U.S. patent application number 15/729291 was filed with the patent office on 2018-02-08 for method for producing composite oxide and composite oxide catalyst.
This patent application is currently assigned to SANTOKU CORPORATION. The applicant listed for this patent is SANTOKU CORPORATION. Invention is credited to Shinya MATSUO, Tadatoshi MUROTA.
Application Number | 20180036714 15/729291 |
Document ID | / |
Family ID | 50477306 |
Filed Date | 2018-02-08 |
United States Patent
Application |
20180036714 |
Kind Code |
A1 |
MATSUO; Shinya ; et
al. |
February 8, 2018 |
METHOD FOR PRODUCING COMPOSITE OXIDE AND COMPOSITE OXIDE
CATALYST
Abstract
Provided are a method for producing a composite oxide and the
composite oxide. The method includes steps of: (a) preparing a Ce
aqueous solution not less than 80 mol % of which Ce ions are
tetravalent, and a Zr aqueous solution; (b1) mixing the Zr aqueous
solution and a portion of the Ce aqueous solution to prepare a
mixed aqueous solution (X1); (c1) hydrothermally processing the
solution (X1); (b2) adding the remainder of the Ce aqueous solution
of step (a) to a colloidal solution (Y1) of a composite salt
obtained from step (c1) to prepare a colloidal solution (Y2) of a
composite salt; (c2) hydrothermally processing the solution (Y2);
(d) mixing a colloidal solution (Y3) of a composite salt obtained
from step (c2) with an alkaline solution and a surfactant to
prepare a precipitate; and (e) calcining the precipitate.
Inventors: |
MATSUO; Shinya; (Kobe-shi,
JP) ; MUROTA; Tadatoshi; (Kobe-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SANTOKU CORPORATION |
Kobe-shi |
|
JP |
|
|
Assignee: |
SANTOKU CORPORATION
Kobe-shi
JP
|
Family ID: |
50477306 |
Appl. No.: |
15/729291 |
Filed: |
October 10, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14434115 |
Apr 8, 2015 |
|
|
|
PCT/JP2013/076662 |
Oct 1, 2013 |
|
|
|
15729291 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C01B 2203/1047 20130101;
B01D 2255/407 20130101; C01B 2203/1064 20130101; B01J 37/08
20130101; C01B 3/40 20130101; C01B 2203/1076 20130101; C01B
2203/0233 20130101; B01J 2523/824 20130101; C01B 2203/1058
20130101; B01J 37/04 20130101; B01J 2523/847 20130101; B01J 37/0201
20130101; Y02T 10/22 20130101; B01D 53/945 20130101; B01J 37/0207
20130101; B01J 37/10 20130101; B01J 23/10 20130101; B01J 37/031
20130101; B01D 2255/20761 20130101; B01J 23/72 20130101; B01J
2523/00 20130101; Y02T 10/12 20130101; B01D 2255/1023 20130101;
C01G 25/00 20130101; B01J 23/464 20130101; B01J 23/894 20130101;
B01D 2255/1021 20130101; B01D 2255/2066 20130101; B01J 23/755
20130101; B01D 2255/20715 20130101; B01J 23/42 20130101; B01J
23/745 20130101; C01B 2203/1082 20130101; Y02P 20/52 20151101; B01D
2255/2065 20130101; B01J 23/002 20130101; B01D 2255/20738 20130101;
B01D 2255/20753 20130101; B01D 2255/1025 20130101; B01J 23/892
20130101; B01J 2523/00 20130101; B01J 2523/3712 20130101; B01J
2523/3718 20130101; B01J 2523/48 20130101; B01J 2523/00 20130101;
B01J 2523/3712 20130101; B01J 2523/3718 20130101; B01J 2523/48
20130101; B01J 2523/824 20130101; B01J 2523/847 20130101 |
International
Class: |
B01J 23/10 20060101
B01J023/10; B01D 53/94 20060101 B01D053/94; B01J 23/00 20060101
B01J023/00; B01J 23/42 20060101 B01J023/42; B01J 23/46 20060101
B01J023/46; B01J 23/72 20060101 B01J023/72; B01J 23/745 20060101
B01J023/745; B01J 23/755 20060101 B01J023/755; B01J 23/89 20060101
B01J023/89; B01J 37/02 20060101 B01J037/02; B01J 37/03 20060101
B01J037/03; B01J 37/04 20060101 B01J037/04; B01J 37/10 20060101
B01J037/10; C01B 3/40 20060101 C01B003/40; C01G 25/00 20060101
C01G025/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 8, 2012 |
JP |
2012-223741 |
Claims
1. A composite oxide obtained by a method comprising the steps of:
(a) preparing at least a cerium aqueous solution 80 to 100 mol % of
which cerium ions are tetravalent, and a zirconium aqueous solution
containing zirconium ions; (b1) mixing said zirconium aqueous
solution and a portion of said cerium aqueous solution prepared in
step (a) to prepare a mixed aqueous solution (X1); (c1)
hydrothermally processing said mixed aqueous solution (X1); (b2)
adding a remainder of said cerium aqueous solution prepared in step
(a) to a colloidal solution (Y1) of a composite salt obtained by
said hydrothermal processing in step (c1) to prepare a colloidal
solution (Y2) of a composite salt; (c2) hydrothermally processing
said colloidal solution (Y2) of a composite salt obtained from step
(b2) ; (d) mixing a colloidal solution (Y3) of a composite salt
obtained by said hydrothermal processing in step (c2) with an
alkaline solution and a surfactant to prepare a precipitate; and
(e) calcining said precipitate, wherein the composite oxide
comprises Ce, Zr, Pr, and oxygen, and wherein the content of Zr is
not less than 20 mol% and not more than 50 mol %, and the content
of Pr is not more than 5 mol %, with respect to the total of the
elements other than oxygen being 100 mol %.
2. A composite oxide catalyst comprising the composite oxide of
claim 1 and a catalytic metal Ni.
3. The composite oxide catalyst according to claim 2 for use as a
catalyst for hydrocarbon steam reforming or purification of exhaust
gas.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 14/434,115 filed Apr. 8, 2015 (pending), which is a National
Stage of International Application No. PCT/JP2013/076662 filed Oct.
1, 2013, claiming priority based on Japanese Patent Application No.
2012-223741 filed Oct. 8, 2012, the contents of all of which are
incorporated herein by reference in their entirety.
FIELD OF ART
[0002] The present invention relates to a method for producing a
composite oxide which finds use as a catalyst for hydrocarbon steam
reforming or purification of exhaust gas, and to a composite oxide
catalyst containing the composite oxide.
BACKGROUND ART
[0003] Fuel cells with high energy conversion efficiency have
recently been developed actively for the purpose of suppression of
global warming. Polymer electrolyte fuel cells (PEFCs) are being
put into practical household or vehicle uses. PEFCs generate
electricity using hydrogen and atmospheric oxygen as fuels, and the
hydrogen is produced by steam reforming of hydrocarbon such as in
city gas. Efficient steam reforming requires a catalyst, and there
have been proposed catalysts such as Ru supported on alumina
(Non-patent Publication 1), Pt, Ru, Rh, Pd, and the like supported
on an oxide solid solution of Zr, Ce, and Fe or Y (Patent
Publication 1), and Pt, Rh, Ni, Co, and the like supported on an
oxide containing Ce, Pr, and the like (Patent Publication 2).
[0004] These catalysts contain a large amount of precious metals,
which adds to cost and uncertainty of supply. Oxidation of the
catalysts significantly deteriorates the rate of reforming
hydrocarbon to hydrogen, which complicates setting of handling and
operating conditions.
[0005] High cost of Pt catalyst, which is used in both anode and
cathode, obstructs popularization of PEFCs. Particularly a large
amount of Pt catalyst is used in the oxygen reduction
1/2O.sub.2+2H.sup.++2e.sup.-.fwdarw.H.sub.2O at cathode. In this
regard, development of catalyst materials which can substitute or
reduce the amount of Pt catalysts is being made actively.
[0006] As a catalyst for purifying exhaust gases used in vehicles
or the like, so-called three-way catalyst is used, which oxidizes
carbon monoxide and hydrocarbon in exhaust gases to carbon dioxide
gas and water, while reduces nitrogen oxide to nitrogen and water.
The three-way catalyst is composed, for example, of a catalytic
metal, Pt, Rh, or Pd, and a co-catalyst, such as Ce, for improving
the catalytic action of the catalytic metal, both supported on a
catalyst support, such as alumina or cordierite. The precious
metals used as such a catalytic metal have problems in cost and
supply, as mentioned above.
PRIOR ART PUBLICATION
Patent Publication 1: JP-2006-181473-A
Patent Publication 2: JP-2008-229604-A
[0007] Non-patent Publication 1: IHI Engineering Review, Vol. 45,
No. 3, p116-120 (2005-9)
SUMMARY OF THE INVENTION
[0008] It is an object of the present invention to provide a method
for producing a composite oxide which finds use as a catalyst for
hydrocarbon steam reforming or purification of exhaust gas, reduces
problems of the above-mentioned catalysts in cost and supply,
achieves a high reforming rate of hydrocarbon to hydrogen even when
oxidized, and is easy to handle, as well as a composite oxide
catalyst containing this composite oxide.
[0009] The present inventors have made intensive researches for
solving the above-mentioned problems to find out that, in the
production of a composite oxide containing Ce and Zr, which is
conventionally effected through one-step hydrothermal processing, a
portion of the raw material cerium aqueous solution is subjected to
mixing before each step of hydrothermal processing, which is
completed in two steps. By this procedure, a composite oxide
containing Ce and Zr is obtained which has particular crystallinity
and specific surface area, and in which a catalytic metal is more
easily dispersed compared to a conventional oxide. Further, by
supporting a catalytic metal on the obtained composite oxide, a
catalyst is obtained which provides high reforming rate of
hydrocarbon to hydrogen and is capable of maintaining the high
reforming rate even when oxidized. Based on the above findings, the
present invention has been completed.
[0010] According to the present invention, there is provided a
method for producing a composite oxide comprising the steps of:
[0011] (a) preparing at least a cerium aqueous solution 80 to 100
mol % of which cerium ions are tetravalent, and a zirconium aqueous
solution containing zirconium ions; [0012] (b1) mixing said
zirconium aqueous solution and a portion of said cerium aqueous
solution prepared in step (a) to prepare a mixed aqueous solution
(X1); [0013] (c1) hydrothermally processing said mixed aqueous
solution (X1); [0014] (b2) adding a remainder of said cerium
aqueous solution prepared in step (a) to a colloidal solution (Y1)
of a composite salt obtained by said hydrothermal processing in
step (c1) to prepare a colloidal solution (Y2) of a composite salt;
[0015] (c2) hydrothermally processing said colloidal solution (Y2)
of a composite salt obtained from step (b2) ; [0016] (d) mixing a
colloidal solution (Y3) of a composite salt obtained by said
hydrothermal processing in step (c2) with an alkaline solution and
a surfactant to prepare a precipitate; and [0017] (e) calcining
said precipitate.
[0018] According to the present invention, there is also provided a
composite oxide obtained by this method.
[0019] According to the present invention, there is further
provided a composite oxide catalyst comprising this composite oxide
and at least one catalytic metal selected from the group consisting
of Ni, Cu, Fe, Pt, Pd, and Rh.
[0020] According to the present invention, there is further
provided a composite oxide catalyst for use as a catalyst for
hydrocarbon steam reforming or purification of exhaust gas, said
composite oxide catalyst comprising the composite oxide mentioned
above and at least one catalytic metal selected from the group
consisting of Ni, Cu, Fe, Pt, Pd, and Rh.
[0021] The method for producing a composite oxide according to the
present invention, wherein the cerium aqueous solution is admixed
in two separate steps (b1) and (b2), provides at low cost without
uncertainty of supply, a composite oxide in which a catalytic metal
is more easily dispersed compared to a conventional oxide. The
method of the present invention also provides a composite oxide
which finds use in a catalyst for hydrocarbon steam reforming or
purification of exhaust gas and which, when used in a catalyst, is
capable of achieving a high reforming rate of hydrocarbon to
hydrogen and of maintaining the high reforming rate even when the
composite oxide is oxidized.
[0022] The present invention will now be explained in detail.
[0023] The method of the present invention includes step (a) of
preparing at least a cerium aqueous solution 80 to 100 mol % of
which cerium ions are tetravalent, and a zirconium aqueous solution
containing zirconium ions.
[0024] The cerium aqueous solution 80 to 100 mol % of which cerium
ions are tetravalent may be, for example, a ceric nitrate solution
or an ammonium ceric nitrate solution, with the former being
preferred.
[0025] The initial concentration of the cerium aqueous solution may
be adjusted to the cerium content of usually 5 to 100 g/l,
preferably 10 to 80 g/l in terms of CeO.sub.2. Too low a
concentrate results in low productivity and is not industrially
advantageous.
[0026] The zirconium aqueous solution containing zirconium ions
prepared in step (a) may be, for example, a zirconium hydroxide
aqueous solution, a zirconium chloride aqueous solution, or a
zirconium nitrate aqueous solution, with a zirconium oxynitrate
aqueous solution being preferred.
[0027] Step (a) may optionally include preparation of, in addition
to the cerium aqueous solution and the zirconium aqueous solution,
a rare earth metal aqueous solution containing ions of rare earth
metals other than cerium, and/or an aqueous solution containing
ions of at least one element (sometimes referred to as element M
hereinbelow) selected from the group consisting of alkaline earth
metal elements, transition metal elements other than Zr, halogen
elements, B, C, Si, and S.
[0028] The aqueous solutions prepared in step (a) usually contain
not less than 10 mol % and not more than 90 mol % of Ce or a
mixture of Ce and other rare earth metals (sometimes referred to as
R hereinbelow), not less than 10 mol % and not more than 90 mol %
of Zr, or not less than 0 mol % and not more than 20 mol % of M,
preferably not less than 50 and not more than 80 mol % of R, not
less than 20 mole % and not more than 50 mol % of Zr, or not less
than 0 mol % and not more than 20 mol % of element M, with respect
to the total of the elements in the resulting composite oxide other
than oxygen being 100 mol %.
[0029] When R contains Pr, the content of Pr in R is preferably not
more than 10 mol %, more preferably not more than 5 mol %.
[0030] A zirconium salt may industrially contain a few molar
percent of Hf, so that Hf is assumed as being included in Zr
herein.
[0031] The method of the present invention includes step (b1) of
mixing the zirconium aqueous solution and a portion of the cerium
aqueous solution prepared in step (a) to prepare a mixed aqueous
solution (X1). In this step, the rare earth metal aqueous solution
containing ions of rare earth metals other than cerium, and/or the
aqueous solution containing ions of at least one element selected
from the group consisting of alkaline earth metal elements,
transition metal elements other than Zr, halogen elements, B, C,
Si, and S, may optionally mixed in the mixed aqueous solution
(X1).
[0032] The alkaline earth metals may be, for example, Mg, Ca, Sr,
or Ba; the rare earth metals other than Ce may be, for example, Sc,
Y, La, Nd, Pr, or Tb; and the transition metal elements other than
Zr may be, for example, Ti, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Ni,
Pd, Pt, Cu, Ag, Zn, Al, Ga, In, Ge, Sn, or Bi.
[0033] A portion of the cerium aqueous solution is subjected to
mixing in this step (b1), and the remainder of the cerium aqueous
solution is subjected to mixing in step (b2) to be discussed below.
The ratio by mass of the portions of the cerium aqueous solution
subjected to mixing in steps (b1) and (b2) is preferably 0.1:99.9
to 30.0:70.0. At a ratio outside this range, the effect of the
cerium aqueous solution subjecting to mixing in two separate
portions may not be sufficient.
[0034] The method of the present invention includes step (c1) of
hydrothermally processing the mixed aqueous solution (X1).
[0035] The hydrothermal processing in step (c1) may be, for
example, holding under heating of the mixed aqueous solution (X1)
to not lower than 60.degree. C. By this holding under heating, a
colloidal solution of a cerium-zirconium composite salt is formed.
A reaction vessel that may be used may either be a sealed or open
vessel, and preferably be an autoclave reactor. The temperature of
the holding under heating is usually not lower than 60.degree. C.,
preferably 60 to 200.degree. C., more preferably 80 to 180.degree.
C. The duration of the holding under heating is usually 10 minutes
to 48 hours, preferably 30 minutes to 36 hours, more preferably 1
hour to 24 hours. With the holding under heating under insufficient
conditions, crystallinity is not increased, and the specific
surface area and the crystallinity of the eventually resulting
composite oxide may not fall within the desired ranges.
[0036] The method of the present invention includes step (b2) of
adding the remainder of the cerium aqueous solution prepared in
step (a) to a colloidal solution (Y1) of a composite salt obtained
by the hydrothermal processing to prepare a colloidal solution (Y2)
of a composite salt. In this step, the rare earth metal aqueous
solution containing ions of rare earth metals other than cerium,
and/or the aqueous solution containing ions of at least one element
selected from the group consisting of alkaline earth metal
elements, transition metal elements other than Zr, halogen
elements, B, C, Si, and S, may optionally mixed in the colloidal
solution (Y2) of a composite salt.
[0037] The method of the present invention includes step (c2) of
hydrothermally processing the colloidal solution (Y2) of a
composite salt.
[0038] The hydrothermal processing in step (c2) may be performed
according to the hydrothermal processing in step (c1).
[0039] The method of the present invention includes step (d) of
mixing a colloidal solution (Y3) of a composite salt obtained by
the hydrothermal processing in step (c2) with an alkaline solution
and a surfactant to prepare a precipitate.
[0040] Step (d) is a neutralization step with an alkaline solution,
which may be, for example, sodium hydroxide, potassium hydroxide,
aqueous ammonia, or a mixture thereof, with aqueous ammonia being
particularly preferred.
[0041] The surfactant may be, for example, anionic surfactant such
as ethoxycarboxylate, nonionic surfactant such as alcohol
ethoxylate, polyethylene glycol, carboxylic acid, or a mixture
thereof, with carboxylic acid being particularly preferred.
[0042] The carboxylic acid may preferably be saturated carboxylic
acid, such as decanoic, lauric, myristic, or palmitic acid, with
lauric acid being particularly preferred.
[0043] The amount of the surfactant to be added is usually 1 to 50
parts by mass, preferably 5 to 30 parts by mass, based on 100 parts
by mass of the composite oxide to be obtained. At less than 1 part
by mass, the specific surface area and the crystallinity of the
eventually resulting composite oxide may not fall under the desired
ranges.
[0044] The surfactant may be used as it is in a solid form, or in
the form of a solution prepared by diluting or dissolving the
surfactant in a solvent such as alcohol or pure water. The mixing
may be carried out in a known mixer.
[0045] The obtained precipitate may be separated by, for example,
Nutsche method, centrifugation, or filter pressing. The obtained
precipitate may be washed with water as necessary. Further, the
obtained precursor may be dried to an appropriate extent. The
drying may be carried out at about 60 to 200.degree. C.
[0046] The method of the present invention includes step (e) of
calcining the obtained precipitate.
[0047] In step (e), the calcination may be preceded by pre-baking.
The temperature of the pre-baking is usually 250 to 700.degree. C.,
preferably 300 to 500.degree. C. The pre-baking may be carried out
in the air or oxygen. The duration of the pre-baking may suitably
be decided taking the pre-baking temperature into consideration,
and may usually be 1 to 10 hours.
[0048] The pre-baked composite oxide is pulverized and then
calcined. The calcining temperature is usually 500 to 1200.degree.
C., preferably 700 to 1100.degree. C., more preferably 800 to
1050.degree. C. The calcining may be carried out in the air or
oxygen, with oxygen being preferred. The duration of the calcining
may suitably be decided taking the calcining temperature into
consideration, and may usually be 1 to 10 hours.
[0049] The obtained composite oxide may be pulverized into a
desired particle size as necessary. For example, when used as a
composite oxide in a hydrocarbon steam reforming catalyst, the
composite oxide preferably has a mean particle diameter of 1 to 50
.mu.m.
[0050] The obtained composite oxide may be made into a desired
catalyst by supporting at least one catalytic metal selected from
the group consisting of Ni, Cu, Fe, Pt, Pd, and Rh. The catalytic
metal may be supported on the composite oxide through a
conventional method, for example, by impregnating the composite
oxide with an aqueous solution of a catalytic metal, followed by
calcination. The calcination temperature is usually 250 to
800.degree. C., preferably 300 to 600.degree. C. The calcination
may be carried out in the air or oxygen, with oxygen being
preferred. The duration of the calcination may suitably be decided
taking the calcination temperature into consideration, and may
usually be 1 to 10 hours.
[0051] Some of the catalyst according to the present invention may
exhibit the catalytic performance as it is after the calcination,
but may be subjected to activation treatment such as reduction
and/or oxidation as necessary.
[0052] It is generally advantageous that the composite oxide
obtained by the method of the present invention, when used as a
catalyst, has a larger specific surface area. Aside from this, the
present inventors have found out that higher crystallinity of a
composite oxide supporting a catalytic metal results in more
effective catalytic performance. Thus, the present inventors have
adopted composite oxides having high crystallinity with a specific
surface area being maintained as large as possible. Such composite
oxides are composed microscopically of two or more very similar
CaF.sub.2 or the like phases, and it is assumed that good catalytic
performance is exhibited due to oxygen tightly taken in at the
boundaries of such similar phases and migrated smoothly to thereby
reduce the catalytic metal. Two or more very similar CaF.sub.2 or
the like phases preferably develop when the composite oxide has the
above-mentioned composition, specific surface area, and
crystallinity, to exhibit good catalytic performance.
[0053] The catalyst of the present invention preferably provides a
rate of reforming methane to hydrogen of not lower than 40%,
preferably not lower than 80%, as determined by heating the
catalyst under oxygen flow from the room temperature to 600.degree.
C. over 1.5 hours, holding the catalyst at 600.degree. C. for 1
hour, and measuring the methane steam reforming.
[0054] The methane steam reforming, as referred to herein, may be
determined under the conditions discussed below.
[0055] The determination of methane steam reforming may be started
by measuring out 50.0 mg of the catalyst, and fixing the catalyst
in a fixed-bed reaction tube (inner diameter 11 mm) made of quartz
glass with the upper and lower sides of the catalyst held between
quartz glass wool. Then hydrogen gas is flown into the reaction
tube at 100 ml/min, while the tube is heated from the room
temperature to 600.degree. C. over 1.5 hours. The tube, when
reaches 600.degree. C., is held for 1 hour to reduce the catalyst.
After the reduction, the hydrogen gas is stopped, and nitrogen gas
is introduced to evacuate the hydrogen gas from the tube. After
thorough evacuation of the hydrogen gas, using nitrogen gas as a
carrier gas and methane and water at 1:3, nitrogen gas, methane
gas, and water steam are introduced into the reaction tube at 90
ml/min, 2.5 ml/min, and 7.5 ml/min, respectively, and measurement
of the rate of reforming methane to hydrogen is started. The
measurement is made by sampling the outlet gas four times at
13-minute intervals, analyzing each sample gas by gas
chromatography, and taking the average. This procedure is referred
to as measurement (1).
[0056] After measurement (1), oxygen gas is flown into the reaction
tube at 100 ml/min, and the tube is held for 1 hour to oxidize the
catalyst. Then the oxygen gas is stopped, and nitrogen gas is
introduced to evacuate the oxygen gas from the tube. After thorough
evacuation of the oxygen gas, the rate of reforming methane to
hydrogen is measured in the same way as in measurement (1). This
procedure is referred to as measurement (2).
[0057] After measurement (2), hydrogen gas is flown into the tube
at 100 ml/min, and the tube is held for 1 hour to reduce the
catalyst. After the reduction, the hydrogen gas is stopped, and
nitrogen gas is introduced to evacuate the hydrogen gas from the
tube. After thorough evacuation of the hydrogen gas, the rate of
reforming methane to hydrogen is measured in the same way as in
measurement (1). This procedure is referred to as measurement
(3).
[0058] After measurement (3), nitrogen gas is flown into the
reaction tube at 90 ml/min while the temperature is lowered to the
room temperature. Then, oxygen gas is flown into the tube at 100
ml/min while the temperature is raised from the room temperature up
to 600.degree. C. over 1.5 hours. When the temperature reaches
600.degree. C., the tube is held for 1 hour to oxidize the
catalyst. After the oxidization, the oxygen gas is stopped, and
nitrogen gas is introduced to evacuate the oxygen gas from the
tube. After thorough evacuation of the oxygen gas, the rate of
reforming methane to hydrogen is measured in the same way as in
measurement (1). This procedure is referred to as measurement
(4).
[0059] After measurement (4), hydrogen gas is flown into the
reaction tube at 100 ml/min, and the tube is held for 1 hour to
reduce the catalyst. After the reduction, the hydrogen gas is
stopped, and nitrogen gas is introduced to evacuate the hydrogen
gas from the tube. After thorough evacuation of the hydrogen gas,
the rate of reforming methane to hydrogen is measured in the same
way as in measurement (1). This procedure is referred to as
measurement (5).
[0060] The rate of reforming is calculated as follows using the
values of methane (CH.sub.4), carbon dioxide (CO.sub.2), and carbon
monoxide (CO) measured in the gas chromatography. Rate of reforming
(%)=(1-CH.sub.4/(CH.sub.4+CO.sub.2+CO)).times.100
[0061] The catalyst according to the present invention may be used
as a substitute for a Pt catalyst in PEFC, catalysts for purifying
exhaust gases, or the like, and may preferably be used as a
hydrocarbon steam reforming catalyst.
EXAMPLES
[0062] The present invention will now be explained with reference
to Examples and Comparative Examples, which do not intend to limit
the present invention.
Example 1
[0063] A portion (5 mass % of the whole) of an aqueous solution of
cerium nitrate prepared, not less than 90% of which cerium ions
were tetravalent, was mixed with an aqueous solution of zirconium
oxynitrate and an aqueous solution of praseodymium nitrate so as to
give a composition ratio of 12.0 mol % Ce, 80.0 mol % Zr, and 8.0
mol % Pr, to prepare a 886 ml of a mixed solution at a
concentration of 8.7 g/l in terms of oxides, and the obtained mixed
solution was placed in a 1 litter separable flask. The separable
flask was equipped with a stirrer and a Dimroth condenser tube, and
the mixed solution was hydrothermally processed at 98.degree. C.
for 8 hours, and cooled down to the room temperature to obtain a
colloidal solution (Y1) of cerium-zirconium-praseodymium composite
salt.
[0064] To the solution (Y1) of the composite salt thus obtained,
the remainder (95 mass % of the whole) of the aqueous solution of
cerium nitrate not less than 90% of which cerium ions were
tetravalent, was added so as to give a compositional ratio of 73.2
mol % Ce, 24.4 mol % Zr, and 2.4 mol % P, to prepare a 1 litter of
a colloidal solution (Y2) of cerium-zirconium-praseodymium
composite salt at a concentration of 30.5 g/l in terms of oxides.
The colloidal solution (Y2) of the composite salt thus obtained was
hydrothermally processed at 98.degree. C. for 20 hours in the same
way as above, and cooled down to the room temperature to obtain a
colloidal solution (Y3) of cerium-zirconium-praseodymium composite
salt.
[0065] The solution (Y3) of the composite salt was added into an
alkaline solution of 23.7 g of ammonium laurate dissolved in 315 ml
of 12.5% ammonia solution under stirring at 50 ml/min to obtain a
precursor of a composite oxide in a gel form. The gel was subjected
to filtration and washing to obtain a filter cake, which was
pre-baked at 400.degree. C. for 5 hours, and then calcined in
oxygen at 1000.degree. C. for 3 hours. The composite oxide thus
obtained was measured with ICP to find that the compositional ratio
was 73.2 mol % Ce, 24.4 mol % Zr, and 2.4 mol % Pr, with respect to
the total of Ce, Zr, and Pr being 100 mol %. After that, the
composite oxide was impregnated with nickel nitrate and palladium
nitrate so as to have 5.00 mol % Ni and 1.25 mol % Pd as catalytic
metals, with respect to the total of Ce, Zr, and Pr being 100 mol
%, and calcined in oxygen at 500.degree. C. for 3 hours to obtain a
catalyst. The catalyst thus obtained was analyzed with ICP to find
that the Ni and Pd contents were 5.00 mol % and 1.25 mol %,
respectively, with respect to the total of Ce, Zr, and Pr being 100
mol %.
[0066] The catalyst of the composite oxide thus obtained was
subjected to the determination of the methane steam reforming as
discussed above. The results are shown in Table 1.
Examples 2 to 6
[0067] A composite oxide and a catalyst were prepared in the same
way as in Example 1, except that the calcination temperature and
the Ni and Pd contents were changed as shown in Table 1. The
obtained catalyst was subjected to the determination of the methane
steam reforming. The results are shown in Table 1.
Comparative Example 1
[0068] An aqueous solution of cerium nitrate not less than 90% of
which cerium ions were tetravalent was mixed with zirconium
hydroxide and an aqueous solution of praseodymium nitrate so as to
give a compositional ratio of 73.2 mol % Ce, 24.4 mol % Zr, and 2.4
mol % Pr, to prepare a 1 litter of a mixed solution at a
concentration of 30 g/l in terms of oxides, and the obtained mixed
solution was placed in a 1 litter separable flask. The separable
flask was equipped with a stirrer and a Dimroth condenser tube, and
held under heating at 98.degree. C. for 20 hours. After the holding
under heating, the flask was cooled down to the room temperature to
obtain a colloidal solution of cerium-zirconium-praseodymium
composite salt. The solution of the composite salt was added into
415 ml of 12.5% aqueous ammonia under stirring at 50 ml/min to
obtain a precursor of a composite oxide in a gel form. The gel was
subjected to filtration and washing to obtain a filter cake. To the
obtained filter cake, 3 g of ammonium laurate dissolved in pure
water was added and mixed. Then the mixture was pre-baked at
400.degree. C. for 5 hours to obtain a composite oxide. The
obtained composite oxide was calcined in oxygen at 1000.degree. C.
for 3 hours. The resulting composite oxide was measured with ICP to
find that the compositional ratio was 73.2 mol % Ce, 24.4 mol % Zr,
and 2.4 mol % Pr.
[0069] The composite oxide was impregnated with an aqueous solution
of nickel nitrate so as to have 6.25 mol % Ni with respect to the
total of Ce, Zr, and Pr being 100 mol %, and calcined in oxygen at
500.degree. C. for 3 hours to obtain a catalyst. The catalyst thus
obtained was analyzed with ICP to find that the Ni content was 6.25
mol % with respect to the total of Ce, Zr, and Pr being 100 mol
%.
[0070] The obtained catalyst was subjected to the determination of
the methane steam reforming as discussed above. The results are
shown in Table 1.
Comparative Examples 2 to 4
[0071] A composite oxide and a catalyst were prepared in the same
way as in Examples 2 to 4, except that the calcination temperature
was changed as shown in Table 1. The obtained catalyst was
subjected to the determination of the methane steam reforming. The
results are shown in Table 1.
Comparative Examples 5 to 7
[0072] A composite oxide and a catalyst were prepared in the same
way as in Comparative Example 1, except that the zirconium
hydroxide was replaced with an aqueous solution of zirconium
oxynitrate, and the calcination temperature and the Ni and Pd
contents were changed as shown in Table 1. The obtained catalyst
was subjected to the determination of the methane steam reforming.
The results are shown in Table 1.
TABLE-US-00001 TABLE 1 Calci- nation Reforming rate temper-
Measure- Measure- Measure- Measure- Measure- Ce Zr Pr Total Ni Pd
ature ment ment ment ment ment (mol %) (mol %) (mol %) (mol %) (mol
%) (mol %) (.degree. C.) (1) (2) (3) (4) (5) Example 1 73.2 24.4
2.4 100 5.00 1.25 1000 92.2 93.0 91.3 90.8 88.8 Example 2 73.2 24.4
2.4 100 6.125 0.125 1000 89.8 87.9 88.2 87.5 86.1 Example 3 73.2
24.4 2.4 100 6.2375 0.0125 1000 84.8 83.9 83.5 82.2 80.7 Example 4
73.2 24.4 2.4 100 6.25 0 1000 92.1 90.9 91.6 90.0 90.5 Example 5
73.2 24.4 2.4 100 6.125 0.125 800 86.6 85.6 82.3 82.9 81.8 Example
6 73.2 24.4 2.4 100 6.25 0 800 87.2 83.4 82.3 81.2 79.9 Com. Ex. 1
73.2 24.4 2.4 100 6.25 0 1000 90.3 90.6 90.8 90.3 89.8 Com. Ex. 2
73.2 24.4 2.4 100 6.125 0.125 600 76.1 74.7 72.1 75.0 71.1 Com. Ex.
3 73.2 24.4 2.4 100 6.2375 0.0125 600 73.4 73.8 68.9 71.9 68.0 Com.
Ex. 4 73.2 24.4 2.4 100 6.25 0 600 68.4 0 65.1 66.3 64.6 Com. Ex. 5
73.2 24.4 2.4 100 5.00 1.25 1000 88.5 89.3 87.6 87.2 85.2 Com. Ex.
6 73.2 24.4 2.4 100 6.125 0.125 1000 86.2 84.4 84.7 84.0 82.7 Com.
Ex. 7 73.2 24.4 2.4 100 6.25 0 800 83.7 80.1 79.0 78.0 76.7
Example 7
[0073] A portion (5 mass % of the whole) of an aqueous solution of
cerium nitrate prepared, not less than 90% of which cerium ions
were tetravalent, was mixed with an aqueous solution of zirconium
oxynitrate and an aqueous solution of praseodymium nitrate so as to
give a compositional ratio of 4.3 mol % Ce, 87.0 mol % Zr, and 8.7
mol % Pr, to prepare a 919 ml of a mixed solution at a
concentration of 16.0 g/l in terms of oxides, and the obtained
mixed solution was placed in a 1 litter separable flask. The
separable flask was equipped with a stirrer and a Dimroth condenser
tube, and the mixed solution was hydrothermally processed at
98.degree. C. for 8 hours, and cooled down to the room temperature
to obtain a colloidal solution (Y1) of
cerium-zirconium-praseodymium composite salt.
[0074] To the solution (Y1) of the composite salt thus obtained,
the remainder (95 mass % of the whole) of the aqueous solution of
cerium nitrate not less than 90% of which cerium ions were
tetravalent, was added so as to give a compositional ratio of 47.6
mol % Ce, 47.6 mol % Zr, and 4.8 mol % Pr, to prepare a 1 litter of
a colloidal solution (Y2) of cerium-zirconium-praseodymium
composite salt at a concentration of 30.8 g/l in terms of oxides.
The colloidal solution (Y2) of the composite salt thus obtained was
hydrothermally processed at 98.degree. C. for 20 hours in the same
way as above, and cooled down to the room temperature to obtain a
colloidal solution (Y3) of cerium-zirconium-praseodymium composite
salt.
[0075] The solution (Y3) of the composite salt was added into an
alkaline solution of 23.7 g of ammonium laurate dissolved in 315 ml
of 12.5% ammonia solution under stirring at 50 ml/min to obtain a
precursor of a composite oxide in a gel form. The gel was subjected
to filtration and washing to obtain a filter cake, which was
pre-baked at 400.degree. C. for 5 hours, and then calcined in
oxygen at 1000.degree. C. for 3 hours. The composite oxide thus
obtained was measured with ICP to find that the compositional ratio
was 47.6 mol % Ce, 47.6 mol % Zr, and 4.8 mol % Pr with respect to
the total of Ce, Zr, and Pr being 100 mol %. After that, the
composite oxide was impregnated with nickel nitrate and palladium
nitrate so as to have 5.00 mol % Ni and 1.25 mol % Pd as catalytic
metals, with respect to the total of Ce, Zr, and Pr being 100 mol
%, and calcined in oxygen at 500.degree. C. for 3 hours to obtain a
catalyst. The catalyst thus obtained was analyzed with ICP to find
that the Ni and Pd contents were 5.00 mol % and 1.25 mol %,
respectively, with respect to the total of Ce, Zr, and Pr being 100
mol %. The catalyst of the composite oxide thus obtained was
subjected to the determination of the methane steam reforming as
discussed above. The results are shown in Table 2.
Examples 8 to 13
[0076] A composite oxide and a catalyst were prepared in the same
way as in Example 7, except that the calcination temperature and
the Ni and Pd contents were changed as shown in Table 2. The
obtained catalyst was subjected to the determination of the methane
steam reforming. The results are shown in Table 2.
Comparative Example 8
[0077] An aqueous solution of cerium nitrate not less than 90% of
which cerium ions were tetravalent was mixed with zirconium
hydroxide and an aqueous solution of praseodymium nitrate so as to
give a compositional ratio of 47.6 mol % Ce, 47.6 mol % Zr, and 4.8
mol % Pr, to prepare a 1 litter of a mixed solution at a
concentration of 30 g/l in terms of oxides, and the obtained mixed
solution was placed in a 1 litter separable flask. The separable
flask was equipped with a stirrer and a Dimroth condenser tube, and
held under heating at 98.degree. C. for 20 hours. After the holding
under heating, the flask was cooled down to the room temperature to
obtain a colloidal solution of cerium-zirconium-praseodymium
composite salt. The solution of the composite salt was added into
415 ml of 12.5% aqueous ammonia under stirring at 50 ml/min to
obtain a precursor of a composite oxide in a gel form. The gel was
subjected to filtration and washing to obtain a filter cake. To the
obtained filter cake, 3 g of ammonium laurate dissolved in pure
water was added and mixed. Then the mixture was pre-baked at
400.degree. C. for 5 hours to obtain a composite oxide. The
obtained composite oxide was calcined in oxygen at 1000.degree. C.
for 3 hours. The resulting composite oxide was measured with ICP to
find that the compositional ratio was 47.6 mol % Ce, 47.6 mol % Zr,
and 4.8 mol % Pr.
[0078] The composite oxide was impregnated with an aqueous solution
of nickel nitrate so as to have 6.25 mol % Ni with respect to the
total of Ce, Zr, and Pr being 100 mol %, and calcined in oxygen at
500.degree. C. for 3 hours to obtain a catalyst. The catalyst thus
obtained was analyzed with ICP to find that the Ni content was 6.25
mol % with respect to the total of Ce, Zr, and Pr being 100 mol
%.
[0079] The obtained catalyst was subjected to the determination of
the methane steam reforming as discussed above. The results are
shown in Table 2.
Comparative Examples 9 to 12
[0080] A composite oxide and a catalyst were prepared in the same
way as in Examples 7 and 9 to 11, except that the calcination
temperature was changed as shown in Table 2. The obtained catalyst
was subjected to the determination of the methane steam reforming.
The results are shown in Table 2.
Comparative Examples 13 and 14
[0081] A composite oxide and a catalyst were prepared in the same
way as in Comparative Example 8, except that the calcination
temperature and the Ni and Pd contents were changed as shown in
Table 2. The obtained catalyst was subjected to the determination
of the methane steam reforming. The results are shown in Table
2.
TABLE-US-00002 TABLE 2 Calci- nation Reforming rate temper-
Measure- Measure- Measure- Measure- Measure- Ce Zr Pr Total Ni Pd
ature ment ment ment ment ment (mol %) (mol %) (mol %) (mol %) (mol
%) (mol %) (.degree. C.) (1) (2) (3) (4) (5) Example 7 47.6 47.6
4.8 100 5.00 1.25 1000 94.4 95.3 93.8 93.3 92.4 Example 8 47.6 47.6
4.8 100 5.625 0.625 1000 93.6 93.3 91.8 91.3 90.2 Example 9 47.6
47.6 4.8 100 6.125 0.125 1000 68.8 69.5 60.3 74.6 65.5 Example 10
47.6 47.6 4.8 100 6.2375 0.0125 1000 77.0 69.7 68.3 67.7 66.0
Example 11 47.6 47.6 4.8 100 6.25 0 1000 94.3 0 92.3 91.2 91.7
Example 12 47.6 47.6 4.8 100 6.125 0.125 800 86.4 82.3 78.4 80.9
77.6 Example 13 47.6 47.6 4.8 100 6.25 0 800 82.5 73.9 69.9 86.6
83.2 Com. Ex. 8 47.6 47.6 4.8 100 6.25 0 1000 93.6 0 91.5 89.9 90.6
Com. Ex. 9 47.6 47.6 4.8 100 5.00 1.25 600 86.8 87.0 83.0 86.6 83.2
Com. Ex. 10 47.6 47.6 4.8 100 6.125 0.125 600 84.1 83.2 80.4 82.1
79.0 Com. Ex. 11 47.6 47.6 4.8 100 6.2375 0.0125 600 81.6 76.4 73.3
74.4 71.4 Com. Ex. 12 47.6 47.6 4.8 100 6.25 0 600 79.6 0 72.2 71.2
72.0 Com. Ex. 13 47.6 47.6 4.8 100 5.00 1.25 1000 90.6 91.5 90.0
89.6 88.7 Com. Ex. 14 47.6 47.6 4.8 100 5.625 0.625 1000 89.9 89.6
88.1 87.6 86.6
* * * * *