Ammonia Synthesis Rate Research Articles

A Sucker-Reactor Polyoxometalate Assembled Superstructures for Efficient Photocatalytic Nitrogen Fixation.

Designing a reaction system that integrates reactant capture and transformation in an artificial photosynthesis system to achieve high reaction efficiency remains challenging. Here, an ionic liquid (IL) -polyoxometalate (POM) superstructure photocatalyst (P2HPMo) is reported, where the anisotropy of the superstructure is allowed by adjusting the alkyl chain lengths of ILs. Experimental data and theoretical simulation show that ILs and POM serve as the "sucker" and "reactor" of the reaction system to capture and transform the reactants, respectively. In particular, the addition of quaternary phosphorous IL cations is not only conducive to the adsorption of N2 but also effectively promotes the activation of N2 by manipulating the energy band and electronic structure. Consequently, the synthesized P2HPMo exhibits an ammonia synthesis rate of 98 µmol·gcat -1·h-1, which is one of the highest values available in a sacrificial agent-free system.

Ni‐MOF‐74 Derived Carbon‐Based Ni Catalysts for Efficient Catalytic Ammonia Synthesis via Pulsed DBD Plasma

ABSTRACTDesigning efficient noble metal‐free catalysts for plasma‐catalytic ammonia synthesis is significant and challenging. Carbon‐based metal catalysts were prepared at different pyrolysis temperatures using the Ni‐MOF‐74 precursor. The effects of Ni‐MOF‐74 and its derived carbon‐based metal catalysts on pulsed dielectric barrier discharge (DBD) plasma ammonia synthesis were investigated. The results showed that Ni‐MOF‐74‐300 with both the MOF structure and nickel metal particles exhibited the best catalytic performance for ammonia synthesis. The ammonia synthesis rate reached 41.38 mmol g−1 h−1, whereas the nitrogen conversion rate was as high as 1.54% with an energy yield of 3.04 g kWh−1. Compared to the situation of plasma only, the ammonia synthesis rate, nitrogen conversion rate, and energy yield were increased by 28.46 times, 5.7 times, and 5.5 times, respectively.

Scalable ammonia synthesis on the modified crystal structure of Cu3PS4 electrocatalyst

Ammonia production, which is vital for agricultural and industrial applications, typically relies on energy-intensive processes that contribute to global CO2 emissions. Electrochemical nitrogen reduction is a promising alternative, although it faces challenges such as low yield and selectivity. Transition-metal-based catalysts, particularly Cu, are promising for overcoming these limitations. Cu3PS4 catalysts were synthesized and evaluated using a 9 cm2-scale electrode, revealing enhanced performance attributed to change in the crystal and electronic structure of Cu, facilitating N2 adsorption and improving the reaction activity. Notably, the ammonia synthesis rate reached 128 μg h-1 mgcat-1 at −1.0 V vs. RHE and faradaic efficiency was 34 % at −0.8 V vs. RHE. These findings provide potential insights into the improvement of practical electrochemical synthesis of ammonia.

Highly active manganese nitride-europium nitride catalyst for ammonia synthesis

The development of efficient catalysts for ammonia synthesis under mild conditions is critical for establishing a carbon-neutral society powered by renewable ammonia. While significant effort has been focused on Fe and Ru-based catalysts, there have been very limited studies on manganese-based catalysts for ammonia synthesis because of their low intrinsic catalytic activity. Herein, we report that the synergy between manganese nitride (Mn4N) and europium nitride (EuN) yields an ammonia synthesis rate that is 41 and 25 times higher than that of neat Mn4N and EuN, respectively. Detailed studies suggest that a [Eu-N-Mn] species at the interface of Mn4N and EuN plays a pivotal role in ammonia synthesis. Compositing of Mn4N with other rare earth metal nitrides such as LaN, PrN, and CeN also leads to a significant enhancement in catalytic activity. This work broadens the scope of advanced nitride catalysts for ammonia synthesis.

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.

Ammonia synthesis rate over a wide operating range: from experiments to validated kinetic models

With the increasing demand for flexible operation of ammonia production, the feasibility of using reaction kinetic models to predict the performance of a Haber Bosch reactor in a wide operating range must be evaluated. This study compares the feasibility of a lumped Temkin rate expression with a more complex lumped microkinetic model in predicting turnover rates across diverse temperatures and feed compositions. Evaluation and validation were carried out through ammonia synthesis experiments on a magnetite‐based industrial catalyst at temperatures ranging from 548 K to 773 K and H2:N2 ratios between 4:1 to 1:1 at 90 bar. While excellent agreement between model predictions and experiments was observed at 648 K, significant discrepancies emerged at 548 K. These findings are valueable for both state‐of‐the‐art ammonia synthesis reactors and green ammonia plants utilizing electrolysis‐derived hydrogen, where flexible operating conditions are paramount. Moreover, integrating site density as a function of temperature and the partial pressure of H2 into the lumped microkinetic model marks a notable advancement, promising enhanced precision in addressing varied operating conditions.

Nanosecond pulsed gliding arc plasma for ammonia synthesis: better insight from discharge mode and vibrational temperature

Low-temperature plasma technology is a promising technological route to achieve green and efficient ammonia synthesis at ambient temperature and pressure. In this work, a Laval nozzle type gliding arc plasma reactor was designed for the direct synthesis of ammonia from N2 and H2 discharges ignited by a high voltage nanosecond pulsed power supply to investigate the effect of different electrode gaps, pulse voltages, and V N2:V H2 on ammonia synthesis. The nanosecond pulsed plasma discharges were characterized through oscilloscope and optical emission spectroscopy (OES). The maximum rate of NH3 synthesis was 538.12 μmol·h−1 at 1.5 mm electrode gap, 16 kV peak pulse voltage, 6 kHz pulse repetition frequency, 100 ns pulse width, 100 ns pulse rising edge, 100 ns pulse falling edge, and 200 mL·min−1 total gas flow rate with V N2:V H2 = 1:1. It was demonstrated that the discharge mode of the nanosecond pulsed gliding arc plasma can transit from a unipolar state to a bipolar state determined by the duty cycle accompanied with higher discharge power and vibrational temperature. Bipolar discharge mode is beneficial to improve the efficiency of plasma ammonia synthesis because of it can strengthen the plasma discharge and increase the vibrational temperature. The ammonia synthesis rate and N2 conversion rate increased with the increase of the discharge power and vibrational temperature.

Reinforced BiOBr for visible-light-driven nitrogen fixation: A synergistic effect of cocatalyst and oxygen vacancies

Photocatalytic nitrogen fixation is a promising long-term strategy for NH3 synthesis, with the development of effective and durable photocatalysts being crucial for achieving high-efficiency N2 to NH3 conversion. In this study, we employed vacancy and interface engineering to create bismuth (Bi) nanoparticles on hierarchical oxygen-deficient BiOBr microspheres using a one-step solvothermal approach. These Bi-decorated BiOBr microspheres, featuring oxygen vacancies, achieved a high photocatalytic ammonia synthesis rate of 222.3 μmol·g−1·h−1 in pure water under visible light irradiation, which is 3.25 times higher than that of the original BiOBr. Atomic-scale images of the interface between the defective regions of BiOBr and the Bi cocatalyst and several other material characterizations confirmed that the enhanced photoreduction activity of Bi/BiOBr is due to the synergistic effects of the metal Bi and the oxygen vacancies. These results present a straightforward and practical method for designing efficient photocatalysts for nitrogen fixation.

Contribution of vibrational excited molecular nitrogen to ammonia synthesis using an atmospheric-pressure plasma jet

The contribution of atomic nitrogen is fairly possible in plasma-assisted catalytic synthesis of ammonia since it has high adsorption probabilities on solid surfaces. On the other hand, recently, the contribution of vibrational excited molecular nitrogen to ammonia synthesis has been discussed. In this work, we compared the fluxes of atomic nitrogen and vibrational excited molecular nitrogen with the rate of plasma-assisted ammonia synthesis. We employed an atmospheric-pressure nitrogen plasma jet, and the spatial afterglow of the plasma jet and a hydrogen flow irradiated the surface of a ruthenium catalyst. The fluxes of atomic nitrogen and vibrational excited molecular nitrogen were measured by two-photon absorption laser-induced fluorescence spectroscopy and laser Raman scattering, respectively. The synthesis rate of ammonia had a positive correlation with the flux of vibrational excited molecular nitrogen, while the variation of the synthesis rate with the gas flow rate was opposite to the flux of atomic nitrogen. The experimental results indicate the contribution of vibrational excited molecular nitrogen to the synthesis of ammonia using the atmospheric-pressure plasma, where the flux of vibrational excited molecular nitrogen is more than four orders of magnitude higher than that of atomic nitrogen.

Dielectric barrier discharge plasma-assisted catalytic ammonia synthesis: synergistic effect of Ni-MOF-74 catalyst and nanosecond pulsed plasma

Ammonia is one of the most important chemical raw materials in both manufacture and life of human. Traditionally Haber-Bosch method for ammonia synthesis involves high temperature and high pressure conditions, leading to significant energy consumption and environmental pollution. Non-thermal plasma (NTP) is a promising alternative approach to ammonia synthesis at low temperature and atmospheric pressure. In this study, the synergistic effect of nanosecond pulsed dielectric barrier discharge (np-DBD) and Ni-MOF-74 catalyst was investigated in ammonia synthesis by utilizing nitrogen and hydrogen as feedstock. The results demonstrated that the plasma catalytic-synthesis process parameters play a crucial role in the synthesis process of ammonia. The highest ammonia synthesis rate of 5145.16 μmol·g−1·h−1 with an energy efficiency of 1.27 g·kWh−1 was observed in the presence of the Ni-MOF-74 catalyst, which was 3.7 times higher than that without Ni-MOF-74 catalyst. The synergistic effect of Ni-MOF-74 catalyst and nanosecond pulsed plasma was explored by in-situ plasma discharge diagnostics.

Photoexcitation Altered Reaction Pathway Greatly Facilitate Ammonia Synthesis Over Isolated Ru Sites

AbstractAmmonia, poised as a carbon‐neutral energy carrier, holds immense promise in reshaping the future energy landscape. Despite the enduring importance of the Haber–Bosch process in ammonia production, its substantial carbon emissions and energy demands necessitate more sustainable pathways. Here, an advanced ammonia synthesis route, enhanced by photoexcitation is demonstrated, which fundamentally modifies the activation pathways of N2 molecules. This alteration significantly lowers the reaction activation energy, resulting in remarkably improved reaction efficiency. The impact of light excitation culminates in an unprecedented ammonia synthesis rate of 18 mmol g−1 h−1, surpassing the traditional thermal catalytic process by 2.57‐fold. More importantly, light assistance reduces the thermal energy input by ≈16%, making it comparable to thermal catalysis while substantially improving energy utilization. This work introduces a greener strategy for ammonia synthesis, pushing the century‐old fossil‐fueled Haber–Bosch process to a new frontier.

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.

Tailoring the surface acidity of catalyst to enhance nonthermal plasma-assisted ammonia synthesis rates

We report nonthermal plasma-assisted catalytic ammonia synthesis from N2 and H2 molecules at near ambient conditions in a custom-built coaxial dielectric barrier discharge plasma reactor. Here, we strategically designed catalysts to facilitate dissociation of strong nitrogen bond and desorption of NH3 molecules. This work demonstrates the use of empty orbitals of boron doped in graphitic carbon nitride (BCN) to activate nitrogen molecules, by creating electron-deficient sites, under nonthermal plasma conditions. Transition metals (Co and Fe) further contribute to the ammonia generation by altering the amount of weak acid sites of the BCN catalyst. As a result, at 20.16 kJ L−1, the maximum ammonia synthesis rate of ∼2.48mmolg−1h−1 was achieved by Co-BCN that corresponds to energy efficiency of 2.09 g-NH3 kWh−1, which was ca. 2.89-folds higher than that of plasma only. Evidently, dual mechanisms at play, leading to enhanced ammonia synthesis rates. Our strategy of tailoring catalyst structure provides a roadmap for engineering synergy with nonthermal plasma towards targeted applications.

Ammonia synthesis over cesium-promoted mesoporous-carbon-supported ruthenium catalysts: Impact of graphitization degree of the carbon support

Carbon-supported ruthenium catalysts facilitate electrically-assisted Haber–Bosch ammonia synthesis. However, the relationship between carbon supports and catalytic performance remains ambiguous. We developed ordered mesoporous carbon plates (MCPs) with varying graphitization degrees as Cs-promoted Ru catalyst supports, examining correlations between ammonia synthesis rate and key structural parameters, included graphitization degree, Ru nanoparticle size, and Cs/Ru ratio. High-graphitization-degree carbon supports resisted methanation and facilitated formation of reductive activation enabled dynamic Cs0 species as electronic promotor, induced by spillover hydrogen from the Ru surface to CsOH. Density functional theory calculations further revealed that CsOH alleviated hydrogen poisoning. Notably, the catalyst supported on MCP-1100—which exhibited the highest graphitization degree among the supports and superior stability—with 10 wt% 2.3-nm-sized Ru nanoparticles and Cs/Ru = 2.5 achieved high ambient-pressure ammonia synthesis rates (7.9–43 mmolNH3·g−1·h−1) below 410 °C. Furthermore, it functioned under intermittent operating conditions, potentially integrating renewable-electricity-based electrolytic hydrogen production.

Regulating oxygen vacancies by Zn atom doping to anchor and disperse promoter Ba on MgO support to improve Ru-based catalysts activity for ammonia synthesis.

In heterogeneous catalysis, surface defects are widely regarded as an effective means to enhance the catalytic performance of catalysts. In this study, the oxygen vacancy-rich Mg(1-X)ZnXO solid solution support was successfully prepared by doping a small amount of Zn into MgO nanocrystals. Based on this support, Ru/Ba-Mg(1-X)ZnXO catalyst for ammonia synthesis was prepared. Characterization using TEM, EPR, XPS, and DFT calculations confirmed the successful substitution of Zn atoms for Mg atoms leading to the formation of more oxygen vacancies (OVs). N2-TPD, SEM and TEM analyses revealed that a small amount of Zn had minimal influence on the surface morphology and the size of Ru nanoparticles. The abundance of OVs in the support was identified as the primary factor enhancing the catalytic activity. XPS, H2-TPD and kinetics experiment studies further elucidated the mechanism by which OVs promote the reaction, with OVs serving as an anchor point for the promoter Ba on the MgO support and promoted the dispersion of Ba. This anchoring effect not only enhanced the electron density on Ru, favoring the dissociation of the N[triple bond, length as m-dash]N bond, but also mitigated hydrogen poisoning. As a result,the ammonia synthesis rate reached 1.73 mmol g-1 h-1. Furthermore, the CO2-TPD and H2-TPR analyses indicated that Zn doping effectively promotes the metal-support interaction (MSI) and surface alkalinity. The findings of this study offers valuable insights for the design of defective modified catalyst supports.

Ammonia synthesis via a protonic ceramic electrolysis cell (PCEC) using LaCu0.1Fe0.9O3−δ catalyst

A LCuF-based cell has a higher ammonia synthesis rate and faradaic efficiency than a LF-based cell because Cu doping generates more electrocatalytic active sites.

MgAl layered double hydroxide (LDH) for promoting ammonia synthesis in non-thermal plasma: Role of surface oxygen vacancy

Here, the MgAl layered double hydroxide (LDH) supports and relevant metal on LDH catalysts (i.e., Ni, Co, and Ru) were prepared and investigated under non thermal plasma (NTP) conditions to probe the role of surface oxygen vacancy (OV) in NTP-assisted ammonia (NH3) synthesis. The findings show that OV on the LDH carrier is highly beneficial to NH3 formation under NTP conditions, and concentration of OV on the LDH can be regulated by the post-synthesis calcination and hydrogen plasma etching. Additionally, loading of active metal species on the LDH could promote the NH3 synthesis further due to presence of multiple reaction pathways and the synergy between the surface OV and metal sites in such NTP-catalytic systems. As the result, the catalysts developed by this work showed high ammonia synthesis rates of 4.42−4.52 mmol g−1 h−1 and energy efficiencies of 1.67−1.71 gNH3 kWh−1, respectively. The findings of the work pave the way for the rational design and optimization of highly efficient catalysts with dual active sites for intensifying the NTP-catalytic ammonia synthesis.

Catalytic Behavior of K-doped Fe/MgO Catalysts for Ammonia Synthesis Under Mild Reaction Conditions.

An important part of realizing a carbon-neutral society using ammonia will be the development of an inexpensive yet efficient catalyst for ammonia synthesis under mild reaction conditions (<400 °C, <10 MPa). Here, we report Fe/K(3)/MgO, fabricated via an impregnation method, as a highly active catalyst for ammonia synthesis under mild reaction conditions (350 °C, 1.0 MPa). At the mentioned conditions, the activity of Fe/K(3)/MgO (17.5 mmol h-1 gcat -1 ) was greater than that of a commercial fused iron catalyst (8.6 mmol h-1 gcat -1 ) currently used in the Haber-Bosch process. K doping was found to increase the ratio of Fe0 on the surface and turnover frequency of Fe in our Fe/K(3)/MgO catalyst. In addition, increasing the pressure to 3.0 MPa at the same temperature led to a significant improvement of the ammonia synthesis rate to 29.6 mmol h-1 gcat -1 , which was higher than that of two more expensive, benchmark Ru-based catalysts, which are also potential alternative catalysts. A kinetics analysis revealed that the addition of K enhanced the ammonia synthesis activity at ≥300 °C by changing the main adsorbed species from NH to N which can accelerate dissociative adsorption of nitrogen as the rate limiting step in ammonia synthesis.

Co‐Ni/MOF‐74 catalyst packed‐bed DBD plasma for ammonia synthesis

AbstractNonthermal plasma (NTP) provides a potential and sustainable route for the synthesis of ammonia. In this work, a Co–Ni/MOF‐74 catalyst was developed to synthesize ammonia from N2 and H2 in a dielectric barrier discharge (DBD) plasma at low temperature and atmospheric pressure. Co–Ni/MOF‐74 showed the highest ammonia synthesis rate up to 2608.70 μmol g−1 h−1 at 200°C, with V(N2):V(H2) ratio of 1:1 and specific energy input of 33.27 kJ L−1. The catalytic activity was increased by 19.57% for Co–Ni/MCM‐41 and 375% for Co‐Ni/Al2O3, respectively. It was observed that the average electric field (E) and power efficiency were enhanced while adding Co–Ni/MOF‐74 to the reaction system.

Self-sacrificed BiOBr template-assisted synthesis of α-Bi2O3/Bi3O4Br heterojunctions with oxygen vacancies for enhanced photocatalytic nitrogen fixation

The catalytic conversion of nitrogen to ammonia is one of the most significant processes in nature and the chemical industry. However, the traditional Haber-Bosch process of ammonia synthesis consumes substantial energy and emits a large amount of carbon dioxide. The efficiency of photocatalytic N2 activation is severely limited by the lack of N2 adsorption sites and poor carrier utilization. Herein, an efficient α-Bi2O3/Bi3O4Br heterojunction is proposed with a photocatalytic nitrogen fixation activity of 238.67 μmol·g−1·h−1. Compared with the BiOBr precursor, α-Bi2O3 and Bi3O4Br, the α-Bi2O3/Bi3O4Br heterojunction with oxygen vacancies can improve the adsorption and activation capacity of N2 and promote the separation efficiency of charge carrier pairs by accommodating photogenerated electrons under visible light through the mechanism of N-type semiconductors. Therefore, oxygen vacancies and heterojunction engineering of semiconductive nanomaterials provide a promising method for the rational design of photocatalysts to enhance the rate of ammonia synthesis under mild conditions.