Molecular sieve abstract
Mesoporous molecular sieve substances having a structure exhibiting
a hexagonal arrangement of straight channels uniform in diameter,
superior over MCM-41 substances of Mobil Co. in thermal stability
and hydrothermal stability, can be prepared by the methods characterized
in using various organic or inorganic salts.
Molecular sieve claims
What is claimed is:
1. A method for preparing a mesoporous molecular sieve substance,
comprising the steps of:
(A) mixing an aqueous ammonia solution, a silicate, and an alkyltrimethylammonium
halide as a surfactant, represented by the following formula I:
where n is an integer of 12 to 18 and X is Cl or Br, to prepare
a mixed aqueous solution;
(B) subjecting the mixed aqueous solution formed in step (A) to
hydrothermal reaction, adjusting its pH and re-subjecting it to
hydrothermal reaction to prepare a hydrothermally treated aqueous
solution;
(C) adding to the hydrothermally treated solution of step (B) one
or more water-soluble organic or inorganic salts which are capable
of binding to a monovalent cation;
(D) subjecting the solution resulting from step (C) to hydrothermal
reaction, adjusting its pH and re-subjecting to hydrothermal reaction;
(E) subjecting the solution resulting from step (D) to hydrothermal
reaction for a suitable period at a suitable temperature while maintaining
its pH, so as to give precipitates of a molecular sieve substance;
(F) filtering, washing and drying the precipitates of the molecular
sieve substance; and
(G) calcining the dried precipitates.
2. The method in accordance with claim 1 wherein said surfactant
is selected from the group consisting of hexadecyltrimethylammonium
chloride, dodecyltrimethyl ammonium bromide, tetradecyltrimethylammonium
bromide and octadecyltrimethylammonium bromide.
3. The method in accordance with claim 1 wherein said silicate
is sodium silicate.
4. The method in accordance with claim 1 wherein said water-soluble
organic or inorganic salts are selected from the group consisting
of LiCl, NaCl, KCl, RbCl, CH.sub.3 COONa, NaBr, CH.sub.3 COOK, Na.sub.2
SO.sub.4 NaNO.sub.3 NaClO.sub.4 NaClO.sub.3 ethylenediaminetetraacetic
acid tetrasodium salt, adipic acid disodium salt, 13-benzenedisulfonic
acid disodium salt and nitrilotriacetic acid sodium salt.
5. The method in accordance with claim 1 wherein said water-soluble
organic or inorganic salts and said silicate were used at an amount
of 0.5 to 16.0 moles and 1.0 to 15.0 moles, respectively, per mole
of the alkyltrimethylammonium halide of the formula I.
6. The method in accordance with claim 1 wherein said calcining
step is carried out at a temperature of 500 to 600.degree. C.
7. A method for preparing a mesoporous molecular sieve substance,
comprising the steps of:
(1) mixing an aqueous ammonia solution, a silicate, one or more
salts selected from the group consisting of aluminates, borates
and acid salts of 3d transition metals on the periodic table and
an alkyltrimethylammonium halide as a surfactant, represented by
the following formula I:
wherein n is an integer of 12 to 18 and X is Cl or Br, to prepare
a mixed aqueous solution;
(2) subjecting the mixed aqueous solution formed in step (1) to
hydrothermal reaction, adjusting its pH and re-subjecting it to
hydrothermal reaction to prepare a hydrothermally treated solution;
(3) adding to the hydrothermally treated solution of step (2) one
or more water-soluble organic or inorganic salts which are capable
of binding to a monovalent cation;
(4) subjecting the solution resulting from step (3) to hydrothermal
reaction, adjusting its pH and re-subjecting to hydrothermal reaction;
(5) subjecting the solution resulting from step (4) to hydrothermal
reaction for a suitable period at a suitable temperature while maintaining
its pH, so as to give precipitates of a molecular sieve substance;
(6) filtering, washing and drying the precipitates of the molecular
sieve substance; and
(7) calcining the dried precipitates.
8. The method in accordance with claim 7 wherein said aluminate
is sodium aluminate.
9. The method in accordance with claim 7 wherein said water-soluble
organic or inorganic salts, said silicate and one or more salts
selected from the group consisting of aluminates, borates and acid
salts of 3d transition metals on periodic table were used at an
amount of 0.5 to 16.0 moles, 1.0 to 15.0 moles and 0.0025 to 0.40
mole, respectively, per mole of the alkyl trimethylammonium halide
of the formula I.
10. The method in accordance with claim 7 wherein said surfactant
is selected from the group consisting of hexadecyltrimethylammonium
chloride, dodecyltrimethyl ammonium bromide, tetradecyltrimethylammonium
bromide and octadecyltrimethylammonium bromide.
11. The method in accordance with claim 7 wherein said silicate
is sodium silicate.
12. The method in accordance with claim 7 wherein said water-soluble
organic or inorganic salts are selected from the group consisting
of LiCl, NaCl, KCl, RbCl, CH.sub.3 COONa, NaBr, CH.sub.3 COOK, Na.sub.2
SO.sub.4 NaNO.sub.3 NaClO.sub.4 NaClO.sub.3 ethylenediaminetetraacetic
acid tetrasodium salt, adipic acid disodium salt, 13-benzenedisulfonic
acid disodium salt and nitrilotriacetic acid sodium salt.
13. The method in accordance with claim 7 wherein said calcining
step is carried out at a temperature of 500 to 600.degree. C.
Molecular sieve description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to a mesoporous molecular
sieve substance and methods for preparing the same. More particularly,
this invention relates to a mesoporous molecular sieve substance
having a structure exhibiting a hexagonal arrangement of straight
channels uniform in diameter, superior over MCM-41 manufactured
by Mobil Co. in thermal stability and hydrothermal stability, and
is concerned with methods for preparing the mesoporous molecular
sieve substance.
2. Description of the Prior Art
Generally, porous substances are divided by pore size, for example,
pore sizes smaller than 2 nm classified as microporous substances,
between 2 and 50 nm classified as mesoporous substances and larger
than 50 nm classified as macroporous substances. Of the porous substances,
those having uniform channel, such as zeolite, are defined as molecular
sieves and up to hundreds of types of species have been found and
synthesized thus far. Zeolites play an important role as catalysts
or carriers in modern chemical industries by virtue of their characteristics
including selective adsorptivity, acidity and ion exchangeability.
However, the molecular size of a reactant which can be utilized
in catalyst conversion reactions, etc. is limited by the pore size
of zeolite because zeolite is a microporous molecular sieve. For
example, when ZSM-5 zeolite is applied in a catalytic cracking reaction,
its reactivity becomes significantly decreased as the reactant changes
from n-alkane to cycloalkane and further to branched alkane. Hence,
an enormous effort has been made all over the world to synthesize
molecular sieves having larger pores than that of zeolite. As a
result, AlPO.sub.4 VPI-5 Cloverlite and JDF-20 having larger pore
size than that of zeolite were developed by many researchers. However,
these molecular sieves cannot exceed the microporous limit.
Recently, a group of researchers in Mobil Co. reported a series
of mesoporous molecular sieves, named MCM-41 in U.S. Pat. Nos.
5057296 and 5102643. According to these patents, MCM-41 has
a structure exhibiting hexagonal arrangement of straight channels,
such as honeycomb, on a silica plate. Recent research reports illustrate
that MCM-41 is synthesized through a liquid crystal template pathway.
That is, in an aqueous solution, surfactants form a liquid crystal
structure which is surrounded by silicate ions and the liquid crystal
structure is associated with MCM-41 substance via a hydrothermal
reaction and then, removed by calcination at a temperature of 500
to 600.degree. C., to prepare MCM-41. At this time, its pore size
can be adjusted in a range of from 1.6 up to 10 nm by modulating
the kinds of surfactants or synthesis conditions. Thus, MCM-41 is
of mesoporosity with larger pore size than that of existing molecular
sieves, such as zeolite, and is being actively researched for characterization
and application in many laboratories. Since MCM-41 is a mesoporous
molecular sieve, which has regularly arranged channels, it is used
for study on adsorption characteristics of various gases as well
as used as a carrier for conductive polymer, organometallic compound
and poly acid by virtue of its large pores. Further, another type
MCM-41 whose framework atoms are partly substituted with other elements,
such as aluminum, boron, manganese, iron, vanadium, titanium, etc,
has been developed for application to apply for a catalytic reactions
of macro organic compound or for use in catalytic carriers.
As mentioned above, the application examples of MCM-41 in various
fields are reported. However, one of the most important physical
properties of MCM-41 for the application is thermal stability. According
to the early researchers, after being subjected to calcination to
remove template materials, MCM-41 samples undergo structure contraction
ranging from 20 to 25% relative to pre-calcination, although exhibiting
a little difference depending on synthesis conditions. This contraction
is attributed to the fact that the silanol groups are condensed
by the calcination. However, recent research data shows that, if
the equilibrium of silicate condensation reaction is moved toward
the product by controlling pH of the reactants during the hydrothermal
synthesis of MCM-41 the condensation of the silanol group is already
completed, so that the weak thermal stability can be surmounted
and a considerable improvement can be brought into the uniformity
of structure. The MCM-41 thus obtained was reportedly found not
to undergo structural decomposition even at 500.degree. C. under
1 atm in the presence of 100% water vapor, in addition to being
only slightly contracted in structure even upon heating up to 900.degree.
C. under an oxygen atmosphere.
Superior in thermal stability as it is, the MCM-41 however, starts
to be slowly destructurized in water heated at 60.degree. C. or
higher, which is ascribed to the hydrolysis of the silicate constituents.
12 hrs after being heated in boiling water of 100.degree. C., the
MCM-41 completely loses its structural characteristics. This poor
hydrothermal stability serves as a serious limiting factor in the
case of requiring 60.degree. C. or higher, for example, in using
a titanium-substituted molecular sieve in a partial oxidation reaction,
in a catalyst conversion reaction needing a hydrothermal condition
in which hydrogen peroxide is used as an oxidizing agent or in impregnating
in the molecular sieve a transition metal, such as platinum, as
a catalytically active ingredient.
Therefore, active research and development efforts have been made
for an improvement in the hydrothermal stability of mesoporous molecular
sieves.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to overcome
the above problems encountered in the prior art and to provide a
method for preparing a novel mesoporous molecular sieve substance
significantly improved in hydrothermal stability.
It is another object of the present invention to provide the novel
mesoporous molecular sieve substance.
In accordance with an aspect of the present invention, there is
provided a method for preparing a mesoporous molecular sieve substance,
comprising the steps of:
(A) mixing an aqueous ammonia solution, a silicate, and an alkyltrimethylammonium
halide as a surfactant, represented by the following formula I:
wherein n is an integer of 12 to 18 and X is Cl or Br, to prepare
a mixed aqueous solution;
(B) subjecting the mixed aqueous solution to hydrothermal reaction,
adjusting its pH and re-subjecting it to hydrothermal reaction;
(C) adding in the mixed aqueous solution one or more water-soluble
organic or inorganic salts which are capable of binding to a monovalent
cation;
(D) repeating the procedure of step (B);
(E) subjecting the reaction solution to hydrothermal reaction for
a suitable period at a suitable temperature while maintaining its
pH, so as to give precipitates of desired molecular sieve substances;
(F) filtering, washing and drying the precipitates of the molecular
sieve substances; and
(G) calcining the dried precipitates.
In accordance with another aspect of the present invention, there
is provided a method for preparing a mesoporous molecular sieve
substance, comprising the steps of:
(1) mixing an aqueous ammonia solution, a silicate, one or more
salts selected from the group consisting of aluminates, borates
and acid salts of 3d transition metals on the periodic table and
an alkyltrimethyl ammonium halide as a surfactant, represented by
the formula I:
wherein n is an integer of 12 to 18 and X is Cl or Br, to prepare
a mixed aqueous solution;
(2) subjecting the mixed aqueous solution to hydrothermal reaction,
adjusting its pH and re-subjecting it to hydrothermal reaction;
(3) adding in the mixed aqueous solution one or more water-soluble
organic or inorganic salts which are capable of binding to a monovalent
cation;
(4) repeating the procedure of step (2);
(5) subjecting the reaction solution to hydrothermal reaction for
a suitable period at a suitable temperature while maintaining its
pH, so as to give precipitates of desired molecular sieve substances;
(6) filtering, washing and drying the precipitates of the molecular
sieve substances; and
(7) calcining the dried precipitates.
In accordance with a further aspect of the present invention, there
are provided mesoporous molecular sieve substances, prepared by
the above methods, having a structure exhibiting a hexagonal arrangement
of straight channels uniform in diameter.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objectives and aspects of the invention will become apparent
from the following description of embodiments with reference to
the accompanying drawings in which:
FIG. 1 is a transmission electronic microphotograph showing KIT-3
substance prepared in accordance with an embodiment of the present
invention;
FIG. 2 shows X-ray diffraction patterns obtained from the KIT-3
substance of FIG. 1;
FIG. 3 shows N.sub.2 adsorption-desorption isotherms at liquid
N.sub.2 temperature for the KIT-3 substance of FIG. 2 after calcination;
FIG. 4 shows the pore size distribution curve for the KIT-3 substance,
obtained from N.sub.2 adsorption-desorption isotherms of FIG. 3
by means of the Horvath-Kawazoe method;
FIG. 5 shows the change in the X-ray diffraction pattern of KIT-3
substance with the alkyl chain length of alkyltrimethylammonium
halide, a surfactant used in Example I;
FIG. 6 shows X-ray diffraction patterns of the KIT-3 substance
prepared by using EDTANa.sub.4 as a salt in Example II;
FIG. 7 shows X-ray diffraction patterns of the KIT-3 substance
prepared by using CH.sub.3 COONa as a salt in Example III;
FIG. 8 shows X-ray diffraction patterns of the KIT-3 substance
prepared by using LiCl as a salt in Example IV;
FIG. 9 shows X-ray diffraction patterns of the KIT-3 substance
prepared by using NaCl as a salt in Example V;
FIG. 10 shows X-ray diffraction patterns of the KIT-3 substance
prepared by using KCl as a salt in Example VI;
FIG. 11 shows X-ray diffraction patterns of the KIT-3 substance
prepared by using NaNO.sub.3 as a salt in Example VII;
FIG. 12 shows X-ray diffraction patterns of the KIT-3 substance
prepared by using Na.sub.2 SO.sub.4 as a salt in Example VIII;
FIG. 13 shows solid phase MAS aluminum-27 NMR spectra of AlKIT-3
substance, in which aluminum is partly substituted for frame silicon
(Si/Al=40), according to various treatments; and
FIG. 14 shows temperature programmed desorption (TPD) results of
ammonia gas for AlKIT-3 substance (Si/Al=40), according to various
treatments.
DETAILED DESCRIPTION OF THE INVENTION
MCM-41 a mesoporous molecular sieve, is prepared through a liquid
crystal template passage using surfactant as a structure-inducing
material. Various preparation methods of MCM-41 have been reported
in recent years. In the present invention, there is provided a novel
molecular sieve KIT-3 based on the method disclosed in J. Chem.
Soc., Chem. Commun., 1995 at 711 authored by the present inventors.
As a surfactant used in the present invention, alkyltrimethylammonium
halide of the formula I is used. Preferred are dodecyltrimethylammonium
bromide (DTABr), tetradecyltrimethyl ammonium bromide (TTABr), hexadecyltrimethylammonium
chloride (HTACl), and octadecyltrimethyl ammonium bromide (OTABr).
In the methods according to the present invention, the silicate
used in steps (A) and (1) may be an aqueous sodium silicate solution
(Na/Si=0.5) which is obtained by dissolving a colloid silica, such
as that sold by DuPont under the tradename of "Ludox HS40"
(40 wt % SiO.sub.2) in a 1 M sodium hydroxide, but is not limited
to this.
An example of one or more salts selected from the group consisting
of aluminates, borates and acid salts of the 3d transition metal
on the periodic table, used in step (1), includes sodium aluminate
(NaAlO.sub.2).
According to the preparation method for KIT-3 the pH of the reactant
solutions is controlled three times to, for example, 10.2 by neutralization
with a weak acid, for example, acetic acid. The present invention
is characterized in that, after the first pH controlling step, a
hydrothermal reaction is carried out, followed by addition of salts.
This allows for a significantly improved molecular sieve in thermal
stability and hydrothermal stability. That is, in contrast with
co-pending U.S. Pat. application Ser. No. 08/788159 filed Jan.
24 1997 to the present assignee, the content of which is incorporated
herein by reference, the present invention additionally comprises
the two hydrothermal reactions and pH control as in the step (B)
or (2) and the addition of salt as in step (C) or (3), resulting
in the production of a mesoporous substance quite different in pore
structure from that of the above prior U.S. patent application.
While the mesoporous substance of the above prior U.S. patent application
is structurized in such a manner that channels uniform in diameter
are randomly arranged interconnecting with one another in a three-dimensional
way, that of the present invention is structured in such a way that
uniform mesopores show a hexagonal arrangement of straight channels,
such as honeycomb.
Well known to the experts in the art, the term "hydrothermal
reaction" as used herein refers to a reaction in water while
heating in an open or closed reactor.
The organic or inorganic salts used in the steps (C) and (3) are
those that are able to bind to monovalent cations, such as Li.sup.+,
Na.sup.+, K.sup.+, Rb.sup.+ and NH.sub.4.sup.+, and also dissolve
in water. Preferred examples include LiCl, NaCl, KCl, RbCl, CH.sub.3
COONa, NaBr, CH.sub.3 COOK, Na.sub.2 SO.sub.4 NaNO.sub.3 NaClO.sub.4
NaClO.sub.3 ethylenediamine tetraacetic acid tetrasodium salt (EDTANa.sub.4),
adipic acid disodium salt, 13-benzendisulfonic acid disodium salt
and nitrilotriacetic acid sodium salt.
In steps (A) and (1), the silicate is preferably used at an amount
of 1.0 to 15.0 moles per mole of alkyltrimethylammonium halide.
The aqueous ammonia solution serves to smoothly promote the function
of the surfactant and may be not used in some cases. In step (1),
the salt selected from the group consisting of aluminum acid salts,
boron acid salts, the acid salts of the 3d transition metal on the
periodic table and the combinations thereof, is preferably added
in a range of 0.0025 to 0.4 moles based on one mole of the alkyltrimethylammonium
halide of the formula I.
In steps (B) and (2), the hydrothermal reaction is suitably carried
out at a temperature of 80 to 120.degree. C. for a time of 1 to
2 days. The hydrothermal reactions in the other steps are conducted
under the same conditions.
In steps (C) and (3), the water-soluble organic or inorganic salt
capable of forming a bond with monovalent cation is preferably used
in an amount of 0.5 to 16.0 moles per mole of the alkyltrimethylammonium
halide of the formula I.
It is preferable that the calcination of the final step be carried
out at 500 to 600.degree. C. in air.
A detailed description will be given of KIT-3 below, in conjugation
with the accompanying drawings.
FIG. 1 is a transmission electron micrograph showing the KIT-3
substance prepared from a reaction comprising SiO.sub.2 :HTACl:Na.sub.2
O:(NH.sub.4).sub.2 O:H.sub.2 O (molar ratio, 4:1:1:0.15:200) in
the following Example I. As shown in FIG. 1 the KIT-3 substance
has a structure in which mesopores are in a hexagonal arrangement
of straight channels, such as honeycomb. Similar electron microphotographs
could be obtained from all of the other KIT-3 substances prepared
in the present invention.
FIG. 2 shows X-ray diffraction patterns of the KIT-3 substances
of FIG. 1 in which reference character "a" stands for
KIT-3 substance before calcination and reference character "b"
for KIT-3 substance after calcination. In the X-ray diffraction
patterns, the peaks showing the hexagonal arrangement can be read
in low angle ranges, irrespective of calcination and designated
as (100), (110), (200), (210) and (300).
FIG. 3 shows nitrogen adsorption-desorption isotherms at liquid
nitrogen temperatures for the KIT-3 of FIG. 1 which has undergone
the calcination of Example I. According to these isotherms, the
nitrogen adsorption is abruptly increased around 0.4 of P/P.sub.0.
FIG. 4 shows a size distribution curve for the channels of KIT-3
obtained from the nitrogen adsorption-desorption isotherms at liquid
nitrogen temperature by the Horvath-Kawazoe method. As seen, the
channels of KIT-3 are of quite narrow size distribution at 3.0 nm
(the line width is not more than 1 nm at medium height). Similar
curves (not shown) could be obtained by such nitrogen adsorption-desorption,
irrespective of the kinds of salt used during the synthesis of the
KIT-3. Referring to FIG. 5 there are X-ray diffraction plots showing
the change of d.sub.100 with the alkyl chain length of the formula
I surfactant. The salt used for this synthesis of KIT-3 was EDTANa.sub.4
which was added at 8 moles per mole of surfactant. As seen in FIG.
5 d.sub.100 of the X-ray diffraction patterns increases from 2.5
to 4.6 nm regularly as the alkyl chain length of the formula I surfactant
extends from 12 for "a" through 14 for "b" to
16 for "c" and then, to 18 for "d".
With reference to FIGS. 6 through 12 there are shown X-ray diffraction
patterns that are dependent on the salts added during the synthesis
of KIT-3 which include EDTANa.sub.4 CH.sub.3 COONa, LiCl, NaCl,
KCl, NaNO.sub.3 and Na.sub.2 SO.sub.4. In these figures, the X-ray
diffraction patterns on the left panel are for the KIT-3 obtained
by calcining KIT-3 substances and then removing surfactant from
them, whereas the patterns on the right panel are for the KIT-3
obtained by calcining KIT-3 substances and then immersing them in
boiling water for 12 hrs.
FIG. 6 is the synthesis results of KIT-3 using EDTANa.sub.4. As
will be illustrated in Example II later, the X-ray diffraction patterns
of KIT-3 after the samples are calcined, followed by the removal
of surfactant from them, are on the left panel whereas the patterns
after the samples are calcined, followed by subjecting them to hydrothermal
reaction for 12 hrs are on the right panel. The numerals on the
patterns in the figure represent the mole number of EDTANa.sub.4
added per mole of hexadecyl trimethylammonium, a surfactant. In
this case, EDTANa.sub.4 is used at an amount of 0 to 16 moles per
mole of the surfactant. As apparent from the figure, the KIT-3 synthesized
without using any salt is completely destructurized when it is immersed
in boiling water for 12 hrs. On the other hand, the addition of
the salt during the synthesis of KIT-3 results in stabilizing the
structure of the corresponding KIT-3. That is, as seen, the hydrothermal
stability of the structure increases as the mole ratio of the EDTANa.sub.4
to the surfactant increases to a certain value, for example, 8.
The mole ratio higher than such optimal value, on the contrary,
makes the hydrothermal stability have a tendency to decrease. This
case will be, in detail, illustrated in Example II, later.
In FIGS. 7 through 12 there are displayed the X-ray diffraction
patterns of the KIT-3 which are obtained by using as a salt CH.sub.3
COONa, LiCl, NaCl, KCl, NaNO.sub.3 and Na.sub.2 SO.sub.4 respectively,
and calcining the corresponding KIT-3 substances, as will be described
in Examples III through VIII, respectively. The diffraction patterns
on the left panel in these figures are obtained from the calcined
substances while the patterns on the right panel from the calcined
substances but further processed through the hydrothermal treatment
in boiling water for 12 hrs. As in FIG. 6 the numerals on the patterns
each mean the mole number of the salt added per mole of hexadecyltrimethyl
ammonium chloride, a surfactant. Like FIG. 6 FIGS. 7 through 12
show that, as the salts are added at more amounts, the hydrothermal
stability becomes increased to the extent beyond which the hydrothermal
stability declines. For each case, when 2 moles of CH.sub.3 COONa,
3 moles of LiCl, 3 moles of NaCl, 2 moles of KCl, 2 moles of NaNO.sub.3
2 moles of Na.sub.2 SO.sub.4 per mole of hexadecyl trimethylammonium
chloride were added, the hydrothermal stability of the corresponding
KIT-3 was found to have maximal hydrothermal stability.
In the following Example IX, parts of silicon present in the frame
of the mesoporous molecular sieve KIT-3 were substituted by aluminum,
resulting in a different mesoporous molecular sieve, named "AlKIT-3"
(Si/Al=10 to 200). In this synthesis, EDTANa.sub.4 was added. The
X-ray diffraction pattern (not shown) thereof shows that the structure
of AlKIT-3 is identical to that of KIT-3.
With reference to FIGS. 13 and 14 the results obtained from the
test of AlKIT-3 (Si/Al=40) for thermal stability and hydrothermal
stability are shown. FIG. 13 is solid phase magic angle spin (MAS)
aluminum-27 nuclear magnetic resonance (NMR) for the AlKIT-3 obtained
before calcination (a), after calcination (b), after temperature
was maintained at 500.degree. C. for 2 hrs under an oxygen atmosphere
with a water vapor of 2.3 kPa (c), and after being placed in boiling
water of 100.degree. C. for 12 hrs (d). As demonstrated in FIG.
13 AlKIT-3 like KIT-3 is not able to be destructured by the above
thermal or hydrothermal treatments by virtue of the salt added,
but AlKIT-3 also allows the substituted aluminum in the frame to
maintain the tetrahedral structure of the mesoporous sieve. In addition,
FIG. 14 is temperature programmed desorption (TPD) of ammonia for
the AlKIT-3 obtained after calcination (a), after temperature was
maintained at 500.degree. C. for 2 hrs under an oxygen atmosphere
with a water vapor of 2.3 kPa (b), and after being placed in boiling
water of 100.degree. C. for 12 hrs (c). As seen in FIG. 14 AlKIT-3
has almost the same acid point after calcination (a), even after
being treated at 500.degree. C. for 2 hrs under an oxygen atmosphere
with a water vapor of 2.3 kPa (b) or after being placed in boiling
water of 100.degree. C. for 12 hrs (c). Consequently, AlKIT-3 is
superior in hydrothermal stability as well as thermal stability.
A better understanding of the present invention may be obtained
in light of following examples which are set forth to illustrate,
but are not to be construed to limit, the present invention.
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