JPH0572710B2 - - 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 for a phosphoric acid fuel cell, platinum, which is commonly used as a catalyst in phosphoric acid fuel cells, can be poisoned by the carbon monoxide, especially at low temperatures. It is well known that there is a phenomenon in which the output characteristics of a phosphoric acid fuel cell are significantly reduced due to this.

Therefore, in order to prevent this development, 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. This is a method of directly reducing ruthenium metal in the phase.

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 ruthenium chloride aqueous solution is gradually concentrated from the large pores, and gradually collects in the small pores and eventually precipitates.
Catalysts prepared through such a process generally have poor dispersibility and are expected to have poor support strength with the carrier.

[Purpose of the invention]

The purpose of this invention is to provide a safer method for preparing a platinum-ruthenium catalyst that eliminates the conventional problems of poor dispersibility of ruthenium and weak support strength with a carrier, and does not use hydrogen gas. shall be.

[Key points of the invention]

In this invention, after sufficiently contacting a platinum-supported catalyst with an aqueous ruthenium chloride solution, the PH of the system is brought to an alkaline side, and the temperature of the system is raised to a temperature at which sufficient reduction of ruthenium chloride occurs. is added, and then a reducing agent is gradually added to reduce ruthenium chloride in the liquid phase, and at the same time, ruthenium is supported on the platinum-supported catalyst. Therefore, in the present invention, the method for preparing the supported platinum catalyst may be appropriately selected from known methods.

[Embodiments of the invention]

Example 1 10g of 10wt% platinum supported catalyst and 400ml of deionized water
Add and disperse. On the other hand, a ruthenium chloride aqueous solution is prepared by dissolving 2.59 g of ruthenium chloride (containing 3 molecules of water of crystallization) in 100 ml of deionized water. Next, an aqueous ruthenium chloride solution is added to the platinum-supported catalyst that has been completely dispersed, and the mixture is stirred at room temperature. After this, 200 ml of 0.1M sodium carbonate aqueous solution is added and further stirred. After that, the temperature of the system is raised to 50°C. After the temperature has been raised, 10 ml of 30 wt% hydrogen peroxide solution is added and stirring is continued for about 5 minutes. After this, while maintaining the temperature of the system, the temperature was increased to 170 °C with continued stirring.
ml of formic acid is added gradually over a period of approximately 1 hour. After the addition is complete, the reaction mass is filtered after further stirring, thoroughly washed with deionized water, and then dried.

Analysis of the prepared platinum-ruthenium catalyst revealed that the amount of platinum supported was 9.2% and the amount of ruthenium supported was 9.3%. Furthermore, as a result of measuring the average crystallite diameter by X-ray diffraction, the average crystallite diameter of platinum on the (111) plane is about 25 Å, and the average crystallite diameter of ruthenium on the (101) plane is about 100 Å. It was hot.

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

(Comparison of characteristics with conventional method) Figure 1 shows a platinum-supported catalyst which is the base material of a platinum-ruthenium catalyst, a platinum-ruthenium catalyst prepared by a conventional method, a catalyst of Example 1, and a catalyst of Example 2.
This figure shows the carbon monoxide poisoning resistance of the anode of the catalyst in a monopolar test.

The test conditions were temperature, 130℃, carbon monoxide concentration, 2
%.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, after the platinum-supported catalyst is brought into sufficient contact with the ruthenium chloride aqueous solution, the pH of the system is brought to the alkaline side, and the system is heated to a temperature at which ruthenium chloride is sufficiently reduced. After raising the temperature, a colloidal aggregation inhibitor was added, and then a reducing agent was gradually added to reduce ruthenium chloride in the liquid phase, and at the same time, ruthenium was supported on the platinum-supported catalyst. The deterioration of the dispersibility of ruthenium due to aggregation of the aqueous occluded ruthenium solution, which was a problem in the conventional method, has been eliminated, and ruthenium can now be supported more uniformly. Furthermore, since ruthenium is supported on the platinum-supported catalyst at the same time as the reduction of ruthenium chloride, the supporting strength of ruthenium is improved, and it is expected that a catalyst with a longer life than conventional catalysts will be obtained.

[Brief explanation of drawings]

Figure 1 shows the carbon monoxide resistance of the anodes of the platinum-supported catalyst which is the base material of the platinum-ruthenium catalyst, the platinum-ruthenium catalyst prepared by the conventional method, the catalyst of Example 1, and the catalyst of Example 2, respectively, in the monopolar test. Graph showing toxic properties. A... Platinum-supported catalyst which is the base of the platinum-ruthenium catalyst, B... Platinum-ruthenium catalyst prepared by a conventional method, C... Catalyst of Example 1, D... Catalyst of Example 2.

Claims (1)

[Scope of Claims] 1. After dispersing the platinum-supported catalyst, add a ruthenium chloride aqueous solution, and after sufficient contact with the platinum-supported catalyst, set the pH of the system to the alkaline side, and raise the temperature of the system to a level sufficient for reduction to occur. The method is characterized in that a mixed catalyst of platinum and ruthenium is obtained by reducing ruthenium chloride to ruthenium by adding a colloidal agglomeration inhibitor after raising the temperature to a temperature and then gradually adding a reducing agent having an aldehyde group. Method for preparing an anode catalyst for phosphoric acid fuel cells. 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.