Ammonia exhibits some unique issues compared to other conventional fuels. Ammonia is a largely used raw material for the production of mainly fertilizers, but also other products. Because of its significantly high calorific value, despite that it does not contain carbon contrary to most of used fuels, it is considered nowadays as a promising free carbon fuel. Combustion of ammonia may be a challenge because of a number issues such as its difficulty in ignition and its tendency to form NO_x. This talk addresses how these drawbacks can be overcome, by exploring some (almost) unique issues of ammonia combustion compared to conventional fuels.

Conventional reactions are mostly driven by heat, light, and electricity. They are named as thermochemistry, photochemistry, and electrochemistry, respectively. Likewise, chemical reaction, caused by mechanical actions, is defined as mechanochemistry, which can deliver energies required to overcome reaction barriers via abrasion, friction, cracking, colliding, and so on. The most representative tool for operating mechanochemistry is ball-milling, which can offer a new tool for ammonia synthesis. To date, ammonia has mainly been produced by the Haber-Bosch process over 110 years. However, it cannot be performed under mild conditions, because of thermodynamic reasons, requiring a large centralized manufacturing facility. Ammonia as one of most efficient hydrogen carriers, a decentralized manufacturing system is urgently developed. We have discovered a new method for the synthesis of ammonia under mild conditions (45 °C and 1 bar) via mechanochemical ball-milling iron (Fe) catalyst in the presence of nitrogen and hydrogen. With this new process, the final concentration of ammonia with potassium (K) promoter has reached as high as 94.5 vol%, which is nearly 4 times higher than the state-of-art Haber-Bosch process (~25 vol%) under harsh conditions (450 °C and 200 bar). Stable nitrogen dissociation at the mild conditions is associated with mechanochemically induced high defect density and violent impact on the Fe catalyst.

This presentation explores the various intricate aspects of the ammonia value chain, encompassing life cycle assessment, energy consumption, and economic viability especially for fossil-fuel driven economies given the real need for decarbonization. Here, we consider the complete supply chain including energy consumption associated with ammonia production, storage, transportation, and utilization. A thorough economic analysis reveals the financial implications, emphasizing the competitiveness of ammonia within the international energy landscape. Through a comprehensive life cycle assessment, the environmental footprint ammonia value chain is evaluated, aiming to align with broader sustainability objectives. Utilizing Qatar as a case study, the nation's visionary roadmap for sustainable ammonia is highlighted, showcasing its strategy to harness ammonia as a central tool for both energy transition and economic transformation. This approach also aids in diversifying the range of higher value products that can be derived from fossil sources such as natural gas. The integration of renewable energy is also explored to further enhance sustainability on the path to transitioning to low-carbon ammonia solutions.

Ammonia (NH₃) has gained interest as a potential energy carrier and a carbon-free fuel during the last decade. However, NH₃ combustion presents multiple challenges, e.g., in terms of flame stability and formation of pollutant nitrogen oxide species. Experimental studies are essential to gain increased understanding of these combustion processes and non-invasive laser-based methods are highly valuable tools in such investigations. This presentation outlines development and application of laser diagnostics for characterization of NH₃ combustion under laminar, turbulent and plasma-assisted conditions. Studies of NH₃ combustion chemistry in laminar flames are presented focusing on some key species together with development of laser/based methods for their measurement. For example, nitric oxide (NO) and nitrous oxide (N₂O). Experimental results and their use in model development and validation are presented for NH₃ flames at atmospheric and elevated pressure. Premixed flames under high turbulent intensity can enter the so-called distributed reaction-zone regime characterized by a broadened reaction layer and a reduced temperature gradient across the flame. Due to the low laminar burning velocity and larger flame thickness, it is easier to achieve such conditions for NH₃ flames. Investigations of premixed NH₃ flames at high turbulent intensity are thus of interest both from fundamental and applied perspectives. This has been carried out with multi-scalar imaging of the NH radical and NO pollutant to characterize flame propagation. Different strategies can be employed to handle challenges with ignition and stability of NH₃ flames, e.g., co-combustion with hydrogen. In plasma-assisted combustion, where the flame is sustained by a pulsed discharge, the chemical reactivity is promoted by creating a non-equilibrium condition with an increased radical pool. The temporal development of this pool and interaction with the flame after discharge has been tracked in premixed laminar NH₃ flames probing species such as the oxygen atom.

With a high hydrogen content (17.6 wt.%), high energy density (4 kWh kg-1), facile storage and transportation, NH₃ has been regarded as a potential energy carrier. The key issue for NH₃ synthesis and decomposition is the development of non-noble metal based, highly active and stable catalysts that can be operated under mild condition. Reduction of dinitrogen to ammonia needs the supply of electron and proton which hydridic hydrogen H‾ could supply; the -N_xH_y intermediates, on the other hand, can be stabilized by alkali or alkaline earth metal cation to lower kinetic barriers in the transformation. The inherent properties of alkali/alkaline earth metal hydrides (denoted as AH) endow them a unique functionality in mediating ammonia synthesis. We developed AH-3d metal composites and A_xRuH₆ complex hydrides for catalytic ammonia synthesis (A = Li, Ca, Ba etc.). These electron-rich and multi-component catalysts favor non-dissociative N₂ activation and lattice hydride-involved hydrogenation. We further disclosed unique behaviors of AH under UV illumination, which enable AH catalytic functional in photo-driven ammonia synthesis.

Green power energy storage such as wind and solar energy is a major national demand to promote the realization of the dual carbon goal. Recently, hydrogen production by water electrolysis, nitrogen reduction and ammonia synthesis of carbon-free fuel has been regarded as a highly competitive green and sustainable technology route. The new thermochemical synthesis of ammonia under mild conditions (≤500 ℃, ≤7 MPa) can significantly reduce energy consumption and is expected to achieve large-scale industrial production, which is of great significance for the consumption of renewable energy such as wind and solar. Due to the extremely inert N≡N bond of nitrogen feedstock, the traditional iron-based ammonia synthesis catalyst used in coal chemical industry under high temperature and high pressure conditions (500-600 °C, 10-15 MPa) has almost no reactivity under mild conditions. The precious metal ruthenium is one of the metals with the highest activity in the synthesis of ammonia, so it is often used in the literature for the thermochemical synthesis of ammonia under mild conditions in the laboratory. However, the high price of ruthenium hinders the large-scale application of ruthenium-based catalysts in the ammonia industry. Therefore, there is an urgent need to develop high-activity, inexpensive and durable transition metal catalysts for thermochemical ammonia synthesis under mild conditions. In this paper, metal-organic framework pyrolysis, dicyandiamide autocatalytic pyrolysis, and lithium-ion intercalation-exfoliation were used to gradually reduce the ruthenium loading of ammonia synthesis catalysts, improve the utilization rate of metal atoms, and realize low-cost and high-efficiency thermochemical ammonia synthesis.

Ammonia is a promising carbon-free alternative fuel for use. The main associated challenges are its relatively low reactivity and high NOx emissions compared to conventional fuels. The co-firing strategy of blending ammonia with a more reactive combustion promoter, such as hydrogen, methane/natural gas, diesel, etc., can effectively facilitate the applications of ammonia in real engines. A detailed ammonia/hydrogen chemical kinetic model is developed over a wide range of engine-relevant conditions and comprehensively validated to describe the combustion of ammonia/hydrogen mixtures using available literature experimental data, including ignition delay times, laminar flame speeds and species concentration profiles. The new model captures very well the combustion properties of pure ammonia and ammonia/hydrogen mixtures at most conditions. The underlying chemistry controlling fuel reactivity and the formation of NOx species will be discussed. Blending ammonia with hydrocarbons leads to potential carbon-nitrogen (C–N) interaction reactions. These play an important role in governing both fuel reactivity and the ‘Thermal DeNO_x’ process of ammonia/hydrocarbon blends However, there remains uncertainties regarding their detailed reaction pathways and rate constants, hampering the development of high-fidelity chemical kinetic models. High-level theoretical kinetic investigations have been performed to determine their accurate rate constants, contributing to the continuous optimization of the ammonia/hydrocarbon chemical kinetic model.

Compared to traditional hydrocarbon fuels, ammonia presents significant challenges as a fuel, including high ignition energy, low reactivity, slow flame propagation, and high NOx emissions, which hinder its use as a renewable fuel. Blending ammonia with fossil fuels like natural gas improves its combustion reactivity and helps mitigate CO2 emissions. However, there is still much to understand about the complex dynamics of ammonia and its blends with hydrocarbons. Key areas such as reaction kinetics mechanisms, ignition properties, flame propagation behaviors, and methods for controlling combustion performance under various conditions require further elucidation. This lecture reviews recent advancements in experiments aimed at developing stable, low-emission combustors for ammonia-fired power generation. Recent burner and flame configurations, including non-swirling jets, single-stage swirl burners, and two-stage burners, are analyzed for their flame stability and pollutant emission potential with ammonia and ammonia blends.

Ammonia is a carbon free hydrogen carrier as a prospective fuel for future power devices de-carbonization, such as gas turbines and internal combustion engines. Significant efforts have been recently devoted to comprehensively understanding the fundamental combustion properties as well as combustion control techniques. This lecture starts with introduction of the recent fundamental ammonia combustion studies, including its ignition behaviors and oxidation chemistry, laminar and turbulent flames structures and turbulent flow-flame interaction. Then by using a model gas turbine combustor, ammonia flame stabilization behaviors and emission characteristics will be presented and discussed. Co-firing strategy and plasma induction on flame stabilization in swirl combustors and the combustion enhancement will also be addressed. Furthermore, a better understanding on NO_x production mechanisms and emission controls over the staged combustion on NO_x mitigation and other techniques will be revealed. Finally, future fundamental research issues and possible directions for ammonia fuels towards more robust, reliable, and low NO_x combustion technologies relevant to gas turbines will be proposed.

The pursuit of global carbon neutrality requires a transition to next-generation energy system predominantly reliant on renewable energy. In such a scenario, the combustion of carbon-free fuels such as ammonia plays an indispensable role in addressing the intermittency of the renewable energy. To phase down the usage of fossil fuels, the co-combustion of green ammonia is emerging as a competitive option in industrial boilers, gas turbines and so on. However, the distinct physicochemical properties of ammonia compared to fossil fuels (coal and natural gas) pose challenges to the large-scale utilization of ammonia due to the weakened flame stability and the elevated NOx propensity in combustion. This study examines the current advancements in the co-combustion of ammonia with fossil fuels. Fundamental research aims to elucidate the competition/cooperation mechanism of ammonia and fossil fuel in the process of rapidly mixing-ignition-steady combustion between fuel and oxidizer. Furthermore, it is necessary to develop accurate and fast numerical simulation model. For application, ammonia combustion requires precise control to manipulate the fuel-N transformation pathway. We demonstrate that, by nitrogen/hydrocarbon separation strategy, the clean and stable ammonia co-combustion with the coal and natural gas can be achieved in a wide range of ammonia blending ratios. We discussed the scaling laws of burner based on dimensionless number, and anticipate the integration of information technology such as artificial intelligence in the future will provide scientific support for the development of the next generation of green power generation system.

Ammonia, as a carbon-free hydrogen carrier, is becoming one of the key energy sources for the low-carbon development of the global economy. However, many challenges remain for its large-scale utilization, including the ammonia cracking process and the rational design of ammonia cracking catalysts. Based on this, our work focuses on the design and preparation of highly active non-noble metal nickel-based catalysts for ammonia cracking. We report Ni-CeO₂ nanocomposite catalysts and CeO₂/Ni inverse catalysts prepared by colloidal solution combustion synthesis and co-precipitation methods, respectively. Both catalysts exhibited high ammonia cracking conversion and long-term stability, which were superior to traditional supported Ni-based catalysts and even many of Ru-based catalysts reported in the literature. These unique structures enhance metal-support interaction and facilitate the breaking of N-H bond, the recombination desorption of N and H adatoms. This study highlights the importance of designing new structural catalysts with enhanced metal-support interaction for boosting ammonia cracking.

The use of fossil fuels results in significant carbon dioxide emission, posing a substantial threat to the development and safety of human society. To mitigate this issue, the use of carbon-free fuels such as ammonia should be promoted. However, ammonia combustion presents certain challenges in combustion community, such as low fuel reactivity and high NO emission. Fundamental understanding of ammonia combustion in different configurations is required to improve the design of practical combustion systems. Moreover, conventional combustion models for predicting turbulent combustion may not be valid for ammonia flames. In this talk, high-fidelity simulations have been performed to understand the underlying physics of ammonia combustion. The complex interactions between turbulence and chemistry are revealed, and the effects of turbulence on ammonia ignition and pollutant formation are explored. The modeling of ammonia turbulent combustion in the context of large eddy simulation is also focused, and new models have been proposed to improve the accuracy of ammonia combustion modeling. In addition, efforts focusing on the understanding and modeling of liquid ammonia spray and combustion have been made by benchmarking with experimental data and high-fidelity direct numerical simulation.

Only few years of intense research have transformed the lithium redox-mediated nitrogen reduction reaction (NRR) from an essentially forgotten process presenting negligible interest to the scientific community into one of the most feasible strategies for sustainable NH3 synthesis. Apart from the plasma-based methods, the Li-mediated NRR is the only currently known process that enables electrosynthesis of ammonia from nitrogen gas at practical yield rates, and it the only process providing faradaic efficiencies close to 100 %. Notwithstanding this success, a range of fundamental and practical challenges are yet to be resolved before the redox-mediated NRR can be transformed into a technology of applied significance. Among others, instability and relatively low energy efficiency, which is thermodynamically limited to approximately 33% (under standard conditions), present major concerns. The presentation will highlight key aspects of our research on the redox-mediated NRR, which aims to resolve the above key challenges, and will present our vision on feasible pathways for future evolution of research in the field. Considerations on increasing energy efficiency of the process beyond the current thermodynamic limit will be briefly discussed.

Ammonia (NH₃) is an essential feedstock for fertilizers and many other chemicals. It is also a flexible long-term energy carrier and zero-carbon fuel. Traditional ammonia production methods heavily rely on fossil fuels, resulting in significant carbon emissions. To address this challenge, the concept of “green ammonia” has emerged, aiming to produce ammonia through renewable energy sources and minimize its carbon footprint. This talk explores the potential of plasma electrification as a promising technology for decentralized green ammonia production under ambient conditions. Plasma, an ionized gas, contains a cascade of energetic electrons and reactive species, which can effectively break the triple bond of N₂ for nitrogen fixation, offering a sustainable alternative to conventional synthesis methods. Plasma processes can be switched on and off instantly, offering great flexibility to leverage intermittent renewable energy resources, such as wind or solar power, to drive the synthesis reaction and enable the decentralized production of ammonia without relying on fossil fuels. The talk will delve into the fundamental principles of plasma electrification and its unique advantages for green ammonia production. We will discuss recent advancements in plasma electrification techniques, particularly non-thermal plasma, showcasing their potential for efficient and scalable green ammonia synthesis, as well as the challenges and future prospects of plasma electrification for decentralized green ammonia production.

Ammonia is a type of high-quality energy with zero carbon emissions. Solid sorption for ammonia is an important technology to achieve efficient energy storage and conversion, but it has the disadvantages of low heat and mass transfer property, unstable sorption performance, and critical adaptability to heat source and environmental temperature. The composite solid sorption technology is researched by the matrix of conductive porous matrix. The anisotropic heat and mass transfer characteristics of thermal conductive consolidate porous matrix is revealed, and the heat and mass transfer intensification of solid sorbents are successfully realized by the anisotropic thermal conductive matrix of expanded nature graphite (ENG). The high-performance composite sorbents of halides with MOFs matrix are developed, and the non-equilibrium solid sorption kinetic models with excellent fitting characteristics are established. After that the cascading cycles with sorption concentration slip characteristics are constructed, which improved the adaptability of the technology to wide heat source temperature ranges, and the specific cooling capacity of solid sorbents is increased by 100% compared with conventional cycles. The achievements formed the novel methods for the efficient utilization of ammonia energy. Based on the achievements, the energy storage and release characteristics of solid sorption ammonia hubs will be studied in the future, which will create a new route for the large scale, safe, and efficient storage and utilization of ammonia energy. 

Hydrogen is considered an ideal zero-carbon energy and can be generated from renewable energy like wind/solar etc., but with low energy density per volume and difficulty for long-term storage. Ammonia is preferred as a suitable hydrogen carrier because of its advantages of easier liquefication, moderate energy density, suitable for long-distance transportation, and well-developed infrastructures for storage and supply. Therefore, utilizing ammonia as a carbon-free fuel become a hot topic in the combustion community. Co-firing ammonia in the existing coal-fired power plants can utilize the existing combustion facilities and reduce CO₂ emissions becomes an attractive and feasible solution. In this presentation, the fundamental research works in the area of NH₃ combustion from laminar burning velocity measurement, kinetic development, and co-firing of NH₃ with pulverized coal will be introduced. The experiments for premixed and staged NH₃/Coal co-firing strategy in an entranced flow reactor will be introduced. NH₃ co-firing performance in 135MW utility boilers will be discussed by CFD simulation. At last, the perspective and challenge of ammonia combustion in the energy system will be discussed.

In the realm of global carbon neutrality, the integrated progression of green transportation and clean energy has emerged as a significant contemporary trend. Implementing carbon reduction strategies at the source, such as employing low-carbon or zero-carbon fuels, stands out as one of the most efficacious methods to mitigate greenhouse gas emissions within the transportation domain. Green ammonia, serving dual roles as a hydrogen carrier and a zero-carbon fuel, exhibits potential for deployment in heavy-duty power equipment like trucks and ships. Nonetheless, ammonia fuel's limited reactivity poses challenges including ignition complexities, sluggish combustion, inadequate emissions, and diminished efficiency in internal combustion engines. Employing high-reactivity fuels such as hydrogen or diesel as combustion enhancers represents an effective approach to rectify the combustion and emission challenges associated with ammonia fuel. This report will give an overview of the current research status, development trends, recent advancements in combustion and emissions, persisting challenges encountered in ammonia-based engines, and finally briefly introduce forthcoming development trends.

Ammonia (NH₃) as a promising carbon-free fuel has attracted massive attention that aim to promote carbon peak and carbon neutrality progress. The CO/NH₃ oxidation chemistry is important for the burnout in ammonia-fueled engines and turbines. Therefore, the oxidation of ammonia and NO formation during NH₃/CO post-combustion is investigated. The experiments are carried out in an entrained flow reactor under different NH₃ concentrations and temperatures. The present work is used to evaluate the ammonia subset of the reaction mechanism under the various  conditions. The oxidation of CO is found to enhance the reaction of am monia. In addition, H₂O₂ may also promote the oxidation of N H₃ . The experimental data under different NH₃/CO ratios is also used to predict the reaction of mixed fuels of hydrocarbons and ammonia.  The catalytic combustion of high concentration NH₃ to produce N₂ and H₂O is also a prospective technology for carbon-free fuel utilization. Hence, the distinct structure-activity relationship and reaction pathways were clearly identified by designing CuO/CeO₂ catalysts for NH₃ reaction. During the combustion of high concentration (~10%) NH₃ , the self-sustained combustion limit, NH₃ conversion efficiency, the distribution of wall temperature, and combustion stability were further revealed. The kinetic model of NH₃ catalytic ignition process was established. And it is found the coexistence of the Mars-van Krevelen (M–K) and Langmuir-Hinshelwood (L–H) mechanism. The M–K mechanism involves adsorbed NH_x by ammonia dehydrogenation route to react with active lattice oxygen, and to produce N₂ and H₂O. Additionally, the contribution of L–H mechanism refers the reaction of adsorbed NH_x species and chemisorbed oxygen or adsorbed HNO through oxidation route.

Chemical looping ammonia synthesis (CLAS) technology is prospective to achieve the efficient storage and conversion of renewable energy under mild conditions. CLAS can decouple the conventional NH₃ synthesis reaction to multiple sub-reactions, which supplies more freedom to regulate the thermodynamic and kinetic properties. The separated sub-reactions are compatible with the fluctuating and intermittent characteristics of renewable energy, and overcome the competing adsorption of N₂ and H₂ on catalyst surface. Owing to the huge elemental reserves, superior catalytic performance and abundant valence states, transition metals (e.g., Cr and Mn) can function as promising nitrogen carriers (NCs) to mediate redox cycles, but their CLAS activity and selectivity are still insufficient. Herein, the novel strategy of composite NCs was proposed to stimulate the CLAS performance, and the enhancement mechanism was investigated with quantitative experiments and DFT calculations. Chromium nitride doped with Co exhibited higher conversion and selectivity of lattice nitrogen to 50.7% and 98.1%, as well as the superior average rate of 466.1 μmol g⁻¹ h⁻¹ in 12 CLAS cycles, which is ∼10 times that of the pristine CrN. Theoretical calculations revealed that the nitrogen vacancies generated in hydrogenation served as active sites for N₂ fixation through the Mars–van Krevelen mechanism. Additionally, Ni-CrN loaded on ZSM-5 supports possessed elevated specific area and CLAS rate of 41.98 m²/g and 343.1 μmol g^-1 h^-1, which are ~4.5 and ~1.4 times that of unsupported NCs respectively. The incorporation of Ni dopants can also enhance the bulk migration and interfacial reaction of lattice nitrogen in Mn-based NCs, where the low content of Ni (~20 wt%) can realize the optimal matching between both processes, thus promoting the activity and selectivity of hydrogenation. This work offers a novel avenue to design efficient NCs for the enhanced CLAS performance.