Plasma-catalyzed reverse water-gas shift reaction

Abstract

The present invention relates to a method for the chemical conversion of a gas mixture comprising carbon dioxide (CO 2) and dihydrogen (H2) using the following RWGS reaction: CO 2 + H 2 → CO + H 2 O in the presence of a catalyst, referred to as catalyst, activated by cold plasma (for example generated by dielectric-barrier discharge (DBD)). The invention also relates to a catalyst and to the use of such a catalyst, activated by cold plasma, in order to produce high-added-value molecules, such as carbon monoxide (CO).

Description

Title: Reverse gas-to-water conversion reaction by plasma catalysis Technical field

[0001] The present invention relates to the field of chemical conversion, in particular to the chemical conversion of carbon dioxide (CO2) and dihydrogen (H2) according to the following RWGS reaction: CO2 + H2 CO + H2O in the presence of a catalyst activated by a cold plasma, for example generated by "dielectric barrier discharge", known as DBD. The invention relates in particular to said conversion process, said catalyst, as well as the use of such a catalyst to produce high added value molecules, such as carbon monoxide (CO). State of the prior art

[0002] The reverse water gas shift reaction (see Equation (1)) is attracting increasing attention for the synthesis of valuable chemicals and fuels. The reverse water gas shift reaction (RWGS) is one of the most promising for the conversion of CO2 to CO, which, in the presence of H2 (e.g., as synthesis gas), can be used for the synthesis of methanol, dimethyl ether (DME), and Fischer-Tropsch fuels [1], [2],

[0003] CO2+ H2->CO + H2O; AIT = 41.09 kJ / molL (Eq. 1)

[0004] The RWGS reaction follows a moderately endothermic process, which must be operated at elevated temperatures. Furthermore, the equilibrium CO2 conversion is limited to ~23% at 300°C and 1 MPa [1], [2]. To achieve 50% CO2 conversion, a temperature of more than 700°C is required with a stoichiometric feed gas composition. Furthermore, the RWGS reaction is always accompanied by a competitive methanation process, which decreases the efficiency of the subsequent syngas utilization. Currently, catalytic conversion is the most widely used strategy for the RWGS reaction. Different types of catalysts have been employed. However, the high cost of noble metals remains a major constraint for their large-scale application [1], [2], [3], [4]. Therefore, further efforts are still required for develop efficient catalysts with higher activity and stability and potential processes to overcome slow kinetics and reduce reaction temperature. Some prior art documents describe catalytic conversion by cold plasma coupled to a catalyst, presented as a promising alternative for CO2 / H2 mixtures compared to thermal catalysis at atmospheric pressure and room temperature. However, the results reported so far do not show sufficiently high energy efficiency and catalytic activity [5], [6], [7], [8], [9],

[0005] The article by Zeng, et al.

[0010] "Plasma-Catalytic CO2 Hydrogenation at Low Temperatures," published in April 2016, IEEE Transactions on Plasma Science, describes the use of copper and / or manganese-based catalysts on AI2O3 supports for the CO2 hydrogenation reaction via DBD plasma. The catalytic and energy yields are not high enough to be exploited on a large scale.

[0006] The object of the present invention is in particular to propose a process for the chemical conversion of carbon dioxide (CO2) and dihydrogen (H2) according to the RWGS reaction in the presence of a catalyst which has high catalytic and energy yields, and which can be exploited on a large scale. Said conversion is carried out in the presence of cold plasma, at temperatures below 400°C.

[0007] The articles by Lina Liu, et al., [11, 12], the patent application

[0013] , the article by L. Yang, et al.

[0014] , and the article by Ching-Shiun Chen, et al.

[0015] do not describe such a plasma-catalysis conversion process in which the catalyst is activated by cold plasma. Summary of the invention

[0008] A first object of the present invention is a process for the chemical conversion of a gas mixture comprising carbon dioxide (CO2) and dihydrogen (H2) according to the following RWGS reaction: CO2 + H2 CO + H2O in the presence of a catalyst, also called a catalytic system, comprising at least one support and at least two promoters, one of which comprises iron. According to the method of the present invention, said catalyst is activated by cold plasma before contacting with the gas mixture to be converted. Furthermore, said conversion is carried out in the presence of cold plasma, also called non-thermal plasma (NTP), at temperatures below 400°C. According to a preferred embodiment, the cold plasma is a plasma generated by dielectric barrier discharge (DBD).

[0009] A second object of the present invention is a catalyst, also called a catalytic system, for converting a gas mixture comprising CO2 and H2 into CO according to the RWGS reaction. This catalyst is activated by cold plasma before contacting with the gas mixture to be converted, for example a plasma generated by dielectric barrier discharge DBD. The catalyst of the present invention is such that it comprises at least one support and at least two promoters, one of which comprises iron. The use of such a catalyst combined with a cold plasma for the conversion of gases in the RWGS reaction makes it possible to overcome all the disadvantages of the prior art present in the thermal process (high temperature and pressure). Such a system makes it possible to synthesize CO from CO2 and H2 under atmospheric conditions with a high yield compared to the studies described in the prior art.In addition, the catalyst offers resistance to pollutants, unlike a thermal process which is particularly vulnerable to pollutants. In addition, it is less bulky, due to the use of a lower quantity of catalyst, around 10 to 50 times less than the catalytic systems used in conventional processes. In addition, it uses less expensive materials compared to thermal processes, which often use noble, rare or precious materials such as rhodium (Rh) or ruthenium (Ru).

[0010] According to a preferred embodiment, said catalyst comprises: - a support comprising alumina, - at least two promoters, one of which comprises iron and the other preferably comprises copper; and - at least one third promoter selected from the group consisting of alkali metals, transition metals, alkaline earth metals, lanthanides, and mixtures thereof.

[0011] A third subject of the present invention relates to the use of a cold plasma activated catalyst for the conversion of a gas mixture comprising carbon dioxide (CO2) and dihydrogen (H2) according to the RWGS reaction, said catalyst comprising at least one support and at least two promoters, one of which comprises iron.

[0012] The present invention overcomes all the drawbacks of traditional thermal catalysis processes, as described in the prior art, and thus achieves high catalytic and energy yields, and is thus capable of being exploited on a large scale. While the RWGS conversion processes of the prior art have a great inertia (which can reach 24 hours for example in the context of large installations) due to the fact that the reactors must be brought to high temperatures, for example of the order of 700-900 °C and up to 50 bars in pressure, the process of the present invention on the contrary presents great flexibility and robustness, due to its speed of implementation which not only allows the conversion reaction to start quickly, but also accepts variations in ratios in the incoming gases while maintaining an average conversion yield much higher than the processes of the prior art. Description of figures

[0013] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings: [Error! Reference source not found.] PFD block diagram of a DBD reactor. Plasma catalysis reactor for the chemical conversion of a gas mixture comprising carbon dioxide (CO2) and dihydrogen (H2) according to the following RWGS reaction: CO2 + H2 -> CO + H2O. The [Error! Reference source not found.] illustrates the experimental setup (PFD diagram) used in one example, the reverse water gas shift reaction (RWGS reaction), by a DBD plasma process coupled to a catalyst (also equivalently referred to as a catalyst) according to one embodiment of the present invention. [Error! Invalid reference for a bookmark. Error! Reference source not found.-2] Tables illustrating the catalytic activity of several catalysts tested in the presence and absence of DBD plasma. The tables show the catalytic activity results obtained in terms of CO2 conversion and CO selectivity. Definitions

[0014] The expression "between ... and ..." (e.g., a range of values) should be understood as including the limits (e.g., the boundary values ​​of that range of values).

[0015] Any description relating to one embodiment is applicable and interchangeable with all other embodiments of the invention.

[0016] The expression "and / or" is to be understood as meaning "and" and "or"; for example, the expression "A and / or B" covers three alternatives and is to be understood as meaning either A and B, or only A, and or only B.

[0017] The expression “N, M and / or P” should be understood as meaning “N and / or M and / or P”.

[0018] The expression "N, M and P" should be understood as meaning "N and M and P".

[0019] 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 term "catalyst" or "catalytic system" refers, in the present invention, to a material promoting the chemical reaction of reactive species, for example, reactant fluids.

[0023] The term "plasma-catalysis" refers, in the present invention, to the coupling of a plasma electrical discharge and a catalyst. For example, the conversion method uses a plasma electrical discharge coupled to a catalyst.

[0024] The term "cold plasma" or "non-thermal plasma (NTP)" refers to a plasma where the distribution of particles (electrons and ions) does not obey a Maxwell-Boltzmann thermal distribution, meaning that the electron temperature is significantly higher than the ion temperature, so the kinetic energy of the ions is much lower than that of the electrons. This type of plasma is often characterized by the presence of a population of highly energetic electrons, while the ions remain at lower energies, hence the term "non-thermal plasma"

[0016] , Dielectric barrier discharge (DBD) is an example of cold plasma or non-thermal plasma, in which the gas is more or less at room temperature, and the average energy of the electrons is between 2 and 5 eV due to the strong electric field in the plasma

[0017] , The temperature of the gas remains close to room temperature. This can be regulated using a heat exchanger system (circulation of a heat transfer fluid) capable of maintaining a constant temperature, thus ensuring control of the system in the event of an exothermic or endothermic reaction.In the present invention, being an endothermic reaction, the gas temperature can be controlled so that it is less than 400°C, less than 350°C, less than 330°C, less than 310°C, or even less than 300°C. If necessary, the gas temperature can be measured by a probe (thermocouple) and the electron temperature by Optical Emission Spectroscopy.

[0025] As used herein, the terms "Reverse Water Gas Shift", "RWGS", "RWGS reaction" or "RWGS equation" refer to the reverse water gas shift reaction according to equation (1).

[0026] The term "hydrogen" should be understood to mean "dihydrogen" or "H2".

[0027] The term "support" or "catalyst support" designates, in the present invention, a solid material or a mixture of solid materials characterized by a high specific surface area, on which the promoter(s) is(are) deposited.

[0028] 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, to increase the efficiency and performance of the catalyst.

[0029] 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

[0030] Process for converting a gas mixture comprising carbon dioxide (CO2) and dihydrogen (H2) according to the RWGS reaction

[0031] A first subject of the present invention relates to a process for converting a gas mixture comprising carbon dioxide (CO2) and dihydrogen (H2) according to the following RWGS reaction: CO2 + H2 CO + H2O characterized in that it is carried out in the presence of a catalyst, activated by cold plasma, said catalyst comprising at least one support and at least two promoters, one of which comprises iron and said conversion being carried out in the presence of cold plasma, at temperatures below 400°C. This process aims to produce molecules with high added value, such as carbon monoxide (CO).

[0032] The inventors 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 an increased efficiency for converting a gas mixture comprising carbon dioxide (CO2) and dihydrogen (H2) according to the RWGS reaction. The structure of the catalyst, i.e. a support-type structure doped by promoters, as well as its composition, and in particular the presence of iron within the catalyst, are essential to the performance of the process of the present invention.

[0033] The gas mixture to be converted according to the RWGS reaction comprises carbon dioxide (CO2) and dihydrogen (H2). It may further comprise other gases such as carbon monoxide (CO), methane (CH4), nitrogen (N2), oxygen (O2), ethene (C2H4) and ethane (C2H6). According to this embodiment, the gas mixture to be converted according to the RWGS reaction comprises, for example, more than 50 mol. % of carbon dioxide (CO2) and dihydrogen (H2), for example, more than 60 mol. %, more than 70 mol. %, more than 80 mol. %, more than 90 mol. %, more than 95 mol. % or even more than 98 mol. %, relative to the total number of moles involved in the RWGS conversion reaction according to the invention. It optionally includes other gases selected from the group consisting of carbon monoxide (CO), methane (CH4), nitrogen (N2), oxygen (O2), ethene (C2H4) and ethane (C2H6), and mixtures thereof.

[0034] The process for converting a gas mixture comprising CO2 and H2 according to said RWGS equation (Eq. 1) is carried out in the presence of the catalyst of the present invention, as well as a cold plasma, preferably a plasma generated by dielectric barrier discharge (DBD). The synergy of plasma catalysis in this process shows great potential for the direct synthesis of carbon monoxide (CO), a high value-added gas used for the synthesis of methanol, dimethyl ether (DME) and Fischer-Tropsch fuels, from CO2 and in the presence of dihydrogen.

[0035] The conversion process of the present invention comprises a first step which consists of activating the catalyst by cold plasma, before feeding the reactor with the gas mixture to be converted. The catalyst according to the invention is activated by cold plasma, that is to say that it is advantageously reduced in situ under cold plasma, preferably a DBD plasma, under H2 as discharge gas. The catalyst activation step is particularly advantageous in the case where its components are in oxidized form.

[0036] The conversion process of the present invention is carried out within a cold plasma reactor, preferably a DBD plasma reactor. The catalyst is typically placed between the electrodes of the cold plasma reactor, before being activated by electrical discharges leading to the formation of cold plasma and thus to the negative or positive polarization of the catalytic sites of the catalyst. The gas mixture to be converted is then introduced into the reactor and circulates between the electrodes of the reactor for the purpose of conversion according to the RWGS reaction. The RWGS conversion reaction is carried out under cold plasma.

[0037] The gas conversion according to the method of the present invention is carried out in the presence of cold plasma, at temperatures below 400°C. According to one embodiment of the present invention, the method is carried out at temperatures below 330°C, below 310°C, below 300°C, or even below 280°C.

[0038] The conversion process may in particular be of the continuous or semi-continuous type, the introduction of the gas mixture to be converted and the extraction of the reaction products each being carried out under continuous or semi-continuous gas flow depending on the availability of energy, which represents an advantage in the process described in this invention given the flexibility of the system and the instantaneous nature of the reaction.

[0039] According to one embodiment of the method of the invention, the catalyst is placed between the electrodes of a DBD reactor, allowing gaseous species to flow through the catalyst, 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 to the activation of the catalyst. 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.

[0040] When implementing the method of the invention, cold plasma is generated and a strong electric field is created, which keeps said catalyst in an activating state, more particularly between the grains of said catalyst or nearby, upstream or downstream of the catalyst, in the gas flow. This strong electric field is typically between 10 3 and 10 10V / m and can vary over time. When the gas mixture is then introduced into the reactor for conversion according to the RWGS reaction, the cold plasma allows the ionization of a portion of the gas and the excitation of atoms and molecules present in the gas phase. The walls of the reactor may typically be made of a metallic material; alternatively, in the case where a DBD reactor is preferentially used for implementing the method of the present invention, the walls of the reactor are made of a dielectric material such as quartz, alumina or ceramic. The reactor may advantageously be cylindrical in shape. In addition to creating a cold plasma state, the strong electric field created is responsible for the negative or positive polarization of the catalytic sites of the catalyst.The latter is typically inserted directly into the reactor to form the catalytic bed through which the gas passes (it is typically not coated on the reactor wall in the form of layers). The structure of the catalyst (in particular the accessibility of the key constituents of the catalyst) and the selection of its constituents is essential to obtain high conversion efficiencies, depending on the gas molecules to be converted. The polarization of the catalytic sites of the catalyst induces adsorption and desorption reactions, essential to the performance of the process of the invention. This performance is possible even at low temperatures (for example at temperatures below 400°C, or even below 350°C, 330°C, 310°C, 300°C or even 280°C). According to the conventional process without polarization, the working temperature is higher, generally of the order of 700°C to 900°C or even 1000°C.

[0041] The reactor comprises at least one inlet allowing it to be supplied with gas to be converted, comprising CO2 and H2, and an outlet for evacuating the products formed, in particular CO.

[0042] According to one embodiment, the method of the present invention comprises the following steps in order: a) Activating the catalyst placed between the electrodes of a cold plasma reactor, preferably a DBD plasma reactor, by generating cold plasma under H2 as discharge gas; b) The introduction of the gas mixture to be converted between the reactor electrodes through the catalyst; c) The conversion under cold plasma of the gas mixture according to the RWGS reaction, for example continuously or semi-continuously, by circulation of the gas flow between the reactor electrodes.

[0043] The process of the present invention may further comprise extraction of reaction products and / or recirculation in the process of the invention. In the industrial process, the carbon monoxide (CO) produced may be separated from the mixture of unconverted gases (CO2, H2) and recovered water by condensation. The mixture of unconverted reactants, carbon dioxide (CO2), and hydrogen may be reintroduced into the reactor. This provides an overall process with 100% conversion, to minimize reactant losses.

[0044] According to one embodiment of the method of the invention, the dihydrogen (H2) is in excess relative to the carbon dioxide (CO2). According to one embodiment of the method of the invention, the dihydrogen (H2) / carbon dioxide (CO2) molar ratio in the gas mixture to be converted varies between 1 and 5 (a H2 / CO2 ratio = 5 means that there are 5 times more H2 molecules than CO2 molecules), for example between 1 and 4, preferably between 1 and 3, between 1 and 2.5, between 1 and 2 or between 1 and 1.5. By way of illustration, the H2 / CO2 ratio can be set at 1.1 ± 0.1, which means that it is likely to vary between 1 and 1.2 (with excess H2).

[0045] As shown in Figure 1, dihydrogen (H2) 1 and CO2 2 are introduced together into the DBD plasma catalytic reactor 7. The incoming gas conduits are each equipped with mass flow meters 4. Before entering the reactor, the incoming flows pass through a pressure gauge 5. The DBD plasma catalytic reactor 7 comprises a catalytic bed 8 and is connected to a plasma generator 6. The product flow 9 is then directed to a water condensation system 10 then a condensed liquid tank 11, a volume flow meter 12, a micro-GC gas analysis system 13, into which the Argon carrier gas (carrier gas for the micro-GC) 3 is introduced, then the vent 14.

[0046] According to one embodiment of the invention, the catalyst of the invention is activated by a DBD plasma by providing an electrical power of less than 35 W / g, for example less than 30 W / g, of catalyst (namely the catalyst present in the reactor, i.e. in the catalytic bed).

[0047] 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 5 Pa. Thus, according to one embodiment of the present invention, the method of the present invention is carried out at a pressure between 1.10 4 Pa and 3.10 5 Pa, for example between 5.10 4 Pa and 2.10 5 Pa or between 8.10 4 Pa and 2.10 5 Pa.

[0048] The conversion process according to the present invention can be carried out under pseudo-adiabatic conditions, i.e. without thermal insulation and without external heating, or under isothermal conditions, i.e. with thermal insulation and / or external heating.

[0049] According to one embodiment of the method of the invention, the DBD plasma is generated by applying a voltage between the two electrodes of between 1 and 25 kV, preferably between 5 and 15 kV, and / or with a frequency of between 1 kHz and 100 kHz. The gas hourly space velocity (GHSV) may in particular be between 1000 h 1 and 150,000 h -1 , preferably less than 100,000 h 1 .

[0050] A cooling system may be 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 water likely to form during the conversion reaction.

[0051] Catalyst according to the invention

[0052] A second subject of the present invention relates to a catalyst for the conversion of a gas mixture comprising carbon dioxide (CO2) and dihydrogen (H2) according to the following RWGS reaction: CO2 + H2 CO + H2O, said conversion being carried out in the presence of a cold plasma and said catalyst comprising at least one support and at least two promoters, one of which comprises iron. Said catalyst is activated by cold plasma before contacting with the gas mixture to be converted.

[0053] The structure of the catalyst of the present invention, a supported catalyst, i.e., a support-type structure doped with promoters, as well as its composition, and in particular the presence of iron within the catalyst, are essential to the performance of the RWGS conversion. The catalyst is distinguished from certain catalysts described in the prior art (this is in particular the case of the perovskite-type catalysts comprising lanthanide described in

[0011] and

[0012] ) in that the latter refer to a specific crystalline structure, while the supported catalyst of the present invention refers to a catalyst which comprises a specific support / promoter structure.

[0054] According to a preferred embodiment, said catalyst comprises: - a support comprising alumina; - at least two promoters, one of which comprises iron and the other preferably comprises copper (each being independently in metallic form or in oxidized form, as detailed below); and - at least one third promoter selected from the group consisting of transition metals, alkaline earth metals, lanthanides, alkali metals and mixtures thereof (each independently in metallic form or in oxidized form, as detailed below).

[0055] In the context of the present invention, the terms "catalytic system" and "catalyst" are equivalent and interchangeable. According to one embodiment of the invention, said catalyst is called a bi / trimetallic catalyst. It should be noted that the notion of bimetallic catalyst and trimetallic catalyst relates in particular to the species present in the catalyst without taking into account the support used. For example, when the catalyst is doped with two promoters, it is then referred to as a bimetallic catalyst; when the catalyst is doped with three promoters, it is then referred to as a trimetallic catalyst.

[0056] The support used in the context of the present invention is notably chosen for its capacity to adsorb reagents and more particularly CO2, for its thermal stability and for its high specific surface area aimed at promoting the plasma-catalyst interface, which makes it possible to offer various reaction pathways in surface chemistry. It is also chosen for its dielectric properties which can impact the properties of the plasma and modify the discharge behavior of the plasma, notably DBD plasma when it is used, the electric field and the electronic density due to the dielectric permittivity and the polarization effect which gives rise to the local electric field.

[0057] The catalyst of the present invention comprises at least one support. The catalyst may in particular comprise several supports, in other words, several support materials, for example two or three distinct support materials.

[0058] According to one embodiment of the present invention, the catalyst support comprises alumina; for example, the support may be made of alumina. For example, the catalyst support may be based on alumina. According to one embodiment, the support comprises or consists of an alumina oxide AI2O3.

[0059] According to one embodiment of the present invention, the catalyst support comprises ceria and / or zirconium, for example in ceria / zirconium form or in oxidized form. A mixed oxide of these materials may for example be used.

[0060] According to one embodiment of the present invention, the catalyst support comprises magnesium. For example, the catalyst support may be based on magnesium. According to one embodiment, the support comprises or consists of magnesium oxide.

[0061] The support(s) used in the context of the present invention may be a commercially available support(s).

[0062] The choice of support(s) can be important given that it(they) impacts the physicochemical properties (basicity, acidity, reducibility, oxygen mobility due to the presence of inherent defects present on said surface...), as well as the textural properties (pore volume, pore diameter, specific surface area...) and the electrical properties (permittivity, conductivity...), which will in turn modulate the catalytic performances of the system.

[0063] A method of preparing the catalyst support is detailed below.

[0064] The catalyst according to the invention makes it possible to produce high added value molecules such as carbon monoxide (CO), during the conversion of a gas mixture comprising carbon dioxide (CO2) and hydrogen (H2) according to the RWGS reaction, in the presence of a catalyst and a cold plasma, preferably a plasma generated by dielectric barrier discharge (DBD), while improving the catalytic performances of the RWGS reaction, i.e. the CO2 conversion rate and the selectivity towards the desired product CO.

[0065] For this purpose, the catalyst according to the present invention comprises at least two promoters, i.e. two or more promoters. In the context of the present invention, the promoters are found in any of their oxidation states and in particular in metallic form or in oxide form. Said promoters act as dopants and impact the physicochemical, textural and conductive properties of the catalyst. The promoters according to the invention advantageously have adequate physicochemical surface properties to help fix the reactants as well as adequate dielectric properties which make it possible to improve the conductivity of the resulting catalyst and which lead to high CO2 conversion rates.

[0066] In the context of the present invention, one of two promoters comprises iron, in metallic form or in oxidized form (FeO, Fe2O3 and / or FesC).

[0067] According to one embodiment of the present invention, said at least two promoters are selected from the group consisting of transition metals. Preferably, the at least two promoters comprise copper and / or iron, each being independently in metallic form and / or in oxidized form. Indeed, in the context of the present invention, copper and / or iron is found in any of its oxidation states and in particular in metallic form or in oxide form (CuO, CU2O, FeO, Fe2O3, and / or FesC).

[0068] According to one embodiment of the present invention, said catalyst comprises at least one support and at least two promoters, and two of these promoters comprise iron and copper, each being independently in metallic form and / or in oxide form.

[0069] According to one embodiment of the invention, the catalyst is such that: - the second promoter comprises copper, in metallic form or in oxidized form; and / or - the support includes alumina.

[0070] According to another embodiment of the invention, the catalyst is such that: - the promoters comprise copper and iron, each independently in metallic form or in oxidized form; and - the support includes alumina.

[0071] According to one embodiment of the present invention, the catalyst according to the present invention comprises at least three promoters, i.e. three or more promoters, for example four promoters.

[0072] According to one embodiment of the present invention, the catalyst comprises at least one third promoter selected from the group consisting of alkali metals, transition metals, alkaline earth metals, lanthanides, and mixtures thereof.

[0073] The at least one third promoter can thus be selected from the group consisting of alkali metals such as cesium, transition metals such as manganese, alkaline earth metals such as calcium and strontium, lanthanides such as lanthanum, and mixtures thereof. In the context of the present invention, the at least one third promoter is found in any of its oxidation states and in particular in metallic form or in oxide form.

[0074] For the purposes of the present invention, the alkali metals may be selected from the group consisting of lithium, sodium, potassium, rubidium, cesium and francium. When the promoter is an alkali metal, it is preferably potassium or cesium, and even more preferably cesium.

[0075] In the context of the present invention, the transition metals may in particular be selected from the group consisting of cobalt, copper, silver, molybdenum, iron, vanadium, manganese, chromium, yttrium, titanium, tantalum, zinc and zirconium. When the promoter is a transition metal, it is preferably yttrium or manganese, and even more preferably manganese.

[0076] For the purposes of the present invention, the alkaline earth metals may be selected from the group consisting of beryllium, magnesium, calcium, strontium, barium and radium. When the promoter is an alkaline earth metal, it is preferably calcium or strontium, and even more preferably calcium.

[0077] In the context of the present invention, the lanthanides may 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 promoter is a lanthanide, it is preferably cerium or lanthanum, and even more preferably lanthanum.

[0078] According to one embodiment of the present invention, the at least one third promoter is selected from the group consisting of calcium, cesium, lanthanum, strontium, manganese and mixtures thereof. More preferably, the at least one third promoter is selected from the group consisting of manganese, cesium and / or mixtures thereof.

[0079] According to one embodiment, the catalyst is trimetallic, doped with 3 promoters, the first of which comprises iron and the second of which comprises copper, their mass content in the catalyst being greater than or equal to 4% or 5% by weight relative to the weight of the support. According to this embodiment, the third promoter may for example comprise cesium, and its mass content in the catalyst may then be greater than or equal to 2% or 3% by weight relative to the weight of the support.

[0080] According to a preferred embodiment, the catalyst is trimetallic, doped with 3 promoters, the first of which is iron and the second of which is copper, their mass content in the catalyst is preferably approximately 5% ± 0.2% by weight relative to the weight of the support. According to this embodiment, the third promoter can be cesium, and its mass content in the catalyst can then be approximately 3% ± 0.5% by weight relative to the weight of the support.

[0081] According to one embodiment of the present invention, the mass content of promoters varies between 0.1% and 40% by weight relative to the weight of the support, preferably between 0.5% and 35% by weight, between 1% and 30% by weight, between 2% and 25% by weight relative to the weight of the support.

[0082] According to one embodiment, the catalyst contains at least 2% by weight, at least 3% by weight, at least 4% by weight or at least 5% by weight of at least one promoter, preferably of each of the two promoters, relative to the total weight of the support. Particularly advantageously, the catalyst comprises approximately 5% ± 1% by weight of copper and / or approximately 5% ± 1% by weight of iron relative to the weight of the support. By convention, a catalyst comprising 5% by weight of copper and 5% by weight of iron on an alumina support is denoted “5Cu5Fe / Al”.

[0083] According to one embodiment, the catalyst comprises: - at least 2% by weight, at least 3% by weight, at least 4% by weight or at least 5% by weight of a promoter comprising iron, in metallic form or in oxidized form, - at least 2% by weight, at least 3% by weight, at least 4% by weight or at least 5% by weight of a promoter comprising copper, in metallic form or in oxidized form, the percentages being expressed relative to the total weight of the support. According to this embodiment, the catalyst may comprise other promoters, preferably a third promoter. The third catalyst may be present within the catalyst at a content of less than or equal to 6% by weight, less than or equal to 5% by weight, less than or equal to 4% by weight, less than or equal to 3% by weight, relative to the total weight of the support.

[0084] The catalyst inserted into the reactor forms a bed and can be in different forms (beads, monoliths, powders, etc.). In the case of powders, the grains forming the powder can, for example, have an average size of between 1 pm and 1 mm, for example between 100 pm and 1 mm, in particular between 200 pm and 800 pm, preferably around 600 pm ± 20 pm. The grain size can in particular be adapted according to the production scale used. The catalyst can also be in the form of balls (in particular by compression of the powder in a mold) with an average size of less than 5 cm.

[0085] Process for preparing the catalyst

[0086] The preparation of the catalyst according to the present invention can be carried out according to different methods.

[0087] The catalyst may in particular be prepared by a process comprising bringing the support into contact with precursors of each of the at least two promoters. This step makes it possible to form a solid comprising the support and the at least two 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. The reduction step may be carried out in situ in the non-thermal plasma device under hydrogen.

[0088] The step of bringing the support into contact with a precursor of each promoter, preferably copper and iron, and optionally a precursor of at least one third promoter, can be carried out by several preparation methods, for example by impregnation, by coprecipitation or by other methods such as the sol-gel reaction or the hydrothermal method, thus bringing the support into contact with a copper precursor, an iron precursor and a precursor of at least one third promoter. The first two specific embodiments (also called sub-variants) are described below in more detail.

[0089] According to one embodiment, the catalyst is such that it comprises at least two promoters which comprise copper and iron, possibly a third promoter. According to this embodiment, the copper precursor, the iron precursor and the precursor of the third promoter 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 can be a mixture of different types of salts and / or oxides of these metals.

[0090] Thus, according to a first variant embodiment of the process for preparing the catalyst, the process for preparing the catalyst according to the invention comprises: - a step of bringing the support comprising alumina into contact with a copper precursor, an iron precursor and possibly one or more precursors of the other promoter(s), and - optionally, a calcination step of the mixture thus obtained, - optionally, a reduction step of the calcined mixture obtained in the previous step.

[0091] According to a second variant embodiment of the process for preparing the catalyst, the process for preparing the catalyst according to the invention comprises: - a step of bringing the support comprising alumina into contact with a copper precursor, an iron precursor and possibly one or more precursors of the other promoter(s), and - a step of calcining the mixture thus obtained, - optionally, a reduction step of the calcined mixture obtained in the previous step.

[0092] According to a third variant embodiment of the process for preparing the catalyst, the process for preparing a catalyst according to the invention comprises: - a step of bringing the support comprising alumina into contact with a copper precursor, an iron precursor and possibly one or more precursors of the other promoter(s), - a step of calcining the mixture thus obtained, and - a reduction step of the calcined mixture obtained in the previous step.

[0093] The step of bringing the components into contact can in particular be carried out by impregnation. More specifically, according to this first sub-variant of embodiment, the method comprises the following steps: 1) a support preparation step, and 2) a step of bringing the components into contact by impregnation.

[0094] Step 1) of preparation of the support itself includes 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. 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 elimination of excess water, in particular by evaporation of the water or filtration, then drying of the resulting solid. The drying step can in particular be carried out at a temperature below 150°C, typically at a temperature of around 100°C, for example for a duration varying between 5 hours and 48 hours. 1.4) calcination of the solid resulting from step 1.3) to lead to the support.

[0095] The product resulting from step 1.3) is calcined, for example at a temperature between 300°C and 600°C. This calcination step can be carried out for 3 hours or more, for example for a duration varying between 3 hours and 6 hours. This step results in the thermal decomposition of the nitrates in order to obtain oxides. Step 2) of bringing the components into contact itself includes the following sub-steps: 2.1) preparation of an aqueous suspension comprising a copper precursor, an iron precursor and one or more precursors of other promoters. During this step, an appropriate mass of each precursor is added to an appropriate volume of solvent, e.g., water. By "appropriate mass" and "appropriate volume" are meant the quantities of precursors and solvent (including water) adequate to achieve the desired mass contents of copper and promoter in the final catalyst. 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 done 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. 2.4) recovery of the solid comprising the support, copper, iron and promoters obtained in step 2.3) by removal of excess water, in particular by evaporation of the water or filtration, then drying of the resulting solid. The drying step can be carried out for example at a temperature below 150°C, typically at a temperature of around 100°C, for example for a period ranging from 7 hours to 48 hours. 2.5) calcination of the solid resulting from step 2.4) to produce the catalyst. 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 3 hours or more, for example for a duration varying between 3 hours and 6 hours. This step results in the thermal decomposition of the nitrates in order to obtain oxides.

[0096] This first sub-variant of implementation is also called wet impregnation process. It consists of impregnating the support with the copper precursor, the iron precursor and the precursor of at least a third promoter.

[0097] The step of bringing the components into contact can alternatively be carried out by coprecipitation. More specifically, according to a second sub-variant of embodiment, the process for preparing the catalyst comprises: 1') a support preparation step, and 2') a step of bringing the support into contact with a precursor of copper, iron and at least one third promoter, this contact being carried out by co-precipitation.

[0098] Step 1) of support preparation consists of preparing an aqueous solution comprising a copper precursor, an iron precursor and the precursors of the other promoters. This step is identical to step 2.1) of the wet impregnation process described previously.

[0099] Step 2') of bringing the components into contact itself includes the following sub-steps: 2.1') ​​adding the support to the solution resulting from step l') 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, sodium carbonate or potassium carbonate, preferably sodium hydroxide. It can be used in the form of a solution, in particular aqueous. The base is gradually added drop by drop 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 copper hydroxide, the iron hydroxide and the hydroxide of the metal used as another 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 copper and the promoter obtained in step 2.3') and its calcination to produce the catalyst. This step is identical to step 2.5) of the wet impregnation process.

[0100] This second sub-variant of implementation allows the precipitation of copper hydroxide, iron hydroxide and the hydroxide of the metal used as a third promoter on the surface of the support.

[0101] Optionally, the step of bringing the components into contact can also be carried out by other preparation methods such as the sol-gel reaction or the hydrothermal method, thus bringing the support into contact with a copper precursor, an iron precursor and a precursor of at least one third promoter. More specifically, according to a third sub-variant embodiment, the step of bringing the support into contact with a copper precursor, an iron precursor and a precursor of at least one third promoter can be carried out by sol-gel reaction or by hydrothermal reaction.

[0102] Use of the catalyst according to the present invention

[0103] Another object of the present invention also relates to the use of a catalyst and cold plasma for the conversion of a gas mixture comprising carbon dioxide (CO2) and dihydrogen (H2) according to the following RWGS reaction: CO2 + H2 CO + H2O, said catalyst comprising at least one support and at least two promoters, one of which includes iron. More particularly, said catalyst is activated by cold plasma before contact with the gas mixture to be converted.

[0104] The present invention relates in particular to the use of a cold plasma activated catalyst for the conversion of a gas mixture comprising carbon dioxide (CO2) and dihydrogen (H2) according to the following RWGS reaction: CO2 + H2 CO + H2O, said catalyst comprising at least one support and at least two promoters, one of which comprises iron.

[0105] The present invention relates in particular to the use of the catalyst of the present invention, as well as a cold plasma, preferably a plasma generated by dielectric barrier discharge (DBD), for converting a gas mixture comprising carbon dioxide (CO2) and dihydrogen (H2) according to the RWGS reaction.

[0106] 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 in converting a gas mixture comprising carbon dioxide (CO2) and dihydrogen (H2) according to the RWGS reaction.

[0107] The present invention also relates to the use of the catalyst according to the invention for the production of carbon monoxide (CO), from a gas mixture comprising carbon dioxide (CO2) and dihydrogen (H2) according to the RWGS reaction.

[0108] Liste des documents cités [1] Miriam Gonzâlez-Castano;Bogdan Dorneanu;Harvey Arellano-Garcia; (2021). The reverse water gas shift reaction: a process systems engineering perspective. Reaction Chemistry & Engineering, https: / / doi.org / 10.1039 / d0re00478b [2] Liu, HX., Li, SQ., Wang, WW. et al. Partially sintered copper-ceria as excellent catalyst for the high-temperature reverse water gas shift reaction. Nat Commun 13, 867 (2022). https: / / doi.org / 10.1038 / s41467-022-28476-5 [3] Abdallah. I. M. Rabee, Dan Zhao, Sebastian Cisneros, Carsten R. Kreyenschulte, Vita Kondratenko, Stephan Bartling, Christoph Kubis, Evgenii V. Kondratenko, Angelika Brückner, Jabor Rabeah, Role of interfacial oxygen vacancies in low-loaded Au-based catalysts for the low-temperature reverse water gas shift reaction, Applied Catalysis B: Environmental, Volume 321, 2023, 122083, ISSN 0926-3373, https: / / doi.Org / 10.1016 / j.apcatb.2022.122083. [4] Chen Xiaodong, Chen Ya, Song Chunyu, Ji Peiyi, Wang Nannan, Wang Wenlong, Cui Lifeng, Recent Advances in Supported Metal Catalysts and Oxide Catalysts for the Reverse Water-Gas Shift Reaction, Frontiers in Chemistry, (8), 2020, https: / / doi.org / 10.3389 / fchem.2020.00709 [5] Lina Liu, Jing Dai, Ziyan Yang, Yuanling Li, Xintai Su, Zhikun Zhang, Plasma-catalytic carbon dioxide conversion by reverse water-gas shift over La0.9Ce0.1B0.5B'0.503-6 perovskite-derived bimetallic catalysts, Chemical Engineering Journal, Volume 431, Part 1, 2022, 134009, ISSN 1385-8947, https: / / doi.Org / 10.1016 / j.cej.2021.134009. [6] Yuhai Sun, Junliang Wu, Yaolin Wang, Jingjing Li, Ni Wang, Jonathan Harding, Shengpeng Mo, Limin Chen, Peirong Chen, Mingli Fu, Daiqi Ye, Jun Huang, and Xin Tu. JACS Au 2022 2 (8), 1800-1810. https: / / doi.org / 10.1021 / jacsau.2c00028 [7] Guido Giammaria, Leon Lefferts, Synergy between dielectric barrier discharge plasma and calcium oxide for reverse water gas shift, Chemical Engineering Journal, Volume 392, 2020, 123806, ISSN 1385-8947, https: / / doi.Org / 10.1016 / j.cej.2019.123806. [8] Shanshan Xu et al 2021 J. Phys. D: Appl. Phys. 54 233001. https: / / doi.org / 10.1088 / 1361- 6463 / abe9el [9] Lina Liu, Sonali Das, Tianjia Chen, Nikita Dewangan, Jangam Ashok, Shibo Xi, Armando Borgna, Ziwei Li, Sibudjing Kawi, Low temperature catalytic reverse water-gas shift reaction over perovskite catalysts in DBD plasma, Applied Catalysis B: Environmental, Volume 265, 2020, 118573, ISSN 0926-3373, https: / / doi.Org / 10.1016 / j.apcatb.2019.118573.

[0010] Y. Zeng and X. Tu, "Plasma-Catalytic CO2 Hydrogenation at Low Temperatures," in IEEE Transactions on Plasma Science, vol. 44, no. 4, pp. 405-411, April 2016, doi: 10.1109 / TPS.2015.2504549.

[0011] Lina Liu, et al., « Low temperature catalytic reverse water-gas shift reaction over perovskite catalysts in DBD plasma », Applied Catalysis B: Environmental, Volume 265, 2020, 118573, ISSN 0926-3373.

[0012] Lina Liu, et al., « Plasma-catalytic carbon dioxide conversion by reverse water-gas shift over La0.9Ce0.1B0.5B'0.503-6 perovskite-derived bimetallic catalysts », Chemical Engineering Journal, Volume 431, Part 1, 2022, 134009, ISSN 1385-8947.

[0013] WO 2022 / 217284 Al - Lanzatech, Inc.

[0014] L. Yang, et al., « CO2 valorisation via reverse water-gas shift reaction using promoted Fe / CeO2-AI2O3 catalysts: Showcasing the potential of advanced catalysts to explore new processes design », Applied Catalysis A: General, Volume 593, 2020, 117442, ISSN 0926-860X.

[0015] Chi ng-Shi un Chen, et al., “Study of iron-promoted Cu / SiO2 catalyst on high temperature reverse water gas shift reaction”, Applied Catalysis A: General, Volume 257, Issue 1, 2004, Pages 97-106, ISSN 0926-860X.

[0016] Chen, FF (1984). “Introduction to Plasma Physics and Controlled Fusion.” Springer. ISBN: 978-0-306-41332-9.

[0017] Friedman, A. (2008). “Plasma Chemistry.” Cambridge University Press. ISBN: 978-0521886678.

[0109] Examples

[0110] The invention is now described in more detail with reference to the following examples, the purpose of which is merely illustrative and not intended to limit the scope of the invention.

[0111] A. Preparation of the different catalysts by wet impregnation

[0112] The various catalysts are prepared by wet impregnation.

[0113] Different supports were used to prepare the catalysts in Table 1 below: 1) A commercial magnesium oxide from Sigma Aldrich (MgO); 2) A commercial ceria oxide from Solvay (Ce); 3) A commercial alumina oxide from Saint Gobain (AI200, Specific surface area=200m 2 / g); 4) A commercial alumina oxide from Saint Gobain (AI220, Specific surface area = 220m 2 / g); 5) A commercial alumina oxide from Saint Gobain (AI260, Specific surface area = 260m 2 / g); 6) A commercial cerium-zirconium mixed oxide from Sigma Aldrich (CZ).

[0114] The catalysts are doped with one or more promoters prepared from an aqueous solution and selected from CufNChh-SHzO Fe(NO3)2.9H2O, Ca(NO3)2.4H2O, SrfNChh, La(NO3)2.6H2O, MnfNOsh.xFbO and CsNCh, (all commercial, Sigma-Aldrich).

[0115] The copper, iron and / or precursor salts used are dissolved in a volume of 50 ml of water, at room temperature and with stirring. The appropriate mass of support (e.g. alumina oxide) is added to the aqueous solution containing the mixture of metal salts and kept stirring for 2 hours. In the case of catalyst 8i “5Cu5Fe3Cs / Al200” (one of the catalytic systems according to the invention), the copper (Cu) content is 5% by mass relative to the weight of the support, that of iron (Fe) is 5% by mass relative to the weight of the support and that of cesium (Cs) is 3% by mass relative to the weight of the support. Said support is based on alumina (Al200). Thus, 0.19 g of nitrate of copper (which represents a content of 5% by weight of copper relative to the weight of the support), 0.36 g of iron nitrate (which represents a content of 5% by weight of iron relative to the weight of the support), 0.044 g of cesium nitrate (which represents a content of 3% by weight of cesium relative to the weight of the support) and 1 g of AI200 support are mixed. The mixture is then placed in a rotary evaporator at 65°C, in order to remove excess water.

[0116] 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 catalyst samples were hand-ground and sieved to an average grain size between 50 and 200 μm.

[0117] B. Conversion of a gas mixture comprising carbon dioxide (CO2) and dihydrogen (H2) according to the RWGS reaction in the presence of different catalysts

[0118] The procedure followed, for example in the presence of catalyst 8i, is as follows: 362 mg of catalyst “5Cu5Fe3Cs / Al200” are placed between the two electrodes of the DBD reactor. A non-thermal DBD plasma at a frequency of 70 kHz is created between the two electrodes: a cylindrical copper electrode placed inside an alumina tube (3 mm diameter), surrounded by a coaxial quartz tube (10 mm internal 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 gap of 2.5 mm, covering a length of about 1 cm. Before the catalytic test, the catalysts are reduced in situ under non-thermal DBD plasma (or cold plasma) under H2 as discharge gas for a duration of 60 minutes.

[0119] Corresponding to a GHSV (Gas Hourly Space Velocity) of 17000 h-1 , the reactor is then supplied with a gas mixture comprising carbon dioxide and dihydrogen (molar ratio H2 / CO2 = 1 / 1) with a total flow rate of 120 ml / min STP (Standard Temperature and Pressure) (60 ml / min STP CO2 and 60 ml / min STP H2), at atmospheric pressure and at a temperature of 20°C.

[0120] The activity and selectivity of the different catalysts tested are measured and reported in Tables 1 and 2.

[0121] The experiments performed and illustrated in Table 2 were carried out using an isothermal reactor surrounded by a jacket heated by a heating system at oil circulation at 250°C. A Julabo oil circulator to control the reactor temperature by pumping thermal oil through a circulation system.

[0122] The following equations were used to estimate the catalytic performance and calculate the CO2 conversion and CO selectivity: Sco = FOUt+ c ° FOUt *100 (Eq. 3) 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.

[0123] C. Results

[0124] Table 1 below lists the catalysts tested in the present tests (“c” indicates a comparative catalyst; “i” indicates a catalyst according to the invention) and indicates the results of the catalytic activity obtained in terms of CO2 conversion and CO selectivity. Table 1: RWGS reaction results - catalyst composition Table 2: RWGS reaction results with 5Cu5Fe3Cs / AI200 catalyst (8i) - plasma significance

[0125] As shown in the results of Table 2, tests 20c and 21c, without cold plasma during the conversion reaction, no change in the composition of the outlet gases is observed (very slight conversion). When the plasma is ignited, and after stabilization, carbon monoxide (CO) is produced at the reactor outlet - Tables 1 and 2, tests 1 to 19. These results demonstrate the importance of the plasma-catalysis combination for the RWGS reaction. Furthermore, prior activation of the catalyst by cold plasma before bringing it into contact with the gas mixture to be converted significantly improves the conversion efficiency (comparison of tests 8i and 19c in particular). Tl

Claims

Claims

1. A process for converting a gas mixture comprising carbon dioxide (CO2) and dihydrogen (H2) according to the following RWGS reaction: CO2+ H2^ CO + H2O characterized in that it is carried out in the presence of a catalyst comprising at least one support and at least two promoters, one of which comprises iron, in metallic form or in oxidized form, said catalyst being activated by cold plasma before contacting with the gas mixture to be converted and said conversion being carried out in the presence of cold plasma, at temperatures below 400°C.

2. The method of claim 1, wherein the catalyst contains at least 2% by weight of at least one promoter, preferably each of the two promoters, relative to the total weight of the support.

3. Method according to one of claims 1 or 2, according to which: - the second promoter comprises copper, in metallic form or in oxidized form; and / or - the support includes alumina.

4. A method according to any one of claims 1 to 3, wherein the catalyst comprises: - a support comprising alumina; - at least two promoters, one of which comprises iron and the other of which comprises copper, each being independently in metallic form or in oxidized form; and - optionally a third promoter selected from the group consisting of alkali metals, transition metals, alkaline earth metals, lanthanides, and mixtures thereof, each independently in metallic form or in oxidized form.

5. A method according to any one of claims 1 to 4, wherein the cold plasma is a plasma generated by dielectric barrier discharge (DBD).

6. Method according to any one of claims 1 to 5, according to which the molar ratio of hydrogen (H2) / carbon dioxide (CO2) in the gas mixture to be converted varies between 1 and 5, preferably between 1 and 3 or even more preferably between 1 and 2.

7. A method according to any one of claims 1 to 6, comprising the following steps in order: a) Activating the catalyst placed between the electrodes of a cold plasma reactor, preferably a DBD plasma reactor, by generating cold plasma under H2 as discharge gas; b) Introducing the gas mixture to be converted through the catalyst between the electrodes of the reactor; and c) Converting under cold plasma the gas mixture according to the RWGS reaction by circulating the gas flow between the electrodes of the reactor.

8. Catalyst for the conversion of a gas mixture comprising carbon dioxide (CO2) and dihydrogen (H2) according to the following RWGS reaction: CO2+ H2^ CO + H2O said conversion being carried out in the presence of a cold plasma, said catalyst comprising at least one support and at least two promoters, one of which comprises iron and said catalyst being activated by cold plasma before contacting with the gas mixture to be converted.

9. A catalyst according to claim 8, wherein: - the second promoter comprises copper, in metallic form or in oxidized form; and / or - the support includes alumina.

10. Catalyst according to any one of claims 8 or 9, according to which the mass content of promoters varies between 0.1% and 40% by weight relative to the weight of the support, preferably between 0.5% and 20% by weight.

11. A catalyst according to any one of claims 8 to 10, comprising: - a support comprising alumina - at least two promoters, one of which comprises iron and the other of which comprises copper, each being independently in metallic form or in oxidized form; and - optionally a third promoter selected from the group consisting of alkali metals, transition metals, alkaline earth metals, lanthanides, and mixtures thereof, each independently in metallic form or in oxidized form.

12. A catalyst according to any one of claims 8 to 11, comprising a third promoter selected from the group consisting of alkali metals, transition metals, alkaline earth metals, lanthanides, and mixtures thereof, each independently being in metallic form or in oxidized form.

13. Use of a catalyst and cold plasma for the conversion of a gas mixture comprising carbon dioxide (CO2) and dihydrogen (H2) according to the following RWGS reaction: CO2+ H2^ CO + H2O said catalyst comprising at least one support and at least two promoters, one of which comprises iron, in metallic form or in oxidized form, said catalyst being activated by cold plasma before contact with the gas mixture to be converted.

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