Continuous Ammonia Research Articles

Domain adaptation through active learning strategies for anomaly classification in wastewater treatment plants

ABSTRACT The increasing use of intermittent aeration controllers in wastewater treatment plants (WWTPs) aims to reduce aeration costs via continuous ammonia and oxygen measurements but faces challenges in detecting sensor and process anomalies. Applying machine learning to this unbalanced, multivariate, multiclass classification challenge requires much data, difficult to obtain from a new plant. This study develops a machine learning algorithm to identify anomalies in intermittent aeration WWTPs, adaptable to new plants with limited data. Utilizing active learning, the method iteratively selects samples from the target domain to fine-tune a gradient-boosting model initially trained on data from 17 plants. Three sampling strategies were tested, with low probability and high entropy sampling proving effective in early adaptation, achieving an F2-score close to the optimal with minimal sample use. The objective is to deploy these models as decision support systems for WWTP management, providing a strategy for efficient model adaptation to new plants, and optimizing labeling efforts.

Reversible Hydrogen Acceptor–Donor Enables Relay Mechanism for Nitrate‐to‐Ammonia Electrocatalysis

AbstractElectrocatalytic nitrate reduction is a crucial process for sustainable ammonia production. However, to maximize ammonia yield efficiency, this technology inevitably operates at the potentials more negative than 0 V vs. RHE, leading to high energy consumption and competitive hydrogen evolution. To eradicate this issue, hydrogen tungsten bronze (HxWO3) as reversible hydrogen donor‐acceptor is partnered with copper (Cu) to enable a relay mechanism at potentials positive than 0 V vs. RHE, which involves rapid intercalation of H into HxWO3 lattice, prompt de‐intercalation of the lattice H and transfer onto Cu, and spontaneous H‐mediated nitrate‐to‐ammonia conversion on Cu. The resulting catalysts demonstrated a high ammonia yield rate of 3332.9±34.1 mmol gcat−1 h−1 and a Faraday efficiency of ~100 % at 0.10 V vs. RHE, displaying a record‐low estimated energy consumption of 17.6 kWh kgammonia−1. Using these catalysts, we achieve continuous ammonia production in an enlarged flow cell at a real energy consumption of 17.0 kWh kgammonia−1.

Reversible Hydrogen Acceptor-Donor Enables Relay Mechanism for Nitrate-to-Ammonia Electrocatalysis.

Electrocatalytic nitrate reduction is a crucial process for sustainable ammonia production. However, to maximize ammonia yield efficiency, this technology inevitably operates at the potentials more negative than 0 V vs. RHE, leading to high energy consumption and competitive hydrogen evolution.To eradicate this issue, hydrogen tungsten bronze (HxWO3) as reversible hydrogen donor-acceptor is partnered with copper (Cu) to enable a relay mechanism at potentials positive than 0 V vs. RHE, which involves rapid intercalation of H into HxWO3 lattice, prompt de-intercalation of the lattice H and transfer onto Cu, and spontaneous H-mediated nitrate-to-ammonia conversion on Cu.The resulting catalysts demonstrated a high ammonia yield rate of 3332.9±34.1 mmol gcat-1 h-1 and a Faraday efficiency of ~100 % at 0.10 V vs. RHE, displaying a record-low estimated energy consumption of 17.6 kWh kgammonia-1. Using these catalysts, we achieve continuous ammonia production in an enlarged flow cell at a real energy consumption of 17.0 kWh kgammonia-1.

Improved Nitrate-to-Ammonia Electrocatalysis through Hydrogen Poisoning Effects.

Electrochemical conversion from nitrate to ammonia is a key step in sustainable ammonia production. However, it suffers from low productive efficiency or high energy consumption due to a lack of desired electrocatalysts. Here we report nickel cobalt phosphide (NiCoP) catalysts for nitrate-to-ammonia electrocatalysis that display a record-high catalytic current density of -702±7 mA cm-2, ammonia production rate of 5415±26 mmol gcat -1 h-1 and Faraday efficiency of 99.7±0.2 % at -0.3 V vs. RHE, affording the estimated energy consumption as low as 22.7 kWh kgammonia -1. Theoretical and experimental results reveal that these catalysts benefit from hydrogen poisoning effects, which leave behind catalytically inert adsorbed hydrogen species (HI*) at Co-hollow sites and thereupon enable ideally reactive HII* at secondary Co-P sites. The dimerization between HI* and HII* for H2 evolution is blocked due to the catalytic inertia of HI* thereby the HII* drives nitrate hydrogenation timely. With these catalysts, the continuous ammonia production is further shown in an electrolyser with a real energy consumption of 18.9 kWh kgammonia -1.

Hydrogen Spillover Mechanism at the Metal-Metal Interface in Electrocatalytic Hydrogenation.

Hydrogen spillover in metal-supported catalysts can largely enhance electrocatalytic hydrogenation performance and reduce energy consumption. However, its fundamental mechanism, especially at the metal-metal interface, remains further explored, impeding relevant catalyst design. Here, we theoretically profile that a large free energy difference in hydrogen adsorption on two different metals (|ΔGH-metal(i)-ΔGH-metal(ii)|) induces a high kinetic barrier to hydrogen spillover between the metals. Minimizing the difference in their d-band centers (Δϵd) should reduce |ΔGH-metal(i)-ΔGH-metal(ii)|, lowering the kinetic barrier to hydrogen spillover for improved electrocatalytic hydrogenation. We demonstrated this concept using copper-supported ruthenium-platinum alloys with the smallest Δϵd, which delivered record high electrocatalytic nitrate hydrogenation performance, with ammonia production rate of 3.45±0.12 mmol h-1 cm-2 and Faraday efficiency of 99.8±0.2 %, at low energy consumption of 21.4 kWh kgamm -1. Using these catalysts, we further achieve continuous ammonia and formic acid production with a record high-profit space.

Hydrogen Spillover Mechanism at the Metal–Metal Interface in Electrocatalytic Hydrogenation

AbstractHydrogen spillover in metal‐supported catalysts can largely enhance electrocatalytic hydrogenation performance and reduce energy consumption. However, its fundamental mechanism, especially at the metal–metal interface, remains further explored, impeding relevant catalyst design. Here, we theoretically profile that a large free energy difference in hydrogen adsorption on two different metals (|ΔGH‐metal(i)−ΔGH‐metal(ii)|) induces a high kinetic barrier to hydrogen spillover between the metals. Minimizing the difference in their d‐band centers (Δϵd) should reduce |ΔGH‐metal(i)−ΔGH‐metal(ii)|, lowering the kinetic barrier to hydrogen spillover for improved electrocatalytic hydrogenation. We demonstrated this concept using copper‐supported ruthenium–platinum alloys with the smallest Δϵd, which delivered record high electrocatalytic nitrate hydrogenation performance, with ammonia production rate of 3.45±0.12 mmol h−1 cm−2 and Faraday efficiency of 99.8±0.2 %, at low energy consumption of 21.4 kWh kgamm−1. Using these catalysts, we further achieve continuous ammonia and formic acid production with a record high‐profit space.

Electrochemical Nitrate Reduction to Ammonia on CuCo Nanowires at Practical Level

AbstractElectrochemical reduction of nitrate (NO3RR) holds great promise for environmentally friendly ammonia production. Tandem catalysis is a promising strategy for boosting the NO3RR and inhibiting side effects, but it is still challenged by lacking well‐designed catalysts to drive this catalytic process. Herein, the study develops the CuCo branched nanowires (CuCo NW) catalyst, which efficiently converts NO3 − to NH3 on Co (111) and Cu (111) crystal facets through a tandem catalysis mechanism. The in situ grown CuCo NW on Cu foam demonstrates a remarkable Faraday efficiency of 90.3% at 1.0 A cm−2 and maintains stable operation for 200 h at 100 and 200 mA cm−2 in a flow reactor. Density functional theory calculations suggest that the initial absorption and subsequent deoxygenation of *NO3 on Co (111) leading to the formation of *NO2, followed by its transfer to Cu (111) and further conversion to *NH3, establish an optimal pathway by managing rate‐determining steps on individual surfaces for NO3RR. To showcase the practical application of the catalyst, the study further develops a scaling‐up prototype reactor for continuous ammonia production, realizing the gram‐level yield rate of 1474.09 mg h−1 and Faraday efficiency of 91.26% at practical‐level 20.0 A.

Long-term continuous ammonia electrosynthesis.

Ammonia is crucial as a fertilizer and in the chemical industry and is considered to be a carbon-free fuel1. Ammonia electrosynthesis from nitrogen under ambient conditions offers an attractive alternative to the Haber-Bosch process2,3, and lithium-mediated nitrogen reduction represents a promising approach to continuous-flow ammonia electrosynthesis, coupling nitrogen reduction with hydrogen oxidation4. However, tetrahydrofuran, which is commonly used as a solvent, impedes long-term ammonia production owing to polymerization and volatility problems. Here we show that a chain-ether-based electrolyte enables long-term continuous ammonia synthesis. We find that a chain-ether-based solvent exhibits non-polymerization properties and a high boiling point (162 °C) and forms a compact solid-electrolyte interphase layer on the gas diffusion electrode, facilitating ammonia release in the gas phase and ensuring electrolyte stability. We demonstrate 300 h of continuous operation in a flow electrolyser with a 25 cm2 electrode at 1 bar pressure and room temperature, and achieve a current-to-ammonia efficiency of 64 ± 1% with a gas-phase ammonia content of approximately 98%. Our results highlight the crucial role of the solvent in long-term continuous ammonia synthesis.

Unraveling the deactivation mechanism of Co-LiH composite catalyst for ammonia synthesis at milder conditions

An efficient ammonia synthesis catalyst that operates under mild conditions has been a long-cherished goal in heterogeneous catalysis. The challenges associated with low-temperature ammonia synthesis arise from both the activation of inert N2 molecules and the presence of scaling relations between reactant dissociation and intermediate adsorption energies. Transition metals-metal hydride (TM-MH) composite catalysts have shown promise to overcome these challenges as both TM and MH actively participate in the reaction, enabling improved ammonia synthesis rates at lower temperatures (150 ºC). Considering this prospect, two types of Co-LiH catalyst were synthesized by ball-milling of precursors (CoCl2 and LiH- denoted as Co-LiH(rxn)) and pure components (Co and LiH- denoted as Co-LiH(pur)), and their catalytic activity was evaluated at several reaction conditions to investigate the stability for long-term operation. Co-LiH(rxn) was found to deactivate in less than 150 h whereas Co-LiH(pur) displayed a continuous production although the synthesis rate was 3 times lower than the former. Structural characterization techniques, such as XRD, SEM, and TEM were used, and it was found that Co metal in the FCC phase was primarily sintered due to its small particle size in the fresh catalyst. Temperature-programmed desorption (TPD) test on the spent Co-LiH(rxn) catalyst also displayed an ammonia release profile similar to that of LiNH2 decomposition, which confirms the presence of ammonia in the spent catalyst structure. Hence, another major finding is speculated that irreversible ammonia absorption by LiH at the target ammonia reaction conditions contributes to the deactivation of the catalyst and the formation of intermediate compounds that are required for continuous ammonia generation in this composite catalyst.

Mechanocatalytic Synthesis of Ammonia: State of the Catalyst During Reaction and Deactivation Pathway.

Ammonia synthesis holds significant importance for both agricultural fertilizer production and emerging green energy applications. Here, we present a comprehensive characterization of a catalyst for mechanochemical ammonia synthesis, based on Cs-promoted Fe. The study sheds light on the catalyst's dynamic evolution under reaction conditions and the origin of deactivation. Initially, elemental Cs converts to CsH, followed by partial CsOH formation due to trace oxygen impurities on the surface of the Fe metal and the equipment. Concurrently, the mechanical milling process comminutes Fe, exposing fresh metallic Fe surfaces. This comminution correlates with an induction period observed during ammonia formation. Critical to the study, degradation of active Cs promoter species (CsH and CsNH2) into inactive CsOH emerged as the primary deactivation mechanism. By increasing the Cs content from 2.2 mol % to 4.2 mol %, we achieved stable, continuous ammonia synthesis for nearly 90 hours, showcasing one of the longest-running mechanocatalytic gas phase reactions. Studies of the temperature dependence of the reaction revealed negligible bulk temperature influence in the range of -10 °C to 100 °C, highlighting the dominance of mechanical action over bulk thermal effects. This study offers insights into the complex interplay between mechanical processing, reactive species, and deactivation mechanisms in mechanocatalytic ammonia synthesis.

Mechanocatalytic Synthesis of Ammonia: State of the Catalyst During Reaction and Deactivation Pathway

AbstractAmmonia synthesis holds significant importance for both agricultural fertilizer production and emerging green energy applications. Here, we present a comprehensive characterization of a catalyst for mechanochemical ammonia synthesis, based on Cs‐promoted Fe. The study sheds light on the catalyst‘s dynamic evolution under reaction conditions and the origin of deactivation. Initially, elemental Cs converts to CsH, followed by partial CsOH formation due to trace oxygen impurities on the surface of the Fe metal and the equipment. Concurrently, the mechanical milling process comminutes Fe, exposing fresh metallic Fe surfaces. This comminution correlates with an induction period observed during ammonia formation. Critical to the study, degradation of active Cs promoter species (CsH and CsNH2) into inactive CsOH emerged as the primary deactivation mechanism. By increasing the Cs content from 2.2 mol % to 4.2 mol %, we achieved stable, continuous ammonia synthesis for nearly 90 hours, showcasing one of the longest‐running mechanocatalytic gas phase reactions. Studies of the temperature dependence of the reaction revealed negligible bulk temperature influence in the range of −10 °C to 100 °C, highlighting the dominance of mechanical action over bulk thermal effects. This study offers insights into the complex interplay between mechanical processing, reactive species, and deactivation mechanisms in mechanocatalytic ammonia synthesis.

Continuous ammonia synthesis from water and nitrogen via contact electrification

We synthesized ammonia (NH3) by bubbling nitrogen (N2) gas into bulk liquid water (200 mL) containing 50 mg polytetrafluoroethylene (PTFE) particles (~5 µm in diameter) suspended with the help of a surfactant (Tween 20, ~0.05 vol.%) at room temperature (25 °C). Electron spin resonance spectroscopy and density functional theory calculations reveal that water acts as the proton donor for the reduction of N2. Moreover, isotopic labeling of the N2 gas shows that it is the source of nitrogen in the ammonia. We propose a mechanism for ammonia generation based on the activation of N2 caused by electron transfer and reduction processes driven by contact electrification. We optimized the pH of the PTFE suspension at 6.5 to 7.0 and employed ultrasonic mixing. We found an ammonia production rate of ~420 μmol L-1 h-1 per gram of PTFE particles for the conditions described above. This rate did not change more than 10% over an 8-h period of sustained reaction.

Optimizing islanded green ammonia and hydrogen production and export from Saudi Arabia

Hydrogen and its derivatives hold significant promise for decarbonizing power and transport. This study proposes a mixed-integer linear optimization model for the flexible production and transportation of islanded green hydrogen and ammonia. Wind and solar databases of three coastal locations across the Kingdom of Saudi Arabia were utilized to provide a holistic geographic perspective. The results show that plant optimization can lead to production levelized costs of ammonia of 383 USD/tonne NH3, and production levelized costs of hydrogen down to 1.57 USD/kg H2 by 2030. The single largest cost driver is the energy cost, representing 60–70 % of the total project cost. In low-wind resource areas, battery storage technology plays a critical role in supplying consistent energy for continuous ammonia synthesis. Transportation to final demand centers in Europe or Asia can lead to additional costs of less than 40 USD/tonne NH3 and less than 0.8 USD/kg H2 via liquid hydrogen route.

Coupling Iron Sludge Addition and Intermittent Aeration for Achieving Simultaneous Methanogenesis, Feammox, and Denitrification in a Single Reactor Treating Fish Sludge.

An integrated anaerobic digestion system for the simultaneous removal of carbon and nitrogen from fish sludge was developed by coupling iron sludge supplementation with intermittent aeration. In terms of nitrogen removal, Fe(III) in iron sludge could trigger Feammox reactions and intermittent aeration could drive the Fe(II)/Fe(III) cycle to sustain continuous ammonia removal. Mass balance analysis suggested that nitrate was the main product of Feammox, which was subsequently removed through heterotrophic denitrification. In terms of carbon removal, the Fe(III)-induced dissimilatory iron reduction (DIR) process significantly promoted fish sludge hydrolysis and provided more simple organics for methanogens and denitrifiers, but aeration showed a negative impact on methanogenesis. To promote nitrogen removal and avoid serious methanogenesis inhibition, different aeration intensities were studied. Results showed that compared with the control without aeration or iron sludge addition, aeration for 5 min every 3 days (150 mL/min) contributed to a 29.0% lower NH4+-N concentration and a 12.1% lower total chemical oxygen demand level on day 28, and the decline in methane yield was acceptable (only 13.5% lower). Simultaneous methanogenesis, Feammox, and denitrification in a single reactor treating fish sludge were achieved, which provides a simple and low-cost strategy for the treatment of organic wastewater.

Cascade N2 Reduction Process with DBD Plasma Oxidation and Electrocatalytic Reduction for Continuous Ammonia Synthesis.

Due to the extremely high bond energy of N≡N (∼941 kJ/mol), the traditional Haber-Bosch process of ammonia synthesis is known as an energy-intensive and high CO2-emission industry. In this paper, a cascade N2 reduction process with dielectric barrier discharge (DBD) plasma oxidation and electrocatalytic reduction as an alternative route is first proposed. N2 is oxidized to be reactive nitrogen species (RNS) by nonthermal plasma, which would then be absorbed by KOH solution and electroreduced to NH4+. It is found that the production of NOx is a function of discharge length, discharge power, and gas flow rate. Afterward, the cobalt catalyst is used in the process of electrocatalytic reduction of ammonia, which shows high selectivity (Faradic efficiency (FE) above 90%) and high yield of ammonia (45.45 mg/h). Finally, the cascade plasma oxidation and electrocatalytic reduction for ammonia synthesis is performed. Also, the performance of the reaction system is evaluated. It is worth mentioning that a stable and sustainable ammonia production efficiency of 16.21 mg/h is achieved, and 22.16% of NOx obtained by air activation is converted into NH4+. This work provides a demonstration for further industrial application of ammonia production with DBD plasma oxidation and electrocatalytic reduction techniques.

Continuous ammonia electrosynthesis using physically interlocked bipolar membrane at 1000 mA cm−2

Electrosynthesis of ammonia from nitrate reduction receives extensive attention recently for its relatively mild conditions and clean energy requirements, while most existed electrochemical strategies can only deliver a low yield rate and short duration for the lack of stable ion exchange membranes at high current density. Here, a bipolar membrane nitrate reduction process is proposed to achieve ionic balance, and increasing water dissociation sites is delivered by constructing a three-dimensional physically interlocked interface for the bipolar membrane. This design simultaneously boosts ionic transfer and interfacial stability compared to traditional ones, successfully reducing transmembrane voltage to 1.13 V at up to current density of 1000 mA cm−2. By combining a Co three-dimensional nanoarray cathode designed for large current and low concentration utilizations, a continuous and high yield bipolar membrane reactor for NH3 electrosynthesis realized a stable electrolysis at 1000 mA cm−2 for over 100 h, Faradaic efficiency of 86.2% and maximum yield rate of 68.4 mg h−1 cm−2 with merely 2000 ppm NO3- alkaline electrolyte. These results show promising potential for artificial nitrogen cycling in the near future.

Continuous ammonia synthesis using Ru nanoparticles based on Li–N2 battery

The exponential increase in carbon dioxide emission has attracted the attention of the international community, and the role of ammonia as a carbon-free energy source has become prominent. The rapid development of renewable energy sources guides humankind toward electrochemical ammonia synthesis. Lithium-mediated nitrogen reduction (LiNR) is a well-recognized and promising approach to the electrochemical synthesis of ammonia and is combined with the Li–N2 battery in the present study. Ru nanoparticle is used as cathode catalyst, H2O is chosen as the proton source for continuous ammonia synthesis, and is beneficial for the reaction of Li and N2 theoretically and experimentally, to produce LiOH and NH3 at the cathode interface. The proton donor also participates in the film formation reaction and the decomposition of cathode products, Li-salt, is verified by charging, so that lithium ions are cyclized and reutilized next time. This article provides a novel application for Li–N2 battery, which can be used as a model for continuous lithium-mediated ammonia synthesis (C-LiNR). Futhermore, it highlights that the ternary roles of the optimal proton source worthy of emphatically study in LiNR.

“Electro-dissolution” of gold nanoclusters for constructing ammonia sensor

• The sensor overcomes the common obstacles in ammonia detection, the high energy barrier of ammonia electrocatalysis and the toxicity of N -ads. • Further improved the electro-dissolution mechanism for ammonia detection by theoretical analysis and expanded the application to more substances. • The economical and facile constructed sensor has excellent reproducibility under high-intensity work both in theory and practice. Overcoming the electrocatalytic energy barrier mediated by Gerischer-Mauerer's mechanism has always been a major challenge in ammonia detection. The previous report [1] that ammonia can electro-dissolve Au gives us inspiration to establish a more efficient and reusable electrochemical transmission technique for ammonia detection and, above all, remove the ammonia electrocatalytic barrier. In this work, the latent electro-dissolution activity of ammonia towards Au was employed to construct the sensing interface. The sensor applied the potentiostatic electrodeposition method to grow Au crystals on the surface of carbon cloth, offering a simple and low-cost alternative for practical production. Additionally, the electro-dissolution sensing method effectively addresses the limitation of high energy barrier and toxic products ( N -ads) in catalytic oxidation of ammonia. Cyclic Voltammetry and Tafel curve demonstrate the electrochemical properties of Au/CC and help to predict the relationship between the ammonia concentration and current through theoretical analysis, which were further confirmed by an i-t curve. We proved that the sensor has excellent reproducibility under high-intensity work in theory and it exhibits high stability over 7 weeks in practice. The economical and facile constructing electrode method and the outstanding performance in long-term reuse greatly reduce the cost. Generally, the sensor is suitable for continuous ammonia monitoring in wastewater and quantitative analysis of products by chemical companies.

Spatial Variation in Cost of Electricity-Driven Continuous Ammonia Production in the United States

Spatial Variation in Cost of Electricity-Driven Continuous Ammonia Production in the United States

Simplified CVD route to near-zero thickness silicon nitride films

Silicon nitride (SiNx, x ∼ 1) thin films were deposited by chemical vapor deposition on silicon oxide (SiO2) substrates by combining controlled pulses of the precursor 1,3,5-tri(isopropyl)cyclotrisilazane (TICZ, C9H27N3Si3) with a continuous ammonia (NH3) plasma. This plasma-assisted pulsed CVD (PPCVD) process enables the integration of the nanoscale thickness and uniformity control achieved in atomic layer deposition with the efficiency of plasma-enhanced CVD (PE-CVD). TICZ was selected because it is a nonpyrophoric stable liquid with a high vapor pressure (∼133 Pa at 70 °C) and could act as a single source for SiNx with both high Si and N contents. An optimized PPCVD process window was identified consisting of a substrate temperature of 350 °C, a TICZ pulse of ≤0.2 s, and a TICZ purge pulse ≥10 s in a continuous direct NH3 plasma at a NH3 flow rate and a power of 40 SCCM and 3000 W, respectively. The as-deposited films were analyzed by x-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry. XPS analysis confirmed the absence of any C inclusion and demonstrated the existence of the 1:1 Si:N ratio. In situ, real-time ellipsometry measurements indicated that SiNx growth occurred in a typical PE-CVD regime. They also yielded an as-grown SiNx average refractive index of ∼1.75.