JPS61181538A - Catalyst for purifying exhaust gas - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a catalyst body that purifies harmful components in exhaust gas mainly generated from internal combustion engines, domestic combustors, etc. .

The present invention relates to a catalyst body that reduces and purifies nitrogen oxides.

Conventional technology Conventionally, as this type of catalyst, a platinum group metal catalyst supported on a carrier mainly composed of lime aluminate (Japanese Patent Application Laid-Open No. 1983-1999)
35888) and those to which titanium oxide is added to suppress sintering of catalyst particles (JP-A-56-126447).
) etc. are known.

Problems to be Solved by the Invention However, the former catalyst suffers from severe thermal deterioration due to sintering of the catalyst material and carrier.

Although the latter catalyst showed considerable improvement in preventing thermal deterioration, it was insufficient in terms of improving low-temperature catalytic activity. In addition, in catalyst bodies that require three-way catalyst performance, such as catalysts for automobile exhaust gas purification, conventional catalyst bodies
Rh is essential.

1/6 to 1/11 fth for Pj used at the same time
is used. On the other hand, the production amount of Rh is less than 1/11 that of platinum! Since the price of Rh is about twice as high as that of platinum, there is a strong desire to reduce the amount of Rh used, and the conventional catalysts described above have been insufficient in this respect as well.

The present invention solves the problems of conventional catalyst bodies as described above, improves the low-temperature catalytic activity of the catalyst body, and also aims to reduce the amount of catalyst used and the corresponding cost reduction, thereby achieving high performance and low cost. The purpose of this invention is to provide a catalytic body.

Means for Solving the Problems The catalyst body of the present invention comprises a carrier comprising a cocatalyst material selected from the group consisting of lanthanum oxide, barium oxide and barium carbonate, and lime aluminate as a binder. It supports a platinum group catalyst material.

Since the lime aluminate used as the functional binder has hydraulic properties, it does not require the sintering process that is required when manufacturing conventional catalyst supports such as cordierite and mullite. A catalyst carrier can be obtained. This increase in specific surface area eliminates the need for wash coat treatment, which is necessary for increasing the specific surface area in the conventional sintered carrier.

Since lime aluminate has a solid base catalytic ability, it exhibits very good activity in purifying harmful components in exhaust gas, particularly hydrocarbon compounds (hereinafter abbreviated as HG).

The content of lime aluminate in the carrier is 16% by weight or more,
It is 50% by weight or less. The content of lime aluminate is 15
If it is less than 50% by weight, sufficient mechanical strength cannot be expected, and if it exceeds 50% by weight, the spalling resistance will be significantly reduced.

Lime aluminate is represented by the general formula mAR203·ncao, and preferably contains alumina of 50% by weight or more and 86% by weight or less, particularly 60% by weight or more.

80% by weight or less is desirable. This is because if the alumina content in the aluminate lime is less than 50% by weight, the thermal deterioration of the catalyst will be significant, and if the alumina content exceeds 85% by weight, the binding strength of the aluminate lime will be significantly weakened. This is because the curing speed becomes extremely high, making it difficult to form complex shapes such as honeycomb shapes.

Lanthanum oxide is a 5-nitrogen compound (hereinafter abbreviated as kiox)
It has excellent adsorption ability for boron, and also has a high affinity for boron.

Therefore, by using the platinum group metals Pt and Pd, the nitrogen oxides contained in the exhaust gas are reduced when the fuel is combusted on the richer side than the stoichiometric air-fuel ratio.
d, and acts as a cocatalyst that significantly improves these properties. Further, barium oxide and barium carbonate have similar effects.

Lanthanum oxide and barium oxide are their chlorides,
hydroxide, acetate, oxalate, sulfate, nitrate, carbonate,
There is a method in which ammonium sulfate or ammonium nitrate is used as a starting material, and the lanthanum compound or barium is used as an oxide, either by firing it before use, or by firing it into a molded product and using it as an oxide. There are methods such as converting a compound into an oxide.

The content of the cocatalyst material of the present invention composed of lanthanum oxide, barium oxide, and barium carbonate in the carrier is preferably 1 weight or more and 50 weight or less. The content is 1
If it is less than 50% by weight, a sufficient effect of the addition of the co-catalyst substance cannot be expected, and if it exceeds 50% by weight, the co-catalyst effect cannot be expected to increase commensurately, and the HC purification ability will actually decrease. come.

In general, when used together with Pt or Pd, lanthanum oxide can reduce Pt in NOx contained in exhaust gas (hereinafter referred to as rich side exhaust gas) emitted when operating in a region where the fuel ratio is higher than the stoichiometric air-fuel ratio. It significantly improves the purification characteristics of Pd, but at the same time reduces the ability to purify HC contained in the exhaust gas (hereinafter referred to as exhaust gas on the lean side) that is generated when the engine is operated under conditions where the fuel is leaner than the stoichiometric air-fuel ratio. Put it away. The same applies to barium oxide and carbonate. This phenomenon is a very serious problem especially when used as an automobile three-way catalyst.

It was difficult to solve this problem with the conventional catalyst body using a sintered catalyst carrier such as cordierite as described above. On the other hand, as mentioned above, since the catalyst carrier of the present invention contains aluminate lime having solid base catalytic ability, it is possible to obtain a catalyst body without a decrease in HC purifying ability even in the exhaust gas on the cylinder side due to the HC purifying effect thereof. can. In addition, lanthanum oxide and barium oxide.

The simultaneous use of cocatalyst materials such as barium carbonate and lime aluminate greatly improves the catalytic activity at low temperatures. Furthermore, by using cerium oxide or titanium oxide together with the above-mentioned promoter, the low-temperature catalytic activity is further increased. In particular, cerium oxide has an oxygen storage ability, so when used as an automobile catalyst, it is desirable because it can provide a wide window width.

Cerium compounds that become cerium oxide when heated include hydroxides, chlorides, acetates, oxalates, sulfates, nitrates, carbonates, ammonium sulfate salts, and ammonium nitrate salts. The content of cerium oxide in the carrier is preferably 6% by weight or more.

It is 63% by weight or less.

Titanium oxide also improves low temperature catalytic activity.

Although the mechanism of action of titanium oxide is not clear, in general, some composite metal oxides containing titanium are known as metal oxide semiconductors. In the present invention, a metal oxide semiconductor of lanthanum and titanium is also used. It is thought that this partially forms, acting as a co-catalyst and improving the catalytic activity. Good results can be obtained regardless of whether the titanium oxide used has an anatase or rutile structure. The content of titanium oxide in the carrier is preferably 2% by weight or more and 50% by weight or less.

The shape of the carrier of the present invention can be any shape such as granular, .

The platinum group catalyst material used in the present invention is Pj.

There are Pd, Rh, and Ru, and platinum group metal compounds that become these metals by reduction and decomposition can be used by dissolving them in a solvent such as water or alcohol.

Note that the carrier desirably contains a heat-resistant base aggregate. This is because the mechanical strength and heat-resistant strength of the catalyst body can be improved. Heat-resistant base aggregates include silica-based base aggregate, silica-alumina-based base aggregate, and alumina-based base aggregate. Minerals include silicate minerals, mullite, corundum, sillimanite, β-alumina, as well as magnesia, chromium,
Dolomite, Magex black, and Kuromag type materials can be used.

Example The present invention will be explained in detail below.

<Examples 1 to 8> Lanthanum oxide (La205), barium oxide, barium carbonate, lime aluminate, titanium oxide, cerium oxide (Ce0z), and silica as a heat-resistant base aggregate were used as the first
After blending with the composition shown in the table, adding an appropriate amount of water and kneading, the cell wall thickness is 0.26 mtx and the cell density is 400 cells/i.
After extrusion molding into a honeycomb shape of n, and curing and drying,
It was burnt off at 00°C and used as a carrier.

The catalyst bodies of Examples 1 to 8 were obtained by supporting 1 mg of platinum per 1 cc of the carrier using chloroplatinic acid.

<Comparative Examples 1 to 3> The carrier having the composition of Comparative Example 1.2 shown in Table 1 was used in Examples 1 to 8.
A catalyst body of Comparative Example 1.2 was obtained by supporting the same amount of platinum as in the above example. In addition, a cordierite honeycomb molded body with an alumina coating layer (average cell wall thickness 0.26 mm, cell density 400 cells/i, 2)
Comparison in which lanthanum nitrate was used and thermally decomposed to support lanthanum oxide in an amount equal to 2 parts by weight relative to the molded weight, and then 1 mg of platinum was supported per 1C of the support in the same manner as in the above example. A catalyst body of Example 3 was obtained.

(The following is a blank space) <Examples 9 to 11> Examples 9 to 11 in which platinum, palladium, rhodium, or ruthenium was supported in the amount shown in Table 2 on the non-nicum molded body used as the carrier in Example 1. A catalyst body was prepared. For supporting each platinum group metal.

Chlorides were used for platinum and palladium, and nitrates were used for rhodium and ruthenium, which were thermally decomposed and used as platinum group metals.

The various catalyst bodies prepared above were subjected to the following catalyst performance test. That is, an engine with a displacement of 2000 cc is used, the torque is adjusted at a rotation speed of 1800 rpm, the catalyst inlet temperature is soo°C ± 10°C, and the space velocity relative to the catalyst is 5ooo.

I ran the engine as hr. Under these conditions.

The air-fuel ratio (A/F is abbreviated below) was varied from 14.0 to 15.0, and the ternary components (-carbon oxide C, hereinafter abbreviated as GO), HQ, No,) at each M/F value were determined. Purification ability was measured. Table 2 shows the NOx purification rate on the lynch side (14,4 A/F) and the HC on the lean side (14,8 A/F) for each catalyst body.

It shows the CO purification rate.

Next, a test gas containing 0.21% Go, 1000 ppm Go, and 10% moisture was prepared, and this was heated from 200°C to 400°C.
The GO purification rate was 50% when the flow was carried out at a space velocity of 50,000 hr through a catalyst body whose temperature was varied up to 00°C.
The catalyst body temperature was measured as 2Tso (°C). The results are also shown in Table 2.

(Hereinafter referred to as "Kinshiro") As is clear from Table 2, the catalyst body using lime aluminate, lanthanum oxide, and the barium compound of the present invention is superior to the catalyst body using conventional lime aluminate (example). 1,2
), the NOx purification ability of platinum on the rich side is significantly improved, and it is thought that it is possible to largely replace the NOx purification ability of rhodium in this region with platinum and palladium. . A similar improvement in purification performance was obtained with palladium. Also, lanthanum, barium oxide and barium carbonate of the present invention.

By using titanium oxide or cerium oxide at the same time, the catalytic activity of the catalyst can be improved.
It was possible to reduce the activation temperature by 30-40'C.

Furthermore, while the conventional catalyst body coated with lanthanum using a cordierite carrier has low catalytic activity towards lean side p''Hc, Go, the catalyst body using lime aluminate of the present invention has high activity. Indicated.

Further, by using rhodium or ruthenium together with platinum and/or palladium, an even better catalyst could be obtained.

<Examples 12 to 22> The content of lime aluminate in the carrier was varied as shown in Table 3, and molded bodies were prepared in the same manner as in Example 1, with no catalyst material supported. Compressive strength in cell direction (
A-axis compressive strength) and spalling resistance tests were conducted. Spalling resistance test: 900°C every 60°C from 500°C
The temperature inside the furnace at which cracks first appeared in the compact was defined as the spalling resistance temperature (°C). The results are shown in Table 3.

(Margin below) As is clear from Table 3, if the content of lime aluminate in the compact is less than 15% by weight, the compressive strength will be low, and if it exceeds 60% by weight, the spalling resistance will be poor. decreased.

<Example 23> The content of lime aluminate in the molded body was 30% by weight,
Various molded bodies were prepared in the same manner as in Example 1, with the content of lanthanum oxide varied from 0.1 to 70% by weight and the balance being silica, and platinum was added to each 1 cc of molded body.
mg was supported. For each, the NOx purification ability at 14.4 μm/F, which was the same as that for Example 1,
14.8 HC purification ability at A/F was tested. The results are shown in the figure.

As is clear from the figure, a sufficient addition effect of lanthanum oxide can be obtained from 1% by weight or more, and the HC purification rate decreases when the amount exceeds 60% by weight. Therefore, the desirable addition amount of lanthanum oxide is 1% by weight.
The content is not less than 50% by weight.

Effects of the Invention As described above, according to the present invention, the catalytic activity at low temperatures is improved, and when used in a three-way catalyst for automobiles, the NOx purification ability of platinum and palladium on the rich side is significantly increased. By reducing the amount of rhodium required, costs can be reduced.

[Brief explanation of the drawing]

The figure shows the N content versus the lanthanum oxide content in the carrier.
It is a figure showing or and HC purification rate.

Claims (4)

[Claims] (1) one or more promoter substances selected from the group consisting of lanthanum oxide, barium oxide, and barium carbonate;
A catalyst body for exhaust gas purification, characterized in that a platinum group catalyst substance is supported on a carrier composed of lime aluminate as a binder. (2) The catalyst body for exhaust gas purification according to claim 1, wherein the carrier has a cocatalyst substance content of 1.0% by weight or more and 50% by weight or less. (3) The lime aluminate content in the carrier is 15% by weight.
The catalyst body for exhaust gas purification according to claim 1, wherein the amount is 50% by weight or less. (4) The exhaust gas purifying catalyst body according to claim 1, wherein the carrier contains at least one of cerium oxide and titanium oxide.