Molecular sieve abstract
A boron-containing molecular sieve having the CHA crystal structure
and comprising (1) silicon oxide and (2) boron oxide or a combination
of boron oxide and aluminum oxide, iron oxide, titanium oxide, gallium
oxide and mixtures thereof is prepared using a quaternary ammonium
cation derived from 1-adamantamine, 3-quinuclidinol or 2-exo-aminonorbornane
as structure directing agent. The molecular sieve can be used for
minimizing cold start emissions from engines.
Molecular sieve claims
1. A process for treating a cold-start engine exhaust gas stream
containing hydrocarbons and other pollutants consisting of flowing
said engine exhaust gas stream over a molecular sieve bed which
preferentially adsorbs the hydrocarbons over water to provide a
first exhaust stream, and flowing the first exhaust gas stream over
a catalyst to convert any residual hydrocarbons and other pollutants
contained in the first exhaust gas stream to innocuous products
and provide a treated exhaust stream and discharging the treated
exhaust stream into the atmosphere, the molecular sieve bed characterized
in that it comprises a boron-containing molecular sieve having the
CHA crystal structure and comprising (1) silicon oxide and (2) boron
oxide or a combination of boron oxide and aluminum oxide, iron oxide,
titanium oxide, gallium oxide and mixtures thereof.
2. The process of claim 1 wherein oxide (2) is more than 50% boron
oxide on a molar basis.
3. The process of claim 1 wherein the oxides comprise silicon oxide
and boron oxide.
4. The process of claim 1 wherein the engine is an internal combustion
engine.
5. The process of claim 4 wherein the internal combustion engine
is an automobile engine.
6. The process of claim 1 wherein the engine is fueled by a hydrocarbonaceous
fuel.
7. The process of claim 1 wherein the molecular sieve has deposited
on it a metal selected from the group consisting of platinum, palladium,
rhodium, ruthenium, and mixtures thereof.
8. The process of claim 7 wherein the metal is platinum.
9. The process of claim 7 wherein the metal is palladium.
10. The process of claim 7 wherein the metal is a mixture of platinum
and palladium.
Molecular sieve description
[0001] This application claims the benefit under 35 USC 119 of
copending Provisional Application No. 60/632022 filed Nov. 30
2004.
BACKGROUND
[0002] Chabazite, which has the crystal structure designated "CHA",
is a natural zeolite with the approximate formula Ca.sub.6Al.sub.12Si.sub.24O.sub.72.
Synthetic forms of chabazite are described in "Zeolite Molecular
Sieves" by D. W. Breck, published in 1973 by John Wiley &
Sons. The synthetic forms reported by Breck are: zeolite "K-G",
described in J. Chem. Soc., p. 2822 (1956), Barrer et al.; zeolite
D, described in British Patent No. 868846 (1961); and zeolite R,
described in U.S. Pat. No. 3030181 issued Apr. 17 1962 to Milton
et al. Chabazite is also discussed in "Atlas of Zeolite Structure
Types" (1978) by W. H. Meier and D. H. Olson.
[0003] The K-G zeolite material reported in the J. Chem. Soc. Article
by Barrer et al. is a potassium form having a silica:alumina mole
ratio (referred to herein as "SAR") of 2.3:1 to 4.15:1.
Zeolite D reported in British Patent No. 868846 is a sodium-potassium
form having a SAR of 4.5:1 to 4.9:1. Zeolite R reported in U.S.
Pat. No. 3030181 is a sodium form which has a SAR of 3.45:1 to
3.65:1.
[0004] Citation No. 93:66052y in Volume 93 (1980) of Chemical Abstracts
concerns a Russian language article by Tsitsishrili et al. in Soobsch.
Akad. Nauk. Gruz. SSR 1980 97(3) 621-4. This article teaches that
the presence of tetramethylammonium ions in a reaction mixture containing
K.sub.2O--Na.sub.2O--SiO.sub.2--Al.sub.2O.sub.3--H.sub.2O promotes
the crystallization of chabazite. The zeolite obtained by the crystallization
procedure has a SAR of 4.23.
[0005] The molecular sieve designated SSZ-13 which has the CHA
crystal structure, is disclosed in U.S. Pat. No. 4544538 issued
Oct. 1 1985 to Zones. SSZ-13 is prepared from nitrogen-containing
cations derived from 1-adamantamine, 3-quinuclidinol and 2-exo-aminonorbornane.
Zones discloses that the SSZ-13 of U.S. Pat. No. 4544538 has a
composition, as-synthesized and in the anhydrous state, in terms
of mole ratios of oxides as follows:
[0006] (0.5 to 1.4)R.sub.2O:(0 to 0.5)M.sub.2O:W.sub.2O.sub.3:(greater
than 5)YO.sub.2
[0007] wherein M is an alkali metal cation, W is selected from
aluminum, gallium and mixtures thereof, Y is selected from silicon,
germanium and mixtures thereof, and R is an organic cation. U.S.
Pat. No. 4544538 does not, however, disclose boron-containing
SSZ-13.
[0008] U.S. Pat. No. 6709644 issued Mar. 23 2004 to Zones et
al., discloses zeolites having the CHA crystal structure and having
small crystallite sizes. It does not, however, disclose a CHA zeolite
containing boron. It is disclosed that the zeolite can be used for
separation of gasses (e.g., separating carbon dioxide from natural
gas), and in catalysts used for the reduction of oxides of nitrogen
in a gas stream (e.g., automotive exhaust), converting lower alcohols
and other oxygenated hydrocarbons to liquid products, and for producing
dimethylamine.
[0009] Gaseous waste products resulting from the combustion of
hydrocarbonaceous fuels, such as gasoline and fuel oils, comprise
carbon monoxide, hydrocarbons and nitrogen oxides as products of
combustion or incomplete combustion, and pose a serious health problem
with respect to pollution of the atmosphere. While exhaust gases
from other carbonaceous fuel-burning sources, such as stationary
engines, industrial furnaces, etc., contribute substantially to
air pollution, the exhaust gases from automotive engines are a principal
source of pollution. Because of these health problem concerns, the
Environmental Protection Agency (EPA) has promulgated strict controls
on the amounts of carbon monoxide, hydrocarbons and nitrogen oxides
which automobiles can emit. The implementation of these controls
has resulted in the use of catalytic converters to reduce the amount
of pollutants emitted from automobiles.
[0010] In order to achieve the simultaneous conversion of carbon
monoxide, hydrocarbon and nitrogen oxide pollutants, it has become
the practice to employ catalysts in conjunction with air-to-fuel
ratio control means which functions in response to a feedback signal
from an oxygen sensor in the engine exhaust system. Although these
three component control catalysts work quite well after they have
reached operating temperature of about 300.degree. C., at lower
temperatures they are not able to convert substantial amounts of
the pollutants. What this means is that when an engine and in particular
an automobile engine is started up, the three component control
catalyst is not able to convert the hydrocarbons and other pollutants
to innocuous compounds.
[0011] Adsorbent beds have been used to adsorb the hydrocarbons
during the cold start portion of the engine. Although the process
typically will be used with hydrocarbon fuels, the instant invention
can also be used to treat exhaust streams from alcohol fueled engines.
The adsorbent bed is typically placed immediately before the catalyst.
Thus, the exhaust stream is first flowed through the adsorbent bed
and then through the catalyst. The adsorbent bed preferentially
adsorbs hydrocarbons over water under the conditions present in
the exhaust stream. After a certain amount of time, the adsorbent
bed has reached a temperature (typically about 150.degree. C.) at
which the bed is no longer able to remove hydrocarbons from the
exhaust stream. That is, hydrocarbons are actually desorbed from
the adsorbent bed instead of being adsorbed. This regenerates the
adsorbent bed so that it can adsorb hydrocarbons during a subsequent
cold start.
[0012] The prior art reveals several references dealing with the
use of adsorbent beds to minimize hydrocarbon emissions during a
cold start engine operation. One such reference is U.S. Pat. No.
3699683 in which an adsorbent bed is placed after both a reducing
catalyst and an oxidizing catalyst. The patentees disclose that
when the exhaust gas stream is below 200.degree. C. the gas stream
is flowed through the reducing catalyst then through the oxidizing
catalyst and finally through the adsorbent bed, thereby adsorbing
hydrocarbons on the adsorbent bed. When the temperature goes above
200.degree. C. the gas stream which is discharged from the oxidation
catalyst is divided into a major and minor portion, the major portion
being discharged directly into the atmosphere and the minor portion
passing through the adsorbent bed whereby unburned hydrocarbon is
desorbed and then flowing the resulting minor portion of this exhaust
stream containing the desorbed unburned hydrocarbons into the engine
where they are burned.
[0013] Another reference is U.S. Pat. No. 2942932 which teaches
a process for oxidizing carbon monoxide and hydrocarbons which are
contained in exhaust gas streams. The process disclosed in this
patent consists of flowing an exhaust stream which is below 800.degree.
F. into an adsorption zone which adsorbs the carbon monoxide and
hydrocarbons and then passing the resultant stream from this adsorption
zone into an oxidation zone. When the temperature of the exhaust
gas stream reaches about 800.degree. F. the exhaust stream is no
longer passed through the adsorption zone but is passed directly
to the oxidation zone with the addition of excess air.
[0014] U.S. Pat. No. 5078979 issued Jan. 7 1992 to Dunne, which
is incorporated herein by reference in its entirety, discloses treating
an exhaust gas stream from an engine to prevent cold start emissions
using a molecular sieve adsorbent bed. Examples of the molecular
sieve include faujasites, clinoptilolites, mordenites, chabazite,
silicalite, zeolite Y, ultrastable zeolite Y, and ZSM-5.
[0015] Canadian Patent No. 1205980 discloses a method of reducing
exhaust emissions from an alcohol fueled automotive vehicle. This
method consists of directing the cool engine startup exhaust gas
through a bed of zeolite particles and then over an oxidation catalyst
and then the gas is discharged to the atmosphere. As the exhaust
gas stream warms up it is continuously passed over the adsorption
bed and then over the oxidation bed.
SUMMARY OF THE INVENTION
[0016] This invention generally relates to a process for treating
an engine exhaust stream and in particular to a process for minimizing
emissions during the cold start operation of an engine. Accordingly,
the present invention provides a process for treating a cold-start
engine exhaust gas stream containing hydrocarbons and other pollutants
consisting of flowing said engine exhaust gas stream over a molecular
sieve bed which preferentially adsorbs the hydrocarbons over water
to provide a first exhaust stream, and flowing the first exhaust
gas stream over a catalyst to convert any residual hydrocarbons
and other pollutants contained in the first exhaust gas stream to
innocuous products and provide a treated exhaust stream and discharging
the treated exhaust stream into the atmosphere, the molecular sieve
bed characterized in that it comprises a boron-containing molecular
sieve having the CHA crystal structure and comprising (1) silicon
oxide and (2) boron oxide or a combination of boron oxide and aluminum
oxide, iron oxide, titanium oxide, gallium oxide and mixtures thereof.
Preferably, oxide (2) is more than 50% boron oxide on a molar basis.
[0017] The present invention further provides such a process wherein
the engine is an internal combustion engine, including automobile
engines, which can be fueled by a hydrocarbonaceous fuel.
[0018] Also provided by the present invention is such a process
wherein the molecular sieve has deposited on it a metal selected
from the group consisting of platinum, palladium, rhodium, ruthenium,
and mixtures thereof.
DETAILED DESCRIPTION
[0019] As stated this invention generally relates to a process
for treating an engine exhaust stream and in particular to a process
for minimizing emissions during the cold start operation of an engine.
The engine consists of any internal or external combustion engine
which generates an exhaust gas stream containing noxious components
or pollutants including unburned or thermally degraded hydrocarbons
or similar organics. Other noxious components usually present in
the exhaust gas include nitrogen oxides and carbon monoxide. The
engine may be fueled by a hydrocarbonaceous fuel. As used in this
specification and in the appended claims, the term "hydrocarbonaceous
fuel" includes hydrocarbons, alcohols and mixtures thereof.
Examples of hydrocarbons which can be used to fuel the engine are
the mixtures of hydrocarbons which make up gasoline or diesel fuel.
The alcohols which may be used to fuel engines include ethanol and
methanol. Mixtures of alcohols and mixtures of alcohols and hydrocarbons
can also be used. The engine may be a jet engine, gas turbine, internal
combustion engine, such as an automobile, truck or bus engine, a
diesel engine or the like. The process of this invention is particularly
suited for hydrocarbon, alcohol, or hydrocarbon-alcohol mixture,
internal combustion engine mounted in an automobile. For convenience
the description will use hydrocarbon as the fuel to exemplify the
invention. The use of hydrocarbon in the subsequent description
is not to be construed as limiting the invention to hydrocarbon
fueled engines.
[0020] When the engine is started up, it produces a relatively
high concentration of hydrocarbons in the engine exhaust gas stream
as well as other pollutants. Pollutants will be used herein to collectively
refer to any unburned fuel components and combustion byproducts
found in the exhaust stream. For example, when the fuel is a hydrocarbon
fuel, hydrocarbons, nitrogen oxides, carbon monoxide and other combustion
byproducts will be found in the engine exhaust gas stream. The temperature
of this engine exhaust stream is relatively cool, generally below
500.degree. C. and typically in the range of 2000 to 400.degree.
C. This engine exhaust stream has the above characteristics during
the initial period of engine operation, typically for the first
30 to 120 seconds after startup of a cold engine. The engine exhaust
stream will typically contain, by volume, about 500 to 1000 ppm
hydrocarbons.
[0021] The engine exhaust gas stream which is to be treated is
flowed over a molecular sieve bed comprising the molecular sieve
of this invention to produce a first exhaust stream. The molecular
sieve is described below. The first exhaust stream which is discharged
from the molecular sieve bed is now flowed over a catalyst to convert
the pollutants contained in the first exhaust stream to innocuous
components and provide a treated exhaust stream which is discharged
into the atmosphere. It is understood that prior to discharge into
the atmosphere, the treated exhaust stream may be flowed through
a muffler or other sound reduction apparatus well known in the art.
[0022] The catalyst which is used to convert the pollutants to
innocuous components is usually referred to in the art as a three-component
control catalyst because it can simultaneously oxidize any residual
hydrocarbons present in the first exhaust stream to carbon dioxide
and water, oxidize any residual carbon monoxide to carbon dioxide
and reduce any residual nitric oxide to nitrogen and oxygen. In
some cases the catalyst may not be required to convert nitric oxide
to nitrogen and oxygen, e.g., when an alcohol is used as the fuel.
In this case the catalyst is called an oxidation catalyst. Because
of the relatively low temperature of the engine exhaust stream and
the first exhaust stream, this catalyst does not function at a very
high efficiency, thereby necessitating the molecular sieve bed.
[0023] When the molecular sieve bed reaches a sufficient temperature,
typically about 150-200.degree. C., the pollutants which are adsorbed
in the bed begin to desorb and are carried by the first exhaust
stream over the catalyst. At this point the catalyst has reached
its operating temperature and is therefore capable of fully converting
the pollutants to innocuous components.
[0024] The adsorbent bed used in the instant invention can be conveniently
employed in particulate form or the adsorbent can be deposited onto
a solid monolithic carrier. When particulate form is desired, the
adsorbent can be formed into shapes such as pills, pellets, granules,
rings, spheres, etc. In the employment of a monolithic form, it
is usually most convenient to employ the adsorbent as a thin film
or coating deposited on an inert carrier material which provides
the structural support for the adsorbent. The inert carrier material
can be any refractory material such as ceramic or metallic materials.
It is desirable that the carrier material be unreactive with the
adsorbent and not be degraded by the gas to which it is exposed.
Examples of suitable ceramic materials include sillimanite, petalite,
cordierite, mullite, zircon, zircon mullite, spondumene, alumina-titanate,
etc. Additionally, metallic materials which are within the scope
of this invention include metals and alloys as disclosed in U.S.
Pat. No. 3920583 which are oxidation resistant and are otherwise
capable of withstanding high temperatures.
[0025] The carrier material can best be utilized in any rigid unitary
configuration which provides a plurality of pores or channels extending
in the direction of gas flow. It is preferred that the configuration
be a honeycomb configuration. The honeycomb structure can be used
advantageously in either unitary form, or as an arrangement of multiple
modules. The honeycomb structure is usually oriented such that gas
flow is generally in the same direction as the cells or channels
of the honeycomb structure. For a more detailed discussion of monolithic
structures, refer to U.S. Pat. Nos. 3785998 and 3767453.
[0026] The molecular sieve is deposited onto the carrier by any
convenient way well known in the art. A preferred method involves
preparing a slurry using the molecular sieve and coating the monolithic
honeycomb carrier with the slurry. The slurry can be prepared by
means known in the art such as combining the appropriate amount
of the molecular sieve and a binder with water. This mixture is
then blended by using means such as sonification, milling, etc.
This slurry is used to coat a monolithic honeycomb by dipping the
honeycomb into the slurry, removing the excess slurry by draining
or blowing out the channels, and heating to about 100.degree. C.
If the desired loading of molecular sieve is not achieved, the above
process may be repeated as many times as required to achieve the
desired loading.
[0027] Instead of depositing the molecular sieve onto a monolithic
honeycomb structure, one can take the molecular sieve and form it
into a monolithic honeycomb structure by means known in the art.
[0028] The adsorbent may optionally contain one or more catalytic
metals dispersed thereon. The metals which can be dispersed on the
adsorbent are the noble metals which consist of platinum, palladium,
rhodium, ruthenium, and mixtures thereof. The desired noble metal
may be deposited onto the adsorbent, which acts as a support, in
any suitable manner well known in the art. One example of a method
of dispersing the noble metal onto the adsorbent support involves
impregnating the adsorbent support with an aqueous solution of a
decomposable compound of the desired noble metal or metals, drying
the adsorbent which has the noble metal compound dispersed on it
and then calcining in air at a temperature of about 400.degree.
to about 500.degree. C. for a time of about 1 to about 4 hours.
By decomposable compound is meant a compound which upon heating
in air gives the metal or metal oxide. Examples of the decomposable
compounds which can be used are set forth in U.S. Pat. No. 4791091
which is incorporated by reference. Preferred decomposable compounds
are chloroplatinic acid, rhodium trichloride, chloropalladic acid,
hexachloroiridate (IV) acid and hexachlororuthenate. It is preferable
that the noble metal be present in an amount ranging from about
0.01 to about 4 weight percent of the adsorbent support. Specifically,
in the case of platinum and palladium the range is 0.1 to 4 weight
percent, while in the case of rhodium and ruthenium the range is
from about 0.01 to 2 weight percent.
[0029] These catalytic metals are capable of oxidizing the hydrocarbon
and carbon monoxide and reducing the nitric oxide components to
innocuous products. Accordingly, the adsorbent bed can act both
as an adsorbent and as a catalyst.
[0030] The catalyst which is used in this invention is selected
from any three component control or oxidation catalyst well known
in the art. Examples of catalysts are those described in U.S. Pat.
Nos. 4528279; 4791091; 4760044; 4868148; and 4868149
which are all incorporated by reference. Preferred catalysts well
known in the art are those that contain platinum and rhodium and
optionally palladium, while oxidation catalysts usually do not contain
rhodium. Oxidation catalysts usually contain platinum and/or palladium
metal. These catalysts may also contain promoters and stabilizers
such as barium, cerium, lanthanum, nickel, and iron. The noble metals
promoters and stabilizers are usually deposited on a support such
as alumina, silica, titania, zirconia, aluminosilicates, and mixtures
thereof with alumina being preferred. The catalyst can be conveniently
employed in particulate form or the catalytic composite can be deposited
on a solid monolithic carrier with a monolithic carrier being preferred.
The particulate form and monolithic form of the catalyst are prepared
as described for the adsorbent above.
[0031] The molecular sieve used in the adsorbent bed comprises
a boron-containing molecular sieve having the CHA framework topology.
Boron-containing CHA molecular sieves can be suitably prepared from
an aqueous reaction mixture containing sources of sources of an
oxide of silicon; sources of boron oxide or a combination of boron
oxide and aluminum oxide, iron oxide, titanium oxide, gallium oxide
and mixtures thereof; optionally sources of an alkali metal or alkaline
earth metal oxide; and a cation derived from 1-adamantamine, 3-quinuclidinol
or 2-exo-aminonorbornane. The mixture should have a composition
in terms of mole ratios falling within the ranges shown in Table
A below: TABLE-US-00001 TABLE A YO.sub.2/W.sub.aO.sub.b .sup. >2-2000
OH--/YO.sub.2 0.2-0.45 Q/YO.sub.2 0.2-0.45 M.sub.2/nO/YO.sub.2 0-0.25
H.sub.2O/YO.sub.2 22-80
wherein Y is silicon; W is boron or a combination of boron and
aluminum, iron, titanium, gallium and mixtures thereof; M is an
alkali metal or alkaline earth metal; n is the valence of M (i.e.,
1 or 2) and Q is a quaternary ammonium cation derived from 1-adamantamine,
3-quinuclidinol or 2-exo-aminonorbornane (commonly known as a structure
directing agent or "SDA").
[0032] The quaternary ammonium cation derived from 1-adamantamine
can be a N,N,N-trialkyl-1-adamantammonium cation which has the formula:
where R.sup.1 R.sup.2 and R.sup.3 are each independently a lower
alkyl, for example methyl. The cation is associated with an anion,
A.sup.-, which is not detrimental to the formation of the molecular
sieve. Representative of such anions include halogens, such as fluoride,
chloride, bromide and iodide; hydroxide; acetate; sulfate and carboxylate.
Hydroxide is the preferred anion. It may be beneficial to ion exchange,
for example, a halide for hydroxide ion, thereby reducing or eliminating
the alkali metal or alkaline earth metal hydroxide required.
[0033] The quaternary ammonium cation derived from 3-quinuclidinol
can have the formula: where R.sup.1 R.sup.2 R.sup.3 and A are
as defined above.
[0034] The quaternary ammonium cation derived from 2-exo-aminonorbornane
can have the formula: where R.sup.1 R.sup.2 R.sup.3 and A are
as defined above.
[0035] The reaction mixture is prepared using standard molecular
sieve preparation techniques. Typical sources of silicon oxide include
fumed silica, silicates, silica hydrogel, silicic acid, colloidal
silica, tetra-alkyl orthosilicates, and silica hydroxides. Sources
of boron oxide include borosilicate glasses and other reactive boron
compounds. These include borates, boric acid and borate esters.
Typical sources of aluminum oxide include aluminates, alumina, hydrated
aluminum hydroxides, and aluminum compounds such as AlCl.sub.3 and
Al.sub.2(SO.sub.4).sub.3. Sources of other oxides are analogous
to those for silicon oxide, boron oxide and aluminum oxide.
[0036] It has been found that seeding the reaction mixture with
CHA crystals both directs and accelerates the crystallization, as
well as minimizing the formation of undesired contaminants. In order
to produce pure phase boron-containing CHA crystals, seeding may
be required. When seeds are used, they can be used in an amount
that is about 2-3 weight percent based on the weight of YO.sub.2.
[0037] The reaction mixture is maintained at an elevated temperature
until CHA crystals are formed. The temperatures during the hydrothermal
crystallization step are typically maintained from about 120.degree.
C. to about 160.degree. C. It has been found that a temperature
below 160.degree. C., e.g., about 120.degree. C. to about 140.degree.
C., is useful for producing boron-containing CHA crystals without
the formation of secondary crystal phases.
[0038] The crystallization period is typically greater than 1 day
and preferably from about 3 days to about 7 days. The hydrothermal
crystallization is conducted under pressure and usually in an autoclave
so that the reaction mixture is subject to autogenous pressure.
The reaction mixture can be stirred, such as by rotating the reaction
vessel, during crystallization.
[0039] Once the boron-containing CHA 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 crystals.
The drying step can be performed at atmospheric or subatmospheric
pressures.
[0040] The boron-containing CHA molecular sieve has a composition,
as-synthesized and in the anhydrous state, in terms of mole ratios
of oxides as indicated in Table B below:
[0041] As-Synthesized Boron-containing CHA Composition TABLE-US-00002
TABLE B YO.sub.2/W.sub.cO.sub.d 20-2000 M.sub.2/nO/YO.sub.2 0-0.03
Q/YO.sub.2 0.02-0.05
where Y, W, M, n and Q are as defined above.
[0042] The boron-containing CHA molecular sieves, as-synthesized,
have a crystalline structure whose X-ray powder diffraction ("XRD")
pattern shows the following characteristic lines: TABLE-US-00003
TABLE I As-Synthesized Boron-Containing CHA XRD 2 Theta.sup.(a)
d-spacing (Angstroms) Relative Intensity.sup.(b) 9.68 9.13 S 14.17
6.25 M 16.41 5.40 VS 17.94 4.94 M 21.13 4.20 VS 25.21 3.53 VS 26.61
3.35 W-M 31.11 2.87 M 31.42 2.84 M 31.59 2.83 M .sup.(a).+-.0.10
.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.
[0046] The X-ray powder diffraction patterns were determined by
standard techniques. The radiation was the K-alpha/doublet of copper
and a scintillation counter spectrometer with a strip-chart pen
recorder was used. The peak heights I and the positions, as a function
of 2 Theta where Theta is the Bragg angle, were read from the spectrometer
chart. From these measured values, the relative intensities, 100.times.l/lo,
where lo is the intensity of the strongest line or peak, and d,
the interplanar spacing in Angstroms corresponding to the recorded
lines, can be calculated.
[0047] Variations in the diffraction pattern can result from variations
in the mole ratio of oxides from sample to sample. The molecular
sieve produced by exchanging the metal or other cations present
in the molecular sieve with various other cations yields a similar
diffraction pattern, although there can be shifts in interplanar
spacing as well as variations in relative intensity. Calcination
can also cause shifts in the X-ray diffraction pattern. Also, the
symmetry can change based on the relative amounts of boron and aluminum
in the crystal structure. Notwithstanding these perturbations, the
basic crystal lattice structure remains unchanged.
[0048] Boron-containing CHA molecular sieves are useful in adsorption,
in catalysts useful in converting methanol to olefins, synthesis
of amines (such as dimethylamine), in the reduction of oxides of
nitrogen in gasses (such as automobile exhaust), and in gas separation.
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