Plasma-Enhanced Catalytic Synthesis of Ammonia over a Ni/Al2O3 Catalyst at Near-Room Temperature: Insights into the Importance of the Catalyst Surface on the Reaction Mechanism

Promoted Two-Step Ammonia Synthesis with CoOOH/Co foam at Ampere-Level Current Density and Nearly 100% Faraday Efficiency from Air and Water

Ammonia (NH3) is regarded as an essential hydrogen storage material in the new energy field, and plasma-electrocatalytic synthesis of NH3 (PESA) is an alternative to the traditional Haber-Bosch process. Here, a bifunctional catalyst CoOOH/CF is proposed to enhance the PESA process. Benefiting from the efficient activation of O2 by CoOOH/CF, NOx - yield rate can reach the highest value of 171.90 mmol h-1 to date. Additionally, CoOOH holds a more negative d-band center, thereby exhibiting weaker adsorption toward NO*, lowering the energy barrier for the rate determining step, resulting in a high NH3 yield rate (302.55 mg h-1 cm-2 at -0.8 V) with ampere-level NH3 current density (2.86 A cm-2 at -0.8 V) and nearly 100% Faraday efficiency (FE, 99.8% at -0.6 V). Moreover, CoOOH/CF achieves an excellent 4.54 g h-1 NH3 yield rate with 97.9% FE in an enlarged electrolyzer, demonstrating the feasibility of PESA on a large scale.

Production of 1,3-propanediol via in situ glycerol hydrogenolysis in aqueous phase reforming using bimetallic W-Ni/CeO2

The production of 1,3-propanediol via in situ glycerol hydrogenolysis and aqueous phase reforming is a promising technique to ensure high product yield with shorter reaction times and lower costs, as demonstrated in this study by investigating the effect of tungsten (W) doping on Ni/CeO2 catalysts. Physicochemical properties of catalyst were determined using XRD, H2-TPR, NH3-TPD, BET, and FESEM-EDX techniques, and the catalytic performance was investigated at 230 °C, 20 bar, and 5 wt.% glycerol in an autoclave batch reactor. W doping ranging from 1-7% improved the catalyst's performance, with 3% W in 10% Ni/CeO₂ (3W10NC) achieving the highest yield (2.4%), selectivity (33.3%), and a good conversion rate (72.18%). The effect of reaction parameter on the 3W10NC catalyst showed that increasing pressure and temperature from the initial parameters had a detrimental effect on 1,3-propanediol attributed to the phenomenon called over-hydrogenolysis. Increasing the glycerol concentration to 20 wt.% also had a positive effect, resulting in the highest 1,3-propanediol yield of 22.27%. The effect of reaction time study revealed that the yield of 1,3-propanediol continued to increase steadily, reaching 38.29% after 4 h of reaction under the optimal conditions of 230 °C, 20 bar, and 20 wt.% glycerol. The kinetic study confirmed that the reaction follows first-order reaction with activation energy of 20.104 kJ mol-1. The catalyst reusability test revealed a decrease in the yield of 1,3-propanediol to 32.55%, likely due to deactivation caused by sintering and leaching, as indicated by the FESEM micrograph, EDX spectra, and NH3-TPD.

Photoselectively modulating main products by changing the wavelength of visible light over D-π-A-D conjugated polymers

The diversity of catalytic products determines the difficulty of selective product modulation, which usually relies on adjusting the catalyst and reaction conditions to obtain different main products selectively. Herein, we synthesized D-π-A-D conjugated organic polymers (TH-COP) using cyclotriphosphonitrile, alkyne, 2H-benzimidazole, and sulfur units as electron donors, π bridges, electron acceptors, and electron donors, respectively. TH-COP exhibited excellent photoinduced carrier separation and redox ability under different visible light wavelengths, and the main products of its CO2 reduction are CH4 (1000.0 μmol g-1) and CO (837.0 μmol g-1) under 400-420 nm and 420-560 nm, respectively. In addition, TH-COP could completely convert phenylmethyl sulfide to methyl phenyl sulfone at 400-420 nm and diphenyl disulfide at 480-485 nm in yields up to 95 %. This study presents a novel strategy for the targeted fabrication of various main products using conjugated polymers by simply changing the wavelength range of visible light.

Recent Advances in Ammonia Synthesis: From Haber-Bosch Process to External Field Driven Strategies

Ammonia, a pivotal chemical feedstock and a potential hydrogen energy carrier, demands efficient synthesis as a key step in its utilization. The traditional Haber-Bosch process, known for its high energy consumption, has spurred researchers to seek ammonia synthesis under milder conditions. Advances in surface science and characterization technologies have deepened our understanding of the microscopic reaction mechanisms of ammonia synthesis. This article concentrates on gas-solid phase ammonia synthesis, initially exploring the latest breakthroughs and improvements in thermal catalytic synthesis. Building on this, it especially focuses on emerging external field-driven alternatives, such as photocatalysis, photothermal catalysis, and low-temperature plasma catalysis strategies. The paper concludes by discussing the future prospects and objectives of nitrogen fixation technologies. This comprehensive review is intended to provide profound insights for overcoming the inherent thermodynamic and kinetic constraints in traditional ammonia synthesis, thereby fostering a shift towards "green ammonia" production and significantly reducing the energy footprint.

Plasma-Driven Efficient Conversion of CO2 and H2O into Pure Syngas with Controllable Wide H2/CO Ratios over Metal-Organic Frameworks Featuring In Situ Evolved Ligand Defects

While the mild production of syngas (a mixture of H2 and CO) from CO2 and H2O is a promising alternative to the coal-based chemical engineering technologies, the inert nature of CO2 molecules, unfavorable splitting pathways of H2O and unsatisfactory catalysts lead to the challenge in the difficult integration of high CO2 conversion efficiency with produced syngas with controllable H2/CO ratios in a wide range. Herein, we report an efficient plasma-driven catalytic system for mild production of pure syngas over porous metal-organic framework (MOF) catalysts with rich confined H2O molecules, where their syngas production capacity is regulated by the in situ evolved ligand defects and the plasma-activated intermediate species of CO2 molecules. Specially, the Cu-based catalyst system achieves 61.9 % of CO2 conversion and the production of pure syngas with wide H2/CO ratios of 0.05 : 1-4.3 : 1. As revealed by the experimental and theoretical calculation results, the in situ dynamic structure evolution of Cu-containing MOF catalysts favors the generation of coordinatively unsaturated metal active sites with optimized geometric and electronic characteristics, the adsorption of reactants, and the reduced energy barriers of syngas-production potential-determining steps of the hydrogenation of CO2 to *COOH and the protonation of H2O to *H.

Plasma Catalysis Modeling: How Ideal Is Atomic Hydrogen for Eley-Rideal?

Plasma catalysis is an emerging technology, but a lot of questions about the underlying surface mechanisms remain unanswered. One of these questions is how important Eley-Rideal (ER) reactions are, next to Langmuir-Hinshelwood reactions. Most plasma catalysis kinetic models predict ER reactions to be important and sometimes even vital for the surface chemistry. In this work, we take a critical look at how ER reactions involving H radicals are incorporated in kinetic models describing CO2 hydrogenation and NH3 synthesis. To this end, we construct potential energy surface (PES) intersections, similar to elbow plots constructed for dissociative chemisorption. The results of the PES intersections are in agreement with ab initio molecular dynamics (AIMD) findings in literature while being computationally much cheaper. We find that, for the reactions studied here, adsorption is more probable than a reaction via the hot atom (HA) mechanism, which in turn is more probable than a reaction via the ER mechanism. We also conclude that kinetic models of plasma-catalytic systems tend to overestimate the importance of ER reactions. Furthermore, as opposed to what is often assumed in kinetic models, the choice of catalyst will influence the ER reaction probability. Overall, the description of ER reactions is too much "ideal" in models. Based on our findings, we make a number of recommendations on how to incorporate ER reactions in kinetic models to avoid overestimation of their importance.

In Situ Ambient Pressure Photoelectron Spectroscopy Study of the Plasma-Surface Interaction on Metal Foils

The plasma-surface interface has sparked interest due to its potential of creating alternative reaction pathways not available in typical gas-surface reactions. Currently, there are a limited number of in situ studies investigating the plasma-surface interface, restricting the development of its application. Here, we report the use of in situ ambient pressure X-ray photoelectron spectroscopy in tandem with an optical spectrometer to characterize the hydrogen plasma's interaction with metal surfaces. Our results demonstrate the possibility to monitor changes on the metal foil surface in situ in a plasma environment. We observed an intermediate state from the metal oxide to an -OH species during the plasma environment, indicative of reactive hydrogen radicals at room temperature. Furthermore, the formation of metal-carbides in the hydrogen plasma environment was detected, a characteristic absent in gas and vacuum environments. These findings illustrate the significance of performing in situ investigations of the plasma-surface interface to better understand and utilize its ability to create reactive environments at low temperature.

Plasma-Assisted Sustainable Nitrogen-to-Ammonia Fixation: Mixed-phase, Synergistic Processes and Mechanisms

Ammonia plays a crucial role in industry and agriculture worldwide, but traditional industrial ammonia production methods are energy-intensive and negatively impact the environment. Ammonia synthesis using low-temperature plasma technology has gained traction in the pursuit of environment-benign and cost-effective methods for producing green ammonia. This Review discusses the recent advances in low-temperature plasma-assisted ammonia synthesis, focusing on three main routes: N2+H2 plasma-only, N2+H2O plasma-only, and plasma coupled with other technologies. The reaction pathways involved in the plasma-assisted ammonia synthesis, as well as the process parameters, including the optimum catalyst types and discharge schemes, are examined. Building upon the current research status, the challenges and research opportunities in the plasma-assisted ammonia synthesis processes are outlined. The article concludes with the outlook for the future development of the plasma-assisted ammonia synthesis technology in real-life industrial applications.

Modelling the effect of surface charging on plasma synthesis of ammonia using DFT

Non-equilibrium plasma has been found to have a synergistic effect on catalytic synthesis of NH3. The non-equilibrium plasma and catalyst surface together could affect NH3 synthesis through several mechanisms. Charging of the catalyst surface in the presence of non-equilibrium plasma is one such mechanism. We employed density functional theory (DFT) calculations to understand the effect of surface charge on surface reactivity of γ-Al2O3 supported single metal atom catalysts and a metal cluster. We investigated the effect of surface charge on adsorption energies of common adsorbates involved in NH3 synthesis. It is found that adsorption energy of N, N2, H, H2, NH and NH2 on metal atoms increases by up to ∼1.2 eV, whereas NH3 desorption is increased by up to 0.45 eV upon surface charging. The present results provide a new mechanism of plasma enhanced catalysis potentially explaining why Ni, Pt and Co have better catalytic performance compared to Ru and Fe in ammonia plasma catalysis. Furthermore, we found that the correlations between adsorption energies of adsorbates change significantly with surface charging. These findings suggest that surface charging might play an important role in plasma synthesis of NH3.

Plasma-induced nitrogen vacancy-mediated ammonia synthesis over a VN catalyst

Plasma catalysis has recently been recognized as a promising route for artificial N2 reduction under mild conditions. Here we report a highly active VN catalyst for plasma-catalytic NH3 synthesis via the typical Mars-van Krevelen (MvK) mechanism. Our results indicate that NH3 synthesis occurs through the continuous regeneration and elimination of nitrogen vacancies on the VN surface. With this strategy, the VN catalyst achieves a superhigh NH3 yield of 143.2 mg h-1 gcat.-1 and a competitive energy efficiency of 1.43 gNH3 kW h-1.

A Study on the Role of Electric Field in Low-Temperature Plasma Catalytic Ammonia Synthesis via Integrated Density Functional Theory and Microkinetic Modeling

Low-temperature plasma catalysis has shown promise for various chemical processes such as light hydrocarbon conversion, volatile organic compounds removal, and ammonia synthesis. Plasma-catalytic ammonia synthesis has the potential advantages of leveraging renewable energy and distributed manufacturing principles to mitigate the pressing environmental challenges of the energy-intensive Haber-Bosh process, towards sustainable ammonia production. However, lack of foundational understanding of plasma-catalyst interactions poses a key challenge to optimizing plasma-catalytic processes. Recent studies suggest electro- and photoeffects, such as electric field and charge, can play an important role in enhancing surface reactions. These studies mostly rely on using density functional theory (DFT) to investigate surface reactions under these effects. However, integration of DFT with microkinetic modeling in plasma catalysis, which is crucial for establishing a comprehensive understanding of the interplay between the gas-phase chemistry and surface reactions, remains largely unexplored. This paper presents a first-principles framework coupling DFT calculations and microkinetic modeling to investigate the role of electric field on plasma-catalytic ammonia synthesis. The DFT-microkinetic model shows more consistent predictions with experimental observations, as compared to the case wherein the variable effects of plasma process parameters on surface reactions are neglected. In particular, predictions of the DFT-microkinetic model indicate electric field can have a notable effect on surface reactions relative to other process parameters. A global sensitivity analysis is performed to investigate how ammonia synthesis pathways will change in relation to different plasma process parameters. The DFT-microkinetic model is then used in conjunction with active learning to systematically explore the complex parameter space of the plasma-catalytic ammonia synthesis to maximize the amount of produced ammonia while inhibiting reactions dissipating energy, such as the recombination of H2 through gas-phase H radicals and surface-adsorbed H. This paper demonstrates the importance of accounting for the effects of electric field on surface reactions when investigating and optimizing the performance of plasma-catalytic processes.

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.

Impact of the geometric structure parameter on the performance of dielectric barrier reactor for toluene removal

The reasonable geometry design of non-thermal plasma (NTP) reactor is significant for its performance. However, optimizing the reactor structure has received insufficient attention in the studies on removing volatile organic compounds by NTP. Several dielectric barrier discharge (DBD) reactors with various barrier thicknesses and discharge gaps were designed, and their discharge characteristics and toluene degradation performance were explored comprehensively. The number and intensity of current pulses, discharge power, emission spectrum intensity and gas temperature of the DBD reactors increased as barrier thickness decreased. The toluene removal efficiency and mineralization rate increased from 23.2-87.1% and 5.3-27.9% to 81.7-100% and 15.9-51.3%, respectively, when the barrier thickness reduced from 3 to 1 mm. With the increase of discharge gap, the breakdown voltage, discharge power, gas temperature and residence time increased, while the discharge intensity decreased. The reactor with the smallest discharge gap (3.5 mm) exhibited the highest toluene removal efficiency (78.4-100%), mineralization rate (15.6-40.9%) and energy yield (8.4-18.7 g/kWh). Finally, the toluene degradation pathways were proposed based on the detected organic intermediates. The findings can provide critical guidance for designing and optimizing of DBD reactor structures.

Plasma-Promoted Ammonia Decomposition over Supported Ruthenium Catalysts for COx -Free H2 Production

The efficient decomposition of ammonia to produce COx -free hydrogen at low temperatures has been extensively investigated as a potential method for supplying hydrogen to mobile devices based on fuel cells. In this study, we employed dielectric barrier discharge (DBD) plasma, a non-thermal plasma, to enhance the catalytic ammonia decomposition over supported Ru catalysts (Ru/Y2 O3 , Ru/La2 O3 , Ru/CeO2 and Ru/SiO2 ). The plasma-catalytic reactivity of Ru/La2 O3 was found to be superior to that of the other three catalysts. It was observed that both the physicochemical properties of the catalyst (such as support acidity) and the plasma discharge behaviours exerted significant influence on plasma-catalytic reactivity. Combining plasma with a Ru catalyst significantly enhanced ammonia conversion at low temperatures, achieving near complete NH3 conversion over the 1.5 %-Ru/La2 O3 catalyst at temperatures as low as 380 °C. Under a weight gas hourly space velocity of 2400 mL gcat -1  h-1 and an AC supply power of 20 W, the H2 formation rate and energy efficiency achieved were 10.7 mol gRu -1  h-1 and 535 mol gRu -1 (kWh)-1 , respectively, using a 1.5 %-Ru/La2 O3 catalyst.

Regulating oxygen vacancies and hydroxyl groups of α-MnO2 nanorods for enhancing post-plasma catalytic removal of toluene

Although nonthermal plasma (NTP) technology has high removal efficiency for volatile organic compounds (VOCs), it has limited carbon dioxide (CO2) selectivity, which hinders its practical application. In this study, α-MnO2 nanorods with tunable oxygen vacancies and hydroxyl groups were synthesized by two-step hydrothermal process to enhance their activity for deep oxidation of toluene. Hydrochloric acid (HCl) was used to assist in synthesis of α-MnO2 nanorods with tunable oxygen vacancies, furtherly, more hydroxyl groups were introduced to HCl-assisted synthesized α-MnO2 by K+ supplement. The results showed that the as-synthesized nanorods exhibited superior activity, improved by nearly 30% removal efficiency of toluene compared to pristine MnO2 at SIE = 339 J/L, and reaching high COx selectivity of 72% at SIE = 483 J/L, successfully promoting the deep oxidation of toluene. It was affirmed that oxygen vacancies played an important role in toluene conversion, improving the conversion of ozone (O3) and resulting in higher mobility of surface lattice oxygen species. Besides, the enhancement of deep oxidation performance was caused by the increase of hydroxyl groups concentration. In-situ DRIFTS experiments revealed that the adsorbed toluene on catalyst surface was oxidized to benzyl alcohol by surface lattice oxygen, and hydroxyl groups were also found participating in toluene adsorption. Overall, this study provides a new approach to designing catalysts for deep oxidation of VOCs.

A Bifunctional Catalyst for Green Ammonia Synthesis from Ubiquitous Air and Water

Ammonia (NH3 ) is essential for modern agriculture and industry, and, due to its high hydrogen density and no carbon emission, it is also expected to be the next-generation of "clean" energy carrier. Herein, directly from air and water, a plasma-electrocatalytic reaction system for NH3 production, which combines two steps of plasma-air-to-NOx - and electrochemical NOx - reduction reaction (eNOx RR) with a bifunctional catalyst, is successfully established. Especially, the bifunctional catalyst of CuCo2 O4 /Ni can simultaneously promote plasma-air-to-NOx - and eNOx RR processes. The easy adsorption and activation of O2 by CuCo2 O4 /Ni greatly improve the NOx - production rate at the first step. Further, CuCo2 O4 /Ni can also resolve the overbonding of the key intermediate of * NO, and thus reduce the energy barrier of the second step of eNOx RR. Finally, the "green" NH3 production achieves excellent FENH3 (96.8%) and record-high NH3 yield rate of 145.8 mg h-1  cm-2 with large partial current density (1384.7 mA cm-2 ). Moreover, an enlarged self-made H-type electrolyzer improves the NH3 yield to 3.6 g h-1 , and the obtained NH3 is then rapidly converted to a solid of magnesium ammonium phosphate hexahydrate, which favors the easy storage and transportation of NH3 .

Binary Heterogroup-Templated Scaffolds of Polyoxopalladates as Precatalysts for Plasma-Assisted Ammonia Synthesis

In addition to improving the synthetic efficiency, the template method can do a lot more in the chemistry of polyoxopalladates (POPs), such as the establishment of novel metal-oxo scaffolds. In this endeavor, a binary system comprising heterogroups of nonmetallic {As/SiO4} and metallic {VO4/5} successfully fulfills the templated growth of two POPs with unprecedented seesaw- and spindle-like prototypes. Of these, self-aggregation of heterogroups beacons an effective route to break the highly symmetrical PdII-oxo matrix and to force the arrangement of addenda in a nonconventional manner. Aside from the interest in their structural features, the as-made POPs are available for immobilization on the mesoporous SBA-15 as precatalysts for ammonia synthesis. The outer cover of heterogroups in the POP precursors contributes to the ultrafine size and uniform distribution of derived Pd0 nanoparticles (PdNPs). With the help of plasma activation on H2 and N2, such PdNPs-SBA15 catalysts significantly improve the production performance of NH3, showcasing the maximum synthesis rate of 64.42 μmol/(min·gcat) with the corresponding energy yield as high as 4.38 g-NH3/kWh.

Dielectric barrier discharge plasma catalysis as an alternative approach for the synthesis of ammonia: a review

Numerous researchers have attempted to provide mild reactions and environmentally-friendly methods for NH3 synthesis. Research on non-thermal plasma-assisted ammonia synthesis, notably the atmospheric-pressure nonthermal plasma synthesis of ammonia over catalysts, has recently gained attention in the academic literature. Since non-thermal plasma technology circumvents the existing crises and harsh conditions of the Haber-Bosch process, it can be considered as a promising alternative for clean synthesis of ammonia. Non-thermal dielectric barrier discharge (DBD) plasma has been extensively employed in the synthesis of ammonia due to its particular advantages such as the simple construction of DBD reactors, atmospheric operation at ambient temperature, and low cost. The combination of this plasma and catalytic materials can remarkably affect ammonia formation, energy efficiency, and the generation of by-products. The present article reviews plasma-catalysis ammonia synthesis in a dielectric barrier discharge reactor and the parameters affecting this synthesis system. The proposed mechanisms of ammonia production by this plasma catalysis system are discussed as well.

Electrochemical nitrogen fixation on single metal atom catalysts

The electrochemical reduction of nitrogen (eNRR) offers a promising alternative to the Haber-Bosch (H-B) process for producing ammonia under moderate conditions. However, the inertness of dinitrogen and the competing hydrogen evolution reaction pose significant challenges for eNRR. Thus, developing more efficient electrocatalysts requires a deeper understanding of the underlying mechanistic reactions and electrocatalytic activity. Single atom catalysts, which offer tunable catalytic properties and increased selectivity, have emerged as a promising avenue for eNRR. Carbon and metal-based substrates have proven effective for dispersing highly active single atoms that can enhance eNRR activity. In this review, we explore the use of atomically dispersed single atoms on different substrates for eNRR from both conceptual and experimental perspectives. The review is divided into four sections: the first section describes eNRR mechanistic pathways, the second section focuses on single metal atom catalysts (SMACs) with metal atoms dispersed on carbon substrates for eNRR, the third section covers SMACs with metal atoms dispersed on non-carbon substrates for eNRR, and the final section summarizes the remaining challenges and future scope of eNRR for green ammonia production.

Insights into the Role of Nanorod-Shaped MnO2 and CeO2 in a Plasma Catalysis System for Methanol Oxidation

Published papers highlight the roles of the catalysts in plasma catalysis systems, and it is essential to provide deep insight into the mechanism of the reaction. In this work, a coaxial dielectric barrier discharge (DBD) reactor packed with γ-MnO₂ and CeO₂ with similar nanorod morphologies and particle sizes was used for methanol oxidation at atmospheric pressure and room temperature. The experimental results showed that both γ-MnO₂ and CeO₂ exhibited good performance in methanol conversion (up to 100%), but the CO₂ selectivity of CeO₂ (up to 59.3%) was much higher than that of γ-MnO₂ (up to 28.6%). Catalyst characterization results indicated that CeO₂ contained more surface-active oxygen species, adsorbed more methanol and utilized more plasma-induced active species than γ-MnO₂. In addition, in situ Raman spectroscopy and Fourier transform infrared spectroscopy (FT-IR) were applied with a novel in situ cell to reveal the major factors affecting the catalytic performance in methanol oxidation. More reactive oxygen species (O₂^2-, O^2-) from ozone decomposition were produced on CeO₂ compared with γ-MnO₂, and less of the intermediate product formate accumulated on the CeO₂. The combined results showed that CeO₂ was a more effective catalyst than γ-MnO₂ for methanol oxidation in the plasma catalysis system.

Developing a microwave-driven reactor for ammonia synthesis: insights into the unique challenges of microwave catalysis

Reactor requirements grow with scale as new phenomena can become more and more relevant, creating trends that we've observed in the development of microwave-driven ammonia synthesis – a technique with a unique combination of high output and energy efficiency.

Computational Screening of Metal-Organic Frameworks for Ammonia Capture from H2/N2/NH3 Mixtures

The separation of ammonia from H₂/N₂/NH₃ mixtures is an important step in ammonia decomposition for hydrogen production and ammonia synthesis from H₂ and N₂ based nonaqueous technologies. Metal-organic frameworks (MOFs) are considered as potential materials for capturing ammonia. In the present work, high-throughput screening of 2932 Computation-Ready Experimental MOFs (CoRE MOFs) was carried out for ammonia capture from H₂/N₂/NH₃ mixtures by Grand Canonical Monte Carlo (GCMC) simulations. It was found that the high-performing MOFs are characterized by tube-like channels, moderate LCD (largest cavity diameter) (4-7.5 Å), and high Q _st ⁰(NH₃) (the isosteric heat of NH₃ adsorption) (>45 kJ/mol). MOFs with high NH₃ adsorption capacity often feature moderate surface area, while the surface area of MOFs with high NH₃ selectivity is relatively lower, which limits the NH₃ adsorption capacity. Q _st ⁰ and the Henry's constant (K _H ) are two energy descriptors describing the interactions between adsorbents and adsorbates. The former has a stronger correlation with the adsorption selectivity, while the latter has a stronger correlation with the adsorption capacity. By analyzing the molecular density distribution of adsorbates in high-performing MOFs, it was found that unsaturated coordinated metal sites provide the main functional binding sites for NH₃. Most MOFs with high NH₃ selectivity have multiple different metal nodes or other atoms except C, O, and H, such as N and P. Multiple metal nodes and nonmetallic atoms provide more functional binding sites. Finally, the adsorption behavior with various concentrations of gas mixtures was examined to verify the universality of the screening calculations, and the effect of framework flexibility on adsorption performance was explored.

Plasma-Catalytic CO2 Hydrogenation over a Pd/ZnO Catalyst: In Situ Probing of Gas-Phase and Surface Reactions

Plasma-catalytic CO₂ hydrogenation is a complex chemical process combining plasma-assisted gas-phase and surface reactions. Herein, we investigated CO₂ hydrogenation over Pd/ZnO and ZnO in a tubular dielectric barrier discharge (DBD) reactor at ambient pressure. Compared to the CO₂ hydrogenation using Plasma Only or Plasma + ZnO, placing Pd/ZnO in the DBD almost doubled the conversion of CO₂ (36.7%) and CO yield (35.5%). The reaction pathways in the plasma-enhanced catalytic hydrogenation of CO₂ were investigated by in situ Fourier transform infrared (FTIR) spectroscopy using a novel integrated in situ DBD/FTIR gas cell reactor, combined with online mass spectrometry (MS) analysis, kinetic analysis, and emission spectroscopic measurements. In plasma CO₂ hydrogenation over Pd/ZnO, the hydrogenation of adsorbed surface CO₂ on Pd/ZnO is the dominant reaction route for the enhanced CO₂ conversion, which can be ascribed to the generation of a ZnO _x overlay as a result of the strong metal-support interactions (SMSI) at the Pd-ZnO interface and the presence of abundant H species at the surface of Pd/ZnO; however, this important surface reaction can be limited in the Plasma + ZnO system due to a lack of active H species present on the ZnO surface and the absence of the SMSI. Instead, CO₂ splitting to CO, both in the plasma gas phase and on the surface of ZnO, is believed to make an important contribution to the conversion of CO₂ in the Plasma + ZnO system.

A review of the advances in catalyst modification using nonthermal plasma: Process, Mechanism and Applications

With the continuous development of catalytic processes in chemistry, biology, organic synthesis, energy generation and many other fields, the design of catalysts with novel properties has become a new paradigm in both science and industry. Nonthermal plasma has aroused extensive interest in the synthesis and modification of catalysts. An increasing number of researchers are using plasma for the modification of target catalysts, such as modifying the dispersion of active sites, regulating electronic properties, enhancing metal-support interactions, and changing the morphology. Plasma provides an alternative choice for catalysts in the modification process of oxidation, reduction, etching, coating, and doping and is especially helpful for unfavourable thermodynamic processes or heat-sensitive reactions. This review focuses on the following points: (i) the fundamentals behind the nonthermal plasma modification of catalysts; (ii) the latest research progress on the application of plasma modified catalysts; and (iii) main challenges in the field and a vision for future development.

Shielding Protection by Mesoporous Catalysts for Improving Plasma-Catalytic Ambient Ammonia Synthesis

Plasma catalysis is a promising technology for decentralized small-scale ammonia (NH3) synthesis under mild conditions using renewable energy, and it shows great potential as an alternative to the conventional Haber-Bosch process. To date, this emerging process still suffers from a low NH3 yield due to a lack of knowledge in the design of highly efficient catalysts and the in situ plasma-induced reverse reaction (i.e., NH3 decomposition). Here, we demonstrate that a bespoke design of supported Ni catalysts using mesoporous MCM-41 could enable efficient plasma-catalytic NH3 production at 35 °C and 1 bar with >5% NH3 yield at 60 kJ/L. Specifically, the Ni active sites were deliberately deposited on the external surface of MCM-41 to enhance plasma-catalyst interactions and thus NH3 production. The desorbed NH3 could then diffuse into the ordered mesopores of MCM-41 to be shielded from decomposition due to the absence of plasma discharge in the mesopores of MCM-41, that is, "shielding protection", thus driving the reaction forward effectively. This promising strategy sheds light on the importance of a rational design of catalysts specifically for improving plasma-catalytic processes.

Tuning the local electronic structure of SrTiO3 catalysts to boost plasma-catalytic interfacial synergy

Boosting plasma-catalyst synergy to enhance volatile organic compounds (VOCs) decomposition remains a challenge. Herein, rich oxygen vacancies (V_O) were engineered into the SrTiO₃ catalysts through a facile nitrogen incorporation strategy for the plasma-catalytic decomposition of toluene and ethyl acetate. 100% toluene conversion with 81% CO₂ selectivity at a competitive energy efficiency was achieved under ambient conditions. The characterization results and theoretical calculations evidenced that the partial substitution of oxygen by nitrogen triggered the electronic reconstruction and local disorder, thus modulating the electronic properties and coordination structures contributed to the formation of V_O-Ti³⁺ pairs. Quasi in-situ EPR, operando OES, and operando DRIFTS originally demonstrated that the V_O-Ti³⁺ pairs as active sites promoted the plasma-catalytic synergy instead of isolated V_O. Importantly, the V_O-Ti³⁺ pairs with favorable electron transfer characteristics energetically preferred to capture and utilize vibrationally excited oxygen species. And the lattice oxygen supplied by the V_O-Ti³⁺ pairs were more vigorously activated by the plasma to participate in the surface/interface reaction. This work advances our understanding of the real active sites in plasma-catalytic interfacial synergy and thus paving the way for the rational design of efficiently heterogeneous catalysts.

Emerging Materials and Methods toward Ammonia-Based Energy Storage and Conversion

Efficient storage and conversion of renewable energies is of critical importance to the sustainable growth of human society. With its distinguishing features of high hydrogen content, high energy density, facile storage/transportation, and zero-carbon emission, ammonia has been recently considered as a promising energy carrier for long-term and large-scale energy storage. Under this scenario, the synthesis, storage, and utilization of ammonia are key components for the implementation of ammonia-mediated energy system. Being different from fossil fuels, renewable energies normally have intermittent and variable nature, and thus pose demands on the improvement of existing technologies and simultaneously the development of alternative methods and materials for ammonia synthesis and storage. The energy release from ammonia in an efficient manner, on the other hand, is vital to achieve a sustainable energy supply and complete the nitrogen circle. Herein, recent advances in the thermal-, electro-, plasma-, and photocatalytic ammonia synthesis, ammonia storage or separation, ammonia thermal/electrochemical decomposition and conversion are summarized with the emphasis on the latest developments of new methods and materials (catalysts, electrodes, and sorbents) for these processes. The challenges and potential solutions are discussed.

Nitrate Capture Investigation in Plasma-Activated Water and Its Antifungal Effect on Cryptococcus pseudolongus Cells

This research investigated the capture of nitrate by magnesium ions in plasma-activated water (PAW) and its antifungal effect on the cell viability of the newly emerged mushroom pathogen Cryptococcus pseudolongus. Optical emission spectra of the plasma jet exhibited several emission bands attributable to plasma-generated reactive oxygen and nitrogen species. The plasma was injected directly into deionized water (DW) with and without an immersed magnesium block. Plasma treatment of DW produced acidic PAW. However, plasma-activated magnesium water (PA-Mg-W) tended to be neutralized due to the reduction in plasma-generated hydrogen ions by electrons released from the zero-valent magnesium. Optical absorption and Raman spectra confirmed that nitrate ions were the dominant reactive species in the PAW and PA-Mg-W. Nitrate had a concentration-dependent antifungal effect on the tested fungal cells. We observed that the free nitrate content could be controlled to be lower in the PA-Mg-W than in the PAW due to the formation of nitrate salts by the magnesium ions. Although both the PAW and PA-Mg-W had antifungal effects on C. pseudolongus, their effectiveness differed, with cell viability higher in the PA-Mg-W than in the PAW. This study demonstrates that the antifungal effect of PAW could be manipulated using nitrate capture. The wide use of plasma therapy for problematic fungus control is challenging because fungi have rigid cell wall structures in different fungal groups.

Synergistic Catalysis of the Synthesis of Ammonia with Co-Based Catalysts and Plasma: From Nanoparticles to a Single Atom

In this study, a series of Co nanoparticles (NPs) with different sizes and Co single-atom catalysts (SACs) with different cobalt-nitrogen coordination numbers (Co-N2, Co-N3, and Co-N4) were synthesized and applied to the synthesis of ammonia catalyzed by plasma at low temperatures and atmospheric pressures. Under the same reaction conditions, the yield of nitrogen obtained from the reduction to ammonia over a series of Co NP catalysts varies with the Co particle size. The smaller the size of the Co NPs, the greater the number of exposed active centers, and the catalytic activity is higher. Among the Co SACs, the best catalyst was Co-N2 with two coordinated nitrogen atoms, and the ammonia yield was 181 mg·h-1·gcat-1. The experimental and theoretical calculations were consistent in that a low Co-N coordination number was beneficial to the adsorption and dissociation of N2, thereby enhancing the reduction activity of N2 and promoting the increase of ammonia production.

Al2O3-Supported Transition Metals for Plasma-Catalytic NH3 Synthesis in a DBD Plasma: Metal Activity and Insights into Mechanisms

N2 fixation into NH3 is one of the main processes in the chemical industry. Plasma catalysis is among the environmentally friendly alternatives to the industrial energy-intensive Haber-Bosch process. However, many questions remain open, such as the applicability of the conventional catalytic knowledge to plasma. In this work, we studied the performance of Al2O3-supported Fe, Ru, Co and Cu catalysts in plasma-catalytic NH3 synthesis in a DBD reactor. We investigated the effects of different active metals, and different ratios of the feed gas components, on the concentration and production rate of NH3, and the energy consumption of the plasma system. The results show that the trend of the metal activity (common for thermal catalysis) does not appear in the case of plasma catalysis: here, all metals exhibited similar performance. These findings are in good agreement with our recently published microkinetic model. This highlights the virtual independence of NH3 production on the metal catalyst material, thus validating the model and indicating the potential contribution of radical adsorption and Eley-Rideal reactions to the plasma-catalytic mechanism of NH3 synthesis.

Decarbonization in ammonia production, new technological methods in industrial scale ammonia production and critical evaluations

With the synthesis of ammonia with chemical methods, global carbon emission is the biggest threat to global warming. However, the dependence of the agricultural industry on ammonia production brings with it various research studies in order to minimize the carbon emission that occurs with the ammonia synthesis process. In order to completely eliminate the carbon emissions from ammonia production, both the hydrogen and the energy needed for the operation of the process must be obtained from renewable sources. Thus, hydrogen can be produced commercially in a variety of ways. Many processes are discussed to accompany the Haber Bosch process in ammonia production as potential competitors. In addition to parameters such as temperature and pressure, various plasma catalysts are being studied to accelerate the ammonia production reaction. In this study, various alternative processes for the capture, storage and complete removal of carbon gas released during the current ammonia production are evaluated and the current conditions related to the applicability of these processes are discussed. In addition, it has been discussed under which conditions it is possible to produce larger capacities as needed in the processes studied in order to reduce carbon gas emissions during ammonia production in order to provide raw material source for fertilizer production and energy sector. However, if the hydrogen gas required for ammonia production is produced using a solid oxide electrolysis cell, the reduction in the energy requirement of the process and in this case the reduction of energy costs shows that it will play an important role in determining the method to be used for ammonia production. In addition, it is predicted that working at lower temperature (<400 °C) and pressure (<10 bar) values in existing ammonia production technologies, despite increasing possible energy costs, will significantly reduce process operating costs.

Nanomaterials for the electrochemical nitrogen reduction reaction under ambient conditions

As an important chemical product and carbon-free energy carrier, ammonia has a wide range of daily applications in several related fields. Although the industrial synthesis method using the Haber-Bosch process could meet production demands, its huge energy consumption and gas emission limit its long-time development. Therefore, the clean and sustainable electrocatalytic N2 reduction reaction (NRR) operating under conditions have attracted great attention in recent years. However, the chemical inertness of N2 molecules makes it difficult for this reaction to proceed. Therefore, rationally designed catalysts need to be introduced to activate N2 molecules. Here, we summarize the recent progress in low-dimensional nanocatalyst development, including the relationship between the structure and NRR performance from both the theoretical and experimental perspectives. Some insights into the development of NRR electrocatalysts from electronic control aspects are provided. In addition, the theoretical mechanisms, reaction pathways and credibility studies of the NRR are discussed. Some challenges and future prospects of the NRR are also pointed out.

Enhancement of plasma-catalytic oxidation of ethylene oxide (EO) over FeMn catalysts in a dielectric barrier discharge reactor

In this work, an integrated system combining non-thermal plasma (NTP) and FeMn catalysts was developed for ethylene oxide (EO) oxidation. The effect of Fe/Mn molar ratio on the oxidation rate of EO and energy yield of the plasma-catalytic process has been investigated as a function of specific energy density (SED). Compared with the case of using plasma alone, the combination of plasma and FeMn catalysts greatly enhanced the reaction performance by the factor of 25.2% to 97.6%. The maximum oxidation rate of 98.8% was achieved when Fe₁Mn₁ catalyst was placed in the dielectric barrier discharge (DBD) reactor at the SED of 656.1 J·L^-1. The highest energy yield of 2.82 g·kWh^-1 was obtained at the SED of 323.2 J·L^-1 over the Fe₁Mn₁ catalyst. The interactions between Fe and Mn species resulted in larger specific surface area of the catalyst. Moreover, the reducibility of the catalysts was improved, while more surface adsorbed oxygen (O_ads) was detected on the catalyst surfaces. Moreover, the redox cycles between Fe and Mn species facilitated consumption and supplementation of reactive oxygen species, which contributed to the plasma-catalytic oxidation reactions. The major reaction products of plasma-induced EO oxidation over the FeMn catalysts, including CH₃COOH, CH₃CHO, CH₄, C₂H₆ and C₂H₄, were observed using the FT-IR analyzer and GC-MS instrument. The reaction mechanisms of EO oxidation were discussed in terms of both gas-phase reaction and catalyst surface reaction. The redox cycles between Fe and Mn species facilitated the plasma reaction and accelerated the deep oxidation of by-products.

Cu/HZSM-5 Sorbent Treated by NH3 Plasma for Low-Temperature Simultaneous Adsorption-Oxidation of H2S and PH3

In this study, an NH₃ plasma-treated Cu/HZSM-5 sorbent was introduced to simultaneously remove H₂S and PH₃ in low-temperature and low-oxygen environments. The effects of the Cu loading amounts, modification methods, and plasma-treatment conditions on the adsorption-oxidation performance of the sorbents were investigated. From the performance test results, the sorbent treated by NH₃ plasma with the specific energy input (SEI, electrical input energy to the unit volume of gas) value of 1 J·mL^-1 (Cu/HZSM-5-[S1]) was identified as having the highest breakthrough capacities of 108.9 mg S·g^-1 and 150.9 mg P·g^-1 among all of the materials tested. After three times of regeneration, the sorbent can still maintain the ideal performance. The results of Fourier transform infrared (FT-IR) spectroscopy and CO₂ temperature-programmed desorption (CO₂-TPD) indicated that the NH₃ plasma treatment can introduce amino groups (functional groups) onto the sorbent surface, which greatly increases the number and strength of the basic sites on the sorbent surface. Results of N₂ adsorption/desorption isotherms and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) showed that the morphology of the sorbent changed after the plasma treatment, which exposed more active sites (copper species). In situ IR spectra showed that the amino groups are continuously consumed during the reaction process, indicating that these amino groups can help sorbents to capture gas molecules. Moreover, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses indicated that CuO is the main active species and the consumption of CuO and accumulation of the reaction products on the surface and inner pores of the sorbent are the primary reasons for the deactivation of the sorbent.

Plasma-Induced Catalytic Conversion of Nitrogen and Hydrogen to Ammonia over Zeolitic Imidazolate Frameworks ZIF-8 and ZIF-67

Microporous crystals have emerged as highly appealing catalytic materials for the plasma catalytic synthesis of ammonia. Herein, we demonstrate that zeolitic imidazolate frameworks (ZIFs) can be employed as efficient catalysts for the cold plasma ammonia synthesis using an atmospheric dielectric barrier discharge reactor. We studied two prototypical ZIFs denoted as ZIF-8 and ZIF-67, with a uniform window pore aperture of 3.4 Å. The resultant ZIFs displayed ammonia synthesis rates as high as 42.16 μmol NH₃/min gcat. ZIF-8 displayed remarkable stability upon recycling. The dipole-dipole interactions between the polar ammonia molecules and the polar walls of the studied ZIFs led to relatively low ammonia uptakes, low storage capacity, and high observed ammonia synthesis rates. Both ZIFs outperform other microporous crystals including zeolites and conventional oxides in terms of ammonia production. Furthermore, we demonstrate that the addition of argon to the reactor chamber can be an effective strategy to improve the plasma environment. Specifically, the presence of argon helped to improve the plasma uniformity, making the reaction system more energy efficient by operating at a low specific energy input range allowing abundant formation of nitrogen vibrational species.