Molecular sieve abstract
The present invention relates to new crystalline molecular sieve
SSZ-70 prepared using a N,N'-diisopropyl imidazolium cation as a
structure-directing agent, methods for synthesizing SSZ-70 and processes
employing SSZ-70 in a catalyst.
Molecular sieve claims
What is claimed is:
1. A process for the reduction of oxides of nitrogen contained
in a gas stream wherein said process comprises contacting the gas
stream with a molecular sieve, the molecular sieve having a mole
ratio greater than about 15 of (1) silicon oxide to (2) an oxide
selected from aluminum oxide, gallium oxide, iron oxide, boron oxide,
titanium oxide, vanadium oxide and mixtures thereof and having,
after calcination, the X-ray diffraction lines of Table II.
2. The process of claim 1 conducted in the presence of oxygen.
3. The process of claim 1 wherein said molecular sieve contains
a metal or metal ions capable of catalyzing the reduction of the
oxides of nitrogen.
4. The process of claim 3 wherein the metal is cobalt, copper,
platinum, iron, chromium, manganese, nickel, zinc, lanthanum, palladium,
rhodium or mixtures thereof.
5. The process of claim 1 wherein the gas stream is the exhaust
stream of an internal combustion engine.
6. The process of claim 4 wherein the gas stream is the exhaust
stream of an internal combustion engine.
Molecular sieve description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to new crystalline molecular sieve
SSZ-70 a method for preparing SSZ-70 using a N,N'-diisopropyl imidazolium
cation as a structure directing agent and the use of SSZ-70 in catalysts
for the reduction of oxides of nitrogen in a gas stream.
2. State of the Art
Because of their unique sieving characteristics, as well as their
catalytic properties, crystalline molecular sieves and zeolites
are especially useful in applications such as hydrocarbon conversion,
gas drying and separation. Although many different crystalline molecular
sieves have been disclosed, there is a continuing need for new zeolites
with desirable properties for gas separation and drying, hydrocarbon
and chemical conversions, and other applications. New zeolites may
contain novel internal pore architectures, providing enhanced selectivities
in these processes.
Crystalline aluminosilicates are usually prepared from aqueous
reaction mixtures containing alkali or alkaline earth metal oxides,
silica, and alumina. Crystalline borosilicates are usually prepared
under similar reaction conditions except that boron is used in place
of aluminum. By varying the synthesis conditions and the composition
of the reaction mixture, different zeolites can often be formed.
SUMMARY OF THE INVENTION
The present invention is directed to a family of crystalline molecular
sieves with unique properties, referred to herein as "molecular
sieve SSZ-70" or simply "SSZ-70". Preferably, SSZ-70
is obtained in its silicate, aluminosilicate, titanosilicate, vanadosilicate
or borosilicate form. The term "silicate" refers to a
molecular sieve having a high mole ratio of silicon oxide relative
to aluminum oxide, preferably a mole ratio greater than 100 including
molecular sieves comprised entirely of silicon oxide. As used herein,
the term "aluminosilicate" refers to a molecular sieve
containing both aluminum oxide and silicon oxide and the term "borosilicate"
refers to a molecular sieve containing oxides of both boron and
silicon. It should be noted that the mole ratio of oxide (1) to
oxide (2) can be infinity, i.e., there is no oxide (2) in the molecular
sieve. In these cases, the molecular sieve is an essentially all-silica
In accordance with this invention, provided a process for the reduction
of oxides of nitrogen contained in a gas stream in the presence
of oxygen wherein said process comprises contacting the gas stream
with a molecular sieve, the molecular sieve having a mole ratio
greater than about 15 of (1) silicon oxide to (2) an oxide selected
from aluminum oxide, gallium oxide, iron oxide, boron oxide, titanium
oxide, vanadium oxide and mixtures thereof, and having, after calcination,
the X-ray diffraction lines of Table II. The molecular sieve may
contain a metal or metal ions (such as cobalt, copper, platinum,
iron, chromium, manganese, nickel, zinc, lanthanum, palladium, rhodium
or mixtures thereof) capable of catalyzing the reduction of the
oxides of nitrogen, and the process may be conducted in the presence
of a stoichiometric excess of oxygen. In a preferred embodiment,
the gas stream is the exhaust stream of an internal combustion engine.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an X-ray diffraction pattern of SSZ-70 after it has been
FIG. 2 is an X-ray diffraction pattern of SSZ-70 in the as-synthesized
form, i.e., prior to calcination with the SDA still in the pores
of the SSZ-70.
DETAILED DESCRIPTION OF THE INVENTION
The present invention comprises a family of crystalline molecular
sieves designated herein "molecular sieve SSZ-70" or simply
"SSZ-70". In preparing SSZ-70 a N,N'-diisopropyl imidazolium
cation (referred to herein as "DIPI") is used as a structure
directing agent ("SDA"), also known as a crystallization
template. The SDA useful for making SSZ-70 has the following structure:
The SDA cation is associated with an anion (X.sup.-) which may
be any anion that is not detrimental to the formation of the molecular
sieve. Representative anions include halogen, e.g., fluoride, chloride,
bromide and iodide, hydroxide, acetate, sulfate, tetrafluoroborate,
carboxylate, and the like. Hydroxide is the most preferred anion.
SSZ-70 is prepared from a reaction mixture having the composition
shown in Table A below.
TABLE-US-00001 TABLE A Reaction Mixture Typical Preferred YO.sub.2/B.sub.2O.sub.3
5 60 10 60 OH--/YO.sub.2 0.10 0.50 0.20 0.30 Q/YO.sub.2 0.05 0.50
0.10 0.20 M.sub.2/n/YO.sub.2 0 0.40 0.10 0.25 H.sub.2O/YO.sub.2
30 80 35 45 F/YO.sub.2 0 0.50 0
where Y is silicon; M is an alkali metal cation, alkaline earth
metal cation or mixtures thereof; n is the valence of M (i.e., 1
or 2); F is fluorine and Q is a N,N'-diisopropyl imidazolium cation.
In practice, SSZ-70 is prepared by a process comprising:
(a) preparing an aqueous solution containing sources of at least
two oxides capable of forming a crystalline molecular sieve and
a DIPI cation having an anionic counterion which is not detrimental
to the formation of SSZ-70;
(b) maintaining the aqueous solution under conditions sufficient
to form crystals of SSZ-70; and
(c) recovering the crystals of SSZ-70.
Accordingly, SSZ-70 may comprise the crystalline material and the
SDA in combination with metallic and non-metallic oxides bonded
in tetrahedral coordination through shared oxygen atoms to form
a cross-linked three dimensional crystal structure. Typical sources
of silicon oxide include silicates, silica hydrogel, silicic acid,
fumed silica, colloidal silica, tetra-alkyl orthosilicates, and
silica hydroxides. Boron can be added in forms corresponding to
its silicon counterpart, such as boric acid.
A source zeolite reagent may provide a source of boron. In most
cases, the source zeolite also provides a source of silica. The
source zeolite in its deboronated form may also be used as a source
of silica, with additional silicon added using, for example, the
conventional sources listed above. Use of a source zeolite reagent
for the present process is more completely described in U.S. Pat.
No. 5225179 issued Jul. 6 1993 to Nakagawa entitled "Method
of Making Molecular Sieves", the disclosure of which is incorporated
herein by reference.
Typically, an alkali metal hydroxide and/or an alkaline earth metal
hydroxide, such as the hydroxide of sodium, potassium, lithium,
cesium, rubidium, calcium, and magnesium, is used in the reaction
mixture; however, this component can be omitted so long as the equivalent
basicity is maintained. The SDA may be used to provide hydroxide
ion. Thus, it may be beneficial to ion exchange, for example, the
halide to hydroxide ion, thereby reducing or eliminating the alkali
metal hydroxide quantity required. The alkali metal cation or alkaline
earth cation may be part of the as-synthesized crystalline oxide
material, in order to balance valence electron charges therein.
The reaction may also be carried out using HF to counterbalance
the OH-contribution from the SDA, and run the synthesis in the absence
of alkali cations. Running in the absence of alkali cations has
the advantage of being able to prepare a catalyst from the synthesis
product, by using calcination alone, i.e., no ion-exchange step
(to remove alkali or alkaline earth cations) is necessary. In using
HF, the reaction operates best when both the SDA and HF have mole
ratios of 0.50 relative to YO.sub.2 (e.g., silica).
The reaction mixture is maintained at an elevated temperature until
the crystals of the SSZ-70 are formed. The hydrothermal crystallization
is usually conducted under autogenous pressure, at a temperature
between 100.degree. C. and 200.degree. C., preferably between 135.degree.
C. and 160.degree. C. The crystallization period is typically greater
than 1 day and preferably from about 3 days to about 20 days.
Preferably, the molecular sieve is prepared using mild stirring
During the hydrothermal crystallization step, the SSZ-70 crystals
can be allowed to nucleate spontaneously from the reaction mixture.
The use of SSZ-70 crystals as seed material can be advantageous
in decreasing the time necessary for complete crystallization to
occur. In addition, seeding can lead to an increased purity of the
product obtained by promoting the nucleation and/or formation of
SSZ-70 over any undesired phases. When used as seeds, SSZ-70 crystals
are added in an amount between 0.1 and 10% of the weight of first
tetravalent element oxide, e.g. silica, used in the reaction mixture.
Once the molecular sieve crystals have formed, the solid product
is separated from the reaction mixture by standard mechanical separation
techniques such as filtration. The crystals are water-washed and
then dried, e.g., at 90.degree. C. to 150.degree. C. for from 8
to 24 hours, to obtain the as-synthesized SSZ-70 crystals. The drying
step can be performed at atmospheric pressure or under vacuum.
SSZ-70 as prepared has a mole ratio of (1) silicon oxide to (2)
boron oxide greater than about 15; and has, after calcination, the
X-ray diffraction lines of Table II below. SSZ-70 further has a
composition, as synthesized (i.e., prior to removal of the SDA from
the SSZ-70) and in the anhydrous state, in terms of mole ratios,
shown in Table B below.
TABLE-US-00002 TABLE B As-Synthesized SSZ-70 YO.sub.2/B.sub.2O.sub.3
20 60 M.sub.2/n/YO.sub.2 0 0.03 Q/YO.sub.2 0.02 0.05 F/YO.sub.2
where Y, M, n and Q are as defined above.
SSZ-70 can be an essentially all-silica material. As used herein,
"essentially all-silica" means that the molecular sieve
is comprised of only silicon oxide or is comprised of silicon oxide
and only trace amounts of other oxides, such as aluminum oxide,
which may be introduced as impurities in the source of silicon oxide.
Thus, in a typical case where oxides of silicon and boron are used,
SSZ-70 can be made essentially boron free, i.e., having a silica
to boron oxide mole ratio of .infin.. SSZ-70 is made as a borosilicate
and then the boron can then be removed, if desired, by treating
the borosilicate SSZ-70 with acetic acid at elevated temperature
(as described in Jones et al., Chem. Mater., 2001 13 1041-1050)
to produce an essentially all-silica version of SSZ-70.
If desired, SSZ-70 can be made as a borosilicate and then the boron
can be removed as described above and replaced with metal atoms
by techniques known in the art. Aluminum, gallium, iron, titanium,
vanadium and mixtures thereof can be added in this manner.
It is believed that SSZ-70 is comprised of a new framework structure
or topology which is characterized by its X-ray diffraction pattern.
SSZ-70 as-synthesized, has a crystalline structure whose X-ray
powder diffraction pattern exhibit the characteristic lines shown
in Table I and is thereby distinguished from other molecular sieves.
TABLE-US-00003 TABLE I As-Synthesized SSZ-70 2 Theta.sup.(a) d-spacing
(Angstroms) Relative Intensity (%).sup.(b) 3.32 26.6 VS 6.70 13.2
VS 7.26 12.2 S 8.78 10.1 S 13.34 6.64 M 20.02 4.44 S 22.54 3.94
M 22.88 3.89 M 26.36 3.38 S-VS 26.88 3.32 M .sup.(a).+-. 0.15 .sup.(b)The
X-ray patterns provided are based on a relative intensity scale
in which the strongest line in the X-ray pattern is assigned a value
of 100: W(weak) is less than 20; M(medium) is between 20 and 40;
S(strong) is between 40 and 60; VS(very strong) is greater than
Table IA below shows the X-ray powder diffraction lines for as-synthesized
SSZ-70 including actual relative intensities.
TABLE-US-00004 TABLE IA 2 Theta.sup.(a) d-spacing (Angstroms) Relative
Intensity (%) 3.32 26.6 84 6.70 13.2 100 7.26 12.2 45 8.78 10.1
44 13.34 6.64 26 20.02 4.44 46 22.54 3.94 33 22.88 3.89 36 26.36
3.38 61 26.88 3.32 31 .sup.(a).+-. 0.15
After calcination, the SSZ-70 molecular sieves have a crystalline
structure whose X-ray powder diffraction pattern include the characteristic
lines shown in Table II:
TABLE-US-00005 TABLE II Calcined SSZ-70 2 Theta.sup.(a) d-spacing
(Angstroms) Relative Intensity (%) 7.31 12.1 VS 7.75 11.4 VS 9.25
9.6 VS 14.56 6.08 VS 15.61 5.68 S 19.60 4.53 S 21.81 4.07 M 22.24
4.00 M-S 26.30 3.39 VS 26.81 3.33 VS .sup.(a).+-. 0.15
Table IIA below shows the X-ray powder diffraction lines for calcined
SSZ-70 including actual relative intensities.
TABLE-US-00006 TABLE IIA 2 Theta.sup.(a) d-spacing (Angstroms)
Relative Intensity (%) 7.31 12.1 67 7.75 11.4 93 9.25 9.6 79 14.56
6.08 68 15.61 5.68 49 19.60 4.53 58 21.81 4.07 38 22.24 4.00 41
26.30 3.39 99 26.81 3.33 80 .sup.(a).+-. 0.15
The X-ray powder diffraction patterns were determined by standard
techniques. The radiation was the K-alpha/doublet of copper. The
peak heights and the positions, as a function of 2.theta. where
.theta. is the Bragg angle, were read from the relative intensities
of the peaks, and d, the interplanar spacing in Angstroms corresponding
to the recorded lines, can be calculated.
The variation in the scattering angle (two theta) measurements,
due to instrument error and to differences between individual samples,
is estimated at .+-.0.15 degrees.
The X-ray diffraction pattern of Table I is representative of "as-synthesized"
or "as-made" SSZ-70 molecular sieves. Minor variations
in the diffraction pattern can result from variations in the silica-to-boron
mole ratio of the particular sample due to changes in lattice constants.
In addition, sufficiently small crystals will affect the shape and
intensity of peaks, leading to significant peak broadening.
Representative peaks from the X-ray diffraction pattern of calcined
SSZ-70 are shown in Table II. Calcination can also result in changes
in the intensities of the peaks as compared to patterns of the "as-made"
material, as well as minor shifts in the diffraction pattern. The
molecular sieve produced by exchanging the metal or other cations
present in the molecular sieve with various other cations (such
as H.sup.+ or NH.sub.4.sup.+) yields essentially the same diffraction
pattern, although again, there may be minor shifts in the interplanar
spacing and variations in the relative intensities of the peaks.
Notwithstanding these minor perturbations, the basic crystal lattice
remains unchanged by these treatments.
Crystalline SSZ-70 can be used as-synthesized, but preferably will
be thermally treated (calcined). Usually, it is desirable to remove
the alkali metal cation by ion exchange and replace it with hydrogen,
ammonium, or any desired metal ion. The molecular sieve can be leached
with chelating agents, e.g., EDTA or dilute acid solutions, to increase
the silica to alumina mole ratio. The molecular sieve can also be
steamed; steaming helps stabilize the crystalline lattice to attack
The molecular sieve can be used in intimate combination with hydrogenating
components, such as tungsten, vanadium, molybdenum, rhenium, nickel,
cobalt, chromium, manganese, or a noble metal, such as palladium
or platinum, for those applications in which a hydrogenation-dehydrogenation
function is desired.
Metals may also be introduced into the molecular sieve by replacing
some of the cations in the molecular sieve with metal cations via
standard ion exchange techniques (see, for example, U.S. Pat. Nos.
3140249 issued Jul. 7 1964 to Plank et al.; U.S. Pat. No. 3140251
issued Jul. 7 1964 to Plank et al.; and U.S. Pat. No. 3140253
issued Jul. 7 1964 to Plank et al.). Typical replacing cations
can include metal cations, e.g., rare earth, Group IA, Group IIA
and Group VIII metals, as well as their mixtures. Of the replacing
metallic cations, cations of metals such as rare earth, Mn, Ca,
Mg, Zn, Cd, Pt, Pd, Ni, Co, Ti, Al, Sn, and Fe are particularly
The hydrogen, ammonium, and metal components can be ion-exchanged
into the SSZ-70. The SSZ-70 can also be impregnated with the metals,
or the metals can be physically and intimately admixed with the
SSZ-70 using standard methods known to the art.
Typical ion-exchange techniques involve contacting the synthetic
molecular sieve with a solution containing a salt of the desired
replacing cation or cations. Although a wide variety of salts can
be employed, chlorides and other halides, acetates, nitrates, and
sulfates are particularly preferred. The molecular sieve is usually
calcined prior to the ion-exchange procedure to remove the organic
matter present in the channels and on the surface, since this results
in a more effective ion exchange. Representative ion exchange techniques
are disclosed in a wide variety of patents including U.S. Pat. No.
3140249 issued on Jul. 7 1964 to Plank et al.; U.S. Pat. No.
3140251 issued on Jul. 7 1964 to Plank et al.; and U.S. Pat.
No. 3140253 issued on Jul. 7 1964 to Plank et al.
Following contact with the salt solution of the desired replacing
cation, the molecular sieve is typically washed with water and dried
at temperatures ranging from 65.degree. C. to about 200.degree.
C. After washing, the molecular sieve can be calcined in air or
inert gas at temperatures ranging from about 200.degree. C. to about
800.degree. C. for periods of time ranging from 1 to 48 hours, or
more, to produce a catalytically active product especially useful
in hydrocarbon conversion processes.
Regardless of the cations present in the synthesized form of SSZ-70
the spatial arrangement of the atoms which form the basic crystal
lattice of the molecular sieve remains essentially unchanged.
SSZ-70 can be formed into a wide variety of physical shapes. Generally
speaking, the molecular sieve can be in the form of a powder, a
granule, or a molded product, such as extrudate having a particle
size sufficient to pass through a 2-mesh (Tyler) screen and be retained
on a 400-mesh (Tyler) screen. In cases where the catalyst is molded,
such as by extrusion with an organic binder, the SSZ-70 can be extruded
before drying, or, dried or partially dried and then extruded.
SSZ-70 can be composited with other materials resistant to the
temperatures and other conditions employed in organic conversion
processes. Such matrix materials include active and inactive materials
and synthetic or naturally occurring zeolites as well as inorganic
materials such as clays, silica and metal oxides. Examples of such
materials and the manner in which they can be used are disclosed
in U.S. Pat. No. 4910006 issued May 20 1990 to Zones et al.,
and U.S. Pat. No. 5316753 issued May 31 1994 to Nakagawa, both
of which are incorporated by reference herein in their entirety.
SSZ-70 may be used for the catalytic reduction of the oxides of
nitrogen in a gas stream. Typically, the gas stream also contains
oxygen, often a stoichiometric excess thereof. Also, the SSZ-70
may contain a metal or metal ions within or on it which are capable
of catalyzing the reduction of the nitrogen oxides. Examples of
such metals or metal ions include cobalt, copper, platinum, iron,
chromium, manganese, nickel, zinc, lanthanum, palladium, rhodium
and mixtures thereof.
One example of such a process for the catalytic reduction of oxides
of nitrogen in the presence of a zeolite is disclosed in U.S. Pat.
No. 4297328 issued Oct. 27 1981 to Ritscher et al., which is
incorporated by reference herein. There, the catalytic process is
the combustion of carbon monoxide and hydrocarbons and the catalytic
reduction of the oxides of nitrogen contained in a gas stream, such
as the exhaust gas from an internal combustion engine. The zeolite
used is metal ion-exchanged, doped or loaded sufficiently so as
to provide an effective amount of catalytic copper metal or copper
ions within or on the zeolite. In addition, the process is conducted
in an excess of oxidant, e.g., oxygen.