JP2001089101A - Method for selectively removing co in hydrogen gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for selectively removing CO, for efficiently carrying out a reaction for reducing the CO concentration within a prescribed temperature range, i.e., the temperature range in which the oxidation reaction of the CO can be efficiently carried out and the side reaction such as a methanation reaction (CO+3H2O→CH4+H2O) is suppressed to efficiently reduce the CO concentration. SOLUTION: This method for selectively removing the CO in a hydrogen gas comprises bringing a mixed gas obtained by mixing a gas consisting essentially of the hydrogen and containing the CO, with oxygen gas, into contact with a catalyst for selectively oxidizing the CO to convert the CO into CO2, and a catalyst of Ru carried by a carrier containing Ce is used as the catalyst for selectively oxidizing the CO.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing CO 2 in hydrogen gas.
In the fuel cell power generation device, more preferably, it is contained in hydrogen gas obtained by reforming methanol or the like supplied to the fuel electrode side of the fuel cell. CO that is selectively oxidized and removed.
It relates to a selective removal method.

[0002]

2. Description of the Related Art A polymer electrolyte fuel cell uses the same platinum-based electrode catalyst as a phosphoric acid fuel cell.
Unlike the phosphoric acid fuel cell, the polymer electrolyte fuel cell is operated at a low temperature (usually 100 ° C. or lower).
The poisoning of the electrode catalyst due to this is an important problem.

Accordingly, as a fuel for a fuel cell using a platinum-based electrode catalyst, pure hydrogen is preferable, but it is obtained by fuel reforming of methanol or the like, which is inexpensive, has excellent storage properties, and is easy to set up in a public supply system. It is common to use a hydrogen-containing gas.

However, such a reformed gas contains a considerable concentration of CO in addition to hydrogen, and this CO is converted into CO ₂ that is harmless to the platinum electrode catalyst.
Development of a technique for reducing the O concentration is strongly desired. At that time, the CO concentration is usually 100 ppm or less, preferably 4 ppm.
It is considered desirable to reduce the concentration to a low concentration of 0 ppm or less.

As one of means for reducing the CO concentration in the reformed gas, a shift reaction (CO + H ₂ O → CO ₂ + H
It has been proposed to use ₂ ). However, such a reaction alone has a limit in reducing the CO concentration due to restrictions on chemical equilibrium, and it is generally difficult to reduce the CO concentration to 1% or less.

Therefore, as a means for reducing the CO concentration to a lower concentration, oxygen or air is introduced into the reformed gas to reduce the C concentration.
There has been proposed a CO selective oxidation method in which O is oxidized to CO ₂ and removed.

As an oxidation catalyst for oxidizing CO to CO ₂ , an alumina catalyst supporting a noble metal has been used. However, it is very difficult for such a noble metal-supported alumina catalyst to selectively oxidize a trace amount of CO in a large amount of hydrogen, and usually, more than stoichiometric oxygen is introduced. However, with the excessive introduction of oxygen, the oxidation reaction of hydrogen proceeds, which causes a decrease in the efficiency of the fuel cell. Therefore, in order to remove CO by oxidation, it is desired to realize a high-performance CO removal method capable of selectively oxidizing a trace amount of CO contained in a large amount of hydrogen with a minimum amount of oxygen.

[0008] The CO selective oxidation reaction is an exothermic reaction, and the temperature of the catalyst layer greatly increases as the reaction proceeds. When the temperature of the catalyst actually increases, the reverse shift reaction (C
O ₂ + H ₂ → CO + H ₂ O), combustion reaction of hydrogen (H ₂ +
1 / 2O ₂ → H ₂ O) or methanation reaction (CO + 3
Undesirable reactions such as H ₂ → CH ₄ + H ₂ O) proceed, and a problem arises in that the CO concentration cannot be sufficiently reduced.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a CO selective oxidation and removal method for efficiently performing a reaction for reducing a CO concentration within a predetermined temperature range in order to efficiently reduce the CO concentration. , A temperature at which the CO oxidation reaction is sufficiently performed, and a methanation reaction (CO + 3H
It is an object of the present invention to provide a CO selective oxidation removal method in which a CO reduction reaction is performed in a temperature range in which a side reaction such as ₂ → CH ₄ + H ₂ O) is suppressed.

[0010]

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors have found that the use of a specific catalyst has a
The present inventors have found that the CO concentration can be sufficiently reduced over a wide temperature range of 200 ° C., and reached the present invention.

According to a first aspect of the present invention, there is provided a method for selectively removing CO from hydrogen gas, wherein a mixed gas obtained by mixing oxygen with a gas containing hydrogen as a main component and containing CO is brought into contact with a CO selective oxidation catalyst to selectively remove CO. Is a method for selectively removing CO in the hydrogen gas by oxidizing to CO ₂ , wherein the carrier containing Ce is used as the CO selective oxidation catalyst.
It is characterized by using a catalyst supporting u.

The method for selectively removing CO from hydrogen gas according to claim 2 is the method for selectively removing CO from hydrogen gas according to claim 1, wherein the selective oxidation of CO is carried out at 80 to 200.
It is characterized in that it is performed in a temperature range of ° C.

The method for selectively removing CO from hydrogen gas according to claim 3 is the method for selectively removing CO from hydrogen gas according to claim 1 or 2, wherein the content of Ce in the carrier is 5 to 5.
20% by weight.

According to a fourth aspect of the present invention, there is provided the method for selectively removing CO from hydrogen gas according to any one of the first to third aspects, wherein the carrier comprises alumina, titania, silica, And zirconia.

The method for selectively removing CO from hydrogen gas according to claim 5 is the method for selectively removing CO from hydrogen gas according to any one of claims 1 to 4. It is characterized by containing 5 to 5% by weight.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, a gas obtained by mixing oxygen with a gas containing hydrogen as a main component and containing CO is brought into contact with a catalyst in which Ru is carried on a carrier containing Ce to selectively oxidize CO. This is a method of selectively removing CO in the hydrogen gas by converting the hydrogen gas into CO ₂ .

As the gas containing hydrogen as a main component and containing CO, hydrogen gas obtained by steam reforming of alcohol or partial oxidation of hydrocarbon can be used. Here, the gas containing hydrogen as a main component and containing CO means a gas containing 40% by volume or more of hydrogen in all the gases.

In order to selectively remove CO from the CO-containing hydrogen gas, oxygen gas is mixed with the CO-containing hydrogen gas. The mixing of the oxygen gas with the CO-containing hydrogen gas is O ₂ / CO (molar ratio) = 0.5-3. With such a mixing ratio, the consumption of H ₂ is minimized,
CO can be selectively removed.

Selective CO from such CO-containing hydrogen gas
CO selective oxidation catalyst and the CO-containing hydrogen gas
The mixed gas in which oxygen is mixed is brought into contact with the gas. Contact method
Is not particularly limited, but under normal pressure, a temperature of 80 to 200 ° C.
It is preferable to perform in the temperature range. Under such conditions, CO selective acid
When the reaction is carried out, CO + H₂O → CO₂+ H ₂
While the shift reaction is carried out efficiently, CO 2₂+ H₂→
CO + H₂O (reverse shift reaction), H₂+ 1 / 2O₂→ H
₂O (hydrogen combustion reaction) and CO + 3H₂→ CH₄+ H
₂O (methanation reaction) is suppressed and CO is sufficiently low
Can be reduced.

As the CO selective oxidation catalyst, a catalyst in which Ru is supported on a carrier containing Ce is preferably used. Such a carrier is suitably selected from the group consisting of alumina, titania, silica and zirconia.

The Ce content in the carrier is 5 to 20 in the carrier.
% By weight. Within this range, Ce can be contained with good dispersibility without reducing the surface area of the carrier. Further, when Ce is contained in the carrier, O ₂ storage is facilitated and Ru can be supported in a high dispersion, so that CO can be selectively removed.

In order for Ce to be contained in the carrier, as a raw material compound of Ce, inorganic acid salts, carbonates, ammonium salts, organic acid salts, halides, oxides, sodium salts of Ce,
Although an ammine complex compound or the like can be used in combination, it is particularly preferable to use a water-soluble salt from the viewpoint of improving the catalyst performance. The content method is not limited to a special method, and various methods such as a known evaporation method, a precipitation method, an impregnation method, and an ion exchange method can be used as long as the components are not significantly unevenly distributed. In particular, the impregnation method is preferable for supporting on alumina, from the viewpoint of increasing dispersibility.

Next, the carrier containing Ce was heated to 80 ° C to 1 ° C.
It is dried at 80 ° C., and then calcined at 300 ° C. to 500 ° C. in the air and / or under air flow. It is preferable that the sintering temperature be in such a temperature range since Ce can be contained while maintaining the surface area of the carrier.

If Ce is contained in the carrier, F
e, Ca, Mg, Mn, La, Nd, Sm, Pr, Gd
And other components may be contained.

The thus obtained Ce-containing carrier has R
u. Ru is 0.5 to 0.5% in the CO selective oxidation catalyst.
If it is contained in an amount of 5% by weight, the oxidizing activity of CO is insufficient if the content is low, and the oxidizing activity corresponding to the supported concentration cannot be obtained if the content is high. Also, by including Ru in the CO selective oxidation catalyst, a reformed gas that can be supplied to the fuel electrode side of the fuel cell can be obtained.

As a raw material compound of Ru, inorganic acid salts, carbonates, ammonium salts, organic acid salts, halides, oxides, sodium salts, ammine complex compounds and the like can be used in combination. It is preferable to use a salt of from the viewpoint of improving the catalyst performance. The method for supporting Ru on the carrier is not limited to a special method, and various methods such as a known evaporation to dryness method, a precipitation method, an impregnation method, and an ion exchange method may be used unless significant uneven distribution of components is involved. Can be.

Next, the Ru-impregnated Ce-containing carrier was
It is dried at a temperature of from 180C to 180C, and then calcined at 300C to 600C in the air and / or in the flow of air. If the calcination temperature is less than 200 ° C., salt decomposition is insufficient, and
If the temperature exceeds 0 ° C., the degree of dispersion of Ru decreases, which is not preferable.

Next, the obtained Ru-containing Ce-containing catalyst is pulverized to a particle size of 24 to 42 mesh. By grinding to such a particle size, performance evaluation can be performed with good reproducibility.

After that, the pulverized catalyst particles are filled in a predetermined reaction vessel, and are heated at 200 to 600 ° C. in a hydrogen stream at a temperature of 0.5 to 500 ° C.
After reducing for 2 hours, a CO selective oxidation catalyst used in the present invention is obtained. A mixture of the above-mentioned CO-containing hydrogen gas and oxygen gas was mixed with the thus-obtained CO selective oxidation catalyst at a flow rate of 25%.
CO can be selectively oxidized and removed by flowing at ~ 150 cm ³ / min.

In the method for selective removal of CO of the present invention, a catalyst comprising Ru supported on a carrier containing at least Ce is used to remove C.
When the O selective oxidation is performed, the temperature range in which the CO concentration can be sufficiently reduced becomes wider as compared with the case where a conventional carrier containing no Ce is used. Therefore, by using the CO selective removal method of the present invention, it is possible to obtain a hydrogen gas having an extremely low CO concentration without performing strict temperature control.

[0031]

The present invention will be described below with reference to the following examples and comparative examples. The present invention is not limited to the following examples.

[0032]Example 1, Comparative Examples 1-2 Al containing Ce₂O₃Preparation of catalyst supporting Ru on carrier
In doing so, first A1 containing Ce₂O₃Prepare the carrier
Was. Preparation of carrier containing Ce dissolved cerium nitrate
Using an aqueous solution as the impregnating solution, Ce content was reduced to 8% by weight.
A1 ₂O₃The carrier was impregnated and supported. Then 15
A1 containing Ce after drying at 0 ° C and firing at 400 ° C₂O
₃A carrier was obtained.

Next, Ru, which is a CO selective oxidation active component, is used.
It was impregnated supported on _A1 2 _{O 3} support containing the Ce.
For carrying Ru, an aqueous solution (3.6% by weight) in which ruthenium nitrate was dissolved was used as an impregnation solution. The loading amount of Ru was set to 5% by weight. Then at 150 ° C 4
Drying at 350 ° C. for 1 hour.
to obtain a catalyst carrying Ru (catalyst 1) to _A1 2 _{O 3} support containing e.

Similar to the method described above, for comparison,
Was prepared catalyst carrying Pt (catalyst 3) to _A1 2 _{O 3} carrier containing not including Ce _A1 2 _{O 3} carrier catalyst supporting Ru (catalyst 2) and ce.

Each of these three types of catalysts (catalysts 1 to 3) is sized to 24 to 42 mesh and filled in a predetermined reaction vessel, and then reduced at 350 ° C. for 1 hour in a hydrogen stream to obtain C.
An O selective oxidation catalyst was obtained.

In the evaluation of the obtained CO selective oxidation catalyst, the composition in a dry state was H ₂ = 75% as a model gas.
A gas prepared by bubbling a mixed gas of CO ₂ = 24.5% and CO = 0.5% so as to have an absolute humidity of 10% was used. In addition, for the CO selective oxidation catalyst, O
_A mixture obtained by mixing oxygen gas so that the molar ratio of ₂ to CO [O ₂ ] / [CO] = 1.5 is supplied so that the gas flow rate / catalyst volume becomes about 10,000 h ⁻¹ on a dry gas basis. Then, the outlet CO concentration was measured while changing the temperature.

FIG. 1 shows the relationship between the outlet CO concentration and the temperature. As shown in FIG. 1, a catalyst in which Ru is supported on an Al ₂ O ₃ carrier that does not contain Ce (catalyst 2) and A containing Ce
In the case where a catalyst (catalyst 3) with Pt supported on an l ₂ O ₃ carrier is used, the CO concentration can be reduced to 40 ppm or less, which is the CO concentration allowable as a fuel gas supplied to the fuel cell, by 180 It was limited to a narrow temperature range around ℃. On the other hand, when a catalyst in which Ru is supported on an Al ₂ O ₃ carrier containing Ce (catalyst 1) is used, 80 to 20
CO concentration of 40ppm over a wide temperature range of 0 ° C
It was able to reduce to below.

In the catalyst of the present embodiment in which Ru is supported on a carrier containing Ce (catalyst 1), the temperature range in which the CO concentration can be sufficiently reduced is wide as described above. O ₂ storage is facilitated by using, in addition to the effect of having a CO oxidation activity more from a low temperature,
This is because the use of a carrier containing Ce has an effect of supporting Ru, which is a CO oxidation active component, in a higher dispersion.

FIG. 2 shows the Ru content depending on the presence or absence of Ce.
Shows differences in diffusivity. Al containing Ce ₂O₃Ru on the carrier
Supported catalyst (catalyst 1) and Ce-free Al₂O₃Responsible
The ratio of the Ru dispersion to the catalyst (Catalyst 2) carrying Ru on the body
In comparison, Al containing Ce₂O₃Ru supported on carrier
The catalyst (catalyst 1) has a higher Ru dispersion degree, but bears Pt.
With the supported catalyst, the above-mentioned effects cannot be obtained.
It is clear that the effect is characteristic of the Ru-supported catalyst
It became. The degree of dispersion of Ru can be measured with a noble metal dispersion degree measuring device (C
O-pulse adsorption method).

Example 2 In the same manner as in Example 1, the Al ₂ O ₃ support containing Ce
A catalyst supporting u was prepared. The content of Ce was 15% by weight, and the supported amount of Ru was 5% by weight (catalyst 4).
Drying and baking were performed in the same manner as in Example 1. After sizing to 24 to 42 mesh, the mixture was filled in a predetermined reaction vessel, and dried under a hydrogen stream.
Reduction treatment was performed at 50 ° C. for 1 hour.

Next, using the same model gas as in Example 1, a CO selective oxidation reaction was performed. As a result, 80 to 20
CO concentration of 40ppm over a wide temperature range of 0 ° C
It was able to reduce to below.

Example 3 In the same manner as in Example 1, the Al ₂ O ₃ carrier containing Ce
A catalyst supporting u was prepared. The content of Ce was 8% by weight, and the supported amount of Ru was 1% by weight (catalyst 5). Drying and calcination were performed in the same manner as in Example 1. After sizing to 24-42 mesh, the mixture was filled in a predetermined reaction vessel, and dried in a stream of hydrogen.
Reduction treatment was performed at 0 ° C. for 1 hour. Next, a CO selective oxidation reaction was performed using the same model gas as in Example 1. As a result, over a wide temperature range of 100 to 200 ° C., CO 2
The concentration could be reduced to 40 ppm or less.

[0043] In the same manner as in Example 4 Example 1, R to _A1 2 _{O 3} carrier containing Ce
A butterflies carrying u were prepared. The content of Ce was 8% by weight, and the supported amount of Ru was 0.5% by weight (catalyst 6). Drying and baking were performed in the same manner as in Example 1, and
After sizing the mesh, the mixture was filled in a predetermined reaction vessel and subjected to a reduction treatment at 350 ° C. for 1 hour in a hydrogen stream. Then, Example 1
Using a model gas similar to that described above, a CO selective oxidation reaction was performed. As a result, the CO concentration could be reduced to 40 ppm or less in a wide temperature range of 120 to 200 ° C.

Example 5, Comparative Example 3 In the same manner as described in Example 1, 8% by weight of C
A catalyst in which 5% by weight of Ru is supported on a ZrO2 support containing e (catalyst 7) and a catalyst in which 5% by weight of Ru is supported on a ZrO2 support not containing Ce (catalyst 8) are prepared by an impregnation method. did. Drying and baking were performed in the same manner as in Example 1. After sizing to 24-42 mesh, the mixture was filled in a predetermined reaction vessel, and reduced at 350 ° C. for 1 hour in a hydrogen stream.

Next, a CO selective oxidation reaction was carried out using the same model gas as in Example 1, and the results are shown in FIG. In the case of using a catalyst in which Ru is supported on a ZrO ₂ carrier not containing Ce (catalyst 8), the temperature range in which the CO concentration can be sufficiently reduced is limited to a narrow temperature range of about 150 to 180 ° C. On the other hand, ZrO ₂ containing Ce
In the case of using a touch butterfly (catalyst 7) supporting Ru on the carrier, the CO concentration can be reduced to a CO concentration allowable as a fuel gas supplied to the fuel cell in a wide temperature range of 100 to 200 ° C. did it.

Examples 6 to 7 A catalyst in which Ru was supported on a SiO ₂ support containing Ce (catalyst 9) and a catalyst in which Ru was supported on a TiO ₂ support containing Ce (catalyst 10) were prepared in the same manner as in Example 1. did. Ce
The content of each catalyst was 8% by weight, and the amount of supported Ru was 5%.
% By weight. Using the same model gas as in Example 1, C
An O selective oxidation reaction was performed. For a catalyst in which Ru is supported on a SiO ₂ support containing Ce (catalyst 9), 100 to 180
In the case of the catalyst (Catalyst 10) in which Ru was supported on a TiO ₂ support containing Ce at 120 ° C., the CO concentration could be reduced at 120 to 200 ° C.

[0047]

According to the CO selective removal method of the present invention, 80
The CO concentration in hydrogen gas can be sufficiently reduced in a wide temperature range of up to 200 ° C., and therefore, a fuel cell vehicle system using a hydrogen-rich gas obtained by reforming methanol or the like can be realized early. It can be expected that the effect of preventing air pollution can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a reaction temperature and a reduction in CO concentration.

FIG. 2 is a graph showing the relationship between the presence or absence of Ce and the degree of Ru dispersion.

FIG. 3 is a diagram showing a relationship between a reaction temperature and a reduction in CO concentration.

Continued on the front page F-term (reference) 4G040 EA02 EA06 EB16 EB32 EC01 EC03 EC04 4G069 AA03 AA08 BA01A BA01B BA02A BA02B BA04A BA04B BA05A BA05B BB02A BB02B BB04A BB04B BC43A BC43B BC70 FB81 CC02A CB81 CC02A 5H027 AA04 AA06 BA01 BA16

Claims (5)

[Claims] 1. A mixed gas in which oxygen is mixed with a gas containing hydrogen as a main component and containing CO, is brought into contact with a CO selective oxidation catalyst to selectively oxidize CO and convert it to CO ₂ , A method for selectively removing CO in a gas, comprising using a catalyst in which Ru is supported on a carrier containing Ce as the CO selective oxidation catalyst. 2. The method according to claim 1, wherein the selective CO oxidation reaction is carried out at 80 to 200.
The method for selectively removing CO from hydrogen gas according to claim 1, wherein the method is performed in a temperature range of ° C. 3. The method for selectively removing CO from hydrogen gas according to claim 1, wherein the content of Ce in the carrier is 5 to 20% by weight. 4. The CO in hydrogen gas according to claim 1, wherein said carrier is selected from the group consisting of alumina, titania, silica and zirconia.
Selective removal method. 5. The method for selectively removing CO from hydrogen gas according to claim 1, wherein 0.5 to 5% by weight of Ru is contained in the CO selective oxidation catalyst.