JPS61197034A - Preparation method of platinum supported catalyst - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] This invention relates to a method for preparing a highly dispersed supported platinum catalyst comprising platinum and a carrier.

[Prior art and its problems]

Conventionally, as a platinum catalyst used in an electrochemical cell, a method using platinum black prepared by a well-known method is known. However, when platinum black is used as a catalyst, the specific surface area of platinum is small, and satisfactory characteristics cannot be obtained.11. There wasn't. Therefore, in order to obtain a platinum catalyst having a large specific surface area, a method has been adopted in which a porous fine powder having a relatively high surface area, such as carbon plastic, is used as a carrier and platinum fine particles are supported on the carrier. Conventional techniques for preparing this platinum-supported catalyst can be broadly classified into the following three types.

First, the first method (hereinafter referred to as gas phase reduction method) is as follows:
A method is known in which a carrier is impregnated with a platinum salt such as an aqueous solution of chloroplatinic acid, water is removed by drying, and then the carrier is directly subjected to hydrogen reduction at a predetermined temperature in a hydrogen stream. However, in this method, depending on the type of carrier, the platinum salt may not be adsorbed onto the carrier surface, but may simply be absorbed into the pores between the carriers or within the carrier, and this may require drying. The platinum salt aqueous solution is gradually concentrated within the pores. As a result, the crystallite diameter of platinum increased (corresponding to a decrease in the specific surface area of platinum), and a platinum catalyst with a high surface area as expected could not be obtained. Furthermore, it was difficult to uniformly disperse platinum on the surface of the carrier by concentrating the platinum salt aqueous solution. Furthermore, other problems include:
In order to directly reduce the dried platinum salt-impregnated powder in a hydrogen stream to obtain a platinum-supported catalyst, the temperature is usually 100°C to 400°C.
It must be heated to a high temperature. Therefore, if the treatment is carried out under these conditions, platinum sintering (increase in the diameter of platinum particles) will occur, and the platinum specific surface area will further decrease.

Next, as a second method (hereinafter referred to as thermal decomposition method), dinitrodiammine platinum()'1(NHa)z(
Using NO2)2), dissolve it in 30% nitric acid, bring it into contact with carbon plastic, let it blend well and dry it, then treat it in an air stream at 260°C to thermally remove the platinum salt. There is a method to obtain a platinum-supported catalyst by decomposing the platinum. However, in this case as well, because the platinum salt is absorbed into the powder and dried, the platinum crystallite diameter increases due to concentration similar to the gas phase reduction method. . Furthermore, during thermal decomposition of platinum salts, sintering of platinum and disappearance of carbon plastic as a carrier are expected, and it is thought that a catalyst with the expected characteristics cannot necessarily be obtained.

The third method (hereinafter referred to as gas phase reduction method) is as follows:
As disclosed in Japanese Patent Application Laid-Open No. 54-92588, a chloroplatinic acid aqueous solution is added to carbon black dispersed in water, and after sufficient contact, the chloroplatinic acid is reduced using sodium dithionate. There is a way. However,
It was found that this method was difficult to support a predetermined type of platinum on the carrier and was not practical.

[Purpose of the invention]

This invention eliminates the conventional drawbacks, and eliminates unnecessary increases in platinum crystallite diameter at the pulley stage of platinum-supported catalysts.
To provide a method for safely supporting a uniformly dispersed platinum-supported catalyst in a short time, and moreover, reliably supporting the required amount of platinum! purpose.

[Key points of the invention]

In this invention, after bringing the platinum salt into sufficient contact with a hydrophilically treated carrier so that the platinum salt water bath solution can contact the carrier surface better and more fully, the pH of the system is adjusted to an alkali level of 13 (ill).
By reducing the platinum salt using a reducing agent under conditions that allow sufficient reduction to occur, and at the same time adsorbing the reduced platinum onto the surface of the carrier, a high surface area and high dispersion of platinum with a small platinum crystallite diameter can be supported. The catalyst can be prepared reliably, safely, and in a short time.

[Embodiments of the invention]

The present invention will be explained below based on examples.

(Example 1) Acetylene resin as catalyst carrier 9
A 10 wt% nitric acid aqueous solution 360- was added to t, and the temperature was raised to ω°C while stirring, and stirring was continued at this temperature for 3 hours. After 3 hours, the cake was drained and thoroughly washed with deionized water until the pH was near. Next, this cake was mixed with 500 g of a 2.1 f-Pt/l aqueous solution of chloroplatinic acid.
The mixture was thoroughly dispersed in M and stirred at room temperature for 2 hours so that the acetylene chloride and chloroplatinic acid came into sufficient contact with each other. A 0.1M sodium chloride 11um aqueous solution was added to this, and the pH was adjusted to 9.
．． Adjusted to 5. After this, 213 d of 0.1M formic acid aqueous solution
was added dropwise to the stirring liquid over about 10 minutes. After the dropwise addition was completed, the reaction mixture was raised while stirring and the temperature was raised to (1)°C. After further raising the temperature, heating and stirring were continued for 2 hours. after that,
The reaction @ was filtered off and the cake was washed with warm water at ω°C. After washing, the cake was vacuum dried under heating at 50° C. for 10 hours to obtain a platinum-supported catalyst. As a result of evaluating the physical properties of the obtained catalyst, the platinum specific surface area was 180'/7-Pt, and the amount of platinum supported was 10
It was 00%.

In addition, in Example 1, 10
wt% nitric acid aqueous solution was used, but instead of the nitric acid aqueous solution, a 1.6 moL'l hydrochloric acid aqueous solution, IN sulfuric acid, or 0.6 moL'l nitric acid aqueous solution was used. A similar effect can be obtained by using IN acetic acid, and there are various other embodiments that can be modified without departing from the gist of the present invention. Below, some modifications of the first embodiment that obtained the same results as the first embodiment will be introduced.

1. In Example 1, the carrier was pretreated at 50° C. for 2 hours.

2) In Example 1, in order to adjust the pH, J 0. I
N-to a (using JH aqueous solution.

3. In Example 1, p) i=
Adjusted to 9.5.

4. In Example 1, 0.1Ni-formic acid water bath solution was replaced with 0.1Ni-formic acid water bath solution. Reduction is carried out at ω°C for 1 hour using an IN-Schelic acid aqueous solution.

5. In the oxidation step 111, reduction is carried out using so,tl'J-formaldehyde at a temperature of 1 hour at °C.

6. Instead of gradually dispersing the pretreated carrier in the chloroplatinic acid water bath solution in Example 1, after dispersing the pretreated carrier in a deionized fishing rod of 500 d, 5o;V-P t/'y
Gradually add the chloroplatinic acid aqueous solution with sufficient stirring,
Bring the carrier into sufficient contact with the platinum salt.

[Effects of the Invention] As is clear from the above explanation, according to this invention number, since the carrier was subjected to hydrophilic treatment before being brought into contact with the platinum salt aqueous solution, contact between the carrier and the platinum salt was more difficult than in the past. The results showed that a uniformly dispersed platinum-supported catalyst having a wider platinum ratio [ffi product] could be obtained. Furthermore, since a liquid phase reduction method is employed, unnecessary heat is not applied during the reduction of the platinum salt, and platinum Q) sintering is improved. Furthermore, since platinum was adsorbed onto the surface of the Platinum Power S carrier during reduction, the dispersibility of platinum and the strength of its support on the carrier were improved. Saraban also had the effect that the required platinum-supported catalyst could be obtained without repeating a single process.

Claims (1)

[Claims] 1) After sufficient contact between the hydrophilically treated catalyst carrier and the platinum salt, the pH of the system is brought to an alkaline level, a reducing agent is added, and the platinum salt is reduced under conditions that allow reduction of the platinum salt. A method for preparing a supported platinum catalyst, characterized by carrying out the following steps. 2) A method for preparing a platinum-supported catalyst according to claim 1, characterized in that an acid aqueous solution is used for the hydrophilic treatment of the catalyst carrier. 3) A method for preparing a supported platinum catalyst according to claim 2, characterized in that a strong acid such as nitric acid, hydrochloric acid, or sulfuric acid is used as the aqueous acid. 4) A method for preparing a supported platinum catalyst according to claim 1, characterized in that the treatment temperature is from 40°C to 90°C. 5) In the method according to claim 1, the pH
is 9 or more, preferably 9.5 or more. 6) In the method described in claim 1, the pH adjusting reagent is NaOH, KOH, Na_2CO_3, K_2
A method for preparing a supported platinum catalyst, characterized by using CO_3 or aqueous ammonia. 7) A method for preparing a supported platinum catalyst according to claim 1, wherein the platinum salt is chloroplatinic acid. 8) A method for preparing a platinum-supported catalyst according to claim 1, wherein the reducing agent is a reagent having a substituent corresponding to an aldehyde group, such as formic acid, formalin, or sodium oxate. . 9) A method for preparing a supported platinum catalyst according to claim 1, wherein the reducing agent is hydrazine, borohydride, sodium or oxalic acid. 10) A method for preparing a supported platinum catalyst according to claim 1, characterized in that the temperature at which reduction of the platinum salt can occur is from 40°C to 90°C, preferably from 50°C to 60°C.