Molecular sieve abstract
The present invention provides a carbon molecular sieve prepared
by forming carbon nanorods or carbon nanotubes with a uniform diameter
inside pores of siliceous mesoporous molecular sieve and a process
for preparing the same. The process for preparing a carbon molecular
sieve of the present invention comprises the steps of; adsorbing
a mixture of an aqueous carbohydrate solution and an acid or a precursor
of carbon polymer into pores of mesoporous silica molecular sieve
template, and polymerizing; heating the mesoporous molecular sieve
including polymeric material at 400 to 1400.degree. C. under vacuum
condition or without oxygen to accomplish thermal decomposition
of the polymeric material included in the pores; and, reacting the
heated mesoporous molecular sieve with hydrofluoric acid or aqueous
sodium hydroxide solution and removing the template to obtain a
carbon molecular sieve. The carbon molecular sieve of the invention
is superior in terms of the hydrogen adsorption effect and the activity
for oxygen reduction, which makes possible its universal application
for the development of adsorbents for organic materials, sensors,
electrodes, and materials for fuel cells and hydrogen storage.
Molecular sieve claims
What is claimed is:
1. A process for preparing a carbon molecular sieve, comprising:
providing a template having an internal structure defining pores;
contacting a composition with the template so as for the template
to absorb and retain the composition in the pores thereof, wherein
the composition comprises a polymerizable compound comprising carbons;
polymerizing the polymerizable compound while being retained in
the pores of the template, thereby forming a polymeric material
having carbons retained in the pores of the template; subjecting
the template and the polymeric material retained therein to heating
sufficient to thermally decompose the polymeric material and to
substantially remove non-carbon elements therefrom; and removing
the template.
2. The process of claim 1 wherein the removal of the template
comprises contacting the template with an acid or base.
3. The process of claim 2 wherein the acid comprises hydrofluoric
acid, and the base comprises a sodium hydroxide.
4. The process of claim 2 wherein the acid or base for removal
of the template is in an aqueous or alcoholic solution.
5. The process of claim 1 wherein the template comprises a molecular
sieve.
6. The process of claim 1 wherein the template comprises a mesoporous
silica molecular sieve.
7. The process of claim 1 wherein the mesoporous silica molecular
sieve comprises aluminum.
8. The process of claim 1 wherein the pores of the template comprises
one-dimensional pores interconnected one another.
9. The process of claim 8 wherein the size of the one-dimensional
pores is from about 1 nm to about 50 nm.
10. The process of claim 8 wherein the size of the one-dimensional
pores is from about 2 nm to about 20 mm.
11. The process of claim 1 wherein the template comprises SBA-15
Aluminum SBA-15 SBA-3 or Aluminum SBA-3.
12. The process of claim 1 wherein the polymerizable compound
comprises a carbohydrate.
13. The process of claim 12 wherein the carbohydrate is selected
from the group consisting of sucrose, xylose and glucose.
14. The process of claim 12 wherein the composition further comprises
an acid.
15. The process of claim 14 wherein the acid is selected from
the group consisting of sulfuric acid, hydrochloric acid, nitric
acid, sulfonic acid and methylsulfonic acid.
16. The process of claim 1 wherein the polymerizable compound
comprises a non-carbohydrate precursor of a polymer.
17. The process of claim 16 wherein the non-carbohydrate precursor
is selected from the group consisting of furfuryl alcohol, aniline,
acetylene and propylene.
18. The process of claim 1 wherein the heating for the thermal
decomposition of the polymeric material is performed under vacuum
or without oxygen.
19. The process of claim 1 wherein the heating is to heat the
polymeric material at a temperature of from about 400.degree. C.
to about 1400.degree. C.
20. A carbon molecular sieve produced by the process of claim 1.
21. A carbon molecular sieve comprising an internal structure of
carbon atoms, which defines at least partly substantially uniform
pores, wherein the pores have a diameter of from about 1 nm to about
50 nm.
22. The carbon molecular sieve of claim 21 wherein the pore size
is from about 2 nm to about 20 nm.
23. The carbon molecular sieve material of claim 21 wherein the
volume of the pores is from about 1.0 cm.sup.3/g to about 3.0 cm.sup.3/g.
24. The carbon molecular sieve of claim 21 wherein a Brunauer-Emmett-Teller
(BET) specific surface area is from about 1000 m.sup.3/g to about
3000 m.sup.3/g.
25. The carbon molecular sieve of claim 21 where the carbon atoms
form nano-lines which form a substantially uniform hexagonal structure,
and wherein the pores have substantially a single uniform diameter.
26. The carbon molecular sieve of claim 21 where the carbon atoms
form nano-tubes which form a substantially uniform hexagonal structure,
and wherein the pores have substantially two uniform diameters.
27. A method of storing hydrogen, comprising: providing a composition
comprising the carbon molecular sieve of claim 21; and contacting
hydrogen with the composition so that the carbon molecular sieve
in the composition can absorb and retain the hydrogen in the internal
structure thereof.
Molecular sieve description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a carbon molecular sieve
and a process for preparing the same, more specifically, to a carbon
molecular sieve prepared by forming carbon nanorods or carbon nanotubes
with a uniform diameter inside pores of siliceous mesoporous molecular
sieve and a process for preparing the same.
[0003] 2. Description of the Related Art
[0004] In general, molecular sieves are known as a class of materials
in which pores with a uniform size form a well-ordered structure,
e.g., zeolite. The molecular sieves, due to their uniform pore size,
show a high selectivity on the molecules with specific molecular
sizes, which makes their practical applications such as catalysts,
catalyst substrates, or adsorbents. Many studies have been actively
performed on the carbon molecular sieves possessing several advantages
of high thermal stability, hydrothermal stability, chemical resistance,
and hydrophobicity, over the conventional metal oxide molecular
sieves such as zeolite. The carbon molecular sieves, though they
have pores with a relatively uniform size when compared to carbon
black, are proved less satisfactory in the senses that their pore
sizes less than 0.5 nm and irregular arrangement of the pores have
limited their applications only to the adsorption or separation
of small molecules.
[0005] Recently, it has been reported that a carbon molecular sieve
with a uniform pore size and structural regularity can be prepared
by using mesoporous silica molecular sieve template MCM-48. Academic
society has paid attention to the carbon molecular sieve with structural
regularity described above as a promising carbon molecular sieve
with a uniform pore size and structural regularity. The carbon molecular
sieves have been prepared by using mesoporous molecular sieve MCM-48
and a newly developed catalyst carbonization process. Continued
studies have revealed that several carbon molecular sieves with
structural diversity can be prepared by using mesoporous molecular
sieves such as SBA-1 SBA-15 KIT-1 and MSU-1 as templates, and
focused on the application of these materials to catalyst supports,
adsorbents for organic materials, sensors, electrode materials,
and materials for hydrogen storage. Especially, it is expected to
have tremendous effect on the hydrogen battery and related areas
if hydrogen can be stored with a high efficiency. However, the carbon
molecular sieve that can efficiently store hydrogen has not been
yet reported in the art.
[0006] Therefore, there are strong reasons for developing and exploring
a novel carbon molecular sieve that can store hydrogen in an efficient
manner.
SUMMARY OF THE INVENTION
[0007] The present inventors have made an effort to develop a carbon
molecular sieve that can efficiently store hydrogen, observed that
if the pores of the carbon molecular sieve are of one-dimensional
structure or have a bundle structure of carbon nanotubes connected
to one another, the materials can be applied for hydrogen storage,
and discovered that a carbon molecular sieve in which carbon nanorods
or carbon nanotubes with a uniform size are hexagonally arranged,
can be prepared by using mesoporous molecular sieve with one-dimensional
pore structure as a template and then forming carbon nanorods or
carbon nanotubes with a uniform diameter inside pores of the siliceous
mesoporous molecular sieve.
[0008] An aspect of the present invention provides a process for
preparing a carbon molecular sieve. The process comprises: providing
a template having an internal structure defining pores; contacting
a composition with the template so as for the template to absorb
and retain the composition in the pores thereof, wherein the composition
comprises a polymerizable compound comprising carbons; polymerizing
the polymerizable compound while being retained in the pores of
the template, thereby forming a polymeric material having carbons
retained in the pores of the template; subjecting the template and
the polymeric material retained therein to heating sufficient to
thermally decompose the polymeric material and to substantially
remove non-carbon elements therefrom; and removing the template.
[0009] In the process, the removal of the template comprises contacting
the template with an acid or base. The acid comprises hydrofluoric
acid, and the base comprises a sodium hydroxide. The acid or base
for removal of the template is in an aqueous or alcoholic solution.
The template comprises a molecular sieve. The template comprises
a mesoporous silica molecular sieve. The mesoporous silica molecular
sieve comprises aluminum. The pores of the template comprises one-dimensional
pores interconnected one another. The size of the one-dimensional
pores is from about 1 nm to about 50 nm. The size of the one-dimensional
pores is from about 2 nm to about 20 nm. The template comprises
SBA-15 Aluminum SBA-15 SBA-3 or Aluminum SBA-3. The polymerizable
compound comprises a carbohydrate. The carbohydrate is selected
from the group consisting of sucrose, xylose and glucose. The composition
further comprises an acid. The acid is selected from the group consisting
of sulfuric acid, hydrochloric acid, nitric acid, sulfonic acid
and methylsulfonic acid. The polymerizable compound comprises a
non-carbohydrate precursor of a polymer. The non-carbohydrate precursor
is selected from the group consisting of furfuryl alcohol, aniline,
acetylene and propylene. The heating for the thermal decomposition
of the polymeric material is performed under vacuum or without oxygen.
The heating is to heat the polymeric material at a temperature of
from about 400.degree. C. to about 1400.degree. C.
[0010] Another aspect of the present invention provides a carbon
molecular sieve produced by the above-described process.
[0011] A further aspect of the present invention provides a carbon
molecular sieve comprising an internal structure of carbon atoms,
which defines at least partly substantially uniform pores, wherein
the pores have a diameter of from about 1 nm to about 50 nm. The
pore size is from about 2 nm to about 20 nm. The volume of the pores
is from about 1.0 cm.sup.3/g to about 3.0 cm.sup.3/g. A Brunauer-Emmett-Teller
(BET) specific surface area is from about 1000 m.sup.3/g to about
3000 m.sup.3/g. The carbon atoms form nano-lines which form a substantially
uniform hexagonal structure, and wherein the pores have substantially
a single uniform diameter. The carbon atoms form nano-tubes which
form a substantially uniform hexagonal structure, and wherein the
pores have substantially two uniform diameters.
[0012] A still further aspect of the present invention provides
a method of storing hydrogen. The method comprises providing a composition
comprising the above-described carbon molecular sieve; and contacting
hydrogen with the composition so that the carbon molecular sieve
in the composition can absorb and retain the hydrogen in the internal
structure thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The above and the other objects and features of the present
invention will become apparent from the following descriptions given
in conjunction with the accompanying drawings.
[0014] FIG. 1 shows a transmission electron micrograph of CMK-3
structure.
[0015] FIG. 2 shows X-ray diffraction ("XRD") patterns
of SBA-15 and CMK-3.
[0016] FIG. 3 shows a graph showing nitrogen adsorption isotherm
of CMK-3 and the inserted picture shows pore size distribution
of CMK-3 obtained by Kruk-Jaroniec-Sayari method from the nitrogen
adsorption isotherm.
[0017] FIG. 4 shows XRD patterns of CMK-3 prepared by using various
mixed solutions.
[0018] FIG. 5a shows XRD patterns of hexagonal mesoporous silica
molecular sieves depending on the mixed ratios of surfactants.
[0019] FIG. 5b shows XRD patterns of CMK-3 prepared by using the
hexagonal mesoporous silica molecular sieve as a template.
[0020] FIG. 6 shows an XRD pattern of CMK-3 prepared by using acetylene.
[0021] FIG. 7 shows an electron micrograph of CMK-5 structure.
[0022] FIG. 8 shows XRD patterns of SBA-15 and CMK-5.
[0023] FIG. 9 shows a graph showing nitrogen adsorption isotherm
of CMK-5 and the inserted picture shows pore size distribution
of CMK-5 obtained by Kruk-Jaroniec-Sayari method from the nitrogen
adsorption isotherm.
[0024] FIG. 10 shows XRD patterns of CMK-5 prepared by using the
variable amount of furfuryl alcohol.
[0025] FIG. 11 shows a graph showing the activity change of platinum
catalyst for oxygen reduction depending on the content of platinum
supported on CMK-5 and carbon black.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0026] The process for preparing a carbon molecular sieve of the
present invention comprises the steps of; adsorbing a mixture of
an aqueous carbohydrate solution and an acid or a precursor of a
carbon polymer into pores of mesoporous silica molecular sieve template,
and then drying and polymerizing; heating the mesoporous molecular
sieve including polymeric material at 400 to 1400.degree. C. under
vacuum condition or without oxygen to accomplish thermal decomposition
of the polymeric material included in the pores; and, reacting the
heated mesoporous molecular sieve with hydrofluoric acid or aqueous
sodium hydroxide solution and removing the template to obtain a
carbon molecular sieve.
[0027] The process for preparing a carbon molecular sieve is illustrated
in more detail.
Step 1
Polymerization of Starting Material
[0028] A mixture of an aqueous carbohydrate solution and an acid
or a precursor of carbon polymer (carbon source of carbon polymer)
is adsorbed into pores of mesoporous silica molecular sieve template
and polymerized at the temperature of 60 to 100.degree. C.: Molecular
sieves with one-dimensional pores ranging 1 to 50 nm, preferably
2 to 20 nm which are inter-connected by micropores, preferably SBA-15
or SBA-3 may be used as the mesoporous silica molecular sieve template.
Water-soluble monosaccharides, disaccharides or polysaccharides
may be preferably used as the carbohydrates, more preferably, sucrose,
xylose, or glucose. The acid includes sulfuric acid, hydrochloric
acid, nitric acid, sulfonic acid, and methylsulfonic acid that can
condense or polymerize the precursors of carbohydrates or polymers,
and furfuryl alcohol, aniline, acetylene, or propylene is preferred
for the precursor of carbon polymer. The above procedure may be
repeated several times depending on the type and the amount of carbon
compounds.
Step 2
Thermal Decomposition
[0029] The mesoporous molecular sieve including the polymeric materials
obtained above is heated at 400 to 1400.degree. C. under vacuum
condition or without oxygen to accomplish thermal decomposition
of the polymeric materials included in the pores, by which the polymerized
carbon compounds in the pores are thermally decomposed, and most
of the components except carbon become disappeared.
Step 3
Removal of Template
[0030] The heated mesoporous molecular sieve is reacted with hydrofluoric
acid or aqueous sodium hydroxide solution, and then the template
is removed to obtain a carbon molecular sieve: This step may be
repeated several times depending on the type and the amount of carbon
compounds, or the reaction can be performed with the addition of
ethanol to hydrofluoric acid or aqueous sodium hydroxide solution.
[0031] The carbon molecular sieve prepared by the above- described
process is a material in which carbon nanorods or carbon nanotubes
with a uniform diameter have the hexagonal arrangement. A rod-type
carbon molecular sieve prepared by using SBA-15 or a mesoporous
silica molecular sieve with similar hexagonal structure as a template
and sucrose, acetylene, or furfuryl alcohol under acid catalysis
is named as "CMK-3" and a tube-type carbon molecular sieve
prepared by using an aluminum grafted mesoporous molecular sieve
as a template and condensing furfuryl alcohol is named as "CMK-5".
[0032] CMK-3 and CMK-5 can be used as the supports for the materials
with catalytic activity, which makes possible their application
in adsorbents for organic materials, sensors, electrodes, and materials
for fuel cells and hydrogen storage. Actually, in the course of
the reduction of oxygen that occurs at the cathode of a cell, the
CMK-5 material supported with platinum showed more than 10 times
higher activity compared to a fuel cell electrode material of Vulcan
XC-72 carbon. In addition, it was also observed that CMK-5 supported
with platinum underwent the violent oxidation with flames when methanol
or ethanol was added to the material, indicating that the platinum
catalyst prepared by supporting platinum on CMK-5 would show a high
activity when applied to methanol and ethanol fuel cells.
[0033] The present invention is further illustrated by the following
examples, which should not be taken to limit the scope of the invention.
EXAMPLE 1
Preparation of CMK-3
[0034] After preheating a mixture of 0.5 g EO.sub.20PO.sub.70EO.sub.20
(Pluronic P123 BASF) and 10 mL of 1.6M aqueous hydrochloric acid
solution at a temperature of 35.degree. C., 1.1 g tetraethylorthosilicate
(TEOS, 98%, Acros) was added to the mixture, and stirred for 6 min.
The reaction mixture was then reacted for 24 h at 35.degree. C.,
and 12 h at 100.degree. C. respectively. The precipitate was filtered
and dried at 100.degree. C. to yield mesoporous molecular sieve
SBA-15 (see: Zhao et al., Science, 279:548 1998).
[0035] SBA-15 was added to a mixture of 5.3 g of 20% (w/w) aqueous
sucrose solution and 0.08 mL sulfuric acid, and then the reaction
mixture was slowly heated to 140.degree. C. to dry and polymerize
the reaction mixture. The unreacted sulfuric acid and water adsorbed
in the pores were removed by heating at 200.degree. C. under vacuum,
followed by thermal decomposition. Then, SBA-15 template was removed
with 10% (w/w) aqueous hydrofluoric acid to give a carbon molecular
sieve CMK-3 (see: FIGS. 1 and 2). FIGS. 1 and 2 show a transmission
electron micrograph of CMK-3 and XRD patterns of SBA-15 and CMK-3
respectively. As shown in FIG. 1 carbon nanolines are well connected
in the uniform hexagonal structure, and CMK-3 perfectly maintains
the structure of SBA-15 used as a template. FIG. 2 also shows that
CMK-3 perfectly maintains the structure of SBA-15 because the diffraction
peaks corresponding to the hexagonal structure appear in identical
patterns as shown in XRD patterns of SBA-15 and CMK-3 prepared by
using SBA-15 as a template. Nitrogen adsorption-desorption experiment
was performed to examine the pore distribution of the prepared CMK-3
(see: FIG. 3). FIG. 3 shows a graph showing nitrogen adsorption
isotherm of CMK-3 and the inserted picture shows pore size distribution
of CMK-3 obtained by Kruk-Jaroniec-Sayari method from the nitrogen
adsorption isotherm. As shown in FIG. 3 CMK-3 was observed to have
characteristic features of mesoporous molecular sieve that has uniform
mesopores with a diameter of 4.0 nm, a BET (Brunauer-Emmett-Teller)
adsorption area of 1520 m.sup.2/g, and a pore volume of 1.3 cm.sup.3/g.
EXAMPLE 2
Preparation of CMK-3 With Varied Amount of Sucrose
[0036] Three kinds of CMK-3 were prepared in a similar fashion
as above, except that a mixed solution of 4.8 g of 15.8% (w/w) aqueous
sucrose solution and 0.04 mL sulfuric acid, a mixed solution of
5.0 g of 20% (w/w) aqueous sucrose solution and 0.06 mL sulfuric
acid, or a mixed solution of 5.3 g of 20% (w/w) aqueous sucrose
solution and 0.04 mL sulfuric acid was retreated before thermal
decomposition, and then their XRD patterns were analyzed, respectively
(see: FIG. 4). FIG. 4 shows XRD patterns of CMK-3 prepared by using
various mixed solutions, where the numbers represent the amount
of sucrose contained in each solution. As shown in FIG. 4 the XRD
patterns were changed depending on the amount of sucrose.
EXAMPLE 3
Preparation of CMK-3 Using Hexagonal Mesoporous Silica Materials
Prepared by Using Surfactant Mixture
[0037] A mixture of 14.29 g Ludox HS40 (colloid silica, DuPont,
U.S.A.) and 100 g of 1M aqueous sodium hydroxide solution prepared
at 80.degree. C. for 2 h was added to the preheated mixture of a
surfactant mixture of hexadecyltrimethylammonium bromide (HTABr,
Acros, 99%), C.sub.16H.sub.33(OC.sub.2H.sub.5).sub.2 (Brij 52 Aldrich),
and C.sub.16H.sub.33(OC.sub.2H.sub.5).sub.10 (Brij 56 Aldrich)
and hydrochloric acid at 35.degree. C., and then the resulting mixture
was stirred for 5 min. After the resultant was further reacted for
12 h at 35.degree. C., and 12 h at 100.degree. C., the precipitate
was filtered and dried at 100.degree. C. to yield hexagonal mesoporous
silica molecular sieve (see: Kim and Stucky, Chem. Commun., p1159
2000), where the ratio of the mixed surfactant, HTABr:C.sub.16H.sub.33
(OC.sub.2H.sub.5).sub.2:C.sub.16H.sub.33 (OC.sub.2H.sub.5).sub.10
was 0:0.14:0.86 0.33:0.09:0.57 0.66:0.05:0.29 or 1:0:0 (w/w/w),
respectively.
[0038] After the addition of 1 g of each hexagonal mesoporous silica
molecular sieve prepared above to a mixture of 5.3 g of 20% (w/w)
aqueous sucrose solution and 0.08 mL sulfuric acid, the mixture
was slowly heated to 140.degree. C. to dry and polymerize the reaction
mixture. The unreacted sulfuric acid and water adsorbed in the pores
were removed by heating at 200.degree. C. under vacuum, followed
by thermal decomposition at 900.degree. C. under vacuum. Then, the
hexagonal mesoporous silica molecular sieve was removed with 10%
(w/w) aqueous hydrofluoric acid to yield CMK-3 and XRD analysis
was performed for the hexagonal mesoporous silica molecular sieve
and CMK-3 (see: FIGS. 5a and 5b). FIG. 5a shows XRD patterns of
hexagonal mesoporous silica molecular sieves depending on the mixed
ratios of surfactants and FIG. 5b shows XRD patterns of CMK-3 prepared
by using the hexagonal mesoporous silica molecular sieve described
above as a template. The numbers shown in the figures represent
the mixed ratios of the surfactants. As shown in FIGS. 5a and 5b,
the pore sizes of CMK-3 were varied while maintaining the identical
structure of the hexagonal mesoporous silica molecular sieve when
the mixed ratios of the surfactants were changed.
EXAMPLE 4
Preparation of CMK-3 Using Acetylene
[0039] SBA-15 prepared in Example 1 was added to a solution of
anhydrous aluminum chloride (AlCl.sub.3) in anhydrous ethanol, and
then stirred for 1 h at room temperature. The precipitate was filtered,
washed with anhydrous ethanol, and then dried at 140.degree. C.
Calcination of the dried precipitate was made for 5 h at 550.degree.
C. under air stream to give AlSBA-15 in which aluminum is grafted
onto SBA-15 ( see: Ryoo et al., Chem. Commun., p2225 1997).
[0040] CMK-3 was prepared in an analogous manner as in Example
1 except that 1 g AlSBA-15 obtained above was subjected to a vacuum
condition at 400.degree. C. and adsorbed under the flow of acetylene
gas for 30 min at 800.degree. C. (see: FIG. 6). FIG. 6 shows an
XRD pattern of CMK-3 prepared by using acetylene, which shows similar
XRD pattern to those of CMK-3 prepared in Examples 1 to 3 with minor
differences.
EXAMPLE 5
Preparation of CMK-5
[0041] After AlSBA-15 prepared in Example 4 was subjected to a
vacuum condition, 1 g of furfuryl alcohol per 1 g of AlSBA-15 was
added under nitrogen, and the resulting mixture was heated for 3
h at 35.degree. C. under reduced pressure to promote the uniform
adsorption of furfuryl alcohol. CMK-5 was prepared by the polymerization
at 95.degree. C. for 12 h followed by the thermal decomposition
by heating at 900.degree. C. under vacuum, and then removal of AlSBA-15
template with 10% (w/w) aqueous hydrofluoric acid solution. The
pore size distribution of CMK-5 was measured by the same method
described in Example 1 (see: FIGS. 7 8 and 9). FIG. 7 shows an
electron micrograph of CMK-5 structure, demonstrating that in the
case of CMK-5 unlike CMK-3 pores of SBA-15 was not filled with
carbon nanorods, rather, formed with nanotubes. It is assumed that
furfuryl alcohol was condensed from the surface by the action of
aluminum grafted on the surface of SBA-15 frame that functions as
an acid site. FIG. 8 shows XRD patterns of SBA-15 and CMK-5 and
shows the characteristic feature that the intensity of peak (100)
of CMK-5 is extremely small. FIG. 9 shows a graph showing nitrogen
adsorption isotherm of CMK-5 and the inserted picture shows pore
size distribution of CMK-5 obtained by Kruk-Jaroniec-Sayari method
from the nitrogen adsorption isotherm. As shown in FIG. 9 CMK-5
presents the characters of mesoporous molecular sieves in a sense
that it has two types of mesopores with diameters of 4.2 nm and
6.0 nm, a BET adsorption area of 2050 m.sup.2/g, and a pore volume
of 2.1 cm.sup.3/g, demonstrating that CMK-5 is a carbon molecular
sieve containing two types of mesopores with different sizes.
EXAMPLE 6
Preparation of CMK-5 Using Varied Amount of Furfury Alcohol
[0042] CMK-5 was prepared similarly as in Example 5 except that
the furfuryl alcohol is added in an amount of 1.0 g, 1.2 g, or 2.0
g (see: FIG. 10). FIG. 10 shows XRD patterns of CMK-5 prepared by
using varied amount of furfuryl alcohol, where the numbers represent
the amount of added furfuryl alcohol. As shown in FIG. 10 it was
clearly demonstrated that the basic structure of CMK-5 is not changed
by the addition amount of furfuryl alcohol, while the diameter of
CMK-5 is changed.
EXAMPLE 7
Hydrogen Adsorption Effect of CMK-5
[0043] To evaluate the hydrogen adsorption ability of CMK-5 carbon
black (Vulcan XC-72) and CMK-5 prepared in Example 5 were impregnated
with a solution prepared by dissolving dichlorodihydroplatinum hexahydrate
(H.sub.2PtCl.sub.2.multidot.6H.sub.2O) in acetone, and then acetone
was removed by thorough drying at 60.degree. C. After the reduction
to platinum under hydrogen flow at 300.degree. C. for 2 h followed
by the removal of the adsorbed hydrogen by the treatment under vacuum
at 300.degree. C. for 1 h, each platinum catalyst impregnated with
the platinum content of 50% (w/w) was prepared. And then, the number
of hydrogen atom adsorbed in the platinum catalyst was measured
(see: Table 1).
1TABLE 1 Hydrogen adsorption of each platinum cluster Sample Number
of adsorbed hydrogen per platinum CMK-5 0.5 Carbon black 0.2
[0044] As shown in Table 1 above, in the case of CMK-5 more than
0.5 hydrogen atoms can be adsorbed per platinum atom. The platinum
cluster is distributed on CMK-5 about 2.5 times better than on carbon
black (Vulcan XC-72), when compared to the hydrogen adsorption result
for the platinum cluster prepared by plating the same amount of
platinum on carbon black (Vulcan XC-72) that is practically used
as an electrode for fuel cells.
EXAMPLE 8
Measurement of Activity of Platinum Catalyst for Reduction
[0045] A mixture of nafion and each platinum catalyst (Pt/CMK-5)
was prepared in a similar manner as in Example 7 except that the
amount of plated platinum on CMK-5 or active carbon black (Vulcan
XC-72) was 16.7%, 333%, or 50% (w/w), and sonicated in an aqueous
solution to give the liquid drops, which was added in a dropwise
to a rotational disc electrode made of hyaline carbon. The uniform
film coating of the electrode by drying at 70.degree. C. gave each
rotational disc electrode. The rotational disc electrode was rotated
at 10000 rpm under HClO.sub.4 electrolyte filled with oxygen at
room temperature, and current was measured at 900 mV to measure
the activity of the platinum catalyst for reduction reaction (see:
FIG. 11 Table 2). FIG. 11 shows a graph showing the activity change
of platinum catalyst for oxygen reduction depending on the content
of platinum supported on CMK-5 and carbon black, where ".smallcircle."
represents carbon black (Vulcan XC-72) and ".circle-solid."
represents CMK-5 respectively. As shown in FIG. 11 the activity
of CMK-5 though it is variable depending on the supported amount,
was superior to that of carbon black (Vulvan XC-72) (see: Table
2).
2TABLE 2 Relative activity of platinum catalyst Content of platinum
(%, w/w) Relative activity of CMK-5 to Vulcan XC-72 16.7 2.7 33.3
13.7 50 10.8
[0046] As shown in Table 2 above, it was clearly demonstrated that
the platinum catalyst employing CMK-5 of the invention is superior
to platinum catalyst employing conventional carbon black (Vulcan
XC-72). Therefore, it is expected that the platinum catalyst prepared
by supporting platinum on CMK-5 will show a high activity when applied
to methanol and ethanol fuel cells.
[0047] As clearly described and demonstrated above, the present
invention provides a carbon molecular sieve prepared by forming
carbon nanorods or carbon nanotubes with a uniform diameter inside
pores of siliceous mesoporous molecular sieve and a process for
preparing the same. The carbon molecular sieve of the invention
is prepared by adsorbing a mixture of an aqueous carbohydrate solution
and an acid or a precursor of a carbon polymer into pores of mesoporous
silica molecular sieve template, polymerizing, and heat treatment.
The carbon molecular sieve of the invention is superior in terms
of the hydrogen adsorption effect and the activity for oxygen reduction,
which makes possible its universal application for the development
of adsorbents for organic materials, sensors, electrodes, and materials
for fuel cells and hydrogen storage. |