Apparatus and method

Abstract

According to a first aspect of the present invention, a method for producing NO from nitrogen and oxygen x An apparatus for forming a plasma comprising a gliding arc discharge (GAD) device configured to generate a plasma, an inlet for a feed gas including nitrogen and oxygen, and a NO x a passageway including an outlet for a gas adsorption and desorption stoichiometric plasma (GAD) for reacting, in use, nitrogen and oxygen in the generated plasma to produce NO from at least a portion of the nitrogen and oxygen. x Forming a passage and forming NO x and a post-discharge vessel for adjusting the NO2 / NO ratio therein to 1:2 to 2:1.

Description

[Technical field]

[0001] The present invention relates to an apparatus and method for nitrogen fixation, in particular, to an apparatus and method for nitrogen fixation using a gliding arc discharge (GAD) device, and in particular, to an apparatus and method for ammonia synthesis. [Background technology]

[0002] Nitrogen is an essential component for all living organisms, as it is a component of nucleic acids. Although elemental nitrogen constitutes approximately 78% of the Earth's atmosphere, its chemically inert characteristics make it unavailable to most living organisms. Nitrogen fixation, which converts inert atmospheric nitrogen into chemically useful nitrogen compounds (ammonia, nitric oxide, nitrates, etc.), is an important process for sustaining life on Earth. In nature, nitrogen fixation is the process by which atmospheric nitrogen is converted into NO x This can be achieved by lightning, which converts nitrogen to ammonia (NO and NO2), or by biological processes that produce ammonia from nitrogen by the enzyme nitrogenase, but they cannot provide enough fixed N2 to feed a growing population.

[0003] Over the past century, large-scale nitrogen fixation has been achieved, mainly by the industrial Haber-Bosch (HB) process, in which ammonia is synthesized from nitrogen and hydrogen. Unfortunately, the HB process is an energy-intensive process with a large CO2 footprint, since it operates at high temperatures (400-600 °C) and pressures (200-400 atm), accounting for 1-2% of global energy use. The HB process also accounts for more than 1% of global CO2 emissions, and utilizes hydrogen derived from fossil fuels such as natural gas. Therefore, there is a need to develop greener and more sustainable technologies for carbon-neutral ammonia production under milder conditions, preferentially driven by renewable energy sources.

[0004] To this end, electrocatalysis, photocatalysis, and plasma (e.g., plasma-electrochemical and plasma-catalysis) technologies have been proposed as alternatives for producing ammonia. Among them, non-thermal plasma (NTP) technology has attracted attention as a decentralized, on-demand nitrogen fixation due to the following advantages: The plasma process for nitrogen fixation can be operated under ambient pressure and temperature, thus significantly reducing the reactor size and capital costs. The plasma process can be switched on and off instantly due to the fast reaction, providing great flexibility to be coupled with renewable energy sources, especially intermittent renewable energy sources such as wind and solar. More noteworthy, nitrogen fixation using plasma technology has a lower theoretical limit of energy consumption than the conventional HB process. This is because the energetic electrons generated by NTP can activate inactive N2 molecules by electron impact excitation and dissociation, and convert N2 into nitrogen compounds (ammonia, nitric oxide, etc.) without additional heating.

[0005] Currently, most studies using NTP for nitrogen fixation focus on the direct synthesis of ammonia from N2 and H2. However, results show that this approach suffers from a trade-off between low energy consumption and high ammonia yield. For example, a high NH3 yield of 6.4% can only be achieved with a very high energy consumption of 81 MJ per mole of NH3, whereas a low energy consumption of 2 MJ per mole of NH3 is accompanied by an ultra-low yield of NH3 (<0.1%). However, separation of NH3 from such a dilute gas mixture is very energy intensive. In addition, the process requires expensive green hydrogen to produce CO2-neutral ammonia.

[0006] Therefore, there is increasing interest in developing more environmentally friendly and sustainable technologies for producing ammonia directly from N2 or air without using hydrogen. xCoupling the synthesis with electrocatalytic reduction of nitrate / nitrite offers a very promising route for ammonia production. In addition, NO generated from air can be used to x can also be used directly in the production of fertilizer. x Reduction of the energy consumption of production and rational design of highly active, highly selective and highly stable electrocatalysts are important for achieving environmentally friendly and energy efficient ammonia production directly from air. Summary of the Invention [Problem to be solved by the invention]

[0007] One object of the present invention is, inter alia, to convert air into gaseous NO x , nitrate / nitrite intermediates, and ammonia as the end product, which at least partially obviates or mitigates at least some of the disadvantages of the prior art, whether specified herein or elsewhere.

[0008] For example, an object of the present invention is to provide a method for producing high NO x NO direct from air with concentration, tunable NO2 / NO ratio, and low energy consumption x The present invention provides an apparatus for providing plasma-assisted synthesis of

[0009] For example, it is an object of embodiments of the present invention to provide an apparatus for providing plasma-assisted synthesis of aqueous nitrate / nitrite intermediates with high nitrate / nitrite concentrations and tunable nitrate / nitrite ratios.

[0010] For example, an object of an embodiment of the present invention is to produce NO at low temperatures using a plasma electrocatalysis system. x The present invention provides a method for synthesizing ammonia from

[0011] For example, it is an object of embodiments of the present invention to provide an apparatus and / or method for synthesizing ammonia that does not require additional heating and can be performed at ambient pressure.

[0012] For example, it is an object of embodiments of the present invention to provide an apparatus and / or method for synthesizing ammonia that does not require H2 as a source and does not have a substantial CO2 footprint.

[0013] For example, an object of embodiments of the present invention is to provide ammonia production (or NO2 generation) that may be integrated with renewable energy sources (e.g., wind and solar), in particular the use of intermittent renewable energy during peak loads for localized or distributed energy storage. x The present invention provides an apparatus and / or method for generating a liquid crystal display. [Means for solving the problem]

[0014] According to the invention there is provided an apparatus as set out in the accompanying claims.A method is also provided.Other features of the invention will become apparent from the dependent claims and the following description. [Brief description of the drawings]

[0015] For a better understanding of the invention and to show how exemplary embodiments thereof may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which:

[0016] [Figure 1A] FIG. 1A depicts the experimental setup diagrammatically. [Diagram 2] For a gas flow rate of 1 SLM, a power of 17 W and an applied voltage frequency of 6 kHz, FIG. 2A shows the NOx concentration at different N2 / O2 ratios, and FIG. 2B shows the energy consumption and NO selectivity of NOx production at different N2 / O2 ratios. [Diagram 3] FIG. 3 shows the NOx concentration and energy consumption of NOx production at different applied voltage frequencies for an air gas flow rate of 1 SLM and a power output of 15 W. [Figure 4]FIG. 4A shows digital photographs of a gliding arc discharge with increasing power at an applied voltage frequency of 6 kHz, FIG. 4B shows digital photographs of a gliding arc discharge with increasing power at an applied voltage frequency of 11 kHz, and FIG. 4C shows digital photographs of a gliding arc discharge with increasing power at an applied voltage frequency of 40 kHz. [Diagram 5] For a gas flow rate of 1 SLM, FIG. 5A shows the NOx concentration at different discharge powers and frequencies, FIG. 5B shows the NO and NO2 selectivity at different discharge powers and frequencies, and FIG. 5C shows the energy consumption of NOx production at different discharge powers and frequencies. [Figure 6] For a gas flow rate of 1 SLM, and an applied voltage frequency of 6 kHz, FIG. 6A shows digital photographs of the gliding arc discharge when the power is increased with a 100 kΩ resistor in the circuit, and FIG. 6B shows digital photographs of the gliding arc discharge when the power is increased without a 100 kΩ resistor in the circuit. [Figure 7] For a gas flow rate of 1 SLM and an applied voltage frequency of 6 kHz, FIG. 7A shows the NOx concentration, energy consumption of NOx production with and without a 100 kΩ resistor, and FIG. 7B shows the NOx selectivity with and without a 100 kΩ resistor. [Figure 8] FIG. 8A shows digital photographs of the gliding arc discharge with increasing flow rate at a fixed power of 18 W and an applied frequency of 40 kHz, and FIG. 8B shows digital photographs of the gliding arc discharge with increasing flow rate at a fixed power of 21 W and an applied frequency of 6 kHz. [Figure 9] For frequencies of 6 kHz and 40 kHz, at fixed powers of 21 W and 18 W, FIG. 9A shows the NOx concentration at different flow rates, the energy consumption of NOx production, and FIG. 9B shows the NO selectivity at different flow rates. [Figure 10]At a discharge power of 18 W and a flow rate of 1.5 SLM, FIG. 10A shows the pH and electrical conductivity of the aqueous solution in the acrylic cylindrical container at different discharge times using water as the absorption solution, FIG. 10B shows the concentrations of nitrate and nitrite in the aqueous solution at different discharge times using water as the absorption solution, and FIG. 10C shows the concentrations of nitrate and nitrite in the aqueous solution at different discharge times using 1 M KOH as the absorption solution. [Figure 11] FIG. 11 shows the LSV curves of Co(OH)2 on different conductive substrates (carbon cloth, carbon paper, and Ni foam) in the electrolysis of nitrate to produce ammonia. [Figure 12] FIG. 12 shows the LSV curves of Co(OH)2 / Ni foam, Co / Ni foam, and Co3O4 / Ni foam in the electrolysis of ammonia production from nitrates. [Figure 13(1)] Figure 13A shows the LSV curves of Co / Ni foam at different concentrations of nitrate (concentration of KOH = 1 M), and Figure 13B shows the faradaic efficiency towards ammonia production from 0.2 to -1.0 V in 1 M KOH containing different concentrations of nitrate. [Figure 13(2)] Figure 13C shows the LSV curves of Co / Ni foam at different concentrations of nitrite (concentration of KOH = 1 M), and Figure 13D shows the faradaic efficiency towards ammonia production from 0.2 to -1.0 V in 1 M KOH containing different concentrations of nitrite. [Figure 14(1)] FIG. 14A shows the LSV curves of Co / Ni foam at different concentrations of KOH using nitrate solution (nitrate concentration = 0.1 M), and FIG. 14B shows the faradaic efficiency towards ammonia production from 0.2 to -1.0 V at different concentrations of KOH containing 0.1 M nitrate. [Figure 14(2)] FIG. 14C shows the LSV curves of Co / Ni foam at different concentrations of nitrite using nitrite solution (nitrite concentration = 0.1 M), and FIG. 14D shows the faradaic efficiency towards ammonia production from 0.2 to -1.0 V at different concentrations of KOH containing 0.1 M nitrite. [Figure 15A]FIG. 15A shows the LSV curves of Co / Ni foam using plasma activated solution (discharge time=30 min, 1 M KOH as absorption solution, discharge power=18 W, flow rate=1.5 SLM) in an acrylic cylindrical container. [Figure 16] For NOx production (air GAD, 50 Hz, total gas flow 2.8 SLM), FIG. 16A shows the effect of discharge power on NOx concentration and FIG. 16B shows the effect of discharge power on energy consumption. [Figure 17] For NOx production (air GAD, 50 Hz, discharge power 28 W), FIG. 17A shows the effect of total gas flow rate on NOx concentration, and FIG. 17B shows the effect of total gas flow rate on energy consumption. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Device According to a first aspect, NO x An apparatus for forming a gliding arc discharge (GAD) device configured to generate a plasma; Inlets for feed gases containing nitrogen and oxygen and NO x a passageway extending at least partially through said GAD device, said passageway including an outlet for a nitrogen and oxygen gas, said nitrogen and oxygen reacting in a generated plasma to thereby produce NO from at least a portion of said nitrogen and oxygen. x a passageway forming NO formed x A post-discharge vessel for adjusting the NO2 / NO ratio in the gas to 1:2 to 2:1. An apparatus is provided that includes:

[0018] This device converts nitrogen and oxygen from a source such as air into NO x Preferably, the feed gas is air. In one example, the feed gas is dry air, preferably containing less than 1% water by weight. The apparatus is suitable for forming gaseous NO xFor the avoidance of doubt, the nitrogen and oxygen are provided in gaseous form. Other gases such as those normally found in air, e.g. argon, may be used in combination with the nitrogen and oxygen.

[0019] NO x defines nitrogen oxides, appropriately nitric oxide (NO) and nitrogen dioxide (NO2).

[0020] Other gaseous products may be formed, such as N2O, N2O5 and / or ozone. However, these gaseous products are preferably present in small amounts and are not affected by NO x is the major product formed in a molar percentage relative to the total products, for example 90% or more, suitably 95% or more, for example 99% or more or 99.9% or more.

[0021] The apparatus of the first embodiment includes a GAD apparatus which may alternatively be referred to as a gliding arc plasma apparatus.

[0022] Gliding arc plasma is a type of low-temperature, non-equilibrium plasma. Compared to other types of low-temperature plasma, the gliding arc is about 10 times 23 m -3 The plasma has a very high electron density (close to that of a thermal plasma), which results in desirable energy efficiency for chemical synthesis such as nitrogen fixation.

[0023] Typically, a gliding arc plasma device includes two divergent electrodes, and the arc is initiated at the shortest distance between the electrodes, then driven by the gas flow, and the length of the arc column increases with voltage. The potential to induce and sustain the gliding arc discharge can be supplied by a direct current (DC), alternating current (AC) or pulsed power source. It is therefore understood that the electrodes are conductors. The electrodes may be any suitable metal.

[0024] Preferably, the gliding arc discharge device of the present invention is powered by alternating current (AC).

[0025] In one example, the gliding arc discharge device includes a pair (i.e., two) of thin divergent stainless steel electrodes. The electrodes may be suitably elliptical shaped, such as a quarter of an ellipse. An electrode having a quarter elliptical shape suitably has a minor axis and a major axis, for example, the electrode may have a minor axis length of 40 mm and a major axis length of 80 mm. The electrodes suitably have a thickness of up to 5 mm, such as 4 mm or up to 3 mm. In one example, the electrodes have a thickness of 3 mm. The electrodes are suitably fixed symmetrically on a support, such as a clear quartz support. However, any suitable support may be used. The support is suitably flat.

[0026] In one example, the support has a thickness of at most 15 mm, suitably at most 12 mm or at most 10 mm. In one example, the support has a thickness of 10 mm. The support preferably has a thickness of at most 5 mm, for example at most 4 mm or at most 3 mm. In one example, the support has a thickness of 2 mm. The support preferably comprises a rectangular cross-section.

[0027] However, these dimensions may be modified depending on the size of the gliding arc discharge device and scaled up or down accordingly.

[0028] The feed gas (including nitrogen and oxygen, preferably air) is introduced through a nozzle. The nozzle is preferably cylindrical with a diameter of up to 5 mm, for example up to 2 mm. In one example, the nozzle has a diameter of 1 mm. The nozzle is suitably positioned above the tip of the electrode, for example, positioned 5 mm above the tip of the electrode, with the narrowest gap distance being 2 mm.

[0029] In one example, the feed gas uses a mixture of nitrogen and oxygen with different N2 / O2 ratios, which is controlled by varying the nitrogen and oxygen gas flows while keeping the total flow the same. In one example, the N2 to O2 flow ratio is 1.5. In one example, the N2 to O2 flow ratio is 4, i.e., similar to the ratio found in air.

[0030] The nitrogen and oxygen gas flow rates are controlled by a nitrogen mass flow controller with a gas flow rate range of 0.05-1 SLM and an oxygen mass flow controller with a gas flow rate range of 0.05-1 SLM. In one example, the feed gas is air, and the flow rate is controlled by a mass flow controller with a range of 0.5-10 SLM.

[0031] In one example, the gas pressure is controlled by a gas regulator. In one example, the pressure is atmospheric pressure.

[0032] In one example, the GAD device is powered by a pulsed power supply having a voltage range of 0-20 kV, a pulse width range of 1 ns-1 ms, a rise time of 50 ns, a fall time of 50 ns, and / or a frequency range of 1 Hz-100 kHz. In one example, the GAD device is powered by an AC power supply with a peak-to-peak voltage range of 0-10 kV regulated through a transformer, and a fixed frequency of 50 Hz, or optionally an adjustable frequency range of 1 Hz-100 kHz. When the GAD device is powered by a power supply, one of the electrodes of the GAD is suitably grounded and the other is suitably connected to the high voltage output of the power supply.

[0033] In one example, the apparatus includes an external heat source to provide additional heat to the reaction when in use. However, this is not preferred. In one preferred example, the apparatus does not include an external heat source or does not include any external heat source.

[0034] The device may include additional safety features. For example, the device may include an additional cooling source to reduce the temperature when the device is in use. However, this is not preferred. In a preferred embodiment, the device does not include any cooling source.

[0035] For example, conventional devices often operate at high temperatures and are therefore energy intensive. Additionally and / or alternatively, conventional devices typically require cooling to attenuate heating due to the exothermic nature of the process. In contrast, the device according to the first embodiment may not require additional cooling due to the relatively low reaction temperature.

[0036] The GAD device may include a catalyst. In one example, the GAD device does not include a catalyst.

[0037] The device is formed NO x The post-discharge chamber includes a post-discharge chamber for adjusting the NO2 / NO ratio in the chamber to 1:2 to 2:1. In one example, the NO2 / NO ratio is 1:1.

[0038] In one example, the post-discharge vessel is fluidly connected to an outlet of the GAD device. In one example, the post-discharge vessel and the GAD device are coupled by using high temperature resistant tubing to connect the inlet of the post-discharge vessel and the outlet of the GAD device.

[0039] In one example, the tube is a rubber tube.

[0040] The inventors have NO x It has been established that the NO2 / NO ratio in the post-discharge vessel may be controlled by changing the dimensions of the post-discharge vessel. Preferably, the post-discharge vessel is a cylindrical post-discharge vessel.

[0041] In one example, a cylindrical post-discharge vessel has a length of 1000 mm, an inner diameter of 4 mm, an outer diameter of 6 mm, and a total volume of 50 cm 3 In one example, a cylindrical post-discharge vessel has a length of 5000 mm, an inner diameter of 4 mm, an outer diameter of 6 mm, and a total volume of 250 cm 3 In one example, a cylindrical post-discharge vessel has a length of 15000 mm, an inner diameter of 4 mm, and an outer diameter of 6 mm, with a total volume of 755 cm 3 It is.

[0042] In one preferred example, the post-discharge vessel is a cylindrical vessel made from a plastic material, such as acrylic, however, any suitable material can be used.

[0043] In one example, the post-discharge vessel includes a microporous membrane that divides the vessel into two portions. x A solution, for example an aqueous solution, may be added to one portion of the post-discharge vessel to absorb the NO. A second portion of the post-discharge vessel absorbs the NO. x Includes.

[0044] The microporous membrane prevents the penetration of aqueous solutions into the gaseous portion while allowing gaseous NO x into the solution. Any suitable membrane material may be used. In one example, the membrane is a metal, such as nickel, cobalt, or stainless steel.

[0045] In one example, the diameter of the microporous membrane is 10 to 100 mm, for example, 20 to 80 mm, for example, 60 mm.

[0046] In one example, the thickness of the membrane is 0.05-0.5 mm, such as 0.1-0.3 mm, for example 0.2 mm.

[0047] In one example, the pitch of the microporous membrane is 350 to 500 μm, for example 380 to 480 μm, for example 450 μm or 480 μm.

[0048] In one example, the pore size is from 5 to 100 μm, for example from 10 to 70 μm, such as 20 μm or 50 μm.

[0049] In one example, the microporous membrane has a diameter of 60 mm, a thickness of 0.2 mm, a pitch of 450 μm, and a pore size of 50 μm. In one preferred example, the microporous membrane has a diameter of 60 mm, a thickness of 0.2 mm, a pitch of 480 μm, and a pore size of 20 μm.

[0050] In one example, the diameter of the vessel is 70 mm and the height of the vessel is 120 mm.

[0051] The device is NO x to ammonia. In one example, the apparatus includes electrochemical means, preferably including an H-cell arranged as a divided electrochemical cell.

[0052] In one example, a divided electrochemical cell includes two compartments connected via a diaphragm, an ion-permeable membrane or a salt bridge. Preferably, one compartment is known as the working compartment. The other compartment is known as the counter compartment.

[0053] Preferably, both the working and counter compartments contain an electrolyte. Preferably, the working and reference electrodes are disposed within the electrolyte in the working compartment. Suitably, the counter electrode is disposed within the electrolyte in the counter compartment.

[0054] In one example, the reference electrode is a Hg / HgO or saturated calomel electrode (SCE) electrode. In one example, the counter electrode comprises platinum. The counter electrode may suitably be platinum foil.

[0055] In one example, the diaphragm includes and / or is a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer membrane, such as a circular Nafion™ perfluorinated membrane.

[0056] In use, the electrochemical means allows the electrochemical reduction of the nitrate / nitrite solution obtained from the vessel after discharge at a specific potential on the working electrode, thereby producing ammonia and other trace products such as, for example, up to 10% nitrite if nitrate is present in the working electrolyte.

[0057] The working electrode may comprise an electrocatalyst, suitably comprising a transition metal, for example cobalt or nickel. The electrocatalyst is suitably provided on a support.

[0058] In one example, the support includes and / or is a carbon cloth, such as CeTech wos 1009. In one example, the support is a commercially available carbon paper, such as Toray TGP-H-060. In one example, the support is nickel foam.

[0059] In one example, the electrocatalysts containing cobalt or nickel are synthesized by electrodeposition. In one example, the electrocatalysts are synthesized in a single chamber cell at 20° C. using a conductive substrate as the working electrode, a SCE as the reference electrode, and a platinum foil as the counter electrode.

[0060] In one example, the catalyst comprises Co(OH)2 nanoarrays. Suitably, the Co(OH)2 nanoarrays may be directly electrodeposited onto carbon paper from an aqueous solution of cobalt nitrate hexahydrate at a potential of -1.0 V vs. SCE.

[0061] In one example, the catalyst comprises Ni(OH)2 nanoarrays. Suitably, the Ni(OH)2 nanoarrays may be directly electrodeposited onto carbon paper from an aqueous solution of nickel nitrate hexahydrate at a potential of -1.0 V vs. SCE.

[0062] In one example, the catalyst comprises Co-Ni(OH)2 nanoarrays. Suitably, the Co-Ni(OH)2 nanoarrays may be directly electrodeposited onto carbon paper from a mixed aqueous solution of cobalt nitrate hexahydrate and nickel nitrate hexahydrate at a potential of -1.0 V vs. SCE.

[0063] The inventors have established that cobalt-containing electrocatalysts are particularly suitable for nitrate / nitrite reduction towards ammonia. The conductive substrate can have an effect on the catalytic performance of the electrocatalyst.

[0064] In one example, the catalyst comprises Co(OH)2 nanoarrays, which are directly electrodeposited onto carbon cloth from an aqueous solution of cobalt nitrate hexahydrate at a potential of -1.0 V vs. SCE.

[0065] In one example, the catalyst comprises Co(OH)2 nanoarrays, which are directly electrodeposited onto nickel foam from an aqueous solution of cobalt nitrate hexahydrate at a potential of -1.0 V vs. SCE.

[0066] The present inventors have established that nickel foam substrates are particularly suitable for the electrochemical reduction of nitrates / nitrites towards ammonia.

[0067] In one example, the catalyst comprises Co3O4 nanoarrays, which may be synthesized by annealing Co(OH)2 deposited on nickel foam at 300 °C for 120 min with a heating rate of 2 °C / min.

[0068] In one preferred embodiment, the catalyst comprises Co. In one particularly preferred embodiment, the catalyst consists essentially of a Co metal film. The Co film catalyst has a current density of 1 A / dm 2 Cobalt chloride hexahydrate, boric acid, and dibasic ammonium citrate may be directly electrodeposited onto the nickel foam at a current density of 1000 .mu.m.

[0069] In one example, no extra equipment is used to change the state (i.e., motion) of the working solution, and the working solution is defined as static. In one preferred example, the working solution is stirred, for example at 400 rpm, using a magnetic stirrer and magnetic stir bars. Suitably, the working solution may be defined as fluid.

[0070] In one example, when electrolysis is performed in an alkaline solution, e.g., 1 M KOH, Hg / HgO is used as the reference electrode. In one example, when electrolysis is performed in a neutral solution, e.g., 0.5 M K2SO4, SCE is used as the reference electrode.

[0071] The device may include additional safety features. For example, the device may include a heating source to increase the temperature when the device is in use. However, in a preferred embodiment, a heating source is not required. In one embodiment, the device is used at low temperatures, and therefore no additional heating source is required.

[0072] This provides a significant advantage over conventional devices that often operate at high temperatures and pressures and are therefore energy intensive. Additionally and / or alternatively, conventional devices for ammonia production typically require H2 as a resource, usually derived from CH4, and therefore have a CO2 footprint. In contrast, the device according to the first embodiment does not require H2.

[0073] method According to a second aspect of the present invention, a method for producing NO from nitrogen and oxygen x A method of forming generating a plasma using a gliding arc discharge (GAD) device; The nitrogen and oxygen are reacted in the generated plasma, thereby producing NO from at least a portion of the nitrogen and oxygen. x forming a The NO formed x and adjusting the NO2 / NO ratio in the mixture to 1:2 to 2:1. A method is provided that includes:

[0074] In one example, the method is carried out using an apparatus according to the first aspect.

[0075] NO x The nitrogen, oxygen, plasma and GAD apparatus may be as described in relation to the first aspect. The method may include any of the steps and / or features described in relation to the first aspect, mutatis mutandis.

[0076] NO formed x The appropriate adjustment of the NO2 / NO ratio in the post-discharge vessel according to the first embodiment is carried out.

[0077] According to a further aspect of the present invention there is provided a method for synthesizing ammonia, comprising the steps of: (a) NO obtained from the method of the second embodiment x is reacted with an aqueous solution to form the NO x forming nitrates / nitrites from at least a portion of (b) electrochemically reducing the nitrate / nitrates obtained in step (a) to ammonia. A method is provided that includes:

[0078] Suitably, step (a) is carried out in a post-discharge vessel as defined according to the second aspect.

[0079] Suitably, step (b) is carried out using electrochemical means as defined in the first aspect, suitably an H-type cell.

[0080] Suitably, step (b) comprises applying a potential to a working electrode in an H-type cell and the nitrates / nitrites are electrochemically reduced to ammonia. Suitably, step (b) is carried out over a catalyst comprising cobalt and / or nickel, suitably consisting essentially of cobalt, supported on a conductive substrate.

[0081] The reaction temperature of the second embodiment (i.e. the temperature at which the nitrogen and oxygen are exposed to the generated plasma) is at most 400° C., more preferably at most 300° C. or at most 250° C. This reaction temperature may appropriately be described as a “low” temperature.

[0082] In one example, the method includes external heating of the nitrogen and oxygen, for example using an external heat source. However, this is not preferred. In one preferred example, the method does not include external heating. In this manner, the reaction temperature is provided, for example at least partially and / or completely, by the generated plasma.

[0083] The method according to the second aspect offers a significant advantage over conventional methods, since the reaction may be carried out at relatively low temperatures without an external heat source. This reduces the energy consumption and capital costs of the process. Additionally and / or alternatively, it is not necessary to remove heat from the process or to provide a process to prevent overheating of the process.

[0084] Additionally and / or alternatively, because the reaction may be carried out at a relatively low temperature, the process may be started (i.e., switched on) and / or paused or terminated (i.e., switched off) as needed, e.g., immediately or instantly, since no pre-heating is required.

[0085] Since the generated plasma reaches a steady state in a relatively short time, the method may be stopped and then restarted without any additional waiting time, which improves the efficiency of the process. In this way, the process offers great flexibility for integration with renewable energy sources such as wind and solar, especially the use of intermittent renewable energy during peak loads for local or distributed energy storage.

[0086] The reaction pressure (i.e., the pressure at which the nitrogen and oxygen, preferably air, are exposed to the generated plasma) is about ambient pressure. It should be understood that about ambient pressure is the substantially natural pressure of the environment, for example, about 101 kPa.

[0087] In one example, the method includes exposing nitrogen and oxygen, preferably air, to a plasma generated in the presence of another gas, e.g., an inert gas such as argon. In one example, only pure nitrogen and oxygen are used. In one example, air is used.

[0088] In one example, the N2 / O2 ratio of the feed gas is in the range of 0.05 to 19, preferably in the range of 0.67 to 4. In one preferred example, the feed gas is air, which contains nitrogen and oxygen at normal atmospheric levels. The use of air means that no additional energy is required to prepare the feed gas.

[0089] The power of the discharge may be defined by equation (1).

number

[0090] In one example, the discharge output defined by formula (1) is in the range of 6 W to 41 W, preferably in the range of 15 W to 30 W, with the power supply frequency being 40 kHz.

[0091] NO x The energy consumption of production may be defined by equation (2).

number

[0092] In one example, NO defined by formula (2) x Energy consumption of EC NOX is at most 17.6 MJ / mol, preferably at most 1.5 MJ / mol, more preferably at most 1.2 MJ / mol.

[0093] In one example, the air flow rate is in the range of 0.5 SLM to 4 SLM, preferably in the range of 1 SLM to 2 SLM, with the power supply frequency being 40 kHz.

[0094] In one example, the GAD device circuit includes a 100 kΩ resistor to limit the discharge current. In one preferred example, the GAD device circuit does not include a resistor. In this way, no extra energy is required in the resistor, and NO x The energy consumption of production is reduced.

[0095] The energy consumption of nitrate / nitrite production in the post-discharge vessel may be defined by equation (3).

number

[0096] In one example, NO defined by formula (3) x Energy consumption of EC 硝酸塩 / 亜硝酸塩 is at most 6.5 MJ / mol, preferably at most 4.7 MJ / mol, more preferably at most 3.5 MJ / mol.

[0097] Since the generated plasma reaches a steady state in a relatively short time, the method may be stopped and then restarted without any additional waiting time, which improves the efficiency of the process. In this way, the process offers great flexibility for integration with renewable energy sources such as wind and solar, especially the use of intermittent renewable energy during peak loads for local or distributed energy storage. In one example, the power supply is connected to a portable solar power generator.

[0098] The potential of an H-type cell may be described relative to the reversible hydrogen electrode (RHE) by the following equation: E RHE =E Hg / HgO +0.098+0.059×pH (4) E RHE =E SCE +0.2412+0.059×pH (5)

[0099] In one example, to determine a suitable potential for ammonia production, electrolysis is performed at working electrode potentials ranging from 0.2 V vs. RHE to −1.0 V vs. RHE, as defined by equations (4) and (5).

[0100] In one example, the electrolysis is performed at a K2SO4 concentration of 0.5M. In one example, the electrolysis is performed at a KOH concentration of 0.1M and a K2SO4 concentration of 0.45M. In one example, the electrolysis is performed at a KOH concentration of 0.5M and a K2SO4 concentration of 0.25M. In one preferred example, the electrolysis is performed at a KOH concentration of 1M.

[0101] In one example, to determine the appropriate concentration of nitrate / nitrite for ammonia production, electrolysis is performed at nitrate / nitrite concentrations between 0.005M and 0.2M.

[0102] Faraday efficiency FE towards NH3 production NH3 may be defined by equation (6).

number

[0103] In one example, the method comprises a faradaic efficiency, F, defined by equation (6), of at least 80%, preferably at least 90%, more preferably at least 95%. NH3 has.

[0104] Ammonia production rate (mmol / h / cm) at a specific applied potential 2 or mg / h) may be defined by equations (7) and (8).

number

[0105] In one example, the method comprises providing a flow rate of at least 3 mmol / h / cm 2 , preferably at least 4 mmol / h / cm 2 , more preferably at least 5 mmol / h / cm 2 The ammonia production rate R is defined by the following equation (7): NH3 has.

[0106] The energy consumption of ammonia production from nitrate / nitrite in electrolysis may be defined by equation (9):

number

[0107] In one example, the energy consumption of ammonia production from nitrate / nitrite in electrolysis, EC, defined by equation (9), NH3 is at most 0.61 MJ / mol, preferably at most 0.32 MJ / mol, more preferably at most 0.06 MJ / mol.

[0108] Total energy consumption T of ammonia production from air using plasma and electrolysis processes ECNH3 may be defined by equation (10).

number

[0109] However, as will be appreciated by one of ordinary skill in the art, the values ​​set forth herein may be modified.

[0110] use According to a further aspect of the present invention there is provided the use of a catalyst comprising a Co metal film in the electrochemical reduction of nitrates and / or nitrites to ammonia.

[0111] The Co metal film, electrochemical reduction, nitrate, nitrite and ammonia may be as described in relation to the first and / or second and / or further aspects. The use may include any of the steps and / or features described in relation to the first and / or second and / or further aspects, mutatis mutandis.

[0112] definition Throughout this specification, the terms "comprising" or "comprises" mean including the specified components but not excluding the presence of other components. The terms "consisting essentially of" or "consists essentially of" mean including the specified components but excluding other components, except for materials present as impurities, unavoidable materials present as a result of the process used to provide the components, and components added for purposes other than achieving the technical effect of the invention, such as colorants.

[0113] The terms "consisting of" or "consists of" mean the inclusion of the specified elements but the exclusion of other elements.

[0114] Where appropriate, depending on the context, use of the words "comprises" or "comprising" may be interpreted to include the meanings "consists essentially of" or "consisting essentially of", as well as "consists of" or "consisting of".

[0115] The optional features described herein may be used individually or, where appropriate, in combination with each other, particularly in such combinations as are described in the appended claims. The optional features of each aspect or exemplary embodiment of the invention described herein are also applicable to all other aspects or exemplary embodiments of the invention, where appropriate. In other words, a person skilled in the art reading this specification should consider the optional features of each aspect or exemplary embodiment of the invention as interchangeable and combinable between different aspects and exemplary embodiments. EXAMPLES

[0116] experiment The following procedures were used in the examples below.

[0117] Arc voltage was measured by a high voltage probe (Tektronix P6015A) and current was measured by a current monitor (Pearson 2877). Electrical signals (arc voltage, current) were recorded by a 4-channel digital oscilloscope (Tektronix MDO 3054, 500 MHz, 2.5 GS / s) with a sampling rate of 5 Mpts / record to ensure accurate measurements.

[0118] The gaseous reaction products were analyzed using a Fourier transform infrared (FTIR) spectrometer (Bruker Tensor II) at 2 cm -1 The spectra were analyzed online with a wavenumber resolution of 100 nm and each spectrum was obtained by averaging 16 scans. To ensure a stable discharge, the absorption spectrum was recorded 10 min after the discharge was ignited and each measurement was repeated at least three times. x To quantitatively analyze the concentration of NO, precise calibration gas mixtures (NO or NO2 in argon) with a wide range of concentrations were introduced into the gas cell by a mass flow controller.

[0119] The concentrations of nitrate, nitrite and ammonia in the aqueous solutions were measured by spectrophotometry using a microplate reader (Thermo Scientific Varioskan® Flash Reader). For the detection of nitrite, 100 μL of Griess reagent was added to 100 μL of sample and the absorbance was measured at 540 nm. For the detection of nitrate, 100 μL of saturated VCl3 was added to the sample, then 100 μL of Griess reagent was added to the above solution and the solution was incubated at 37 °C for 12 h to ensure the complete reduction of nitrate by VCl3, after which the absorbance was measured at 540 nm. Finally, the nitrate concentration was obtained by subtracting the nitrite concentration from the total concentration of nitrate and nitrite. For the detection of ammonia, 100 μL of potassium sodium tartrate was added to 100 μL of sample, followed by adding 100 μL of Nessler's reagent to the above solution and measuring the absorbance at 420 nm. All measurements were calibrated by using a standard curve.

[0120] Example: Ammonia production by plasma electrolysis process Example 1: NO at different N2 / O2 ratios x Generate The experimental setup is depicted diagrammatically in Figure 1. Experiments were carried out in a flat-gliding arc reactor using either a mixture of nitrogen and oxygen at atmospheric pressure or dry air as feed gas.

[0121] The gliding arc reactor consists of two thin diverging stainless steel electrodes (3 mm thick) fixed symmetrically in a transparent flat (10 mm thick) quartz vessel with rectangular cross section (100 x 60 mm) to achieve uniform drag of the arc column by the surrounding gas flow and a high processing fraction. The feed gas was introduced through a cylindrical nozzle of 1 mm diameter, which was located 5 mm above the tip of the electrodes and had a narrowest gap distance of 2 mm.

[0122] Supply gas: a mixture of N2 and O2; gas flow rate: 1 SLM; discharge power: 17 W; applied voltage frequency: 6 kHz.

[0123] Figure 2A shows NO measured at different N2 / O2 ratios. x (NO and NO2) concentrations are shown. Both NO and NO2 concentrations follow a parabolic trend with increasing N2 fraction. NO concentration increases with increasing N2 fraction until it reaches a maximum value of 10900 ppm at an N2 / O2 ratio of 4, whereas NO2 concentration reaches its maximum value (10850 ppm) at an N2 / O2 ratio of 1.5.

[0124] FIG. 2B shows the selectivity of NO and NO x The energy consumption of production is shown as a function of the N2 / O2 ratio. At N2 / O2 ratios below 0.11, increasing the N2 fraction results in slightly lower NO selectivity. After this point, NO selectivity increases with varying N2 / O2 ratio, as NO2 production by NO oxidation becomes less dominant at low O2 fractions, with the highest N2 / O2 ratio giving the highest NO selectivity of 81.6%. x The energy consumption for production drops sharply with increasing N fraction when the N2 / O2 ratio is lower than 0.43, and continues to decrease to a minimum value of 1.26 MJ / mol when the optimum N2 / O2 ratio (1.5) is reached, after which the energy consumption starts to increase. Clearly, too much or too little N2 is not effective for efficient NO production. x production is unfavorable because both N2 and O2 are precursors for the formation of NO and NO2.

[0125] Interestingly, at an N2 / O2 ratio of 4, which is similar to the composition of air, the energy consumption (1.35 MJ / mol) is only 7% higher than the optimized N2 / O2 feed ratio, which indicates that air is a better source of NO x This is because no additional energy is required to prepare pure O2 and N2. Therefore, in the following experiments, we will use only air as a feed gas to generate NO x Focus on generation.

[0126] Example 2: NO at different frequencies x Generate Figure 3 shows the NO2 emission at different applied voltage frequencies at a constant discharge power (supply gas: air; gas flow rate: 1 SLM; discharge power: 15 W). x The generation performance is compared. Obviously, a higher or lower applied voltage frequency does not necessarily result in a higher NO x A frequency of 40 kHz gives the best performance, in which case NO x Concentration and NO x The energy consumption of production can reach 15500 ppm and 1.41 MJ / mol, respectively. Similar results are seen at 20 kHz. Frequencies of 6 kHz, 25 kHz, 30 kHz and 43 kHz show slightly worse performance, with the worst NO x The generation performance is observed at 11 kHz.

[0127] Example 3: NO at different discharge powers and frequencies x Generate Figure 4 shows that the gliding arc exhibited different phenomena at different frequencies with increasing discharge power (supply gas: air; gas flow rate: 1 SLM).

[0128] FIG. 4A shows digital photographs of the gliding arc discharge upon increasing power at a frequency of 6 kHz. Under the lowest discharge power, the arc can only propagate a short distance. Increasing the power from 8 W to 11 W significantly increases the propagation distance and arc length, and further increasing the power only slightly increases the propagation distance but results in a larger plasma volume and a more diffuse appearance. The discharge contains numerous bright filamentary arcs at low power upstream of the gliding arc. The evolution process from a mode containing numerous short bright arcs (short-arc mode) to a mode containing long propagating arcs (diffuse mode) upon increasing the power was also observed at frequencies of 8 kHz, 11 kHz, 25 kHz, 30 kHz, and 43 kHz. This short-arc mode is most prominent at 11 kHz, where the upstream arc is even brighter and less likely to be dragged down, as shown in FIG. 4B. Interestingly, but differently, the discharge cannot sustain itself in the short-arc mode at frequencies of 20 kHz and 40 kHz. As shown in Figure 4C, the gliding arc discharge appears directly in a diffusion mode at the lowest discharge power, and the arc propagates slightly downwards as the power increases.

[0129] Figure 5 shows the NO x Concentration, NO x Selectivity and NO x The energy consumption of production is shown as a function of the discharge power. In FIG. 5A, NO x It can be seen that the NO concentration increases at higher discharge powers and more rapidly at lower discharge powers for all frequencies. x Concentrations are consistently observed at 20 kHz and 40 kHz with fixed discharge power. 11 kHz has the lowest NO x The concentration of NO is consistent with the results above. x It has an effect on the generation of the best frequency NO x Generates high power, worst frequency NO x At frequencies of 6 kHz and 11 kHz, the highest discharge powers can be achieved at 35 W and 21 W, respectively.

[0130] FIG. 5B shows NO x The effect of frequency and discharge power on selectivity is shown. For all frequencies, increasing power results in significant NO2 selectivity (lower NO selectivity) under low power (<24 W), and further power increase increases NO selectivity only slightly. This can be partly explained by the fact that increasing power results in a longer propagation distance and a larger volume of plasma region, as mentioned earlier. As a result, previously formed NO molecules are more likely to be oxidized to NO2 by excited O2 with a longer residence time in the plasma region. As shown in Figure 4, the propagation distance increases significantly under low power, consistent with the increase in NO2 selectivity upon increasing power. The highest and lowest NO2 selectivities are 36.1% and 47.8%, which are achieved at the lowest power of 6 kHz and the highest power of 40 kHz.

[0131] In Figure 5C, NO x The calculated energy consumption for generation drops sharply with increasing power (<15 W) for frequencies of 6 kHz and 11 kHz. The rapid decrease in energy consumption with increasing power at low power at frequencies of 6 kHz and 11 kHz closely follows the discharge behavior at these frequencies. As shown in Figures 4A and 4B, the discharge evolves from a short arc mode to a diffusion mode with a longer propagation distance and a larger plasma volume with increasing power at low power. In contrast, at frequencies of 20 kHz and 40 kHz, the energy consumption does not change much with increasing power, as the discharge operates directly in the diffusion mode, as seen in Figure 4C. For all frequencies, NO x The optimum power for generation is between 15W and 30W, with further power increases resulting in only slightly higher energy consumption. Under the optimum power, the energy consumption can reach about 1.29MJ / mol at 20kHz and 40kHz, while the numbers are 1.34MJ / mol and 1.39MJ / mol for 6kHz and 11kHz, respectively.

[0132] Example 4: NO with limited discharge current x Generate Discharge current is NO x The effect on the generation was investigated by limiting the discharge current with a resistor of 100 kΩ. The experiments are carried out at a frequency of 6 kHz and an air flow rate of 1 SLM.

[0133] In Figure 6, the discharge can be sustained at a much lower power of about 5 W with a 100 kΩ resistor. For comparison, the minimum power to maintain a gliding arc without resistance is about 8 W. Note that the arc propagation distance is close at the lowest discharge power with or without current limiting, indicating that current limiting does not change the discharge mode at this frequency, but at low discharge powers. Visually, the arc plasma upstream of the discharge region is much brighter when operating the discharge at low power without current limiting, whereas the discharge becomes more uniform when current limiting.

[0134] Figure 7 shows NO x Concentration, NO x Selectivity, and NO x The effect of limiting the discharge current on the energy consumption of production is plotted as a function of the discharge power. x The concentration is about 1400 ppm, which is lower than the 8 W case without current limiting (1800 ppm), but the selectivity of NO is higher in the former case. Note that at the same output of about 8 W, the NO concentration is higher when the current is limited. x The concentration can reach 6000 ppm, and therefore the energy consumption is only 1 / 3 of that without current limiting. This is reasonable, because at the same power of 8 W, the discharge clearly shows different modes, the short arc mode without current limiting, and the diffuse glow type mode with current limiting, and as mentioned above, the short arc mode is NO x This is because it consumes more energy to generate the NOx. In fact, at discharge powers below 12W, the NOx generated by limiting the current is xThe energy consumption of the generation is significantly lower than that without current limiting, mainly due to the fact that the discharge is in a different mode, as clearly shown in FIG.

[0135] However, when the power is further increased to above 12 W, the advantage of limiting the discharge current starts to disappear because the non-current-limited discharge transitions to a diffuse glow-like mode. From the perspective of the overall energy input, limiting the current by using a high-value resistor is not encouraged because a lot of energy is dissipated by the resistor in the form of heat. For example, the resistor power and resistor temperature can reach about 35 W and 200° C. at an optimal power of 15 W, and these values ​​are even higher at higher powers. If the energy spent on the resistor is not used properly and efficiently, the overall energy efficiency of the system will be quite low.

[0136] Example 5: NO at different flow rates x Generate 8A and 8B show digital photographs of the gliding arc discharge at increasing flow rates at fixed powers of 21 W and 18 W at applied frequencies of 6 kHz and 40 kHz, respectively, except for the first case at 40 kHz, which is in glow mode (supply gas: air) and has a power of 22 W.

[0137] Figure 8 shows the discharge phenomenon exhibiting different patterns when increasing the flow rate at frequencies of 6 kHz and 40 kHz. The gliding arc was observed in the flow rate range of 0.5 to 2.5 SLM, and when the flow rate was further increased at a frequency of 6 kHz, the power supply could not sustain the gliding arc at 21 W. Differently, at 40 kHz, we observed a static glow type discharge at flow rates of 0.5 SLM and 0.75 SLM, and the gliding arc could operate at a higher maximum flow rate (4 SLM). Notably, when the flow rate was increased, the propagation distance decreased and the arc became brighter and more uneven.

[0138] In Figure 9, NO x Concentration, NO xSelectivity, and NO x The effect of flow rate on the energy consumption of production is seen. As shown in Figure 8, when the discharge operates in a static glow type mode, the energy consumption is significantly higher than that in the gliding arc mode. NO x The concentration steadily decreases with increasing flow rate at both frequencies, and this is also true for NO2 selectivity. For example, at 6 kHz, the lowest flow rate gives the highest NO2 selectivity (83%), and NO2 selectivity decreases almost linearly with increasing flow rate. Lower flow rates indicate a longer residence time, and therefore previously formed NO molecules are more likely to be oxidized to NO2. However, flow rates that are too high or too low can result in energy-efficient NO2 selectivity. x It is not useful for production.

[0139] As shown in Figure 9B, the optimal gas flow rates at 6 kHz and 40 kHz are 1.25 SLM and 1.5 SLM, respectively. The corresponding energy consumption is 1.28 MJ / mol and 1.23 MJ / mol at optimal conditions. A low flow rate benefits from a long propagation distance but suffers from high concentration of products, whereas a high flow rate can overcome the effect of high concentration of products but results in a short propagation distance and non-uniform discharge.

[0140] Example 6: NO in aqueous solution x Formation of nitrate / nitrite by absorption of NO generated by the GAD device x is first introduced into the post-discharge vessel to obtain a suitable NO2 / NO ratio, and then NO x was introduced into a vessel containing 100 mL of solution, and NO x The reaction of nitrate with the solution produced nitrate / nitrite.

[0141] FIG. 10A shows the NO xThe pH and electrical conductivity of the aqueous solution in an acrylic cylindrical vessel at different discharge times using water as an absorbent solution under the optimal discharge conditions for production (discharge power: 18 W, applied frequency: 40 kHz, flow rate: 1.5 SLM) are shown. The vessel used in this experiment has a length of 15 m, and the NO2 selectivity increases from 34.5% to 68%. The pH drops sharply from 5.9 to 2.1 at 2.5 min of discharge time, and then drops further with increasing discharge time. At 30 min of discharge time, the pH reaches about 1. The electrical conductivity of the solution increases almost linearly with increasing discharge time, reaching about 25000 μs / cm at 30 min of discharge time.

[0142] FIG. 10B shows the concentrations of nitrate and nitrite in the solution at different discharge times. Both nitrate and nitrite concentrations increase with increasing discharge time. The concentration of nitrate increases almost linearly with increasing discharge time, reaching a value of about 100 mM at a discharge time of 30 minutes, while the value of nitrite at the same discharge time is only 5 mM. The concentration of nitrate in the solution is more than 10 times higher than that of nitrite, especially at longer discharge times, which indicates that NO x This is due to the high NO2 selectivity in the

[0143] To achieve high nitrite selectivity in aqueous solution, NO x The NO2 selectivity in the column was adjusted to about 50% using a 5 m long post-discharge chamber, and 1 M KOH solution was used as the capture solution.

[0144] FIG. 10C shows the concentration of nitrate and nitrite in solution at different discharge times using 1M KOH as the capture solution. As with water as the capture solution, both nitrate and nitrite concentrations increase with increasing discharge time. The difference is that the concentration of nitrite is much higher than that of nitrate at all discharge times. The former reaches about 130 mM at a discharge time of 30 minutes, while the latter figure is about 7.5 mM. Therefore, in this case, a solution with high nitrite selectivity is obtained.

[0145] Example 7: Ammonia production from electrolysis using Co(OH)2 catalysts supported on different conductive substrates Nitrate solution concentration: 0.1M, KOH concentration: 1M

[0146] FIG. 11 shows the LSV curves of Co(OH)2 on carbon cloth, carbon paper and Ni foam in electrolysis to produce ammonia from a standard electrolyte containing 0.1 M nitrate and 1 M KOH. When the potential is higher than −0.1 V vs. RHE, the current density for both curves is about 0 mA / cm 2 The current density of the LSV curves for Co(OH)2 on Ni foam starts to decrease at a potential of about -0.12 V vs. RHE, while the potentials for Co(OH)2 on carbon cloth and carbon paper are about -0.2 V vs. RHE. After the drop point where the current density starts to decrease rapidly with decreasing potential, the current density decreases at a similar rate with decreasing potential for Co(OH)2 on all types of conductive substrates.

[0147] The current density of the LSV curve of Co(OH)2 on Ni foam is -650 mA / cm at a potential of -0.56 V vs. RHE. 2 At the same potential, the current density of the LSV curves of Co(OH)2 on carbon cloth and carbon paper is -391mA / cm 2 and -331mA / cm 2 Apparently, Co(OH)2 on Ni foam has higher activity than Co(OH)2 on other substrates, probably due to the 3D porous structure of Ni foam. In the following examples, Ni foam was used as the conductive substrate.

[0148] Example 8: Ammonia production from electrolysis using different catalysts including cobalt supported on Ni foam Nitrate solution concentration: 0.1M, KOH concentration: 1M

[0149] FIG. 12 shows the LSV curves of Co(OH)2 / Ni foam, Co / Ni foam, and Co3O4 / Ni foam in electrolysis to produce ammonia from a standard electrolyte containing 0.1 M nitrate and 1 M KOH. The current density of the LSV curves of Co(OH)2 on Ni foam and Co3O4 on Ni foam is both about 0 mA / cm when the potential is higher than −0.0 V vs. RHE. 2 The current density of the LSV curves for Co on Ni foam begins to decrease at a potential of about 0.17 V vs. RHE, while the potentials for Co(OH)2 on Ni foam and Co3O4 on Ni foam are about -0.17 V vs. RHE. After the drop point where the current density starts to decrease rapidly with decreasing potential, the current density decreases at approximately the same rate with decreasing potential for all catalysts, including cobalt on Ni foam.

[0150] The absolute values ​​of the LSV curves of Co on Ni foam are larger than those of Co(OH)2 and Co3O4 in the potential range of 0.1 V vs. RHE to -1.0 V vs. RHE, especially in the potential range of -0.2 V vs. RHE to -0.5 V vs. RHE. For example, the current density of the LSV of Co on Ni foam is -648 mA / cm at a potential of -0.4 V vs. RHE. 2 At the same potential, the current density of the LSV curves of Co(OH)2 on Ni foam and Co3O4 on Ni foam is -388mA / cm 2 and -212mA / cm 2 From the above examples, it can be seen that Co on Ni foam has higher activity than Co(OH)2 and Co3O4. In the following examples, Co on Ni foam was used as the catalyst.

[0151] Example 9: Ammonia production from electrolysis using Co / Ni foam at different concentrations of KOH Concentration of nitrate solution: 0.1M, Catalyst: Co / Ni foam

[0152] FIG. 14A shows the LSV curves of Co / Ni foam at different concentrations of KOH (0.0M, 0.1M, 0.5M, and 1M) using nitrate solution as the nitrogen source. The absolute value of the LSV curve is higher at higher KOH concentrations in the potential range of −0.2 V vs. RHE to −0.2 V vs. RHE, indicating that the catalyst has higher activity in a more alkaline environment. For example, at a potential of −0.8 V vs. RHE, the current density is −1270 mA / cm in 1 M KOH solution. 2 However, when electrolysis was performed in 0.5M, 0.1M, and 0M KOH solutions, the current density was −658mA / cm 2 , -390mA / cm 2 , and -154mA / cm 2 It only reaches that level.

[0153] FIG. 14B shows the faradaic efficiency of nitrate towards ammonia using Co / Ni foam as catalyst with different concentrations of KOH (0.0M, 0.1M, 0.5M, and 1M). The faradaic efficiency of nitrate towards ammonia is similar at different concentrations of KOH, and they are all above 90% when the potential is higher than −0.9V vs. RHE. Combining the current density and faradaic efficiency at different concentrations of KOH, higher concentrations of KOH are preferred since they have higher ammonia production rates.

[0154] Figure 14C shows the LSV curves of Co / Ni foam at different concentrations of KOH (0.0M, 0.1M, 0.5M, and 1M) using nitrite solution as the nitrogen source. The absolute value of the LSV curve is higher at higher KOH concentrations in the potential range of -0.2 V vs. RHE to -0.2 V vs. RHE, indicating that the catalyst has higher activity in a more alkaline environment. This is the same trend as when nitrate is used as the nitrogen source.

[0155] FIG. 14D shows the faradaic efficiency of nitrate towards ammonia using Co / Ni foam as catalyst with different concentrations of KOH (0.0M, 0.1M, 0.5M, and 1M). The faradaic efficiency of nitrate towards ammonia is similar at different concentrations of KOH, and they are all above 90% when the potential is higher than −0.9V vs. RHE, which is the same trend as when nitrate is used as the nitrogen source. Combining the current density and faradaic efficiency at different concentrations of KOH, higher concentrations of KOH favor a higher ammonia production rate.

[0156] Example 11: Ammonia production from electrolysis using Co / Ni foam as catalyst at different concentrations of nitrate / nitrite KOH concentration: 1M FIG. 13A shows the LSV curves of Co / Ni foam at different concentrations of nitrate (0.005M, 0.02M, 0.05M, 0.1M, and 0.2M). The absolute value of the LSV curve is higher with higher concentrations of nitrate in the potential range of −0.2 V vs. RHE to −0.2 V vs. RHE, indicating that the catalyst has higher activity with higher concentrations of nitrate. For example, at a potential of −0.8 V vs. RHE, the current density is −1410 mA / cm for 0.2 M nitrate solution. 2 When electrolyzed in 0.1M, 0.05M, 0.02M and 0.005M KOH solutions, the current density was -1269mA / cm 2 , -1103mA / cm 2 , -636mA / cm 2 reaches.

[0157] FIG. 14B shows the faradaic efficiency of nitrate towards ammonia using Co / Ni foam as catalyst at different nitrate concentrations (0.005M, 0.02M, 0.05M, 0.1M, and 0.2M). At 0.2M nitrate concentration, the faradaic efficiency remains above 90% at all potentials ranging from 0.2V vs. RHE to -1.0V vs. RHE. A similar trend of faradaic efficiency can be observed at 0.1M nitrate concentration, except for potential at -1.0V vs. RHE, which has a faradaic efficiency of 88%. At 0.05M nitrate concentration, the faradaic efficiency remains above 90% at potentials higher than -0.5V vs. RHE and starts to decrease almost linearly with decreasing potential. At lower nitrate concentrations, the faradaic efficiency starts to decrease at higher potentials. Combining the current density and faradaic efficiency at different concentrations of nitrate, a high concentration of nitrate favors a higher ammonia production rate as a result of the higher activity of the catalyst and the higher faradaic efficiency towards ammonia.

[0158] Figure 13A shows the LSV curves of Co / Ni foam at different concentrations of nitrite (0.005 M, 0.02 M, 0.05 M, 0.1 M, and 0.2 M). The absolute value of the LSV curve is higher with higher concentrations of nitrite in the potential range of -0.2 V vs. RHE to -0.2 V vs. RHE, which indicates that the catalyst has higher activity with higher concentrations of nitrite, which is the same trend as when nitrate is used as the nitrogen source.

[0159] FIG. 14B shows the faradaic efficiency of nitrite towards ammonia using Co / Ni foam as catalyst with different concentrations of nitrite (0.005M, 0.02M, 0.05M, 0.1M, and 0.2M). At 0.2M nitrite concentration, the faradaic efficiency remains above 90% at all potentials ranging from 0.2V vs. RHE to -1.0V vs. RHE. A similar trend of faradaic efficiency can be observed at 0.1M nitrite concentration, except for potential of -1.0V vs. RHE. At lower nitrite concentrations, the faradaic efficiency starts to decrease at higher potentials, which is the same trend as when nitrate is used as the nitrogen source. Combining the current density and faradaic efficiency at different concentrations of nitrite, a higher concentration of nitrite favors a higher ammonia production rate as a result of the higher activity of the catalyst and the higher faradaic efficiency towards ammonia.

[0160] Example 12: Ammonia production from electrolysis using Co / Ni foam as catalyst and plasma activated solution as working electrolyte FIG. 15A shows the LSV curves of Co / Ni foam using plasma activated solution in an acrylic cylindrical container (discharge time: 30 min, 1 M KOH as absorption solution, discharge power: 18 W, flow rate: 1.5 SLM, nitrate concentration: 7.5 mM, nitrite concentration: 130 mM). The LSV curves of the Co / Ni foam using the plasma activated solution are similar to those using the 0.1 M nitrite solution in 1 M KOH.

[0161] Table 1 below provides a summary of the results.

[0162] [Table 1] a. NO in electrolysis x Optimized energy consumption for production + energy consumption for ammonia production

[0163] Example 13: NO2-rich NO from air using a gliding arc reactor x Plasma synthesis of Further experiments were carried out as follows.

[0164] The flat GAD reactor used in this study contains two diverging stainless steel electrodes (60 mm long, 18 mm wide) placed 3 mm downstream of the nozzle exit with the narrowest gap of 2 mm. The GAD reactor was connected to an AC high-voltage neon transformer with a maximum peak-to-peak voltage of 10 kV and a fixed frequency of 50 Hz. The applied voltage was measured by a high-voltage probe (Testec, TT-HVP 15HF) and the arc current was recorded by a current monitor (Magnelab CT-E0.5). The electrical signal was sampled using a four-channel digital oscilloscope (Tektronix, MDO3024). The discharge power was determined by the integral of the applied voltage multiplied by the arc current. The gas temperature in the GAD reactor was measured by a fiber optic thermometer (Omega, FOB102) with the fiber placed 70 mm downstream of the nozzle exit.

[0165] Air (Zero grade, BOC) was used as a reactant and was introduced into the DBD reactor by a mass flow controller (Omega, FMA-2404). The gas product was delivered at a flow rate of 0.5 cm -1 The analysis was performed using an online Fourier transform infrared (FTIR) spectrometer (FTIR-4200, Jasco) with a resolution of 100 nm. The effluent gas was passed through a standard gas cell with a path length of 10 cm placed in the FTIR. The products from air GAD were determined as NO and NO2 in all working conditions, and the sum of their concentrations was expressed as NO x The concentrations of these products were defined as the concentration of NO and NO2. Calibration gases with known concentrations of NO and NO2 diluted in N2 were used to quantify the concentrations of these products. Each experiment was repeated three times, and the margin of error in this work was within 3%. The total gas flow rate was 2.8-4.0 L / min, and the discharge power was 24-38 W, resulting in a specific energy input (SEI) ranging from 450 to 814 J / L.

[0166] NO2 and NO were found to be the predominant products in this process. Figure 16A shows that increasing the discharge power from 24 W to 38 W increased the overall NO x Figure 16B shows that when the discharge power is increased from 24 W to 38 W, the NO x The energy consumption for synthesis is 0.66MJ / mol NO x from 0.76 MJ / mol NO x This indicates that the lower the discharge power, the higher the NO x These results suggest that the generation of NOx can result in lower energy consumption. Within the test range, the lowest energy consumption was 0.66 MJ / mol NOx at a discharge power of 24 W. x It was.

[0167] Individual NO2 and NO concentrations and overall NO x showed the same trend with increasing total flow rate, as shown in Figure 17A. x The concentration of NO increased from 2.8 to 3.0 SLM, reached a maximum value of 20271 ppm at 3.0 SLM, and then linearly decreased to 15846 ppm at a total flow rate of 4.0 SLM. The concentrations of NO2 and NO also reached peak values ​​of 16563 ppm and 3709 ppm, respectively, at a gas flow rate of 3.0 SLM. Figure 17B shows the NO x The effect of total gas flow rate on the energy consumption of the synthesis is shown. x The energy consumption of the synthesis decreased slightly with increasing total flow rate from 2.8 to 3.2 SLM, and then increased by 0.65 MJ / mol NO with increasing total flow rate up to 4.0 SLM. x In particular, NO x The minimum energy consumption for synthesis (0.65 MJ / mol NO x ) was achieved at the highest total flow rate of 4.0 SLM.

Claims

1. NO from nitrogen and oxygen ｘ 1. An apparatus for forming a a gliding arc discharge (GAD) device configured to generate a plasma; Inlets for feed gases containing nitrogen and oxygen and NO ｘ a passageway extending at least partially through the GAD device, wherein in use the nitrogen and oxygen react in a generated plasma to thereby convert NO from at least a portion of the nitrogen and oxygen. ｘ a passageway forming The formed NO ｘ Inside NO ２ / NO ratio to adjust to 1:2 to 2:1, and An apparatus comprising:

2. 10. The apparatus of claim 1, wherein the post-discharge vessel includes a microporous membrane that divides the vessel into two portions.

3. The device is ｘ 3. The apparatus of claim 1 or claim 2, further comprising means for converting

4. The above NO ｘ 4. The apparatus of claim 3, wherein the means for converting to ammonia is an electrochemical means, preferably an electrochemical means including an H-type cell arranged as a divided electrochemical cell.

5. 5. The apparatus of claim 4, wherein the divided electrochemical cell includes a working electrode that includes an electrocatalyst that includes cobalt or nickel.

6. 2. Apparatus according to claim 1, wherein the nitrogen and oxygen react in the generated plasma at a temperature of up to 300°C, preferably at a temperature of up to 250°C.

7. 2. The apparatus of claim 1, wherein the supply gas is air.

8. 10. The apparatus of claim 1, wherein the GAD device includes at least one pair of diverging electrodes, preferably diverging steel electrodes.

9. Nitrogen and oxygen to NO ｘ 1. A method of forming a generating a plasma using a gliding arc discharge (GAD) device; The nitrogen and oxygen are reacted in the generated plasma, thereby converting NO from at least a portion of the nitrogen and oxygen. ｘ and forming The formed NO ｘ Inside NO ２ adjusting the NO / NO ratio to 1:2 to 2:1; A method comprising:

10. 10. The method of claim 9, wherein the method comprises reacting air with nitrogen and oxygen in the generated plasma.

11. A method for synthesizing ammonia, comprising: (a) NO obtained from claim 9 ｘ is reacted with an aqueous solution to form the NO ｘ forming nitrates / nitrites from at least a portion of the (b) electrochemically reducing the nitrates / nitrites obtained in step (a) to ammonia; A method comprising:

12. 12. The method of claim 11, wherein step (b) comprises applying a potential to a working electrode in an H-type cell.

13. 13. A method according to claim 12, wherein step (b) is carried out over a catalyst comprising cobalt and / or nickel, preferably consisting essentially of cobalt, supported on a conductive substrate.

14. Use of a catalyst comprising a Co metal film in the electrochemical reduction of nitrates and / or nitrites to ammonia.

Images