Process and catalyst for the production of hydrogen by decomposition of ammonia by plasma catalysis

Abstract

The present invention relates to a process for converting a gas comprising NH3 into dihydrogen and dinitrogen in the presence of a cold plasma, preferably a plasma generated by dielectric barrier discharge (DBD), and of a catalyst comprising a support that comprises alumina, nickel, and at least one promoter comprising iron. The invention also relates to a catalyst of this kind, and to the use thereof for producing molecules with high added value, such as hydrogen (H2).

Description

Title: Process and catalyst for the production of hydrogen by plasma catalysis decomposition of ammonia Technical field

[0001] The present invention belongs to the field of chemical conversion, in particular the conversion of a gas or a mixture of gases comprising ammonia (NH3) to produce dihydrogen (H2) and dinitrogen (N2). The invention relates in particular to the process for converting NH3 into H2 and N2, in the presence of a catalyst and a cold plasma, for example generated by dielectric barrier discharge, known as DBD, thus allowing chemical conversion via plasma-catalysis. The invention also relates to said catalyst, to the process for preparing this catalyst and to the use of the catalyst to convert ammonia and produce a high added value molecule such as hydrogen. State of the prior art

[0002] With the sharp increase in energy demand and the impact of fossil fuels on the environment, the search for new energy resources is attracting increasing attention.

[0003] Hydrogen fuel is seen as an ideal candidate to solve the energy and environmental crisis. Furthermore, its use in fuel cell vehicles is particularly promising for controlling COx and NOx emissions into the environment from traditional fossil fuels. Hydrogen has a higher energy density (142 MJ / kg) than other fuels. In addition, this molecule is readily available in water and gaseous hydrocarbon fuels. Numerous studies have examined hydrogen production methods such as steam reforming and water splitting [1].

[0004] Ammonia gas (NH3) is a promising candidate for hydrogen transport and storage. In addition, 150 Mt of NH3 are produced annually and used worldwide. Due to its storage characteristics, NH3 is more advantageous than other hydrogen energy carriers: on the one hand, NH3 has a higher gravimetric density than other fuels; on the other hand, the cost of stored energy per volume of NH3 is three times lower than that of hydrogen. Ammonia decomposition is notably used in at least two different fields related to energy and environmental sciences: it can be used to supply COx-free hydrogen to fuel cells and it can also be used to remove ammonia from the reformate of internal gasification and regeneration power plants. combined cycle (IGCC), a technology that could be widely deployed in the future as a CO2 removal pathway.

[0005] In recent years, NH3 decomposition has received great attention due to its potential use in COx-free H2 production for fuel cells. Traditional heterogeneous catalysis according to Eq. 1 (Eq. 1) has been, so far, the main route for NH3 decomposition[1], [2], [3].

[0006] Given the high chemical stability of NH3, traditional thermal catalysis processes require high gas pressures and a significant amount of energy (thermal energy), including temperatures in the range of 500°C to 800°C, to promote catalyst activation, shift the thermodynamic equilibrium, and ensure acceptable yields. High-temperature catalytic reactions not only result in high energy consumption but also potential catalyst deactivation due to sintering of the metal active sites and coke formation on the catalyst surface. Thermal processes are generally catalyzed by noble metals, such as Ir, Pd, Pt, Rh, and Ru, under stable operation. The noble metal ruthenium (Ru) has the best catalytic activity for ammonia decomposition, but its cost and scarcity limit its large-scale commercialization.Unfortunately, the very slow rate of recombinant desorption of adsorbed nitrogen atoms (N. ads ) on the surface of cheap metal catalysts inhibits the entire process of ammonia decomposition, unless the reaction is carried out at high temperature (about 500°C-800°C) [1], [2], [3].

[0007] Therefore, the search for new processes capable of operating at low temperatures and temperature-stable catalysts is of great interest.

[0008] Various studies have been carried out to develop cold plasma chemical synthesis technologies, making it possible to overcome the aforementioned temperature problems. Among these technologies, dielectric barrier discharge (DBD), particularly coupled with the presence of a heterogeneous catalyst (plasma-catalysis), has been described [4], [5].

[0009] Different catalytic systems, plasma types, experimental variables and reactors have been tested in the prior art to improve ammonia conversion. However, the efficiency of these systems remains low. Furthermore, the activity, stability and costs of the described catalysts have proven incompatible with industrial use [6], [7].

[0010] The object of the present invention is in particular to propose a process for the chemical conversion of ammonia (NH3) in the presence of a catalyst which exhibits catalytic yields and high energy costs, and capable of being exploited on a large scale, the objective being to obtain hydrogen (H2), while avoiding the use of noble metals.

[0011] None of the documents [6], [7], [8], [9],

[0010] ,

[0011] or

[0012] describes a process for the conversion of ammonia (NH3) by plasma-catalysis in the presence of a cold plasma and a catalyst comprising an alumina-based support, nickel and at least one promoter comprising iron (Fe). Summary of the invention

[0012] A first object of the present invention is a process for converting a gas or a mixture of gases comprising ammonia (NH3) into dihydrogen (H2) and dinitrogen (N2) according to the following reaction: NH3 3 / 2 H2 + 1 / 2 N2 said process being carried out in the presence of cold plasma and a catalyst comprising a support comprising alumina, nickel (Ni), and at least one promoter comprising iron (Fe).

[0013] A second object of the present invention is a catalyst, also called a catalytic system, for converting a gas or a mixture of gases comprising ammonia (NH3) into dihydrogen (H2) and dinitrogen (N2), said conversion being carried out in the presence of a cold plasma, characterized in that the catalyst comprises a support comprising alumina, nickel, and at least one promoter comprising iron (Fe). This catalytic system, which can for example be activated by a DBD plasma, makes it possible to resolve all the disadvantages of the prior art present in the thermal process (high temperature and pressure) and capable of synthesizing H2 from NH3 under atmospheric conditions with a high yield compared to the studies described in the prior art.

[0014] According to a preferred embodiment, said catalyst comprises: - a support comprising alumina, - nickel, - a promoter comprising iron (Fe), and - optionally at least one second promoter: - of transition metal type, and more particularly a promoter comprising cobalt (Co), manganese (Mn), copper (Cu) or silver (Ag); - of lanthanide type, and more particularly a promoter comprising lanthanum (La), cerium (Ce) or gadolinium (Gd); - of alkaline earth type, and more particularly a promoter comprising barium (Ba); and / or - of alkali metal type, and more particularly a promoter comprising potassium (K).

[0015] A third object of the present invention relates to a process for preparing such a catalyst.

[0016] A fourth subject of the present invention relates to the use of the catalyst according to the present invention for the conversion of a gas or a mixture of gases comprising ammonia (NH3), said conversion being carried out in the presence of cold plasma, preferably a plasma generated by dielectric barrier discharge (DBD)

[0017] The present invention makes it possible to overcome all the drawbacks of traditional thermal catalysis processes, as described in the prior art, and thus to obtain high catalytic and energy yields, and is thus capable of being exploited on a large scale. Description of the figures

[0018] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which can be read with reference to the appended drawings: [Figure 1] GC chromatogram of the incoming gas before reaction by combining the 5Ni10FeAl catalytic system with the DBD plasma catalytic reactor. Figure 1 illustrates a GC chromatogram of the incoming gas (containing 100% NH3) in a DBD reactor coupled with the 5Ni10FeAl catalyst. [Figure 2] GC chromatogram of the outgoing ammonia gas after reaction by combining the 5Ni10FeAl catalytic system with the DBD plasma catalytic reactor. Figure 2 illustrates a GC chromatogram of the ammonia gas remaining following the conversion of NH3 in a DBD reactor coupled with the 5Ni10FeAl catalyst. [Table 1] Table showing the catalytic activity (i.e., conversion, selectivity) obtained for several catalysts according to the invention and comparative ones, tested in DBD plasma. Definitions

[0019] In the context of the present invention: - the expression “between … and …” (for example, a range of values) must be understood as including the limits (for example, the limit values ​​of this range of values); - any description relating to an embodiment is applicable and interchangeable with all other embodiments of the invention; - the expression “and / or” must be understood as meaning “and” and “or”; for example, the expression “A and / or B” must be understood as meaning either A and B, or only A, or only B; - the expression “N, M and / or P” must be understood as meaning “N and / or M and / or P”; - the expression “N, M and P” must be understood as meaning “N and M and P”; - when an element or component is included in and / or selected from a list of elements or components, it is to be understood that this individual element or component may be selected and combined with other individual elements, or may be selected to constitute a subgroup of two or more explicitly listed elements or components; also, any element or component cited in a list of elements or components may be omitted from this list.

[0020] The term “DBD – Dielectric Barrier Discharge” designates, in the present invention, an electrical discharge created between two electrically conductive elements separated by one or more dielectric elements.

[0021] The term "dielectric" refers, in the present invention, to an electrically insulating material that provides electrical insulation between the high-voltage network associated with the electrode and the electrically and thermally conductive tube connected to ground via the reactor. This type of electrically insulating material is also used inside the DBD cell to generate a plasma by Dielectric Barrier Discharge (DBD) by promoting the accumulation of electrical charges on the surface of this material.

[0022] The terms "catalyst" and "catalytic system" are interchangeable and refer, in the present invention, to a material promoting the chemical reaction of reactive species, for example, reactant fluids.

[0023] The term “plasma-catalysis” designates, in the present invention, the method which implements an electric discharge of plasma coupled to a catalyst.

[0024] The term "hydrogen" should be understood to mean dihydrogen (H2).

[0025] The term “support” or “catalyst support” designates, in the present invention, a solid material or mixture of solid materials - which can in particular be characterized by its specific surface area, on which the promoter(s) is / are deposited.

[0026] The term "promoter" or "catalyst promoter" refers, as used herein, to a solid material or mixture of solid materials added to the surface of the support material, generally in small amounts, for the purpose of increasing the efficiency and performance of the catalyst.

[0027] Naturally, the invention is described in the foregoing by way of example. It is understood that those skilled in the art are able to carry out different variant embodiments of the invention without departing from the scope of the invention. Detailed description of the invention

[0028] Process for converting a gas comprising NH3

[0029] A first subject of the present invention relates to a process for converting a gas or a mixture of gases comprising ammonia (NH3) into dihydrogen (H2) and dinitrogen (N2) according to the following reaction: NH3^ 3 / 2 H2+ 1 / 2 N2, said process being carried out in the presence of cold plasma and a catalyst comprising: - a support comprising alumina, - nickel, and - at least one promoter comprising iron (Fe).

[0030] The gas in question here comprises NH3 and may also comprise other chemical species. Thus, it may involve converting a gas or a mixture of gases comprising NH3. This process aims to produce molecules with high added value, in particular in gas form. The process of the present invention makes it possible to generate dihydrogen (H2), dinitrogen (N2) or their mixtures, in gas form. The product resulting from the process of the invention may also be in another form, for example partially liquid or anhydrous. In this case, it may be hydrazine, ammonium nitrate, and / or ammonia.

[0031] According to the present invention, the process for converting the gas comprising NH3 is therefore carried out in the presence of a catalyst, as well as a cold plasma, preferably a plasma generated by dielectric barrier discharge (DBD). When implementing the process of the invention, the catalyst is activated by the cold plasma. The synergy of plasma catalysis in this process shows great potential for the direct synthesis of H2, a high value-added gas, from NH3. Said catalyst comprising a support comprising alumina, nickel, and at least one promoter comprising iron (Fe) used in the context of the present conversion, in combination with a cold plasma, is more particularly described below. Thus, the process of the invention is carried out in the presence of a catalyst activated by cold plasma. It should be noted that all of the characteristics described in connection with said catalyst are applicable to the conversion process of the present invention.

[0032] According to one embodiment, the selected catalyst is placed between the electrodes of the DBD reactor, allowing the gaseous species to circulate, and is activated by high voltage electrical discharges (of the order of kV) lasting from nanoseconds to microseconds. This polarization, combined with adsorption, desorption and catalyst / gas interaction, gives rise to the formation of the plasma as well as its activation and the production of hydrocarbons. The electrical energy supplied to the fixed bed in the form of sinusoidal or pulsed high voltage, creates multiple currents on the HV (high voltage) carrier waves, during positive and negative polarization. These streamers, lasting from a few hundred picoseconds to a few tenths of nanoseconds, are responsible for the negative or positive polarization of the catalytic sites.

[0033] Before the conversion step, in particular hydrogenation, the catalytic system according to the invention, in the case where its components are in oxidized form, is advantageously reduced in situ under cold plasma, preferably a DBD plasma, under H2 as discharge gas.

[0034] The catalytic system according to the invention is activated by the creation at the level of the catalytic system (more particularly between the grains of said catalytic system) or nearby (upstream or downstream of the catalytic system, in the gas flow) of a strong electric field, typically between 10 3 and 10 10V / m, which can vary over time. This strong electric field allows the ionization of part of the gas and the excitation of atoms and molecules present in the gas phase. The walls of the reactor are made of a metallic material; alternatively, in the case where a DBD plasma is used, the walls of the reactor are made of a dielectric material such as quartz, alumina or ceramic. The reactor can advantageously be cylindrical in shape. In addition to the creation of a cold plasma state, the strong electric field created is responsible for the negative or positive polarization of the catalytic sites. This polarization induces adsorption and desorption reactions, including at low temperatures (for example at temperatures below 400°C, or even below 350°C). According to the conventional process without polarization, the working temperature is higher, generally in the order of 500°C to 800°C.

[0035] The reactor comprises in particular at least one inlet allowing it to be supplied with gas to be converted, i.e. a gas (or a mixture of gases) comprising NH3, and an outlet for evacuating the products formed, which are also in the form of gas.

[0036] In a variant of the invention, the catalytic system of the invention is activated by a DBD plasma by providing an electrical power of less than 20-35 W / g of catalytic system (i.e. the catalytic system present in the reactor, i.e. in the catalytic bed).

[0037] The conversion reaction is advantageously carried out at a pressure close to or equal to atmospheric pressure (10 5 Pa), for example at a pressure between 1.10 4 Pa and 3.10 5Pa. The conversion reaction can be carried out under pseudo-adiabatic conditions, i.e. without thermal insulation and without external heating, or under adiabatic conditions, i.e. with thermal insulation and without external heating, or under isothermal conditions, i.e. with thermal insulation and / or external heating. The DBD plasma is generated by applying a voltage between the two electrodes of between 1 and 25 kV, preferably between 2 and 20 kV, in particular with a frequency of between 1 kHz and 100 kHz. The gas hourly space velocity (GHSV) is in particular between 1000 h -1 and 150,000 h -1 , preferably it is less than 100,000 h -1 .

[0038] A cooling system is optionally present between the container intended to receive the products generated by the conversion reaction and the outlet of the reactor so as to condense and eliminate the liquid likely to form during the conversion reaction.

[0039] Catalyst according to the invention

[0040] A second subject of the present invention relates to a catalyst for converting a gas or a mixture of gases comprising ammonia (NH3) into dihydrogen (H2) and dinitrogen (N2), said conversion being carried out in the presence of a cold plasma, characterized in that the catalyst comprises an alumina-based support, nickel and at least one promoter comprising iron (Fe). This catalytic system, which can for example be activated by a DBD plasma, makes it possible to overcome all the disadvantages of the prior art present in the thermal process (high temperature and pressure) and capable of synthesizing H2 from NH3 under atmospheric conditions with a high yield compared to the studies described in the prior art.

[0041] Preferably, the catalyst of the present invention does not comprise a noble metal, such as ruthenium (Ru), iridium (Ir), palladium (Pd), platinum (Pt) or rhodium (Rh).

[0042] As demonstrated in the following examples, the combined use of the catalyst according to the invention and a cold plasma, preferably a plasma generated by dielectric barrier discharge (DBD), makes it possible to produce high added value molecules such as hydrogen (H2), while improving the catalytic performance of the reaction, i.e. the conversion rates of NH3 and the selectivity towards the desired product (H2).

[0043] The present invention therefore relates, in general, to a catalyst, comprising: - a support comprising alumina, - nickel, and - at least one promoter comprising iron (Fe).

[0044] According to one embodiment, the present invention relates to a cold plasma activated catalyst.

[0045] In the context of the present invention, the terms "catalytic system" and "catalyst" are interchangeable. According to one embodiment of the invention, said catalytic system is called a mono / bimetallic catalytic system. It should be noted that the notion of monometallic system and bimetallic system relates in particular to the species present in the catalyst without taking into account the support used and nickel. For example, when the catalyst is doped with two promoters, we speak of a bimetallic catalyst; when the catalyst is doped with three promoters, we speak of a trimetallic catalyst.

[0046] The support used in the context of the present invention is based on alumina. It is notably chosen for its capacity to adsorb reagents and more particularly NH3, for its thermal stability and for its specific surface area. It is also chosen for its dielectric properties which can impact the properties of the plasma and modify the discharge behavior of the DBD plasma, the electric field and the electronic density due to the dielectric permittivity and the polarization effect which gives rise to the local electric field. The inventors realized that the use of a support comprising alumina was particularly advantageous, particularly compared to supports described in the literature (e.g. SiO2), with a view to obtaining superior catalytic results for the conversion of NH3.

[0047] The support is likely to impact the physicochemical properties (basicity, acidity, reducibility, oxygen mobility due to the presence of inherent defects present on said surface, etc.), as well as the textural properties (pore volume, pore diameter, specific surface area, etc.) and the electrical properties (permittivity, conductivity, etc.), which in turn modulate the catalytic performance of the system.

[0048] According to the present invention, the support of the catalytic system comprises alumina; in particular, the support may be made of alumina. According to one embodiment, the support is an alumina oxide, for example Al2O3. Thus, the support of the catalytic system may, in addition, comprise other components, for example a mixed oxide and / or cerium.

[0049] In the context of the present invention, the alumina may have any specific surface area (expressed as BET surface area m 2 / g). For example, the specific surface area of ​​alumina is at least 20 m 2 / g and can vary between 50 and 1,000 m 2 / g. For example, the specific surface area of ​​alumina is 200 m 2 / g or 260 m 2 / g. According to one embodiment of the present invention, the catalyst comprises a support comprising alumina having a specific surface area varying between 50 and 1,000 m 2 / g, between 100 and 800 m 2 / g, between 150 and 300 m 2 / g or between 180 and 250 m 2 / g.

[0050] The preparation of the support for the catalytic system is detailed below. The support used in the context of the present invention may also be a commercially available support.

[0051] The catalyst of the present invention also comprises nickel. The nickel of the catalyst according to the present invention may be in any of its oxidation states and in particular in metallic form (in its oxidation state 0) or in oxide form in its oxidation state II (e.g., in the form of nickel (II) oxide (NiO)). The mass content of nickel in the catalytic system may advantageously vary between 0.1% and 50% by weight relative to the weight of the support, for example between 0.5% and 40% or between 1% and 30%; preferably, it is less than 20% or less than 15%. By "weight of the support" is meant "weight of the support comprising the alumina", including when the support comprises elements other than alumina. Particularly advantageously, the catalytic system comprises 5% ± 1% by weight of nickel, relative to the weight of the support.

[0052] By convention, a catalyst comprising 5% by weight of nickel and 10% by weight of iron relative to the weight of a support comprising alumina is denoted “5Ni10FeAl”, “5Ni10Fe-Al” or “5Ni10Fe / Al”.

[0053] The catalyst of the present invention comprises at least one promoter, i.e., one or more promoters. Said at least one promoter acts as a dopant and impacts the physicochemical, textural and conductive properties of the catalyst. The promoter according to the invention advantageously has adequate physicochemical surface properties to help fix the NH3 reagent as well as adequate dielectric properties which make it possible to improve the conductivity of the resulting catalyst and which logically lead to the generation of NH2, NH radicals from NH3, and then their desorption from the catalytic surface, thus promoting the formation of hydrogen.

[0054] The catalyst of the present invention comprises at least one promoter comprising iron (Fe). The iron can be in any oxidation state, and in particular in metallic form or in oxide form. For example, the iron promoter is in the form FeO: iron (II) oxide or ferrous oxide, or Fe2O3 iron (III) oxide or ferric oxide or in the form of a mixed oxide with NiO and Al2O3. An example of a catalyst representative of this embodiment is the 5Ni10Fe-Al catalyst, i.e. a catalyst comprising a support comprising alumina, nickel and a promoter comprising iron.

[0055] The catalyst of the present invention is also capable of comprising at least one second promoter. This second promoter may in particular comprise a chemical element selected from the group consisting of transition metals, alkali metals, alkaline earth metals, lanthanides and mixtures thereof. In the context of the present invention, the promoter is in any of its oxidation states and in particular in metallic form or in oxide form. Thus, according to one embodiment of the present invention, the catalyst comprises at least two promoters, i.e. two or more promoters, for example three or four promoters.

[0056] In the context of the present invention, the transition metals may in particular be selected from the group consisting of copper, cobalt, silver, molybdenum, vanadium, manganese, chromium, yttrium, titanium and tantalum. When the second promoter comprises a chemical element which is a transition metal, this is preferably cobalt (Co), copper (Cu), silver (Ag) and / or manganese (Mn).

[0057] In the context of the present invention, the alkali metals may in particular be selected from the group consisting of lithium, sodium, potassium, rubidium, cesium and francium. When the second promoter comprises a chemical element which is an alkali metal, this is preferably potassium (K) or cesium (Cs), and even more preferably potassium (K).

[0058] In the context of the present invention, the alkaline earths may in particular be selected from the group consisting of barium, calcium and magnesium. When the second promoter comprises a chemical element which is an alkaline earth, this is preferably barium (Ba).

[0059] In the context of the present invention, the lanthanides may in particular be selected from the group consisting of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. When the second promoter comprises a chemical element which is a lanthanide, this is preferably cerium (Ce), gadolinium (Gd) and / or lanthanum (La), and even more preferably cerium (Ce).

[0060] According to one embodiment of the present invention, the catalyst comprises at least one second promoter comprising cobalt (Co), manganese (Mn), copper (Cu) and / or silver (Ag).

[0061] According to one embodiment of the present invention, the catalyst comprises at least one second promoter comprising lanthanum (La), cerium (Ce) and / or gadolinium (Gd).

[0062] According to one embodiment of the present invention, the catalyst comprises at least one second promoter comprising barium (Ba).

[0063] According to one embodiment of the present invention, the catalyst comprises at least one second promoter comprising potassium (K).

[0064] According to a preferred embodiment, the catalyst of the present invention comprises at least one second promoter comprising cobalt (Co). An example of a representative catalyst of this embodiment is the 5Ni10Fe1Co-Al catalyst, i.e. a catalyst comprising two distinct promoters: a promoter comprising Fe and a promoter comprising Co.

[0065] The amount of nickel and / or promoter can be adjusted depending on the nature of the promoter used and / or the type of conversion reaction implemented.

[0066] According to an embodiment of the present invention, the mass content of promoter(s) in the catalytic system varies between 0.1% and 40% by weight relative to the weight of the support, for example between 0.2 and 30% by weight, in particular between 0.3% and 20% by weight, preferably between 0.5% and 15% by weight, in particular between 1% and 12% by weight, even more preferably between 2% and 10% by weight relative to the weight of the support.

[0067] The promoters used for the preparation of the catalysts of the present invention are in any oxidation state, and in particular in metallic form or in oxide form. They are therefore likely to comprise other chemical elements, which are not included in the calculation of the claimed mass content. For example, for a 5Ni10Fe1Co-Al catalyst, if 1 g of support comprising nickel is used, then 0.049 g of Co(NO3)2.6H2O promoter (molar mass: 291.04 g / mol) is used, which corresponds to 0.01 g of Co (molar mass: 58.93 g / mol), or 1% by weight of cobalt relative to the weight of the support. For this catalyst, the mass content of promoters is 11% by weight relative to the weight of the support, or 10% of iron (or "iron promoter") and 1% of cobalt (or "cobalt promoter").

[0068] According to an embodiment of the present invention, the mass content of Fe in the catalytic system varies between 0.1% and 40% by weight relative to the weight of the support, for example between 0.2 and 30% by weight, in particular between 0.3% and 25% by weight, preferably between 0.5% and 20% by weight, in particular between 1% and 15% by weight, even more preferably between 2% and 10% by weight relative to the weight of the support.

[0069] According to an embodiment of the present invention, the mass content of other promoter(s) in the catalytic system (for example a second promoter) varies between 0.1% and 40% by weight relative to the weight of the support, for example between 0.2 and 30% by weight, in particular between 0.3% and 20% by weight, preferably between 0.5% and 15% by weight, in particular between 1% and 12% by weight, even more preferably between 2% and 10% by weight relative to the weight of the support. For example, in addition to the promoter comprising Fe, the catalyst according to the invention comprises from 0.5% to 20% by weight of one or more other promoters (% by weight relative to the weight of the support) selected from the group consisting of cobalt (Co), manganese (Mn), copper (Cu), silver (Ag), lanthanum (La), cerium (Ce), gadolinium (Gd), barium (Ba) and potassium (K).According to another example, in addition to the promoter comprising Fe, the catalyst according to the invention comprises from 0.1% to 4% by weight of a cobalt (Co) (% by weight relative to the weight of the support).

[0070] According to a particular embodiment of the present invention, the catalyst is doped with two promoters, one of which comprises iron (Fe) and the other of which comprises cobalt (Co). This is referred to here as a bimetallic catalyst. According to this embodiment, the mass content of iron in the catalyst may preferably vary between 6% and 14%, between 7% and 13% or between 6 and 12%. For example, the mass content of iron in the catalyst is 10% ± 0.5% by weight relative to the weight of the support. Also, according to this particular embodiment, the mass content of cobalt in the catalyst may preferably vary between 0.1% and 4%, between 0.2 and 3% or between 0.5 and 2%. For example, the mass content of cobalt in the catalyst is 1% ± 0.5% by weight relative to the weight of the support.An example of a catalyst representative of this embodiment is the 5Ni10Fe1Co-Al catalyst, i.e., a catalyst comprising a support comprising alumina, 5% by weight of nickel relative to the weight of the alumina and two distinct promoters: 10% by weight of iron and 1% by weight of cobalt.

[0071] The catalyst may be in various forms, for example in the form of beads, monoliths, powders, or granules. In the case of powders, the grains forming the powder may, for example, have an average size of between 1 μm and 1 mm, for example between 100 μm and 1 mm, in particular between 200 μm and 800 μm, preferably approximately 600 μm ± 20 μm. The grain size may in particular be adapted according to the production scale used. The catalyst may also be in a geometric form, advantageously beads having a size average less than 5 cm. The average catalyst size is adjusted according to the type, as well as the dimensions of the fixed bed reactor used to avoid possible pressure drops.

[0072] According to one embodiment of the present invention, the support, the nickel and the at least one promoter form a homogeneous mixture. In particular, the nickel-modified support and the promoter form a homogeneous mixture. This means that the nickel and the promoter are uniformly distributed throughout the entire volume of the catalyst.

[0073] According to a preferred embodiment, the catalyst of the present invention comprises: - a support comprising alumina, - nickel, - a promoter comprising iron (Fe), and - optionally at least one second promoter: - of transition metal type, and more particularly a promoter comprising cobalt (Co), manganese (Mn), copper (Cu) or silver (Ag); - of lanthanide type, and more particularly a promoter comprising lanthanum (La), cerium (Ce) or gadolinium (Gd); - of alkaline earth type, and more particularly a promoter comprising barium (Ba); and / or - of alkali metal type, and more particularly a promoter comprising potassium (K).

[0074] According to another preferred embodiment, the catalyst of the present invention comprises: - a support comprising alumina, - 0.1% to 50% by weight of nickel (% by weight relative to the weight of the support), - 0.1% to 40% by weight of promoter(s) (% by weight relative to the weight of the support), including at least one promoter comprising iron (Fe), and optionally at least one second promoter: - of transition metal type, and more particularly a promoter comprising cobalt (Co), manganese (Mn), copper (Cu) or silver (Ag); - of lanthanide type, and more particularly a promoter comprising lanthanum (La), cerium (Ce) or gadolinium (Gd); - of alkaline earth type, and more particularly a promoter comprising barium (Ba); and / or - of alkali metal type, and more particularly a promoter comprising potassium (K).

[0075] According to another preferred embodiment, the catalyst of the present invention comprises: - a support comprising alumina, - 0.1% to 50% by weight of nickel (% by weight relative to the weight of the support), and - 0.1% to 40% by weight of promoter(s) (% by weight relative to the weight of the support), including a promoter comprising iron (Fe), and at least one second promoter chosen from promoters comprising cobalt (Co), manganese (Mn), copper (Cu), silver (Ag), lanthanum (La), cerium (Ce), gadolinium (Gd), barium (Ba) and potassium (K).

[0076] According to another preferred embodiment, the catalyst of the present invention comprises: - a support comprising alumina, - 0.1% to 50% by weight of nickel (% by weight relative to the weight of the support), - 0.5% to 20% by weight of an iron (Fe) promoter (% by weight relative to the weight of the support), and - 0.5% to 20% by weight of one or more promoter(s) (% by weight relative to the weight of the support) selected from the group consisting of cobalt (Co), manganese (Mn), copper (Cu), silver (Ag), lanthanum (La), cerium (Ce), gadolinium (Gd), barium (Ba) and potassium (K).

[0077] According to another preferred embodiment, the catalyst of the present invention comprises: - a support comprising alumina, - 0.1% to 50% by weight of nickel (% by weight relative to the weight of the support), - 0.5% to 20% by weight of an iron (Fe) promoter (% by weight relative to the weight of the support), and - 0.1% to 4% by weight of a cobalt (Co) promoter (% by weight relative to the weight of the support).

[0078] Process for the preparation of the catalytic system

[0079] The preparation of the catalytic system according to the present invention can be carried out according to different methods.

[0080] The catalytic system may in particular be prepared by a process comprising bringing the support comprising alumina into contact with a nickel precursor and at least one precursor of the promoter (or promoters). This step makes it possible to form a solid comprising the support, the nickel and the promoter (or promoters). The process optionally comprises a step of calcining the mixture thus obtained. The contacting step is optionally preceded by a step of modifying the support. Furthermore, the optional calcination step is optionally followed by a step of reducing the calcined mixture.

[0081] The step of bringing the support into contact with a nickel precursor and a promoter precursor can be carried out, for example, by impregnation, by coprecipitation or by sol-gel. These three specific embodiments (also called sub-variants) are described below in more detail.

[0082] The nickel precursor and the promoter precursor may be any chemical compound, or mixture of chemical compounds, containing the metal used as active metal / promoter and more particularly may be a salt of said metal, an oxide of said metal or a mixture thereof, preferably a salt of said metal or a mixture of salts of said metal. The salt (designates a non-hydrated salt or a hydrated salt, or even multi-hydrated) of said metal may be, for example, chosen from chloride, nitrate, sulfate, carbonate, acetate, acetylacetonate, tartrate, and citrate of said metal and mixtures thereof, preferably nitrate of said metal. In the case where the promoter is a mixture of several metals, the precursor may be a mixture of different types of salts and / or oxides of these metals.

[0083] The calcination step leads to the oxidation of the various components of the catalytic system (support, nickel and promoter). This optional calcination step can itself be optionally followed by a reduction step, so as to change the oxidation state of the nickel and the promoter (to have nickel and metallic promoter), and possibly that of the support. The reduction can be total or partial, i.e. only a part of the components of the catalytic system can be reduced. The reduction step can be carried out in situ in the non-thermal plasma device under hydrogen.

[0084] Thus, according to a first variant embodiment of the process according to the invention, the process for preparing a catalytic system according to the invention comprises: - a step of bringing the support comprising alumina into contact with a nickel precursor and one or more precursors of the promoter, and - optionally, a step of calcining the mixture obtained following the bringing into contact of the components, - optionally, a step of reducing the calcined mixture obtained in the previous step.

[0085] According to a second variant embodiment of the process according to the invention, the process for preparing a catalytic system according to the invention comprises: - a step of bringing the support comprising alumina into contact with a nickel precursor and one or more precursors of the promoter, and - a step of calcining the mixture obtained following the bringing into contact of the components, - optionally, a step of reducing the calcined mixture obtained in the previous step.

[0086] According to a third variant embodiment of the process according to the invention, the process for preparing a catalytic system according to the invention comprises: - a step of bringing the support comprising alumina into contact with a nickel precursor and one or more precursors of the promoter, and - a step of calcining the mixture obtained following the bringing into contact of the components, - a step of reducing the calcined mixture obtained in the previous step.

[0087] According to a fourth variant embodiment of the process according to the invention, the process for preparing a catalytic system according to the invention comprises: - a step of modifying the support comprising alumina, and - a step of bringing the modified support into contact with a nickel precursor and one or more precursors of the promoter, - optionally a step of calcining the mixture obtained following the contacting of the components, - optionally, a step of reducing the calcined mixture obtained in the previous step.

[0088] The step of bringing the components into contact can in particular be carried out by impregnation. More specifically, according to this first sub-variant embodiment, the method comprises the following steps: 1) a step of preparing the support, and 2) a step of bringing the components into contact by impregnation.

[0089] Step 1) of support preparation itself comprises the following sub-steps: 1.1) preparation of a suspension comprising an alumina precursor or comprising an alumina oxide precursor. According to this step 1.1), the support precursor corresponds to an alumina precursor or a mixture of several precursors. In the case where the support is a mixture, in particular a mixed oxide, of cerium and alumina, a suspension of cerium precursor and a suspension of alumina precursor are advantageously prepared separately and then mixed in a ratio making it possible to obtain the desired Ce / Al molar ratio in the mixture, in particular the final mixed oxide of cerium and alumina. 1.2) mixing of the suspension resulting from step 1.1). The addition of these precursors is carried out in particular at room temperature, for example between 20 and 25°C, with continuous mixing, for 30 min to several hours, for example for 30 min to 3 hours. 1.3) recovery of the solid obtained in step 1.2) by removing excess water, in particular by evaporation of the water or filtration, then drying the resulting solid. The drying step may in particular be carried out at a temperature below 150°C, typically at a temperature of approximately 100°C, for example for a duration varying between 5h and 48h. 1.4) calcination of the solid resulting from step 1.3) to produce the support. The product resulting from step 1.3) is calcined, for example at a temperature between 300°C and 600°C. This calcination step may be carried out for 3h or more, for example for a duration varying between 3h and 6h. This step results in the thermal decomposition of the nitrates in order to obtain oxides.

[0090] Step 2) of bringing the components into contact itself comprises the following substeps: 2.1) preparation of an aqueous suspension comprising a nickel precursor and one or more precursors of the promoters. During this step, an appropriate mass of each precursor is added to an appropriate volume of solvent, for example water. By "appropriate mass" and "appropriate volume" is meant the quantities of precursors and solvent adequate (in particular water) to obtain the desired mass contents of nickel and promoter in the final catalytic system. 2.2) addition of the support resulting from step 1) to the aqueous solution resulting from step 2.1) to give a suspension. 2.3) mixing of the suspension resulting from step 2.2). The addition of these precursors is carried out at room temperature, for example between 20 and 25°C, with continuous mixing, for 30 min to several hours, for example for 30 min to 3 h. 2.4) recovery of the solid comprising the support, nickel and promoters obtained in step 2.3) by removing excess water, in particular by evaporation of the water or filtration, then drying the resulting solid. The drying step can be carried out for example at a temperature below 150°C, typically at a temperature of approximately 100°C, for example for a period ranging from 7h to 48h. 2.5) calcination of the solid resulting from step 2.4) to produce the catalytic system. The product resulting from step 2.4) is calcined, for example at a temperature between 300°C and 600°C. This calcination step can be carried out for 3h or more, for example for a period varying between 3h and 6h. This step results in the thermal decomposition of the nitrates in order to obtain oxides.

[0091] This first sub-variant of realization is also called wet impregnation process. It consists of impregnating the support with the nickel precursor and the promoter precursor.

[0092] The step of bringing the components into contact can alternatively be carried out by coprecipitation. More specifically, according to a second sub-variant embodiment, the method for preparing the catalytic system comprises: 1') a support preparation step, and 2') a step of bringing the support into contact with a nickel precursor and the promoter, this contact being carried out by coprecipitation.

[0093] Step 1') of support preparation consists of preparing an aqueous solution comprising a nickel precursor and the precursors of the promoters. This step is identical to step 2.1) of the wet impregnation process described previously.

[0094] Step 2') of bringing the components into contact itself comprises the following sub-steps: 2.1') ​​adding the support to the solution resulting from step 1') to give a suspension This step is identical to step 2.2) of the wet impregnation process described previously. 2.2') adding a base to the suspension resulting from step 2.1'). During this step, a base is added to the suspension resulting from step 2.1'). This base is advantageously a hydroxide salt, such as sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, preferably sodium hydroxide. It can be used in the form of a solution, in particular an aqueous solution. The base is gradually added dropwise until the pH of the suspension (consisting of a solid suspended in a liquid solution) is between 8 and 12, preferably approximately equal to 10. Step 2.2') can be carried out at a temperature between 60°C and 100°C, in particular between 70°C and 90°C, preferably approximately equal to 80°C. 2.3') mixing of the suspension resulting from step 2.2'). This step aims to precipitate the nickel hydroxide and the hydroxide of the metal used as promoter on the surface of the support. The mixing, in particular by stirring, is for example carried out at a temperature between 60°C and 100°C, preferably approximately equal to 80°C. This mixing step can be carried out for a period of 2 hours or more, typically for approximately 3 hours. 2.4') recovery of the solid comprising the support, the nickel and the promoter obtained in step 2.3') and its calcination to lead to the catalytic system. This step is identical to step 2.5) of the wet impregnation process.

[0095] This second sub-variant of implementation makes it possible to precipitate nickel hydroxide and the hydroxide of the metal used as promoter on the surface of the support.

[0096] The step of bringing the components into contact can also be carried out by sol-gel reaction. More specifically, according to a third sub-variant embodiment, the step of bringing the support into contact with a nickel precursor and a precursor of the promoter is carried out by sol-gel reaction and comprises the following sub-steps: 1'') preparation of a solution comprising a nickel precursor, a precursor of the promoter (or promoters) and a support precursor in citric acid, 2'') adjustment of the pH of the solution 1''), for example to 4, by preferentially adding a strong base solution of NaOH, 3'') reflux heating of the solution of step 2''), and 4'') removal of excess citric acid and recovery of the catalytic system.

[0097] In step 1''), the support precursor corresponds to an alumina precursor, a cerium precursor, a lanthanum precursor or a mixture of alumina precursor, cerium and lanthanum precursor depending on whether the support is alumina, cerium, lanthanum or a mixture of alumina, cerium and lanthanum. In the case where the support is a mixture, in particular a mixed oxide, of alumina, cerium and lanthanum, a solution of alumina precursor, cerium and a solution of lanthanum precursor are advantageously prepared separately and then mixed in a ratio making it possible to obtain the desired Al / Ce and Ce / La molar ratio in the mixture, in particular the final mixed oxide, of alumina, cerium and lanthanum.

[0098] In order to prepare the desired quantity of the catalyst, the precursor of the support, as well as the precursors of nickel (e.g. nickel (II) acetate tetrahydrate) and of the promoter are advantageously dissolved separately in citric acid, in particular with heating (e.g., at 80-120°C, in particular at about 80°C, for 1 hour or more, for example for about 2 hours).

[0099] Step 3'') of reflux heating is carried out for a sufficient time to obtain the gel.

[0100] If the product resulting from step 3'') is a gel, it may be dried in an oven or solidified before carrying out a possible calcination step, in particular using liquid nitrogen, so that the product resulting from step 3'') is a solid.

[0101] The last step 4'') consists of recovering the solid obtained in step 3''), This step is identical to step 2.5) of the wet impregnation process.

[0102] The support used in the process of preparing the catalytic system may also be a commercially available support.

[0103] Use of the catalyst according to the present invention

[0104] The present invention also relates to the use of the catalyst according to the invention for converting a gas or a mixture of gases comprising ammonia (NH3), said conversion being carried out in the presence of cold plasma.

[0105] The present invention relates in particular to the combined use of the catalyst of the present invention, together with a cold plasma, preferably a plasma generated by dielectric barrier discharge (DBD), for converting a gas or a mixture of gases comprising NH3.

[0106] In other words, the present invention relates in particular to the use of the catalyst of the present invention, activated by a cold plasma, preferably a plasma generated by dielectric barrier discharge (DBD), to convert a gas or a mixture of gases comprising NH3.

[0107] The inventors have, in fact, realized that the combination of a catalyst according to the present invention, and a cold plasma, preferably a plasma generated by dielectric barrier discharge (DBD), showed increased efficiency for converting a gas or a mixture of gases comprising NH3 and / or for the production of hydrogen, for example for the production of dihydrogen (H2) and nitrogen gas (N2).

[0108] The present invention also relates to the use of the catalytic system according to the invention for the production of dihydrogen (H2) and dinitrogen (N2), from a gas or a mixture of gases comprising NH3.

[0109] The present invention relates in particular to the combined use of the catalyst of the present invention, together with a cold plasma, preferably a plasma generated by dielectric barrier discharge (DBD), for the production of dihydrogen (H2) and dinitrogen (N2), from a gas or a mixture of gases) comprising NH3.

[0110] In other words, the present invention relates in particular to the use of the catalyst of the present invention, activated by a cold plasma, preferably a plasma generated by dielectric barrier discharge (DBD), for the production of dihydrogen (H2) and dinitrogen (N2), from a gas or a mixture of gases) comprising NH3.

[0111] Liste des documents cités [1] Yoshitsugu Kojima, Masakuni Yamaguchi, Ammonia as a hydrogen energy carrier, International Journal of Hydrogen Energy, 2022, ISSN 0360-3199, https: / / doi.org / 10.1016 / j.ijhydene.2022.05.096. [2] Schüth, F. and Palkovits, R. and Schlögl, R. and Su, D. S., Ammonia as a possible element in an energy infrastructure: catalysts for ammonia decomposition, Energy Environ. Sci., 2012, Volume 5, p. 6278- 6289, http: / / dx.doi.org / 10.1039 / C2EE02865D. [3] Dejiang Zhou;Renwu Zhou;Rusen Zhou;Baowang Liu;Tianqi Zhang;Yubin Xian;Patrick J. Cullen;Xinpei Lu;Kostya (Ken) Ostrikov; (2021). Sustainable ammonia production by non-thermal plasmas: Status, mechanisms, and opportunities. Chemical Engineering Journal, (), –. https: / / doi.org / doi:10.1016 / j.cej.2021.129544 [4] M. Mikhail et al., « Tailoring physicochemical and electrical properties of Ni / CeZrOx doped catalysts for high efficiency of plasma catalytic CO2 methanation », Appl. Catal. B Environ., vol.294, p.120233, oct.2021, https: / / doi.org / 10.1016 / j.apcatb.2021.120233 [5] M. Mikhail et al., « Electrocatalytic behaviour of CeZrOx-supported Ni catalysts in plasma assisted CO2 methanation », Catal Sci Technol, vol. 10, no 14, p. 4532-4543, 2020, https: / / doi.org / 10.1039 / D0CY00312C. [6] Mao Akiyama, Keigo Aihara, Tomiko Sawaguchi, Masahiko Matsukata, Masakazu Iwamoto, Ammonia decomposition to clean hydrogen using non-thermal atmospheric-pressure plasma, International Journal of Hydrogen Energy, Volume 43, Issue 31, 2018, Pages 14493-14497, ISSN 0360- 3199, https: / / doi.org / 10.1016 / j.ijhydene.2018.06.022. [7] Mostafa El-Shafie, Shinji Kambara, Yukio Hayakawa, Plasma-enhanced catalytic ammonia decomposition over ruthenium (Ru / Al2O3) and soda glass (SiO2) materials, Journal of the Energy Institute, Volume 99, 2021, Pages 145-153, ISSN 1743-9671, https: / / doi.org / 10.1016 / j.joei.2021.09.001. [8] Lucentini et al., “Review of the decomposition of ammonia to generate hydrogen” Ind. Eng. Chem. Res.2021,60, 18560-18611, https: / / doi.org / 10.1021 / acs.iecr.1c00843 [9] Demande de brevet CN 101147863 A

[0010] Demande de brevet EP 2332646 A1

[0011] Demande de brevet WO 2021 / 255422 A1

[0012] Yanhhui Yi et al., Plasma-assisted ammonia decomposition over Fe-Ni alloy catalysts for COx-free hydrogen” AIChE J, 65: 691-701, 2019, https: / / doi.org / 10.1002 / aic.16479.

[0112] Examples

[0113] The invention is now described in more detail with reference to the following examples, the purpose of which is illustrative and not intended to limit the scope of the invention.

[0114] A. Preparation of different catalytic systems by wet impregnation

[0115] Several supports were used to prepare various catalytic systems identified more precisely in Table 1 below: 1) A commercial alumina oxide (Al200, Specific surface area = 200m 2 / g, Saint Gobain); 2) A commercial alumina oxide (Al260, Specific surface area=260m 2 / g, Saint Gobain); 3) A commercial mixed ceria zirconia oxide from Sigma Aldrich (CZ); 4) A commercial silica oxide SiO2 (Si160, Specific surface area = 160m 2 / g, Saint Gobain); 5) A commercial magnesium oxide MgO from Sigma Aldrich; 6) A mixed oxide synthesized by the inventors according to the method described previously.

[0116] The various catalysts exemplified here are prepared by wet impregnation.

[0117] The promoter-doped nickel catalytic systems (metal M) were prepared by the method from an aqueous solution of Ni(NO3)2.6H2O (Sigma-Aldrich) and one or more promoter precursors selected from: Fe(NO3)2.9H2O, Co(NO3)2.6H2O, Mn(NO3)2.4H2O, La(NO3)2.6H2O, Y(NO3)2.6H2O, Gd(NO3)3·6H2O, Ba(NO3)2, Ag(NO3), Cs(NO3), Ce(NO3)3·6H2O, Cu(NO3)2.5H2O, NaNO3, and KNO3 (all commercial, Sigma-Aldrich), depending on the desired promoter.

[0118] For example, for the preparation of the 5Ni10Fe-Al catalyst (one of the catalysts according to the invention), the nickel content is 5% by mass relative to the weight of the support and that of the Fe promoter is 10% by mass relative to the weight of the support.

[0119] The appropriate mass of nickel salt and promoter precursor are dissolved in a 50 mL volume of water at room temperature and with stirring. The appropriate mass of carrier is added to the aqueous solution containing the mixture of metal salts and kept stirring for 2 hours. For example, 0.25 g of nickel nitrate (representing a content of 5% by weight of nickel relative to the weight of the carrier), 0.72 g of iron nitrate (representing a content of 10% by weight of iron relative to the weight of the carrier), and 1 g of carrier are mixed according to the previous procedure. The mixture is then placed in a rotary evaporator at 60°C to remove excess water.

[0120] After impregnation and water evaporation, all samples were collected, dried in an oven at 100°C for 8 h, and then calcined in air at 550°C for 4 h with a temperature ramp of 10°C / min. After calcination, the catalytic system samples were hand-ground and sieved to an average grain size between 50 and 200 μm.

[0121] The different catalysts prepared according to the method described above are listed in Table 1 below.

[0122] B. Conversion of gas comprising NH3 in the presence of different catalysts

[0123] The procedure for hydrogen production using a catalytic plasma reactor is as follows: 320 mg of catalyst to be tested, corresponding to a GHSV (Gas Hourly Space Velocity) of 22000 h -1, are placed between the electrodes of the DBD reactor; the reactor is supplied with ammonia gas with a total flow rate of 160 mL / min STP (Standard Temperature and Pressure), at atmospheric pressure and a temperature of 20°C.

[0124] A non-thermal dielectric barrier discharge (DBD) plasma is created between two electrodes: a cylindrical copper electrode placed inside an alumina tube (3 mm diameter), surrounded by a coaxial quartz tube (10 mm inner diameter, 1 mm thickness), and a steel wire wrapped around the outer surface of the quartz tube, acting as a ground electrode (grounded via an external 2 nF capacitor). In this configuration, a discharge is sustained in a 2.5 mm gap, covering a length of approximately 1 cm. Before catalytic testing, the as-synthesized catalytic systems are reduced in situ under non-thermal DBD plasma under H2 as a discharge gas for a duration of 60 minutes.

[0125] The activity and selectivity of the promoter and non-promoter catalysts under DBD plasma conditions are evaluated in an experimental setup comprising a cylindrical reactor. quartz tubular, a DBD plasma generator, and corresponding devices for gas supply and analysis.

[0126] Without plasma, no change in the composition of the outlet gases is observed. When the plasma is ignited, and after stabilization, hydrogen and nitrogen are produced at the outlet.

[0127] The following equations were used to estimate the catalytic performance and calculate the NH3 conversion, and the H2 and N2 selectivity: ^^^ (Eq.2) ^ ^ ^^^ ^ ^ ^ ( % ) = ^ ^ ^^ ^^ ^^^ × ^^^ (Eq.3) ^^ ^ ^^^ ^^^ ^ ^ ^ ^ ( %) = ^ ^ ^ ^^ × ^^^ (Eq.4) ^^ ^ ^^ ^^^ ^^^ where F in and F out respectively denote the inlet and outlet flow rate (mol / s) of the species considered at the inlet and outlet of the reactor.

[0128] C. Results

[0129] Table 1 below illustrates and summarizes a list of the catalysts tested and shows the catalytic activity results obtained in terms of NH3 conversion, and H2 and N2 selectivity. [Table 1]

[0130] Figure 1 illustrates the GC chromatogram of the incoming gas before reaction (containing 100% NH3) by combining the 5Ni10FeAl catalyst system (catalyst 12i in Table 1 above) with the DBD plasma catalytic reactor.

[0131] Figure 2 illustrates the GC chromatogram of the ammonia gas remaining after reaction following the conversion of NH3 by combining the 5Ni10FeAl catalyst system (catalyst 12i in Table 1 above) with the DBD plasma catalytic reactor.

Claims

Claims

1. A process for converting a gas or a mixture of gases comprising ammonia (NH3) into dihydrogen (H2) and dinitrogen (N2) according to the following reaction: 3 1 ^^ ^ → ^ + ^ 2 ^ 2 ^characterized in that it is carried out in the presence of cold plasma and a catalyst comprising: - a support comprising alumina, - nickel, and - at least one promoter comprising iron (Fe).

2. A process according to claim 1, wherein the catalyst further comprises at least one second promoter: - of the transition metal type, and more particularly a promoter comprising cobalt (Co), manganese (Mn), copper (Cu), or silver (Ag); - of the lanthanide type, and more particularly a promoter comprising lanthanum (La), cerium (Ce), or gadolinium (Gd); - of the alkaline earth type, and more particularly a promoter comprising barium (Ba); and / or - of the alkali metal type, and more particularly a promoter comprising potassium (K).

3. A method according to claim 1 or 2, wherein: - the mass content of promoter(s) in the catalyst varies from 0.1% to 40% by weight relative to the weight of the support, preferably from 0.5% to 20% by weight; or - the mass content of iron in the catalyst varies from 0.1% to 40% by weight relative to the weight of the support, preferably from 0.5% to 20% by weight.

4. A method according to any one of the preceding claims, wherein the catalyst comprises at least one second promoter comprising cobalt (Co).

5. A method according to any one of the preceding claims, wherein: - the mass content of iron varies from 6% to 14% relative to the weight of the support; and / or - the mass content of cobalt varies from 0.1% to 4% relative to the weight of the support.

6. A method according to any one of the preceding claims, wherein the support is an alumina oxide.

7. A method according to any one of the preceding claims, wherein the nickel content in the catalyst varies between 0.1% and 50% by weight relative to the weight of the support, preferably less than 20%.

8. A method according to any one of the preceding claims, wherein the cold plasma is generated by dielectric barrier discharge (DBD).

9. A method according to any one of the preceding claims, wherein the catalyst comprises: - a support comprising alumina, - 0.1% to 50% by weight of nickel (% by weight relative to the weight of the support), and - 0.1% to 40% by weight of promoter(s) (% by weight relative to the weight of the support), including an iron promoter (Fe), and at least one second promoter selected from cobalt (Co), manganese (Mn), copper (Cu), silver (Ag), lanthanum (La), cerium (Ce), gadolinium (Gd), barium (Ba) and potassium (K).

10. Catalyst for the conversion of a gas or mixture of gases comprising ammonia (NH3) into dihydrogen (H2) and dinitrogen (N2) according to the following reaction: 3 1 ^^. ^ → ^ + ^ 2 ^ 2 ^ The conversion being carried out in the presence of a cold plasma, characterized in that the catalyst comprises: - a support comprising alumina, - nickel, and - at least one promoter comprising iron (Fe).

11. Catalyst according to claim 10, further comprising at least one second promoter: - of the transition metal type, and more particularly a promoter comprising cobalt (Co), manganese (Mn), copper (Cu) or silver (Ag); - of the lanthanide type, and more particularly a promoter comprising lanthanum (La), cerium (Ce) or gadolinium (Gd); - of the alkaline earth type, and more particularly barium (Ba); and / or - of the alkali metal type, and more particularly potassium (K).

12. Catalyst according to claim 10 or 11, wherein the mass content of promoter(s) in the catalyst varies between 0.1% and 40% by weight relative to the weight of the support, preferably between 0.5% and 20% by weight.

13. Catalyst according to any one of claims 10 to 12, comprising: - 0.1% to 50% by weight of nickel (% by weight relative to the weight of the support), - 0.5% to 20% by weight of iron (Fe) (% by weight relative to the weight of the support), and - 0.5% to 20% by weight of one or more promoter(s) (% by weight relative to the weight of the support) selected from the group consisting of cobalt (Co), manganese (Mn), copper (Cu), silver (Ag), lanthanum (La), cerium (Ce), gadolinium (Gd), barium (Ba) and potassium (K).

14. A catalyst according to any one of claims 10 to 13, comprising at least a second promoter comprising cobalt (Co), wherein: - the iron mass content varies from 6 to 14% by weight of the support; and / or - the cobalt mass content varies from 0.1% to 4% by weight of the support.

15. Use of the catalyst according to any one of claims 10 to 14, for the conversion of a gas or gas mixture comprising ammonia (NH3), said conversion being carried out in the presence of cold plasma, preferably a dielectric barrier discharge (DBD) plasma.

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