JP2011163286A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the NOx reduction ratio without increasing the dimensions of an exhaust emission control device over the whole. <P>SOLUTION: The exhaust emission control device includes an NOx absorption/reduction catalyst 12 on the way of an exhaust pipe 11, and is configured to reduce NOx to control exhaust emission by adding a gas oil 4 (fuel) as a reducing agent on an upstream side of the NOx absorption/reduction catalyst 12. The NOx absorption/reduction catalyst 12 is formed by molding a catalyst raw material itself into a flow-through type honeycomb shape without using a carrier, and the shaped body is burned to form a porous structure, in which exhaust gas 9 can pass through. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device.

Conventionally, exhaust purification is carried out with an exhaust purification catalyst installed in the middle of the exhaust pipe. As this type of exhaust purification catalyst, NOx in exhaust gas is oxidized when the exhaust air-fuel ratio is lean. Thus, a NOx occlusion reduction catalyst having the property of temporarily storing in the form of nitrate and decomposing and releasing NOx through the intervention of unburned HC, CO, etc. when the O ₂ concentration in the exhaust gas decreases is reduced and purified. Are known.

In such a NOx occlusion reduction catalyst, when the occlusion amount of NOx increases and reaches the saturation amount, no more NOx can be occluded, so that the exhaust gas flowing into the NOx occlusion reduction catalyst periodically It is necessary to decompose and release NOx by reducing the O ₂ concentration.

For example, when used in a gasoline engine, the operating air-fuel ratio of the engine is reduced (the engine is operated at a rich air-fuel ratio), thereby reducing the O ₂ concentration in the exhaust gas and unburned HC in the exhaust gas. It is possible to promote the decomposition and release of NOx by increasing reducing components such as CO and CO. However, when the NOx storage reduction catalyst is used as an exhaust purification device of a diesel engine, it is difficult to operate the engine at a rich air-fuel ratio. is there.

For this reason, a means for adding fuel (HC) to the exhaust gas upstream of the NOx storage reduction catalyst is newly provided, and the added fuel reacts with O ₂ on the NOx storage reduction catalyst as a reducing agent, It is necessary to actively reduce the O ₂ concentration in the exhaust gas to regenerate the NOx storage reduction catalyst (see, for example, Patent Document 1).

JP 2000-356127 A

  However, since the conventional NOx occlusion reduction catalyst is made by coating a cordierite carrier, when an attempt is made to increase the amount of catalyst to achieve a higher NOx reduction rate than before, the increase in the amount of catalyst will be increased. There is a problem that a substantial increase in the volume of the corresponding cordierite carrier is caused, and an increase in the size of the entire exhaust gas purification apparatus cannot be avoided.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to improve the NOx reduction rate without causing an increase in the size of the entire exhaust gas purification apparatus.

  The present invention is an exhaust emission control device equipped with a NOx storage reduction catalyst in the middle of an exhaust pipe and configured to reduce and purify NOx by adding fuel as a reducing agent upstream of the NOx storage reduction catalyst, The NOx occlusion reduction catalyst is formed by molding the catalyst raw material itself into a flow-through honeycomb type without using a carrier and firing the molded body so as to form a porous structure through which exhaust gas can pass. It is what.

  Thus, in this way, since the catalyst raw material itself is molded without using a carrier to form a NOx occlusion reduction catalyst, it is possible to increase all the volume previously occupied by the carrier as a catalyst raw material. Thus, the amount of catalyst can be greatly increased without increasing the overall size of the exhaust purification device.

  Moreover, since the flow-through honeycomb-shaped molded body is fired so as to form a porous structure through which exhaust gas can pass, the diffusibility of exhaust gas passing through the NOx storage reduction catalyst is improved and the exhaust The contact area between the gas and the catalyst will be greatly increased, and the NOx reduction performance per unit catalyst amount will be greatly improved as compared with the prior art.

  Further, in the present invention, the inlets of the respective channels partitioned in a lattice pattern of the NOx occlusion reduction catalyst are alternately sealed, and the outlets of the channels whose inlets are not sealed are sealed, and the respective channels It is preferable that only the exhaust gas that has passed through the partition wall partitioning the exhaust gas is discharged to the downstream side, and the NOx occlusion reduction catalyst has a filter function for collecting particulates in the exhaust gas.

  In this way, since the NOx storage reduction catalyst can be used as a particulate filter, it becomes possible to collect particulates without securing a new particulate filter mounting space. In addition, it is possible to burn and remove the particulates collected in the interior during the desulfurization treatment of the NOx storage reduction catalyst.

  As the catalyst raw material for the NOx occlusion reduction catalyst, for example, it is possible to use a mixture of barium carbonate and potassium carbonate on alumina supporting platinum and rhodium. If such a catalyst raw material is used, NOx occlusion catalyst can be used. It becomes possible to form the reduction catalyst satisfactorily by using only the catalyst raw material without using a carrier.

  According to the exhaust emission control device of the present invention described above, various excellent effects as described below can be obtained.

  (I) According to the invention described in claim 1 of the present invention, since the catalyst raw material itself is molded without using a carrier to form a NOx occlusion reduction catalyst, the volume occupied by the carrier so far is reduced. All of this can be increased as a catalyst raw material, and the diffusibility of exhaust gas passing through the NOx occlusion reduction catalyst is achieved by firing a flow-through honeycomb-shaped molded body so as to form a porous structure through which exhaust gas can pass. And the contact area between the exhaust gas and the catalyst can be greatly increased, and the NOx reduction performance per unit catalyst amount can be greatly improved as compared with the prior art. The NOx reduction rate can be improved.

  (II) According to the invention described in claim 2 of the present invention, the NOx occlusion reduction catalyst can also be used as a particulate filter. Therefore, the particulates can be obtained without newly securing a space for mounting the particulate filter. In addition, the particulates trapped inside can be burned and removed during the desulfurization treatment of the NOx storage reduction catalyst.

  (III) According to the invention described in claim 3 of the present invention, the NOx occlusion reduction catalyst can be satisfactorily molded only from the catalyst raw material without using the carrier, and the liquid phase can be obtained by using no carrier. It is also possible to avoid the problem that the potassium carbonate moves to the carrier side and NOx occlusion performance decreases.

It is the schematic which shows an example of the form which implements this invention. FIG. 2 is a perspective view with a part cut away showing details of the NOx occlusion reduction catalyst of FIG. 1. It is the graph which compared NOx reduction rate with the conventional NOx storage reduction catalyst. It is the schematic which shows another form example of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an example of an embodiment for carrying out the present invention. In FIG. 1, reference numeral 1 denotes a diesel engine. The diesel engine 1 includes a turbocharger 2, and intake air guided from an air cleaner 3. 4 is sent to the compressor 2 a of the turbocharger 2 through the intake pipe 5, and the intake air 4 pressurized by the compressor 2 a is sent to the intercooler 6 to be cooled, and further from the intercooler 6 to the intake manifold 7. The intake 4 is guided to the cylinder 8 and distributed to each cylinder 8 of the diesel engine 1.

  The exhaust gas 9 discharged from each cylinder 8 of the diesel engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 10, and the exhaust gas 9 that has driven the turbine 2b is exhausted (exhaust flow path). 11 is passed through the NOx occlusion reduction catalyst 12 in the middle of the exhaust pipe 11, and after the NOx occlusion is reduced by the NOx occlusion reduction catalyst 12, it is discharged outside the vehicle.

  The exhaust pipe 11 on the inlet side of the NOx storage reduction catalyst 12 is provided with a fuel addition device 16 that guides the light oil 14 (fuel) from the light oil tank 13 by the pump 15 and injects it toward the NOx storage reduction catalyst 12. The NOx occlusion reduction catalyst 12 is regenerated using the light oil 14 added by the fuel addition device 16 as a reducing agent.

  Here, as shown in FIG. 2, the NOx occlusion reduction catalyst 12 is a mixture of barium carbonate and potassium carbonate in alumina supporting platinum and rhodium without using a conventional cordierite carrier. As the catalyst material, the catalyst material itself is molded into a flow-through honeycomb type, and the molded body is fired so as to form a porous structure through which the exhaust gas 9 can pass.

  When forming the catalyst raw material into a flow-through honeycomb type, the catalyst raw material is put into a conventionally known extruder and extruded from a discharge port while kneading with a screw, and the flow through is performed depending on the shape of the die attached to the discharge port. It is sufficient that the catalyst raw material is molded into the honeycomb type, and when firing so as to form a porous structure, particles of resin, carbon, etc. that are burned down under high temperature conditions at the time of firing to form voids May be mixed with the catalyst raw material as a pore former.

  Thus, in this way, since the catalyst raw material itself is molded without using the cordierite carrier to form the NOx occlusion reduction catalyst 12, all of the volume previously occupied by the cordierite carrier is used as the catalyst raw material. As a result, the amount of catalyst can be significantly increased without increasing the size of the entire exhaust gas purification apparatus.

  In addition, since the flow-through honeycomb-shaped molded body is fired so as to form a porous structure through which the exhaust gas 9 can pass, the diffusibility of the exhaust gas 9 passing through the NOx storage reduction catalyst 12 is improved. As a result, the contact area between the exhaust gas 9 and the catalyst is greatly increased, and the NOx reduction performance per unit catalyst amount is greatly improved as compared with the prior art.

  Here, it should be further noted that in this embodiment, since the catalyst raw material is a mixture of barium carbonate and potassium carbonate on alumina supporting platinum and rhodium, the cordierite carrier can be used as before. For example, there is a concern that liquid phase potassium carbonate (barium carbonate is a solid phase) moves to the cordierite carrier side and the NOx occlusion ability decreases, but such a concern is avoided by not using the cordierite carrier. There is also a merit.

  Therefore, according to the above embodiment, the catalyst raw material itself is molded without using the cordierite carrier to form the NOx occlusion reduction catalyst 12, so that all the volume occupied by the cordierite carrier up to now is taken as the catalyst raw material. Furthermore, the diffusibility of the exhaust gas 9 passing through the NOx occlusion reduction catalyst 12 is obtained by calcining the flow-through honeycomb-shaped molded body so as to form a porous structure through which the exhaust gas 9 can pass. In addition, the contact area between the exhaust gas 9 and the catalyst can be greatly increased, and the NOx reduction performance per unit catalyst amount can be greatly improved as compared with the prior art. Therefore, the NOx reduction rate can be improved.

  In fact, in the verification experiment by the present inventor, as shown by a graph in FIG. 3, compared with a conventional NOx occlusion reduction catalyst (shown by curve A in FIG. 3) formed by coating a catalyst raw material on a cordierite carrier. It is confirmed that the NOx occlusion reduction catalyst (shown by curve B in FIG. 3) of the present embodiment in which the catalyst raw material itself is molded and calcined can obtain a higher NOx reduction rate in all active temperature ranges. Has been.

  FIG. 4 shows another embodiment of the present invention. In this embodiment, the inlets of the respective flow paths 12a partitioned in a lattice pattern of the NOx storage reduction catalyst 12 are alternately sealed and the inlets are closed. The NOx occlusion reduction catalyst is configured such that only the exhaust gas 9 passing through the partition wall 12b partitioning each flow path 12a by sealing the outlet of the unsealed flow path 12a is discharged to the downstream side. 12 is provided with a filter function for collecting particulates in the exhaust gas 9.

  In this way, the NOx occlusion reduction catalyst 12 can be used as a particulate filter, so it is possible to collect particulates without newly securing a particulate filter mounting space. In addition, it is possible to burn and remove the particulates collected in the NOx storage reduction catalyst 12 during the desulfurization process.

That is, in the exhaust gas 9 of the diesel engine 1, SO ₂ gas derived from the sulfur content contained in the light oil of the fuel is present, so this SO ₂ gas is similar to NOx on the NOx occlusion reduction catalyst 12. However, since this sulfate is more stable than nitrate, even if fuel is added to regenerate the NOx storage reduction catalyst 12, the NOx is stored. As a result of the fact that only a part of the sulfate stored in the storage reduction catalyst 12 is released and remains, the recovery rate of the NOx storage site of the NOx storage reduction catalyst 12 becomes small, and the storage capacity decreases. There is.

Therefore, for example, the diesel engine 1 is set in an idling state, and the flow rate of the exhaust gas 9 is narrowed down. Then, the light oil 14 is intermittently added to the inlet side of the NOx storage reduction catalyst 12 by the fuel addition device 16, and this light oil 14 is stored in the NOx. with lowering the O ₂ concentration in the surrounding oxygen is reacted on the reduction catalyst 12 to raise the catalyst bed temperature due to the reaction heat up to 650 to 700 ° C. desulfurization temperature, SO ₂ gas sulfate from the NOx storage-reduction catalyst 12 The desulfurization process to be released as is performed.

At this time, the particulates trapped inside the NOx occlusion reduction catalyst 12 start to burn from around 600 ° C. in the process of raising the catalyst bed temperature to the desulfurization temperature condition of 650 to 700 ° C., and substantially SO ₂ gas. Most of it will be burned away by the beginning of the release.

  Note that the exhaust emission control device of the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

9 exhaust gas 11 exhaust pipe 12 NOx storage reduction catalyst 12a flow path 12b partition wall 14 light oil (fuel)
16 Fuel addition device

Claims (3)

  An exhaust purification apparatus equipped with a NOx storage reduction catalyst in the middle of an exhaust pipe and configured to reduce and purify NOx by adding fuel as a reducing agent upstream of the NOx storage reduction catalyst, the NOx storage reduction Exhaust gas purification characterized in that the catalyst raw material itself is molded into a flow-through honeycomb type without using a carrier, and the molded body is fired to form a porous structure through which exhaust gas can pass. apparatus.   The inlet of each flow path partitioned in a lattice pattern of the NOx occlusion reduction catalyst is alternately sealed, and the outlet of the flow path where the inlet is not sealed is sealed, and passes through the partition wall partitioning each flow path. 2. The exhaust gas according to claim 1, wherein only the exhaust gas is discharged to the downstream side, and the NOx occlusion reduction catalyst is provided with a filter function for collecting particulates in the exhaust gas. Purification equipment.   The exhaust emission control device according to claim 1 or 2, wherein barium carbonate and potassium carbonate are mixed with alumina supporting platinum and rhodium to form a catalyst raw material.

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