Improved catalyst for manufacturing MWCNT

Abstract

The present invention relates to an iron-free supported catalyst for the selective conversion of hydrocarbons to carbon nanotubes, said catalyst comprising cobalt and vanadium as active catalytic metals in any oxidation state on a catalyst support comprising aluminum oxide hydroxide, wherein the mass ratio of cobalt to vanadium is between 2 and 15, and the mass ratio of cobalt to aluminum is between 5.8 and 10. -2 ~5.8 10 -1 and - the mass ratio of vanadium to aluminum is 5.8 10 -3 ~8.7 10 -2 The present invention also relates to a method for producing said iron-free supported catalyst and a method for producing carbon nanotubes using said iron-free supported catalyst.

Description

Technical Field

[0001] The present invention relates to a supported catalyst system for the conversion of hydrocarbons to carbon nanotubes, particularly an iron-free supported catalyst system for the production of multi-walled carbon nanotubes with improved selectivity and yield.

Background Art

[0002] Carbon nanostructures (CNSs) are a general term for nano-sized carbon structures having various shapes such as nanotubes, nanohairs, fullerenes, nanocones, nanohorns, and nanorods. Carbon nanostructures are widely used in various technical applications because they have very excellent properties.

[0003] Carbon nanotubes (CNTs) are tubular materials composed of hexagonally arranged carbon atoms and have a diameter of approximately 1 to 100 nm. Carbon nanotubes exhibit insulating, conductive, or semiconductive properties depending on their inherent chirality. Carbon nanotubes have a structure in which carbon atoms are strongly covalently bonded to each other. Due to this structure, carbon nanotubes have a tensile strength approximately 100 times that of steel, high flexibility and elasticity, and are chemically stable.

[0004] Carbon nanotubes are classified into three types: single-walled carbon nanotubes (SWCNTs) consisting of a single sheet and having a diameter of about 1 nm, double-walled carbon nanotubes (DWCNTs) consisting of two sheets and having a diameter of about 1.4 to about 3 nm, and multi-walled carbon nanotubes (MWCNTs) consisting of three or more sheets and having a diameter of about 5 to about 100 nm.

[0005] Due to their high chemical stability, flexibility, and elasticity, carbon nanotubes are being considered for commercialization and application in various industrial fields such as, for example, aerospace, fuel cells, composite materials, biotechnology, pharmaceuticals, electrical / electronics, and semiconductor industries.

[0006] Carbon nanotubes are generally manufactured using various methods such as arc discharge, laser cutting, and chemical vapor deposition. However, arc discharge and laser cutting are not suitable for the mass production of carbon nanotubes and require high arc manufacturing costs or expensive laser equipment. Catalytic chemical vapor deposition (CCVD) of hydrocarbons on a metal catalyst offers higher yield and quality compared to other methods and simplifies the manufacturing process on an industrial scale.

[0007] Most research conducted on CCVD technology currently focuses on developing new catalysts and reaction conditions to control the type (single-walled, double-walled, or multi-walled), diameter, length, and purity of carbon nanotubes. The structure, physical properties, and chemical properties of carbon nanotubes are related to their conductivity, mechanical strength, and thermal, optical, and magnetic properties.

[0008] International Publication No. 2003 / 004410 discloses a wide variety of metal oxide systems (Co, Fe, Ni, V, Mo, and Cu, etc.) and catalyst supports (Al(OH)3, Ca(OH)2, Mg(OH)2, Ti(OH)4, Ce(OH)4, and La(OH)3, etc.) for the production of single-walled and multi-walled carbon nanotubes. In this document, various metals and metal mixtures are tested for their selectivity properties, i.e., their ability to selectively produce single-walled, double-walled, or multi-walled carbon nanotubes with respect to a specific proportion of amorphous carbon or fibers simultaneously formed during the reaction.

[0009] European Patent Publication No. 2883609 relates to an impregnated supported catalyst and a carbon nanotube aggregate comprising the impregnated supported catalyst, wherein the impregnated supported catalyst is prepared by successively adding polycarboxylic acid and precursors of primary (Co) and secondary (Fe,Ni) catalyst components to precursors of primary (Mo) and secondary (V) active components to obtain a clear aqueous metal solution, impregnating an aluminum-based granular support with the clear aqueous metal solution, followed by drying and calcination, and the supported catalyst is 0.8-1.5 g / cm³ 3 It is disclosed that it has a bulk density of [value].

[0010] U.S. Patent No. 9,956,546 discloses a catalyst for producing carbon nanotubes, comprising a support and a supported metal graphitide catalyst, wherein the metal graphitide catalyst is a multi-component metal catalyst comprising a primary catalyst and an auxiliary catalyst, the primary catalyst being selected from Co, Fe and mixtures thereof, and the auxiliary catalyst being V, and the catalyst being a supported catalyst obtained by calcining aluminum hydroxide at a first calcination temperature of 250°C to 500°C to form a support, supporting a catalyst metal precursor on the support, and calcining the catalyst metal precursor supported on the support at a second calcination temperature of 450°C to 800°C.

[0011] European Patent Publication No. 3053877 describes a method for producing carbon nanotubes, 1 m 2 The present invention discloses a method comprising the steps of forming a support by first calcining a support precursor having a BET specific surface area of ​​less than / g at a temperature of 100 to 450°C, supporting a metal graphitized catalyst on the support, preparing a supported catalyst by second calcining the catalyst supported on the support at a temperature of 100 to 500°C, and forming carbon nanotubes by contacting the supported catalyst with a carbon source in a gas phase, wherein the support precursor is aluminum trihydrate and the metal graphitized catalyst is a binary metal catalyst selected from Co / Mo, Co / V, Fe / Mo, and Fe / V.

[0012] U.S. Patent Publication 2008213160 discloses a method for synthesizing a supported catalyst for the production of multi-walled carbon nanotubes, comprising the steps of: mixing Al(OH)3 powder having a particle size of less than about 80 μm with an aqueous solution of iron and cobalt salt; forming a paste overall; drying the paste until a powder with a moisture concentration of less than about 5% by mass is obtained; selecting a particle size fraction of the supported catalyst having a particle size of less than about 63 μm; and producing nanotubes using the supported catalyst having a particle size of less than about 63 μm.

[0013] Korean Patent No. 101781252 discloses a method for producing carbon nanotube aggregates, comprising the steps of: heat-treating a carrier precursor containing layered metal hydroxide and non-layered metal hydroxide to form a porous carrier; supporting a catalyst metal or catalyst metal precursor on the carrier to form a supported catalyst; and forming carbon nanotube aggregates by bringing the supported catalyst and a carbon-containing compound into contact with each other under a heated area to form bundled and entangled carbon nanotube aggregates. The catalyst metal is a combination of elements selected from iron, cobalt and nickel, elements selected from titanium, vanadium and chromium, and elements selected from molybdenum (Mo) and tungsten (W).

[0014] European Patent Publication No. 3156125 describes a method for producing carbon nanotube aggregates, - A step of mixing the carrier with an aqueous solution of a metal graphitized catalyst precursor to form a paste. - A process of drying the paste to remove water, followed by calcination to obtain a supported catalyst, and, - A process of contacting a supported catalyst with a carbon-containing compound under heating conditions and allowing them to react with each other. Includes, - To control the bulk density of carbon nanotubes, the rate of water removal from the paste is adjusted to 5-30% by mass. Graphitization catalysts are binary or multicomponent catalysts containing only iron (Fe) or one or more metals selected from cobalt (Co), molybdenum (Mo), and vanadium (V).

[0015] European Patent Publication No. 3053880 describes a method for producing carbon nanotube aggregates, comprising the steps of: calcining aluminum hydroxide at a first calcination temperature of 100°C to 500°C to form a support; supporting a catalyst metal precursor on the support; calcining the catalyst-containing support at a second calcination temperature of 100°C to 800°C to obtain a supported catalyst; and contacting the supported catalyst with a carbon-containing compound under heating to cause a reaction between them, resulting in a carbon nanotube aggregate yield of 10 kg / m³. 3The first calcination temperature, second calcination temperature, amount of supported catalyst, or reaction time are controlled to achieve the above bulk density. The catalyst metal includes Fe, Co, Mo, V, or a combination of two or more of these. The metal graphitization catalyst may be a composite catalyst consisting of a main catalyst and an auxiliary catalyst. In this case, the main catalyst may include iron (Fe) or cobalt (Co), and the auxiliary catalyst may be molybdenum (Mo), vanadium (V), or a combination thereof. To prepare the supported catalyst, an organic acid is added to the catalyst metal in a molar ratio of 5:1 to 30:1.

[0016] Carbon nanotubes are attracting attention as a potential electrode material for lithium batteries.

[0017] A typical lithium-ion battery utilizes a carbon anode (negative electrode) and a lithified transition metal oxide cathode (positive electrode) located on the opposite side of a microporous polymer separator.

[0018] A lithium-ion battery starts with all the lithium in the cathode, and as it charges, some of this lithium moves to the anode and is incorporated into the carbon anode.

[0019] Lithium-ion battery failure is a result of dendrite formation within the battery. Dendrites are tiny metallic deposits that can form inside a battery. Dendrite formation generally begins at the anode and, if it extends through the separator to the cathode, forms an internal short circuit.

[0020] If iron impurities from any electrode dissolve in the electrolyte, there is a significant risk that these impurities will migrate to the anode and initiate dendrite growth through deposition. For this reason, iron-free materials are required for the electrodes.

[0021] When MWCNTs are used as electrode material, there is a risk of battery failure caused by these dendrites.

[0022] Consequently, MWCNTs containing interstitial iron components obtained by methods using catalyst systems that include iron-based graphitization catalysts should be avoided.

[0023] Therefore, there is a demand for MWCNTs produced by a CCVD process of hydrocarbons on iron-free metal catalysts, which offers improved selectivity and productivity. [Prior art documents] [Patent Documents]

[0024] [Patent Document 1] International Publication No. 2003 / 004410 [Patent Document 2] European Patent Publication No. 2883609 [Patent Document 3] U.S. Patent No. 9956546 [Patent Document 4] European Patent Publication No. 3053877 [Patent Document 5] U.S. Patent Publication No. 2008213160 [Patent Document 6] Korean Patent No. 101781252 [Patent Document 7] European Patent Publication No. 3156125 [Patent Document 8] European Patent Publication No. 3053880 [Overview of the Initiative] [Problems that the invention aims to solve]

[0025] The object of this invention is to disclose an iron-free catalyst for the production of MWCNTs, a method for preparing the same, and the use of these carbon nanotubes in batteries. [Means for solving the problem]

[0026] The present invention relates to an iron-free supported catalyst for the selective conversion of hydrocarbons to carbon nanotubes, wherein the catalyst contains cobalt and vanadium as active catalyst metals in any oxidation state on a catalyst support containing aluminum hydroxide, - The mass ratio of cobalt to vanadium is from 2 to 15, - The mass ratio of cobalt to aluminum is 5.8 × 10 -2 ~5.8 × 10 -1 and, - The mass ratio of vanadium to aluminum is 5.8 × 10 -3 ~8.7 × 10 -2 is disclosed.

[0027] Preferred embodiments of the present invention include one or more of the following features: - The mass ratio of cobalt to vanadium is from 3.0 to 11, - The mass ratio of cobalt to aluminum is 1.2 × 10 -1 ~4.3 × 10 -1 and, - The mass ratio of vanadium to aluminum is 1.2 × 10 -2 ~5.8<00 / / × 10 -2 is, - The iron-free catalyst of the present invention further contains molybdenum as an active catalyst, - The mass ratio of molybdenum to aluminum is 1.2 × 10 -3 ~2.3 × 10 -2 and, - The mass ratio of cobalt to the combined mass of vanadium and molybdenum is from 2 to 15, - An iron-free molybdenum containing the catalyst of the present invention, - The mass ratio of molybdenum to aluminum is 1.7 × 10 -3 ~1.7 × 10-2 , and, - The mass ratio of cobalt to the combined mass of vanadium and molybdenum is 3 to 11. -The catalyst support of the present invention comprises aluminum hydroxide and / or aluminum oxide and hydroxyl acid Based on the total amount of aluminum oxide, it contains at least 30% by mass of aluminum hydroxide oxide, - The iron-free catalyst exhibited the maximum diffraction peak at a 2θ angle of 35° to 38° in XRD patterns recorded at 2θ angles of 10° to 80°. If we define the intensity of the maximum diffraction peak and the intensity of the diffraction peak at a 2θ angle of -17° to 22° as "a" and "b", respectively, then the ratio b / a is in the range of 0.10 to 0.7, and, When the intensity of the diffraction peak at a 2θ angle from -63° to 67° is defined as "c", it is disclosed that the ratio c / a is in the range of 0.51 to 0.7.

[0028] Preferred embodiments of the method for producing an iron-free supported catalyst of the present invention have one or more of the following characteristics: -A water-based mixture of aluminum hydroxide and a catalyst precursor is heated at a predetermined temperature of at least 100°C for at least 1 hour, at least 0.1 m 3 Dryed with an airflow of / h, - A water-based mixture of aluminum hydroxide and a catalyst precursor is contained in a predetermined temperature between 100 and 150°C for a period of 1 to 10 hours, with a concentration of 0.1 m 3 / h~1m 3 It is dried by the airflow contained within / h. -A water-based mixture of aluminum hydroxide and a catalyst precursor is dried by spray drying. - The dry mixture is contained in temperatures between 200 and 600°C for a period of 1 to 24 hours, 0.1 m 3 / h ~1m 3 It is fired in the airflow contained within / h. - The calcined product has a volume median particle size (D) of less than 450 μm. 50 ) is ground into a powder having the following properties: - Aluminum hydroxide, 5-16 m 2 Characterized by the specific surface area (BET) contained within / g, -Aluminum hydroxide is selected from gibbsite or bayerite. - Cobalt-based precursors, vanadium-based precursors, molybdenum-based precursors and The carrier precursor has a purity of at least 95%, - Cobalt-based precursors include cobalt(II) acetate tetrahydrate and / or cobalt(II) nitrate. Six It is a hydrate, with a vanadium-based precursor being ammonium metavanadate and a molybdenum-based precursor being ammonium heptamolybdate tetrahydrate. -The polycarboxylic acid is a mixture of citric acid and malic acid, with a molar ratio of malic acid to citric acid of 0.5 to 5.

[0029] Preferred embodiments of the method for producing an iron-free supported catalyst of the present invention have one or more of the following characteristics: -A water-based mixture of aluminum hydroxide and a catalyst precursor is heated at a predetermined temperature of at least 100°C for at least 1 hour, at least 0.1 m 3 Dryed with an airflow of / h, - A water-based mixture of aluminum hydroxide and a catalyst precursor is contained in a predetermined temperature between 100 and 150°C for a period of 1 to 10 hours, with a concentration of 0.1 m 3 / h~1m 3 It is dried by the airflow contained within / h. -A water-based mixture of aluminum hydroxide and a catalyst precursor is dried by spray drying. - The dry mixture is contained in temperatures between 200 and 600°C for a period of 1 to 24 hours, 0.1 m 3 / h~1m 3 It is fired in the airflow contained within / h. - The calcined product has a volume median particle size (D) of less than 450 μm. 50 ) is ground into a powder having the following properties: - Aluminum hydroxide, 5-16 m 2Characterized by the specific surface area (BET) contained within / g, -Aluminum hydroxide is selected from gibbsite or bayerite. - The cobalt-based precursor, vanadium-based precursor, molybdenum-based precursor, and carrier precursor have a purity of at least 95%. - The cobalt-based precursor is cobalt(II) acetate tetrahydrate and / or cobalt(II) nitrate tetrahydrate, the vanadium-based precursor is ammonium metavanadate, and the molybdenum-based precursor is ammonium heptamolybdate tetrahydrate. - The polycarboxylic acid is a mixture of citric acid and malic acid, with a molar ratio of malic acid to citric acid of 0.5 to 5. We will disclose this.

[0030] The present invention relates to a method for producing multi-walled carbon nanotubes from an iron-free supported catalyst, comprising the following steps: - The process of filling the reactor with catalyst, A process of heating the catalyst to a temperature within the range of -500℃ to 900℃. A process of supplying a carbon source to the reactor while maintaining a temperature between -500°C and 900°C. - A step of contacting the catalyst with a carbon source for at least 1 minute. Further disclosures include methods that include the following:

[0031] Preferred embodiments of the method for producing multi-walled carbon nanotubes of the present invention have one or more of the following features: - The space time of the catalyst and carbon source is 0.1 to 0.8 gh / mol. - The carbon source is selected from the group consisting of methane, ethylene, acetylene, methanol, ethanol, and mixtures thereof. We will disclose this.

[0032] The present invention further discloses a multilayer carbon nanotube obtained by a method for producing a multilayer carbon nanotube of the present invention, comprising 0.1 to 13% by mass, preferably 1 to 10% by mass, of an iron-free supported catalyst, wherein the iron-free supported catalyst is obtained by a method for preparing an iron-free supported catalyst of the present invention.

[0033] The present invention further discloses a polymer matrix containing the multilayer carbon nanotubes obtained by the method of the present invention.

[0034] The present invention further discloses the use of the multilayer carbon nanotubes obtained by the method of the present invention in batteries. [Modes for carrying out the invention]

[0035] The present invention discloses an iron-free supported catalyst that produces increased selectivity in the production of multilayer nanotubes having specific properties, wherein the improved multilayer selectivity is obtained in high yield while reducing catalyst consumption. The present invention also discloses an economically attractive method for obtaining the supported catalyst.

[0036] In this invention, an iron-free catalyst means reducing the iron content as much as possible, except for unavoidable trace amounts. Nevertheless, the iron content within the total transition metal content is less than 1000 ppm, preferably less than 500 ppm, more preferably less than 200 ppm, and most preferably less than 100 ppm.

[0037] In a first embodiment of the present invention, the supported catalyst is an iron-free two-component catalyst comprising, firstly, a cobalt-based catalyst component and secondly, a vanadium-based catalyst component, preferably both in the form of oxides, and is supported on a carrier comprising aluminum oxide (Al2O3) and / or aluminum hydroxide (Al(OH)3) and aluminum hydroxide oxide (AlO(OH)) (hereinafter referred to as "carrier element").

[0038] In a second embodiment of the present invention, the supported catalyst is an iron-free three-component graphitizing catalyst comprising, firstly, a cobalt-based catalyst component, secondly, a vanadium-based catalyst component, and a molybdenum-based catalyst component, preferably all in the form of oxides, and is supported on a carrier comprising aluminum oxide and / or aluminum hydroxide and aluminum hydroxide oxide (hereinafter referred to as "carrier elements").

[0039] Preferably, the support precursor is aluminum hydroxide, more preferably gibbsite or bayerite.

[0040] Preferably, the carrier precursor has a volume median particle size (D) of less than 70 μm. 50 ) and 20m 2 Characterized by a specific surface area of ​​less than / g.

[0041] Preferably, the carrier precursor is 3 to 18 m 2 / g, preferably 5-16m 2 Gibbsite is characterized by its specific surface area per gram.

[0042] Preferably, the cobalt-based catalyst precursor of the graphitization catalyst is obtained from a cobalt-based precursor, and the precursor is Co(NO3) 2· 6H2O, Co2(CO)8 and Co(O a c) Cobalt salts, cobalt oxides, or cobalt compounds such as 24H2O.

[0043] Preferably, the vanadium-based catalyst precursor of the graphitization catalyst is obtained from a vanadium-based precursor, and the precursor is a vanadium salt such as NH4VO3, a vanadium oxide, or a vanadium compound.

[0044] Preferably, the molybdenum-based catalyst precursor of the graphitization catalyst is obtained from a molybdenum-based precursor, and the precursor is (NH4)6Mo7O 24· These are molybdenum salts, molybdenum oxides, or molybdenum compounds such as 4H2O, Mo(CO)6, or (NH4)2MoS4.

[0045] The present invention relates to a method for producing the supported catalyst, comprising the following steps: -Additional steps: -The method of the first embodiment involves adding a specific amount of water containing a specific amount of one or more polycarboxylic acids and / or salts of those polycarboxylic acids to a specific amount of one or more vanadium-based precursors and mixing until a clear solution is obtained. -The method of the second embodiment involves adding a specific amount of water containing a specific amount of one or more polycarboxylic acids and / or salts of those polycarboxylic acids to a specific amount of one or more vanadium-based precursors and a specific amount of one or more molybdenum-based precursors, and mixing until a clear solution is obtained. - A step of contacting one or more cobalt-based precursors with an aqueous solution containing a vanadium-based precursor and an optional molybdenum-based precursor, wherein the one or more cobalt-based precursors are added in the form of a powder, a wet powder, or an aqueous solution, or in any form having the water content contained in the powder and aqueous solution. - Add the carrier precursor and mix for at least 1 minute. -By appropriate means, preferably at a fixed predetermined temperature of at least 100°C, for at least 1 hour, at least 0.1 m 3 A process of drying the mixture with an airflow of / h, -By appropriate means, preferably at a fixed predetermined temperature of at least 200°C, for at least 1 hour, at least 0.1 m 3 A process of firing the mixture with an airflow of / h, - The calcined product has a volume median particle size (D) of less than 450 μm. 50 ) The process of crushing, Methods including the following are also disclosed.

[0046] The polycarboxylic acid used in the method of the present invention is selected from the group consisting of dicarboxylic acids, tricarboxylic acids, tetracarboxylic acids, and mixtures thereof. Examples of these polycarboxylic acids include oxalic acid, succinic acid, tartaric acid, malic acid, and fumaric acid. ,stomachIt contains taconic acid, citraconic acid, mesaconic acid, citric acid, 2-butene-1,2,3-tricarboxylic acid, and 1,2,3,4-butanetetracarboxylic acid.

[0047] In this invention, a polycarboxylic acid salt means a polycarboxylic acid in which at least one carboxylic acid group is converted to an ammonium salt or an alkali metal salt.

[0048] In this case, the polycarboxylic acid is citric acid or malic acid, and the salt of the polycarboxylic acid is an ammonium salt.

[0049] The addition involves adding one or more polycarboxylic acids and / or salts thereof such that the resulting aqueous solution contains 0.5 to 25%, more preferably 4 to 15%, of the polycarboxylic acids and / or salts.

[0050] In this method, the polycarboxylic acid used is a mixture of citric acid and malic acid, with a malic acid / citric acid molar ratio of 0.5 to 5, preferably 1.5 to 2.5.

[0051] In the method of the first embodiment, 1000 g of the carrier precursor is added to an aqueous mixture obtained by mixing an aqueous solution containing 5 to 70 g of a vanadium-based precursor in 300 to 3000 g of water with 80 to 850 g of a cobalt-based precursor, either as a powder or as an aqueous mixture containing up to 3000 g of water.

[0052] In the method of the second embodiment, 1000 g of the carrier precursor is added to an aqueous mixture obtained by mixing an aqueous solution containing 5 to 70 g of vanadium-based precursor and 1 to 15 g of molybdenum precursor in 300 to 3000 g of water, and 80 to 850 g of cobalt-based precursor as a powder or as an aqueous mixture containing up to 3000 g of water.

[0053] In the method according to the present invention, Water containing one or more polycarboxylic acids and / or salts of polycarboxylic acids is added to a vanadium-based precursor and an optional molybdenum-based precursor at a temperature between -20 and 90°C, preferably between 50 and 70°C, and mixed, for example, by means of a paddle mixer, for a period of 5 to 60 minutes, preferably between 10 and 20 minutes. - A cobalt-based precursor, either as a powder, a wet precursor, or an aqueous solution, is added to an aqueous solution containing a vanadium-based precursor and an optional molybdenum precursor. When adding as a wet precursor or an aqueous solution, water is added to the cobalt-based precursor at a temperature between 20 and 90°C, preferably between 50 and 70°C, and mixed for a period of 5 to 60 minutes, preferably 10 to 20 minutes. - The carrier precursor is added to an aqueous solution containing a cobalt-based precursor, a vanadium-based precursor, and an optional molybdenum precursor, and mixed (to avoid aggregation). -After the addition of the carrier precursor is complete, the resulting paste is further mixed for a period of 5 to 60 minutes, preferably 10 to 20 minutes. - Transfer the paste to a ceramic crucible with a large opening: -As the first step, the temperature is raised to a range of 100 to 150°C, preferably between 110 and 130°C, for a period of 60 to 600 minutes, preferably between 150 and 330 minutes, and the temperature is 0.1 to 1.0 m. 3 Preferably, 0.4 to 0.6 m between / h 3 With an airflow of / h, heating is performed, and the temperature is obtained using a heating gradient that is between 1.0 and 5.0°C / min, and further, -As a second step, the temperature is raised to a range of 200-600°C, preferably between 220-550°C, more preferably between 250-550°C, for a period of 1-24 hours, preferably between 60-600 minutes, more preferably between 150-330 minutes, with a duration of 0.1-1.0 m 3 Preferably, 0.4 to 0.6 m between / h 3 Heating is performed with an airflow of / h, and the temperature is obtained using a heating gradient that is between 1.0 and 5.0°C / min. - The calcined product has a volume median particle size (D) of less than 450 μm, preferably less than 250 μm. 50 It is crushed into pieces.

[0054] After both heating cycles, the carrier precursor is converted into a calcined product, i.e., a carrier containing one or more components selected from the group consisting of hydroxides, hydroxide oxides, and oxides, while the catalyst precursor is converted into an oxide, and the graphitization catalyst is preferably present as a mixed oxide.

[0055] The type of heat source used in both heating cycles is not limited to induction heating, radiant heating, laser, IR, microwave, plasma, UV, or surface plasmon heating.

[0056] The inventors observed that the BET of the support precursor, Al(OH)3, is an important parameter for obtaining an iron-free supported catalyst that enables the production of MWCNTs with high carbon yield.

[0057] In the method of the present invention, the BET of the Al(OH)3 support precursor is 3 to 18 m 2 Between / g, preferably 5-16 m 2 It is contained within the / g range.

[0058] The conversion of gibbsite to boehmite, as studied by X-ray diffraction, is described, for example, in Applied Catalysis A: General 167 (1998), pp. 203-213 by A.M.D. Cruz et al.

[0059] Qualitative and quantitative analysis of aluminum hydroxide oxide (boehmite) in aluminum oxide (bauxite) by X-ray diffraction is described, for example, in GAB Soares et al., Rev. Esc. Minas, 2014, vol.67, n.1, pp.41-46.

[0060] The inventors have found that while the presence of aluminum hydroxide oxide in iron-free supported catalysts can be reliably and easily identified by X-ray diffraction, this quantification is susceptible to uncertainty and should be limited to estimating the mass percentage of AlO(OH) relative to the total of Al2O3, Al(OH)3, and AlO(OH).

[0061] In any case, the inventors observed that aluminum hydroxide oxide was present in an amount of at least 30% by mass, preferably at least 40% by mass, more preferably at least 50% by mass, most preferably at least 60% by mass, and even more preferably at least 70% by mass, of the total of Al2O3, Al(OH)3, and AlO(OH).

[0062] In the method of the present invention, the first heating cycle intended to dry the paste may be replaced by alternative drying methods or combinations thereof that are well known in the art. Among these, flash drying and spray drying are widely used.

[0063] A typical supported catalyst according to the present invention is given by formula (Co v V w )O y .(carrier)z or (Co v V w Mo x )O y It is represented by (carrier) z.

[0064] Iron-free two-component graphitization catalysts are: -Aluminum hydroxide oxide, preferably based on the total of aluminum oxide, aluminum hydroxide, and aluminum hydroxide oxide, comprising at least 30% by mass of aluminum hydroxide oxide. - The mass ratio of cobalt to aluminum is 5.8 10 -2 ~5.8 10 -1 Preferably 1.2 10 -1 ~4.3 10 -1 And, - The mass ratio of vanadium to aluminum is 5.8 10 -3 ~8.7 10-2 Preferably 1.2 10 -2 ~5.8 10 -2 That is, It is characterized by this.

[0065] Iron-free two-component graphitization catalysts are further characterized by having a cobalt-to-vanadium mass ratio between 2 and 15, preferably between 3.0 and 11.

[0066] Iron-free three-component graphitization catalysts are: -Aluminum hydroxide oxide, preferably based on the total of aluminum oxide, aluminum hydroxide, and aluminum hydroxide oxide, comprising at least 30% by mass of aluminum hydroxide oxide. - The mass ratio of cobalt to aluminum is 5.8 10 -2 ~5.8 10 -1 Preferably 1.2 10 -1 ~4.3 10 -1 And, - The mass ratio of vanadium to aluminum is 5.8 10 -3 ~8.7 10 -2 Preferably 1.2 10 -2 ~5.8 10 -2 And, - The mass ratio of molybdenum to aluminum is 1.2 10 -3 ~2.3 10 -2 Preferably 1.7 10 -3 ~1.7 10 -2 That is, It is characterized by the following.

[0067] The iron-free three-component graphitization catalyst is further characterized by the ratio of the mass of cobalt to the combined mass of vanadium and molybdenum being between 2 and 15, preferably between 3.0 and 11.

[0068] The iron-free supported catalyst of the present invention is characterized by an XRD pattern recorded at a 2θ angle of 10° to 80°, having the maximum diffraction peak defined as "a" at a 2θ angle of 35° to 38°. - The ratio b / a of the intensity of the diffraction peak at a 2θ angle of 17° to 22°, defined as "b", to the intensity of the maximum diffraction peak "a", is in the range of 0.10 to 0.7, preferably in the range of 0.12 to 0.7, and more preferably in the range of 0.14 to 0.7. - The ratio c / a, which is defined as the intensity of the diffraction peak at a 2θ angle of 63° to 67° defined as "c", to the intensity of the maximum diffraction peak "a", is in the range of 0.51 to 0.7, and, - Meets both criteria b / a (0.10~0.7) and c / a (0.51~0.7).

[0069] To prepare MWCNT, a supported iron-free catalyst is brought into contact with a carbon source in a gas phase.

[0070] By using a supported catalyst, carbon nanotubes can be grown by chemical vapor deposition synthesis through the decomposition of a carbon source, and carbon nanotube aggregates can be produced.

[0071] In chemical vapor deposition synthesis, an iron-free graphitization catalyst is packed into the reactor, and then a carbon source in the gas phase is supplied to the reactor at ambient pressure and high temperature to produce carbon nanotube aggregates grown on the supported catalyst. As described above, carbon nanotubes grow by the thermal decomposition of hydrocarbons as the carbon source. The thermally decomposed hydrocarbons permeate and saturate the graphitization catalyst, and carbon is deposited from the saturated graphitization catalyst to form a hexagonal ring structure.

[0072] Chemical vapor deposition synthesis can be carried out by a method in which a supported catalyst is supplied into a reactor, and at least one carbon source selected from the group consisting of C1-C6 saturated hydrocarbons, C1-C6 unsaturated hydrocarbons, C1-C2 alcohols, and mixtures thereof is optionally introduced into the reactor together with a reducing gas (e.g., hydrogen) and a carrier gas (e.g., nitrogen) at a temperature between 500 and about 900°C, preferably between 600 and 800°C, and more preferably between 650 and 750°C. Carbon nanotubes can be grown for 1 minute to 5 hours, preferably between 1 minute and 30 minutes, after the carbon source has been introduced onto the supported catalyst.

[0073] Preferably, the space time, defined as the mass in grams of the supported catalyst divided by the flow rate of the reactant stream in moles / hour under standard temperature and pressure conditions, is between 0.1 and 0.8 gh / mol, preferably between 0.2 and 0.6 gh / mol, during a period of 10 to 30 minutes, preferably 15 to 25 minutes.

[0074] The type of heat source for the heat treatment in the preparation method of MWCNT is not limited to induction heating, radiant heating, laser, IR, microwave, plasma, UV, or surface plasmon heating.

[0075] Any carbon source capable of supplying carbon and existing in the gas phase at temperatures above 300°C can be used in chemical vapor deposition synthesis, without particular limitations. The gas phase carbonaceous material may be any carbon-containing compound, but is preferably a compound consisting of up to six carbon atoms, more preferably a compound consisting of up to four carbon atoms. Examples of these gas phase carbonaceous materials include, but are not limited to, carbon monoxide, methane, ethane, ethylene, methanol, ethanol, acetylene, propane, propylene, butane, butadiene, pentane, pentene, cyclopentadiene, hexane, cyclohexane, benzene, and toluene. These gas phase carbonaceous materials may be used individually or in mixtures thereof. A mixed gas of a reducing gas (e.g., hydrogen) and a carrier gas (e.g., nitrogen) transports the carbon source, prevents the carbon nanotubes from burning at high temperatures, and aids in the decomposition of the carbon source.

[0076] The iron-free catalyst of the present invention can produce MWCNTs with a carbon yield between 800 and 2500% by mass, preferably between 1000 and 2400% by mass, and more preferably between 1100 and 2300% by mass.

[0077] The carbon yield by mass is, 100(m tot -m cat ) / m cat Defined as, m tot m is the total mass of the product after the reaction. cat This is the mass of the catalyst used in the reaction. [Examples]

[0078] The following exemplary embodiments are merely illustrative of the present invention and are not intended to limit or define the scope of the invention.

[0079] Example 1 Synthesis of an iron-free two-component graphitization catalyst At 60°C, 5000 parts by mass of water containing 277 parts by mass of citric acid and 387 parts by mass of malic acid was added to 333 parts by mass of ammonium metavanadate, and the mixture was mixed for 15 minutes using a paddle mixer to obtain the first aqueous solution.

[0080] Similarly, at 60°C, 5000 parts by mass of water were added to 4109 parts by mass of cobalt(II) acetate tetrahydrate, and the mixture was mixed for 15 minutes using a paddle mixer to obtain a second aqueous solution.

[0081] The second aqueous solution was added to the first aqueous solution and mixed for 15 minutes using a paddle mixer.

[0082] A mixture of the first and second aqueous solutions contains 15 m 2 13,333 parts by mass of aluminum hydroxide (Apyral® 200 SM-Nabaltec) having a specific surface area (BET) of 1 / g was added and mixed for 15 minutes using a paddle mixer.

[0083] Subsequently, the paste obtained in this manner is transferred to a ceramic crucible with a large opening and subjected to a heating process, with the paste heated at a temperature gradient of 2°C / min and 0.5m 3 The sample was heated to 120°C using an airflow of 1 / h and maintained at 120°C for 5 hours.

[0084] After 5 hours at 120°C, the paste is further heated to a temperature of 400°C using a heating gradient of 2°C / min, and 0.5m 3 The temperature was maintained at 400°C for 5 hours while maintaining an airflow of 1 / h.

[0085] The solid material obtained in this way is cooled to room temperature and then ground using a conical grinder to a volume median particle size (D) of 120 μm. 50 It was ground into a powder characterized by ).

[0086] Example 2 Synthesis of an iron-free three-component graphitization catalyst Example 1 was repeated at 60°C, except that 5000 parts by mass of water containing 277 parts by mass of citric acid and 387 parts by mass of malic acid was added to 340 parts by mass of ammonium metavanadate and 64 parts by mass of ammonium heptamolybdate tetrahydrate to obtain a first aqueous solution. A second aqueous solution was obtained at 60°C by adding 5000 parts by mass of water to 4931 parts by mass of cobalt(II) acetate tetrahydrate.

[0087] A mixture of the first and second aqueous solutions contains 15 m 2 13,333 parts by mass of aluminum hydroxide (Apyral® 200 SM-Nabaltec) having a specific surface area (BET) of 1 / g was added and mixed for 15 minutes using a paddle mixer.

[0088] Examples 3-8 In Examples 3-8, - The vanadium-based precursor is ammonium metavanadate. - The molybdenum-based precursor is ammonium heptamolybdate tetrahydrate. -The cobalt-based precursors in Examples 3 and 5-8 are cobalt(II) acetate tetrahydrate. - The cobalt-based precursor of Example 4 is cobalt(II) nitrate. Six It is a hydrate, -The Al(OH)3 in Example 3 is 5.4m 2 ALOLT 59 AF (Inotal) is characterized by a BET of / g, -The Al(OH)3 in Example 4 is 4m 2 Hydral 710 (Huber) is characterized by a BET of / g, -The Al(OH)3 in Examples 5 and 6 is 3.5m 2 Apyral 40 CD (Nabaltec) characterized by a BET of / g, -The Al(OH)3 in Examples 7 and 8 was 10-12 m 2 This is Martinal OL-111 LE (Huber) characterized by a BET of / g.

[0089] Examples 3-7 were carried out using the same process conditions as Example 1, namely the mixing temperature and time, drying and firing conditions (temperature, heating gradient, time, airflow), and a D of approximately 120 μm. 50 The preparation was carried out using grinding conditions to obtain the following, except that a cobalt-based precursor was added as a powder to an aqueous solution containing a vanadium-based precursor and an optional molybdenum-based precursor, the aqueous solution containing 5000 parts by mass of water.

[0090] Example 8 is a comparative example in which a carrier precursor was calcined before being added to an aqueous mixture containing a cobalt-based precursor, a vanadium-based precursor, and a molybdenum-based precursor. First, the carrier precursor was impregnated with water and stirred at 60°C for 12 hours before drying at 60°C and 100 mbar. Subsequently, the dried carrier precursor was calcined at 400°C for 5 hours under a nitrogen atmosphere, and then the calcined carrier was added to the aqueous mixture of catalyst precursors. The aqueous mixture containing the cobalt-based precursor, vanadium-based precursor, and molybdenum-based precursor was obtained by adding the cobalt-based precursor as a powder to an aqueous solution containing the vanadium-based precursor, molybdenum base, and 5000 parts by mass of water. The resulting paste was heated with a heating gradient of 2°C / min and 0.5 m 3 The paste was heated to 120°C using an airflow of 1 / h and maintained at 120°C for 5 hours. Subsequently, the paste was further heated to a temperature of 400°C using a heating gradient of 2°C / min, and 0.5m 3 The sample was maintained at 400°C for 5 hours while keeping the airflow at / h. No diffraction peaks corresponding to boehmite or AlO(OH) were detected.

[0091] Table 1 reports the amounts of catalyst precursors, support precursors, and polycarboxylic acids and / or salts thereof for Examples 3 to 8, expressed as parts per 5000 parts by mass of water.

[0092] [Table 1]

[0093] Synthesis of MWCNT 1.0 g of the iron-free graphitized supported catalyst of Examples 1 to 8 was spread in a quartz container and then placed at the center of a quartz tubular reactor having an inlet and an outlet.

[0094] The center of the quartz tube reactor in which the container containing the catalyst was installed was heated to a temperature of 700 °C.

[0095] Subsequently, ethylene gas, nitrogen and hydrogen were flowed into the quartz tube reactor at flow rates of 1.744 l / min (C2H4), 0.857 l / min (N2) and 0.286 l / min (H2) for 20 minutes.

[0096] Table 2 shows the carbon yields (column 8) of MWCNT (Examples A to H) (column 1) prepared using the catalysts of Examples 1 to 8 (column 2).

[0097] Table 2 further shows - the ratio of cobalt to aluminum of the supported catalyst (column 3), - the ratio of vanadium to aluminum of the supported catalyst (column 4), - the ratio of molybdenum to aluminum of the supported catalyst (column 5), - the ratio of cobalt to vanadium of the iron-free binary graphitized supported catalyst and the ratio of cobalt to vanadium and molybdenum of the iron-free ternary graphitized supported catalyst (column 6), - the BET (m <0> 2 2 / g) of each Al(OH)₃ support precursor (column 7).

[0098]

Table 2

[0099] As is clear from Table 2, in contrast to MWCNTs obtained by the method using an iron-free supported catalyst (Example 8) in which the support precursor is calcined before impregnation with the catalyst precursor, the iron-free supported catalysts of the present invention (Examples 1-7) yield MWCNTs (Examples A-G) with a carbon yield of at least 800%. The MWCNTs with the highest carbon yield were 10-15m 2 The iron-free supported catalyst is obtained from an Al(OH)3 support precursor characterized by the BET contained between / g. The iron-free supported catalyst of Example 8 (=Comparative Example) is obtained when the supported catalyst is 10-12m 2 Despite being prepared from an Al(OH)3 support precursor with a BET of 1 / g, MWCNTs (Example H) yield a carbon yield of 554%. In the iron-free supported catalyst of Example 8 (=Comparative Example), no diffraction peaks corresponding to boehmite and AlO(OH) were detected.

[0100] To their surprise, the inventors observed that, unlike multi-walled carbon nanotubes obtained from a supported catalyst obtained from the same dry mixture calcined at temperatures above 600°C, calcination temperatures between 200°C and 600°C yielded multi-walled carbon nanotubes with a high carbon yield.

[0101] The inventors also observed that the drying method has a similar, albeit lesser, effect on the carbon yield of the final multi-walled carbon nanotubes.

[0102] The effect of the firing temperature is reflected in the ratio of the intensity of the diffraction peaks in the XRD pattern of the supported catalyst, recorded in the 2θ range of 10° to 80°.

[0103] In the XRD pattern, the diffraction peak with maximum intensity at a 2θ angle of 35° to 38° is defined as "a". If the intensity of the diffraction peak at a 2θ angle of 17° to 22° is defined as "b", and the intensity of the diffraction peak at a 2θ angle of 63° to 67° is defined as "c", then multi-walled carbon nanotubes with high carbon yield can be prepared using an iron-free supported catalyst that satisfies both intensity ratio (b / a and c / a) conditions, where the ratio b / a is between 0.10 and 0.7, and the ratio c / a is between 0.51 and 0.7.

[0104] Table 3 reports the 2θ angle values, the net intensity at the 2θ angle, and the intensity ratios b / a and c / a of the supported catalyst obtained from different drying methods and firing temperatures.

[0105] Table 4 reports the carbon yield in mass% of MWCNTs obtained from the iron-free supported catalyst of Example 2 in Example B, for the following catalyst precursor drying: - Heat the precursor paste with a 2°C / min heating gradient and 0.5m 3 Heat to 120°C using an airflow of / h, and dry at 120°C for 5 hours; - The precursor paste is diluted so that 10,000 parts of precursor paste are converted to 25,000 parts of precursor dispersion, and the fluid is thoroughly pumped peristally into a Yamato Scientific GB-210A spray dryer with the following settings: -Blower: 0.5m 3 / h (=hot airflow for drying)) - Sprayer: 0.1 MPa (= air pressure required to generate spray) - Drying temperature: 150°C (= air temperature at the inlet of the drying column) -Pump: 7 (=The flow rate of the pumped liquid, which depends on the pump speed and the viscosity of the liquid, and therefore its dilution. In this experiment, the flow rate is 17 g / min and equals + / -.)

[0106] The inventors observed that calcination of a dry mixture of aluminum hydroxide and catalyst precursor at a temperature of 700°C yielded multi-walled carbon nanotubes with a lower carbon yield, and that the intensity ratio (b / a) was not satisfied at the calcination temperature of 700°C. No diffraction peaks corresponding to boehmite or AlO(OH) were detected.

[0107] The decrease in carbon yield by mass% of MWCNTs in Example B (carbon yield = 2076%) compared to the carbon yield by mass% was obtained by repeating Example B, which uses the iron-free three-component graphitization catalyst of Example 2, by calcining at 550°C and 700°C for 5 hours each. Therefore, a decrease in carbon yield of approximately 14% was observed for the catalyst of Example 2 calcined at 550°C for 5 hours (carbon yield = 1781%) compared to the carbon yield of Example B, while a decrease in carbon yield of 42% was observed for the catalyst of Example 2 calcined at 700°C for 5 hours (carbon yield = 1211%) compared to the carbon yield of Example B.

[0108] The spray-dried iron-free three-component graphitization catalyst from Example 2, which was calcined at 600°C for 1 hour, yielded MWCNTs with a carbon yield of 1840%.

[0109] [Table 3]

[0110] [Table 4]

Claims

1. An iron-free supported catalyst for the selective conversion of hydrocarbons to carbon nanotubes, The catalyst, based on the total amount of aluminum hydroxide and / or aluminum oxide and aluminum hydroxide oxide determined by X-ray diffraction, contains at least 30% by mass of aluminum hydroxide oxide on a catalyst support, and includes cobalt and vanadium as active catalyst metals in any oxidation state. The iron-free supported catalyst is In the XRD patterns recorded at 2θ angles from 10° to 80°, the maximum diffraction peak is found at 2θ angles from 35° to 38°. "a" represents the intensity of the maximum diffraction peak at a 2θ angle between 35° and 38°. If we define "b" as the intensity of the maximum diffraction peak at a 2θ angle from -17° to 22°, then the ratio b / a is between 0.10 and 0.

7. If we define "c" as the intensity of the diffraction peak at a 2θ angle from -63° to 67°, then the ratio c / a is in the range of 0.51 to 0.

7. The iron-free supported catalyst is - The mass ratio of cobalt to vanadium is 2 to 15. - The mass ratio of cobalt to aluminum is 5.8 × 10 －２ ~5.8 x 10 －１ , and, - The mass ratio of vanadium to aluminum is 5.8 × 10⁻⁶ －３ ~8.7 x 10 －２ It is a catalyst.

2. - The mass ratio of cobalt to vanadium is 3.0 to 11. - The mass ratio of cobalt to aluminum is 1.2 × 10⁻⁶ －１ ~4.3 x 10 －１ , and, - The mass ratio of vanadium to aluminum is 1.2 × 10⁻⁶ －２ ~5.8 x 10 －２ The iron-free supported catalyst according to claim 1.

3. As an additional active catalyst, it contains molybdenum. - The mass ratio of molybdenum to aluminum is 1.2×10 －３ to 2.3×10 －２ and - An iron-free catalyst according to claim 1 or 2, wherein the mass ratio of cobalt to the combined mass of vanadium and molybdenum is 2 to 15.

4. - The mass ratio of molybdenum to aluminum is 1.7 × 10⁻⁶ －３ ~1.7 x 10 －２ , and, - The iron-free catalyst according to claim 3, wherein the mass ratio of cobalt to the combined mass of vanadium and molybdenum is 3 to 11.

5. The iron-free catalyst according to any one of claims 1 to 4, wherein the catalyst support contains at least 40% by mass of aluminum hydroxide oxide, based on the total amount of aluminum hydroxide and / or aluminum oxide and aluminum hydroxide oxide determined by X-ray diffraction.

6. A method for producing an iron-free supported catalyst according to any one of claims 1 to 5, comprising the following steps: - A step of contacting an aqueous solution containing one or more polycarboxylic acids and / or salts of polycarboxylic acids with one or more vanadium-based precursors and optionally one or more molybdenum-based precursors. - A step of contacting one or more cobalt-based precursors with an aqueous solution containing the vanadium-based precursor and optionally additional molybdenum-based precursors to form an aqueous mixture of catalyst precursors. -3 to 18m ２ A step of contacting aluminum hydroxide having BET contained between / g with the water-based mixture containing the catalyst precursor to form a water-based mixture of aluminum hydroxide and the catalyst precursor, - A step of drying the water-based mixture of aluminum hydroxide and catalyst precursor to form a dry mixture. A step of firing the dry mixture at a temperature between -200°C and 600°C to form a fired product containing at least 30% by mass of aluminum hydroxide oxide, based on the total amount of aluminum hydroxide and / or aluminum oxide and aluminum hydroxide oxide determined by X-ray diffraction. - A method comprising the step of grinding the calcined product into a powder.

7. The water-based mixture of aluminum hydroxide and the catalyst precursor is heated at a predetermined temperature of at least 100°C for at least 1 hour and at least 0.1 m ３ The method according to claim 6, wherein the drying is performed with an airflow of / h.

8. The water-based mixture of aluminum hydroxide and the catalyst precursor is contained in a predetermined temperature between 100 and 150°C for a period of 1 to 10 hours, for a duration of 0.1 m ３ / h~1m ３ The method according to claim 6 or 7, wherein the airflow contained within the interval / h is used for drying.

9. The method according to claim 6, wherein the water-based mixture of aluminum hydroxide and the catalyst precursor is dried by spray drying.

10. The aforementioned dry mixture is contained in a temperature between 220 and 550°C for a period of 1 to 24 hours, and the duration is 0.1 m. ３ / h~1m ３ The method according to any one of claims 6 to 9, wherein firing is performed with an airflow contained between / h.

11. The aforementioned fired product has a volume median particle size (D) of less than 450 μm. ５０ The method according to any one of claims 6 to 10, wherein the material is ground into a powder having the following properties:

12. Aluminum hydroxide, 5-16 m ２ The method according to any one of claims 6 to 11, characterized by the specific surface area (BET) contained between / g.

13. The method according to any one of claims 6 to 12, wherein the aluminum hydroxide is selected from gibbsite or bayerite.

14. The method according to any one of claims 6 to 13, wherein the cobalt-based precursor, the vanadium-based precursor, the molybdenum-based precursor, and the carrier precursor have a purity of at least 95%.

15. The cobalt-based precursor is cobalt(II) acetate tetrahydrate and / or cobalt(II) nitrate hexahydrate. The vanadium-based precursor is ammonium metavanadate, and The method according to any one of claims 6 to 14, wherein the molybdenum-based precursor is ammonium heptamolybdate tetrahydrate.

16. The method according to any one of claims 6 to 15, wherein the polycarboxylic acid is a mixture of citric acid and malic acid, and the molar ratio of malic acid to citric acid is 0.5 to 5.

17. A method for producing multi-walled carbon nanotubes from an iron-free supported catalyst according to any one of claims 1 to 5, obtained by the method according to any one of claims 6 to 16, comprising the following steps: - A step of filling the reactor with the catalyst, A step of heating the catalyst to a temperature within the range of -500°C to 900°C, A step of supplying a carbon source to the reactor while maintaining a temperature between -500°C and 900°C. - A method comprising the step of contacting the catalyst with the carbon source for at least one minute.

18. The method according to claim 17, wherein the space time of the catalyst and carbon source is 0.1 to 0.8 g.h / mol, and is defined as the mass in grams of the supported catalyst divided by the reaction stream flow rate in moles / h units under standard temperature and pressure conditions.

19. The method according to claim 17 or 18, wherein the carbon source is selected from the group consisting of methane, ethylene, acetylene, methanol, ethanol, and mixtures thereof.

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