Method and catalysts for plasma-catalytic reforming of methane

Abstract

The present invention relates to a method for converting a gas or a gas mixture comprising methane (CH4), according to the CH4 reforming reactions (DRM or SRM), characterised in that it is carried out in the presence of cold plasma and a catalyst, such as a nickel-based catalyst, said catalyst comprising a support comprising a mixture of alumina and cerium in a molar ratio of between 80 / 20 and 30 / 70. It also relates to said catalyst and to the use thereof for converting a gas or a gas mixture comprising CH4, activated by cold plasma, preferably generated by dielectric barrier discharge (DBD), to produce molecules with high added value, such as hydrogen, CO, gaseous hydrocarbons, liquid hydrocarbons, aromatics, oxygenated compounds (alcohols, acids, ketones, esters, ethers, aldehydes, etc.), and / or liquid fuels.

Description

Title: Process and catalysts for plasma-catalyzed methane reforming Technical field

[0001] The present invention belongs to the field of chemical conversion, in particular the conversion of a gas or a mixture of gases comprising methane (CH4) to produce high added value molecules such as hydrogen (H2), carbon monoxide (CO), gaseous hydrocarbons, liquid hydrocarbons, in particular oxygenates (alcohols, acids, ketones, esters, ethers, aldehydes, etc.), aromatics, as well as liquid fuels. The invention relates in particular to the process for converting CH4 using a catalytic system in the presence of a cold plasma. The invention also relates to said catalyst capable of being activated by a cold plasma, for example generated by dielectric barrier discharge (DBD), thus allowing chemical conversion via plasma catalysis. The invention also relates to a process for preparing such a catalyst and to the use of the catalyst for producing high added value molecules. State of the prior art

[0002] With the sharp increase in energy demand and the environmental impact of fossil fuels, the search for new energy resources is gaining increasing attention. Greenhouse gas (GHG) emissions are a global environmental issue that raises concerns about future human health and sustainable living. While reducing GHG emissions is an important goal that all sectors should strive to achieve, GHG recovery is an effective strategy for GHG management, particularly in the energy and industrial process sectors. Methane (CH4) is a potent greenhouse gas, capable of trapping approximately 28 times more heat from the atmosphere than carbon dioxide (CO2) over a 100-year period.This means that despite its much lower concentration in the atmosphere compared to CO2, CH4 contributes significantly to climate change. Reducing or otherwise recovering CH4 emissions is therefore crucial to combat 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 vast majority of H2 on the market today is produced industrially by steam reforming of CH4 (SRM) according to Eq. 1 (Eq. 1). However, steam reforming Steam is highly endothermic. It is typically carried out at high temperature (700°C- 1000°C), under a pressure of around 25 bars, and catalyzed by noble metal catalysts. CH4+ H2O = 3H2+ CO, AH 29 8K = 206 kJ / mol (Eq. 1)

[0005] It is possible to implement the CH4 steam reforming reaction at low temperature in a non-thermal plasma called cold plasma, where electrons are involved to drive the chemical reactions at low temperature. In the literature, it has been reported that such can take place in microwave plasma reactors, sliding arc reactors, radiofrequency plasma reactors and DBD reactors [1], [2], [3]. However, the energy efficiency observed in a DBD plasma coupled with a catalyst is not high enough for industrial use.

[0006] Furthermore, dry CH4 reforming (DRM) according to Eq. 2 (Eq. 2) has attracted considerable interest due to its potential to achieve a sustainable and low-carbon process in chemical industries and oil refineries and to avoid the disadvantages of storage. The chemical conversion of CH4 in the presence of CO2 can be indirect or direct. According to the indirect approach, which has been researched for decades, the mixture of CO2 and CH4 is first converted into syngas products, a mixture of hydrogen (H2) and carbon monoxide (CO). Then, the syngas can be converted into liquid fuels and other oxygenated chemicals by the Fischer-Tropsch FTS process. The direct approach is more attractive, in that it can convert CH4 in the presence of CO2 into high-value syngas and liquid products in a single reaction step. CH4+ CO2= 2H2+ 2CO, ÛH 298K = 247 kJ / mol (Eq. 2)

[0007] Given the high chemical stability of CO2 and CH4, traditional thermal catalysis processes such as CH4 dry reforming (DRM) require high gas pressures and a significant amount of energy (thermal energy), including temperatures in the range of 700°C to 1000°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 the metal active sites and coke formation on the catalyst surface. Thermal processes are typically catalyzed by noble metals, such as Ir, Pd, Pt, Rh, and Ru, in stable operation and with relatively low amounts of carbon deposited on the catalysts.As an alternative to noble metals, a non-noble metal Ni-based catalyst, which has the advantages of wider availability and lower cost, has been reported to possess relatively high activity for DRM [4], .

[0008] Various studies have been carried out to develop cold plasma chemical synthesis technologies, making it possible to overcome the aforementioned temperature problems. Among these technologies, dielectric barrier discharge (DBD), especially coupled with the presence of a heterogeneous catalyst (plasma-catalysis), has been described [5], especially the synergistic effects of plasma and catalysts that lead to better results compared to thermal catalysis [6], [7], Dielectric barrier discharge (DBD), a type of non-thermal plasma (NTP), is a promising technique used in various reactions. It is attracting particular attention in the utilization of CO2 and CH4 through the DRM process due to the scalability possibilities, mild operating conditions, including ease of handling, compactness of the system and versatility of the process.

[0009] Different catalytic systems, plasma types, reactors and experimental conditions have been tested to improve the conversion and selectivity of syngas products. However, the efficiency of these systems remains very low. In addition, the activity, stability and costs of the catalysts have proven incompatible with industrial use. Little effort has been devoted to the direct approach, i.e., the plasma-catalytic synthesis of liquid chemicals (including hydrocarbons) directly from CO2 and CH4 with considerable selectivity under ambient conditions [8],

[0010] There is therefore a need for a hybrid plasma-catalysis process in the presence of an efficient catalyst allowing the conversion reaction of a gas or a mixture of gases comprising CH4, for example using a hybrid cold plasma-catalysis process, said catalyst allowing a reduction in energy consumption in the reaction and / or an improvement in catalytic performance, namely the gas conversion rate, the selectivity and the catalytic stability, the objective being to obtain hydrogen (H2), gaseous hydrocarbons, liquid hydrocarbons with a long carbon chain, as well as oxygenates, preferably by a direct route (in other words in a single step from CH4).

[0011] An object of the present invention is to provide a CH4 conversion process which meets these expectations.

[0012] The conversion process of the present invention uses a catalytic system in the presence of a cold plasma. The catalytic system capable of being activated by cold plasma, notably comprising a support which is a mixture of alumina and cerium in a molar ratio of between 80 / 20 and 30 / 70.

[0013] The article by KHOJA, et al. [9] describes the preparation of the Ni / La2O3-MgAI2O4 catalyst and its use for plasma-assisted dry reforming of methane (DRM). This article does not describe a catalyst comprising a support that is a mixture of alumina and cerium.

[0014] The article by FOO, et al.

[0010] , describes an alumina-based catalyst (Saint Gobain Nopro, USA) which is impregnated with the following solutions: 5Co-15Ni / 80AI2O3 and 2.5Ce-5CO-15Ni / 77.5AI2O3. According to one embodiment, the catalyst may thus comprise cerium. According to this embodiment, the catalyst comprising an alumina-based support may then be impregnated with solutions potentially comprising cerium. However, this article does not describe a catalyst in which the cerium is found at the level of the support and is present in a molar quantity greater than 20%.

[0015] The article by NANDINI, et al.

[0011] describes a catalyst of formula 13.5Ni-2K / 10CeO2-AI2O3, the support of which consists of alumina and 10 wt. % cerium and which is then co-impregnated with nickel and potassium. See paragraph 2.1. This article does not describe a catalyst in which the support is an alumina / cerium mixture in which cerium is present in a molar quantity greater than 20% and which is used in a cold plasma process.

[0016] The article by KHOJA, et al.

[0012] describes the dry reforming of methane (DRM) using a y-AI2O3-MgO catalyst. The use of cerium is not described.

[0017] The article by SONG, et al.

[0013] , describes the production of synthesis gas via DBD using a Ni / y-AI2O3 catalyst. The use of cerium is not described. Summary of the invention

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

[0019] A second object of the present invention is a catalytic system, also called catalyst, for converting a gas or a mixture of gases comprising methane (CH4), according to the methane reforming reactions (DRM or SRM). This catalytic system, which can for example be activated by a DBD plasma, makes it possible to resolve all the drawbacks of the prior art present in the thermal process (high temperature and pressure) and capable of producing synthesis gas (hydrogen, CO), liquid hydrocarbons, gaseous hydrocarbons, aromatics, oxygenated compounds (in particular alcohols, acids, ketones, esters, ethers, aldehydes), and / or liquid fuels in atmospheric conditions with a high yield compared to the studies described in the prior art.

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

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

[0022] A fourth subject of the present invention relates to the use of the catalyst according to the present invention for the conversion of a gas or a mixture of gases comprising methane (CH4), according to the CH4 reforming reactions (DRM or SRM), said conversion being carried out in the presence of cold plasma. The conversion of methane in the context of the present invention makes it possible to produce molecules with high added value, such as hydrogen (Hz), CO, gaseous hydrocarbons, liquid hydrocarbons, aromatics, oxygenated compounds (alcohols, acids, ketones, esters, ethers, aldehydes, etc.), and / or liquid fuels.

[0023] The present invention makes it possible to overcome all the drawbacks of traditional thermal catalysis processes, as described in the prior art, and thus to obtain high catalytic and energy yields, and is thus capable of being exploited on a large scale. Description of figures

[0024] 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 attached drawings:

[0025] [Figure 1] PFD block diagram of a DBD plasma reactor. Plasma catalysis reactor for dry reforming of methane. Figure 1 illustrates the experimental setup (PFD diagram) used in an example of dry reforming of CH4, DRM, by a DBD plasma process coupled with the catalyst of the present invention.

[0026] [Figure 2] GC-FID spectrum of the organic liquid obtained by combining the 8Ni5Co2K-CeAI200 (50-50) catalytic system with the DBD plasma catalytic reactor. Figure 2 illustrates a GC-FID spectrum of the liquid obtained during the reaction of CH4 and CO2 in a DBD plasma reactor coupled with the 8Ni5Co2K-CeAI200 (50-50) catalyst.

[0027] [Figure 3] GC-MS (mass spectrometer) spectrum of the organic liquid obtained by combining the 8Ni5Co2K-CeAI200 (50-50) catalytic system with the DBD plasma catalytic reactor. Figure 3 illustrates a GC-MS spectrum of the liquid obtained during the reaction of CH4 and CO2 in a DBD plasma reactor coupled with the 8Ni5Co2K-CeAI200 (50-50) catalyst.

[0028] [Figure 4] PFD block diagram of a DBD plasma reactor. Plasma catalysis reactor for steam reforming of methane. Figure 4 illustrates the experimental setup (PFD diagram) used in an example of steam reforming of CH4, SRM, by a DBD plasma process coupled with the catalyst of the present invention.

[0029] [Table 1] Table showing the catalytic activity (i.e., conversion, selectivity) obtained for several catalysts according to the invention and comparative ones, tested in DBD plasma, in the dry reforming reaction of methane (DRM).

[0030] [Table 2] Table showing the catalytic activity (i.e., conversion, selectivity) obtained for several catalysts according to the invention and comparative ones, tested in DBD plasma, in the steam reforming of methane (SRM) reaction. Definitions

[0031] 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).

[0032] Any description relating to one embodiment is applicable and interchangeable with all other embodiments of the invention.

[0033] The expression "and / or" is to be understood as meaning "and" and "or"; for example, the expression "A and / or B" is to be understood as meaning either A and B, or only A, or only B.

[0034] The expression "N, M and / or P" should be understood as meaning "N and / or M and / or P".

[0035] The expression "N, M and P" should be understood as meaning "N and M and P".

[0036] 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.

[0037] 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.

[0038] The term "dielectric" designates, in the present invention, an electrically insulating material which makes it possible to ensure 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 electrical insulating material is also used inside the DBD cell to generate plasma by Dielectric Barrier Discharge (DBD) by promoting the accumulation of electrical charges on the surface of this material.

[0039] The terms "catalyst" and "catalytic system" are interchangeable and refer, in the present invention, to a material promoting the chemical reaction of reactive species, for example, reactant fluids.

[0040] The term “plasma-catalysis” designates, in the present invention, the method which implements an electric discharge of plasma coupled to a catalyst.

[0041] The term “support” or “catalyst support” designates, in the present invention, a solid material or mixture of solid materials - which can in particular be characterized by its specific surface area, on which the promoter(s) is / are deposited.

[0042] The term "promoter" or "catalyst promoter" refers, as used herein, to a solid material or mixture of solid materials added to the surface of the support material, generally in small amounts, for the purpose of increasing the efficiency and performance of the catalyst.

[0043] The term "hydrogen" should be understood to mean "dihydrogen" or "H2".

[0044] The term "carbon monoxide" should be understood to mean "CO".

[0045] The term "syngas" should be understood to mean "synthesis gas" or "a mixture of H2 and CO".

[0046] The term “DRM” should be understood as meaning “Dry Reforming of Methane” or "dry reforming of methane" or "reforming of a mixture of the gas containing methane and carbon dioxide."

[0047] The term "SRM" should be understood as meaning "Steam Reforming of Methane" or "reforming of methane with steam" or "reforming of a mixture of gas containing methane and water vapor".

[0048] The term "methane reforming" or "methane reforming reactions" should be understood to cover both dry reforming of methane (DRM) and steam reforming of methane (SRM).

[0049] 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

[0050] Process for converting a gas or a mixture of gases comprising methane

[0051] A first subject of the present invention relates to a process for converting a gas or a mixture of gases comprising methane (CH4), characterized in that it is carried out in the presence of a cold plasma and a catalyst, said catalyst comprising a support comprising a mixture of alumina and cerium in a molar ratio of between 80 / 20 and 30 / 70, and preferably nickel and optionally at least one promoter. According to one embodiment, the cold plasma is a plasma generated by dielectric barrier discharge (DBD). In particular, the methane (CH ) conversion process according to the invention is carried out according to the CH steam reforming reactions (DRM or SRM).

[0052] According to a first embodiment, the method for converting a gas or a mixture of gases according to the present invention comprises methane (CH4) and water vapor (H2O). According to this embodiment, the method generates 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).

[0053] According to a second embodiment, the method for converting a gas or a mixture of gases according to the present invention comprises methane (CH4) and carbon dioxide (CO2). This embodiment aims to produce high value-added molecules of 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 reforming reaction of CH4(DRM).

[0054] When a hydrocarbon gas is generated, it is preferably ethane, ethene, propane, propene, butane, butene, pentane, hexane or mixtures thereof.

[0055] When an alcohol is generated, it is preferably methanol, ethanol, propanol, butanol, phenol, their isomers and / or their mixtures, more preferably methanol or ethanol.

[0056] When an acid is generated, it is preferably formic acid, acetic acid, propanoic acid, butanoic acid, pentanoic acid, gallic acid or mixtures thereof, more preferably acetic acid.

[0057] When an ether is generated, it is preferably methyl tert-butyl ether (MTBE), ethyl tert-butyl ether ETBE, cyclic ethers, non-cyclic ethers or mixtures thereof, more preferably MTBE.

[0058] When a liquid hydrocarbon is generated, it is preferably aromatic type molecules (benzene, toluene, xylene, etc.), more complex molecules or their mixtures, more preferably benzene.

[0059] When liquid fuel is generated, it is preferably C7->C15 or their mixtures, more preferably C12 diesel.

[0060] According to the present invention, the CH4 conversion process is therefore carried out in the presence of a catalyst, as well as a cold plasma, preferably a plasma generated by dielectric barrier discharge (DBD). The synergy of plasma catalysis in this process shows great potential for the direct synthesis of high value-added molecules, as demonstrated in the examples. Said catalyst comprises a support comprising a mixture of alumina and cerium in a molar ratio of between 80 / 20 and 30 / 70. Such a catalyst also preferably comprises nickel. Such a catalyst optionally comprises at least one promoter. The catalyst is used in combination with a cold plasma. It should be noted that all of the characteristics described in connection with said catalyst are applicable to the conversion process of the present invention.

[0061] According to the present invention, the process for converting a gas or a mixture of gases comprising methane (CH4), in particular according to the CH4 reforming reactions (DRM or SRM), is characterized in that it is carried out in the presence of a cold plasma and a catalyst, said catalyst comprising a support comprising, or consisting essentially of, a mixture of alumina and cerium in a molar ratio of between 80 / 20 and 30 / 70. Preferably, the catalyst also comprises nickel.

[0062] 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), characterized in that it is carried out in the presence of a cold plasma and a catalyst, said catalyst comprising a support comprising, or consisting essentially of, a mixture of alumina and cerium in a molar ratio of between 80 / 20 and 30 / 70. Preferably, the catalyst also comprises nickel.

[0063] 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), characterized in that it is carried out in the presence of a cold plasma and a catalyst, said catalyst comprising a support comprising, or consisting essentially of, a mixture of alumina and cerium in a molar ratio of between 80 / 20 and 30 / 70. Preferably, the catalyst also comprises nickel.

[0064] According to these two embodiments, the catalyst optionally comprises at least one promoter.

[0065] The products obtained according to these conversion processes depend in particular on the molar ratio between CH4, CO2 and / or water vapor used to carry out the conversion reaction, a ratio that a person skilled in the art can determine according to the desired products. For example, reducing the CO2 / CH4 ratio leads to the generation of CH3 radicals, thus promoting the formation of long-chain products, such as ethanol, and reducing the selectivity towards methanol.

[0066] The synergy of plasma catalysis in this process is effective for the direct synthesis of syngas, chemicals and value-added liquid fuels from CO2 and CH4 or the direct synthesis of syngas, chemicals and gaseous hydrocarbons from H2O and CH4, as demonstrated in the following examples.

[0067] According to one embodiment of the method of the invention, the selected and prepared catalyst is placed between the electrodes of a DBD plasma reactor, allowing gaseous species to flow through the catalyst, and is activated by high voltage electrical discharges (of the order of kV) of a duration of the order of nanoseconds to microseconds. This polarization, combined with adsorption, desorption and catalyst / gas interaction, gives rise to the formation of the plasma, as well as its activation and the production of hydrogen. 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 of a few hundred picoseconds to a few tenths of nanoseconds, are responsible for the negative or positive polarization of the catalytic sites.

[0068] Before the gas mixture conversion step, the catalyst according to the invention, in the case where its components are in oxidized form, is advantageously reduced in situ under cold plasma, preferably a DBD plasma, under H2 as discharge gas.

[0069] When implementing the method of the invention, a strong electric field is created, which activates said catalyst, more particularly between the grains of said catalyst or nearby, upstream or downstream of the catalyst, in the gas flow. This strong electric field is typically between 10 3 and 10 10V / m and can vary over time. It 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 plasma 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 the creation of a cold plasma state, the strong electric field created is responsible for the negative or positive polarization of the catalytic sites. This polarization induces adsorption and desorption reactions even at low temperatures (for example at temperatures below 450°C, or even below 400°C).Without polarization (conventional process), the working temperature is higher, generally 700°C to 1000°C.

[0070] The reactor comprises in particular at least one inlet allowing it to be supplied with gas to be converted, comprising CH4 and CO2, or CH4 and H2O in gas form, and an outlet for evacuating the products formed, in liquid and / or gas form.

[0071] According to one embodiment of the method of the invention, the molar ratio of carbon dioxide (CO2) / methane (CH4) or the molar ratio of water vapor (H Z O) / methane (CH4) in the gas mixture to be converted varies between 1 and 5, for example between 1 and 4, preferably between 1 and 3.

[0072] In a variant of the invention, the catalyst of the invention is activated by a DBD plasma by providing an electrical power of less than 30-35 W / g of catalyst (i.e. the catalytic system present in the reactor, i.e. in the catalytic bed).

[0073] The conversion reaction is advantageously carried out at a pressure close to or equal to atmospheric pressure (10 5 Pa), for example at a pressure between 1.10 4 Pa and 3.10 5Pa. The conversion reaction can be carried out under pseudo-adiabatic conditions, i.e. without thermal insulation and without external heating, or under adiabatic conditions, i.e. with thermal insulation and without external heating, or under isothermal conditions, i.e. with thermal insulation and / or external heating. The DBD plasma is generated by applying a voltage between the two electrodes of between 1 and 25 kV, preferably between 5 and 20 kV, in particular with a frequency of between 1 kHz and 100 kHz. The gas hourly space velocity (GHSV) is in particular between 1000 h 1 and 150,000 h 1 , preferably less than 100,000 h 1 .

[0074] A cooling system is optionally present between the container intended to receive the products generated by the conversion reaction and the outlet of the reactor so as to condense and eliminate the liquid products which could be formed during the conversion reaction.

[0075] Catalytic system or catalyst according to the invention

[0076] A second subject of the present invention relates to a catalyst for the conversion of a gas or a mixture of gases comprising methane (CH4), said conversion being carried out in the presence of a cold plasma and said catalyst comprising a support comprising a mixture of alumina and cerium in a molar ratio of between 80 / 20 and 30 / 70. In particular, the conversion is carried out according to the CH4 reforming reactions (DRM or SRM).

[0077] Preferably, the catalyst of the present invention does not comprise a noble metal, such as ruthenium (Ru), iridium (Ir), palladium (Pd), platinum (Pt) or rhodium (Rh).

[0078] The catalyst of the present invention is capable of being activated by cold plasma, when it is used in the process of the invention.

[0079] According to one embodiment of the present invention, said catalyst comprises: - a support which comprises a mixture of alumina and cerium in a molar ratio of between 80 / 20 and 30 / 70, and - nickel, and - optionally at least one promoter, for example of alkali metal type, alkaline earth type, transition metal type and / or lanthanide type, i.e. a promoter comprises at least one chemical element belonging to alkali metals, alkaline earth metals, transition metals, and / or lanthanides (including mixtures thereof).

[0080] According to another embodiment of the present invention, said catalyst consists essentially of: - a support which comprises a mixture of alumina and cerium in a molar ratio of between 80 / 20 and 30 / 70, and - nickel. According to this embodiment, the catalyst does not comprise a promoter.

[0081] According to a preferred embodiment, said catalyst essentially consists of: - a support which comprises a mixture of alumina and cerium in a molar ratio of between 80 / 20 and 30 / 70, - nickel, and - at least one promoter of alkali metal type, alkaline earth type, transition metal type and / or lanthanide type, i.e. a promoter comprising at least one chemical element belonging to the alkali metals, alkaline earth metals, transition metals, and / or lanthanides (including mixtures thereof).

[0082] The catalytic 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 cerium-modified alumina.

[0083] In the context of the present invention, the terms "catalytic system" and "catalyst" are interchangeable. According to one embodiment of the invention, said catalytic system is called a mono / bi / trimetallic catalytic system. It should be noted that the notion of monometallic system, bimetallic system and trimetallic system relates in particular to the species present in the catalyst without taking into account the support used and nickel. For example, when the catalyst is doped with a promoter in addition to nickel, we speak of a monometallic catalyst; when the catalyst is doped with two promoters in addition to nickel, we speak of a bimetallic catalyst; when the catalyst is doped with three promoters in addition to nickel, we speak of a trimetallic catalyst.

[0084] The support used in the context of the present invention is notably chosen for its capacity to adsorb reagents and more particularly CO2, for its thermal stability and for its optimized 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 DBD plasma, the electric field and the electron density due to the dielectric permittivity and the polarization effect which gives rise to the local electric field.

[0085] According to the present invention, the catalyst support comprises, in particular is constituted by or consists of, a mixture of alumina and cerium. More specifically, the support according to the invention comprises a mixture of alumina and cerium, in particular a mixed oxide AlCe, and the alumina / cerium (Al / Ce) molar ratio is between 80 / 20 and 30 / 70. The alumina / cerium (Al / Ce) molar ratio is, for example, between 75 / 25 and 35 / 65, between 73 / 28 and 40 / 60 or between 71 / 29 and 42 / 58. The alumina / cerium ratio may, for example, be approximately 70 / 30 +1. According to this embodiment, the Al / Ce molar ratio 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.The inventors noted that the presence of cerium in the crystal lattices of alumina allows for a higher number of defects on the surface of the support, which promotes the mobility of oxygen on the surface of said support and thus leads to increased catalytic performance.

[0086] According to one embodiment, the support consists of a mixture of alumina oxide, for example AI2O3 and cerium oxide CeO2.

[0087] In the context of the present invention, the alumina may have any specific surface area (expressed as BET surface area m 2 / g)- For example, the specific surface area of ​​alumina is at least 20 m 2 / g and can vary between 50 and 1,000 m 2 / g. For example, the specific surface area of ​​alumina is 200 m 2 / g or 260 m 2 / g. According to one embodiment of the present invention, the catalyst comprises a support comprising alumina having a specific surface area varying between 50 and 1,000 m 2 / g, between 100 and 800 m 2 / g, between 150 and 300 m 2 / g or between 180 and 250 m 2 / g.

[0088] When the catalyst comprises nickel, it may be in any of its oxidation states and in particular in metallic form (in its oxidation state 0) or in oxide form in its oxidation state II (e.g. in the form of nickel (II) oxide (NiO)). The mass content of nickel in the catalyst may advantageously vary between 0.1% and 50% by weight relative to the weight of the support, for example between 1% and 40% or between 2% and 30%; preferably, it is less than 25% or less than 20%. By "weight of the support" is meant "weight of the support comprising the alumina", including when the support comprises elements other than alumina. Particularly advantageously, the catalytic system comprises approximately 8% ± 1% or 10% ± 1% by weight of nickel relative to the weight of the support.

[0089] By convention, a catalyst comprising 8% by weight of nickel relative to the weight of a support comprising alumina and cerium is designated by “8Ni-CeAI”, “8Ni-CeAI” or “8Ni-CeAI”.

[0090] According to one embodiment, the present invention relates to a cold plasma activated catalyst.

[0091] The combined use of the catalyst according to the invention and a cold plasma makes it possible to produce molecules with high added value such as hydrogen (H2), CO and gaseous hydrocarbons, liquid hydrocarbons, in particular oxygenates (alcohols, acids, ketones, esters, ethers, aldehydes, etc.), aromatics, as well as heavy fuels such as diesel, during the conversion, in particular reforming, of the gas comprising CH4, for example 1 / a gas mixture comprising CH4 and CO2, and optionally CO and H2, or for example 2 / a gas mixture comprising CH4 and H2O, and optionally CO and H2. The catalytic performances of the reaction are improved, i.e. the conversion rates of CO2 and / or CH4 and / or the selectivity towards the desired product (liquid fuel and / or synthesis gas).In particular, the catalyst combination according to the invention / cold plasma advantageously makes it possible to produce such molecules in a single step from CH4.

[0092] According to one embodiment, the catalytic system according to the present invention does not comprise a promoter. For example, an example of a catalyst according to the invention not comprising a promoter is the Ni-CeAI catalyst, i.e. a catalyst comprising a support comprising a mixture of Ce and AI, as well as Ni. More particularly, it may be a 10Ni-CeAI (50-50) catalyst, i.e. comprising a support with an alumina / cerium (Al / Ce) molar ratio = (50 / 50) and 10% by weight of Ni relative to the weight of the CeAI support.

[0093] According to another embodiment, the catalytic system according to the present invention comprises at least one promoter, i.e. one or more promoters. Said at least one promoter acts as a dopant and impacts the physicochemical, textural as well as conductive properties of the catalytic system. The promoter according to the invention advantageously has adequate physicochemical surface properties to help fix the reactants as well as adequate dielectric properties which make it possible to improve the conductivity of the resulting catalytic system and which logically lead to the generation of CH3 radicals from CH4, thus promoting the formation of long-chain carbon products (long-chain oxygenated species and particularly long-chain liquid hydrocarbons).

[0094] Thus, in the context of the present invention, the at least one promoter may in particular comprise a chemical element selected from the group consisting of alkalis, transition metals, alkaline earths, lanthanides and their mixtures; more particularly, from the group consisting of alkalis, such as potassium (K), transition metals such as cobalt (Co), copper (Cu), zinc (Zn), manganese (Mn), yttrium (Y), and iron (Fe), alkaline earths 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 of its oxidation states and in particular in metallic form or in oxide form.

[0095] For the purposes of the present invention, the alkali metals may be selected from the group consisting of lithium, sodium, potassium, rubidium, cesium, and francium. When the promoter comprises a chemical element that is an alkali metal, it is preferably potassium (K) or cesium (Cs), and even more preferably potassium (K).

[0096] In the context of the present invention, the transition metals 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, this is preferably cobalt (Co) or iron (Fe), and even more preferably cobalt (Co).

[0097] In the context of the present invention, the alkaline earths 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, this is preferably magnesium (Mg).

[0098] For the purposes 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 that is a lanthanide, it is preferably yttrium (Y) or lanthanum (La), and even more preferably yttrium (Y).

[0099] According to one embodiment of the present invention, the catalyst promoter is selected from the group consisting of potassium (K), cesium (Cs), cobalt (Co), iron (Fe), magnesium (Mg), yttrium (Y), lanthanum (La), 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.

[0100] According to one embodiment of the present invention, the mass content of promoter in the catalyst 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 0.5% 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.

[0101] The promoters used for the preparation of the catalysts of the present invention are found in any oxidation state, and in particular in metallic form or in oxide form. They are therefore likely to comprise other chemical elements, which do not fall within the calculation of the claimed mass content. For example, for an 8Ni2K-CeAI catalyst, if 1 g of support comprising nickel is used, then 0.051 g of KNO3 promoter (molar mass: 101.1 g / mol) is used, which corresponds to 0.02 g of K (molar mass: 39.1 g / mol), or 2% by weight of potassium relative to the weight of the support. For this catalyst, the mass content of promoter (only one in this example, “K promoter”) is 2% by weight relative to the weight of the support.

[0102] The quantity of nickel and / or promoter can be adjusted depending on the nature of the promoter used and / or the type of conversion reaction implemented, i.e. depending on the type of product generated by the conversion reaction, in particular reforming of methane into synthesis gas and / or hydrocarbons.

[0103] According to one embodiment of the present invention, the catalyst according to the present 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 present invention comprises a single promoter which comprises potassium (K). The chemical element potassium may, for example, be introduced into the catalyst in the form of a precursor, for example in the form of potassium nitrate KNO3. More particularly, it may be an 8Ni2K-CeAI (30-70) catalyst, i.e. comprising a support with a molar ratio alumina / cerium (Al / Ce) = (70 / 30), 8% by weight of Ni relative to the weight of the CeAI support and 2% by weight of potassium (K) promoter.

[0104] According to one embodiment of the present invention, the catalyst according to the present invention comprises at least two promoters in addition to nickel, i.e. two or more promoters, for example two promoters (it is then bimetallic) or three promoters in addition to nickel (it is then trimetallic).

[0105] According to a particular embodiment, the catalyst is bimetallic, doped with two promoters in addition to nickel, one of the two promoters being potassium (K), its mass content in the catalytic system is preferably about 2% ± 0.2% by weight relative to the weight of the support, while the second promoter is cobalt (Co), its mass content in the catalytic system is preferably about 5% ± 0.5% by weight relative to the weight of the support. More particularly, it may be a 8NI5Co2K-CeAI (30-70) catalyst, i.e. comprising a support with a molar ratio alumina / cerium (Al / Ce) = (70 / 30), 8% by weight of Ni relative to the weight of the support, 2% by weight of potassium (K) promoter and 5% by weight of cobalt (Co) promoter.

[0106] The catalytic system can come in different forms (balls, 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 catalytic system can also be found in the form of balls (in particular by compression of the powder in a mold) having an average size of less than 5 cm.

[0107] According to one embodiment of the present invention, the alumina / ceria support, the nickel and optionally the promoter(s) form a homogeneous mixture. This means that the nickel and the promoter(s) are distributed uniformly throughout the entire volume of the catalyst.

[0108] According to a preferred embodiment of the present invention, said catalyst comprises: - a support which comprises a mixture of alumina and cerium in a molar ratio of between 80 / 20 and 30 / 70, and - nickel, and - 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).

[0109] Process for the preparation of the catalytic system

[0110] The preparation of the catalytic system according to the present invention can be carried out according to different methods.

[0111] According to a first variant, the catalytic system is prepared by bringing the support into contact with a nickel precursor and at least one precursor of the promoter (or promoters). This step makes it possible to form a solid comprising the support, the nickel and the promoter (or promoters). This contacting step is optionally: preceded by a step of modifying the support; and / or followed by a step of calcining the mixture thus obtained, itself optionally followed by a step of reducing this calcined mixture.

[0112] The calcination step leads to the oxidation of the different components of the catalytic system (support, nickel and promoter). This optional calcination step can itself be optionally followed by a reduction step, so as to change the oxidation state of the nickel and the promoter (to have nickel and metallic promoter), and possibly that of the support. The reduction can be total or partial, that is to say that only a part of the components of the catalytic system can be reduced. The reduction step can be carried out in situ in the non-thermal plasma device under hydrogen.

[0113] The step of bringing the support into contact with a nickel precursor and a promoter precursor can be carried out for example by impregnation or by coprecipitation.

[0114] The nickel precursor and the promoter precursor can be any chemical compound, or mixture of chemical compounds, containing the metal used as the 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.

[0115] According to a first embodiment, the method for preparing the catalytic system comprises a step 1) of preparing the support and a step 2) of bringing the support into contact with a nickel precursor and at least one precursor of the promoter. According to this embodiment, the contacting is carried out by impregnation. More specifically, according to this embodiment, the method comprises the following steps:

[0116] 1) preparation of support: a) preparation of an aqueous solution comprising a cerium precursor and an alumina oxide or comprising 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 2 cerium precursors and an alumina precursor. In the case where the support is a mixture, in particular a mixed oxide, of cerium and alumina, a cerium precursor solution and an 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, in particular the final mixed oxide of cerium and alumina. b) mixing of the suspension resulting from step a). The addition of these precursors is carried out in particular at room temperature, in particular from 20 to 25°C with continuous mixing, in particular from 30 min to several hours, for example from 30 min to 3 h. c) recovery of the solid obtained in step b) 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, typically for a period ranging from 7 hours to 48 hours.d) calcination of the solid resulting from step c) to provide the support. The product resulting from step c) is then 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 period ranging from 3 hours to 6 hours. This step results in the thermal decomposition of the nitrates in order to obtain oxides.

[0117] 2) contact a) preparing an aqueous solution comprising a nickel precursor and one or more precursors of the promoters, b) adding the support resulting from 1) to the aqueous solution resulting from step a) to give a suspension, In step a), an appropriate mass of each precursor is added to an appropriate volume of solvent, for example water. "Appropriate mass" and "appropriate volume" means the quantities of precursors and solvent (in particular water) adequate to obtain the desired mass contents of nickel and promoter in the final catalytic system. c) mixing the suspension resulting from step b). The addition of these precursors is carried out in particular at room temperature, in particular from 20 to 25°C with continuous mixing, in particular from 30 min to several hours, for example from 30 min to 3 h. d) recovery of the solid comprising the support, the nickel and the promoters obtained in step b) by elimination of the 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 approximately 100°C, typically for a period ranging from 7 h to 48 h. e) calcination of the solid resulting from step d) to give the catalyst called the catalytic system. The product resulting from step c) is then 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 period ranging from 3 hours to 6 hours. This step results in the thermal decomposition of the nitrates in order to obtain oxides.

[0118] This first embodiment is also called the wet impregnation process. It consists of impregnating the support with the nickel precursor and the promoter precursor.

[0119] According to a second embodiment, the method for preparing the catalytic system comprises a support preparation step and bringing the support into contact with a nickel precursor and the promoter, this contact being carried out by co-precipitation and comprising the following steps:

[0120] a') preparation of an aqueous solution comprising a nickel precursor and the precursors of the promoters (this step is identical to step 2 a) of the wet impregnation process). b') addition of the support to the solution resulting from step a') to give a suspension (this step is identical to step 2 b) of the wet impregnation process). c') addition of a base to the suspension resulting from step b'). During this step, a base is added to the suspension resulting from step b'). This base is advantageously a hydroxide salt such as sodium or potassium hydroxide or sodium or potassium carbonate, in particular sodium hydroxide. It can be used in the form of a solution, in particular an aqueous solution. The base is added gradually drop by drop until the pH of the suspension (consisting of a solid suspended in a liquid solution) is between 8 and 12, preferably equal to approximately 10. Step c') is advantageously carried out at a temperature between 60°C and 100°C, in particular between 70°C and 90°C, preferably equal to approximately 80°C. d') mixing of the suspension resulting from step c'). This step aims to precipitate the nickel hydroxide and the hydroxide of the metal used as promoter on the surface of the support. The mixing, in particular by stirring, is advantageously carried out at a temperature between 60°C and 100°C, preferably equal to approximately 80°C. This mixing step can be carried out for a period of 2 hours or more, typically for approximately 3 hours.e') recovery of the solid comprising the support, the nickel and the promoter obtained in step d') and its calcination to give the catalyst called the catalytic system (this step is identical to step 2 e) of the wet impregnation process). This method allows the precipitate of nickel hydroxide and the hydroxide of the metal used as promoter on the surface of the support.

[0121] Use of the catalyst according to the present invention

[0122] The present invention also relates to the use of the catalyst, in the presence of cold plasma for the conversion of a gas or a mixture of gases comprising CHU, according to the CHi reforming reactions (DRM or SRM), said catalyst comprising a support which is a mixture of alumina and cerium in a molar ratio of between 80 / 20 and 30 / 70. According to one embodiment, the cold plasma is a plasma generated by dielectric barrier discharge (DBD).

[0123] The present invention relates in particular to the combined use of the catalyst of the present invention, together with a cold plasma, for the conversion of a gas mixture comprising methane (CHi) and water vapor (H2O), according to the steam reforming reaction (SRM), aimed at generating synthesis gas, liquid oxygenates and / or gaseous hydrocarbons.

[0124] The present invention also relates to the combined use of the catalyst of the present invention, as well as a cold plasma, for the conversion of a gas mixture comprising methane (CH4) and carbon dioxide (CO2), according to the dry methane reforming reaction (DRM), aimed at producing high added value molecules of synthesis gas (hydrogen, CO), liquid hydrocarbons, gaseous hydrocarbons, aromatics, oxygenated compounds (in particular alcohols, acids, ketones, esters, ethers, aldehydes), and / or liquid fuels.

[0125] 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 barrier discharge dielectric (DBD), showed increased efficiency in converting a gas mixture including methane according to methane reforming reactions (DRM or SRM).

[0126] List of cited documents [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. [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. [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. [4] C. Shi, S. Wang, X. Ge, S. Deng, B. Chen, et 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, avr. 2021, https: / / doi.Org / 10.1016 / j.jcou.2021.101462 [5] H. Puliyalil, D. Lasic Jurkovic, V. D. B. C. Dasireddy, et 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 [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 [7] M. Mikhail et al., « Electrocatalytic behaviour of CeZrOx-supported Ni catalysts in plasma assisted CO2 methanation », Catal Sci Technol, vol. 10, no 14, p. 4532-4543, 2020, https: / / doi.org / 10.1039 / D0CY00312C [8] A. Wang, J. H. Harrhy, S. Meng, P. He, L. Liu, et H. Song, « Nonthermal plasma-catalytic conversion of biogas to liquid chemicals with low coke formation », Energy Convers. Manag., vol. 191, p. 93-101, juill. 2019, https: / / doi.Org / 10.1016 / j.enconman.2019.04.026 [9] Asif Hussain Khoja, Muhammad Tahir, Nor Aishah Saidina Amin, Process optimization of DBD plasma dry reforming of methane over Ni / La2O3MgAI2O4 using multiple response surface methodology, International Journal of Hydrogen Energy, Volume 44, Issue 23, 2019, Pages 11774- 11787, ISSN 0360-3199, https: / / doi.Org / 10.1016 / j.ijhydene.2019.03.059.

[0010] Say Yei Foo, Chin Kui Cheng, Tuan-Huy Nguyen, Adesoji A. Adesina, Kinetic study of methane CO2 reforming on Co-Ni / AI2O3 and Ce-Co-Ni / AI2O3 catalysts, Catalysis today, Volume 164, Issue 1, 2011, Pages 221-226, ISSN 0920-5861, https: / / doi.Org / 10.1016 / j.cattod.2010.10.092.

[0011] A. Nandini, K.K. Pant, S.C. Dhingra, Kinetic study of the catalytic carbon dioxide reforming of methane to synthesis gas over Ni-K / CeO2-AI2O3 catalyst, Applied Catalysis A: General, Volume 308, 2006, Pages 119-127, ISSN 0926-860X, https: / / doi.Org / 10.1016 / j.apcata.2006.04.014.

[0012] Asif Hussain Khoja, Muhammad Tahir, Nor Aishah Saidina Amin, Cold plasma dielectric barrier discharge reactor for dry reforming of methane over Ni / v-AI2O3-MgO nanocomposite, Fuel Processing Technology, Volume 178, 2018, Pages 166-179, ISSN 0378-3820, https: / / doi.Org / 10.1016 / j.fuproc.2018.05.030.

[0013] Hyung Keun Song, Jae-Wook Choi, Sung Hoon Yue, Hwaung Lee, Byung-Ki Na, Synthesis gas production via dielectric barrier discharge over Ni / y-AI2O3 catalyst, Catalysis Today, Volume 89, Issues 1-2, 2004, Pages 27-33, ISSN 0920-5861, https: / / doi.Org / 10.1016 / j.cattod.2003.ll.009.

[0127] Exemples

[0128] The invention is now described in more detail with reference to the following examples, the purpose of which is illustrative and not intended to limit the scope of the invention.

[0129] A. Preparation of the different catalysts by wet impregnation

[0130] Several supports were used to prepare various catalysts from Tables 1 and 2 below: 1) A commercial alumina oxide (TH, Specific surface area = 80m 2 / g, Sasol); 2) A commercial alumina oxide (AI200, Specific surface area = 200m 2 / g, Saint Gobain); 3) A commercial alumina oxide (AI260, Specific surface area = 260m 2 / g, Saint Gobain); 4) A commercial silica oxide (Sil60, Specific surface area = 160m 2 / g, Saint Gobain); 5) Mixed Cerium-Aluminum (CeAI) oxides of different molar compositions, synthesized by the inventors according to the method described above.

[0131] The catalyst is prepared by two successive impregnation sequences. In other words, a first wet impregnation for the preparation of the ceria-modified alumina support according to method 1) above up to the calcination step. After calcination, a new impregnation step, this time only of nickel and the promoter(s), is carried out on the catalytic system resulting from the first impregnation.

[0132] The promoter-doped nickel catalysts (metal M) were prepared by the method from an aqueous solution of Ni(NO3)2-6H2O (Sigma-Aldrich and one or more promoter precursors selected from: 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 commercial, Sigma-Aldrich), depending on the desired promoter.

[0133] For example, for the preparation of the 8Ni5Co2K-CeAI catalyst (one of the preferred catalysts of the invention), the nickel content is 8% by mass relative to the weight of the support, that of the Co promoter is 5% by mass relative to the weight of the support and that of the K promoter is 2% by mass relative to the weight of the support. A 10Ni-CeAI catalyst without promoter was also prepared as an inventive example according to the present invention.

[0134] The appropriate mass of nickel salt and that of the promoter precursor(s) are dissolved in a volume of 50 mL of water, 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. For example, for the preparation of the 8Ni5Co2K-CeAI catalyst, 0.396 g of nickel nitrate (content 8% by weight), 0.155 g of cobalt nitrate (content 5% by weight), 0.052 g of potassium nitrate (content 2% by weight) and 1 g of support are mixed according to the previous procedure. The mixture is then placed in a rotary evaporator for 2 h at 65°C, in order to remove excess water.

[0135] After impregnation and water evaporation, all samples were collected, dried in an oven at 100°C for 8 h, and then calcined in air at 550°C for 4 h with a temperature ramp of 10°C / min. After calcination, the catalytic system samples were hand-ground and sieved to an average grain size between 50 and 200 μm.

[0136] The different catalysts prepared according to the method described above are listed in Tables 1 and 2 below.

[0137] B. Conversion of a gas or a mixture of gases including CH4 in the presence of different catalytic systems

[0138] Dry methane reformaae reaction (DMR)

[0139] The procedure for the production of hydrogen and liquid hydrocarbons using a catalytic plasma reactor is as follows: 357 mg of catalyst to be tested, corresponding to a GHSV (Gas Hourly Space Velocity) of 17000 h 1, are placed between the electrodes of the DBD reactor; the reactor is supplied with a mixture of methane and carbon dioxide (50% vol CO2) with 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.

[0140] Steam reforma e methane (SRM) reaction

[0141] The procedure for the production of hydrogen and gaseous hydrocarbons using a catalytic plasma reactor is as follows: 400 mg of catalyst to be tested, and a 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 (Gas Hourly Space Velocity) of 20 00 h 1, are placed between the electrodes of the DBD plasma reactor; the reactor is supplied with a gas mixture containing carbon monoxide and water vapor; the water is first propelled by an inert gas (Ar), then circulates through a mass flow controller, it is then vaporized and mixed with the 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.

[0142] A non-thermal electric barrier discharge (DBD) plasma was created between two electrodes: a cylindrical copper electrode placed inside an alumina tube (3 mm diameter), surrounded by a coaxial quartz tube (10 mm inner diameter, 1 mm thickness), and a steel wire wrapped around the outer surface of the quartz tube, acting as a ground electrode (grounded via an external 2 nF capacitor). In this configuration, a discharge was sustained in a 2.5 mm gap, covering a length of approximately 1 cm. Before the catalytic test, the as-synthesized catalytic systems were reduced in situ under non-thermal DBD plasma under H2 as the discharge gas for a duration of 60 minutes.

[0143] The activity and selectivity of the promoter and non-promoted catalysts under DBD plasma conditions are evaluated in an experimental setup comprising a cylindrical quartz tubular reactor, a DBD plasma generator, and corresponding devices for gas feeding and analysis. A schematic representation of the DBD plasma setup is provided in Figure 1 (DRM) and Figure 4 (SRM).

[0144] Without plasma, no change in the composition of the outlet gases is observed. When the plasma is ignited, and after stabilization, production of synthesis gas and liquid / gaseous hydrocarbons is obtained at the outlet.

[0145] The following equations 3 to 8 were used to estimate the catalytic performance and calculate CO2 conversion, CH4 conversion, H2 and CO selectivity: Sco( 100 (Eq. 5) (Eq. 6) a SRM reaction where F m 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.

[0146] C. Results

[0147] Table 1 below indicates the catalysts tested and shows the results of the catalytic activity obtained in terms of conversion, selectivity and yield, from a gas mixture comprising CH4 and CO2 (DRM). Figures 2 and 3 show the GC-FID and GC-MS spectra of the organic liquid obtained by combining the catalytic system 8Ni5Co2K-CeAI200 (50-50) with the DBD plasma catalytic reactor, respectively. These figures confirm the presence of acetic acid, acetone, molecules with Molar mass = 77 g / mol which represents the phenyl group, molecules with 12 carbons (MM = 140 g / mol) and molecules larger than C12 with MM = 207, 213 and 281. The density of this organic liquid obtained is equal to 920 kg / m 3 .

[0148] It is found that the 8Ni2K-CeAI200 catalysts according to the invention 8i, 13i and 18i, which have an Al / Ce molar ratio in the range 80 / 20 and 30 / 70, have a better catalytic efficiency in the conversion of CH4 and CO2 compared to a catalyst not comprising cerium (8Ni2K-CeAI200 comparative test 7c), or compared to catalysts comprising cerium outside the claimed molar ratio (comparative tests 17c, 19c and 20c). Indeed, the catalytic efficiencies in the conversion of CH4 and CO2 of the catalysts according to the invention are significantly greater than 50%, whereas those of the comparative catalysts are all less than 50%.

[0149] It is therefore necessary to respect a compromise between the molar quantity of alumina and cerium at the level of the support of the catalytic system to obtain better conversion efficiencies of CH4 to CO2.

[0150] It can also be noted that 8Ni2K-CeAI200 catalysts with an Al / Ce molar ratio of less than 30 / 70 - in the table above, molar ratio 20 / 80 (test 19c) and molar ratio 10 / 90 (test 20c) - do not allow the production of high added value liquids.

[0151] Although Table 1 below does not specify it, the inventive catalysts 5Ni5Co-CeAI200 (30-70) (AI / Ce=70 / 30) of test 14i and 8Ni5Co2K-CeAI200 (50-50) of test 15i allow produce a large quantity of liquids. These catalysts comprising a cobalt promoter are therefore very efficient for the direct approach DRM conversion in a single step.

[0152] Despite its high-performance catalytic results, the 10Ni5Ce-AI200 catalyst of test 3c in which cerium is not present in a mixture with alumina at the support level, does not allow liquids to be obtained. [Table 1]

[0153] Table 2 below indicates the catalysts tested and shows the results of the catalytic activity obtained in terms of conversion, selectivity and yield, from a gas mixture comprising CH4 and H2O (SRM). [Table 2]

Claims

Demands

1. A process for converting a gas or a mixture of gases comprising methane (CH4) according to CH4 reforming reactions, characterized in that it is carried out in the presence of a cold plasma and a catalyst, said catalyst comprising a support comprising a mixture of alumina and cerium in a molar ratio between 80 / 20 and 30 / 70.

2. The method according to claim 1, wherein the catalyst also comprises: - nickel, and / or - at least one promoter selected from the group consisting of alkali metals, alkaline earth metals, transition metals, lanthanides and mixtures thereof.

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

4. A method according to any one of claims 2 or 3, wherein the mass content of promoter in the catalytic system varies between 0.1% and 40% by weight relative to the weight of the support, preferably between 0.5% and 25% by weight.

5. A method 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 relative to the weight of the support, preferably less than 30%.

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

7. A process according to any one of the preceding claims, for converting a gas mixture comprising methane (CH4) and carbon dioxide (CO2) according to the dry methane reforming (DMR) reaction, characterized in that it generates synthesis gas, liquid hydrocarbons, gaseous hydrocarbons, aromatics, oxygenated compounds (including alcohols, acids, ketones, esters, ethers, aldehydes), and / or liquid fuels.

8. A process according to any one of claims 1 to 6, for converting a gas mixture comprising methane (CP) and water vapor (H2O) according to the steam methane reforming (SRM) reaction, characterized in that it generates synthesis gas, liquid oxygenated compounds and / or gaseous hydrocarbons.

9. Catalyst for the conversion of a gas or gas mixture comprising methane (CP) according to CH4 reforming reactions, comprising a support comprising a mixture of alumina and cerium in a molar ratio between 80 / 20 and 30 / 70.

10. Catalyst according to claim 9, said catalyst being activated by cold plasma, preferably generated by dielectric barrier discharge (DBD).

11. Catalyst according to any one of claims 9 or 10, also comprising: - nickel, and / or - at least one promoter selected from the group consisting of alkali metals, alkaline earth metals, transition metals, lanthanides and mixtures thereof.

12. Catalyst according to claim 11, wherein at least one promoter is: - of the alkaline type, and more specifically potassium; and / or - of the transition metal type and more particularly selected from the group consisting of cobalt, copper, iron, yttrium and their mixtures.

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

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

15. Use of the catalyst according to any one of claims 9 to 14, for the conversion of a gas or a mixture of gases comprising methane (CH4) according to the reactions of CH4 reforming, said conversion being carried out in the presence of cold plasma, preferably generated by dielectric barrier discharge (DBD).

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