Plasma assisted nitrogen oxide production from air: Using pulsed powered gliding arc reactor for a containerized plant

Selective Electrocatalytic Conversion of Nitric Oxide to High Value-Added Chemicals

The artificial disturbance in the nitrogen cycle has necessitated an urgent need for nitric oxide (NO) removal. Electrochemical technologies for NO conversion have gained increasing attention in recent years. This comprehensive review presents the recent advancements in selective electrocatalytic conversion of NO to high value-added chemicals, with specific emphasis on catalyst design, electrolyte composition, mass diffusion, and adsorption energies of key intermediate species. Furthermore, the review explores the synergistic electrochemical co-electrolysis of NO with specific carbon source molecules, enabling the synthesis of a range of valuable chemicals with C─N bonds. It also provides in-depth insights into the intricate reaction pathways and underlying mechanisms, offering valuable perspectives on the challenges and prospects of selective NO electrolysis. By advancing comprehension and fostering awareness of nitrogen cycle balance, this review contributes to the development of efficient and sustainable electrocatalytic systems for the selective synthesis of valuable chemicals from NO.

Carbon Support Enhanced Mass Transfer and Metal-Support Interaction Promoted Activation for Low-Concentrated Nitric Oxide Electroreduction to Ammonia

The electrochemical NO reduction reaction (NORR) is a promising approach for both nitrogen cycle regulation and ammonia synthesis. Due to the relatively low concentration of the NO source and poor solubility of NO in solution, mass transfer limitation is a serious but easily overlooked issue. In this work, porous carbon-supported ultrafine Cu clusters grown on Cu nanowire arrays (defined as Cu@Cu/C NWAs) are prepared for low-concentration NORR. A high Faradaic efficiency (93.0%) and yield rate (1180.5 μg h-1 cm-2) of ammonia are realized on Cu@Cu/C NWAs at -0.1 V vs a reversible hydrogen electrode (RHE), which are far superior to those of Cu NWAs and other reported performances under similar conditions. The construction of a porous carbon support can effectively decrease the NO diffusion kinetics and promote NO coverage for subsequent highly effective conversion. Moreover, the favorable metal-support interaction between ultrafine Cu clusters and carbon support enhances the adsorption of NO and decreases the barrier for *HNO formation in comparison with that of pure Cu NWAs. Overall, the whole NORR can be fully strengthened on Cu@Cu/C NWAs at low NO concentrations.

Coupling of N2 and O2 in the Gas Phase to Synthesize Nitric Oxide at Room Temperature: A Zeldovich-Like Strategy

Dinitrogen (N2) activation and its chemical transformations are some of the most challenging topics in chemistry. Herein, we report that heteronuclear metal anions AuNbBO- can mediate the direct coupling of N2 and O2 to generate NO molecules. N2 first forms the nondissociative adsorption product AuNbBON2- on AuNbBO-. In the following reactions with two O2 molecules, two NO molecules are gradually released, with the formation of AuNbBO2N- and AuNbBO3-. In the reaction with the first O2, the generated nitrene radical (N••-) originating from the dissociated N2, induces the activation of O2. Subsequently, the second O2 is anchored and forms a superoxide radical (O2•-); this radical attacks the other N atom to form an N-O bond, releasing the second NO. The N••- and O2•- radicals play key roles in the reactions. The mechanism adopted in this direct oxidation of N2 by O2 to NO can be labeled as a Zeldovich-like mechanism.

Advanced (photo)electrocatalytic approaches to substitute the use of fossil fuels in chemical production

Electrification of the chemical industry for carbon-neutral production requires innovative (photo)electrocatalysis. This study highlights the contribution and discusses recent research projects in this area, which are relevant case examples to explore new directions but characterised by a little background research effort. It is organised into two main sections, where selected examples of innovative directions for electrocatalysis and photoelectrocatalysis are presented. The areas discussed include (i) new approaches to green energy or H2 vectors, (ii) the production of fertilisers directly from the air, (iii) the decoupling of the anodic and cathodic reactions in electrocatalytic or photoelectrocatalytic devices, (iv) the possibilities given by tandem/paired reactions in electrocatalytic devices, including the possibility to form the same product on both cathodic and anodic sides to "double" the efficiency, and (v) exploiting electrocatalytic cells to produce green H2 from biomass. The examples offer hits to expand current areas in electrocatalysis to accelerate the transformation to fossil-free chemical production.

Energy-Efficient Small-Scale Ammonia Synthesis Process with Plasma-Enabled Nitrogen Oxidation and Catalytic Reduction of Adsorbed NOx

Industrial ammonia production without CO₂ emission and with low energy consumption is one of the technological grand challenges of this age. Current Haber-Bosch ammonia mass production processes work with a thermally activated iron catalyst needing high pressure. The need for large volumes of hydrogen gas and the continuous operation mode render electrification of Haber-Bosch plants difficult to achieve. Electrochemical solutions at low pressure and temperature are faced with the problematic inertness of the nitrogen molecule on electrodes. Direct reduction of N₂ to ammonia is only possible with very reactive chemicals such as lithium metal, the regeneration of which is energy intensive. Here, the attractiveness of an oxidative route for N₂ activation was presented. N₂ conversion to NO_x in a plasma reactor followed by reduction with H₂ on a heterogeneous catalyst at low pressure could be an energy-efficient option for small-scale distributed ammonia production with renewable electricity and without intrinsic CO₂ footprint.

Review of low-temperature plasma nitrogen fixation technology

Nitrogen fixation is essential for all forms of life, as nitrogen is required to biosynthesize fundamental building blocks of creatures, plants, and other life forms. As the main method of artificial nitrogen fixation, Haber–Bosch process (ammonia synthesis) has been supporting the agriculture and chemical industries since the 1910s. However, the disadvantages inherent to the Haber–Bosch process, such as high energy consumption and high emissions, cannot be ignored. Therefore, developing a green nitrogen fixation process has always been a research hotspot. Among the various technologies, plasma-assisted nitrogen fixation technology is very promising due to its small scale, mild reaction conditions, and flexible parameters. In the present work, the basic principles of plasma nitrogen fixation technology and its associated research progress are reviewed. The production efficiency of various plasmas is summarized and compared. Eventually, the prospect of nitrogen fixation using low-temperature plasma in the future was proposed.

From the Birkeland-Eyde process towards energy-efficient plasma-based NO X synthesis: a techno-economic analysis

Plasma-based NO X synthesis via the Birkeland-Eyde process was one of the first industrial nitrogen fixation methods. However, this technology never played a dominant role for nitrogen fixation, due to the invention of the Haber-Bosch process. Recently, nitrogen fixation by plasma technology has gained significant interest again, due to the emergence of low cost, renewable electricity. We first present a short historical background of plasma-based NO X synthesis. Thereafter, we discuss the reported performance for plasma-based NO X synthesis in various types of plasma reactors, along with the current understanding regarding the reaction mechanisms in the plasma phase, as well as on a catalytic surface. Finally, we benchmark the plasma-based NO X synthesis process with the electrolysis-based Haber-Bosch process combined with the Ostwald process, in terms of the investment cost and energy consumption. This analysis shows that the energy consumption for NO X synthesis with plasma technology is almost competitive with the commercial process with its current best value of 2.4 MJ mol N-1, which is required to decrease further to about 0.7 MJ mol N-1 in order to become fully competitive. This may be accomplished through further plasma reactor optimization and effective plasma-catalyst coupling.

A novel energy efficient path for nitrogen fixation using a non-thermal arc

Plasma-assisted nitrogen fixation is a promising sustainable and clean alternative to the classical Haber-Bosch process. However, the high energy consumption and low production rate of plasma-assisted nitrogen fixation limit its application. This study shows that the non-thermal (non-equilibrium) enhancement of the arc plasma significantly reduces the energy consumption of nitrogen fixation. The highest energy efficiency with high NO selectivity is observed with a low specific energy input (SEI). However, the highest production rate is reached at a high SEI. The studied process offers high NO selectivity (up to 95%) with low energy consumption (∼48 GJ per tN) at 0.1 kJ L-1 SEI, which is much lower than the previously reported value of plasma-assisted atmospheric nitrogen fixation and is close to that of the Haber-Bosch process.

Potential of N2/O2 atmospheric pressure needle-water DC microplasmas for nitrogen fixation: nitrite-free synthesis of nitrates

A needle-water DC microplasma system working at atmospheric pressure in N₂/O₂ gas mixtures is used to study the fundamental mechanisms of nitrate/nitrite synthesis in highly complex and yet little-known plasma-water systems. Plasma properties are investigated by means of optical emission spectroscopy while the activated water is analyzed following the treatment using ionic chromatography and UV-Vis absorbance spectroscopy. Experiments highlight that the energy efficiency and selectivity of the process are influenced by the oxygen content and the plasma-induced water heating, with strong differences when the water surface is the anode or the cathode electrode. Nitrates are successfully synthesized without residual nitrites in the solution with a comparatively higher energy efficiency when the water is the cathode. The possible reactions involved in the gas phase and aqueous phase chemistry are presented and future scope for the optimization of the system is discussed.

Plasma Generating—Chemical Looping Catalyst Synthesis by Microwave Plasma Shock for Nitrogen Fixation from Air and Hydrogen Production from Water for Agriculture and Energy Technologies in Global Warming Prevention

Simultaneous generation of plasma by microwave irradiation of perovskite or the spinel type of silica supported porous catalyst oxides and their reduction by nitrogen in the presence of oxygen is demonstrated. As a result of plasma generation in air, NOx generation is accompanied by the development of highly heterogeneous regions in terms of chemical and morphological variations within the catalyst. Regions of almost completely reduced catalyst are dispersed within the catalyst oxide, across micron-scale domains. The quantification of the catalyst heterogeneity and evaluation of catalyst structure are studied using Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy and XRD. Plasma generating supported spinel catalysts are synthesized using the technique developed by the author (Catalysts; 2016; 6; 80) and BaTiO3 is used to exemplify perovskites. Silica supported catalyst systems are represented as M/Si = X (single catalysts) or as M(1)/M(2)/Si = X/Y/Z (binary catalysts) where M; M(1) M(2) = Cr; Mn; Fe; Co; Cu and X, Y, Z are the molar ratio of the catalysts and SiO2 support. Composite porous catalysts are synthesized using a mixture of Co and BaTiO3. In all the catalysts, structural heterogeneity manifests itself through defects, phase separation and increased porosity resulting in the creation of the high activity sites. The chemical heterogeneity results in reduced and oxidized domains and in very large changes in catalyst/support ratio. High electrical potential activity within BaTiO3 particles is observed through the formation of electrical treeing. Plasma generation starts as soon as the supported catalyst is synthesized. Two conditions for plasma generation are observed: Metal/Silica molar ratio should be > 1/2 and the resulting oxide should be spinel type; represented as MaOb (a = 3; b = 4 for single catalyst). Composite catalysts are represented as {M/Si = X}/BaTiO3 and obtained from the catalyst/silica precursor fluid with BaTiO3 particles which undergo fragmentation during microwave irradiation. Further irradiation causes plasma generation, NOx formation and lattice oxygen depletion. Partially reduced spinels are represented as MaOb–c. These reactions occur through a chemical looping process in micron-scale domains on the porous catalyst surface. Therefore; it is possible to scale-up this process to obtain NOx from MaOb for nitric acid production and H2 generation from MaOb–c by catalyst re-oxidized by water. Re-oxidation by CO2 delivers CO as fuel. These findings explain the mechanism of conversion of combustion gases (CO2 + N2) to CO and NOx via a chemical looping process. Mechanism of catalyst generation is proposed and the resulting structural inhomogeneity is characterized. Plasma generating catalysts also represent a new form of Radar Absorbing Material (RAM) for stealth and protection from radiation in which electromagnetic energy is dissipated by plasma generation and catalytic reactions. These catalytic RAMs can be expected to be more efficient in frequency independent microwave absorption.

Sustainable Non-Thermal Plasma-Assisted Nitrogen Fixation-Synergistic Catalysis

In this Minireview, the multiple chemical synergies present in catalytic non-thermal plasma-assisted nitrogen fixation (NTPNF) are uncovered through a critical exploration of the underlying mechanisms, during which the catalyst, plasma, and reactants play different roles. For the gas-phase NTPNF, the synergies consist of different aspects of the catalytic pathways such as electron-impact dissociation; Zeldovich mechanism in the PNO interactions; and Eley-Rideal, Langmuir-Hinshelwood, surface adsorption, and diffusion mechanisms for the plasma-catalyst interactions. The synergies within the gas-liquid NTPNF involve contributions of plasma and UV excitation to the gas-phase reactions and the UV excitation of molecules at the liquid-surface interface, which improves synthesis of aqueous nitrate, nitrite, and ammonium products. Based on the various synergistic mechanisms during NTPNF, future potential applications are proposed for how NTPNF could benefit the sustainable nitrogen fixation industry.

Recent Progress of Plasma-Assisted Nitrogen Fixation Research: A Review

Nitrogen is an essential element to plants, animals, human beings and all the other living things on earth. Nitrogen fixation, which converts inert atmospheric nitrogen into ammonia or other valuable substances, is a very important part of the nitrogen cycle. The Haber-Bosch process plays the dominant role in the chemical nitrogen fixation as it produces a large amount of ammonia to meet the demand from the agriculture and chemical industries. However, due to the high energy consumption and related environmental concerns, increasing attention is being given to alternative (greener) nitrogen fixation processes. Among different approaches, plasma-assisted nitrogen fixation is one of the most promising methods since it has many advantages over others. These include operating at mild operation conditions, a green environmental profile and suitability for decentralized production. This review covers the research progress in the field of plasma-assisted nitrogen fixation achieved in the past five years. Both the production of NOx and the synthesis of ammonia are included, and discussion on plasma reactors, operation parameters and plasma-catalysts are given. In addition, outlooks and suggestions for future research are also given.

In situ plasma-assisted atmospheric nitrogen fixation using water and spray-type jet plasma

In this study, a sustainable nitrogen fixation process was presented under atmospheric conditions and without introducing hydrogen or any catalyst. The novel in situ synthesis in this study used an advanced spray-type jet plasma, which significantly improved the fixation rate of nitrite, nitrate, and ammonium. Furthermore, the mechanism focusing on the co-synthesis of the abovementioned three nitrogen compounds was proposed based on the synergistic interactions between the gas-phase plasma and liquid surface dissociation.