JPH054135B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a catalyst body for exhaust gas purification that oxidizes and purifies carbon monoxide and hydrocarbons generated from various combustion appliances and cooking appliances into harmless substances. Structures of Conventional Examples and Their Problems Conventional catalyst bodies containing lime aluminate were constructed by using lime aluminate and manganese dioxide or a platinum group metal. put it here,
Although the former catalyst body constructed using manganese dioxide has strong poisoning resistance, it has the problem that when exposed to temperatures of 600°C or higher, the catalytic activity decreases due to thermal transfer of manganese. In addition, the latter catalyst using a platinum group metal is susceptible to poisoning by the platinum group metal in the catalyst in small amounts, and if a large amount of platinum group metal is used to make it resistant to poisoning, it becomes an expensive catalyst. At the same time, the dispersibility of the catalyst material decreases,
Thermal deterioration of the catalyst body due to sintering is accelerated,
The problem was that the catalyst life was shortened. Purpose of the Invention The present invention has been made to solve the above-mentioned conventional problems, and its object is to obtain a catalyst body for exhaust gas purification that has excellent heat resistance and toxicity resistance. Structure of the Invention The present invention is an exhaust gas purifying catalyst body containing at least lime aluminate and a delahousite type composite metal oxide. Description of Examples The delafosite type composite metal oxide used in the present invention is represented by the general formula A ⁺ B ³⁺ O ₂ and has a trivalent metal B
It has a layered structure consisting of an octahedral layer in which oxygen is spread out in the plane sharing edges, and a monovalent metal A that connects this layer with linear two-coordination bonds. . In the present invention, the metals used as the metal A are Cu, Ag, Pd, and Pt, and the metals B are Al, Cr, Ga, Fe, Co, Rh,
Selected from La, Y, and Mn. Delafuosite type composite metal oxide has oxidation catalytic performance and oxidizes and purifies carbon monoxide (hereinafter referred to as CO) and hydrocarbon compounds (hereinafter referred to as HC) into carbon dioxide and water. This catalytic action is due to the fact that oxygen in the delafousite complex metal oxide adsorbs and desorbs oxygen through heating and cooling, and oxygen in the delafousite complex metal oxide has a high degree of freedom and can easily participate in the reaction. Among delafousite type composite metal oxides, those containing Cu and Ag have semiconducting properties, and those containing Pd and Pt exhibit metallic conductivity. This is thought to be due to the fact that movement tends to occur quickly. For example, a delafosite-type composite metal oxide (credonerite) composed of Cu as metal A and Mn as metal B can be heated at 1100°C from room temperature.
When heated and cooled to temperatures above 900°C, structural oxygen is released, and upon cooling, oxygen is occluded again at around 900°C. According to the results of X-ray analysis, during the above heating and cooling cycle, this metal oxide adsorbs and desorbs oxygen while maintaining its delta phossite structure, and the amount of oxygen that changes during the heating and cooling process is about 25% of the total oxygen amount. It was %. In this way, it is thought that in the delafousite type composite metal oxide described above, the composition ratio of oxygen to the two types of metals as described above changes depending on the thermal environment and atmosphere. Therefore, the delafosite type composite metal oxide used in the present invention may include, in addition to the one represented by the above-mentioned general formula ABO ₂ , a composite metal oxide in which the oxygen ratio has been changed by a small amount as long as the delafosite type structure is not destroyed. It includes. Delafuosite type composite metal oxides can be prepared in the same manner as ordinary composite oxides. That is, it may be prepared by hydrolyzing a mixed aqueous solution of each metal salt with aqueous ammonia or urea. When used as a catalyst, usually
Use one that has been fired at 400 to 600°C for several hours. The delafosite type composite metal oxide used in the present invention is preferably contained in the catalyst body in an amount of 5% by weight or more and 50% by weight or less. If it is less than 5% by weight, sufficient catalytic activity cannot be obtained, and if it exceeds 50% by weight, the mechanical strength of the catalyst body will decrease rapidly. In the present invention, lime aluminate is used together with the above-described delafosite type composite metal oxide. Lime aluminate, also called alumina cement, is a hydraulic binder and is generally mAl ₂ O ₃ .
Expressed as nCaO. This lime aluminate reacts with water even at room temperature, forms hydrates, and bonds strongly. When this hydrate is fired at 340°C or higher, the hydrated water is removed, and at the same time, the hydrated bond becomes porous. Therefore, a porous catalyst body can be obtained by constructing a catalyst body containing delafosite as a catalyst substance using lime aluminate as a binder and firing it at the above-mentioned temperature or higher. This is excellent not only in that it is possible to obtain a catalyst body without sintering, but also in that it is possible to obtain a porous catalyst body which is highly desirable as a catalyst body. On the other hand, catalyst bodies made of materials that require sintering, such as cordierite and mullite, which are the raw materials for conventional catalyst supports, and delafosite-type composite metal oxides have extremely small porosity through sintering, which is desirable. It is difficult to obtain a catalyst body with catalytic activity. The aluminate lime used in the present invention preferably has an alumina content of 50% by weight or more and 85% by weight or less, particularly preferably 60% by weight or more and 80% by weight or less. If the alumina content contained in the aluminate lime is less than 50% by weight, thermal deterioration of the catalyst body becomes significant, and if the alumina content exceeds 85% by weight, the mechanical strength of the catalyst body decreases rapidly. In the present invention, it is possible to obtain a catalyst body having sufficient catalytic properties with just the above structure, but it is also possible to further use a heat-resistant base aggregate. Heat-resistant base aggregates that can be used in the present invention include silica-based base aggregate, silica-alumina-based base aggregate, and alumina-based base aggregate, and the mineral phase includes silicate minerals, mullite, corundum, It is preferable to use sillimanite, β-alumina, magnesia, chromium, dolomite, magne black, and chromag-based materials.
Also, depending on the operating temperature of the catalyst, the constant temperature side (300 to 700
℃), it is preferable to use a general granular base aggregate, and for high temperatures (700℃ or higher), it is preferable to use a heat-resistant granular base aggregate. More specifically, examples of the silica base aggregate include silica stone. These base aggregates have SiO ₂ as a main component. Silica-alumina base aggregates include siyamoto, waxite, high alumina, etc.
_The main component is _SiO2 - _Al2O3 . As alumina base aggregate, α-Al ₂ O ₃ , β-Al ₂ O ₃ , γ-Al ₂ O ₃ , ρ
−Al ₂ O ₃ etc. More commonly used main mineral phases include silicate minerals, mullite, corundum, sillimanite, and β-alumina. These base aggregates can be crushed to a certain extent, or commercially available conical silica sand, alumina, siyamoto, etc. can be used.Generally, commercially available silica sand or siyamoto is used. It's convenient. Furthermore, for the purpose of increasing heat resistance, heat-resistant fibers such as dealkalized glass fibers, fibrous iron wires, and silica/alumina fibers may optionally be added. In addition, carboxymethyl cellulose, methyl cellulose, polyvinyl alcohol,
By adding clay compounds such as alcohol and bentonite, molding becomes easier. With the above configuration of the present invention, an oxidation catalyst body having very good catalytic performance can be obtained, but
Furthermore, it is also possible to construct a three-way catalyst using the catalyst of the present invention, which is constructed as follows. A catalyst body for exhaust gas purification comprising a catalyst body formed from at least lime aluminate and a delafosite type composite metal oxide, supporting a platinum group metal containing Rh. As mentioned above, the delafousite type composite metal oxide has an oxidation catalytic ability and also has the property of adsorbing and desorbing oxygen. Therefore, the delafosite type composite metal oxide not only functions as an oxidation catalyst but also exhibits a good oxygen storage effect. Therefore, compared to conventional three-way catalysts, it is possible to obtain a catalyst body with a wider window width and to significantly reduce the amount of platinum group metal used. Next, specific examples of the present invention will be described. Example 1 Lime aluminate, CuMnO ₂ as a delahousite type composite metal oxide, silica as a heat-resistant base aggregate,
For comparison, γ-MnO ₂ was used, and the compositions No. 1 to No. 3 shown in Table 1 were dry mixed, an appropriate amount of water (approximately 20% by weight) was added, and 50
After forming into a honeycomb shape with cells/cm ² and cell wall thickness of 0.3 mm, the catalyst bodies were cured, dried, and fired at 500° C. to obtain catalyst bodies of each composition. This is shown in Table 1.
A test gas of 500 ppm CO, 1000 ppm HC (propane), and residual air was passed through the catalyst bodies No. 1 to No. 3 at 300°C and a space velocity (hereinafter referred to as SV) of 20000 h ^-1 , and the oxidation catalytic performance of the catalyst bodies was was tested. In addition, the catalyst bodies No. 1 to No. 3 prepared by the method described above were heated at 800℃-5
After the heat treatment for several hours, the above-mentioned oxidation catalytic ability test was conducted again. In addition, the mechanical strength before and after the 800°C heat treatment was measured as transverse rupture strength. The results are shown in Table 1. As is clear from Table 1, although the conventional catalyst body using manganese dioxide has good initial performance, the catalytic performance is significantly deteriorated by heat. In addition, in terms of mechanical strength, the use of a heat-resistant base aggregate causes less thermal strength deterioration of the catalyst body.

[Table] Example 2 Honeycomb-shaped catalyst body No. 1 and catalyst body No. 2 were obtained using the same preparation method as in Example 1 using the formulation shown in Table 2. In addition, after forming catalyst No. 2 into a honeycomb shape, curing, and drying, the amount of Pt was 0.005wt.
% of chloroplatinic acid, and then thermally decomposed and calcined at 500°C. The prepared catalyst bodies No. 1 and No. 2
An oxidation catalytic ability test was conducted on the catalyst body under the same conditions as in Example 1 using a test gas of 500 ppm CO and residual air. This result was applied to the catalyst bodies No. 1 and No.
The initial performance was set as 2. Next, this catalyst body No. 1, No.
2 was placed in the exhaust gas of an engine operated with gasoline containing 0.01 mg/lead at 600°C for 10 hours, and the catalyst body was poisoned with lead. Here, the engine had a displacement of 2000 c.c., was operated at an air/heat ratio of 14.6, a rotational speed of 2000 rpm, and a dynamo torque of 10 Kgm. Regarding the catalyst bodies No. 1 and No. 2 that were poisoned in this way, the same
A CO purification ability test was conducted, and this was taken as the oxidation catalyst performance after the life test. The results are shown in Table 2. As is clear from Table 2, the catalytic performance of the platinum-supported catalyst body rapidly decreased in the above life test. On the other hand, the catalyst body of the present invention showed good catalytic performance even after being poisoned.

[Table] Example 3 As shown in Table 3, in delafosite type composite metal oxide ABO ₂ , as metal A, Ca, Ag,
Pd, Pt, and metal B, Al, Cr, Ga,
Using various oxides using Fe, Co, Rh, La, Y, and Mn, this and lime aluminate were mixed at a ratio of 20:80, and a honeycomb-shaped catalyst body was prepared using the same preparation method as in Example 1. (No. 1 to No. 15 in Table 3) were obtained. Next, for each of these catalyst bodies, the SV was set to 20000 h ^-1 under the test gas and temperature conditions shown in Example 2.
The oxidation catalyst ability was tested by changing the temperature to 40000 h ^-1 . The results are shown in Table 3. As is clear from Table 3, all the delafosite type composite metal oxides used in the present invention have good properties.
CuMnO ₂ showed the best CO purification ability, and even when the space velocity increased from 20,000 h ^-1 to 40,000 h ^-1 , the reduction in purification rate was very small.

[Table] Example 4 As shown in Table 4, the amount of lime aluminate used as the binder was 45% by weight, and CuMnO ₂ was used as the delafosite type composite metal oxide.
The content of CuMnO ₂ was varied from 3% to 52% by weight, and the remaining amount was silica.
Table Nos. 1 to 9) were each prepared in the same manner as in Example 1 to obtain honeycomb molded bodies. This catalyst body was subjected to the same CO purification ability test as in Example 2 and the transverse rupture strength was measured, and the results are shown in Table 4. As is clear from Table 4, the CO purification ability is
If CuMnO ₂ is less than 5% by weight, almost no effect is obtained by adding it, and the CO purification ability of the catalyst is extremely low.
Moreover, when it exceeds 50% by weight, the CO purification ability is very good, but the transverse rupture strength decreases rapidly.

【table】

[Table] Example 5 Lime aluminate was prepared in the same manner as in Example 1.
After molding and curing, honeycomb catalyst bodies No. 1 to No. 9 were obtained by changing the firing temperature from 200°C to 500°C with a composition of 70% by weight and 30% by weight of CuMnO ₂ (No. 5). table). Next, the apparent porosity of these catalyst bodies No. 1 to No. 9 is
In addition to measuring according to JIS-R2205, the CO purification ability of each catalyst was tested using the test gas and space velocity shown in Example 2 at a catalyst temperature of 200°C. The results are shown in Table 5. As is clear from the results, the firing temperature is 340℃
If it is below, the porosity is small and the catalytic activity is also small.
A catalyst body having sufficient catalytic ability cannot be obtained.

[Table] Example 6 A honeycomb catalyst body was obtained by the same preparation method as in Example 1 with a blend of 70% by weight of lime aluminate and 30% by weight of CuMnO ₂ . Here, catalyst bodies were obtained using the aluminate lime in which the alumina content was varied from 40% by weight to 90% by weight, respectively, by the above-mentioned method. The transverse rupture strength of catalyst bodies using lime aluminate with various alumina contents was measured, and the results are shown in the figure. As is clear from the figure, when the alumina content in the lime aluminate exceeds 85% by weight, the transverse rupture strength (mechanical strength) decreases rapidly. Further, the above-mentioned catalyst body was subjected to the CO purification performance test described in Example 2. The catalysts were tested immediately after preparation, after preparation, heat treated at 800°C for 5 hours, and after preparation, heat treated at 1000°C for 5 hours. The results are shown in the figure. As is clear from the figure, immediately after preparation, the catalyst body of the present invention has good catalytic ability regardless of the alumina content in the aluminate lime, but the alumina content in the aluminate lime is less than 50% by weight. The catalytic body of
Heat treatment at 800℃ causes a rapid decrease in catalytic ability.
Furthermore, even after heat treatment at 1000°C, if the alumina content in the aluminate lime is 50% by weight or more, a catalyst body with good catalytic performance can be obtained. In particular, if the alumina content is 60% by weight or more, even in this heat treatment, the catalyst body can be obtained. A good catalyst body with little decrease in performance can be obtained. Example 7 A honeycomb catalyst body was prepared using the same preparation method as in Example 1, using the proportions of lime aluminate, CuMnO ₂ and silica shown in Table 6, and the amounts of Pt and silica also shown in Table 6. Rh was supported by thermal decomposition using chloroplatinic acid and rhodium chloride to prepare catalyst bodies No. 1 and No. 2 shown in Table 6, respectively. This was installed in the engine exhaust gas path, and the three-way catalyst performance of the two catalyst bodies was compared. The engine has a displacement of 2000
Using a cc engine, the air-fuel ratio was varied from 14.0 to 15.0 at an engine speed of 2000 rpm and a torque of 6 kgm, the exhaust gas catalyst inlet temperature was 400°C, and the exhaust gas components,
HC, CO and nitrogen oxides (NO _x ) all 80
The air-fuel ratio width that is purified by % or more is defined as the window width,
The three-way catalyst performance was evaluated based on this window width. Performance evaluation was carried out immediately after the preparation of the catalyst body and after the poisoning treatment using leaded gasoline shown in Example 2.
I went around. The results are shown in Table 6. As is clear from Table 6, the catalyst body of the present invention has a lower amount of platinum group metals and has better life characteristics than the conventional catalyst body (No. 2) using only platinum group metals. was gotten.

[Table] Effects of the Invention As described above, according to the present invention, a catalyst having excellent heat resistance and toxicity resistance can be obtained.

[Brief explanation of the drawing]

The figure is a diagram showing the CO purification rate and transverse rupture strength change of the catalyst body with respect to the alumina content contained in the aluminate lime used in the catalyst body of the present invention.

Claims (1)

[Scope of Claims] 1 Contains at least lime aluminate and a delahousite type composite metal oxide, the delahousite type composite metal oxide is a compound represented by the general formula ABO ₂ , and the A site metal is: Cu, Ag,
The metal at the B site is selected from Pd and Pt.
A catalyst body for exhaust gas purification characterized by being selected from Al, Cr, Ga, Fe, Co, Rh, La, Y, and Mn. 2. The exhaust gas purifying catalyst body according to claim 1, characterized in that the delafosite type composite metal oxide is contained in an amount of 5% by weight or more and 50% by weight or less. 3 Alumina content contained in lime aluminate is 50
The catalyst body for exhaust gas purification according to claim 1, characterized in that the content is at least 85% by weight. 4. The catalyst body for exhaust gas purification according to claim 1, characterized in that a platinum group metal containing rhodium is supported on a molded body composed of at least lime aluminate and a delafosite type composite metal oxide.