OXYDES DE CERIUM, OXYDES DE ZIRCONIUM, OXYDES MIXTES CE/ZR ET SOLUTIONS SOLIDES CE/ZR PRESENTANT UNE STABILITE THERMIQUE ET UNE CAPACITE DE STOCKAGE D'OXYGENE AMELIOREES

CERIUM OXIDES, ZIRCONIUM OXIDES, CE/ZR MIXED OXIDES AND CE/ZR SOLID SOLUTIONS HAVING IMPROVED THERMAL STABILITY AND OXYGEN STORAGE CAPACITY

Abrégé français

Production d'oxydes de cérium, d'oxydes de zirconium, d'oxydes mixtes (Ce, Zr)O2 et de solutions solides (Ce, Zr) O2 avec répartition de la grandeur des particules, aire spécifique, capacité de stockage d'oxygène et volume poreux améliorés par l'adjonction d'un additif tel qu'un tensioactif anionique ou non ionique pendant la formation des oxydes ou des précurseurs de ces derniers.

Abrégé anglais

The production of cerium oxides, zirconium oxides, (Ce, Zr)O2 mixed oxides and
(Ce, Zr)O2 solid solutions having improved particle size distribution, surface
area, oxygen storage capacity and pore volume by the addition of an additive,
such as an anionic or nonionic surfactant, during the formation of the or
oxides or precursors thereof.

Revendications

What is claimed is:
1. A process comprising the reaction of a cerium solution, zirconium solution,
a
base, optionally an oxidizing agent, and an additive selected from the group
consisting of:
a) anionic surfactants;
b) nonionic surfactants;
c) polyethylene glycols;
d) carboxylic acids; and
e) carboxylate salts.
2. The process of claim 1 further comprising the step of washing or
impregnating
with an alkoxylated compound and/or an additive selected from the group
consisting of:
a) anionic surfactants;
b) carboxylic acids; and
c) carboxylate salts.
3. The process according to claim 1 wherein the reaction is an aqueous
precipitation or coprecipitation.
4. The process according to claim 1 wherein the reaction is co-
thermohydrolysis.
5. The process according to claim 1 where in the additive is represented by
the
formula:
R1-((CH2)x-O)n-R2
wherein R1 and R2 represent a linear or non-linear alkyl, aryl, and/or
alkylaryl
group or H or OH or Cl or Br or I; n is a number between about 1 and about
100; x is a number from about 1 to about 4 and R1 and R2 can contain an
alcohol group, a CO group, or a S-C group.
28

6. The process according to claim 5 wherein the additive comprises a methoxy,
ethoxy or propoxy group.
7. The process according to claim 1 wherein the anionic surfactants are
selected
from the group consisting of carboxylates, phosphates, sulfates, sulfonates
and
mixtures thereof.
8. The process according to claim 7 wherein the nonionic surfactants are
selected
from the group consisting of:
acetylenic surfactants, alcohol ethoxylates, alkanolamides, amine oxides,
ethoxylated alkanolamides, ethoxylated long chain amines, ethylene
oxide/propylene oxide (EO/PO) co-polymers, sorbitan derivatives; ethylene
glycol, propylene glycol, glycerol and polyglyceryl esters plus their
ethoxylated derivatives; alkyl amines; alkyl imidazolines; ethoxylated oils
and
fats; alkyl phenol derivatives and mixtures thereof.
9. The process according to claim 8 wherein the nonionic surfactants are
selected
from the group consisting of:
a) octyl phenols of about 12 EO such as represented by the formula:
<IMG>
b) nonylphenol ethoxylated polyethylene glycols of about 9 EO
represented by the formula:
<IMG>
c) nonylphenols having from about 5 to about 14 EO;
d) tristyrylphenol ethoxylates;
e) ethylene glycol n-butyl ethers represented by the formula:
29

<IMG>
f) diethylene glycol n-butyl ethers represented by the formula:
<IMG>
g) triethylene glycol n-butyl ethers represented by the formula:
<IMG>
h) alkanolamides represented by the formulae:
<IMG>
i) tallowamines, ethoxylated represented by the formula:
<IMG>
j) lauryl dimethylamine oxides represented by the formula:
30

<IMG>.
10. The process according to claim 7 wherein the anionic surfactants are
selected
from the group consisting of:
a) ethoxycarboxylates of the formula: R-O(CH2CH2O) x CH2COO-, which
includes ether carboxylates of the formula:
<IMG>
wherein R is an alkyl or alkylaryl group, M+ can be ammonium, potassium,
sodium or trithanolamine, and n can be from about 1 to about 13;
b) ester carboxylates of the formula: R1-CH2-C[C(O)O](OH)(-R2);
c) sarcosinates of the formula: R-C(O)N(CH3)CH2COO;
d) phosphate esters of the formulae (HO)(OR)P(O)2 and (RO)2P(O)2
<IMG>
where R is an alkyl or alkyaryl group, n is moles of ethylene oxide (and/or
propylene oxide) and M is hydrogen, sodium, potassium, or other counterion;
e) alcohol sulfates;
f) alcohol ether sulfates;
g) sulfated alkanolamide ethoxylate;
h) sulphosuccinates;
i) taurates;
j) isethionates;
31

R-C(O)CH2CH2SO3-
k) alkyl benzene sulfonates;
l) fatty acid and diester sulfonates;
m) .alpha.-sulfo fatty acid esters;
n) alkyl naphthalene sulfonates;
o) formaldehyde naphthalene sulfonates;
p) olefin sulfonates; and
q) petroleum sulphonates.
11. The process of claim 1 wherein the ethoxylated nonionic surfactants and
polyethylene glycols are added to the salt solution, base solution or both
before reaction.
12. The process of claim 9 wherein the alkanolamides are added to the salt
solutions, water, oxidizing agent or any combination thereof before reaction.
13. The process of claim 1 wherein the carboxylic acids are added to the base
solution before reaction.
14. The process of claim 1 wherein the additive is added based on the weight
percent of the reaction media and reagents at from about 1 % to about 35 %.
15. A method for improving the thermal stability, surface area, porosity,
and/or
oxygen storage capacity of cerium oxides, zirconium oxides, (Ce, Zr)O2
mixed oxides or (Ce, Zr)O2 solid solutions by preparing a cerium hydroxide,
zirconium hydroxide, cerium/zirconium mixed hydroxide or hydroxide of a
cerium/zirconium solid solution in the presence of an additive selected from
the group consisting of:
a) anionic surfactants;
b) nonionic surfactants;
32

c) polyethylene glycols;
d) carboxylic acids; and
e) carboxylate salts.
16. The method of claim 15 wherein the process for preparation is
co-thermohydrolysis or an aqueous coprecipitation.
17. Cerium oxides, zirconium oxides, (Ce, Zr)O2 mixed oxides or (Ce, Zr)O2
solid solutions having a total pore volume of greater than about 0.5 ml/g
after
calcination under air at about 500°C for about 2 hours.
18. An oxide according to claim 17 having a total pore volume of greater than
about 0.8 ml/g after calcination under air at about 500°C for about 2
hours.
19. A (Ce, Zr)O2 mixed oxide or (Ce, Zr)O2 solid solution having a total pore
volume of greater than about 0.5 ml/g after calcination under air at about
500°C for about 2 hours.
20. A (Ce, Zr)O2 mixed oxide or (Ce, Zr)O2 solid solution having a surface
area
greater than about 25 m2/g after calcination under air at about 900°C
for about
6 hours.
21. The (Ce, Zr)O2 mixed oxide or (Ce, Zr)O2 solid solution according to claim
20 wherein the surface area is greater than about 30 m2/g after calcination
under air at about 900°C for about 6 hours.
22. A (Ce, Zr)O2 mixed oxide or (Ce, Zr)O2 solid solution having an oxygen
storage capacity of greater than about 2 ml O2/g after calcination under air
at
about 900°C for about 2 hours.
33

23. The (Ce, Zr)O2 mixed oxide or (Ce, Zr)O2 solid solution according to claim
22 wherein said mixed oxide or solid solution is cerium rich.
24. A (Ce, Zr)O2 mixed oxide or (Ce, Zr)O2 solid solution having:
a) a total pore volume of greater than about 0.5 ml/g after calcination
under air at about 500°C for about 2 hours;
b) a surface area of greater than about 25 m2/g after calcination under air
at about 900°C for about 6 hours; and
c) an oxygen storage capacity of greater than about 2 ml O2/g after
calcination under air at 900 ° C for about 2 hours.
25. A (Ce, Zr)O2 mixed oxide or (Ce, Zr)O2 solid solution according to claim
24
wherein the total pore volume is greater than about 0.6 ml/g after calcination
at about 500°C for about 2 hours; the surface area is greater than
about 30
m2/g after calcination at about 900°C for about 6 hours; and the oxygen
storage capacity is greater than about 2.6 ml O2/g after calcination at
500°C
for about 2 hours.
26. A (Ce, Zr)O2 mixed oxide or (Ce, Zr)O2 solid solution having an oxygen
storage capacity of greater than about 2 ml O2/g after calcination at about
900°C for about 2 hours, a total pore volume of greater than about 0.5
ml/g
after calcination at about 500°C for about 2 hours, or a surface area
of greater
than about 25 m2/g after calcination at about 900°C for about 6 hours,
said
(Ce, Zr)O2 mixed oxide or (Ce, Zr)O2 solid solution prepared by a process
comprising the step of preparing a (Ce, Zr)O2 mixed hydroxide precipitate or
a hydroxide of a (Ce, Zr)O2 solid solution precipitate by reacting a solution
of
cerium salt, a solution of zirconium salt, a base, an additive selected from
the
group consisting of:
a) anionic surfactants;
b) nonionic surfactants;
c) polyethylene glycols; and
34

d) carboxylic acids; and
e) carboxylate salts;
and optionally an oxidizing agent.
27. A process comprising the step of washing or impregnating cerium
hydroxides,
oxides, hydroxy carbonates or carbonates; zirconium hydroxides, oxides,
hydroxy carbonates or carbonates; cerium/zirconium mixed hydroxides,
oxides, hydroxy carbonates or carbonates; or cerium/zirconium hydroxides,
oxides, hydroxy carbonates or carbonates solid solutions with an additive
selected from the group consisting of: anionic surfactants; carboxylic acids;
and carboxylate salts.
28. A dehydrogenation catalyst comprising: an active support selected from the
group consisting of:
(Ce, Zr)O2 mixed oxide or (Ce, Zr)O2 solid solution having:
a) a total pore volume of greater than about 0.5 ml/g after calcination
under air at about 500°C for about 2 hours;
b) a surface area of greater than about 25 m2/g after calcination under air
at about 900 ° C for about 6 hours; and
c) an oxygen storage capacity of greater than about 2 ml O2/g after
calcination under air at 900°C for about 2 hours.
29. A (Ce, Zr)O2 mixed oxide or (Ce, Zr)O2 solid solution according to claim
28
wherein the total pore volume is greater than about 0.6 ml/g after calcination
at about 500°C for about 2 hours; the surface area is greater than
about 30
m2/g after calcination at about 900°C for about 6 hours; and the oxygen
storage capacity is greater than about 2.6 ml O2/g after calcination at
500°C
for about 2 hours.

30. A method for preparing styrene comprising the step of conversion of
ethylbenzene to styrene utilizing a dehydrogenation catalyst comprising an
active support prepared by the process comprising the steps of:
washing or impregnating cerium hydroxides, oxides, hydroxy carbonates or
carbonates; zirconium hydroxides, oxides, hydroxy carbonates or carbonates;
cerium/zirconium mixed hydroxides, oxides, hydroxy carbonates or
carbonates; or cerium/zirconium hydroxides, oxides, hydroxy carbonates or
carbonates solid solutions with an additive selected from the group consisting
of: anionic surfactants; carboxylic acids; and carboxylate salts.
31. A method for preparing styrene comprising the step of conversion of
ethylbenzene to styrene utilizing a dehydrogenation catalyst comprising an
active support selected from the group consisting of:
(Ce, Zr)O2 mixed oxides or (Ce, Zr)O2 solid solutions having:
a) a total pore volume of greater than about 0.5 ml/g after calcination
under air at about 500°C for about 2 hours;
b) a surface area of greater than about 25 m2/g after calcination under air
at about 900°C for about 6 hours; and
c) an oxygen storage capacity of greater than about 2 ml O2/g after
calcination under air at 900°C for about 2 hours.
32. A method of catalysis for exhaust gas systems comprising the steps of:
reacting a cerium solution, zirconium solution, a base, an additive selected
from the group consisting of:
a) anionic surfactants;
b) nonionic surfactants;
c) polyethylene glycols;
d) carboxylic acids; and
e) carboxylate salts; and
optionally an oxidizing agent.
36

33. A method of catalysis for exhaust gas systems comprising:
(Ce, Zr)O2 mixed oxides or (Ce, Zr)O2 solid solutions having:
a) a total pore volume of greater than about 0.5 ml/g after calcination
under air at about 500°C for about 2 hours;
b) a surface area of greater than about 25 m2/g after calcination under air
at about 900°C for about 6 hours; and
c) an oxygen storage capacity of greater than about 2 ml O2/g after
calcination under air at 900°C for about 2 hours; and
mixtures thereof.
34. A method of catalysis for exhaust gas systems comprising a product of the
process comprising the steps of: washing or impregnating cerium hydroxides,
oxides, hydroxy carbonates or carbonates; zirconium hydroxides, oxides,
hydroxy carbonates or carbonates; cerium/zirconium mixed hydroxides,
oxides, hydroxy carbonates or carbonates; or cerium/zirconium hydroxide,
oxides, hydroxy carbonates or carbonates solid solutions with an additive
selected from the group consisting of: anionic surfactants; carboxylic acids;
and carboxylate salts.
35. A catalytic converter comprising the product of the process comprising the
steps of:
reacting a cerium solution, zirconium solution, a base, an additive selected
from the group consisting of:
a) anionic surfactants;
b) nonionic surfactants;
c) polyethylene glycols;
d) carboxylic acids; and
e) carboxylate salts; and
optionally an oxidizing agent.
37

36. A catalytic converter comprising the product of the process comprising the
steps of:
washing or impregnating cerium hydroxide, oxide, hydroxy carbonate or
carbonate; zirconium hydroxide, oxide, hydroxy carbonate or carbonate;
cerium/zirconium mixed hydroxides, oxides, hydroxy carbonate or carbonates;
or cerium/zirconium hydroxides, oxides or carbonates solid solutions with an
additive selected from the group consisting of: anionic surfactants;
carboxylic
acids; and carboxylate salts.
38

Description

CA 02285228 1999-09-30
WO 98/45212 PCT/ITS98/06437
CERIUM OXIDES, ZIRCONIUM OXIDES, Ce/Zr ~D OXIDES AND
Ce/Zr SOLID SOLUTIONS HAVING IIVVIPROVED THERMAL STABILITY
AND OXYGEN STORAGE CAPACITY
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to the production of cerium oxides, zirconium
oxides, cerium and zirconium mixed oxides or solid solutions (also hydroxides
and
carbonates) having improved thermal stability and oxygen storage capacity. The
oxides, hydroxides or carbonates have a fme particle size distribution, very
high
surface area, oxygen storage capacity and release capacity, and are useful in
many
applications including catalytic converters, catalysis for the manufacture of
styrene
and catalysis for gas exhaust systems.
Background of the Invention
Oxides of cerium and zirconium, and particularly cerium. and zirconium
(Ce,Zr)OZ mixed oxides and solid solutions, are used for many applications,
including
catalysts used in automotive catalytic converters and the like. Such oxides
are
typically formed by known precipitation techniques which involve the formation
of
precursors to, or the solid oxides in a liquid medium. When such oxides are to
be
used, for example, in catalytic converters, it is desirable to maximize the
thermal
stability of the compounds, as defined by the stability of the surface area of
the
material after aging at high temperature. It is also desirable to maximize the
surface
area of such mined oxides in order to provide improved catalytic properties.
In
addition to (Ce,Zr)OZ mixed oxides, the present invention also relates to
cerium
oxides, zirconium oxides, and mixtures thereof as well as cerium and zirconium
(Ce,Zr)OZ solid solutions (where substitution between cerium and zirconium in
the
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SUBSTITUTE SHEET (RULE 26)

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network of the oxide, as opposed to being two different phases, is one phase)
all of
which can be utilized as catalysts or as .catalyst supports.
Increasingly stringent vehicle emissions standards make exhaust system
operating conditions increasingly severe. The majority of modern gasoline
fueled cars
are equipped with so-called three-way catalysts to afterneat their exhaust
gases. The
purpose of this system is to convert simultaneously carbon monoxide,
hydrocarbons
and nitrogen oxides by means of a precious metal based heterogeneous catalyst,
whereby the engine's air-to-fuel ratio is controlled to obtain exhaust gas
compositions
that guarantee optimal conversions. Cerium-zirconium oxides are widely used in
three-way catalysts for automotive exhaust treatment. Three-way automotive
catalysts
consist of precious metals (platinum, rhodium, etc.), promoters and supports
such as
y-alumina. It is known that the addition of CeO, as a promoter results in an
improvement of the dynamic performance for the removal of carbon monoxide
(CO),
nitrogen oxides (NOx) and hydrocarbons (Hcs) . However, the high temperature
conditions of use in an automotive engine lead to significant degradation
including
surface area loss of supports, sintering of supported precious metals and
deactivation
of added cerium.
It is known that cerium oxides and zirconium oxides and cerium and zirconium
mixed oxides can be used as a catalyst or as a catalyst support. It is also
well known
that a catalyst is generally more effective when the contact surface between
the
catalyst and the reagents is larger. For this purpose, it is necessary for the
catalyst to
be maintained in the most divided state possible, that is, that the solid
particles which
compose it be as small and individualized as possible. The fundamental role of
the
support, therefore, is to maintain the catalyst particles or crystallites in
contact with
the reagents, in the most divided state possible. During the extended use of a
catalyst
support, a decrease in the specific surface occurs due to the coalescence of
the very
fine micropores. During this coalescence, part of the catalyst is surrounded
by the
body of the support and can no longer be in contact with the reagents.
An object of the present invention is to provide a method for producing cerium
oxides, zirconium oxides, cerium and zirconium (Ce,Zr)OZ mixed oxides, and
cerium
and zirconium (Ce,Zr)OZ solid solutions having improved thermal stability,
surface
2
SUBSTITUTE SHEET (RULE ~6j
_.T ...

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area, porosity, and/or oxygen storage capacity. The method is preferred for
use in
producing cerium oxides, (Ce,Zr)Oz mixed oxides and (Ce,Zr)OZ solid solutions
having improved thermal stability, surface area, porosity, and/or oxygen
storage
capacity.
Another object of the present invention is cerium oxides, zirconium oxides,
(Ce,Zr)Oz mixed oxides, and (Ce,Zr)OZ solid solutions compositions having
improved
thermal stability surface area, porosity, and/or oxygen storage capacity. The
oxides,
mixed oxides and solid solutions produced can have very high surface areas,
very
high oxygen storage capacities and low particle size.
These and other objects of the present invention will be more readily apparent
from the following description.
SUMMARY OF THE INVENTION
The present invention provides a novel way to improve the thermal stability,
surface area, porosity, and/or oxygen storage capacity of cerium oxides,
zirconium
oxides, (Ce,Zr)OZ mixed oxides, and (Ce,Zr)O, solid solutions obtained by
processes
such as precipitation, co-precipitation or thermohydrolysis, by introducing an
additive, such as an anionic surfactant and/or nonionic surfactant, during the
formation of the oxide or precursors thereof. By additionally washing or
impregnating
with an alkoxylated compound and/or additive, thermal stability, surface area,
porosity, and/or oxygen storage capacity can be even further improved.
All ratios, proportions and percentages herein are by weight, unless otherwise
specified. "Comprising," as used herein, means various components can be
conjointly employed. Accordingly, the terms "consisting essentially of" and
"consisting of ' are embodied in the term "comprising. "
DETAILED DESCRIPTION OF THE INVENTION
The thermal stability of inorganic compounds can be defined as the stability
of
the surface area when material is aged at high temperature. For many
applications,
particularly catalysis, high surface area and highly stable materials are
required by
end users. In accordance with the present invention, cerium and zirconium
mixed
oxides and solid solutions are produced having improved thermal stability,
surface
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area, porosity, and/or oxygen storage capacity. The invention is also useful
for
producing cerium oxides, zirconium oxides and mixtures of cerium oxides and
zirconium oxides having improved thermal stability, surface area, porosity,
and/or
oxygen storage capacity.
Many methods have been developed for the preparation of high surface area
oxides, mixed oxides and solid solutions. They generally fall into four basic
steps:
synthesis of precursors, treatment of precursors before conversion to oxides,
conversion of precursors to mixed oxides, and post treatment of mixed oxide
material.
The methods of synthesis to produce precursors for oxides include: aqueous
precipitation or coprecipitation, organic coprecipitation, spray
coprecipitation, and
hydrothermal techniques. These are conventional methods known in the art. The
method of the present invention is preferred for use with aqueous
precipitation or
coprecipitation and hydrothermal techniques. Most preferably, the method of
the
present invention is utilized with aqueous precipitation or coprecipitation.
Typically, processes which precipitate hydrous hydroxides in water are acid
base neutralizations or ion exchange reactions. This method typically involves
thermal treatment to obtain high surface area oxides. The soluble salts which
are
frequently used include nitrates, carbonates, and halides which are typically
"neutralized" by adding them to an aqueous ammonia solution, forming metal
hydroxides. This is by far the most commonly used method for preparing
precursors
for oxide powders. Conventional processes, co-thermohydrolysis and aqueous
coprecipitation, are generally described separately below:
Co-thermoh, dro , ~i
The first stage of the co-thermohydrolysis process involves preparing a
mixture, in aqueous medium, of at least a soluble cerium compound, preferably
a salt,
and or at least a soluble zirconium compound, preferably a salt. The mixture
can be
obtained either from solid compounds which are dissolved in water, or directly
from
aqueous solutions of these compounds, followed by mixing, in any order, of the
defined solutions.
Of the water soluble cerium compounds, one example is Ce IV salts, such as
nitrates including ceric ammonium nitrate, that are suitable for the present
invention.
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T.. ....,..

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Preferably, a cerium nitrate is used. The cerium IV salt solution can contain
some
cerium III. However, it is preferred that the salt contains at least about 85
% cerium
IV . An aqueous solution of cerium nitrate can be obtained by reacting nitric
acid with
a hydrated ceric oxide, prepared by a standard reaction of cerium III salt
solution,
carbonate for instance, with an ammonia solution in the presence of hydrogen
peroxide, an oxidizing agent. Ceric nitrate solutions obtained by electrolytic
oxidation of a cerous nitrate may also be used.
The aqueous solution of cerium IV salt can have some free acid, for instance a
normality ranging from about 0.1 to about 4 N. In the present invention, it is
possible
to use either a solution containing some free acid or a pre-neutralized
solution by
addition of a base, such as an aqueous solution of ammonia or alkaline
hydroxides,
e.g., sodium, potassium, etc. Preferably an ammonia solution is used to reduce
the
free acidity. In this case, it is possible to define the neutralization rate
(r) of the initial
solution by the following equation:
r = (ns-nz)~n~
wherein n, represents the total number of moles of Ce IV present in the
solution after
neutralization, n2 represents the number of OH~ ions effectively used to
neutralize the
initial free acidity from the Ce IV aqueous solution, and n3 represents the
total number
of moles of OH~ ions from the base added. When a neutralization step is used,
excess
base can be used in order to ensure the complete precipitation of the Ce(OH)4
species.
Preferably, r is lower than about 1, more preferably about 0.5 .
The soluble zirconium salts used in the invention can be, for instance,
zirconium sulfate, zirconyl nitrate or zirconyl chloride.
The amount of cerium and zirconium contained in the mixture substantially
corresponds to the stoichiometric proportion required to obtain the final
desired
composition.
Once the mixture is obtained, it is then heated. This thermal treatment,
called
thermohydrolysis, is carried out at a preferred temperature of between about
80 °C and
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the critical temperature of the reacting medium, typically between about 80
and about
350°C, more preferably between about 90 and about 200°C.
The heating stage can be carried out under air or under an inert gas such as
nitrogen. Any suitable reaction time can be used, usually between about 2 and
about
24 hours. The thermal treatment can be performed under atmospheric pressure or
under any higher pressure such as the saturated vapor pressure. When the
temperature is higher than the reflux temperature of the reaction medium
(usually
higher than about 100°C}, for instance between about 150 and about
350°C, the
reaction is performed in a closed reactor or autoclave. The pressure can be
equal to
the autogenic pressure and can be correlated to the chosen temperature. It is
also
possible to increase the pressure in the reactor. If required, some additional
base can
be added directly after the heating stage into the reaction medium in order to
improve
the yield of the reaction.
After the heating stage, a solid precipitate is recovered from the reactor and
separated from the mother liquor by any process known by the state of art, for
example filtration, settling or centrifugation.
The obtained precipitate optionally can be washed or impregnated with one or
several alkoxylated compounds, as more fully described below. In one
embodiment,
the precipitate is then dried, under air conditions for instance, at a
temperature
ranging from about 80 to about 300°C, preferably from about 100 to
about 150°C.
The drying stage is preferably performed until substantially no more weight
loss is
observed. Conventional drying techniques such as spray drying can be utilized.
After the optional drying step, the recovered precipitate is then calcined.
This
allows the formation of a crystalline phase. Usually, the calcination is
carried out at
temperatures ranging from about 200 to about 1000°C. The calcination
temperature is
typically higher than about 30(?°C, and preferably ranges from about
400 to about
800°C.
In accordance with the present invention an additive, e.g., a nonionic
surfactant and or an anionic surfactant, can be added to the salt solutions,
the base,
the reactor, and/or reaction media. The formation of the hydroxide (or other
precursor) is to be in the presence of the additive preferably during the
6
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CA 02285228 1999-09-30
WO 98/45212 PCT/US98/06437
thermohydrolysis/heating stage or the optional additional neutralization
stageladdition
of base and most preferably during the optional neutralization stage.
In a preferred embodiment of the thermohydrolysis, the additive is added to
the reactor during the neutralization stage.
As~i~eous Conrecipitation
The aqueous precipitation or coprecipitation method comprises preparing a
hydroxide (also referred to in the art as being an aqueous oxide) or carbonate
or
hydroxy carbonate by reacting a salt solution and a base in the presence of an
additive, such as an anionic and/or nonionic surfactant, possibly in the
presence of an
oxidizing agent, and separating the precipitate obtained, possibly washing or
IS impregnating it (preferably with an alkoxylated compound), and /or drying
or
calcining it.
The first stage of the co-precipitation process is the preparation of a
mixture in
an aqueous medium of at least a soluble cerium compound, preferably a salt, at
least a
soluble zirconium compound, preferably a salt, or both. The mixture can be
obtained
either from solid compounds which are dissolved in water, or directly from
aqueous
solutions of these compounds, followed by mixing, in any order, of the defined
solutions. According to the present invention the reaction of the base and
cerium and
or zirconium compound (e.g., salt) solutions is done in the presence of an
additive.
The cerium salt solution used can be any aqueous cerium salt solution, in the
cerous and or ceric state, which is soluble in the conditions of preparation,
in
particular a cerous chloride or cerium nitrate solution in the cerous or ceric
state or a
mixture of the same. Suitable water soluble cerium compounds include cerium
III
salts, and cerium nitrates or halides, e.g., chlorides, for instance. The
zirconium salt
solution used can be any aqueous zirconium salt solution which is soluble in
the
conditions of preparation. The soluble zirconium salts used in the invention
can be
nitrates, sulfates or halides, for instance, zirconium sulfate, zirconyl
nitrate or
zirconyl chloride. Zr (IV) salts can be utilized.
It is preferable to utilize a cerium or zirconium salt with a high degree of
metal purity, preferably greater than about 90 % , more preferably greater
than about
7
SUBSTITUTE SHEET (RULE 26)

CA 02285228 1999-09-30
WO 98/45212 PCT/US98/06437
95 % and most preferably above about 99 % . It is recognized that the Ce
and/or Zr
salts can comprise additional elements, such as Rare Earth elements, e.g., Pr
or La,
in varying amounts such as about 2 % . The amount of cerium and/or zirconium
contained in the mixture corresponds to the stoichiometric proportion required
to
obtain the final desired composition.
IO Optionally an oxidizing agent can be used. Among the oxidizing agents which
are suitable are solutions of sodium, potassium or ammonium perchlorate,
chlorate,
hypochlorite, or persulfate, hydrogen peroxide or air, oxygen or ozone. An
oxidizing
agent, preferably hydrogen peroxide, can be added to the cerium/zirconium
mixture
or to the cerium or zirconium salt before mixing together. The amount of
oxidizing
agent in relation to the salts to be oxidized can vary within wide limits. It
is generally
greater than the stoichiometry and preferably corresponds to an excess.
The precipitation can be carried out by the reaction of the salt solution or
solutions and a base solution. The base solution can be added to the cerium
and or
zirconium salt solution to precipitate out the hydroxides or carbonates or
hydroxy
carbonates (or the salt solutions can be added to the base solution). The base
can be
an ammonia solution or alkaline hydroxide solution, e.g., sodium, potassium,
etc., or
sodium, potassium or ammonia carbonate or bicarbonate solution. The base
solution
used can, in particular, be an aqueous solution of ammonia or of sodium or
potassium
hydroxide. An ammonia solution is preferably used. The normality of the base
solution is not a critical factor in accordance with the invention; it can
vary within
wide limits. A preferred range is between about 1 and about 5 N, more
preferably
between about 2 and about 3 N. The quantity of the base solution utilized is
determined such that the pH of the reaction medium is preferably greater than
about
7. In the case of batch precipitation, the amount of base solution added is
preferably at
least the amount required to precipitate out Ce(OH)4 and or Zr(OH)4.
The precipitation is carried out on a batch or continuous basis. In the case
of
a continuous precipitation, the pH of the reaction is typically maintained
between
about 7 and about 11, preferably between about 7.5 and about 9.5. Generally,
the
mixing time in the reaction medium is not a critical factor and can vary
within wide
limits; generally between about 15 minutes and about 2 hours are selected. The
8
SUBSTITUTE SHEET (RULE 26)
...... .. . T. _....._..... ..... .........._.___._..._...__.......... ..
...... . _.

CA 02285228 1999-09-30
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residence time of the material in the reactor is typically at least about 15
minutes,
preferably at least about 30 minutes. The reaction can be carried out at any
suitable
temperature such as room temperature.
After the reaction stage, a solid precipitate is recovered from the reactor
and
separated from the mother liquor by any process known in the state of art, for
example filtration, settling or centrifugation. The precipitate can be
separated by
conventional solid/liquid separation techniques such as decantation, drying,
filtration
and /or centrifugation. The obtained precipitate can then be washed.
Optionally, the
obtained precipitate can then be washed or impregnated with one or several
alkoxylated compounds, as described below.
The next stage of the process is calcination of the material, either with or
without an intermediate drying step. This allows the formation of a
crystalline solid
solution phase. Usually, the calcination is carried out at temperatures
ranging from
about 200 to about 1000°C. Calcination temperatures of greater than
about 300°C are
suitable, preferably ranging from about 350 to about 800°C.
As previously discussed, (Ce, Zr)OZ mixed oxides can be prepared by
various processes. Salts of Ce(III) and Zr(IV), nitrates for instance, can be
mixed
together and precipitated by adding a base such as sodium hydroxide or
ammonia.
Adequate precipitation conditions must be used to obtain the mixed oxide phase
after calcination at high temperature. This process also requires the use of a
base as
a precipitating agent. In any case, the precipitate is separated from the
mother
liquor by any known techniques such as filtration, decantation or
centrifugation.
Once washed, the precipitate is either dried at about 120°C and
calcined at a
minimum temperature of about 400°C or directly calcined at the same
temperature.
The final preferred product is a pure mixed oxide with little or no organics
since
they are removed as a result of calcination.
Additives:
The use of an additive, e.g., ethoxylated alcohols or surfactants of anionic
or
nonionic nature, during co-precipitation, hydrothermolysis or the like, in
order to
improve the thermal stability, surface area, oxygen storage capacity, and or
porosity
of oxides or their precursors, preferably (Ce, Zr)Oz mixed oxides, hydroxides
and
9
SUBSTITUTE SHEET (RULE 26)

CA 02285228 1999-09-30
WO 98/45212 PCT1US98/06437
carbonates is provided. The process is suitable for the production of cerium
oxides,
zirconium oxides, (Ce, Zr)Oz mixed oxides, (Ce, Zr)OZ solid solutions, and the
corresponding hydroxides or carbonates or hydroxy carbonates thereof, or
mixtures
thereof. The process is preferred for use in preparing cerium oxides, (Ce,
Zr)OZ
mixed oxides, (Ce, Zr)O~ solid solutions and mixtures thereof and most
preferably
for preparing (Ce, Zr)OZ mixed oxides and (Ce, Zr)Oz solid solutions.
In the current invention, an additive, such as a surfactant of anionic or
nonionic nature, is present during the formation of the cerium, zirconium or
(Ce,Zr) oxides) (mixed or solid solution) or precursors thereof, preferably
during
co-precipitation. The additive can generally be added to the: Metal salt
solution,
e.g., the Zr salt solution or Ce salt solution, a mixture of Ce and Zr salt
solution, a
base solution water, oxidizing agent or the reactor or reaction media.
Optionally
additional alkoxylated compounds or additives can also be added to the
precipitate
(generally in the form of a wet cake) obtained after liquid/solid separation
or during
the liquid/solid separation stage.
The additives can generally be described by the general formula:
Rn((CHz)x O)n RZ
where R, and Rz represent a linear or non-linear alkyl, aryl, and/or alkylaryl
group
or H or OH or Cl or Br or I; n is a number between about 1 and about 100; and
x is
a number from about 1 to about 4. R, and RZ can contain an alcohol group, a CO
group, a S-C group etc. Preferred are compounds comprising alkoxy groups,
particularly methoxy, ethoxy and propoxy groups which can generate an
improvement of the thermal stability, surface area, porosity and or oxygen
storage
capacity.
Anionic and nonionic surfactants suitable for use herein are described in
Handbook of Surfacta"rc, M. R. Porter, Blackie & Son Ltd., Glasgow; 1991, pp.
54 to 115, which is incorporated herein by reference. The terms "anionic
surfactant" , "nonionic surfactant" or "additive" as used herein encompass
mixtures
of surfactants as well as mixtures of other types of additives. The additive
of the
SUBSTITUTE SHEET (RULE 26)
T

CA 02285228 1999-09-30
WO 98/45212 PCT/US98/06437
present invention can advantageously be provided in the form of an aqueous
solution
having a relatively minor amount of the additive, e.g., anionic or nonionic
surfactant.
The additive preferably comprises less than about SO wt. % of the aqueous
solution,
and more preferably comprises from about 0.1 % to about 30 wt. % of an aqueous
solution. A preferred commercially available additive suitable for use is sold
by
Rhone-Poulenc Inc. under the tradename IGEPAL~ nonionic ethoxylates.
Anionic surfactants suitable for use include: carboxylates, phosphates,
sulfates
and sulfonates.
Suitable carboxylates have the general formula R-CHZC(O)O' and include:
a) ethoxycarboxylates of the formula: R-O(CHzCHzO)xCHzC00-, which includes
ether carboxylates of the formula:
R-O-(CH,CH20)~CHZ~i -O'M+
O
wherein R is an alkyl or alkylaryl group, M+ can be ammonium, potassium,
sodium or trithanolamine, and n2 can be from about 1 to about 13;
b) ester carboxylates of the formula: R,-CHz C[C(O)O](OH)(-Rz); and
c) sarcosinates of the formula: R-C(O)N(CH3)CHZCOO-
Phosphates have the general formula: RZP04 and include:
a) phosphate esters of the formulae {HO)(OR)P(O)2 and (RO)ZP(O)2
RO(CHZCH20)~ - O RO(CHZCH20)~ O
\P % \ P
MO~ \ OM RO(CHZCH j~ ~ OM
where R is an alkyl or alkyaryl group, n is moles of ethylene oxide (and/or
propylene
oxide) and M is hydrogen, sodium, potassium, or other counterion.
Suitable sulfates have the general formula: ROS03- and include:
a) alcohol sulfates;
b) alcohol ether sulfates; and
c) sulfated alkanolamide ethoxylate.
Suitable sulfonates have the general formula: RS03 and include:
a) sulphosuccinates;
b) taurates;
11
SUBSTITUTE SHEET (RULE 26)

CA 02285228 1999-09-30
WO 98/45212 PCT/US98/06437
S c) isethionates;
R-C(O)CHZCHZS03
d) alkyl benzene sulfonates;
e) fatty acid and diester sulfonates;
f) a-sulfo fatty acid esters;
g) alkyl naphthalene sulfonates;
h) formaldehyde naphthalene sulfonates;
i) olefin sulfonates; and
j) petroleum sulphonates.
Nonionic surfactants suitable for use include: acetylenic surfactants; alcohol
ethoxylates; alkanolamides; amine oxides; ethoxylated alkanolamides;
ethoxylated
long chain amines; ethylene oxide/propylene oxide (EO/PO) co-polymers;
sorbitan
derivatives; ethylene glycol, propylene glycol, glycerol and polyglyceryl
esters plus
their ethoxylated derivatives; alkyl amines; alkyl imidazolines; ethoxylated
oils and
fats; and alkyl phenol ethoxylates (ethoxylated alkyl phenols).
Preferred nonionic surfactants include the ethoxylated alkyl phenols supplied
by Rhone-Poulenc Inc. under the trademark "IGEPAL"~ and including:
-IGEPAL~ CA 720 : octyl phenol of about 12 EO such as represented by the
formula:
CsH~7 O _ O H
12
-IGEPAL~ CO 630 : nonylphenol ethoxylated polyethylene glycol or
nonophenol of about 9 EO such as represented by the formula:
O
CgH~g \ / O ~ v H
Additionally, IGEPAL~ CO 630 is well characterized in Phvsio-Chemical
Prot~~rties of Selected Anionic Cationic and Nonionic Surfactants, N. M. Van
Os
12
SUBSTITUTE SHEET (RULE 26)
T

CA 02285228 1999-09-30
WO 98/45212 PCT/IJS98/06437
et al., Amsterdam, 1993, pp. 312-316, 318 and 342 which is incorporated herein
by
reference.
Also useful are IGEPAL~ RC nonionic surfactants and IGEPAL~ DN
nonionic surfactants (dodecyl phenol + 5 to 14 EO) which are supplied by Rhone-
Poulenc Inc.
Also useful are tristyrylphenol ethoxylates.
Other preferred nonionics are glycol monoethers supplied by Dow Chemical
under the tradename "DOWANOL" and including:
-DOWANOL : ethylene glycol n-butyl ether
Bu~~'~OH
-DOWANOL DB : diethylene glycol n-butyl ether
Bu~~O~ OOH
-DOWANOL TBH : triethylene glycol n-butyl ether and higher
Bu~O,-,.~4~.~O~~~OH
Other preferred nonionic surfactants for use include the alkanolamides which
are the simplest members of the polyoxyethylene alkylamide family. Their
formula
can be either R~C(O)NH(CHZCHZOH) or R,C(O)N(CHZCHZOH)2 where R,
represents a linear or non-linear alkyl group comprising from about 1 to about
50°C
or H. Monoalcoholamides are generally solids while dialcoholamides are
generally
liquids. Both types can be used, preferably with coprecipitation. They include
those
sold by Rhone-Poulenc Inc. under the trademark "ALKAMIDE"~ and including:
-ALKAMIDE LE~
13
SUBSTITUTE SHEET (RULE 26)

CA 02285228 1999-09-30
WO 98/45212 PCT/US98106437
O
~~~ OH
C~~H2a N
~' ~~ OH
-ALKAMIDE~ L203
O
~I
~~ OH
C11H23 ' NH
Other preferred nonionic surfactants include ethoxylated amines such as
those sold under the trademark "RHODAMEEN" by Rhone-Poulenc Inc. and
including:
-RhodameenVP 532 SPB : Tallowamines, ethoxylated
(CH2CH20)x-H
R-N
~ (CH2CH20)y-H
Other preferred nonionic surfactants include amine oxides including those
supplied by Rhone-Poulenc Inc. under the trademark "Rhodamox"~ and including:
-Rhodamox LO : lauryl dimethylamine oxide
CH3
i
CH3(CH2)~o --N--~ O
CH3
Other additives are the polyethylene glycols. Polyethylene glycols include:
H O'~~; ~ H
14
SUBSTITUTE SHEET (RULE 26)
_.T_ .. . ..

CA 02285228 1999-09-30
WO 98/45212 PCT/US98/06437
Other additives suitable for use are carboxylic acids, both mono and
dicarboxylic acids. The general formula for a carboxylic acid can be
represented as:
O
R---C-OH .
Suitable carboxylic acids are listed:
TRIVIAL NAME STRUCTURE GENEVA NAME
MONOCARBOXYLIC
Formic H-COZH Methanoic acid
Acetic CH3-C02H Ethanoic acid
Propionic CH3-CHZ- COZH Propanic acid
Butyric CH3-CHZ ZCOZH Butanoic acid
Isobutric CH3-CH-COZH 2-Methylpropanoic
acid
CH3
Valeric CH3- CHZ Z COZH Pentanoic acid
Caproic CH3- CHZ 4 COZH Hexanoic acid
Caprylic CH3- CH2- 6 COZH Octanoic acid
Capric CH3- CHZ 8 COZH Decanoic acid
Lauric CH3- CHz ,o COZH Dodecanoic acid
Myristic CH3- CHZ- ,2 COZH Tetradecanoic acid
Palmitic CH3- CHZ-,4 Hexadecanoic acid
COZH
DICARBOXYLIC
Oxalic HOZC-COZH Ethanedioic acid
Malonic HOZC-CHZ-COZH Propanedioic acid
Succinic HOZC-CHz ZCOZH Butanedioic acid
Glutaric HOZC-CHZ-3COZH Pentanedioic acid
Adipic HOZC-CH2-4COZH Hexanedioic acid
Pimelic HOzC-CHZ-SC02H Heptanedioic acid
Suberic HOZC-CHZ 6COZH Octanedioic acid
Azelaic HOZC-CHZ-,COZH Nonanedioic acid
Sebacic HOZC-CHz BCOZH Decanedioic acid
SUBSTITUTE SHEET (RULE 26)

CA 02285228 1999-09-30
WO 98!45212 PCT/US98/06437
Carboxylate salts can also be utilized as additives.
As described previously the additives are to be present during the formation
of
the cerium hydroxide, oxide, hydroxy carbonate and/or carbonate, zirconium
hydroxide, oxide, hydroxy carbonate andlor carbonate, cerium/zirconium (Ce,Zr)
hydroxide, oxide (mixed or solid solution, i.e., one phase), hydroxy carbonate
and/or
carbonate. (For the addition of the nonionic ethoxylates and (e.g., IGEPAL~
surfactants} and the polyethylene glycols, it is preferred that the
ethoxylates be added
to either the metal (e.g., Ce,Zr) salt solution or solutions, preferably a
cerium nitrate
and/or zirconium nitrate aqueous solution, and/or the base solution,
preferably an
ammonia solution. Most preferably, the ethoxylates are added to the nitrate
solutions
and the ammonia solutions prior to reaction. For the amide surfactants (e.g.,
ALKAMIDE~ surfactants), it is preferred to add to the metal (e.g., Ce,Zr) salt
solution or solutions, preferably a cerium nitrate and/or zirconium nitrate
solution,
and/or water and/or the oxidizing agent and mixtures thereof.
For the addition of the carboxylic acid(s), addition to the base solution is
preferred, preferably addition to an ammonia solution.
The determination of an effective amount of addition for the additives is
within
the skill of an artisan. Generally, the additives are added (based on the
weight
percent of the reaction media and reagents) of from about 1 % to about 35 % ,
preferably from about 2 % to about 30 % and most preferably from about 3 % to
about
30%. For the ethoxylated additives, it is generally preferred to utilize from
about
2.5 % to about 35 % and preferably from about 10 % to about 25 % . For the
amide
additives, it is generally preferred to utilize from about 1 % to about 10%
and
preferably from about 2 % to about 5 % . An excess of additive can be utilized
without
detrimentally effecting the benefits of addition.
(~ tp ionatl Washin~/Im~re~,~nation
Most industrial processes which include the precipitation or the creation of a
solid in a liquid medium involve a solid/liquid separation state. Filtration,
decantation
or centrifugation are among the known techniques used for this purpose. After
the
solid/liquid separation is completed, the so-called wet cake comprises
precipitated
16
SUBSTITUTE SHEET (RULE 26)
1 T

CA 02285228 1999-09-30
WO 98/45212 PCT/US98/06437
particles and remaining mother liquor. In most of the processes, the mother
liquor
contains some salts that can contaminate the oxides generated during the next
calcination operation. To reduce the amount of contaminants, washing is needed
during and/or after the solid/Iiquid separation. In cases where the salts used
as raw
materials to make the precipitation are soluble in water, washing is typically
carried
out with water. The volume and temperature of water used for washing determine
the
purity of the material and its thermal stability as well.
The process of the present invention optionally includes the use of
alkoxylated
compounds having greater than 2 carbon atoms during the washing or
impregnating
stage in order to improve the thermal stability of cerium and or zirconium
oxides and
preferably (Ce,Zr)OZ mined oxides and solid solutions. The alkoxylated
compounds
suitable for use herein have greater than 2 carbon atoms.
In the scope of the present invention, the solid oxide material is separated
from
liquid by filtration or any other suitable method. In a preferred embodiment,
the
solid, otherwise called wet cake, is washed during a first stage with water to
remove
the water-soluble salts, nitrates for instance if nitrate solutions are the
raw materials
for the reaction. In a second stage of the preferred embodiment, the wet cake
is
washed or impregnated with a solution containing alkoxylated compounds such as
ethoxylated alcohols, organic compounds or ethoxylated polymers such as PEG.
Once
washed or impregnated, the wet cake is either dried and calcined or directly
calcined.
The final product is a pure mixed oxide having substantially no organics since
they
are removed during calcination.
The alkoxylated compounds of the present invention can be defined by the
general formula:
R, ((CH~xO)~ RZ
wherein R, and Rz represent linear or non-linear alkyl, aryl and/or alkylaryl
groups or
H or OH or Cl or Br or I; n is a number from 1 to 100; and x is a number from
1 to
4. R, and RZ can contain an alcohol group. Of the alkyl groups, methoxy,
ethoxy
17
SUBSTITUTE SHEET (RULE 26)

CA 02285228 1999-09-30
WO 98/45212 PCT/US98/06437
and propoxy groups are preferred in order to generate an improvement in the
thermal
stability of the (Ce,Zr)OZ mixed oxides and solid solutions.
The alkoxylated compound can be of the formula:
R,-((CH~X-O)n OH,
wherein R, is selected from the group consisting of linear and nonlinear alkyl
groups
having from 1 to 20 carbons and fatty hydrocarbon residues having from 8 to 20
carbons, n is from I to 100, and x is from 1 to 4. Preferably, n is from I2 to
40 and
x is from 1 to 3. More preferably, x is 2.
The alkoxylated compound can be of the formula:
H(OCH~~OH or H(OEt)"OH,
wherein the average of n is from 1 to 100.
Examples of suitable alkoxylated compounds can be of the formulae:
O
CgH~g ~ ~ O ~ H
x
wherein the average of x is 9 or from 4 to 15;
O
CgH17 ~ ~ O ~ H
X
wherein the average of x is 12;
~~ OH
C~~H2s ' N
\f \ OH ; and
O
I
~~~~ OH
C11H23 ~ NH
18
SUBSTITUTE SHEET (RULE 26)
~ I

CA 02285228 1999-09-30
WO 98/45212 Pc.T.~JS9biU6437
- Commercially available alkoxylated compounds suitable for use are sold by
Rhone-Poulenc Inc. under the trade names: IGEPAL'~ CO 630, IGEPAL~ CA 720,
,ALKrII~iIDE'~ LE, and ALKrIMIDE'' L203.
The alkoxylated compound can alternatively be of the formula:
Rz O ((CHz)~ O)il OH,
R3
wherein RZ and Rj are the same or different and are independently selected
from the
group consisting of hydrogen and linear and nonlinear alkyl groups having from
1 to
carbons, n is from 1~ to 100, and x is from 1 to 4. Preferably, n is from (2
to 40
and x is from 1 to 3. More preferably, x is 2.
The alkoxylated compound can further be of the formula:
RaO-((CH~xO)~ H,
wherein R, is selected from the group consisting of linear and noniir_ear
alkyl groups
having from 1 to 20 carbons, n is from 1 to 100, and x is from 1 to 4.
Preferably, n
is from 12 to 40 and x is from 1 to 3. More preferably, n is 3, and x is 2.
The alkoxylated compound can further be of the formula:
~'S-((CH~z~~n H,
35
wherein R, is selected from the group consisting of linear and nonlinear alkyl
groups
having from 1 to 20 carbons, n is from 1 to 100, and x is from 1 to 4.
Preferably, n
is from 4 to 40 and x is ~rom 1 to 3. More preferably, x is 2.
The alkoxylated compound can also be of the formula:
CH,
R6-(OCHZCH~n(O-CH2-CH~m OH.
19
SUBSTITUTE SHEEP (RULE 26)
AMENDED SHEET

CA 02285228 1999-09-30
WO 98/45212 PCT/US98/06437
S wherein R6 is selected from the group consisting of linear and nonlinear
alkyl groups
having from 1 to 20 carbons, n is from 1 to 100, and m is from 0 to 300
preferably 0
to 100. Preferably, n is from 12 to 40 and m is from 1 to 40.
The alkoxylated compound can alternatively be of the formula:
CH 3
HO-(CHZCH20)o(CHZCHO)m(CHZCH20)p H,
wherein o is from 0 to 300, m is from 0 to 300, and p is from 0 to 300.
The alkoxylated compound can further be of the formula:
R,-(O(CH~X)n Cl,
wherein R, is selected from the group consisting of linear and nonlinear alkyl
groups
having from 1 to 20 carbons, n is from 1 to 100, and x is from 1 to 4.
Preferably, n
is from 4 to 40 and x is from 1 to 3. More preferably, x is 2.
The alkoxylated compound can further be of the formula:
CH3 CH3
HO-(CH,CH20)rt,(CHzCH20)P(CHZCHO)q H,
wherein m is from 0 to 300, p is from 0 to 300, and q is from 0 to 300 and
having an
average molecular weight of from about 40 to about 8,000.
The alkoxylated compound can comprise, or be derived from, compounds as
listed below:
- Polyoxyalkylenated (polyethoxyethylenated, polyoxypropyhamad,
polyoxybutylenated) alkylphenols in which the alkyl substituent is
Cb C,2 and containing from 5 to 25 oxyalkylene units; examples
include Tritons X-45, X-114, X-100 and X-102, marketed by
Rohm & Haas Co.;
- glucosamide, glucamide, and glycerolamide;
- polyoxyalkylenated C6 Cu aliphatic alcohols containing from 1 to
25 oxyalkylene (oxyethylene, oxypropylene) units; examples
SUBSTtTUTE SHEET (RULE 26)
t i

CA 02285228 1999-09-30
WO 98/45212 PCT/US98/06437
include Tergitol 15-S-9 and Tergitol 24-L-6, marketed by Union
Carbide Corp.; Neodol 45-9, Neodol 23-65, Neodol 45-7 and
Neodol 45-4, marketed by Shell Chemical Co.; and Kyro KOB
marketed by the Procter & Gamble Co.;
- the products resulting from the condensation of ethylene oxide, the
compound resulting from the condensation of propylene oxide with
propylene glycol, such as the Pluronics marketed by BASF;
- the products resulting from the condensation of ethylene oxide, the
compound resulting from the condensation of propylene oxide with
ethylenediamine, such as the Tetronics marketed by BASF;
- amine oxides such as (C,o C,g alkyl) dimethylamine oxides and
(C6 C~ alkoxy) ethyldihydroxyethylamine oxides;
- the alkylpolyglycosides described in U.S. Patent No. 4,565,647;
- C6-CZO fatty acid amides;
- C6-C~ alkamides, preferably utilized at low concentrations;
- ethoxylated fatty acids; and
- ethoxylated amines.
The alkoxylated compound of the present invention can advantageously be
provided in the form of an aqueous solution having a relatively minor amount
of the
alkoxylated compound. The alkoxylated compound preferably comprises less than
about 50 wt. % of the aqueous solution, and more preferably comprises from
about
0.1 to about 30 wt. % of the aqueous solution. A preferred commercially
available
compound suitable for use is sold by Rhone-Poulenc Inc. under the tradename
IGEPAL~ CA 720 surfactant.
The alkoxylated compounds can also be utilized as additives as described
above. Conversely, the additives as described above can be utilized in the
washing or
impregnation of carbonates, hydroxides or oxides of cerium, zirconium, Ce/Zr
mixed
or solid solutions. Preferred additives for use are carboxylic acids,
carboxylate salts
and anionic surfactants. An embodiment of the present invention is the washing
or
impregnation utilizing the additives, preferably additives which are not
ethoxylated.
Impregnation is addition of the alkoxylated compound and/or additive,
preferably with
21
SUBSTITUTE SHEET (RULE 26)

CA 02285228 1999-09-30
WO 98/45212 PCT/US98/06437
mixing, to the oxide, hydroxide or carbonate, preferably in the form of a wet
cake,
followed by calcining. The preferred impregnation surfactant is an ethoxylated
atkylphenol. The alkoxyleted compound or additive is usually added at an
amount
equal to the weight of total oxide, hydroxide or carbonate in the wet cake.
The
material is then calcined at a temperature high enough to ensure removal of
carbonaceous remnants from the oxide, hydroxide or carbonate.
For example instead of being present during the formation, a carboxylic acid,
such as lauric acid, can be utilized in the washing or impregnation of a
hydroxide,
oxide or carbonate of cerium, zirconium, cerium/zirconium mixed or solid
solutions.
A preferred embodiment would be a carboxylic acid dissolved in aqueous ammonia
or
the like for washing or impregnation. The preferred mole ratio range for
ammonia
(NH3) to carboxylic acid is about 0 to about 4, preferably about 1.5 to about
3.5.
Oxides and Solid Solutions
Mixed oxides or solid solutions produced utilizing the additives typically
have
a weight ratio of Ce02 to ZrOz of from about 5:95 to about 95:5, preferably
from
about 95:5 to about 40:60. The mixed oxides and solid solutions, preferably
being
cerium rich, have a very high surface area, for example, greater than about 25
m 2I g,
preferably greater than about 30 m2/g, and more preferably greater than about
35 mZ/g
after calcination at about 900°C for about 6 hours. "Cerium rich"
refers to cerium
zirconium mixed oxides having a formula of (CeXZr,_x)OZ where x is greater
than or
equal to about 0.5. The mixed oxides and solid solutions, preferably being
cerium
rich, also have a very high oxygen storage capacity, for example, greater than
about
2, preferably greater than about 2.6 ml OZ/g after calcination at about
500°C for about
2 hours.
The surface area of the oxides and mixed oxides produced in accordance with
the present invention is designated as B.E.T. determined by nitrogen
adsorption
according to the standard procedure ASTM D 3663-78 established from the method
by BRUNAUER -EMMET - TELLER described in journal of the Americ n
Chemical Society, 60, 309 (1938). Thermal stability is designated as the
surface area
of any powdery inorganic material after aging at a given temperature for a
certain
time. In the current invention, 10 g of material are calcined in a muffle
furnace for
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about 6 hours at about 900°C. After this aging stage, the surface area
of the material
was measured by the method previously described.
Oxides produced with the addition of additives as described herein provide for
cerium oxides, zirconium oxides, cerium/zirconium mixed oxides or
cerium/zirconium solid solutions having a total pore volumes greater than
about 0.5
ml/g after calcination at about 500°C for about 2 hours, preferably
from about 0.5 to
about 1 ml/g after calcination at about 500°C for about 2 hours and
most preferably
greater than about 0.6 or 0.8 after calcination at about 500°C for
about 2 hours.
The following examples illustrate various aspects of the invention and are not
intended to limit the scope thereof.
Example I:
Using a co-precipitation method and a nitrate solution of cerium and
zirconium, a mixed oxide composition of: Ce02 = 80 wt % ZrOz = 20 wt % is
prepared. By reacting the various salts in stoichiometric amounts and adding
ammonia to the mixed nitrates to reach a pH of about 9, the mixed hydroxides,
corresponding to about 30 g of dried rare earth oxides (REO) are precipitated
out
from the solution and filtered on a Buchner filter. The cake is washed with
about
12.5 ml of deionized water per gram of oxide, then calcined for about 2 hours
at
about 500°C. The thermal stability of the product is evaluated after
calcination
under air in a muffle furnace at about 900°C for about 6 hours. The
surface area is
measured at about 22 mz/g by the B.E.T. method (Micromeretics Gemini 2360).
Example 2:
The experiment described in Example 1 is repeated. However, an IGEPAL~
CA 720 (Octyl Phenol containing 12 EO groups) surfactant is added during the
preparation of the Ce/Zr mixed oxide. The ratio moles of surfactant to moles
of
total metal is about 1.11. The surfactant is added into the nitrate metal
solution and
the ammonia solution. The concentration of pure surfactant is about 20 % in
the
nitrate solution and about 30 % in the ammonia solution. The obtained wet cake
is
washed with about 12.5 ml of deionized water per g of oxide, and calcined as
in
Example 1. The surface area measured after calcination under air at about
900°C
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S for about 6 hours is about 33 m2/g. The increase is about 47.5 % compared to
the
product made without surfactant.
Example 3:
The conditions used in Example 1 are utilized again. However, the mixed
oxide is prepared in the presence of an Alkamide LE~ surfactant, which is an
alkanolamide with a C" chain. The amount of surfactant added is 0.13 moles per
mole of metals. All the alkanolamide is added to the mixed nitrate solution.
The
surface area measured after calcination under air at about 900°C for
about 6 hours
is about 35 mz/g. This example further demonstrates the effect a small amount
of
surfactant has on the improvement of thermal stability.
Exam Ip a 4:
In this example a Zr rich mixed oxide is prepared. The stoichiometric
amounts of Ce nitrate solution and Zr nitrate solution are mixed to obtain a
product
with the following composition: 80 wt % Zr02 and 20 wt % Ce02. The mixed
oxide is precipitated using the procedure described in Example 1. The surface
area
after calcination under air at about 900°C for about 6 hours is about
32 m2/g.
Example 5:
The conditions used in Example 4 are utilized. In this case however, the
mixed oxides are precipitated in the presence of IGEPAL~ CA 720 surfactant
(Phenol Aromatic Ethoxylated - nonionic). The amount of surfactant used is
0.96
moles per mole of metal. IGEPAL~ CA 720 surfactant is added to both the
ammonia solution (concentration of surfactant is about 20 wt% ) and to the
nitrate
solution (concentration of surfactant is about 22 wt % ). The thermal
stability after
calcination under air at about 900°C for about 6 hours is about 38
m2/g, indicated
an improvement of approximately I9 % compared to the product made without
surfactant.
Examr,,de 6:
Oxygen Storage Capacity (OSC) is measured on the sample obtained in
Example 1. OSC is obtained using alternate pulses of CO and OZ in He passed
through the mixed oxide bed at about 400°C in order to simulate rich
and lean
conditions in an engine. CO is diluted to about 5 % in He and OZ to about 2.5
% in
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the same inert gas. The continuous flow rate of He is about 10.1.h-' and the
catalyst volume is about 0.1 cm3. O2, CO and COZ are measured using gas
chromatography. OSC is evaluated from the alternate pulses. The result is
about
1.6 ml OZ/g of mixed oxide (~0.1).
xample 7:
The OSC is measured on the sample prepared according to Example 2,
precipitated in the presence of an EO-surfactant. The result is about 2.4 ml
OZ/g of
mixed oxide (~0.1). The addition of surfactant had a significant effect on the
OSC
Increase.
Example 8:
A pure cerium dioxide is prepared by adding ammonia to a solution of Ce
nitrate in order to reach a pH value of about 9Ø The precipitated hydroxide
is
filtered on a Buchner filter and washed with about 12.5 ml of deionized water
per
gram of oxide. The surface area measured after calcination under air at about
900°C for about 6 hours is about 2 m2/g.
Example 9:
Example 8 is repeated. However, the precipitation is carried out in the
presence of a Alkamide LE~ surfactant. The concentration of surfactant in the
Ce
nitrate solution is about 2 weight percent. The surface area measured after
calcination at about 900°C for about 6 hours is about 4 mz/g. This
demonstrates the
improvement of the thermal stability of pure ceria by using a surfactant in
the
process.
Exam In a 10:
A co-thermohydrolysis procedure as described above is performed. This
example illustrates the preparation of a cerium-zirconium mixed oxide
(Ceo.,SZro.u02). Combine a solution of ceric nitrate and zirconyi nitrate in
the
stoichiometric proportions required to obtain the desired composition. The
nitrate
solution is preneutralized with NH40H to diminish the acidity. The
concentration
of the mixture (expressed in oxides of the different elements) is adjusted to
about 80
g/l. The mixture is heated in an autoclave reactor at about 150°C for
about 4
hours. For the pulp which is obtained in this way, add about 27 g of Alkamide
LE~
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surfactant. An ammonia solution is added to the previously described mixture
until
the pH is greater than about 8.5. The reaction mixture is heated to boiling
for
about 2 hours. After decanting the liquid from the solid, the resulting solid
is
resuspended and heated at about 100°C for about 1 hour. The product is
then
filtered and calcined at about 600°C for about 2 hours. The surface
area is
IO measured at about 32 mZ/g after calcination under air at about 900°C
for about 6
hours. Without the additive, the surface area is measured at about 19 m2/g
after
calcination under air at about 900°C for about 6 hours.
Example 11:
Utilizing a Mercury porosimeter supplied by Micromeritics samples of
Ce02/ZrOz 80/20 % wt. mixed oxides prepared by coprecipitation are evaluated
for
pore volume (measured after calcination under air at about 500°C for
about two
hours):
Sample A: prepared according to the coprecipitation method of Example 1
without
surfactant additive achieves a total pore volume mllg of about 0.35.
Sample B: prepared in accordance with Example 3 by addition of a nonionic
surfactant, Alkamide LE~ surfactant (Lauramide DEA) supplied by Rh6ne-Poulenc
Inc., achieves a total pore volume ml/g of about 0.88.
Sample C: prepared in accordance with Example 2 by addition of a nonionic
surfactant, IGEPAL~ CA-720 surfactant (Octyl Phenol Aromatic Ethoxylate)
supplied
by Rhone-Poulenc Inc., achieves a total pore volume ml/g of about 0.72.
Example 12:
Using a coprecipitation method, a nitrate solution of cerium and zirconium is
added to an aqueous solution containing ammonia and lauric acid, to prepare a
mixed oxide of composition: 80 wt % Ce02 and 20 wt % Zr02. By reacting the
various salts in stoichiometric amounts and adding to an ammonia solution
which
contains Iauric acid, the hydroxides, corresponding to 22.5 g of dried rare
earth
oxides (REO) are precipitated out from the solution and filtered on a Buchner
funnel. The ratio moles of lauric acid/moles of total metal is 0.2. The lauric
acid
is added only to the ammonia solution. The obtained wet cake is washed with
12.5
ml of deionized water per g of oxide and calcined under air for about 2 hours
at
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about 500°C. The thermal stability of the product is evaluated after
calcination
under air in a muffle furnace at about 900°C for about 6 hours. The
surface area is
measured at about 34 m2/g by the B.E.T. method (Micromeritics Gemini 2360).
The increase is about 49.0 % compared to the product made without lauric acid.
Lauric acid can be represented by the formula: CH3(CHz),oC(O)OH
Exam 1~ a 13:
The thermal stability is measured for two samples, by measuring the surface
area by the B.E.T. method (Micromeritics Gemini 2360 Norcross, Ga.) of three
samples which are aged (under air) for about 6 hours at about 900°C,
about
1000 ° C, and about 1100 ° C . The curves are shown below in
Figure 1.
Sample A: prepared according to the coprecipitation method of Example 1
without additive.
Sample B: prepared according to Example 2 by the addition of a nonionic
surfactant, Igepal~ CA-720 surfactant (Octyl Phenol Aromatic Ethoxylate)
supplied
by Rhone-Poulenc Inc.
Figure 1
30
w 25
a
_s
20 - - Sample A I
d
d 15 Sample B I
H
0'
900 1000 1100
templerature (C)
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5+
w