JPS63256134A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To make the deterioration of activity small by regulating the average particle diameter of calcium aluminate to 0.5-5mum by means of atomization. CONSTITUTION:In a catalyst consisting of both a heat resistant inorganic oxide carrier contg. calcium aluminate as a binder and fused silica as an aggregate, and catalytic components carried thereon, the average particle diameter of calcium aluminate is regulated to 0.5-5mum by atomization. Thereby the surface area of calcium aluminate occupied in unit area is made large and the catalytic component of palladium is uniformly dispersed and carried. By such a way, when using it for the catalyst for purifying exhaust gas, the deterioration of activity can be remarkably made small.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a catalyst body for purifying exhaust gas of a combustion apparatus using gaseous fuel such as natural gas or propane, and liquid fuel such as petroleum.

Conventional technology Traditionally, a porous body was made by mixing lime aluminate as a binder, fused silica as an aggregate, and an inorganic oxide consisting of titanium dioxide, adding molding aids, etc., and kneading with water. The catalyst carrier was obtained by pressure molding, followed by solidification, curing, and drying.

After that, for exhaust gas purification, the catalyst was further immersed in an acidic aqueous solution of palladium salt to support the catalyst, and then heated to 900°C in air.
A catalyst body was obtained by heat treatment for 1 hour.

Problems to be Solved by the Invention When the catalyst body obtained by such a conventional method is used for exhaust gas purification, its initial performance is relatively hard;
There was a problem in that the catalytic activity decreased over time.

The present invention is intended to solve these problems, and aims to improve the composition of the carrier and improve its purification ability.

Means for Solving the Problems The present invention provides a catalyst body comprising a heat-resistant inorganic oxide loss body containing lime aluminate as a binder and at least fused silica as an aggregate, and a catalyst supported on the same. The average particle size of lime aluminate has been increased by 0.5 μm compared to the conventional 5 to 10 μm.
It is made into fine particles of ~6 μm.

Function When a palladium catalyst is supported on a support mainly composed of lime aluminate, fused silica, or titanium dioxide, a method of immersing the support in an acidic aqueous solution such as palladium chloride or palladium nitrate is generally used.

Compared to fused silica and titanium dioxide, the surface of lime aluminate is more basic, so when immersed in a catalyst solution, palladium is likely to be supported mainly on the surface of lime aluminate due to an acid-base reaction. Therefore, by making the particles of lime aluminate finer and increasing the surface area of lime aluminate per unit area, the palladium catalyst can be uniformly dispersed and supported. As a result, when used in a catalyst body for exhaust gas purification,
This results in a significantly smaller decrease in activity.

Example Examples of the present invention will be described in detail below.

The carrier is made by thoroughly mixing 40 parts of lime aluminate (by weight, same hereinafter) as a binder, 46 parts of fused silica as an aggregate, 10 parts of titanium dioxide, and 5 parts of carboxymethyl cellulose as a molding aid. Water was added and kneaded. This mixed wire material was extruded into a honeycomb shape using a die, solidified, cured, and dried at 100°C. 9oo in the air
The molding aid was completely removed by heat treatment at .degree. C. to obtain four types of carriers having different particle sizes of lime aluminate as shown in Table 1. Among these, carrier C is a conventional example. Next, these four types of carriers were immersed in a palladium nitrate aqueous solution to support 0.19% of palladium per apparent volume of the carrier.
Reduction treatment was performed at 0°C for 1 hour.

Table 1 Average particle size of lime aluminate in the catalyst body Under the same conditions as under kerosene combustion exhaust gas for the above four types of catalyst bodies,
A continuous exposure test was conducted at a temperature of 90° C., and the ability to purify carbon oxide was measured to determine the life characteristics of the catalyst. - The measurement conditions for the carbon oxide purification ability are shown in Table 2, and the changes over time in the carbon monoxide purification ability of the catalyst are shown in the figure.

As shown in Table 2 - Carbon oxide purification performance measurement conditions diagram, the conventional catalyst C has a relatively large decrease in carbon monoxide purification performance as the exposure time increases.

The catalyst body, in which the average particle diameter of lime aluminate is 17 μm, which is larger than that of the conventional example, shows an even more significant decrease. On the other hand, catalyst bodies A and B using lime aluminate with average particle diameters of 1 and 5 μm
Compared with Conventional Example C, the initial characteristics are also higher, and the deterioration of the purification ability over time is significantly smaller.

Table 3 shows the results of determining the amount of elements exposed on the surface of the carrier before supporting the catalyst using a simple quantitative method using a point analysis method using an X-ray microanalyzer.

Table 3 Point analysis of exposed surface of carrier (unit: wt%) T present on the surface of carrier with small average particle size of lime aluminate
It can be seen that the amount of iO decreases and the amounts of Ca and At increase. This is thought to be because the larger the average particle size of lime aluminate, the more fine particles of titanium dioxide (average particle size 0.2 μm) come out to the surface during extrusion molding.

As shown in Table 3, carriers A and B have a large amount of basic Ca on their surfaces. Therefore, when the carrier is immersed in an acidic aqueous solution of palladium nitrate, the palladium catalyst is more uniformly dispersed and supported than other C and D catalysts, and as shown in the figure, it has excellent initial performance and heat-resistant life characteristics. Conceivable.

From the results of the above examples, it is possible to further reduce the particle size of lime aluminate, but the average particle size is 0.6 μm.
Grinding to a size smaller than m leads to a significant increase in material cost and poses a practical problem.

In this example, the case where lime aluminate, fused silica, and titanium dioxide were used as the constituent materials of the carrier was described, but even if alumina such as hydraulic alumina or activated alumina is used instead of titanium dioxide, the same results will be obtained. was recognized.

Effects of the Invention As described above, according to the present invention, by micronizing the average particle size of lime aluminate to 0.6 to 6 μm, a catalyst with excellent initial characteristics and longevity of carbon monoxide purification ability in exhaust gas can be obtained. The effect of being able to provide a medium can be obtained.

[Brief explanation of drawings]

The figure shows the life characteristics of carbon monoxide purification ability when exposed at 900° C. for a long time.

Claims (1)

[Claims] In a catalyst body consisting of a heat-resistant inorganic oxide support containing lime aluminate as a binder and at least fused silica as an aggregate, and a catalyst supported on this, the lime aluminate has an average particle size of 0.5 A catalyst body for exhaust gas purification characterized by having fine particles of ~5 μm.