JP5158792B2 - Catalyst for electrochemical oxidation of carbon monoxide - Google Patents

Description

  The present invention relates to a catalyst for electrochemical oxidation of carbon monoxide and use thereof.

  The polymer electrolyte fuel cell is easy to handle due to its low operating temperature, and has excellent startability and operational operability, such as fast start-up time. Furthermore, it has a high current density and can be reduced in size and weight. For this reason, it is attracting attention as a small-capacity power source and a mobile power source. In a polymer electrolyte fuel cell, a platinum catalyst is mainly used as an anode catalyst. However, when hydrogen obtained by reforming natural gas, methanol, gasoline, or the like is used as a fuel, it is generated by reforming. There is a problem that carbon monoxide is strongly adsorbed on platinum and greatly reduces the catalytic function.

  As a fuel electrode of such a low-temperature fuel cell that is susceptible to catalyst poisoning by carbon monoxide, a catalyst for fuel electrode having CO poisoning resistance using a combination of a transition metal or an alloy thereof and a specific organometallic complex, etc. Has been reported (for example, Patent Document 1). However, an effective catalyst for actively oxidizing and removing carbon monoxide has not been reported.

  On the other hand, as a gas sensor that electrically detects carbon monoxide, an ionization electrode and a reference electrode are connected to a proton conductor, and a proton current generated by an oxidation reaction of carbon monoxide at the ionization electrode is detected to detect a gas monoxide concentration. There is known a sensor having a structure for measuring (Patent Document 2).

This gas sensor is disadvantageous in that it is expensive because a large amount of noble metal catalyst such as platinum is used as the ionization electrode, and the detection sensitivity is inferior because the overvoltage of carbon monoxide oxidation is high.
JP-A-14-329500 Japanese Patent Publication No. 5-39509

  The present invention has been made in view of the current state of the prior art as described above, and its main purpose is to perform electrochemical oxidation of carbon monoxide suitable for use in a gas monoxide sensor, a fuel cell anode, and the like. It is to provide a novel catalyst effective for the reaction.

  The present inventor has intensively studied to achieve the above-described object. As a result, among rhodium porphyrin complexes, in particular, a specific rhodium porphyrin complex in which at least one carboxyalkyl group is substituted on the pyrrole ring has been known to have excellent activity as a catalyst for electrochemical oxidation of carbon monoxide. I found the characteristic. In addition, when the rhodium porphyrin complex is supported on a conductive carrier, particularly carbon black, carbon monoxide can be oxidized with high efficiency at a low overvoltage and dispersed on the carrier in a very fine state. Since it can be supported, it has been found that even when the amount of noble metal used is greatly reduced, it has sufficient catalytic activity. Furthermore, it discovered that about the water-soluble compound in this rhodium porphyrin complex, it has the outstanding activity as an electrochemical oxidation catalyst of carbon monoxide also in the state of aqueous solution. The present invention has been completed based on these findings.

That is, the present invention provides the following catalyst for electrochemical oxidation of carbon monoxide and its use.
1. The following chemical formula (1):

(Wherein R _{1 to} R ₈ are the same or different and each represents a hydrogen atom, an alkyl group, a hydroxyalkyl group, an alkenyl group, a group: —SO ₃ M ₁ (wherein M ₁ represents a hydrogen atom, an alkali metal or -NH is _4), or a group: -R ₉ -COOM ₂ (wherein, R ₉ represents a linear or branched alkylene group, M ₂ is a hydrogen atom or an alkali metals) Provided that at least one of R _{1 to} R ₈ is a rhodium porphyrin represented by the group: —R ₉ —COOM ₂ , or rhodium 2,4-diacetyldeuteroporphyrin dimethyl ester. Catalyst for electrochemical oxidation of carbon monoxide.
2. In the chemical formula (1), at least two of R _{1 to} R ₈ are groups: —R ₉ —COOM ₂ (wherein R ₉ is a linear or branched alkylene group, and M ₂ is a hydrogen atom or electrochemical oxidation catalyst for carbon monoxide according to 1 which is a is) alkali metals.
3. In the chemical formula (1), R ₆ and R ₇ groups: -R ₉ -COOM ₂ (wherein, R ₉ represents a linear or branched alkylene group, M ₂ is a hydrogen atom or an alkali metals 3. A catalyst for electrochemical oxidation of carbon monoxide according to item 2 above.
4). Item 4. The catalyst for electrochemical oxidation of carbon monoxide according to any one of Items 1 to 3, wherein rhodium porphyrin is supported on a conductive carrier.
5. Item 5. The catalyst according to Item 4 , wherein the conductive support is carbon black.
6). 6. An anode for a polymer electrolyte fuel cell comprising the catalyst according to any one of items 1 to 5 and an anode catalyst material.
7). 6. A carbon monoxide sensor comprising the catalyst according to any one of items 1 to 5 as a catalyst component for oxidizing carbon monoxide in a carbon monoxide detector.
8). In the carbon monoxide oxidation removal apparatus in the anode gas for a polymer electrolyte fuel cell including an electrolyte solution, a working electrode, a counter electrode, and a power supply device, as a catalyst for oxidizing carbon monoxide in the working electrode,
An apparatus for removing carbon monoxide from an anode gas, comprising the catalyst according to any one of items 1 to 5.
9. 6. An anode for a polymer electrolyte fuel cell using carbon monoxide as a fuel, comprising the catalyst according to any one of items 1 to 5 as an anode catalyst substance.
10. A solid polymer fuel cell using carbon monoxide as a fuel, comprising the anode electrode according to item 9 as a constituent element.
11. 4. A method for oxidizing carbon monoxide, wherein carbon monoxide is electrochemically oxidized in an aqueous solution containing the catalyst according to any one of items 1 to 3.
12 A platinum catalyst poisoned by carbon monoxide is brought into contact with an aqueous solution containing the catalyst according to any one of the above items 1 to 3 at a potential at which the carbon monoxide is oxidized and removed by the catalyst. A method for recovering the catalytic activity of a platinum catalyst.

  The catalyst for electrochemical oxidation of carbon monoxide of the present invention has the following chemical formula (1)

(Wherein R _{1 to} R ₈ are the same or different and each represents a hydrogen atom, an alkyl group, a hydroxyalkyl group, an alkenyl group, a group: —SO ₃ M ₁ (wherein M ₁ represents a hydrogen atom, an alkali) A metal or —NH ₄ ), or a group —R ₉ —COOM ₂ (wherein R ₉ is a linear or branched alkylene group, and M ₂ is a hydrogen atom, an alkali metal or an alkyl group). However, at least one of R _{1 to} R ₈ is a rhodium porphyrin represented by the group: —R ₉ —COOM ₂ ).

The rhodium porphyrin represented by the chemical formula (1) has the reaction formula:
CO + H ₂ O → CO ₂ + 2H ⁺ + 2e−
It has an excellent activity for the electrochemical oxidation reaction of carbon monoxide represented by: Therefore, by electrochemically oxidizing carbon monoxide in the presence of the rhodium porphyrin, it becomes possible to efficiently oxidize carbon monoxide with a low overvoltage.

  Furthermore, the rhodium porphyrin represented by the chemical formula (1) has a high activity for the electrochemical oxidation reaction of carbon monoxide, and has a structure in which the ligand used is mainly close to a natural product. It is a highly safe and inexpensive compound.

  In the above chemical formula, the alkyl group is linear or branched having about 1 to 5 carbon atoms such as methyl, ethyl, isopropyl, n-propyl, t-butyl, sec-butyl, n-butyl, isobutyl, n-pentyl and the like. A chain-like lower alkyl group is preferred.

  As the alkyl group portion of the hydroxyalkyl group, a straight chain having about 1 to 5 carbon atoms such as methyl, ethyl, isopropyl, n-propyl, t-butyl, sec-butyl, n-butyl, isobutyl, n-pentyl or the like A branched lower alkyl group can be exemplified. The hydroxy group can be substituted on any carbon atom of the alkyl group.

  Examples of the alkenyl group include linear or branched alkenyl groups having 2 to 6 carbon atoms such as vinyl, allyl, 2-butenyl, 3-butenyl, 1-methylallyl, 2-pentenyl, 2-hexenyl and the like. Can do.

In the group: —SO ₃ M ₁ , M ₁ is a hydrogen atom, an alkali metal, or —NH ₄ . Among these, examples of the alkali metal include K and Na.

In the group: —R ₉ —COOM ₂ , as the alkylene group represented by R ₉ , for example, methylene, ethylene, trimethylene, 2-methyltrimethylene, 2,2-dimethyltrimethylene, 1-methyltrimethylene, methylmethylene C1-C6 linear or branched alkylene groups such as ethylmethylene, tetramethylene, pentamethylene and hexamethylene groups. The alkyl group and alkali metal represented by M ₂ are the same as those described above.

In the rhodium porphyrin represented by the chemical formula (1), a compound in which two or more of R _{1 to} R ₈ are a group: —R ₉ —COOM ₂ is particularly suitable for an electrochemical oxidation reaction of carbon monoxide. And has high activity.

  Hereinafter, among the rhodium porphyrin compounds, preferred compounds will be described.

  In the above chemical formulas, a group bonded to the porphyrin ring, carbon atom or oxygen atom:-represents a methyl group, and a group bonded to the porphyrin ring:

Represents a vinyl group.

Among the rhodium porphyrins represented by the chemical formula (1), R ₆ and R ₇ are groups: —R ₉
The compound which is -COOM ₂ has high activity, and in particular, the compound in which M ₂ is a hydrogen atom or an alkali metal exhibits very high activity for the electrochemical oxidation reaction of carbon monoxide. Is. In addition to the group: —R ₉ —COOM ₂ , it preferably has a substituent having higher electron donating property or higher water solubility than the alkyl group, and is a hydroxyalkyl group, alkenyl group, or group: —SO It is more preferable to contain 2 or more ₃ M _1, and it is particularly preferable to have 2 or more hydroxyalkyl groups or groups: —SO ₃ M ₁ .

  The rhodium porphyrin represented by the chemical formula (1) has the chemical formula (2).

(Wherein R _{1 to} R ₈ are the same as above) and can be obtained by forming a chelate with a rhodium atom. For example, it can be synthesized by the method described in Inorganica Chimica Acta 25 (1977) 215-218. That is, after the porphyrin compound represented by the chemical formula (2) is sufficiently dissolved in a solvent such as ethanol, a rhodium salt, a complex or the like is added thereto and heated to reflux, and the reaction mixture is purified by a usual method. By doing so, the target rhodium porphyrin can be obtained. As the rhodium salt or complex, tetracarbonyldi-μ-chlorodirhodium is desirable. The solvent to be used is not particularly limited as long as it can dissolve both the porphyrin compound and the rhodium salt, but ethanol and methanol are preferable. The heating reflux temperature is not particularly limited as long as it is lower than the boiling point of the solvent, but when ethanol is used, it is preferably about 60 ° C to 70 ° C.

  The above rhodium porphyrin can stabilize rhodium porphyrin by supporting intermolecular reactions such as dimerization reaction and disproportionation reaction by supporting it on a conductive carrier. It can have a high catalytic activity for the oxidation reaction. This is presumably because the rhodium porphyrin is strongly adsorbed and supported on the carrier by the interaction with the conductive carrier.

  The conductive carrier is not particularly limited, and for example, various carriers conventionally used as catalyst carriers for polymer electrolyte fuel cells can be used. Specific examples of such a carrier include carbonaceous materials such as carbon black, activated carbon, and graphite. Among these, carbon black has a strong interaction with rhodium porphyrin represented by the above chemical formula and has a strong function of stabilizing rhodium porphyrin. Further, it has excellent conductivity and a large specific surface area. As a particularly preferred substance.

The shape of the conductive carrier is not particularly limited, and for example, a conductive carrier having an average particle diameter of about 0.1 to 100 μm, preferably about 1 to 10 μm can be used. Further, when carbon black is used, for example, specific surface area by BET method is preferably one in the range of about 100~800m ² / g, more preferably being within the range of about 200 to 300 m ² / g . As a specific example of such a carbon black, those commercially available under the trade name Vulcan XC-72R (Cabot) can be used.

  As a method for supporting the conductive carrier, for example, a known method such as a dissolution drying method or a gas phase method can be applied.

  For example, in the dissolution drying method, rhodium porphyrin is dissolved in an organic solvent, and a conductive carrier is added to this solution. For example, the rhodium porphyrin is adsorbed on the carrier by stirring for several hours, and then the organic solvent is dried. Just do it. In addition, when rhodium porphyrin is contained in a large amount in an organic solvent, rhodium porphyrin is adsorbed on a conductive support until equilibrium is reached, and then filtered to remove rhodium porphyrin not adsorbed on the conductive support. Thus, only the rhodium porphyrin interacting with the carrier can be left on the surface of the carrier.

  In this method, the organic solvent can be used without particular limitation as long as it can dissolve rhodium porphyrin. For example, a lower alcohol such as ethanol can be suitably used.

  If the dispersion obtained by filtration is further washed with an organic solvent until the washing liquid becomes transparent, rhodium porphyrin, which has a weak interaction with the conductive carrier, can be washed away and firmly adsorbed on the conductive carrier. It is possible to obtain a highly active catalyst containing only the rhodium porphyrin.

  In the case of carrying by a vapor phase method, for example, a known method such as a plasma vapor deposition method, a CVD method, or a heating vapor deposition method can be adopted.

  The amount of rhodium porphyrin supported on the conductive carrier is not particularly limited. For example, rhodium porphyrin may be supported at about 20 μmol to 80 μmol per 1 g of the conductive carrier, and about 30 μmol to 70 μmol is supported. Is preferred.

  Since the catalyst for electrochemical oxidation of carbon monoxide of the present invention containing rhodium porphyrin as an active ingredient can oxidize oxygen monoxide with high selectivity, various catalysts that require such characteristics are used. Can be used for applications.

  For example, in a polymer electrolyte fuel cell using hydrogen gas containing carbon monoxide obtained by reforming natural gas, methanol, gasoline, etc. as a fuel, carbon monoxide is selected by using it in combination with an anode catalyst material. Thus, an anode having excellent carbon monoxide poisoning resistance can be obtained.

As the anode catalyst material in the anode electrode in this case, for example, a known catalyst such as platinum can be used. The ratio of the carbon monoxide electrochemical oxidation catalyst and the anode catalyst material of the present invention is not particularly limited. For example, the ratio is suitably determined from the range of about 50 to 500 parts by weight of the latter with respect to 100 parts by weight of the former. That's fine. The catalyst for electrochemical oxidation of carbon monoxide and the anode catalyst material may be supported on separate conductive carriers, or may be supported on the same carrier. In the case of supporting the same carrier, for example, a method of supporting rhodium porphyrin by various methods described above on a carrier supporting a catalyst material such as platinum, a carrier supporting rhodium porphyrin, Furthermore, a method of supporting a catalyst substance such as platinum can be applied.

  The structure of the anode electrode and the structure of the polymer electrolyte fuel cell using this anode electrode are not particularly limited, and may be the same as that of a known fuel cell.

  In addition, the carbon monoxide electrochemical oxidation catalyst of the present invention can be used, for example, as a sensor for detecting carbon monoxide using an electrode reaction. In this case, a sensor including the catalyst of the present invention as a carbon monoxide oxidation catalyst is used, and detection methods include a method of detecting a current generated by an oxidation reaction of carbon monoxide, a method of detecting a potential difference, and a proton. A detection method or the like can be employed. For example, like the sensor in the gas detector described in Japanese Patent Publication No. 5-39509, an ionization electrode for oxidizing carbon monoxide by an electrode reaction to generate protons, a proton conductor, and a proton conductor A proton conductor gas sensor having a reference electrode for receiving protons from the gas, reacting with oxygen in the atmosphere and discharging it as water can be obtained. In the gas sensor having such a structure, the catalyst of the present invention can be used as a catalyst for oxidizing carbon monoxide in the ionization electrode.

  In addition, the catalyst for electrochemical oxidation of carbon monoxide of the present invention is, for example, a solid polymer fuel cell using a reformed gas obtained by reforming natural gas, methanol, gasoline or the like as an anode gas. In the above, before supplying the anode gas to the fuel cell, the carbon monoxide contained in the anode gas can be used as a catalyst for oxidizing carbon monoxide in a carbon monoxide oxidation removing apparatus for oxidizing and removing carbon monoxide by electrolysis. Such a carbon monoxide oxidation removal device has, for example, an electrolytic solution, a working electrode, a counter electrode, and a power supply device as basic components.

  A schematic diagram of the carbon monoxide removal apparatus is shown in FIG. The carbon monoxide oxidation removal apparatus can basically have the same structure as that of various ordinary electrolysis apparatuses. As the electrolytic solution, for example, a sulfuric acid solution of about 0.1 to 1M can be used. The catalyst of the present invention is used as a catalyst for oxidizing carbon monoxide at the working electrode. In the working electrode, a conductive material such as a carbon electrode may be used as a base material, and the catalyst of the present invention may be fixed to the base material with a conductive binder. There is no particular limitation on the counter electrode, and various electrodes used in a normal electrolysis apparatus can be used. For example, a platinum electrode can be used. As the power supply device, for example, a constant voltage power supply (potentiostat) or the like can be used. Further, in order to set the working electrode at a predetermined potential, a reference electrode is usually installed in the electrolyte solution. As the reference electrode, various electrodes used in a normal electrolysis apparatus can be used. For example, a silver / silver chloride electrode can be used.

  In the carbon monoxide oxidation removing apparatus, for example, an anode gas is bubbled into the electrolyte solution by a method such as bubbling, and a positive voltage is applied to the working electrode with respect to the reference electrode using a constant voltage power source (potentiostat) during the ventilation. By applying, carbon monoxide contained in the anode gas can be electrochemically oxidized with high selectivity. At this time, by using the catalyst of the present invention as a working electrode catalyst, carbon monoxide can be electrochemically oxidized at a low overvoltage without oxidizing the fuel gas, and the anode gas can be purified. Become. By supplying the exhaust gas from the carbon monoxide oxidation removal apparatus to the polymer electrolyte fuel cell, it is possible to supply high purity hydrogen gas to the fuel cell.

  Furthermore, the catalyst for electrochemical oxidation of carbon monoxide of the present invention can be used as an anode catalyst for a polymer electrolyte fuel cell using carbon monoxide as a fuel. Normally, it is known that carbon monoxide is contained in the fuel gas even a little, but it is known that it causes catalyst poisoning. It can be used as fuel.

  When the catalyst of the present invention is used as an anode catalyst, the structure of the anode electrode and the structure of the polymer electrolyte fuel cell using this anode electrode are not particularly limited except that the catalyst of the present invention is used as an anode catalyst material. It may be similar to a known fuel cell. That is, the polymer electrolyte membrane, the electrode catalyst, the membrane-electrode assembly, the cell structure and the like may be the same as those of a known solid polymer fuel cell.

  For example, conventionally known various metals and metal alloys can be used as the cathode catalyst metal. Specific examples include various metal catalysts including platinum, palladium, iridium, rhodium, ruthenium, platinum-ruthenium, or a supported catalyst in which these catalyst fine particles are dispersed on a carrier such as carbon.

  Polymer electrolyte membranes include perfluorocarbon, styrene-divinylbenzene copolymer, polybenzimidazole and other ion exchange resin membranes, inorganic polymer ion exchange membranes, organic-inorganic composite polymer ion exchange membranes, etc. Can be used.

  The joined body of the solid polymer electrolyte membrane and the electrode catalyst can be produced by a known method. For example, a method in which a catalyst ink produced by mixing catalyst powder and an electrolyte solution is thinned and then hot-pressed on the electrolyte membrane or directly applied and dried on the polymer membrane is applied.

  A fuel battery cell can be produced by sandwiching both surfaces of the obtained membrane-electrode assembly between current collectors such as carbon paper and carbon cloth and incorporating them into the cell.

  In the fuel cell using the catalyst of the present invention as an anode catalyst, carbon monoxide may be supplied to the anode as a fuel, and air or oxygen may be supplied or naturally diffused on the cathode side.

  The operating temperature of the fuel cell of the present invention varies depending on the electrolyte membrane to be used, but is usually about 0 ° C to 100 ° C, preferably about 10 ° C to 80 ° C.

Further, among the rhodium porphyrins represented by the general formula (1), a water-soluble compound, for example, a compound having a group: —SO ₃ M ₁ is subjected to electrochemical oxidation of carbon monoxide even in an aqueous solution state. It has excellent activity as a catalyst. Therefore, by introducing carbon monoxide into the aqueous solution in which the water-soluble rhodium porphyrin represented by the general formula (1) is dissolved, the electrochemical oxidation reaction of carbon monoxide can proceed in the aqueous solution. For example, when an electrode reaction using a platinum electrode is performed in an aqueous solution containing carbon monoxide, poisoning by the carbon monoxide of the platinum electrode can be suppressed by making water-soluble rhodium porphyrin present in the aqueous solution. .

  Further, when a platinum catalyst used as an anode catalyst of a fuel cell is poisoned by carbon monoxide, an aqueous solution containing a water-soluble rhodium porphyrin is brought into contact with the poisoned platinum catalyst, whereby a catalyst for the platinum catalyst is obtained. Activity can be restored. For example, the catalytic activity of the poisoned platinum catalyst can be recovered by supplying an aqueous solution containing rhodium porphyrin to the fuel gas supply path of the fuel cell and bringing the aqueous solution into contact with the platinum catalyst.

  When rhodium porphyrin is used as an aqueous solution, the concentration of rhodium porphyrin is not particularly limited, but can be, for example, about 0.05 mM to 2 mM. Moreover, about reaction temperature, it can be set as about 25 to 80 degreeC, for example.

According to the catalyst for electrochemical oxidation of carbon monoxide of the present invention, carbon monoxide can be efficiently oxidized at a low overvoltage. In particular, a compound having two or more hydroxyalkyl groups or groups: —SO ₃ M ₁ has high activity for electrochemical oxidation of carbon monoxide. Furthermore, the catalyst of the present invention is a low-cost and highly safe substance having a structure close to that of natural porphyrin.

  In addition, when rhodium porphyrin is supported on a conductive carrier, intermolecular reaction can be suppressed and rhodium porphyrin can be stabilized, and has high catalytic activity for electrochemical oxidation reaction of carbon monoxide. It will be a thing.

  When the conductive support is carbon black, rhodium porphyrin can be dispersed and supported in a state close to atomic units, so that the amount of catalyst metal used can be greatly reduced, and it is inexpensive and highly active monoxide. It can be a catalyst for electrochemical oxidation of carbon.

  Also, when rhodium porphyrin is used as an aqueous solution, it can exhibit excellent catalytic activity for the electrochemical oxidation reaction of carbon monoxide.

  Hereinafter, the present invention will be described in more detail with reference to production examples and examples.

Production Example 1
Example of production of rhodium hematoporphyrin IX

A rhodium hematoporphyrin IX represented by the following formula was produced by the following method.

  First, the following chemical formula

30 mg of a commercially available hematoporphyrin IX represented by the following formula was dissolved in 100 mL of ethanol, and then tetracarbonyldi-μ-chlorodirhodium (I) ([Rh ₂ Cl ₂ (CO) ₄ ]) was added to 10.6. mg was added, and the mixture was heated to reflux at 70 ° C. for 5 hours. The refluxed solution was concentrated with a rotary evaporator, dissolved in ethanol, and ultraviolet / visible spectrum (UV-vis spectrum) was measured to confirm the formation of the target compound. FIG. 2 shows an absorbance curve of an ultraviolet / visible spectrum. In FIG. 2, curve A corresponds to hematoporphyrin IX used as a raw material, and curve B is a spectroscopic curve corresponding to rhodium hematoporphyrin IX, which is the target product.

Example 1
Production of rhodium hematoporphyrin IX-supported carbon catalyst The rhodium hematoporphyrin IX obtained in Production Example 1 was dissolved in 10 mL of ethanol to a concentration of 0.7 mM, and carbon black (specific surface area 250 m ² / g , Trade name: Vulcan XC 72R, manufactured by Cabot) was added. After sealing the container, dispersibility was improved by placing it in an ultrasonic cleaner for 1 minute.

  The porphyrin solution in which carbon black was suspended was stirred with a magnetic stirrer for 3 hours, and then the solvent was removed by suction filtration using No. 5C quantitative filter paper manufactured by Toyo Filter Paper Co., Ltd. The carbon black on the filter paper was recovered to obtain a rhodium hematoporphyrin IX-supported carbon catalyst. The amount of rhodium hematoporphyrin IX supported on the obtained rhodium hematoporphyrin IX supported carbon catalyst was 68 μmol / g.

Evaluation of catalytic activity The rhodium hematoporphyrin IX-supported carbon catalyst obtained by the above method was crushed in a mortar, and 5 mg was suspended in 0.5 mL of a mixed solvent (water: ethanol = 1: 1), and then 5 μL 5% Nafion solution (Aldrich) was added. This suspension was placed in an ultrasonic cleaner for 5 minutes to be well dispersed, and then 2 μL was placed on a rotating disk electrode and dried.

The oxygen reduction activity of the catalyst was evaluated using a potentiostat (ALS model 711B) manufactured by ALS. The rotational speed was controlled using a rotational speed control device (BAS RDE-1) manufactured by BAS Co., Ltd. A glassy carbon rotating disk electrode coated with a catalyst was used as a working electrode, a platinum electrode as a counter electrode, and an Ag / AgCl / KCl (sat.) Electrode as a reference electrode. As the electrolyte, 0.1 MH ₂ SO ₄ was used.

A cyclic voltammogram (CV) of rhodium porphyrin-supported carbon in the absence of carbon monoxide is shown as curve A in FIG. After injecting carbon monoxide gas into the electrolytic cell for 7 minutes and measuring the linear sweep voltammogram while rotating the electrode at 6400 rpm, an increase in oxidation current was observed (curve B), and CO was catalyzed by the rhodium porphyrin complex. It can be seen that it is electrochemically oxidized. Under carbon monoxide saturation, the oxidation current starts to increase from around -0.18 V (Ag / AgCl / KCl (sat.) Standard), indicating that the oxidation of carbon monoxide proceeds at a low overvoltage.

Example 2
In the same manner as in Production Example 1, using the commercially available protoporphyrin IX, the following chemical formula

Rhodium protoporphyrin IX represented by The obtained rhodium protoporphyrin IX was supported on carbon black by the same method as in Example 1. The supported amount of rhodium protoporphyrin IX was 54 μmol / g.

  Using the obtained rhodium protoporphyrin IX-supported carbon catalyst, the catalytic activity for the electrochemical oxidation reaction of carbon monoxide was evaluated in the same manner as in Example 1. The results are shown in FIG.

A cyclic voltammogram (CV) of rhodium porphyrin-supported carbon in the absence of carbon monoxide is shown as curve A in FIG. When carbon monoxide gas was blown into the electrolytic cell for 7 minutes and CV was measured, an increase in oxidation current was observed (curve B), and CO was oxidized electrochemically by the catalytic action of the rhodium porphyrin complex. Recognize. Under carbon monoxide saturation, the oxidation current starts to increase from around -0.14 V (Ag / AgCl / KCl (sat.)), Indicating that the oxidation of carbon monoxide proceeds at a low overvoltage.

Examples 3-6
Rhodium porphyrin complexes shown in Table 1 below were prepared by the same method as in Production Example 1, and the catalytic activity for the electrochemical oxidation reaction of carbon monoxide was evaluated by the same method as in Example 1.

Table 1 shows the potential (mV) at 5 μA, the current value (μA) at 0 V, and the maximum current value (μA) obtained from the cyclic voltammogram (CV) measured by the method described above.

Example 7
In the same manner as in Production Example 1 (however, water was used instead of ethanol and the reflux temperature was 95 ° C.), and commercially available deuteroporphyrin (2,4) disulfonic acid was used.

The rhodium deuteroporphyrin (2,4) disulfonic acid represented by these was produced. The obtained rhodium deuteroporphyrin (2,4) disulfonic acid was supported on carbon black by the same method as in Example 1.

  Using the obtained rhodium deuteroporphyrin (2,4) disulfonic acid-supported carbon catalyst, the catalytic activity for the electrochemical oxidation reaction of carbon monoxide was evaluated in the same manner as in Example 1. The results are shown in FIG.

A cyclic voltammogram (CV) of rhodium porphyrin-supported carbon in the absence of carbon monoxide is shown as curve A in FIG. When carbon monoxide gas was blown into the electrolytic cell for 7 minutes and CV was measured, an increase in oxidation current was observed (curve B), and CO was oxidized electrochemically by the catalytic action of the rhodium porphyrin complex. Recognize. Under carbon monoxide saturation, the oxidation current starts to increase from around −0.2 V (Ag / AgCl / KCl (sat.)), Indicating that the oxidation of carbon monoxide proceeds at a low overvoltage.

Evaluation of electrochemical carbon monoxide oxidation ability of rhodium deuteroporphyrin (2,4) disulfonic acid in aqueous solution Rhodium deuteroporphyrin (2,4) disulfonic acid was added to 0.1 MH ₂ SO ₄ as an electrolyte.
The catalytic activity for the electrochemical oxidation reaction of carbon monoxide using a solution dissolved in 0.1 mM as a measurement sample, using a glassy carbon electrode as a working electrode, a platinum electrode as a counter electrode, and a reversible hydrogen electrode as a reference electrode Evaluated. The measurement temperature was 60 ° C.

A cyclic voltammogram (CV) of the rhodium porphyrin-carrying carbon measured in the absence of carbon monoxide is shown as curve A in FIG. When carbon monoxide gas was blown into the electrolytic cell for 7 minutes and the cyclic voltammogram was measured, an increase in oxidation current was observed, indicating that CO was electrochemically oxidized by the catalytic action of the rhodium porphyrin complex. (Curve B
). Under carbon monoxide saturation, the oxidation current begins to rise even at 0.2 V or less (RHE standard), indicating that the oxidation of carbon monoxide proceeds at a low overvoltage.

Confirmation test of platinum catalyst poisoning suppression effect of rhodium deuteroporphyrin (2,4) disulfonic acid aqueous solution (1) Platinum catalyst poisoning suppression effect by aqueous solution containing rhodium porphyrin confirmed. A platinum rotating disk electrode was used as the working electrode, a reversible hydrogen electrode as the reference electrode, and a platinum electrode as the counter electrode. The electrolyte used was 0.1 MH ₂ SO ₄ . The measurement was performed at 60 ° C.

  First, pure hydrogen gas was blown into the electrolytic solution for 20 minutes, and then the electrode potential was maintained at 0.05 V while hydrogen gas was blown, and the electrode was rotated at 3600 rpm to perform amperometry. The results are shown in FIG.

As is clear from FIG. 7, when the potential holding to 0.05 V was started, a hydrogen oxidation current by the platinum electrode was observed. When the gas blown into the electrolytic solution was switched to hydrogen gas containing 0.1% CO at 553 seconds after the start of potential holding, the hydrogen oxidation current decreased rapidly. This shows that the platinum catalyst was poisoned by CO. Furthermore, the gas blown from the hydrogen gas containing 0.1% CO to the pure hydrogen gas was switched 1210 seconds after the start of the potential holding. From FIG. 7, it can be confirmed that the hydrogen oxidation current gradually recovers but the speed is slow. When an aqueous solution of rhodium deuteroporphyrin (2,4) disulfonic acid was added to 0.1 mM in the electrolyte solution (after 1950 seconds after the start of potential holding), the hydrogen oxidation current recovered rapidly. Furthermore, when the hydrogen gas containing 0.1% CO was switched again after 3044 seconds, the hydrogen oxidation current decreased, but the rate of decrease was smaller than when the complex was not present in the electrolyte.

  From the above results, the presence of rhodium deuteroporphyrin (2,4) disulfonic acid in the aqueous solution can recover the activity of the platinum catalyst poisoned with CO, and further suppress the poisoning of the platinum catalyst with CO. I understand.

  (2) Even when hydrogen containing 0.01% CO is used instead of hydrogen gas containing 0.1% CO, the platinum catalyst poisoning suppression effect is confirmed by the same method as in (1) above. did. The results are shown in FIG.

First, when the potential holding to 0.05 V was started, a hydrogen oxidation current by a platinum electrode was observed. Next, when the gas was switched to hydrogen gas containing 0.01% CO in 500 seconds after the start of potential holding, the hydrogen oxidation current decreased rapidly, and it was confirmed that the platinum catalyst was poisoned by 0.01% CO. .

  When the hydrogen gas was returned to pure hydrogen gas in 1720 seconds after the start of potential holding, the hydrogen oxidation ability began to recover. When an aqueous solution of rhodium deuteroporphyrin (2,4) disulfonic acid was added to 0.1 mM in the electrolytic solution 2080 seconds after the start of potential holding, the recovery of the hydrogen oxidation current was accelerated.

  After that, when hydrogen gas containing 0.01% CO is returned again in 2330 seconds after the start of potential holding, the hydrogen oxidation current decreases, but the rate of decrease is suppressed, and the decrease stops in a certain current region ( 3500 seconds to 4500 seconds after the start of potential holding). This suggests that the removal rate of CO on the platinum catalyst by the rhodium porphyrin complex is faster than the poisoning rate of the platinum catalyst by CO.

Thereafter, the hydrogen gas is returned to pure hydrogen gas in 4580 seconds after the start of potential holding, and after 5330 seconds, an aqueous solution of rhodium deuteroporphyrin (2,4) disulfonic acid is 0.286 mM in total in the electrolyte.
It was added to become. Under this condition, no decrease in current is observed even when switching to hydrogen gas containing 0.01% CO in 5808 seconds after starting the potential holding, and hydrogen oxidation is performed even if switching to hydrogen gas containing 0.1% CO in 6526 seconds. The rate of current decrease was greatly suppressed.

  From the above results, the presence of rhodium deuteroporphyrin (2,4) disulfonic acid in the aqueous solution can restore the activity of the platinum catalyst poisoned with CO, and further suppress the poisoning of the platinum catalyst with CO. Was confirmed.

Examples 7-8, 10-12 and Reference Example 9
The rhodium porphyrin complexes shown in Table 2 and Table 3 below were prepared by the same method as in Production Example 1, and the catalytic activity for the electrochemical oxidation reaction of carbon monoxide was evaluated by the same method as in Example 1.

Tables 2 and 3 show the potential (mV) at 5 μA, the current value at 0 V (μA), and the maximum current value (μA) obtained from the cyclic voltammogram (CV) measured by the above method. Show.

Schematic of a carbon monoxide oxidation removal apparatus. The absorbance curve of the ultraviolet-visible spectrum about the rhodium hematoporphyrin IX obtained in Production Example 1. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows cyclic voltammetry measurement results for a rhodium hematoporphyrin IX-supported carbon catalyst in Example 1. FIG. 3 is a drawing showing the results of cyclic voltammetry measurement for the rhodium protoporphyrin IX-supported carbon catalyst in Example 2. FIG. FIG. 6 shows cyclic voltammetry measurement results for rhodium deuteroporphyrin (2,4) disulfonic acid-carrying carbon in Example 7. FIG. The figure which shows the measurement result of the cyclic voltammetry about the rhodium deuteroporphyrin (2,4) disulfonic acid aqueous solution in Example 7. FIG. The figure which shows the result of the confirmation test (CO / H2 1000ppm) of the platinum catalyst poisoning suppression effect in Example 7. The drawing which shows the result of the confirmation test (CO / H2 100ppm) of the platinum catalyst poisoning suppression effect in Example 7.

Claims (12)

The following chemical formula (1):

(Wherein R _{1 to} R ₈ are the same or different and each represents a hydrogen atom, an alkyl group, a hydroxyalkyl group, an alkenyl group, a group: —SO ₃ M ₁ (wherein M ₁ represents a hydrogen atom, an alkali, A metal or —NH ₄ ), or a group: —R ₉ —COOM ₂ (wherein R ₉ is a linear or branched alkylene group, and M ₂ is a hydrogen atom or an alkali metal). Provided that at least one of R _{1 to} R ₈ is a rhodium porphyrin represented by a group: —R ₉ —COOM ₂ , or rhodium 2,4-diacetyldeuteroporphyrin dimethyl ester. Catalyst for electrochemical oxidation of carbon oxide.
In the chemical formula (1), at least two of R _{1 to} R ₈ are groups: —R ₉ —COOM ₂ (wherein R ₉ is a linear or branched alkylene group, and M ₂ is a hydrogen atom or electrochemical oxidation catalyst for carbon monoxide according to claim 1 which is a is) alkali metals.
In the chemical formula (1), _{R 6} and _{R 7 groups:} -R 9 -COOM ₂ (wherein, _{R 9} represents a linear or branched alkylene group, _{M 2} is a hydrogen atom or an alkali metals The catalyst for electrochemical oxidation of carbon monoxide according to claim 2.
The catalyst for electrochemical oxidation of carbon monoxide according to any one of claims 1 to 3, wherein rhodium porphyrin is supported on a conductive carrier. The catalyst according to claim 4 , wherein the conductive support is carbon black.
An anode for a polymer electrolyte fuel cell, comprising the catalyst according to claim 1 and an anode catalyst material. A carbon monoxide sensor comprising the catalyst according to claim 1 as a catalyst component for oxidation of carbon monoxide in a carbon monoxide detector. In the carbon monoxide oxidation removal apparatus in the anode gas for a polymer electrolyte fuel cell including an electrolytic solution, a working electrode, a counter electrode, and a power supply device, as a catalyst for oxidizing carbon monoxide in the working electrode, An apparatus for removing carbon monoxide from an anode gas, comprising the catalyst according to any one of the above. An anode electrode for a polymer electrolyte fuel cell using carbon monoxide as a fuel, comprising the catalyst according to any one of claims 1 to 5 as an anode catalyst material. A solid polymer fuel cell using carbon monoxide as a fuel, comprising the anode electrode of claim 9 as a constituent element. A method for oxidizing carbon monoxide, wherein carbon monoxide is electrochemically oxidized in an aqueous solution containing the catalyst according to any one of claims 1 to 3. A platinum catalyst poisoned by carbon monoxide is brought into contact with an aqueous solution containing the catalyst according to any one of claims 1 to 3 at a potential at which the carbon monoxide is oxidized and removed by the catalyst. A method for recovering the catalytic activity of a platinum catalyst.

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