Green ammonia production technologies: A review of practical progress

Integration of electrocoagulation and solar energy for sustainable wastewater treatment: a thermodynamic and life cycle assessment study

This study presents an innovative approach to sustainable wastewater treatment by integrating electrocoagulation (EC) with solar energy and biogas. The research evaluates the performance of an EC reactor in terms of chemical oxygen demand (COD) removal efficiency under varying current densities, demonstrating enhanced COD removal rates with increased current densities, achieving up to 95.3% at 1500 A/m2. Life cycle assessment (LCA) is employed to compare the environmental impacts of different energy sources for powering the EC system. The findings indicate that biogas derived from domestic waste offers a lower environmental impact compared to natural gas, coal, hydro, solar, and wind. The study further explores the potential of solar energy in Turkey, particularly in Istanbul, where high solar radiation could be harnessed. However, the efficiency of photovoltaic (PV) panels is affected by temperature, with an observed efficiency decrease of approximately 0.5% per degree Celsius increase in temperature. Effective cooling strategies are thus essential for optimizing PV performance. The integration of EC with solar energy, powered by biogas, not only enhances wastewater treatment efficiency but also contributes to reduced greenhouse gas emissions and energy costs. This combined approach presents a viable solution for both domestic and industrial wastewater treatment, especially in remote or off-grid areas.

Climate change mitigation potential and economic evaluation of selected technical adaptation measures and innovations in conventional arable farming in Germany

Agriculture accounts for a large proportion of global greenhouse gas (GHG) emissions. It is therefore crucial to identify effective and efficient GHG mitigation potentials in agriculture, but also in related upstream sectors. However, previous studies in this area have rarely undertaken a cross-sectoral assessment. There is also a gap in research on the GHG mitigation potential of innovations such as green ammonia in arable farming at a larger spatial scale. The study therefore aimed to analyze how selected technological adaptations or innovations can be used to contribute to efficient and effective cross-sectoral GHG mitigation in conventional arable farming systems. Germany, one of the largest agricultural producers and contributors of GHG emissions from agriculture in the EU, was chosen as a case study. The GHG mitigation potential and abatement cost of four selected measures were analyzed using an integrated land use model and life cycle assessment. Their GHG mitigation potential varied between 0.3 Mt CO2-eq. for nitrification inhibitors under lower mitigation rate assumptions and 4.7 Mt CO2-eq. for green ammonia with upper mitigation rate assumptions on GHG emission impacts, i. e. rather high mitigation. While crop varieties based on new genomic technologies (NGT) were introduced at no GHG abatement cost, the average mitigation costs ranged from 48 € for the use of nitrification inhibitors (upper mitigation rate) to 1233 € per t CO2-eq. for N sensors (lower mitigation rate). There were also regional differences due to different land use structures, regional farm sizes, economic and agronomic conditions. Based on these results we recommend for agricultural and environmental policy to foster the use of nitrification inhibitors due to the identified GHG reduction potential and the comparatively low GHG abatement costs. Additionally, the use of green ammonia in fertilizer production should be further promoted. Although the results are exemplary for Germany, they can be very informative for other EU Member States with comparable socio-economic and agronomic conditions.

A review of chemical kinetic mechanisms and after-treatment of amino fuel combustion

Ammonia is a highly promising carbon-neutral fuel. The use of ammonia as a fuel for internal combustion engines can reduce fossil energy consumption and greenhouse gas emissions. However, the high ignition energy required for ammonia and the slow flame propagation rate result in low combustion efficiency when ammonia is used directly in internal combustion engines. The combination of ammonia with highly reactive fuels improves combustion quality and increases efficiency. However, the combustion of these combined fuels generates particulate matter, CO, hydrocarbon, and significant amounts of NOx. Therefore, pollutant emissions must be reduced through after-treatment technologies. In this paper, a series of combustion and post-treatment challenges faced by amino fuel combustion in internal combustion engines are extensively discussed and the combustion reaction mechanisms of different amino fuels are also analyzed. The paper then reviews five key technologies applicable to the reprocessing of amino fuels, including selective catalytic reduction, selective catalytic reduction filter technology, electrochemical methods for NOx removal, direct catalytic decomposition of N2O, and ammonia sliding catalysts. An in-depth discussion of the catalytic materials and reaction mechanisms involved in these technologies is also provided in this paper. Finally, the paper summarizes the main technical challenges that must be addressed for the future application of amino fuels in internal combustion engines. These discussions can serve as an essential reference for developing and applying critical technologies for combustion control and pollutant treatment of amino fuels.

Light-driven nitrogen fixation routes for green ammonia production

The global goal for decarbonization of the energy sector and the chemical industry could become a reality by a massive increase in renewable-based technologies. For this clean energy transition, the versatile green ammonia may play a key role in the future as a fossil-free fertilizer, long-term energy storage medium, chemical feedstock, and clean burning fuel for transportation and decentralized power generation. The high energy-intensive industrial ammonia production has triggered researchers to look for a step change in new synthetic approaches powered by renewable energies. This review provides a comprehensive comparison of light-mediated N2 fixation technologies for green ammonia production, including photocatalytic, photoelectrocatalytic, PV-electrocatalytic and photothermocatalytic routes. Since these approaches are still at laboratory scale, we examine the most recent developments and discuss the open challenges for future improvements. Last, we offer a technoeconomic comparison of current and emerging ammonia production technologies, highlighting costs, barriers, recommendations, and potential opportunities for the real development of the next generation of green ammonia solutions.

Technology Readiness and Emerging Prospects of Coupled Catalytic Reactions for Sustainable Chemical Value Chains

Transitioning from both the direct and indirect use of fossil fuels to the renewable and sustainable resources of the near future demands a focal shift in catalysis research - from investigating catalytic reactions in isolation to developing coupled reactions for modern chemical value chains. In this Perspective, we discuss the status and emerging prospects of coupled catalytic reactions across various scales and provide key examples. Besides being a sustainable and essential alternative to current fossil-based processes, the coupling of catalytic reactions offers novel and scalable pathways to value-added chemicals. By emphasizing the specific requirements and challenges arising from coupled reactions, we aim to identify and underscore research needs that are critical to expedite their development and to fully unlock their potential for chemical and fuel production.

Nitric oxide recovery from hydrogen combustion streams. A clean pathway for the sustainable production of nitrogen compounds

This work proves that nitric oxide (NO) can be successfully recovered from hydrogen flue gas streams in nitric acid, opening new pathways for NO control in combustion streams. Recovering NO from hydrogen combustion streams allows for increasing the combustion temperature in the turbine, reducing the fuel consumption per kWh, while obtaining a building block for nitric acid production. The solubility of nitric oxide is determined in amines, ethanol, and nitric acid solutions at a laboratory scale, suitable candidates for nitric oxide absorption. The solubility of nitric oxide in amines and ethanol is very low (0.009 mol/L/bar & 0.018 mol/L/bar respectively) compared with nitric acid (0.23 mol/L/bar), which is in the same range as the solubility of CO2 in amines solutions. Nitric acid, in addition to having good NO solubility, also presents high selectivity towards nitric oxide and easy recovery of nitric oxide by simply raising the temperature. Finally, a fugacity-activity coefficient model combining the Peng-Robinson (PR) equation of state with the Non-Random Two-Liquid (NRTL) activity coefficient model is proposed as a thermodynamic model to represent the NO-HNO3-H2O equilibrium, giving as a result an average absolute deviation between the experimental results and the model predictions of only 5%.

Challenges and Advancements in the Electrochemical Utilization of Ammonia Using Solid Oxide Fuel Cells

Solid oxide fuel cells utilized with NH3 (NH3-SOFCs) have great potential to be environmentally friendly devices with high efficiency and energy density. The advancement of this technology is hindered by the sluggish kinetics of chemical or electrochemical processes occurring on anodes/catalysts. Extensive efforts have been devoted to developing efficient and durable anode/catalysts in recent decades. Although modifications to the structure, composition, and morphology of anodes or catalysts are effective, the mechanistic understandings of performance improvements or degradations remain incompletely understood. This review informatively commences by summarizing existing reports on the progress of NH3-SOFCs. It subsequently outlines the influence of factors on the performance of NH3-SOFCs. The degradation mechanisms of the cells/systems are also reviewed. Lastly, the persistent challenges in designing highly efficient electrodes/catalysts for low-temperature NH3-SOFCs, and future perspectives derived from SOFCs are discussed. Notably, durability, thermal cycling stability, and power density are identified as crucial indicators for enhancing low-temperature (550 °C or below) NH3-SOFCs. This review aims to offer an updated overview of how catalysts/electrodes affect electrochemical activity and durability, offering critical insights for improving performance and mechanistic understanding, as well as establishing the scientific foundation for the design of electrodes for NH3-SOFCs.

Enhanced Photocatalytic Nitrogen Reduction via Bismuth Nanoparticle-Decorating ZnCdS Solid Solution

The construction of photocatalysts with a surface plasmon resonance effect (SPR) has been demonstrated as a highly effective strategy for enhancing photocatalytic efficiency. In this paper, we synthesized a catalyst with bismuth metal loaded on ZnCdS nanospheres for an efficient photocatalytic nitrogen reduction reaction (PNRR). The SPR effect induced by Bi nanoparticles under light excitation significantly promoted the ammonia production efficiency of the photocatalyst. Under air ambient conditions with lactic acid as the sacrificial agent, the photocatalytic NH4+ yield of 3% Bi@ZnCdS was 58.93 μmol·g-1·h-1, which exhibited an approximately 7.7 times that of the pure phase ZnCdS. The experimental characterization results demonstrate that the incorporation of metallic bismuth enhances the light absorption capacity of the catalyst and improves the separation efficiency of the photogenerated carriers. Theoretical calculations proved that Bi NPs provide more photogenerated electrons to convert N2 to NH3 for solid-solution ZnCdS. This work presents a novel concept for the development of advanced plasma nanomaterials to enhance the photocatalytic nitrogen fixation reaction.

Ultra-Low Loading of Gold on Nickel Foam for Nitrogen Electrochemistry

Ammonia (NH3) is widely used in various fields, and it is also considered a promising carbon free energy carrier, due to its high hydrogen content. The nitrogen reduction reaction (NRR), which converts nitrogen into ammonia by using protons from water as the hydrogen source, is receiving a lot of attention, since effective process optimization would make it possible to overcome the Haber-Bosch method. In this study, we used a solution-based approach to obtain functionalized porous Ni foam substrates with a small amount of gold (<0.1 mg cm-1). We investigated several deposition conditions and obtained different morphologies. The electrochemical performance of various catalysts on the hydrogen evolution reaction (HER) and NRR has been characterized. The ammonia production yield was determined by chronoamperometry experiments at several potentials, and the results showed a maximum ammonia yield rate of 20 µg h-1 mgcat-1 and a Faradaic efficiency of 5.22%. This study demonstrates the potential of gold-based catalysts for sustainable ammonia production and highlights the importance of optimizing deposition conditions to improve the selectivity toward HER.