WO2011020970A2 - Supported fe/mo catalyst, process for preparing same and use for the manufacture of nanotubes - Google Patents

Supported fe/mo catalyst, process for preparing same and use for the manufacture of nanotubes Download PDF

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Publication number
WO2011020970A2
WO2011020970A2 PCT/FR2010/051716 FR2010051716W WO2011020970A2 WO 2011020970 A2 WO2011020970 A2 WO 2011020970A2 FR 2010051716 W FR2010051716 W FR 2010051716W WO 2011020970 A2 WO2011020970 A2 WO 2011020970A2
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Prior art keywords
catalyst material
carbon
catalyst
iron
substrate
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PCT/FR2010/051716
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French (fr)
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WO2011020970A3 (en
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Patrice Gaillard
Serge Bordere
Daniel Cochard
Philippe Serp
Brigitte Caussat
Julien Beausoleil
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Arkema France
Institut National Polytechnique
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Publication of WO2011020970A2 publication Critical patent/WO2011020970A2/en
Publication of WO2011020970A3 publication Critical patent/WO2011020970A3/en

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    • B01J35/40—
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/84—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • B01J23/85—Chromium, molybdenum or tungsten
    • B01J23/88—Molybdenum
    • B01J23/881—Molybdenum and iron
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/0201—Impregnation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/158—Carbon nanotubes
    • C01B32/16—Preparation
    • C01B32/162—Preparation characterised by catalysts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/02—Boron or aluminium; Oxides or hydroxides thereof
    • B01J21/04—Alumina

Definitions

  • the present invention relates to novel supported Fe / Mo catalysts. It also relates to the process for preparing these catalysts and their use for the manufacture of nanotubes, especially carbon nanotubes.
  • CNTs carbon nanotubes
  • CNTs have been intensively researched to replace powdered carbon black powder, which is difficult to handle in all its applications.
  • the CNTs furthermore have the advantage of conferring improved mechanical properties and electrical and / or thermal conduction properties on any composite material containing them, at least equal to those of the pulverulent carbon black, at lower contents.
  • Their good mechanical properties and especially resistance to elongation are related in part to their very high aspect ratios (length / diameter).
  • SWNT synchronym for Single Wall Nanotubes
  • MWNT acronym for Multi Wall Nanotubes
  • Carbon nanotubes can be manufactured using various processes such as electrical discharge, laser ablation, chemical vapor deposition (CVD in abbreviation) or physical vapor deposition (PVD abbreviation).
  • CVD in abbreviation chemical vapor deposition
  • PVD abbreviation physical vapor deposition
  • the CVD process involves injecting a source of carbon-rich gas into a reactor containing a high temperature metal catalyst. In contact with the metal, the gas source decomposes into graphitic plane NTC and hydrogen.
  • the catalyst consists of a catalytic metal such as iron, cobalt, nickel, supported by a solid substrate, in the form of grains, and chemically inert, such as alumina, silica, magnesia or still carbon.
  • the gaseous carbon sources generally used are methane, ethane, ethylene, acetylene or benzene.
  • CNTs are synthesized by contacting a catalyst containing iron (e.g. Fe3 ⁇ 4, Fe on a carbon support, Fe on an alumina carrier or Fe on a carbon fibril support) with a rich gaseous compound carbon, such as a hydrocarbon, in the presence of another gas capable of reacting with the carbon-rich gaseous compound.
  • a catalyst containing iron e.g. Fe3 ⁇ 4, Fe on a carbon support, Fe on an alumina carrier or Fe on a carbon fibril support
  • a rich gaseous compound carbon such as a hydrocarbon
  • the catalyst has a structure different from that of a supported catalyst since it is obtained by coprecipitation, on the one hand, of a solution of iron salts and molybdenum salts and, on the other hand, a solution of aluminum salts.
  • a first type is obtained by placing in contact with a catalytic material with a carboxylate.
  • MagChem ® by MARTIN MARIETTA has a particle size of at most 50 ⁇ m and is used as a paste.
  • Another type of catalyst is formed by co-precipitation of catalytic metals with aluminum or magnesium compounds
  • Example X This complex process induces a filling of the porosity of the support and leads to a catalyst whose active phase is diluted throughout the support. It is not therefore a supported catalyst.
  • Yet another type of catalyst consists of particular compositions deposited on carbon fiber aggregates (Example XI). Again, the percentage of iron in the catalyst is well below 25% by weight.
  • catalysts suitable for the preparation of carbon nanotubes which comprise alumina impregnated with iron and molybdenum and contain less than 25% by weight of iron, are described (catalysts A and B) in the document WO 02/081371.
  • Example 2 discloses (Example 2) a process for manufacturing a catalyst intended for the preparation of carbon nanotubes, without mentioning the quantities of the impregnation solutions used and therefore the percentage by weight of iron. in the catalyst.
  • the present inventors have found that a very particular Fe / Mo type catalyst supported on porous alumina, allowed to obtain a very high productivity at a CNT synthesis reaction temperature of 620 to 680 0 C, the productivity being calculated as follows:
  • the invention thus aims at providing a supported catalyst material, for the preparation of nanotubes, in particular carbon, said material being in the form of solid particles, said particles comprising a porous substrate having a BET specific surface area greater than 50 m 2 / g, preferably between 70 and 400 m 2 / g, in the form of particles having a larger dimension of between 75 and 500 microns, supporting a catalytic layer of a mixture of iron and molybdenum, said catalytic layer representing from 30% to 70% by weight.
  • the iron content being at least 25%, preferably from 30% to 40% of the total mass of the catalyst material, and the ratio iron / molybdenum mass being between 11 and 1.5, preferably between 5 and 2.
  • iron and mobdenum reference is made to these metals in the elemental state, that is to say in the oxidation state 0, or the oxidized state. However, it is preferred that these metals are primarily in the elemental state.
  • the substrate is a substrate that is chemically inert with respect to molybdenum, iron and the carbon source, under the operating conditions of the CNT synthesis method by the CVD technique; it represents from 30% to 70% by weight of the total mass of the catalyst.
  • this substrate may be inorganic. It is especially chosen from alumina, an activated carbon, silica, a silicate, magnesia, titanium oxide, zirconia, a zeolite or carbon fibers.
  • the substrate is alumina, in particular of the gamma or theta type.
  • the porosity of the substrate can be measured by nitrogen adsorption, a method well known to those skilled in the art.
  • the macroscopic shape of the substrate particles, and particles of catalyst material can be globally substantially spherical or not.
  • the invention also applies to grains of macroscopic shape more or less flattened (flakes, discs ...) and / or elongated (cylinders, rods, ribbons ).
  • the shape and size of the particles are adapted to allow the formation of a fluidized bed of the catalyst material.
  • the substrate particles have a larger dimension of between 75 and 150 microns, more preferably between 80 and 100 microns, as measured by laser granulometry.
  • the use of particles of this size makes it possible to use the substrate in solid form, in the dry state, in an impregnation process and thus to obtain a catalyst material having a higher iron content than the catalysts obtained by liquid impregnation, in particular.
  • the catalyst grains thus obtained can also be used in a fluidized bed, and thus more easily lead to the production of multi-walled carbon nanotubes.
  • the catalyst material is in the form of spherical particles having a unimodal particle size distribution, the equivalent diameter of the particles being between 80% and 120% of the average particle diameter of the catalyst material.
  • the particles of catalyst material may have a broad or bimodal particle size distribution, with an equivalent diameter ranging from 20 to 600%.
  • the catalyst material according to the invention comprises particles of alumina supporting a catalytic layer, the mass percentages of the various constituents being 32 for iron, 12 for molybdenum and 56 for alumina, relative to total mass of the catalyst material.
  • the invention extends to a process for preparing the catalyst material described above, by impregnating the dry substrate with an impregnating solution comprising an iron salt and a molybdenum salt.
  • the solution may be an alcoholic or aqueous solution.
  • the iron salt may be iron nitrate, and in particular iron nitrate nonahydrate.
  • the molybdenum salt may be ammonium molybdate, and in particular ammonium molybdate tetrahydrate.
  • the impregnation solution is an aqueous solution of iron nitrate nonahydrate and ammonium molybdate tetrahydrate.
  • the impregnation step is preferably carried out under a dry gas sweep, preferably under a sweep of air. It is carried out at a temperature measured in situ ranging from 100 to 150 ° C., preferably approximately 120 ° C.
  • the quantity of impregnation solution, at any time, in contact with the substrate is generally just sufficient to ensuring the formation of a film or a layer on the surface of the substrate particles.
  • this impregnation step makes it possible to obtain a catalyst material containing more than 25% by weight of iron. It is also easier to implement than the co-precipitation or liquid impregnation processes of the art. and does not require the use of carboxylate, or additional filtration step.
  • the process for preparing the catalytic material according to the invention also comprises a drying step at a temperature ranging, for example, from 150 to 250 ° C., measured in situ, advantageously followed by a denitrification step, preferably under an inert atmosphere at a temperature ranging from 350 to 45O 0 C, measured in situ.
  • the invention also extends to a catalyst material obtained by a process according to the invention as defined above.
  • the invention also extends to a method for manufacturing nanoparticles of material chosen from silicon, carbon, boron, and a mixture of these elements, optionally associated with nitrogen or doped with nitrogen, characterized in that at least one catalyst material according to the invention is used.
  • the invention is a reaction for the selective production of carbon nanotubes by thermal decomposition of a source of gaseous carbon.
  • the invention more particularly relates to a process for selectively producing carbon nanotubes by decomposition of a carbon source in the gaseous state, comprising the following steps:
  • step b) contacting a carbon source (alkane or alkene), preferably ethylene, with the catalyst material of step b), to form on the surface of said catalyst material carbon nanotubes and hydrogen by catalytic decomposition of said carbon source;
  • a carbon source alkane or alkene
  • the carbon source is an alkane such as methane or ethane or preferably an alkene which may be selected from the group consisting of ethylene, isopropylene, propylene, butene, butadiene, and mixtures thereof.
  • This source of carbon may be of renewable origin as described in patent application EP 1 980 530.
  • the alkene preferably used is ethylene.
  • the carbon source and preferably ethylene, is mixed in step c) with a stream of hydrogen.
  • the carbon / hydrogen source ratio can in this case be between 90/10 and 60/40, preferably between 70/30 and 80/20.
  • step c) is carried out with an ethylene / hydrogen mixture in a ratio of 75/25.
  • the different steps are preferably carried out simultaneously and continuously in the same reactor.
  • this process may comprise other steps (preliminary, intermediate or subsequent), as long as they do not adversely affect the production of carbon nanotubes.
  • the catalyst material is reduced in situ in said reactor, between steps a) and b).
  • the catalytic layer is not oxidized at the moment when the catalyst material is used for the synthesis of CNTs.
  • a step of grinding the nanotubes in situ or ex situ may be considered, before or after step d). It is also possible to provide a step of chemical and / or thermal purification of the nanotubes before or after step d).
  • the productivity obtained with the process of the invention is particularly high, since it is always greater than 15, even greater than 25.
  • the carbon nanotubes formed are less likely to agglomerate than in the processes described in US Pat. prior art.
  • the invention also extends to carbon nanotubes that can be obtained according to the method described above. It is advantageously multi-walled nanotubes, comprising for example from 5 to 15, and preferably from 7 to 10, graphene sheets wound concentrically.
  • the nanotubes obtained according to the invention usually have a mean diameter ranging from 0.1 to 200 nm, preferably from 0.1 to 100 nm, more preferably from 0.4 to 50 nm and better still from 1 to 30 nm and advantageously a length of more than 0.1 microns and advantageously from 0.1 to 20 microns, for example about 6 microns.
  • Their length / diameter ratio is advantageously greater than 10 and most often greater than 100.
  • Their specific surface area is for example between 100 and 600 m 2 / g and their apparent density may especially be between 0.01 and 0.5 g. / cm 3 and more preferably between 0.07 and 0.2 g / cm 3 .
  • the invention also relates to the use of nanotubes, which can be obtained as described above, in composite materials to impart improved electrical and / or thermal conduction properties and / or mechanical properties, in particular resistance to corrosion. elongation, improved.
  • CNTs can be used in macromolecular compositions intended for the packaging of electronic components or the manufacture of fuel lines (fuel oil) or coatings or paints (antistatic coating), or in thermistors or electrodes for supercapacities or for the manufacture of structural parts for aeronautical, nautical or automotive fields.
  • FIG. 1 is a graph obtained from Examples 5 to 7 and representing the productivity expressed as the ratio between the carbon mass of the CNTs and the catalyst mass gc / gcatai yS eur as a function of the temperature,
  • FIG. 2 is a graph obtained from example 5 and representing the productivity as a function of the molybdenum content
  • FIG. 3 is a microscopic photograph showing nanotubes obtained in example 5.
  • a catalyst is prepared under the same conditions as in Example 1 but adjusting the amount of ammonium molybdate to obtain a catalyst with 32% by weight of iron and 6% by weight of molybdenum.
  • a catalyst is prepared under the same conditions as in Example 1, but by adjusting the amount of ammonium molybdate to obtain a catalyst with, in masses, 32% iron and 3% molybdenum.
  • a catalyst is prepared under the same conditions as in Example 1, but without adding ammonium molybdate and adjusting the amount of solution injected to obtain a 32% iron catalyst.
  • a catalytic test is carried out by putting a mass of about 2.3 g of catalyst layer in a reactor of 5 cm in diameter and 1 m in effective height.
  • the mixture is heated at 65 ° C. under 2.66 L / min of nitrogen for 30 minutes and then a reduction stage is maintained for 30 minutes under 2 L / min of nitrogen and 0.66 L / min of hydrogen. Once this stage is over, an ethylene flow rate of 2 L / min and 0.66 L / min of hydrogen. After 60 minutes, the heating was stopped and the reactor was cooled under a nitrogen flow of 2.66 L / min.
  • the amount of product formed is evaluated by calculating the mass remaining after a calcination of about 2 g of the composite at 800 ° C. for 6 hours. At the same time, an estimate of the quality of the nanotubes is made by microscopy.
  • the productivity of the catalysts according to the invention is improved with respect to the catalyst of the prior art.
  • Molybdenum enrichment improves productivity and activity, as illustrated in Figure 2.
  • Example 7 Catalytic Test at 600 ° C.
  • Example 1 With the catalyst of Example 1, a catalytic test is carried out as in Example 5, but at a temperature of 600 ° C.
  • the productivity of the catalysts according to the invention is dependent on the reaction temperature and is maximum at 65 ° C., as also illustrated in FIG.
  • the nanotubes obtained can then be introduced into a polymer matrix in order to produce composite materials with improved mechanical and / or thermal and / or conductive properties.

Abstract

The invention relates to a catalyst material for preparing nanotubes, especially carbon nanotubes, said material being in the form of solid particles, said particles comprising a porous substrate having a BET specific surface area of greater than 50 m2/g, preferably between 70 and 400 m2/g, covered with at least one catalytic layer of a mixture of iron and molybdenum, said catalytic layer representing from 30% to 70%, preferably from 40 to 55% by weight of the total weight of the catalyst material, the iron content being at least 25%, preferably from 30% to 40% by weight of the total weight of the catalyst material, and the iron/molybdenum weight ratio being between 11 and 1.5, preferably between 5 and 2. The invention also relates to the process for preparing same and to a process for the synthesis of CNTs using this catalyst material.

Description

CATALYSEUR Fe/Mo SUPPORTE, SON PROCEDE DE PREPARATION ET UTILISATION POUR LA FABRICATION DE NANOTUBES FE / Mo SUPPORTED CATALYST, PROCESS FOR PREPARING THE SAME, AND USE IN THE MANUFACTURE OF NANOTUBES
La présente invention concerne de nouveaux catalyseurs Fe/Mo supportés. Elle concerne également le procédé de préparation de ces catalyseurs et leur utilisation pour la fabrication de nanotubes, notamment de carbone . The present invention relates to novel supported Fe / Mo catalysts. It also relates to the process for preparing these catalysts and their use for the manufacture of nanotubes, especially carbon nanotubes.
De nombreux travaux ont porté sur des catalyseurs de type métal de transition supporté, en particulier pour la fabrication de nanotubes de carbone (NTC) .  Many studies have focused on supported transition metal catalysts, in particular for the manufacture of carbon nanotubes (CNTs).
Les NTC font l'objet depuis ces dernières années d'une recherche intensive, en vue de remplacer la poudre de noir de carbone pulvérulent et difficile à manipuler dans toutes ses applications. Les NTC présentent en outre l'avantage de conférer des propriétés mécaniques et des propriétés de conduction électrique et/ou thermique améliorées à tout matériau composite les contenant, au moins égales à celles du noir de carbone pulvérulent, à des teneurs plus faibles. Leurs bonnes propriétés mécaniques et notamment de résistance à 1 ' élongation sont liées en partie à leurs rapports de forme (longueur/diamètre) très élevés.  In recent years, CNTs have been intensively researched to replace powdered carbon black powder, which is difficult to handle in all its applications. The CNTs furthermore have the advantage of conferring improved mechanical properties and electrical and / or thermal conduction properties on any composite material containing them, at least equal to those of the pulverulent carbon black, at lower contents. Their good mechanical properties and especially resistance to elongation are related in part to their very high aspect ratios (length / diameter).
Ils se composent d'un ou plusieurs feuillets graphitiques agencés de façon concentrique autour d'un axe longitudinal. Pour des nanotubes composés d'un seul feuillet, on parle de SWNT (acronyme anglais de Single Wall Nanotubes) et pour des nanotubes composés de plusieurs feuillets concentriques, on parle alors de MWNT (acronyme anglais de Multi Wall Nanotubes) . Les SWNT sont en général plus difficiles à fabriquer que les MWNT.  They consist of one or more graphitic sheets arranged concentrically about a longitudinal axis. For nanotubes composed of a single sheet, we speak of SWNT (acronym for Single Wall Nanotubes) and for nanotubes composed of several concentric layers, this is called MWNT (acronym for Multi Wall Nanotubes). SWNTs are generally more difficult to manufacture than MWNTs.
Les nanotubes de carbone peuvent être fabriqués selon différents procédés comme la décharge électrique, l'ablation laser, le dépôt chimique en phase vapeur (CVD en abréviation) ou le dépôt physique en phase vapeur (PVD en abréviation) . Carbon nanotubes can be manufactured using various processes such as electrical discharge, laser ablation, chemical vapor deposition (CVD in abbreviation) or physical vapor deposition (PVD abbreviation).
Selon la Demanderesse, le procédé de fabrication des NTC le plus prometteur en termes de qualité des NTC, de reproductibilité des caractéristiques des NTC, et de productivité est le procédé CVD. Ce procédé consiste à injecter une source de gaz riche en carbone, dans un réacteur renfermant un catalyseur métallique porté à haute température. Au contact du métal, la source de gaz se décompose en NTC à plan graphitique et en hydrogène. En général, le catalyseur est constitué d'un métal catalytique tel que le fer, le cobalt, le nickel, supporté par un substrat solide, sous forme de grains, et chimiquement inerte, tel que l'alumine, la silice, la magnésie ou encore le carbone.  According to the Applicant, the most promising method of manufacturing CNTs in terms of CNT quality, reproducibility of CNT characteristics, and productivity is the CVD process. This process involves injecting a source of carbon-rich gas into a reactor containing a high temperature metal catalyst. In contact with the metal, the gas source decomposes into graphitic plane NTC and hydrogen. In general, the catalyst consists of a catalytic metal such as iron, cobalt, nickel, supported by a solid substrate, in the form of grains, and chemically inert, such as alumina, silica, magnesia or still carbon.
Les sources gazeuses de carbone généralement utilisées sont le méthane, l'éthane, l'éthylène, l'acétylène ou le benzène.  The gaseous carbon sources generally used are methane, ethane, ethylene, acetylene or benzene.
A titre d'exemple de documents décrivant ce procédé CVD, on peut citer le document WO 86/03455 d'Hyperion Catalysis International Inc. que l'on peut considérer comme l'un des brevets de base sur la synthèse des NTC. Ce document décrit des fibrilles de carbone (ancienne dénomination des NTC) quasi cylindriques, dont le diamètre est compris entre 3,5 et 70 nm et dont le rapport de forme est supérieur ou égal à 100, ainsi que leur procédé de préparation .  By way of example of documents describing this CVD process, mention may be made of WO 86/03455 of Hyperion Catalysis International Inc. which can be considered as one of the basic patents on the synthesis of CNTs. This document describes carbon fibrils (former NTC designation) almost cylindrical, whose diameter is between 3.5 and 70 nm and whose aspect ratio is greater than or equal to 100, and their method of preparation.
Les NTC sont synthétisés par mise en contact d'un catalyseur contenant du fer (par exemple Fe3θ4, Fe sur un support de charbon, Fe sur un support d'alumine ou Fe sur un support en fibrille carbonée) avec un composé gazeux riche en carbone, tel qu'un hydrocarbure, en présence d'un autre gaz capable de réagir avec le composé gazeux riche en carbone. La synthèse est réalisée à une température choisie dans la gamme allant de 85O0C à 12000C. Le catalyseur est préparé par imprégnation à sec, par précipitation ou par imprégnation en voie humide. CNTs are synthesized by contacting a catalyst containing iron (e.g. Fe3θ 4, Fe on a carbon support, Fe on an alumina carrier or Fe on a carbon fibril support) with a rich gaseous compound carbon, such as a hydrocarbon, in the presence of another gas capable of reacting with the carbon-rich gaseous compound. The synthesis is carried out at a chosen temperature in the range from 85O 0 C to 1200 0 C. The catalyst is prepared by dry impregnation, precipitation or wet impregnation.
D'autres documents décrivent des améliorations de ce procédé, telles que l'utilisation d'un lit fluidisé continu de catalyseur, qui permet de contrôler l'état d'agrégation du catalyseur et des matériaux carbonés formés (voir par exemple WO 02/94713A1 au nom de l'Université de Tsinghua et FR 2 826 646 INPT) .  Other documents describe improvements in this process, such as the use of a continuous fluidized bed of catalyst, which makes it possible to control the state of aggregation of the catalyst and of the carbonaceous materials formed (see, for example, WO 02 / 94713A1 on behalf of Tsinghua University and FR 2 826 646 INPT).
De nombreux travaux ont aussi porté sur l'amélioration du catalyseur, notamment par combinaison de différents métaux catalytiques . Ainsi, US 2001/00036549 d'Hyperion Catalysis International Inc. a décrit des catalyseurs bimétalliques supportés de type Fe/Mo et Fe/Cr et a montré qu'un dopage en molybdène de l'ordre de 1 à 2% en masse permettait de doubler la productivité par rapport à un catalyseur monométallique de fer, dans une gamme de températures de 5000C à 15000C, mais qu'un dopage au-delà de 2,5% faisait chuter la productivité. On peut également citer la demande de brevet US 2008/0003169 qui décrit des catalyseurs de type Fe/Mo/alumine permettant une bonne productivité. Cependant, dans ce cas, le catalyseur présente une structure différente de celle d'un catalyseur supporté puisqu'il est obtenu par co-précipitation, d'une part, d'une solution de sels de fer et de sels de molybdène et, d'autre part, d'une solution de sels d'aluminium. Many studies have also focused on improving the catalyst, especially by combining different catalytic metals. Thus, US 2001/00036549 of Hyperion Catalysis International Inc. has described supported bimetallic catalysts of Fe / Mo and Fe / Cr type and has shown that a molybdenum doping of the order of 1 to 2% by weight made it possible to doubling the productivity compared to a monometallic iron catalyst, in a temperature range of 500 0 C to 1500 0 C, but doping above 2.5% lowered productivity. We can also mention the US patent application 2008/0003169 which describes Fe / Mo / alumina type catalysts for good productivity. However, in this case, the catalyst has a structure different from that of a supported catalyst since it is obtained by coprecipitation, on the one hand, of a solution of iron salts and molybdenum salts and, on the other hand, a solution of aluminum salts.
La Demanderesse a proposé dans sa demande de brevet WO 2006/082325 un nouveau type de catalyseur supporté pouvant combiner plusieurs types de métaux. Cependant, ce document se concentre uniquement sur des exemples de catalyseur Fe/alumine.  The Applicant has proposed in his patent application WO 2006/082325 a new type of supported catalyst that can combine several types of metals. However, this document focuses only on examples of Fe / alumina catalyst.
Par ailleurs, le document US 2004/162216 divulgue différents types de catalyseurs pour la production de nanotubes de carbone. Un premier type est obtenu par mise en contact d'un matériau catalytique avec un carboxylate.Furthermore, document US 2004/162216 discloses various types of catalysts for the production of carbon nanotubes. A first type is obtained by placing in contact with a catalytic material with a carboxylate.
Il conduit à un catalyseur renfermant bien moins de 25% de fer (Exemples I-VI I et IX) ou dont le substrat (la magnésieIt leads to a catalyst containing well less than 25% of iron (Examples I-VI I and IX) or whose substrate (magnesia
MagChem® de MARTIN MARIETTA) a une taille de particule d'au plus 50 μm et est utilisé sous forme de pâte. Un autre type de catalyseur est formé par co-précipitation des métaux catalytiques avec des composés d'aluminium ou de magnésiumMagChem ® by MARTIN MARIETTA) has a particle size of at most 50 μm and is used as a paste. Another type of catalyst is formed by co-precipitation of catalytic metals with aluminum or magnesium compounds
(Exemple X) . Ce procédé complexe induit un remplissage de la porosité du support et conduit de ce fait à un catalyseur dont la phase active est diluée dans l'ensemble du support. Il ne s'agit donc pas d'un catalyseur supporté. Un autre type encore de catalyseur est constitué de compositions particulières déposées sur des agrégats de fibres de carbone (Exemple XI) . Là encore, le pourcentage de fer du catalyseur est bien inférieur à 25% en poids. (Example X) This complex process induces a filling of the porosity of the support and leads to a catalyst whose active phase is diluted throughout the support. It is not therefore a supported catalyst. Yet another type of catalyst consists of particular compositions deposited on carbon fiber aggregates (Example XI). Again, the percentage of iron in the catalyst is well below 25% by weight.
D'autres exemples de catalyseurs adaptés à la préparation de nanotubes de carbone, qui comprennent de l'alumine imprégnée de fer et de molybdène et renferment moins de 25% en poids de fer, sont décrits (catalyseurs A et B) dans le document WO 02/081371.  Other examples of catalysts suitable for the preparation of carbon nanotubes, which comprise alumina impregnated with iron and molybdenum and contain less than 25% by weight of iron, are described (catalysts A and B) in the document WO 02/081371.
Enfin, le document WO 2008/100325 divulgue (Exemple 2) un procédé de fabrication d'un catalyseur destiné à la préparation de nanotubes de carbone, sans mentionner les quantités des solutions d'imprégnation mises en oeuvre et donc le pourcentage en poids de fer dans le catalyseur.  Finally, the document WO 2008/100325 discloses (Example 2) a process for manufacturing a catalyst intended for the preparation of carbon nanotubes, without mentioning the quantities of the impregnation solutions used and therefore the percentage by weight of iron. in the catalyst.
Malgré ces divers développements, il existe toujours un besoin en de nouveaux catalyseurs, qui permettent d'améliorer encore la productivité des réactions de synthèse des NTC, à environ 650 0C, dans lesquelles ils sont utilisés. Despite these various developments, there is still a need for new catalysts, which can further improve the productivity of CNT synthesis reactions at about 650 0 C, in which they are used.
Les présents inventeurs ont trouvé qu'un catalyseur très particulier de type Fe/Mo supporté sur alumine poreuse, permettait d'obtenir une productivité très élevée à une température de réaction de synthèse des NTC de 620 à 680 0C, la productivité étant calculée de la façon suivante : The present inventors have found that a very particular Fe / Mo type catalyst supported on porous alumina, allowed to obtain a very high productivity at a CNT synthesis reaction temperature of 620 to 680 0 C, the productivity being calculated as follows:
( ÇTc / ÇTcatalyseur )  (ÇTc / ÇCatalyst)
où gc est la masse de carbone formé et gCataiyseur est la masse de catalyseur mis en oeuvre. g where c is the mass of carbon formed and g y C atai sor is the mass of catalyst used.
L'invention vise ainsi à proposer un matériau catalyseur supporté, pour la préparation de nanotubes, notamment de carbone, ledit matériau étant sous forme de particules solides, lesdites particules comprenant un substrat poreux de surface spécifique BET supérieure à 50 m2/g, de préférence comprise entre 70 et 400 m2/g, sous forme de particules ayant une plus grande dimension comprise entre 75 et 500 microns, supportant une couche catalytique d'un mélange de fer et de molybdène, ladite couche catalytique représentant de 30% à 70%, de préférence de 40 à 55% en masse de la masse totale du matériau catalyseur, la teneur en fer étant d'au moins 25%, de préférence de 30% à 40% de la masse totale du matériau catalyseur, et le ratio massique fer/molybdène étant compris entre 11 et 1,5, de préférence entre 5 et 2. The invention thus aims at providing a supported catalyst material, for the preparation of nanotubes, in particular carbon, said material being in the form of solid particles, said particles comprising a porous substrate having a BET specific surface area greater than 50 m 2 / g, preferably between 70 and 400 m 2 / g, in the form of particles having a larger dimension of between 75 and 500 microns, supporting a catalytic layer of a mixture of iron and molybdenum, said catalytic layer representing from 30% to 70% by weight. %, preferably from 40 to 55% by weight of the total mass of the catalyst material, the iron content being at least 25%, preferably from 30% to 40% of the total mass of the catalyst material, and the ratio iron / molybdenum mass being between 11 and 1.5, preferably between 5 and 2.
Il est entendu, dans la présente description, que par "fer" et "molybdène", il est fait référence à ces métaux à l'état élémentaire, c'est-à-dire à l'état d'oxydation 0, ou à l'état oxydé. On préfère toutefois que ces métaux se trouvent principalement à l'état élémentaire.  It is understood, in the present description, that by "iron" and "molybdenum", reference is made to these metals in the elemental state, that is to say in the oxidation state 0, or the oxidized state. However, it is preferred that these metals are primarily in the elemental state.
Le substrat est un substrat inerte chimiquement vis- à-vis du molybdène, du fer et de la source de carbone, dans les conditions opératoires du procédé de synthèse des NTC par la technique CVD ; il représente de 30 % à 70 % en masse de la masse totale du catalyseur. Avantageusement, ce substrat peut être inorganique. Il est notamment choisi parmi l'alumine, un charbon actif, la silice, un silicate, la magnésie, l'oxyde de titane, la zircone, une zéolithe, ou encore des fibres de carbone. Selon un mode de réalisation avantageux, le substrat est de l'alumine, notamment de type gamma ou thêta. The substrate is a substrate that is chemically inert with respect to molybdenum, iron and the carbon source, under the operating conditions of the CNT synthesis method by the CVD technique; it represents from 30% to 70% by weight of the total mass of the catalyst. Advantageously, this substrate may be inorganic. It is especially chosen from alumina, an activated carbon, silica, a silicate, magnesia, titanium oxide, zirconia, a zeolite or carbon fibers. According to a mode of Advantageously, the substrate is alumina, in particular of the gamma or theta type.
La porosité du substrat peut être mesurée par l'adsorption d'azote, méthode bien connue de l'homme du métier.  The porosity of the substrate can be measured by nitrogen adsorption, a method well known to those skilled in the art.
La forme macroscopique des particules de substrat, et des particules de matériau catalyseur, peut être globalement sensiblement sphérique ou non. L'invention s'applique aussi à des grains de forme macroscopique plus ou moins aplatie (flocons, disques...) et/ou allongée (cylindres, bâtonnets, rubans...).  The macroscopic shape of the substrate particles, and particles of catalyst material, can be globally substantially spherical or not. The invention also applies to grains of macroscopic shape more or less flattened (flakes, discs ...) and / or elongated (cylinders, rods, ribbons ...).
Selon l'invention, la forme et la dimension des particules sont adaptées pour permettre la formation d'un lit fluidisé du matériau catalyseur. Dans la pratique, pour assurer une productivité correcte, on préfère que les particules de substrat aient une plus grande dimension comprise entre 75 et 150 microns, plus préférentiellement entre 80 et 100 microns, telle que mesurée par granulométrie laser. L'utilisation de particules de cette taille permet en effet de mettre en oeuvre le substrat sous forme solide, à l'état sec, dans un procédé d'imprégnation et d'obtenir ainsi un matériau catalyseur présentant un taux de fer plus important que les catalyseurs obtenus par imprégnation en voie liquide, notamment. Les grains de catalyseur ainsi obtenus peuvent en outre être mis en oeuvre dans un lit fluidisé, et conduire ainsi plus aisément à l'obtention de nanotubes de carbone multi- parois .  According to the invention, the shape and size of the particles are adapted to allow the formation of a fluidized bed of the catalyst material. In practice, to ensure correct productivity, it is preferred that the substrate particles have a larger dimension of between 75 and 150 microns, more preferably between 80 and 100 microns, as measured by laser granulometry. The use of particles of this size makes it possible to use the substrate in solid form, in the dry state, in an impregnation process and thus to obtain a catalyst material having a higher iron content than the catalysts obtained by liquid impregnation, in particular. The catalyst grains thus obtained can also be used in a fluidized bed, and thus more easily lead to the production of multi-walled carbon nanotubes.
Par ailleurs, selon une forme d'exécution de l'invention, le matériau catalyseur est sous forme de particules sphériques ayant une répartition granulométrique unimodale, le diamètre équivalent des particules étant compris entre 80 % et 120 % du diamètre moyen des particules du matériau catalyseur. Selon d'autres formes d'exécution, les particules de matériau catalyseur peuvent avoir une répartition granulométrique large ou bimodale, avec un diamètre équivalent allant de 20 à 600%. Furthermore, according to one embodiment of the invention, the catalyst material is in the form of spherical particles having a unimodal particle size distribution, the equivalent diameter of the particles being between 80% and 120% of the average particle diameter of the catalyst material. . According to other forms In one embodiment, the particles of catalyst material may have a broad or bimodal particle size distribution, with an equivalent diameter ranging from 20 to 600%.
De façon avantageuse, le matériau catalyseur selon l'invention comprend des particules d'alumine supportant une couche catalytique, les pourcentages massiques des différents constituants étant de 32 pour le fer, 12 pour le molybdène et 56 pour l'alumine, par rapport à la masse totale du matériau catalyseur.  Advantageously, the catalyst material according to the invention comprises particles of alumina supporting a catalytic layer, the mass percentages of the various constituents being 32 for iron, 12 for molybdenum and 56 for alumina, relative to total mass of the catalyst material.
L'invention s'étend à un procédé de préparation du matériau catalyseur décrit précédemment, par imprégnation du substrat sec avec une solution d'imprégnation comprenant un sel de fer et un sel de molybdène. La solution peut être une solution alcoolique ou aqueuse. Le sel de fer peut être un nitrate de fer, et notamment le nitrate de fer nonahydraté. Le sel de molybdène peut être le molybdate d'ammonium, et notamment le molybdate d'ammonium tétrahydraté . De façon avantageuse, la solution d'imprégnation est une solution aqueuse de nitrate de fer nonahydraté et de molybdate d'ammonium tétrahydraté.  The invention extends to a process for preparing the catalyst material described above, by impregnating the dry substrate with an impregnating solution comprising an iron salt and a molybdenum salt. The solution may be an alcoholic or aqueous solution. The iron salt may be iron nitrate, and in particular iron nitrate nonahydrate. The molybdenum salt may be ammonium molybdate, and in particular ammonium molybdate tetrahydrate. Advantageously, the impregnation solution is an aqueous solution of iron nitrate nonahydrate and ammonium molybdate tetrahydrate.
L'étape d'imprégnation est réalisée de préférence sous balayage de gaz sec, de préférence sous balayage d'air. Elle est effectuée à une température mesurée in situ allant de 100 à 15O0C, de préférence d'environ 12O0C. Avantageusement, la quantité de solution d'imprégnation, à tout moment, en contact avec le substrat est généralement juste suffisante pour assurer la formation d'un film ou d'une couche à la surface des particules de substrat. The impregnation step is preferably carried out under a dry gas sweep, preferably under a sweep of air. It is carried out at a temperature measured in situ ranging from 100 to 150 ° C., preferably approximately 120 ° C. Advantageously, the quantity of impregnation solution, at any time, in contact with the substrate is generally just sufficient to ensuring the formation of a film or a layer on the surface of the substrate particles.
Comme indiqué précédemment, cette étape d'imprégnation permet d'obtenir un matériau catalyseur renfermant plus de 25% en poids de fer. Elle est par ailleurs plus simple à mettre en oeuvre que les procédés de co-précipitation ou d'imprégnation en voie liquide de l'art antérieur et ne nécessite pas l'utilisation de carboxylate, ni d'étape supplémentaire de filtration. As indicated above, this impregnation step makes it possible to obtain a catalyst material containing more than 25% by weight of iron. It is also easier to implement than the co-precipitation or liquid impregnation processes of the art. and does not require the use of carboxylate, or additional filtration step.
Le procédé de préparation du matériau catalytique selon l'invention comprend en outre une étape de séchage à une température allant par exemple de 150 à 25O0C, mesurée in situ, avantageusement suivie d'une étape de dénitrification, de préférence sous atmosphère inerte à une température allant de 350 à 45O0C, mesurée in situ. The process for preparing the catalytic material according to the invention also comprises a drying step at a temperature ranging, for example, from 150 to 250 ° C., measured in situ, advantageously followed by a denitrification step, preferably under an inert atmosphere at a temperature ranging from 350 to 45O 0 C, measured in situ.
L'invention s'étend aussi à un matériau catalyseur obtenu par un procédé selon l'invention tel que défini ci- dessus .  The invention also extends to a catalyst material obtained by a process according to the invention as defined above.
L'invention s'étend également à un procédé de fabrication de nanoparticules de matériau choisi parmi le silicium, le carbone, le bore, et un mélange de ces éléments, éventuellement associés à l'azote ou dopés à l'azote, caractérisé en ce qu'on utilise au moins un matériau catalyseur selon l'invention.  The invention also extends to a method for manufacturing nanoparticles of material chosen from silicon, carbon, boron, and a mixture of these elements, optionally associated with nitrogen or doped with nitrogen, characterized in that at least one catalyst material according to the invention is used.
Avantageusement et selon l'invention, il s'agit d'une réaction de fabrication sélective de nanotubes de carbone par décomposition thermique d'une source de carbone gazeuse. Ainsi, l'invention concerne plus particulièrement un procédé de fabrication sélective de nanotubes de carbone par décomposition d'une source de carbone à l'état gazeux, comprenant les étapes suivantes :  Advantageously and according to the invention, it is a reaction for the selective production of carbon nanotubes by thermal decomposition of a source of gaseous carbon. Thus, the invention more particularly relates to a process for selectively producing carbon nanotubes by decomposition of a carbon source in the gaseous state, comprising the following steps:
a) l'introduction, notamment la mise en lit fluidisé, dans un réacteur, d'un matériau catalyseur tel que défini précédemment ,  a) introducing, in particular the fluidized bed, into a reactor, a catalyst material as defined above,
b) le chauffage dudit matériau catalyseur à une température allant de 620 à 68O0C, de préférence d'environ 65O0C ; b) heating said catalyst material at a temperature ranging from 620 to 68O 0 C, preferably about 65O 0 C;
c) la mise en contact d'une source de carbone (alcane ou alcène) , de préférence de l'éthylène, avec le matériau catalyseur de l'étape b) , pour former en surface dudit matériau catalyseur des nanotubes de carbone et de l'hydrogène par décomposition catalytique de ladite source de carbone ; c) contacting a carbon source (alkane or alkene), preferably ethylene, with the catalyst material of step b), to form on the surface of said catalyst material carbon nanotubes and hydrogen by catalytic decomposition of said carbon source;
d) la récupération des nanotubes de carbone produits en c) .  (d) the recovery of the carbon nanotubes produced in (c).
La source de carbone est un alcane comme le méthane ou l'éthane ou de préférence un alcène qui peut être choisi dans le groupe comprenant l'éthylène, 1 ' isopropylène, le propylène, le butène, le butadiène, et leurs mélanges. Cette source de carbone peut être d'origine renouvelable comme décrit dans la demande de brevet EP 1 980 530. L'alcène préférablement utilisé est l'éthylène.  The carbon source is an alkane such as methane or ethane or preferably an alkene which may be selected from the group consisting of ethylene, isopropylene, propylene, butene, butadiene, and mixtures thereof. This source of carbon may be of renewable origin as described in patent application EP 1 980 530. The alkene preferably used is ethylene.
Avantageusement et selon l'invention, la source de carbone, et de préférence l'éthylène, est mélangée dans l'étape c) à un flux d'hydrogène.  Advantageously and according to the invention, the carbon source, and preferably ethylene, is mixed in step c) with a stream of hydrogen.
Le ratio source de carbone/hydrogène peut dans ce cas être compris entre 90/10 et 60/40, de préférence entre 70/30 et 80/20. De façon avantageuse, on met en œuvre l'étape c) avec un mélange éthylène/hydrogène dans un ratio de 75/25.  The carbon / hydrogen source ratio can in this case be between 90/10 and 60/40, preferably between 70/30 and 80/20. Advantageously, step c) is carried out with an ethylene / hydrogen mixture in a ratio of 75/25.
Les différentes étapes sont de préférence mises en oeuvre simultanément et en continu dans un même réacteur.  The different steps are preferably carried out simultaneously and continuously in the same reactor.
En outre, ce procédé peut comprendre d'autres étapes (préliminaires, intermédiaires ou subséquentes), pour autant qu'elles n'affectent pas négativement la production de nanotubes de carbone.  In addition, this process may comprise other steps (preliminary, intermediate or subsequent), as long as they do not adversely affect the production of carbon nanotubes.
Ainsi, avantageusement, le matériau catalyseur est réduit in situ dans ledit réacteur, entre les étapes a) et b) . Ainsi, la couche catalytique n'est pas oxydée au moment où le matériau catalyseur est utilisé pour la synthèse des NTC.  Thus, advantageously, the catalyst material is reduced in situ in said reactor, between steps a) and b). Thus, the catalytic layer is not oxidized at the moment when the catalyst material is used for the synthesis of CNTs.
Si nécessaire, une étape de broyage des nanotubes in situ ou ex situ peut être envisagée, avant ou après l'étape d) . Il est aussi possible de prévoir une étape de purification chimique et/ou thermique des nanotubes avant ou après l'étape d) . If necessary, a step of grinding the nanotubes in situ or ex situ may be considered, before or after step d). It is also possible to provide a step of chemical and / or thermal purification of the nanotubes before or after step d).
La productivité obtenue avec le procédé de l'invention est particulièrement élevée, puisqu'elle est toujours supérieure à 15, même supérieure à 25. De plus, les nanotubes de carbone formés ont moins tendance à s'agglomérer que dans les procédés décrits dans l'art antérieur .  The productivity obtained with the process of the invention is particularly high, since it is always greater than 15, even greater than 25. In addition, the carbon nanotubes formed are less likely to agglomerate than in the processes described in US Pat. prior art.
L'invention s'étend aussi aux nanotubes de carbone susceptibles d'être obtenus suivant le procédé décrit précédemment. Il s'agit avantageusement de nanotubes multi- parois, comprenant par exemple de 5 à 15, et de préférence de 7 à 10, feuillets de graphène enroulés de façon concentrique. Les nanotubes obtenus selon l'invention ont habituellement un diamètre moyen allant de 0,1 à 200 nm, de préférence de 0,1 à 100 nm, plus préférentiellement de 0,4 à 50 nm et, mieux, de 1 à 30 nm et avantageusement une longueur de plus de 0,1 μm et avantageusement de 0,1 à 20 μm, par exemple d'environ 6 μm. Leur rapport longueur/diamètre est avantageusement supérieur à 10 et le plus souvent supérieur à 100. Leur surface spécifique est par exemple comprise entre 100 et 600 m2 /g et leur densité apparente peut notamment être comprise entre 0,01 et 0,5 g/cm3 et plus préférentiellement entre 0,07 et 0,2 g/cm3. The invention also extends to carbon nanotubes that can be obtained according to the method described above. It is advantageously multi-walled nanotubes, comprising for example from 5 to 15, and preferably from 7 to 10, graphene sheets wound concentrically. The nanotubes obtained according to the invention usually have a mean diameter ranging from 0.1 to 200 nm, preferably from 0.1 to 100 nm, more preferably from 0.4 to 50 nm and better still from 1 to 30 nm and advantageously a length of more than 0.1 microns and advantageously from 0.1 to 20 microns, for example about 6 microns. Their length / diameter ratio is advantageously greater than 10 and most often greater than 100. Their specific surface area is for example between 100 and 600 m 2 / g and their apparent density may especially be between 0.01 and 0.5 g. / cm 3 and more preferably between 0.07 and 0.2 g / cm 3 .
L'invention porte également sur l'utilisation des nanotubes, susceptibles d'être obtenus comme décrit précédemment, dans des matériaux composites pour leur conférer des propriétés de conduction électrique et/ou thermique améliorées et/ou des propriétés mécaniques, notamment de résistance à 1 ' élongation, améliorées. En particulier, les NTC peuvent être utilisés dans des compositions macromoléculaires destinées à l'emballage de composants électroniques ou à la fabrication de conduites d'essence (fuel Une) ou de revêtements ou peintures (coating) antistatiques, ou dans des thermistors ou des électrodes pour supercapacités ou encore pour la fabrication de pièces de structure pour les domaines aéronautique, nautique ou automobile. The invention also relates to the use of nanotubes, which can be obtained as described above, in composite materials to impart improved electrical and / or thermal conduction properties and / or mechanical properties, in particular resistance to corrosion. elongation, improved. In particular, CNTs can be used in macromolecular compositions intended for the packaging of electronic components or the manufacture of fuel lines (fuel oil) or coatings or paints (antistatic coating), or in thermistors or electrodes for supercapacities or for the manufacture of structural parts for aeronautical, nautical or automotive fields.
D'autres buts, caractéristiques et avantages de l'invention apparaissent à la lecture de la description suivante de ses exemples de réalisation qui se réfère aux figures annexées dans lesquelles :  Other objects, features and advantages of the invention appear on reading the following description of its exemplary embodiments which refers to the appended figures in which:
la figure 1 est un graphique obtenu à partir des exemples 5 à 7 et représentant la productivité exprimée comme le rapport entre la masse de carbone des NTC et la masse de catalyseur gc/gcataiySeur en fonction de la température, FIG. 1 is a graph obtained from Examples 5 to 7 and representing the productivity expressed as the ratio between the carbon mass of the CNTs and the catalyst mass gc / gcatai yS eur as a function of the temperature,
la figure 2 est un graphique obtenu à partir de l'exemple 5 et représentant la productivité en fonction de la teneur en molybdène,  FIG. 2 is a graph obtained from example 5 and representing the productivity as a function of the molybdenum content,
la figure 3 est une photographie microscopique représentant des nanotubes obtenus à l'exemple 5.  FIG. 3 is a microscopic photograph showing nanotubes obtained in example 5.
L'invention sera décrite plus en détail par référence aux exemples suivants qui sont donnés à titre purement illustratif et nullement limitatif.  The invention will be described in more detail with reference to the following examples which are given purely by way of illustration and in no way limitative.
EXEMPLES Exemple 1 : Préparation d'un catalyseur 32Fel2Mo/Al2O3 EXAMPLES Example 1: Preparation of a Catalyst 32Fel2Mo / Al 2 O 3
Dans un réacteur de IL muni d'une double enveloppe chauffé à 12O0C, on introduit 100 g d'alumine Puralox® SCCa-5/150 de diamètre médian égal à environ 85 μm et de surface spécifique 160 m2/g, et on balaie à l'air. Au moyen d'une pompe, on injecte alors en continu 600 mL d'une solution de nitrate de fer et de molybdate d'ammonium contenant 675 g/L de nitrate de fer nonahydraté et 65 g/L de molybdate d'ammonium tétrahydraté . La durée d'addition est fixée à 25h. Le catalyseur est ensuite chauffé in-situ à 22O0C sous balayage d'air sec pendant 8 heures puis placé dans un four à moufle à 4000C pendant 8 heures. On obtient un catalyseur à 32% en fer et 12% en molybdène, les pourcentages étant des pourcentages massiques par rapport à la masse de catalyseur. In an IL reactor equipped with a jacketed jacket heated to 120 ° C., 100 g of Puralox ® SCCa-5/150 alumina having a median diameter of about 85 μm and a specific surface area of 160 m 2 / g are introduced, and we sweep in the air. By means of a pump, 600 ml of a solution of iron nitrate and ammonium molybdate containing 675 g / l of iron nitrate nonahydrate and 65 g / l of ammonium molybdate tetrahydrate are then continuously injected. The duration of addition is fixed at 25h. The catalyst is then heated in situ at 20 ° C. under a dry air sweep for 8 hours and then placed in a muffle furnace at 400 ° C. for 8 hours. A catalyst containing 32% iron and 12% molybdenum is obtained, the percentages being percentages by weight relative to the mass of catalyst.
Exemple 2 : Préparation d'un catalyseur 32Fe6Mo/Al2θ3 Example 2 Preparation of a Catalyst 32Fe6Mo / Al 2 θ 3
On prépare un catalyseur dans les mêmes conditions que dans l'exemple 1 mais en ajustant la quantité de molybdate d'ammonium pour obtenir un catalyseur avec 32% en masse de fer et 6% en masse de molybdène. A catalyst is prepared under the same conditions as in Example 1 but adjusting the amount of ammonium molybdate to obtain a catalyst with 32% by weight of iron and 6% by weight of molybdenum.
Exemple 3 : Préparation d' un catalyseur 32Fe3Mo/Al2θ3Example 3 Preparation of a Catalyst 32Fe3Mo / Al 2 O 3
On prépare un catalyseur dans les mêmes conditions que dans l'exemple 1, mais en ajustant la quantité de molybdate d'ammonium pour obtenir un catalyseur avec, en masses, 32% de fer et 3% de molybdène. A catalyst is prepared under the same conditions as in Example 1, but by adjusting the amount of ammonium molybdate to obtain a catalyst with, in masses, 32% iron and 3% molybdenum.
Exemple 4 (comparatif) : Préparation d'un catalyseur 32Fe/Al2O3 Example 4 (Comparative): Preparation of a 32Fe / Al 2 O 3 Catalyst
On prépare un catalyseur dans les mêmes conditions que dans l'exemple 1, mais sans ajouter de molybdate d'ammonium et en ajustant la quantité de solution injectée pour obtenir un catalyseur à 32% de fer.  A catalyst is prepared under the same conditions as in Example 1, but without adding ammonium molybdate and adjusting the amount of solution injected to obtain a 32% iron catalyst.
Exemple 5 : Test catalytique à 6500C Example 5 Catalytic Test at 650 ° C.
Avec chacun des catalyseurs des exemples 1 à 4 ci- dessus, on pratique un test catalytique en mettant une masse d'environ 2,3 g de catalyseur en couche dans un réacteur de 5 cm de diamètre et de 1 m de hauteur efficace. On chauffe à 65O0C sous 2,66 L/min d'azote pendant 30 minutes puis on maintient un palier de réduction pendant 30 minutes sous 2 L/min d'azote et 0,66 L/min d'hydrogène. Une fois ce palier terminé, on introduit un débit d'éthylène de 2 L/min et de 0,66 L/min d'hydrogène. Après 60 minutes, on arrête le chauffage et on refroidit le réacteur sous un courant d'azote de 2,66 L/min. La quantité de produit formé est évaluée en calculant la masse restante après une calcination d'environ 2 g du composite à 8000C pendant 6 heures. Parallèlement, une estimation de la qualité des nanotubes est faite par microscopie. With each of the catalysts of Examples 1 to 4 above, a catalytic test is carried out by putting a mass of about 2.3 g of catalyst layer in a reactor of 5 cm in diameter and 1 m in effective height. The mixture is heated at 65 ° C. under 2.66 L / min of nitrogen for 30 minutes and then a reduction stage is maintained for 30 minutes under 2 L / min of nitrogen and 0.66 L / min of hydrogen. Once this stage is over, an ethylene flow rate of 2 L / min and 0.66 L / min of hydrogen. After 60 minutes, the heating was stopped and the reactor was cooled under a nitrogen flow of 2.66 L / min. The amount of product formed is evaluated by calculating the mass remaining after a calcination of about 2 g of the composite at 800 ° C. for 6 hours. At the same time, an estimate of the quality of the nanotubes is made by microscopy.
Les résultats sont présentés dans le tableau 1 ci-dessous :  The results are shown in Table 1 below:
TABLEAU 1  TABLE 1
Figure imgf000014_0001
Figure imgf000014_0001
La productivité des catalyseurs selon l'invention est améliorée par rapport au catalyseur de l'art antérieur. Un enrichissement en molybdène permet d'améliorer la productivité et l'activité, ce qu'illustre la figure 2. The productivity of the catalysts according to the invention is improved with respect to the catalyst of the prior art. Molybdenum enrichment improves productivity and activity, as illustrated in Figure 2.
Sur la figure 3, on voit que les NTC formés présentent une longueur importante et qu'il n'y a pas d'agrégation des grains de catalyseur. Exemple 6 : Test catalytique à 700 0C In FIG. 3, it can be seen that the CNTs formed have a large length and that there is no aggregation of the catalyst grains. Example 6 Catalytic Test at 700 ° C.
Avec le catalyseur de l'exemple 1, on pratique un test catalytique comme dans l'exemple 5, mais à une température de 7000C. Exemple 7 : Test catalytique à 600 0C With the catalyst of Example 1, a catalytic test is carried out as in Example 5, but at a temperature of 700 ° C. Example 7 Catalytic Test at 600 ° C.
Avec le catalyseur de l'exemple 1, on pratique un test catalytique comme dans l'exemple 5, mais à une température de 6000C. With the catalyst of Example 1, a catalytic test is carried out as in Example 5, but at a temperature of 600 ° C.
Les résultats obtenus aux exemples 6 et 7, sont présentés dans le tableau 2 ci-après et sur la figure 1.  The results obtained in Examples 6 and 7 are shown in Table 2 below and in Figure 1.
TABLEAU 2 TABLE 2
Figure imgf000015_0001
Figure imgf000015_0001
La productivité des catalyseurs selon l'invention est dépendante de la température de réaction et est maximale à 65O0C, comme illustré également à la figure 1. The productivity of the catalysts according to the invention is dependent on the reaction temperature and is maximum at 65 ° C., as also illustrated in FIG.
Les nanotubes obtenus peuvent alors être introduits dans une matrice polymérique afin de réaliser des matériaux composites à propriétés mécaniques et/ou thermiques et/ou conductrices améliorées.  The nanotubes obtained can then be introduced into a polymer matrix in order to produce composite materials with improved mechanical and / or thermal and / or conductive properties.

Claims

REVENDICATIONS
1. Matériau catalyseur supporté pour la préparation de nanotubes, notamment de carbone, ledit matériau étant sous forme de particules solides, lesdites particules comprenant un substrat poreux de surface spécifique BET supérieure à 50 m2/g, de préférence comprise entre 70 et 400 m2/g, sous forme de particules ayant une plus grande dimension comprise entre 75 et 500 microns, supportant une couche catalytique d'un mélange de fer et de molybdène, ladite couche catalytique représentant de 30% à 70%, de préférence de 40 à 55% en masse de la masse totale du matériau catalyseur, la teneur en fer étant d'au moins 25%, de préférence de 30% à 40% en masse de la masse totale du matériau catalyseur, et le ratio massique fer/molybdène étant compris entre 11 et 1,5, de préférence entre 5 et 2. 1. Supported catalyst material for the preparation of nanotubes, in particular carbon, said material being in the form of solid particles, said particles comprising a porous substrate with a BET specific surface area greater than 50 m 2 / g, preferably between 70 and 400 m 2 / g, in the form of particles having a larger dimension of between 75 and 500 microns, supporting a catalytic layer of a mixture of iron and molybdenum, said catalytic layer representing from 30% to 70%, preferably from 40 to 55% by weight of the total mass of the catalyst material, the iron content being at least 25%, preferably 30% to 40% by weight of the total mass of the catalyst material, and the mass ratio iron / molybdenum being between 11 and 1.5, preferably between 5 and 2.
2. Matériau catalyseur selon la revendication 1 dans lequel le substrat est choisi parmi l'alumine, un charbon actif, la silice, un silicate, la magnésie, l'oxyde de titane, la zircone, une zéolithe ou des fibres de carbone, de préférence le substrat est de l'alumine.  2. Catalyst material according to claim 1, in which the substrate is chosen from alumina, an active carbon, silica, a silicate, magnesia, titanium oxide, zirconia, a zeolite or carbon fibers, preferably the substrate is alumina.
3. Matériau catalyseur selon la revendication 1 ou 2, caractérisé par le fait que les particules de substrat ont une plus grande dimension comprise entre 80 et 100 microns.  3. Catalyst material according to claim 1 or 2, characterized in that the substrate particles have a larger dimension of between 80 and 100 microns.
4. Matériau catalyseur selon l'une quelconque des revendications 1 à 3, caractérisé par le fait que le substrat est en alumine et que les pourcentages massiques des différents constituants sont de 32 pour le fer, 12 pour le molybdène et 56 pour l'alumine, par rapport à la masse totale de matériau catalyseur.  4. Catalyst material according to any one of claims 1 to 3, characterized in that the substrate is alumina and the mass percentages of the various constituents are 32 for iron, 12 for molybdenum and 56 for alumina , relative to the total mass of catalyst material.
5. Procédé de préparation du matériau catalyseur selon l'une quelconque des revendications 1 à 4, par imprégnation du substrat sec avec une solution d'imprégnation de sel de fer et de sel de molybdène, de préférence de nitrate de fer et molybdate d'ammonium, ladite imprégnation étant de préférence réalisée sous balayage de gaz sec. 5. Process for the preparation of the catalyst material according to any one of claims 1 to 4, by impregnation of the dry substrate with an impregnation solution of iron salt and molybdenum salt, preferably iron nitrate. and ammonium molybdate, said impregnation being preferably carried out under dry gas scavenging.
6. Procédé selon la revendication 5, caractérisé par le fait que l'imprégnation s'effectue à une température, mesurée en situ, allant de 100 à 15O0C, de préférence à environ 12O0C. 6. Process according to claim 5, characterized in that the impregnation is carried out at a temperature, measured in situ, ranging from 100 to 150 ° C., preferably at about 120 ° C.
7. Procédé selon l'une quelconque des revendications précédentes dans lequel la quantité de solution d'imprégnation, à tout moment, en contact avec le substrat est juste suffisante pour assurer la formation d'un film à la surface des particules de substrat.  A process according to any one of the preceding claims wherein the amount of impregnating solution at all times in contact with the substrate is just sufficient to provide for the formation of a film on the surface of the substrate particles.
8. Procédé selon l'une des revendications 5 à 7, qui comprend en outre une étape de séchage à une température allant de 150 à 25O0C, mesurée in situ, éventuellement suivie d'une étape de dénitrification, de préférence sous atmosphère inerte à une température allant de 350 à 45O0C, mesurée in situ. 8. Method according to one of claims 5 to 7, which further comprises a drying step at a temperature ranging from 150 to 250 ° C., measured in situ, optionally followed by a denitrification step, preferably under an inert atmosphere. at a temperature ranging from 350 to 45O 0 C, measured in situ.
9. Procédé de fabrication de nanotubes de carbone, comprenant les étapes suivantes : a) l'introduction, notamment la mise en lit fluidisé, dans un réacteur, d'un matériau catalyseur tel que défini à l'une quelconque des revendications 1 à 4 ou préparé selon l'une quelconque des revendications 5 à 8,  9. A process for manufacturing carbon nanotubes, comprising the following steps: a) the introduction, in particular the fluidized bed, into a reactor, of a catalyst material as defined in any one of claims 1 to 4; or prepared according to any one of claims 5 to 8,
b) le chauffage dudit matériau catalyseur à une température allant de 620 à 68O0C, de préférence d'environb) heating said catalyst material at a temperature ranging from 620 to 68O 0 C, preferably about
65O0C ; 65O 0 C;
c) la mise en contact d'une source de carbone, de préférence de l'éthylène, avec le matériau catalyseur de l'étape b) , pour former en surface dudit catalyseur des nanotubes de carbone et de l'hydrogène par décomposition catalytique de ladite source de carbone;  c) contacting a source of carbon, preferably ethylene, with the catalyst material of step b), to form on the surface of said catalyst carbon nanotubes and hydrogen by catalytic decomposition of said carbon source;
d) la récupération des nanotubes de carbone produits en c) . (d) the recovery of the carbon nanotubes produced in (c).
10. Procédé selon la revendication 9, caractérisé en ce que la source de carbone est un alcane tel que le méthane ou l'éthane, un alcène tel que l'éthylène, ou leurs mélanges . 10. The method of claim 9, characterized in that the carbon source is an alkane such as methane or ethane, an alkene such as ethylene, or mixtures thereof.
11. Procédé selon la revendication 9 ou 10, caractérisé en ce que la source de carbone est mélangée dans l'étape c) à un flux d'hydrogène.  11. The method of claim 9 or 10, characterized in that the carbon source is mixed in step c) with a flow of hydrogen.
12. Procédé selon la revendication 11, dans lequel le ratio source de carbone/hydrogène est compris entre 90/10 et 60/40, de préférence entre 70/30 et 80/20.  12. The method of claim 11, wherein the carbon / hydrogen source ratio is between 90/10 and 60/40, preferably between 70/30 and 80/20.
13. Procédé selon la revendication 12, dans lequel la source de carbone est l'éthylène et le ratio éthylène/hydrogène est de 75/25.  The process according to claim 12, wherein the carbon source is ethylene and the ethylene / hydrogen ratio is 75/25.
14. Procédé selon l'une quelconque des revendications 9 à 13, caractérisé en ce que le matériau catalyseur est réduit in situ dans ledit réacteur.  14. Process according to any one of claims 9 to 13, characterized in that the catalyst material is reduced in situ in said reactor.
15. Nanotubes de carbone susceptibles d'être obtenus suivant le procédé de l'une quelconque des revendications 9 à 14.  15. Carbon nanotubes obtainable by the method of any one of claims 9 to 14.
16. Utilisation des nanotubes de carbone selon la revendication 15, dans des matériaux composites pour leur conférer des propriétés de conduction électrique et/ou thermique améliorées et/ou des propriétés mécaniques, notamment de résistance à 1 ' élongation, améliorées.  16. Use of carbon nanotubes according to claim 15, in composite materials to impart improved electrical and / or thermal conduction properties and / or improved mechanical properties, especially resistance to elongation.
17. Utilisation des nanotubes de carbone selon la revendication 16, dans des compositions macromoléculaires destinées à l'emballage de composants électroniques ou à la fabrication de conduites d'essence (fuel Une) ou de revêtements ou peintures (coating) antistatiques, ou dans des thermistors ou des électrodes pour supercapacités ou encore pour la fabrication de pièces de structure dans les domaines aéronautique, nautique ou automobile.  17. The use of carbon nanotubes according to claim 16, in macromolecular compositions intended for the packaging of electronic components or for the manufacture of fuel lines (fuel oil) or antistatic coatings or paints (coating), or in thermistors or electrodes for supercapacities or for the manufacture of structural parts in the aeronautical, nautical or automotive fields.
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