Molecular sieve abstract
The present invention is directed to a large-pore aluminosilicate
molecular sieve comprising alumina and silica, where the ratio of
SiO.sub.2 /Al.sub.2 O.sub.3 ranges from about 75 to 600 and its
method of preparation. The large-pore aluminosilicate molecular
sieve of the present invention has the ability to catalyze reactions
involving particularly bulky transition states or large molecules.
Molecular sieve claims
What is claimed is:
1. A method of preparing an aluminosilicate molecular sieve that
comprises alumina and silica in a ratio of SiO.sub.2 /Al.sub.2 O.sub.3
ranging from about 75 to 600 said molecular sieve having an x-ray
diffraction pattern that includes at least the d-spacing lines set
forth in Table 1 said method comprising the step of
Molecular sieve description
BACKGROUND OF THE INVENTION
A number of reactions involving bulky transition states or large
molecules cannot be carried out using commercially available aluminosilicate
zeolites, since the critical pore diameter of these aluminosilicate
zeolites does not allow the facile ingress and egress of such molecules.
As a result, reactions involving particularly bulky transition states
or large molecules are often conducted using environmentally undesirable
catalysts, such as chlorided alumina or liquid-phase acids, such
as sulfuric acid.
A large-pore silica, 14-membered ring, molecular sieve was described
for the first time by K. J. Balkus et al in "Synthesis and
Characterization of UTD-1: A Novel Zeolite Molecular Sieve"
in ACS Petroleum Chemicals Preprints, Volume 40 page 296 (1995),
and "Molecular Sieve Synthesis Using Metallocenes as Structure
Directing Agents" in Mat. Res. Soc. Symp. Proc., Volume 368
page 369 (1995). Specifically, this large-pore silica molecular
sieve is identified as UTD-1 a 14-membered ring, all-silica molecular
sieve. UTD-1 is disclosed in U.S. Pat. No. 5489424.
In the article "Molecular Sieve Synthesis Using Metallocenes
as Structure Directing Agents", K. J. Balkus, Jr. et al suggest
incorporating aluminum into UTD-1 in an amount such that the Si/Al
ratio is greater than 350 (corresponding to a SiO.sub.2 /Al.sub.2
O.sub.3 ratio of greater than 700), to enhance the catalytic activity
of UTD-1. However, the reference fails to describe or suggest the
incorporation of greater amounts of alumina or the method by which
aluminum is incorporated into the molecular sieve framework. To
date, the synthesis of a large-pore, 14-membered ring, true aluminosilicate
molecular sieve, namely a zeolite comprising alumina and silica,
has not been reported.
The article further indicates that crystals of the UTD-1 silica
molecular sieve are large "bundles of two dimensional planks
. . . about 2 microns across."
SUMMARY OF THE INVENTION
The present invention is directed to a large-pore aluminosilicate
molecular sieve, having a nominal critical pore diameter of about
7.5 .ANG., comprising alumina and silica, where the ratio of SiO.sub.2
/Al.sub.2 O.sub.3 ranges from about 75 to 600 and its method of
preparation. The large-pore aluminosilicate molecular sieve of the
present invention has the ability to catalyze reactions involving
particularly bulky transition states or large molecules, specifically,
the conversion of toluene.
As used herein, the term "aluminosilicate molecular sieve"
or "zeolite" refers to a molecular sieve having alumina
and silica, which is substantially free of phosphorus and boron.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is the X-ray diffraction pattern for the aluminosilicate
molecular sieve of the present invention having a SiO.sub.2 /Al.sub.2
O.sub.3 ratio of about 200 as-synthesized.
FIG. 2 is the X-ray diffraction pattern for the aluminosilicate
molecular sieve of the present invention having a SiO.sub.2 /Al.sub.2
O.sub.3 ratio of about 100 as-synthesized.
FIG. 3 is an NMR spectrum that shows Al is in the framework of
the molecular sieve of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to a novel large-pore aluminosilicate
molecular sieve comprising alumina and silica, where the molecular
sieve has an average crystal size of less than 2 microns; an "a"
unit cell dimension of greater than 18.83 .ANG.; and an x-ray diffraction
pattern that includes at least the lines set forth in Table 1 below.
TABLE 1 MOST SIGNIFICANT XRD REFLECTIONS OF MCM-64 Degrees d-spacing,
Relative Two-theta in .ANG. Intensity 6.0 14.70 .+-. 0.32 S 7.5
11.67 .+-. 0.40 M 14.6 6.09 .+-. 0.09 M 18.1 4.90 .+-. 0.11 M 19.6
4.53 .+-. 0.15 M 21.2 4.20 .+-. 0.04 S 22.0 4.04 .+-. 0.10 M
Table 2 shows additional lines of the x-ray diffraction pattern
for the molecular sieve of the present invention.
TABLE 2 SIGNIFICANT XRD REFLECTIONS OF MCM-64 Degrees d-spacing,
Relative Two-theta in .ANG. Intensity 6.0 14.7 S 7.5 11.7 M 14.6
6.1 M 18.1 4.9 M 19.5 4.5 M 21.2 4.2 S 22.1 4.0 M 22.5 3.9 M 24.3
3.7 MW 24.8 3.6 MW 26.2 3.4 W 28.3 3.15 W 29.8 3.0 W 32.4 2.8 W
The aluminosilicate molecular sieve of the present invention may
be prepared by using a cobalt metal complex, such as bis(pentamethylcyclopentadienyl)
cobalt (lll) ion [(Cp*).sub.2 Co] or a bis(partially methylated
cyclopentadienyl) cobalt (lll) ion having at least three methyl
groups, as the directing agent.
The aluminosilicate molecular sieve of the present invention may
be prepared from a reaction mixture containing a source of sodium
ions and/or hydroxide ions such as NaOH or [(Cp*).sub.2 Co]OH; a
source of aluminum such as NaAlO.sub.2 aluminum oxide or aluminum
sulfate; a directing agent such as [(Cp*).sub.2 Co] ion, in the
form of [(Cp*).sub.2 Co]OH or a chloride or other salt of [(Cp*).sub.2
Co] ion; and a source of silica such as a pyrogenic silica (e.g.,
Cab-O-Sil M5), precipitated silicas, silica gels, silica sols, or
soluble silicates (e.g., tetraethylorthosilicate) in the following
mole ratios:
H.sub.2 O/SiO.sub.2 =20 to 80
Na.sup.+ /SiO.sub.2 =0 to 0.2
OH.sup.- /SiO.sub.2 =0.1 to 0.3
[(Cp*).sub.2 Co]/SiO.sub.2 =0.05 to 0.2
SiO.sub.2 /Al.sub.2 O.sub.3 =75 to 600
The preferred mole ratios for H.sub.2 O/SiO.sub.2 is from about
40 to 60; for Na.sup.+ /SiO.sub.2 from about 0.05 to 0.15; for
OH.sup.- /SiO.sub.2 from about 0.15 to 0.25; for [(Cp*).sub.2 Co]/SiO.sub.2
from about 0.05 to 0.15; and for SiO.sub.2 /Al.sub.2 O.sub.3 from
about 100 to 300.
Crystallization of the aluminosilicate molecular sieve from the
above-described reaction mixture requires from about 2 to 50 days;
at a temperature of from about 150 to 200.degree. C.
The as-synthesized form of the aluminosilicate molecular sieve
is then calcined at a temperature of about 300 to 400.degree. C.
in N.sub.2 then at 500 to 550.degree. C. in air to destroy the
cobalt metal complex. The calcined molecular sieve may optionally
be treated to remove sodium ions, e.g., with a solution of NH.sub.4.sup.+
ion.
The aluminosilicate molecular sieve prepared from the bis(pentamethylcyclopentadienyl)
cobalt (lll) ion [(CP*).sub.2 Co] directing agent has a nominal
critical pore diameter of about 7.5 .ANG.; an average crystal size
of less than 2 microns, preferably ranging from 0.01 to 1.0 micron
and more preferably ranging from 0.05 to 0.5 micron; an "a"
unit cell dimension of greater than 18.83 .ANG.; and an x-ray diffraction
pattern that includes at least the lines set forth in Table 1 above.
This embodiment of the aluminosilicate molecular sieve of the present
invention is a 14-membered ring, aluminosilicate molecular sieve
and is referred to hereinafter as MCM-64.
The following examples illustrate the preparation of MCM-64 using
bis(pentamethylcyclopentadienyl) cobalt (lll) ion [(CP*).sub.2 Co]
as the directing agent.
EXAMPLE 1
The metal complex of [(Cp*).sub.2 Co] was prepared as described
in Example 1 of U.S. Pat. No. 5489424.
MCM-64 was prepared as a substantially single phase product by
combining water, 50% NaOH, 47% NaAlO.sub.2 7% [(Cp*).sub.2 Co]OH
aqueous solution and silica, specifically Cab-O-Sil M-5 and stirring
until well mixed. The mole ratio of the reactants were:
H.sub.2 O/SiO.sub.2 =60
Na.sup.+ /SiO.sub.2 =0.1
OH.sup.- /SiO.sub.2 =0.2
[(Cp*).sub.2 Co]/SiO.sub.2 =0.1
SiO.sub.2 /Al.sub.2 O.sub.3 =200
Crystallization of the aluminosilicate molecular sieve was carded
out at a temperature of 175.degree. C. in an unstirred, teflon-lined
autoclave, and was deemed to be complete after approximately 28
days. FIG. 1 shows the characteristic x-ray diffraction pattern
for this sample.
The off-yellow, as-synthesized form was then calcined, first at
350.degree. C. in N.sub.2 then at 538.degree. C. in air to destroy
the cobalt metal complex. The resultant blue powder was treated
with NH.sub.3 gas and then exchanged with 1M NH.sub.4 NO.sub.3.
The unit cell dimensions of this MCM-64 sample were:
a (.ANG.) b (.ANG.) c (.ANG.) MCM-64 as-synthesized 18.866 8.382
23.533 MCM-64 calcined 18.989 8.410 23.144
The average crystal size of both the as-synthesized and calcined
forms of this MCM-64 sample was less than about 1 micron.
The as-synthesized form of this MCM-64 sample, when examined by
NMR, was found to have a framework SiO.sub.2 /Al.sub.2 O.sub.3 ratio
of approximately 160. All alumina in the sample was in the framework
as shown by the single peak in FIG. 3.
EXAMPLE 2
MCM-64 was prepared as a substantially single phase product by
combining water, 50% NaOH, 47% NaAlO.sub.2 9% [(Cp*).sub.2 Co]OH
aqueous solution and silica, specifically Cab-O-Sil M-5 and stirring
until well mixed. The mole ratio of the reactants were:
H.sub.2 O/SiO.sub.2 =60
Na.sup.+ /SiO.sub.2 =0.1
OH.sup.- /SiO.sub.2 =0.2
[(CP*).sub.2 Co]/SiO.sub.2 =0.1
SiO.sub.2 /Al.sub.2 O.sub.3 =100
Crystallization of the aluminosilicate molecular sieve was carried
out at a temperature of 175.degree. C. in an unstirred, teflon-lined
autoclave, and was deemed to be complete after approximately 35
days. FIG. 2 shows the characteristic x-ray diffraction pattern
for this sample.
The off-yellow, as-synthesized form was treated as described in
Example 1. The average crystal size of this MCM-64 sample was about
1 micron.
COMPARATIVE EXAMPLE
An attempt was made to prepare an aluminosilicate molecular sieve
where the mole ratios of the reactants were the same as in Examples
1 and 2 except that the mole ratio of SiO.sub.2 /Al.sub.2 O.sub.3
was about 50. Crystallization of a molecular sieve was unsuccessful
after six weeks at 347.degree. C.
EXAMPLE 3
The aluminosilicate molecular sieve of Example 1 after calcination
and removal of sodium ions, was tested for activity. Specifically,
activity was confirmed in a test reaction with toluene. At 470.degree.
C., toluene conversion was 7.5% to benzene and a mixture of xylenes.
The presence of higher molecular weight compounds in the product
demonstrated the ability to convert toluene via disproportionation.
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