Improved catalyst for mwcnt production

Abstract

The present invention relates to an improved catalyst for MWCNT production. The present invention also relates to an iron-free supported catalyst for the selective conversion of hydrocarbons into carbon nanotubes, said catalyst comprising cobalt and vanadium as active catalytic metals in any oxidation state on a catalyst support comprising hydroxyl alumina, wherein: - the mass ratio of cobalt to vanadium is between 2 and 15; - the mass ratio of cobalt to aluminum is between 5.8 x 10 ‑2 and 5.8 x 10 ‑1 ; and - the mass ratio of vanadium to aluminum is between 5.8 x 10 ‑3 and 8.7 x 10 ‑2 . The present invention also relates to a method for the preparation of said iron-free supported catalyst and to a method for the preparation of carbon nanotubes using said iron-free supported catalyst.

Description

[0001] This application is a divisional application of Chinese patent application 202180038525.2, filed on May 27, 2021, entitled "Improved catalyst for MWCNT production". Technical Field

[0002] This invention relates to a supported catalyst system for converting hydrocarbons into carbon nanotubes, and more particularly to an iron-free supported catalyst system for a method of producing multi-walled carbon nanotubes with improved selectivity and yield. Background Technology

[0003] Carbon nanostructures (CNS) refer to carbon structures of various shapes and sizes at the nanoscale, such as nanotubes, nanohairs, fullerenes, nanocones, nanohorns, and nanorods. Carbon nanostructures have wide applications in various technologies due to their superior properties.

[0004] Carbon nanotubes (CNTs) are tubular materials composed of carbon atoms arranged in a hexagonal pattern, with diameters ranging from approximately 1 to 100 nm. Due to their inherent chirality, carbon nanotubes exhibit insulating, conductive, or semi-conductive properties. They possess a structure in which carbon atoms are strongly covalently bonded to each other. Because of this structure, carbon nanotubes have a tensile strength approximately 100 times that of steel, exhibit high flexibility and elasticity, and possess chemical stability.

[0005] Carbon nanotubes are classified into three types: single-walled carbon nanotubes (SWCNTs), which consist of a single sheet and have a diameter of about 1 nm; double-walled carbon nanotubes (DWCNTs), which consist of two sheets and have a diameter of about 1.4 to about 3 nm; and multi-walled carbon nanotubes (MWCNTs), which consist of three or more sheets and have a diameter of about 5 to about 100 nm.

[0006] Due to their high chemical stability, flexibility, and elasticity, carbon nanotubes are being investigated for commercialization and applications in various industrial sectors, such as aerospace, fuel cells, composite materials, biotechnology, pharmaceuticals, electrical / electronics, and semiconductor industries.

[0007] Carbon nanotubes are typically produced using various techniques, such as arc discharge, laser ablation, and chemical vapor deposition. However, arc discharge and laser ablation are not suitable for large-scale production of carbon nanotubes and require high costs for arc generation or expensive laser equipment. Catalytic chemical vapor deposition (CCVD) of hydrocarbons over a metallic catalyst offers higher yields and quality compared to other methods and simplifies the industrial-scale manufacturing process.

[0008] Currently, most research in CCVD technology 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, and chemical properties of carbon nanotubes are related to their electrical conductivity, mechanical strength, and thermal, optical, and magnetic properties.

[0009] WO 03 / 004410A1 discloses various metal oxide systems (e.g., Co, Fe, Ni, V, Mo, and Cu) and catalyst supports (e.g., Al(OH)3, Ca(OH)2, Mg(OH)2, Ti(OH)4, Ce(OH)4, and La(OH)3) for the production of single-walled and multi-walled carbon nanotubes. This paper tests the selectivity of various metals and metal mixtures, i.e., the ability of the catalyst to selectively produce single-walled, double-walled, or multi-walled nanotubes relative to a certain proportion of amorphous carbon or fibers formed simultaneously during the reaction.

[0010] EP 2883609 A1 discloses an impregnated supported catalyst and a carbon nanotube aggregate containing the impregnated supported catalyst. The impregnated supported catalyst is prepared by sequentially adding a polycarboxylic acid and precursors of a first (Co) and a second (Fe, Ni) catalyst to precursors of a first (Mo) and a second (V) catalyst component to obtain a transparent aqueous metal solution. An aluminum-based particulate support is then impregnated with the transparent aqueous metal solution, followed by drying and calcination. The bulk density of the supported catalyst is 0.8 to 1.5 g / cm³. 3 .

[0011] US 9956546 A1 discloses a catalyst for the production of carbon nanotubes, comprising a support and a graphitized metal catalyst supported on the support, wherein the graphitized metal catalyst is a multi-component metal catalyst comprising a main catalyst and a co-catalyst, wherein the main catalyst is selected from Co, Fe and mixtures thereof, and the co-catalyst is V, wherein the catalyst is a supported catalyst obtained by calcining aluminum hydroxide at a primary calcination temperature of 250°C to 500°C to form a support, loading a catalytic metal precursor onto the support, and calcining the catalytic metal precursor loaded on the support at a secondary calcination temperature of 450°C to 800°C.

[0012] EP 3053877 A1 discloses a method for producing carbon nanotubes, comprising: primary calcination at a temperature of 100 to 450 °C to produce nanotubes with a diameter of 1m. 2A support precursor with a BET specific surface area of ​​less than / g is used to form a support. A graphitized metal catalyst is loaded onto the support. The catalyst loaded on the support is calcined twice at a temperature of 100 to 500 °C to prepare a supported catalyst. The supported catalyst is then contacted with a carbon source in the gas phase to form carbon nanotubes. The support precursor is aluminum trioxide, and the graphitized metal catalyst is a binary metal catalyst selected from Co / Mo, Co / V, Fe / Mo, and Fe / V.

[0013] US2008213160 A1 discloses a method for synthesizing a supported catalyst to produce multi-walled carbon nanotubes, comprising the steps of: mixing Al(OH)3 powder with a particle size less than about 80 micrometers with an aqueous solution of iron and cobalt salts to form a paste; drying the paste until a powder with a moisture content of less than about 5% by weight is obtained; selecting a particle size fraction of the supported catalyst of less than about 63 μm; and producing nanotubes using the supported catalyst with a particle size of less than about 63 μm.

[0014] KR 101781252 discloses a method for producing carbon nanotube aggregates, comprising: heat-treating a support precursor containing layered metal hydroxide and non-layered metal hydroxide to form a porous support; loading a catalyst metal or a catalyst metal precursor onto the support to form a supported catalyst; and forming carbon nanotube aggregates, wherein the supported catalyst and a carbon-containing compound are brought into contact with each other under heating to form bundles and entangled carbon nanotube aggregates. The catalyst metal incorporates elements selected from iron, cobalt, and nickel; elements selected from titanium, vanadium, and chromium; and elements selected from molybdenum (Mo) and tungsten (W).

[0015] EP 3156125 A1 discloses a method for producing carbon nanotube aggregates, comprising:

[0016] - The support is mixed with an aqueous solution of a graphitized metal catalyst precursor to form a paste;

[0017] - The paste is dried to remove moisture, and then calcined to obtain a supported catalyst; and

[0018] - The supported catalyst is brought into contact with a carbonaceous compound under heating to allow them to react.

[0019] -The water removal rate of the paste is adjusted to 5 to 30% by weight to control the bulk density of carbon nanotubes.

[0020] Graphitization catalysts are catalysts containing only iron (Fe) or binary or multi-component catalysts containing one or more metals selected from cobalt (Co), molybdenum (Mo), and vanadium (V).

[0021] EP 3053880 A1 discloses a method for preparing carbon nanotube aggregates, comprising: calcining aluminum hydroxide at a primary calcination temperature of 100°C to 500°C to form a support; loading a catalytic metal precursor onto the support; calcining the catalyst-containing support at a secondary 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 react with each other, wherein the primary calcination temperature, the secondary calcination temperature, the amount of the supported catalyst, or the reaction time are controlled so that the bulk density of the carbon nanotube aggregates is 10 kg / m³. 3 The above. Catalytic metals include Fe, Co, Mo, V, or combinations of two or more thereof. Graphitized metal catalysts can be composite catalysts consisting of a main catalyst and a co-catalyst. In this case, the main catalyst may include iron (Fe) or cobalt (Co), and the co-catalyst may be molybdenum (Mo), vanadium (V), or combinations thereof. To prepare supported catalysts, organic acids are added in a molar ratio of 5:1 to 30:1 relative to the catalytic metal.

[0022] Carbon nanotubes have attracted attention as a potential electrode material in lithium batteries.

[0023] A typical lithium-ion battery uses a carbon anode (negative electrode) and a lithium-ion transition metal oxide cathode (positive electrode) located on opposite sides of a microporous polymer separator.

[0024] The lifespan of a lithium-ion cell begins with all the lithium in the cathode, and during charging, a certain proportion of that lithium moves to the anode and embeds itself in the carbon anode.

[0025] Failures in lithium-ion batteries result from the formation of dendrites within the battery. Dendrites are microscopic metal deposits that can form within the cell. Dendrite formation typically begins at the anode and creates internal shortcuts as it extends through the separator to the cathode.

[0026] When any iron impurities from the electrode dissolve in the electrolyte, there is a significant risk that these impurities may migrate to the anode side and induce dendrite growth through deposition. Therefore, iron-free materials are required as electrode materials.

[0027] When MWCNT is used as an electrode material, there is a risk of battery failure caused by these dendrites.

[0028] Therefore, MWCNTs containing interstitial iron components should be avoided, as they are obtained through catalytic systems containing iron-based graphitized catalysts.

[0029] Therefore, there is a need for MWCNTs produced above an iron-free metal catalyst via a hydrocarbon-based CCVD process with improved selectivity and productivity.

[0030] Purpose of the invention

[0031] The purpose of this invention is to disclose an iron-free catalyst for preparing MWCNTs, a method for preparing the same, and the use of these carbon nanotubes in batteries. Summary of the Invention

[0032] This invention discloses an iron-free supported catalyst for the selective conversion of hydrocarbons into carbon nanotubes. The catalyst comprises cobalt and vanadium as active catalytic metals in any oxidation state on a catalyst support containing alumina hydroxyl.

[0033] - The mass ratio of cobalt to vanadium is between 2 and 15;

[0034] - The mass ratio of cobalt to aluminum is 5.8 to 10. -2 and 5.8 10 -1 Between; and

[0035] - The mass ratio of vanadium to aluminum is between 5.8 and 10. -3 and 8.7 10 -2 between.

[0036] Preferred embodiments of the present invention disclose one or more of the following features:

[0037] - The mass ratio of cobalt to vanadium is between 3.0 and 11;

[0038] - The mass ratio of cobalt to aluminum is 1.2 to 10. -1 and 4.3 10 -1 Between; and

[0039] - The mass ratio of vanadium to aluminum is 1.2 to 10. -2 and 5.8 10 -2 between;

[0040] -The iron-free catalyst of the present invention further comprises molybdenum as an active catalyst, wherein:

[0041] - The mass ratio of molybdenum to aluminum is 1.2 to 10. -3 and 2.3 10 -2 Between; and

[0042] - The mass ratio of cobalt to the total mass of vanadium and molybdenum is between 2 and 15;

[0043] - Iron-free molybdenum comprising the catalyst of the present invention, wherein:

[0044] - The mass ratio of molybdenum to aluminum is 1.7 to 10. -3 and 1.7 10 -2 Between; and

[0045] - The mass ratio of cobalt to the total mass of vanadium and molybdenum is between 3 and 11;

[0046] - The catalyst support of the present invention comprises at least 30% by weight of aluminum hydroxide, based on the total amount of aluminum hydroxide and / or aluminum oxide and aluminum hydroxide;

[0047] - In the XRD patterns recorded in the 2θ range of 10° to 80°, the iron-free catalyst exhibits the largest diffraction peak at a 2θ angle of 35° to 38°, where...

[0048] - When the intensity of the maximum diffraction peak and the intensity of the diffraction peak at an angle of 17° to 22° are defined as "a" and "b" respectively, the ratio b / a is in the range of 0.10 to 0.7.

[0049] - When the intensity of the diffraction peak at the 2θ angle between 63° and 67° is defined as "c", the ratio c / a is in the range of 0.51 to 0.7.

[0050] This invention also discloses a method for preparing an iron-free supported catalyst, comprising the following steps:

[0051] - Contact an aqueous solution containing one or more polycarboxylic acids and / or polycarboxylic acids with one or more vanadium-based precursors and optionally one or more molybdenum-based precursors.

[0052] - Contact one or more cobalt-based precursors with an aqueous solution containing a vanadium-based precursor and optionally an additional molybdenum-based precursor to form an aqueous mixture of catalytic precursors;

[0053] - Make BET in 3 and 18m 2 Aluminum hydroxide at a ratio of / g is contacted with an aqueous mixture containing a catalytic precursor to form an aqueous mixture of aluminum hydroxide and a catalytic precursor;

[0054] - Dry the aqueous mixture of aluminum hydroxide and the catalytic precursor to form a dry mixture;

[0055] - Calcination of a dried mixture at a temperature of at least 200°C to form a calcined product;

[0056] - Grind the calcined product into powder.

[0057] A preferred embodiment of the method for preparing the iron-free supported catalyst of the present invention discloses one or more of the following features:

[0058] - An aqueous mixture of aluminum hydroxide and a catalytic precursor is heated at a predetermined temperature of at least 100°C with a concentration of at least 0.1 m... 3 Drying time is at least 1 hour with an air flow rate of / h;

[0059] - At a predetermined temperature between 100 and 150°C, at 0.1m 3 / h and 1m 3An air flow rate between / h was used to dry the water-based mixture of aluminum hydroxide and the catalyst precursor over a period of time between 1 hour and 10 hours.

[0060] - The aqueous mixture of aluminum hydroxide and the catalytic precursor is dried by spray drying;

[0061] - At temperatures between 200 and 600°C, at a speed of 0.1m 3 / h to 1m 3 An air flow rate between / h is used to calcine the dried mixture over a period of 1 to 24 hours;

[0062] - Grind the calcined product to a volume median particle diameter (D) 50 Powders smaller than 450 micrometers;

[0063] Aluminum hydroxide is characterized by a specific surface area (BET) of 5 to 16 m². 2 Between / g;

[0064] - Aluminum hydroxide is selected from gibbsite or diaspore;

[0065] - Cobalt-based precursors, vanadium-based precursors, molybdenum-based precursors, and support precursors have a purity of at least 95%.

[0066] - 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.

[0067] - Polycarboxylic acids are mixtures of citric acid and malic acid, wherein the molar ratio of malic acid to citric acid is between 0.5 and 5.

[0068] This invention also discloses a method for preparing multi-walled carbon nanotubes from the iron-free supported catalyst, comprising the following steps:

[0069] - Load the catalyst into the reactor;

[0070] - Heat the catalyst to a temperature between 500°C and 900°C;

[0071] - Supply carbon source to the reactor while maintaining the temperature between 500°C and 900°C;

[0072] - Allow the catalyst to contact the carbon source for at least 1 minute.

[0073] A preferred embodiment of the method for preparing multi-walled carbon nanotubes of the present invention discloses one or more of the following features:

[0074] - The space-time interval between the catalyst and the carbon source is between 0.1 and 0.8 gh / mol;

[0075] - The carbon source is selected from methane, ethylene, acetylene, methanol, ethanol and mixtures thereof.

[0076] The present invention also discloses multi-walled carbon nanotubes obtained by the preparation method of the present invention, comprising 0.1-13% by weight, preferably 1-10% by weight, of an iron-free supported catalyst, wherein the iron-free supported catalyst is obtained by the preparation method of the iron-free supported catalyst of the present invention.

[0077] The present invention also discloses a polymer matrix containing the multi-walled carbon nanotubes obtained by the method of the present invention.

[0078] The present invention also discloses the use of the multi-walled carbon nanotubes obtained by the method of the present invention in batteries. Detailed Implementation

[0079] This invention discloses a supported iron-free catalyst that produces improved selectivity in the production of multi-walled nanotubes with specific properties, the improved multi-walled selectivity being obtained in high yields while reducing catalyst consumption. The invention also discloses an economically attractive method for obtaining the supported catalyst.

[0080] The iron-free catalyst referred to in this invention means that the iron content is minimized, except for unavoidable trace amounts. However, the iron content in 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.

[0081] In a first embodiment of the invention, the supported catalyst is an iron-free bicomponent catalyst comprising a first cobalt-based catalytic component and a second vanadium-based catalytic component, both preferably in oxide form, and supported on a support comprising alumina (Al2O3) and / or aluminum hydroxide (Al(OH)3) and aluminum hydroxyoxide (AlO(OH)) (further referred to as "support element").

[0082] In a second embodiment of the present invention, the supported catalyst is an iron-free three-component graphitized catalyst, comprising a first cobalt-based catalytic component, a second vanadium-based catalytic component, and a molybdenum-based catalytic component, all preferably in the form of oxides, and supported on a support containing alumina and / or aluminum hydroxide and aluminum hydroxya (further referred to as a "support element").

[0083] Preferably, the carrier precursor is aluminum hydroxide, more preferably gibbsite or diaspore.

[0084] Preferably, the carrier precursor is characterized by a median volumetric particle diameter (D) of less than 70 μm. 50 ) and less than 20m 2 Specific surface area per g.

[0085] Preferably, the carrier precursor is gibbsite, characterized by a specific surface area of ​​3 to 18 m². 2 Between / g, preferably between 5 and 16m 2 Between / g.

[0086] Preferably, the cobalt-based catalytic precursor of the graphitized catalyst is obtained from a cobalt-based precursor, which is a cobalt salt, cobalt oxide, or a cobalt compound, such as Co(NO3)2·6H2O; Co2(CO)8 and CO(OAC)2·4H2O.

[0087] Preferably, the vanadium-based catalytic precursor of the graphitized catalyst is obtained from a vanadium-based precursor, which is a vanadium salt, vanadium oxide, or vanadium compound such as NH4VO3.

[0088] Preferably, the molybdenum-based catalytic precursor of the graphitized catalyst is obtained from a molybdenum-based precursor, which is a molybdenum salt, molybdenum oxide, or molybdenum compound, such as (NH4)6Mo7O. 24 .4H2O; Mo(CO)6 or (NH4)2MoS4.

[0089] The present invention also discloses a method for preparing the supported catalyst, comprising the following steps:

[0090] -In the method of the first embodiment, a specific amount of water containing a specific amount of one or more polycarboxylic acids and / or their salts is added to a specific amount of one or more vanadium-based precursors and mixed until a transparent solution is obtained;

[0091] - In the method of the second embodiment, a specific amount of water containing a specific amount of one or more polycarboxylic acids and / or their salts is added to a specific amount of one or more vanadium-based precursors and a specific amount of one or more molybdenum-based precursors, and mixed until a transparent solution is obtained;

[0092] - Contact one or more cobalt-based precursors with an aqueous solution containing a vanadium-based precursor and optionally a molybdenum-based precursor, wherein the one or more cobalt-based precursors are added to a powder or wetted powder or aqueous solution or in any form having a water content contained between the powder and the aqueous solution;

[0093] - Add the carrier precursor and mix for at least 1 minute;

[0094] - The mixture is dried by a suitable method, preferably at a fixed predetermined temperature of at least 100°C with a flow rate of at least 0.1 m. 3 Drying time is at least 1 hour with an air flow rate of / h;

[0095] - The mixture is calcined by a suitable method, preferably at a fixed predetermined temperature of at least 200°C with a flux of at least 0.1 m. 3 Calcination for at least 1 hour at an air flow rate of / h;

[0096] - Grind the calcined product to a volumetric median particle diameter (D). 50 (less than 450μm)

[0097] The polycarboxylic acids used in the method of the present invention are preferably selected from dicarboxylic acids, tricarboxylic acids, tetracarboxylic acids, and mixtures thereof. Examples of such polycarboxylic acids include oxalic acid, succinic acid, tartaric acid, malic acid, fumaric acid, malic acid, itaconic acid, citraconic acid, mesoconic acid, citric acid, 2-butene-1,2,3-tricarboxylic acid, and 1,2,3,4-butanetetracarboxylic acid.

[0098] For salts of polycarboxylic acids, the present invention refers to polycarboxylic acids in which at least one carboxylic acid group is converted into an ammonium or alkali metal salt.

[0099] Preferably, the polycarboxylic acid is citric acid or malic acid; preferably, the polycarboxylic acid salt is an ammonium salt.

[0100] Preferably, the amount of one or more polycarboxylic acids and / or their salts added is such that the resulting aqueous solution contains between 0.5% and 25%, more preferably between 4% and 15% of polycarboxylic acids and / or their salts.

[0101] Preferably, the polycarboxylic acid used in the method of the present invention is a mixture of citric acid and malic acid, wherein the molar ratio of malic acid to citric acid is between 0.5 and 5, preferably between 1.5 and 2.5.

[0102] In the method of the first embodiment, 1000g of the carrier precursor is added to an aqueous mixture obtained by mixing an aqueous solution containing 5 to 70g of vanadium-based precursor and 80 to 850g of cobalt-based precursor in water between 300 and 3000g, either as a powder or as an aqueous mixture containing up to 3000g of water.

[0103] In the method of the second embodiment, 1000g of the carrier precursor is added to an aqueous mixture obtained by mixing an aqueous solution containing 1 to 15g of molybdenum precursor, 5 to 70g of vanadium-based precursor, and 80 to 850g of cobalt-based precursor in water between 300 and 3000g, either as a powder or as an aqueous mixture containing up to 3000g of water.

[0104] In the method according to the present invention:

[0105] - At a temperature between 20 and 90°C, preferably between 50 and 70°C, water containing one or more polycarboxylic acids and / or polycarboxylic acids is added to the vanadium-based precursor and optionally the molybdenum-based precursor and mixed, for example by a paddle mixer, for a period of 5 to 60 minutes, preferably between 10 and 20 minutes.

[0106] - Add the cobalt-based precursor, in powder form, as a wetted precursor, or as an aqueous solution, to an aqueous solution containing a vanadium-based precursor and optionally a molybdenum precursor; when added as a wetted precursor or as an aqueous solution, add water to the cobalt-based precursor and mix for 5 to 60 minutes, preferably 10 to 20 minutes, at a temperature between 20 and 90°C, preferably between 50 and 70°C.

[0107] - Add the carrier precursor to the aqueous solution containing the cobalt-based precursor, the vanadium-based precursor and optionally the molybdenum precursor and mix (to avoid clumping);

[0108] - After the carrier precursor is added, the resulting paste is further mixed for 5 to 60 minutes, preferably 10 to 20 minutes;

[0109] - Transfer the paste to a ceramic crucible with a large opening, and:

[0110] -As a first step, heat to between 100 and 150°C, preferably between 110 and 130°C.

[0111] The temperature is maintained between 60 and 600 minutes, preferably between 150 and 330 minutes, using a heating gradient between 1.0 and 5.0 °C / min; and 0.1 to 1.0 m 3 Between / h, preferably 0.4 to 0.6m 3 The airflow rate between / h is obtained;

[0112] And subsequently

[0113] - As a second step, heating is performed to a temperature between 200 and 600°C, preferably between 220 and 550°C, more preferably between 250 and 550°C, for a duration between 1 hour and 24 hours, preferably between 60 and 600 minutes, more preferably between 150 and 330 minutes, wherein the temperature is achieved using a heating gradient between 1.0 and 5.0°C / min and a current between 0.1 and 1.0 m. 3 Between / h, preferably 0.4 to 0.6m 3 The airflow rate between / h is obtained;

[0114] - Grind the calcined product to a volumetric median particle diameter (D). 50 The micrometer size is less than 450 μm, preferably less than 250 μm.

[0115] After two heating cycles, the support precursor is converted into a calcined product, i.e., the support, which contains one or more components selected from hydroxides, hydroxy oxides and oxides, while the catalyst precursor is converted into an oxide, wherein the graphitized catalyst is preferably present as a mixed oxide.

[0116] The type of heat source used in the two heating cycles is not limited; for example, it can be induction heating, radiation heating, laser, IR, microwave, plasma, UV, or surface plasma heating.

[0117] The inventors have observed that the BET of the support precursor Al(OH)3 is an important parameter for obtaining an iron-free supported catalyst capable of producing MWCNTs with high carbon yield.

[0118] In the method according to the present invention, the BET of the Al(OH)3 support precursor is at 3 and 18 m 2 Between / g, preferably between 5 and 16m 2 Between / g.

[0119] The transformation of gibbsite to boehmite by X-ray diffraction studies is described, for example, by AMdA. Cruz et al. in Applied Catalysts is A: General 167 (1998), pp. 203-213.

[0120] Qualitative and quantitative analysis of hydroxyalumina (boehmite) in alumina (bauxite) by X-ray diffraction, as described by GABSoares in Rev. Esc. Minas, 2014, vol. 67, n. 1, pp. 41-46.

[0121] The inventors have experienced that the presence of aluminum hydroxide in iron-free supported catalysts can be easily and definitively identified by X-ray diffraction, but this quantification is subject to uncertainty and should therefore be limited to an estimate of the weight percentage of AlO(OH), in terms of the total amount of Al2O3, Al(OH)3 and AlO(OH).

[0122] In addition, the inventors have observed that the amount of aluminum hydroxyaluminate present is at least 30% by weight, preferably at least 40% by weight, more preferably at least 50% by weight, most preferably at least 60% by weight, and even at least 70% by weight, based on the total amount of Al2O3, Al(OH)3 and AlO(OH).

[0123] In the method of this invention, the first heating cycle aimed at drying the paste can be replaced by alternative drying methods or combinations thereof known in the art. Among these, flash drying or spray drying are widely used.

[0124] A typical supported catalyst according to the present invention is composed of formula (Co) v V w )O y (Carrier) z or (Co) v V w Mox )O y (Carrier) z express.

[0125] The iron-free two-component graphitization catalyst is characterized by:

[0126] - It contains aluminum hydroxide, preferably at least 30% by weight, based on the total weight of aluminum oxide, aluminum hydroxide and aluminum hydroxide;

[0127] - The mass ratio of cobalt to aluminum is 5.8 to 10. -2 and 5.8 10 -1 Between 1.2 and 10, the preferred value is 1.2 10. -1 and 4.3 10 -1 between;

[0128] - The mass ratio of vanadium to aluminum is 5.8 to 10. -3 and 8.7 10 -2 Between 1.2 and 10, the preferred value is 1.2 10. -2 and 5.8 10 -2 between.

[0129] A further feature of this iron-free bicomponent graphitization catalyst is that the mass ratio of cobalt to vanadium is between 2 and 15, preferably between 3.0 and 11.

[0130] The iron-free three-component graphitization catalyst is characterized by:

[0131] - It contains aluminum hydroxide, preferably at least 30% by weight, based on the total weight of aluminum oxide, aluminum hydroxide and aluminum hydroxide;

[0132] - The mass ratio of cobalt to aluminum is 5.8 to 10. -2 and 5.8 10 -1 Between 1.2 and 10, the preferred value is 1.2 10. -1 and 4.3 10 -1 between;

[0133] - The mass ratio of vanadium to aluminum is 5.8 to 10. -3 and 8.7 10 -2 Between 1.2 and 10, the preferred value is 1.2 10. -2 and 5.8 10 -2 Between; and

[0134] - The mass ratio of molybdenum to aluminum is 1.2 to 10. -3 and 2.3 10 -2 Between 1.7 and 10, the preferred value is between 1.7 and 10. -3 and 1.7 10 -2 between.

[0135] A further characteristic of the iron-free three-component graphitization catalyst is that the ratio of cobalt mass to the total mass of vanadium and molybdenum is between 2 and 15, preferably between 3.0 and 11.

[0136] The iron-free supported catalyst of the present invention is characterized in that the XRD pattern recorded in the 2θ range of 10° to 80° has a maximum diffraction peak defined as "a" at a 2θ angle of 35° to 38°, wherein

[0137] - The ratio of the intensity of the diffraction peak at a 2θ angle of 17° to 22°, defined as “b”, to the maximum diffraction peak intensity “a”, b / 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;

[0138] - The ratio of the diffraction peak intensity "c" at a 2θ angle of 63° to 67° to the maximum diffraction peak intensity "a" is defined as c / a, which is in the range of 0.51 to 0.7; and

[0139] - Complies with the standards of b / a (0.10 to 0.7) and c / a (0.51 to 0.7).

[0140] To prepare MWCNTs, the supported iron-free catalyst is brought into contact with a carbon source in the gas phase.

[0141] The use of supported catalysts allows for the growth of carbon nanotubes through chemical vapor-phase synthesis via carbon source decomposition, resulting in the formation of carbon nanotube aggregates.

[0142] According to the chemical vapor phase synthesis method, an iron-free graphitized catalyst is loaded into a reactor, and then a gaseous carbon source is supplied to the reactor under ambient pressure and high temperature to produce carbon nanotube aggregates, wherein the carbon nanotubes are grown on a supported catalyst. As described above, the carbon nanotubes are grown through the thermal decomposition of hydrocarbons, which serve as the carbon source. The thermally decomposed hydrocarbons permeate and saturate in the graphitized catalyst, and carbon is deposited from the saturated graphitized catalyst to form a hexagonal ring structure.

[0143] Chemical vapor phase synthesis can be carried out as follows: a supported catalyst is supplied to a reactor, and at least one carbon source selected from C1-C6 saturated hydrocarbons, C1-C6 unsaturated hydrocarbons, C1-C2 alcohols, and mixtures thereof, along with optionally a reducing gas (e.g., hydrogen) and a carrier gas (e.g., nitrogen), is introduced into the reactor at a temperature equal to or below the melting point of the graphitization catalyst, for example, between about 500 and 900 °C, preferably between 600 and 800 °C, and more preferably between 650 and 750 °C. After the carbon source is introduced into the supported catalyst, carbon nanotubes can grow from 1 minute to 5 hours, preferably from 1 minute to 30 minutes.

[0144] Preferably, under standard temperature and pressure conditions, within a time period of 10 to 30 minutes, more preferably 15 to 25 minutes, the time-space ratio defined as the weight of the supported catalyst in grams divided by the flow rate of the reactant stream in moles per hour is between 0.1 and 0.8 gh / mol, more preferably between 0.2 and 0.6 gh / mol.

[0145] There are no restrictions on the type of heat source used for heat treatment in the preparation method of MWCNT, such as induction heating, radiation heating, laser, IR, microwave, plasma, UV or surface plasma heating.

[0146] For chemical vapor phase synthesis, any carbon source that is available in carbon and can exist in the gaseous phase at temperatures above 300°C can be used without particular limitation. The gaseous carbon-containing material can be any carbon-containing compound, but is preferably a compound consisting of up to 6 carbon atoms, more preferably a compound consisting of up to 4 carbon atoms. Examples of such gaseous carbon-containing 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 gaseous carbon-containing materials can be used alone or in mixtures thereof. A mixture of reducing gas (such as hydrogen) and carrier gas (such as nitrogen) transports the carbon source, prevents the carbon nanotubes from burning at high temperatures, and facilitates the decomposition of the carbon source.

[0147] The iron-free catalyst according to the invention allows for the production of MWCNTs with a carbon yield between 800 and 2500 wt%, preferably between 1000 and 2400 wt%, and more preferably between 1100 and 2300 wt%.

[0148] Carbon production, as a percentage by weight, is defined as:

[0149] 100(m tot -m cat ) / m cat

[0150] Where m tot It is the total weight of the products after the reaction, m cat This is the weight of the catalyst used in the reaction.

[0151] Example

[0152] The following illustrative examples are intended to illustrate the invention only and are not intended to limit or otherwise restrict the scope of the invention.

[0153] Example 1: Synthesis of an iron-free two-component graphitization catalyst.

[0154] At 60°C, 5000 parts by weight of water containing 277 parts by weight of citric acid and 387 parts by weight of malic acid were added to 333 parts by weight of ammonium metavanadate, and the mixture was stirred for 15 minutes using a paddle mixer to produce a first aqueous solution.

[0155] Similarly, at 60°C, 5000 parts by weight of water were added to 4109 parts by weight of cobalt(II) acetate tetrahydrate and mixed for 15 minutes using a paddle mixer to obtain a second aqueous solution.

[0156] Add the second aqueous solution to the first aqueous solution and mix using a paddle mixer for 15 minutes.

[0157] Add 13333 parts by weight of a specific surface area (BET) of 15 m² to the mixture of the first and second aqueous solutions. 2 / g aluminum hydroxide ( Mix SM-Naba l tec) and use a paddle mixer for 15 minutes.

[0158] The resulting paste is then transferred to a ceramic crucible with a large opening and subjected to a heating process, wherein the paste is heated at a temperature gradient of 2 °C / min and a flow rate of 0.5 m. 3 The air flow rate is heated to 120°C at a rate of / h and maintained at 120°C for 5 hours.

[0159] After 5 hours at 120℃, the paste was further heated to 400℃ at a heating gradient of 2℃ / min and held at 400℃ for 5 hours, while maintaining a 0.5m [temperature value missing]. 3 / h airflow.

[0160] The resulting solid material is cooled to room temperature and then ground using a conical mill to a particle size characterized by a median particle diameter (D). 50 () is a powder with a particle size of 120 μm.

[0161] Example 2: Synthesis of an iron-free three-component graphitization catalyst

[0162] Example 1 was repeated, except that 5000 parts by weight of water containing 277 parts by weight of citric acid and 387 parts by weight of malic acid were added to 340 parts by weight of ammonium metavanadate and 64 parts by weight of ammonium heptamolybdate tetrahydrate at 60°C to obtain a first aqueous solution. A second aqueous solution was obtained by adding 5000 parts by weight of water to 4931 parts by weight of cobalt(II) acetate tetrahydrate at 60°C.

[0163] Add a specific surface area (BET) of 15 m² to the mixture of the first and second aqueous solutions. 2 / g of 13333 parts by weight of aluminum hydroxide ( SM-Nabal tec), and mix for 15 minutes using a paddle mixer.

[0164] Examples 3 to 8

[0165] In Examples 3 to 8:

[0166] -The vanadium-based precursor is ammonium metavanadate;

[0167] -The molybdenum-based precursor is ammonium heptamolybdate tetrahydrate;

[0168] -For Examples 3 and 5 to 8, the cobalt-based precursor is cobalt(II) acetate tetrahydrate;

[0169] - For Example 4, the cobalt-based precursor is cobalt(II) nitrate tetrahydrate.

[0170] - The Al(OH)3 in Example 3 is ALOLT 59AF (Inotal), characterized by a BET of 5.4m. 2 / g

[0171] - The Al(OH)3 in Example 4 is Hydro 710 (Huber), characterized by a BET of 4m. 2 / g;

[0172] - The Al(OH)3 in Examples 5 and 6 is Apyral 40CD (Nabal tec), characterized by a BET of 3.5m. 2 / g;

[0173] - The Al(OH)3 in Examples 7 and 8 is Martinal OL-111LE (Huber), characterized by a BET of 10. -12 m 2 / g.

[0174] Examples 3 to 7 were prepared using the process conditions of Example 1, namely the mixing temperature and time period, drying and calcination conditions (temperature, heating gradient, time, air flow rate), and the D for obtaining approximately 120 μm. 50 The grinding conditions are the same, but the cobalt-based precursor is added as a powder to an aqueous solution containing a vanadium-based precursor and optionally a molybdenum-based precursor, the aqueous solution containing 5000 parts by weight of water.

[0175] Example 8 is a comparative example in which the support precursor was calcined before addition and then mixed with an aqueous mixture containing cobalt-based, vanadium-based, and molybdenum-based precursors. The support precursor was first impregnated with water and stirred at 60°C for 12 hours before drying at 60°C and 100 mbar. Subsequently, the dried support precursor was calcined at 400°C for 5 hours under a nitrogen atmosphere, and then the calcined support was added to the aqueous mixture of catalyst precursors. An aqueous mixture containing cobalt-based, vanadium-based, and molybdenum-based precursors was obtained by adding the cobalt-based precursor as powder to an aqueous solution containing vanadium-based, molybdenum-based, and 5000 parts by weight of water. A heating gradient of 2°C / min and 0.5 m... 3 The resulting paste was heated to 120°C at an air flow rate of / h and held at 120°C for 5 hours. Subsequently, the paste was further heated to 400°C at a heating gradient of 2°C / min and held at 400°C for 5 hours, while maintaining a 0.5m... 3 Air flow rate of / h. No diffraction peaks corresponding to boehmite AlO(OH) were detected.

[0176] In Table 1, the amounts of catalyst precursor, support precursor and polycarboxylic acid and / or its salts in 5000 parts by weight of water are reported for Examples 3 to 8.

[0177] Example vector precursor cobalt precursor Vanadium precursor Molybdenum precursor Citric acid malic acid Citric acid disalt 3 3335 835 35 85 35 4 3335 970 100 5 50 85 5 6667 2667 267 33 200 296 6 6250 1200 70 60 135 120 7 6665 1810 225 55 140 195 8 2500 1430 65 10 105

[0178] Table 1

[0179] Synthesis of MWCNT

[0180] 1.0 g of the iron-free supported graphitization catalysts of Examples 1 to 8 were dispersed in a quartz container and then placed in the center of a quartz tubular reactor with an inlet and an outlet.

[0181] The center of the quartz tube reactor (where the container containing the catalyst is located) is heated to a temperature of 700°C.

[0182] Subsequently, ethylene gas, nitrogen, and hydrogen were allowed to flow through 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.

[0183] Table 2 shows the carbon yields (column 8) of MWCNTs (Examples A to H) (column 1) prepared using the catalysts of Examples 1 to 8 (column 2).

[0184] In addition, Table 2 shows:

[0185] - Cobalt to aluminum ratio of supported catalysts (Column 3);

[0186] - The ratio of vanadium to aluminum in supported catalysts (Column 4);

[0187] - The ratio of molybdenum to aluminum in supported catalysts (Column 5);

[0188] - The ratio of cobalt to vanadium in the iron-free two-component graphitized supported catalyst, and the ratio of cobalt to vanadium and molybdenum in the iron-free three-component graphitized supported catalyst (Column 6).

[0189] -BET(m) of each Al(OH)3 support precursor 2 / g)(Column 7).

[0190]

[0191] Table 2

[0192] As can be clearly seen from Table 2, compared with the MWCNT method obtained using an iron-free supported catalyst (Example 8), the iron-free supported catalyst according to the present invention (Examples 1 to 7) produced MWCNTs with a carbon yield of at least 800% (Examples A to G), wherein the support precursor was impregnated with the catalyst precursor. Before Calcined. MWCNT with the highest carbon yield was obtained from an iron-free supported catalyst prepared from an Al(OH)3 supported precursor, characterized by BET values ​​between 10 and 15 m. 2 Between / g. Example 8 (= Comparative Example) showed that the iron-free supported catalyst produced MWCNT (Example H) with a carbon yield of 554%, although the supported catalyst had a BET of 10. -12 m 2 / g Al(OH)3 support precursor preparation. For the iron-free supported catalyst of Example 8 (= Comparative Example), no diffraction peaks corresponding to boehmite AlO(OH) were detected.

[0193] The inventors were surprised to observe that, compared with multi-walled carbon nanotubes produced by a supported catalyst obtained from the same dry mixture but calcined at a temperature above 600°C, calcination temperatures of the dry mixture of aluminum hydroxide and the catalytic precursor between 200°C and 600°C resulted in multi-walled carbon nanotubes with high carbon yields.

[0194] The inventors also observed that the drying method also affected the carbon yield of the final multi-walled carbon nanotubes, albeit to a lesser extent.

[0195] The effect of calcination temperature is reflected in the ratio of diffraction peak intensities in the XRD patterns of the supported catalyst recorded in the 2θ range from 10° to 80°.

[0196] In the XRD pattern, the diffraction peak with the highest intensity at a 2θ angle between 35° and 38° is defined as "a". When the intensity of the diffraction peak at a 2θ angle between 17° and 22° is defined as "b", and the intensity of the diffraction peak at a 2θ angle between 63° and 67° is defined as "c", multi-walled carbon nanotubes were prepared with high carbon yield when two conditions were met, namely, the intensity ratios (b / a and c / a) were between 0.10 and 0.7, and the intensity ratio (c / a) was between 0.51 and 0.7.

[0197] Table 3 reports the 2θ angle, net strength at the 2θ angle, and strength ratios b / a and c / a of the supported catalysts obtained by different drying methods and calcination temperatures.

[0198] Table 4 reports the carbon yield of MWCNT for Example B obtained from the iron-free supported catalyst of Example 2, in weight % for the following dry catalyst precursors:

[0199] - At 120℃ for 5 hours, with a heating gradient of 2℃ / min and 0.5m 3 An air flow rate of / h heats the precursor paste to 120°C;

[0200] - Dilute the precursor paste to convert 10,000 parts of precursor paste into 25,000 parts of precursor dispersion, with sufficient flowability for peristaltic pumping to a GB-210A spray dryer from Yamato Scientific, which has the following settings:

[0201] - Blower: 0.5m 3 / h (=Flow rate of hot air used for drying)

[0202] - Atomizer: 0.1MPa (=Air pressure to produce spray)

[0203] - Drying temperature: 150℃ (=Air temperature at the inlet of the drying column)

[0204] - Pump: 7 (= The flow rate of the pumped liquid, which depends on the pump speed and the viscosity of the liquid, and therefore on its dilution. In this experiment, the flow rate is approximately (+ / -) 17 g / min.)

[0205] The inventors have observed that calcining a dry mixture of aluminum hydroxide and the catalytic precursor at 700°C results in multi-walled carbon nanotubes with lower carbon yields; the intensity ratio (b / a) is not satisfied at the calcination temperature of 700°C. No diffraction peaks corresponding to boehmite (AlO(OH)) were detected.

[0206] When Example B was repeated using the iron-free three-component graphitization catalyst of Example 2, but calcined at 550°C and 700°C for 5 h respectively, a reduced carbon yield (by weight) was obtained relative to the carbon yield of MWCNT of Example B (carbon yield = 2076%). Therefore, a decrease of approximately 14% in carbon yield was observed for the catalyst of Example 2 relative to the carbon yield of Example B, but calcined at 550°C for 5 h (carbon yield = 1781%), while a decrease of 42% in carbon yield was observed for the catalyst of Example 2 relative to the carbon yield of Example B, but calcined at 700°C for 5 h (carbon yield = 1211%).

[0207] The spray-dried, iron-free, three-component graphitization catalyst of Example 2 was calcined at 600°C for 1 hour to obtain MWCNTs with a carbon yield of 1840%.

[0208]

[0209] Table 3

[0210]

[0211] Table 4

Claims

1. An iron-free supported catalyst for carbon nanotube synthesis, said catalyst comprising cobalt and vanadium as active catalytic metals in any oxidation state on a catalyst support, said catalyst support comprising at least 30 wt% aluminum hydroxide, determined by X-ray diffraction based on the total amount of aluminum hydroxide and / or aluminum oxide and aluminum hydroxide, wherein said iron-free catalyst exhibits a maximum diffraction peak at a 2θ angle of 35° to 38° in the XRD pattern recorded in the 2θ range of 10° to 80°, wherein - When the maximum diffraction peak intensity at a 2θ angle of 35° to 38° and the maximum diffraction peak intensity at a 2θ angle of 17° to 22° are defined as "a" and "b" respectively, the ratio of b / a is in the range of 0.10 to 0.7; and - When the maximum diffraction peak intensity at the 2θ angle between 63° and 67° is defined as "c", the c / a ratio is in the range of 0.51 to 0.7: - The mass ratio of cobalt to vanadium is between 2 and 15; - The mass ratio of vanadium to aluminum is 5.8 × 10⁻⁶. -3 and 8.7×10 -2 between.

2. The iron-free supported catalyst according to claim 1, characterized in that: - The mass ratio of cobalt to vanadium is between 3 and 11; - The mass ratio of vanadium to aluminum is 1.2 × 10⁻⁶. -2 and 5.8×10 -2 between.

3. The iron-free catalyst according to claim 1 or 2, wherein it comprises molybdenum as an additional active catalyst, wherein: - The mass ratio of molybdenum to aluminum is 1.2 × 10⁻⁶. -3 and 2.3×10 -2 Between; and - The mass ratio of cobalt to the total mass of vanadium and molybdenum is between 2 and 15.

4. The iron-free catalyst according to claim 3, characterized in that: - The mass ratio of molybdenum to aluminum is 1.7 × 10⁻⁶. -3 and 1.7×10 -2 Between; and - The mass ratio of cobalt to the total mass of vanadium and molybdenum is between 3 and 11.

5. The iron-free catalyst according to any one of claims 1 to 2 and 4, wherein the catalyst support comprises at least 40% by weight of aluminum hydroxide based on the total amount of aluminum hydroxide and / or aluminum oxide and aluminum hydroxyoxide.

6. A method for producing a catalyst precursor of the iron-free supported catalyst of any one of claims 1 to 5, comprising the following steps: - Contact an aqueous solution containing one or more polycarboxylic acids and / or polycarboxylic acids with one or more vanadium-based precursors and optionally one or more molybdenum-based precursors; - Contact one or more cobalt-based precursors with an aqueous solution containing a vanadium-based precursor and optionally an additional molybdenum-based precursor to form an aqueous mixture of catalytic precursors; - Make BET in 3 and 18m 2 Aluminum hydroxide at a ratio of / g is contacted with an aqueous mixture containing a catalytic precursor to form an aqueous mixture of aluminum hydroxide and the catalytic precursor.

7. The method according to claim 6, wherein the aluminum hydroxide is characterized by a specific surface area BET of 5 and 16 m². 2 Between / g.

8. The method according to claim 6 or 7, wherein the aluminum hydroxide is selected from gibbsite or diaspore.

9. The method according to claim 6 or 7, wherein the cobalt-based precursor, vanadium-based precursor, molybdenum-based precursor and aluminum hydroxide have a purity of at least 95%.

10. The method according to claim 6 or 7, wherein 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.

11. The method according to claim 6 or 7, wherein the polycarboxylic acid is citric acid, malic acid, or a mixture of malic acid and citric acid.

12. The method according to claim 6 or 7, wherein at a predetermined temperature of at least 100°C and at least 0.1 m 3 The aqueous mixture of aluminum hydroxide and catalytic precursor is dried at an air flow rate of / h for at least 1 hour.

13. The method according to claim 6 or 7, wherein at a predetermined temperature between 100 and 150°C, at 0.1m 3 / h and 1m 3 The aqueous mixture of aluminum hydroxide and catalytic precursor is dried at an air flow rate between 1 hour and 10 hours.

14. The method according to claim 6 or 7, wherein the aqueous mixture of the aluminum hydroxide and the catalytic precursor is dried by spray drying.

15. A method for producing the iron-free catalyst according to claim 1, wherein the dried mixture obtained according to any one of claims 12-14 is subjected to a temperature of 220 to 550°C at 0.1 m 3 / h to 1m 3 The calcination process is carried out at an air flow rate of / h for a period of time between 1 and 24 hours.

16. The method of claim 15, wherein the calcined product is ground to a median particle diameter Dv. 50 Powder with a particle size of less than 450 μm.

17. A method for preparing multi-walled carbon nanotubes from an iron-free supported catalyst according to any one of claims 1-5, comprising the following steps: - Load the catalyst into the reactor; - Heat the catalyst to a temperature between 500°C and 900°C; - Supply carbon source to the reactor while maintaining the temperature between 500°C and 900°C; - A period of time during which the catalyst is in contact with the carbon source for at least 1 minute.

18. The method of claim 17, wherein the space-time between the catalyst and the carbon source is between 0.1 and 0.8 gh / mol, wherein the space-time is defined as the weight of the supported catalyst in grams divided by the flow rate of the reactant stream in moles per hour under standard temperature and pressure conditions.

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

20. Multi-walled carbon nanotubes obtained by the method according to any one of claims 17 to 19, comprising 0.1 to 13% by weight of a catalyst according to any one of claims 1 to 5, wherein alumina hydroxyaluminate has been partially or completely converted to alumina.

21. The multi-walled carbon nanotube of claim 20, wherein the multi-walled carbon nanotube comprises between 1 and 10% by weight of a catalyst.

22. A polymer matrix comprising the multi-walled carbon nanotubes according to claim 20 or 21.

23. The electrodes of a secondary battery comprising multi-walled carbon nanotubes according to claim 20 or 21.

Images