Classifications

• • 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
  • B01J23/74—Iron group metals
  • B01J23/745—Iron
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82B—NANOSTRUCTURES FORMED BY MANIPULATION OF INDIVIDUAL ATOMS, MOLECULES, OR LIMITED COLLECTIONS OF ATOMS OR MOLECULES AS DISCRETE UNITS; MANUFACTURE OR TREATMENT THEREOF
  • B82B3/00—Manufacture or treatment of nanostructures by manipulation of individual atoms or molecules, or limited collections of atoms or molecules as discrete units
  • B82B3/0009—Forming specific nanostructures
• • 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
  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
  • B01J35/391—Physical properties of the active metal ingredient
  • B01J35/393—Metal or metal oxide crystallite size
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B2202/00—Structure or properties of carbon nanotubes
  • C01B2202/06—Multi-walled nanotubes
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B2202/00—Structure or properties of carbon nanotubes
  • C01B2202/20—Nanotubes characterized by their properties
  • C01B2202/36—Diameter

Definitions

• the invention relates to the production of ordered carbon nanotubes.
• Ordered carbon nanotubes in the sense of the present invention have a tabular structure with a diameter of between 0.4 nm and 30 nm and a length greater than 100 times their diameter, in particular between 1000 and 100,000 times their diameter. They may be associated with metal catalyst particles or free of these particles (following purification). Carbon nanotubes have been described for a long time (S. Iijima "Helical nanotubes of graphitic carbon” Nature, 354, 56 (1991)), but are not yet exploited on an industrial scale. They could nonetheless be the subject of numerous applications, and in particular be greatly useful and advantageous in the manufacture of composite materials, flat screens, spikes for atomic force microscopes, storage of hydrogen or other gases, as catalytic supports ...
• WO-03002456 discloses a method for selectively producing ordered fluidized bed carbon nanotubes in the presence of a supported iron-on-alumina catalyst comprising from 1% to 5% by weight of highly fluidized CVD-dispersed atomic iron on alumina grains of about 120 ⁇ m or 150 ⁇ m.
• the deposited iron particles are dispersed and have a size of the order of 3 to 6 nm. This method makes it possible to obtain a good selectivity and a good yield (greater than 90%) with respect to the carbon source.
• the highly dispersed catalysts with low metal loading make it possible to obtain good metallic catalytic activity A * (grams of nanotubes formed per gram of metal per hour) and catalytic activity.
• the object of the invention is to propose a process which makes it possible simultaneously to obtain a high productivity, in particular of the order of or greater than 25%, a high activity, in particular of the order of or greater than 10%, and a selectivity. very high - especially greater than 90%, or even close to 100% - in carbon nanotubes produced - especially in multiwall nanotubes -.
• the object of the invention is more particularly to provide a method for producing ordered carbon nanotubes-in particular multiwall nanotubes-having a kinetics and a performance compatible with the constraints of an industrial scale operation.
• the invention relates to a process for the selective production of ordered carbon nanotubes by decomposition of a source of carbon in the gaseous state brought into contact with at least one solid catalyst supported in the form of grains, called catalyst, porous alumina support carrying a so-called ferrous, non-oxidized metal deposition of at least one transition metal whose iron characterized in that a supported catalyst mainly formed of catalyst grains is used:
• the ferrous metal deposition covers more than 75% of the surface of the macroscopic form (without taking into account the porosity) of the alumina support.
• the ferrous metal deposit is in the form of at least one cluster formed of a plurality of agglutinated metal bulbs.
• the ferrous metal deposit forms a homogeneous continuous ferrous metal surface layer. formed of metal bulbs.
• Each cluster-in particular the ferrous metal layer- is formed of bulbs, that is to say of rounded and globular swellings agglutinated to each other.
• the inventors have indeed found that the specific catalyst that constitutes a non-oxidized ferrous metal deposition - in particular made in the form of clusters, or a continuous layer of bulbs - covering more than 75% of the alumina support, has a much higher performance than the known catalysts, and in particular simultaneously makes it possible to obtain high activity and productivity with carbon nanotube selectivity close to 100% .
• the ferrous metal deposition is adapted to cover the alumina support so that its pores are rendered inaccessible. It should be noted that the fact that these pores (mesopores in the case of a mesoporous alumina) are made inaccessible by the metal deposition can be easily verified by a simple measurement of the variation of the specific surface area due to the presence of the deposit. Ferrous metal and / or by the calculation of the volume of mesopores and / or residual micropores and / or XPS analysis to demonstrate that the constituent chemical elements of the alumina support are no longer accessible on the surface.
• the composition according to the invention has a specific surface area corresponding to that of grains whose pores are inaccessible.
• each catalyst grain has a non-oxidized ferrous metal deposit forming a homogeneous continuous surface layer extending in at least a portion of a closed surface around a porous alumina core.
• Continuous layer means that it is possible to travel continuously throughout the surface of this layer, without having to cross a portion of another kind (including a portion free of non-oxidized ferrous metal deposition).
• the ferrous metal deposit is not dispersed on the surface of each grain of alumina, but instead forms a continuous layer of area apparently corresponding to that of the grains.
• This layer is moreover “homogeneous” in that it is formed of iron or a plurality of metals including iron, and has a solid composition identical in all its volume.
• the expression "closed surface” is used in the topological sense of the term, that is to say a surface that delimits and surrounds an internal finite space which is the heart of the grain, and which can take various forms (sphere, polyhedron). , prism, torus, cylinder, cone ).
• the ferrous metal deposition forms the outer layer of the catalyst grains immediately after its manufacture and if the catalyst composition is not brought into contact with an oxidizing medium. If the catalyst composition is vented to atmosphere, an oxide layer may form at the periphery. This oxide layer can, if necessary, be removed by a step of
• the ferrous metal deposit is derived from an elemental metal deposit (that is to say in which one (or more) metal (s) is (are) deposited (s) in the state element (s), that is to say in atomic or ionic form) made in a single step on the alumina support.
• the ferrous metal layer is part of an elemental ferrous metal deposit made in a single step on the solid alumina support.
• a single-stage elemental metal deposit can result in particular from a vacuum evaporation deposition (PVD), or a chemical vapor deposition (CVD), or an electrochemical deposition.
• the catalyst composition used in a process according to the invention differs in particular from a composition obtained by grinding metallurgically manufactured pure metal parts.
• a single-stage elemental metal deposit is formed of crystalline microdomains of the metal (s).
• Such a metal deposit elementary is formed of bulbs (rounded and globular bulges) metallic agglutinated to each other.
• the bulbs have an average size of between 10 nm and 1 ⁇ m, in particular between 30 nm and 100 nm.
• the ferrous metal deposition covers from 90% to 100% of the surface of the macroscopic form (envelope surface considered without taking into account the porosity) of the grains, which is itself a closed surface.
• This proportion of coverage of the alumina support surface by ferrous metal deposition can be determined by XPS analysis.
• the ferrous metal deposit thus extends 90% to 100% of a closed surface.
• the ferrous metal deposition extends over a thickness greater than 0.5 ⁇ m, in particular of the order of 2 to 20 ⁇ m.
• the ferrous metal deposition of each catalyst grain extends superficially with an average apparent surface area (on the outside surface of the grain) greater than 2.10 3 ⁇ m 2 . More particularly, advantageously and according to the invention, the ferrous metal deposition of each catalyst grain extends superficially with an average apparent surface area of between 10 ⁇ m and 1.5 ⁇ 10 5 ⁇ m 2 .
• the unoxidized ferrous metal deposition of each catalyst grain extends superficially with a global average dimension developed greater than 35 microns.
• the overall average dimension developed is the equivalent radius of the disk circumscribing the ferrous metal deposit after having virtually developed it in a plane.
• the unoxidized ferrous metal deposition of each catalyst grain extends superficially with an overall average developed dimension of between 200 ⁇ m and 400 ⁇ m.
• a process according to the invention is characterized in that a supported catalyst is used in the form of grains whose shapes and size are adapted to allow the formation of a bed fluidized of these catalyst particles, in that a fluidized bed of the catalyst particles is produced in a reactor, and in that the source of carbon in the reactor is continuously delivered in contact with the catalyst particles under clean conditions; to ensure the fluidization of the bed of catalyst grains, the decomposition reaction and the formation of nanotubes.
• a supported catalyst having a mean particle size (D50) of between 100 ⁇ m and 200 ⁇ m is used.
• the shape of the catalyst grains may be globally substantially spherical or not.
• the invention also applies to a process in which catalyst grains of more or less flattened form (flakes, discs, etc.) and / or elongated (cylinders, rods, ribbons, etc.) are used.
• each grain comprises a core of alumina covered with a gangue formed of said ferrous metal deposit.
• the ferrous metal deposit forms a metal gangue covering the entire surface of the porous alumina support and rendering its pores inaccessible.
• each grain depends on that of the alumina core, and the conditions under which ferrous metal deposition is formed on that core.
• the alumina has a specific surface area greater than 100 m 2 / g.
• the supported catalyst has a specific surface area of less than 25 m 2 / g.
• the thickness of the ferrous metal deposition may extend at least partly in the thickness of the porous alumina core and / or at least partly in the thickness relative to the porous core. It is not always easy to determine precisely and clearly the interface between the porous alumina core impregnated with ferrous metal deposition and the pure ferrous metal layer extending out of the alumina core and their relative arrangement.
• a supported catalyst comprising more than 20% by weight, in particular of the order of 40%, of ferrous metal deposition is used.
• the ferrous metal deposit is exclusively made of iron.
• the ferrous metal deposition is formed of iron and at least one metal selected from nickel and cobalt. It is known in particular that it is possible to use a bi ⁇ metal catalyst Fe-Ni or Fe-Co with similar results to a catalyst of pure iron, all things being equal elsewhere.
• the ferrous metal deposit is mainly iron.
• the supported catalyst composition used in a process according to the invention is advantageously formed mainly of such grains, that is to say contains more than 50% of such grains, preferably more than 90% of such grains.
• the invention extends to a process for the selective production of ordered carbon nanotubes in which a supported catalyst composition exclusively formed, with impurities, of such grains, that is to say the grains of which all comply with all or some of the characteristics defined above or below.
• a quantity of carbon source such as the ratio of the mass of the starting carbon source - in particular of the mass of carbon introduced into the reactor per hour - on the metal mass is used.
• the supported catalyst, in particular present in the reactor is greater than 100.
• the carbon source is ethylene.
• Other carbonaceous gases can be used.
• FIG. 1 is a diagram of an example of an installation for the manufacture of a catalyst composition that can be used in a process according to the invention
• FIG. 2 is a diagram of an example of an installation for the preparation of carbon nanotubes with a method according to the invention
• FIG. 3 is a micrograph of the surface of a grain of a catalytic composition that can be used in a process according to the invention obtained in example 1,
• FIGS. 4 and 5 are micrographs of the surface of the grains of a catalytic composition obtained in Example 2 that can be used in a process according to the invention
• FIG. 6 is a graph showing the distribution of the diameters of the nanotubes obtained in example 4,
• FIGS. 7a and 7b are microscopic photographs at two different scales representing nanotubes obtained in Example 4.
• FIG. 1 is a diagram of an installation for implementing a method of manufacturing a divided solid catalyst composition used in a method according to the invention.
• This installation comprises a reactor, called a deposition reactor 20 for the synthesis of the catalytic composition by chemical vapor deposition (CVD), which comprises a glass sublimator 1 into which the organometallic precursor is introduced.
• This sublimator comprises a sintered plate and can be brought to the desired temperature by a heated bath 2.
• the neutral carrier gas 3, for example helium, which entrains the vapors of the organometallic precursor used is stored in a bottle and admitted to the sublimator 1 using a flow regulator (not shown).
• the sublimator 1 is connected to a lower glass compartment 4, which comprises a sintered plate, into which is introduced water vapor which serves to activate the decomposition of the organometallic precursor.
• the presence of water makes it possible to obtain a non-oxidized metal deposit (thanks to the reaction of movement of the gas with water), free of impurity, and thus a very active catalyst.
• the compartment 4 has a thermostatically controlled double jacket at a temperature which can be adjusted by means of a temperature controller (not shown).
• the steam is entrained by and with a neutral carrier gas, for example nitrogen, stored in a bottle and admitted to the compartment 4 using a flow regulator (not shown).
• a neutral carrier gas feed 6, for example nitrogen is intended to adjust the flow rates so as to be in the fluidization conditions.
• This carrier gas 6 is stored in a bottle and admitted into compartment 4 using a flow regulator (not shown).
• the upper part of the compartment 4 is sealingly connected to a fluidization column 7 made of glass, for example 5 cm in diameter, which is equipped at its base with a gas distributor.
• This column 7 jacketed is thermostatically controlled at a temperature that can be adjusted by means of a temperature controller 8.
• the upper part of the column 7 is connected to a vacuum pump 9 via a trap, to retain the decomposition gases released.
• the implementation protocol of the examples relating to the preparation of the catalysts according to the invention by CVD is as follows.
• a precursor mass Ma is introduced into the sublimator 1.
• a mass Ms of alumina support grains is poured into the column 7 and a quantity of water is introduced into the compartment 4 with the aid of a syringe (for example of the order of 20 g).
• the vacuum is made in the assembly formed of compartment 4 and column 7.
• the temperature of the bed is brought to T1.
• the sublimator 1 is brought to the temperature Ts and the pressure is set to the value Pa throughout the equipment by introducing the carrier gases 3, 5 and 6 (total flow Q). The deposit then begins and lasts a while.
• the temperature is brought back to ambient temperature by slow cooling and the vacuum pump 9 is stopped.
• the catalytic granular composition is removed from column 7 under an inert gas atmosphere (for example nitrogen): it is ready to be used for the manufacture of nanorubes in a reactor growth 30.
• the growth reactor 30 is composed of a quartz fluidization column (for example 2.6 cm in diameter) provided at its center with a dispensing plate (sintered in quartz) 11 on which the powder is placed. catalytic granular composition.
• the column 10 can be brought to the desired temperature by means of an oven 12 which can slide vertically vertically along the fluidization column 10.
• the oven 12 has either a high position where it does not heat not the fluidized bed, a low position where it provides heating of the bed.
• the gases 13 neutral gas such as helium, carbon source and hydrogen
• the gases 13 are stored in bottles and are admitted into the fluidization column by means of flow regulators 14.
• the fluidization column 10 is sealingly connected to a trap 15 for collecting any fine particles of catalytic granular composition or a mixture of catalytic granular composition and nanotubes.
• the height of the column 10 is adapted to contain, in operation, the fluidized bed of the catalyst grains. In particular, it is at least 10 to 20 times the gaseous height, and must correspond to the heated zone. In the examples, a column 70 cm in height, heated to 60 cm high by oven 12, is chosen.
• the protocol for implementing examples relating to the production of nanotubes according to the invention is as follows:
• a mass Mc of granular supported catalyst is introduced into the fluidization column 10 under an inert gas atmosphere.
• the furnace 12 Since the furnace 12 is in a low position relative to the catalytic bed, its temperature is brought to the desired value Tn for the synthesis of the nanotubes, either under an inert gas atmosphere or under a mixture of inert gas and hydrogen ( reactive gas).
• the carbon source, the hydrogen and a complement of neutral gas are introduced into the column 10.
• the total flow rate Q x provides the bed with a bubbling regime at the temperature Tn, without firing.
• the growth of the nanotubes then begins and lasts a time ta.
• the oven 12 is placed in the high position relative to the catalytic bed, the gas flow rates corresponding to the carbon source and to the hydrogen are stopped and the temperature is brought back to ambient temperature by slow cooling. .
• the carbon nanotubes associated with the metal particles and attached to the support grains are extracted from the growth reactor 30 and stored without any particular precautions.
• the amount of carbon deposited is measured by weighing and by gravimetric thermal analysis.
• the nanotubes thus produced are analyzed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) for size and dispersion measurements and by X-ray crystallography and Raman spectroscopy to evaluate the crystallinity of the nanotubes.
• TEM transmission electron microscopy
• SEM scanning electron microscopy
• a catalyst composition is prepared at 24% by weight of
• the organometallic precursor is pentacarbonyl iron
• the support is mesoporous alumina- ⁇ (pore volume 0.54 cm 3 g -1 ) sieved between 120 ⁇ m and 150 ⁇ m and having a specific surface area of 160 m 2 g 4 .
• the composition obtained is formed of alumina grains covered with iron bulb clusters (the average bulb size is of the order of 20 nm), covering the surface of the alumina with a surface composition having 22% of aluminum as measured by XPS analysis (FIG. 3).
• This example is aimed at the preparation of a catalyst composition supported at 40% by mass of iron on alumina (Al 2 O 3 ) as indicated in Example 1, but with the following operating conditions:
• the composition obtained is formed of alumina grains completely covered with an iron matrix consisting of iron bulb clusters of 30 nm to 300 nm ( Figures 4 and 5).
• the specific surface area of the final material is 8 m 2 g -1 and the XPS analyzes show that the aluminum is no longer present on the surface.
• Multilayer carbon nanotubes are manufactured from the catalyst of Example 1 at 24% FeZAl 2 O 3 in an installation according to Figure 2, from ethylene gas as a carbon source.
• Multilayer carbon nanotubes are manufactured from the catalyst of Example 2 at 40% FeZAl 2 O 3 in an installation according to Figure 2, from ethylene gas as a carbon source.
• the operating conditions are as follows:
• FIG. 6 also shows that the diameter of the nanotubes obtained in Example 4 is in the majority of the order of 10 nm to 25 nm, whereas the grains of the composition have a diameter of the order of 150 ⁇ m and the bulbs iron sizes from 30 to 300 nm. Again, this result is surprising, inexplicable and goes against all previous teachings.
• FIGS. 7a and 7b show the high selectivity of the nanotubes produced in Example 4, which are thus directly usable, particularly in view of the small proportion of residual porous support in the nanotubes that had to be eliminated in the previous processes. known.
• Multilayer carbon nanotubes are manufactured from a 5% FeZAl 2 O 3 catalyst obtained as indicated in Example 1 with the operating conditions:
• the carbon nanotubes are prepared in a plant according to Figure 2, from ethylene gas as a carbon source.
• a 20% by weight FeZAl 2 O 3 catalyst composition is prepared by the fluidized bed CVD method described above.
• the carrier gas is nitrogen.
• the organometallic precursor is pentacarbonyl iron
• the support is non-porous ⁇ -alumina (specific surface area (BET method) of 2 m 2 / g).
• the resulting composition is formed of gangue-coated alumina particles formed of iron bulb clusters completely covering the surface of the alumina with a surface composition where aluminum is absent as measured by XPS analysis.
• Multilayer carbon nanotubes are manufactured from this iron catalyst on non-porous alumina in an installation according to FIG. 2, from ethylene gas as a carbon source.

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• 2004
  • 2004-06-23 FR FR0406804A patent/FR2872150B1/fr active Active
• 2005
  • 2005-06-21 CN CN2005800212288A patent/CN101018736B/zh not_active Expired - Fee Related
  • 2005-06-21 JP JP2007517354A patent/JP4866345B2/ja not_active Expired - Fee Related
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