Ammonia Synthesis Process Research Articles

Dynamic Simulation and Optimization for Load Regulation Strategies of the Green Ammonia Synthesis Process

Dynamic Simulation and Optimization for Load Regulation Strategies of the Green Ammonia Synthesis Process

Localized High-Concentration Electrolyte in Li-Mediated Nitrogen Reduction for Ammonia Synthesis.

The lithium-mediated nitrogen reduction reaction (Li-NRR) is a promising green alternative to the Haber-Bosch process for ammonia synthesis. The solid electrolyte interphase (SEI) is crucial for high efficiency and stability, as it regulates reactant diffusion and suppresses side reactions. The SEI properties are greatly influenced by the Li+ ion solvation structure, which is controllable through electrolyte engineering. Although anion-derived SEI enhances selectivity and stability, it has typically been engineered using high-concentration electrolytes (HCEs), which face mass transfer, viscosity, and cost issues. In this study, a localized high-concentration electrolyte (LHCE) in the Li-NRR is first introduced, enabling the formation of anion-derived SEI in a low-concentration electrolyte (LCE) by enhancing the Li-anion coordination using an antisolvent. Among various antisolvents, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) achieves the highest ammonia Faradaic efficiency (73.6 ± 2.5%), more than double that of the LCE (34.3 ± 2.8%) and exceeding the HCE (56.0 ± 2.8%). Systematic calculations and experimental analyses show that the LHCE exhibits anion-rich solvation structures and formsthin, inorganic SEI. Moreover, the LHCE has advantages of low viscosity and high N2 solubility, which facilitate mass transport. This study suggests the application of LHCE as an effective electrolyte engineering strategy to enhance the Li-NRR efficiency.

Carbon-neutral design of ammonia synthesis process using oxy-fuel combustion-based carbon capture: Carbon-techno-economic comparison

This study proposes a novel blue ammonia synthesis process by applying oxy-fuel combustion to simplify the CO2 capture process. Generally, ammonia production requires N2 as the primary feedstock, prompting the deployment of an air separation unit (ASU) to supply N2. However, the ASU also produces O2 as a byproduct, which remains unused in conventional air combustion processes. Therefore, this study introduces oxy-fuel combustion that harnesses surplus O2, thereby overcoming the limitations of amine-based CO2 capture units in the conventional process. In the proposed process, high-purity CO2 is separated through simple water condensation. This eliminates the significant thermal energy consumption required for amine solution regeneration and avoids the additional cost of distillation columns. Instead, only an increase in the ASU scale is required to supply the oxygen necessary for combustion. A comprehensive carbon-techno-economic analysis compares the proposed oxy-fuel combustion-based process with a conventional air combustion-based process involving amine-based CO2 capture. Remarkably, the proposed system achieved a 61% reduction in CO2 emissions compared with the conventional system and demonstrated the highest return on investment at 19.5%. These findings suggest that oxy-fuel combustion significantly enhances the potential of blue ammonia as a low-carbon energy carrier.

Radiocatalytic ammonia synthesis from nitrogen and water.

The development of alternative methods to the Haber-Bosch process for ammonia (NH3) synthesis is a pressing and formidable challenge. Nuclear energy represents a low-carbon, efficient and stable source of power. The harnessing of nuclear energy to drive nitrogen (N2) reduction not only allows 'green' NH3 synthesis, but also offers the potential for the storage of nuclear energy as a readily transportable zero-carbon fuel. Herein, we explore radiocatalytic N2 fixation to NH3 induced by γ-ray radiation. Hydrated electrons (e- aq) that are generated from water radiolysis enable N2 reduction to produce NH3. Ru-based catalysts synthesized by using γ-ray radiation with excellent radiation stability substantially improve NH3 production in which the B5 sites of Ru particles may play an important role in the activation of N2. By benefitting from the remarkable penetrating power of γ-ray radiation, radiocatalytic NH3 synthesis can proceed in an autoclave under appropriate pressure conditions, resulting in an NH3 concentration of ≤5.1mM. The energy conversion efficiency of the reaction is as high as 563.7mgNH3·MJ-1. This radiocatalytic chemistry broadens the research scope of catalytic N2 fixation while offering promising opportunities for converting nuclear energy into chemical energy.

Plant-wide modeling and techno-economic optimization of a low-pressure microwave-assisted ammonia synthesis process with adsorption separation

Ammonia production has traditionally been done by using the Haber-Bosch process, that operates at extremely high pressure (200–300 bar), has a large carbon footprint, and requires significant energy. For ammonia to be used as a hydrogen carrier, it is desired that it is produced by using modular technologies under benign conditions, yet the economics remain commercially viable. This paper investigates a novel technology for ammonia synthesis by using a microwave-assisted low-pressure reactor. Microwave reactors are compact and can be readily modularized and started/shutdown thus making them ideal to be integrated with the electric grid or with regional/local renewable-based electric generation facilities. For separation of unreacted reactants from the product ammonia, if the traditional condensation separation technology used in the high-pressure Haber-Bosch process is used, then the separation process needs to be operated under cryogenic condition thus adversely affecting the economics. A solid sorbent based separation technology is investigated in this paper. A kinetic model for the microwave-catalytic synthesis process is used. An isotherm model is developed for MgCl2–Si adsorbent and used for modeling the dynamic adsorption-desorption cycle. A plant-wide model with heat and mass integration is developed. An economic model is developed and used for economic optimization by using an equation-oriented approach. Since the adsorption-desorption process is dynamic, for techno-economic optimization, a reduced order model for the key performance measures of the adsorption-desorption process as a function of its input and decision variable is developed under cyclic steady-state conditions. For the optimized MW-assisted process, the levelized cost of ammonia is $772/mt as opposed to $808/mt for the conventional Haber-Bosch process for a hydrogen price of $2.07/kg. The MW-assisted process is found to be economically viable in the US market if the hydrogen price is below $4/kg.

Cross-domain fault diagnosis for multimode green ammonia synthesis process based on DA-CycleGAN

Green ammonia is a crucial strategy for reducing carbon emissions and promoting sustainable development. However, in industrial applications, the production load of the ammonia synthesis section must be adjusted to accommodate fluctuations in renewable energy generation and hydrogen production. Consequently, the green ammonia synthesis process operates under multiple conditions with varying production loads. The operations of this multimode process introduce new challenges for process safety. Traditional fault diagnosis methods experience significant performance degradation when production conditions change. In new conditions, only a small number of normal samples can be obtained, and no fault samples are available. To address this issue, a novel transfer learning method named DA-CycleGAN is proposed for the multimode green ammonia synthesis process. This method combines a two-dimensional generation model based on CycleGAN (Cycle-Consistent Generative Adversarial Networks) with domain adaptation to enhance model performance in cross-domain tasks. The feasibility of the proposed method was initially validated using the benchmark Tennessee-Eastman process for fault diagnosis. Subsequently, a case study of the green ammonia synthesis process demonstrated that it significantly enhances performance in multimode processes, ensuring process safety and reducing losses for industrial applications.

A bioinspired Fe/Mo bimetallic nitride catalyst for efficient electrochemical ammonia synthesis and Zn-nitrate battery

The electrocatalytic nitrate reduction reaction to ammonia (NRA) offers a promising alternative to traditional ammonia synthesis methods. In nature, enzymes containing molybdenum and iron sites catalyze the reduction of nitrate and nitrite ions. Drawing inspiration from these enzymes, we synthesized a carbon-coated nano-octahedra of FeMo-based nitride (FeMoN@C NO) by pyrolyzing phosphomolybdic acid hydrate (POM) doped Fe-NH2-MIL-101 to catalyze NRA. Experimental results demonstrate that in an alkaline environment, FeMoN@C NO exhibits a suitable hydrogen evolution reaction (HER) capacity, and the protons or hydroxyls produced effectively facilitate the hydrogenation reaction in the ammonia synthesis process. Additionally, the introduction of Mo increases the number of active sites and effectively reduces the thermodynamic barrier in NRA, thereby enhancing the rate of ammonia synthesis. As a result, FeMoN@C NO displays outstanding NH3 Faradaic efficiency (FE) of 98.2 % and an NH3 yield of 434.16 µmol/h cm−2. Building upon the excellent electrocatalytic properties of FeMoN@C NO, a new Zn-nitrate battery system is assembled in this work, which exhibits an outstanding peak power density of 3.23 mW cm−2 and an FE of 91.58 % for NH3 production. This work provides a new perspective for designing enzyme-mimicking nitrate reduction catalysts and broadens the application of Zn-based batteries.

Nature's Catalyst: Investigating the Mechanisms behind Nitrogenase's N2rr Activity

Electrochemical nitrogen reduction reaction (eNRR), one of the most studied problems in catalysis, has the potential to replace the century-old Haber-Bosch process for ammonia synthesis. However, a low-cost, highly selective and efficient catalyst for eNRR is yet to be discovered. Nitrogenase, a naturally occurring biocatalyst responsible for nitrogen conversion to ammonia under ambient conditions, is the most efficient catalyst for eNRR. The Iron-Molybdenum cofactor (FeMo-co) in the enzyme is identified as the catalytic part with bridging irons being active sites. Despite decades of work the exact mechanism of its operation and various intermediates along the pathway are still debated. We revisit eNRR on FeMo-co and decipher the key mechanisms at play.Most studies on FeMo-co tend to ignore the magnetic nature of transition metals (TMs) in the cofactor. Proper treatment of these TMs (Fe and Mo) is necessary to pinpoint the intermediates and potential limiting step along the eNRR pathway. We start with an iterative optimization of the Hubbard U parameter to capture the correct magnetic structure of the cofactor. We also explore the effect of local chemical environment including, H-coverage and various ligands attached to the cofactor, on its activity and selectivity. The potential limiting step is found to be sensitive to the magnetic orientation of the TMs in the cofactor and it is thus imperative to provide the U correction to capture the true bottleneck of eNRR. The cofactor also shows an affinity towards a medium H-coverage under eNRR operating conditions. These findings provide a comprehensive and elaborate view of nitrogen reduction on FeMo-co and insights from this study paves the path towards designing heterogeneous counterparts to the catalyst.Acknowledgments:This work was supported by the U.S. Department of Energy, via Grant DE-FOA-0002676 to the SUNCAT Center for Interface Science and Catalysis.

A Durable Vanadium Disulfide-Based Catalyst for Nitrate Reduction and Insights on in-Line Ammonia Detection By Mass Spectrometry

Ammonia is critical to agriculture worldwide and is a renewable fuel. The dominant process for ammonia synthesis, Haber-Bosch, is fossil-fuel dependent, energy intensive and highly centralized. Electrochemical N2 or NO3 - reduction promises to provide a decentralized and environmentally friendly route to ammonia synthesis. Electrochemical ammonia synthesis research is challenging due to typically low amounts of ammonia produced relative to environmental levels. In this two-part presentation, a VS2-based nitrate reduction catalyst, which has shown exceptional activity, selectivity, and durability, will be discussed. The proposed mechanism of nitrate reduction on VS2 will be discussed along with thorough characterization of the catalyst material, and we will present density functional theory mechanistic insight of nitrate reduction on VS2. Various experimental controls used in the VS2 nitrate reduction experiments, including Ar purge and NMR characterization experiments will also be detailed. Additionally, a test platform for nitrogen or nitrate reduction catalysts in a gas-diffusion electrode architecture with in-line NH3 and 15NH3 monitoring by multi-turn TOF-MS will be discussed. This part of the presentation will detail some advantages of our analytical approach that stem from the low limit of detection and high mass resolution. Finally, we will address areas of opportunity in electrochemical ammonia generation.

The synergistic effect of Cl doping and Bi coupling to promote the carrier separation of BiOBr for efficient photocatalytic nitrogen reduction

Photocatalytic nitrogen reduction reaction (NRR) is a sustainable process for ammonia synthesis under mild conditions. However, photocatalytic NRR activity and are generally limited by inefficient carrier separation and transfer. Therefore, parallel engineering of bulk phase doping and surface coupling is critical to achieving the goal of efficient NRR. In this study, Cl doped BiOBr nanosheet assemblies (BiOBr/Cl) were constructed in delicately designed deep eutectic solvents (DESs), combined with ionothermal methods at low temperatures and Bi3+ exsolution reduction strategy at high temperatures. The unique liquid state and reducibility of DESs induce the reduction of Bi3+ and the in situ coupling of Bi quantum dots at the surface of BiOBr/Cl nanosheets along with the construction of Bi-BiOBr/Cl nanosheet assemblies. The experimental results show that Cl doping could reduce the exciton dissociation energy and promote its dissociation to free carriers. Bi quantum dots could form tightly coupled Schottky junction with BiOBr/Cl enabling the efficient and unidirectional transmission of photogenerated electrons from BiOBr/Cl to metal Bi. The formed electron deficient region at Schottky interface promotes the adsorption and activation of N2. The hierarchical structure of Bi-BiOBr/Cl nanosheet assembly benefits to providing more N2 adsorption active sites. The DFT calculation shows that the accumulation of high concentration of active hydrogen in Bi-BiOBr/Cl leads to a significant decrease of energy barrier of the first step hydrogenation of N2. Bi-BiOBr/Clis more inclined to adsorb nitrogen for NRR in comparison with H* for hydrogen production. The synergistic effect of Cl doping and Bi coupling result in a high NRR activity of Bi-BiOBr/Cl photocatalyst of 6.67 mmol·g−1·h−1, which was 11.3 times higher than that of initial BiOBr. This study provides a promising strategy for designing highly active NRR photocatalysts with high efficiency carrier dissociation and transport.

Confined dual functionalized ionic liquids in metal-organic frameworks for selective NH3 adsorption

The capture and separation of ammonia (NH3), a typical hydrogen-rich, carbon-free, but highly corrosive and pungent odorous gas, is significantly important for resource utilization, sustainable development and environment protection. The combination of functionalized ionic liquids (ILs) and porous supports to develop novel porous composites for NH3 adsorption is an efficient way to achieve the above goals. In this work, dual functionalized IL (DFIL) simultaneously containing Lewis acidic sites and hydrogen bond sites supported porous Zr-MOF (Zr-bptc) with high stability and reversibility are developed for NH3 adsorption. The DFIL confined in the nanopores not only provides high NH3 affinity, but also reduces the pore size to form selective NH3 diffusion pathways. Thus, the highest NH3 adsorption capacity of 10.26 mmol/g at 1 bar and 25 °C was achieved by DFIL@Zr-bptc-50 wt%. Especially, the optimal composites showed high NH3/N2 IAST of 3146.21 for NH3/N2 (0.5/99.5, v/v) and 593.97 for NH3/N2 (5/95, v/v), which is 269 % and 346 % higher than that of pristine Zr-bptc, respectively, indicating the composites have great potential for low-concentration NH3 separation. Moreover, the mixed gas breakthrough experiments demonstrated that optimal DFIL@Zr-bptc also exhibits outstanding NH3/N2 separation performance under simulative conditions including ammonia synthesis process and air purification. In addition, the DFIL@Zr-bptc composites show great structural stability and recyclability. This work provides a feasible way to design novel porous IL composites for NH3 efficient removal and recovery.

Interface reconstruction of MXene-Ti3C2 doped CeO2 nanorods for remarked photocatalytic ammonia synthesis

Prospective photocatalytic ammonia synthesis process has received more attentions but quite challenging with the low visible light utilization and weak N2 molecule absorption ability around the photocatalysts. Herein, interface reconstruction of MXene-Ti3C2/CeO2 composites with high-concentration active sites through the carbon-doped process are presented firstly, and obvious transition zones with the three-phase reaction interface are formed in the as-prepared catalysts. The optimal co-doped sample demonstrates an excellent photo response in the visible light region, the strongest chemisorption activity and the most active sites. Moreover, much more in-situ extra oxygen defects are also produced under light irradiation. It is expected that the double decorated catalyst shows a remarked ammonia production rate of above 0.76 mmol gcal−1·h−1 under visible-light illumination and a higher apparent quantum efficiency of 1.08 % at 420 nm, which is one of the most completive properties for the photocatalytic N2 fixation at present.

Boosting electroreduction of nitrate to ammonia by modulating the crystalline phase of Fe2O3

Electrocatalytic nitrate reduction reaction (NO3RR) provides an alternative to the conventional Haber-Bosch process for ammonia synthesis and is an effective method for removal of nitrate ions from polluted waters, which is highly significant from both energy and environmental perspectives. However, NO3RR involves the complex eight-electron process alongside various nitrogen-containing intermediates and is also in competition with hydrogen evolution reaction, thus demanding highly active and selective electrocatalysts. In this work we prepare a Ni-doped Fe2O3 electrocatalyst via a solvent-free route. It is found that the addition of Ni induces the crystalline-phase transformation of Fe2O3 from γ-Fe2O3 to α-Fe2O3. The density functional theory (DFT) results reveal that compared to γ-Fe2O3, α-Fe2O3 gives rise to a lower potential-determining step (PDS) energy barrier, leading to the more thermodynamically favourable reaction. By modulating the crystalline phase, the optimal catalyst achieves high ammonia yield rates of > 5000 μg h−1 cm−2 and faradaic efficiencies of > 90 %, showcasing its high electrocatalytic activity and selectivity. From this perspective, this paper provides new insights and strategies for the green nitrate-to-ammonia conversion.

Optimal Design of an Absorbent-Enhanced Ammonia Synthesis Process for Solar Thermochemical Energy Storage

Optimal Design of an Absorbent-Enhanced Ammonia Synthesis Process for Solar Thermochemical Energy Storage

Mechanism of synthesis ammonia over atomically dispersed Ni/BCN catalyst under atmospheric pressure and low-temperature conditions

In industry, ammonia synthesis process typically requires high temperatures (400 ∼ 500 °C) and high pressures (20 ∼ 40 MPa), resulting in high energy consumption and high carbon emissions. Exploring the direct ammonia synthesis with N2 and H2 under mild conditions without the assistance of electrochemical or photochemical energy, represents a promising approach. In this study, atomically dispersed Ni loaded on B-doped CN catalyst (Ni/BCN) was prepared by a liquid phase one-pot method, which achieved efficient ammonia synthesis under mild conditions of 101.3 kPa and 80 °C, with an ammonia yield of 114 μmol h−1 gcat-1 after 10 h. Further experimental studies combined with the characterization of catalyst morphology, bulk phase structure, and surface chemical state reveal the mechanism of ammonia synthesis under mild conditions. The appearance of nitrogen vacancies on Ni/BCN can promote the electron delocalization of stable N≡N bonds in N2, facilitating the activation of N2. B, C and N bond with each other to form a hybrid BCN carrier, which promotes the electron transfer on the surface. Our findings suggest a general approach to engineer catalysts that can drive critical reactions pertinent to energy conservation, low-carbon, and sustainability.

Microwave-Mediated ammonia synthesis over Co2Mo3N catalysts at low pressures

The Haber-Bosch process for ammonia (NH3) synthesis is a major contributor to greenhouse gas emissions and is responsible for > 2 % of the world’s energy consumption each year encouraging the need for alternative renewable-based options. This study investigates an earth-abundant ternary metal nitride (i.e., Co2Mo3N) catalyst to develop a renewable-based NH3 synthesis approach, utilizing an energy-efficient microwave-assisted route. Using a combination of spectroscopic and catalytic measurements coupled with surface analysis techniques, Co2Mo3N was evaluated as a stable and efficient NH3 synthesis catalyst. Results presented here demonstrate NH3 synthesis on Co2Mo3N at ∼420 ℃ and ambient pressure yield ∼0.7 mmolNH3.gcat-1.h−1 and up to ∼12 mmolNH3.gcat-1.h−1 at 28 bar under microwave irradiation. Co2Mo3N displayed an activation energy of ∼72 kJ.mol−1 and yielded NH3 following first-order kinetics with respect to both H2 and N2. These studies illustrate the potential of using this catalyst for a sustainable, cost-effective, and environmentally friendly approach to producing NH3.

Learning-Based Model Reduction and Predictive Control of an Ammonia Synthesis Process

Learning-Based Model Reduction and Predictive Control of an Ammonia Synthesis Process

Design Principle of Molybdenum-Based Metal Nitrides for Lattice Nitrogen-Mediated Ammonia Production.

Chemical looping ammonia synthesis (CLAS) is a promising technology for reducing the high energy consumption of the conventional ammonia synthesis process. However, the comprehensive understanding of reaction mechanisms and rational design of novel nitrogen carriers has not been achieved due to the high complexity of catalyst structures and the unrevealed relationship between electronic structure and intrinsic activity. Herein, we propose a multistage strategy to establish the connection between catalyst intrinsic activity and microscopic electronic structure fingerprints using density functional theory computational energetics as bridges and apply it to the rational design of metal nitride catalysts for lattice nitrogen-mediated ammonia production. Molybdenum-based nitride catalysts with well-defined structures are employed as prototypes to elucidate the decoupled effects of electronic and geometrical features. The electron-transfer and spin polarization characteristics of the magnetic metals are constructed as descriptors to disclose the atomic-scale causes of intrinsic activity. Based on this design strategy, it is demonstrated that Ni3Mo3N catalysts possess the highest lattice nitrogen-mediated ammonia synthesis activity. This work reveals the structure-activity relationship of metal nitrides for CLAS and provides a multistage perspective on catalyst rational design.

Boosting Electrochemical Nitrogen Reduction via Axial Coordination Engineering on Single‐Iron‐Atom Catalysts

AbstractElectrocatalytic nitrogen (N2) reduction reaction (NRR) presents a sustainable alternative to the Haber–Bosch process for ammonia (NH3) synthesis. Iron phthalocyanine (FePc) is demonstrated as a promising catalyst for the electrocatalytic NRR. However, FePc with planar symmetric Fe‐N4 sites exhibits poor N2 adsorption and activation capabilities, resulting in an unsatisfactory NRR performance. Herein, an axial oxygen coordination strategy is developed to optimize the local electron distribution on FePc for improving N2 adsorption and activation. The as‐obtained FePc‐O‐CP shows a superior NH3 yield rate (59.72 µg h−1 mg−1cat.) and a considerable Faradaic efficiency (13.76%) in 0.1 m HCl. Density functional theory (DFT) calculations verify that the axial oxygen ligand on FePc inhibits the adsorption of H+ and enhances the N2 adsorption and activation, thereby greatly promoting NH3 generation. This work reveals the significance of regulating the local coordination environment of single‐atom catalysts for improving electrocatalytic NRR performance and provides a feasible strategy for the rational design of atomic‐scale active sites.

Design, global energy integration, and sustainability analyses of a process coupling renewable energy water electrolysis for hydrogen production with ammonia synthesis

The conventional ammonia synthesis process typically depends on fossil energy and faces challenges such as low utilization of elements and high CO2 emissions, leading to unsatisfactory economic performance. In order to achieve green synthesis and sustainable development of ammonia, this study constructed a process for renewable energy water electrolysis hydrogen production coupled with ammonia synthesis. The process includes: PEM electrolysis water hydrogen production coupling synthesis ammonia (PEM-GHtA) and SOEC electrolysis water hydrogen production coupling synthesis ammonia (SOEC-GHtA). Compared to traditional ammonia synthesis, the new process eliminates the use of carbon conversion for hydrogen production. Instead, it utilizes green electrolysis to split water into hydrogen and oxygen, leading to enhanced energy efficiency and decreased carbon emissions. By employing modeling, simulation, global energy integration, and conducting technical and economic analysis of the new process, this study elucidates the technical advantages and economic competitiveness of the new process over the traditional ammonia synthesis process. According to the analysis results, the utilization rates of hydrogen element in the PEM-GHtA and SOEC-GHtA processes are 92.64% and 92.59%, and the utilization rate of nitrogen element is 90.56% and 90.50%, respectively, much higher than the traditional ammonia synthesis process. In addition, the SOEC-GHtA demonstrated improved energy efficiency, achieving a range of 72.19–75.08%. The CO2 emissions of the two green ammonia synthesis processes are 0.17–0.81 t CO2/t NH3, much lower than the 1.6–3.6 t CO2/t NH3 of the traditional ammonia synthesis process. Based on the current market price, the production cost of green ammonia is relatively high, which has no economic advantage over the traditional ammonia synthesis process. Considering the future implementation of carbon taxes and the decreasing prices of renewable energy electricity to 0.014 $/kWh, the production costs of PEM-GHtA and SOEC-GHtA will be reduced to 359.7 $/t NH3 and 343.5 $/t NH3 respectively. In comparison to the traditional process (403.1–514.7 $/t NH3), the new process offers substantial economic benefits and shows promising prospects for further development.