U.S. patent number RE34,853 [Application Number 07/594,076] was granted by the patent office on 1995-02-07 for preparation of monolithic catalyst supports having an integrated high surface area phase.
This patent grant is currently assigned to Corning Incorporated. Invention is credited to Thomas P. DeAngelis, Irwin M. Lachman.
United States Patent |
RE34,853 |
DeAngelis , et al. |
February 7, 1995 |
Preparation of monolithic catalyst supports having an integrated
high surface area phase
Abstract
A method of preparing a monolithic catalyst support having an
integrated high surface area phase is provided. A plasticized batch
of ceramic matrix material intimately mixed with high surface area
powder is formed into the desired shape for the monolith and then
heated to sinter the ceramic. The resulting monolith has a strong
substrate of the ceramic matrix material and a high surface area
phase provided by the high surface area powder extruded with the
batch.
Inventors: |
DeAngelis; Thomas P. (East
Amherst, NY), Lachman; Irwin M. (Corning, NY) |
Assignee: |
Corning Incorporated (Corning,
NY)
|
Family
ID: |
24863952 |
Appl.
No.: |
07/594,076 |
Filed: |
October 9, 1990 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
712885 |
Mar 18, 1985 |
04637995 |
Jan 20, 1987 |
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Current U.S.
Class: |
502/439; 502/64;
502/355; 502/524; 502/351; 502/263; 502/527.19 |
Current CPC
Class: |
B01J
37/08 (20130101); B01J 37/0009 (20130101); Y10S
502/524 (20130101) |
Current International
Class: |
B01J
37/08 (20060101); B01J 37/00 (20060101); B01J
020/28 (); B01J 035/00 () |
Field of
Search: |
;502/527,439,64,263,351,355,524 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1442653 |
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Aug 1969 |
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DE |
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111843 |
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Aug 1980 |
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JP |
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1064018 |
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Apr 1967 |
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GB |
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1142800 |
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Feb 1969 |
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GB |
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1315553 |
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Mar 1973 |
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GB |
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Primary Examiner: Dees; Carl F.
Attorney, Agent or Firm: van der Sterre; Kees
Claims
We claim:
1. A method of preparing a monolithic catalyst support which
comprises:
(a) providing a substantially homogeneous body comprising an
admixture of
(i) a first phase sinterable ceramic matrix material, in
particulate form finer than 200 mesh, selected from the group
consisting of cordierite, mullite, alpha-alumina, lithium
aluminosilicate, and mixtures of these, and
(ii) a second phase high surface area catalyst-support material
having a crystalline size no larger than 0.2 microns and a surface
area of at least 40 m.sup.2 /g, said catalys-support material
consisting of transition metal sulfide; a mixture of transition
metal sulfides; porous oxide selected from the group consisting of
.[.alumina,.]. zirconia, spinel, silica, zeolite, titania,
.[.and.]. mixtures of these.Iadd., and mixtures of the preceeding
with alumina; .Iaddend.or a mixture of said sulfide and said oxide
materials;
(b) forming the resultant body into a desired shape; and
(c) heating the shaped body at a temperature sufficient to sinter
the first phase matrix material.
2. A method of claim 1 in which mixing step (a) is performed using
50-90 parts by weight of the first phase material and 10-50 parts
by weight of the second phase material.
3. A method of claim 2 in which mixing step (a) is performed using
1-30 part by weight of a binder material.
4. A method of claim 3 in which the second phase material has a
surface area of at least 100 m.sup.2 /g and is selected from the
group consisting of .[.alumina,.]. silica, zeolite, .[.and.].
mixtures of these.Iadd., and mixtures of the preceeding with
alumina.
5. A method of claim 4 in which .[.the second phase material is
alumina, and.]. the binder is methyl cellulose, a silicone resin,
or mixtures of these.
6. A method of claim 4 in which the second phase material is silica
and the binder is methyl cellulose, a silicone resin, or mixture of
these.
7. A method of claim 4 in which the second phase material is a
mixture of silica and alumina and the binder is methyl cellulose, a
silicone resin, or mixtures of these.
8. A method of claim 4 in which the second phase material is a
zeolite and the binder is methyl cellulose, a silicone resin, or
mixture of these.
9. A method of claim 3 in which the second phase material is
titania and the binder is methyl cellulose, a silicone resin, or
mixtures of these.
10. A method of claim 3 in which the second phase material is a
spinel and the binder is methyl cellulose, a silicone resin, or
mixtures of these.
11. A method of claim 3 in which the second phase material is
zirconia or a transition metal sulfide.
12. A method of claim 5, 6, 7, 8, 9, or 10 in which the first phase
sinterable material is cordierite or mullite.
13. A method of claim 5, 6, 7, 8, 9, or 10 in which the first phase
sinterable material is alpha-alumina.
14. A monolithic catalyst support prepared by the method of claim
1.
15. A monolithic catalyst support prepared by the method of claim
12.
16. A monolithic catalyst support prepared by the method of claim
13.
17. A monlithic catalyst support comprising 50-90 parts by weight
of a sintered ceramic matrix material and 10-50 parts per weight of
a high surface area catalyst-support material dispersed throughout
the matrix wherein
(a) the ceramic matrix material consists of cordierite, mullite,
alpha-alumina, lithium aluminosilicate, or mixtures of these;
and
(b) the dispersed catalyst-support material has a surface area of
at least 40 m.sup.2 /g and a crystallite size no larger than about
0.5 microns, and the catalyst-support material consists of
transition metal sulfide; a mixture of transition metal sulfides;
porous oxide selected from the group consisting of .[.alumina,.].
zirconia, spinel, silica, zeolite, titania, .[.and.]. mixtures of
these.Iadd., and mixtures of the preceeding with alumina.Iaddend.;
or a mixture of said sulfide and said oxide materials.
18. A monolithic catalyst support of claim 17 wherein the dispersed
catalyst-support material has a surface area of at least 100
m.sup.2 /g and is .[.alumina,.]. silica, zeolite, .[.or.]. mixture
of these.[...]. .Iadd., or mixtures of the preceeding with alumina.
.Iaddend. .[.19. A monolithic catalyst support of claim 18 wherein
the dispersed
catalyst-support material is a transition alumina..]. 20. A
monolthic catalyst suppport of claim 18 wherein the dispersed
catalyst-support
material is silica. 21. A monolithic catalyst support of claim 17
wherein
the dispersed catalyst-support material is a spinel. 22. A
monlithic catalyst support of claim 17, 18, .[.19,.]. 20, or 21 in
which the ceramic
matrix material is cordierite or mullite. 23. A monolithic
catalyst
support of claim 22 having a surface area of at least 5 m.sup.2 /g.
24. A method of claim 1 in which the second phase material is
.[.alumina,.]. spinel, or a mixture of alumina and silica; and in
which the admixture further comprises up to 20 percent by weight,
based on the weight of the
second phase material, or rare earth oxide. 25. A monolithic
catalyst support of claim 17 wherein the dispersed catalyst-support
material is .[.alumina,.]. spinel, or a mixture of alumina and
silica; and wherein the monolithic catalyst support further
comprises up to 20 percent by weight, based on the weight of the
dispersed catalyst-support material, of rare earth oxide.
Description
BACKGROUND OF THE INVENTION
This invention is directed to monolithic ceramic catalyst supports
and particularly to supports which contain a high surface area
phase incorporated within the ceramic matrix itself.
It conventional ceramic monlithic catalyst consists of a ceramic
support with a coating of high surface material upon which the
catalyst is actually deposited. In particular, the ceramic support
is normally prepared by sintering a mold of clay or other ceramic
material at a high temperature to impart density and strength. This
procedure normally results in a very small surface area, and
consequently the ceramic must be coated with an other material
having a higher surface area, as well as specific chemical
characteristics on which to actually deposit the catalyst. This
procedure of depositing a high surface area "wash coat" on the low
surface area ceramic wall is disclosed, for example, in U.S. Pat.
Nos. 2,742,437 and 3,824,196.
Catalyst supports of this kind suffer from several disadvantages.
In service, the supports are exposed to a flow of gases which often
contain dusts or particulate matter, which can cause the high
surface area coating to flake off the underlying ceramic support.
This phenomenon can also occur where the support is exposed to
thermal cycling becuase the wash coat and the underlying ceramic
material often have different thermal expansion coefficients.
Furthermore, catalysts deposited on the high surface area wash coat
are susceptible to poisoning, such as by lead or phosphorous in
service in automobile converters, and therefore must be
periodically regenerated or replaced.
U.S. Pat. No. 4,294,806 discloses the preparation of monolithic
supports by extrusion of an alumina ceramic material into the shape
of a honeycomb, calcining the material, and then sintering only the
front portion. This procedure is said to make the support more
abrasion resistant. However, the bulk of the support remains
unsintered, so that even thourgh it retains high surface area, the
support would lack high strength. U.S. Pat. No. 4,151,121 discloses
the preparation of a catalyst by dispersing zeolite and a high
surface area alumina (on which a catalytic metal is supported) in a
hydrogel of a porous oxide matrix material (such as alumina, clay,
silica-alumina composites, and the like) to form a composite
mixture. The composite is spray dried, washed free of salts, and
then flash dried. Ths method produces catalyst materials in which
the high surface material is embedded within a matrix, and thereby
somewhat protected from abrasion or poisoning. However, the method
is not suitable for the preparation of catalyst support structures
that are in monolithic form, the kind normally used in the services
where these problems are most prevalent or most severe. British
Pat. No. 1,064,018 discloses tubular catalyst supports prepared by
forming a paste of alpha-alumina, active alumina, and hydrargillite
(a high surface area alumina trihydrate), extruding the paste to
form tubular elements, and firing the elements.
It is an object of the present invention to provide a monolithic
support having a high surface area which is not easily abraded and
which supports catalysts in a manner that resists poisoning. It is
a further object of the invention to provide a monolithic support
which has good mechanical properties while retaining the porosity
and high surface area necessary for proper catalytic functioning
These and other objects are met by the invention to be
described.
SUMMARY OF THE INVENTION
The present invention provides a method of preparing a monolithic
ceramic support for a catalyst, which support has a high surface
area phase intimately mixed with, and incorporated into, the
ceramic material itself. The method comprises providing a
substantially homogenous body comprising an admixture of (i) a
ceramic matrix material, in particulate from finer than 200 mesh,
selected from cordierite, mullite, alpha-alumina, lithium
aluminosilicate, and mixtures of these, and (ii) a high surface
area support material having a crystallite size no larger than 0.2
microns and a surface area of at least 40 m.sup.2 /g. The support
material may comprise .[.a catalyst-support oxide (e.g. alumina,
zirconia, silica, spinel, titania, zeolite), a transition metal
sulfide, or mixtures of these..]. .Iadd.transition metal sulfide; a
mixture of transition metal sulfides; porous oxide selected from
the group consisting of zirconia, spinel, silica, zeolite, titania,
mixtures of these and mixtures of the preceeding with alumina; or a
mxiture of said sulfide and said oxide materials. .Iaddend.
The mixed body is formed into a desired shape and then heated to
sinter the ceramic matrix material.
The monolithic support prepared in this manner comprises a ceramic
matrix, as a first phase, sintered to a desirable level of
strength, and a second high surface area phase well dispersed
within the ceramic matrix on which to actually support catalyst. It
has been recognized that ceramic, although sintered, is itself
porous and that the high surface area material, even though within
the walls of the ceramic, is accessible to the target gas stream
and provides suitable surface area and extended catalyst life. The
embedded high surface area material, upon which catalytically
active materials are deposited, is protected from abrasion, and it
is thought that the ceramic acts as a filter, by reaction or
adsorption, to eliminate poisons before they can contact and
adversely affect the catalyst itself. Another advantage of the
monolithic supports of this invention, compared to those heretofore
used, is the lower weight attributable to replacement of the denser
ceramic material with the lighter high surface area phase and the
elimination of the conventional washcoat. In those applications
requiring the catalyst to be thermally activated and to function
quiclky, such as in automotive catalyic convertors, the reduced
thermal mass in the present monolith permits the " light off"
temperature to be reached quickly.
DETAILED DESCRIPTION OF THE INVENTION
In the method of the present invention, a sinterable, ceramic
matrix material and a high surface area material are combined into
a single plasticized batch which is formed into a desired shape for
the monolithic support. In this manner, the high surface area phase
is incorporated into the monolith itself, eliminating the
heretofore required step of coating a pre-formed sintered ceramic,
which itself normally has low porosity and surface area, with an
additional high surface area substance on which catalyst is
actually supported. Accordingly, the present invention provides a
monolithic support having strength, due to the sintered ceramic
phase, and available surface area, due to the embedded high surface
area materials.
The high surface area materials suitable for use in the present
invention are porous oxides and transition metal sulfides,
generally in fine powder form, havig a crystallite size of 0.2
microns or smaller and a surface area of at least 40 square meters
per gram of weight (m.sup.2 /g), preferably at least 100 m.sup.2
/g, and most preferably at least 200 m.sup.2 g. This surface area
may be present in the material naturally or may manifest itself
after calcining. The practice of this invention contemplates either
case. (As used herein, "Calcining" means heating a material to a
temperature below that at which the material begins to shrink or
sinter.) With respect to the oxides, they are preferably
.[.alumina.]. silica, a spinel, titania, zircomia, or a zeolite.
Mixtures of the oxides can also be used. The invention is not
limited to these particular oxides, however, and as those skilled
in the art will recognize, the invention contemplates the use of
other materials which are commonly used as catalyst supports and
which have the above-described characteristics.
The aluminas useful.[.as.]. .Iadd.in .Iaddend.the high surface are
a material of this invention are those which, before or upon
calcining, provide gamma-alumina or other transition aluminas
having the specified crystallite size and surface area. Colloidal
gamma-alumina can be used directly, or "alumina-precursors" such as
alpha-alumina monohydrate, or aluminum chlorohydrate can also be
used. When alpha-alumina monohydrate isused, the particle size can
be from less than 1 micron up to about 100 microns. Suitable
commercially available materials of this kind are Kaiser SA
substrate alumina, available from the Kaiser Chemical Division of
Kaiser Aluminum Corporation, and the Catapal.RTM. aluminas
available from the chemical division of Conoco Corporation. The
colloidal gamma-alumina is preferably in the form of particles not
exceeding 1 micron. The aluminum chlorohydrate is generally in the
form of an aqueous solution of aluminum chloride, preferably with
an alumina content of at least 20% by weight. Suitable products of
this kind are the Chlorohydrol.RTM., Rehydrol.RTM., and
Rehabond.RTM. alumina products available from Reheis Chemical
Company.
Spinels useful in the present invention are the magnesium aluminate
spinels heretofore used as catalyst supports, including spinel
solid solutions in which magnesium is partially replaced by such
other metals as manganese, cobalt, zirconium, or zinc. Preferred
spinels are magnesium aluminate spinels having 1-7 percent by
weight alumina in excess of 1:1 MgO.Al.sub.2 O.sub.3 spinel; that
is, those having about 72.0-73.5 weight percent Al.sub.2 O.sub.3
(balance MgO). Spinels of this kind are available on order from
Baikowski International Corporation of Charlotte, N.C., or can be
prepared by co-precipitation or wet-mixing precursor powders of
alumina and magnesia, followed by drying and calcining. Such a
procedure is described in U.S. Pat. No. 4,239,656, the disclosure
of which is hereby incorporated by Reference. As a supplement to
this disclosure, however, it has been found that calcining of the
spinels should normally not exceed 1300.degree. C. for 2-2.5 hours.
Calcining temperatures below 1200.degree. C. are preferred.
Suitable alumina precursor powders for preparation of the spinels
are commercially available as Kaiser SA hydrated alumina or Conoco
CATAPAL SB alumina (boehmite alpha-alumina monohydrate). Magnesium
oxide component powders found to be suitable are magnesium
hydroxide slurry, about 40 weight percent MgO, available from Dow
Chemical Company, or hydrated magnesium carbonate.
High surface area silicas useful as the high surface area phase are
the amorphous silicas of about 1-10 microns or sub-micron particle
size such as CABOSIL EH-5 colloidal silica, available from Cabot
Corporation. Silica precursors, such as an aqueous suspension of
colloidal silicate, can also be used. High surface area titanias
suitable for use are also commercially available, such as P25
TiO.sub.2 available from DeGussa Corporation. Titania precursors
such as hydrolyzed titanium isopropoxide can also be used.
The use of zeolites to provide high surface area in various
catalytic and molecular sieving operations is well known. Readily
available zeolites useful in the present invention include the
crystalline aluminosilicate zeolites with the art-recognized
designations. A, X, and Y, and silicalite. Zeolites A, X, And Y,
and their methods of preparation, are disclosed in U.S. Pat. Nos.
2,882,243; 2,882,244; and 3,130,007; respectively. Disclosures of
these patents is incorporated by reference. Silicalite is described
in NATURE (271), No. 5645 (1978).
Composites of alumina and silica also can form the basis for the
high surface area agglomerates. Alumina-silica composites are
commercially available from Davison Chemical Division of W. R.
Grace Company and from the Norton Company, or can be prepared by
the gel processes as described, for example, in U.S. Pat. Nos.
4,129,522 and 4,039,474. Alternatively, alumina and silica or their
precursors can be mixed directly during the preparation of the
monoliths as described below.
Transition metal sulfides, such as cerium sulfide, nickel sulfide,
iron sulfide, titanium sulfide, and chromium sulfide, or mixtures
can be combined with cordierite, mullite, alpha-alumina, lithium
alumino-silicates or mixtures.
When the high surface area material is an alumina, spinel, or a
mixture of alumina and silica, it is preferred to add up to about
20 percent by weight (based on the alumina, spinel, or
alumina-silica mixture weight) of a rare earth oxide. The preferred
rare earth oxides are those of the "cerium subgroup", that is,
elements of atomic number 57-62, particularly cerium and lanthanum.
Cerium oxide is most preferred. Paticularly useful spinels, for
example, are those in which about 1 to 20 percent by weight, based
on the total spinel weight, of cerium oxide is present. Cerium
oxide is incorporated by adding, for example, cerium acetate,
cerium carbonate, or cerium nitrate to the other precursor powders
during the spinel preparation. In like manner, particularly useful
mixtures of alumina and silica are those in which about 5 percent
by weight, based on the total alumina and silica dry weight, of
cerium oxide is present.
The transition metal sulfides preferable for use in the present
invention are cerium sulfide, nickel sulfide, iron sulfide,
titanium sulfide, and chromium sulfide. Mixtures of these can also
be used.
The preferred high surface area materials are silica, the magnesium
aluminate spinels, and the transition aluminas.
The ceramic material, which forms the high-strength matrix phase of
the monolith, is comprised of any of the well known sinterable
materials capable of providing mechanical strength and good thermal
properties in monolithic supports as heretofore prepared by those
skilled in the art. Preferably the ceramic is selected from
cordierite, mullite, alphaalumina, and lithium alumino-silicates.
Mixtures of these can also be used to the extent that the chosen
materials are compatible and will not degrade each other, as those
skilled in the art will recognize. To cordierite can be in the
precursor or "raw" form, as in U.S. Pat. No. 3,885,977, which
becomes true cordierite upon heating, but it is preferably
pre-reacted. The use of raw cordierite is disclosed in the U.S.
Pat. No. 3,885,977. When raw cordierite is used, it is preferred
that up to 10% by total weight of B.sub.2 O.sub.3 be added to the
raw batch to promote the actual cordierite formation and to impart
strength.
The ceramic material can contain substantial amounts of a component
which causes intracrystalline and intercrystalline microcracking to
occur. Such microcracking enhances the thermal shock resistance of
monolithic supports based on these ceramics and is therefore
desirable when the monoliths, in service, may be exposed to rapid
changes in temperature. Ceramic materials which contain such a
component, and are therefore contemplated for use within the
present invention are disclosed in U.S. Pat. Nos. 3,528,831;
3,549,400; and 3,578,471; all issued to I. M. Lachman. A preferred
microcracking agent for addition to the ceramic material is
aluminum titanate, which is normally incorporated into the ceramic
matrix as a "solid solution" with the basis ceramic material. An
aluminum titanate solid solution with mullite is disclosed in U.S.
Pat. No. 4,483,944 to Day, et al. The disclosures of the four
above-mentioned patents are incorporated herein by reference.
The monolithic supports are prepared by mixing the sinterable
ceramic materials with the high surface area materials described
above and, optionally, a binder. Generally about 10-50 parts by
weight of the high surface area material will be combined with
50-90 parts by weight of the ceramic material. Preferably, 1-30
parts by weight of binder will also be used. Any binder material
conventionally used in ceramic catalyst support manufacture is
suitable. Examples are disclosed in:
"Ceramics Processing Before Firing," ed. by George Y. Onoda, Jr.
& L. L. Hench, John Wiley & Sons, New York
"Study of Several Groups of Organic Binders Under Low-Pressure
Extrusion," C. C. Treischel & E. W. Emrich,
Jour. Am. Cer. Soc. (29), pp. 129-132, 1946 "Organic (Temporary)
Binders for Ceramic Systems," S. Levine, Ceramic Age, (75) No. 1,
pp. 39+, January 1960
"Temporary Organic Binders for Ceramic Systems," S. Levine, Ceramic
Age, (75) No. 2, pp. 25+, February 1960.
Preferred are methyl cellulose or a silicone resin. The silicone
resins preferred for use are Dow Corning Corporation's Q6-2230
silicone resin or those described in U.S. Pat. No. 3,090,691 to
Weyer. The most preferred binder is methyl cellulose, available as
Methocel.RTM. A4M from the Dow Chemical Company. It is preferred to
use at least some methyl cellulose in addition to silicone resin as
a binder. Up to about 1 percent by weight, based upon total mixture
weight, of a surfactant, such as sodium stearate, can also be used
to facilitate mixing and flow for subsequent processing. The mixing
step should be performed in a liquid, such as water, which acts as
a further plasticizer. When the binder is a silicone resin, it is
preferred to use isopropyl alcohol in addition to water. Normally,
the dry ingredients as first pre-mixed and then combined with the
liquid plasticizer and any wet ingredients.
The most preferred ceramic materials for use in this invention are
the pre-reacted cordierite and mullite, including mullite with a
microcracking agent. The ceramic material should be in particulate
form, preferably of a size finer than 200 mesh (U.S. Standard) and
most preferably finer than 325 mesh (U.S. Standard). With such
characteristics, the ceramic material can normally be sintered as
temperatures below those at which the surface area of the
incorporated porous oxides or sulfides would be adversely
affected.
The monoliths are prepared by combining the components to form a
homogeneous or substantially homogeneous mixture. Conventional
mixing equipment can be used, but the use of a mix muller is
preferred. To effect further mixing, the batch can subsequently be
extruded through a "noodling" die one or more times. The noodling
die can form, for example, ribbons-like or tubular shapes, or
shapes having circular or polygonal cross-section. Ultimately, the
batch is formed into the desired shape of the monolithic support,
preferably by extrusion through a die, but another method, for
example, is injection molding. The method of this invention is
particularly well suited to the preparation of supports in the
shape of, for example, thin-walled honeycombs and wagon-wheels.
Finally, the shapes are heated to a temperature and for a time
sufficient to sinter the ceramic material. Optionally, this
heating/sintering step can be preceeded by drying the shapes at
about 100.degree.-120 .degree. C. The heating/sintering generally
takes place at 700.degree.-1300.degree. C., although when silicone
resin is used as a binder for the ceramic matrix, particularly when
the ceramic has a high alumina content, temperatures as low as
500.degree. C. may be sufficient. Temperatures below about
1100.degree. C. are preferred. When the high surface area support
material is a zeolite, temperatures below 800.degree. C. are
preferred. With the reaction of high surface area by the embedded
material, despite the temperatures used to sinter the ceramic, the
monolithic support preferably has an overall surface area of at
least 5-10 square meters per gram, more preferably at least 20
m.sup.2 /g, and most preferably at least 40 m.sup.2 /g. Although
some sintering of the embedded material may take place, it is
expected that the crystalline size of this material will grow no
larger than about 0.5 microns. Crystalline size can be determined
by scanning or transmission electron microscopy.
The monolithic supports of this invention may have some catalytic
activity of their own by virtue of the chemistry and structure of
the high surface area phase. The support may further carry
additional catalytically active ingredients dispersed throughout,
but generally more concentrated at the high surface area sites
provided by the embedded oxide and sulfide materials. These
additional catalytic ingredients can be incorporated into the
monolith by methods by methods known in the art. Preferably, these
ingredients will be dposited onto the high surface phase after
fabricating and sintering the final structure.
The monolithic supports of this invention are useful in most
applications in which it is necessary to catalytically convert
undesirable components in a gas stream prior to the stream's
further processing or exhaustion to the atmosphere. The supports
have good thermal shock resistance, particularly when the ceramic
matrix phase is microcracked, and are therefore useful in
applications in which they might be exposed to rapid and frequent
changes in temperature. Capability to withstand thermal shock makes
the supports of this invention particularly well suited for
catalyzing the conversion of truck or automotive exhaust gasses to
less noxious forms.
The following examples are illustrative, but not limiting, of the
invention.
EXAMPLE 1
A mixture of 91 weight % Kaiser SA alumina and 9 weight % cerium
nitrate was prepared by intensively dry-mixing the ingredients. The
mixture was calcined at 900.degree. C. for six hours, after which
time the surface area of the resultant powder was determined to be
120 m.sup.2 /g. A paste of this powder was prepared by mixing 500
grams of the powder with 750 ml of distiled water, 30 grams of zinc
oxide, 30 grams of nickel oxide green, and 60 cc glacial acetic
acid. An extrusion batch was prepared by charging 20 parts by
weight of the paste, 80 parts of pre-reacted cordierite (milled to
a particle size finer than 200 mesh), 37 parts of distilled water,
0.5 part sodium stearate, and 6.0 parts of methyl cellulose to a
mix muller. The batch was mixed until substantial homogeneity and
plasticity were attained. The batch was extruded through a die to
form homeycomb monoliths of one-inch diameter having 200 square
openings per square inch. The honeycombs were heated at various
temperatures between 1000.degree. C. and 1300.degree. C. for six
hours. Strength of the supports was not quantitatively determined,
but the supports were characterized as weak, although they were
capable of handling. Properties of the supports are listed below
according to heating temperature.
______________________________________ Mean BET Pore Linear Surface
Heating Porosity Size Shrinkage Area Temp (.degree.C.) (%)
(Microns) (%) (m.sup.2 /g) ______________________________________
1000 41 0.4 0.0 24 1100 40 0.45 0.9 15 1200 42 1.4 2.9 1 1300 41
1.6 3.9 -- ______________________________________
Honeycomb catalysts fired at 1100.degree. C. were loaded with the
appropriate noble metals to test the conversions of each of HC, CO
and various nitrogen oxides (NO.sub.x) in gas streams. The
temperature at which a 50% conversion rate for each contaminant was
reached is recorded below.
______________________________________ Noble Metal 50% Conversion
Temperature (.degree.C.) Loading (gms/Ft.sup.3) HC CO NOx
______________________________________ 19 330 330 330 29 340 320
315 37 350 325 325 47 330 305 305
______________________________________
EXAMPLE 2
A combination of 83.8 weight parts of Kaiser SA alumina, 8.44 parts
cerium nitrate, 3.9 parts zinc oxide, 3.9 parts nickel oxide green,
and 100 parts distilled water was mixed until a plasticized batch
(the "alumina/cerium nitrate batch") was attained. The batch was
calcined at 500.degree. C. for six hours to develop high surface
area. An extrusion batch was prepared by charging 20 parts by
weight of the calcined alumina/cerium nitrate batch, 80 parts by
weight of pre-reacted cordierite (milled to a particle size finer
than 200 mesh), 43.5 parts of distilled water, 0.5 part sodium
sterate, and 6.0 parts of methyl celluloe to a mix muller. The
batch was mixed until substantial homogeneity and plasticity were
attained. The batch was then extruded through a die to form
honeycomb monoliths of one-inch diameter having 400 square openings
per square inch. The honeycombs were heated at various temperatures
between 1000.degree. C. and 1300.degree. C. for six hours. Strength
of the supports was not quantitatively determined, but the supports
were characterized as weak, although they were capable of handling.
Properties of the supports are listed below according to heating
temperature.
______________________________________ Thermal Expansion Mean
Linear BET Coefficient Heating Poro- Pore Shrink- Surface
RT-1000.degree. C. Temp sity Size age Area (cm/cm .degree.C.
.times. (.degree.C.) (%) Microns (%) (m.sup.2 /g) 10.sup.7)
______________________________________ 1000 43 0.4 0.0 26 -- 1100
43 0.9 1.4 14 26 1200 43 1.7 4.4 1 23 1300 36.5 1.9 6.4 -- 27
______________________________________
Honeycomb catalysts fired at 1100.degree. C. were loaded with the
appropriate noble metals to test the conversions of each of HC, Co,
and varius nitrogen oxides (NO.sub.x) in gas streams. The
temperature at which a 50% conversion rate for each contaminant was
reached is recorded below.
______________________________________ Noble Metal 50% Conversion
Temperature (.degree.C.) Loading (gms/Ft.sup.3) HC CO NOx
______________________________________ 9 365 345 345 18 345 330 330
27 345 325 325 36 325 305 305 44 330 310 310
______________________________________
EXAMPLE 3
Example 3A Ingredients: 20 parts by weight of the calcined
alumina/cerium mitrate batch of Example 2; 80 parts of raw
cordierite batch, containing B.sub.2 O3.
Example 3B Ingredients: 20 parts by weight of the uncalcined
alumina/cerium nitrate batch of Example 2; 80 parts of raw
cordierite batch, containing B.sub.2 O3.
The compositions of Examples 3A and 3B were each mixed, separately,
according to the precedure of Example 2, with 6 parts by weight of
methyl cellulose, 0.5 part sodium stearate, and sufficient
distilled water to obtain plasticity. The batches were extruded as
honeycombs and fired as in Example 2. X-ray diffraction indicated
that cordierite was not fully formed until a firing temperature of
1140.degree. C. was reached in both examples. Surface area of the
honeycombs was 8 m.sup.2 /g at a firing temperature of 1100.degree.
C. and 0.7 m.sup.2 /g at a temperature of 1140.degree. C. It is
thought that the high surface area alumina phase was sintered by
virtue of the intimate mixing with the cordierite phase and the
B.sub.2 O.sub.3, which is a sintering aid.
EXAMPLE 4
The following compositions were prepared for the fabrication of
honeycomb monolithic supports. Figures represent parts by weight
(dry, fired weights for the inorganic ingredients).
______________________________________ Ingredient Ex. 4A Ex. 4B Ex.
4C ______________________________________ Pre-reacted cordierite
80.0 80.0 80.0 (325 mesh) Kaiser SA Medium Al.sub.2 O.sub.3 20.0
17.1 17.0 Methyl Cellulose 4.0 5.0 5.0 Sodium Stearate 0.5 0.5 0.5
CeO.sub.2 (Reagent Grade) -- 1.3 -- ZrO.sub.2 -- 1.3 -- Cr.sub.2
O.sub.3 (Reagent Grade) -- -- 1.0 Bastnesite (Molycorp #4010) -- --
2.0 ______________________________________
In Example 4A, the ingredients were dry mixed overnight in a roll
mixer. In Examples 4B and 4C, all ingredients but the methyl
cellulose and sodium stearate were wet milled overnight in
trichloroethylene, after which they were dried and dry-blended with
the remaining two ingredients. The subsequent procedure for all
examples was as follows: The ingredients were placed into a mix
muller and mulled with sufficient distilled water until a
well-plasticized batch was obtained. The batches were then
separately extruded through a spaghetti die at least twice to
effect further mixing and, finally, extruded through a honeycomb
die to form a shape having 400 square cells per square inch with a
wall thickness of 6 mils. The honeycombs were steam dried and then
fired in electrically heated furnaces, in air, at
50.degree.-100.degree. C./hr. to a maximum temperature of
800.degree.-1200.degree. C. with a six hour hold at the maximum
temperature. Generally, there was a short hold at 300.degree. C. to
burn out the binder. Properties of the honeycomb, according to
maximum firing temperature, are shown below in the table.
__________________________________________________________________________
Mean Pore BET Thermal Expansion Heating Density Open Porosity Size
Surface Area Coefficient Example Temp (.degree.C.) (g/cc) (%)
(Microns) (m.sup.2 g) (in./in. .degree.C. .times. 10.sup.7)
Hardness
__________________________________________________________________________
4A 800 1.41 31.3 0.25 50.9 -- Soft 1000 1.29 35.1 0.3 28.9 25.3
Soft 1100 1.32 38.3 0.35 24.7 -- Soft 1200 1.31 39.3 0.5 11.9 --
Soft 4B 800 1.41 31.6 0.3 45.2 -- Soft 1000 1.39 36.4 0.35 24.3
23.3 Medium Hard 1100 1.44 38.3 0.35 24.4 -- Medium Hard 1200 1.46
41.3 0.9 8.6 -- Hard 4C 800 1.36 33.9 0.3 44.2 -- Soft 1000 1.40
40.6 0.35 26.65 26.2 Soft 1100 1.37 41.8 0.4 23.0 -- Medium Hard
1200 1.42 43.8 0.9 11.2 -- Medium Hard
__________________________________________________________________________
EXAMPLE 5
A mixture of the following ingredients was prepared: 80 parts by
weight of pre-reacted cordierite (particle size finer than 200
mesh), 20 parts by weight of CABOSIL fumed silica, 6 parts by
weight methyl cellulose, 0.6 part sodium stearate. Teh mixture was
dry blended by rolling overnight, after which it was charged to a
mix muller and mulled with sufficient distilled water to 60 produce
a well-plasticized batch. The batch was extruded through a
spaghetti die two times and then through a honeycomb die to form a
shape having 200 square cells per square inch with a wall thickness
of 15 mils. The honeycombs were steam dried and then fired as in
Example 4. Properties of the honeycombs, according to firing
temperature, are shown in the table below.
______________________________________ Linear BET Shrink- Open Mean
Pore Surface Heating age Density Porosity Size Area Temp
(.degree.C.) (%) (g/cc) (%) (Microns) (m.sup.2 /g)
______________________________________ 700 0 1.06 52.1 0.1 41.9 900
0 1.06 51.6 0.2 33.8 1030 5 1.22 46.3 2.0 4.7 1100 7 1.23 43.5 2.5
0.7 1300 5 1.28 44.3 3.0 0.3 1400 5 1.41 36.4 3.8 0.3
______________________________________
All samples fired at temperatures of 1000.degree. C. and above
exhibited significant strength and could be easily handled without
breaking.
* * * * *