The development of alternative approaches to the conventional Haber–Bosch ammonia synthesis process is a very challenging task. Extrinsic stimuli such as plasma could provide greater flexibility in materials selection and process innovation for dinitrogen fixation. Hydride (hydrogen anion, H‾)-containing materials have recently shown promise in thermal ammonia synthesis, whereas the interactions of hydrides and N₂ under plasma conditions have rarely been investigated. Herein we explore plasma-assisted nitrogen fixation to NH₃ mediated by a series of alkali and alkaline earth metal hydrides. The chemical responses of these metal hydrides under nitrogen plasma differ significantly from one another. And the plasma nitrogen fixation behaviors of these hydrides are different from those observed under normal thermal conditions. NaH and KH, which cannot react with N₂ under normal thermal conditions, can fix much larger amount of nitrogen under plasma conditions as compared to others. The subsequent thermal-hydrogenation of fixed N produces NH₃ facilely. Based on these experimental observations, a plasma-thermal hybrid chemical looping ammonia synthesis process has been proposed. This hybrid ammonia loop effectively prevents NH₃ from plasma-induced cracking, a challenging obstacle to overcome in plasma-catalytic ammonia synthesis.

Ammonia has emerged as a key candidate in the global push for decarbonization, with its potential as a carbon-free fuel and hydrogen carrier. Its existing global infrastructure enables rapid deployment and large-scale integration into energy systems. Our research centers on ammonia as a future energy vector, particularly when blended with renewable fuels such as methanol, ethanol, dimethyl ether, and dimethoxymethane. These fuels not only enhance engine performance but also reduce emissions. We have extensively studied ammonia and its blends, generating experimental data under extreme pressure and temperature conditions. By integrating these data with theoretical chemistry and chemical kinetics modeling, we have gained valuable insights into the combustion behavior and fuel kinetics of ammonia-alcohol/ether blends. These insights are critical for optimizing these blends for practical applications in engines like spark ignition, which are vital to achieving a decarbonized energy future. Ammonia-renewable fuel blends present a scalable and sustainable solution, crucial for addressing the ongoing environmental crisis and meeting the increasing energy demands of a growing global population. Our work contributes significantly to developing these NH3-blends as a viable pathway toward a sustainable energy future.

This talk will present how certain materials separately manipulate electrons and hydrogen in the presence of nitrogen to create ammonia. In the first part, we will explain how group 14 clathrates, typically known for their thermoelectric properties, in fact have low work functions, making them effective Haber-Bosch catalyst supports. In the second part, as time permits, we will show how some hydride-based solids give enhanced reactivity over unusual element sites (Ti, V, Ca, etc.) and overcome the hydrogen poisoning often encountered in Ru-based catalysts.

Ammonia has received attention as an alternative hydrogen carrier and a potential fuel for thermal propulsion systems with a lower carbon footprint. However, there are numerous challenges, particularly around safety and ammonia’s energy conversion performance. One strategy for high power density in ammonia applications will be direct injection of liquid ammonia. Understanding the evaporation and mixing processes associated with this is important for model development. This presentation will focus on the challenges and opportunities for ammonia as a future energy vector for propulsion systems, in particular focusing on supporting modelling efforts. Subsequently a look ahead to future directions of research will be explored.

This presentation explains the technologies for simultaneously controlling flame stability and nitrogen oxide (NOx) emissions in the combustion of pure ammonia. Ammonia, with its inherently low burning velocity, faces significant challenges in maintaining a stable flame even under premixed combustion conditions. To address these challenges, various approaches such as hydrogen and fossil fuel co-combustion, plasma assistance, and preheating have been extensively studied. However, to fully realize the long-term potential of ammonia as a carbon-free fuel, the development of new combustor designs optimized specifically for pure ammonia is essential. This study focuses on a recently developed high-swirl tangential combustor designed to enhance flame stability in ammonia combustion. Furthermore, it analyzes the effectiveness of a newly proposed staged combustion technique that employs secondary ammonia injection for NOx reduction. Finally, the presentation briefly introduces ongoing ammonia-based research and development projects in South Korea.

Ammonia is regarded as a promising alternative fuel in internal combustion engine for its potential to reduce carbon emissions, and ammonia spray combustion technology has received intense research interests. However, key impact factors of liquid ammonia spray process and effects of combustion optimization strategy on liquid ammonia-fueled engines are still not well understood.

In this report, we presented a new spray model for liquid ammonia injection, and numerically investigated spray characteristics under diesel-engine conditions. Furthermore, large eddy simulation of ammonia-diesel high pressure injection dual fuel (HPDF) combustion mode has been performed to evaluate the applicability of exhaust gas recirculation strategy in this mode. This report will provide potential support to optimize operation strategy of liquid ammonia-fueled engines.

In future carbon-free energy systems, fuel flexibility stands as a critical requirement for the development of various combustors, encompassing applications such as gas turbines, boilers, furnaces, and stoves. This necessity arises from the diverse and evolving nature of energy sources, especially those low-carbon fuels, thus demanding adaptable combustion technologies. To address the gas turbine application of ammonia (NH3) which belongs to low-combustion reactivity and low-calorific-value fuels, a new strategy is proposed: co-firing NH3 with high reactivity fuels (such as hydrogen) and fuels with high specific properties (such as dimethyl ether and butane) to achieve methane-equivalent thermochemical properties. Tuning fuel thermochemical properties, including calorific value, Wobbe Index, and combustion characteristics, enables their direct use in existing gas fuel combustors without extensive mechanical modifications.‎

Oxide-supported transition metal catalysts are essential for numerous chemical reactions, ‎determining the efficiencies and ‎‎sustainability of many industrial ‎processes. How metals interact with gaseous reactants and support ‎underneath, i.e., metal-reactant ‎interaction (MRI) and metal-support interaction (MSI), are two cornerstones of supported metal ‎catalysts‎. MRI determines activity and selectivity‎, where the nature of the active sites and their structure sensitivity are the keys to rational design of efficient catalysts but have been debated for decades. While MSI is vital in ‎stabilizing dispersed catalysts and impacting a variety of interfacial processes, including ‎charge transfer, chemical composition, perimeter sites, particle morphology, ‎and encapsulation.‎ The significance of MSI makes its modulation one of the few strategies for enhancing catalytic ‎performance, but developing a fundamental theory has been challenging because of the intricate interfaces. To address these challenges, here, we harness the power of interpretable machine learning, domain knowledge, theoretical and experimental data to establish a general theory of MRI and MSI grounded in topological under-coordinated number, metallophilicity and oxophilicity. The theory developed applies to other metal catalysts and metal compound supports.‎

Carbon-free fuel ammonia contributes to the decarbonization of energy consumption structure. Blending ammonia with conventional carbon-based fuels can often reduce soot emission while improving the combustion performance of ammonia. Effects of adding ammonia are divided into three categories, namely dilution, thermal and chemical effects. Of these, regulation mechanism of chemical effect was the most complex. Chemical effect of added ammonia on soot formation characteristics during hydrocarbons pyrolysis was comprehensively revealed via gas-solid coupling in this work. Nitrogenous species introduced by ammonia addition firstly combined with small hydrocarbons, which led to the decrease of C2 and C4 species, and hindered the conversion of benzene to large PAHs, and available carbon necessary for soot growth was consumed. Besides, increased nitrogen content in soot particles and the presence of nitrogenous functional groups on their surface reliably proved that nitrogen-containing species can preempt the reactive sites on PAHs surface to form saturated nitrogen atoms, which reduced soot reactivity and inhibited soot surface growth, directly reflecting in the decrease of primary soot particles diameter. Future research should focus on the interactions between nitrogen-containing species and hydrocarbons lager than C3 at broad pressures, to accurately understand detailed mechanisms by which adding ammonia regulates soot emission.

Ammonia has recently gained interest as a zero-carbon fuel and a potent hydrogen vector. Ammonia suffers from low flame speed and fuel-bound NOx emissions. Recent studies have investigated the applicability of ammonia as a net-zero combustion solution. This lecture will shed light on the recent advancement of ammonia as a fuel using different innovative techniques. The potential of this fuel, along with various shortcomings and challenges will be discussed in different configurations. Particular importance will be given towards NOx formation and mitigation techniques. Research have shown that NO and NO2 emissions peaks around Φ = 0.8 – 0.9 and drops more at the rich side of combustion, whereas N2O becomes a concern below Φ = 0.7. The lecture will further discuss world’s 1^st in-situ cracker development and ammonia fed 1MW steam boiler demonstration. Finally, reflections will be made on future works and ammonia’s position in the Net Zero world.

Recent developments on gaseous ammonia/air combustion indicate that NH₃ will be an important energy vector in a carbon-neutral society by 2050. Rich-lean ammonia two-stage combustion was able to reduce NOx emissions in exhaust gas to the order of 100 ppm at 16% O₂ concentration and zero unburned NH₃ emissions. The world's first 50-kw gaseous ammonia gas turbine system was constructed in Fukushima, Japan. However, ammonia is commercially available as a liquid in high-pressure cylinders at room temperature. Therefore, it has been reported that considerable energy is consumed by the vaporizer and compressor in converting liquid ammonia to gaseous ammonia. On the other hand, high pressure is thermodynamically crucial in improving the efficiency of gas turbine systems. Therefore, ammonia gas turbines at high pressures using liquid ammonia spray combustion contribute to improving the efficiency of the entire gas turbine system, including peripheral equipment. However, when high-pressure liquid ammonia is released through a nozzle below saturation pressure, the liquid is superheated, resulting in severe flash boiling (flash spray) and two-phase mixed flow. Therefore, the numerical analysis of LNH₃ flash spray involves the gas phase (continuous phase), the liquid phase (discontinuous phase), and the interaction between the two phases. Furthermore, the resulting two-phase mixed flow has a very low temperature due to the high latent heat of LNH₃. Therefore, a preheated air stream is essential for the stable combustion of the LNH₃ spray.

As ammonia emerges as a key player in the energy transition, the efforts to unravel its fundamental behavior have intensified, aiming to enable its widespread use as an energy carrier. Although the past decade has seen impressive advances in theoretical research and kinetic modeling of ammonia pyrolysis and oxidation mechanisms, a comprehensive understanding of its chemistry has not yet been fully achieved. This lecture provides an overview of the state of the art in ammonia kinetics, discussing the theoretical and modeling challenges lying ahead, and highlighting the remaining gaps in the knowledge of its chemistry. In particular, the unsolved issues in the low-temperature chemistry of ammonia and the third-body collision efficiencies in affecting flame propagation and extinction are thoroughly discussed. Finally, the potential of combining ammonia with other carbon-neutral energy carriers is explored in order to optimize the energy portfolio, tailor blends to meet specific user needs, and enhance the fuel flexibility of combustion devices.

Distributed NH₃ production next to farmers can reduce emissions from transport, NH₃ storage volume, shortage risks, and price volatility generated by conventional world-scale production. Technologies for small-scale NH₃ production, such as plasma reactors, have been recently proposed, but the high production cost in these plants makes plasma technology not attractive. To promote this technology, the environmental benefits should be considered in decision making. In this study, we propose to estimate the environmental impacts using the life cycle assessment methodology and internalize the impacts into the estimated NH₃ production cost in Australia.  Multi-objective optimization was used to address the economic potential of distributed non-thermal plasma (NTP) plants, benchmarked to a centralized Haber-Bosch plant. The carbon emissions of centralized production were 2.6 tCO₂-eq/t NH₃, where 16% corresponded to transport. NTP plants reached a rate of -0.84 tCO₂-eq/t NH₃, using solar energy. NTP plants would produce NH₃ at $796 to $2,204 per tonne, which could decrease to $145 per tonne when internalizing the environmental benefits. If the climate change impacts of conventionally made NH₃ in Australia are accounted for, it would cost the public administration between $229 million and $5.3 billion annually, which could be used to promote cleaner technologies.

Electrides are distinguished by several key characteristics, including a low work function and strong electron-donating ability. These compounds have demonstrated significant potential in various catalytic reactions, such as ammonia synthesis, ammonia decomposition, and CO2 hydrogenation. Research into electride materials, whether experimental or computational, generally follows an empirical rule: electrides should exist within an electron-rich system where the sum of the standard oxidation states of the anions and cations is positive. Recent studies have identified a new class of electrides with electron-deficient properties, characterized by a negative sum of the standard oxidation states of anions and cations. This discovery was made through a combination of high-throughput calculations, machine learning, and experimental validation. The synthesized electron-deficient electride exhibits a promising balance between chemical stability and catalytic performance for ammonia synthesis, maintaining its effectiveness even after being washed with water for five days. Moreover, further research has demonstrated that this electron-deficient electride excels in ammonia oxidation catalysis in aqueous environments. These preliminary findings suggest that electron-deficient electrides offer new avenues for developing ammonia energy catalysts with both excellent stability and high performance.

Understanding the mechanism of NOx formation and destruction is a prerequisite for the development of effective NOx mitigation techniques in ammonia flames. Nevertheless, quantitative and spatially resolved NO/N2O concentration data in canonical laminar ammonia flames are surprisingly scarce. We developed a NO/N2O measurement method combining microprobe sampling and calibration-free mid-infrared laser absorption spectroscopy and realized spatially-resolved detection with high accuracy and large dynamic ratio. The fidelity of the method has been rigorously tested before being applied to perform a comprehensive parametric study on NO and N2O formation in NH3-CH4 co-fired burner-stabilized premixed flames. The effects of NH3 fuel ratio, equivalence ratio and flame temperature on NO/N2O formation has been experimentally determined. The present study not only provide extensive spatially-resolved NO/N2O data in ammonia flames that is urgently needed for the development and validation of NH3 combustion mechanisms, the comparison between neat CH4 and NH3-cofired also points to a fact that traditional NOx mitigation technique that are popular in combustion of hydrocarbon fuels may not be appropriate in NH3 flames. Perhaps most interestingly, the present experimental results show an oxygen-enriched oxidizer can in some cases reduce NO emission from NH3 flames.

Ammonia-fueled solid oxide fuel cell (SOFC) is a promising energy conversion technology due to its high efficiency and carbon-free characteristics. In typical nickel-based anodes, the ammonia decomposition and electrochemical oxidation are directly coupled, which determines the performance of ammonia-fueled SOFCs. In this lecture, the mechanism studies and stack integration of ammonia-fueled SOFCs will be introduced. The reaction mechanism is studied by patterned anode experiments and elementary reaction modeling. Multiscale models from the electrode, to the unit and stack are developed for understanding the coupling effect of reaction and transport processes. At last, advanced heat management strategies are proposed and compact stack integration is realized based on ammonia fuel.

Understanding fundamental mechanism of explosions of ammonia blends is important for the safe transportation and use of ammonia. Blending ammonia with high-reactivity fuels, such as hydrogen and dimethyl ether (DME), is a promising way to improve the combustion performance of ammonia. However, this leads to a higher risk of explosions since the reactivity of the mixtures is increases. While combustion and explosions of ammonia, hydrogen or DME have been scrutinized in previous work, fundamental mechanism of explosion of ammonia blended with hydrogen/DME received less attention and deserves further study. In this lecture, I will start by discussing the chemical kinetics mechanism of NH3/DME/H2 mixed combustion. Next, the lecture will show experiments of the dynamics of NH3/DME/Air premixed flames under different initial conditions. The effect of hydrogen addition on the propagation of NH3/Air and NH3/DME/Air premixed flames will be also talked. Then, I will present experimental and theoretical investigation of the explosion characteristics of NH3/DME/H2/Air premixtures. Results, that address the prediction of explosion overpressures of various low-carbon fuels such as H2, DME, and NH3/DME, will be presented.

Ammonia synthesis is one of the most important catalytic processes in the chemical industry. While Fe and Ru are efficient for N≡N bond cleavage, low cost and earth abundant elements such as Ni and Co exhibit much poorer activity due to their weak nitrogen adsorption energy. Here, we report that Ni, Co-loaded rare-earth nitride works as stable and highly efficient catalyst for ammonia synthesis along with a new mechanism. A high density of nitride vacancies is formed with low formation energy, which enables N2 activation at the vacancy sites. Consequently, the reaction rate and turnover frequency (TOF) of the nitride catalysts are quite high at 400 °C and under ambient pressure, and even comparable to those of Ru-based catalysts. Kinetic analysis and isotope experiments combined with density functional theory (DFT) calculations indicate that the nitrogen vacancies generated play a dominant role in the reaction mechanism, and contribute to both the adsorption and activation of N2 molecules. These results indicate the potential role of vacancy sites in the reaction cycles, and provide a new catalyst design concept for earth-abundant catalysts in ammonia synthesis.

Over the past two decades, there has been growing interest in developing catalysts to enable Haber-Bosch ammonia synthesis under milder conditions than currently pertain. Rational catalyst design requires theoretical guidance and clear mechanistic understanding. Recently, a spin-mediated promotion mechanism was proposed to activate traditionally unreactive magnetic materials such as cobalt (Co) for ammonia synthesis by introducing hetero metal atoms bound to the active site of the catalyst surface. We combined theory and experiment to validate this promotion mechanism on the La/Co and NbN/Co system. By conducting elaborate model catalyst studies on Co single crystals and mass-selected Co nanoparticles at ambient pressure, we identified the active site for ammonia synthesis over Co based catalysts, as well as the spin mediated promotion mechanism with promotors of different chemical states.