U.S. patent application number 12/032094 was filed with the patent office on 2008-10-02 for method for production of carbon monoxide-reduced hydrogen-containing gas.
This patent application is currently assigned to Idemitsu Kosan Co., Ltd.. Invention is credited to Hiroyuki Endo, Tetsuya FUKUNAGA, Satoshi Hachiya, Masatoshi Shibata, Kozo Takatsu.
Application Number | 20080241039 12/032094 |
Document ID | / |
Family ID | 18290449 |
Filed Date | 2008-10-02 |
United States Patent
Application |
20080241039 |
Kind Code |
A1 |
FUKUNAGA; Tetsuya ; et
al. |
October 2, 2008 |
METHOD FOR PRODUCTION OF CARBON MONOXIDE-REDUCED
HYDROGEN-CONTAINING GAS
Abstract
A method for the oxidative removal of carbon monoxide from a
hydrogen containing gas employing a catalyst for the selective
oxidation of carbon monoxide is provided.
Inventors: |
FUKUNAGA; Tetsuya;
(Sodegaura-shi, JP) ; Takatsu; Kozo;
(Sodegaura-shi, JP) ; Shibata; Masatoshi;
(Sodegaura-shi, JP) ; Hachiya; Satoshi;
(Sodegaura-shi, JP) ; Endo; Hiroyuki;
(Sodegaura-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Idemitsu Kosan Co., Ltd.
Tokyo
JP
|
Family ID: |
18290449 |
Appl. No.: |
12/032094 |
Filed: |
February 15, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10847857 |
May 19, 2004 |
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12032094 |
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09831908 |
Jun 19, 2001 |
6780386 |
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PCT/JP99/06535 |
Nov 24, 1999 |
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10847857 |
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Current U.S.
Class: |
423/247 |
Current CPC
Class: |
B01J 23/58 20130101;
Y02E 60/50 20130101; H01M 8/0662 20130101; C01B 3/583 20130101;
C01B 2203/044 20130101; B01J 23/462 20130101; Y02P 70/50 20151101;
C10K 3/04 20130101; C01B 2203/047 20130101 |
Class at
Publication: |
423/247 |
International
Class: |
C10K 3/04 20060101
C10K003/04; B01D 53/62 20060101 B01D053/62; C01B 3/16 20060101
C01B003/16 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 26, 1998 |
JP |
10-335604 |
Claims
1. A method for producing a CO-reduced, hydrogen-containing gas,
which comprises selectively oxidizing carbon monoxide in a gas of
essentially hydrogen, with oxygen in the presence of a CO oxidation
catalyst comprising ruthenium with an alkali metal held on a
carrier of titania and alumina, wherein the weight ratio of titania
to alumina falls between 1/99 and 15/85, and the amount of
ruthenium falls between 0.3 and 3% by weight of the carrier.
2. The method for producing a hydrogen-containing gas as claimed in
claim 1, wherein the gas of essentially hydrogen is obtained by
reforming or partially oxidizing a hydrogen-producing starting
material.
3. The method for producing a hydrogen-containing gas as claimed in
claim 1, wherein the hydrogen-containing gas produced is for fuel
cells.
4. The method for producing a CO-reduced, hydrogen-containing gas
according to claim 1, wherein the alkali metal is at least one
selected from the group consisting of potassium, cesium, rubidium,
sodium and lithium.
5. The method for producing a CO-reduced hydrogen-containing gas
according to claim 1, wherein the carrier of titania and alumina
comprises titania adhering onto a shaped alumina.
6. The method for producing a CO-reduced hydrogen-containing gas as
claimed in claim 5, wherein the shaped alumina is solid grains or
powder of alumina.
7. The method for producing a CO-reduced hydrogen-containing gas as
claimed in claim 2, wherein the gas of essentially hydrogen is
obtained by reforming or partially oxidizing a hydrogen-producing
starting material.
8. The method for producing a CO-reduced hydrogen-containing gas as
claimed in claim 5, wherein the gas of essentially hydrogen is
obtained by reforming or partially oxidizing a hydrogen-producing
starting material.
9. The method for producing a hydrogen-containing gas as claimed in
claim 4, wherein the hydrogen-containing gas produced is for fuel
cells.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of prior U.S.
patent application Ser. No. 10/847,857, filed May 19, 2004, which
is a continuation application of U.S. patent application Ser. No.
09/831,908, filed Jun. 19, 2001, which is the national stage
application of PCT/JP99/06535, filed Nov. 24, 1999. The parent
application claims priority to Japanese Application No. 10-335604,
filed Nov. 26, 1998.
TECHNICAL FIELD
[0002] The present invention relates to a method for producing a
hydrogen-containing gas through oxidative removal of carbon
monoxide from a carbon monoxide-containing, hydrogen-containing
gas.
BACKGROUND ART
[0003] Fuel cells for power generation do not so much pollute the
environment and their energy loss is low. Other advantages are that
they can be installed in any desired site, and they are easy to
increase, and are easy to handle. Accordingly, fuel cells are
specifically noticed these days. Various types of fuel cells are
known that differ in the type of fuel and electrolyte for them and
in the operating temperature. Hydrogen-oxygen fuel cells
(low-temperature-working fuel cells) in which hydrogen serves as a
reducing agent (active material) and oxygen (e.g., air) serves as
an oxidizing agent have been developed most of all, and will be
more and more popularized in future.
[0004] Various types of hydrogen-oxygen fuel cells are known that
differ in the type of electrolyte and the type of electrode
therein. Typical examples are phosphate-type fuel cells, KOH-type
fuel cells, and solid polymer-type fuel cells. In these fuel cells,
especially those capable of operating at low temperatures such as
solid polymer-type fuel cells, platinum (platinum catalyst) is used
for the electrodes, and it is easily poisoned with CO (carbon
monoxide). Therefore, if CO of higher than a predetermined level is
in the fuel for them, the power-generating capability of the fuel
cells is lowered. If the CO concentration in the fuel is too high,
the fuel cells could not generate power at all, and this is a
serious problem.
[0005] Therefore, pure hydrogen is preferred for the fuel for these
fuel cells having such a platinum-type electrode catalyst. From the
practical viewpoint, however, hydrogen-containing gas is generally
used for them. This is obtained through steam reforming of various
types of ordinary fuels (for example, methane or natural gas (LNG);
petroleum gas (LPG) such as propane, butane; various types of
hydrocarbon fuels such as naphtha, gasoline, kerosene, gas oil;
alcohol fuels such as methanol; town gas, and other fuels for
hydrogen production), for which public supply systems have been
established. Therefore, a fuel-cell power-generation system
equipped with a fuel-reforming unit is now being popularized.
However, the reformed gas generally contains a relatively high
concentration of CO in addition to hydrogen. Accordingly, it is
much desired to develop a technique for converting CO in the
reformed gas into CO.sub.2 that is harmless to platinum-type
electrode catalysts, to thereby reduce the CO concentration in the
fuel for fuel cells. For this, it is desirable that the CO
concentration in the fuel is lowered generally to at most 100 ppm,
preferably to at most 10 ppm.
[0006] To solve the problem as above, a technique of utilizing
shift reaction of the following formula (1) (aqueous gas shift
reaction) has been proposed for reducing the CO concentration in
fuel gas (hydrogen-containing reformed gas) for fuel cells.
CO+H.sub.2O.dbd.CO.sub.2+H.sub.2 (1)
[0007] However, reducing the CO concentration in fuel gas through
only the shift reaction is limited, as the chemical equilibrium in
the reaction is limited. In general, therefore, it is difficult to
reduce the CO concentration in fuel gas to at most 1% through the
shift reaction.
[0008] Accordingly, for further reducing the CO concentration in
fuel gas, proposed is a method of introducing oxygen or an
oxygen-containing gas (e.g., air) into fuel gas to thereby convert
CO therein into CO.sub.2. However, fuel gas contains a large amount
of hydrogen. Therefore, when CO in fuel gas is oxidized, then
hydrogen therein is also oxidized, and, after all, the CO
concentration in fuel gas could not be satisfactorily reduced.
[0009] To solve the problem, a method of using a catalyst for
selectively oxidizing only CO will be proposed in the process of
introducing oxygen or an oxygen-containing gas into fuel gas so as
to oxidize CO therein into CO.sub.2.
[0010] For CO oxidation catalysts, heretofore known are various
catalysts of Pt/alumina, Pt/SnO.sub.2, Pt/C, Co/TiO.sub.2,
hopcalite, and Pd/alumina. However, these catalysts are not well
resistant to moisture, and their reaction temperature range is low
and narrow. In addition, their selectivity for CO is low. Fuel gas
for fuel cells contains only a minor amount of CO in a majority of
hydrogen. Therefore, if the catalysts are used for reducing the
minor amount of CO in fuel gas to a lowered concentration of at
most 10 ppm, a large amount of hydrogen in fuel gas must be
sacrificed through oxidation.
[0011] Japanese Patent Laid-Open No. 201702/1993 discloses a method
for producing a CO-free, hydrogen-containing gas for automobile
fuel cells, which comprises selectively removing CO from a
hydrogen-rich, CO-containing gas. The catalyst used in this is Rh
or Ru held on an alumina carrier, but this is problematic in that
it is applicable to only a gas having a low CO concentration.
[0012] Japanese Patent Laid-Open No. 258764/1993 discloses a method
of processing a methanol-reformed gas (containing 20% by volume of
CO.sub.2 and from 7 to 10% by volume of CO, in addition to
hydrogen) with an Fe--Cr catalyst to thereby reduce the CO
concentration of the gas to 1% by volume, followed by further
reducing the CO concentration of the gas through methanation with a
catalyst having a catalytic metal component of Rh, Ni or Pd. In the
method, CO still remaining in the processed gas is removed through
plasma oxidation. The method provides a reformed gas for solid
polymer-type fuel cells, and the gas does not poison the platinum
catalyst for the electrode in the cells. However, as requiring a
plasma generator, the method is problematic in that the reaction
apparatus for it shall be large. In addition, the temperature for
methanation in the method falls between 150 and 500.degree. C. At
such a high reaction temperature, not only CO but also CO, is
methanated, and the methanation consumes a large amount of hydrogen
in the gas. For these reasons, the method is unsuitable for CO
removal from a hydrogen-containing gas for fuel cells.
[0013] Japanese Patent Laid-Open No. 131531/1997 discloses a
catalyst for removing CO from a hydrogen-containing gas, and the
catalyst comprises ruthenium and an alkali metal compound and/or an
alkaline earth metal compound held on a titania carrier. However,
this discloses nothing about a combination of titania and alumina
for the carrier of the catalyst. In addition, this suggests nothing
about the fact that the catalyst with a carrier of titania and
alumina combined is significantly superior to the catalyst with a
carrier of titania or alumina alone.
[0014] The present invention has been made in consideration of the
above-mentioned viewpoints, and its object is to provide a CO
oxidation catalyst which is effective for selectively oxidizing and
removing CO from a hydrogen-containing gas in a broad reaction
temperature range, especially even at relatively high temperatures;
to provide a method for producing the catalyst; and to provide a
method of using the catalyst for producing a hydrogen-containing
gas, especially for producing a hydrogen-containing gas favorable
to fuel cells.
DISCLOSURE OF THE INVENTION
[0015] We, the present inventors have assiduously studied, and, as
a result, have found that a catalyst of ruthenium held on a carrier
of titania and alumina is effective for selectively oxidizing and
removing CO from a hydrogen-containing gas in a broad reaction
temperature range. On the basis of this finding, we have completed
the present invention.
[0016] Specifically, the invention is summarized as follows:
[0017] (1) A CO oxidation catalyst of ruthenium held on a carrier
of titania and alumina.
[0018] (2) A CO oxidation catalyst of ruthenium with an alkali
metal and/or an alkaline earth metal held on a carrier of titania
and alumina.
[0019] (3) The CO oxidation catalyst of above (1) or (2), wherein
the weight ratio of titania to alumina falls between 0.1/99.9 and
90/10.
[0020] (4) The CO oxidation catalyst of above (2) or (3), wherein
the alkali metal is at least one selected from potassium, cesium,
rubidium, sodium and lithium.
[0021] (5) The CO oxidation catalyst of any of above (2) to (4),
wherein the alkaline earth metal is at least one selected from
barium, calcium, magnesium and strontium.
[0022] (6) A method for producing a CO oxidation catalyst of
ruthenium with an alkali metal and/or an alkaline earth metal held
on a carrier of titania and alumina, which comprises applying a
solution of ruthenium and a solution of an alkali metal and/or an
alkaline earth metal to the carrier.
[0023] (7) The method for producing a CO oxidation catalyst of
above (6), wherein a mixed solution of ruthenium and an alkali
metal and/or an alkaline earth metal is applied to the carrier.
[0024] (8) A method for producing a CO-reduced, hydrogen-containing
gas, which comprises selectively oxidizing carbon monoxide in a gas
of essentially hydrogen, with oxygen in the presence of the
catalyst of any of above (1) to (5) or the catalyst produced in the
process of above (6) or (7).
[0025] (9) The method for producing a hydrogen-containing gas of
above (8), wherein the gas of essentially hydrogen is obtained by
reforming or partially oxidizing a hydrogen-producing starting
material.
[0026] (10) The method for producing a hydrogen-containing gas of
above (8) or (9), wherein the hydrogen-containing gas produced is
for fuel cells.
BEST MODES OF CARRYING OUT THE INVENTION
[0027] Embodiments of the invention are described hereinunder.
[0028] First described are the CO-removing catalyst (CO oxidation
catalyst) of the invention, which is for removing CO from a gas of
essentially hydrogen, and a method for producing the catalyst.
[0029] The carrier for the catalyst of the invention is composed of
titania and alumina. As held on the carrier of titania and alumina,
the catalyst of the invention is superior to the catalyst of
ruthenium or ruthenium and an alkali metal compound and/or an
alkaline earth metal compound held on a titania carrier or an
alumina carrier, which is disclosed in Japanese Patent Laid-Open
No. 131531/1997, in that its activity for CO oxidation and removal
is high in a broader temperature range, especially at relatively
higher temperatures. In addition, as compared with the catalyst
held on a titania carrier, the catalyst of the invention held on an
alumina/titania carrier is easy to produce and shape, and has high
mechanical strength and abrasion resistance, always keeping its
high mechanical strength at any temperature at which it serves for
CO oxidation.
[0030] For producing the carrier composed of titania and alumina,
employable is any method capable of producing the carrier composed
of the two. For example, preferred is a method of mixing titania
and alumina, or a method of applying titania to shaped alumina
(including alumina grains and powder). For mixing titania and
alumina, for example, employed is a method of mixing titania powder
with alumina powder or pseudo-boehmite alumina, along with water,
then shaping the resulting mixture, drying and calcining it. For
shaping it, for example, the mixture may be generally molded
through extrusion. An organic binder may be added thereto for
improving the moldability of the mixture. Titania may be mixed with
an alumina binder to give a good carrier of titania and alumina.
Water may be added to a mixed solution of a titanium alkoxide and
an aluminium alkoxide dissolved in a solvent such as alcohol. In
this, the alkoxides are hydrolyzed, and the co-precipitated solid
is shaped, dried and calcined in the same manner as above to give a
carrier of titania and alumina. Preferably, the weight ratio of
titania/alumina of the carrier falls between 10/90 and 90/10.
[0031] On the other hand, titania may be adhered to shaped alumina,
for example, as follows. Titania powder (this may carry a catalytic
metal, and the metal-carrying titania powder will be mentioned
hereinunder), and optionally an organic binder and pseudo-boehmite
alumina powder are added to and well dispersed in an organic
solvent. Shaped alumina is dipped in the resulting mixture (this is
generally in the form of slurry).
[0032] After the mixture has well penetrated into the shaped
alumina and the titania powder has adhered thereto, the shaped
alumina is taken out of the mixture. With that, the shaped alumina
is dried and calcined. Apart from the process, a titanium alkoxide
or titanium tetrachloride, and shaped alumina are added to an
alcohol, to which is added water to hydrolyze the titanium alkoxide
or titanium tetrachloride. Then, the shaped alumina with titanium
hydroxide having deposited thereon is dried and calcined. As in the
titania-adhering methods, titania may be applied to shaped alumina
in any desired manner so that the shaped alumina can carry titania.
In the titania/alumina carrier thus produced according to the
method of adhering titania to shaped alumina, the weight ratio of
titania/alumina preferably falls between 0.1/99.9 and 50/50, more
preferably between 0.5/99.5 and 50/50, even more preferably between
1/99 and 50/50. In the two methods mentioned above, the weight
ratio of titania/alumina of the carrier produced preferably falls
between 0.1/99.9 and 90/10, more preferably between 0.5/99.5 and
90/10, even more preferably between 1/99 and 90/10.
[0033] The starting material of alumina for the method of producing
the carrier may be any and every one that contains aluminium
atom(s). It includes, for example, aluminium nitrate, aluminium
hydroxide, aluminium alkoxides, pseudo-boehmite alumina, a-alumina,
and .gamma.-alumina. Pseudo-boehmite alumina, a-alumina and
y-alumina are obtained from aluminium nitrate, aluminium hydroxide
and aluminium alkoxides. Depending on the method of producing the
carrier, the starting material easy to use is selected.
[0034] The starting material of titania may also be any and every
one that contains titanium atom(s). It includes, for example,
titanium alkoxides, titanium tetrachloride, amorphous titania
powder, anatase titania powder, and rutile titania powder.
Amorphous titania powder, anatase titania powder and rutile titania
powder are obtained from titanium alkoxides and titanium
tetrachloride. Depending on the method of producing the carrier,
the starting material easy to use is selected.
[0035] The carrier is composed of titania and alumina, but may
contain any other refractory inorganic oxide. For example, it may
contain zirconia and silica. The zirconia source may be any and
every one that contains zirconium atom(s), for which, for example,
employable are zirconium hydroxide, zirconium oxychloride,
zirconium oxynitrate, zirconium tetrachloride, and zirconia powder.
Zirconia powder is obtained from zirconium hydroxide, zirconium
oxychloride, zirconium oxynitrate, and zirconium tetrachloride. The
silica source may be any and every one that contains silicon
atom(s), for which, for example, employable are silicon
tetrachloride, sodium silicate, ethyl silicate, silica gel, and
silica sol. Silica gel is obtained from silicon tetrachloride,
sodium silicate, ethyl silicate, and silica sol.
[0036] Next described is how to apply ruthenium to the carrier.
[0037] For applying ruthenium to the carrier, for example, a
ruthenium salt is first dissolved in water or ethanol to prepare a
catalyst solution. The ruthenium salt includes, for example,
RuCl.sub.3.nH.sub.2O, Ru(NO.sub.3).sub.3,
Ru.sub.2(OH).sub.2Cl.sub.47NH.sub.33H.sub.2O,
K.sub.2(RUCl.sub.5(H.sub.2O)),
(NH.sub.4).sub.2(RuCl.sub.5(H.sub.2O), K.sub.2(RuCl.sub.5(NO)),
RuBr.sub.3nH.sub.2O, Na.sub.2RuO.sub.4, Ru(NO)(NO.sub.3).sub.3,
(Ru.sub.3O(OAc).sub.6(H.sub.2O).sub.3)OAcnH.sub.2O,
K.sub.4(Ru(CN).sub.6)nH.sub.2O, K.sub.2(Ru(NO.sub.2).sub.4(OH)NO)),
(Ru(NH.sub.3).sub.6)Cl.sub.3, (Ru(NH.sub.3).sub.6)Br.sub.3,
(Ru(NH.sub.3).sub.6)Cl.sub.2, (Ru(NH.sub.3).sub.6)Br.sub.2,
(Ru.sub.3O.sub.2(NH.sub.3).sub.14)Cl.sub.6H.sub.2O,
(Ru(NO)(NH.sub.3).sub.5)Cl.sub.3,
(Ru(OH)(NO)(NH.sub.3).sub.4)(NO.sub.3).sub.2,
RuCl.sub.2(PPh.sub.3).sub.3, RuCl.sub.2(PPh.sub.3).sub.4,
(RuClH(PPh.sub.3).sub.3)C.sub.7H.sub.8, RuH.sub.2(PPh.sub.3).sub.4,
RuClH(CO)(PPh.sub.3).sub.3, RuH.sub.2(CO)(PPh.sub.3).sub.3,
(RuCl.sub.2(cod))n, Ru(CO).sub.12, Ru(acac).sub.3,
(Ru(HCOO)(CO.sub.2)n, Ru.sub.2I.sub.4(p-cymene).sub.2. Of these,
preferred are RuCl.sub.3.nH.sub.2O, and
Ru.sub.2(OH).sub.2Cl.sub.4.7NH.sub.3.3H.sub.2O, as easy to
handle.
[0038] For applying ruthenium to the carrier, the catalyst solution
as above may be applied to the carrier in any ordinary method of
dipping, co-precipitation or competitive adsorption. The condition
for the treatment may be suitably selected, depending on the method
employed. In general, the carrier is kept in contact with the
catalyst solution at a temperature falling between room temperature
and 90.degree. C., for 1 minute to 10 hours.
[0039] The amount of ruthenium to be held on the carrier is not
specifically defined, but, in general, it preferably falls between
0.05 and 10% by weight, more preferably between 0.3 and 3% by
weight of the carrier. If the ruthenium content is smaller than the
lowermost limit, the CO conversion activity of the catalyst will be
low; but if too large, the amount of ruthenium held on the carrier
is excessive over the necessary amount thereof, and the cost of the
catalyst thereby increases.
[0040] After ruthenium has been applied to the carrier, it is
dried. For drying it, for example, employable is any known drying
method of spontaneous drying, evaporation to dryness, rotary
evaporation, or air drying. After having been thus dried, this is
calcined generally at 350 to 550.degree. C., preferably at 380 to
500.degree. C., for 2 to 6 hours, preferably 2 to 4 hours.
[0041] Next described is how to apply an alkali metal and/or an
alkaline earth metal to the carrier. First described is how to
apply an alkali metal to the carrier. For the alkali metal,
preferred are potassium, cesium, rubidium, sodium and lithium.
[0042] For applying the alkali metal to the carrier, a catalyst
solution is prepared by dissolving an alkali metal salt in water or
ethanol, and this is applied to the carrier. The alkali metal salt
includes K salts such as K.sub.2B.sub.10O.sub.16, KBr, KBrO.sub.3,
KCN, K.sub.2CO.sub.3, KCl, KClO.sub.3, KClO.sub.4, KF, KHCO.sub.3,
KHF.sub.2, KH.sub.2PO.sub.4, KH.sub.5(PO.sub.4).sub.2, KHSO.sub.4,
KI, KIO.sub.3, KIO.sub.4, K.sub.4I.sub.2O).sub.9, KN.sub.3,
KNO.sub.2, KNO.sub.3, KOH, KPF.sub.6, K.sub.3PO.sub.4, KSCN,
K.sub.2SO.sub.3, K.sub.2SO.sub.4, K.sub.2S.sub.2O.sub.3,
K.sub.2S.sub.2O.sub.5, K.sub.2S.sub.2O.sub.6,
K.sub.2S.sub.2O.sub.8, K(CH.sub.3COO); Cs salts such as CsCl,
CsClO.sub.3, CsClO.sub.4, CsHCO.sub.3, CSI, CsNO.sub.3,
Cs.sub.2SO.sub.4, Cs(CH.sub.3COO)Cs.sub.2CO.sub.3, CsF; Rb salts
such as Rb.sub.2B.sub.10O.sub.16, RbBr, RbBrO.sub.3, RbCl,
RbClO.sub.3, RbClO.sub.4, RbI, RbNO.sub.2,
Rb.sub.2SO.sub.4,Rb(CH.sub.3COO), Rb.sub.2CO.sub.3; Na salts such
as Na.sub.2B.sub.4O.sub.7, NaB.sub.10O.sub.16, NaBr, NaBrO.sub.3,
NaCN, Na.sub.2CO.sub.3, NaCl, NaClO, NaClO.sub.3, NaClO.sub.4NaF,
NaHCO.sub.3, NaHPO.sub.3, Na.sub.2HPO.sub.3, Na.sub.2HPO.sub.4,
NaH.sub.2PO.sub.4, Na.sub.3HP.sub.2O.sub.6,
Na.sub.2H.sub.2P.sub.2O.sub.7, NaI, NaIO.sub.3, NaIO.sub.4,
NaN.sub.3, NaNO.sub.2, NaNO.sub.3, NaOH, Na.sub.2PO.sub.3,
Na.sub.3PO.sub.4, Na.sub.4P.sub.2O.sub.7, Na.sub.2S, NaSCN,
Na.sub.2SO.sub.3, Na.sub.2SO.sub.4, Na.sub.2S.sub.2O.sub.5,
Na.sub.2S.sub.2O.sub.6, Na(CH.sub.3COO); and Li salts such as
LiBO.sub.2, Li.sub.2B.sub.4O.sub.7, LiBr, LiBrO.sub.3,
Li.sub.2CO.sub.3, LiCl, LiClO.sub.3, LiClO.sub.4, LiHCO.sub.3,
Li.sub.2HPO.sub.3, LiI, LiN.sub.3, LiNH.sub.4SO.sub.4, LiNO.sub.2,
LiNO.sub.3, LiOH, LiSCN, Li.sub.2SO.sub.4, Li.sub.3VO.sub.4.
[0043] Described is how to apply an alkaline earth metal to the
carrier. For the alkaline earth metal, preferred are barium,
calcium, magnesium and strontium.
[0044] For applying the alkaline earth metal to the carrier, a
catalyst solution is prepared by dissolving an alkaline earth metal
salt in water or ethanol, and this is applied to the carrier. The
alkaline earth metal salt includes Ba salts such as BaBr.sub.2,
Ba(BrO.sub.3).sub.2, BaCl.sub.2, Ba(ClO.sub.2).sub.2,
Ba(ClO.sub.3).sub.2, Ba(ClO.sub.4).sub.2, BaI.sub.2,
Ba(N.sub.3).sub.2, Ba(NO.sub.2).sub.2, Ba(NO.sub.3).sub.2,
Ba(OH).sub.2, BaS, BaS.sub.2O.sub.6, BaS.sub.4O.sub.6,
Ba(SO.sub.3NH.sub.2).sub.2; Ca salts such as CaBr.sub.2, CaI.sub.2,
CaCl.sub.2, Ca(ClO.sub.3).sub.2, Ca(IO.sub.3).sub.2,
Ca(NO.sub.2).sub.2, Ca(NO.sub.3).sub.2, CaSO.sub.4,
CaS.sub.2O.sup.3, CaS.sub.2O.sub.6, CaSO.sub.3NH.sub.2).sub.2,
Ca(CH.sub.3COO).sub.2, Ca(H.sub.2PO.sub.4).sub.2; Mg salts such as
MgBr.sub.2, MgCO.sub.3, MgCl.sub.2, Mg(ClO.sub.3).sub.2, MgI.sub.2,
Mg(IO.sub.3).sub.2, Mg(NO.sub.2).sub.2, Mg(NO.sub.3).sub.2,
MgSO.sub.3, MgSO.sub.4, MgS.sub.2O.sub.6, Mg(CH.sub.3COO).sub.2,
Mg(OH).sub.2, Mg(ClO.sub.4).sub.2; Sr salts such as SrBr.sub.2,
SrCl.sub.2, SrI.sub.2, Sr(NO.sub.3).sub.2, SrO, SrS.sub.2O.sub.3,
SrS.sub.2O.sub.6, SrS.sub.4O.sub.6, Sr(CH.sub.3COO).sub.2,
Sr(OH).sub.2.
[0045] For applying the alkali metal and the alkaline earth metal
to the carrier, the catalyst solution as above may be applied to
the carrier in any ordinary method of dipping, co-precipitation or
competitive adsorption. The condition for the treatment may be
suitably selected, depending on the method employed. In general,
the carrier is kept in contact with the catalyst solution at a
temperature falling between room temperature and 90.degree. C., for
1 minute to 10 hours.
[0046] Ruthenium, the alkali metal and the alkaline earth metal may
be applied to the carrier in any order. If possible, these may be
applied to the carrier all at a time. Preferably, these are applied
to the carrier all at a time. In case where these are applied to
the carrier all at a time, a mixed catalyst solution containing
ruthenium, an alkali metal and an alkaline earth metal is prepared,
and this is applied to the carrier. The method of applying these
metals to the carrier all at a time is preferred, as it is simple
and the cost for catalyst production is reduced. In addition, the
activity of the catalyst produced in the method is high.
[0047] Apart from the methods of applying the active metals to the
carrier that has been formed previously, also employable is still
another method of first applying the active metals to titania,
followed by adhering the titania thus carrying the active metals to
alumina to produce the catalyst of the invention. Anyhow, the
method for producing the catalyst of the invention is not
specifically defined, so far as the catalyst produced comprises
ruthenium and other active metals held on a titania/alumina
carrier.
[0048] The amount of the alkali metal and the alkaline earth metal
to be held on the carrier is not specifically defined, but, in
general, it preferably falls between 0.01 and 10% by weight, more
preferably between 0.03 and 3% by weight of the carrier. If the
metal content is smaller than the lowermost limit, the activity of
the catalyst to selectively oxidize CO will be low; but if too
large, the activity of the catalyst to selectively oxidize CO will
lower, and, in addition, the amount of the metals held on the
carrier is excessive over the necessary amount thereof, and the
cost of the catalyst thereby increases.
[0049] After the alkali metal and the alkaline earth metal have
been applied to the carrier, it is dried. For drying it, for
example, employable is any known drying method of spontaneous
drying, evaporation to dryness, rotary evaporation, or air drying.
After having been thus dried, this is calcined generally at 350 to
550.degree. C., preferably at 380 to 500.degree. C., for 2 to 6
hours, preferably 2 to 4 hours.
[0050] The shape and the size of the catalyst thus produced are not
specifically defined. The catalyst may have any desired shape and
structure as in ordinary catalysts, for example, in any form of
powers, spheres, granules, honeycombs, foams, fibers, cloths,
plates, and rings. The method of shaping the catalyst is not
specifically defined. For example, the catalyst may be molded
through extrusion; or it may be adhered to honeycomb or ring
substrates.
[0051] Next described is a method of using the catalyst for
oxidizing carbon monoxide in a gas of essentially hydrogen, with
oxygen so as to produce a CO-reduced, hydrogen-containing gas. The
catalyst produced in the manner as above is generally calcined, and
the active metals therein are generally in the form of their
oxides. Before using it, the catalyst is reduced with hydrogen. For
reducing it with hydrogen, in general, the catalyst is exposed to
hydrogen streams at a temperature falling between 250 and
550.degree. C., preferably between 300 and 530.degree. C., for 1 to
5 hours, preferably for 1 to 2 hours.
[0052] In the presence of the thus-processed catalyst therein,
oxygen is added to a hydrogen-containing gas, which consists
essentially of hydrogen and which contains at least CO, to thereby
selectively oxidize CO in the gas. The CO oxidation method of the
invention is favorable for selective CO removal from a gas of
essentially hydrogen, which is obtained by reforming or partially
oxidizing a hydrogen-producing material capable of being converted
into a hydrogen-containing gas by reforming or partially oxidizing
it (this is hereinafter referred to as "reformed gas"), and is
applied to production of a hydrogen-containing gas for fuel cells,
to which, however, the invention is not limited.
[0053] The method of oxidative removal of CO from a gas of
essentially hydrogen for producing a hydrogen-containing gas for
fuel cells is described below.
1. Step of Reforming or Partial Oxidation of a Material for
Hydrogen Production:
[0054] In the invention, CO in a reformed gas having been obtained
by reforming various types of materials for hydrogen production is
selectively oxidized with hydrogen in the presence of a catalyst to
remove it from the gas, to thereby produce a hydrogen-containing
gas of which the CO content is fully reduced. The process of
reformed gas production may be any desired one that has heretofore
been carried out or proposed in the art for hydrogen production,
especially for that in fuel cell systems, as will be described
hereinunder. Therefore, in fuel cell systems equipped with a
gas-reforming unit, the reformed gas produced may be used directly
in the invention as it is.
[0055] First described is how to reform or partially oxidize a
material for hydrogen production. The material for hydrogen
production is meant to indicate a material capable of being
converted into a hydrogen-rich gas through its steam reforming or
partial oxidation, and includes, for example, hydrocarbons such as
methane, ethane, propane, butane; hydrocarbon-containing materials
such as natural gas (LNG), naphtha, gasoline, kerosene, gas oil,
fuel oil, asphalt; alcohols such as methanol, ethanol, propanol,
butanol; oxygen-containing compounds such as methyl formate, methyl
tert-butyl ether, dimethyl ether; and also various types of town
gases, LPG, synthetic gases, and coals. The matter of selecting the
material for hydrogen production herein from those depends on
various related conditions such as the scale of fuel cell systems
and the material supply situation. In general, preferred are
methanol, methane or LNG, propane or LPG, naphtha or lower
saturated hydrocarbons, and town gases.
[0056] The technique of reforming or partial oxidation (this is
hereinafter referred to as "reforming technique") includes, for
example, steam reforming or partial oxidation, combination of steam
reforming and partial oxidation, autothermal reforming, and other
reforming reactions. Of those, steam reforming is the most popular.
To some specific materials, however, partial oxidation or other
reforming techniques (for example, thermal reforming such as
pyrolysis, and other various catalytic reforming reactions such as
catalytic decomposition and shift reaction) may apply, if
desired.
[0057] Also if desired, reforming reactions of different types may
be combined. For example, steam reforming is generally accompanied
by endothermic reaction, and it may be combined with partial
oxidation that compensates for the part of endothermic reaction
(the combination is autothermal reforming). As the case may be, CO
having been side-produced in steam reforming may be reacted with
H.sub.2O in shift reaction, so that a part of the side product, CO
is converted into CO.sub.2 and H.sub.2 to thereby reduce the CO
content of the reformed gas. In that manner, steam reforming may be
combined with any type of other reactions. If desired, after having
been subjected to partial oxidation in the absence of a catalyst or
to catalytic partial oxidation, the processed gas may be further
subjected to steam reforming in the latter stage of the process. In
this case, the heat having been generated through the former-stage
partial oxidation may be directly used in the latter-stage steam
reforming of endothermic reaction.
[0058] Steam reforming, one typical embodiment of reforming
reaction is described below.
[0059] In steam reforming, in general, the catalyst and the
reaction condition are so selected that the hydrogen absorption of
the gas being processed can be as large as possible. In this,
however, it is difficult to completely inhibit side production of
CO. Even if steam reforming is combined with shift reaction, the CO
content reduction in the reformed gas is limited. In fact, in steam
reforming of hydrocarbons such as methane, it is desirable that the
condition is optimized for better selectivity of the following
reaction (2) or (3), to thereby increase the hydrogen yield and
retard side production of CO.
CH.sub.4+2H.sub.2O.fwdarw.4H.sub.2+CO.sub.2 (2)
CnHm+2nH.sub.2O.fwdarw.(2n+m/2)H.sub.2+nCO.sub.2 (3)
[0060] Similarly, in steam reforming of methanol, it is also
desirable that the condition is optimized for better selectivity of
the following reaction (4):
CH.sub.3OH+H.sub.2O.fwdarw.3H.sub.2+CO.sub.2 (4)
[0061] Further, CO may be modified and reformed according to the
shift reaction of formula (1) mentioned above. However, since the
shift reaction is equilibrium reaction, a relatively large amount
of CO still remains in the reformed gas. Therefore, the gas
reformed through the reaction (this is the gas of essentially
hydrogen that shall be processed in the present invention--the same
shall apply hereinunder) shall contain CO.sub.2, non-reacted steam
and some CO, in addition to the majority of hydrogen.
[0062] Various types of catalysts are known effective for the
reforming reaction mentioned above, and a desired one is selected
from these depending on the type of the starting material to be
processed and the type of the reaction for reforming, and on the
other reaction conditions. Some of the catalysts are mentioned
below. For steam reforming of hydrocarbons and methanol, for
example, Cu--ZnO catalysts, Cu--Cr.sub.2O.sub.3 catalysts,
catalysts of Ni held on carrier, Cu--Ni--ZnO catalysts, Cu--Ni--MgO
catalysts, and Pd--ZnO catalysts are effective. For catalytic
reforming or partial oxidation of hydrocarbons, for example,
catalysts of Pt, Ni or Ru held on carrier are effective.
[0063] The reforming apparatus to be employed herein is not
specifically defined, and may be any and every one generally
employed in ordinary fuel cell systems. However, since most
reforming reactions of steam reforming or decomposition are
accompanied by endothermic reaction, generally preferred are
reaction units and reactors of good heat supply thereto (for
example, heat-exchangeable reaction units). Such reaction units
are, for example, multi-tubular reactors and plate-fin reactors.
Regarding the mode of heat supply to these, for example, the
reactors may be heated with a burner or a heating medium, or may be
heated through catalyst combustion for partial oxidation, to which,
however, the invention is not limited.
[0064] The condition for reforming reaction shall be suitably
determined, as varying depending on the material to be processed,
the type of reforming reaction, the catalyst used, the type of the
reaction unit used, and the reaction mode in the unit. Anyhow, it
is desirable that the reaction condition is so selected that the
conversion of the starting material can be the largest (preferably
up to 100% or nearly 100%) and that the hydrogen yield can be the
largest. If desired, the non-reacted hydrocarbon and alcohol may be
recovered and recycled in the reaction system. Also if desired, the
formed or non-reacted CO.sub.2 and water may be removed from the
reaction system.
2. Step of Selective Oxidation (Conversion) and Removal of CO:
[0065] In the manner as above, obtained is a desired reformed gas
which has a large hydrogen content and from which the other
components of the starting material than hydrogen, such as
hydrocarbons and alcohols have been fully removed.
[0066] In the invention, oxygen is added to the starting gas
(reformed gas) of which the majority is hydrogen and which contains
a minor amount of CO, to thereby selectively oxidize (convert) the
CO therein into CO.sub.2. In this, therefore, the oxidation of
hydrogen must be minimized as much as possible. In addition, in
this, the conversion of CO.sub.2 having been formed or having
existed in the starting gas into CO must be retarded (this is
because the hydrogen in the starting gas may cause reverse-shift
reaction). Before used for the selective oxidation, the catalyst of
the invention is generally in a reduced condition. Therefore, if
not, or that is, if the catalyst is not reduced, it is desirable
that the catalyst is reduced with hydrogen before it is used for
the selective oxidation. The catalyst of the invention produces a
good result in selective oxidation and removal of CO not only from
the starting gas having a low CO.sub.2 content but also from any
others having a high CO.sub.2 content. In fuel cell systems, in
general, used is a reformed gas having an ordinary-level CO.sub.2
content, or that is, a reformed gas having a CO.sub.2 content of
from 5 to 33% by volume, but preferably a reformed gas having a
CO.sub.2 content of from 10 to 25% by volume, more preferably from
15 to 20% by volume.
[0067] On the other hand, the starting gas obtained through steam
reforming generally contains steam, but the steam content of the
starting gas to be processed in the invention is preferably as
small as possible. In general, the starting gas contains from about
5 to 30% of steam, and its steam content on this level causes no
problem in processing the starting gas with the catalyst of the
invention.
[0068] Still another advantage of the catalyst of the invention is
that not only the CO content of the starting gas having a low CO
content (of at most 0.6% by volume) can be effectively reduced, but
also the CO content of any others having a relatively high CO
content (of from 0.6 to 2.0% by volume) can also be effectively
reduced.
[0069] In the hydrogen-containing gas production method of the
invention, the catalyst of the invention or the catalyst produced
according to the method of the invention is used. In this method,
even when the starting gas has a high CO.sub.2 content of 15% by
volume or more, selective conversion and removal of CO from it is
still possible even at relatively high temperatures falling between
60 and 300.degree. C. In this, the conversion and removal of CO
from the starting gas is accompanied by endothermic reaction, like
the side reaction, a hydrogen oxidation therein. Therefore, the
heat having been generated through the reaction in the method may
be effectively recovered and recycled in fuel cells for increasing
the power generation efficiency of the fuel cells.
[0070] In general, it is desirable that the oxygen gas to be added
to the reformed gas is pure oxygen (O.sub.2), air or oxygen-rich
air. The amount of the oxygen gas to be added is preferably so
controlled that the ratio of oxygen/CO (by mol) falls between 0.5
and 5, more preferably between 1 and 4. If the ratio is too small,
the CO removal will be low; but if too large, it is unfavorable
since the hydrogen consumption will increase.
[0071] The reaction pressure is not specifically defined. For fuel
cells, in general, it may fall between atmospheric pressure and 10
kg/cm.sup.2G, but preferably between atmospheric pressure and 5
kg/cm.sup.2G. If the reaction pressure is set too high, the power
for pressure elevation must be large, which, however, is
uneconomical. In particular, reaction pressure higher than 10
kg/cm.sup.2G is undesirable as it must be controlled according to
high-pressure gas regulations, and, in addition, such high reaction
pressure is not safe as being critical for the possibility of
explosion.
[0072] The reaction may be effected generally at a temperature not
lower than 60.degree. C., preferably falling between 60 and
300.degree. C. In such an extremely broad temperature range, the
reaction is stable and selective for CO conversion. If the reaction
temperature is lower than 60.degree. C., the reaction speed will be
low at such a low temperature, and if so, the degree of CO removal
(conversion) through the reaction will be low within the
practicable range of GHSV (gas hourly space velocity) for the
reaction.
[0073] In general, it is preferable that the reaction is effected
at GHSV falling between 5,000 and 100,000 hr.sup.-1. GHSV indicates
the hourly space velocity of the gas supplied in the reactor, based
on the standard-state volume velocity of the gas supplied and
passing through the catalyst layer and on the apparent volume of
the catalyst layer. If GHSV is too small, a large amount of the
catalyst is needed; but if too large, the CO removal will lower.
Preferably, GHSV for the reaction falls between 6,000 and 60,000
hr.sup.-1. In this step of CO conversion and removal, the CO
conversion reaction is endothermic reaction, and this therefore
elevates the temperature of the catalyst layer. If the temperature
of the catalyst layer is elevated too much, the selectivity of the
catalyst for CO conversion and removal is generally lowered.
Accordingly, it is undesirable that too much CO is reacted on a
small amount of the catalyst within a short period of time. To that
effect, too large GHSV is often undesirable.
[0074] The reaction unit for the CO conversion and removal is not
specifically defined, and may be any and every one that satisfies
the above-mentioned requirements for the reaction. However, since
the conversion reaction is endothermic reaction, preferred for it
are reaction units or reactors that ensure easy removal of reaction
heat from them for facilitating good temperature control therein.
Concretely, for example, preferred are heat-exchangeable,
multi-tubular or plate-fin reactors. As the case may be, a coolant
medium may be circulated in or around the catalyst layer.
[0075] Of the hydrogen-containing gas thus produced according to
the method of the invention, the CO content is satisfactorily
reduced, as so mentioned hereinabove. Accordingly, the gas does not
poison or deteriorate the platinum electrode catalyst in fuel
cells, and therefore it significantly prolongs and increases the
life and the power generation efficiency and capability of fuel
cells. In addition, in the method of producing the
hydrogen-containing gas of the invention, the heat having been
generated through the CO conversion reaction can be recovered.
Moreover, even a hydrogen-containing gas having a relatively high
CO content can be well processed according to the method of the
invention, and the CO content of the gas can be well lowered to a
practicable level. In general, the CO content of the
hydrogen-containing gas for fuel cells is preferably at most 100
ppm, more preferably at most 50 ppm, even more preferably at most
10 ppm. According to the method of the invention, it is surely
possible to produce the hydrogen-containing gas of the preferred
level, in a broad reaction condition.
[0076] The hydrogen-containing gas obtained in the invention is
favorable to the fuel for various types of H.sub.2-combusting fuel
cells, especially for those at least having platinum (platinum
catalyst) for the fuel electrode (negative electrode), for example,
low-temperature-working fuel cells such as phosphate-type fuel
cells, KOH-type fuel cells, and solid polymer-type fuel cells.
[0077] When an oxygen-introducing unit and a CO conversion unit
both to be driven according to the method of the invention is
installed in a space between the reforming unit (in case where a
modifying unit is after the reforming unit, this is considered as a
part of the reforming unit) and the fuel cell unit in a
conventional fuel cell system; or when the catalyst of the
invention is used for the CO conversion and removal catalyst in a
fuel cell system equipped with an oxygen-introducing unit and a
conversion reactor unit, and when the reaction condition for the CO
conversion with the catalyst is controlled in the manner described
hereinabove, the fuel cell system thus constructed is superior to
any other conventional ones.
EXAMPLES
[0078] The invention is described more concretely with reference to
the following Examples, which, however, are not intended to
restrict the scope of the invention.
Example 1
[0079] 160 g of rutile-type titania (TiO.sub.2, Ishihara Sangyo's
CR-EL, having a surface area of 7 m.sup.2/g) and 59.7 g of
pseudo-boehmite alumina powder (Shokubai Kasei Kogyo's Cataloid-AP)
were mixed, and well kneaded with ion-exchanged water in a kneader,
and the water content of the resulting mixture was controlled to be
enough for extrusion. Through an extruder, this was pelletized into
columnar pellets having a diameter of 2 mm and a length of from 0.5
to 1 cm, and then dried in a drier at 120.degree. C. for 24 hours.
Next, this was calcined in a furnace at 500.degree. C. for 4 hours.
This is carrier 1. The ratio by weight of titania/alumina of the
carrier 1 is 80/20.
[0080] 10 g of the carrier 1 was metered, to which was applied a
dipping solution that had been prepared separately by adding 4.75
cc of ethanol to 5.25 cc of an ethanol solution of ruthenium
chloride (containing 0.952 g of Ru in 50 cc). This was heated at
60.degree. C. to evaporate and remove ethanol, and calcined in a
muffle furnace at 120.degree. C. for 2 hours and then at
500.degree. C. for 4 hours. This is ruthenium-carrying carrier
1.
[0081] Next, 10 cc of an aqueous solution containing 0.0259 g of
potassium nitrate, which had been prepared separately, was applied
to the ruthenium-carrying carrier 1. This was heated at 60.degree.
C. to evaporate and remove water, and calcined in a muffle furnace
at 120.degree. C. for 2 hours and then at 500.degree. C. for 4
hours. This is catalyst 1. The composition of the catalyst 1 is
shown in Table 1. The crash strength of the catalyst 1 is 1.2
kg/mm, and this proves the durability of the catalyst 1 in use in
ordinary conditions.
Example 2
[0082] Carrier 2 having a ratio by weight of titania/alumina of
50/50, ruthenium-carrying carrier 2 and catalyst 2 were produced in
the same manner as in Example 1, for which, however, used were 100
g of rutile-type titania (this is the same as in Example 1) and 149
g of pseudo-boehmite alumina powder (this is the same as in Example
1) in place of 160 g of rutile-type titania and 59.7 g of
pseudo-boehmite alumina powder. The composition of the catalyst 2
is shown in Table 1.
Example 3
[0083] 14.2 g of titanium tetraisopropoxide (TTIP, Wako Pure
Chemical Industries special-grade chemical) was dissolved in 97 ml
of isopropyl alcohol, to which was added 5.25 g of diethanolamine,
and stirred for 2 hours. Next, a solution of 3.6 ml of isopropyl
alcohol in 1.8 g of water was gradually added to it, and then
stirred for 2 hours. 25 ml of the resulting solution was metered,
to which was added 10 g of activated alumina (Sumitomo Chemical's
KHD24) that had been dressed to be 16 to 32-mesh grains. This was
left as it was for 1 hour, and the alumina grains were taken out
through filtration, and well washed with isopropyl alcohol. The
grains were calcined in a muffle furnace at 120.degree. C. for 2
hours and then at 500.degree. C. for 4 hours. This is carrier 3.
The carrier 3 has titania adhering onto the solid grains of alumina
(alumina grains). The ratio by weight of titania/alumina of the
carrier 3 is 1/99.
[0084] 10 g of the carrier 3 was metered, to which was applied a
dipping solution that had been prepared separately by adding 4.75
cc of ethanol to 5.25 cc of an ethanol solution of ruthenium
chloride (containing 0.952 g of Ru in 50 cc). This was heated at
60.degree. C. to evaporate and remove ethanol, and calcined in a
muffle furnace at 120.degree. C. for 2 hours and then at
500.degree. C. for 4 hours. This is ruthenium-carrying carrier
3.
[0085] Next, 10 cc of an aqueous solution containing 0.0259 g of
potassium nitrate, which had been prepared separately, was applied
to the ruthenium-carrying carrier 3. This was heated at 60.degree.
C. to evaporate and remove water, and calcined in a muffle furnace
at 120.degree. C. for 2 hours and then at 500.degree. C. for 4
hours. This is catalyst 3. The composition of the catalyst 3 is
shown in Table 1.
Example 4
[0086] 3 g of activated alumina (Sumitomo Chemical's KHD24) that
had been dressed to be 16 to 32-mesh grains was dipped in a titania
dispersion of 0.8 g of rutile-type titania (TiO.sub.2, Ishihara
Sangyo's CR-EL, having a surface area of 7 m.sup.2/g) and 0.3 g of
pseudo-boehmite alumina powder (Shokubai Kasei Kogyo's Cataloid-AP)
in 2 ml of a dispersion medium (ion-exchanged water/polyoxyethylene
(10) octylphenyl ether (from Wako Pure Chemical
Industries)/acetylacetone=50/1/1 by volume), to thereby make
titania adhere onto the alumina grains. The alumina grains were
taken out through filtration, washed and dried. The grains were
calcined in a muffle furnace at 120.degree. C. for 2 hours and then
at 500.degree. C. for 4 hours. This is carrier 4. The carrier 4 has
titania adhering onto the solid grains of alumina (alumina grains).
The ratio by weight of titania/alumina of the carrier 4 is
15/85.
[0087] 3.84 g of the carrier 4 was metered, and dipped in 2 ml of
an ethanol solution of ruthenium chloride that had been prepared
separately (the solution contains 38.4 mg of Ru). This was heated
at 60.degree. C. to evaporate and remove ethanol, and calcined in a
muffle furnace at 120.degree. C. for 2 hours and then at
500.degree. C. for 4 hours. This is ruthenium-carrying carrier
4.
[0088] Next, the ruthenium-carrying carrier 4 was dipped in 5 ml of
an aqueous solution of potassium nitrate that had been prepared
separately (this contains 3.0 mg of K). With that, this was heated
at 60.degree. C. to evaporate and remove water, and calcined in a
muffle furnace at 120.degree. C. for 2 hours and then at
500.degree. C. for 4 hours. This is catalyst 4. The composition of
the catalyst 4 is shown in Table 1.
Example 5
[0089] Catalyst 5 of this Example is the ruthenium-carrying carrier
1 produced in Example 1. Its composition is shown in Table 1.
Comparative Example 1
[0090] 10 g of rutile-type titania (TiO.sub.2, Ishihara Sangyo's
CR-EL, having a surface area of 7 m.sup.2/g) was dipped in 5.25 cc
of an ethanol solution of ruthenium chloride that had been prepared
separately (this contains 0.952 g of Ru in 50 cc). This was heated
at 60.degree. C. to evaporate and remove ethanol, and calcined in a
muffle furnace at 120.degree. C. for 2 hours and then at
500.degree. C. for 4 hours. This is catalyst 6 (powdery catalyst).
Its carrier is titania alone. The composition of the catalyst 6 is
shown in Table 1. Before Ru was applied thereto, pelletizing the
starting titania into columnar pellets was tried through extrusion
in the same manner as in Example 1, but in vain.
Comparative Example 2
[0091] 10 g of the catalyst 6 produced in Comparative Example 1 was
metered, to which was applied a dipping solution that had been
prepared separately by dissolving 0.0259 g of potassium nitrate in
5.25 ml of ion-exchanged water. This was heated at 60.degree. C. to
evaporate and remove water, and calcined in a muffle furnace at
120.degree. C. for 2 hours and then at 500.degree. C. for 4 hours.
This is catalyst 7 (powdery catalyst). Its carrier is titania
alone. The composition of the catalyst 7 is shown in Table 1.
Comparative Example 3
[0092] A dipping solution that had been prepared separately by
adding 4.75 cc of ethanol to 5.25 cc of an ethanol solution of
ruthenium chloride (containing 0.952 g of Ru in 50 cc) was applied
to 10 g of activated alumina (Sumitomo Chemical's KHD24) that had
been dressed to be 16 to 32-mesh grains. This was heated at
60.degree. C. to evaporate and remove ethanol, and calcined in a
muffle furnace at 120.degree. C. for 2 hours and then at
500.degree. C. for 4 hours. This is catalyst 8. Its carrier is
alumina alone. The composition of the catalyst 8 is shown in Table
1.
Comparative Example 4
[0093] To 10 g of the catalyst 8 produced in Comparative Example 3,
applied was a dipping solution that had been prepared separately by
dissolving 0.0259 g of potassium nitrate in 10 ml of ion-exchanged
water. This was heated at 60.degree. C. to evaporate and remove
water, and calcined in a muffle furnace at 120.degree. C. for 2
hours and then at 500.degree. C. for 4 hours. This is catalyst 9.
Its carrier is alumina alone. The composition of the catalyst 9 is
shown in Table 1.
Example 6
[0094] 10 g of the carrier 1 produced according to the process of
Example 1 was metered, and dipped in a dipping solution that had
been prepared separately by dissolving 0.263 g of ruthenium
chloride (containing 38.03% of ruthenium metal) and 0.026 g of
potassium nitrate. This was dried at 60.degree. C., and then
calcined in air at 500.degree. C. for 4 hours. This is catalyst 10.
Its composition is shown in Table 1.
Example 7
[0095] 10 g of the carrier 1 produced according to the process of
Example 1 was metered, and sprayed with 2.0 cc of a dipping
solution (this is the same as in Example 6), with stirring under
reduced pressure. This was dried at 120.degree. C., and then
calcined at 500.degree. C. for 4 hours. This is catalyst 11. Its
composition is shown in Table 1.
Example 8
[0096] 0.263 g of ruthenium chloride (containing 38.03% of
ruthenium metal) and 0.026 g of potassium nitrate were dissolved in
5.5 cc of water to prepare a dipping solution. 10 g of the carrier
3 produced according to the process of Example 3 was metered, and
sprayed with the dipping solution, with stirring under reduced
pressure. This was dried at 120.degree. C., and then calcined at
500.degree. C. for 4 hours. This is catalyst 12. Its composition is
shown in Table 1.
Example 9
[0097] Ruthenium and potassium were applied to the carrier 1
produced according to the process of Example 1, in the manner
mentioned below.
[0098] 0.263 g of ruthenium chloride (containing 38.03% of
ruthenium metal) was dissolved in 2.0 cc of water to prepare a
dipping solution. 10 g of the carrier 1 was metered, dipped in the
dipping solution, then dried at 60.degree. C., and thereafter
calcined in air at 500.degree. C. for 4 hours. This is
ruthenium-carrying carrier 5.
[0099] 0.026 g of potassium nitrate was dissolved in 2.0 cc of
water to prepare a dipping solution. The ruthenium-carrying carrier
5 was dipped in the dipping solution, and then dried at 60.degree.
C. This was calcined in air at 500.degree. C. for 4 hours. This is
catalyst 13. Its composition is shown in Table 1.
Example 10
[0100] 0.263 g of ruthenium chloride (containing 38.03% of
ruthenium metal) was dissolved in 2.0 cc of water to prepare a
dipping solution. 10 g of the carrier 1 was metered, and sprayed
with the dipping solution with stirring under reduced pressure.
This was dried at 120.degree. C., and then calcined in air at
500.degree. C. for 4 hours. This is ruthenium-carrying carrier
6.
[0101] 0.026 g of potassium nitrate was dissolved in 2.0 cc of
water to prepare a dipping solution. The ruthenium-carrying carrier
6 was sprayed with the dipping solution with stirring under reduced
pressure, and then dried at 120.degree. C. This was calcined in air
at 500.degree. C. for 4 hours. This is catalyst 14. Its composition
is shown in Table 1.
Example 11
Comparative Example 5
Selective Oxidation of CO Gas
[0102] Before in use, each catalyst was dressed to be 16 to 32-mesh
grains. Concretely, the catalysts 1, 2, 5, 10, 11, 13 and 14 each
were ground, while the catalysts 6 and 7 each were shaped into
tablets, using a tablet-shaping machine, and then ground; and each
catalyst powder was dressed to be 16 to 32-mesh grains. The other
catalysts were in the form of 16 to 32-mesh grains, and they were
used as they were. The catalyst was packed into a fixed bed flow
reactor, and hydrogen gas passed through it to reduce the catalyst
at 500.degree. C. for 1 hour.
[0103] A gas of essentially hydrogen was processed in the reactor
for selective oxidation of CO therein, under the condition shown in
Table 2. The reaction temperature was varied in a range within
which the CO concentration in the processed gas was reduced to at
most 10 ppm. The results are given in Table 3. As in this, the
catalyst activity was evaluated on the basis of the temperature
range within which the CO concentration in the processed gas was
reduced to at most 10 ppm.
TABLE-US-00001 TABLE 1 Titania/Alumina Ratio in Carrier of
Catalyst, and Amount of Metal Held by the Carrier Method of
TiO.sub.2/Al.sub.2O.sub.3 (by Ruthenium Potassium Catalyst Catalyst
weight) (wt. %) (wt. %) Production Catalyst 1 80/20 1.0 0.1 Example
1 Catalyst 2 50/50 1.0 0.1 Example 2 Catalyst 3 1/99 1.0 0.1
Example 3 Catalyst 4 15/85 1.0 0.1 Example 4 Catalyst 5 80/20 1.0
0.0 Example 5 Catalyst 6 100/0 1.0 0.0 Co. Ex. 1 Catalyst 7 100/0
1.0 0.1 Co. Ex. 2 Catalyst 8 0/100 1.0 0.0 Co. Ex. 3 Catalyst 9
0/100 1.0 0.1 Co. Ex. 4 Catalyst 10 80/20 1.0 0.1 Example 6
Catalyst 11 80/20 1.0 0.1 Example 7 Catalyst 12 1/99 1.0 0.1
Example 8 Catalyst 13 80/20 1.0 0.1 Example 9 Catalyst 14 80/20 1.0
0.1 Example 10
TABLE-US-00002 TABLE 2 CO Oxidation Condition Items Reaction
Condition Reaction Pressure atmospheric pressure Reaction
Temperature 50 to 350.degree. C. Gas Hourly Space Velocity 10,000
hr.sup.-1 (GHSV) Composition of Gas Processed (vol. %) Hydrogen
74.4 Carbon Monoxide 0.6 Carbon Dioxide 15 Oxygen 2 Nitrogen 8
TABLE-US-00003 TABLE 3 Result of CO Oxidation Reaction Temperature
Catalyst Range (.degree. C.)* Example 11 Catalyst 1 90-300 Catalyst
2 100-300 Catalyst 3 85-300 Catalyst 4 110-270 Catalyst 5 85-280
Catalyst 10 70-300 Catalyst 11 60-300 Catalyst 12 75-300 Catalyst
13 80-270 Catalyst 14 75-270 Comp. Example 5 Catalyst 6 50-250
Catalyst 7 95-200 Catalyst 8 110-250 Catalyst 9 90-250 *This is the
reaction temperature range (.degree. C.) within which the CO
concentration in the processed gas was reduced to at most 10
ppm.
[0104] The catalysts carrying the same metal are compared in point
of the high-activity temperature range for selective CO oxidation.
As in Table 3, the catalysts with the active metal on a carrier of
titania and alumina combined (catalysts 1 to 5, and catalysts 10
and 14) are active in a broader temperature range than the
catalysts with the active metal on a carrier of titania or alumina
alone (catalysts 6 to 9). In particular, the former catalysts are
active at high temperatures. Regarding their shapability including
the mechanical strength of the shaped catalysts, the catalysts with
the active metal held on a carrier of titania and alumina combined
are superior to those with the active metal held on a carrier of
titania alone.
INDUSTRIAL APPLICABILITY
[0105] The method of the invention is effective for selective
conversion and removal of CO from a gas of essentially hydrogen
within a broad temperature range. When used in hydrogen-oxygen fuel
cells, the method prevents the platinum electrode (hydrogen
electrode) from being poisoned by CO, and therefore prolongs the
cell life and stabilizes the cells for power generation.
* * * * *