Method and catalyst for plasma catalytic reforming of methane

Abstract

The present invention relates to a method for the conversion of a gas or gas mixture containing methane (CH4) according to the CH4 reforming reaction (DRM or SRM), which is carried out in the presence of a low-temperature plasma and a catalyst, characterized in that the catalyst comprises a support comprising a mixture of alumina and cerium in a molar ratio of 80 / 20 to 30 / 70. It also relates to the catalyst, a method for preparing such a catalyst and their use for the conversion of a gas or gas mixture containing CH4, preferably activated by a low-temperature plasma generated by a dielectric barrier discharge (DBD), to produce high-added molecules such as hydrogen, CO, gaseous hydrocarbons, liquid hydrocarbons, aromatics, oxygenated compounds (alcohols, acids, ketones, esters, ethers, aldehydes, etc.) and / or liquid fuels.

Description

[Technical field]

[0001] The present invention relates to the field of chemical conversion, in particular the conversion of gases or mixtures of gases including hydrogen (H2), carbon monoxide (CO), gaseous and liquid hydrocarbons, in particular methane (CH4), to produce high added value molecules such as oxygenates (alcohols, acids, ketones, esters, ethers, aldehydes, etc.), aromatics, and even liquid fuels. In particular, the present invention relates to a method for converting CH4, which implements a catalytic system in the presence of low temperature plasma. The present invention also relates to said catalysts, which can be activated by low temperature plasma (e.g. generated by dielectric barrier discharge (DBD)), thereby enabling chemical conversions via plasma catalysis. The present invention also relates to a method for preparing such catalysts, and to the use of the catalysts to produce high added value molecules. [Background technology]

[0002] The huge increase in energy demand and the impact of fossil fuels on the environment have led to increased attention in the search for new energy resources. Greenhouse gas (GHG) emissions are a global environmental problem that raises concerns about human health and sustainable lifestyles in the future. If the reduction of GHG emissions is the main objective that all sectors should strive to reach, GHG capture is an effective strategy to manage GHGs, especially in the energy and industrial process sectors. Methane (CH4) is a powerful greenhouse gas. It can trap about 28 times more heat in the atmosphere than carbon dioxide (CO2) over a period of 100 years. This means that CH4 contributes significantly to climate change, despite its lower concentration in the atmosphere when compared to CO2. Therefore, the reduction or capture of CH4 emissions is important to limit global warming.

[0003] Catalytic reforming of CH4 is a process widely used in industry to convert natural gas into H2 or synthesis gas (H2 and CO). It is based on different processes, namely steam reforming of CH4 (SRM), partial oxidation of CH4 and dry reforming of CH4 with CO2 (DRM).

[0004] The majority of H2 present on the market is currently produced in industry by steam reforming (SRM) of CH4, according to Equation 1. However, steam reforming is highly endothermic. It is typically carried out at high temperatures (700°C-1,000°C), pressures in the range of 25 bar, and catalyzed by precious metal-based catalysts.

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[0005] Low-temperature dry reactions for reforming CH4 can be carried out in non-thermal plasmas, so-called cold plasmas, in which electrons are involved in carrying out chemical reactions at low temperatures. In the literature, it has been reported that these can be carried out in microwave plasma reactors, gliding arc reactors, radio frequency plasma reactors and DBD reactors (Non-Patent Document 1, Non-Patent Document 2, Non-Patent Document 3). However, the energy efficiency observed in DBD plasmas combined with catalysts is not high enough for industrial applications.

[0006] Moreover, dry reforming of CH4 (DRM) according to Equation 2 has attracted great interest due to its ability to implement a sustainable and low carbon emission process in the chemical industry and oil refining and to avoid storage defects. The chemical conversion of CH4 in the presence of CO2 can be indirect or direct. According to the indirect approach, which has been the subject of research for several decades, a mixture of CO2 and CH4 is first converted into a synthesis gas product, which is a mixture of hydrogen (H2) and carbon monoxide (CO). The synthesis gas may then be converted into liquid fuels and other oxygenated chemical products by the Fischer-Tropsch FTS process. The direct approach is more interesting because it allows the conversion of CH4 into high-value synthesis gas and liquid products in a single reaction step in the presence of CO2.

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[0007] Considering the high chemical stability of CO2 and CH4, conventional thermal catalytic processes such as dry reforming of CH4 (DRM) require high gas pressure and large amounts of energy (thermal energy), especially temperatures in the range of 700°C to 1,000°C, to promote catalyst activation, shift the thermodynamic equilibrium, and ensure acceptable yields. High-temperature catalytic reactions not only result in high energy consumption, but also in potential catalyst deactivation due to sintering of metal active sites and formation of coke on the catalyst surface. Generally, thermal processes are catalyzed by noble metals such as Ir, Pd, Pt, Rh, and Ru with stable operation and with a relatively small amount of carbon deposited on the catalyst. As an alternative to noble metals, non-noble Ni-based catalysts have the advantages of greater availability and lower cost, and have been reported to have relatively high activity for DRM (Non-Patent Document 4).

[0008] Various studies are being carried out to develop techniques for chemical synthesis by low-temperature plasma, which would allow overcoming the temperature problems mentioned above. Among these techniques, dielectric barrier discharge (DBD) has been described (Non-Patent Document 5), especially in combination with the presence of heterogeneous catalysts (plasma catalysts), and a synergistic effect between plasma and catalysts leading to better results, especially when compared to thermal catalysis (Non-Patent Documents 6, 7). Dielectric barrier discharge (DBD), a type of non-thermal plasma (NTP), is a promising technique used in various reactions. It has attracted particular attention in the use of CO2 and CH4 through the DRM process, due to the scaling possibilities, mild operating conditions, especially the ease of handling, the compactness of the system and the versatility of the process.

[0009] Various catalytic systems, plasma types, reactors and test conditions have been tested to improve the conversion and selectivity of synthesis gas products. However, the efficiency of these systems is still very low. In addition, the activity, stability and cost of the catalysts have proven unsuitable for industrial applications. Little effort has been invested in the direct approach, i.e., plasma-catalyzed synthesis of liquid chemical products (including hydrocarbons) directly from CO2 and CH4 with considerable selectivity under ambient conditions (Non-Patent Document 8).

[0010] Therefore, there is a need for a hybrid plasma catalytic process in the presence of an effective catalyst that allows the conversion reaction of a gas or mixture of gases containing CH4, for example using a hybrid low-temperature plasma-catalysis process, which allows a reduction in the energy consumption in the reaction and / or an improvement in the catalytic performance, i.e., gas conversion rate, selectivity and catalyst stability. The aim is to obtain hydrogen (H2), gaseous hydrocarbons, liquid hydrocarbons with long carbon chains and oxygenated compounds, preferably directly (in other words, in a single step from CH4). Summary of the Invention [Problem to be solved by the invention]

[0011] The object of the present invention is to provide a method for converting CH4 that meets these expectations.

[0012] The conversion method of the invention is carried out in the presence of a low-temperature plasma with a catalytic system. The catalytic system that can be activated by low-temperature plasma in particular comprises a support that is a mixture of alumina and cerium in a molar ratio comprised between 80 / 20 and 30 / 70.

[0013] The paper by KHOJA, et al. (Non-Patent Document 9) describes the preparation of the catalyst Ni / La2O3-MgAl2O4 and its use for dry reforming of methane (DRM) via DBD plasma. The paper does not describe a catalyst containing a support that is a mixture of alumina and cerium.

[0014] The article by FOO, et al. (Non-Patent Document 10) describes an alumina-based catalyst (Saint Gobain Nopro, USA) that is impregnated with the following solution: 5Co-15Ni / 80Al2O3 et 2.5Ce-5CO-15Ni / 77.5Al2O3. According to one embodiment, the catalyst may therefore contain cerium. According to this embodiment, the catalyst comprising the alumina-based support may subsequently be impregnated with a solution potentially containing cerium. Nevertheless, this article does not describe a catalyst in which cerium is found at the level of the support and is present in a molar amount of more than 20%.

[0015] The paper by NANDINI, et al. (Non-Patent Document 11) describes a catalyst of formula 13.5Ni-2K / 10CeO2-Al2O3, the support of which consists of alumina and 10% by weight of cerium, which is then co-impregnated with nickel and potassium. See paragraph 2.1. The paper does not describe a catalyst in which the support has a molar amount of cerium greater than 20% and which is an alumina / cerium mixture used in low-temperature plasma processes.

[0016] The paper by KHOJA, et al. (Non-Patent Document 12) describes the dry reforming of methane (DRM) using the catalyst γ-Al2O3-MgO. The use of cerium is not described.

[0017] The paper by SONG, et al. (Non-Patent Document 13) describes the production of synthesis gas via DBD using the catalyst Ni / γ-Al2O3. The use of cerium is not described. [Means for solving the problem]

[0018] A first object of the invention relates to a method for converting a gas or a mixture of gases containing CH4 according to a methane (CH4) reforming reaction (DRM or SRM), which is carried out in the presence of a low-temperature plasma and a catalyst, characterized in that the catalyst comprises a support comprising a mixture of alumina and cerium in a molar ratio between 80 / 20 and 30 / 70. According to one embodiment, the low-temperature plasma is a plasma generated by dielectric barrier discharge (DBD).

[0019] A second object of the invention is a catalytic system, also called catalyst, that allows the conversion of a gas or mixture of gases containing methane (CH4) according to the methane reforming reaction (DRM or SRM), for example activated by DBD plasma, which allows to overcome all the deficiencies of the prior art present in thermal processes (high temperature and pressure) allowing the production of synthesis gas (hydrogen, CO), liquid hydrocarbons, gaseous hydrocarbons, aromatics, oxygenated compounds (in particular alcohols, acids, ketones, esters, ethers, aldehydes) and / or liquid fuels, with high yields under atmospheric conditions, when compared to the works described in the prior art.

[0020] According to a preferred embodiment, the catalyst comprises: A support which is a mixture of alumina and cerium in a molar ratio of 80 / 20 to 30 / 70; Nickel, and / or at least one promoter of an alkali metal species, an alkaline earth metal species, a transition metal species, and / or a lanthanide species (including mixtures thereof).

[0021] A third object of the present invention relates to a process for preparing such a catalyst.

[0022] A fourth object of the invention relates to the use of the catalyst according to the invention for the conversion of a gas or mixture of gases containing CH4 according to a methane (CH4) reforming reaction (DRM or SRM), the conversion being carried out in the presence of a low-temperature plasma. The conversion of methane in the context of the invention allows the production of high-added-value molecules such as hydrogen (H2), CO, gaseous hydrocarbons, liquid hydrocarbons, aromatics, oxygenated compounds (alcohols, acids, ketones, esters, ethers, aldehydes) and / or liquid fuels. Effect of the Invention

[0023] The present invention overcomes all the deficiencies of the conventional thermal catalysis methods as described in the prior art, thereby making it possible to obtain high catalytic and energy efficiency, and thus large-scale application. [Brief description of the drawings]

[0024] Other characteristics, objects and advantages of the invention will become apparent from the following description, which is given by way of example only and is non-limiting, and which must be read in conjunction with the accompanying drawings, in which:

[0025] [Figure 1] PFD functional diagram of DBD plasma reactor. Plasma catalytic reactor for dry reforming of methane. Figure 1 shows the experimental setup (PFD diagram) used in an example of dry reforming (DRM) of CH4 by DBD plasma process combined with the catalyst of the present invention. [Diagram 2]GC-FID spectrum of organic liquid obtained by combining the catalytic system 8Ni5Co2K-CeAl200(50-50) with a DBD plasma catalytic reactor. Figure 2 shows the GC-FID spectrum of the liquid obtained during the reaction of CH4 with CO2 in a DBD plasma reactor combined with the catalyst 8Ni5Co2K-CeAl200(50-50). [Diagram 3] GC-MS spectrum (mass spectrometer) of organic liquid obtained by combining the catalytic system 8Ni5Co2K-CeAl200(50-50) with a DBD plasma catalytic reactor. Figure 3 shows the GC-MS spectrum of the liquid obtained during the reaction of CH4 with CO2 in a DBD plasma reactor combined with the catalyst 8Ni5Co2K-CeAl200(50-50). [Figure 4] PFD functional diagram of DBD plasma reactor. Plasma catalytic reactor for steam reforming of methane. Figure 4 shows the experimental setup (PFD diagram) used in an example of steam reforming (SRM) of CH4 by DBD plasma process combined with the catalyst of the present invention.

[0026] Table 1 shows the catalytic activity (ie conversion, selectivity) obtained for some catalysts according to the invention and comparative catalysts tested in DBD plasma in a methane dry reforming reaction (DRM).

[0027] Table 2 shows the catalytic activity (ie conversion, selectivity) obtained for some catalysts according to the invention and comparative catalysts tested in DBD plasma in a methane steam reforming reaction (SRM). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] definition

[0029] Expressions such as "from" (eg, a range of values) should be understood as including boundaries (eg, the limits of this value range).

[0030] Any description of one embodiment is applicable and interchangeable with all other embodiments of the invention.

[0031] The term "and / or" should be understood as meaning "and" and "or", for example, the term "A and / or B" should be understood as meaning either A and B, or A only, or B only.

[0032] The phrase "N, M and / or P" should be understood to mean "N and / or M and / or P."

[0033] The phrase "N, M and P" should be understood to mean "N and M and P."

[0034] When an element or component is included in and / or selected from a list of elements or components, it is to be understood that the individual element or component may be selected and combined with other individual elements, or may be selected to form a subset of two or more of the exclusively listed elements or components, and further, any element or component mentioned in the list of elements or components may be excluded from the list.

[0035] In the present invention, the term "DBD - Dielectric Barrier Discharge" refers to a discharge that occurs between two conductive elements that are separated by one or more dielectric elements.

[0036] In the present invention, the term "dielectric" refers to an electrically insulating material that makes it possible to ensure electrical insulation between the high voltage network associated with the electrodes and the electrically and thermally conductive tube grounded through the reactor. This type of electrically insulating material is also used inside a Dielectric Barrier Discharge (DBD) cell to generate a DBD plasma by promoting the accumulation of charges on the surface of this material.

[0037] As used herein, the terms "catalyst" and "catalyst system" are used interchangeably and refer to a material that promotes a chemical reaction of a reactive species (eg, a reagent fluid).

[0038] In the present invention, the term "plasma catalysis" refers to the process of conducting a plasma discharge in combination with a catalyst.

[0039] For the purposes of the present invention, the term "support" or "catalyst support" refers to a solid material or mixture of solid materials, which may be characterized in particular by the specific surface area on which the promoter is deposited.

[0040] As used herein, the term "promoter" or "catalyst promoter" refers to a solid material or mixture of solid materials added to the surface of a support material, generally in small amounts, that is intended to enhance the efficiency and performance of the catalyst.

[0041] The term "hydrogen" should be understood to mean "hydrogen" or "H2".

[0042] The term "carbon monoxide" should be understood to mean "CO."

[0043] The term "syngas" should be understood to mean "synthetic gas" or "a mixture of H2 and CO".

[0044] The term "DRM" should be understood to mean "Dry Reforming of Methane", or "dry reforming of methane", or "reforming of a mixture of gases containing methane and carbon dioxide".

[0045] The term "SRM" should be understood to mean "steam reforming of methane", or "reforming of methane with steam", or "reforming of a mixture of gases containing methane and steam".

[0046] The term "methane reforming" or "methane reforming reaction" should be understood to encompass both dry reforming of methane (DRM) and steam reforming of methane (SRM).

[0047] Of course, the present invention has been described above by way of example, and of course, those skilled in the art can make different modifications thereto without departing from the scope of the present invention.

[0048] Detailed Description of the Invention

[0049] Process for converting a gas or mixture of gases containing methane

[0050] A first object of the invention relates to a method for converting a gas or a mixture of gases comprising methane (CH4), which is carried out in the presence of a low-temperature plasma and a catalyst, characterized in that the catalyst comprises a support comprising a mixture of alumina and cerium in a molar ratio of 80 / 20 to 30 / 70, preferably containing nickel and optionally at least one promoter. According to one embodiment, the low-temperature plasma is a plasma generated by dielectric barrier discharge (DBD). In particular, the method for converting methane (CH4) according to the invention is carried out according to the CH4 reforming reaction with steam (DRM or SRM).

[0051] According to a first embodiment, the method for converting a gas or gas mixture according to the invention comprises methane (CH4) and water vapor (H2O). According to this embodiment, the method produces synthesis gas (i.e., H2 and CO), liquid oxygenated compounds and / or gaseous hydrocarbons. In particular, the method for converting methane (CH4) according to this embodiment is carried out according to the CH4 reforming reaction (SRM).

[0052] According to a second embodiment, the method for converting a gas or gas mixture according to the invention comprises methane (CH4) and carbon dioxide (CO2). This embodiment is aimed at producing high added value molecules from synthesis gas (H2, CO), liquid hydrocarbons, gaseous hydrocarbons, aromatics, oxygenated compounds (in particular alcohols, acids, ketones, esters, ethers, aldehydes) and / or liquid fuels. In particular, the method for converting methane (CH4) according to this embodiment is carried out according to the dry CH4 reforming reaction (DRM).

[0053] If a gaseous form of hydrocarbon is produced, it preferably consists of ethane, ethene, propane, propene, butane, butenes, pentane, hexane or mixtures thereof.

[0054] If alcohol is produced, it preferably comprises methanol, ethanol, propanol, butanol, phenol, isomers and / or mixtures thereof, more preferably methanol or ethanol.

[0055] If an acid is produced, it preferably comprises formic acid, acetic acid, propanoic acid, butyric acid, pentanoic acid, gallic acid or mixtures thereof, more preferably acetic acid.

[0056] If an ether is produced, it preferably comprises methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), a cyclic ether, an acyclic ether or mixtures thereof, more preferably MTBE.

[0057] If liquid hydrocarbons are produced, this will preferably consist of molecules of the aromatic type (benzene, toluene, xylenes, etc.), more complex molecules or mixtures thereof, with benzene being more preferred.

[0058] If a liquid fuel is produced, it is preferred that this consists of C7 to C15 or mixtures thereof, with diesel C12 being more preferred.

[0059] According to the invention, the method for converting CH4 is therefore carried out in the presence of a catalyst and a low-temperature plasma, preferably generated by dielectric barrier discharge (DBD). The synergistic effect of the plasma catalyst in this method shows a great possibility for the direct synthesis of high-added-value molecules, as demonstrated in the examples. The catalyst comprises a support comprising a mixture of alumina and cerium in a molar ratio of 80 / 20 to 30 / 70. Preferably, the catalyst also comprises nickel. Optionally, the catalyst comprises at least one promoter. The catalyst is used in combination with a low-temperature plasma. It is noted that all the features described in connection with the catalyst are applicable to the conversion method of the invention.

[0060] According to the invention, a method for converting a gas or a mixture of gases containing methane (CH4), in particular by CH4 reforming reaction (DRM or SRM), is characterized in that it is carried out in the presence of a low-temperature plasma and a catalyst, the catalyst comprising a support comprising or essentially consisting of a mixture of alumina and cerium in a molar ratio of 80 / 20 to 30 / 70. Preferably, the catalyst also comprises nickel.

[0061] According to one embodiment, the present invention relates to a method for converting a gas or a mixture of gases comprising methane (CH4) and carbon dioxide (CO2), which is carried out in the presence of a low-temperature plasma and a catalyst, characterized in that the catalyst comprises a support comprising or essentially consisting of a mixture of alumina and cerium in a molar ratio of 80 / 20 to 30 / 70. Preferably, the catalyst also comprises nickel.

[0062] According to another embodiment, the present invention relates to a method for converting a gas or a mixture of gases comprising methane (CH4) and water (H2O), which is carried out in the presence of a low-temperature plasma and a catalyst, characterized in that the catalyst comprises a support comprising or consisting essentially of a mixture of alumina and cerium in a molar ratio of 80 / 20 to 30 / 70, preferably also comprising nickel.

[0063] According to these two embodiments, the catalyst optionally comprises at least one promoter.

[0064] In particular, the products obtained according to these conversion processes vary according to the molar ratio between CH4, CO2 and / or steam used to carry out the conversion reaction, which can be determined by the skilled artisan according to the desired products. For example, a decrease in the CO2 / CH4 ratio generates CH3 radicals, which promotes the formation of long-chain products such as ethanol and reduces the selectivity towards methanol.

[0065] The synergistic effect of plasma catalysis in this process has proven effective for the direct synthesis of value-added synthesis gas, chemical products and liquid fuels from CO2 and CH4, or the direct synthesis of synthesis gas, chemicals and gaseous hydrocarbons from H2O and CH4, as demonstrated in the examples below.

[0066] According to one embodiment of the method of the present invention, the selected and prepared catalyst is placed between the electrodes of a DBD plasma reactor, allowing gas species to circulate through the catalyst and activated by a high voltage discharge (in the range of several kV) for a period ranging from a few nanoseconds to a few microseconds. This polarization leads to the formation of plasma and its activation and the production of hydrogen, combined with adsorption, desorption and catalyst / gas interactions. The electrical energy supplied to the fixed bed in a sinusoidal or pulsed high voltage form generates multiple currents on the HV (high voltage) carrier during positive and negative polarization. These streamers, from hundreds of picoseconds to a few tenths of a nanosecond, are responsible for the negative or positive polarization of the catalytic sites.

[0067] Prior to the step of converting the gas mixture, the catalyst according to the invention, if its components are in oxidized form, is advantageously reduced in situ under a low-temperature plasma, preferably a DBD plasma, under H2 as discharge gas.

[0068] During the process of the invention, a strong electric field is generated, which activates the catalyst, more particularly between the particles of the catalyst or in the gas stream upstream or downstream of the catalyst and in close proximity to them. This strong electric field is usually of about 10 3 ~10 10 V / m and can vary over time. This allows ionization of some gases as well as excitation of atoms and molecules present in the gas phase. The reactor walls may be made of a metal material, or alternatively, if a DBD plasma reactor is preferably used to carry out the method of the invention, the reactor walls are made of a dielectric material such as quartz, alumina or ceramic. Advantageously, the reactor may be cylindrical. In addition to the generation of the low-temperature plasma state, the strong electric field generated is responsible for the negative or positive polarization of the catalytic sites. This polarization induces adsorption and desorption reactions even at low temperatures (for example, temperatures below 450°C or below 400°C). In the absence of polarization (conventional processes), the operating temperatures are even higher, typically between 700°C and 1,000°C.

[0069] In particular, the reactor comprises at least one inlet allowing the supply of the gases to be converted, which include CH4 and CO2, or CH4 and H2O in gaseous form, and an outlet for discharging the products formed, which are in liquid and / or gaseous form.

[0070] According to one embodiment of the process of the present invention, the carbon dioxide (CO2) / methane (CH4) or water vapor (H2O) / methane (CH4) molar ratio in the gas mixture to be converted varies from 1 to 5, for example from 1 to 4, preferably from 1 to 3.

[0071] In a variant of the invention, the catalyst of the invention is activated by DBD plasma by supplying less power than 30-35 W / g of catalyst (i.e. the catalyst system present in the reactor, so-called catalyst bed).

[0072] Advantageously, the conversion reaction is carried out in a manner similar to that described for example in 1.10 4 Pa~3.10 5 Pressure between atmospheric pressure (10 Pa) 5 The conversion reaction may be carried out under pseudoadiabatic conditions, i.e. without insulation and without external heating, or under adiabatic conditions, i.e. with insulation and without external heating, or under isothermal conditions, i.e. with adiabatic and / or external heating. The DBD plasma is generated by applying a voltage between two electrodes of 1-25 kV, preferably 5-20 kV, at a frequency, in particular, of 1 kHz-100 kHz. In particular, the gas hourly space velocity (GHSV) is greater than 1,000 h -1 ~150,000h -1 Preferably for 100,000 hours -1 is less than.

[0073] Optionally, a cooling system is present between the vessel intended to receive the products resulting from the conversion reaction and the outlet of the reactor for condensing and removing liquid products that may be formed during the conversion reaction.

[0074] Catalytic system or catalyst according to the invention

[0075] A second object of the present invention relates to a catalyst for the conversion of a gas or mixture of gases containing methane (CH4), the conversion being carried out in the presence of a low-temperature plasma, the catalyst comprising a support comprising a mixture of alumina and cerium in a molar ratio between 80 / 20 and 30 / 70, in particular the conversion being carried out according to the CH4 reforming reaction (DRM or SRM).

[0076] Preferably, the catalyst of the present invention does not contain any precious metals such as ruthenium (Ru), iridium (Ir), palladium (Pd), platinum (Pt) or rhodium (Rh).

[0077] The catalyst of the present invention may be activated by low temperature plasma during the performance of the process of the present invention.

[0078] According to one embodiment of the present invention, the catalyst comprises: a support comprising a mixture of alumina and cerium in a molar ratio of 80 / 20 to 30 / 70; - Nickel, - optionally at least one promoter, for example a promoter of the alkali metal, alkaline earth metal, transition metal and / or lanthanide type, i.e. a promoter comprising at least one chemical element belonging to the alkali metal, alkaline earth metal, transition metal and / or lanthanide classes (including mixtures thereof), Includes.

[0079] According to another embodiment of the present invention, the catalyst comprises: a support comprising a mixture of alumina and cerium in a molar ratio of 80 / 20 to 30 / 70; and -nickel, It essentially consists of: According to this embodiment, the catalyst does not include any promoter.

[0080] According to a preferred embodiment, the catalyst comprises: a support comprising a mixture of alumina and cerium in a molar ratio of 80 / 20 to 30 / 70; - Nickel, at least one promoter, such as a promoter of the alkali metal, alkaline earth metal, transition metal and / or lanthanide type, i.e. a promoter comprising at least one chemical element belonging to the alkali metal, alkaline earth metal, transition metal and / or lanthanide classes (including mixtures thereof); Includes.

[0081] The catalyst system is characterized in that the support comprises a mixture of alumina and cerium. According to one embodiment, the support consists essentially of a mixture of alumina and cerium. For example, it comprises a cerium-modified alumina.

[0082] In the context of the present invention, the terms "catalyst system" and "catalyst" are interchangeable. According to one embodiment of the present invention, the catalyst system is a so-called monometallic / bimetallic / trimetallic catalyst system. It should be noted that the concepts monometallic, bimetallic and trimetallic relate to the species present in the catalyst, without taking into account the support and nickel used in particular. For example, if the catalyst is doped with a promoter in addition to nickel, we speak of a monometallic catalyst. If the catalyst is doped with two promoters in addition to nickel, we speak of a bimetallic catalyst. If the catalyst is doped with three promoters in addition to nickel, we speak of a trimetallic catalyst.

[0083] In particular, the support used in the context of the present invention is selected for its ability to adsorb reagents, more particularly CO2, for its thermal stability and for its optimized specific surface area, which is intended to promote a plasma-catalyst interface that allows the provision of various reaction pathways in the surface chemistry, and also for its dielectric properties, which affect the properties of the plasma and modify the discharge behavior, electric field and electron density of the DBD plasma, due to the dielectric constant and polarization effects that give rise to local electric fields.

[0084] According to the invention, the support of the catalyst comprises a mixture of alumina and cerium, in particular formed by this mixture or consisting of this mixture. More specifically, the support according to the invention comprises a mixture of alumina and cerium, in particular the mixed oxide AlCe, with an alumina / cerium (Al / Ce) molar ratio of 80 / 20 to 30 / 70. For example, the alumina / cerium (Al / Ce) molar ratio is 75 / 25 to 35 / 65, 73 / 28 to 40 / 60, or 71 / 29 to 42 / 58. For example, the alumina / cerium ratio may be about 70 / 30±1. According to this embodiment, the Al / Ce molar ratio influences the physicochemical properties (basicity, acidity, reducibility, oxygen transfer, etc. due to the presence of inherent defects present on the surface) and the textural properties (pore volume, pore size, specific surface area, etc.) and the electrical properties (dielectric constant, electrical conductivity, etc.), thus modulating the catalytic performance of the system. The inventors have noted that the presence of cerium in the crystalline network of alumina allows for a large amount of defects at the support surface, which facilitate oxygen transfer at the surface of the support, thereby resulting in improved catalytic performance.

[0085] According to one embodiment, the support consists of a mixture of alumina oxide, for example Al2O3, and cerium oxide, CeO2.

[0086] In the context of the present invention, alumina is any specific surface area (BET surface area m 2 For example, the specific surface area of ​​alumina may be at least 20 m 2 / g, especially 50 to 1,000m 2 For example, the specific surface area of ​​alumina may vary between 200 m 2 / g or 260m 2 According to one embodiment of the present invention, the catalyst has a molecular weight of 50 to 1,000 m 2 / g, 100-800m 2 / g, 150-300m 2 / g or 180~250m 2 The support includes an alumina-containing support having a specific surface area that varies in .mu.m / g.

[0087] When the catalyst comprises nickel, the latter may be in any of its oxidation states, in particular in metallic form (under its oxidation state 0) or in oxidic form under its oxidation state II (for example in the form of nickel(II) oxide (NiO)). Advantageously, the mass content of nickel in the catalyst may vary between 0.1% and 50% by weight, for example between 1% and 40% by weight, or between 2% and 30% by weight, relative to the weight of the support, being less than 25% or less than 20%. By "weight of the support", it is to be understood that this is the "weight of the support including alumina", including when the support comprises elements other than alumina. In a particularly advantageous manner, the catalytic system comprises about 8% ± 1% by weight, or 10% ± 1% by weight, of nickel relative to the weight of the support.

[0088] By convention, a catalyst containing 8% nickel by weight based on the weight of the support containing alumina and cerium is designated as "8Ni-CeAl", "8Ni-CeAl" or "8Ni-CeAl".

[0089] According to one embodiment, the present invention relates to a low-temperature plasma activated catalyst.

[0090] The combination of the catalyst according to the invention with low-temperature plasma allows the production of high-added molecules such as hydrogen (H2), CO and gaseous and liquid hydrocarbons, especially oxygenates (alcohols, acids, ketones, esters, ethers, aldehydes), aromatics and heavy fuels such as diesel during the conversion, especially the reforming of gases containing CH4, for example a gas mixture containing 1 / CH4 and CO2, possibly CO and H2, or for example a gas mixture containing 2 / CH4 and H2O, possibly CO and H2. The catalytic performance of the reaction, i.e. the conversion of CO2 and / or CH4, and / or the selectivity of the desired products (liquid fuels and / or synthesis gas), are improved. In particular, the combination of the catalyst according to the invention / low-temperature plasma advantageously allows the production of such molecules in a single step from CH4.

[0091] According to one embodiment, the catalyst system according to the invention does not contain any promoter.For example, an example of the catalyst according to the invention without promoter is a catalyst Ni-CeAl, i.e. a mixture of Ce and Al, and a catalyst containing a support containing Ni.More specifically, it can be a catalyst 10Ni-CeAl(50-50), i.e. a support with a molar ratio of alumina / cerium (Al / Ce) of (50 / 50) and a catalyst containing 10% by weight of Ni relative to the weight of the support, which is a support CeAl.

[0092] According to another embodiment, the catalytic system according to the invention comprises at least one promoter, i.e. one or more promoters, which act as dopants and influence the physicochemical, textural and conductive properties of the catalytic system. Advantageously, the promoter according to the invention has favorable surface physicochemical properties that aid in the immobilization of the reagents and favorable dielectric properties that allow to improve the electrical conductivity of the system obtained and that logically give rise to the production of CH3 radicals from CH4, thereby promoting the formation of long-chain carbon products (long-chain oxygenated species and especially long-chain liquid hydrocarbons).

[0093] Thus, in the context of the present invention, the at least one promoter is selected from the group consisting of alkali metals, transition metals and alkaline earth metals, lanthanides and mixtures thereof, and more particularly may comprise a chemical element selected from the group consisting of alkali metals such as potassium (K), transition metals such as cobalt (Co), copper (Cu), zinc (Zn), manganese (Mn), yttrium (Y) and iron (Fe), alkaline earth metals such as magnesium (Mg), lanthanides such as yttrium or lanthanum (La), and mixtures thereof. In the context of the present invention, the promoter is in any one of its oxidation states, in particular in metallic or oxidic form.

[0094] In the context of the present invention, the alkali metal may be selected from the group consisting of lithium, sodium, potassium, rubidium, cesium and furan. When the promoter comprises a chemical element which is an alkali metal, the latter is preferably potassium (K) or cesium (Cs), and even more preferably potassium (K).

[0095] In the context of the present invention, the transition metal may be selected from the group consisting of copper, cobalt, silver, iron, zinc, manganese, vanadium, manganese, chromium, yttrium, titanium and tantalum. When the promoter comprises a chemical element which is a transition metal, the latter is preferably cobalt (Co) or iron (Fe), even more preferably cobalt (Co).

[0096] In the context of the present invention, the alkaline earth metal may in particular be selected from the group consisting of magnesium, barium, calcium and strontium. When the promoter comprises a chemical element which is an alkaline earth, the latter is preferably magnesium (Mg).

[0097] In the context of the present invention, the lanthanides may be selected from the group consisting of lanthanum, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. When the promoter comprises a chemical element which is a lanthanide, the latter is preferably yttrium (Y) or lanthanum (La), and even more preferably yttrium (Y).

[0098] According to one embodiment of the present invention, the promoter of the catalyst is selected from the group consisting of potassium (K), cesium (Cs), cobalt (Co), iron (Fe), magnesium (Mg), yttrium (Y), lanthanum (Ia), manganese (Mn) and mixtures thereof. More preferably, the promoter is selected from the group consisting of potassium (K), cobalt (Co), iron (Fe), yttrium (Y) and mixtures thereof.

[0099] According to one embodiment of the invention, the mass content of promoter in the catalyst varies between 0.1% and 40% by weight, for example between 0.2% and 30% by weight, in particular between 0.5% and 25% by weight, preferably between 1% and 20% by weight, in particular between 1% and 15% by weight, even more preferably between 1% and 9% by weight, relative to the weight of the support.

[0100] The promoters used to prepare the catalysts of the invention are in any oxidation state, in particular in metallic or oxidic form. They can therefore contain other chemical elements, which are not taken into account in the calculation of the claimed mass contents. For example, for the catalyst 8Ni2K-CeAl, 1 g of support containing nickel is used, then 0.051 g of promoter KNO3 (molar mass: 101.1 g / mol) is used. This corresponds to 0.02 g of K (molar mass: 39.1 g / mol), i.e. 2% by weight of potassium relative to the weight of the support. For this catalyst, the mass content of the promoter (there is only one in this example, the "K promoter") is 2% by weight relative to the weight of the support.

[0101] The amount of nickel and / or promoter may be adjusted according to the nature of the promoter used and / or the type of conversion reaction being carried out, i.e. according to the type of products resulting from the conversion reaction (in particular for reforming methane to synthesis gas and / or hydrocarbons).

[0102] According to one embodiment of the invention, the catalyst according to the invention is monometallic, i.e. it comprises a single promoter in addition to nickel. In particular, according to a preferred embodiment, the catalyst according to the invention comprises a single promoter comprising potassium (K). For example, the potassium chemical element may be introduced into the catalyst in the form of a precursor, for example in the form of potassium nitrate KNO3. More particularly, it may consist of the catalyst 8Ni2K-CeAl(30-70), i.e. a catalyst comprising a support with an alumina / cerium (Al / Ce) molar ratio of (70 / 30) and 8% by weight of Ni and 2% by weight of potassium (K) promoter relative to the weight of the support CeAl.

[0103] According to one embodiment of the invention, the catalyst according to the invention comprises at least two promoters in addition to nickel, i.e. more than one promoter, for example two promoters (which in this case consist of two metals) or three promoters in addition to nickel (which in this case consist of three metals).

[0104] According to a particular embodiment, the catalyst is bimetallic doped with two promoters in addition to nickel, one of which is potassium (K) whose mass content in the catalytic system is preferably 2% ±0.2% by weight relative to the weight of the support, while the second cobalt (Co) promoter has a mass content in the catalytic system of preferably about 5% ±0.5% by weight relative to the weight of the support. More particularly, it may consist of the catalyst 8Ni5Co2K-CeAl(30-70), i.e. a support with an alumina / cerium (Al / Ce) molar ratio of (70 / 30) and a catalyst comprising 8% by weight of Ni and 2% by weight of potassium (K) promoter and 5% by weight of cobalt (Co) promoter relative to the weight of the support.

[0105] The catalyst system may be in various forms (beads, monoliths, powders, etc.). In the case of powders, the particles forming the powder have an average diameter of, for example, 1 μm to 1 mm, for example 100 μm to 1 mm, in particular 200 μm to 800 μm, preferably about 600 μm ± 20 μm. In particular, the diameter of the particles may be adapted according to the production scale used. The catalyst system may also be in the form of beads (in particular by compaction of the powder in a mold) with an average diameter of less than 5 cm.

[0106] According to one embodiment of the present invention, the alumina / serine support, nickel and optionally the promoter form a homogeneous mixture, meaning that the nickel and the promoter are uniformly distributed throughout the volume of the catalyst.

[0107] According to a preferred embodiment of the present invention, the catalyst comprises a support comprising a mixture of alumina and cerium in a molar ratio of 80 / 20 to 30 / 70; - Nickel, at least one promoter selected from the group consisting of potassium (K), cesium (Cs), cobalt (Co), iron (Fe), magnesium (Mg), yttrium (Y), lanthanum (La) and mixtures thereof, preferably potassium (K) or a mixture of potassium (K) and cobalt (Co), Includes.

[0108] Method for preparing the catalyst system

[0109] The preparation of the catalyst system according to the invention may be carried out according to different processes.

[0110] According to a first variant, the catalytic system is prepared by contacting the support with a nickel precursor and at least one precursor of the promoter(s). This step makes it possible to form a solid comprising the support, nickel and the promoter(s). This contacting step can optionally be carried out by: - preceded by a step of modifying the carrier; and / or followed by a step of calcining the mixture thus obtained, optionally followed by a step of reducing the calcined mixture.

[0111] The calcination step results in the oxidation of the different components of the catalytic system (support, nickel and promoter). This optional calcination step is then optionally followed by a reduction step in order to change the oxidation state of the nickel and promoter (with nickel and metal promoter) and possibly the oxidation state of the support. The reduction may be complete or partial, i.e. only some of the components of the catalytic system may be reduced. The reduction step may be carried out in situ in a non-thermal plasma under hydrogen.

[0112] The step of contacting the support with the nickel precursor and the promoter precursor may be carried out, for example, by impregnation or co-precipitation.

[0113] The nickel precursor and the precursor of the promoter may be any compound or mixture of compounds containing the metal used as active metal / promoter, more particularly the salt of the metal, the oxide of the metal or a mixture thereof, preferably the salt of the metal or a mixture of the salts of the metal. For example, the salt of the metal (meaning the non-hydrated or hydrated, polyhydrated salt) may be selected from the chloride, nitrate, carbonate, acetate, acetylacetonate, tartrate and citrate of the metal and mixtures thereof, preferably the nitrate of the metal. If the promoter is a mixture of several metals, the precursor may be a mixture of different salts and / or oxides of these metals.

[0114] According to a first embodiment, the method for preparing the catalytic system comprises step 1) of preparing a support and step 2) of contacting the support with a nickel precursor and at least one precursor of a promoter. According to this embodiment, the contacting is carried out by impregnation. More specifically, according to this embodiment, the method comprises the following steps:

[0115] 1) Preparation of the carrier: a) Preparation of an aqueous solution containing a cerium precursor and an alumina oxide or containing a cerium precursor and an alumina precursor. In step a), the support precursor corresponds to a cerium precursor, an alumina precursor or a mixture of two cerium and alumina precursors. When the support is a mixture of cerium and alumina, in particular a mixed oxide, the cerium precursor solution and the alumina precursor solution are advantageously prepared separately and then mixed in a ratio making it possible to obtain the desired Al / Ce molar ratio in the mixture of cerium and alumina, in particular in the mixed final oxide. b) Mixing the suspension obtained from step a), in particular adding these precursors at room temperature, in particular at 20-25° C. with continuous mixing, in particular for 30 minutes to several hours, for example 30 minutes to 3 hours. c) recovery of the solid obtained in step b) by removal of excess water, in particular by evaporation or filtration of the water, followed by drying of the solid obtained. For example, the drying step may be carried out at a temperature below 150° C., usually at a temperature of about 100° C., for a period ranging from 7 h to 48 h. d) Calcination of the solid obtained from step c) to obtain the support. The product obtained from step c) is then calcined at a temperature, for example between 300° C. and 600° C. This calcination step may be carried out for a period of 3 hours or more, for example ranging from 3 hours to 6 hours, which results in the thermal decomposition of the nitrates to obtain the oxides.

[0116] 2) Contact a) preparing an aqueous solution comprising a nickel precursor and one or more precursors of a promoter; b) adding the carrier obtained from 1) to the aqueous solution obtained from step a) to obtain a suspension; During step a), an appropriate mass of each precursor was added to an appropriate volume of solvent (e.g. water). By "appropriate mass" and "appropriate volume" one should understand suitable amounts of precursor and solvent (especially water) to obtain the desired mass contents of nickel and promoter in the final catalyst system. c) mixing the suspension obtained from step b); In particular, the addition of these precursors is carried out at room temperature, in particular at 20-25° C. with continuous mixing, in particular for 30 minutes to several hours, for example 30 minutes to 3 hours. d) recovery of the solid comprising the support, nickel and promoter obtained in step b) by removing excess water, in particular by evaporation or filtration of the water, followed by drying of the solid obtained. For example, the drying step may be carried out at a temperature below 150° C., typically at a temperature of about 100° C., for a period ranging from 7 hours to 48 hours. e) Calcination of the solid obtained from step d) to obtain the so-called catalytic system. The product obtained from step c) is then calcined at a temperature, for example between 300° C. and 600° C. This calcination step may be carried out for a period of 3 hours or more, for example ranging from 3 hours to 6 hours, which results in the thermal decomposition of the nitrates to obtain the oxides.

[0117] This first embodiment is also called the wet impregnation process. It consists of impregnation of the support with a nickel precursor and a precursor of the promoter.

[0118] According to a second embodiment, a method for preparing a catalyst system comprises the steps of preparing a support and contacting the support with a nickel precursor and a promoter, the contacting being carried out by co-precipitation, and comprises the steps of:

[0119] a') Preparation of an aqueous solution containing the nickel precursor and the promoter precursor (this step is identical to step 2a) of the wet impregnation process). b') Addition of a support to the solution obtained from step a') to obtain a suspension (this step is identical to step 2b) of the wet impregnation process). c') Addition of a base to the suspension obtained from step b'). During this step, a base is added to the suspension obtained from step b'). Advantageously, this base is a hydroxide salt, such as sodium or potassium hydroxide, or potassium carbonate, and in particular sodium hydroxide. It may be used in the form of a solution, in particular an aqueous solution. The base is slowly added dropwise until the pH of the suspension (consisting of the solids in suspension, which is a solution) is equal to between 8 and 12, preferably about 10. Advantageously, step c') is carried out at a temperature between 60°C and 100°C, in particular between 70°C and 90°C, preferably equal to about 80°C. d') mixing of the suspension obtained from step c'), the purpose of which is to precipitate the hydroxides of the metals used as promoters on the surface of the nickel hydroxide and of the support. Advantageously, the mixing, in particular the mixing by stirring, is carried out at a temperature equal to 60°C to 100°C, preferably about 80°C. This mixing step may be carried out for a period of more than 2 hours, usually about 3 hours. e') Recovery and calcination of the solid comprising the support, nickel and promoter obtained in step d' to obtain the so-called catalytic system (this step is identical to step 2e) of the wet impregnation process). This method makes it possible to precipitate the hydroxides of the metals used as promoters on the surface of the nickel hydroxide and the support.

[0120] Use of the catalyst according to the invention

[0121] The invention also relates to the use of a catalyst in the presence of a low-temperature plasma for the conversion of a gas or a mixture of gases containing CH4 by a CH4 reforming reaction (DRM or SRM), said catalyst comprising a support which is a mixture of alumina and cerium in a molar ratio of 80 / 20 to 30 / 70. According to one embodiment, the low-temperature plasma is a plasma generated by dielectric barrier discharge (DBD).

[0122] In particular, the present invention relates to the use of the catalyst of the present invention in combination with low temperature plasma for the conversion of a gas mixture comprising methane (CH4) and water vapor (HO) via a steam reforming reaction (SRM) intended to produce synthesis gas, oxygenated liquid compounds and / or gaseous hydrocarbons.

[0123] The present invention also relates to the use of the catalyst of the present invention in combination with low-temperature plasma for the conversion of gas mixtures comprising methane (CH4) and carbon dioxide (CO2) by dry reforming of methane (DRM) with the aim of producing high added value molecules such as synthesis gas (hydrogen, CO), liquid hydrocarbons, gaseous hydrocarbons, aromatics, oxygenated compounds (in particular alcohols, acids, ketones, esters, ethers, aldehydes) and / or liquid fuels.

[0124] Indeed, the inventors have realised that the combination of a catalyst according to the invention with a low temperature plasma, preferably a plasma generated by a dielectric barrier discharge (DBD), has shown increased efficiency for converting gas mixtures containing methane by the methane reforming reaction (DRM or SRM). [Prior art documents] [Non-patent literature]

[0125] [Non-Patent Document 1] M.Boudjeloud, A.Boulahouache, C.Rabia, N.Salhi, La-doped supported Ni catalysts for steam reforming of methane, International Journal of Hydrogen Energy, Volume 44, Issue 20, 2019, Pages 9906-9913, ISSN 0360-3199, https: / / doi.org / 10.1016 / j.ijhydene.2019.01.140 Non-Patent Document 2 Qi Wang, Huiliang Shi, Binhang Yan, Yong Jin, Yi Cheng, Steam enhanced carbon dioxide reforming of methane in DBD plasma reactor, International Journal of Hydrogen Energy, Volume 36, Issue 14, 2011, Pages 8301-8306, ISSN 0360-3199, https: / / doi.org / 10.1016 / j.ijhydene.2011.04.084 Non-Patent Document 3 Xiaobing Zhu, Xiaoyu Liu, Hao-Yu Lian, Jing-Lin Liu, Xiao-Song Li, Plasma catalytic steam methane reforming for distributed hydrogen production, Catalysis Today, Volume 337, 2019, Pages 69-75, ISSN 0920-5861, https: / / doi.org / 10.1016 / j.cattod.2019.05.015 Non-Patent Document 4 C. Shi, S. Wang, X. Ge, S. Deng, B. Chen, et al. J. Shen, ‘‘A review of different catalytic systems for dry reforming of methane: Conventional catalysis-alone and plasma-catalytic system’’, J. CO2 Util., vol. 46, p. 101462, Apr. 2021, https: / / doi.org / 10.1016 / j.jcou.2021.101462 [Non-Patent Document 5] H. Puliyalil, D. Lasic Jurkovic, V. D. B. C. Dasireddy, et al. B. Likozar, ‘‘A review of plasma-assisted catalytic conversion of gaseous carbon dioxide and methane into value-added platform chemicals and fuels’’, RSC Adv., vol. 8, no 48, p. 27481-27508, 2018, https: / / doi.org / 10.1039 / C8RA03146K [Non-Patent Document 6] M. Mikhail et al., ‘‘Tailoring physicochemical and electrical properties of Ni / CeZrOx doped catalysts for high efficiency of plasma catalytic CO2 methanation’’, Appl. Catal. B Environ., vol. 294, p. 120233, Oct. 2021, https: / / doi.org / 10.1016 / j.apcatb.2021.120233 [Non-Patent Document 7] M.Mikhail et al.,''Electrocatalytic behavior of CeZrOx-supported Ni catalysts in plasma assisted CO2 methanation'',Catal Sci Technol,vol

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[0126] The invention will now be described in more detail with reference to the following examples, the purpose of which is illustrative and is not intended to limit the scope of the invention.

[0127] A. Preparation of different catalysts by wet impregnation

[0128] Several supports were used to prepare the various catalysts in Tables 1 and 2 below. 1) Commercially available alumina oxide (TH, specific surface area = 80 m 2 / g,Sasol), 2) Commercially available alumina oxide (Al200, specific surface area = 200 m 2 / g,Saint Gobain), 3) Commercially available alumina oxide (Al260, specific surface area = 260 m 2 / g,Saint Gobain), 4) Commercially available silica oxide (Si160, specific surface area = 160 m 2 / g,Saint Gobain), 5) Cerium-aluminium (CeAl) mixed oxides of different molar compositions, synthesized by the inventors according to the method described above.

[0129] The catalyst is prepared by two successive impregnation sequences: a first wet impregnation for the preparation of an alumina support modified with ceria according to method 1) above until the calcination step. After calcination, a new step of impregnation with only nickel and promoters is carried out on the catalyst system obtained from the first impregnation.

[0130] Catalysts with nickel doped with promoter (metal M) were prepared by a method from an aqueous solution of Ni(NO3)2.6H2O (Sigma-Aldrich) and one or more promoter precursors selected from among Cu(NO3)2.3H2O, Co(NO3)2.6H2O, Mn(NO3)2.4H2O, La(NO3)2.6H2O, Y(NO3)2.6H2O, Fe(NO3)2.9H2O, Mg(NO3)2.6H2O, Zn(NO3)2.6H2O, NaNO3 and KNO3 (all commercially available, Sigma-Aldrich) depending on the desired promoter.

[0131] For example, for the preparation of catalyst 8Ni5Co2K-CeAl (one of the preferred catalysts of the present invention), the nickel content is 8% by weight relative to the weight of the support, the promoter Co content is 5% by weight relative to the weight of the support, and the promoter K content is 2% by weight relative to the weight of the support. The promoter-free catalyst 10Ni-CeAl was prepared as an inventive example according to the present invention.

[0132] A suitable mass of nickel salt and a suitable mass of promoter precursor are dissolved in water with a volume of 50 mL at room temperature and under stirring. A suitable mass of carrier is added to the aqueous solution containing the mixture of metal salts and kept stirring for 2 hours. For example, for the preparation of catalyst 8Ni5Co2K-CeAl, 0.396 g of nickel nitrate (content of 8 wt%), 0.155 g of cobalt nitrate (content of 5 wt%), 0.052 g of potassium nitrate (content of 2 wt%) and 1 g of carrier are mixed according to the above procedure. Then, to remove excess water, the mixture is placed in a rotary evaporator at 65°C for 2 hours.

[0133] After impregnation and evaporation of water, all samples were collected and dried in an oven at 100 °C for 8 h. They were then calcined in air at 550 °C for 4 h with a temperature gradient of 10 °C / min. After calcination, the catalyst system samples were hand-ground and screened to an average particle size of 50-200 μm.

[0134] Different catalysts prepared according to the above method are listed in Tables 1 and 2 below.

[0135] B. Conversion of gases or gas mixtures containing CH4 in the presence of different catalytic systems

[0136] Dry Methane Reforming (PRM) Reaction

[0137] The procedure for producing hydrocarbons and liquid hydrocarbons by catalytic plasma reactor is as follows: 17,000h -1 357 mg of the catalyst to be tested, corresponding to a GHSV (space velocity) of 1000 s, were placed between the electrodes of a DBD reactor, which was fed with a mixture of methane and carbon dioxide (50% CO2 by volume) at a total flow rate of 120 mL / min STP (standard temperature and pressure) (60 mL / min STP CO2 and 60 mL / min STP CH4) at atmospheric pressure and a temperature of 20 °C.

[0138] Steam methane reforming (SRM) reaction

[0139] The procedure for producing hydrogen and gaseous hydrocarbons by catalytic plasma reactor is as follows: 400 mg of the tested catalyst, 2,000 h -1A total flow rate of 150 mL / min STP (standard temperature and pressure) (75 mL / min STP H2O and 75 mL / min STP CH4) at atmospheric pressure and a temperature of 20° C., corresponding to a GHSV (space velocity) of 10 ...

[0140] A non-thermal dielectric barrier discharge (DBD) plasma was generated between two electrodes: a copper cylindrical electrode placed inside an alumina tube (diameter 3 mm) surrounded by a quartz coaxial tube (inner diameter 10 mm, thickness 1 mm) and a steel wire wrapped around the outer surface of the quartz tube acting as a ground electrode (grounded via an external capacitor of 2 nF). In this configuration, the discharge was maintained in a space of 2.5 mm over a length of about 1 cm. Prior to catalytic testing, the synthesized catalytic system was reduced in situ under non-thermal DBD plasma for a period of 60 min under H2 as the discharge gas.

[0141] The activity and selectivity of catalysts with and without promoters under DBD plasma conditions are evaluated in an experimental setup comprising a quartz tubular cylindrical reactor, a DBD plasma generator and corresponding equipment for gas supply and analysis. A schematic diagram of the DBD plasma setup is shown in Figure 1 (DRM) and Figure 4 (SRM).

[0142] In the absence of plasma, no change in the composition of the outlet gas is observed. After the plasma is ignited and stabilized, production of synthesis gas and liquid / gaseous hydrocarbons is obtained at the outlet.

[0143] The following Equations 3-8 were used to evaluate the catalytic performance and calculate the CO2 conversion, CH4 conversion, H2 and CO selectivity.

number

number

number

number

number

number

[0144] C. Results

[0145] Table 1 below indicates the catalysts tested and gives the results of catalytic activity obtained in terms of conversion, selectivity and yield of a gas mixture containing CH4 and CO2 (DRM). Figures 2 and 3 show the GC-FID and GC-MS spectra of the organic liquid obtained by combining, respectively, the catalytic system 8Ni5Co2K-CeAl200(50-50) with the DBD plasma catalytic reactor. These figures confirm the presence of acetic acid, acetone, a molecule with molar mass = 77 g / mol representing a phenyl group, a molecule with 12 carbons (MM = 140 g / mol) and molecules larger than C12 with MM = 207, 213 and 281. The density of the obtained organic liquid is 920 kg / m 3 is equal to.

[0146] It can be seen that the catalysts 8Ni2K-CeAl200 according to the invention 8i, 13i and 18i, having Al / Ce molar ratios in the range of 80 / 20 to 30 / 70, have better catalytic yields for CH4 and CO2 conversion when compared to catalysts without cerium (8Ni2K-Al200 Comparative Test 7c) or with cerium outside the claimed molar ratios (Comparative Tests 17c, 19c and 20c). Indeed, the catalytic yields for CH4 and CO2 conversion of the catalysts according to the invention are significantly higher than 50%, while the catalytic yields of the comparative catalysts are all below 50%.

[0147] Therefore, it is necessary to meet the trade-off between the molar amount of alumina and the molar amount of cerium in the support of the catalyst system to obtain better conversion yields of CH4 and CO2.

[0148] Furthermore, it is noted that catalyst 8Ni2K-CeAl200 (with Al / Ce molar ratios below 30 / 70 in the table above, molar ratios of 20 / 80 (test 19c) and 10 / 90 (test 20c)) did not allow the production of high added value liquids.

[0149] Although not specified in Table 1 below, the catalysts of the present invention, 5Ni5Co-CeAl200(30-70) (Al / Ce=70 / 30) in Test 14i and 8Ni5Co2K-CeAl200(50-50) in Test 15i, allow the production of large amounts of liquids. Therefore, these catalysts with cobalt promoters are very effective for a direct approach to DRM conversion in a single step.

[0150] Despite this high performance catalyst result, it was not possible to obtain liquid with catalyst 10Ni5Ce-Al200 of test 3c, in which there was no cerium mixed with the alumina support. [Table 1]

[0151] Table 2 below lists the catalysts tested and the catalytic activity results obtained in terms of conversion, selectivity and yield of a gas mixture containing CH4 and H2O (SRM). [Table 2]

Claims

1. Methane (CH ４ ) CH according to the reforming reaction ４ 1. A process for converting a gas or a mixture of gases comprising:

2. The catalyst is Nickel, and / or at least one promoter selected from the group consisting of alkali metals, alkaline earth metals, transition metals, lanthanides, and mixtures thereof; The method of claim 1 further comprising:

3. The at least one promoter is Accelerators of the alkaline type, more particularly containing potassium (K), a promoter comprising one of the transition metal species, more particularly cobalt (Co), copper (Cu), zinc (Zn), manganese (Mn), yttrium (Y), iron (Fe) or mixtures thereof; a promoter comprising said alkaline earth metal species, more particularly magnesium (Mg), and / or A promoter of the lanthanide type, more particularly comprising yttrium, lanthanum (La) or mixtures thereof. The method of claim 2 , wherein

4. 4. The process according to claim 2 or 3, wherein the mass content of the promoter in the catalytic system varies from 0.1% to 40% by weight, preferably from 0.5% to 25% by weight, relative to the weight of the support.

5. 5. The process according to any one of claims 2 to 4, wherein the mass content of nickel in the catalytic system varies between 0.1% and 50% by weight, preferably less than 30% by weight, relative to the weight of the support.

6. The method according to any one of claims 1 to 5, wherein the low temperature plasma is generated by dielectric barrier discharge (DBD).

7. According to the dry methane reforming (DRM) reaction, methane (CH ４ ) and carbon dioxide (CO ２ 7. The method according to claim 1 for the conversion of a gas mixture comprising toluene, toluene, toluene- ...

8. According to the steam methane reforming (SRM) reaction, methane (CH ４ ) and water vapor (H ２ 7. The method according to claim 1 for converting a gas mixture comprising oxygen, a volatile organic compound ...

9. The CH ４ Methane (CH ４ 1. A catalyst for converting a gas or gas mixture containing cerium, the catalyst comprising a support comprising a mixture of alumina and cerium in a molar ratio of from 80 / 20 to 30 / 70.

10. 10. The catalyst of claim 9, wherein the catalyst is activated by low temperature plasma, preferably generated by dielectric barrier discharge (DBD).

11. Nickel, and / or at least one promoter selected from the group consisting of alkali metals, alkaline earth metals, transition metals, lanthanides, and mixtures thereof; The catalyst of claim 9 or 10, further comprising:

12. The at least one promoter is of the alkaline species, more particularly potassium, and / or of the transition metal species, more particularly selected from the group consisting of cobalt, copper, iron, yttrium and mixtures thereof The catalyst of claim 11, wherein

13. Catalyst according to claim 11 or 12, according to which the mass content of said promoter in the catalytic system varies from 0.1% to 40% by weight, preferably from 0.5% to 25% by weight, relative to the weight of the support.

14. Catalyst according to any one of claims 11 to 13, according to which the mass content of nickel in the catalytic system varies between 0.1% and 50% by weight, preferably less than 30% by weight, relative to the weight of the support.

15. Methane (CH ４ ) CH according to the reforming reaction ４ 15. Use of a catalyst according to any one of claims 9 to 14 for the conversion of a gas or mixture of gases comprising:

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