JPH07256107A - Production of noble metal alloy catalyst - Google Patents

Abstract

PURPOSE:To provide a method for producing a noble metal alloy catalyst by which the control of an alloy compsn. is facilitated and a desired alloy compsn. can be obtd. by increasing the rate of carrying of a heavy metal by the control of the temp. of a plating soln. during a reaction. CONSTITUTION:A noble metal or noble metal alloy catalyst carried on a powdery carrier is dispersed in hot water to prepare a catalyst slurry. A plating soln. of pH 10.5-13.0 contg. a heavy metallic salt, a chelating agent. and a reducing agent is prepd. and put in the catalyst slurry and electroless plating is carried out at a low temp. The resultant noble metal or noble metal alloy catalyst plated with the heavy metal and carried on the carrier is washed, dried and subjected to alloying treatment by heating in a required atmosphere. A reduction reaction of the heavy metallic salt is allowed to proceed slowly and a point of time when the reduction reaction finishes practically and teaching does not occur yet is easily ascertained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a noble metal alloy catalyst containing heavy metals, which is used in fuel cells and the like.

[0002]

2. Description of the Related Art Conventionally, the following method has been considered as a method for producing a noble metal alloy catalyst of this type. In this method, first, a platinum or platinum alloy catalyst supported on carbon powder is dispersed in boiling hot water and allowed to cool to obtain a catalyst slurry. On the other hand, a mixed solution of one or two heavy metal salts of chromium, manganese, iron, cobalt, nickel and copper, a chelating agent and a reducing agent is built in the plating bath to prepare a plating bath having a pH of about 10.5 to 13.0. Then, the plating bath is poured into the catalyst slurry all at once, stirred for 1 hour to perform electroless plating, filtered, washed several times with water until the washing liquid becomes neutral, and dried at a temperature of 60 ° C. Next, a method of performing alloying treatment by heating platinum or a platinum alloy, which is plated with a heavy metal and supported on a carrier, at a temperature of 900 ° C. under a hydrogen stream. Among the platinum alloy catalysts produced by the above method, in the case of supporting nickel and / or cobalt on platinum or a platinum alloy, a mixed solution for preparing a plating solution for electroless plating is, for example, nickel chloride and / or cobalt chloride, It contains sodium tartrate as a chelating agent and hydrazine chloride as a reducing agent. Then, in order to adjust the pH of this mixed solution into a plating solution, it is possible if the chemicals to be mixed are completely dissolved into a solution, which is prepared using a 50% NaOH (sodium hydroxide) solution. The electroless plating using the prepared plating solution is performed by adding the plating solution to the catalyst slurry and then stirring for 1 hour so that the reduction of nickel and / or cobalt is sufficiently completed.

[0003]

However, in the conventional method for producing a noble metal alloy catalyst, supporting of heavy metals is not sufficient, and a desired alloy composition cannot be obtained, and
There is a problem that it is difficult to control the alloy composition. It is considered that the factor affecting the loading rate of the heavy metal is that the temperature of the plating solution during the plating reaction is too high. That is, when the temperature of the plating solution during the reaction is high, the reduction reaction proceeds rapidly, but the heavy metal once supported melts at a high speed. Further, it is considered that the other factor is that the ripening of the mixed solution before the pH adjustment is insufficient and the chelating of the heavy metal by the chelating agent is not sufficient. Therefore, in the present invention, by suppressing the temperature of the plating solution during the reaction and increasing the loading rate of heavy metals, a desired alloy composition can be obtained, and at the same time, the production of a noble metal alloy catalyst that can facilitate control of the alloy composition. The purpose is to provide a method. Further, another object of the present invention is to further increase the load of heavy metals by controlling the temperature of the plating solution during the reaction and further aging the mixed solution before pH adjustment to further increase the heavy metal loading rate. An object of the present invention is to provide a method for producing a noble metal alloy catalyst capable of obtaining an alloy composition and further facilitating control of the alloy composition.

[0004]

In order to solve the above problems, the first method for producing a noble metal alloy catalyst according to the present invention comprises dispersing a noble metal or noble metal alloy catalyst supported on a powdery carrier in hot water. While preparing a catalyst slurry, a plating bath composed of a mixed solution of a heavy metal salt, a chelating agent and a reducing agent is prepared to prepare a plating solution having a pH of 10.5 to 13.0, and the plating solution is added to the catalyst slurry. The method is characterized in that electroless plating is performed at a low temperature, a noble metal or noble metal alloy catalyst, which is plated with a heavy metal and supported on a carrier, is washed and dried, and then heated in a required atmosphere to be alloyed. Carbon or the like is used as the carrier. The noble metal or noble metal alloy catalyst is preferably platinum or a platinum alloy catalyst. Further, it is preferable that the heavy metal salt is nickel chloride and / or cobalt chloride, the chelating agent is sodium tartrate, and the reducing agent is hydrazine chloride. On the other hand, the second method for producing a noble metal or noble metal alloy catalyst is characterized in that, in the first method, the mixed solution is sufficiently stirred at the time of establishing the plating bath and before adjusting the pH. The stirring time is preferably 30 minutes to 90 minutes. The temperature of the low-temperature electroless plating solution is preferably 5 to 40 ° C.
A more preferable temperature of the low temperature electroless plating solution is 20 to 30 ° C. The required atmosphere is preferably a hydrogen stream. The heating temperature of the alloying treatment is preferably around 800 to 1100 ° C. further,
A more preferable heating temperature for the alloying treatment is 900 to 950 ° C.
Is.

[0005]

In the first method for producing a noble metal alloy catalyst of the present invention, the reduction reaction of heavy metals proceeds relatively slowly, the reduction reaction is completed, and it is easy to determine when elution does not occur. On the other hand, in the second method for producing a noble metal alloy catalyst, in addition to the action of the first method, the ripening of the mixed solution is sufficient, and the heavy metal is chelated with the chelating agent and easily reduced. If it is less than 10 minutes, the chelation is incomplete, and if it exceeds 90 minutes, the chelation does not proceed any more and the time is wasted. If the temperature of the low-temperature electroless plating solution is lower than 5 ° C, the reduction reaction becomes too slow and takes a long time, and if it exceeds 40 ° C, the reduction reaction becomes fast and it becomes difficult to determine. Moreover, the heating temperature of the alloying treatment is
If it is less than 800 ° C, alloying becomes insufficient, and if it exceeds 900 ° C, there arises a problem that the alloy composition varies depending on particles. Further, from the viewpoint of device design, the range of 900 to 950 ° C is preferable.

[0006]

EXAMPLES Examples of the present invention will be described below together with comparative examples and conventional examples.

[0007]

[Example 1] Platinum 2.92 using carbon powder as a carrier
13.8 g of carbon-supported platinum catalyst supporting g of the catalyst was wetted with 200 ml of boiling hot water and dispersed with an ultrasonic homogenizer for 2 minutes while stirring to form a catalyst slurry, then at 21 ° C.
Cooled down. Next, nickel chloride 1.90 as a heavy metal salt.
g and cobalt chloride 1.89 g Sodium tartrate 28.93 g as a chelating agent, and hydrazine hydrochloride as a reducing agent 1
3.20 g was dissolved in pure water to prepare a 300 ml mixed solution, and this mixed solution was stirred as it was at a temperature of about 19 ° C. for 60 minutes. Then
A 50% NaOH solution was added to the mixed solution to adjust the pH, and a plating solution having a pH of 12.9 and a solution temperature of 24.3 ° C. was prepared while cooling halfway. Next, the plating solution was added to the catalyst slurry all at once, and electroless plating was performed while stirring for 20 minutes. The temperature of the slurry plating solution during electroless plating was 24 to 26 ° C. The nickel- and cobalt-plated carbon-supported platinum catalyst was collected by filtration, washed with water several times until the washing water became neutral, dried at a temperature of 60 ° C, and finally at a temperature of 900 ° C in a hydrogen stream. Then, the platinum particles were alloyed with nickel and cobalt plated thereon.

Atomic absorption spectrometry of the waste liquid after plating revealed that only 4.6% of the input amount of nickel and 3.6% of the input amount of cobalt remained, and platinum was not detected. or,
The alloy composition in the obtained platinum alloy catalyst was analyzed by ICP emission spectrometry and atomic absorption spectrometry. As a result, platinum was 50.0 atomic%, nickel was 25.5 atomic%, and cobalt was 24.5 atomic%.

[0009]

Example 2 Carbon powder was used as a carrier on which platinum 2.80 was applied.
13.3 g of carbon-supported platinum catalyst supporting g of water was wetted with 200 ml of boiling hot water and dispersed with an ultrasonic homogenizer for 2 minutes while stirring to make a catalyst slurry, then at 20 ° C.
Cooled down. Next, as a heavy metal salt, cobalt chloride 3.80
g, 29.14 g of sodium tartrate as a chelating agent, and 13.29 g of hydrazine hydrochloride as a reducing agent are dissolved in pure water.
A 20 ml mixed solution was prepared, and this mixed solution was directly stirred at a temperature of about 17 ° C. for 40 minutes. Next, add 50% NaOH solution to the mixed solution to adjust the pH, and while cooling on the way to pH 12.8,
A plating solution at 23.8 ° C was prepared. Next, the plating solution was added to the catalyst slurry all at once, and electroless plating was performed while stirring for 25 minutes. The temperature of the slurry plating solution during electroless plating was 22 to 24 ° C. The cobalt-plated carbon-supported platinum catalyst was collected by filtration, washed with water several times until the washing water became neutral, dried at a temperature of 60 ° C, and finally heated at a temperature of 900 ° C in a hydrogen stream. Then, an alloying treatment of platinum particles and cobalt plated on the platinum particles was performed.

Atomic absorption spectrometry of the waste liquid after plating revealed that only 6.2% of the input amount of cobalt remained and platinum was not detected. Further, when the alloy composition in the obtained platinum alloy catalyst was subjected to IPC emission spectroscopic analysis and atomic absorption spectrometry, the results were 48.9% platinum and 51.1 atomic% cobalt.

[0011]

Example 3 Carbon powder was used as a carrier and platinum 3.62 was added thereto.
140g of carbon-supported platinum catalyst carrying g was wetted with 200ml of boiling hot water and dispersed with an ultrasonic homogenizer for 2 minutes with stirring to make a catalyst slurry, then at 20 ° C.
Cooled down. Then, as a heavy metal salt, cobalt chloride 4.68
g, 35.88 g of sodium tartrate as a chelating agent, and 16.37 g of hydrazine hydrochloride as a reducing agent are dissolved in pure water.
A 390 ml mixed solution was prepared, and this mixed solution was directly stirred at a temperature of about 17 ° C. for 80 minutes. Next, a 50% NaOH solution was added to the mixed solution to adjust the pH, and a plating solution having a pH of 12.9 and a solution temperature of 27.9 ° C. was prepared while cooling halfway. Next, the plating solution was added to the catalyst slurry all at once, and electroless plating was performed while stirring for 15 minutes. The temperature of the slurry plating solution during electroless plating was 26 to 28 ° C. The cobalt-plated carbon-supported platinum catalyst was collected by filtration, washed with water until the washing water became neutral, dried at a temperature of 60 ° C, and finally heated at a temperature of 900 ° C in a hydrogen stream. The platinum particles were alloyed with the plated cobalt.

Atomic absorption spectrometry of the waste liquid of the plating solution revealed that only 6.0% of the input amount of cobalt remained and platinum was not detected. Further, the alloy composition in the obtained platinum alloy catalyst was subjected to IPC emission spectroscopic analysis and atomic absorption spectrometry, whereby platinum 49.6 atomic% and cobalt 50.4 atomic% were obtained.
Met.

[0013]

[Comparative Example 1] Platinum 2.89 was prepared by using carbon powder as a carrier.
13.7 g of carbon-supported platinum catalyst supporting g of water was wetted with 200 ml of boiling hot water and dispersed with an ultrasonic homogenizer for 2 minutes with stirring to form a catalyst slurry, and then 28 ° C.
Cooled down. Next, nickel chloride 1.97 as a heavy metal salt.
g and cobalt chloride 1.96 g, sodium tartrate as a chelating agent 29.99 g, and hydrazine chloride as a reducing agent
13.68 g was dissolved in pure water to prepare a 330 ml mixed solution. Then, add 50% NaOH solution to the mixed solution to adjust the pH, and p
A H12.7 plating solution was prepared. Next, the plating solution was added to the catalyst slurry all at once, and electroless plating was performed while stirring for 5 minutes. The temperature of the slurry plating solution during electroless plating was 31 to 32 ° C. The nickel- and cobalt-plated carbon-supported platinum catalyst was collected by filtration, washed with water until the washing water became neutral, dried at a temperature of 60 ° C, and finally at a temperature of 900 ° C in a hydrogen stream. The platinum particles and the nickel and cobalt plated on the platinum particles were alloyed by heating.

Atomic absorption spectrometry of the waste liquid after plating revealed that 34.6% of the input amount of nickel and 4.8% of the input amount of cobalt remained, and platinum was not detected. When the alloy composition in the obtained platinum alloy catalyst was subjected to IPC emission spectroscopy and atomic absorption spectrometry, platinum was 53.8 at%, nickel was 19.3 at%, and cobalt was 26.9 at%.

[0015]

[Comparative Example 2] Platinum 2.87 was prepared by using carbon powder as a carrier.
13.8g of carbon-supported platinum catalyst carrying g was wetted with 200ml of boiling hot water and dispersed with an ultrasonic homogenizer for 2 minutes with stirring to make a catalyst slurry, then at 13 ° C.
Cooled down. Next, as a heavy metal salt, nickel chloride 1.95
g and cobalt chloride 1.94 g, sodium tartrate 29.79 g as a chelating agent, and hydrazine hydrochloride 1 as a reducing agent 1
3.59 g was dissolved in pure water to prepare a 330 ml mixed solution. Next, a 50% NaOH solution was added to the mixed solution to adjust the pH, and a plating solution having a pH of 12.9 and a solution temperature of 16.0 ° C. was prepared while cooling halfway. Next, the plating solution was added to the catalyst slurry all at once, and electroless plating was performed while stirring for 15 minutes. The temperature of the slurry plating solution during electroless plating was 15 to 16 ° C. The nickel- and cobalt-plated carbon-supported platinum catalyst was collected by filtration, washed with water until the washing water became neutral, dried at a temperature of 60 ° C, and finally at a temperature of 900 ° C in a hydrogen stream. The platinum particles and the nickel and cobalt plated on the platinum particles were alloyed by heating.

When atomic absorption analysis of the waste liquid after plating was carried out, 26.8% of the input amount of nickel and 6.0% of the input amount of cobalt remained, and platinum was not detected. Further, the alloy composition in the obtained platinum alloy catalyst was subjected to IPC emission spectroscopic analysis and atomic absorption spectrometric analysis. As a result, platinum was 52.6 at%, nickel was 20.8 at%, and cobalt was 26.6 at%.

[0017]

[Comparative Example 3] Platinum 2.90 was used with carbon powder as a carrier.
13.7 g of carbon-supported platinum catalyst supporting g of water was wetted with 200 ml of boiling hot water and dispersed with an ultrasonic homogenizer for 2 minutes while stirring to make a catalyst slurry, then at 22 ° C.
Cooled down. Next, nickel chloride 1.97 as a heavy metal salt.
g and cobalt chloride 1.96 g, sodium tartrate as a chelating agent 30.10 g, and hydrazine hydrochloride as a reducing agent 1
3.73 g was dissolved in pure water to prepare a 330 ml mixed solution. Next, a 50% NaOH solution was added to the mixed solution to adjust the pH, and a plating solution having a pH of 12.8 and a solution temperature of 24.2 ° C. was prepared while cooling halfway. Next, the plating solution was added to the catalyst slurry all at once, and electroless plating was performed while stirring for 60 minutes. The reaction was completed in 18 minutes, and the temperature of the slurry plating solution during electroless plating was 24 to 26 ° C. The nickel- and cobalt-plated carbon-supported platinum catalyst was collected by filtration, washed with water until the washing water became neutral, dried at a temperature of 60 ° C, and finally at a temperature of 900 ° C in a hydrogen stream. The platinum particles and the nickel and cobalt plated on the platinum particles were alloyed by heating.

Atomic absorption spectrometry of the waste liquid after plating revealed that 14.5% of the input amount of nickel and 10.6% of the input amount of cobalt remained, and platinum was not detected. When the alloy composition in the obtained platinum alloy catalyst was subjected to IPC emission spectroscopy and atomic absorption spectrometry, the results were 51.1 at% platinum, 23.8 at% nickel, and 25.1 at% cobalt.

[0019]

[Prior art example] Carbon powder used as a carrier 2.86 g of platinum
13.7 g of the carbon-supported platinum catalyst carrying C was wetted with 200 ml of boiling hot water, and was dispersed with an ultrasonic homogenizer for 2 minutes while stirring to obtain a catalyst slurry. Next, as a heavy metal salt, 1.95 g of nickel chloride and 1.94 of cobalt chloride.
g, 29.72 g of sodium tartrate as a chelating agent, and 13.16 g of hydrazine hydrochloride as a reducing agent are dissolved in pure water.
A mixed solution of 330 ml was prepared. Then add 50% NaOH to the mixture.
The solution was added to adjust the pH to prepare a plating solution having a solution temperature of 65.4 ° C. Next, the plating solution was added to the catalyst slurry all at once, and electroless plating was performed while stirring for 60 minutes. Then, the carbon-supported platinum catalyst plated with nickel and cobalt was collected by filtration, washed with water until the washing water became neutral, dried at a temperature of 60 ° C., and finally, in a hydrogen stream.
It was heated at a temperature of 900 ° C. to alloy the platinum particles with nickel and cobalt plated on them.

When the atomic absorption analysis of the waste liquid after plating was carried out, 98.4% of the input amount of nickel and 74.8% of the input amount of cobalt remained, and platinum was not detected. When the alloy composition in the obtained platinum alloy catalyst was subjected to IPC emission spectroscopy and atomic absorption spectrometry, platinum was 87.3 atomic%, nickel was 0.5 atomic%, and cobalt was 12.2 atomic%.

[0021]

As described above, according to the first method for producing a noble metal alloy catalyst of the present invention, the method for reducing heavy metals proceeds relatively slowly, the reduction reaction is completed, and elution does not occur yet. Since it is easy to determine the time point, a desired alloy composition can be obtained and the alloy composition can be easily controlled by increasing the loading ratio of the heavy metal. Further, according to the second method for producing a noble metal alloy catalyst, in addition to the effect of the first method, the ripening of the mixed solution is sufficient, and the heavy metal is chelated with the chelating agent and easily reduced, so The desired alloy composition can be obtained, and the alloy composition can be controlled more easily.

Claims (11)

[Claims] 1. A plating bath comprising a mixture of a heavy metal salt, a chelating agent and a reducing agent, while a precious metal or precious metal alloy catalyst supported on a powdery carrier is dispersed in hot water to form a catalyst slurry. To prepare a plating solution with a pH of 10.5 to 13.0, put this plating solution in the catalyst slurry and perform electroless plating at low temperature, and wash the noble metal or noble metal alloy catalyst carried on the carrier by plating heavy metals. A method for producing a precious metal alloy catalyst, which comprises drying and then heating in a required atmosphere for alloying treatment. 2. The method for producing a noble metal alloy catalyst according to claim 1, wherein the carrier is carbon. 3. The method for producing a noble metal alloy catalyst according to claim 1, wherein the noble metal or noble metal alloy catalyst is platinum or a platinum alloy catalyst. 4. The heavy metal salt is nickel chloride and / or cobalt chloride, and the chelating agent is sodium tartrate.
The method for producing a noble metal alloy catalyst according to claim 1, 2 or 3, wherein the reducing agent is hydrazine hydrochloride. 5. The mixed solution is sufficiently stirred before adjusting the pH when the plating bath is set up.
3. The method for producing the noble metal alloy catalyst according to 3 or 4. 6. The production of the noble metal alloy catalyst according to claim 1, wherein the mixed solution is stirred for 30 to 90 minutes before the pH adjustment during the construction of the plating bath. Method. 7. The low-temperature electroless plating solution has a temperature of 5 to 40 ° C.,
The method for producing a noble metal alloy catalyst according to 3, 4, 5 or 6. 8. The temperature of a plating solution for the low-temperature electroless plating is 20 to 30 ° C.,
The method for producing a noble metal alloy catalyst according to 3, 4, 5 or 6. 9. The required atmosphere is a hydrogen gas flow, 1, 2, 3, 4, 5, 6, 7 or 8.
A method for producing the noble metal alloy catalyst described. 10. The heating temperature of the alloying treatment is 800 ° C.
The temperature is around 1100 ° C, Claims 1, 2, 3,
4. A method for producing a noble metal alloy catalyst according to 4, 5, 6, 7, 8 or 9. 11. The heating temperature of the alloying treatment is 900 ° C. to 9 ° C.
50 ° C., Claims 1, 2, 3, 4,
A method for producing a noble metal alloy catalyst according to 5, 6, 7, 8 or 9.