JPH057066B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a catalyst body that purifies harmful components in exhaust gas mainly generated from internal combustion engines, domestic combustors, etc., and in particular, oxidizes carbon monoxide and hydrocarbons.
The present invention relates to a catalyst body that reduces and purifies nitrogen oxides. Conventional technology Conventionally, this type of catalyst has been made by supporting a platinum group metal catalyst on a carrier mainly made of lime aluminate (Japanese Patent Application Laid-Open No. 1983-35886), or by adding titanium oxide to suppress sintering of catalyst particles. Added (Tokkai Sho)
56-126447) 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, and the latter catalyst shows considerable improvement in preventing thermal deterioration. The improvement in low-temperature catalyst activity was insufficient. In addition, in catalyst bodies that require three-way catalyst performance, such as catalysts for purifying automobile exhaust gas, Rh is essential in conventional catalyst bodies, and Rh is 1/5 to 1/11 of Pt used at the same time. It is used. On the other hand, the production amount of Rh is less than 1/11 that of platinum, and the price is about 2 times that of platinum.
Since Rh is twice as expensive, there is a strong desire to reduce the amount of Rh used, and the conventional catalysts described above were 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 reduces the amount of catalyst used and the associated cost. The purpose is to provide a catalyst body. Means for Solving the Problems The catalyst body of the present invention has platinum added to a carrier composed of 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 group catalyst material. Function The lime aluminate used as a binder has hydraulic properties, so it does not require the sintering process that is required when manufacturing conventional catalyst supports such as cordierite and mullite. A large catalyst support can be obtained. This increase in specific surface area eliminates the need for wash coating, which is necessary for increasing the specific surface area in the conventional sintered carrier. Since lime aluminate has a solid base catalytic ability, it shows very good activity in purifying harmful components in exhaust gas, especially hydrocarbon compounds (hereinafter abbreviated as HC). The content of lime aluminate in the carrier is 15% by weight
above, and below 50% by weight. If the content of lime aluminate is less than 15% by weight, sufficient mechanical strength cannot be expected, and if it exceeds 50% by weight, the spalling resistance properties will be significantly reduced. Lime aluminate has the general formula mAl ₂ O ₃ nCaO, and contains 50% by weight or more of alumina, 85
It is preferably at most 60% by weight and at most 80% by weight. 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 has excellent adsorption ability for nitrogen oxides (hereinafter abbreviated as NOx) and also has a high affinity for hydrogen. Therefore, by using it together with platinum group metals Pt and Pd, the above-mentioned Pt and Pd can improve the purification characteristics of nitrogen oxides contained in exhaust gas when the fuel is burnt on the richer side than the stoichiometric air-fuel ratio. It acts as a co-catalyst material that contributes and significantly improves this property. Further, barium oxide and barium carbonate have similar effects. Lanthanum oxide and barium oxide are prepared by starting from their chlorides, hydroxides, acetates, oxalates, sulfates, nitrates, carbonates, ammonium sulfates, and ammonium nitrates and calcining them before use, or There is a method in which the molded body is fired and then used as an oxide, and a method in which the lanthanum compound and barium compound are converted into oxides at the same time as the catalyst is supported in the firing process of supporting the catalyst. 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% by weight or more and 50% by weight or less. If the content is less than 1% by weight, a sufficient effect of the addition of the promoter substance cannot be expected, and if it exceeds 50% by weight, not only a commensurate increase in the promoter action cannot be expected, but also the HC purification ability is adversely affected. It starts to decline. In general, when used together with Pt or Pd, lanthanum oxide can reduce NOx contained in the exhaust gas (hereinafter referred to as rich side exhaust gas) produced when operating at a fuel ratio higher than the stoichiometric air-fuel ratio.
Although it significantly improves the purification properties of Pt and Pd,
At the same time, it reduces the ability to purify HC contained in the exhaust gas (hereinafter referred to as exhaust gas on the lean side) generated when the engine is operated under conditions where the fuel is leaner than the stoichiometric air-fuel ratio. The same applies to barium oxide and carbonate. This phenomenon is a very serious problem especially when used as an automobile three-way catalyst, and it is difficult to solve this problem with the catalyst body using the conventional sintered catalyst carrier such as cordierite mentioned above. Ta. On the other hand, as mentioned above, since the catalyst carrier of the present invention contains aluminate lime having solid base catalytic ability, the HC purifying effect thereof makes it possible to obtain a catalyst body without a decrease in HC purifying ability even in lean side exhaust gas. . Further, by simultaneously using cocatalyst materials such as lanthanum oxide, barium oxide, barium carbonate, and lime aluminate, the catalytic activity at low temperatures is greatly improved. Furthermore, by using cerium oxide or titanium oxide together with the above-mentioned promoter, the low-temperature catalytic activity is further increased. In particular, since cerium oxide has oxygen storage ability, when used as an automobile catalyst,
A wide window width can also be obtained, which is desirable. Cerium compounds that become cerium oxide by heating include its hydroxide, chloride, acetate, oxalate,
sulfates, nitrates, carbonates, ammonium sulfates,
Examples include ammonium nitrate salts. A desirable content of cerium oxide in the carrier is 5% by weight or more,
63% by weight or less. Titanium oxide similarly 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, and in the present invention, a metal oxide semiconductor of lanthanum and titanium is partially formed, so that this becomes a co-catalyst. It is thought that this function acts as a catalyst to improve 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 granule or honeycomb shape, and various molding methods such as extrusion molding method and corrugating method can be used. The platinum group catalyst materials used in the present invention include Pt,
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 can be improved, and heat-resistant base aggregates include silica-based base aggregate, silica-alumina-based base aggregate,
There is an alumina base aggregate, and the minerals include silicate minerals, mullite, corundum, sillimanite, β
- Alumina, as well as magnesia, chromium, dolomite, magne black, and chromag-based materials can be used. Examples Examples of the present invention will be described below. <Examples 1 to 8> Lanthanum oxide (La ₂ O ₃ ), barium oxide, barium carbonate, lime aluminate, titanium oxide, cerium oxide (CeO ₂ ), and silica as a heat-resistant base aggregate are shown in Table 1. After mixing with the following composition and adding an appropriate amount of water, the cell wall thickness is 0.25 mm and the cell density is 0.25 mm.
It was extruded into a honeycomb shape of 400 cells/in ² , cured and dried, and then baked at 800°C to form a carrier. The catalysts of Examples 1 to 8 were obtained by supporting 1 mg of platinum per 1 c.c. of the carrier using chloroplatinic acid. <Comparative Examples 1 to 3> Supports having the compositions of Comparative Examples 1 and 2 shown in Table 1 were prepared in the same manner as in Examples 1 to 8, and the same amount of platinum as in the above Examples was supported for comparison. Catalyst bodies of Examples 1 and 2 were obtained. In addition, lanthanum nitrate was used on a cordierite honeycomb molded body (average cell wall thickness 0.25 mm, cell density 400 cells/in ² ) having an alumina coating layer, and by thermal decomposition it was converted into lanthanum oxide at a rate of 2% of the molded weight. After supporting the catalyst in an amount equal to % by weight, a catalyst of Comparative Example 3 was obtained in which 1 mg of platinum was supported per 1 c.c. of the support in the same manner as in the above example.

【table】

[Table] <Examples 9 to 11> Catalyst bodies of Examples 9 to 11 were prepared in which the honeycomb molded body used as the carrier in Example 1 supported platinum, palladium, rhodium, or ruthenium in the amount shown in Table 2. did. 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 catalytic performance tests. That is, an engine with a displacement of 2000 c.c. was used, the torque was adjusted at a rotation speed of 1800 rpm, the catalyst inlet temperature was 500°C ± 10°C, and the engine was operated with a space velocity relative to the catalyst of 50000 hr ^-1 . Under these conditions, the air-fuel ratio (hereinafter abbreviated as A/F) was varied from 14.0 to 15.0, and the ternary components (carbon monoxide (hereinafter referred to as CO), HC, NOx) were purified at each A/F value. The performance was measured. Second
The table shows the NOx purification rate on the rich side (14.4 A/F) and the HC and CO purification rate on the lean side (14.8 A/F) for each catalyst body. Next, a test gas containing 1% O ₂ , 1000 ppm CO, and 10% moisture was prepared, and this was applied to a catalyst body whose temperature was varied from 200°C to 400°C at various space velocities.
The catalyst temperature ^at which the CO purification rate was 50% at that time was measured as T50 (°C). The results are also shown in Table 2.

【table】

[Table] As is clear from Table 2, the catalyst body using lime aluminate, lanthanum oxide, and the barium compound of the present invention is compared with the catalyst body using conventional lime aluminate (Examples 1 and 2). Compared to this, the NOx purification ability of platinum on the rich side has been significantly improved, and it is thought that it is possible to replace much of the NOx purification ability in this area with platinum and palladium, which previously relied on rhodium. . A similar improvement in purification performance was obtained with palladium. Furthermore, by simultaneously using lanthanum, barium oxide, and barium carbonate of the present invention, and titanium oxide or cerium oxide, the catalytic activity of the catalyst can be further improved, and the activation temperature for CO can be lowered to 30 to 40°C.
It was possible to reduce this. Furthermore, compared to the conventional catalyst body using a cordierite carrier and coated with lanthanum, which had low catalytic activity against HC and CO on the lean side, the catalyst body using lime aluminate of the present invention showed high activity. . 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, molded bodies were prepared in the same manner as in Example 1, and without supporting a catalyst substance,
Compressive strength in the cell direction (A-axis compressive strength) and spalling resistance tests were conducted. The spalling resistance test was conducted from 500°C to 900°C at 50°C intervals, and the temperature in the furnace when the molded article first cracked was taken as the spalling resistance temperature (°C). The results are shown in Table 3.

[Table] As is clear from Table 3, when the content of lime aluminate in the compact was less than 15% by weight, the compressive strength was low, and when it exceeded 50% by weight, the spalling resistance was reduced. <Example 23> The content of lime aluminate in the molded body is 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 each of them was loaded with 1 mg of platinum per c.c. did. For each, the same 14.4A/
NOx purification ability at F, HC at 14.8A/F
Purification ability 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 if it exceeds 50% by weight, the HC purification rate on the lean side decreases. Therefore, the desirable addition amount of lanthanum oxide is 1% by weight or more and 50% by weight or less. Effects of the Invention As described above, according to the present invention, the catalyst activity at low temperatures is improved, and when used in a three-way catalyst for automobiles, platinum and palladium are
Since the NOx purification ability is significantly increased, the amount of rhodium required can be reduced, resulting in lower costs.

[Brief explanation of drawings]

The figure shows the NOx and HC purification rates relative to the lanthanum oxide content contained in the carrier.

Claims (1)

[Scope of Claims] 1. A heat-resistant material containing one or more promoter substances selected from the group consisting of lanthanum oxide, barium oxide, and barium carbonate, lime aluminate as a binder, and as necessary. A catalyst body for exhaust gas purification, characterized in that a platinum group catalyst substance is supported on a carrier composed of a base aggregate. 2 The promoter content of the carrier is 1.0% by weight
The catalyst body for exhaust gas purification according to claim 1, wherein the amount is 50% by weight or less. 3. Claim 1, wherein the content of lime aluminate in the carrier is 15% by weight or more and 50% by weight or less.
Catalyst body for exhaust gas purification as described in . 4. Contains one or more promoter substances selected from the group consisting of lanthanum oxide, barium oxide, and barium carbonate, lime aluminate as a binder, and at least one of cerium oxide and titanium oxide, as necessary. A catalyst body for exhaust gas purification, characterized in that a platinum group catalyst substance is supported on a carrier made of a heat-resistant base aggregate.