JP2017155643A - Nox purification device and process of manufacture of nox purification device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a NOx purification device in which reliability in promotion of NOx absorption through adding of ozone is improved.SOLUTION: A NOx purification device is applied to an exhaust system in which ozone can be added to an exhaust passage 11 of an internal combustion engine 10 and comprises an absorption part 20A and a reduction part 20B. The absorption part 20A has first porous carrier to adsorb NOx oxidized by ozone added from an ozone addition part 30. The reduction part 20B has a second porous carrier to cause NOx desorbed from the absorption part 20A to be reduced by the reduction catalyst carried by the second carrier. Then, a carrying amount of oxidation catalyst by the first carrier is none and the first carrier adsorbs NOx.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a NOx purification device that reduces and purifies NOx contained in exhaust gas from an internal combustion engine, and a method for manufacturing the NOx purification device.

A conventional storage-type NOx purification device includes an adsorption part having a carrier carrying an adsorption catalyst and a reduction part having a carrier carrying a reduction catalyst, and adsorbs NOx by the adsorption catalyst and leaves the adsorption catalyst. NOx is reduced with a reduction catalyst. This type of adsorption catalyst can adsorb NO ₂ and NO ₃ but hardly adsorbs NO. Therefore, conventionally, an oxidation catalyst is supported on the carrier of the adsorption section, and NO is oxidized to NO ₂ by this oxidation catalyst to promote NOx adsorption.

Furthermore, in Patent Document 1, NO is oxidized to NO ₂ to promote NOx adsorption by adding ozone to the upstream portion of the adsorption portion and the reduction portion in the exhaust passage. According to this, NOx can be adsorbed even in a low temperature state where the oxidation catalyst is not sufficiently activated.

JP 2008-163887 A

Now, in the conventional NOx purification device in which an oxidation catalyst is supported on the support of the adsorption unit, the present inventors have actually tested the credibility of the effect of promoting NOx adsorption even at low temperatures by adding ozone as described above. I checked it. As a result, it was found that the following problems occur. That is, in a low temperature state, CO in the exhaust gas reacts with NO _2, and thereby NO ₂ becomes NO. That is, in the low temperature, even by oxidizing NO to NO ₂ with ozone, the so produced NO ₂ is will go back to NO by reaction with CO, achieving a sufficient NOx adsorption promoting Ozone I can't.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a NOx purification device that improves the certainty of NOx adsorption promotion by ozone addition and a method for manufacturing the NOx purification device.

  The invention disclosed herein employs the following technical means to achieve the above object. Note that the reference numerals in parentheses described in the claims and in this section indicate the correspondence with the specific means described in the embodiments described later, and do not limit the technical scope of the invention. .

  The disclosed first invention is applied to an exhaust system capable of adding ozone to an exhaust passage (11) of an internal combustion engine (10), and is a NOx purification device that reduces and purifies NOx contained in exhaust gas, and is porous. An adsorbing portion (20A) having a first carrier (23) having a shape and adsorbing NOx oxidized by ozone added to the exhaust passage, and a second carrier (24) having a porous shape, A reduction section (20B, 202B) for reducing NOx desorbed from the second carrier with a reduction catalyst (24a) carried on the second carrier, the amount of the oxidation catalyst carried by the first carrier is zero, and the first carrier Is a NOx purification device that adsorbs NOx.

As described above, CO changes NO ₂ to NO, and this reaction is called a CO inhibition reaction. The present inventors considered that the oxidation catalyst supported on the carrier of the conventional adsorbing part activated CO and promoted CO inhibition reaction, and conducted various tests to confirm this consideration. As a result, the inventors have found that the CO inhibition reaction is suppressed as the amount of the oxidation catalyst supported is reduced, and that the CO inhibition reaction hardly occurs if the amount of the oxidation catalyst supported is reduced to zero.

In view of this point, the first invention is based on the premise that the NOx purification device is applied to an exhaust system to which ozone can be added, and the amount of the oxidation catalyst supported by the first carrier that the adsorption unit has is zero. It is. For this reason, the CO inhibition reaction in which NO ₂ generated by the addition of ozone returns to NO hardly occurs, so that the certainty of the NOx adsorption promotion by the addition of ozone can be improved. Therefore, sufficient NOx adsorption can be realized even at a low temperature at which the catalyst cannot be sufficiently activated.

  A second invention to be disclosed includes an adsorbing portion (1) having a porous first support (23) and adsorbing NOx oxidized by ozone added to an exhaust passage (11) of an internal combustion engine (10). 20A) and a reduction part (20B) having a porous second support (24) and reducing NOx desorbed from the adsorption part by a reduction catalyst (24a) supported on the second support. In the manufacturing method of the NOx purification device, a paste-like first carrier having a zero oxidation catalyst content is applied to the first region (22A) of the surface of the base material (22), and then the surface of the base material (22A). Of these, the second region (22B) adjacent to the first region is coated with a paste-like second carrier containing a reduction catalyst, and then the first carrier and the second carrier are heated together with the base material, thereby The carrier and the second carrier are made porous and baked onto the substrate. It is a manufacturing method of the Ox purifier.

  Here, when the first region to which the first carrier is applied and the second region to which the second carrier is applied are adjacent to each other, in the manufacturing process in which the first carrier and the second carrier are applied at the boundary portion of the region. There may be a slight overlap. In this case, when the first carrier is superimposed on the second carrier, the first carrier is affected by the reduction catalyst carried by the second carrier, and in the portion of the first carrier that is superimposed on the second carrier. The CO inhibition reaction cannot be sufficiently suppressed. On the other hand, when the second carrier is superimposed on the first carrier, there is no problem such that the second carrier is affected by the first carrier and the reducing power is reduced.

  In the second invention in view of these points, since the second carrier is applied after the first carrier is applied, the first carrier is placed on the second carrier at the boundary between the first region and the second region. Superposition can be avoided. Therefore, the risk of the CO inhibition reaction due to the superposition described above can be avoided. Moreover, since the amount of the oxidation catalyst supported by the first carrier becomes zero, it is possible to suppress the occurrence of a CO inhibition reaction as in the first aspect of the invention, and it is possible to improve the certainty of promoting NOx adsorption by adding ozone.

  A third invention to be disclosed has a first support (23) having a porous shape and adsorbs an NOx oxidized by ozone added to the exhaust passage (11) of the internal combustion engine (10) ( 20A) and a reduction part (202B) having a porous second support (24) and reducing NOx desorbed from the adsorption part with a reduction catalyst (24a) supported on the second support. In the manufacturing method of the NOx purification device, a paste-like first carrier having an oxidation catalyst content of zero is applied to the surface of the substrate (22), and then a reduction catalyst is applied to a part of the surface of the first carrier. NOx purification in which a paste-like second carrier containing sapphire is applied, and then the first carrier and the second carrier are heated together with the base material so that the first carrier and the second carrier are made porous and baked on the base material It is a manufacturing method of an apparatus.

  As described above, when the first carrier is superimposed on the second carrier, there is a concern about the CO inhibition reaction, whereas when the second carrier is superimposed on the first carrier, the reduction power is reduced. There is no problem. In the third aspect of the invention in view of this point, after the first carrier is applied, the second carrier is applied to a part of the surface of the first carrier. Thus, the production efficiency can be improved. That is, in the third aspect of the invention, since the manufacturing is performed on the premise that the second carrier is stacked on the first carrier, the first carrier is applied compared to the case where the first carrier is applied to the predetermined first region. It is not necessary to manage the range accurately. Therefore, manufacturing efficiency can be improved. Moreover, since the amount of the oxidation catalyst supported by the first carrier becomes zero, it is possible to suppress the occurrence of a CO inhibition reaction as in the first aspect of the invention, and it is possible to improve the certainty of promoting NOx adsorption by adding ozone.

1 is a diagram showing an outline of a NOx purification system in a first embodiment of the present invention. The perspective view of the NOx purification part which concerns on 1st Embodiment. Sectional drawing of the adsorption | suction part shown in FIG. Sectional drawing of the reduction | restoration part shown in FIG. The flowchart which shows the manufacture procedure of the NOx purification apparatus which concerns on 1st Embodiment. The figure which shows a mode that the adsorption | suction part shown in FIG. 3 adsorb | sucks NOx in ozone environment. The figure which shows the result of having tested the relationship between the characteristic of NOx adsorption rate with respect to NOx adsorption amount, and CO inhibition in the NOx purification apparatus which concerns on the comparative example of 1st Embodiment. The figure which shows the result of having tested the relationship between the characteristic of NOx adsorption rate with respect to NOx adsorption amount, and CO inhibition in the NOx purification apparatus which concerns on 1st Embodiment. The figure which shows the result of having tested the relationship between the temperature of a NOx purification apparatus, and NOx desorption amount. The figure which shows the result of having tested the relationship between an oxidation catalyst carrying amount and NOx adsorption amount decreasing rate. Sectional drawing of the adsorption | suction part which concerns on 2nd Embodiment of this invention. The flowchart which shows the manufacture procedure of the NOx purification apparatus which concerns on 2nd Embodiment. The perspective view of the NOx purification part which concerns on 3rd Embodiment of this invention. Sectional drawing of the NOx purification part which concerns on 4th Embodiment of this invention.

  Hereinafter, a plurality of modes for carrying out the invention will be described with reference to the drawings. In each embodiment, portions corresponding to the matters described in the preceding embodiment may be denoted by the same reference numerals and redundant description may be omitted. In each embodiment, when only a part of the configuration is described, the other configurations described above can be applied to other portions of the configuration.

(First embodiment)
The NOx purification device shown in FIG. 1 is mounted on a vehicle that travels using the output of the engine 10 as a drive source. The engine 10 that is an internal combustion engine is a compression ignition type diesel engine, and light oil that is a hydrocarbon compound is used as a fuel for combustion. The NOx purification device includes a NOx purification unit 20 and an ozone addition unit 30. The NOx purification unit 20 is provided in the exhaust passage 11 of the engine 10. Exhaust gas flowing through the exhaust passage 11 passes through the NOx purification unit 20 and is then discharged from the exhaust outlet 11a. NOx includes NO _{3 and the} like in addition to NO and NO ₂ .

The ozone addition unit 30 adds ozone O ₃ to the upstream side of the NOx purification unit 20 in the exhaust passage 11. When ozone is supplied from the ozone addition unit 30 to the exhaust passage 11, NO in the exhaust is oxidized to NO ₂ by ozone, so that the ratio of NO ₂ increases. The ozone addition unit 30 is controlled to be able to shift between a supply state in which ozone is supplied to the exhaust passage 11 and a stop state in which ozone is not supplied.

  The ozone addition unit 30 includes an ozone passage 31, an ozone generator 32, an air pump 33, an exhaust cutoff valve 34, a pressure sensor 35, an addition nozzle 36, and a control device 37. The ozone passage 31 is connected to the upstream side of the NOx purification unit 20 in the exhaust passage 11. The ozone passage 31 is provided with an ozone generator 32, an air pump 33, an exhaust cutoff valve 34, a pressure sensor 35, and an addition nozzle 36.

  The air pump 33 blows air, which is external air, to the ozone passage 31. The air pump 33 is a centrifugal air pump and is configured by housing an impeller driven by an electric motor in a case. An air pump 33 is provided at the upstream end of the ozone passage 31, and an ozone generator 32 is provided between the air pump 33 and the exhaust passage 11.

  The ozone generator 32 includes a housing that forms a flow path therein, and a plurality of electrodes are disposed in the flow path. These electrodes have a flat plate shape arranged so as to face each other in parallel, and electrodes to which a high voltage is applied and electrodes having a ground voltage are alternately arranged. Air blown by the air pump 33 flows into the housing of the ozone generator 32. This air flows into the flow passage in the housing and flows through the interelectrode passage, which is a passage between the electrodes.

  When the electrode of the ozone generator 32 is energized, electrons emitted from the electrode collide with oxygen molecules contained in the air in the interelectrode passage. Then, ozone is generated from oxygen molecules. That is, the ozone generator 32 generates ozone by changing oxygen molecules into a plasma state by discharge. Therefore, when the ozone generator 32 is energized, ozone is contained in the external air flowing from the ozone generator 32 toward the exhaust passage 11.

  The exhaust cutoff valve 34 is an electromagnetically driven on-off valve, and is provided between the ozone generator 32 and the exhaust passage 11 in the ozone passage 31. When the exhaust cutoff valve 34 is closed, the communication between the ozone passage 31 and the exhaust passage 11 is shut off. This prevents exhaust from flowing back through the ozone passage 31 and reaching the ozone generator 32. The pressure sensor 35 is provided between the ozone generator 32 and the exhaust cutoff valve 34 in the ozone passage 31 and detects the internal pressure of the ozone passage 31 as a passage pressure.

The addition nozzle 36 is attached to the downstream end of the ozone passage 31 and is arranged on the upstream side of the NOx purification unit 20 in the exhaust passage 11. When ozone is added from the addition nozzle 36 to the exhaust passage 11, NOx in the exhaust gas that reaches the NOx purification unit 20 is easily oxidized by ozone. Examples of NOx oxidized by ozone include NO ₂ in which NO is oxidized and NO ₃ in which NO ₂ is oxidized.

  The control device 37 controls the operation of the ozone generator 32, the air pump 33, and the exhaust cutoff valve 34. For example, the NOx amount in the exhaust or the NO amount in the NOx is estimated based on the engine speed, the engine load, and the like. Then, the operations of the ozone generator 32 and the air pump 33 are controlled based on the estimated NO amount so as to add the ozone amount corresponding to the estimated NO amount.

  Further, the control device 37 opens the exhaust cutoff valve 34 when ozone addition is required. However, when the pressure detected by the pressure sensor 35 becomes higher than the pressure in the exhaust passage 11 or when it is predicted to become higher, the exhaust shut-off valve 34 is closed so that the above-described exhaust backflow occurs. Avoid it.

As shown in FIG. 2, the NOx purification unit 20 includes an adsorption unit 20A and a reduction unit 20B. The adsorption unit 20A adsorbs NOx in the exhaust gas oxidized by the ozone added from the ozone addition unit 30. The adsorption force for NO ₂ is larger than the adsorption force for NO, and the adsorption force for NO ₃ is larger than the adsorption force for NO ₂ . Therefore, particularly at low temperatures (for example, 100 ° C. to 200 ° C.), the adsorption power can be increased by supplying ozone to the exhaust and oxidizing NO to NO ₂ or NO ₃ . NOx adsorbed at a low temperature becomes easier to desorb from the adsorbing portion 20A as the amount of NOx adsorbed in the adsorbing portion 20A increases. Also, the higher the temperature, the easier it is to desorb. The reducing unit 20B is disposed downstream of the adsorption unit 20A in the exhaust flow direction, and reduces NOx desorbed from the adsorption unit 20A to N ₂ .

  The NOx purification unit 20 includes a base material 22 that is a skeleton of the adsorption unit 20A and the reduction unit 20B. The base material 22 is a through-flow type honeycomb, and is formed in a lattice shape by cordierite or silicon carbide. The inner part partitioned by the base material 22 in a lattice shape functions as a plurality of lattice passages 21 extending along the exhaust passage 11. In other words, the base material 22 has a cylindrical shape extending in the exhaust flow direction, and a plurality of lattice passages 21 extending in the exhaust flow direction are formed inside the cylinder.

  A portion of the surface of the base material 22 that forms the adsorption portion 20A is referred to as a first region 22A, and a portion of the surface of the base material 22 that forms the reduction portion 20B is referred to as a second region 22B. As shown in FIG. 3, the first carrier 23 is coated on the first region 22 </ b> A on the surface of the base material 22. As shown in FIG. 4, the second carrier 24 is coated on the second region 22 </ b> B on the surface of the substrate 22.

Alumina Al ₂ O ₃ is used as the material of the first carrier 23 and the second carrier 24. The first carrier 23 and the second carrier 24 have a porous shape in which a large number of pores are formed. This porous shape is formed when the gas vaporized inside the paste escapes to the outside by heating the paste-like alumina.

The second carrier 24 carries a reduction catalyst 24a. Noble metals such as Pt, Rh, and Pd are used as the reduction catalyst. The activity of the reduction catalyst 24a is enhanced when its temperature rises to an activation temperature (for example, about 300 ° C.). In a state where the reduction catalyst 24a is sufficiently activated, NOx is easily reduced to nitrogen N ₂ on the reduction catalyst 24a. On the other hand, the first carrier 23 does not carry a catalyst, and the amount of the oxidation catalyst and adsorption catalyst carried by the first carrier 23 is zero.

  Next, the manufacturing method about the NOx purification part 20 among the manufacturing methods of a NOx purification apparatus is demonstrated using FIG. The procedure according to this manufacturing method is a procedure performed by an operator using various manufacturing apparatuses. First, in step S10, a paste as a base material of the first carrier 23 and a paste as a base material of the second carrier 24 are formed. Specifically, powdery alumina is dissolved in a solution to form a paste. Further, the reduction catalyst 24 a is mixed in the paste of the second carrier 24. The paste of the first carrier 23 is not mixed with an oxidation catalyst or an adsorption catalyst.

  Next, in step S <b> 11, the paste-like first carrier 23 formed in step S <b> 10 is applied to the first region 22 </ b> A (see FIG. 2) in the surface of the base material 22. The base material 22 is divided into a first region 22A that is an upstream portion in the exhaust flow direction and a second region 22B that is a downstream portion. The first region 22A and the second region 22B are adjacent to each other. For example, the paste-like first carrier 23 is stored in a container, and the base material 22 is oriented so that the axial direction of the base material 22 coincides with the vertical direction and the first region 22A is on the lower side. adjust. Thereafter, the substrate 22 is lowered by a predetermined amount, and the first region 22A of the substrate 22 is immersed in the paste in the container. Then, the base material 22 is raised and taken out from the container. Thereby, the paste-like first carrier 23 is applied to the first region 22A.

  Next, in step S <b> 12, hot air is blown onto the first carrier 23 applied to the base material 22 to dry the first carrier 23. This prevents the first carrier 23 applied to the base material 22 from dripping.

  Next, in step S <b> 13, the paste-like second carrier 24 formed in step S <b> 10 is applied to the second region 22 </ b> B (see FIG. 2) in the surface of the base material 22. For example, the paste-like second carrier 24 is stored in a container, and the base material 22 is oriented so that the axial direction of the base material 22 coincides with the vertical direction and the second region 22B is on the lower side. adjust. Thereafter, the base material 22 is lowered by a predetermined amount, and the second region 22B of the base material 22 is immersed in the paste in the container. Then, the base material 22 is raised and taken out from the container. Thereby, the paste-like second carrier 24 is applied to the second region 22B.

  Next, in step S <b> 14, hot air is blown onto the second carrier 24 applied to the base material 22 to dry the second carrier 24. This prevents the second carrier 24 applied to the base material 22 from dripping.

  Next, in step S <b> 15, the applied first carrier 23 and second carrier 24 are heated together with the base material 22. Accordingly, the first carrier 23 and the second carrier 24 are formed in a porous shape and are baked onto the base material 22. In the example shown in FIG. 2, the lengths of the first region 22A and the second region 22B in the exhaust passage direction are set to be the same, but one of the first region 22A and the second region 22B is the other. You may set larger than.

Contrary to this embodiment, in the case of a NOx purification device (comparative example) in which platinum Pt as an oxidation catalyst and barium Ba as an adsorption catalyst are supported on the first carrier 23, the CO shown in the upper part of FIG. An inhibitory reaction occurs. That is, even if ozone is added at low temperatures to change NO to NO ₂ or NO ₃ to increase the amount of NOx adsorbed to the adsorption catalyst at low temperatures, CO in the exhaust gas reacts with NO _2. As a result, NO ₂ becomes NO. That is, in the low temperature, even by oxidizing NO to NO ₂ with ozone, the so produced NO ₂ is will go back to NO by reaction with CO, achieving a sufficient NOx adsorption promoting Ozone I can't.

On the other hand, when the amount of the oxidation catalyst and the adsorption catalyst supported by the first carrier 23 is zero, there is no oxidation catalyst that promotes the CO inhibition reaction. Therefore, as shown in the lower part of FIG. No longer occurs. The inventors have found that a phenomenon occurs in which NO ₃ produced by the added ozone is directly adsorbed to the first carrier 23.

  The present inventors conducted the following tests to confirm the above findings, and obtained the test results shown in FIGS.

  In the test according to FIG. 7, an adsorption part 20Ax (comparative example) shown in the upper part of FIG. 6 carrying an oxidation catalyst and an adsorption catalyst is prepared. In the test according to FIG. 8, the adsorption unit 20 </ b> A according to the present embodiment in which the loading amount of the oxidation catalyst and the adsorption catalyst is zero is prepared. In the tests of FIG. 7 and FIG. 8, exhaust gas for test simulating exhaust gas is caused to flow into the adsorbing portions 20A and 20Ax in which the NOx adsorption amount is zero. The test is performed on each of the test exhaust gas containing 1000 ppm of CO and the test exhaust gas not containing CO. Also, the same amount of ozone is added to any test exhaust gas.

Further, in the above test, the amount of NOx is measured on the downstream side of the adsorbing portions 20A and 20Ax when the test exhaust gas is flowing into the adsorbing portions 20A and 20Ax. Therefore, when all the NO ₂ (that is, the NOx inflow amount) in the test exhaust gas flowing into the adsorption portions 20A and 20Ax is adsorbed, the measured NOx amount (that is, the NOx outflow amount) becomes zero. The ratio of the NOx outflow amount to the NOx inflow amount is referred to as the NOx adsorption rate. In this test, the amount of NO contained in the test exhaust gas is adjusted to 200 ppm. Further, the center temperature of the adsorption portions 20A and 20Ax is adjusted to 130 ° C.

  According to the test results of FIG. 7 and FIG. 8, as the test time elapses, when the NOx adsorption amount shown on the horizontal axis increases and exceeds a certain amount, the NOx adsorption rate shown on the vertical axis decreases. I understand. In the case of the comparative example, the NOx adsorption rate decreases remarkably when tested with exhaust gas containing CO, whereas the NOx adsorption rate decreases slowly when tested with exhaust gas not containing CO. It is. This means that the NOx adsorption rate is remarkably reduced due to the CO inhibition reaction. On the other hand, in the present embodiment, the rate of decrease in the NOx adsorption rate is almost the same between the case of containing CO and the case of not containing CO. This means that it is hardly affected by the CO inhibition reaction.

  In the test according to FIG. 9, a sufficient amount of NOx is adsorbed in an environment where ozone exists for each of the adsorption unit 20A according to the present embodiment and the adsorption unit 20Ax according to the comparative example. The temperature of the adsorption portions 20A and 20Ax is gradually increased. Then, the amount of NOx is measured downstream of the adsorption units 20A and 20Ax, and this measured value corresponds to the amount of NOx desorbed from the adsorption units 20A and 20Ax. The solid line in FIG. 9 shows the change in the measured value of the NOx desorption amount when the adsorption unit 20A according to this embodiment is used, and the dotted line in FIG. 9 is the case where the adsorption unit 20Ax according to the comparative example is used. The change in the measured value of the NOx desorption amount is shown.

As the test time elapses, the center temperatures of the adsorption portions 20A and 20Ax shown on the horizontal axis gradually increase, and the NOx desorption amount increases as the temperature rises. In the case of the adsorption part 20Ax according to the comparative example, the NOx desorption amount peaks at two locations of 350 ° C and 570 ° C. The NOx desorption amount peaking at 350 ° C. is assumed to be due to NO ₂ desorption, and the NOx desorption amount peaking at 570 ° C. is due to NO ₃ desorption. Inferred. On the other hand, in the case of the adsorption part 20A according to the present embodiment, the NOx desorption amount peaks at one place at 430 ° C. Since the peak is not at two places but at one place, it is presumed that NOx adsorbed on the first carrier 23 is NO ₃ and that NO ₂ is hardly adsorbed. The test results in FIG. 9 show that the peak of the NOx desorption amount according to this embodiment is lower than that in the comparative example.

  In the test according to FIG. 10, the NOx adsorption amount decrease rate described below is tested by changing the amount of the oxidation catalyst supported in the adsorption unit 20Ax according to the comparative example. 7 and 8, the NOx adsorption amount when the NOx adsorption rate reaches a predetermined value is referred to as a reference adsorption amount. The ratio of the reference adsorption amount when CO is included to the reference adsorption amount when CO is not included in the exhaust gas is called the NOx adsorption amount decrease rate, and the vertical axis in FIG. 10 indicates the NOx adsorption amount decrease rate. In the tests of FIGS. 7 and 9, the weight of Pt contained in each liter of the adsorbing portion 20Ax according to the comparative example (that is, the amount of Pt supported) is set to 1.0 g / L. In the test of FIG. 10, the NOx adsorption amount decrease rate was measured for each of the Pt loadings of 1.0 g / L, 0.5 g / L, 0.2 g / L, and 0.0 g / L. The horizontal axis of 10 indicates the amount of Pt supported.

  The test results in FIG. 10 indicate that the smaller the amount of Pt supported, the smaller the NOx adsorption amount decrease rate and the less the influence of the CO inhibition reaction. It can be seen from the test results of FIGS. 7 to 10 that a sufficient amount of NOx can be adsorbed even if the amount of Pt supported is zero under an environment where ozone is added.

As described above, according to the present embodiment, assuming that the NOx purification unit 20 is applied to an exhaust system to which ozone can be added, the amount of the oxidation catalyst supported by the first carrier 23 included in the adsorption unit 20A is zero. is there. As a result, the CO inhibition reaction in which NO ₂ generated by the addition of ozone returns to NO hardly occurs, so that the certainty of NOx adsorption promotion by ozone at a low temperature can be improved. Therefore, sufficient NOx adsorption can be realized even at a low temperature at which the catalyst cannot be sufficiently activated.

Further, under the ozone is added conditions, NO and NO ₂ is oxidized to NO _3, is NO ₃ was found that the phenomenon is adsorbed directly to the first carrier 23 occurs. Therefore, in this embodiment, since the amount of adsorption catalyst supported is also zero, the material cost of the adsorption unit 20A can be reduced.

  Further, in the present embodiment, the adsorption unit 20A and the reduction unit 20B are arranged side by side in the exhaust flow direction, and the adsorption unit 20A is arranged on the upstream side of the reduction unit 20B in the exhaust flow direction. According to this, by stacking the first carrier 23 and the second carrier 24, the reduction catalyst 24a supported on the second carrier 24 can be compared with the case where the adsorption unit 20A and the reduction unit 20B are stacked and arranged. The first carrier 23 can be disposed at a sufficiently distant position. Therefore, the possibility that the CO inhibition reaction may occur in the adsorption unit 20A due to the influence of the reduction catalyst 24a can be reduced.

  Furthermore, in this embodiment, the base material 22 holding both the first carrier 23 and the second carrier 24 is provided. According to this, since the base material holding the first carrier 23 and the base material holding the second carrier 24 can be shared, the number of parts can be increased compared to the case where each base material is provided separately. Reduction and downsizing of the apparatus can be achieved.

  Further, in this embodiment, alumina is used for the first carrier 23. When alumina is used for the first carrier 23, it has been confirmed that sufficient adsorption performance is exhibited as shown in FIGS.

  Furthermore, in the present embodiment, a paste-like first carrier 23 having an oxidation catalyst content of zero is applied to the first region 22A on the surface of the substrate 22. Thereafter, the paste-like second carrier 24 containing the reduction catalyst 24a is applied to the second region 22B adjacent to the first region 22A in the surface of the base material 22. Thereafter, the first carrier 23 and the second carrier 24 are heated together with the base material 22 so that the first carrier 23 and the second carrier 24 are made porous and baked on the base material 22. Therefore, since the second carrier is applied after the first carrier is applied, it is possible to avoid the first carrier from being superimposed on the second carrier at the boundary between the first region and the second region. Therefore, the risk of the CO inhibition reaction due to the superposition described above can be avoided.

(Second Embodiment)
In the first embodiment, the first carrier 23 is provided in the first region 22A, the second carrier 24 is provided in the second region 22B, and each of the first carrier 23 and the second carrier 24 is the base material 22. Is provided on the surface. In contrast, in the NOx purification unit 202 according to the present embodiment, the first carrier 23 is provided in both the first region 22A and the second region 22B, and the entire surface of the base material 22 is covered with the first carrier 23. It has been broken. And the 2nd support | carrier 24 is provided in the surface of the 1st support | carrier 23 of the part provided in 2nd area | region 22B (refer FIG. 11). That is, the adsorption part 20A according to the present embodiment has the same cross-sectional shape as shown in FIG. 3 as in the first embodiment, and the reduction part 202B according to the present embodiment has the cross-sectional shape shown in FIG.

  Next, the manufacturing method about the NOx purification part 202 among the manufacturing methods of a NOx purification apparatus is demonstrated using FIG. The procedure of this manufacturing method is a procedure performed by an operator using various manufacturing apparatuses. First, in step S20, a paste of the first carrier 23 and the second carrier 24 is formed in the same manner as in step S10 of FIG. The second carrier 24 is mixed with a reduction catalyst 24a, and the first carrier 23 is not mixed with an oxidation catalyst or an adsorption catalyst.

  Next, in step S <b> 21, the pasty first carrier 23 formed in step S <b> 20 is applied to the entire surface of the base material 22. For example, the 1st support | carrier 23 is apply | coated to the whole base material 22 by storing the paste-like 1st support | carrier 23 in the container and immersing the whole base material 22 in the paste in a container. Next, in step S <b> 22, hot air is blown onto the first carrier 23 applied to the base material 22 to dry the first carrier 23.

  Next, in step S23, the paste-like second carrier 24 formed in step S20 is applied to the second region 22B (see FIG. 2) in the surface of the first carrier 23. For example, the paste-like second carrier 24 is stored in a container in the same manner as in step S13 of FIG. Then, the orientation of the base material 22 is adjusted so that the second region 22B is on the lower side, and then the base material 22 is lowered by a predetermined amount, so that the second region 22B is immersed in the paste in the container. Thereafter, the base material 22 is raised and taken out from the container, whereby the paste-like second carrier 24 is applied to the second region 22B. Next, in step S <b> 24, hot air is blown onto the second carrier 24 applied to the base material 22 to dry the second carrier 24.

  Next, in step S25, the coated first carrier 23 and second carrier 24 are heated together with the base material 22 in the same manner as in step S15 of FIG. Bake.

As described above, in the present embodiment as well, in the same manner as in the first embodiment, the amount of the oxidation catalyst supported by the first carrier 23 included in the adsorption unit 20A becomes zero, so that almost no CO inhibition reaction occurs. The certainty of NOx adsorption promotion by ozone can be improved. In addition, in a situation where ozone is added, focusing on NO ₃ being directly adsorbed on the first carrier 23, the amount of adsorption catalyst supported is also reduced to zero, so that the material cost of the adsorption unit 20A can be reduced. .

  In the present embodiment, the second carrier 24 is laminated on the first carrier 23. However, since the first carrier 23 does not carry a catalyst, the reducing ability of the second carrier 24 is high. There is no problem of reducing under the influence of

  Furthermore, in this embodiment, the paste-like 1st support | carrier 23 with which the content of an oxidation catalyst is zero is apply | coated to the whole surface of the base material 22. FIG. Thereafter, a paste-like second carrier 24 containing a reduction catalyst is applied to a portion of the surface of the first carrier 23 corresponding to the second region 22B. Thereafter, the first carrier 23 and the second carrier 24 are heated together with the base material 22 so that the first carrier 23 and the second carrier 24 are made porous and baked on the base material 22. Therefore, in order to manufacture on the premise that the second carrier 24 is stacked on the first carrier 23, the application range of the first carrier 23 is larger than that in the case where the first carrier 23 is applied to the predetermined first region 22A. It is unnecessary to manage with high accuracy. For example, when the base material 22 is lowered and immersed in the paste-like first carrier 23 stored in the container, the amount of the base material 22 to be lowered can be roughly controlled, so that the production efficiency can be improved.

(Third embodiment)
The substrate 22 according to the first embodiment has a through-flow honeycomb shape shown in FIG. 2, but the substrate 22 of the NOx purification section 203 according to the present embodiment is a wall flow honeycomb shown in FIG. Shape. Specifically, for half of the plurality of lattice passages 21 shown in FIG. 2, the inlet of the lattice passage is closed with a sealing wall 25 to form an inflow passage 21a. For the remaining half, the outlet of the lattice passage is closed with a sealing wall 25 to form the outflow passage 21b. According to this configuration, as shown by the arrow in FIG. 13, the exhaust gas flowing in from the inflow port flows through the inflow passage 21a, then flows through the wall of the base material 22 to the adjacent outflow passage 21b, and thereafter Then, it flows through the outflow passage 21b and flows out from the outflow port.

  In this embodiment of the wall flow type as well, the first carrier 23 and the second carrier 24 are provided on the base material 22 in the same manner as in the first or second embodiment, and the first carrier 23 carries the oxidation catalyst. The amount is set to zero. Therefore, since the CO inhibition reaction can be suppressed also in this embodiment, the certainty of NOx adsorption promotion by ozone at a low temperature can be improved.

(Fourth embodiment)
In the second embodiment, the first carrier 23 is provided on the entire surface of the base material 22, and the second carrier 24 is provided in a portion of the first carrier 23 corresponding to the second region 22 </ b> B. In contrast, in the NOx purification unit 204 according to the present embodiment, as shown in FIG. 14, the second carrier 24 is provided on the entire surface of the base material 22, and the first carrier 23 is provided on the entire surface of the second carrier 24. Yes. Specifically, the second carrier 24 is applied to the surface of the base material 22 and the first carrier 23 is applied to the surface of the second carrier 24 in both the first region 22A and the second region 22B. ing.

  That is, in the first embodiment and the second embodiment, the adsorption unit 20A and the reduction unit 20B are arranged side by side in the exhaust flow direction. On the other hand, in the present embodiment, the first carrier 23 that forms the adsorption part and the second carrier 24 that forms the reduction part are stacked on the base material 22, so that the adsorption part and the reduction part are exhausted. It can be said that they are arranged side by side in a direction perpendicular to the flow direction. And the shape of the base material 22 is a through flow type.

According to this embodiment having the above configuration, when NOx is adsorbed at a low temperature, NO ₃ oxidized by ozone is adsorbed by the second carrier 24 exposed in the lattice passage 21. Then, when the NOx desorbed from the second carrier 24 passes through the pores in the first carrier 23 and reaches the reduction part, it is reduced by the reduction catalyst 24a carried on the second carrier 24 in the reduction part. .

  Also in the present embodiment, the amount of the oxidation catalyst supported on the first carrier 23 is set to zero as in the first embodiment or the second embodiment. Therefore, since the CO inhibition reaction can be suppressed also in this embodiment, the certainty of NOx adsorption promotion by ozone at a low temperature can be improved.

(Other embodiments)
The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made as illustrated below. Not only combinations of parts that clearly show that combinations are possible in each embodiment, but also combinations of the embodiments even if they are not explicitly stated unless there is a problem with the combination. Is also possible.

In each of the above embodiments, alumina is used for the first carrier 23, but alumina silica or zeolite may be used, or they may be mixed in combination as appropriate. In short, it is desirable that at least one of alumina, alumina silica, and zeolite is contained in the component of the first carrier 23. In addition to these materials, silica SiO ₂ , ceria CeO, zirconia ZrO ₂ , lanthanum La, and titania TiO ₂ may be used, or they may be appropriately combined and mixed.

  In each of the above embodiments, the amount of adsorption catalyst supported by the first carrier 23 is zero. On the other hand, an adsorption catalyst such as barium may be supported on the first carrier 23.

  The NOx purification unit 20 shown in FIG. 1 is applied to a diesel engine that is a compression self-ignition internal combustion engine, but is an ignition ignition internal combustion engine that directly injects fuel into a combustion chamber. It may be applied to.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 11 ... Exhaust passage, 20, 202, 203, 204 ... NOx purification part, 20A ... Adsorption part, 20B, 202B ... Reduction part, 22 ... Base material, 23 ... 1st support | carrier, 24 ... 2nd support | carrier 24a ... reduction catalyst, 30 ... ozone addition part.

Claims (7)

In an NOx purification device that is applied to an exhaust system that can add ozone to an exhaust passage (11) of an internal combustion engine (10) and that reduces and purifies NOx contained in exhaust gas,
An adsorbing portion (20A) having a porous first support (23) for adsorbing NOx oxidized by ozone added to the exhaust passage;
A reduction part (20B, 202B) having a porous second support (24), and reducing NOx desorbed from the adsorption part with a reduction catalyst (24a) supported on the second support;
With
The NOx purification device in which the amount of the oxidation catalyst supported by the first carrier is zero, and the first carrier adsorbs NOx. The adsorbing part and the reducing part are arranged side by side in the exhaust flow direction,
The NOx purification device according to claim 1, wherein the adsorption unit is disposed upstream of the reduction unit in the exhaust flow direction.   The NOx purification device according to claim 2, further comprising a base material (22) that holds both the first carrier and the second carrier.   The NOx purification device according to any one of claims 1 to 3, wherein the component of the first carrier includes at least one of alumina, alumina silica, and zeolite.   The NOx purification device according to any one of claims 1 to 4, further comprising an ozone addition section (30) for adding ozone to the exhaust passage (11) of the internal combustion engine (10). An adsorbing portion (20A) having a porous first support (23) and adsorbing NOx oxidized by ozone added to the exhaust passage (11) of the internal combustion engine (10);
A reducing unit (20B) having a porous second carrier (24), and reducing NOx desorbed from the adsorption unit with a reduction catalyst (24a) supported on the second carrier;
In a manufacturing method of a NOx purification device comprising:
Applying the paste-like first carrier having an oxidation catalyst content of zero to the first region (22A) on the surface of the substrate (22),
Then, the paste-like second carrier containing the reduction catalyst is applied to the second region (22B) adjacent to the first region of the surface of the substrate,
Thereafter, the first carrier and the second carrier are heated together with the base material, whereby the first carrier and the second carrier are made porous to be baked on the base material. An adsorbing portion (20A) having a porous first support (23) and adsorbing NOx oxidized by ozone added to the exhaust passage (11) of the internal combustion engine (10);
A reducing unit (202B) having a porous second carrier (24), and reducing NOx desorbed from the adsorption unit with a reduction catalyst (24a) supported on the second carrier;
In a manufacturing method of a NOx purification device comprising:
On the surface of the base material (22), the paste-like first carrier having an oxidation catalyst content of zero is applied,
Thereafter, the paste-like second carrier containing the reduction catalyst is applied to a part of the surface of the first carrier,
Thereafter, the first carrier and the second carrier are heated together with the base material, whereby the first carrier and the second carrier are made porous to be baked on the base material.

Images