JPH0464738B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a catalyst body that purifies harmful gas components in exhaust gas discharged from various combustion devices. Configuration of conventional examples and their problems As a catalyst that simultaneously purifies CO and _NO It is a perovskite type complex oxide.

[Formula] (Me is an element selected from Fe, Mn, Cr, V, O
<x<1) and SrTiO ₃ have been proposed. This catalyst is based on the principle that the latter amplifies the catalytic action of the former based on oxygen ion conductivity, and it is an excellent catalyst that exhibits properties comparable to those of precious metals, is highly heat resistant, and is inexpensive. The drawback was that the catalytic activity in the low temperature range of around 100°C was generally low. OBJECTS OF THE INVENTION In view of the above-mentioned problems, the present invention aims to provide an excellent exhaust gas purifying catalyst body with improved low-temperature catalytic activity. Structure of the invention The present invention includes:

[Formula] (Me is an element selected from Fe, Mn, Cr, and V, O<x
By using a catalyst consisting of a two-component system of <1) and SrTiO ₃ with the addition of a noble metal as a co-catalyst, the catalyst body significantly improves low-temperature activity, has heat deterioration resistance, and is inexpensive. It is something. Description of Examples FIG. 1 is a schematic cross-sectional view of a catalyst body showing Example 1. The arrows represent the flow of exhaust gas. 1
is a noble metal catalyst layer. It consists of 6 mg of palladium catalyst uniformly dispersed and supported on 0.5 g of alumina fiber (approximately 3 μm + approximately 10 mm or less, referred to as bulk). 2 is a composite oxide catalyst layer. La _0.35
Similarly, 1.5 g of a composite oxide consisting of 40 mol % of Sr _0.65 Co _0.7 Fe _0.3 O ₃ and 60 mol % of SiTiO ₃ was supported on a 1.5 g bulk. In both cases, the bulk was impregnated with a catalyst component-dispersed polyvinyl alcohol solution adjusted to a predetermined amount, and dried at 500°C.
It was produced by firing after 30 minutes, and the following examples were also produced by the same method. FIG. 2 shows Example 2. 3 is a catalyst layer in which a homogeneous mixture of 0.375 g of the composite oxide used in Example 1 and 6 mg of palladium catalyst is supported on a 0.5 g bulk, and 4 is a catalyst layer in which 1.125 g of a composite oxide is supported on a 1.5 g bulk. Each represents a catalyst layer consisting of: FIG. 3 shows Example 3. In this case, the entire catalyst layer is a homogeneous mixture of 1.5 g of composite oxide and 6 mg of palladium catalyst supported on 2 g of bulk. As a conventional example, a sample was prepared in which 1.5 g of a composite oxide was supported in a 2 g bulk in the same manner. Next, we will show the characteristics of these catalysts. A quartz glass tube reaction vessel having an inner diameter of 25 mm was filled with the catalyst body having the above-described structure, and the catalytic activity was measured while the temperature was controlled in an electric furnace. For the reaction gas
A homogeneous mixed gas consisting of 150 ppmt of CO, 40 ppm of NO ₂ and the remainder of N ₂ was used and was supplied to the catalyst layer at a space velocity of 8000 h ^-1 . The direction of gas flow is the direction indicated by the arrows shown in FIG. 1 and the like. Figure 4 shows the CO removal rate,
Figure 5 shows the NO production rate, and Figure 6 shows the _N2 production rate. The CO removal rate is (inlet CO concentration - outlet CO concentration)/inlet CO concentration x 100 (%)
...(1) NO production rate is outlet NO concentration / inlet NO ₂ concentration x 100 (%) ... (2) N ₂ production rate is (inlet NO _x concentration - outlet NO _x concentration) / inlet NO _x concentration x 100 (%
)...(3) (However, NO _x concentration = NO concentration + NO ₂ concentration). As is clear from the data on these properties, all of the catalyst bodies of the present invention exhibit excellent activity and thermally stable properties. In the conventional example, the activity at 100 to 200°C is low. In addition, in the figure, palladium catalyst (6 mg of palladium catalyst supported in 2 g bulk by the above method)
However, the overall activity was low, and the activity decreased at high temperatures. In order to improve the activity, it is necessary to increase the amount of palladium catalyst, but this comes with the disadvantages of being expensive and increasing the loading density, increasing the possibility of sintering, leading to deterioration of properties at high temperatures. Now. In the catalyst body of the present invention, by positioning a noble metal catalyst with excellent low-temperature activity on the upstream side of the exhaust gas flow path, when an oxidation reaction occurs at low temperature and reaction heat is generated, the composite oxide located on the downstream side This enables a series of catalytic actions in which the complex oxide itself is heated and its own catalytic action is subsequently developed. A similar cycle occurs also in the locations where composite oxide and noble metal coexist as in Examples 2 and 3. Therefore, in this catalyst body, only a small amount of noble metal catalyst is required to cause the entire reaction, making it economically advantageous. In addition, the heat generated by the reaction is almost uniformly dispersed in the catalyst layer, which has the effect of reducing the degree of sintering of the precious metal catalyst itself, which, together with the high heat resistance of the composite oxide, prevents thermal deterioration and extends the lifespan. It is also becoming possible to Next, data comparing this thermal stability will be shown.
Each of the catalyst bodies described above was placed in a reaction vessel, placed in an electric furnace, and a test was conducted in which the temperature of the catalyst layer was alternately changed from 100°C to 900°C while flowing the mixed gas for 500 cycles. The catalytic activity at 200°C was measured every 100 cycles, and the CO removal rate is shown in FIG. 7 as a representative example.
In the case of using only a palladium catalyst, it can be seen that the activity decreases significantly in the very early stage, but each catalyst body of Examples shows very stable performance. As described above, the catalyst of the present invention exhibits excellent low-temperature activity and excellent thermal stability. In the example, the case where Me=Fe was used as the composite oxide was shown, but similar results can be obtained with Mn, Cr, and V. The same holds true when platinum is used as the noble metal catalyst. Only a small amount of precious metal catalyst is required, and it is economically advantageous. The carrier is not limited to bulk, and the material, shape, and supporting method can be selected as appropriate depending on the purpose, such as ceramic or metal. In addition, in the example, the noble metal catalyst was uniformly dispersed and supported, but by adopting a configuration in which the noble metal concentration is high on the upstream side of the exhaust gas flow path and becomes lower toward the downstream side, it is possible to achieve economic efficiency without impairing the characteristics. It is also possible to increase Effects of the invention A catalyst body having a structure in which a composite oxide is used as a main catalyst and a trace amount of a precious metal catalyst is added in combination so that the precious metal catalyst is located on the upstream side of the exhaust gas flow path has low-temperature activity, thermal stability, and economic efficiency. It exhibits excellent performance.

[Brief explanation of the drawing]

Figures 1 to 3 are schematic cross-sectional views of catalyst bodies of different embodiments of the present invention, Figure 4 is a relationship between temperature and CO removal rate, Figure 5 is a relationship between temperature and NO production rate, and Figure 6 is a relationship between temperature and NO production rate. The figure is a diagram showing the relationship between temperature and N ₂ production rate, and Figure 7 is a diagram showing thermal stability shown in terms of CO removal rate. 1... Noble metal catalyst layer, 2, 4... Composite oxide catalyst layer, 3... Mixed layer of noble metal catalyst and composite oxide.

Claims (1)

[Claims] 1 General formula [Formula] (Me is an element selected from Fe, Mn, Cr, V, O<x<
An exhaust gas purification catalyst body characterized in that a composite oxide catalyst consisting of a two-component system consisting of the oxide represented by 1) and SrTiO ₃ and a co-catalyst consisting of a noble metal are used together. 2. The exhaust gas purification catalyst body according to claim 1, characterized in that the noble metal catalyst is located on the upstream side of the exhaust gas flow path, and the composite oxide catalyst is located in contact with each other on the downstream side of the exhaust gas flow path. 3. A patent claim characterized in that the portion of the catalyst body located on the upstream side of the exhaust gas flow path is composed of a mixed layer of a composite oxide catalyst and a noble metal catalyst, and the portion downstream thereof is composed only of the composite oxide catalyst. The exhaust gas purification catalyst body according to item 1. 4. The exhaust gas purification catalyst body according to claim 1, characterized in that the entire body is composed of a mixture of a composite oxide catalyst and a noble metal catalyst.