JP2001149781A - Catalyst for selective oxidation of carbon monoxide in hydrogen-enriched gas and method for removing carbon monoxide using the catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for selectively oxidizing gaseous carbon monoxide in a hydrogen-containing gas, which is activated even in a low temperature region and shows excellent CO removing performance, and a method for removing carbon monoxide by using the catalyst. SOLUTION: One or more metals selected from Fe, Co and Cu are incorporated in the Pt-containing catalyst for selectively oxidizing carbon monoxide as a low-temperature active component. The method for removing carbon monoxide comprises a step to add the necessary amount of oxygen for oxidizing at least a part of carbon monoxide to the hydrogen-rich gas containing carbon monoxide and a step to contact the low-temperature active catalyst with the hydrogen-rich gas thus prepared.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for selectively oxidizing carbon monoxide in fuel gas supplied to an anode electrode of a solid polymer electrolyte fuel cell and a method for removing carbon monoxide using the catalyst.

[0002]

2. Description of the Related Art Solid polymer electrolyte fuel cells have a high output density, operate at low temperatures, and emit little exhaust gas containing harmful substances. It has also attracted attention.

In general, compressed gas or high-purity hydrogen from a liquid hydrogen tank is used as a fuel gas for a fuel cell, and a hydrogen rich gas obtained by reforming a fuel such as alcohol or hydrocarbon with a reformer in advance. Gas is used. But,
When operating (operating) at a low temperature, such as at the time of starting, impurities such as carbon monoxide and carbon gas in the hydrogen-enriched gas poison Pt in the anode electrode catalyst, increase polarization, and decrease output. It is known to end up.

In order to prevent such a problem, Pt is replaced by Pd,
Noble metals such as Rh, Ir, Ru, Os, Au, Sn, W, Cr, Mn, F
An anode electrode alloyed with a base metal such as e, Co, Ni, or Cu is known. However, there is a limit in improving the CO poisoning resistance of the anode electrode catalyst, and in an atmosphere in which the concentration of carbon monoxide in the hydrogen-enriched gas is 100 ppm or more, the poisoning of the electrode catalyst becomes remarkable.

Therefore, a catalyst has been proposed which selectively removes only carbon monoxide without sacrificing hydrogen in the hydrogen-enriched gas. Such a carbon monoxide selective oxidation catalyst includes Pt and Ru.
Such a noble metal is supported on a carrier such as alumina, titania, and zirconia.It is known that oxygen is mixed in an equimolar amount with carbon monoxide contained in a hydrogen-enriched gas and comes into contact with the catalyst. To selectively remove carbon monoxide (US Pat. No. 5,248,566, JP-B-39-21742, JP-A-8-295503, JP-A-10-101302).

[0006]

However, the conventional selective oxidation catalyst for carbon monoxide is strongly affected by the catalyst temperature, is not activated when the catalyst temperature is low, and does not operate unless it is once reduced at a high temperature. There was a problem. Also,
There is a problem that once removed, the CO removal performance is low in a low temperature range.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem.
An object of the present invention is to provide a carbon monoxide selective oxidation catalyst exhibiting removal performance and a method for removing carbon monoxide using the catalyst.

[0008]

In order to achieve the above object,
As a result of intensive studies, the present inventors have found that the combination of a Pt catalyst, which is inferior in low-temperature activity, and at least one transition metal selected from Fe, Co, and Cu, enables the low-temperature, low-temperature selective oxidation catalyst for carbon monoxide. The inventors have found that the activity is dramatically improved, and arrived at the present invention.

That is, the carbon monoxide selective oxidation catalyst of the present invention is characterized in that the Pt catalyst contains at least one transition metal selected from Fe, Co and Cu as a low-temperature activating component.

[0010] Another aspect of the present invention is to add to a hydrogen-enriched gas containing carbon monoxide an amount of oxygen necessary to oxidize at least a portion of the carbon monoxide in the gas; Contacting the oxygen-added gas with the carbon monoxide selective oxidation catalyst.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below step by step.

[A] Carbon monoxide selective oxidation catalyst The carbon monoxide selective oxidation catalyst of the present invention comprises at least Pt.
And one or more metals selected from Fe, Co and Cu. Although Pt alone has insufficient low-temperature activity, low-temperature activity is dramatically improved by using it in combination with one or more low-temperature activation components selected from Fe, Co, and Cu.

(1) Pt There is no particular limitation on the state of Pt, but a metal state or a low-valent oxide state such as PtO or PtO ₂ is preferable.
Two or more of these states may be mixed. Among these, the metal state is particularly preferred.

(2) Low-temperature activating component The low-temperature activating component in the present invention comprises Fe, Co and C
u is at least one metal selected from u. Particularly preferred among these is Fe.

The total amount of the low-temperature activating component is preferably 1 to 70% by weight, and more preferably 5% by weight or more, with [Pt + low-temperature activating component] being 100% by weight. If the low-temperature activating component is less than 1% by weight, a sufficient effect cannot be obtained, and if it exceeds 70% by weight, the maximum CO removal rate is rather lowered, which is not preferable.

When Fe is used alone as a low-temperature activating component, the content of Fe is reduced by setting [Pt + Fe] to 100 wt%.
It is preferably from 5 to 70 wt%, more preferably from 10 to 50 wt%, particularly preferably from 20 to 30 wt%.

There are no particular restrictions on the state of Fe, Co and Cu, but a metal state or a metal oxide state is preferred. Two or more of these states may be mixed. Among these, the metal state is particularly preferred.

(3) Catalyst Preparation Method The catalyst of the present invention preferably uses a carrier in order to increase the effective surface area. The carrier is alumina, titania,
A carrier such as zirconia can be used without particular limitation. The BET specific surface area of the carrier is not particularly limited, but is 150 m ²
/ G or more, more preferably 200 m ² / g or more. Practically, it is 200 to 400 m ² / g.

The loadings of Pt and the low-temperature activating component are not particularly limited, but the total loading of Pt and the low-temperature activating component is preferably 0.1 to 20% by weight, in terms of metal, based on the mass of the catalyst. 10 wt% is more preferred.

In order to support the catalyst of the present invention on a carrier, a conventional method such as impregnation, water absorption, evaporation to dryness and the like can be used. Pt and the low-temperature activating component may be supported at the same time, or may be supported in separate steps. However, it is preferable that the Pt and the low-temperature activation component be supported simultaneously to reduce the number of steps. For example, it is adjusted by adding a mixed solution or suspension of a platinum compound and a low-temperature activation component starting material to a carrier powder, evaporating to dryness, insolubilizing, and then reducing to activate the loading component. be able to.

Examples of the platinum compound include platinum acid, platinum halides (platinum chloride, platinum bromide, platinum iodide, etc.), platinum sulfide, platinum selenide, platinum telluride, halogen acids (chloroplatinic acid, Alkali metal salts and ammonium salts (such as sodium chloroplatinate and sodium platinate), platinum salts of inorganic acids, and organic platinum compounds (trichloroethylene platinum acid) Salts, platinum carbonyl compounds), platinum complexes and the like.

The low-temperature activating component starting materials include Fe,
Soluble salts such as nitrates, acetates and oxalates of Co or Cu may be mentioned.

The method of insolubilizing these compounds after being carried on the carrier powder may be a conventional method, and may be neutralized and precipitated with a suitable acid or alkali.

Next, as a reduction treatment method for activating the supported components, a wet reduction method of treating with a reducing agent such as formic acid, formalin, or hydrazine, or a gas phase reduction method of treating in a gas stream containing hydrogen is used. it can.

When using the wet reduction method, the treatment temperature is usually from room temperature to 100 ° C., and the treatment is performed within 24 hours. Preferably, the processing temperature is 40 to 60 ° C. and the processing time is 30 minutes to 4 hours.

When the gas phase reduction method is used, the hydrogen content in the gas is not limited, but it is preferable to use a gas having a hydrogen content of 5 to 20% by volume (the balance is nitrogen). The processing temperature is usually between room temperature and 250
° C, preferably from 100 to 250 ° C. Processing time is
Usually, it is 10 minutes to 4 hours, preferably 30 minutes to 2 hours.

The catalyst after the reduction treatment can be used as it is, but is preferably used after washing. By washing, insoluble decomposition products of the platinum compound and the low-temperature activation component starting material and decomposition products of the reducing agent can be removed.

[0028] The catalyst of the present invention comprises
It is preferred that all processing temperatures do not exceed 250 ° C. Two
If the treatment is carried out at more than 50 ° C., a change in the state of the catalytic metal, a transfer of the carrier, and the like are likely to occur.

The form in which the catalyst of the present invention is used is not particularly limited. For example, the above catalyst can be mixed with an appropriate binder and molded into various shapes by a molding method such as compression or extrusion. Prior to carrying out the loading treatment of the platinum compound, the carrier may be molded in a predetermined shape in advance. The shape to be molded is not particularly limited, and examples thereof include a spherical shape, a pellet shape, a cylindrical shape, a honeycomb shape, a spiral shape, a granular shape, and a ring shape. The shape, size and the like can be appropriately selected according to use conditions.

Further, the catalyst may be coated on the surface of the fixed-structure supporting substrate to form a catalyst-coated structure. Examples of the integrally-structured support substrate include ceramics such as cordierite and mullite, and metals such as stainless steel and ferrite, which are formed into a honeycomb or foam.

In preparing the catalyst-coated structure, the catalyst of the present invention may be coated on the surface of the support substrate with a suitable binder or without a binder by a method such as wash coating. Alternatively, the catalyst-coated structure may be prepared by first coating only the support on the support substrate, and then supporting the platinum compound and the low-temperature activator starting material.

As the binder, a conventional binder such as alumina sol, silica sol, aluminum nitrate and aluminum acetate can be used.

[B] Method for Removing Carbon Monoxide Next, the method for removing carbon monoxide of the present invention will be described. This process involves adding to a hydrogen-enriched gas containing carbon monoxide the amount of oxygen necessary to oxidize at least some of the CO in the gas, and then contacting the catalyst of the present invention with H2.
_This is a CO removal method in which only CO is selectively oxidized without substantially losing ₂ . This method, for example,
In the polymer electrolyte fuel cell system described below,
Applies to gases derived from shift reactors.

The oxygen added in this manner is usually added as air. Although the oxidation of CO is advantageous to oxygen at a high concentration, an excess of oxygen would also oxidizes H _2. In order to obtain a high CO removal rate without lowering the hydrogen recovery rate, the O ₂ / CO (molar ratio) is preferably set to 0.5 to 2.5, more preferably 0.7 to 1.5.

The contact temperature between the gas and the catalyst is preferably from 60 to 250 ° C, more preferably from 100 to 200 ° C. The gas hourly space velocity (GHSV) is usually 5,000 to 150,000 / hr, preferably 10,000 to 100,000 / hr.

According to the removing method of the present invention, the CO concentration in the gas can be reduced to 100 ppm or less, and if necessary, to 50 ppm or less even at a low temperature such as at the time of starting.

[C] Solid Polymer Electrolyte Fuel Cell System The catalyst of the present invention can be suitably used in a solid polymer electrolyte fuel cell system equipped with a carbon monoxide selective oxidation reactor. According to a preferred embodiment, the solid polymer electrolyte fuel cell system comprises (i) a storage container for a fuel composed of a hydrocarbon and / or an oxygen-containing hydrocarbon, and (ii) the fuel and water, and if necessary, A reformer that supplies air and comes into contact with the reforming catalyst to generate H ₂ , CO, and CO ₂ ;
ii) a shift reactor for adding steam to the reformed gas generated in the reformer and bringing the reformed gas into contact with a catalyst to reduce the CO concentration to 2% by volume or less; and (iv) a gas generated in the shift reactor. It comprises a carbon monoxide selective oxidation reactor for adding a predetermined amount of air to contact with the catalyst of the present invention to reduce the CO concentration to 100 ppm or less, and (v) a solid polymer electrolyte fuel cell.

A system may be configured by combining some of these components or adding other components. For example, when methanol is used as the fuel, a shift reactor can be incorporated into the reformer to form one apparatus. Further, since several percent of H ₂ remains in the anode exhaust gas of the solid polymer electrolyte fuel cell, a catalytic combustor is further provided as a component of the solid polymer electrolyte fuel cell system, and the anode exhaust gas and air Can be introduced into a catalytic combustor to burn residual hydrogen and use the heat of combustion for, for example, the vaporization of methanol as fuel.

In the above-mentioned solid polymer electrolyte fuel cell system, the catalyst of the present invention having high low-temperature activity is used in the selective oxidation reactor for carbon monoxide. Therefore, the catalyst warm-up system is simplified, and the selective oxidation reactor for carbon monoxide is used. It is possible to reduce the size and to supply a gas having a low CO concentration to the subsequent fuel cell. For this reason, CO poisoning of the anode electrode catalyst can be suppressed, and the life of the anode catalyst electrode can be extended.

[0040]

EXAMPLES Hereinafter, the present invention will be described with reference to examples.
The present invention is not limited to these.

EXAMPLE 1 0.21 g of chloroplatinic acid hexahydrate (special grade of Wako Pure Chemical Reagent), 0.25 g of iron nitrate (III) nonahydrate (special grade of Wako Pure Chemical Reagent) and γ- Alumina (TA-2301 manufactured by Sumitomo Chemical)
24.89 g and 100 ml of water were charged, and an appropriate amount of an aqueous potassium hydroxide solution was added to adjust the pH to 10, thereby obtaining a platinum / iron slurry solution.

Separately, 0.26 g of sodium borohydride was added to water
It was dissolved in 21 ml to obtain a reduced solution. While keeping the platinum / iron slurry solution at 50 ° C., a reducing solution was added dropwise over 6 minutes to perform a reducing treatment. The solid obtained after the treatment is filtered, washed with water,
After drying at 0 ° C. for 2 hours, 25 g of an alumina catalyst powder carrying 0.32% Pt and 0.14% Fe was obtained. This powder was compacted with an 8 t compression press and then pulverized, sieved and sized to 80 to 100 mesh to obtain a catalyst sample.

Example 2 In a separable flask, 0.21 g of chloroplatinic acid hexahydrate (special grade of Wako Pure Chemical Reagent), 0.17 g of cobalt (II) nitrate hexahydrate (special grade of Wako Pure Chemical Reagent), and γ- Alumina (TA-23 manufactured by Sumitomo Chemical)
01) 24.89 g and 100 ml of water were charged, and an appropriate amount of an aqueous potassium hydroxide solution was added to adjust the pH to 10 to obtain a platinum / cobalt slurry solution.

Separately, 0.21 g of sodium borohydride was added to water
It was dissolved in 17 ml to obtain a reduced solution. While keeping the platinum / cobalt slurry solution at 50 ° C., the reducing solution was dropped in 5 minutes,
A reduction treatment was performed. The solid obtained after the treatment was filtered, washed with water, and dried at 120 ° C. for 2 hours to obtain 25 g of a 0.32% Pt, 0.14% Co-supported alumina catalyst powder. This powder was compacted with an 8 t compression press and then pulverized, sieved and sized to 80 to 100 mesh to obtain a catalyst sample.

Example 3 In a separable flask, 0.21 g of chloroplatinic acid hexahydrate (special grade of Wako Pure Chemical Reagent), 0.13 g of copper (II) nitrate (special grade of Wako Pure Chemical Reagent), and γ- Alumina (TA-2301 manufactured by Sumitomo Chemical) 2
4.89 g and 100 ml of water were charged, and an appropriate amount of an aqueous potassium hydroxide solution was added to adjust the pH to 10 to obtain a platinum / copper slurry solution.

Separately, 0.21 g of sodium borohydride was added to water
It was dissolved in 16 ml to obtain a reduced solution. While keeping the platinum / copper slurry solution at 50 ° C., a reducing solution was added dropwise over 5 minutes to perform a reducing treatment. The solid obtained after the treatment is filtered, washed with water,
After drying at 0 ° C. for 2 hours, 25 g of 0.32% Pt, 0.14% Cu-supported alumina catalyst powder was obtained. This powder was compacted with an 8 t compression press and then pulverized, sieved and sized to 80 to 100 mesh to obtain a catalyst sample.

Example 4 0.46% Pt, 0.44% Pt / 0.02% Fe (Pt: Fe = 9
5: 5), 0.32% Pt / 0.14% Fe (Pt: Fe = 70: 3)
0), 0.23% Pt / 0.23% Fe (Pt: Fe = 50: 50),
0.14% Pt / 0.32% Fe (Pt: Fe = 30: 70), 0.46
% Fe catalyst was prepared in the same manner as in Example 1;
A catalyst sample was prepared by coating a honeycomb of ch × t30 mm at 50 g / L.

Comparative Example 1 0.29 g of chloroplatinic acid hexahydrate (special grade of Wako Pure Chemical Reagent) and γ-alumina (TA-2301 manufactured by Sumitomo Chemical) were placed in a separable flask.
24.89 g and 100 ml of water were charged, and an appropriate amount of an aqueous potassium hydroxide solution was added to adjust the pH to 10 to obtain a platinum slurry.

Separately, 0.18 g of sodium borohydride was added to water
It was dissolved in 13.8 ml to obtain a reduced solution. The above platinum slurry
While keeping the temperature at 50 ° C., the reducing solution was added dropwise over 5 minutes to perform a reducing treatment. The solid obtained after treatment is filtered, washed with water and
After drying for an hour, 25 g of 0.46% platinum-carrying alumina catalyst powder was obtained. This powder is pressed and crushed by an 8t compression press,
What was sieved and sized to 80 to 100 mesh was used as a catalyst sample.

Performance Evaluation 1 For the catalyst samples obtained in Examples 1 to 3 and Comparative Example 1, the ignition temperature of the selective oxidation of CO in the hydrogen-enriched gas and the CO concentration in the outlet gas before the ignition were obtained by the following methods. (%) Was measured.

0.5 cc catalyst sample in a quartz reaction tube (φ8 mm)
Was set and flowed at 0.33 L / min while gradually heating the following composition gas to 100 to 200 ° C., and the outlet gas was analyzed by gas chromatography. When the CO concentration in the outlet gas became 200 ppm or less, it was determined that ignition had occurred, and the evaluation test was terminated. Table 1 shows the ignition temperature of the catalyst sample, and FIG. 1 shows the CO concentration in the outlet gas (before ignition) at each temperature.

Gas composition H ₂ 43.7% CO 6185 ppm CO ₂ 18.4% O ₂ 0.9% N ₂ 14.3% H ₂ O 22.0%

Table 1 Sample No. Ignition Temperature Example 1 (Pt / Fe) 100 ° C. Example 2 (Pt / Co) 140 ° C. Example 3 (Pt / Cu) 100 ° C. Comparative Example 1 (Pt) 200 ° C.

Performance Evaluation 2 A catalyst sample (Examples 1 to 3 and Comparative Example 1) was set in a quartz reaction tube (φ8 mm) by 0.5 cc each, and the same composition gas as in Performance Evaluation 1 was flowed and ignited once. The temperature of 10
It flowed at 0.33 L / min while adjusting the temperature to 0 to 220 ° C, and the outlet gas was analyzed by gas chromatography. FIG. 2 shows the CO concentration in the outlet gas (after ignition) at each temperature.

Performance Evaluation 3 For the catalyst sample obtained in Example 4, the CO concentration (%) in the outlet gas was measured by the following method.

A catalyst sample (φ1 inch × t30) was placed in a quartz reaction tube.
mm) and set the same composition gas as in the performance evaluation 1 to 100-300.
It flowed at 5.06 L / min while preheating to ° C, and the outlet gas was analyzed by a comprehensive gas analyzer for reforming performance evaluation (BEX-5900CM). FIG. 3 shows the CO concentration in the outlet gas at each temperature.

As is clear from FIG. 1, Comparative Example 1 having no low-temperature activating component hardly operates before ignition, and FIG. It can be seen that the CO removal performance is low in the region (100 to 200 ° C.). On the other hand, it can be seen that the catalyst samples of Examples 1 to 3 have excellent CO removal performance even in a low temperature region.

As can be seen from FIG. 3, the Fe content is
Although the maximum low-temperature activity (about 190 ° C) is exhibited at 50 wt% (x), the maximum purification rate of CO is lower than that of 30 wt% (△), which is preferable when both practicalities are considered. Fe
The content is around 30 wt%.

[0059]

The Pt catalyst has a low-temperature activating component of F
e, the catalyst of the present invention containing one or more metals selected from Co and Cu has a markedly higher selective oxidation activity of carbon monoxide in a low temperature region at the time of start-up and the like than a conventional catalyst. improves. Therefore, the catalyst of the present invention makes it possible to reduce the size of the alcohol removal gas CO removal system and simplify the catalyst warm-up system.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between an inlet gas temperature (° C.) and a CO concentration in an outlet gas (before ignition).

FIG. 2 is a graph showing a relationship between an incoming gas temperature (° C.) and a CO concentration in an outlet gas (after ignition).

FIG. 3 is a graph showing a relationship between an incoming gas temperature (° C.) and a CO concentration in an outlet gas in a Pt / Fe catalyst.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Osamu Usaka, Inventor: 1-4-1, Chuo, Wako, Saitama Prefecture Inside Honda R & D Co., Ltd. (72) Inventor: Shoji Isobe 1-4-1, Chuo, Wako, Saitama No. F-term in Honda R & D Co., Ltd. (Reference) 4G040 EA02 EA03 EB31 4G069 AA03 AA08 BA01A BA01B BA04A BA05A BC31A BC31B BC66A BC66B BC67A BC67B BC75A BC75B CC32 DA05 FC08 5H027 AA06 BA01 BA16

Claims (6)

[Claims] 1. A Pt catalyst containing F as a low-temperature activating component
e. A selective oxidation catalyst for carbon monoxide in a hydrogen-enriched gas, wherein the catalyst contains at least one metal selected from e, Co and Cu. 2. The selective oxidation catalyst for carbon monoxide according to claim 1, wherein the low-temperature activation component is Fe. 3. The catalyst for selective oxidation of carbon monoxide according to claim 2, wherein the content of Fe is 5 to 70% by weight, where the total weight (based on metal) of Pt + Fe is 100% by weight. Carbon monoxide selective oxidation catalyst. 4. A selective oxidation catalyst for carbon monoxide, wherein the catalyst for selective oxidation of carbon monoxide according to claim 1 is carried on a carrier. 5. A hydrogen-enriched gas containing carbon monoxide,
Oxygen necessary for oxidizing at least a part of carbon monoxide is added, and then the gas is contacted with a carbon monoxide selective oxidation catalyst according to any one of claims 1 to 4. Carbon removal method. 6. A selective oxidation reactor for carbon monoxide, comprising the catalyst for selective oxidation of carbon monoxide according to claim 1.