Plasma-catalyzed direct water-gas shift reaction

Abstract

The present invention relates to a method for the chemical conversion of a gas mixture comprising carbon monoxide (CO) and water vapor (H 2 O) using the following WGS reaction: CO + H 2 O → CO 2 + H 2 in the presence of a catalytic system, 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 catalytic system, activated by cold plasma, in order to produce high-added-value molecules, such as hydrogen (H 2).

Description

Title: Direct 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 monoxide (CO) and water vapor (H2O) according to the following WGS reaction: CO + H2O CO2 + H2 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 catalytic system, as well as the use of such a catalyst to produce high added value molecules, such as hydrogen (H2). State of the prior art

[0002] Hydrogen is a clean alternative to conventional fossil fuel-based energy sources and is considered the ideal energy choice for developing a sustainable future.

[0003] The water gas shift reaction (WGS) is a method of choice for increasing the hydrogen (H2) content of a synthesis gas. This process is normally deployed after steam reforming or partial oxidation of natural gas or coal to produce a hydrogen-rich synthesis gas [1].

[0004] The WGS reaction (see Equation 1) is reversible and slightly exothermic. It is sensitive to temperature variations. Too high a temperature significantly increases the reaction rate but favors the reverse reaction "Reverse Water Gas Shift" or "RWGS reaction" which is endothermic (see Equation 2), which limits the conversion rate. A compromise must therefore be found between the reaction rate (high temperature) and the conversion rate (low temperature) [1], [2],

[0005] -41.09 kJ / moL (Eq.l)

[0006] CO2+ H2->CO + H2O; AIT = 41.09 kJ / moL (Eq.2)

[0007] Due to thermodynamic constraints, the WGS reaction is normally carried out in two separate reactors: a high temperature (HTS) reactor and a low temperature (LTS) reactor [1], [2]. According to this approach, the kinetics are favored in the first reactor due to the high temperature, while thermodynamics is favored in the low temperature reactor, resulting in a high H2 yield.

[0008] Typically, the WGS reaction is carried out over iron oxide catalysts in the high temperature region (HTS) (>300°C), followed by the reaction over copper catalysts in the low temperature region (LTS) (200-250°C) to optimize the process from a kinetic and thermodynamic point of view. Coupling the HTS and LTS processes requires careful process design, including the use of heat exchangers for thermal control of the reaction streams, which results in high investment and operating costs [1], [2], [3],

[0009] Furthermore, under WGS reaction conditions, catalyst deactivation due to metal sintering and coking is also problematic, reducing process efficiency and increasing operational costs.

[0010] Activation of reactants through non-thermal plasma (NTP) assisted by WGS reaction with a catalyst is one of the candidates to solve the problems of the prior art. The few studies that have been carried out to date are not satisfactory in terms of stability, efficiency and cost, which limits the use of the system for industrial application [4], [5], [6], [7],

[0011] The object of the present invention is in particular to propose a process for the chemical conversion of carbon monoxide (CO) and water vapor (H2O) according to the following WGS reaction: CO + CO2 + H2 in the presence of cold plasma and a catalyst which has high catalytic and energy yields, said process being capable of being exploited on a large scale. In particular, said catalyst comprises: - at least one support comprising ceria or cerium oxide, - at least one first promoter comprising copper, and - at least one second promoter selected from the group consisting of transition metals, poor metals, lanthanides, and mixtures thereof.

[0012] Patent applications and patents [9-12] do not describe such a plasma-catalysis conversion process in which the catalyst is activated by cold plasma. Summary of the invention

[0013] A first object of the present invention is a process for the chemical conversion of a gas mixture comprising carbon monoxide (CO) and water vapor (H2O) according to the following WGS reaction: CO + H2O CO2 + H2 in the presence of a catalyst, also called a catalytic system, comprising at least one support comprising ceria or cerium oxide, at least one first promoter comprising copper, and at least one second promoter selected from the group consisting of transition metals, poor metals, lanthanides, and mixtures thereof, activated by cold plasma. According to one embodiment, the cold plasma is a plasma generated by dielectric barrier discharge (DBD).

[0014] A second object of the present invention is a catalyst, also called a catalytic system, for converting, preferably in a single step, a gas mixture comprising CO and water vapor into H2. This catalyst, which can for example be activated by cold plasma before contacting with the gas mixture to be converted, for example generated by dielectric barrier discharge DBD. The catalyst of the present invention is such that it comprises at least one ceria support and at least two promoters, one of which comprises copper. The use of such a catalyst combined with a cold plasma for the conversion of gases in the WGS reaction makes it possible to overcome all the disadvantages of the prior art present in the thermal process (coupling of the HTS and LTS processes) and capable of directly synthesizing hydrogen from CO and water vapor 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 smaller quantity of catalyst, on the order of 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 gold or platinum (Pt).

[0015] More specifically, said catalyst comprises: - a support comprising ceria or cerium oxide, - at least one first promoter comprising copper, and - at least one second promoter selected from the group consisting of transition metals, poor metals, lanthanides, and mixtures thereof.

[0016] 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 monoxide (CO) and water vapor (H2O) according to the WGS reaction, said catalyst comprising at least one support comprising ceria or cerium oxide, at least one first promoter comprising copper, and at least one second promoter selected from the group consisting of transition metals, poor metals, lanthanides, and mixtures thereof, activated by cold plasma.

[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. While the WGS conversion processes of the prior art have a high inertia (which can reach 24 hours for example in the context of large-scale installations) due to the fact that the reactors must be brought to high temperatures, for example of the order of 350°C-500°C and up to 80 bars in pressure, the process of the present invention, on the contrary, has great flexibility and robustness, due to its rapid implementation which not only makes it possible to start the conversion reaction 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

[0018] 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 flow diagram for the WGS reaction. DBD-type plasma-catalyzed reactor for the chemical conversion of a gas mixture comprising carbon monoxide (CO) and water vapor (H2O) according to the following WGS reaction CO2 + H2. The [Error! Reference source not found.] illustrates the experimental setup (PFD diagram) used in one example, the water gas reaction (WGS 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 or absence of DBD plasma. The tables [Error! Invalid reference for a bookmark. Error! Reference source not found. -2] indicate in particular the results of the catalytic activity obtained in terms of conversion and selectivity. Definitions

[0019] 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).

[0020] Any description relating to one embodiment is applicable and interchangeable with all other embodiments of the invention.

[0021] 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.

[0022] The expression “N, M and / or P” should be understood as meaning “N and / or M and / or P”.

[0023] The expression "N, M and P" should be understood as meaning "N and M and P".

[0024] 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.

[0025] 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.

[0026] 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 in order to generate a plasma by Dielectric Barrier Discharge (DBD) by promoting the accumulation of electrical charges on the surface of this material.

[0027] 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.

[0028] 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.

[0029] The term "cold plasma" or "non-thermal plasma (NTP)" refers to a plasma where the particle (electron and ion) distribution 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"

[0013] , Dielectric barrier discharge (DBD) is an example of a cold plasma or non-thermal plasma, in which the gas is more or less at room temperature, and the average electron energy is between 2 and 5 eV due to the strong electric field in the plasma

[0014] , The gas temperature 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 context of the present invention, in the case of an exothermic reaction, the gas temperature can be controlled so that it is below 300°C, for example below 280°C or 270°C. If necessary, the gas temperature can be measured by a probe (thermocouple) and the electron temperature by Optical Emission Spectroscopy.

[0030] In the context of the present invention, the terms "Water Gas Shift", "WGS", "WGS reaction" designate the direct conversion reaction of gas to water according to equation 1.

[0031] The term "hydrogen" should be understood to mean "dihydrogen" or "H2".

[0032] 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.

[0033] 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.

[0034] 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

[0035] Process for converting a gas mixture comprising carbon monoxide (CO) and water vapor (H2O) according to the WGS reaction

[0036] A first subject of the present invention relates to a method for converting a gas mixture comprising carbon monoxide (CO) and water vapor (H2O) according to the following WGS reaction: CO2 + Fb in the presence of cold plasma and a catalyst, the latter being activated by cold plasma, preferably a plasma generated by dielectric barrier discharge (DBD), before starting the gaseous species conversion reaction. Said catalyst comprises at least one support comprising ceria or cerium oxide, at least one first promoter comprising copper (in metallic form or in oxidized form) and at least one second promoter selected from the group consisting of transition metals, poor metals, lanthanides, and mixtures thereof, activated by cold plasma (each being independently in metallic form or in oxidized form). This process aims to produce, in a single step, high value-added molecules, such as hydrogen (H2).

[0037] The gas mixture to be converted according to the WGS reaction comprises carbon monoxide (CO) and water vapor (H2O). It may further comprise other gases such as, for example, carbon dioxide (CO2), methane (CH4), nitrogen (N2), oxygen (O2) and / or dihydrogen (H2). According to one embodiment of the present invention, the gas mixture to be converted according to the WGS reaction comprises predominantly carbon monoxide (CO) and water vapor (H2O), and optionally one or more gases selected from the group consisting of carbon dioxide (CO2), methane (CH4), nitrogen (N2), oxygen (O2) and dihydrogen (H2), and mixtures thereof. According to this embodiment, the gas mixture to be converted according to the WGS reaction comprises, for example, more than 50 mol. % of carbon monoxide (CO) and water vapor (H2O), 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 WGS conversion reaction according to the invention.

[0038] The process for converting a gas mixture comprising carbon monoxide (CO) and water vapor (H2O) according to said WGS reaction (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 hydrogen, a high value-added gas, from CO and water vapor.

[0039] 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.

[0040] 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 WGS reaction. The WGS conversion reaction is carried out under cold plasma.

[0041] According to one embodiment of the method of the invention, said conversion is carried out in the presence of cold plasma at temperatures below 300°C, below 290°C, below 280°C or even below 270°C.

[0042] 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 a 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.

[0043] According to one embodiment of the method of the invention, the selected catalyst is placed between the electrodes of a DBD reactor, allowing gaseous species to circulate 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 inventors realized that this catalyst activation step is essential to the performance of the conversion process according to the invention. 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.

[0044] When implementing the method of the invention, the cold plasma is generated and a strong electric field is created, which keeps said catalyst in an activated state, more particularly between the grains of said catalyst or nearby, upstream or downstream of the catalytic system, 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 WGS 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 catalyst constituents) and the selection of its constituents is essential to obtain high conversion efficiencies, depending on. gaseous 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. The polarization performances, as well as the activation of the catalytic sites necessary for the chemical reaction, the rate-limiting steps, are possible in the presence of cold plasma, at low gas temperatures (for example below 300°C, or below 290°C, 280°C or 270°C). According to the conventional process without polarization, the working temperature is higher, generally of the order of 350°C to 500°C and requires 2 steps LTS and HTS.

[0045] The reactor comprises at least one inlet allowing it to be supplied with gas to be converted, comprising CO and water vapor, and an outlet for evacuating the products formed, in particular H2.

[0046] According to one embodiment, the method of the present invention comprises the following steps in order: a) Activation of the catalyst placed between the electrodes of a cold plasma reactor, preferably a DBD plasma reactor, by generation of cold plasma under H2 as discharge gas; b) Introduction of the gas mixture to be converted between the electrodes of the reactor through the catalyst; c) Conversion under cold plasma of the gas mixture according to the WGS reaction, for example continuously or semi-continuously, by circulation of the gas flow between the electrodes of the reactor.

[0047] 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 hydrogen (H2) produced will be separated from the mixture of unconverted gases (CO, H2O) and carbon dioxide (CO2). The mixture of unconverted reactants, carbon monoxide (CO), and water vapor (H2O) will be reintroduced into the reactor. This allows for an overall process with 100% conversion, in order to minimize reactant losses.

[0048] According to one embodiment of the method of the invention, the water vapor (H2O) is in excess relative to the carbon monoxide (CO). According to one embodiment of the method of the invention, the molar ratio of water vapor (H2O) / carbon monoxide (CO) in the gas mixture to be converted varies between 1 and 5 (a ratio of H2O / CO = 5 means that there are 5 times more water molecules than CO 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. For illustration purposes, the H2O / CO ratio can be set at 1.1 ± 0.1, which means that it is likely to vary between 1 and 1.2 (with excess vaporized water).

[0049] As shown in Figure 1, water 1 stored in a tank is first propelled by an inert gas (Ar) 3 and then circulates through a mass flow controller 4. It is then vaporized and then mixed with a flow of CO (carrier gas) 2, also controlled by a mass flow meter 4, using a controlled evaporation and mixing system 6. The gas mixture is then transported along a heated pipe 7 equipped with a pressure gauge 5 to the inside of the DBD plasma catalytic reactor 9. The latter comprises a catalytic bed 10 and is connected to a plasma generator 8. The product flow 11 is then directed to a water condensation system 12 and then a condensed liquid recovery tank 13. The gas flow is measured using a volume flow meter 14. A micro GC 15 into which Argon 3 (carrier gas) is introduced vector for micro-GC) is used to analyze the composition of the gases, then vent 16.

[0050] 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 25 W / g of catalyst (i.e. the catalyst present in the reactor, i.e. in the catalytic bed).

[0051] 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. The conversion reaction 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 temperature control.

[0052] 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 .

[0053] 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 the water vapor which has not reacted during the conversion reaction.

[0054] Catalyst according to the invention

[0055] A second subject of the present invention relates to a catalyst for the conversion of a gas mixture comprising carbon monoxide (CO) and water vapor (H2O) according to the following WGS reaction: CO + H2O CO2 + H2, said conversion being carried out in the presence of a cold plasma.

[0056] More specifically, said catalyst comprises: - a support comprising ceria or cerium oxide, - at least one first promoter comprising copper, and - at least one second promoter selected from the group consisting of transition metals, poor metals, lanthanides, and mixtures thereof.

[0057] For the purposes of the present invention, the terms "catalytic system" and "catalyst" are equivalent and interchangeable.

[0058] According to one embodiment of the invention, said catalyst is called a bi / trimetallic catalyst. It should be noted that the concept of bimetallic or 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, we then speak of a bimetallic catalyst; when the catalyst is doped with three promoters, we then speak of a trimetallic catalyst.

[0059] The support used in the context of the present invention is notably chosen for its capacity to adsorb the reactants and more particularly CO, 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.

[0060] According to one embodiment of the present invention, the catalyst support comprises ceria; in particular, the support may be made of ceria. According to one embodiment or use, the support is a cerium oxide. Thus, the catalyst support may further comprise other components, for example a mixed oxide and / or aluminum and / or zirconium.

[0061] According to one embodiment of the present invention, the catalyst support consists of ceria, and optionally alumina, each being independently in ceria / alumina form or in their corresponding oxidized form.

[0062] According to this embodiment, the catalyst support may in particular consist exclusively of ceria and / or cerium oxide. Alternatively, the catalyst support may consist exclusively of ceria and / or cerium oxide, as well as alumina and / or aluminum oxide. When the catalyst support consists of a mixture of ceria and alumina (including in oxidized form), these species may be present in a Ce / Al mass ratio varying between 10:90 and 90:10, for example 20:80 and 80:20, 40:60 and 75:25 or 50:50 and 70:30.

[0063] According to a preferred embodiment of the present invention, the catalyst support consists of ceria and / or cerium oxide. According to this preferred embodiment, the catalyst support does not comprise other constituents or comprises an amount of other constituents that does not significantly impact its properties. Thus, according to this embodiment, the catalyst support comprises less than 5% by weight of other constituents, less than 4% by weight of other constituents, less than 3% by weight of other constituents, less than 2% by weight of other constituents, less than 1% by weight of other constituents, or even less than 0.1% by weight of other constituents.

[0064] The choice of support is important as it impacts 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 will modulate the catalytic performance of the system.

[0065] The preparation of the catalyst support is detailed below. The support used in the context of the present invention may also be a commercially available support.

[0066] The catalyst according to the invention makes it possible to produce high added value molecules such as hydrogen, during the conversion, in particular the conversion reaction of a gas mixture comprising carbon monoxide (CO) and water vapor (H2O) according to the WGS reaction, in the presence of a catalyst and a cold plasma, preferably a plasma generated by dielectric barrier discharge (DBD), while improving the catalytic performance of the WGS reaction, i.e. the CO conversion rate and the selectivity towards the desired products (hydrogen and carbon monoxide).

[0067] For this purpose, the catalyst according to the present invention comprises at least two promoters. The inventors demonstrate that when the catalyst of the present invention is in the form of a support comprising ceria and comprises at least two promoters, and when said catalyst is furthermore activated by cold plasma before initiating the conversion reaction, the performance of the reaction is significantly higher than that achieved without prior activation of the catalyst, or when the catalyst does not comprise a copper promoter, or when the catalyst does not comprise at least two promoters.

[0068] 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.

[0069] Promoters act as dopants and impact the physicochemical, textural and conductive properties of the catalytic system. The promoters according to the invention advantageously possess adequate physicochemical surface properties to help fix the reactants, as well as adequate dielectric properties which improve the conductivity of the resulting catalyst and which lead to high CO conversion rates.

[0070] Thus, in the context of the present invention, said first promoter comprises copper. In the context of the present invention, copper is in any of its oxidation states and in particular in metallic form or in oxide form (CuO or CU2O). The mass content of copper in the catalyst advantageously varies between 1% and 50% by weight relative to the weight of the support, for example between 2 and 40% by weight, preferably less than 30%. Particularly advantageously, the catalyst comprises between 5 and 16% by weight of copper or between 7 and 13% of copper, for example approximately 10% ± 1% by weight of copper, relative to the weight of the support.

[0071] According to the present invention, the catalyst comprises at least one second promoter selected from the group consisting of transition metals, poor metals, lanthanides, and mixtures thereof, each independently being in metallic form or in oxidized form.

[0072] Thus, within the scope of the present invention, the at least one second promoter is selected from the group consisting of transition metals such as zinc and iron, poor metals such as aluminum and gallium, lanthanides such as lanthanum, and mixtures thereof. In the context of the present invention, the at least one second promoter is in any of its oxidation states and in particular in metallic form or in oxide form.

[0073] In the context of the present invention, the transition metals may in particular be selected from the group consisting of cobalt, silver, iron, copper, molybdenum, vanadium, manganese, chromium, yttrium, titanium, tantalum, zinc and zirconium. When the promoter is a transition metal, it is preferably iron or zinc, and even more preferably zinc.

[0074] In the context of the present invention, the poor metals may be selected from the group consisting of gallium, indium, tin, thallium, lead, bismuth and aluminum. When the promoter is a poor metal, it is preferably gallium or aluminum, and even more preferably aluminum.

[0075] 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.

[0076] According to one embodiment of the present invention, the at least one second promoter of the catalyst is selected from the group consisting of zinc, iron, lanthanum, gallium, aluminum and mixtures thereof, each independently being in metallic form or in oxidized form. More preferably, the at least one second promoter is selected from the group consisting of zinc, aluminum and mixtures thereof, each independently being in metallic form or in oxidized form.

[0077] According to one embodiment, the catalyst preferably comprises two or three promoters. According to this embodiment, the catalyst is bimetallic or trimetallic. Preferably, the bimetallic or trimetallic catalyst consists essentially of a support comprising ceria and / or cerium oxide, and two or three promoters, the first of which comprises copper (in metallic or oxidized form), and the second, and optionally the third, promoter(s) comprises zinc, iron, lanthanum, gallium, aluminum or mixtures thereof (each of these metals being independently in metallic or oxidized form).

[0078] According to one embodiment, the catalyst does not comprise noble, rare or precious materials, such as gold (Au) or platinum (Pt), or comprises an amount of these materials that does not significantly impact its properties. Thus, according to this embodiment, the catalyst comprises less than 3% by weight of noble, rare or precious materials, less than 2% by weight, less than 1% by weight, less than 0.5%, less than 0.1% by weight, or even less than 0.01% by weight of noble, rare or precious materials. Indeed, in the context of the present invention, it uses less expensive materials compared to thermal processes, which often use noble, rare or precious materials, such as gold or platinum.

[0079] According to an 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, 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 11% by weight relative to the weight of the support.

[0080] According to the present invention, the catalyst according to the present invention comprises at least two promoters, i.e. two or more promoters, for example three promoters. According to one embodiment, when the catalyst is trimetallic, doped with 3 promoters, one of which is copper (in metallic form or in oxidized form), its mass content in the catalyst can preferably vary between 8 and 15% ± 0.2% by weight relative to the weight of the support; the second promoter can in particular be zinc (in metallic form or in oxidized form), and its mass content in the catalyst can preferably vary between 3% and 8% ± 0.5% by weight relative to the weight of the support; the third promoter can in particular be aluminum (in metallic form or in oxidized form) and its mass content in the catalyst can preferably vary between 1 and 5% ± 0.5% by weight relative to the weight of the support.

[0081] According to a particular embodiment, the trimetallic catalyst consists of three promoters, one of which is copper (in metallic form or in oxidized form), its mass content in the catalyst is preferably approximately 10% ± 0.2% by weight relative to the weight of the support; the second promoter is zinc (in metallic form or in oxidized form), and its mass content in the catalyst is preferably approximately 5% ± 0.5% by weight relative to the weight of the support; the third promoter is aluminum (in metallic form or in oxidized form), its mass content in the catalyst is preferably approximately 3% ± 0.5% by weight relative to the weight of the support.

[0082] 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 beads (in particular by compression of the powder in a mold) having an average size of less than 5 cm.

[0083] According to one embodiment of the present invention, the support comprising ceria or cerium oxide, and at least two promoters form a homogeneous mixture. This means that the promoters are distributed uniformly throughout the entire volume of the catalyst.

[0084] Process for preparing the catalyst

[0085] The preparation of the catalyst according to the present invention can be carried out according to different methods.

[0086] The catalyst may in particular be prepared by a process comprising bringing the support comprising ceria or cerium oxide into contact with a precursor of the first promoter, copper, and at least one precursor of the second promoter. This step makes it possible to form a solid comprising the support, the copper, and the second 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. The reduction step may be carried out in situ in the non-thermal plasma device under hydrogen.

[0087] The step of bringing the support into contact with a copper precursor and a precursor of the second 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 and a precursor of at least one second promoter. The first two Specific embodiments (also called sub-variants) are described below in more detail.

[0088] The precursor of the copper and the precursor of the second 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 may be a mixture of different types of salts and / or oxides of these metals.

[0089] Thus, according to a first variant embodiment of the process according to the invention, the process for preparing a catalyst according to the invention comprises: - a step of bringing the support comprising ceria or cerium oxide into contact with a copper precursor and one or more precursors of the promoter(s), and - optionally, a calcination step of the mixture obtained following contact between the components, - optionally, a reduction step of the calcined mixture obtained in the previous step.

[0090] According to a second variant embodiment of the process according to the invention, the process for preparing a catalyst according to the invention comprises: - a step of bringing the support comprising ceria or cerium oxide into contact with a copper precursor and one or more precursors of the promoter(s), and - a step of calcining the mixture obtained following contact between the components, - optionally, a reduction step of the calcined mixture obtained in the previous step.

[0091] According to a third variant embodiment of the process according to the invention, the process for preparing a catalyst according to the invention comprises: - a step of bringing the support comprising ceria or cerium oxide into contact with a copper precursor and one or more precursors of the promoter(s), and - a step of calcining the mixture obtained following contact between the components, - a reduction step of the calcined mixture obtained in the previous step.

[0092] According to a fourth variant embodiment of the process according to the invention, the process for preparing a catalyst 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 copper precursor and one or more precursors of the promoter(s), - optionally a calcination step of the mixture obtained following contact of the components, - optionally, 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 support preparation itself includes the following sub-steps: 1.1) preparation of a suspension comprising a ceria precursor or comprising a cerium oxide precursor. According to this step 1.1), the support precursor corresponds to a ceria 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 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. 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.

[0095] 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 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, 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 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 lead to 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 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 realization is also called wet impregnation process. It consists of impregnating the support with the copper precursor and the promoter precursor.

[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 copper precursor and the 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 and the precursors of the 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 hydroxide, 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 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 copper 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 lead to the catalytic system. This step is identical to step 2.5) of the wet impregnation process.

[0100] This second sub-variant of implementation makes it possible to precipitate copper hydroxide and the hydroxide of the metal used as a 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 and a precursor of at least one second promoter.

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

[0103] The present invention also relates to the use of a catalyst and a cold plasma for the conversion of a gas mixture comprising carbon monoxide (CO) and water vapor (H2O) according to the following WGS reaction: CO + H2O CO2 + H2, said catalyst comprising at least one support comprising ceria or cerium oxide, at least one promoter comprising copper, and at least one second promoter selected from the group consisting of transition metals, poor metals, lanthanides, and mixtures thereof, said catalyst being further activated by cold plasma before contacting with the gas mixture to be converted.

[0104] 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 monoxide (CO) and water vapor (H2O) according to the WGS reaction.

[0105] 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 mixture comprising carbon monoxide (CO) and water vapor (H2O) according to the WGS reaction, more particularly when the catalyst has been activated by cold plasma before contacting with the gas mixture to be converted.

[0106] The present invention also relates to the use of the catalyst according to the invention for the production of dihydrogen (H2), from a gas mixture comprising carbon monoxide (CO) and water vapor (H2O) according to the WGS reaction.

[0107] List of cited documents [1] W. Uribe-Soto, J. -F. Portha, J.-M. Commenge, and L. Falk, "A review of thermochemical processes and technologies to use steelworks off-gases," Renew. Sustain. Energy Rev., vol. 74, no. Supplement C, pp. 809-823, Jul. 2017. [2] T. L. LeValley, A. R. Richard, and M. Fan, "The progress in water gas shift and steam reforming hydrogen production technologies - A review," Int. J. Hydrog. Energy, vol. 39, no. 30, pp. 16983-17000, Oct. 2014. [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 nonthermal plasmas: Status, mechanisms, and opportunities. Chemical Engineering Journal, https: / / doi.Org / doi:10.1016 / j.cej.2021.129544 [4] Jingjing Li, Sarayute Chansai, Christopher Hardacre and Xiaolei Fan, Non thermal plasma assisted water-gas shift reactions under mild conditions: state of the art and a future perspective, Catalysis Today, (2022) https: / / doi.Org / 10.1016 / j.cattod.2022.ll.017 [5] Amit K Jaiswal et al 2020 J. Phys. D: Appl. Phys. 53 465205, https: / / doi.Org / 10.1016 / j.cattod.2022.ll.017 [6] Wangkawong, K., Phanichphant, S., Inceesungvorn, B. et al. Kinetics of Water Gas Shift Reaction on Au / CeZrO4: A Comparison Between Conventional Heating and Dielectric Barrier Discharge (DBD) Plasma Activation. Top Catal 63, 363-369 (2020). https: / / doi.org / 10.1007 / sll244-020-01245-8 [7] Xu, S., Chansai, S., Stere, C. et al. Sustaining metal-organic frameworks for water-gas shift catalysis by non-thermal plasma. Nat Catal 2, 142-148 (2019). https: / / doi.org / 10.1038 / s41929-018-0206-2 [8] Miriam Gonzalez-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 [9] Demande de brevet US 2007 / 059235 Al - GM Global Technology Operations LLC

[0010] Demande de brevet US 2008 / 131744 Al - Tetros Innovations LLC

[0011] Brevet EP 1866083 Bl - Université of REGINA

[0012] Demande de brevet WO 2013 / 110716 Al - SGE Scandgreen Energy AB

[0013] Chen, F. F. (1984). "Introduction to Plasma Physics and Controlled Fusion." Springer. ISBN: 978-0-306-41332-9.

[0014] Fridman, A. (2008). "Plasma Chemistry." Cambridge University Press. ISBN: 978- 0521886678.

[0108] Exemples

[0109] 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.

[0110] A. Preparation of the different catalysts by wet impregnation

[0111] The various catalytic systems are prepared by wet impregnation.

[0112] Different supports were used to prepare the catalysts in Tables 1 and 2 below: 1) A commercial cerium oxide from Solvay - Nre002 (Ce); 2) A commercial aluminum oxide from Saint Gobain (AI200, Specific surface area = 200 m 2 / g); 3) A commercial cerium-zirconium mixed oxide from Sigma Aldrich (CZ); and 4) A mixed cerium-aluminium oxide of molar composition Ceo.sAlo.sCh, and synthesized by the inventors according to the method described previously.

[0113] The catalytic systems doped with the copper-based promoter, and with the other promoter(s), are prepared from an aqueous solution comprising Cu(NO3)2.3H2O (Sigma-Aldrich) and one or more promoter precursors selected from Zn(NO3)2.6H2O, AI(NO3)3.9H2O, La(NO3)2.6H2O, and Ga(NO3)2.xH2O, Fe(NO3)2.9H2O (all commercial, Sigma-Aldrich).

[0114] The salts of the precursor(s) of the promoter(s) are dissolved in a volume of water of 50 mL, at room temperature and with stirring. The appropriate mass of support is added to the aqueous solution containing the mixture of metal salts and kept stirring for 2 hours. In the case of the catalyst “10%Cu 5%Zn 3%Al / Ce” (one of the catalysts according to the invention), the content of Cu promoter is 10% by mass relative to the weight of the support, that of Zn promoter is 5% by mass relative to the weight of the support and that of Al promoter is 3% by mass relative to the weight of the support. Thus, 0.38 g of copper nitrate (which represents a content of 10% by weight of copper relative to the weight of the support), 0.227 g of zinc nitrate (which represents a content of 5% by weight of zinc relative to the weight of the support), 0.417 g of aluminum nitrate (which represents a content of 3% by weight of aluminum relative to the weight of the support) and 1 g of Ce support are mixed. The mixture is then placed in a rotary evaporator at 65°C, in order to remove excess water.

[0115] 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 samples were hand-ground and sieved to an average grain size between 50 and 200 μm.

[0116] B. Conversion of a gas mixture comprising carbon monoxide (CO) and water vapor (H2O) according to the WGS reaction in the presence of different catalysts

[0117] An example of the procedure followed for hydrogen production as disclosed in the present invention is as follows: 471 mg of “10%Cu 5%Zn 3%Al / Ce” catalyst is placed between the electrodes of the DBD reactor. A non-thermal dielectric barrier discharge (DBD) plasma is then 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 inner diameter, 1 mm thick), 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. The catalyst is then activated in situ under non-thermal DBD plasma under H2 as the discharge gas for a duration of 60 minutes.

[0118] The reactor is then fed with a mixture of gases containing carbon monoxide and water vapor. The total gas flow rate used during the process is 100 ml / min STP (Standard Temperature and Pressure) at atmospheric pressure and a temperature of 20°C, corresponding to a GHSV (Gas Hourly Space Velocity) of 17,000 h 1 The H2O / CO molar ratio is 1 / 1. The water is first propelled by an inert gas (Ar), then circulated through a mass flow controller. It is then vaporized and mixed with carbon monoxide using a controlled evaporation and mixing system (Bronkhorst CEM). The gas mixture is then transported along a heated pipe to the interior of the DBD plasma reactor.

[0119] The activity and selectivity of the different catalysts tested are measured and reported in Tables 1 and 2.

[0120] 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.

[0121] The following equations were used to estimate the catalytic performance and calculate CO conversion, H2 and CO2 selectivity: Eq.5) 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.

[0122] C. Results

[0123] 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 CO conversion and H2 and CO2 selectivity. Table 1: WGS reaction results - catalyst composition Table 2: WGS reaction results with 10%Cu 5%Zn 3%AI / Ce catalyst - plasma importance

[0124] As shown in the results of Table 2, tests 24c and 25c, 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, hydrogen production is obtained at the reactor outlet - Tables 1 and 2, tests 1 to 23. These results demonstrate the importance of the plasma-catalysis combination for the WGS conversion 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 21i and 23c in particular).

Claims

Claims

1. A process for converting a gas mixture comprising carbon monoxide (CO) and water vapor (H2O) according to the following WGS reaction: characterized in that it is carried out in the presence of a cold plasma and a catalyst comprising: - a support comprising ceria or cerium oxide, - at least one first promoter comprising copper, in metallic form or in oxidized form, and - at least one second promoter selected from the group consisting of transition metals, poor metals, lanthanides, and mixtures thereof, each being independently in metallic form or in oxidized form, said catalyst being activated by cold plasma before contacting with the gas mixture to be converted.

2. The method of claim 1, wherein the second promoter is zinc and / or aluminum, each independently in metallic form or in oxidized form.

3. A method according to either of claims 1 or 2, wherein the catalyst contains at least 2% by weight of promoter comprising copper, relative to the total weight of the support, preferably at least 5% by weight.

4. Method according to one of claims 1 to 3, 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.

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), preferably in a DBD plasma reactor.

6. A method according to any one of claims 1 to 5, wherein the molar ratio of water vapor (H2O) to carbon monoxide (CO) in the gas mixture to be converted varies between 1 and 5, preferably between 1 and 3.

7. A method according to any one of claims 1 to 6, comprising the following steps in order: a) Activation of the catalyst placed between the electrodes of a cold plasma reactor, preferably a DBD plasma reactor, by generation of cold plasma under H2 as discharge gas; b) Introduction of the gas mixture to be converted through the catalyst between the electrodes of the reactor; and c) Conversion under cold plasma of the gas mixture according to the WGS reaction by circulation of the gas flow between the electrodes of the reactor.

8. Catalyst for the conversion of a gas mixture comprising carbon monoxide (CO) and water vapor (H2O) according to the following WGS reaction: said conversion being carried out in the presence of a cold plasma and said catalyst comprising - a support comprising ceria or cerium oxide, - at least one first promoter comprising copper, in metallic form or in oxidized form, and - at least one second promoter selected from the group consisting of transition metals, poor metals, lanthanides, and mixtures thereof, each being independently in metallic form or in oxidized form, 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 catalyst comprises at least 5% by weight of promoter comprising copper, relative to the weight of the support; and / or - the catalyst comprises at least one second promoter selected from the group consisting of zinc, aluminum, and mixtures thereof, each being independently in metallic form or in oxidized form.

10. Catalyst according to any one of claims 8 or 9, comprising at least one second promoter consisting of zinc, in metallic form or in oxidized form.

11. Catalyst according to any one of claims 8 to 10, 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.

12. A catalyst according to any one of claims 8 to 11, wherein the catalyst and promoters form a homogeneous mixture.

13. Use of a catalyst and cold plasma for the conversion of a gas mixture comprising carbon monoxide (CO) and water vapor (H2O) according to the following WGS reaction: said catalyst comprising: - a support comprising ceria or cerium oxide, - at least one first promoter comprising copper, in metallic form or in oxidized form, and - at least one second promoter selected from the group consisting of transition metals, poor metals, lanthanides, and mixtures thereof, each being independently in metallic form or in oxidized form, said catalyst being activated by cold plasma before contacting with the gas mixture to be converted.

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