HK1175431A - Catalyst and methods for producing multi-wall carbon nanotubes - Google Patents

Description

Catalyst and method for producing multi-walled carbon nanotubes

Background

This application claims priority to U.S. provisional patent application No. 61/226,438 filed on 7/17/2009. The entire disclosure of U.S. provisional patent application No. 61/226438 is incorporated herein by reference.

Carbon nanotubes are known to exist in both single-walled and multi-walled configurations. Each configuration provides certain advantages. Single-walled nanotubes are preferred for electronic applications because of the low incidence of structural abnormalities. However, multi-walled nanotubes are generally less expensive and can provide desirable performance in electronic applications if the amount of nanotube walls formed can be controlled. Unfortunately, current methods for producing multi-walled carbon nanotubes do not have the ability to control the amount of wall available in the resulting nanotube structure. As a result, multi-walled carbon nanotubes currently produced are typically about 3-35nm in diameter and include 3-40 concentric graphene (graphene) layers, i.e., the walls of the tubes. Each layer is a cylinder of coaxially arranged carbon atoms with an interlayer spacing of about 0.37 nm. This wide distribution of wall and outer diameter dimensions limits the value of multi-walled nanotubes for electrical conduction applications, thermal conduction applications, and mechanical reinforcement applications.

In contrast, multi-walled nanotubes can provide conductive characteristics that are close to those of single-walled nanotubes if they have a relatively narrow distribution of wall and outer diameters. Furthermore, multi-walled nanotubes can provide such improvements at a lower cost. Further, multi-walled nanotube batches (btach) with narrow distributions of tube wall number and outer diameter provide enhanced thermal conductivity and mechanical strength compared to batches with a wide distribution.

Although one might think of simply separating a narrow distribution of multi-walled carbon nanotubes from the wide distribution of multi-walled carbon nanotubes currently manufactured, the technology to accomplish this task does not exist. Thus, multi-walled nanotubes now available are provided entirely in batches or lots of undesirably broad distribution of wall and outside diameters.

As discussed in detail below, the present invention can provide batches of multi-walled nanotubes having narrow distributions of tube walls and diameters. When mixed with thermoplastics, the narrow distribution range batches can provide significantly improved conductivity characteristics comparable to single-walled nanotubes over currently available multi-walled nanotube batches. The present invention also provides catalysts and methods for making multi-walled nanotube batches with narrow distributions of tube walls and outer diameters.

Summary of the invention

In one embodiment, the present invention provides a catalyst precursor comprising alumina (Al)₂O₃) Magnesium oxide (MgO) and magnesium aluminate (MgAl)₂O₄) As a catalyst support. The catalyst precursor also includes metal oxides of cobalt, iron, and molybdenum. Preferred metal oxides include, but are not necessarily limited toMixed metal oxides limited to one or more of the following: CoFe₂O₄、CoMoO₄、Co_xMoO₄、Fe₂(MoO₄)₃、Co_xFe_yMoO₄(ii) a Wherein x and y represent the atomic ratio of Co and Fe to Mo, and x is from about 1.6 to about 6.5 and y is from about 0.1 to about 10.5. Mixed metal oxides containing two or more metal components are preferred because oxides of a single metal produce carbon fibers and other forms of carbon.

In another embodiment, the present invention provides a process for preparing a catalyst precursor and a catalyst. The method involves first preparing a solution comprising a mixed metal compound of two or more of: a cobalt compound selected from the group consisting of cobalt acetate and cobalt nitrate; an iron compound selected from the group consisting of iron acetate, iron nitrate; a molybdenum compound selected from ammonium heptamolybdate and ammonium dimolybdate; and magnesium nitrate. The solution is reacted with excess aluminum hydroxide powder, the reaction product subsequently forming a paste. The formation of a paste caused agglomeration of the reaction product, resulting in a particle size distribution of about 100 and 1400 microns. The reaction product is then dried, reduced in size and calcined to give the catalyst precursor. The presently preferred particle size distribution of the catalyst precursor is from 70 μm to 150 μm. The conversion of the precursor to the catalyst requires that the catalyst precursor be placed in a reaction chamber suitable for use as a fluidized bed reactor. An inert gas selected from nitrogen, argon or helium is flowed through the reaction chamber to fluidize and preheat the catalyst precursor to the desired reaction temperature. The inert gas is replaced with a blend of ethylene and inert gas when steady state conditions are reached at the desired reaction temperature. During the first 5 minutes of contact with the ethylene and inert gas blend, the catalyst precursor is converted to the desired catalyst. During the conversion process, cobalt and iron oxides are reduced to the corresponding metals. In addition, part of the iron oxide is reduced to iron carbide (Fe)₃C) The molybdenum oxide is reduced to molybdenum carbide (Mo)₂C)。

Still further, the present invention provides a method for producing multi-walled carbon nanotubes, wherein the resulting batch of multi-walled nanotubes has a narrow distribution with respect to the number of walls that make up the nanotubes, and the resulting nanotubes also have a narrow distribution of outer diameters. In the process of the present invention, the catalyst precursor is prepared as discussed above. After the catalyst precursor is converted to the reduced metal catalyst, the ethylene/inert gas flow is continued under the desired reaction conditions for a period of time sufficient to obtain multi-walled carbon nanotubes. The ethylene/inert gas contains from about 10 to about 80 volume percent ethylene and is flowed at a velocity sufficient to fluidize the bed of catalyst particles. After a reaction period of about 10 to about 30 minutes, the gas flow to the reaction chamber is cut off and the (carbonizing) multiwall nanotube-loaded particles are removed. About 95 to about 98% of the resulting carbon product supported by the spent catalyst is carbon nanotubes. About 60 to about 90% of the resulting multi-walled carbon nanotube batch has 3 to 6 walls and an outer diameter of about 3nm to about 7 nm. Thus, the present invention also provides a novel product comprising carbon nanotubes having 3 to 6 walls and an outer diameter of about 3nm to about 7 nm.

Drawings

Figure 1 provides a tabular illustration of the carbon yield and carbon nanotube diameter characteristics of various catalyst compositions on alumina supports.

FIG. 2 provides a graphical illustration of the carbon nanotube diameter distribution of the catalytic composition corresponding to PXE2-282 in FIG. 1.

FIG. 2B provides a graphical illustration of the carbon nanotube diameter distribution of the catalytic composition corresponding to PXE2-285 of FIG. 1.

FIG. 2C provides a graphical illustration of the carbon nanotube diameter distribution of the catalytic composition corresponding to PXE2-288 in FIG. 1.

FIG. 2D provides a graphical illustration of the carbon nanotube diameter distribution of the catalytic composition corresponding to PXE2-295 in FIG. 1.

FIG. 3 is a tabular illustration of the effect of reaction temperature and gas composition on carbon yield and selectivity for smaller diameter tubes.

Fig. 4A depicts the carbon nanotube diameter distribution corresponding to the SMW-100 carbon nanotube product as determined by TEM.

Figure 4B depicts the carbon nanotube diameter distribution corresponding to the MWCNT a carbon nanotube product as determined by TEM.

Figure 4C depicts the carbon nanotube diameter distribution corresponding to the MWCNT B carbon nanotube product as determined by TEM.

Figure 4D depicts the carbon nanotube diameter distribution corresponding to the MWCNT C carbon nanotube product as determined by TEM.

Fig. 5 is a graphical illustration of the volume resistivity of SMW-100 carbon nanotubes in polycarbonate and 3 commercial carbon nanotube products.

Figure 6A is a graphical illustration of the front and back sheet resistance of a composite containing nylon 66 resin loaded with 2.5 wt% SMW-100 carbon nanotubes or 2.5 wt% commercially available multi-wall carbon nanotubes.

Figure 6B is a graphical illustration of the front and back sheet resistance of a composite containing nylon 66 resin loaded with 3.5 wt% SMW-100 carbon nanotubes or 3.5 wt% commercially available multi-wall carbon nanotubes.

Fig. 7 depicts the surface resistivity of thin films comprising different forms of carbon nanotubes.

Detailed description of the preferred embodiments

The following detailed disclosure of the invention will illustrate the catalyst precursor, the process for preparing the catalyst precursor and the process for converting it to the desired catalyst. In addition, the present invention provides methods of producing the claimed batches of multi-walled carbon nanotubes on the catalyst, wherein the carbon nanotube product has a narrow distribution range of tube walls and outer diameters. As used in this specification, "carbon content" refers to the percentage of the final product (carbon nanotubes + catalyst) based on carbon. Therefore, if 250g of the final product is carbon and the final product is 500g in total, the carbon content is 50% or 50.0 (as used in FIG. 1). As used in this specification, "carbon yield" refers to the amount of carbon product produced relative to the amount of catalyst used in the reaction. It is defined as the following formula: (amount of carbon in final product (g)/amount of catalyst (g)) x 100. For example, the carbon yield of a reaction using 250g of the catalyst to produce 250g of the carbon product is 100% ((50g/250g) x100 ═ 100%). As used herein, (including FIGS. 2A-2D; 2A-4D), "frequency" refers to the number of carbon nanotubes in a sample having a specified diameter (x-axis). For example, in FIG. 2A, there are approximately 20 carbon nanotubes with a diameter of approximately 6 nm.

1. Catalyst precursor and catalyst

The catalyst precursor of the present invention has a surface phase of mixed metal oxide supported on alumina and magnesium aluminate particles. Mixed metal oxides are oxides containing two or more metal components. In addition, the surface treatment of the alumina/magnesium aluminate carrier carrying magnesium oxide. The magnesium oxide carried by the alumina/magnesium aluminate particles need not be a surrounding layer. MgO and Al₂O₃Is about 0.02 to 0.04. In other words, for a ratio of 0.02: 1, there are 50 atoms of Al for MgO per atom₂O₃And at a ratio of 0.04: 1, there are 25 atoms of Al for each atom of MgO₂O₃. As noted below, some of the MgO used in these calculations may be converted to MgAl₂O₄。

Preferred surface phases of mixed metal oxides include, but are not limited to, one or more of the following: CoFe₂O₄、CoMoO₄、Co_xMoO₄、Co_xFe_yMoO₄、Fe₂(MoO₄)₃. Typically, the metal oxide is provided on the catalyst precursor at the following weight percent concentrations of the metal: from about 0.5 to about 2.0 Co; about 0.3 to about 2.0% Mo; and about 0 to about 3.0% Fe. Thus, for Co_xFe_yMoO₄X may be about 1.6-6.5 and y may be 0.1-10.5. More preferably, x may be about 3.3 and y is 2.6-6.3. In any event, the metal oxide should be present on the catalyst precursor in an amount sufficient to result in a catalyst comprising the following metal components in weight percent: from about 0.5 to about 2.0 Co; about 0.3 to about 2.0% Mo; and about 0 to about 3.0% Fe. In the resulting catalyst, iron may be used as a reduced metal or carbide (Fe)₃C) And molybdenum may be present as carbide (Mo)₂C) Are present.

Preferably, the weight percent of each metal component, based on the weight of the catalyst precursor composition, is: co from about 0.75 to about 1.5%; mo about 0.5 to about 1.0%; and Fe from about 0.5 to about 2.0%. Accordingly, the active metal components are present in the following atomic ratios, with Mo being a constant value: a Co to Mo ratio of about 1.6 to about 6.5, more preferably about 2.44 to about 4.88, most preferably about 3.3; the ratio of Fe to Mo is from about 0 to about 10.5, more preferably from about 1.75 to about 6.98, and most preferably from about 2.62 to about 6.28.

The presence of Mg ions on the catalyst support can reduce the number of strong acid sites on the surface of the alumina support. By reducing the amount of strong acid sites on the surface of the catalyst support, the use of the improved catalyst can produce primarily carbon nanotubes, and produce significantly reduced amorphous carbon or other carbon products. As discussed below, the catalytic reaction using the improved catalyst may produce at least 90%, preferably greater than 98%, of the carbon nanotubes as the resulting carbon product.

The catalyst precursor of the present invention preferably has a particle size of from about 20 μm to about 500. mu.m. Preferably, the particle size is about 20 μm to 250 μm. More preferably, the catalyst precursor has a particle size of from about 20 μm to about 150 μm. In the presently preferred process discussed below, the particle size ranges from about 70 μm to about 150 μm.

By reducing metal oxides to the corresponding metals and metal carbides, i.e. Fe, Fe₃C. Co DEG and Mo₂C, the catalyst precursor as described above may be converted into catalyst particles. The catalyst particles have the same atomic ratio of metals present as the catalyst precursor. What is needed isThe resulting deposit of metallic cobalt and metallic iron in nanometer size can determine the inside diameter of the multi-walled nanotubes produced on the catalyst particles. In addition, Mo is present₂C may disperse or partition the metallic cobalt, thereby avoiding sintering of the cobalt and providing the desired cobalt particle size. Typically, the resulting metal deposit on the support has a diameter of from about 1.5nm to about 3.0 nm. Preferably, the resulting deposit of reduced iron and reduced cobalt metal is from about 1.5nm to about 2.2nm in diameter. In addition, as noted above, the final catalyst particles have fewer surface acid sites than catalyst particles utilizing only alumina as the support.

In general, the final catalyst particles of the present invention have a particle size of from about 20 μm to about 500. mu.m. Preferably, the particle size is about 20 μm to 250 μm. More preferably, the catalyst precursor particle size is from about 20 μm to about 150 μm. In the presently preferred method of making multi-walled nanotubes discussed below, the presently preferred particle size is from about 70 μm to about 150 μm. The catalyst particles comprise:

a. about 91.0 to 97.6 wt.%, preferably about 94.8 to about 97.3 wt.% gamma alumina (gamma-Al)₂O₃)；

b. About 0.5 to about 3.3 wt.%, preferably 0.5 to 1.0 wt.% Mg (as MgO and MgAl)₂O₄Forms of (d);

c. about 0.5 to about 2.0 wt%, preferably about 0.75 to about 1.5 wt% reduced Co;

d. about 0.3 to about 2.0 wt.%, preferably 0.5 to 1.0 wt.% Mo₂Mo in the form of C; and the number of the first and second groups,

e. about 0 to about 3.0 wt.%, preferably 0.5 to 2.0 wt.% of reduced iron and iron carbide (Fe °, Fe)₃C) Fe in its form.

Typically, less than 2.0 wt% of the catalyst particles may be metal carbides. The atomic ratio of the reduced metal used for catalytic production of multi-walled carbon nanotubes does not vary much from the catalyst precursor because metal carbides are not produced in large quantities.

2. Preparation of the catalystAgent precursor particles and catalyst particles

The present invention provides methods of making catalyst precursors and catalysts suitable for the catalytic formation of multi-walled carbon nanotubes. In particular, the catalysts of the present invention are capable of producing batches of multi-walled carbon nanotubes having a narrow distribution range of wall and diameter.

In a preferred embodiment, the process involves first preparing a solution comprising a mixed metal compound of two or more of: a cobalt compound selected from the group consisting of cobalt acetate and cobalt nitrate; an iron compound selected from the group consisting of iron acetate, iron nitrate; a molybdenum compound selected from ammonium heptamolybdate and ammonium dimolybdate; and magnesium nitrate. Preferred solutions include cobalt acetate, ferric nitrate, ammonium heptamolybdate, and magnesium nitrate in water.

The solution contains a concentration of cobalt ions, regardless of the cobalt compound selected, of from about 20g/L to about 50 g/L; a molybdenum ion concentration of about 10.5g/L to about 70.3 g/L; an iron ion concentration of about 35g/L to about 105 g/L; and, the Mg ion concentration is from about 6.7g/L to about 27.0 g/L. Preferred solutions contain cobalt ions in the range of about 26.7g/L to about 40.0 g/L; molybdenum ions in the range of about 17.6g/L to about 35.2 g/L; iron ion is from about 52.7g/L to about 70.1 g/L; and, the magnesium ion is from about 6.7g/L to about 13.5 g/L. Most preferred are solutions of the following ionic concentrations: cobalt ion was about 33.4 g/L; molybdenum ion was about 17.6 g/L; iron ion is about 63.1 g/L; and magnesium ion was about 6.7 g/L. Proper selection of the metal ion concentration enhances the desired mixed metal oxide formation. It is therefore desirable to provide a reasonable stoichiometric ratio of metals in solution to achieve this result.

The metal ions cited above are then reacted with aluminum hydroxide to give a mixture of metal hydroxide and other ionic compounds, including but not limited to hydroxides whose stoichiometric ratio may differ from that shown below: mg (OH)₂，、Fe(OH)₃、Co(OH)₂、CoMoO₄·nH₂O、Fe₂(MoO₄)₃·nH₂And O. Typically the reaction is carried out at room temperature for about 2-4 hours. The reaction product had a paste-like consistency (consistency)ency), which may promote particle agglomeration. Preferably, the moisture content of the paste is about 20-40% by weight water. More preferably, the paste contains from about 25 to about 30 weight percent water.

If particle agglomeration is desired, the paste-like product can be manipulated (manipulated) to obtain agglomerate particles having a particle size of from about 100 μm to about 1400 μm. Generally the particles may agglomerate during the reaction. Preferably, the agglomerate particles are about 100 μm to about 500 μm. In a preferred method, the agglomerate grains are mixed in a machine that kneads or mixes the paste for about 20 to about 50 minutes. After kneading, the product was aged for about 2 to 3 additional hours. The total length of time may depend on the batch size. For batches of about 200 to about 2000 grams, a preferred kneading time is about 30 minutes. Larger batches may require longer mixing times. After agglomeration, the particles were dried and sieved to separate particles below 1400 μm. Preferably, the sieving step provides particles of about 100 μm to about 500 μm.

The agglomerate is dried to a moisture content of about 10-20% by weight water. Preferably, the dried particles contain less than 15 wt% water. The drying step is preferably carried out at a temperature of about 30 ℃ to 50 ℃.

After drying and sieving, the particles are calcined under flowing gas at a temperature of about 400 ℃ to 600 ℃ for a time of about 3 hours to about 8 hours. More preferably, the calcination step is conducted at a temperature of from about 400 deg.C to 500 deg.C for a period of from about 3.5 hours to about 4.5 hours. Most preferably, the calcination step is carried out at a temperature of about 440 ℃ to 460 ℃ for about 3.5 hours to about 4.5 hours. Preferably, the calcining gas is selected from the group consisting of air, nitrogen, helium and mixtures thereof. Typically, the preferred calcining gas is one that is inert under the conditions of calcination. The drying and calcining steps reduce the agglomerate particle size to a particle size of from about 20 μm to about 500 μm. Alternatively, the particles are sieved prior to calcination and, if necessary, milled so that calcination can produce particles of 20 μm to 250 μm. Preferably, the calcination produces particles of about 20 μm to 200 μm. More preferred are particles of about 20 μm to 150 μm. In the preferred process discussed below, the preferred particle size range is from about 70 μm to about 150 μm. The resulting particles are substantially free of water, i.e., no more than 3% by weight water.

Particle calcination converts the metal hydroxide to the corresponding oxide. For example, calcination of iron hydroxide with molybdate yields iron molybdate (Fe)₂(MoO₄)₃). Similarly, calcination of cobalt hydroxide with molybdate resulted in cobalt molybdate (CoMoO)₄). Further, Fe (OH) during calcination₃And Co (OH)₂Combined to produce CoFe₂O₄. Finally, Mg (OH)₂MgO, aluminum hydroxide (Al (OH) are obtained during calcination₃) Conversion to gamma alumina, i.e. gamma-Al₂O₃. During calcination, Mg (OH)₂Oxidation can also be prevented in gamma-Al₂O₃Strong acid sites are formed on the surface. The resulting surface texture is believed to be similar to a mixed oxide of Mg-Al-O. In any case, MgO-loaded gamma-Al₂O₃Surface acidity significantly lower than in the absence of Mg (OH)₂gamma-Al by calcining₂O₃The surface acidity of (2).

Further, during calcination, in addition to forming the corresponding oxides of magnesium and aluminum, a portion of Mg adjacent to the aluminum hydroxide⁺²The ions produce parallel reactions. In this reaction, the solubility of magnesium ions in alumina is such that magnesium can replace a portion of the alumina tetrahedral structure near the particle surface, thereby producing magnesium aluminate (MgAl)₂O₄) A compound having a spinel-like structure. Magnesium aluminate formation is preferred to CoAl formation₂O₄And FeAlO₃. Thus, this favorable reaction protects the catalytic sites that the catalytic metal reduces and converts on the surface of the resulting support particle. In particular, reduced cobalt acquires the form of nanoparticle-sized domains on the surface of the resulting support, iron becomes reduced iron and iron carbide, and molybdenum becomes molybdenum carbide. Iron carbide and reduced iron disperse the cobalt on the surface of the catalyst support, thereby controlling the internal diameter of the resulting nanotubes.

The resulting catalyst support had a configuration in which magnesium aluminate was bonded to γ -Al mainly at the outer layer of the particles₂O₃In the crystal structure. Further, MgO is supported on the surface of γ alumina. Without being limited by theoryThe MgO on the surface may be a mixed oxide with particulate alumina, i.e., a Mg-Al-O mixed oxide. This configuration results from the reaction of magnesium ions with alumina during calcination. Finally, the preferred catalyst support is preferably free of CoAl₂O₄And FeAlO₃. If FeAlO is present₃Preferably, then the catalyst support comprises less than 0.5 wt% of FeAlO₃. If CoAl is present₂O₄Preferably, then the catalyst support comprises less than 0.5 wt.% CoAl₂O₄。

The presence of magnesium on the surface of the catalyst support particles can reduce the surface acidity of the catalyst precursor support particles, and the resulting catalyst support particles. By reducing the number of acid sites on the surface of the support particles, the method of the present invention can improve the production of carbon nanotubes and reduce the formation of other forms of carbon during the subsequent production of multi-walled carbon nanotubes. In addition, the presence of magnesium ions prevents the formation of CoAl₂O₄And FeAlO₃Loss of catalytic metal can be prevented.

After calcination and particle size reduction, the resulting catalyst precursor particles contain MgO surface-treated catalyst support gamma-Al₂O₃/MgAl₂O₄. In addition, the surface of the catalyst support carries a mixed phase of the cited metal oxides. As noted above, preferred mixed metal oxides include, but are not necessarily limited to: CoFe₂O₄、CoMoO₄、Co_xMoO₄、Fe₂(MoO₄)₃、Co_xFe_yMoO₄In which Co_xFe_yMoO₄And is most preferred.

The resulting catalyst precursor was placed in a reaction chamber. Preferably, the reaction chamber is designed to produce a fluidized bed of catalyst particles as the flowing gas passes through the chamber and the particles located therein. In order to finally convert the catalyst precursor into a catalyst, the precursor must be heated and reacted with a carbon-containing gas. In the following method for producing multi-walled nanotubes, the preferred gaseous carbon compound is ethylene. Catalyst precursor to catalystOccurs at a temperature of about 600 c to 700 c during the first 10 minutes of contact with the gaseous carbon compound. During this time period, the metal oxide is reduced to the corresponding metal and metal carbide discussed above. In addition, Fe is formed₃C and Mo₂C prevents sintering and agglomeration of the reduced cobalt and iron on the surface of the support. Thus, the resulting nanoparticles of reduced cobalt preferably have a diameter of about 1.5nm to about 3.5 nm. More preferably, the reduced cobalt metal particles on the surface of the catalyst support have a diameter of from about 1.5nm to about 2.2 nm. The reduced iron particles have similar sizes, i.e., from about 1.5nm to about 3.5nm, preferably from about 1.5nm to about 2.2 nm.

The obtained catalyst comprises gamma-Al which is subjected to surface treatment by MgO₂O₃/MgAl₂O₄Support, and nanosized Fe on the surface of the support₃C and Mo₂And C particles. The reduced metallic cobalt may be prepared from gamma-Al₂O₃/MgAl₂O₄The carrier may be molybdenum carbide (Mo)₂C) And iron carbide (Fe)₃C) Are present. Alternatively, the reduced iron may be formed from gamma-Al₂O₃/MgAl₂O₄The carrier may be molybdenum carbide (Mo)₂C) And iron carbide (Fe)₃C) Are present.

As discussed above, the resulting catalyst particles have a particle size of from about 20 μm to about 500 μm. Preferably, the particle size is about 20 μm to 250 μm. More preferably, the catalyst particle size is from about 20 μm to about 150 μm. In a presently preferred method of making multi-walled nanotubes, a presently preferred particle size is from about 70 μm to about 150 μm.

The catalyst particles comprise about 91.0-97.6 wt% gamma alumina (gamma-Al)₂O₃) Preferably from about 94.8 to about 97.3 wt%; about 0.5 to about 3.3 wt.% Mg (as MgO and MgAl)₂O₄Form (b) preferably 0.5 to 1.0% by weight; about 0.5 to about 2.0 wt.% reduced Co, preferably about 0.75 to about 1.5 wt.%; about 0.3 to about 2.0 weight percent Mo, as Mo₂Form C, preferably from about 0.5 to about 1.0 wt%; and about 0 to about 3.0 wt.% Fe, as reduced iron and iron carbide (Fe, F)e₃C) Preferably 0.5 to 2.0% by weight. Typically, less than 2.0 wt% of the catalyst particles are metal carbides. The atomic ratio of the reduced metal used for catalytic production of multi-walled carbon nanotubes does not vary much from the catalyst precursor because metal carbides are not produced in large quantities.

In an alternative process for preparing the catalyst precursor, the magnesium nitrate is omitted from the initial solution. In the method, magnesium hydroxide powder is mixed with aluminum hydroxide powder and reacted with a solution of metal compounds including a cobalt compound selected from the group consisting of cobalt acetate, cobalt nitrate, an iron compound selected from the group consisting of iron acetate, iron nitrate, a molybdenum compound selected from the group consisting of ammonium heptamolybdate and ammonium dimolybdate, and mixtures thereof. Preferred solutions include cobalt acetate, ferric nitrate, ammonium heptamolybdate, and magnesium nitrate in water.

The solution contains a concentration of cobalt ions, regardless of the cobalt compound selected, of from about 20g/L to about 50 g/L; a molybdenum ion concentration of about 10.5g/L to about 70.3 g/L; an iron ion concentration of about 35g/L to about 105 g/L; and, the Mg ion concentration is from about 6.7g/L to about 27.0 g/L. Preferred solutions contain cobalt ions in the range of about 26.7g/L to about 40.0 g/L; molybdenum ions in the range of about 17.6g/L to about 35.2 g/L; iron ion is from about 52.7g/L to about 70.1 g/L; and, the magnesium ion is from about 6.7g/L to about 13.5 g/L. Most preferred are solutions of the following ionic concentrations: cobalt ion was about 33.4 g/L; molybdenum ion was about 17.6 g/L; and the iron ion was about 63.1 g/L.

The metal ion solution is then reacted with an excess of aluminum hydroxide powder having a particle size of from about 20 μm to about 150 μm and magnesium hydroxide powder having a particle size of from about 20 μm to about 150 μm. After this reaction, the catalyst precursor and the subsequent catalyst are prepared in the same manner as described above.

Production of multi-walled carbon nanotube batches with narrow distribution range of tube walls and diameters

The following discussion regarding the catalytic production of multi-walled carbon nanotubes is essentially a continuation of the above discussion regarding catalyst precursors and catalyst preparation. After the calcined catalyst precursor is placed in the reactor chamber, the particles are fluidized and converted to catalyst particles. As noted above, the particle size of the catalyst may be from about 20 μm to about 500 μm. Preferably, the particle size is about 20 μm to 250 μm. More preferably, the catalyst precursor particle size is from about 20 μm to about 150 μm. In a presently preferred method of making multi-walled nanotubes, a presently preferred particle size is from about 70 μm to about 150 μm. Thus, the particles are well suited for use in a fluidized bed reactor.

After the catalyst precursor particles are placed in the reaction chamber, a stream of nitrogen is passed through the reaction chamber, thereby fluidizing the particle bed. The nitrogen is heated to a temperature sufficient to raise the temperature within the fluidized bed to between about 600 c and about 700 c. Alternatively, the reaction chamber may be located in a furnace or other suitable heating device. When located in a furnace, the reaction chamber is typically heated by both the furnace and the gas. More preferably, the fluidized bed is preheated to a temperature of from about 600 ℃ to about 650 ℃. Most preferably, the fluidized bed is preheated to a temperature of about 610 ℃ to 630 ℃. It will be appreciated by those skilled in the art that other non-reactive gases such as argon or helium may be substituted for nitrogen. The primary requirement of the preheating step is fluidization of the fluidized bed and heating to the desired temperature without undesirable side reactions.

After the temperature in the fluidized bed has stabilized, the gas flow to the bed is switched from nitrogen to the reactive gas. The reactive gas is a non-reactive carrier gas containing a carbon-containing gas. The preferred carrier gas is nitrogen and the preferred carbon-containing gas is ethylene; however, other carrier gases such as argon or helium work equally well. Preferred blends of ethylene in nitrogen range from about 10 to 80 volume percent by volume. More preferably, the reactive gas contains from about 20 to about 50 volume percent ethylene in nitrogen. Most preferred are reactive gases containing from about 20 to about 40 volume percent ethylene in nitrogen.

The flow rate of the ethylene-containing gas does not depend on the size of the reaction chamber. In contrast, the volume of gas passing through the reaction chamber depends on the grams of catalyst precursor within the reaction chamber. The flow rate is from about 70L/min per kg catalyst precursor to about 150L/min per kg catalyst precursor. More preferably, the flow rate is from about 90L/min per kg catalyst precursor to about 120L/min per kg catalyst precursor.

Initial reaction of the ethylene-containing gas with the catalytic particles reduces the metal oxides to their corresponding metals (Co DEG and Fe DEG) and metal carbides (Mo)₂C and Fe₃C) In that respect This reduction step typically occurs within the first 5 minutes of the reaction process. Preferably, the reaction temperature is from 600 ℃ to 750 ℃. More preferably, the reaction temperature is 610 ℃ to 650 ℃. Most preferably, the reaction temperature is 610 ℃. In addition, the reaction of ethylene with the catalyst precursor and subsequent catalyst particles during the first 10 minutes of the reaction process is exothermic. Therefore, the preferred method maintains the fluidized bed temperature below 670 ℃. Temperature maintenance may be achieved by reducing the temperature of the gases entering the reaction chamber. If a furnace is used, the temperature of the furnace can also be reduced. It is preferred to keep the temperature below 650 deg.c, since higher temperatures will result in increased amorphous carbon production. As the metal oxide is reduced, ethylene gas contacts the resulting catalytic particles and multi-walled carbon nanotubes begin to grow. The reaction process continues for about 10 to about 40 minutes after the metal oxide is reduced to catalytic particles. More preferably, the reaction process after the reduction of the metal oxide is continued for about 15 to 25 minutes.

The resulting carbon product, now loaded with spent catalyst particles, was 98% free of amorphous carbon and other forms of carbon. Thus, 98% of the carbon product was multi-walled carbon nanotubes. Furthermore, the obtained multi-wall carbon nano-tube mainly has 3-8 tube walls. More preferably, the resulting nanotubes loaded with spent catalyst particles have predominantly 3-6 walls and an outer diameter of about 4.0nm to about 7.0 nm. Preferably, at least 60% of the resulting multi-walled carbon nanotubes have 3 to 6 walls and an outer diameter of about 4.0nm to about 7.0 nm. More preferably, the method of the present invention can yield multi-walled carbon nanotubes wherein at least 75% of the resulting multi-walled carbon nanotubes have the required narrow distribution range of 3-6 walls and diameters of about 4.0nm to about 7.0 nm. More preferably, at least 85% of the resulting multi-walled carbon nanotubes loaded with spent catalyst have 3 to 6 walls and an outer diameter of about 4.0nm to about 7.0 nm. Most preferably, the catalyst particles are continuously maintained fluidized, and the present invention can provide spent catalyst loaded multi-walled carbon nanotubes wherein at least 90% of the resulting multi-walled carbon nanotubes can have 3 to 6 walls and a diameter of about 4.0nm to about 7.0 nm.

The following examples and test data do not limit the nature of the invention. Rather, this information will enhance the understanding of the present invention.

Example 1

Purpose(s) to

This example illustrates the effect of various catalyst metal compositions on carbon yield and carbon nanotube diameter.

Method of producing a composite material

Various catalyst precursors were prepared to demonstrate the importance of the catalytic metal to the resulting multi-wall product. The resulting nanotube product used for this comparison is shown in the table of figure 1. For these examples, 600 grams of the catalyst precursor having a particle size of 150-300 microns prepared as discussed above was placed in a fluidized bed reactor. As discussed above, the method of the present invention converts a catalyst precursor to a catalyst and then grows multi-walled carbon nanotubes on the resulting catalyst. For each example provided in fig. 1, the final catalyst was reacted with 40% ethylene in nitrogen at 610 ℃ for 20 minutes with a gas flow rate of 60L/min (mass ratio gas flow/catalyst of 100L/min per kg catalyst).

Results

As depicted in fig. 1, the catalytic metal composition significantly affected the resulting multi-walled nanotube product. For example, tests PXE2-282, PXE2-285, PXE2-292, and PXE2-293 provide data on multi-walled carbon nanotubes prepared with a catalyst containing Co, Mo, and about 0.75 wt% iron to about 1.9 wt% iron. The resulting nanotube batch has a high yield of carbon nanotubes with a bit outer diameter of about 6.72nm to about 8.24nm and a mode outer diameter of about 4.97nm to about 6 nm. 75-85% of these carbon nanotubes have an outer diameter of less than 10 nm. Specifically, PXE2-282 represents multi-walled nanotube batches with a mode diameter of 6.0nm, a median diameter of 8.24nm, and 73% of the batches were less than 10nm in diameter. Similarly, PXE2-285 represents a multi-walled nanotube batch with a mode diameter of 5.38nm, a median diameter of 6.72nm, and 85% of the batch is less than 10nm in diameter. The values of PXE2-292 and PXE2-293 may be readily determined from FIG. 1. As known to those skilled in the art, the term "mode" when used in this manner means the value that occurs most frequently in the data set. Thus, for PXE2-285, the most common diameter of nanotubes within the batch is 6.72 nm.

These results indicate that the catalyst precursor composition comprising Co in an amount of about 0.75 to about 1 wt% of the total metals of the catalyst precursor, Fe in an amount of about 0.75 to about 1.9 wt% of the total metals of the catalyst precursor, and Mo in an amount of about 0.4 to about 0.5 wt% of the total metals of the catalyst precursor yields very high percentage yields of small diameter carbon nanotubes.

In contrast, the lack of iron catalyst precursor particles results in a significant reduction in carbon yield. For example, test PXE2-288 showed that when iron was removed from the precursor catalyst formulation, the carbon yield lost 57%. Interestingly, the resulting product comprised carbon nanotubes with a median outer diameter of 6.98 and a mode outer diameter of 4.68. This suggests that iron is not the reason for obtaining small diameter carbon nanotubes. However, the results seem to suggest that molybdenum plays a role in limiting the diameter of carbon nanotubes. For example, test PXE2-284 produced carbon nanotubes with a median outer diameter and a mode outer diameter of 9.63nm and 11.06nm, respectively. In addition, only 54% of the resulting carbon nanotubes had an outer diameter of less than 10nm, compared to 85% in test PXE2-285, where Mo was used in the precursor composition. Figures 2A-2D further illustrate the effect of removing any pair of carbon nanotube diameter distributions of Fe or Mo from the catalyst precursor. Taken together, these results indicate that iron serves to maintain carbon yield, while molybdenum promotes the production of smaller diameter carbon nanotubes.

Example 2

Purpose(s) to

Referring to fig. 3, this example illustrates the effect of reaction temperature and gas composition on carbon yield and carbon nanotube diameter.

Method of producing a composite material

Catalyst compositions having the formulations PXE2-282 and PXE2-285 of FIG. 1 were used as references in this experiment. To determine the effect of reaction temperature on the resulting nanotube product, the reaction was carried out at a temperature of 610-675 deg.C. Further, these tests determined the effect on the resulting nanotube product due to ethylene concentration changes when ethylene concentration in the gas feed was varied between 30-40%.

Results

Increasing the reaction temperature and/or decreasing the ethylene content of the gas composition from 40% to 30% reduces the carbon yield and increases the carbon nanotube diameter. Thus, to maximize carbon yield and produce small diameter carbon nanotubes, the catalytic reaction should be at about 610 ℃ and the reactive gas mixture contains 40% ethylene.

Example 3

Purpose(s) to

This example compares the electrical conductivity of a composite material comprising mainly small diameter multi-walled carbon nanotubes (diameter 4-8nm) with 3-6 walls and a composite material comprising large diameter carbon nanotubes. This and subsequent examples use a material identified in FIG. 1 as PXE2-282 (referred to as SMW-100) prepared in accordance with the present invention.

Method of producing a composite material

Carbon nanotubes made by the method and catalyst composition of the present invention (hereinafter, SMW-100 refers to multi-walled carbon nanotubes made by the catalyst composition described for PXE2-282 in FIG. 1) were compared to various commercially available carbon nanotubes having diameter distributions as described in Table 1 and FIGS. 4A-D. Table 1 below provides the carbon nanotube diameter distributions for various commercially available multi-walled carbon nanotubes and SMW-100. For example, for SMW-100, 10% of the nanotubes have a diameter of less than 4.2nm, 50% of all nanotubes have a diameter of less than 6.7nm, and 90% of all nanotubes have a diameter of less than 12 nm.

	10％	50％	90％
				SMW-100	4.2nm	6.7nm	12.0nm
MWCNT A	5.5nm	7.8nm	13.0nm
				MWCNT B	7.4nm	12.0nm	16.5nm
MWCNT C	7.1nm	9.9nm	13.3nm

TABLE 1

Polycarbonate Makrolon 2600 PC particles were melt mixed with the carbon nanotube source described in table 1. Melt mixing was carried out on a DSM micro-mixer (15 cm)³) The method comprises the following steps: screw speed-200 rpm; the temperature is 280 ℃; time-5 minutes. From the extruded strands (temperature: 280 ℃, time: 1 minute, pressure: 100kN) were prepared press plates (60mm diameter x0.5mm thickness). The carbon nanotube samples were characterized by TGA and TEM analysis (fig. 4A-D).

Test fixture with Keithley 6517A potentiometer in combination with Keithley 8009 (for resistivity > 10)⁷Ohm cm) or bar test fixture (for resistivity < 10)⁷Ohm cm) was measured. For the purposes of this disclosure, the term percolation threshold refers to the concentration of carbon loading when there is one, and only one, continuous conductive path in the material.

Results

Fig. 5 demonstrates that SMW-100 carbon nanotube material provides the lowest electropercolation threshold. As depicted in fig. 5, a CNT loading of 0.33 wt% can meet the requirements of electro-percolation. As shown in FIG. 5, SMW-100 provides 10 for a load of 0.5-1.0 wt.% load⁴-10²Ohm/cm resistivity reading. In contrast, comparative carbon nanotubes having diameters of 7-9nm (MWNT A), 10-11nm (MWNT C), and 12-15nm (MWNT B) gave percolation thresholds of 0.50 wt%, and 0.55-0.60 wt%, respectively.

Based on the above results, using batches of straight (straight) multi-walled carbon nanotubes having the SMW-100 characteristics provided in table 1 and fig. 1, can provide higher conductivity performance at lower loading levels than other commercially available multi-walled carbon nanotube sources.

Example 4

Purpose(s) to

This study compared the performance of composites based on commercially available multi-walled carbon nanotubes dispersed in nylon 66 resin with composites prepared from SMW-100 carbon nanotubes dispersed in nylon 66 resin.

Method of producing a composite material

Compounding of CNT-nylon 6, 6 was performed by twin screw extrusion. The resulting composite was then injection molded into standard ASTM test bars and test pieces (4 inches by 3.2 millimeters). The conductivity measurements were then carried out on the injection-molded test pieces using a standard ProStat resistance meter, according to the standard ASTM D-257 for volume and surface resistance. The surface resistance was measured at 25 predetermined locations on each surface of the injection molded sheet using a PRF-912B probe, i.e., 25 points on the front surface and 25 points on the back surface of the injection molded sheet. The rigorous testing is designed to discover any minor variations in electrical performance due to material and/or process non-uniformities. The front surface of the sheet corresponds to the location of the ejector pins. The rear surface of the sheet corresponds to the fixed part of the tool (closer to the nozzle). The volume resistance of the patch was measured at 5 positions per sample using a PRF-911 concentric ring, and the data from the front and back of the patch were averaged.

Results

The sheet resistance data is plotted in fig. 6A and 6B. The molded SMW-100 composite exhibited lower and more uniform resistance properties than commercially available multi-walled carbon nanotubes (MWCNTs). The surface resistance of the MWCNT and SMW-100 filled samples was relatively uniform, with the front and back surfaces of the sheet being very consistent.

Furthermore, the composite with SMW-100 based on nylon 6, 6 showed higher conductivity values than the composite with commercially available MWCNT grades based on nylon 6, 6. The SMW-100 composite further exhibited uniform resistance values with a narrower range of standard deviations between test points and between the front and back surfaces of the sheet. As reflected in fig. 6A and 6B, the composite materials prepared from the carbon nanotube material of the present invention, i.e., the nanotube batch with narrow diameter and wall count distributions, have improved electrical conductivity compared to the current materials.

Example 5

Purpose(s) to

This example compares the surface resistivity of films containing the following nanotubes, respectively: SMW-100; single-walled carbon nanotubes (SWNTs); double-walled carbon nanotubes (DWNTs); and, commercially available multi-walled carbon nanotubes (MWCNT B of example 3).

Method of producing a composite material

Carbon nanotube-based films of varying transparency (80-95% transmittance) were prepared using a solution containing 1g carbon nanotubes per liter in 1% Triton-X100 surfactant. The solution was then sonicated and centrifuged. Various carbon nanotube inks were deposited on a PET 505 substrate using a bar coating process.

Results

As shown in FIG. 7, films made with SWNTs having a transparency of 80-90% exhibited higher conductivity than materials with other types of carbon nanotubes in the film. However, the films prepared using the novel batch materials of the present invention, i.e., using SMW-100, have better conductivity properties than films combining conventional DWNTs and MWNTs.

Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification or practice of the invention disclosed herein. Accordingly, the foregoing description is to be considered as merely illustrative of the invention, with the true scope and spirit of the invention being indicated by the following claims.

Claims (109)

1. A catalyst precursor composition comprising:

a carrier; and

a mixed metal oxide on the surface of the support, wherein the mixed metal oxide is selected from the group consisting of: CoFe₂O₄、CoMoO₄、Co_xFe_yMoO₄、Fe₂(MoO₄)₃And blends thereof, and to the use of such polymers,

wherein x and y each represent the atomic ratio of the corresponding metal oxide, wherein x is from about 1.6 to 6.5 and y is from about 0 to 10.5.

2. The catalyst precursor composition of claim 1, wherein x is from about 2.44 to 4.88 and y is from about 1.75 to 6.98.

3. The catalyst precursor composition of claim 1, wherein the mixed metal oxide is selected from the group consisting of: CoFe₂O₄、CoMoO₄、Co_3.3Fe_2.62MoO₄And blends thereof.

4. The catalyst precursor composition of claim 1, wherein the mixed metal oxide is selected from the group consisting of: CoFe₂O₄、CoMoO₄、Co_3.3FeyMoO₄And blends thereof, wherein y can be 2.6 to 6.3.

5. The catalyst precursor composition of any of claims 1-4, wherein the support comprises alumina and magnesium aluminate.

6. The catalyst precursor composition of claim 5, wherein the magnesium oxide is located on the surface of the support.

7. The catalyst precursor composition of claim 6, wherein the alumina is gamma alumina.

8. A catalyst precursor composition comprising:

a support comprising alumina and a magnesium compound; and

a mixed metal oxide on the surface of the support, wherein the metal component of the mixed metal oxide is selected from the group consisting of: cobalt, molybdenum and iron, and the iron,

wherein the cobalt is from about 0.5 to about 2.0 weight percent of the total metal concentration of the catalyst precursor composition, the molybdenum is from about 0.3 to about 2.0 weight percent of the total metal concentration of the catalyst precursor composition, the iron is from about 0 to about 3.0 weight percent of the total metal concentration of the catalyst precursor composition, and the magnesium is from about 0.5 to about 3.3 weight percent of the total metal concentration of the catalyst precursor composition.

9. The catalyst precursor composition of claim 8, wherein the alumina is gamma alumina.

10. The catalyst precursor composition of claim 8, wherein the magnesium compound is magnesium aluminate.

11. The catalyst precursor composition of claim 8, wherein the magnesium oxide is present on the surface of the support.

12. The catalyst precursor composition of claim 8, wherein the catalyst precursor composition has a particle size of about 20 to about 500 microns.

13. The catalyst precursor composition of claim 8, wherein the catalyst precursor composition has a particle size of about 20 to about 250 microns.

14. The catalyst precursor composition of claim 8, wherein the catalyst precursor composition has a particle size of about 20 to about 150 microns.

15. The catalyst precursor composition of claim 8, wherein the catalyst precursor composition is substantially free of FeAlO₃And CoAl₂O₄。

16. The catalyst precursor composition of claim 8, wherein the catalyst precursor composition has less than 0.5 wt% of FeAlO₃And less than 0.5 wt.% CoAl₂O₄。

17. The catalyst precursor composition of claim 8, wherein the cobalt is about 0.75 to about 1.5 weight percent of the total metal concentration of the catalyst precursor composition, the molybdenum is about 0.5 to about 1.0 weight percent of the total metal concentration of the catalyst precursor composition, the iron is about 0.5 to about 2.0 weight percent of the total metal concentration of the catalyst precursor composition, and the magnesium is about 0.5 to about 1.0 weight percent of the total metal concentration of the catalyst precursor composition.

18. A catalyst composition comprising:

a support comprising gamma alumina and magnesium aluminate; and

a surface of said support supporting cobalt, molybdenum, and iron, wherein said cobalt is in the form of metallic cobalt and is in the range of from about 0.5 to about 2.0 weight percent of said catalyst composition, wherein said molybdenum is in the form of molybdenum carbide and is in the range of from about 0.3 to about 2.0 weight percent of the concentration of said catalyst composition, wherein said iron is in the form of metallic iron and iron carbide, and the total iron component is in the range of from about 0 to about 3.0 weight percent of the concentration of said catalyst composition.

19. The catalyst composition of claim 18, wherein gamma alumina is about 91.0 to about 97.6 wt% of the catalyst composition, and wherein MgO and MgAl are present₂O₄The magnesium is in the form of about 0.5 to about 3.3 weight percent of the catalyst composition.

20. The catalyst composition of claim 18, wherein gamma alumina is from about 94.8 to about 97.6 wt% of the catalyst composition, and wherein magnesium is from about 0.5 to about 1.0 wt% of the catalyst composition.

21. The catalyst composition of claim 18 wherein said cobalt is in the form of metallic cobalt and is in the range of from about 0.75 to about 1.5 weight percent of said catalyst composition, wherein said molybdenum is in the form of molybdenum carbide and is in the range of from about 0.5 to about 1.0 weight percent of the concentration of said catalyst composition, and wherein said iron is in the form of metallic iron and iron carbide and the total iron component is in the range of from about 0.5 to about 2.0 weight percent of the concentration of said catalyst composition.

22. The catalyst composition of claim 18, wherein molybdenum carbide and iron carbide comprise from 0 to less than 2.0 wt% of the catalyst composition.

23. The catalyst composition of claim 18 wherein said metallic cobalt is located on the surface of said support as particles having a particle size of from about 1.5nm to about 3.0 nm.

24. The catalyst composition of claim 18 wherein said metallic cobalt is located on the surface of said support as particles having a particle size of from about 1.5nm to about 2.2 nm.

25. The catalyst composition of claim 18, wherein the magnesium oxide is present on the surface of the support.

26. The catalyst composition of claim 18, wherein the particle size of the catalyst composition is from about 20 to about 500 microns.

27. The catalyst composition of claim 18, wherein the particle size of the catalyst composition is from about 20 to about 250 microns.

28. The catalyst composition of claim 18, wherein the particle size of the catalyst composition is from about 20 to about 150 microns.

29. A material composition, comprising:

a plurality of spent catalyst particles supporting carbon products catalytically formed, wherein at least 70% of the carbon products supported by the spent catalyst particles are multi-walled carbon nanotubes, and wherein at least 60% of the multi-walled carbon nanotubes have between about 3 and about 8 walls.

30. The composition of matter of claim 29, wherein at least 98% of the carbon product is multi-walled carbon nanotubes.

31. The composition of matter of claim 29, wherein at least 60% of said multi-walled carbon nanotubes have between 3 and 6 walls.

32. The composition of matter of claim 29, wherein at least 75% of said multi-walled carbon nanotubes have between about 3 and about 8 walls.

33. The composition of matter of claim 29, wherein at least 75% of said multi-walled carbon nanotubes have between 3 and 6 walls.

34. The composition of matter of claim 29, wherein at least 85% of said multi-walled carbon nanotubes have between about 3 and about 8 walls.

35. The composition of matter of claim 29, wherein at least 85% of said multi-walled carbon nanotubes have between 3 and 6 walls.

36. The composition of matter of claim 29, wherein at least 90% of said multi-walled carbon nanotubes have between about 3 and about 8 walls.

37. The composition of matter of claim 29, wherein at least 90% of said multi-walled carbon nanotubes have between 3 and 6 walls.

38. The composition of matter of claim 29, wherein at least 60% of said multi-walled carbon nanotubes have an outer diameter of less than about 7 nm.

39. The composition of matter of claim 29, wherein at least 75% of said multi-walled carbon nanotubes have an outer diameter of about 4nm to about 7 nm.

40. The composition of matter of claim 29, wherein at least 85% of said multi-walled carbon nanotubes have an outer diameter of about 4nm to about 7 nm.

41. The composition of matter of claim 29, wherein at least 90% of said multi-walled carbon nanotubes have an outer diameter of about 4nm to about 7 nm.

42. A method of preparing a catalyst precursor composition comprising:

preparing a solution comprising two or more metal compounds, wherein the metal portion of the compounds is selected from the group consisting of: cobalt, iron, molybdenum, magnesium, and mixtures thereof;

reacting a solution of a metal compound with aluminum hydroxide to obtain a product comprising reaction particles;

drying the particles;

calcining the particles under a flowing gas; and

reducing the size of the particles.

43. The method of claim 42, wherein the cobalt-containing compound is selected from the group consisting of: cobalt acetate and cobalt nitrate; the iron-containing compound is selected from the group consisting of: iron acetate and nitrate; the molybdenum-containing compound is selected from the group consisting of: ammonium heptamolybdate and ammonium dimolybdate; and the magnesium-containing compound is magnesium nitrate.

44. The method of claim 42, wherein the solution comprises cobalt acetate, iron nitrate, ammonium heptamolybdate, and magnesium nitrate.

45. The method of claim 42, wherein the reaction between the metal compound solution and the aluminum hydroxide is conducted at room temperature for a period of about 2 to 4 hours.

46. The method of claim 42, wherein the product of the reaction particles has a paste-like consistency.

47. The method of claim 42, wherein the water content of the product comprising reactive particles is about 20-40% by weight prior to drying.

48. The method of claim 42, wherein the water content of the product comprising reactive particles is about 25-30% by weight prior to drying.

49. The method of claim 42, further comprising the step of manipulating the reactive particles by kneading the particles for a time of from about 20 minutes to about 50 minutes.

50. The method of claim 42, wherein the drying step is performed at a temperature of about 30 ℃ to 50 ℃.

51. The method of claim 42, wherein the drying step produces a moisture content of about 10-20% by weight water.

52. The method of claim 42, wherein the drying step produces a moisture content of less than 15% by weight water.

53. The method of claim 42, wherein the calcining step is conducted at a temperature of from about 400 ℃ to 600 ℃ for a time of from about 3 hours to about 5 hours.

54. The method of claim 42, wherein the calcining step is conducted at a temperature of from about 400 ℃ to about 500 ℃ for a time of from about 3.5 hours to about 4.5 hours.

55. The method of claim 42, wherein the calcining step is conducted at a temperature of from about 440 ℃ to about 460 ℃ for a time of from about 3.5 hours to about 4.5 hours.

56. The method of claim 42, wherein the step of reducing the particle size produces particles of about 20 μm to about 500 μm.

57. The method of claim 42, wherein the step of reducing the particle size produces particles of about 20 μm to about 250 μm.

58. The method of claim 42, wherein the step of reducing the particle size produces particles of about 20 μm to about 150 μm.

59. A method of preparing a catalyst precursor composition comprising:

preparing a solution comprising two or more metal compounds, wherein the metal portion of the compounds is selected from the group consisting of: cobalt, iron, molybdenum, and mixtures thereof;

preparing a mixture of aluminum hydroxide and magnesium hydroxide;

reacting the mixture of aluminum hydroxide and magnesium hydroxide with a solution of a metal compound to obtain a product comprising reaction particles;

drying the particles;

calcining the particles under a flowing gas; and

reducing the size of the particles.

60. The method of claim 59, wherein the calcining step is conducted at a temperature of from about 400 ℃ to about 500 ℃ for a time of from about 3 hours to about 5 hours.

61. The method of claim 59, wherein the calcining step is conducted at a temperature of from about 425 ℃ to about 475 ℃ for a time of from about 3.5 hours to about 4.5 hours.

62. The method of claim 59, wherein the calcining step is conducted at a temperature of from about 440 ℃ to about 460 ℃ for a time of from about 3.5 hours to 4.5 hours.

63. A method of making multi-walled carbon nanotubes, comprising:

placing catalyst precursor particles having a particle size of from about 20 microns to about 500 microns in a reactor chamber, the catalyst precursor composition comprising:

a carrier; and

a phase of mixed metal oxide on the surface of the support, wherein the metal of the mixed metal oxide is selected from the group consisting of: cobalt, molybdenum and iron;

flowing a stream of a non-reactive gas through the reaction chamber at a flow rate sufficient to fluidize the catalyst precursor particles, thereby forming a fluidized bed;

heating the fluidized bed to a temperature of about 600 ℃ to about 750 ℃;

flowing a reactive gas mixture through a reaction chamber while maintaining the fluidized bed at a temperature of about 600 ℃ to about 750 ℃, wherein the flow of the reactive gas reduces the metal oxide of the catalytic precursor composition to yield a composition comprising catalyst particles; and the number of the first and second groups,

the reactive gas mixture continues to flow through the reaction chamber, thereby producing multi-walled carbon nanotubes on the catalyst particles.

64. The method of claim 63, wherein about 60 to about 95% of the resulting multi-walled carbon nanotubes have 3 to 7 walls.

65. A process as claimed in claim 63, wherein the fluidised bed temperature is maintained below 650 ℃ during the passage of the gas through the bed.

66. The method of claim 63, wherein the reactive gas mixture comprises nitrogen and ethylene.

67. The method of claim 66, wherein the reactive gas mixture contains about 10 to 50 volume percent ethylene.

68. The method of claim 66, wherein the reactive gas mixture contains about 20 to 30 volume percent ethylene.

69. The method of claim 63, wherein the gas is passed through the fluidized bed at a flow rate of from about 70L/min per kg catalyst precursor to about 150L/min per kg catalyst precursor.

70. The method of claim 63, wherein the gas is passed through the fluidized bed at a flow rate of from about 90L/min per kg catalyst precursor to about 120L/min per kg catalyst precursor.

71. The method of claim 63, wherein the gas is passed through the fluidized bed at a flow rate of about 100L/min per kg catalyst precursor.

72. The method of claim 63, wherein the reactive gas mixture is flowed through the reaction chamber for a time of about 15 to about 30 minutes after the metal oxide is reduced.

73. The method of claim 63, wherein the catalyst particles are spent catalyst particles supporting the multi-walled carbon nanotubes after the catalytic reaction, and the method further comprises the step of removing the spent catalyst particles supporting the multi-walled carbon nanotubes.

74. A process as set forth in claim 63 wherein the cobalt is from about 0.5 to about 2.0% by weight of the total metal concentration of the catalyst precursor composition, the molybdenum is from about 0.3 to about 2.0% by weight of the total metal concentration of the catalyst precursor composition, and the iron is from about 0 to about 3.0% by weight of the total metal concentration of the catalyst precursor composition.

75. The method of claim 63, wherein the support comprises alumina and magnesium aluminate.

76. A batch of carbon nanotubes, comprising:

multi-walled carbon nanotubes, wherein the multi-walled carbon nanotubes comprise from about 60 to about 100 wt% of the batch, and wherein at least 60% of the multi-walled carbon nanotubes have from about 3 to about 7 walls.

77. The batch of carbon nanotubes of claim 76, wherein at least 75% of the multi-wall carbon nanotubes have between about 3 and about 7 walls.

78. The batch of carbon nanotubes of claim 76, wherein at least 85% of the multi-wall carbon nanotubes have between about 3 and about 7 walls.

79. The batch of carbon nanotubes of claim 76, wherein at least 90% of the multi-wall carbon nanotubes have between about 3 and about 7 walls.

80. The batch of carbon nanotubes of claim 76, wherein at least 60% of the multi-wall carbon nanotubes have an outer diameter of from about 4nm to about 7 nm.

81. The batch of carbon nanotubes of claim 76, wherein at least 75% of the multi-wall carbon nanotubes have an outer diameter of from about 4nm to about 7 nm.

82. The batch of carbon nanotubes of claim 76, wherein at least 85% of the multi-wall carbon nanotubes have an outer diameter of from about 4nm to about 7 nm.

83. The batch of carbon nanotubes of claim 76, wherein at least 90% of the multi-wall carbon nanotubes have an outer diameter of from about 4nm to about 7 nm.

84. The batch of carbon nanotubes of any of claims 76 to 83, wherein said multi-walled carbon nanotubes comprise from about 80 to about 98 weight percent of said batch.

85. A composition comprising multi-walled carbon nanotubes, wherein about 60 to about 90 weight percent of the multi-walled carbon nanotubes have 3 to 7 walls.

86. The composition of matter of claim 85, wherein at least 75% of said multi-walled carbon nanotubes have between about 3 and about 7 walls.

87. The composition of matter of claim 85, wherein at least 85% of said multi-walled carbon nanotubes have between about 3 and about 7 walls.

88. The composition of matter of claim 85, wherein at least 90% of said multi-walled carbon nanotubes have between about 3 and about 7 walls.

89. The composition of matter of claim 85, wherein at least 60% of said multi-walled carbon nanotubes have an outer diameter of between about 4nm and about 7 nm.

90. The composition of matter of claim 85, wherein at least 75% of said multi-walled carbon nanotubes have an outer diameter of between about 4nm and about 7 nm.

91. The composition of matter of claim 85, wherein at least 85% of said multi-walled carbon nanotubes have an outer diameter of between about 4nm and about 7 nm.

92. The composition of matter of claim 85, wherein at least 90% of said multi-walled carbon nanotubes have an outer diameter of between about 4nm and about 7 nm.

93. A batch of carbon nanotubes, comprising:

wherein about 60 to about 100 weight percent of the batch of carbon nanotubes are multi-walled carbon nanotubes, and wherein 50 to about 90 percent of the multi-walled carbon nanotubes have an outer diameter of less than 10 nm.

94. The batch of carbon nanotubes of claim 93, wherein 54-85% of the multi-wall carbon nanotubes have an outer diameter of less than 10 nm.

95. The batch of carbon nanotubes of claim 93, wherein 60 to 75% of the multi-wall carbon nanotubes have an outer diameter of less than 10 nm.

96. The batch of carbon nanotubes of claim 93, wherein said multi-walled carbon nanotubes have a median outer diameter of from about 6.5nm to about 8.5 nm.

97. The batch of carbon nanotubes of claim 93, wherein said multi-walled carbon nanotubes have a median outer diameter of from about 7nm to about 8 nm.

98. The batch of carbon nanotubes of claim 93, wherein said multi-wall carbon nanotubes have a mode outer diameter of from about 4nm to about 7 nm.

99. The batch of carbon nanotubes of claim 93, wherein said multi-wall carbon nanotubes have a mode outer diameter of from about 4.5nm to about 6.7 nm.

100. The batch of carbon nanotubes of claim 93, wherein said multi-wall carbon nanotubes have a mode outer diameter of from about 5.1nm to about 6.2 nm.

101. The batch of carbon nanotubes of any of claims 93-100, wherein said multi-walled carbon nanotubes comprise at least 90% by weight of said batch.

102. The batch of carbon nanotubes of any of claims 93-100, wherein said multi-walled carbon nanotubes comprise at least 98 wt.% of said batch.

103. A composition comprising multi-walled carbon nanotubes, wherein 50-90% of the multi-walled carbon nanotubes have an outer diameter of less than 10 nm.

104. The composition of claim 103, wherein 54-85% of the multi-walled carbon nanotubes have an outer diameter of less than 10 nm.

105. The composition of claim 103, wherein 60-75% of the multi-walled carbon nanotubes have an outer diameter of less than 10 nm.

106. The composition of claim 103, wherein said multi-walled carbon nanotubes have a median outer diameter of from about 6.5nm to about 8.5 nm.

107. The composition of claim 103, wherein said multi-walled carbon nanotubes have a median outer diameter of from about 6.5nm to about 8.5 nm.

108. The composition of claim 103, wherein said multi-walled carbon nanotubes have a mode outer diameter of from about 4nm to about 7 nm.

109. The composition of claim 103, wherein said multi-walled carbon nanotubes have a mode outer diameter of from about 5.1nm to about 6.2 nm.