JPH0572711B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] This invention relates to a method for preparing an anode catalyst used in a phosphoric acid fuel cell.

[Prior art and its problems]

Phosphoric acid fuel cells use hydrogen-rich gas obtained by reforming natural gas, methanol, etc. as their fuel. However, such reformed gas usually contains several percent of carbon monoxide. When such a gas containing carbon monoxide is used as a fuel in a phosphoric acid fuel cell, especially at low temperatures, platinum, which is commonly used as a catalyst in phosphoric acid fuel cells, becomes poisoned by the carbon monoxide. It is well known that the output characteristics of phosphoric acid fuel cells are significantly reduced due to

Therefore, in order to prevent this phenomenon, in phosphoric acid fuel cells that are started or operated at particularly low temperatures, a platinum-ruthenium based catalyst has been often used as an anode catalyst instead of platinum alone. In other words, the resistance of ruthenium to carbon monoxide poisoning is well known.

Next, regarding a specific method for preparing a platinum-ruthenium catalyst, we will introduce the conventional technology and list its problems.

A typical method for preparing a platinum-ruthenium catalyst is to first fully contact a platinum-supported catalyst prepared by a well-known method with an aqueous ruthenium chloride solution, dry it, and then air it with hydrogen gas. directly reduced to ruthenium metal in the phase,
This method is to use it as it is or to further heat treat it to make it into a catalyst.

However, in this method, in the step of bringing the platinum-supported catalyst into contact with ruthenium chloride, ruthenium chloride is occluded in the pores existing inside the platinum-supported catalyst or between the fine particles of the platinum-supported catalyst. be. When this is dried, the occluded aqueous ruthenium chloride solution is gradually concentrated starting from the large pores, and gradually collects in the small pores and eventually precipitates out.
Catalysts prepared through such a process generally have poor dispersibility and are expected to have poor support strength with the carrier. Moreover, it is necessary to prepare a platinum-supported catalyst before preparing a platinum-ruthenium catalyst, which has the disadvantage that the catalyst preparation process becomes long.

[Purpose of the invention]

An object of the present invention is to provide a method for preparing a platinum-ruthenium alloy catalyst that eliminates the conventional drawbacks and prepares a highly dispersible catalyst in a shorter time and by a safer method that does not use hydrogen gas. .

[Key points of the invention]

This invention involves bringing a hydrophilically treated catalyst carrier into sufficient contact with an aqueous chloroplatinic acid solution and an aqueous ruthenium chloride solution, and then bringing the pH of the system to an alkaline level to a temperature at which sufficient reduction of the chloroplatinic acid and ruthenium chloride occurs. After raising the temperature of the system, a colloidal flocculation inhibitor is added, followed by a gradual addition of a reducing agent to reduce chloroplatinic acid and ruthenium chloride in the liquid phase, while simultaneously catalyzing platinum and ruthenium. It is made to be supported on a carrier. Furthermore, after this, a heat treatment is performed to improve the life of the catalyst.

[Embodiments of the invention]

Example 1 400 ml of a 10 wt% nitric acid aqueous solution is added to 9.0 g of acetylene black, and the mixture is heated and stirred at a temperature of about 50° C. for about 2 hours. After this, the acetylene black is separated and thoroughly washed with deionized water until the pH of the system is 7. Next, add 400 ml of deionized water to the washed acetylene black and disperse. Add to this 100 ml of chloroplatinic acid aqueous solution containing 1.0 g of platinum.
and ruthenium chloride (contains 3 molecules of water of crystallization) 2.59
A ruthenium chloride aqueous solution prepared by dissolving 100 ml of deionized water is added thereto, and the mixture is stirred at room temperature. after this
Add 400 ml of 0.1M sodium carbonate aqueous solution and stir further. After that, the temperature of the system is raised to 50°C. After completing the temperature rise, add 20 ml of 30 wt% hydrogen peroxide solution and continue stirring for about 5 minutes. After this, while maintaining the temperature of the system, continue stirring for 300 min.
ml of acid is added gradually over a period of approximately 2 hours. After the addition is complete, and after further stirring, the reaction mass is filtered, thoroughly washed with deionized water, and then dried. next,
The dried platinum-ruthenium mixed catalyst is
A platinum-ruthenium alloy catalyst was obtained by heat treatment at a temperature of 900° C. for about 2 hours in a nitrogen atmosphere. As a result of analyzing the obtained catalyst, the amount of platinum supported was 9.5%.
The amount of ruthenium supported was 9.4%. Also, X
As a result of observation by line diffraction, no individual peaks of platinum and ruthenium were observed, confirming that they were alloyed.

Example 2 In Example 1, sodium acid was used as the reducing agent instead of the acid.

(Comparison of characteristics with conventional method) Figure 1 shows the carbon monoxide poisoning resistance characteristics of the platinum-ruthenium catalyst prepared by the conventional method and the anode of the catalyst of Example 1 in a monopolar test (heat-treated under the same conditions). ). The test conditions were a temperature of 130°C and a carbon monoxide concentration of 2%.

Further, FIG. 2 shows the change over time in the carbon monoxide poisoning resistance of the catalyst of Example 1 after heat treatment and the catalyst before heat treatment.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, after a catalyst carrier subjected to hydrophilic treatment is brought into sufficient contact with chloroplatinic acid and a ruthenium chloride aqueous solution, the pH of the system is brought to the alkaline side, and chloroplatinic acid and ruthenium chloride are brought into contact with each other. After raising the temperature of the system to a temperature at which ruthenium chloride is sufficiently reduced, a colloidal flocculant is added, followed by gradual addition of a reducing agent to reduce chloroplatinic acid and ruthenium chloride in the liquid phase. At the same time, since platinum and ruthenium are supported on the catalyst carrier, the deterioration of the dispersibility of ruthenium due to concentration of the occluded ruthenium aqueous solution, which was a problem in the conventional method, is eliminated, and ruthenium can be supported more uniformly. It became like that. In addition, since platinum and ruthenium are supported on the catalyst carrier at the same time as the reduction of chloroplatinic acid and ruthenium chloride, the supporting strength of platinum and ruthenium is improved, resulting in a longer-life catalyst compared to conventional catalysts. can be expected to be obtained.

Furthermore, compared to conventional methods, the time required for catalyst preparation can be shortened because platinum and ruthenium can be supported simultaneously.

[Brief explanation of drawings]

FIG. 1 is a graph showing the carbon monoxide poisoning resistance characteristics of the platinum-ruthenium catalyst prepared by the conventional method and the anode of the catalyst of Example 1 in a monopolar test.
The figure is a graph showing the change over time in the carbon monoxide poisoning resistance of the catalyst of Example 1, which was heat-treated and which was not heat-treated. A...Platinum-ruthenium catalyst prepared by a conventional method, B...Catalyst of Example 1, C...Heat treatment, D...No heat treatment.

Claims (1)

[Claims] 1. After dispersing the hydrophilically treated catalyst carrier in water, add a chloroplatinic acid aqueous solution and a ruthenium chloride aqueous solution to the catalyst carrier, and after fully contacting the platinum-supported catalyst, adjust the pH of the system to an alkaline state. After raising the temperature of the system to a temperature at which sufficient reduction occurs, a colloidal aggregation inhibitor is added and then a reducing agent having an aldehyde group is gradually added to convert platinum chloride and ruthenium chloride into platinum and ruthenium chloride, respectively. A method for preparing an anode catalyst for a phosphoric acid fuel cell, comprising obtaining a mixed catalyst of platinum and ruthenium by reducing it to ruthenium, and obtaining a platinum-ruthenium alloy catalyst by heat-treating the mixed catalyst. 2. In the method described in claim 1,
A method for preparing an anode catalyst for a phosphoric acid fuel cell, characterized in that sodium carbonate is used as a reagent to make the pH of the system alkaline. 3. In the method described in claim 1,
A method for preparing an anode catalyst for a phosphoric acid fuel cell, characterized in that formic acid is used as a reducing agent. 4. In the method described in claim 1,
A method for preparing an anode catalyst for a phosphoric acid fuel cell, characterized in that sodium formate is used as a reducing agent. 5. In the method described in claim 1,
A method for preparing an anode catalyst for a phosphoric acid fuel cell, characterized in that a hydrogen peroxide solution is used as a colloidal aggregation inhibitor. 6. A method for preparing an anode catalyst for a phosphoric acid fuel cell, characterized in that a nitric acid aqueous solution is used as the hydrophilic treatment agent in the method according to claim 1.