JPH09173841A - Catalyst for cleaning exhaust gas from diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the discharge of particulate and sulfate contained in an exhaust gas from a diesel engine and improve a HC and CO cleaning rate in a low temperature zone. SOLUTION: This catalyst for cleaning an exhaust gas from a diesel engine is structurally designed so that a heat-resistant inorganic oxide layer containing a catalytic component deposited on a catalyst carrier. In this case, the heat- resistant inorganic oxide layer composed of at least, one type of component selected from among silica, titania and zirconia, and potassium titanate. In addition, the heat-resistant inorganic oxide layer contains at least, one type of catalytic component selected from among platinum, palladium and rhodium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst. Specifically, carbon monoxide (C, which is a harmful component contained in the exhaust gas from a diesel engine)
O), hydrocarbons (HC) and soluble organic components (SO
F: Soluble Organic Fractio
The present invention relates to an exhaust gas purifying catalyst for a trap type for removing n) or an open type for straight flow.

[0002]

2. Description of the Related Art With regard to gasoline engines, harmful regulations in exhaust gas have been steadily reduced due to strict regulations on exhaust gas and progress in technology capable of coping with the regulations. However, regarding the diesel engine, due to the unique fact that harmful components are mainly emitted as particulates, the regulations and the development of technology are behind the gasoline engine,
The development of an exhaust gas purification device that can reliably purify is desired.

As a diesel engine exhaust gas purifying apparatus which has been developed to date, a trap type (without a catalyst and a catalyst) and an open type SOF decomposition catalyst are roughly classified. Of these, the trap type without catalyst is
It traps particulates contained in the exhaust gas of a diesel engine to suppress emissions, and is usually used when regenerating a catalyst support that burns and removes SOF and soot (dry suit) that are accumulated particulates.
Since heating is required, there are problems such as cracking of the catalyst support.

Further, the trap type with catalyst purifies particulates contained in the exhaust gas of a diesel engine together with CO and HC.
Japanese Patent Publication No. 75 discloses a catalyst for purifying exhaust gas, which carries palladium and at least one selected from praseodymium, neodymium and samarium. On the other hand, open type SOF decomposition catalyst is, for example, Japanese Patent Publication No. 3-382.
As disclosed in Japanese Patent Publication No. 55, a catalyst in which an oxidation catalyst such as a platinum group metal is carried on a catalyst carrying layer such as activated alumina is used as in the case of a gasoline engine.
As a result, S in the particulate along with CO and HC
Purify by oxidizing and decomposing OF. This open type SOF decomposition catalyst has a drawback that the removal rate of dry suit is low, but the amount of dry suit can be reduced by improving the diesel engine and the fuel itself, and a large amount of regeneration processing device is not required. It is being studied because of its merits.

[0005]

However, it has been difficult to reduce the emission amount of particulates with the above-mentioned conventional catalysts for trap-type and open-type exhaust gas purification that carry the catalyst. That is, the activated alumina layer used in the conventional catalyst has a property of adsorbing SO ₂ . Therefore, SO ₂ contained in the exhaust gas from the diesel engine is adsorbed on the activated alumina layer, and when the temperature of the catalyst becomes high, the adsorbed SO ₂ is oxidized by the catalytic action of the catalytic metal. Therefore, since SO ₂ is discharged as SO ₃ , there is a problem that the amount of particulates increases. This is because SO ₂ is not measured as particulates, but SO ₃ is measured as particulates. Particularly in a diesel engine, oxygen gas is sufficiently present in the exhaust gas and SO ₂
Oxidation reaction easily occurs. SO ₃ easily reacts with water vapor present in a large amount in the exhaust gas to form sulfuric acid mist. On the other hand, when SO ₂ is released as it is, SO ₃ is produced by reacting with O ₃ in the atmosphere, but SO ₂ is generated in the atmosphere.
And O ₃ do not have a high probability of reacting with each other, it takes time to generate SO ₃ , and there is no problem as compared with the case where SO ₃ is released into the atmosphere. Therefore, we want to reduce the release of SO ₃ into the atmosphere as much as possible.

The present invention has been made in view of the above circumstances, and suppresses the release of sulfates, and HC, C
The purpose is to improve the purification rate of O 2.

[0007]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventors have found that a catalyst composition that can improve the purification performance of the catalyst and suppress the release of sulfate as compared with the conventional catalysts. Heading The present invention has been completed. That is, the diesel engine exhaust gas-purifying catalyst of the present invention is an exhaust gas-purifying catalyst having a heat-resistant inorganic oxide layer containing a catalyst component on a catalyst support, and the heat-resistant inorganic oxide layer is silica. , Titania, and zirconia, and potassium titanate, and the heat-resistant inorganic oxide layer contains at least one catalyst component of platinum, palladium, and rhodium. Is characterized by.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The catalyst for purifying exhaust gas of a diesel engine of the present invention comprises a heat resistant inorganic oxide layer containing at least one selected from silica, titania, and zirconia.
Formed with potassium titanate. When the heat-resistant inorganic oxide layer has the above-described structure, it is possible to suppress the release of sulfate and improve the purification rate of HC and CO in the low temperature range.

The amount of potassium titanate contained in the heat-resistant inorganic oxide layer is 20 per unit volume of the catalyst.
It is preferably -60 g. If the amount of potassium titanate supported is less than 20 g / L, sufficient catalytic activity may not be obtained. Further, if the supported amount exceeds 60 g / L, even if the supported amount of potassium titanate is further increased, the activity is slightly improved and it is not preferable. Particularly, when the supported amount is 30 to 40 g / L, it is more preferable in terms of catalyst activity and cost.

The coating amount on the support of one or more selected from silica, titania, and zirconia constituting the heat-resistant inorganic oxide layer is 40 to 80 g per 1 liter of the unit volume of the catalyst. Is preferred. If the coating amount is less than 40 g / L, sufficient catalytic activity may not be obtained. Further, if the coating amount exceeds 80 g / L, even if the coating amount is further increased, the activity is slightly improved and it is not preferable. In particular, the coat amount is 50
When it is up to 70 g / L, it is more preferable in terms of catalytic activity and cost.

At least one of silica, titania, and zirconium used in the heat-resistant inorganic oxide layer is preferably in the form of powder or sol, and although it may be used alone, it is desirable to mix powder and sol. The particle size of the inorganic oxide is preferably 60 μm or less. For inorganic oxides of 60 μm or more, catalyst components such as platinum, palladium,
A catalyst supporting at least one kind of rhodium cannot obtain sufficient catalytic activity.

The amount of platinum supported on the catalyst component is preferably 0.01 to 5.0 g per 1 liter of the unit volume of the catalyst. If the amount of platinum supported is less than 0.01 g / L, sufficient catalytic activity may not be obtained. Further, when the amount of platinum supported exceeds 5.0 g / L, even if the amount of platinum supported is further increased, the improvement in activity is slight and expensive. Especially,
A platinum loading of 0.1 to 3.0 g / L is more preferable in terms of catalytic activity and cost.

The amount of palladium supported is 1 unit volume of the catalyst.
It is preferably 0.1 to 5.0 g per liter.
When the amount of palladium supported is less than 0.1 g / L, sufficient catalytic activity may not be obtained. Further, when the amount of palladium carried exceeds 5.0 g / L, even if the amount of palladium carried is further increased, the activity is slightly improved and becomes expensive. Particularly, the amount of palladium carried is 0.5 to 3.0 g / L
Is more preferable in terms of catalyst activity and cost.

The amount of rhodium supported is preferably 0.01 to 1.0 g per 1 liter of the unit volume of the catalyst.
If the amount of rhodium supported is less than 0.01 g / L, sufficient catalytic activity may not be obtained. Further, when the amount of rhodium carried exceeds 1.0 g / L, even if the amount of rhodium carried is further increased, the activity improvement is slight and expensive.
In particular, when the supported amount of rhodium is 0.05 to 0.5 g / L, it is more preferable in terms of catalytic activity and cost.

According to the present invention, by incorporating a potassium titanate component in the heat-resistant inorganic oxide layer, sulfate can be suppressed and, further, a function of removing harmful components such as HC, CO and SOF at a low temperature range is large. Can be improved. In the exhaust gas-purifying catalyst of the present invention, the heat-resistant inorganic oxide layer is preferably composed of potassium titanate and at least one of silica, titania, and zirconia. Zeolite may be contained, but in that case, it is preferable that the silica / alumina ratio is as high as about 30/1 to 100/1. The heat-resistant inorganic oxide layer containing at least one of silica, titania, and zirconia absorbs less SO ₂ , and produces less SO ₃ by reacting with a catalyst component such as platinum.

As described above, alumina such as activated alumina is not preferable because it absorbs SO ₂ a lot and a large amount of SO ₃ is produced by the reaction with a catalyst component such as platinum. The silica, titania, and zirconia constituting the heat-resistant inorganic oxide layer of the present invention preferably have a particle size of 60 μm or less. If the particle size exceeds 60 μm, sufficient catalytic activity cannot be obtained. The mechanism is not clear, but it is presumed as follows.

The catalyst for purifying exhaust gas from diesel engine of the present invention comprises a mixed layer of potassium titanate and at least one of silica, titania and zirconia, and at least one of platinum, palladium and rhodium which are catalyst components. Is. The mixed layer comprises at least one of potassium titanate and silica, titania, and zirconia.
The seeds are uniformly mixed, and powdered silica, titania,
And potassium titanate is present in contact with at least one of zirconia, or at least one of silica, titania, and zirconia is present in contact with the periphery of potassium titanate.

The catalyst component supported on the thus-formed mixed layer is supported on at least one of potassium titanate, silica, titania, and zirconia. The catalyst component supported on potassium titanate changes its electronic state due to the effect of K ₂ O, which is an alkaline component stably existing in potassium titanate, and suppresses the SO ₂ oxidation reaction. Also, most of the catalyst components supported on at least one of silica, titania, and zirconia contain at least one of silica, titania, and zirconia.
Since the seed is in contact with potassium titanate, the electronic state is changed by K ₂ O in potassium titanate, and the oxidation reaction of SO ₂ can be suppressed.

Siri not mixed with potassium titanate
White for at least one of mosquito, titania, and zirconia
In the case of a catalyst supporting a catalyst component such as gold, the catalyst component such as platinum
HC and SO in the exhaust gas above_TwoBoth of the oxidation reactions
Waking up and purifying HC and SO _TwoBy the oxidation reaction of
Fate is generated. From this, silica and titani
A, and at least one of zirconia is 70 g / L or less
At the top, K in potassium titanate_TwoNot in contact with O
The number of sites is increased, and the amount of sulfate produced is increased. Ma
At least silica, titania, and zirconia
When the particle size of one kind exceeds 60 μm, silica, titania,
And an increase in the amount of at least one of zirconia
The effect increases the number of parts that are not in contact with potassium titanate.
In addition, a large amount of sulfate is generated on the catalyst component
It is.

From the above, the catalyst for purifying diesel engine exhaust gas of the present invention is a catalyst in which a catalyst component is carried on a component obtained by uniformly contact-mixing potassium titanate with at least one of silica, titania, and zirconia. ,
It is a catalyst that can purify HC in exhaust gas at a low temperature and produces a small amount of sulfate at a high temperature. The exhaust gas purifying catalyst of the present invention does not substantially contain alumina as a component for forming the heat resistant inorganic oxide layer, except for those mixed as impurities.

The most suitable catalyst for purifying exhaust gas of diesel engine of the present invention is a catalyst in which at least one of platinum, palladium and rhodium is contained as a catalyst component in a heat resistant inorganic oxide containing potassium titanate and silica. preferable.

[0022]

EXAMPLES The present invention will be described in detail below with reference to examples, but it goes without saying that the scope of the present invention is not limited to these examples. Example 1 A cordierite monolithic support having a cell size of 400 cells / in ² , a diameter of 80 mm, and a length of 95 mm was applied to silica powder (40 g) having an average particle diameter of 10 μm, and the average minor axis and major axis were 0.5 μm and 15 μm, respectively. Of potassium titanate (40 g), silica sol (silica solid content: 20 g) and deionized water (100 g) are coated, dried, and calcined at 500 ° C. for 1 hour to obtain silica and silica on the monolith support. A heat resistant inorganic oxide layer containing potassium titanate was formed. This heat-resistant inorganic oxide layer is formed of silica and potassium titanate in amounts of 60 g and 40 g, respectively, per 1 liter of the unit volume of the catalyst.

Next, the support was immersed in an aqueous solution of chloroplatinic acid to carry 1.0 g of platinum per unit volume of the catalyst to obtain a catalyst 1 shown in Table 1. Example 2 A cordierite monolithic support having a cell size of 400 cells / in ² , a diameter of 80 mm, and a length of 95 mm was used, and titania powder (40 g) having an average particle size of 0.7 μm and an average minor axis and a major axis of 0.5 μm, respectively. , 15 μm potassium titanate (40 g), titania sol (titania solid content 2
0 g) and deionized exchanged water (100 g) are coated, dried and then calcined at 500 ° C. for 1 hour,
A heat resistant inorganic oxide layer containing titania and potassium titanate was formed on a monolith support. This heat-resistant inorganic oxide layer is formed of titania and potassium titanate in amounts of 60 g and 40 g, respectively, per 1 liter of the unit volume of the catalyst.

Next, the support was dipped in a palladium nitrate solution to carry 1.0 g of palladium per 1 liter of the catalyst in a unit volume to obtain a catalyst 2 shown in Table 1. The catalyst composition is shown in Table 1. (Example 3) A monolithic support made of cordierite having a cell size of 400 cells / in ² , a diameter of 80 mm, and a length of 95 mm was added to a zirconia powder (80 g) having an average particle diameter of 0.5 μm, and an average short diameter and a long diameter of 0.5 μm. , 15 μm potassium titanate powder (50 g), zirconia sol (20 g of zirconia solids) and deionized exchanged water (150 g) were coated, dried and calcined at 500 ° C. for 1 hour to give a monolith support. A heat resistant inorganic oxide layer containing zirconia and potassium titanate was formed thereon.
In this heat-resistant inorganic oxide layer, zirconia and potassium titanate are added to 100 parts of each per unit volume of the catalyst.
g, 50 g.

Next, the support was dipped in a rhodium nitrate solution to carry 1.0 g of rhodium per unit volume of the catalyst to obtain a catalyst 3 shown in Table 1. (Example 4) The catalyst 1 obtained in Example 1 was further immersed in a rhodium nitrate solution to carry 0.2 g / L of rhodium per unit volume of the catalyst to obtain a catalyst 4 shown in Table 1.

(Example 5) The catalyst 2 obtained in Example 2 was further immersed in a rhodium nitrate solution to give a catalyst of 0.
A catalyst 5 shown in Table 1 was obtained by supporting 2 g / L of rhodium. (Example 6) The heat-resistant inorganic oxide layer formed on the support in Example 1 was immersed in an aqueous solution of chloroplatinic acid, then a solution of palladium nitrate, and then a solution of rhodium nitrate to form 0.5 g / L of the catalyst per unit volume. Platinum and palladium, and 0.
A catalyst 6 shown in Table 1 was obtained by supporting 2 g / L of rhodium.

[0027]

[Table 1]

(Comparative Example 1) 400 cells / in ² , diameter 8
A cordierite monolithic support having a length of 0 mm and a length of 95 mm was coated with activated alumina powder having an average particle size of 5 μm
g), a hydrated alumina (5 g) and deionized exchanged water (150 g) are coated and dried, then 5
Firing was performed at 00 ° C. for 1 hour to form a heat resistant inorganic oxide layer composed of activated alumina on the monolith support.

Next, the monolith support having the heat-resistant inorganic oxide layer as a support was immersed in an aqueous solution of chloroplatinic acid to carry 1.0 g / L of platinum per unit volume of the catalyst, and the results are shown in Table 1. Catalyst A was obtained. (Comparative Example 2) A silica powder (100 g) having a mean particle diameter of 5 μm, a silica sol (50 g in terms of silica solid content) and deionization were applied to a monolithic support made of cordierite having a diameter of 80 mm and a length of 95 mm and 400 cells / in ² . Water (100
g) was coated and dried, and then baked at 500 ° C. for 1 hour to form a heat resistant inorganic oxide layer composed of silica on the monolith support.

Next, the support B having the heat-resistant inorganic oxide layer formed thereon is immersed in an aqueous solution of chloroplatinic acid to carry 1.0 g / L of platinum per unit volume of the catalyst, and the catalyst B shown in Table 1 is used.
I got (Comparative Example 3) 400 cells / in ² , diameter 80 mm, length 95 mm, made of cordierite monolith support, titania powder (100 g) having an average particle size of 0.7 μm, titania sol (solid content 20 g) and deionized. Exchanged water (200
g) was coated and dried, and then baked at 500 ° C. for 1 hour to form a heat-resistant inorganic oxide layer composed of titania on the monolith support.

Next, the support having the heat-resistant inorganic oxide layer formed thereon was immersed in an aqueous solution of palladium nitrate to carry 1.0 g / L of palladium per unit volume of the catalyst to prepare the catalyst C shown in Table 1. Obtained. (Comparative Example 4) A zirconia powder (100 g) having a mean particle size of 0.7 μm, a zirconia sol (solid content: 20 g) and a desorbed material were applied to a cordierite monolithic support having a diameter of 80 mm and a length of 95 mm of 400 cells / in ² . Deionized water (2
00g) and then dried to obtain a slurry of 500
The mixture was baked at 1 ° C. for 1 hour to form a heat resistant inorganic oxide layer composed of zirconia on the monolith support.

Next, the support having the heat-resistant inorganic oxide layer formed thereon was dipped in an aqueous solution of rhodium nitrate to carry 1.0 g / L of rhodium per unit volume of the catalyst to prepare Catalyst D shown in Table 1. Obtained. (Comparative Example 5) The catalyst A obtained in Comparative Example 1 was further immersed in a rhodium nitrate solution to carry 0.2 g / L of rhodium per unit volume of the catalyst to obtain a catalyst E shown in Table 1.

(Comparative Example 6) The catalyst B shown in Table 1 was prepared by further immersing the catalyst B obtained in Comparative Example 2 in a rhodium nitrate solution to carry 0.2 g / L of rhodium per unit volume of the catalyst.
I got (Comparative Example 7) The catalyst C obtained in Comparative Example 3 was further immersed in a rhodium nitrate solution to carry 0.2 g / L of rhodium per unit volume of the catalyst to obtain a catalyst G shown in Table 1.

(Comparative Example 8) The amount of platinum supported on the catalyst A of Comparative Example 1 was reduced to half, and the catalyst A was immersed in a palladium nitrate solution and a rhodium nitrate solution to give 0.5 per unit volume of the catalyst.
A catalyst H shown in Table 1 was obtained by supporting platinum and palladium in an amount of g / L and rhodium in an amount of 0.2 g / L.

(Comparative Example 9) The amount of platinum supported on the catalyst B of Comparative Example 2 was reduced to half, and the catalyst B was immersed in a palladium nitrate solution and a rhodium nitrate solution to give 0.5 per unit volume of the catalyst.
A catalyst I shown in Table 1 was obtained by supporting platinum and palladium in an amount of g / L and rhodium in an amount of 0.2 g / L. (Evaluation method) A catalyst was attached to a 3.6-liter direct-injection diesel engine, and the engine was operated for 500 hours at a full throttle at the rated point, and then H
C, CO, particulates and HC, C of catalyst output gas
O and particulates were analyzed and the purification rate was calculated by the following formula. The temperature of the incoming gas at this time was 250 ° C., the particulates were collected on the filter using a dilution tunnel to collect the SOF, and the particulates on the filter were quantified by Soxhlet extraction. Next, the torque was set to 25 kW, the catalyst introduction gas temperature was set to 350 ° C., the particulates of the incoming gas and the catalyst outgoing gas were analyzed, and the purification rate was calculated.

[0036]

[Equation 1] The results are shown in Table 1.

As shown in Table 1, each of the catalysts in the examples had 25
Maintains a high purification rate of HC and CO at 0 ° C, and further 350 ° C
The conversion rate of particulates is excellent. On the other hand, in the comparative example which does not contain potassium titanate and has the same amount of the catalyst metal supported as in the example, HC and CO at the same level at 250 ° C.
However, the conversion rate of particulates shows a negative value. This indicates that SO ₂ is oxidized by the oxygen gas contained in the exhaust gas of the diesel engine to generate SO ₃ . This is SO
_{This is because 2} is not measured as particulates, but SO ₃ is measured as particulates. In particular, in the case of a platinum catalyst, the oxidation reaction is likely to proceed and the negative value of the particulate conversion rate is large.

Although the conversion rate of particulates is slightly improved by using rhodium in the catalyst, it can be seen that the comparative example has a smaller conversion rate of particulates as compared with the Examples having the same amount of catalyst metal. Furthermore, the results in Table 1 show that the catalyst containing SiO ₂ in the heat-resistant inorganic oxide layer has a higher HC and CO purification ability than other catalysts and a high particulate conversion rate.

As described above, in the diesel engine exhaust gas purifying catalyst of this embodiment, the conversion rate of particulates can be increased by making potassium titanate (40 g / L amount) present in the heat resistant inorganic oxide layer. As a result, the discharge of particulates can be suppressed.

[0040]

According to the diesel engine exhaust gas purifying catalyst of the present invention having the heat-resistant inorganic oxide layer having the above-mentioned constitution and containing potassium titanate, the purifying rate of CO and HC in the exhaust gas discharged from the diesel engine is improved. Can be enhanced in the low temperature range, and the generation of particulates can be suppressed.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Sakano, Nagakute-cho, Aichi-gun, Aichi Prefecture, Nagatoji 1 1 at 41 Yokochi, Toyota Central Research Institute Co., Ltd. (72) Inventor, Yoko Kumai Nagakute-machi, Aichi-gun, Aichi Prefecture 1st 41st of the Yokomichi Toyota Central Research Institute Co., Ltd. (72) Inventor Tetsuo Nagami 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Norihiko Aono 7800 Chihama, Daito Town, Ogasa County, Shizuoka Prefecture Address Cataler Industry Co., Ltd. (72) Inventor Koichi Kasahara 7800 Chihama, Daito-cho, Ogasa-gun, Shizuoka Prefecture Cataler Industry Co., Ltd. (72) Inventor Shigeji Matsumoto 7800 Chihama, Daito-cho, Shizuoka Prefecture Cataler Industry Co., Ltd.

Claims (3)

[Claims] 1. A catalyst for exhaust gas purification having a heat-resistant inorganic oxide layer containing a catalyst component on a catalyst support, wherein the heat-resistant inorganic oxide layer is at least one selected from silica, titania, and zirconia. And a potassium titanate, and the heat-resistant inorganic oxide layer contains at least one catalyst component of platinum, palladium, and rhodium. . 2. The amount of potassium titanate constituting the heat-resistant inorganic oxide layer is 20 to 60 g per liter of contact volume.
The catalyst for purifying exhaust gas from a diesel engine according to claim 1, wherein 3. The catalyst for purifying exhaust gas of diesel engine according to claim 1, wherein the heat-resistant inorganic oxide layer contains at least silica.