Method and catalyst for methane plasma-catalytic reforming

Abstract

The invention relates to a method for converting a methane (CH4)-containing gas or gas mixture according to a CH4 reforming reaction (DRM or SRM), characterised in that it is carried out in the presence of a cold plasma and a catalyst comprising a support comprising a mixture of alumina and cerium in a molar ratio of between 80 / 20 and 30 / 70. The invention also relates to said catalyst, to a method for producing said catalyst and to the use thereof for the conversion of CH4-containing gases or gas mixtures, the catalyst being activated by a cold plasma, preferably generated by dielectric barrier discharge (DBD), thereby producing high value added molecules, such as hydrogen, CO, gaseous hydrocarbons, liquid hydrocarbons, aromatics, oxygenates (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 methane (CH4)-containing gases or gas mixtures to produce high value-added molecules, such as hydrogen (H2), carbon monoxide (CO), gaseous hydrocarbons, liquid hydrocarbons, in particular oxygen-containing compounds (alcohols, acids, ketones, esters, ethers, aldehydes, etc.), aromatic hydrocarbons and liquid fuels. In particular, the present invention relates to a method for converting CH4 by a catalytic system in the presence of cold plasma. The present invention also relates to the catalyst, which can be activated by cold plasma, such as cold plasma generated by dielectric barrier discharge (DBD), so that chemical conversion can be achieved by plasma-catalysis. The present invention also relates to a method for preparing the catalyst and the use of the catalyst for producing high value-added molecules. Background Art

[0002] With the strong growth in energy demand and the impact of fossil fuels on the environment, the search for new energy sources has received increasing attention. Greenhouse gas (GHG) emissions are a global environmental issue that raises concerns about future human health and sustainable living patterns. If reducing GHG emissions is the main goal that all sectors should strive to achieve, then recycling GHGs is an effective strategy for managing GHGs, especially in the energy and industrial process sectors. Methane (CH4) is a powerful greenhouse gas that traps 28 times more heat in the atmosphere than carbon dioxide (CO2) over a 100-year period. This means that, although CH4 has much lower concentrations in the atmosphere than CO2, it has a large impact on climate change. Therefore, reducing or recycling CH4 emissions is essential to combat global warming.

[0003] Catalytic reforming of CH4 is an industrially widely used process for converting natural gas into H2 or syngas ((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] Most of the H2 currently available on the market is produced industrially by steam reforming (SRM) of CH4 according to Equation 1 (Equation 1). However, steam reforming is highly endothermic. It is usually carried out at high temperatures (700°C-1000°C) at a pressure of 25 bar and catalyzed by precious metal-based catalysts.

[0005] CH4+H2O=3H2+CO,ΔH 298K =206 kJ / mol (Formula 1)

[0006] Low-temperature dry reactions for reforming CH4 can be carried out in non-thermal plasmas (so-called cold plasmas), where electrons participate in the chemical reaction at low temperatures. In the literature, it is reported that these can occur in microwave plasma reactors, gliding arc reactors, radio frequency plasma reactors and DBD reactors [1], [2], [3]. However, it is noted that the energy efficiency in DBD plasmas combined with catalysts is not high enough for industrial use.

[0007] In addition, dry reforming (DRM) of CH4 according to Equation 2 (Equation 2) has received great attention because it has the potential to implement sustainable and low carbon emission processes in the chemical industry and refineries and avoid the disadvantages of storage. The chemical conversion of CH4 in the presence of CO2 can be indirect or direct. According to the indirect method, which has been the subject of research for decades, a mixture of CO2 and CH4 is first converted into a synthesis gas product, i.e. a mixture of hydrogen (H2) and carbon monoxide (CO). The synthesis gas can then be converted into liquid fuels and other oxygen-containing chemical products by a Fischer-Tropsch FTS process. The direct method is more attractive because it allows the conversion of CH4 into high value-added synthesis gas and liquid products in the presence of CO2 in a single reaction step.

[0008] CH4+CO2=2H2+2CO,ΔH 298K =247 kJ / mol (Formula 2)

[0009] Given the high chemical stability of CO2 and CH4, conventional thermal catalytic processes, such as dry reforming of CH4 (DRM), require high gas pressures and large amounts of energy (heat), especially temperatures of 700°C to 1000°C, to promote catalyst activation, change thermodynamic equilibrium, and ensure acceptable yields. High-temperature catalytic reactions not only lead to high energy consumption, but also to possible catalyst deactivation due to sintering of metal active sites and formation of coke on the catalyst surface. In general, thermal processes are catalyzed by precious metals (e.g., Ir, Pd, Pt, Rh, and Ru), which are stable in operation and have relatively little carbon deposition on the catalyst. As an alternative to precious metals, catalysts based on non-precious metal Ni (which have the advantage of being more readily available and less expensive) have been reported to have relatively high activity for DRM [4].

[0010] Different studies have been conducted to develop cold plasma chemical synthesis techniques that overcome the above-mentioned temperature problems. Among these techniques, dielectric barrier discharge (DBD) has been described, especially in combination with the presence of heterogeneous catalysts (plasma-catalysis) [5], in particular the synergistic effect of plasma and catalyst leading to better results compared to thermal catalysis [6], [7]. Dielectric barrier discharge (DBD), a non-thermal plasma (NTP), is a promising technology for various reactions. It has received particular attention in the use of CO2 and CH4 via DRM processes due to its scalability, mild operating conditions (especially easy handling), compactness of the system and versatility of the process.

[0011] 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 low. In addition, the activity, stability, and cost of the catalysts have proven to be unsuitable for industrial use. Little effort has been devoted to direct methods, i.e., the synthesis of liquid chemical products (including hydrocarbons) directly from CO2 and CH4 by plasma-catalysis with reasonably high selectivity under ambient conditions [8].

[0012] Therefore, there is a need for a hybrid plasma-catalytic method in the presence of an effective catalyst to subject a CH4-containing gas or gas mixture to a conversion reaction, such as using a hybrid cold plasma-catalytic process, wherein the catalyst is capable of reducing the reaction energy consumption and / or improving the catalytic performance, i.e., the gas conversion rate, selectivity and catalytic stability, with the aim of obtaining hydrogen (H2), gaseous hydrocarbons, liquid hydrocarbons with long carbon chains and oxygen-containing compounds, preferably directly (in other words, from CH4 in a single step).

[0013] The object of the present invention is to provide a process for converting CH4 which meets these expectations.

[0014] The conversion process of the invention utilizes a catalytic system in the presence of a cold plasma. The catalytic system that can be activated by cold plasma comprises in particular a support that is a mixture of aluminum oxide and cerium in a molar ratio between 80 / 20 and 30 / 70.

[0015] The article by KHOJA et al. [9] describes the preparation of the catalyst Ni / La2O3-MgAl2O4 and its use for dry reforming of methane (DRM: dry reforming of methane) by DBD plasma. The article does not describe a catalyst comprising a support which is a mixture of alumina and cerium.

[0016] The article by FOO et al.

[10] describes an alumina-based catalyst (Saint Gobain Nopro, USA) impregnated with the following solutions: 5Co-15Ni / 80Al2O3 and 2.5Ce-5CO-15Ni / 77.5Al2O3. According to one embodiment, the catalyst may thus contain cerium. According to this embodiment, the catalyst comprising an alumina-based support may then be impregnated with a solution which may contain cerium. However, the article does not describe a catalyst in which cerium is present at the level of the support and in a molar content greater than 20%.

[0017] The article by NANDINI et al.

[11] describes a catalyst of formula 13.5Ni-2K / 10CeO2-Al2O3, whose support consists of alumina and 10 wt.% cerium, which is then co-impregnated with nickel and potassium. See 2.1. The article does not describe a catalyst in which the support is an alumina / cerium mixture, in which the molar content of cerium is higher than 20%, which is used in a cold plasma process.

[0018] The article by KHOJA et al.

[12] describes the use of the catalyst γ-Al2O3-MgO for the dry reforming of methane (DRM: dry reforming of methane). The use of cerium is not described.

[0019] The article by SONG et al.

[13] describes the production of synthesis gas by DBD using a Ni / γ-Al2O3 catalyst. The use of cerium is not described. Summary of the invention

[0020] A first object of the present invention relates to a method for converting a gas or a gas mixture containing methane (CH4) according to a CH4 reforming reaction (DRM or SRM), characterized in that the method is carried out in the presence of a cold plasma and a catalyst comprising a support comprising a mixture of aluminum oxide and cerium in a molar ratio between 80 / 20 and 30 / 70. According to one embodiment, the cold plasma is a plasma generated by a dielectric barrier discharge (DBD).

[0021] A second object of the invention is a catalytic system, also called catalyst, allowing the conversion of methane (CH4)-containing gases or gas mixtures according to the methane reforming reaction (DRM or SRM). This catalytic system, which can be activated by DBD plasma, for example, can solve all the disadvantages of the prior art in thermal processes (high temperature and high pressure) and can produce synthesis gas (hydrogen, CO), liquid hydrocarbons, gaseous hydrocarbons, aromatic hydrocarbons, oxygenates (in particular alcohols, acids, ketones, esters, ethers, aldehydes) and / or liquid fuels under atmospheric conditions with higher yields than the studies described in the prior art.

[0022] According to a preferred embodiment, the catalyst comprises:

[0023] - a support which is a mixture of alumina and cerium in a molar ratio between 80 / 20 and 30 / 70;

[0024] - Nickel; and / or

[0025] - at least one promoter of the alkali metal type, alkaline earth metal type, transition metal type and / or lanthanide type (including mixtures thereof).

[0026] A third object of the present invention relates to a method for preparing said catalyst.

[0027] A fourth object of the invention relates to the use of the catalyst according to the invention for converting a gas or gas mixture containing methane (CH4) according to a CH4 reforming reaction (DRM or SRM), said conversion being carried out in the presence of a cold plasma. In the present invention, the conversion of methane allows the production of high added value molecules such as hydrogen (H2), CO, gaseous hydrocarbons, liquid hydrocarbons, aromatics, oxygenates (alcohols, acids, ketones, esters, ethers, aldehydes, etc.) and / or liquid fuels.

[0028] The present invention allows to overcome all the drawbacks of the traditional thermocatalytic methods described in the prior art, obtaining a high catalytic and energetic efficiency, thus making it possible to exploit them on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Other features, objects and advantages of the present invention will become apparent from the following description which is intended to be illustrative only and not restrictive, and which should be read with reference to the accompanying drawings:

[0030] [ Figure 1 ]PDF functional diagram of DBD plasma reactor. Plasma catalytic reactor for methane dry reforming. Figure 1 An experimental setup (PFD diagram) used in an example of dry reforming (DRM) of CH4 by a DBD plasma process combined with the catalyst of the present invention is shown.

[0031] [ Figure 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 Shown is the GC-FID spectrum of the liquid obtained by the reaction of CH4 and CO2 in a DBD plasma reactor combined with the catalyst 8Ni5Co2K-CeAl200 (50-50).

[0032] [ Figure 3 ] GC-MS spectrum (mass spectrum) of organic liquid obtained by combining the catalytic system 8Ni5Co2K-CeAl200 (50-50) with a DBD plasma catalytic reactor. Figure 3The GC-MS spectrum of the liquid obtained by the reaction of CH4 and CO2 in a DBD plasma reactor combined with the catalyst 8Ni5Co2K-CeAl200 (50-50) is shown.

[0033] [ Figure 4 ]PDF functional diagram of DBD plasma reactor. Plasma catalytic reactor for methane steam reforming. Figure 4 An experimental setup (PFD diagram) used in an example of steam reforming (SRM) of CH4 by a DBD plasma process combined with the catalyst of the present invention is shown.

[0034] [Table 1] The table shows the catalytic activities (ie, conversion, selectivity) of several catalysts of the present invention and comparative catalysts tested in DBD plasma in the dry reforming reaction of methane (DRM).

[0035] [Table 2] The table shows the catalytic activities (ie, conversion, selectivity) of several catalysts of the present invention and comparative catalysts tested in DBD plasma in the steam reforming reaction of methane (SRM). DETAILED DESCRIPTION

[0036] definition

[0037] The expression "between ... and ..." (eg, a numerical range) should be understood to include the limit value (eg, the limit value of the numerical range).

[0038] Any description relating to one embodiment is applicable to and interchangeable with all other embodiments of the invention.

[0039] The expression “and / or” should be understood as both “and” and “or”; for example, the expression “A and / or B” should be understood as A and B, or only A, or only B.

[0040] The expression "N, M and / or P" should be understood to mean "N and / or M and / or P".

[0041] The expression "N, M and P" should be understood to mean "N and M and P".

[0042] Where elements or ingredients are included in and / or selected from a list of elements or ingredients, it should be understood that individual elements or ingredients may be selected and combined with other individual elements, or may be selected to form a subset of two or more of the elements or ingredients explicitly listed; furthermore, any element or ingredient mentioned in a list of elements or ingredients may be omitted from that list.

[0043] In the present invention, the term "DBD-Dielectric Barrier Discharge" refers to a discharge generated between two conductive elements separated by one or more dielectric elements.

[0044] In the present invention, the term "dielectric" refers to an electrically insulating material that ensures electrical insulation between the high voltage grid associated with the electrodes and the electrically conductive and thermally conductive pipes that are grounded through the reactor. This type of electrically insulating material is also used inside DBD cells to generate dielectric barrier discharge (DBD) plasma by promoting the accumulation of charge on the surface of this material.

[0045] In the present invention, the terms "catalyst" and "catalytic system" are used interchangeably and refer to a material that promotes a chemical reaction of an active species (eg, a reagent fluid).

[0046] In the present invention, the term "plasma-catalysis" refers to a process in which a plasma discharge combined with a catalyst is performed.

[0047] In the present invention, the term "support" or "catalyst support" refers to a solid material or a mixture of solid materials, particularly characterized by the specific surface area on which the promoter is deposited.

[0048] In the present invention, the term "promoter" or "catalyst promoter" refers to a solid material or a mixture of solid materials that is usually added to the surface of a support material in a small amount to improve the efficiency and performance of the catalyst.

[0049] The term "hydrogen" should be understood to mean "hydrogen gas" or "H2".

[0050] The term "carbon monoxide" shall be understood to mean "CO".

[0051] The term "synthesis gas" should be understood to mean "synthesis gas" or "a mixture of H2 and CO".

[0052] The term "DRM" is understood to mean "dry reforming of methane" or "reforming of a gas containing methane and carbon dioxide".

[0053] The term "SRM" is understood to mean "steam methane reforming" or "reforming of methane and steam" or "reforming of a gas containing methane and water vapor".

[0054] The term "methane reforming" or "methane reforming reaction" is understood to cover dry reforming of methane (DRM) and steam reforming of methane (SRM).

[0055] Of course, the present invention has been described above by way of example. Of course, those skilled in the art will be able to implement different variations of the present invention without departing from the scope of the present invention.

[0056] Process for converting methane-containing gases or gas mixtures

[0057] A first object of the present invention relates to a method for converting a gas or gas mixture containing methane (CH4), characterized in that the method is carried out in the presence of a cold plasma and a catalyst, the catalyst comprising a carrier and preferably nickel and optionally at least one promoter, the carrier comprising a mixture of aluminum oxide and cerium in a molar ratio between 80 / 20 and 30 / 70. According to one embodiment, the cold plasma is a plasma generated by a dielectric barrier discharge (DBD). In particular, the method of converting methane (CH4) according to the invention is carried out according to the reforming reaction of CH4 with steam (DRM or SRM).

[0058] According to a first embodiment, the method of the invention for converting a gas or a gas mixture comprises methane (CH4) and water vapor (H2O). According to this embodiment, the method produces synthesis gas (i.e. H2 and CO), liquid oxygen-containing compounds and / or gaseous hydrocarbons. In particular, the method for converting methane (CH4) of this embodiment is carried out according to a CH4 reforming reaction (SRM).

[0059] According to a second embodiment, the method of the invention for converting a gas or a gas mixture comprises methane (CH4) and carbon dioxide (CO2). This embodiment aims to produce high value-added molecular synthesis gas (H2, CO), liquid hydrocarbons, gaseous hydrocarbons, aromatic hydrocarbons, oxygen-containing compounds (especially alcohols, acids, ketones, esters, ethers, aldehydes) and / or liquid fuels. In particular, the method for converting methane (CH4) of this embodiment is carried out according to a CH4 dry reforming reaction (DRM).

[0060] In the case of the generation of hydrocarbons in gaseous form, these preferably consist of ethane, ethylene, propane, propylene, butane, butene, pentane, hexane or a mixture thereof.

[0061] In case an alcohol is produced, it preferably consists of methanol, ethanol, propanol, butanol, phenol, isomers and / or mixtures thereof, more preferably methanol or ethanol.

[0062] In case an acid is generated, it preferably consists of formic acid, acetic acid, propionic acid, butyric acid, valeric acid, gallic acid or a mixture thereof, more preferably acetic acid.

[0063] In case an ether is produced, it preferably consists of methyl tert-butyl ether (MTBE), ethyl tert-butyl ether ETBE, cyclic ethers, acyclic ethers or mixtures thereof, more preferably MTBE.

[0064] In case liquid hydrocarbons are produced, they are preferably composed of aromatic molecules (benzene, toluene, xylenes, etc.), more complex molecules or mixtures thereof, more preferably benzene.

[0065] In case a liquid fuel is produced, it preferably consists of C7→C15 or a mixture thereof, more preferably diesel C12.

[0066] Therefore, according to the present invention, the method for converting CH4 is carried out in the presence of a catalyst and a cold plasma, preferably a plasma generated by a dielectric barrier discharge (DBD). As shown in the examples, the synergistic effect of plasma catalysis in the method shows great potential for the direct synthesis of high value-added molecules. The catalyst comprises a carrier, which comprises a mixture of aluminum oxide and cerium in a molar ratio between 80 / 20 and 30 / 70. Preferably, the catalyst also comprises nickel. Optionally, the catalyst comprises at least one promoter. The catalyst is used in combination with a cold plasma. It should be noted that all the features described about the catalyst are applicable to the conversion method of the present invention.

[0067] According to the invention, a method for converting a gas or gas mixture containing methane (CH4), in particular according to a CH4 reforming reaction (DRM or SRM), is characterized in that it is carried out in the presence of a cold plasma and a catalyst comprising a support comprising or essentially consisting of a mixture of aluminum oxide and cerium in a molar ratio between 80 / 20 and 30 / 70. Preferably, the catalyst also comprises nickel.

[0068] According to one embodiment, the present invention relates to a method for converting a gas or a gas mixture containing methane (CH4) and carbon dioxide (CO2), characterized in that it is carried out in the presence of a cold plasma and a catalyst, the catalyst comprising a support, the support comprising or essentially consisting of a mixture of aluminum oxide and cerium in a molar ratio between 80 / 20 and 30 / 70. Preferably, the catalyst also comprises nickel.

[0069] According to another embodiment, the present invention relates to a method for converting a gas or a gas mixture containing methane (CH4) and water (H2O), characterized in that it is carried out in the presence of a cold plasma and a catalyst comprising a support comprising or essentially consisting of a mixture of aluminum oxide and cerium in a molar ratio between 80 / 20 and 30 / 70. Preferably, the catalyst also comprises nickel.

[0070] According to both embodiments, the catalyst optionally comprises at least one promoter.

[0071] In particular, the products obtained from these conversion processes depend on the molar ratio of CH4, CO2 and / or water vapor used to carry out the conversion reaction, which can be determined by those skilled in the art based on the desired product. For example, a reduction in the CO2 / CH4 ratio leads to the production of CH3 free radicals, thereby promoting the formation of long-chain products (such as ethanol) and reducing the selectivity to methanol.

[0072] As shown in the following examples, the synergistic effect of plasma catalysis in this method is proven to be effective for the direct synthesis of value-added syngas, chemical products and liquid fuels from CO2 and CH4 or the direct synthesis of syngas, chemical products and gaseous hydrocarbons from H2O and CH4.

[0073] 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 so that the gaseous material circulates through the catalyst and the catalyst is activated by a high voltage discharge (in the range of several kV) in a few nanoseconds to a few microseconds. This polarization, combined with adsorption, desorption and catalyst / gas interactions, leads to the formation of plasma and the activation of plasma and the generation of hydrogen. The electrical energy supplied to the fixed bed in the form of sinusoidal or pulsed high voltage generates multiple currents on the HV (high voltage) carrier during positive and negative polarization. These streamers, which range from hundreds of picoseconds to a few tenths of a nanosecond, are responsible for the negative or positive polarization of the catalytic sites.

[0074] Prior to the step of converting the gas mixture, the catalyst according to the invention, in the case of its components in oxidized form, is advantageously reduced in situ under a cold plasma, preferably a DBD plasma, with H 2 as discharge gas.

[0075] During the implementation of the method of the invention, a strong electric field is generated in the gas flow, which activates the catalyst, more specifically between or near the particles of the catalyst, upstream or downstream of the catalyst. 3 and 10 10 V / m, and can change over time. It is able to ionize part of the gas and excite the atoms and molecules present in the gas phase. The walls of the reactor can generally be made of a metal material; alternatively, in the case where a DBD plasma reactor is preferably used to implement the method of the present invention, the walls of the reactor are made of a dielectric material such as quartz, alumina or ceramic. Advantageously, the reactor can be cylindrical. In addition to producing a cold plasma state, the strong electric field generated is also responsible for the negative or positive polarization of the catalytic sites. Even at low temperatures (for example, at temperatures below 450°C or below 400°C), this polarization causes adsorption and desorption reactions. The operating temperature is higher when there is no polarization (conventional process), generally 700°C to 1000°C.

[0076] In particular, the reactor comprises at least one inlet capable of supplying the gas to be converted, including CH4 and CO2 or CH4 and H2O in gaseous form, and an outlet for discharging the products formed in liquid and / or gaseous form.

[0077] According to one embodiment of the process of the invention, the carbon dioxide (CO2) / methane (CH4) molar ratio or the water vapor (H2O) / methane molar ratio in the gas mixture to be converted varies between 1 and 5, for example between 1 and 4, preferably between 1 and 3.

[0078] In one variant of the invention, the catalyst of the invention is activated by DBD plasma by providing an electrical power of less than 30-35 W / g catalyst (catalytic system present in the reactor, ie the catalytic bed).

[0079] Advantageously, the conversion reaction is carried out at a pressure close to or equal to atmospheric pressure (10 5 Pa) pressure, for example, 1.10 4 Pa and 3.10 5 The DBD plasma is generated by applying a voltage between 1 and 25 kV, preferably between 5 and 20 kV, between two electrodes, in particular at a frequency between 1 kHz and 100 kHz. In particular, the gas hourly space velocity (GHSV) is 1000 h / s. -1 and 150000h -1 Between, preferably less than 100000h -1 .

[0080] Optionally, there is a cooling system between the container for receiving the product produced by the conversion reaction and the outlet of the reactor in order to condense and remove liquid products that may be formed during the conversion reaction.

[0081] Catalytic system or catalyst of the present invention

[0082] A second object of the invention relates to a catalyst for the conversion of a gas or gas mixture containing 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 between 80 / 20 and 30 / 70. In particular, the conversion is carried out according to a CH4 reforming reaction (DRM or SRM).

[0083] Preferably, the catalyst of the present invention does not contain any noble metals, such as ruthenium (Ru), iridium (Ir), palladium (Pd), platinum (Pt) or rhodium (Rh).

[0084] During the implementation of the method of the present invention, the catalyst of the present invention can be activated by cold plasma.

[0085] According to one embodiment of the present invention, the catalyst comprises:

[0086] a support comprising a mixture of alumina and cerium in a molar ratio between 80 / 20 and 30 / 70, and

[0087] - Nickel, and

[0088] - optionally at least one promoter, for example of the alkali metal type, alkaline earth metal type, transition metal type and / or lanthanide type, i.e. the promoter comprises at least one chemical element belonging to the group consisting of alkali metals, alkaline earth metals, transition metals and / or lanthanides (including mixtures thereof).

[0089] According to another embodiment of the present invention, the catalyst consists essentially of:

[0090] a support comprising a mixture of alumina and cerium in a molar ratio between 80 / 20 and 30 / 70, and

[0091] -nickel.

[0092] According to this embodiment, the catalyst does not contain any promoter.

[0093] According to a preferred embodiment, the catalyst consists essentially of:

[0094] a support comprising a mixture of alumina and cerium in a molar ratio between 80 / 20 and 30 / 70, and

[0095] - Nickel, and

[0096] - at least one promoter of the alkali metal type, alkaline earth metal type, transition metal type and / or lanthanide type, ie the promoter comprises at least one chemical element belonging to the group consisting of alkali metals, alkaline earth metals, transition metals and / or lanthanides (including mixtures thereof).

[0097] The catalytic system is characterized in that the support comprises a mixture of aluminum oxide and cerium. According to one embodiment, the support consists essentially of a mixture of aluminum oxide and cerium. For example, it comprises cerium-modified aluminum oxide.

[0098] In the present invention, the terms "catalytic system" and "catalyst" are interchangeable. According to one embodiment of the present invention, the catalytic system is a so-called mono / bi / trimetallic catalytic system. It should be noted that the concepts of monometallic system, bimetallic system and trimetallic system specifically relate to the substances present in the catalyst, regardless of the support and the nickel used. For example, in the case where the catalyst is doped with one promoter in addition to nickel, we call it a monometallic catalyst; in the case where the catalyst is doped with two promoters in addition to nickel, we call it a bimetallic catalyst; in the case where the catalyst is doped with three promoters in addition to nickel, we call it a trimetallic catalyst.

[0099] In particular, the support used in the present invention is selected based on its ability to adsorb reagents (more particularly CO2), its thermal stability and its optimized specific surface area (intended to promote the plasma-catalyst interface, allowing various reaction pathways in surface chemistry). It is also selected for its dielectric properties, which affect the properties of the plasma and change the discharge behavior, electric field and electron density of the DBD plasma due to the dielectric constant and the polarization effect that generates the local electric field.

[0100] According to the present invention, the support of the catalyst comprises, in particular is formed by or consists of a mixture of aluminum oxide and cerium. More specifically, the support of the present invention comprises a mixture of aluminum oxide and cerium, in particular a mixed oxide AlCe, with an aluminum oxide / cerium (Al / Ce) molar ratio between 80 / 20 and 30 / 70. For example, the aluminum oxide / cerium (Al / Ce) molar ratio is between 75 / 25 and 35 / 65, between 73 / 28 and 40 / 60 or between 71 / 29 and 42 / 58. For example, the ratio of aluminum oxide / cerium is about 70 / 30±1. According to this embodiment, the Al / Ce molar ratio affects the physicochemical properties (basicity, acidity, reducibility, oxygen mobility due to the presence of inherent defects on the surface, etc.) as well as textural properties (pore volume, pore size, specific surface area, etc.) and electrical properties (dielectric constant, conductivity, etc.), which in turn adjust the catalytic performance of the system. The inventors have noted that the presence of cerium in the alumina crystal network allows for more defects on the support surface, which promotes the mobility of oxygen on the support surface, thereby improving the catalytic performance.

[0101] According to one embodiment, the support consists of a mixture of aluminum oxide (eg Al2O3) and cerium oxide CeO2.

[0102] In the present invention, the alumina may have any specific surface area (measured in BET surface area m 2 For example, the specific surface area of ​​aluminum oxide is at least 20 m 2 / g, especially at 50 and 1000m 2 / g. For example, the specific surface area of ​​alumina is 200m 2 / g or 260m 2 According to one embodiment of the present invention, the catalyst comprises a carrier, the carrier comprises a catalyst having a specific surface area between 50 and 1000 m 2 / g, between 100 and 800m 2 / g, between 150 and 300m 2 / g or between 180 and 250m 2 / g of aluminum oxide.

[0103] In the case where the catalyst comprises nickel, the latter may be in any of its oxidation states and in particular in metallic form (oxidation state 0) or in the form of an oxide in oxidation state II (for example in the form of nickel(II) oxide (NiO)). Advantageously, the mass content of nickel in the catalyst may be between 0.1% and 50% by weight, for example between 1% and 40% or between 2% and 30%, relative to the weight of the support; preferably lower than 25% or lower than 20%. "The weight of the support" is to be understood as the "weight of the support comprising alumina", including when the support comprises elements other than alumina. In a particularly advantageous manner, the catalytic system comprises about 8% by weight ± 1% by weight or 10% by weight ± 1% by weight of nickel, relative to the weight of the support.

[0104] By convention, a catalyst comprising 8 wt% nickel relative to the weight of the support comprising alumina and cerium is denoted as "8Ni-CeAl", "8Ni-CeAl" or "8Ni-CeAl".

[0105] According to one embodiment, the present invention is directed to cold plasma activated catalysts.

[0106] The combined use of the catalyst of the present invention and cold plasma allows the production of high value-added molecules such as hydrogen (H2), CO and gaseous hydrocarbons, liquid hydrocarbons, especially oxygen-containing compounds (alcohols, acids, ketones, esters, ethers, aldehydes, etc.), aromatic hydrocarbons and heavy fuels such as diesel in the conversion process, especially reforming a gas containing CH4, such as 1 / a gas mixture containing CH4 and CO2, possibly also CO and H2, or such as 2 / a gas mixture containing CH4 and H2O, possibly also CO and H2. The catalytic performance of the reaction, i.e., the conversion rate of CO2 and / or CH4 and / or the selectivity of the desired product (liquid fuel and / or synthesis gas) is improved. In particular, the catalyst / cold plasma combination of the present invention advantageously allows the production of these molecules from CH4 in a single step.

[0107] According to one embodiment, the catalytic system of the present invention does not contain any promoter. For example, an example of a catalyst of the present invention that does not contain a promoter is a catalyst Ni-CeAI, i.e. a catalyst comprising a carrier containing a mixture of Ce and Al and Ni. More specifically, it can be composed of a catalyst 10Ni-CeAl (50-50), i.e. a carrier comprising alumina / cerium (Al / Ce) in a molar ratio = (50 / 50) and 10% by weight of Ni relative to the weight of the carrier CeAl.

[0108] According to another embodiment, the catalytic system of the present invention comprises at least one promoter, i.e. one or more promoters. The at least one promoter acts as a dopant and affects the physicochemical, textural and conductive properties of the catalytic system. Advantageously, the promoter of the present invention has suitable surface physicochemical properties to help fix the reagent, as well as suitable dielectric properties, which allow to improve the conductivity of the resulting system and logically lead to the generation of CH3 radicals from CH4, thereby promoting the formation of long carbon chain products (oxygen-containing substances with long chains and liquid hydrocarbons with particularly long chains).

[0109] Thus, in the present invention, at least one promoter may comprise in particular a chemical element selected from the group consisting of alkali metals, transition metals and alkaline earth metals, lanthanides and mixtures thereof; more particularly, selected from 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 present invention, the promoter is in any of its oxidation states, and in particular in metallic form or in oxide form.

[0110] In the present invention, the alkali metal may be selected from the group consisting of lithium, sodium, potassium, rubidium, cesium and francium. When the promoter comprises an alkali metal chemical element, the latter is preferably potassium (K) or cesium (Cs), even more preferably potassium (K).

[0111] In 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 transition metal chemical element, the latter is preferably cobalt (Co) or iron (Fe), even more preferably cobalt (Co).

[0112] In 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 an alkaline earth chemical element, the latter is preferably magnesium (Mg).

[0113] In the present invention, the lanthanide element 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 lanthanide chemical element, the latter is preferably yttrium (Y) or lanthanum (La), even more preferably yttrium (Y).

[0114] 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.

[0115] According to one embodiment of the present invention, the mass content of the promoter in the catalyst is between 0.1 wt % and 40 wt %, for example between 0.2 wt % and 30 wt %, in particular between 0.5 wt % and 25 wt %, preferably between 1 wt % and 20 wt %, in particular between 1 wt % and 15 wt %, even more preferably between 1 wt % and 9 wt %, relative to the weight of the carrier.

[0116] The promoters used to prepare the catalyst of the present invention are in any oxidation state, and in particular in metallic or oxide form. Therefore, they may contain other chemical elements that are not taken into account when calculating the claimed mass content. For example, for catalyst 8Ni2K-CeAl, if 1g of a nickel-containing carrier is used, 0.051g of promoter KNO3 (molar mass: 101.1g / mol) is used, which corresponds to 0.02g K (molar mass: 39.1g / mol), i.e. potassium of 2% by weight relative to the weight of the carrier. For this catalyst, the mass content of the promoter (only one in this example, "K promoter") is 2% by weight relative to the weight of the carrier.

[0117] The nickel and / or promoter content can be adjusted depending on the nature of the promoter used and / or the type of conversion reaction performed, ie the type of product produced by the conversion reaction, in particular the reforming of methane into synthesis gas and / or hydrocarbons.

[0118] According to one embodiment of the present invention, the catalyst of the present invention is monometallic, i.e. it contains a single promoter in addition to nickel. In particular, according to a preferred embodiment, the catalyst of the present invention contains a single promoter containing potassium (K). For example, the potassium chemical element can be introduced into the catalyst in the form of a precursor, for example in the form of potassium nitrate KNO3. More specifically, it can be composed of a catalyst 8Ni2K-CeAl(30-70), i.e. a carrier containing an aluminum oxide / cerium (Al / Ce) molar ratio = (70 / 30), 8% by weight of Ni and 2% by weight of potassium (K) promoter relative to the weight of the carrier CeAl.

[0119] According to one embodiment of the present invention, the catalyst of the present invention comprises at least two promoters in addition to nickel, ie two or more promoters, for example two promoters (which is a bimetallic catalyst) or three promoters (which is a trimetallic catalyst) in addition to nickel.

[0120] According to a specific embodiment, the catalyst is a bimetallic catalyst doped with two promoters in addition to nickel, one of the two promoters being potassium (K), preferably present in an amount of about 2% by weight ± 0.2% by weight relative to the weight of the support, and a second cobalt (Co) promoter, preferably present in an amount of about 5% by weight ± 0.5% by weight relative to the weight of the support. More specifically, it may be composed of a catalyst 8Ni5Co2K-CeAl (30-70), i.e. a support comprising an alumina / cerium (Al / Ce) molar ratio = (70 / 30), 8% by weight of Ni relative to the weight of the support, 2% by weight of a potassium (K) promoter and 5% by weight of a cobalt (Co) promoter.

[0121] The catalytic system may be in various forms (beads, monoliths, powders, etc.). In powder form, the average size of the particles forming the powder may be between 1 μm and 1 mm, for example between 100 μm and 1 mm, in particular between 200 μm and 800 μm, preferably about 600 μm ± 20 μm. In particular, the size of the particles may be adjusted according to the production scale adopted. The catalytic system may also be in the form of beads (in particular by pressing the powder in a mold) having an average size of less than 5 cm.

[0122] According to one embodiment of the invention, the alumina / cerium support, the nickel and optionally the promoter form a homogeneous mixture. This means that the nickel and the promoter are evenly distributed throughout the volume of the catalyst.

[0123] According to a preferred embodiment of the present invention, the catalyst comprises:

[0124] a support comprising a mixture of alumina and cerium in a molar ratio between 80 / 20 and 30 / 70, and

[0125] - Nickel, and

[0126] - 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).

[0127] Method for preparing a catalytic system

[0128] The preparation of the catalyst system of the present invention can be carried out according to different methods.

[0129] According to a first variant, the catalytic system is prepared by contacting the support with a nickel precursor and with at least one promoter (or promoters) precursor. This step allows the formation of a solid comprising the support, the nickel and the promoter (or promoters). This contacting step may:

[0130] - before a step of modifying the support; and / or

[0131] - This is followed by a step of calcining the mixture thus obtained, which itself may optionally be followed by a step of reducing the calcined mixture.

[0132] The calcination step results in oxidation of the different components of the catalytic system (support, nickel and promoter). In turn, the optional calcination step may optionally be followed by a reduction step, thereby changing the oxidation state of the nickel and promoter (with nickel and metallic promoter), and possibly the oxidation state of the support. The reduction may be total or partial, i.e. only part of the components of the catalytic system may be reduced. The reduction step may be performed in situ in a non-thermal plasma device under hydrogen.

[0133] The step of contacting the support with the nickel precursor and the promoter precursor may be carried out, for example, by impregnation or coprecipitation.

[0134] The nickel precursor and the promoter precursor can be any compound or mixture of compounds containing the metal used as the active metal / promoter, more specifically, a salt of the metal, an oxide of the metal or a mixture thereof, preferably a salt of the metal or a mixture of salts of the metal. For example, the salt of the metal (referring to a non-hydrated salt or a hydrated salt, or a multi-hydrated salt) can be selected from chlorides, nitrates, sulfates, carbonates, acetates, acetylacetonates, tartrates and citrates of the metal and mixtures thereof, preferably nitrates of the metal. In the case where the promoter is a mixture of several metals, the precursor can be a mixture of different types of salts and / or oxides of these metals.

[0135] According to a first embodiment, the method for preparing the catalytic system comprises the steps of 1) preparing a support and 2) contacting the support with a nickel precursor and at least one promoter precursor. According to this embodiment, the contacting is performed by impregnation. More specifically, according to this embodiment, the method comprises the steps of:

[0136] 1) Vector preparation:

[0137] a) preparing an aqueous solution comprising a cerium precursor and aluminum oxide or comprising a cerium precursor and an aluminum oxide precursor. In step a), the support precursor corresponds to a cerium precursor, an aluminum oxide precursor or a mixture of a cerium precursor and an aluminum oxide precursor.

[0138] In case 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 proportion to obtain the desired Al / Ce molar ratio in the mixture, in particular the final mixed oxide of cerium and alumina.

[0139] b) mixing the suspension obtained in step a). In particular, the addition of these precursors is carried out at room temperature, in particular at 20 to 25° C. with continuous mixing, in particular for 30 minutes to several hours, for example 30 minutes to 3 hours.

[0140] c) recovering the solid obtained in step b) by removing excess water, in particular by evaporating the water or filtering, and then drying the solid obtained. For example, the drying step can be carried out at a temperature below 150° C., typically at a temperature of about 100° C., typically for 7 to 48 hours.

[0141] d) calcining the solid obtained in step c) to obtain a carrier.

[0142] The product obtained in step c) is then calcined, for example at a temperature between 300° C. and 600° C. The calcination step may be carried out for 3 hours or more, for example 3 to 6 hours. This step results in thermal decomposition of the nitrate to obtain the oxide.

[0143] 2) Contact

[0144] a) preparing an aqueous solution comprising a nickel precursor and one or more promoter precursors,

[0145] b) adding the carrier obtained in step 1) to the aqueous solution obtained in step a) to obtain a suspension,

[0146] During step a), an appropriate mass of each precursor is added to an appropriate volume of solvent, such as water. "Appropriate mass" and "appropriate volume" should be understood as the appropriate amount of precursor and solvent (especially water) to obtain the desired mass content of nickel and promoter in the final catalytic system.

[0147] c) mixing the suspension obtained in step b).

[0148] In particular, the addition of these precursors is carried out at room temperature, in particular at 20 to 25° C. with continuous mixing, in particular for 30 minutes to several hours, for example 30 minutes to 3 hours.

[0149] d) recovering the solid comprising the support, nickel and the promoter obtained in step b) by removing excess water, in particular by evaporating the water or filtering, and then drying the obtained solid. For example, the drying step can be carried out at a temperature below 150° C., typically at a temperature of about 100° C., typically for 7 to 48 hours.

[0150] e) calcining the solid obtained in step d) to obtain the so-called catalytic system.

[0151] The product obtained in step c) is then calcined, for example at a temperature between 300° C. and 600° C. The calcination step may be carried out for 3 hours or more, for example 3 to 6 hours. This step results in thermal decomposition of the nitrate to obtain the oxide.

[0152] The first embodiment is also referred to as the wet impregnation process. It comprises impregnating the support with a nickel precursor and a promoter precursor.

[0153] According to a second embodiment, the method for preparing a catalytic 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 coprecipitation and comprising the steps of:

[0154] a') preparing an aqueous solution comprising a nickel precursor and a promoter precursor (this step is the same as step 2a) of the wet impregnation process).

[0155] b') adding the carrier to the solution obtained in step a') to obtain a suspension (this step is the same as step 2b) of the wet impregnation process).

[0156] c') Adding a base to the suspension obtained in step b'). During this step, a base is added to the suspension obtained in step b'). Advantageously, this base is a hydroxide salt, such as sodium hydroxide or potassium hydroxide or sodium carbonate 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 dropwise gradually until the pH value of the suspension (consisting of a suspension of solids in a liquid solution) is between 8 and 12, preferably equal to 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.

[0157] d') mixing the suspension obtained in step c'). The purpose of this step is to precipitate nickel hydroxide and the metal hydroxide used as promoter on the surface of the support. Advantageously, the mixing is carried out at a temperature between 60° C. and 100° C., preferably equal to about 80° C., in particular by stirring. The mixing step can be carried out for 2 hours or more, generally for about 3 hours.

[0158] e') recovering the solid comprising the support, nickel and promoter obtained in step d') and calcining it to obtain the so-called catalytic system (this step is the same as step 2e) of the wet impregnation process).

[0159] This method allows the precipitation of nickel hydroxide and the metal hydroxide used as a promoter on the surface of the support.

[0160] Use of the catalyst of the present invention

[0161] The invention also relates to the use of a catalyst for converting a CH4-containing gas or gas mixture according to a CH4 reforming reaction (DRM or SRM) in the presence of a cold plasma, the catalyst comprising a support, the support being a mixture of alumina and cerium in a molar ratio between 80 / 20 and 30 / 70. According to one embodiment, the cold plasma is a plasma generated by a dielectric barrier discharge (DBD).

[0162] In particular, the present invention relates to the combined use of the catalyst of the present invention and cold plasma for converting a gas mixture containing methane (CH4) and water vapor (H2O) according to a steam reforming reaction (SRM) to produce synthesis gas, liquid oxygenates and / or gaseous hydrocarbons.

[0163] The present invention also relates to the use of the catalyst and cold plasma combination of the present invention for converting a gas mixture containing methane (CH4) and carbon dioxide (CO2) according to the methane dry reforming reaction (DRM) to produce high value-added molecules such as synthesis gas (hydrogen, CO), liquid hydrocarbons, gaseous hydrocarbons, aromatic hydrocarbons, oxygen-containing compounds (especially alcohols, acids, ketones, esters, ethers, aldehydes) and / or liquid fuels.

[0164] In fact, the inventors have recognized that the combination of the catalyst of the invention and a cold plasma, preferably a plasma generated by a dielectric barrier discharge (DBD), increases the efficiency of converting a methane-containing gas mixture according to the methane reforming reaction (DRM or SRM).

[0165] List of References

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[0171] [6]M.Mikhail et al.,《Tailoring physicochemical and electricalproperties of Ni / CeZrOx doped catalysts for high efficiency of plasmacatalytic CO2 methanation》,Appl.Catal.B Environ.,vol.294,p.120233,oct.2021,https: / / doi.org / 10.1016 / j.apcatb.2021.120233

[0172] [7]M.Mikhail et al.,《Electrocatalytic behaviour of CeZrOx-supportedNi catalysts in plasma assisted CO2 methanation》,Catal Sci Technol,vol.10,no14,p.4532-4543,2020,https: / / doi.org / 10.1039 / DOCY00312C

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[0174] [9]Asif Hussain Khoja,Muhammad Tahir,Nor Aishah Saidina Amin,Processoptimization of DBD plasma dry reforming of methane over Ni / La2O3MgAI2O4using multiple response surface methodology,International Journal f HydrogenEnergy,Volume 44,Issue 23,2019,Pages 11774-11787,ISSN 0360-3199,https: / / doi.org / 10.1016 / j.ijhydene.2019.03.059.

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[10] Say Yei Foo,Chin Kui Cheng,Tuan-Huy Nguyen,Adesoji A.Adesina,Kinetic study of methane CO2 reforming on Co-Ni / Al2O3 and Ce-Co-Ni / Al2O3catalysts,Catalysis today,Volume 164,lssue 1,2011,Pages 221-226,ISSN 0920-5861,https: / / doi.org / 10.1016 / j.cattod.2010.10.092.

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[13] Hyung Keun Song, Jae-Wook Choi, Sung Hoon Yue, Hwaung Lee, Byung-KiNa, Synthesis gas production via dielectric barrier discharge over Ni / γ-Al2O3catalyst, Catalysis Today, Volume 89, lssues 1-2, 2004, Pages 27-33, ISSN 0920-5861, https: / / doi.org / 10.1016 / j.cattod.2003.11.009.

[0179] Example

[0180] The present invention will now be described in more detail with reference to the following examples, which are illustrative but not intended to limit the scope of the present invention.

[0181] A. Preparation of different catalysts by wet impregnation

[0182] Several supports were used to prepare various catalysts in Tables 1 and 2 below:

[0183] 1) Commercially available alumina (TH, specific surface area = 80 m 2 / g, Sasol);

[0184] 2) Commercially available alumina (Al200, specific surface area = 200m 2 / g, Saint Gobain);

[0185] 3) Commercially available alumina (Al260, specific surface area = 260 m 2 / g, Saint Gobain);

[0186] 4) Commercially available silicon dioxide (Si160, specific surface area = 160 m 2 / g, Saint Gobain);

[0187] 5) The inventors synthesized mixed oxides of cerium-aluminum (CeAl) of different molar compositions according to the aforementioned method.

[0188] The catalyst is prepared by two consecutive impregnation steps. In other words, a ceria-modified alumina support is prepared according to the above-described method 1) by a first wet impregnation until the calcination step. After calcination, a new step is carried out on the catalytic system obtained by the first impregnation, this time only with nickel and promoter.

[0189] Nickel-containing catalysts doped with promoters (metal M) were prepared by this method from an aqueous solution of Ni(NO3)2·6H2O (Sigma-Aldrich) and one or more promoter precursors selected from the following: 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.

[0190] For example, to prepare catalyst 8Ni5Co2K-CeAl (one of the preferred catalysts of the present invention), the nickel content is 8 wt % relative to the weight of the carrier, the content of the promoter Co is 5 wt % relative to the weight of the carrier, and the content of the promoter K is 2 wt % relative to the weight of the carrier. As an inventive example of the present invention, catalyst 10Ni-CeAl without a promoter is also prepared.

[0191] Under room temperature and stirring, the nickel salt and promoter precursor of appropriate mass are dissolved in 50mL volume of water. The support of appropriate mass is added to the aqueous solution containing the metal salt mixture and stirred for 2 hours. For example, in order to prepare the catalyst 8Ni5Co2K-CeAl, 0.396g nickel nitrate (content 8 wt%), 0.155g cobalt nitrate (content 5 wt%) and 0.052g potassium nitrate (content 2 wt%) and 1g support are mixed according to the aforementioned procedure. The mixture is then placed in a rotary evaporator at 65°C for 2 hours to remove excess water.

[0192] After impregnation and evaporation of water, all samples were collected, dried in an oven at 100°C for 8 hours, and then calcined at 550°C in air for 4 hours at a temperature rate of 10°C / min. After calcination, samples of the catalytic system were manually ground and sieved to an average particle size between 50 and 200 μm.

[0193] The various catalysts prepared according to the above method are listed in Table 1 and Table 2 below.

[0194] B. Conversion of CH4-containing gases or gas mixtures in the presence of different catalytic systems

[0195] Methane dry reforming (PRM) reaction

[0196] The steps for producing hydrogen and liquid hydrocarbons by a catalytic plasma reactor are as follows: 357 mg of the catalyst to be tested is placed between the electrodes of the DBD reactor, corresponding to a GHSV (gas hourly space velocity of 17000 h -1 ); a mixture of methane and carbon dioxide (50% by volume CO2) was supplied to the reactor at atmospheric pressure and a temperature of 20°C, 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).

[0197] Steam Methane Reforming (SRM) reaction

[0198] The steps for producing hydrogen and gaseous hydrocarbons by a catalytic plasma reactor are as follows: 400 mg of the catalyst to be tested is placed between the electrodes of a DBD plasma reactor at atmospheric pressure and a temperature of 20°C, with a total flow rate of 150 ml / min STP (standard temperature and pressure) (75 ml / min STP H2O and 75 ml / min STP CH4), corresponding to 2000 h -1 The reactor was supplied with a gas mixture containing carbon monoxide and water vapor; the water was first propelled by an inert gas (Ar), then circulated through a mass flow controller, and then evaporated and mixed with carbon monoxide using a controlled evaporation and mixing system (Bronkhorst CEM). The gas mixture was then transported into the DBD plasma reactor through a heated pipeline.

[0199] A non-thermal dielectric barrier discharge (DBD) plasma was generated between two electrodes: a cylindrical electrode made of copper was placed inside a tube made of alumina (3 mm in diameter), surrounded by a coaxial tube made of quartz (10 mm in inner diameter, 1 mm in thickness), and a steel wire wrapped around the outer surface of the tube made of quartz served as a ground electrode (grounded through an external capacitor of 2 nF). In this configuration, the discharge was sustained within a space of 2.5 mm and covered a length of about 1 cm. Prior to the catalytic test, the synthesized catalytic system was reduced in situ under non-thermal DBD plasma in H2 as the discharge gas for 60 min.

[0200] The activity and selectivity of the catalysts with and without promoters under DBD plasma conditions were evaluated in an experimental setup, which included a tubular cylindrical reactor made of quartz, a DBD plasma generator, and the corresponding gas supply and analysis equipment. Figure 1 (DRM) and Figure 4 (SRM) shown.

[0201] Without the aid of plasma, no changes in the outlet gas composition were observed. When the plasma was ignited, after stabilization, synthesis gas and liquid / gaseous hydrocarbons were obtained at the outlet.

[0202] The following equations 3 to 8 were used to estimate the catalytic performance and calculate the conversion of CO2, the conversion of CH4, and the selectivity of H2 and CO:

[0203]

[0204]

[0205]

[0206]

[0207] H2 / CO=S H2 / S CO (Formula 7)

[0208] SRM reactions

[0209] Among them, F in and F out Refers to the inlet and outlet flow rates of the substance under consideration at the reactor inlet and outlet respectively (mol / s).

[0210] C. Results

[0211] Table 1 below shows the catalysts tested and shows the catalytic activity results in terms of conversion, selectivity and yield obtained from a gas mixture containing CH4 and CO2 (DRM). Figure 2 and Figure 3 The GC-FID and GC-MS spectra of the organic liquid obtained by combining the catalytic system 8Ni5Co2K-CeAl200 (50-50) with the DBD plasma catalytic reactor are shown respectively. These figures confirm the presence of acetic acid, acetone, molecules with a molar mass = 77 g / mol (representing phenyl), molecules with 12 carbons (MM = 140 g / mol) and molecules greater than C12 (MM = 207, 213 and 281). The density of the organic liquid obtained is equal to 920 kg / m 3 .

[0212] It can be noted that the catalysts 8Ni2K-CeAl200 (8i, 13i and 18i) of the invention with an Al / Ce molar ratio of 80 / 20 to 30 / 70 have better catalytic yields in terms of CH4 and CO2 conversions compared to catalysts without cerium (8Ni2K-Al200, comparative test 7c) or compared to catalysts containing cerium in excess of the required molar ratio (comparative tests 17c, 19c and 20c). In fact, the catalytic yields of the catalysts of the invention in terms of CH4 and CO2 conversions are much higher than 50%, while the catalytic yields of the comparative catalysts are all lower than 50%.

[0213] Therefore, it is necessary to observe a trade-off between the molar amounts of alumina and cerium on the support of the catalytic system to obtain better conversion yields of CH4 and CO2.

[0214] Furthermore, it can be noted that the catalyst 8Ni2K-CeAl200 with an Al / Ce molar ratio lower than 30 / 70, in the table with a molar ratio of 20 / 80 (Test 19c) and a molar ratio of 10 / 90 (Test 20c), does not produce a high added value liquid.

[0215] Although not specifically described in Table 1 below, the catalyst 5 Ni5Co-CeAl200 (30-70) (Al / Ce=70 / 30) of the present invention of Run 14i and the catalyst 8 Ni5Co2K-CeAl200 (50-50) of Run 15i allow the production of large amounts of liquid. Therefore, these catalysts containing a cobalt promoter are very effective for a single-step heavy DRM direct conversion process.

[0216] Despite its high catalytic performance, the catalyst 10Ni5Ce-Al200 of test 3c (in which cerium was not mixed with alumina on the support) could not be obtained as a liquid.

[0217] [Table 1]

[0218] Table 2 below shows the catalysts tested and shows the catalytic activity results in terms of conversion, selectivity and yield obtained from a gas mixture containing CH4 and H2O (SRM).

[0219] catalyst <![CDATA[X CH4 Conversion rate [%]]]> <![CDATA[Y H2 Yield [%]]]> Gaseous hydrocarbon production 1’i 10Ni-CeAl200(30 / 70) 64 67 O 2’i 15Ni-CeAl200(30 / 70) 41 47 O 3’i 7Ni3La-CeAl200(30 / 70) 51 56 O 4’i 10Ni3La-CeAl200(30 / 70) 47 52 O 5’i 10Ni3Fe-CeAl200(30 / 70) 40 45 O 6’i 10Ni3Y-CeAl200(30 / 70) 54 58 O 7’i 10Ni3Co-CeAl200(30 / 70) 51 55 O 8’i 10Ni3Mg-CeAl200(30 / 70) 45 50 O 9’c 10Ni-Al200 33 40 O 10’c 10Cu-Al200 7 14 O

[0220] [Table 2]

Claims

1. A method for converting a gas or a gas mixture containing methane (CH4) according to a CH4 reforming reaction, characterized in that: The method is carried out in the presence of a cold plasma and a 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 further 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 of claim 2, wherein at least one accelerator is: - accelerators of the alkali metal type, more particularly accelerators comprising potassium (K), - a promoter of transition metal type, more particularly a promoter comprising cobalt (Co), copper (Cu), zinc (Zn), manganese (Mn), yttrium (Y), iron (Fe) or a mixture thereof, - an alkaline earth metal type promoter, more particularly a promoter comprising magnesium (Mg), and / or - Lanthanide-type promoters, more particularly promoters comprising yttrium, lanthanum (La) or mixtures thereof.

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

5. The process according to any one of claims 2 to 4, wherein the mass content of nickel in the catalytic system is 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 of the preceding claims, wherein the cold plasma is generated by a dielectric barrier discharge (DBD).

7. A method according to any one of the preceding claims for converting a gas mixture containing methane (CH4) and carbon dioxide (CO2) according to a dry reforming of methane (DRM) reaction, characterized in that They produce synthesis gas, liquid hydrocarbons, gaseous hydrocarbons, aromatic hydrocarbons, oxygenates (especially alcohols, acids, ketones, esters, ethers, aldehydes) and / or liquid fuels.

8. A method according to any one of the preceding claims 1 to 6 for converting a gas mixture containing methane (CH4) and water vapor (H2O) according to a steam reforming of methane (SRM) reaction, characterized in that It produces synthesis gas, liquid oxygenates and / or gaseous hydrocarbons.

9. A catalyst for converting a gas or gas mixture containing methane (CH4) according to a CH4 reforming reaction, comprising a carrier comprising a mixture of alumina and cerium in a molar ratio between 80 / 20 and 30 / 70.

10. The catalyst according to claim 9, which is activated by cold plasma, preferably produced by dielectric barrier discharge (DBD).

11. The catalyst according to claim 9 or 10, further 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. The catalyst of claim 11, wherein at least one promoter is: - alkali metal type, more particularly potassium; and / or - of transition metal type, more particularly chosen from the group consisting of cobalt, copper, iron, yttrium and mixtures thereof.

13. The catalyst according to claim 11 or 12, wherein the mass content of the promoter in the catalytic system is between 0.1 wt% and 40 wt%, preferably between 0.5 wt% and 25 wt%, relative to the weight of the carrier.

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

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

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