JPH0375202B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to an apparatus for purifying harmful gas components in exhaust gas. Conventional configurations and their problems There is a strong demand for purification treatment of exhaust gas emitted from various household combustion appliances, and in order to deal with this, conventional methods have been developed that use heat-resistant and corrosion-resistant wire mesh as a catalyst. Alternatively, a method of using a solution in which catalyst powder is dispersed in a solution of an organic binder and depositing it on the wire mesh described above and firing it is an example of a relatively inexpensive and easy-to-configure method. There is. However, it has the disadvantage of poor reliability, such as the wire mesh itself gradually oxidizing and deteriorating, reducing its initial purification ability, or the supported catalyst falling off due to differences in thermal expansion with the wire mesh.
In the former case, oxidizing gases such as nitrogen oxides ( _NOx ) and carbon monoxide (CO) in exhaust gas,
Another problem is that it is difficult to simultaneously process reducing gases such as hydrocarbons (HC). Purpose of the Invention In view of the above-mentioned problems, the present invention provides an exhaust gas purification device that is highly reliable and easy to implement, using a catalyst that can efficiently treat oxidizing gas components and reducing gas components in exhaust gas at the same time. That is. Structure of the Invention The present invention is based on the general formula La _1-X/2 Sr _1+X/2 Co _1-x M _x O ₃
(Me is an element selected from Fe, Mn, Cr, V, and Ti, O<X<1), and is a perovskite-type composite oxide that has the ability to simultaneously reduce oxidizing gases and oxidize reducing gases. This is an exhaust gas purification device that uses as a catalyst and supports this on a heat-resistant metal porous body such as a metal net with enamel. By determining the composition as shown in the above formula, the catalyst used in the present invention can have the highest catalytic activity and excellent stability. However, by utilizing the buffering effect of enamel during catalyst operation, it is possible to prevent the catalyst from falling off and also to prevent oxidative deterioration of the metal porous body, thereby increasing reliability. Description of Examples FIG. 1 shows an example of the activity of an oxide catalyst having the composition La _1-x Sr _x Co _1-y Fe _y O ₃ . As a catalyst, a composite oxide obtained by mixing oxides or carbonates of each component element so as to have a predetermined composition and firing the mixture was molded into 1 g/pellet and sintered. Four pellets were placed in a reaction vessel with a fixed volume, and a homogeneous mixed gas of 100 ppm CO, 5% O ₂ , and the balance N ₂ adjusted to atmospheric pressure was introduced, and the gas pressure inside the reaction vessel was measured 1 minute after contact with the catalyst. was measured, and the rate of change was taken as the catalytic activity. The temperature was 300°C. From the figure, when y=0, x=0.5, when y=0.3, x=0.65,
It can be seen that the activity is maximized when each element ratio is x=0.8 at y=0.6 and x=1.0 at y=1.0. Figure 2 shows an example of _NO2 decomposition activity for the same catalyst. Pellet 45 produced in the same manner as above
The samples were filled into a quartz tube with an inner diameter of 20 mm, and the tube was fixed in an electric furnace to maintain the temperature at 300°C. Then, a homogeneous mixed gas of 40 ppm NO ₂ and the balance N ₂ was flowed into the catalyst layer at SV = 10000 h ^-1 , and when a steady state was reached, the NO ₂ concentration on the outlet side was measured and the rate of decrease with respect to the inflow gas concentration was determined. It is something. In this case, as in the case of CO oxidation, y=O and x=0.5, y=0.3 and x=0.65, y=0.6
We obtained the results that the NO ₂ reduction rate is maximum when each element ratio is x = 0.8, y = 1.0, and x = 1.0. The oxide composition showing the activity peak in the above is
La _0.5 Sr _0.5 CoO ₃ , La _0.35 Sr _0.65 Co _0.7 Fe _0.3 O ₃ , La _0.2
Sr _0.8 Co _0.4 Fe _0.6 O ₃ and SrFeO ₃ were formed. by the way
In LaCoO ₃ , Co has a valence of +3, but when La at the A site is replaced with Sr ²⁺ , Co ⁴⁺ is generated. Furthermore, assuming that Fe substituting Co at the B site enters with a valence of +4, Co ³⁺ and Co ⁴⁺ will exist in equal amounts in the four oxides due to the electrically neutral condition. In other words, it is thought that high activity can be imparted by determining the amount of substitution at the A site and B site so that Co ³⁺ and Co ⁴⁺ are present in equal amounts. That is, the B site substitution element Me
If the amount of is x, then the highly active catalyst composition is La _1-X/2
It can be expressed as Sr _1+X/2 Co _1-x Me _x O ₃ . Next, an example of the purification device will be described. As an example, when x=0.3, that is, La _0.35
Sr _0.65 Co _0.7 Me _0.3 O ₃ (Me=Fe, Mn, Cr, V, Ti)
An oxide catalyst expressed as follows is supported on an expanded metal mesh made of stainless steel SUH21 with high melting point enamel. High-melting point enamel with a melting point of approximately 900°C was applied to a stainless steel SUH21 wire mesh with a diameter of 120 mm by spraying, and on top of this, the composite oxide synthesized in the same manner as described above was powdered into a powder approximately 300 mesh in size. Spray it on the surface evenly. This was heat-treated at a predetermined temperature to obtain a net in which the catalyst powder was evenly and firmly supported. FIG. 3 shows a cross section of the main part of the metal mesh supporting the catalyst. The catalyst particles 1 are not completely covered with the enamel 2, but are supported on the wire mesh 3 so that the surface is exposed as shown in the figure, and exhibits the function as a catalyst. FIG. 4 is a schematic sectional view showing the net 4 attached to the upper part of the combustion tube of a commercially available portable gas stove. The exhaust gas generated in the combustion section 5 passes through the flow path 6 and reaches the exhaust gas purification device 4, where it is purified and discharged. The table below shows the changes in the CO and NO ₂ concentrations in the exhaust gas after passing through the purifier when this gas stove is burned. Note that the CO concentration before passing through the purification device is 37 ppm, and the NO ₂ concentration is 6 ppm. The data includes the concentration during the first combustion and the concentration after repeating the cycle of 30 minutes of combustion and 30 minutes of extinguishing 5000 times. The exhaust gas temperature on the upstream side of the purification device during combustion is approximately 700°C. As a comparative example, a metal mesh made of stainless steel SUH21 itself and a similar catalyst powder uniformly dispersed in a 10% by weight aqueous solution of methyl cellulose were uniformly applied to the metal mesh made of stainless steel SUH21 and baked to support it. was subjected to the reaction. The amount of catalyst supported was approximately 1 g in both the examples and comparative examples.
It was hot. The catalyst composition in the table is La _0.35 Sr _0.65
Shown as Me in Co _0.7 Me _0.3 O ₃ .

[Table] The amount of catalyst supported after 5000 cycles of combustion test was approximately 0.4 to 0.6 g using the conventional method, whereas the amount of catalyst supported using the present invention showed almost no change from the initial amount supported. Ta. There is a slight difference in thermal expansion between the catalyst oxide and the metal mesh, and when supported directly, the catalyst gradually falls off, whereas when supported with enamel, the enamel softens slightly during catalytic operation, resulting in a buffering effect. This is thought to be effective in preventing catalyst particles from falling off. Furthermore, looking at the loading state after the combustion cycle test,
It can be seen that the surface of the catalyst particles is not covered with enamel and maintains its initial state, which greatly contributes to maintaining and stabilizing the characteristics. The metal mesh used may be made of heat-resistant and corrosion-resistant steel other than stainless steel SUH21, and the enamel used must be of low melting point.
It can be appropriately selected and configured depending on the conditions of use. Effects of the Invention As described above, the exhaust gas purification device of the present invention can efficiently process oxidizing gas and reducing gas at the same time.
Moreover, it has excellent characteristic stability and high reliability. Furthermore, it has features such as being relatively inexpensive and easy to configure.

[Brief explanation of drawings]

Figure 1 shows the CO oxidation activity of La _1-x Sr _x Co _1-y Fe _y O ₃ , Figure 2 also shows the NO ₂ decomposition activity,
FIG. 3 is a sectional view of a main part of the catalyst-supporting metal mesh, and FIG. 4 is a schematic sectional view of the combustion section of a gas stove with a catalyst purification device. 1...Catalyst particles, 2...Enamel layer, 3...Metal part.

Claims (1)

[Claims] 1 General formula La _1-X/2 Sr _1+X/2 Co _1-x Me _x O ₃ (Me is Fe,
A type of element selected from Mn, Cr, V, Ti, O<X<
An exhaust gas purification device in which a perovskite-type composite oxide catalyst represented by 1) is supported on a metal porous body using enamel.