JPS5923861B2 - Catalyst and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Catalysts commonly used at present are those in which one or more metals or oxides having catalytic ability are supported in the form of powder on the surface of a carrier usually made of alumina or silica.

Furthermore, the lifetime of catalysts is an important factor that determines their catalytic ability. When using a three-dimensional irregular network porous material with interconnected pores made of metals such as iron and nickel as shown in Figure 1, there are sufficient pores 1 and the surface area of the skeleton 2 is large, making it difficult to use alumina or silica. It has a high strength and is suitable as a carrier. However, if fine metal powder with catalytic ability is directly supported on the surface of the skeleton 2 and used as a catalyst, the external heat required for the catalytic reaction and the reaction heat of the catalyst will cause the skeleton to
Diffusion occurs between the metal and the catalyst metal, and the catalytic ability is significantly reduced, and the skeleton 2 of the three-dimensional network porous body supporting the metal powder with catalytic ability becomes brittle and no longer plays its role as a support. . The object of the present invention is to eliminate these drawbacks of metal carriers and to make them sufficiently usable as carriers. That is, as shown in FIG. 2, a diffusion prevention layer 3 made of a chromium layer with good adhesion is formed on the surface of the skeleton 2 of a metal three-dimensional network porous body having communicating pores, and furthermore, a diffusion prevention layer 3 made of a chromium layer with good adhesion is formed thereon. It supports a catalyst layer 4 formed by baking metal powder. In the catalyst configured in this way, the diffusion prevention layer 3 consisting of a chromium layer between the carrier metal and the metal powder having catalytic ability prevents performance deterioration due to diffusion of the catalyst layer 4 into the skeleton 2 of the carrier during high-temperature use. , the life of the catalyst can be significantly improved. Generally, an electroplating method and a chromium diffusion infiltration method (powder method, gas method, etc.) can be considered for forming the chromium layer.

If a chromium layer with good adhesion is not provided, the chromium layer will peel off from the carrier metal when a metal powder with catalytic ability is baked or used as a catalyst, and it will no longer function as a diffusion prevention layer. When electroplating is used, chromium is simply deposited on the metal carrier, and heat treatment is required to provide adhesion, and even with that treatment, the degree of adhesion is not good. With the gas method, it is difficult to uniformly deposit a chromium layer on objects with complex shapes, such as three-dimensional irregular network structure porous metal bodies with communicating pores as shown in Figure 1.
In addition, productivity is low and there are many problems with the equipment. The conventional powder method requires a long period of time at a high temperature of 1000 DEG C. for 5 to 10 hours, resulting in a thin precipitated chromium layer that does not function as a diffusion prevention layer. The present invention also provides a method for forming a chromium layer that compensates for these drawbacks. It is well known that in the powder method, there is generally a process of precipitation of chromium on the substrate surface and a process of diffusion of the precipitated chromium into the substrate, but these processes are said to be carried out in parallel. The present invention is characterized in that it has been clarified that the precipitation process takes place mainly within one hour, and the diffusion process takes place in the subsequent time, and that the precipitation process is applied in such a short time. That is, the powder method is applied under the conditions that the chromium layer has the necessary thickness to function as a diffusion prevention layer and also has a diffusion layer of several micrometers that provides adhesion. The conditions of the powder method will be explained below.

Figure 3 shows a three-dimensional irregular network porous body made of nickel with continuous pores, and the powder composition is chromium powder and alumina powder in a weight ratio of 1:1, and the total weight of the chromium powder and alumina powder is 3%. % of ammonium chloride was placed in a container together with a porous material, sealed, and treated in a hydrogen atmosphere at 1000°C.

As can be seen from FIG. 3, a thick chromium layer was deposited within one hour and then decreased with time. FIG. 4 shows the thickness of the precipitated layer and the thickness of the diffusion layer when a three-dimensional network porous body of nickel and powder having the same composition as in FIG. 3 were used at each temperature for a treatment time of 1 hour. As these figures show, the most suitable conditions are 85°C to 1050°C for 1 hour. If the temperature is longer than 1 hour or at a high temperature of 1050° C. or higher, the diffusion layer becomes thicker, which is not preferable.

It goes without saying that by increasing the amount of chromium in the powder, it is possible to process at even lower temperatures. Under these conditions, a chromium layer as the diffusion prevention layer 3 shown in FIG. 2 was provided, supporting metal powder having catalytic ability, and the life of the catalyst could be significantly improved.

Width 50m7! LS length 100mm. A metal porous body having a three-dimensional irregular network structure made of nickel having a thickness of 10 mm and a density of 0.52 densities was coated with Al2O38O by weight. Crl
8 weight? , HN4Cl2 weight? Embedded in the mixed powder of J. H
This was maintained at 1000° C. for 0.5 hours in two air streams to form a metallic chromium layer with a thickness of about 201Dn on the entire surface of the network skeleton.

As comparison materials, the porous body without the metal chromium layer formation treatment and the porous body with an Alf) 3 layer formed instead of the metal chromium layer were prepared. Platinum was supported as a catalytic metal on the skeletal surface of these catalyst carriers, and a life test was conducted with the exhaust gas temperature set at 850° C. as a catalyst for purifying automobile exhaust gas. The results were as shown in the table below. The life of comparative material (2) is reduced due to diffusion of the catalytic metal into the carrier.

The tensile strength of the carrier is after the life, and not only the comparative material (2) but also the comparative material (1) in which an Al2O3 layer was formed had severe embrittlement, and the strength was significantly lower than that of the catalyst of the present invention. Since the catalyst according to the present invention has a porosity of 90% or more,
It is extremely lightweight, has a large surface area, has good catalytic performance, and has unprecedented strength.

[Brief explanation of drawings]

Fig. 1 is a perspective view of a metal three-dimensional irregular network porous body with communicating pores used in the present invention, Fig. 2 is a cross-sectional view of the catalyst skeleton according to the present invention, and Fig. 3 is a powder obtained by chromium diffusion infiltration method. FIG. 4 is a diagram showing changes over time in the thickness of the chromium layer precipitated by the chromium diffusion method and the thickness of the diffusion layer, and FIG. 1...Empty 2...Skeleton, 3...
...Diffusion prevention layer, 4...Catalyst layer.

Claims (1)

[Scope of Claims] 1. A diffusion prevention layer made of metallic chromium is formed on the entire surface of the network skeleton of a porous metal body having a three-dimensional irregular network structure with continuous pores, and a diffusion prevention layer made of metal chromium and a metal having active catalytic ability are formed on the entire surface of the network skeleton of a porous metal body having a three-dimensional irregular network structure with continuous pores. Or a catalyst characterized by being baked and supported with an oxide. 2 Applying a diffusion infiltration method using a powder method under the conditions of 1050°C or less and within 1 hour, a diffusion prevention layer made of chromium is applied to the entire surface of the network skeleton of a metal porous body having a three-dimensional irregular network structure with communicating pores. 1. A method for producing a catalyst, which comprises forming a catalyst and baking and supporting a metal and/or oxide having an active catalytic ability thereon.