JPH10118454A - Apparatus for purifying exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attempt remarkable reduction of nitrogen oxide contained in exhaust gas over a wide temperature range. SOLUTION: An apparatus is constituted so that between an exhaust manifold 3 and an exhaust muffler 4 of an exhaust conduit 2, an oxidation catalyst 5 is arranged on the upstream side of the flow of exhaust gas, a reduction catalysts 6, 7 are arranged on the downstream side, and a hydrocarbon reducing agent is supplied from a space between them by a pump 8. In the oxidation catalyst 5, an active component of platinum or palladium is carried on an alumina carrier. A reduction catalyst is formed in two-stage structure, a reduction catalyst 6 in which at least one kind of active component selected from a group consisting of gold, silver, cobalt, and copper is carried on an alumina carrier are arranged in a preceding stage on the upstream side of the flow of exhausts gas, and a reduction catalyst 7 in which an active component of platinum, rhodium, or indium is carried on an alumina carrier is arranged in a succeeding stage on the downstream side. NO2 , after being converted into NO once, is converted into N2 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the internal combustion engine, more particularly to an exhaust gas purifying device capable of reducing the high concentration of oxygen is nitrogen oxides in the exhaust gas contained in (NO _X) from a diesel engine or the like.

[0002]

2. Description of the Related Art Catalysts capable of reducing nitrogen oxides (NO _x ) contained in exhaust gas containing nitrogen oxides and excess air, typically exhaust gas from diesel engines, include:
Conventionally, zeolite (Cu-ZSM-5) has been proposed, but this catalyst has a problem in durability because it is easily deteriorated by coexisting steam and heat, and has not been put to practical use. Currently commonly used catalysts include metal oxides such as alumina (Al ₂ O ₃ ), silica (Si
O _2), zirconia (ZrO ₂₎ or the like as a carrier, it becomes an acid salt of the noble metal dissolved in water as an active ingredient solution,
For example, the carrier is immersed in an aqueous solution of chloroplatinic acid (H ₂ PtCl ₆ .nH ₂ O), dried, fired, and supported.
In particular, platinum / alumina (Pt / Al ₂ O ₃ ) is mainly used because of its high conversion of nitrogen oxides to nitrogen (N ₂ ).

[0003] However, in the case of using any of the catalysts (including zeolite), the conversion of nitrogen oxides is attempted by utilizing the high-temperature activity of the catalyst. For example, in a low temperature range of 200 ° C. or lower, the high-temperature activity of the catalyst cannot be used, and the conversion performance of nitrogen oxides is extremely low. Therefore, there is a problem in that nitrogen oxides are hardly converted and are released to the atmosphere as they are until the temperature of the catalyst rises.

[0004] Therefore, an exhaust gas purifying apparatus provided with these catalysts has not yet obtained satisfactory exhaust gas purifying performance.

[0005]

SUMMARY OF THE INVENTION Therefore, the present invention provides an exhaust gas purifying apparatus capable of effectively reducing nitrogen oxides in exhaust gas containing nitrogen oxides and high-concentration oxygen in a wide temperature range. The purpose is to:

[0006]

Means for Solving the Problems As a result of intensive studies, the present inventor has found that the exhaust gas is brought into contact with the oxidation catalyst and then brought into contact with the reduction catalyst in the presence of a reducing agent, whereby the presence of the oxidation catalyst is reduced. Under nitrogen monoxide (NO) nitrogen dioxide (N
O ₂ ), and then, in the presence of a reducing catalyst, nitrogen dioxide reacts with the hydrocarbon-based reducing agent in a highly selective manner to form nitrogen (N
₂ ), and as a result, it was found that nitrogen oxides could be significantly reduced. As a result, an exhaust gas purifying apparatus of the present invention was proposed.

That is, in the exhaust gas purifying apparatus of the present invention, which is disposed in an exhaust pipe for discharging exhaust gas from an internal combustion engine to the outside, an oxidation catalyst is provided upstream of the flow of the exhaust gas. A reduction catalyst is provided on the downstream side, and a supply means for the hydrocarbon-based reducing agent is connected to an exhaust pipe at a position between the oxidation catalyst and the reduction catalyst. . Here, the oxidation catalyst means a catalyst that works to oxidize nitrogen oxides, and the reduction catalyst means a catalyst that works to reduce nitrogen oxides.

[0008] Preferably, the oxidation catalyst is an active component comprising platinum or palladium supported on an alumina carrier, and the reduction catalyst is one selected from the group consisting of rhodium, iridium, gold, cobalt and copper. The above active components are supported on an alumina carrier.

Another preferred embodiment of the reduction catalyst has a two-stage structure, and the upstream stage upstream of the exhaust gas flow has at least one member selected from the group consisting of gold, silver, cobalt and copper. Is disposed on the alumina carrier, and an active component selected from platinum, rhodium or iridium is carried on the alumina carrier at a downstream stage on the downstream side. In this case, the exhaust gas comes into contact with the preceding catalyst body and then comes into contact with the latter catalyst body. Therefore, once oxidized by the oxidation catalyst, NO
Nitrogen oxide converted to ₂ is mixed with hydrocarbon as a reducing agent, NO ₂ and hydrocarbon react on the reduction catalyst,
NO ₂ is reduced to N ₂ . NO ₂ has strong oxidizing power,
Strongly adsorbed on the active metal, in which that the hydrocarbon is adsorbed, because the reduction reaction of the NO _X occurs, further increases the rate of reduction of nitrogen oxides.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The following embodiments of the present invention will be described in detail, but the scope of the present invention is not limited thereto.

[0011] As shown in structure diagram 1 and 2 of the exhaust gas purifying device, the exhaust pipe 2, between the specific and the exhaust manifold 3 and the exhaust muffler 4, the exhaust gas purification device 1 of the present invention Will be arranged. FIG. 1 shows a reduction catalyst having a one-stage configuration, and FIG. 2 shows a reduction catalyst having a two-stage configuration. 1 and 2 have a common configuration, and the configuration is indicated using the same reference numeral.

In the apparatus shown in FIG. 1, between the exhaust manifold 3 and the exhaust muffler 4 in the exhaust pipe 2, an exhaust gas comprising an oxidation catalyst 5 and a reduction catalyst 6 is applied to the flow of the exhaust gas. A purifying device 1 is provided. In particular,
An oxidation catalyst 5 is provided on the upstream side, and a reduction catalyst 6 is provided on the downstream side. The oxidation catalyst body 5 and the reduction catalyst body 6 are arranged at an interval, and the supply means 8 for the hydrocarbon-based reducing agent is provided at the position between the oxidation catalyst body 5 and the reduction catalyst body 6 in the exhaust line. 2 is connected.

In the apparatus shown in FIG. 2, between the exhaust manifold 3 and the exhaust muffler 4 in the exhaust pipe 2, an oxidation catalyst 5 and reduction catalysts 6, 7 are provided for the flow of exhaust gas. An exhaust gas purification device 1 is provided. Specifically, the oxidation catalyst 5 is provided on the upstream side, and the reduction catalysts 6 and 7 are provided on the downstream side. The oxidation catalyst 5 and the reduction catalyst 6 are arranged at an interval, and the supply means 7 for supplying a hydrocarbon-based reducing agent is exhausted at a position between the oxidation catalyst 5 and the reduction catalysts 6 and 7. It is connected to the pipeline 2.

In practice, a reducing agent is pumped by a pump 9 and a proper flow rate of the reducing agent is sent to an injection nozzle via a regulating valve (not shown). The reducing agent will be injected and supplied.
In addition, both the oxidation catalyst body and the reduction catalyst body are housed in an outer cylinder such as a casing (not shown) by a known method. While the exhaust gas emitted from the internal combustion engine, for example, the engine 10 passes through the exhaust pipe 2 and is exhausted to the outside, the exhaust gas is contacted with the exhaust gas purification device 1, specifically, the catalyst body sequentially from the upstream side. Will do.

Structure and Production Method of Catalyst Body The oxidation catalyst body preferably has an active component made of platinum or palladium supported on an alumina carrier from the viewpoints of catalytic activity and heat resistance. As an alumina carrier, γ
- alumina, can be used which BET specific surface area are commercially available about 1 to 500 ² / g. However,
What can be used is not limited to these.
For example, palladium and rhodium may be used as active ingredients, and zirconia, silica and titania may be used as carriers. When the reduction catalyst has a one-stage structure, one or more active components selected from the group consisting of rhodium, iridium, gold, cobalt and copper are preferably used in view of catalytic activity and heat resistance. It is carried on a carrier, but is not limited to this. For example, platinum, silver, nickel and iron could be used as active ingredients, and zirconia, silica and titania could be used as carriers. The carrier has a particle diameter of 0.1 to
A powder of about 50 μm is preferred.

In a more preferred embodiment, the reduction catalyst has a two-stage structure, and at the upstream stage upstream of the exhaust gas flow, at least one member selected from the group consisting of gold, silver, cobalt and copper. A reduction catalyst in which the active component is supported on an alumina carrier is provided, and a reduction catalyst in which an active component made of platinum, rhodium or iridium is supported on the alumina carrier is provided downstream of the downstream stage.

The active ingredient is immersed in a carrier, and a powdery carrier is immersed in an aqueous solution obtained by dissolving a water-soluble compound containing the active ingredient, ie, a nitrate, chloride, metal chloride, or various complex salts in water. , Dried, crushed to about 10 to 50 μm, and baked to be supported. Examples of the compound include dinitrodiammine platinum (Pt)
(NH ₃ (NO ₂ )) ₂ ), palladium nitrate (Pd (N
O ₃ ) ₃ ), rhodium nitrate (Rh (NO ₃ ) ₃ ), silver nitrate (AgNO ₃ ), cobalt nitrate ((Co (NO ₃ ) ₂ ),
Copper nitrate (CuNO ₃ ), ruthenium chloride (RuCl ₃ ),
Cobalt chloride (CoCl ₂ ), copper chloride (CuCl ₂ ), rhodium chloride (Rh (NO ₃ ) ₃ ), chloroplatinic acid (H ₂ Pt)
Cl ₆ ), iridic acid chloride (H ₂ IrCl ₂ ), and chloroauric acid (HAuCl ₄ .nH ₂ O) can be used. The loading is not limited to the impregnation method, and can be performed using various known methods such as a deposition (concentration) method and an ion exchange method. Further, two or more methods can be used in combination. Drying is usually performed in air at 100 to 150 ° C. for 2 to 2 hours.
It is performed for 3 hours, and the calcination is usually 300 to 500
C. for 3-5 hours. The firing atmosphere is appropriately selected from an oxidizing atmosphere, a reducing flame, or a reducing atmosphere composed of a hydrogen gas containing a hydrogen stream, depending on the type of the compound as a precursor. The content of the active ingredient is usually 0.1
-10% by weight. Note that 10% by weight is an upper limit determined from the fact that even if it exceeds this, it is not possible to expect a corresponding improvement in the catalytic activity, and therefore may be exceeded.

Further, as another method, instead of being supported on the carrier in the form of metal ions, fine particles comprising an active metal or a metal oxide may be supported on the carrier by being fixed to the carrier using a binder.

The form of the catalyst body may be a monolith type such as a honeycomb body or a type such as a pellet. In the case of a monolith type, a catalyst component obtained by supporting an active component on a carrier is mixed with an inorganic binder such as silica sol or alumina sol and water to form a slurry, which is made of ceramics such as cordierite or stainless steel. It can be formed by coating a three-dimensional structure made of a heat and corrosion resistant metal. Usually, by weight, the catalyst components (active components + carrier):
Inorganic binder: water = 70-90: 5-30: 100-
A slurry is prepared at a ratio of 150 (parts by weight). The inorganic binder can be replaced by an organic binder up to 20 parts by weight. The structure is immersed in the obtained slurry, pulled up, dried in the air at 100 to 150 ° C. for 2 to 3 hours, and subsequently dried at 300 to 500 ° C. in the air for 3 hours.
By calcining for up to 5 hours, a finished catalyst in which the structure is coated with a layer of the catalyst component is obtained. The amount of coating on the structure is 20 to 200 g per unit volume of the structure.
/ L is preferred. In the case of molding into pellets, a catalyst component comprising an active component supported on a carrier is kneaded with an inorganic binder such as silica sol or alumina sol and water. Usually, a slurry is prepared by combining the catalyst component (active component + carrier): inorganic binder: water = 70 to 90: 5 to 30:10 to 15 by weight. In addition, the inorganic binder,
Up to 20% by weight can be replaced by an organic binder. The obtained kneaded material is granulated into pellets having a particle size of 5 to 10 mm, dried in the air at 100 to 150 ° C for 2 to 3 hours, and subsequently fired in the air at 300 to 500 ° C for 3 to 5 hours. By doing so, a finished catalyst in the form of a pellet is obtained.

[0020] Examples of the hydrocarbon reductant hydrocarbon reducing agent, for example, as gaseous, methane, ethane, propane, propylene, butylene, etc., as a liquid, pentane, hexane, octane, heptane, benzene , A single component such as toluene and xylene, and a mineral oil such as gasoline, kerosene, light oil and heavy oil can be used. In the apparatus of the present invention, gasoline and light oil can be used, and therefore, it is advantageous in particular to purify exhaust gas from an internal combustion engine using these as fuel, since there is no need to prepare a separate reducing agent. In addition, a hydrocarbon may use only 1 type and may use 2 or more types together.

[0021]

Example 1 Preparation of Catalyst Body Example 1 ( Production of Oxidation Catalyst Body 5 (Pt / Al ₂ O ₃ )): γ-alumina powder having a particle diameter of 1 μm (BET:
(200 m ² / g, 100 g) was immersed, pulled up, dried in the air at 150 ° C. for 3 hours, pulverized back to the original size, and fired at 500 ° C. in the air for 5 hours. Alumina sol and water were added to this powder in a weight ratio of powder: alumina sol: water = 80: 20: 150 to form a slurry. A honeycomb body made of cordierite was immersed in the obtained slurry, pulled up, and aired. After drying at 150 ° C. for 3 hours in air,
For 5 hours to obtain a finished catalyst. The supported amount of platinum was 2 g / L. The amount of coating on the honeycomb body was 150 g / L.

(Preparation of Reduction Catalyst 6 (Co / Al ₂ O ₃ )): A γ-alumina powder (BET: 200 m ² / g, 1000 g) having a particle size of 1 μm was immersed in an aqueous solution of cobalt nitrate and pulled up. After drying at 150 ° C. in the air for 3 hours and pulverizing, it was calcined at 500 ° C. in the air for 5 hours. Alumina sol and water were added to this powder in a weight ratio of powder: alumina sol: water = 80: 20: 150 to form a slurry. A honeycomb body made of cordierite was immersed in the obtained slurry, pulled up, and aired. After drying at 150 ° C. for 3 hours in air,
For 5 hours to obtain a completed catalyst body. The supported amount of cobalt was 1.8 g / L. Further, the coating amount on the honeycomb body was 180 g / L.

(Preparation of Reduction Catalyst 7 (Cu / Al ₂ O ₃ )): A γ-alumina powder (BET: 200 m ² / g, 1000 g) having a particle size of 1 μm is immersed in an aqueous solution of iridic acid chloride and pulled up. After drying in air at 150 ° C. for 3 hours, pulverizing back to the original size,
Calcination was performed at 5 ° C. for 5 hours. Alumina sol and water were added to this powder in a weight ratio of powder: alumina sol: water = 8.
At 0: 20: 150, they were combined into a slurry, a honeycomb body made of cordierite was immersed in the obtained slurry, pulled up, and dried at 150 ° C. in the air for 3 hours, and subsequently, at 500 ° C. in the air for 5 hours. Calcination gave a finished catalyst. The supported amount of iridium was 2.1 g / L. The amount of coating on the honeycomb body was 250 g / L.
Met.

Comparative Example 1 (Preparation of Catalyst) A Cu / Al ₂ O ₃ catalyst in the form of a honeycomb was treated in the same manner as in Example 1 to obtain a catalyst.

Example 2 (Preparation of Catalyst) An oxidation catalyst 5 (Pt / Al ₂ O ₃ ) and a reduction catalyst 6 (C
o / Al ₂ O ₃ ) and the reduction catalyst 7 (Cu / Al ₂ O ₃ ) were all produced in the form of pellets. Specifically, alumina sol and water are added to a powder carrying each corresponding active ingredient in a weight ratio of powder: alumina sol: water = 8.
Except for mixing at 0:20:15 and kneading and granulation into pellets, the same treatment as in Example 1 was carried out to obtain a finished catalyst. That is, in Example 1 and Example 2, the composition of the active component of each catalyst was the same.

Comparative Example 2 (Preparation of Catalyst) A Cu / Al ₂ O ₃ catalyst in the form of a pellet was treated in the same manner as in Example 2 to obtain a catalyst.

Evaluation Test of Catalyst Activity A catalyst body (strictly speaking, a casing containing the catalyst body) is provided in the exhaust gas purifying apparatus shown in FIG. 2 for the catalyst bodies of Examples 1 and 2. The catalysts of Comparative Examples 1 and 2 were provided in the exhaust gas purifying apparatus shown in FIG. Therefore, in Comparative Examples 1 and 2, Cu / A
l ₂ O ₃ catalyst only so that is disposed.

A simulation test was conducted under the following conditions. The reducing agent was supplied by pumping and injecting it into an exhaust pipe. Reaction gas Composition: NO: 1,000 ppm C ₃ H ₆ : 30 ppm O ₂ : 10% SO ₂ : 20 ppm H ₂ O: 4% N ₂ : Remaining Space velocity (SV): 20,000 h ⁻¹ Reducing agent Type: Propylene (100%) Flow rate: 20 mL / min The results are shown in FIGS. 3 and 4. That is, FIG. 3 shows various catalyst inlet temperatures (temperatures of exhaust gas at the inlet of the catalyst body 5) when the catalyst body of Example 1 is provided and when the catalyst body of Comparative Example 1 is provided. FIG. 4 is a diagram showing a comparison between nitrogen oxide (NO _x ) reduction rates (%), and FIG.
Nitrogen oxide (NO _x ) reduction rate at various catalyst inlet temperatures (temperature of exhaust gas at the inlet of catalyst body 5) when catalyst body of Comparative Example 2 is provided and when catalyst body of Comparative Example 2 is provided It is the figure which showed and compared (%). When the exhaust gas purifying device of the example was used, nitrogen oxides were significantly reduced as compared with the case where the exhaust gas purifying device of the comparative example was used.

[0029]

According to the exhaust gas purifying apparatus of the present invention,
Nitrogen oxides contained in exhaust gas can be significantly reduced over a wide temperature range.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a cross section of one embodiment of an exhaust gas purification device of the present invention.

FIG. 2 is a diagram schematically showing a cross section of another embodiment of the exhaust gas purifying apparatus of the present invention.

FIG. 3 is a diagram showing a comparison between nitrogen oxide (NO _x ) reduction rates (%) when the catalyst body of Example 1 is provided and when the catalyst body of Comparative Example 1 is provided. .

FIG. 4 is a diagram showing a comparison between nitrogen oxide (NO _x ) reduction rates (%) when the catalyst body of Example 2 is provided and when the catalyst body of Comparative Example 2 is provided. .

[Explanation of symbols]

1: Exhaust gas purifier, 2: Exhaust line, 3: Exhaust manifold, 4: Exhaust muffler, 5: Oxidation catalyst, 6,
7: reduction catalyst, 8: supply means of hydrocarbon-based reducing agent,
9: Pump, 10: Engine

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01J 23/46 311 B01J 23/50 A 23/50 23/52 A 23/52 23/72 A 23/72 23/89 A23 / 75 F01N 3/08 B 23/89 3/10 A F01N 3/08 3/28 301E 3/10 B01D 53/34 129B 3/28 301 53/36 102H B01J 23/74 311A

Claims (4)

[Claims] 1. An exhaust gas purifying device disposed in an exhaust pipe for discharging exhaust gas from an internal combustion engine to the outside, wherein an oxidation catalyst is provided on an upstream side with respect to a flow of the exhaust gas. An exhaust gas purifying apparatus, wherein a reduction catalyst is provided on the downstream side, and a supply means for a hydrocarbon-based reducing agent is connected to an exhaust pipe at a position between the oxidation catalyst and the reduction catalyst. . 2. The apparatus according to claim 1, wherein the oxidation catalyst is an active component comprising platinum or palladium supported on an alumina carrier. 3. The method according to claim 1, wherein the reduction catalyst is rhodium, iridium,
3. The device according to claim 1, wherein at least one active component selected from the group consisting of gold, cobalt and copper is supported on an alumina carrier. 4. The reduction catalyst has a two-stage structure, and one or more active components selected from the group consisting of gold, silver, cobalt and copper are provided in the upstream stage upstream of the flow of exhaust gas. A reduction catalyst body supported on a carrier is provided, and a reduction catalyst body formed by supporting an active component selected from platinum, rhodium or iridium on an alumina carrier is provided at a downstream stage downstream. 3. The method according to claim 1, wherein
An apparatus according to claim 1.