we focus on applying the doped nickel hydroxide materials to increase the performance for ammonia oxidation to nitrate and nitrite. Co, Mn and Cu as dopants showed promising results. Furthermore, it became clear that the reaction was dependent on e Ni(II)/Ni(III) equilibrium as the reaction also occurs through indirect oxidation via the charged NiOOH phase. Under continuous operation at 25 mA/cm² a high faradaic efficiency is obtained with a 97% NO₂^-:NO₃^- selectivity. 

The above sparks interest in further investigation of NiCu_0.2 as promising catalyst in chapter 3, while taking into account the significant of the setup layout. The setup contains a Nafion 117 membrane to keep the counter electrode and nitrite separate, as it would otherwise result in reduction of the nitrite to nitrogen gas or back to ammonia. The Ni_0.8Cu_0.2(OH)₂ can perform ammonia oxidation, with limited oxygen evolution, from 2.5 up to 400 mA/cm². At high initial ammonia concentration of 1 M, more than 75% was able to be converted in 3 hours at this 400 mA/cm² with a faradaic efficiency of 96%. Thus, this work reveals a potential approach for replacing the Ostwald process with electrochemistry within the near future.
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Since the industrial revolution in the 1760s, the CO2 concentration in the atmosphere has been rising incessantly driving global warming closer to the point of no return. The world requires urgent actions to not only reduce CO2 emissions but also capture the CO2 for utilization to mitigate the future environmental crisis. CO2 hydrogenation to CH3OH offers an alternative to produce a feasible and economic substitute for oil. This technology also resembles the nearly 100 years old CH3OH synthesis processes from syngas containing H2, CO, and CO2. The conventional Cu/ZnO/Al2O3 catalyst has also been applied for more than 50 years, and its high performance stems from synergies between Cu and ZnO. However, the true nature of the interfacial sites is still extensively debated. Moreover, lower temperature and higher pressure are thermodynamically favorable for maximum CO2 conversion and CH3OH selectivity according to Le Châtelier’s principle and beneficial in terms of energy consumption and catalyst stability against sintering. The limitation in the catalytic performance of Cu/ZnO/Al2O3 in such conditions demands the exploration of novel catalysts.

Part I of this dissertation is dedicated to gaining a deeper understanding of Cu-ZnO synergistic structure as well as other Cu-based catalysts. In Chapter 2, we proposed a greener synthesis route for Cu/ZnO catalysts via urea hydrolysis of acetate precursors that can achieve comparable activity to commercial Cu/ZnO/Al2O3 catalysts without producing wastewater. Co-precipitated Cu-Zn hydroxycarbonate mineral-like precursors are crucial for a high inter-dispersion between CuO and ZnO after calcination and providing Cu-ZnO interfacial sites for the reaction. In Chapter 3, the effects of key process conditions, namely temperature and pressure, on CO2 hydrogenation over a commercial Cu/ZnO/Al2O3 catalyst were investigated using a space-resolved study. The gradients of reactants/products concentration and catalyst bed temperature within the catalytic reactor can reveal the significant effect of temperature on the dominant reaction pathways. CH3OH is formed through direct CO2 hydrogenation at low temperatures, while CH3OH formation is mediated via CO which is formed by a reverse water–gas shift reaction at a high temperature. Although pressure did not influence the reaction pathway, higher pressure helped suppress CH3OH decomposition to CO. In Chapter 4, the decisive roles of peripheral promoters to Cu nanoparticles in promoting CH3OH selectivity were elucidated. The model Cu-based catalysts (Cu-M/SiO2, M = Zn, Ga, and In) were prepared via surface organometallic chemistry (SOMC). The M+ sites played important roles in stabilizing formate species spillovered from Cu and determining the reactivity of formate hydrogenation. Improving the spillover and tuning the reactivity of formate help suppress formate decomposition to CO over Cu and ultimately boost CH3OH selectivity.

Part II is dedicated to exploring the novel catalysts for low-temperature CO¬2 hydrogenation, as well as, gaining a deeper understanding of the state-of-the-art Re/TiO2 catalyst. In Chapter 5, the bifunctionality of Re supported on TiO2 was deciphered, where metallic Re functions as the H2 activator and cationic Re as the CO2 activator. Re/TiO2 suffers from additional CH4 formation, and the active intermediates and reaction pathways for CH3OH and CH4 were identified. Understanding the nature of active sites and reaction mechanisms over Re/TiO2 led to approaches for CH4 selectivity mitigation in Chapter 6. Exploring various transition metals under low-temperature conditions provided insights into the formate stabilization of the coinage metals (Cu, Ag, and Au). Since the balance between metallic and cationic Re limited the CH3OH selectivity of Re/TiO2, the addition of Ag complemented the role of cationic Re. A synergistic interplay between Ag and Re did not only improve CH3OH selectivity significantly by suppressing intermediates in the reaction pathways toward CH4 but also exhibited superior stability.

Finally, the dissertation conveys a message that obtaining the definitive synthesis of well-defined active sites, expansive structure-activity relationships, and comprehensive reaction mechanisms are the major prerequisites for the rational design of novel catalysts.
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CH4 and CO2 are ideal candidates in the context of C1 chemistry as alternatives to oil-based feedstocks for chemicals and fuels production, due to their abundancy, low cost and potential to develop a closed carbon cycle.

Large scale utilisation of CO2 in the chemical industry is currently limited to a few applications (e.g. synthesis of urea, carboxylic acids, food industry) and generally requires high purity feedstock. Integrated processes that combine CO2 capture from diluted sources (e.g. industrial flue gases, air) and its conversion to value-added chemicals represent a solution to enhance the utilisation of CO2 and mitigate its emissions. CH4 is an abundant hydrocarbon with diversified sources ranging from fossil-based (natural gas, shale gas) to renewable ones (biomass, biogas), which can potentially substitute oil for the synthesis of valuable chemicals and fuels, including higher hydrocarbons. At the moment, however, CH4 utilisation is circumscribed to combustion for heat and energy production or energy-intensive production of H2 and syngas (H2 + CO) via steam reforming, resulting in a high carbon footprint.

In general, the thermodynamic stability of CO2 and CH4 molecules imposes severe limitations to their exploitation as chemical feedstocks, in terms of low conversion efficiencies and control on the selectivity of products. Their efficient conversion requires harsh reaction conditions (high temperatures and pressures, highly chemically reactive substances) at which the stability of the desired products is threatened, resulting in low selectivity. In this scenario, catalysis is essential to identify functional materials and develop new catalytic processes able to maximise the selective conversion of CO2 and CH4 feedstocks to value-added products.

Unsteady-state operation in catalysis is an option to overcome the thermodynamic constraints imposed by the conventional steady-state operation. Integrated CO2 capture and conversion, sorption-enhanced reactions, chemical looping combustion are examples of intrinsically unsteady-state catalytic processes that demonstrated enhanced performances compared to their steady state analogues. Moreover, the analysis of the transient catalytic behaviour developed in unsteady-state conditions leads to a deeper understanding of the catalytic processes in terms of identification of specific reactant-catalyst interactions, the steps involved in products formation and the mechanism of catalyst deactivation.

This dissertation deals with the catalytic activation of CO2 and CH4 molecules targeting at their valorisation to important chemical commodities as CO (syngas) and light hydrocarbons. Unsteady-state catalysis is explored as a means to overcome thermodynamic constraints associated to the conventional CO2 and CH4 conversion routes.... ... Read more

Capturing and utilizing the emissions of CO₂ has become a method to reduce the occurring emissions from industrial flue gases. One of the methodologies to capture and use the CO₂ is through the CO₂ capture and reduction (CCR) process. This process uses a bi-functional catalyst to capture CO₂ from diluted gas streams and subsequently reduce it to CO in the presence of H₂. The obtained product (syngas) can be further used as feedstock in for example the Fischer-Tropsch process. To implement a novel technology in industry, the
technology itself should be economical feasible.

To determine the feasibility of the process a technoeconomical analysis is executed. The analysis uses process parameters obtained by evaluating the catalytic activity of the bifunctional catalysts. Two catalytic
systems have been evaluated: Cu-K/𝛾-Al₂O₃ and FeCrCuK/PMG20. Effect on the synthesis conditions of Cu-K/𝛾-Al₂O₃ were also investigated. Cu-K/𝛾-Al₂O₃
without additional drying steps during the synthesis shows a higher CO₂ capacity and a faster CO production rate compared to the other catalysts. Furthermore, to
estimate the H₂ requirement in an industrialized process the consumption of H2 during the process has been quantified.

To ensure a continuous process operation, a two reactor process has been proposed in the techno-economical analysis. The sizing and subsequent cost of the process equipment has been determined by utilizing the obtained process parameters. Besides the capital costs, the operating costs were also estimated to determine the profitability of the process. After the monetary benefit of selling the syngas was determined, it could be stated that the process is profitable under certain conditions. The process is profitable if the used H₂ source has a buying price below $1.8 per kilogram. If sales of allowances is possible, the buying price of H₂ needs to be below $2.4 to ensure a profitable process.

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Increasing tensions over global warming, talks about a sustainable future and a huge imbalance in closure of the carbon cycle indicate a response for developing efficient conversion of CO2 and syngas obtained from renewable sources. Thermochemical conversion of carbon oxides (CO and CO2) in combination with hydrogen to produce methanol in the presence of catalyst provides a pathway to close this carbon cycle. Steady state activity tests were carried out in a small integral reactor for methanol synthesis from a mixture of either CO/H2 or CO2/H2. The temperature was varied from 200 to 300°C, while the total pressure was held constant for CO/H2 at 85 bar and CO2/H2 at 60 bar keeping stoichiometric flow of hydrogen at GHSV of 24,000 hr¡1. Four different metal oxides namely ZnO, ZrO2,MgO and CeO2 were investigated for support effects on active Cu along with different combinations among them while keeping commercial catalyst as the benchmark. Catalysts were prepared using urea hydrolysis method. It was found that ZrO2 and MgO show higher selectivity however the latter does not exhibit comparable conversion as the commercial catalyst for CO2 hydrogenation. Detailed GHSV study for Cu-ZrO2 paint a completely different picture showing higher methanol selectivity (64%) with increasing space velocity (at GHSV of 32,000 hr¡1). In case of COhydrogenation, commercial catalyst performs the best, albeit displaying signs of carbon deposition at higher temperature (280°, 300°C). This situation is circumvented by employing ZnO/MgO combination as a support. Cu-CeO2 exhibited characteristics of an excellent water gas shift catalyst. This led to a novel configuration of mixed bed consisting of Cu-CeO2 with commercial catalyst. Results indicate that this combination improves themethanol yield by atleast 30% as compared to commercial catalyst at a high GHSV of 24,000 hr¡1. ... Read more