JP4997967B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification device for an internal combustion engine.

  Conventionally, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-89246, an exhaust gas purifying apparatus having a NOx occlusion reduction type catalyst (hereinafter referred to as “NSR catalyst”) is known. More specifically, the NSR catalyst has a catalytic function for purifying nitrogen oxide (NOx), hydrocarbon (HC), etc. contained in the combustion gas discharged from the internal combustion engine, and stores NOx in the catalyst. And a catalyst having a function. During lean operation where the reducing agent is insufficient, NOx that is not purified by the catalyst may be released to the atmosphere. According to the NSR catalyst, NOx can be occluded inside the catalyst, and during the rich or stoichiometric operation after the catalyst activation, the occluded NOx can be reacted with a reducing agent such as HC for purification.

  Further, at the time of cold start of the internal combustion engine that does not exhibit catalytic activity, the NOx oxidation reaction is not activated, and the above-described occlusion reaction is not performed efficiently. Therefore, according to the conventional system, ozone is added to the exhaust gas at the cold start. Ozone can oxidize NOx in the gas phase. For this reason, even before the catalytic activity is expressed, NOx can be effectively oxidized, and the storage amount of NOx can be increased.

JP 2002-89246 A

  However, since ozone is easily pyrolyzed, the use of ozone is limited to a region where the catalyst temperature is relatively low. For this reason, there was a possibility that NOx that could not be occluded was released to the atmosphere in the temperature range from the upper limit of usable ozone to the manifestation of the activity of the NSR catalyst.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an exhaust gas purification device for an internal combustion engine that can improve NOx purification performance.

In order to achieve the above object, a first invention is an exhaust gas purification apparatus provided in an exhaust passage of an internal combustion engine,
NOx retention material;
Ozone introducing means for introducing ozone into the exhaust gas upstream of the NOx holding material;
A three-way catalyst disposed on a flow path through which NOx desorbed from the NOx holding material flows;
A selective reduction catalyst prepared such that the activity is exhibited at a temperature lower than that of the three-way catalyst;
Oxygen introducing means for introducing oxygen into the exhaust gas upstream of the selective catalytic reduction catalyst;
Temperature acquisition means for acquiring the temperature of the selective catalytic reduction catalyst;
Control means for controlling the operation of the ozone introduction means and the oxygen introduction means,
The control means stops the introduction of ozone by the ozone introduction means and starts the introduction of oxygen by the oxygen introduction means when the temperature of the selective catalytic reduction catalyst reaches an activation expression temperature. To do.

The second invention is the first invention, wherein
The selective reduction catalyst and the three-way catalyst are separate bodies,
The selective reduction catalyst is arranged upstream of the three-way catalyst.

The third invention is the first or second invention, wherein
The NOx holding material and the three-way catalyst are separate bodies,
The NOx holding material is arranged upstream of the three-way catalyst.

Moreover, 4th invention is 1st or 2nd invention,
The NOx holding material and the three-way catalyst are an integrated NOx occlusion reduction type catalyst.

The fifth invention is the invention according to any one of the first to fourth inventions,
The oxygen introducing means stops oxygen introduction when the selective catalytic reduction catalyst reaches an activity loss temperature.
Further, the sixth invention is the invention according to any one of the first to fifth inventions,
The control means starts introduction of ozone by the ozone introduction means when the selective catalytic reduction catalyst has not reached the activity expression temperature.

According to the first invention, a selective reduction catalyst (hereinafter referred to as “SCR catalyst”) and a three-way catalyst are arranged in the exhaust passage of the internal combustion engine. The SCR catalyst is prepared so as to be activated at a temperature lower than that of the three-way catalyst, and has a function of purifying by reacting NOx and HC in a lean atmosphere. Therefore, according to the present invention, it is possible to effectively purify NOx that could not be occluded or adsorbed by the NOx holding material before the three-way catalyst is activated, and improve the NOx purification performance.
Further, the SCR catalyst can purify NOx and HC by reacting in an excess of oxygen. According to the present invention, oxygen is introduced from the upstream side of the SCR catalyst when the temperature of the SCR catalyst reaches the activity expression temperature, so that the inside of the SCR catalyst can be in an oxygen-excess atmosphere. Therefore, according to the present invention, NOx that cannot be purified by the NOx holding material can be purified by the SCR catalyst, and the NOx purification efficiency can be improved.
Further, after the temperature of the SCR catalyst reaches the activation temperature and the purification process in the SCR catalyst is started, it is not always necessary to store or adsorb NOx in the NOx holding material. According to the present invention, since the addition of ozone is stopped while the NOx purification process is being performed in the SCR catalyst, the use of ozone can be suppressed and the system efficiency can be improved.

  According to the second invention, the SCR catalyst is disposed upstream of the three-way catalyst in the exhaust passage of the internal combustion engine. For this reason, according to the present invention, the activity of the SCR catalyst can be rapidly exhibited at the time of cold start of the internal combustion engine. Further, after the activity of the three-way catalyst is developed to some extent, NOx that has not been purified by the SCR catalyst can be purified by the three-way catalyst, and the NOx purification performance can be improved.

  Further, the occlusion element supported on the NOx holding material is considered to be a catalyst poison for the noble metal of the catalyst. According to the third invention, since the NOx holding material and the three-way catalyst are separately arranged in the exhaust passage of the internal combustion engine, the activity of the three-way catalyst can be further increased. In addition, since the three-way catalyst is arranged downstream of the NOx holding material, after the activity of the three-way catalyst is developed to some extent, the NOx that has not been occluded or adsorbed by the NOx holding material is purified in the three-way catalyst. NOx purification performance can be improved.

  According to the fourth invention, since the NOx occlusion reduction type catalyst in which the NOx holding material and the three-way catalyst are integrated is used, the desorbed NOx can be efficiently reacted on the catalyst. Moreover, since the number of parts is reduced by integrating, manufacturing cost can be suppressed.

Further, when the temperature of the SCR catalyst rises and the activity decreases, NOx cannot be effectively purified in the SCR catalyst. According to the fifth aspect , when the activity of the SCR catalyst is lost, the introduction of oxygen is stopped and the inside of the catalyst becomes a stoichiometric atmosphere. For this reason, according to the present invention, NOx can be effectively purified by using a three-way catalyst.

  Several embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted. The present invention is not limited to the following embodiments.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
FIG. 1 is a diagram for explaining the configuration of the first embodiment of the present invention. As shown in FIG. 1, the exhaust gas purifying apparatus 10 of the present embodiment is an internal combustion engine (hereinafter also simply referred to as “engine”).
12 is attached.

An exhaust pipe 14 is connected to the exhaust side of the engine 12. An exhaust purification catalyst 20 is disposed in the middle of the exhaust pipe 14. Inside the exhaust purification catalyst 20, an NSR catalyst 22 in which platinum (Pt) and barium carbonate (BaCO ₃ ) which are noble metals are supported on a ceramic carrier is disposed. Pt functions as an active site that activates an oxidation reaction of CO, HC, etc., or a reduction reaction of NOx. BaCO ₃ functions as a NOx storage agent that stores NOx as nitrate.

Further, on the upstream side of the NSR catalyst 22 inside the exhaust purification catalyst 20, a selective reduction type catalyst 24 (hereinafter referred to as "SCR catalyst 24") in which copper (Cu) is supported on a zeolitic ZSM-5 carrier is provided. Has been placed. Cu functions as an active site that activates an oxidation reaction of HC or the like or a reduction reaction of NOx. A temperature sensor 26 is disposed on the SCR catalyst 24. Hereinafter, the carrier carrying Pt or Cu is referred to as “catalyst”, and the carrier carrying BaCO ₃ is referred to as “NOx holding material”.

The exhaust gas purification device 10 of the present embodiment includes an ozone supply device 30. The ozone supply device 30 is configured to generate ozone (O ₃ ) using oxygen introduced from the air port 32 and inject it from the ozone injection port 34. The ozone supply device 30 can also inject the air introduced from the air port 32 as it is from the ozone injection port 34. The ozone injection port 34 is arranged on the upstream side of the SCR catalyst 24 and is arranged so as to inject ozone toward the downstream side. The configuration, function, and the like of the ozone supply device 30 are not the main part of the present invention and are well-known techniques, and thus detailed description thereof is omitted.

  The system according to the present embodiment includes an ECU (Electronic Control Unit) 50 as shown in FIG. The ozone supply device 30 described above is connected to the output unit of the ECU 50. In addition to the temperature sensor 26 described above, various sensors for detecting the operating condition and operating state of the engine 12 are connected to the input unit of the ECU 50. The ECU 50 calculates an ozone injection timing and an injection amount based on various types of input information, and drives the ozone supply device 30.

[Operation of Embodiment 1]
(NOx occlusion reduction operation using ozone)
Next, the operation of this embodiment will be described with reference to FIGS. On the catalyst of the NSR catalyst 22 disposed inside the exhaust purification catalyst 20, NOx reacts with HC or CO and is decomposed into N ₂ , H ₂ O, CO _{2 and the} like. Thereby, NOx contained in the exhaust gas is effectively purified. However, at the time of cold start of the internal combustion engine 12 where the NSR catalyst 22 has not reached the activation temperature, the three-way activity is low and NOx contained in the exhaust gas cannot be purified.

  Therefore, in the present embodiment, NOx that cannot be purified is occluded and the situation where it is released to the atmosphere is suppressed. As means for storing NOx, ozone is introduced into the exhaust gas. More specifically, when the engine 12 is cold started, ozone generated by the ozone supply device 30 is injected from the ozone injection port 34 toward the NSR catalyst 22.

FIG. 2 is a schematic diagram for explaining the NOx occlusion reaction, and is an enlarged view showing the inside of the NSR catalyst 22. As shown in this figure, before the exhaust purification catalyst 20 is activated at a low temperature, NOx reacts with ozone in the gas phase and is oxidized. More specifically, the following reaction occurs.
NO + O ₃ → NO ₂ + O ₂ (1)
NO ₂ + O ₃ → NO ₃ + O ₂ (2)
NO ₂ + NO ₃ → N ₂ O ₅ (3)
(NO ₂ + NO ₃ ← N ₂ O ₅ )

NOx oxidized to NO ₂ , NO ₃ , or N ₂ O ₅ is occluded as a nitrate such as Ba (NO ₃ ) _{2 in} the NOx holding material. Thereby, NOx can be occluded effectively, and the situation where NOx is released into the atmosphere before the three-way activity of the exhaust purification catalyst 20 can be effectively suppressed.

The stored NOx reacts with a reducing agent such as HC contained in the exhaust gas and is purified after the NSR catalyst 22 is activated. FIG. 3 is a schematic diagram for explaining the reduction reaction of NOx, and is an enlarged view showing the inside of the NSR catalyst 22. As shown in this figure, after the catalyst activity, the adsorbed NOx is reduced by a reducing agent such as HC contained in the exhaust gas, and decomposed into N ₂ , H ₂ O, CO _{2 and the} like. Thus, NOx occlusion and reduction reaction can be efficiently performed to effectively purify NOx occluded before the catalyst activity.

In the above NOx occlusion reaction, NO ₂ , NO ₃ , N ₂ O ₅ , or HNO ₃ produced by reacting these nitrogen oxides with water can be occluded, the NOx occlusion amount by the form NO ₂ is limited. Therefore, by the above reaction formula (2) is actively performed, if it is possible to much NO ₂ in the form of NO _3, it is possible to dramatically increase a NOx storage amount.

However, since the activation energy required for the reaction of the above equation (2) is higher than the energy required for the reaction of the above equation (1), the reaction of the above equation (1) takes precedence over the reaction of the above equation (2). Get up. Therefore, when the molar amount of ozone contained in the exhaust gas is less than the molar amount of NO are not occur only to the above reaction formula (1), NO is only so that the not oxidized to NO _2.

Therefore, the ozone introduction amount is controlled so that the molar amount of ozone introduced into the exhaust gas is larger than the molar amount of NO contained in the exhaust gas. Accordingly, the NO ₂ by the reaction of the equation (2) can be oxidized to NO _3, it is possible to increase the NOx storage amount.

Preferably, if the amount of ozone introduced is controlled so that the molar amount of ozone introduced into the exhaust gas is at least twice the molar amount of NO contained in the exhaust gas, most of the NO Can be oxidized to NO ₃ , and the NOx occlusion amount can be dramatically increased.

(NOx purification operation by SCR catalyst)
As described above, in the present embodiment, ozone is injected toward the NSR catalyst 22 when the engine 12 is cold started. Thus, NOx discharged from the engine 12 is effectively occluded before the three-way activity of the NSR catalyst 22 is expressed, and the release to the atmosphere is suppressed.

  However, since ozone causes thermal decomposition at a high temperature, use of ozone is limited to a temperature range where the catalyst temperature is 300 ° C. or lower. For this reason, the range from the upper limit value at which ozone can be used to the temperature at which the activity of the NSR catalyst 22 is exhibited cannot be stored in the NSR catalyst 22 even if ozone is added, and can be effectively purified. Since it cannot be performed, NOx that could not be stored is released to the atmosphere.

  Therefore, in the first embodiment, the SCR catalyst 24 is disposed inside the exhaust purification catalyst 20. The SCR catalyst 24 is activated at a temperature lower than that of the NSR catalyst 22, and is prepared so that NOx and HC can be selected and purified in a temperature range where ozone cannot be used. For this reason, even if the NSR catalyst 22 cannot store and purify NOx, the NOx that could not be stored by the SCR catalyst 24 can be purified, and the NOx purification performance can be improved.

  Note that the SCR catalyst 24 can exhibit its purification performance in an oxygen-excess atmosphere. In the present embodiment, an oxygen-excess atmosphere is formed by introducing air into the SCR catalyst 24. More specifically, in the activation temperature range of the SCR catalyst 24, the introduction of ozone from the ozone supply device 30 is stopped, and air is introduced instead. Thereby, NOx that could not be stored in the NSR catalyst 22 can be effectively purified by the SCR catalyst 24.

[Specific Processing in Embodiment 1]
FIG. 4 is a flowchart of a routine executed to efficiently purify NOx in the system shown in FIG. In the routine shown in FIG. 4, first, the temperature Ts of the SCR catalyst 24 is acquired (step S100). Here, specifically, it is calculated based on the output signal of the temperature sensor 26.

  Next, it is determined whether or not the temperature Ts of the SCR catalyst 24 acquired in step S100 is lower than a predetermined temperature T1 (step S102). The temperature T1 is a temperature at which the activity of the SCR catalyst 24 is manifested, and the SCR catalyst 24 is prepared so that the T1 is in the vicinity of the upper limit of the ozone usable temperature.

  If the establishment of Ts <T1 is recognized in step S102, it is determined that the activity of the SCR catalyst 24 has not yet developed, and the process proceeds to the next step, where ozone is added to the exhaust purification catalyst 20. (Step S104). Here, specifically, the ozone supply device 30 is driven, and ozone is injected from the ozone injection port 34. As a result, NOx is occluded in the NSR catalyst 22.

  On the other hand, if the establishment of Ts <T1 is not recognized in step S102, it is determined that the temperature of the SCR catalyst 24 is higher than the activity expression temperature, the process proceeds to the next step, and is acquired in step S100. It is determined whether or not the temperature Ts of the SCR catalyst 24 is lower than a predetermined temperature T2 (step S106). The temperature T2 is a temperature at which the activity of the SCR catalyst 24 is lost, and the SCR catalyst 24 is prepared so that the T2 is close to the temperature at which the activity of the NSR catalyst 22 is expressed.

  If the establishment of Ts <T2 is recognized in step S106, it is determined that the region is where the activity of the SCR catalyst 24 is expressed, the process proceeds to the next step, and air is added to the exhaust purification catalyst 20. (Step S108). Here, specifically, the supply of ozone by the ozone supply device 30 is first stopped. Next, the air introduced into the ozone supply device 30 from the air port 32 is jetted from the ozone jet port 34. Thereby, the atmosphere around the SCR catalyst 24 becomes an oxygen-excess atmosphere, and the NOx purification performance in the SCR catalyst 24 is exhibited.

  On the other hand, if the establishment of Ts <T2 is not recognized in step S106, it is determined that the activity in the NSR catalyst 22 is expressed, the process proceeds to the next step, the ozone supply device 30 is stopped, and the exhaust purification catalyst 20 is reached. Addition of air to is stopped (step S110). Thereby, NOx is purified in the NSR catalyst 22.

  As described above, according to the first embodiment, the addition of ozone to the exhaust purification catalyst is stopped in the temperature range from the upper limit value of the temperature at which ozone can be used to the temperature at which the activity of the NSR catalyst 22 is manifested. Instead, oxygen is added. As a result, the SCR catalyst 24 can be in an oxygen-excess atmosphere, so that the NOx can be effectively purified in the SCR catalyst 24 even in a temperature range where the NSR catalyst 22 cannot store and purify NOx. , NOx purification performance can be improved.

  Incidentally, in Embodiment 1 described above, ozone is generated by the ozone supply device 30 and injected from the ozone injection port 34 toward the exhaust purification catalyst 20, but the configuration of the ozone supply device 30 is limited to this. I can't. That is, if ozone can be added to the exhaust gas introduced into the exhaust purification catalyst 20, an ozone generator may be arranged in the exhaust pipe 14, or the exhaust pipe 14 upstream of the exhaust purification catalyst 20 from the ozone supply device 30. The configuration may be such that ozone is introduced.

In the first embodiment described above, SCR catalyst 24 as the temperature T1 are available temperature upper limit vicinity of the ozone, the temperature T2 is prepared so that the activity onset current temperature near the NSR catalyst 22 However, T1 and T2 are not limited to this. That is, the NOx purification performance can be improved if the active region of the SCR catalyst 24 overlaps with the active region of the SCR catalyst 24 as much as possible in the temperature region between the upper limit of the usable temperature of ozone and the activity expression temperature of the NSR catalyst 22.

In Embodiment 1 described above, BaCO ₃ is used as the NOx storage agent, but the material is not limited to this. That is, alkali metals such as Na, K, Cs, and Rb, alkaline earth metals such as Ba, Ca, and Sr, and rare earth elements such as Y, Ce, La, and Pr may be used as necessary. Further, the material of the catalyst used for the NSR catalyst 22 is not limited to Pt, and Rh, Pd, etc., which are noble metal materials, may be used as necessary. Further, the catalyst used for the SCR catalyst 24 is not limited to Cu, and a transition metal such as Fe may be used as necessary.

In the first embodiment described above, the NSR catalyst 22 in which Pt, which is a noble metal, and BaCO ₃ functioning as a NOx storage agent is supported on a ceramic carrier is disposed inside the exhaust purification catalyst 20. However, the configuration of the arranged NSR catalyst 22 is not limited to this. That is, according to the gas phase reaction of ozone shown in the above formulas (1) and (2), NOx can be oxidized without being on the catalyst. It is also possible to separate and carry a noble metal. More specifically, the NOx storage agent and the noble metal may be supported separately on the upstream side and the downstream side of the carrier, or the carrier may be supported separately on the upper layer side and the lower layer side. Good. In the case where the layers are separated and supported, it is preferable to arrange the noble metal in the upper layer of the NOx storage agent and reduce the NOx released from the NOx storage agent with the noble metal.

In the first embodiment described above, the SCR catalyst 24 corresponds to the “selective reduction catalyst” in the first invention .

  In the first embodiment described above, the NSR catalyst 22 corresponds to the “NOx occlusion reduction type catalyst” in the fourth invention.

In the first embodiment described above, the temperature sensor 26 corresponds to the “temperature acquisition means” in the first invention, and the temperature T1 corresponds to the “activity expression temperature” in the first invention. Further, the “ control means” according to the first aspect of the present invention is realized by the ECU 50 executing the processing of step 106 described above.

In the first embodiment described above, the temperature T2 corresponds to the “activity loss temperature” in the first aspect of the invention, and the ECU 50 executes the processing of step 106 to thereby execute the first step . The “ control means” in the invention is realized.

In the first embodiment described above, the ECU 50 executes the process of step 108, and the “ control means” in the fifth aspect of the invention executes the process of step 102. The “control means” in the sixth aspect of the invention is realized.

Evaluation test for the first embodiment
[Configuration of experimental apparatus]
Next, an evaluation test conducted for confirming the effect of the invention shown in Embodiment 1 will be described with reference to FIGS. FIG. 5 is a diagram for explaining the configuration of the experimental apparatus for this evaluation test. As shown in FIG. 5, the experimental apparatus includes a model gas generator 100. The model gas generator 100 can generate a simulated gas of exhaust gas discharged from an internal combustion engine by mixing gases supplied from a plurality of types of gas cylinders 102.

  A catalyst test body 200 is disposed downstream of the model gas generator 100. An electric furnace for controlling the catalyst test body 200 to a desired temperature is disposed around the catalyst test body 200. The specific configuration of the catalyst test body 200 will be described later.

  Exhaust gas analyzers 110 and 112 and an ozone analyzer 114 are connected downstream of the catalyst test body 200. The components of the simulated gas generated by the model gas generator 100 are analyzed by these analyzers after passing through the catalyst test body 200.

  Further, the experimental apparatus shown in FIG. 5 includes an apparatus for introducing an injection gas containing ozone upstream of the catalyst test body 200. More specifically, this experimental apparatus includes an oxygen cylinder 122. An ozone generator 120 is connected downstream of the oxygen cylinder 122 via a flow rate control unit 124. The ozone generator 120 is a device that generates ozone using oxygen supplied from the oxygen cylinder 122. The ozone generator 120 is connected upstream of the catalyst test body 200 via an ozone analyzer 126 and a flow rate control unit 128. The oxygen cylinder 122 is directly connected to the upstream side of the ozone analyzer 126 via a separately provided flow control unit 130. According to such a configuration, it becomes possible to individually control the amount of ozone and the amount of oxygen contained in the injected gas.

The measurement equipment used in the experimental apparatus for this evaluation test is shown below.
Ozone generator 120: Iwasaki Electric OP100W
Ozone analyzer 126: Sugawara business EG600
Ozone analyzer 114: Sugawara business EG2001B
Exhaust gas analyzer 110: HORIBA, Ltd. MEXA9100D
(Measures HC, CO, NOx)
Exhaust gas analyzer 112: HORIBA, Ltd. VAI-510
(Measures CO ₂ )

  Next, a specific configuration of the catalyst test body 200 will be described in detail. FIG. 6 is a cross-sectional view schematically showing the inside of the catalyst test body 200 of this experimental apparatus. In this evaluation test, as the catalyst test body 200, the catalyst test body 200a is used in Experiment 1, and the catalyst test body 200b is used in Experiment 2. FIG. 6A is a cross-sectional view schematically showing the inside of the catalyst test body 200a used in Experiment 1. FIG. As shown in FIG. 6A, a catalyst sample 204 is disposed upstream and a catalyst sample 206 is disposed downstream of the quartz tube 202 of the catalyst test body 200a. Catalyst samples 204 and 206 were prepared by the following procedure.

(Procedure for making catalyst sample 204)
First, a cordierite honeycomb of φ30 mm × L25 mm, 4 mil / 400 cpsi was coated with H-type ZSM-5 type zeolite (Si / Al ratio = 40). The coating amount is 120 g / L. Next, Cu was ion-exchanged using an aqueous solution containing Cu nitrate here, dried, and then fired at 450 ° C. for 1 hour. The supported amount of Cu is 4 g / L.

(Procedure for making catalyst sample 206)
First, γ-Al ₂ O ₃ was coated on a cordierite honeycomb of φ30 mm × L25 mm, 4 mil / 400 cpsi. The coating amount is 120 g / L. Next, barium acetate was supported on the water and fired at 500 ° C. for 2 hours. The supported amount of barium acetate is 0.2 mol / L. This catalyst was immersed in a solution containing ammonium hydrogen carbonate and dried at 250 ° C. Furthermore, Pt was supported using an aqueous solution containing dinitrodiammine platinum, dried, and then fired at 450 ° C. for 1 hour. The supported amount of Pt is 4 g / L.

  On the other hand, FIG. 6B is a cross-sectional view schematically showing the inside of the catalyst test body 200b used in Experiment 2. As shown in FIG. 6B, a catalyst sample 208 is disposed inside the quartz tube 202 of the catalyst test body 200b. The catalyst sample 208 was prepared by the following procedure.

(Procedure for making catalyst sample 208)
First, a cordierite honeycomb of φ30 mm × L50 mm, 4 mil / 400 cpsi was coated with γ-Al ₂ O ₃ . The coating amount is 120 g / L. Next, barium acetate was supported on the water and fired at 500 ° C. for 2 hours. The amount of barium acetate supported is 0.1 mol / L. This catalyst was immersed in a solution containing ammonium hydrogen carbonate and dried at 250 ° C. Furthermore, Pt was supported using an aqueous solution containing dinitrodiammine platinum, dried, and then fired at 450 ° C. for 1 hour. The supported amount of Pt is 2 g / L.

[Experimental conditions]
The experimental conditions in this evaluation test are shown below.
Temperature: Control in the range of 30 ° C to 500 ° C Temperature rise rate: 10 ° C / min.
Simulated gas composition: C ₃ H ₆ (1000 ppm)
CO (7000ppm)
NO (1500ppm)
O ₂ (7000ppm)
CO ₂ (10%)
H ₂ O (3%)
Remaining N ₂
Simulated gas flow rate: 30L / min.
Injection gas composition: O ₃ (30000ppm)
Balance O ₂
(Injection of only O ₂ is possible by controlling the ozone generator 120)
Injection gas flow rate: 6 L / min.

[Test method]
The experiment was performed by raising the temperature of the electric furnace arranged around the catalyst test body 200 from the low temperature side. An injection gas containing ozone was injected in the range of 30 ° C. to 250 ° C., and an injection gas containing only oxygen was injected from 250 ° C. to 300 ° C. At a temperature of 300 ° C. or higher, the injection gas was stopped and only the simulated gas was injected. The experiment was conducted in Experiment 1 using catalyst samples 204 and 206 and Experiment 2 using catalyst sample 208. The purification rate refers to the amount of NOx discharged to the downstream of the catalyst test body 200 (hereinafter referred to as “discharged NOx amount”) from the NOx amount introduced into the catalyst test body 200 within the test time (hereinafter referred to as “introduced NOx amount”) The value obtained by subtracting “)” was calculated by dividing by the amount of introduced NOx at a 100-minute rate.
Introduced NOx amount = NOx concentration in simulated gas × simulated gas flow rate × test time (4)
Exhaust NOx amount = NOx concentration downstream of catalyst 200 × gas flow rate (simulated gas + injected gas) × test time (5)
Purification rate = (introduction NOx amount−exhaust NOx amount) / introduction NOx amount × 100 (6)

[Test results]
FIG. 7 is a diagram showing purification rates of various components in Experiment 1 and Experiment 2. As shown in FIG. 7, it is confirmed that the catalyst test body 200a used in Experiment 1 has a higher purification rate for any of NOx, HC, and CO than the catalyst test body 200b. Thereby, the effect of using the SCR catalyst in addition to the NSR catalyst can be confirmed.

Embodiment 2. FIG.
[Characteristic Configuration of Embodiment 2]
Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 8 is a diagram for explaining the configuration of the second embodiment. In the exhaust gas purifying apparatus 40 shown in FIG. 8, the same reference numerals are given to the elements common to the exhaust gas purifying apparatus 10 shown in FIG.

As shown in FIG. 8, in the exhaust gas purification device 40 of the present embodiment, an exhaust purification catalyst 42 is disposed in the middle of the exhaust pipe 14. Inside the exhaust purification catalyst 42, a NOx holding material 44 in which barium carbonate (BaCO ₃ ) is supported on a ceramic carrier is disposed. On the downstream side of the NOx holding material 44, an SCR catalyst 46 in which copper (Cu) is supported on a zeolitic ZSM-5 carrier is disposed. Further, on the further downstream side of the SCR catalyst 46, a three-way catalyst 48 in which a noble metal (Pt) is supported on a ceramic carrier is disposed. BaCO ₃ functions as a NOx storage agent that stores NOx as nitrate. Further, Cu and Pt function as active sites that activate an oxidation reaction of CO, HC, or the like, or a reduction reaction of NOx.

  The exhaust gas purification device 40 of this embodiment includes an ozone supply device 30. Further, an ozone injection port 34 that injects ozone toward the NOx holding material 44 is disposed upstream of the NOx holding material 44.

[Characteristic operation of the second embodiment]
In the exhaust gas purification apparatus 10 of the first embodiment described above, the SCR catalyst 46 is used in combination with the NSR catalyst 22. Thus, NOx can be effectively purified in a period in which NOx can not be occluded and purified by the NSR catalyst 22, and NOx purification performance can be improved.

  However, in general, the NSR catalyst has a lower purification efficiency than the three-way catalyst. This is thought to be because the NOx storage agent supported on the NSR catalyst becomes a catalyst poison for the noble metal.

  Therefore, in the second embodiment, the exhaust purification catalyst 42 in which the NOx holding material and the three-way catalyst are separately disposed is used. As shown in FIG. 8, in the exhaust purification catalyst 42, the NOx holding material 44 is arranged separately from the three-way catalyst 48, so that the activity of the three-way catalyst 48 can be further increased. In addition, since the three-way catalyst 48 is arranged downstream of the NOx holding material 44, after the activity of the three-way catalyst 48 is expressed to some extent, the NOx that has not been occluded in the NOx holding material 44 is purified by the three-way catalyst 48. The NOx purification performance can be improved.

  If the three-way catalyst 48 is arranged upstream of the SCR catalyst 46, the reducing agent contained in the exhaust gas reacts with the introduced oxygen in the three-way catalyst 48, and the reducing agent becomes the SCR catalyst 46. It will be consumed before it is introduced. In this regard, according to the second embodiment, since the three-way catalyst 48 is disposed downstream of the SCR catalyst 46, a reducing agent can be efficiently introduced into the SCR catalyst 46, and NOx purification in the SCR catalyst 46 can be performed. Efficiency can be improved.

  By the way, in Embodiment 2 mentioned above, although the exhaust purification catalyst 42 which equips the inside with the NOx holding | maintenance material 44, the SCR catalyst 46, and the three way catalyst 48 is used, the structure of a catalyst is not restricted to this. That is, these catalysts do not have to be integrated as the exhaust purification catalyst 42, and may be configured separately in the exhaust pipe 14.

  In the second embodiment described above, ozone is injected from the ozone injection port 34 disposed upstream of the NOx holding material 44 toward the NOx holding material 44. However, the configuration for adding ozone is as follows. Not limited to. That is, as long as ozone can be added to the exhaust gas introduced into the NOx holding material 44, an ozone generator may be arranged in the exhaust pipe 14, or the ozone injection port 34 may be an exhaust pipe upstream of the NOx holding material 44. 14 may be arranged.

  Moreover, in Embodiment 2 mentioned above, it is supposed that oxygen is injected from the ozone injection port 34 using the ozone supply apparatus 30, However, The structure which adds oxygen is not restricted to this. That is, as long as the SCR catalyst 46 can be made to have excess oxygen, oxygen may be introduced into the exhaust gas using another device such as a pump. Further, if oxygen in the exhaust gas upstream of the SCR catalyst 46 is introduced, the introduction location is not particularly limited, and for example, a configuration in which oxygen is introduced into the exhaust manifold may be used.

In Embodiment 2 described above, BaCO ₃ is used as the NOx storage agent, but the material is not limited to this. That is, alkali metals such as Na, K, Cs, and Rb, alkaline earth metals such as Ba, Ca, and Sr, and rare earth elements such as Y, Ce, La, and Pr may be used as necessary. The material of the catalyst used for the three-way catalyst 48 is not limited to Pt, and Rh, Pd, etc., which are noble metal materials, may be used as necessary. Further, the catalyst used for the SCR catalyst 46 is not limited to Cu, and a transition metal such as Fe may be used as necessary.

  In the second embodiment, the NOx holding material 44 is the “NOx holding material” in the first invention, the SCR catalyst 46 is the “selective reduction catalyst” in the first invention, and the three-way catalyst. No. 48 corresponds to the “three-way catalyst” in the first invention.

Evaluation test for Embodiment 2
[Configuration of experimental apparatus]
Next, with reference to FIG. 9 and FIG. 10, an evaluation test performed to confirm the effect of the invention shown in Embodiment 2 will be described. As an experimental apparatus for this evaluation test, an experimental apparatus in which the catalyst test body 200 of the experimental apparatus shown in FIG. 5 is changed to a catalyst test body 300 described later is used.

  Next, a specific configuration of the catalyst 300 will be described in detail. FIG. 9 is a cross-sectional view schematically showing the inside of the catalyst test body 300 of the experimental apparatus. In this evaluation test, Experiment 1 using the catalyst test body 300a and Experiment 2 using the catalyst test body 300b were performed. FIG. 9A is a cross-sectional view schematically showing the inside of the catalyst test body 300a used in Experiment 1. FIG. As shown in FIG. 9A, the catalyst sample 304 is arranged upstream, the catalyst sample 306 is arranged in the middle, and the catalyst sample 308 is arranged downstream in the quartz tube 302 of the catalyst test body 300a. Catalyst samples 304, 306, and 308 were prepared by the following procedure.

(Procedure for making catalyst sample 304)
First, γ-Al ₂ O ₃ was coated on a cordierite honeycomb of φ30 mm × L25 mm, 4 mil / 400 cpsi. The coating amount is 120 g / L. Next, barium acetate was supported on the water and fired at 500 ° C. for 2 hours. The supported amount of barium acetate is 0.2 mol / L. This catalyst was immersed in a solution containing ammonium hydrogen carbonate and dried at 250 ° C.

(Procedure for making catalyst sample 306)
First, a cordierite honeycomb of φ30 mm × L25 mm, 4 mil / 400 cpsi was coated with H-type ZSM-5 type zeolite (Si / Al ratio = 40). The coating amount is 120 g / L. Next, Cu was ion-exchanged using an aqueous solution containing Cu nitrate here, dried, and then fired at 450 ° C. for 1 hour. The supported amount of Cu is 4 g / L.

(Procedure for making catalyst sample 308)
First, a cordierite honeycomb of φ30 mm × L50 mm, 4 mil / 400 cpsi was coated with γ-Al ₂ O ₃ . The coating amount is 120 g / L. Next, Pt was supported thereon using an aqueous solution containing dinitrodiammine platinum, dried, and calcined at 450 ° C. for 1 hour. The supported amount of Pt is 2 g / L.

  On the other hand, FIG. 9B is a cross-sectional view schematically showing the inside of the catalyst test body 300b used in Experiment 2. As shown in FIG. 9B, the catalyst sample 310 is disposed upstream and the catalyst sample 312 is disposed downstream of the quartz tube 302 of the catalyst test body 300b. The catalyst sample 310 has the same configuration as the catalyst test body 204 used in the evaluation test of the first embodiment, and the catalyst sample 312 has the same configuration as the catalyst test body 206 used in the evaluation test. Omitted.

[Experimental conditions]
The experimental conditions in this evaluation test are shown below.
Temperature: Control in the range of 30 ° C to 500 ° C Temperature rise rate: 10 ° C / min.
Simulated gas composition: C ₃ H ₆ (1000 ppm)
CO (7000ppm)
NO (1500ppm)
O ₂ (7000ppm)
CO ₂ (10%)
H ₂ O (3%)
Remaining N ₂
Simulated gas flow rate: 30L / min.
Injection gas composition: O ₃ (30000ppm)
Balance O ₂
(Injection of only O ₂ is possible by controlling the ozone generator 120)
Injection gas flow rate: 6 L / min.

[Test method]
The experiment was conducted by raising the temperature of the electric furnace arranged around the catalyst test body 300 from the low temperature side. An injection gas containing ozone was injected in the range of 30 ° C. to 250 ° C., and an injection gas containing only oxygen was injected from 250 ° C. to 300 ° C. At a temperature of 300 ° C. or higher, the injection gas was stopped and only the simulated gas was injected. The experiment was run 1 using catalyst samples 304, 306 and 308 and run 2 using catalyst samples 310 and 312. The purification rate was calculated based on the above equation (5).

[Test results]
FIG. 10 is a diagram showing the purification rates of various components in Experiment 1 and Experiment 2. As shown in FIG. 10, it is confirmed that the catalyst test body 300a used in Experiment 1 has a higher purification rate for any of NOx, HC, and CO than the catalyst test body 300b. Thereby, the effect which separated and arrange | positioned the NOx holding | maintenance material and the three way catalyst can be confirmed.

It is a figure for demonstrating the structure of Embodiment 1 of this invention. It is a schematic diagram for demonstrating the occlusion reaction of NOx using ozone. It is a schematic diagram for demonstrating the reduction reaction of NOx. It is a flowchart of the routine performed in Embodiment 1 of the present invention. FIG. 3 is a diagram for explaining a configuration of an evaluation test experimental apparatus according to the first embodiment. 2 is a cross-sectional view schematically showing the inside of a catalyst test body 200. FIG. It is a figure which shows the purification rate of the various components in Experiment 1 and Experiment 2. It is a figure for demonstrating the structure of Embodiment 2 of this invention. 2 is a cross-sectional view schematically showing the inside of a catalyst test body 300. FIG. It is a figure which shows the purification rate of the various components in Experiment 1 and Experiment 2.

Explanation of symbols

10 Exhaust Gas Purification System 12 Internal Combustion Engine (Engine)
14 Exhaust pipe 20 Exhaust purification catalyst 22 NOx storage reduction catalyst (NSR catalyst)
24 selective reduction catalyst (SCR catalyst)
26 Temperature sensor 30 Ozone supply device 32 Air port 34 Ozone injection port 40 Exhaust gas purification device 42 Exhaust purification catalyst 44 NOx holding material 46 Selective reduction type catalyst (SCR catalyst)
48 Three-way catalyst 50 ECU (Electronic Control Unit)
100 Model gas generator 102 Gas cylinder 110, 112 Exhaust gas analyzer 114 Ozone analyzer 120 Ozone generator 122 Oxygen cylinder 124, 128, 130 Flow control unit 126 Ozone analyzer 200 Catalyst specimen 202 Quartz tube 204, 206 Catalyst sample 300 Catalyst sample 302 Quartz tube 304, 306, 308, 310, 312 Catalyst sample

Claims (6)

An exhaust gas purification device provided in an exhaust passage of an internal combustion engine,
NOx retention material;
Ozone introducing means for introducing ozone into the exhaust gas upstream of the NOx holding material;
A three-way catalyst disposed on a flow path through which NOx desorbed from the NOx holding material flows;
A selective reduction catalyst prepared such that the activity is exhibited at a temperature lower than that of the three-way catalyst;
Oxygen introducing means for introducing oxygen into the exhaust gas upstream of the selective catalytic reduction catalyst;
Temperature acquisition means for acquiring the temperature of the selective catalytic reduction catalyst;
Control means for controlling the operation of the ozone introduction means and the oxygen introduction means,
The control means stops the introduction of ozone by the ozone introduction means and starts the introduction of oxygen by the oxygen introduction means when the temperature of the selective catalytic reduction catalyst reaches an activation expression temperature. An exhaust gas purification device for an internal combustion engine. The selective reduction catalyst and the three-way catalyst are separate bodies,
The exhaust gas purification device for an internal combustion engine according to claim 1, wherein the selective reduction catalyst is disposed upstream of the three-way catalyst. The NOx holding material and the three-way catalyst are separate bodies,
The exhaust gas purifying device for an internal combustion engine according to claim 1 or 2, wherein the NOx holding material is arranged upstream of the three-way catalyst.   The exhaust gas purifying device for an internal combustion engine according to claim 1 or 2, wherein the NOx holding material and the three-way catalyst are an integrated NOx storage reduction catalyst. Wherein, when the selective reduction catalyst has reached the activation loss temperature, the internal combustion engine of any one of claims 1 to 4, characterized in that stopping the introduction of oxygen by the oxygen introduction means Exhaust gas purification device.   The internal combustion engine according to any one of claims 1 to 5, wherein the control means starts introduction of ozone by the ozone introduction means when the selective catalytic reduction catalyst has not reached the activation expression temperature. Engine exhaust gas purification device.

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