US20050025695A1

US20050025695A1 - Catalyst and process to produce nanocarbon materials in high yield and at high selectivity at reduced reaction temperatures

Info

Publication number: US20050025695A1
Application number: US10/628,842
Authority: US
Inventors: Bhabendra Pradhan
Original assignee: Individual
Current assignee: Columbian Chemicals Co
Priority date: 2003-07-28
Filing date: 2003-07-28
Publication date: 2005-02-03
Also published as: EP1654406A2; AR044387A1; BRPI0413069A; WO2005016853A3; TW200505788A; EP1654406A4; JP2007500121A; CN1833055A; KR20060052923A; WO2005016853A2

Abstract

A carbon nanofiber system is synthesized with very high purity (above 95%), selectivity of the carbon morphology, and exceptionally high yield. A custom made catalyst with a particle size of ≦10 nm and a high surface area (>50 m²/g), provides a higher morphological selectivity and higher yield. The reactivity of these catalyst particles is maintained even after 24 hours reaction such that yield exceeds 200 g carbon per gram of catalyst. The catalysts which are key to the products and yields achieved are prepared to specific parameters (size distribution, composition and crystallinity) specified and via a flame synthesis process as taught in U.S. Pat. No. 6,132,653.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

None

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable

REFERENCE TO A “MICROFICHE APPENDIX”

Not applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to the production of Nanocarbon materials. More particularly, the present invention relates to an improved catalyst and process to produce Nanocarbon materials in high yield and high selectivity and at reduced reaction temperatures.
2. General Background of the Invention
Nano-structured materials, more particular carbon nano structure materials, are gaining importance for various commercial applications. Such applications include their use to store molecular hydrogen, to serve as catalyst supports, as reinforcing components of polymeric composites, for use in electromagnetic shielding and for use in various types of batteries and other energy storage devices. Carbon nano-structure materials are generally prepared from the decomposition of carbon containing gases over selected catalytic metal surfaces at temperatures ranging from about 500° C. to about 1200° C.
For example, carbon nanofibers can be used in lithium ion batteries, wherein the anode would be comprised of graphitic nanofibers. The graphite sheets are substantially perpendicular or parallel to the longitudinal axis of the carbon nanofiber. Example of such a use can be found in U.S. Pat. No. 6,503,660 which is contained in the information disclosure statement submitted herewith. Furthermore U.S. Pat. No. 5,879,836 teaches the use of fibrils as a material for the lithium ion battery anode. Fibrils are described as being composed of parallel layers of carbon in the form of a series of concentric tubes disposed about a longitudinal axis rather than as multi-layers of flat graphite sheets.
Furthermore in U.S. Pat. No. 6,485,858 the graphite nanofibers possess structures in which the graphite sheets are aligned in the direction either substantially perpendicular or substantially parallel to the fiber axis and designated as platelet and ribbon respectively. In addition, the exposed surfaces of the nanofibers are comprised of at least 95% edge regions in contrast to conventional graphites that are comprised almost entirely of basal plane regions and very little edge sites.
Other references include “Catalytic Growth of Carbon Filaments,” which is an article from the Chemical Engineering Department of Auburn University dated 1989, wherein it discusses the formation of filamentous carbon. Another source of information is an article entitled “A Review of Catalytic Grown Carbon Nanofibers,” published by the Material Research Society, in 1993. In that article, carbon nanofibers are discussed as being produced in a relatively large scale through a catalytic decomposition of certain hydrocarbons on small metal particles.
In all cases, as was discussed above, synthesizing a pure carbon nanomaterial is challenging. Most of the applications of these materials require pure carbon nanomaterials systems. Therefore, it would be beneficial to provide a system of producing pure carbon nanomaterials where the carbon system can be synthesized with very high purity (greater than 95%), high crystallinity, selectivity of the carbon morphology, and exceptionally high yield. Furthermore, a custom made catalyst with a particular particle size and high surface area would give a higher selectivity and higher reactivity.

BRIEF SUMMARY OF THE INVENTION

In the present invention, a carbon nanofiber system is synthesized with very high purity (above 95%), high crystallinity, selectivity of the carbon morphology, and exceptionally high yield. A custom made catalyst with an average single crystal-particle size of <10 nm and a high surface area (>50 m²/g), provides a higher morphological selectivity and higher reactivity than heretofore attainable. The reactivity of these catalyst particles is maintained even after 24 hours reaction such that yield exceeds 200 g carbon per gram of catalyst. The catalysts which are key to the products and yield achieved are prepared to specific parameters (size distribution, composition and crystallinity) specified and via a flame synthesis process as taught in U.S. Pat. No. 6,132,653. The disclosure of U.S. Pat. No. 6,132,653, is totally incorporated herein by reference thereto.
For purposes of this application the terms used herein will have the following definitions: “Purity” is defined as carbon content with the impurity understood to comprise the catalyst.
“Selectivity” is defined as fraction of the carbonaceous product possessing the intended morphology (orientation of graphene layers); and “yield” is defined as weight carbon produced divided by weight of catalysts; in such catalytic processes, this is also sometimes expressed as turnover.
Therefore, it is a principal object of the present invention to synthesize a pure carbon nanomaterial with extremely high purity, high selectivity, of the carbon morphology and exceptionally high yield.
It is a further object of the present invention to synthesize a pure carbon nanomaterial in the presence of a custom made catalyst having a particular particle size, surface area, and chemical composition to provide the high morphological selectivity, yield, and purity.
It is a further object of the present invention to produce a carbon nanomaterial in the presence of a custom made catalyst so that over a given amount of time the yield exceeds 200 g carbon/g of catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the nature, objects, and advantages of the present invention, reference should be had to the following detailed description, read in conjunction with the following drawings, wherein like reference numerals denote like elements and wherein:
FIG. 1 is a graph of the Effect of Time on Growth of the carbon nanofiber in the presence of the Iron oxide catalyst over a 24 hour period;
FIG. 2 is a graph of the Effect of Time on Growth of the carbon nanofiber in the presence of an Iron:Nickel catalyst over a 24 hour period;
FIG. 3 illustrates the specific morphology of the carbon microstructure of the carbon nanofiber produced in the presence of the Iron oxide catalyst as described in relation to FIG. 1;
FIG. 4 is a high resolution view of the specific morphology of the carbon microstructure of the carbon nanofiber produced in the presence of the Iron oxide catalyst as described in relation to FIG. 1.
FIG. 5 illustrates the specific morphology of the carbon microstructure of the carbon nanofiber produced in the presence of the Iron:Nickel catalyst as described in relation to FIG. 2;
FIG. 6 is a high resolution view of the specific morphology of the carbon microstructure of the carbon nanofiber produced in the presence of the Iron:Nickel catalyst as described in relation to FIG. 2;
FIG. 7 is a graph of the production of nanocarbon fibers having platelet morphology prepared with Iron oxide catalyst compared with a conventional catalyst; and
FIG. 8 is a graph of the production of nanocarbon fibers having tubular morphology prepared with Iron:Nickel catalyst compared with a conventional catalyst.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS PROCESS FOR PRODUCING THE CATALYSTS

The production of the catalyst utilized in the production of the nanofibers disclosed herein is similar to that disclosed in U.S. Pat. No. 6,132,653, referenced and incorporated earlier herein.
List of metals that can be used as part of the catalyst are as follows:

Fe, Ni, Co, Mo, Cu, La, Ag, Au and alloys.

The Nanocarbon Materials Produced with the Catalysts

Reference is now made to the table and information below which discusses the properties of the material as produced with the new catalyst as described above (flame synthesized) and a conventional catalyst (co-precipitated)

TABLE 2


	New Catalyst	Conventional or
	(flame	Commercial Catalyst
Properties	synthesized)	(co-precipitation)

Chemical form	Metal Oxide	Pre-reduced Metal with
		thin cover of oxide
Size (nm)	˜10	500-2000
Morphology	Single Crystal	Polycrystalline
Surface area	˜130	<20
(m²/g)
Packing density	Lower than bulk	Same as bulk

Experimental Detail to Achieve Results Above:

a. Conventional or Commercial Catalyst:
A known amount of pre-reduced catalyst (0.1 g) was placed in a ceramic boat or a quartz cylinder. The boat was then transferred into a quartz reactor (ø=47 mm). The reactor was flushed for 30 min with nitrogen gas with a flow rate of 200 sccm. The reactor was heated up to 450° C. with a heating rate of 5° C./min under 10-20% H₂(balanced with N₂). This was held for 1 h at this temperature. The temperature was then increased to reaction temperature 600° C. for iron or 650° C. for iron-nickel catalyst in 30 min under N₂flow. Once the set temperature was stabilized, the reaction gas (CO/H₂or C₂H₄/H₂) was introduced into the reactor for different periods of time (1, 2, 4, 6, 8 and 24 h).
b. New Catalyst:
A known amount of oxide catalyst (0.1 g) was placed in ceramic boat or a quartz cylinder. The boat was then transferred into the quartz reactor (ø=47 mm). The reactor was flushed for 30 min with nitrogen gas with a flow rate of 200 sccm. The reactor was heated up to 450° C. with a heating rate of 5° C./min under 10-20% H₂(balanced with N₂). This was held for 1 h at this temperature than the temperature was increased to reaction temperature 550° C. for iron oxide and iron-nickel oxide catalyst in 30 min under N₂flow. Once the set temperature was stabilized, the reaction gas (CO/H2 or C₂H₄/H₂) was introduced into the reactor for different periods of time (1, 2, 4, 6, 8 and 24 h).
The Iron oxide catalyst utilized with CO:H₂::4::1 at 550° C. produces a specific morphology of the carbon micro structure where the graphite planes are perpendicular to the carbon growth axis as seen in FIGS. 3 and 4. In comparison to the commercial catalyst, this trial shows a better carbon yield (2 to 3 time higher) and at 50° C. lower synthesis temperature (550° vs 600° C.). There is a greater than 99.6% purity of the carbon product which can be reached in the system. Morphological selectivity is 100%.
In the second example, an Iron:Nickel catalyst was used, with C₂H₂:H₂::1:4 at 550° C. to produce a specific morphology of the carbon micro structure, i.e., where the graphite planes are parallel and/or at an angle to the carbon growth axis, as seen in FIGS. 5 and 6. In comparison to other conventional or commercial catalyst, this trial shows a better carbon yield (2 to 3 times higher) and at 100° C. lower synthesis temperature (5500 vs 650° C.). A greater than 99.2% purity of the carbon product can be reached in this system. Morphological selectivity is >95%. In the two examples used above, the catalyst can be a metal oxide catalyst selected from the metals including iron, nickel, cobalt, lanthanum, gold, silver, molybdenum, iron-nickel, iron-copper and their alloys.
c. Fluid Bed Process Option:
A known amount of oxide catalyst (0.1-1.2 g) was placed in a ebullated fluid-bed reactor with Al₂O₃(14.9-13.8 g) The reactor was flushed for 30 min with nitrogen gas with a flow rate of 1000 sccm. The reactor was heated up to 450° C. with a heating rate of 5° C./min under 10-20% H₂(balanced with N₂). This was held for 1 h at this temperature then the temperature was increased to a reaction temperature 550° C. for iron-nickel oxide catalyst in 30 min under N₂flow. Once the set temperature was stabilized, the reaction gas (C₂H₄/H₂) was introduced into the reactor for a known period of time (2 h). The yield can reach to 140 g carbon/g catalyst.
Reference is now made to FIG. 1 which shows the graph of the effect of time on growth of carbon nanofibers utilizing an iron oxide catalyst with CO:H₂::4:1 at 550° C. In this graph, the carbon nanofibers produced comprise the carbon platelet morphology as seen in FIGS. 3 and 4. With reference to FIG. 1: As the process continues over some 24 hour period, the metal content as a percentage weight of the product decreases to 0.3% and the yield of carbon per gram of catalyst was >300 g/g. It also shows that the catalytic particle was still active even after the 24 hours reaction time. In this particular example, the iron oxide catalyst, with CO:H₂::4:1 at 550° C. produced a specific morphology of the carbon micro structure, i.e., where the graphite planes are perpendicular to the carbon growth axis, again as depicted in FIGS. 3 and 4. Furthermore, in comparison to the commercial catalyst, as stated earlier this trial shows a better carbon yield (2-3 times higher) and at 50° C. lower synthesis temperature. This provides a 99.7 pure carbon product and with a morphological selectivity of 100%. As seen in FIGS. 3 and 4, the specific morphology of the carbon microstructure shows the graphite planes perpendicular to the carbon growth axis.
Turning now to FIG. 2, the graph depicts utilizing the iron-nickel catalyst with C₂H₂:H₂::1:4 at 550° C. The carbon nanofibers which were produced as shown in this graph resulted in a specific morphology of the carbon micro structure, i.e., where the graphite planes are parallel or at an angle to the growth axis as seen in FIGS. 5 and 6. In comparison to the conventional catalyst, this shows a better carbon yield and at a 100° C. lower synthesis temperature. Again there is a 99.6% purity of the carbon product and morphological selectivity is >95%. At the end of a 24 hour reaction period, the metal content of the product was 0.4% while the yield of carbon was between 200 and 250 g/g catalyst.
In both of these systems, as shown in FIGS. 1 and 2, there can be reached a 99% carbon in an 8 hour reaction time. These results are shown in the following tables.
In each of these tables and as depicted in FIGS. 7 and 8 respectively, both the Iron catalyst and the Iron:Nickel catalyst respectively produced a carbon nanomaterial platelet or tubular morphology at lower temperature, >95% morphological selectivity, higher yield and lower impurity of metal than the commercial or conventional catalysts.
For Platelet Morphology, Catalyst Iron, CO:H₂::4:1.

Temperature Selectivity Yield Impurity

Catalyst (° C.) (visual) (g/6 h) (metal)

Flame 550 100 77 1.3

Commercial 600 90 50 2

(J. T. Baker)
For Tubular Morphology, Catalyst Iron:Nickel::8:2, C₂H₄:H₂::1:4

Temperature Selectivity Yield Impurity

Catalyst (° C.) (visual) (g/6 h) (metal)

Flame 550 >95 81 1.25

CCC 650 60 26.33 3.8

Produced

Conventional

The “CCC Produced Conventional” catalyst was prepared utilizing a liquid precipitation process. Iron, nickel, and copper metal nitrates were utilized. The metal nitrates were stoichimetrically mixed in H₂O and rapidly stirred at room temperature. Ammonium bicarbonate is added to a pH ˜9, and stirred ˜5 minutes. A precipitate forms overnight; the precipitate is washed and dried. Metal carbonate is dried at 110° C. for 24 hrs. and then calcinated in air for 4 hrs. at 400° C. Metal oxides are ball milled for 6 hrs. and reduced in 10% H2 in N2 at 500° C. for 20 hrs. in 200 sccm flow. Metal powder is passivated in 2% O₂in N2 at room temperature for 1 hour. This technique and the reaction taking place, as shown below, are referenced in R. J. Best and W. W. Russel, J. Am. Chem. Soc. 76, 8383 (1954). $M ({NO}_{3}) \times \frac{{NH}_{4} {HCO}_{3}}{H_{2} O} > M ({CO}_{3}) \times \frac{air}{400^{°} C .} > M_{2} O \times \frac{10 % H_{2}}{500^{°} C .} > M$
Powder Catalyst Synthesis by Flame/Plasma Process:
A mixture of nitrate/sulfate salt of metal (Fe, Ni and Cu) ethanolic solution were prepared and vaporized/atomized into either flame or plasma torch and powder of pure oxide or mixed metal oxide were obtained by this process. U.S. Pat. No. 6,123,653 (Oct. 17, 2000).
In general, the process for producing nanocarbon materials, is undertaken by providing a catalyst with an average particle size of ≦10 nm and a surface area greater than 50 m2/g, although this may vary. Next, carbonaceous reactants are reacted in the presence of the catalyst over a given period of time to produce carbon nanofibers with over 99% purity and a morphological selectivity approaching 100% with higher reactivity.
The catalyst, produced by the method described in U.S. Pat. No. 6,123,653, incorporated herein by reference, is a metal oxide catalyst selected from the metals including iron, nickel, cobalt, lanthanum, gold, silver, molybdenum, iron-nickel, iron-copper and their alloys. There may be other suitable metal oxides which may be found as experimentation continues. The catalyst, itself, is prepared to specific parameters (size distribution, composition and crystallinity) specified and via a flame synthesis process; and it possesses a single crystal morphology. By utilizing the catalyst from the group identified, the resulting yield of carbon nanomaterial is ≧140 g carbon per g catalyst, but it may be more, while the morphology of the carbon micro structure comprises graphite planes of controllable orientation (depending on catalyst composition and carbonaceous feedstock) perpendicular or parallel to the carbon growth axis resulting in the 99.6% purity of the carbon product.
The foregoing embodiments are presented by way of example only; the scope of the present invention is to be limited only by the following claims.

Claims

1. A process for producing nanocarbon materials, comprising the following steps:

a. providing a catalyst with a particle size of ≦10 nm and a surface area greater than 50 m2/g;

b. reacting carbonaceous feedstocks in the presence of the catalyst over a given period of time to produce carbon nanofibers with over 99% purity and a morphological selectivity approaching 100% in yields ≧140 g carbon/g catalyst with higher reactivity.

2. The process in claim 1, wherein the catalyst is a metal oxide catalyst selected from the metals including iron, nickel, cobalt, lanthanum, gold, silver, molybdenum, iron-nickel, iron-copper and their alloys.

3. The process in claim 1, wherein the catalyst is prepared to specific parameters (size distribution, composition and crystallinity) specified and via a flame synthesis process.

4. The catalyst in claim 1, wherein the catalyst possesses a single crystal morphology.

5. The process in claim 1, wherein the yield of carbon nanomaterial resulted in ≧140 g carbon per g/catalyst.

6. The process in claim 1, wherein the morphology of the carbon micro structure can be selectively controlled to achieve various desired orientations in selectivities of ≧90%.

7. A process for producing nanocarbon materials, comprising the following steps:

a. providing a metal oxide catalyst with a particle size of about ≦10 nm and a surface area greater than 50 m2/g;

b. reacting carbonaceous feedstocks in the presence of the catalyst over a given period of time to produce carbon nanofibers with over 99% purity and a morphological selectivity approaching 100% with yield ≧140 g carbon/g catalyst.

8. The process in claim 7, wherein the reaction took place at a temperature not exceeding 550 C.

9. The process in claim 7, wherein the purity of carbon nanofibers was >99% after 8 hours reaction time.

10. The process in claim 7, wherein the metal oxide catalyst is selected from a group of metals including iron, nickel, cobalt, lanthanum, gold, silver, molybdenum, iron-nickel, iron-copper and their alloys.

11. Carbon nanofibers of high purity and high reactivity, produced by the steps of:

a. providing a metal oxide catalyst with a particle size of ≦10 nm and a surface area greater than 50 m2/g;

b. reacting carbonaceous feedstocks in the presence of the catalyst over a given period of time to produce the carbon nanofibers with over 99% purity and a selectivity approaching 100% with higher reactivity.

12. The carbon nanofibers produced by the process in claim 11, wherein the metal oxide catalyst is selected from a group of metals including iron, nickel, cobalt, lanthanum, gold, silver, molybdenum, iron-nickel, iron-copper and their alloys.

13. The carbon nanofibers produced by the process in claim 11, wherein the purity of carbon nanofibers was ≧99% in after 8 hours reaction time.

14. A carbon nanofiber, of the type produced in the presence of an metal oxide catalyst, the carbon nanofiber comprising at least 99% pure carbon, and produced at high yield, and >90% morphological selectivity.

15. The carbon nanofiber in claim 14, wherein the metal oxide catalyst is selected from a group of metals including iron, nickel, cobalt, lanthanum, gold, silver, molybdenum, iron-nickel, iron-copper and their alloys.

16. A carbon nanofiber composition exhibiting 90% Selectivity to a single morphology as produced.

17. The composition in claim 16, wherein the morphology comprises graphene layers oriented parallel to the fiber axis.

18. The composition in claim 16, wherein the morphology comprises graphene layers oriented perpendicular to the fiber axis.

19. The composition of claim 16, wherein the morphology comprises graphene layers oriented at a specific and equal (±10°) angle to the fiber axis.