JPS6186944A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To obtain a catalyst for purifying exhaust gas enhanced in heat resistance and poisoning resistance, by constituting a molded body by mixing and baking at least calcium aluminate and delafossite composite metal oxide. CONSTITUTION:Calcium aluminate containing 50-85wt% of an alumina component and delafossite composite metal oxide represented by ABO2 (wherein an A-site is Cu, Ag, Pd or Pt and a B-site is Al, Cr, Ga, Fe, Co Rh, La, Y or Mn) are mixed and baked to obtain a catalyst for purifying exhaust gas. The delafossite composite metal oxide constituting the catalyst is pref. 5-50wt%. Furthermore, as the constitutional component of the catalyst, a heat resistant base aggregate such as a silica base aggregate or silica-alumina base aggregate can be compounded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a catalyst for purifying exhaust gas that oxidizes and purifies hydrocarbons into harmless substances.

Structure of conventional examples and their problems Conventional catalyst bodies containing lime aluminate are constructed by using lime aluminate and manganese dioxide or platinum group metal. Here, although the former catalyst composed of manganese dioxide has strong resistance to poisoning,
When exposed to temperatures of 0° C. or higher, the catalytic activity is reduced due to thermal transition of manganese. The latter type of catalyst using platinum or a different metal is susceptible to poisoning by contaminated platinum group metals in small amounts, and is expensive if a large amount of platinum group metal is used to provide excellent poisoning resistance. This has the problem that the dispersibility of the catalytic material is reduced, which promotes thermal deterioration of the catalytic material due to sintering, and shortens the catalyst life.

OBJECTS OF THE INVENTION The present invention has been made in order 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 delafossite type composite metal oxide.

Description of Examples The delafossite-type composite metal oxide used in the present invention is represented by the general formula A+B3+02, and is an octahedral layer centered on trivalent metal B, with oxygen spreading in the plane sharing edges. and a monovalent metal A that connects these layers with linear two-coordination bonds. In the present invention, the metals used as the metal A are Cu, Aq, Pd, and pt, and the metals B are Ad, Cr, Ga, and F.
e, Co, Rh, La.

Selected from Y and Mn.

The delafossite-type composite metal oxide has oxidation catalytic performance, and is capable of oxidizing carbon oxide (hereinafter referred to as CO) and hydrocarbon compounds (
(hereinafter referred to as HC) is oxidized and purified into carbon dioxide and water. This catalytic action is due to the fact that delafossite-type composite metal oxides can participate in the reaction by heating and cooling, and that bluffosite-type fractured metal oxides containing Cu and Ag have semiconductor properties. In addition, since those containing Pd and Pt exhibit metallic conductivity, this is thought to be due to the fact that electron movement within the bluffsite-type composite oxide tends to occur quickly. It will be done.

For example, a bluffsite-type fractured metal oxide (credonerite) composed of Cu as metal A and Mn as metal B will have a structure at 900°C or higher when heated and cooled from room temperature to 1000°C. Oxygen is released, and oxygen is stored again at around 900°C by cooling. From the results of the X@ analysis, it was found that during the heating and cooling cycle described above, this metal oxide adsorbs and desorbs oxygen while maintaining the bluffsite structure, and the amount of oxygen that changes during the heating and cooling process is approximately equal to the total amount of oxygen. There were about 25 people in charge.

Thus, in the delafossite-type composite metal oxide described above, the groove bottom ratio of oxygen to the two types of metals as described above is thought to change depending on the thermal environment and atmosphere. Therefore, the delafosa, ite-type composite metal oxide used in the present invention, in addition to that represented by the general formula AB○2 described above, has the oxygen ratio that has undergone multiple changes within the range that does not destroy the bluff-osite type groove structure. It also includes composite metal oxides.

The delafossite 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 60% by weight or less. If it is less than 5% by weight, sufficient catalytic activity will not be obtained, and if it exceeds 5Q% by weight, the mechanical strength of the catalyst body will sharply decrease.

The present invention uses lime aluminate together with the above-mentioned delafossite type composite metal oxide.

Aluminate lime, also called alumina cement, is a hydraulic binder and is generally expressed as mAt203.nCaO. This lime aluminate reacts with water even at room temperature, forms a hydrate, and forms a strong bond.

When this hydrate is fired at 340° C. or higher, the hydrated water is removed, and at the same time, the water conservancy becomes porous. Therefore, a porous catalyst body can be obtained by constructing a catalyst body containing a catalytic substance, bluffsite, 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, the porosity of the catalyst body, which is made of the conventional catalyst support raw materials cordierite and 'i-myrite, which require sintering treatment, and delafossite-type composite metal oxide, has extremely small porosity due to sintering. Therefore, it is difficult to obtain a catalyst having a desired catalytic activity.

The aluminate lime used in the present invention preferably has an alumina content of 6Q or more and 85 or less by weight,
In particular, it is preferably 60% by weight or more and 80% by weight or less. If the alumina content contained in the aluminate lime is less than 5Q% by weight, the thermal deterioration of the catalyst body will be significant, and if the alumina content exceeds 85% by weight, the mechanical strength of the catalyst body will decrease drastically. .

In the present invention, although it is possible to obtain a catalyst body having sufficient catalytic properties with the above-mentioned structure alone, there is also a support material, and as a mineral phase, silicate mineral, mullite, corundum, sillimanite, β-alumina, and even magnesia, chromium,
It is preferable to use dolomite, magekuro, and chromag type materials. Also, depending on the operating temperature of the catalyst, the low temperature side (300
~700℃), a general granular base aggregate is used, and the high temperature side (
7001C or higher), it is preferable to use a heat-resistant granular base aggregate.

To explain in more detail, examples of the silica-based aggregate include silica stone. These base aggregates mainly contain SiO2. Examples of the silica-alumina base aggregate include Nyamonoto, Rouseki, and high alumina, and the main component is SiO2-A12O3. α-A1203 as alumina base aggregate
．． β-A1203. There are γ-A1203゜ρ-AIO, etc. More common major mineral phases are silicate minerals, mullite, and corundum.

Norimanite, β-alumina, etc. are used. These base aggregates can be crushed to a certain extent, or commercially available base aggregates such as conical silica sand, alumina, and Nyamonoto can be used.Generally, it is best to use commercially available silica sand or chamotte. It is 1 Sarari.

Furthermore, for the purpose of increasing the excitement of the town, heat-resistant fibers such as dealkalized glass fibers, fibrous iron wire, silica/alumina*, and gi(f) may optionally be added.

By adding a compound, molding becomes easier.

With the configuration of the present invention described above, it is possible to obtain an oxidation catalyst having very good catalytic performance, but it is also possible to configure a three-way catalyst using the catalyst of the present invention. Configure it as follows.

At least lime aluminate and bluffsite die-cut alloy
Platinum Sl containing Rh is added to the catalyst body formed from a platinum oxide.
Catalyst for exhaust gas purification composed of supporting metal.

As mentioned above, the delafossite type composite metal oxide has an oxidation catalytic ability and also has the property of adsorbing and desorbing oxygen. Therefore, the delafossite 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 metals used.

Next, specific examples of the present invention will be described.

<Example 1> Lime aluminate, CuMn○2. as delafossite type composite metal oxide. Silica as a heat-resistant base aggregate.

And for comparison, using γ-M n 02, those with compositions of 1 to 116.3 shown in Table 1 were dry mixed, an appropriate amount of water (approximately 2Q% by weight) was added, and 50 <
After forming into a honeycomb shape with a cell wall thickness of 0.3 cm and a cell wall thickness of 0.3 cm, the catalyst bodies were cured, dried, and calcined at 500°C to obtain catalyst bodies having respective compositions. This plate 1- shown in Table 1
A test gas of Co 500ppm, HC (propane) 10001)Pm, and residual air was flowed through the A3 catalyst body at 300°C and a space velocity (hereinafter referred to as SV) of 20.0OOh to test the oxidation catalytic ability of the catalyst body. . Further, the catalyst bodies of Flats 1 to 3 prepared by the method described above were heat-treated for 80C)C-5 hours, and then the oxidation catalytic ability test described above was conducted again. In addition, the mechanical strength before and after the 800C 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 using manganese dioxide has good initial performance, the catalyst performance is significantly deteriorated by heat. In addition, (in the case of strong IW), the use of a heat-resistant base aggregate results in less thermal strength deterioration of the catalyst body.

<Example 2> A honeycomb-shaped catalyst body A1 and a catalyst body A2 were obtained using the formulation shown in Table 2 and the same adjustment method as in Example 1. The catalyst plate 2 was formed into a nicam shape, cured, dried, supported with chloroplatinic acid having a pt amount of o, ooswt, and then thermally decomposed and calcined at 500°C. Regarding this prepared catalyst body j61゜116,2,
An oxidation catalyst ability test was conducted under the same conditions as in Example 1 using a test gas containing 500 ppm of Co and residual air. The results are summarized in the above catalyst plate 1. This is the initial performance of A2. Next, this catalyst body AI, &2 was placed in the exhaust gas of an engine operated with gasoline containing lead of ○-o1rrtq/(J) for 10 hours.
The catalyst was placed at 600°C and poisoned with lead. Here, the engine had a displacement of 2000 cc, was operated at an air-fuel ratio of 14.6 degrees, a rotational speed of 200 rpm, and a dynamo torque of 10 KVrQ. Catalyst body A1 poisoned in this way. A2 was subjected to the same Co purification ability test as described above, 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 catalyst supporting platinum is
As a result of the above life test, the catalyst performance suddenly decreased. On the other hand, the catalyst body of the present invention showed good catalytic performance even after detoxification.

Table 2 (Example 3) As shown in Table 3, in the dephosite type composite metal △ oxide AB02, as metal A, Ca, Ag,
Pd.

pt and metal B, AI, Cr, Ga,
Fe.

Using various oxides using Co, Rh, La, Y, and Mn, this and lime aluminate were mixed at a ratio of 20:80,
Honeycomb-shaped catalyst bodies (AG 1 to AG 15 in Table 3) were obtained by the same preparation method as in Example 1. Next, for each of these melting media, under the test gas and temperature conditions shown in Example 2, the SV was set to 20ρ○○h and 40. The oxidation catalyst ability was tested instead of ○ooh. The results are shown in Table 3.

As is clear from Table 3, all of the bluffsite-type composite metal oxides used in the present invention showed good CO purification ability, but CuMnO2 was particularly good, with a space velocity of 20,000 Even when increasing from 40,000 h-1 to 40,000 h-1, the reduction in purification rate was very small.

The following margin is <Example 4> As shown in Table 4, the amount of lime aluminate used as the binder was 46% by weight, CuM n O2 was used as the delafossite type composite metal oxide, and this was variously changed. , a catalyst body with the remaining amount of silica (Table 4)
) were prepared in the same manner as in Example 1, and obtained as non-nicum molded bodies. This IIl insect repellent was subjected to the same coli purifying ability test as in Example 2, and the transverse rupture strength was measured, and the results are shown in Table 4.

Moreover, when the content exceeds 60% by weight, the transverse rupture strength decreases rapidly, although the C◯ resistance is always good.

Table 4 (Example 5) The same method as in Example 1 was used to mold and cure the mixture of 70% by weight of lime aluminate and 230% by weight of CuMnO, and then the firing temperature was varied from 200°C to 500°C. to obtain honeycomb catalyst bodies A1-71;9 (fifth
table).

Next, the apparent porosity of this tentative body/I61 to A9 is Tl5
-R2205, and the CO purification ability of each catalyst was tested using the test gas shown in Example 2, varying the space velocity, and setting the catalyst temperature to 200'C. 6th result
Shown in the table.

As is clear from the results, when the calcination temperature is lower than 340'C, the porosity is low, the catalytic activity is also low, and a catalyst body having sufficient catalytic ability cannot be obtained.

Table 5 (Example 6) A honeycomb catalyst body was obtained by the same preparation method as in Example 1 with a composition of 70 parts by weight of lime aluminate and 30 parts by weight of CuMnO. Here, the alumina content in the alumin M stone was varied from 4o to 9o:11-% by weight, and catalyst bodies were obtained by removing the above-mentioned force.

The transverse rupture strength of the catalyst using lime aluminate containing the alumina of this chimney was measured, and the results are shown in Figure 47. As is clear from Figure 47, when the alumina content in the aluminate lime exceeds 85% by weight, the transverse rupture strength (mechanical strength) decreases rapidly.

Moreover, regarding the above-mentioned catalyst body, the Co
Purification performance tests were conducted. The catalysts were tested immediately after preparation, after preparation and heat-treated at 8°C for 5 hours, and after preparation and heat-treated at 1000'C for 5 hours. The results are shown in the AI diagram.

As is clear from the He diagram, immediately after preparation, the catalyst body of the present invention has good catalytic ability regardless of the alumina content in the lime, but the alumina content in the aluminate lime is 50% by weight. The catalytic ability of a catalyst body with a temperature lower than 8oQ°C decreases rapidly by heat treatment at 8oQ°C. Furthermore, even after heat treatment at 100°C, a catalyst body with good catalytic performance can be obtained when the alumina content in the aluminate lime is 50% by weight or more, and in particular,
Alumina content is 60. When the fi ratio is higher than the fi ratio, a good catalyst body with little decrease in catalytic performance can be obtained even in this heat treatment.

<Example 7> By the same preparation method as Example 1, lime aluminate and Cu
A honeycomb catalyst body was prepared with M n O2 and silica in the proportion shown in Table 6, and P in the amount also shown in Table 6 was added.
t (!: Rh was supported by thermal decomposition using chloroplatinic acid and rhodium chloride, and AI and A shown in Table 6 were prepared.
A catalyst body of No. 2 was prepared. This was installed in the engine exhaust gas path, and the three-way catalyst performance of the two catalyst bodies was compared. The engine used was one with a displacement of 2000 CCO and an engine rotation speed of 200 rpm.

The air-fuel ratio was changed from 14.0 to 15.0 at a torque of 6 to 7 m, the exhaust gas catalyst inlet temperature was set to 400°C, and the exhaust gas components, HC, Co, and nitrogen oxides (NOx) were all s
The three-way catalyst performance was evaluated based on the air-fuel ratio range in which the air-fuel ratio was purified by 0% or more as the window width. Performance evaluation was performed twice: immediately after the preparation of the catalyst body and after the poisoning treatment using leaded gasoline shown in Example 2. 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 (flat 2) using 7% of platinum group metals. I got something.

Table 6 Effects of the Invention As described above, according to the present invention, a catalyst body having excellent heat resistance and poisoning resistance can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS The figure is a diagram showing the change in co-purification rate and transverse rupture strength of the catalyst body with respect to the alumina content contained in the lime aluminate used in the catalyst body of the present invention.

Claims (5)

[Claims] (1) A catalyst body for exhaust gas purification characterized by containing at least lime aluminate and a delafossite type composite metal oxide. (2) The delafossite type composite metal oxide is ABO_2
It is a compound represented by the general formula, and the metal at the A site is
selected from Cu, Aq, Pd, and Pt, and the metal at the B site is Al, Cr, Ga, Fe, Co, Rh, La,
The catalyst body for exhaust gas purification according to claim 1, characterized in that the catalyst body is selected from Y and Mn. (3) The exhaust gas purifying catalyst body according to claim 1, characterized in that the delafossite type composite metal oxide is contained in an amount of 5% by weight or more and 50% by weight or less. (4) The exhaust gas purifying catalyst body according to claim 1 or 4, wherein the alumina content contained in the aluminate lime is 50% by weight or more and 85% by weight or less. (5) A catalyst 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 delafossite type composite oxide. Medium.