U.S. patent application number 13/518735 was filed with the patent office on 2012-12-06 for complex oxide, method for producing same, and exhaust gas purifying catalyst.
This patent application is currently assigned to ANAN KASEI CO., LTD.. Invention is credited to Naotaka Ohtake, Kazuhiko Yokota.
Application Number | 20120309614 13/518735 |
Document ID | / |
Family ID | 44195840 |
Filed Date | 2012-12-06 |
United States Patent
Application |
20120309614 |
Kind Code |
A1 |
Ohtake; Naotaka ; et
al. |
December 6, 2012 |
COMPLEX OXIDE, METHOD FOR PRODUCING SAME, AND EXHAUST GAS PURIFYING
CATALYST
Abstract
Disclosed are a composite oxide which is capable of maintaining
a large volume of pores even used in a high temperature
environment, and which has excellent heat resistance and catalytic
activity, as well as a method for producing the composite oxide and
a catalyst for exhaust gas purification employing the composite
oxide. The composite oxide contains cerium and at least one element
selected from aluminum, silicon, or rare earth metals other than
cerium and including yttrium, at a mass ratio of 85:15 to 99:1 in
terms oxides, and has a property of exhibiting a not less than 0.30
cm.sup.3/g, preferably not less than 0.40 cm.sup.3/g volume of
pores with a diameter of not larger than 200 nm, after calcination
at 900.degree. C. for 5 hours, and is suitable for a co-catalyst in
a catalyst for vehicle exhaust gas purification.
Inventors: |
Ohtake; Naotaka; (Anan-shi,
JP) ; Yokota; Kazuhiko; (Shanghai, CN) |
Assignee: |
ANAN KASEI CO., LTD.
Tokushima
JP
|
Family ID: |
44195840 |
Appl. No.: |
13/518735 |
Filed: |
December 24, 2010 |
PCT Filed: |
December 24, 2010 |
PCT NO: |
PCT/JP2010/073306 |
371 Date: |
August 3, 2012 |
Current U.S.
Class: |
502/263 ;
502/303; 502/304 |
Current CPC
Class: |
B01D 2255/2061 20130101;
B01J 37/0205 20130101; B01D 2255/2068 20130101; B01J 23/63
20130101; B01J 35/1066 20130101; B01J 23/10 20130101; B01J 37/0018
20130101; B01D 2257/404 20130101; B01D 2255/2065 20130101; B01J
35/1042 20130101; C01F 17/206 20200101; B01D 2255/30 20130101; C01F
17/34 20200101; C01P 2006/16 20130101; B01D 2257/702 20130101; B01D
2255/9202 20130101; B01J 37/031 20130101; B01D 2255/2066 20130101;
B01D 2257/502 20130101; C01P 2006/14 20130101; B01D 2255/2092
20130101; B01D 2255/2063 20130101; B01J 35/1038 20130101; B01J
37/088 20130101; C01F 17/32 20200101; B01J 35/108 20130101; B01D
53/94 20130101; B01J 37/035 20130101 |
Class at
Publication: |
502/263 ;
502/304; 502/303 |
International
Class: |
B01J 23/10 20060101
B01J023/10 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 25, 2009 |
JP |
2009-294338 |
Claims
1. A composite oxide comprising cerium and at least one element
selected from aluminum, silicon, or rare earth metals other than
cerium and including yttrium, at a mass ratio of 85:15 to 99:1 in
terms oxides, and having a property of exhibiting a not less than
0.30 cm.sup.3/g volume of pores with a diameter of not larger than
200 nm, after calcination at 900.degree. C. for 5 hours.
2. The composite oxide according to claim 1 having a property of
exhibiting a not less than 0.40 cm.sup.3/g volume of pores with a
diameter of not larger than 200 nm, after calcination at
900.degree. C. for 5 hours.
3. The composite oxide according to claim 1 having a property of
exhibiting a not less than 0.50 cm.sup.3/g volume of pores with a
diameter of not larger than 200 nm, after calcination at
900.degree. C. for 5 hours.
4. The composite oxide according to claim 1, having a property of
exhibiting a not less than 0.32 cm.sup.3/g volume of pores with a
diameter of not larger than 200 nm, after calcination at
800.degree. C. for 5 hours.
5. The composite oxide according to claim 1, comprising at least
silicon as said at least one element selected from aluminum,
silicon, or rare earth metals other than cerium and including
yttrium, and having a property of exhibiting a not less than 0.60
cm.sup.3/g volume of pores with a diameter of not larger than 200
nm, after calcination at 900.degree. C. for 5 hours.
6. The composite oxide according to claim 1, wherein said rare
earth metals other than cerium and including yttrium comprise at
least one element selected from the group consisting of yttrium,
lanthanum, praseodymium, and neodymium.
7. A method for producing a composite oxide comprising the steps
of: (a) providing a cerium solution not less than 90 mol % of which
cerium ions are tetravalent, (b) heating and maintaining said
cerium solution obtained from step (a) up to and at not lower than
60.degree. C., (c) adding an oxide precursor of at least one
element selected from aluminum, silicon, or rare earth metals other
than cerium and including yttrium, to a cerium suspension obtained
through said heating and maintaining, (d) heating and maintaining
said cerium suspension containing said oxide precursor of at least
one element selected from aluminum, silicon, or rare earth metals
other than cerium and including yttrium, up to and at not lower
than 100.degree. C., (e) neutralizing said suspension obtained from
step (d), (f) adding a surfactant to said suspension neutralized in
step (e) to obtain a precipitate, and (g) calcining said
precipitate.
8. The method according to claim 7, wherein a cerium content of
said cerium solution in step (a) is 5 to 100 g/L in terms of
CeO.sub.2.
9. A catalyst for exhaust gas purification comprising the composite
oxide according to claim 1.
Description
FIELD OF ART
[0001] The present invention relates to a composite oxide which may
be used as a catalyst, functional ceramics, solid electrolyte for
fuel cells, abrasive, and the like, particularly suitably used as a
co-catalyst material in catalysts for purifying vehicle exhaust gas
and the like, and which has a large pore volume, causing excellent
catalytic performance, as well as to a method for producing the
composite oxide and a catalyst for exhaust gas purification
employing the composite oxide.
BACKGROUND ART
[0002] Catalysts for purifying vehicle exhaust gas and the like are
composed of a catalytic metal such as platinum, palladium, or
rhodium, and a co-catalyst for enhancing the catalyst action of
such metal, both supported on a catalyst support made of, for
example, alumina or cordierite. The co-catalyst material absorbs
oxygen under the oxidizing atmosphere and desorbs oxygen under the
reducing atmosphere, and functions to optimally maintain the
air/fuel ratio so that the catalyst for exhaust gas purification
can efficiently purify noxious components in exhaust gases, such as
hydrocarbons, carbon monoxide, and nitrogen oxides.
[0003] Efficiency of a catalyst for purifying exhaust gas is
generally proportional to the contact area between the active
species of the catalytic metal and exhaust gas. It is also
important to maintain the air/fuel ratio at optimum, for which the
pore volume of a co-catalyst should be made larger to maintain
oxygen absorbing and desorbing capability at a high level. However,
a co-catalyst, such as cerium-containing oxides, is apt to be
sintered during use at high temperatures, e.g., for exhaust gas
purification. This results in reduction of its pore volume, causing
aggregation of the catalytic metals and decrease in the contact
area between exhaust gas and the catalytic metals, which leads to
reduction of efficiency in purifying exhaust gases.
[0004] In the light of the above, for improving the heat resistance
of cerium oxide, Patent Publication 1 proposes a method of
producing a cerium composite oxide containing cerium and other rare
earth metal elements. The method includes the steps of: forming a
liquid medium containing a cerium compound; heating the medium at a
temperature of at least 100.degree. C.; separating the precipitate
obtained at the end of the preceding step from the liquid medium;
adding thereto a solution of a compound of rare earth other than
cerium to form another liquid medium; heating the medium thus
obtained at a temperature of at least 100.degree. C.; bringing the
reaction medium obtained at the end of the preceding heating step
to a basic pH to obtain a precipitate; and separating and calcining
the precipitate.
[0005] The composite oxide obtained by this method is described to
have a porosity of at least 0.2 cm.sup.3/g provided by pores having
a diameter of at most 200 nm, after calcining at 1000.degree. C.
for 5 hours.
[0006] However, the largest porosity provided by pores having a
diameter of at most 200 nm of the composite oxides disclosed in the
specific examples in Patent Publication 1, is 0.24 cm.sup.3/g after
calcining at 1000.degree. C. for 5 hours, and the porosity of this
composite oxide after calcining at 900.degree. C. for 5 hours is
0.25 cm.sup.3/g provided by pores having a diameter of at most 200
nm. Thus further improvement is demanded.
[0007] Patent Publication 2 proposes, for the improvement of
thermal stability of cerium oxide (ceria), a composition containing
ceria and from about 5 to 25 mole % based on the moles of ceria of
a ceria stabilizer selected from the group consisting of La, Nd, Y,
and mixtures thereof. This composition is described to be prepared
by mixing a ceria precursor with from 5 to 25 mole % of a ceria
stabilizer selected from the group consisting of La, Nd, Y and
mixtures thereof; forming an intimate mixture of the ceria
precursor and the ceria stabilizer by either evaporation of the
mixture of the preceding step or precipitation of the mixture of
the preceding step as a hydroxide or a carbonate; and calcining the
resulting intimate mixture.
[0008] However, as a property of the resulting composition,
stabilized ceria, Patent Publication 2 is silent about the volume
of pores with a diameter of not larger than 200 nm after
calcination at 900.degree. C. for 5 hours. Besides, the method
disclosed in this publication does not provide a composite oxide
having a larger volume of pores with a diameter of not larger than
200 nm after calcination at 900.degree. C. for 5 hours, than the
composite oxide taught in Patent Publication 1.
PRIOR ART PUBLICATIONS
Patent Publications
[0009] Patent Publication 1: WO-2008-156219-A
[0010] Patent Publication 2: JP-4-214026-A
SUMMARY OF THE INVENTION
[0011] It is an object of the present invention to provide a
composite oxide which is capable of maintaining a large pore volume
even in use in a high temperature environment, which brings about
excellent heat resistance and catalytic activity, and which is
particularly suitable for a co-catalyst for a catalyst for exhaust
gas purification, as well as a catalyst for exhaust gas
purification utilizing the composite oxide.
[0012] It is another object of the present invention to provide a
method for producing a composite oxide which realizes easy
production of the composite oxide of the present invention capable
of maintaining a large pore volume even in use in a high
temperature environment.
[0013] According to the present invention, there is provided a
composite oxide comprising cerium and at least one element selected
from aluminum, silicon, or rare earth metals other than cerium and
including yttrium, at a mass ratio of 85:15 to 99:1 in terms of
oxides, and having a property of exhibiting a not less than 0.30
cm.sup.3/g volume of pores with a diameter of not larger than 200
nm, after calcination at 900.degree. C. for 5 hours.
[0014] According to the present invention, there is also provided a
method for producing a composite oxide comprising the steps of:
[0015] (a) providing a cerium solution not less than 90 mol % of
which cerium ions are tetravalent,
[0016] (b) heating and maintaining said cerium solution obtained
from step (a) up to and at not lower than 60.degree. C.,
[0017] (c) adding an oxide precursor of at least one element
selected from aluminum, silicon, or rare earth metals other than
cerium and including yttrium, to a cerium suspension obtained
through said heating and maintaining,
[0018] (d) heating and maintaining said cerium suspension
containing said oxide precursor up to and at not lower than
100.degree. C.,
[0019] (e) neutralizing said suspension obtained from step (d),
[0020] (f) adding a surfactant to said suspension neutralized in
step (e) to obtain a precipitate, and
[0021] (g) calcining said precipitate.
[0022] According to the present invention, there is further
provided a catalyst for exhaust gas purification comprising the
composite oxide of the present invention.
[0023] The composite oxide according to the present invention
contains at least one element selected from aluminum, silicon, or
rare earth metals other than cerium and including yttrium
(sometimes referred to as the particular rare earth metals
hereinbelow) at the particular ratio, and is capable of maintaining
a large pore volume even in use in a high temperature environment.
Thus the composite oxide according to the present invention, when
used as a co-catalyst in a catalyst for exhaust gas purification,
provides particularly effective purification of exhaust gas.
[0024] The method for producing a composite oxide according to the
present invention includes the steps (a) to (g), in particular,
step (f) of adding a surfactant after step (e), so that the
composite oxide according to the present invention may be obtained
conveniently.
EMBODIMENTS OF THE INVENTION
[0025] The present invention will now be explained in detail.
[0026] The composite oxide according to the present invention has a
property of exhibiting a not less than 0.30 cm.sup.3/g volume of
pores, preferably a not less than 0.40 cm.sup.3/g volume of pores,
more preferably a not less than 0.50 cm.sup.3/g volume of pores,
with a diameter of not larger than 200 nm after calcination at
900.degree. C. for 5 hours. In particular, the composite oxide of
the present invention, when containing at least silicon as the at
least one element selected from aluminum, silicon, or rare earth
metals other than cerium and including yttrium as will be discussed
later, has a property of exhibiting preferably a not less than 0.60
cm.sup.3/g volume of pores with a diameter of not larger than 200
nm after calcination at 900.degree. C. for 5 hours.
[0027] The composite oxide of the present invention has a property
of exhibiting usually a not less than 0.32 cm.sup.3/g volume of
pores, preferably a not less than 0.42 cm.sup.3/g volume of pores,
more preferably a not less than 0.52 cm.sup.3/g volume of pores,
with a diameter of not larger than 200 nm after calcination at
800.degree. C. for 5 hours. The upper limit of the volume of pores
with a diameter of not larger than 200 nm after calcination at
900.degree. C. or 800.degree. C. for 5 hours, is not particularly
limited, and may be about 0.80 cm.sup.3/g. With a less than 0.30
cm.sup.3/g volume of pores, excellent catalytic function may not be
brought about when the composite oxide is used in a catalyst for
exhaust gas purification.
[0028] As used herein, the volume of pores is a value obtained by
measuring a volume of pores with a diameter of not larger than 200
nm by means of mercury porosimetry.
[0029] The composite oxide according to the present invention has
the above-mentioned property, and contains cerium and at least one
element selected from aluminum, silicon, or the particular rare
earth metals, at a mass ratio of 85:15 to 99:1, preferably 85:15 to
95:5, in terms of oxides. If the oxide of cerium and at least one
element selected from aluminum, silicon, or the particular rare
earth metals, has a cerium content of less than 85 mass % or more
than 99 mass % in terms of CeO.sub.2, excellent catalytic function
may not be brought about.
[0030] The particular rare earth metals may preferably be yttrium,
lanthanum, praseodymium, neodymium, samarium, europium, gadolinium,
terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium,
or a mixture of two or more of these, with yttrium, lanthanum,
praseodymium, neodymium, or a mixture of two or more of these being
particularly preferred.
[0031] In the present invention, yttrium is expressed in terms of
Y.sub.2O.sub.3, lanthanum in terms of La.sub.2O.sub.3, cerium in
terms of CeO.sub.2, praseodymium in terms of Pr.sub.6O.sub.11,
neodymium in terms of Nd.sub.2O.sub.3, samarium in terms of
Sm.sub.2O.sub.3, europium in terms of Eu.sub.2O.sub.3, gadolinium
in terms of Gd.sub.2O.sub.3, terbium in terms of Tb.sub.4O.sub.7,
dysprosium in terms of Dy.sub.2O.sub.3, holmium in terms of
Ho.sub.2O.sub.3, erbium in terms of Er.sub.2O.sub.3, thulium in
terms of Tm.sub.2O.sub.3, ytterbium in terms of Yb.sub.2O.sub.3,
lutetium in terms of Lu.sub.2O.sub.3, aluminum in terms of
Al.sub.2O.sub.3, and silicon in terms of SiO.sub.2.
[0032] The production method according to the present invention
realizes easy production of the composite oxide of the present
invention with good reproducibility, and includes step (a) of
providing a cerium solution not less than 90 mol % of which cerium
ions are tetravalent.
[0033] The cerium solution used in step (a) may be, for example, a
ceric nitrate solution or ammonium ceric nitrate, with the ceric
nitrate solution being particularly preferred.
[0034] In step (a), the initial concentration of the cerium
solution not less than 90 mol % of which cerium ions are
tetravalent, may be adjusted to usually 5 to 100 g/L cerium,
preferably 5 to 80 g/L, more preferably 10 to 70 g/L in terms of
CeO.sub.2. Usually water is used for the adjustment of the
concentration of the cerium solution, and deionized water is
particularly preferred. If the initial concentration is too high,
the crystallinity of the precipitate to be discussed later is not
sufficiently high, and sufficient volume of pores cannot be formed
for holding the oxide precursor of at least one element selected
from aluminum, silicon, or the particular rare earth metals to be
discussed later, resulting in an insufficient volume of pores of
the ultimate composite oxide for exhibiting the desired property.
Too low an initial concentration leads to low productivity, which
is not industrially advantageous.
[0035] In the present production method, next step (b) of heating
and maintaining the cerium solution obtained from step (a) up to
and at not lower than 60.degree. C. is carried out to cause
reaction of the cerium solution. By way of step (b) of heating and
maintaining, cerium oxide hydrate is generated from the cerium
solution to form a cerium suspension. A reactor to be used in step
(b) may either be a sealed- or open-type vessel. An autoclave
reactor may preferably be used.
[0036] Instep (b), the temperature at which the cerium solution is
heated and maintained is not lower than 60.degree. C., preferably
60 to 200.degree. C., more preferably 80 to 180.degree. C., most
preferably 90 to 160.degree. C. The duration of heating and
maintaining is usually 10 minutes to 48 hours, preferably 30
minutes to 36 hours, more preferably 1 hour to 24 hours. With
insufficient heating and maintaining, the crystallinity of the
precipitate to be discussed later is not sufficiently high, and a
sufficient volume of pores cannot be formed for holding the oxide
precursor of at least one element selected from aluminum, silicon,
or the particular rare earth metals to be discussed later,
resulting in an insufficient volume of pores of the ultimate
composite oxide for exhibiting the desired property. Too long a
period of heating and maintaining is not industrially
advantageous.
[0037] The present method further includes step (c) of adding an
oxide precursor of at least one element selected from aluminum,
silicon, or rare earth metals other than cerium and including
yttrium, to a cerium suspension obtained through said step (b) of
heating and maintaining.
[0038] The oxide precursor may be any compound which may be
converted to an oxide of at least one element selected from
aluminum, silicon, or the particular rare earth metals, through an
oxidation treatment, such as calcining, and may be, for example, a
nitric acid solution of at least one of the particular rare earth
metals, aluminum nitrate, colloidal silica, siliconate, or
quaternary ammonium silicate sol.
[0039] The amount of the precursor to be added may be adjusted so
that the ratio of cerium in the cerium suspension to at least one
element selected from aluminum, silicon, or the particular rare
earth metals, is usually 85:15 to 99:1, preferably 85:15 to 95:5,
by mass in terms of oxides. If the oxide of cerium and at least one
element selected from aluminum, silicon, or the particular rare
earth metals, has a cerium content of less than 85 mass % or more
than 99 mass % in terms of CeO.sub.2, the resulting composite oxide
may not have a volume of pores for exhibiting the desired
property.
[0040] Step (c) may be carried out after the cerium suspension
obtained through the heating and maintaining in step (b) is
cooled.
[0041] Such cooling may usually be carried out under stirring
according to a commonly known method. The cooling may either be
natural cooling by leaving the suspension to stand, or forced
cooling with cooling tubes. The cooling may be carried out down to
usually 40.degree. C. or lower, preferably about a room temperature
of 20 to 30.degree. C.
[0042] In step (c), before adding the precursor, the salt
concentration of the cerium suspension may be adjusted by removing
the mother liquor from the cerium suspension or by adding water.
The removal of the mother liquor may be effected, for example, by
decantation, Nutsche method, centrifugation, or filter-pressing. In
this case, a slight amount of cerium is removed with the mother
liquor, so the amounts of the precursor and water to be added next
may be adjusted, taking this removed amount of cerium into
consideration.
[0043] The present method includes step (d) of heating and
maintaining the cerium suspension containing the precursor up to
and at not lower than 100.degree. C., preferably 100 to 200.degree.
C., more preferably 100 to 150.degree. C.
[0044] In step (d), the duration of the heating and maintaining may
be usually 10 minutes to 6 hours, preferably 20 minutes to 5 hours,
more preferably 30 minutes to 4 hours.
[0045] In step (d) of heating and maintaining, at lower than
100.degree. C., the crystallinity of the precipitate to be
discussed later is not sufficiently high, resulting in an
insufficient volume of pores of the ultimate composite oxide for
exhibiting the desired property. Too long a period of heating and
maintaining is not industrially advantageous.
[0046] The present method includes step (e) of neutralizing the
suspension obtained from step (d). By this neutralization in step
(e), cerium oxide hydrate containing the precursor is generated in
the suspension.
[0047] The neutralization in step (e) may be effected by adding a
base, for example, sodium hydroxide, potassium hydroxide, aqueous
ammonia, ammonia gas, or a mixture thereof, with aqueous ammonia
being particularly preferred.
[0048] The neutralization may be carried out by adding a base to
the suspension obtained from step (d) under stirring, or in case of
ammonia gas, by bubbling the suspension with ammonia gas in a
reactor under stirring. Usually, the neutralization may be carried
out so as to generate a precipitate in the suspension at about pH 7
to 9, preferably pH 7 to 8.5.
[0049] Step (e) may be carried out after the cerium suspension
obtained through the heating and maintaining in step (d) is
cooled.
[0050] Such cooling may usually be carried out under stirring
according to a commonly known method. The cooling may either be
natural cooling by leaving the suspension to stand, or forced
cooling with cooling tubes. The cooling may be carried out down to
usually 40.degree. C. or lower, preferably about a room temperature
of 20 to 30.degree. C.
[0051] The present method includes step (f) of adding a surfactant
to the suspension neutralized in step (e) to obtain a
precipitate.
[0052] The surfactant used in step (f) may be, for example, an
anionic surfactant, such as ethoxycarboxylate, a nonionic
surfactant, such as alcohol ethoxylate, polyethylene glycol,
carboxylic acid, or a mixture thereof, with carboxylic acid being
particularly preferred.
[0053] The carboxylic acid may preferably be a saturated carboxylic
acid, such as decanoic, lauric, myristic, or palmitic acid, with
lauric acid being particularly preferred.
[0054] The amount of the surfactant to be added in step (f) is
usually 5 to 50 parts by mass, preferably 7 to 40 parts by mass,
more preferably 10 to 30 parts by mass, based on 100 parts by mass
of the total of cerium, aluminum, silicon, and the particular rare
earth metals in the suspension neutralized in step (e) in terms of
oxides. With the amount smaller than the above range, the pore
volume of the ultimate composite oxide may not be sufficient for
exhibiting the desired property. The amount exceeding the above
range will impact the pore volume little, and is not industrially
advantageous.
[0055] The surfactant to be used in step (f), if in a solid form,
may be dissolved in water or aqueous ammonia to be used as a
surfactant solution. Here, the concentration of the surfactant is
not particularly limited as long as the solution is stable, and may
usually be 10 g/L to 500 g/L, preferably about 50 to 300 g/L, for
workability and efficiency.
[0056] In step (f), it is preferred to have a retention time after
adding the surfactant, in order to cause the cerium oxide hydrate
containing the precursor present in the suspension, which has been
neutralized in step (e), to uniformly adsorb the surfactant on its
surface. The retention time may usually be 10 minutes to 6 hours,
preferably 20 minutes to 5 hours, more preferably 30 minutes to 4
hours. The retention may preferably be carried out while the
precipitate is stirred.
[0057] If step (f) of adding the surfactant is performed, for
example, after step (c) and before step (d), or after step (d) and
before step (e), the effect of the addition cannot be achieved, and
the pore volume of the ultimate composite oxide is insufficient for
exhibiting the desired property. Thus step (f) must be carried out
after step (e).
[0058] Through step (f), a slurry of the precipitate of cerium
oxide hydrate containing the precursor may be obtained, which is
highly crystalline and on which particle surface the surfactant has
uniformly been adsorbed. The precipitate may be separated by, for
example, Nutsche method, centrifugation, or filter-pressing. The
precipitate may optionally be washed with water as necessary. For
improving efficiency in the subsequent step (g), the precipitate
may optionally be dried as appropriate. Such drying may be carried
out at about 60 to 200.degree. C.
[0059] The present method includes step (g) of calcining the
precipitate thus obtained. The temperature for the calcining is
usually 250 to 700.degree. C., preferably 300 to 600.degree. C.
[0060] The duration of the calcination in step (g) may suitably be
determined in view of the calcination temperature, and may usually
be 1 to 10 hours.
[0061] The composite oxide powder obtained by the method of the
present invention may be made into a desired particle size by
pulverization. For example, for use as a co-catalyst in a catalyst
for exhaust gas purification, the composite oxide powder preferably
has an average particle size of 1 to 50 .mu.m.
[0062] The catalyst for exhaust gas purification according to the
present invention is not particularly limited as long as it
incorporates a co-catalyst containing the composite oxide of the
present invention, and the method of production thereof and other
materials to be used may be, for example, conventional.
EXAMPLES
[0063] The present invention will now be explained in more detail
with reference to Examples and Comparative Examples, which are not
intended to limit the present invention.
Example 1
[0064] This example relates to a composite oxide of cerium oxide
and lanthanum oxide at a mass ratio of 90:10.
[0065] 50 g of a ceric nitrate solution in terms of CeO.sub.2
containing not less than 90 mol % tetravalent cerium ions was
measured out, and adjusted to a total amount of 1 L with pure
water. The obtained solution was heated to 100.degree. C.,
maintained at this temperature for 30 minutes, and allowed to cool
down to the room temperature, to thereby obtain a cerium
suspension.
[0066] After the mother liquor was removed from the cerium
suspension thus obtained, 20.8 ml of a lanthanum nitrate solution
(5.2 g in terms of La.sub.2O.sub.3) was added, and the total volume
was adjusted to 1 L with pure water.
[0067] Then the cerium suspension containing a precursor of
lanthanum oxide was maintained at 120.degree. C. for 2 hours,
allowed to cool, and neutralized to pH 8.5 with aqueous
ammonia.
[0068] To a slurry resulting from the neutralization, an ammonium
laurate solution prepared by dissolving 10.4 g of lauric acid in
1.2% aqueous ammonia was added, and stirred for 30 minutes. The
obtained slurry was subjected to solid-liquid separation through a
Nutsche filter to obtain a filter cake. The cake was calcined in
the air at 300.degree. C. for 10 hours to obtain composite oxide
powder mainly composed of cerium oxide with 10% by mass of
lanthanum oxide.
[0069] For determination of its properties, the obtained composite
oxide powder was calcined in the air at 800.degree. C. for 5 hours
or at 900.degree. C. for 5 hours, and then subjected to measurement
of the volume of pores with a diameter of not larger than 200 nm,
by means of mercury porosimetry. The results are shown in Table
1.
Example 2
[0070] This example relates to a composite oxide of cerium oxide
and lanthanum oxide at a mass ratio of 85:15.
[0071] Composite oxide powder mainly composed of cerium oxide with
15% by mass of lanthanum oxide was prepared in the same way as in
Example 1, except that the amount of the lanthanum nitrate solution
was 33.2 ml (8.3 g in terms of La.sub.2O.sub.3). The properties of
the composite oxide powder thus obtained were evaluated in the same
way as in Example 1. The results are shown in Table 1.
Example 3
[0072] This example relates to a composite oxide of cerium oxide
and praseodymium oxide at a mass ratio of 90:10.
[0073] Composite oxide powder mainly composed of cerium oxide with
10% by mass of praseodymium oxide was prepared in the same way as
in Example 1, except that the lanthanum nitrate solution was
replaced with 20.5 ml of a praseodymium nitrate solution (5.2 g in
terms of Pr.sub.6O.sub.11). The properties of the composite oxide
powder thus obtained were evaluated in the same way as in Example
1. The results are shown in Table 1.
Example 4
[0074] This example relates to a composite oxide of cerium oxide,
lanthanum oxide, and praseodymium oxide at a mass ratio of
90:5:5.
[0075] Composite oxide powder mainly composed of cerium oxide with
5% by mass each of lanthanum oxide and praseodymium oxide was
prepared in the same way as in Example 1, except that the amount of
the lanthanum nitrate solution was 10.4 ml (2.6 g in terms of
La.sub.2O.sub.3), and 10.3 ml of a praseodymium nitrate solution
(2.6 g in terms of Pr.sub.6O.sub.11) was added at the same time.
The properties of the composite oxide powder thus obtained were
evaluated in the same way as in Example 1. The results are shown in
Table 1.
Example 5
[0076] This example relates to a composite oxide of cerium oxide
and neodymium oxide at a mass ratio of 90:10.
[0077] Composite oxide powder mainly composed of cerium oxide with
10% by mass of neodymium oxide was prepared in the same way as in
Example 1, except that the lanthanum nitrate solution was replaced
with 23.5 ml of a neodymium nitrate solution (5.2 g in terms of
Nd.sub.2O.sub.3). For determination of its properties, the
composite oxide powder thus obtained was subjected to the
evaluation of the volume of pores with a diameter of not larger
than 200 nm after calcination at 900.degree. C. for 5 hours in the
same way as in Example 1. The results are shown in Table 1.
Example 6
[0078] This example relates to a composite oxide of cerium oxide
and yttrium oxide at a mass ratio of 90:10.
[0079] Composite oxide powder mainly composed of cerium oxide with
10% by mass of yttrium oxide was prepared in the same way as in
Example 1, except that the lanthanum nitrate solution was replaced
with 22.9 ml of a yttrium nitrate solution (5.2 g in terms of
Y.sub.2O.sub.3). For determination of its properties, the composite
oxide powder thus obtained was subjected to the evaluation of the
volume of pores with a diameter of not larger than 200 nm after
calcination at 900.degree. C. for 5 hours in the same way as in
Example 1. The results are shown in Table 1.
Example 7
[0080] This example relates to a composite oxide of cerium oxide
and aluminum oxide at a mass ratio of 90:10.
[0081] Composite oxide powder mainly composed of cerium oxide with
10% by mass of aluminum oxide was prepared in the same way as in
Example 1, except that the lanthanum nitrate solution was replaced
with 38.2 g of aluminum nitrate nonahydrate (5.2 g in terms of
Al.sub.2O.sub.3). For determination of its properties, the
composite oxide powder thus obtained was subjected to the
evaluation of the volume of pores with a diameter of not larger
than 200 nm after calcination at 900.degree. C. for 5 hours in the
same way as in Example 1. The results are shown in Table 1.
Example 8
[0082] This example relates to a composite oxide of cerium oxide,
lanthanum oxide, praseodymium oxide, and aluminum oxide at a mass
ratio of 85:5:5:5.
[0083] Composite oxide powder mainly composed of cerium oxide with
5% by mass each of lanthanum oxide, praseodymium oxide, and
aluminum oxide was prepared in the same way as in Example 1, except
that the amount of the lanthanum nitrate solution was 11.2 ml (2.8
g in terms of La.sub.2O.sub.3), and 11.1 ml of a praseodymium
nitrate solution (2.8 g in terms of Pr.sub.6O.sub.11) and 20.6 g of
aluminum nitrate nonahydrate (2.8 g in terms of Al.sub.2O.sub.3)
were added at the same time. For determination of its properties,
the composite oxide powder thus obtained was subjected to the
evaluation of the volume of pores with a diameter of not larger
than 200 nm after calcination at 900.degree. C. for 5 hours in the
same way as in Example 1. The results are shown in Table 1.
Example 9
[0084] This example relates to a composite oxide of cerium oxide
and silicon oxide at a mass ratio of 90:10.
[0085] Composite oxide powder mainly composed of cerium oxide with
10% by mass of silicon oxide was prepared in the same way as in
Example 1, except that the lanthanum nitrate solution was replaced
with 25.4 g of colloidal silica (5.2 g in terms of SiO.sub.2). For
determination of its properties, the composite oxide powder thus
obtained was subjected to the evaluation of the volume of pores
with a diameter of not larger than 200 nm after calcination at
900.degree. C. for 5 hours in the same way as in Example 1. The
results are shown in Table 1.
Example 10
[0086] This example relates to a composite oxide of cerium oxide,
lanthanum oxide, praseodymium oxide, and silicon oxide at a mass
ratio of 85:5:5:5.
[0087] Composite oxide powder mainly composed of cerium oxide with
5% by mass each of lanthanum oxide, praseodymium oxide, and silicon
oxide was prepared in the same way as in Example 1, except that the
amount of the lanthanum nitrate solution was 11.2 ml (2.8 g in
terms of La.sub.2O.sub.3), and 11.1 ml of praseodymium nitrate
solution (2.8 g in terms of Pr.sub.6O.sub.11) and 13.7 g of
colloidal silica (2.8 g in terms of SiO.sub.2) were added at the
same time. For determination of its properties, the composite oxide
powder thus obtained was subjected to the evaluation of the volume
of pores with a diameter of not larger than 200 nm after
calcination at 900.degree. C. for 5 hours in the same way as in
Example 1. The results are shown in Table 1.
Comparative Examples 1 to 4
[0088] Various composite oxide powders were prepared in the same
way as in Examples 1 to 4, except that the treatment with the
ammonium laurate solution was eliminated. That is, these composite
oxides were prepared by the production method disclosed in Patent
Publication 1. The properties of the composite oxide powders thus
obtained were evaluated in the same way as in Example 1. The
results are shown in Table 1.
Comparative Example 5
[0089] Composite oxide powder mainly composed of cerium oxide with
10% by mass of lanthanum oxide was prepared in the same way as in
Example 1, except that the ammonium laurate solution was added
immediately after the addition of the lanthanum nitrate solution.
For determination of its properties, the composite oxide powder
thus obtained was subjected to the evaluation of the volume of
pores with a diameter of not larger than 200 nm after calcination
at 900.degree. C. for 5 hours in the same way as in Example 1. The
results are shown in Table 1.
Comparative Example 6
[0090] Composite oxide powder mainly composed of cerium oxide with
10% by mass of lanthanum oxide was prepared in the same way as in
Example 1, except that the ammonium laurate solution was added
immediately before the neutralization with aqueous ammonia. For
determination of its properties, the composite oxide powder thus
obtained was subjected to the evaluation of the volume of pores
with a diameter of not larger than 200 nm after calcination at
900.degree. C. for 5 hours in the same way as in Example 1. The
results are shown in Table 1.
TABLE-US-00001 TABLE 1 Composition of Ce + Volume of pores
(cm.sup.3/g) ME in terms of oxides (.ltoreq.200 nm) (mass %)
800.degree. C./5 h 900.degree. C./5 h Example 1 Ce/La = 90/10 0.64
0.53 Example 2 Ce/La = 85/15 0.36 0.32 Example 3 Ce/Pr = 90/10 0.41
0.36 Example 4 Ce/La/Pr = 90/5/5 0.50 0.44 Example 5 Ce/Nd = 90/10
-- 0.33 Example 6 Ce/Y = 90/10 -- 0.31 Example 7 Ce/Al = 90/10 --
0.38 Example 8 Ce/La/Pr/Al = 85/5/5/5 -- 0.35 Example 9 Ce/Si =
90/10 -- 0.68 Example 10 Ce/La/Pr/Si = 85/5/5/5 -- 0.70 Comp. Ex. 1
Ce/La = 90/10 0.22 0.21 Comp. Ex. 2 Ce/La = 85/15 0.21 0.22 Comp.
Ex. 3 Ce/Pr = 90/10 0.23 0.23 Comp. Ex. 4 Ce/La/Pr = 90/5/5 0.26
0.25 Comp. Ex. 5 Ce/La = 90/10 -- 0.15 Comp. Ex. 6 Ce/La = 90/10 --
0.21 ME stands for one or more elements selected from aluminum,
silicon, and rare earth metals other than cerium and including
yttrium.
[0091] As clearly seen from the results in Table 1, the composite
oxides of Examples prepared by the method of the present invention
exhibited larger volumes of pores compared to the composite oxides
of Comparative Examples 1 to 4 prepared by the method disclosed in
Patent Publication 1, after calcination under the same conditions.
It is assumed that, in Comparative Examples 1 to 4, during the
course of calcining the filter cake to obtain a composite oxide,
evaporation of moisture present at the interface of the particles
in the precipitate induced aggregation of the particles, and
sufficient volume of pores could not be achieved. In contrast, in
the composite oxides of Examples prepared by the method of the
present invention, the surfactant was adsorbed uniformly on the
surface of the particles in the precipitate to hydrophobize the
particle surface, which prevented aggregation of the particles
caused by the moisture evaporation during calcining. As a result,
the composite oxides of Examples were able to maintain, even after
the calcination at high temperature, large volumes of pores which
cannot be achieved by the composite oxides disclosed in Patent
Publication 1.
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