Molecular sieve abstract
The present invention relates to new molecular sieve SSZ-71 prepared
using a N-benzyl-14-diazabicyclo[2.2.2]octane cation as a structure-directing
agent, methods for synthesizing SSZ-71 and processes employing SSZ-71
in a catalyst.
Molecular sieve claims
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 produced by the method comprising:
(1) preparing an as-synthesized molecular sieve having a composition,
as synthesized and in the anhydrous state, in terms of mole ratios
as follows: TABLE-US-00017 YO.sub.2/WO.sub.d 15-.infin. M.sub.2/n/YO.sub.2
0-0.03 Q/YO.sub.2 0.02-0.05
wherein Y is silicon, germanium or a mixture thereof; W is zinc,
titanium or mixtures thereof; d is 1 or 2 (i.e., d is 1 when W is
divalent or 2 when W is tetravalent); M is an alkali metal cation,
alkaline earth metal cation or mixtures thereof; n is the valence
of M (i.e., 1 or 2); and Q is a N-benzyl-14-diazabicyclo[2.2.2]octane
cation, the as-synthesized molecular sieve having the X-ray diffraction
lines of Table I; (2) thermally treating the as-synthesized molecular
sieve at a temperature and for a time sufficient to remove the N-benzyl-14-diazabicyclo[2.2.2]octane
cation from the molecular sieve; and (3) optionally, replacing at
least part of the zinc and/or titanium with a metal selected from
the group consisting of aluminum, gallium, iron, boron, indium,
vanadium and mixtures thereof.
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.
Molecular sieve description
[0001] This application claims the benefit under 35 USC 119 of
Provisional Application No. 60/639211 filed Dec. 23 2004.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to new molecular sieve SSZ-71
a method for preparing SSZ-71 using a N-benzyl-14-diazabicyclo[2.2.2]octane
cation as a structure directing agent and the use of SSZ-71 in catalysts
for, e.g., hydrocarbon conversion reactions.
[0004] 2. State of the Art
[0005] 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.
[0006] 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
[0007] The present invention is directed to a family of molecular
sieves with unique properties, referred to herein as "molecular
sieve SSZ-71" or simply "SSZ-71". Preferably, SSZ-71
is in its silicate, zincosilicate, aluminosilicate, titanosilicate,
germanosilicate, vanadosilicate, ferrosilicate 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 "zincosilicate"
refers to a molecular sieve containing both zinc oxide and silicon
oxide. 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.
[0008] In accordance with this invention, there is provided 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 produced by the method comprising:
[0009] (1) preparing an as-synthesized molecular sieve having a
composition, as synthesized and in the anhydrous state, in terms
of mole ratios as follows: TABLE-US-00001 YO.sub.2/WO.sub.d 15-.infin.
M.sub.2/n/YO.sub.2 0-0.03 Q/YO.sub.2 0.02-0.05
[0010] wherein Y is silicon, germanium or a mixture thereof; W
is zinc, titanium or mixtures thereof; d is 1 or 2 (i.e., d is 1
when W is divalent or 2 when W is tetravalent); M is an alkali metal
cation, alkaline earth metal cation or mixtures thereof; n is the
valence of M (i.e., 1 or 2); and Q is a N-benzyl-14-diazabicyclo[2.2.2]octane
cation, the as-synthesized molecular sieve having the X-ray diffraction
lines of Table I; [0011] (2) thermally treating the as-synthesized
molecular sieve at a temperature and for a time sufficient to remove
the N-benzyl-14-diazabicyclo[2.2.2]octane cation from the molecular
sieve; and [0012] (3) optionally, replacing at least part of the
zinc and/or titanium with a metal selected from the group consisting
of aluminum, gallium, iron, boron, indium, vanadium and mixtures
thereof.
[0013] 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.
DETAILED DESCRIPTION OF THE INVENTION
[0014] The present invention comprises a family of molecular sieves
designated herein "molecular sieve SSZ-71" or simply "SSZ-71".
In preparing SSZ-71 a N-benzyl-14-diazabicyclo[2.2.2]octane cation
(referred to herein as "benzyl DABCO") is used as a structure
directing agent ("SDA"), also known as a crystallization
template. The SDA useful for making SSZ-71 has the following structure:
[0015] 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.
[0016] Benzyl DABCO and a method for making it are disclosed in
U.S. Pat. No. 5653956 issued Aug. 5 1997 to Zones.
[0017] SSZ-71 is prepared from a reaction mixture having the composition
shown in Table A below. TABLE-US-00002 TABLE A Reaction Mixture
Typical Preferred YO.sub.2/WO.sub.d >15 >30 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 10-80 15-45
where Y is silicon, germanium or a mixture thereof; W is zinc,
titanium or mixtures thereof; d is 1 or 2 (i.e., d is 1 when W is
divalent or 2 when W is tetravalent); M is an alkali metal cation,
alkaline earth metal cation or mixtures thereof; n is the valence
of M (i.e., 1 or 2); and Q is a N-benzyl-14-diazabicyclo[2.2.2]octane
cation.
[0018] In practice, SSZ-71 is prepared by a process comprising:
[0019] (a) preparing an aqueous solution containing sources of at
least one oxide capable of forming a molecular sieve and a benzyl
DABCO cation having an anionic counterion which is not detrimental
to the formation of SSZ-71; [0020] (b) maintaining the aqueous solution
under conditions sufficient to form SSZ-71; and [0021] (c) recovering
the SSZ-71.
[0022] SSZ-71 can be prepared as a zincosilicate or titanosilicate.
However, once the SSZ-71 is made, the zinc and/or titanium can be
replaced with other metals by techniques well known in the art.
Accordingly, SSZ-71 may comprise the molecular sieve 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. The metallic and non-metallic
oxides comprise one or a combination of oxides of (1) a first tetravalent
element(s), and (2) one or a combination of a divalent element(s),
trivalent element(s), pentavalent element(s), second tetravalent
element(s) different from the first tetravalent element(s) or mixture
thereof. The first tetravalent element(s) is preferably selected
from the group consisting of silicon, germanium and combinations
thereof. More preferably, the first tetravalent element is silicon.
The divalent element, trivalent element, pentavalent element and
second tetravalent element (which is different from the first tetravalent
element) is preferably selected from the group consisting of zinc,
aluminum, gallium, iron, boron, titanium, indium, vanadium and combinations
thereof. More preferably, the divalent or trivalent element or second
tetravalent element is zinc, aluminum, titanium or boron.
[0023] Silicon can be added as silicon oxide or Si(OC.sub.2H.sub.5).sub.4.
Zinc can be added as a zinc salt such as zinc acetate. Titanium
can be added as Ti(OC.sub.2H.sub.5).sub.4.
[0024] A source zeolite reagent may provide a source of metals.
In most cases, the source zeolite also provides a source of silica.
The source zeolite 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 is 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.
[0025] Typically, an alkali metal hydroxide and/or an alkaline
earth metal hydroxide, such as the hydroxide of sodium, potassium,
lithium, cesium, rubidium, calcium, strontium, barium 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 material, in order to balance valence electron
charges therein.
[0026] The reaction mixture is maintained at an elevated temperature
until the crystals of the SSZ-71 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.
[0027] Optionally, the molecular sieve is prepared using mild stirring
or agitation.
[0028] During the hydrothermal crystallization step, the SSZ-71
crystals can be allowed to nucleate spontaneously from the reaction
mixture. The use of SSZ-71 or SSZ-42 (disclosed in U.S. Pat. No.
5653956 issued Aug. 5 1997 to Zones) 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-71 over any undesired phases. When used as seeds,
as-synthesized SSZ-71 or SSZ-42 crystals (containing the SDA) 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.
[0029] 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-71 crystals. The
drying step can be performed at atmospheric pressure or under vacuum.
[0030] SSZ-71 as prepared has a mole ratio of an oxide selected
from silicon oxide, germanium oxide and mixtures thereof to an oxide
selected from zinc oxide, titanium oxide and mixtures thereof greater
than about 15. SSZ-71 further has a composition, as synthesized
(i.e., prior to calcination of the SSZ-71) and in the anhydrous
state, in terms of mole ratios, shown in Table B below. TABLE-US-00003
TABLE B As-Synthesized SSZ-71 YO.sub.2/WO.sub.d >15 M.sub.2/n/YO.sub.2
0-0.03 Q/YO.sub.2 0.02-0.05
where Y, W, d, M, n and Q are as defined above.
[0031] SSZ-71 can be made with a mole ratio of YO.sub.2/WO.sub.d
of 00 i.e., there is essentially no WO.sub.d present in the SSZ-71.
In this case, the SSZ-71 would be an all-silica material or a germanosilicate.
If SSZ-71 is prepared as a zincosilicate, the zinc can be removed
and replaced with metal atoms by techniques known in the art. See,
for example, U.S. Pat. No. 6117411 issued Sep. 12 2000 to Takewaki
et al. Metals such as aluminum, gallium, iron, boron, titanium,
indium, vanadium and mixtures thereof may be added in this manner.
[0032] It is believed that SSZ-71 is comprised of a new framework
structure or topology which is characterized by its X-ray diffraction
pattern. SSZ-71 as-synthesized, has a structure whose X-ray powder
diffraction pattern exhibit the characteristic lines shown in Table
I and Table II and is thereby distinguished from other molecular
sieves. The XRD data shown in Table I and IA was obtained from a
sample of SSZ-71 prepared in the presence of sodium hydroxide. The
XRD data shown in Table II and IIA was obtained from a sample of
SSZ-71 prepared in the presence of strontium hydroxide. TABLE-US-00004
TABLE I As-Synthesized Zn-SSZ-71 Prepared with NaOH 2 Theta.sup.(a)
d-spacing (Angstroms) Relative Intensity.sup.(b) 5.64 15.7 S 8.65
10.2 S 13.65 6.49 M 17.06 5.20 M 20.32 4.37 M 20.64 4.30 VS 23.12
3.85 M 24.08 3.70 VS 26.15 3.41 M 26.57 3.35 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 60.
[0033] Table IA below shows the X-ray powder diffraction lines
for as-synthesized Zn-SSZ-71 prepared with NaOH including actual
relative intensities. TABLE-US-00005 TABLE IA 2 Theta.sup.(a) d-spacing
(Angstroms) Relative Intensity (%) 5.64 15.7 60 8.65 10.2 57 11.40
7.8 5 11.95 7.4 7 13.11 6.75 7 13.65 6.49 21 14.34 6.18 5 17.06
5.20 29 17.84 4.97 4 18.23 4.87 10 18.84 4.71 12 19.49 4.55 18 20.32
4.37 37 20.64 4.30 100 21.55 4.12 16 22.03 4.03 16 23.12 3.85 34
24.08 3.70 62 25.29 3.52 20 25.52 3.49 20 26.15 3.41 29 26.57 3.35
33 27.15 3.28 9 28.55 3.13 18 30.00 2.98 8 30.80 2.90 5 31.68 2.82
10 32.45 2.76 5 33.16 2.70 7 34.92 2.57 11 35.61 2.52 14 36.90 2.44
12 38.82 2.32 14 40.26 2.24 12 .sup.(a).+-.0.15
[0034] TABLE-US-00006 TABLE II As-Synthesized Zn-SSZ-71 prepared
with Sr(OH).sub.2 2 Theta.sup.(a) d-spacing (Angstroms) Relative
Intensity.sup.(b) 5.65 15.6 VS 8.69 10.2 VS 16.99 5.22 S 19.52 4.55
M 20.60 4.31 VS 23.13 3.85 M 24.01 3.71 S 24.23 3.67 M 26.14 3.41
M 26.52 3.36 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 60.
[0035] Table IIA below shows the X-ray powder diffraction lines
for as-synthesized SSZ-71 (Zn-SSZ-71 prepared with Sr(OH).sub.2)
including actual relative intensities. TABLE-US-00007 TABLE IIA
2 Theta.sup.(a) d-spacing (Angstroms) Relative Intensity (%) 5.65
15.6 84 8.69 10.2 67 11.36 7.8 5 11.94 7.4 5 13.17 6.7 7 13.68 6.5
20 14.34 6.18 6 15.31 5.79 2 16.99 5.22 42 18.24 4.86 8 18.79 4.72
17 19.52 4.55 26 20.34 4.37 23 20.60 4.31 100 21.59 4.12 13 22.06
4.03 16 23.13 3.85 37 24.01 3.71 41 24.23 3.67 25 25.25 3.53 20
25.52 3.49 23 26.14 3.41 36 26.52 3.36 30 27.10 3.29 12 28.52 3.13
22 29.85 2.99 6 30.24 2.96 2 30.84 2.90 3 31.64 2.83 11 32.44 2.76
5 33.11 2.71 5 34.86 2.57 6 35.63 2.52 14 36.10 2.49 6 .sup.(a).+-.0.15
[0036] 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.
[0037] 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.
[0038] The X-ray diffraction pattern of Table I is representative
of "as-synthesized" or "as-made" SSZ-71 molecular
sieves. Minor variations in the diffraction pattern can result from
variations in the silica-to-zinc or silica-to-titanium 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.
[0039] 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.
[0040] SSZ-71 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 also
be steamed; steaming helps stabilize the molecular sieve to attack
from acids.
[0041] 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.
[0042] 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. No. 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 preferred.
[0043] The hydrogen, ammonium, and metal components can be ion-exchanged
into the SSZ-71. The SSZ-71 can also be impregnated with the metals,
or the metals can be physically and intimately admixed with the
SSZ-71 using standard methods known to the art.
[0044] 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.
[0045] 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.
[0046] Regardless of the cations present in the synthesized form
of SSZ-71 the spatial arrangement of the atoms which form the basic
crystal lattice of the molecular sieve remains essentially unchanged.
[0047] SSZ-71 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-71 can be extruded before drying, or, dried or partially
dried and then extruded.
[0048] SSZ-71 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.
[0049] SSZ-71 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-71
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.
[0050] 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.
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