JP2006320854A - Selective reduction type catalyst and exhaust gas purifier of engine for use therein - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively prevent NOx from releasing to the atmosphere even at relatively low temperatures relating to a selective reduction type catalyst making NOx contained in an exhaust gas of a diesel engine react with a urea liquid to decompose, and an exhaust gas purifier of an engine for use therein. <P>SOLUTION: The selective reduction type catalyst is equipped with a carrier 26 partitioned by porous partition walls and mutually and parallely formed with a plurality of through holes, and active ingredients having a catalyst action and supported by the partition walls. The mutually adjucent inlets and outlets of the plurality of through holes are alternatively sealed, and the partition walls supported with the active ingredients are composed so as to impermiate ammonium nitrate of particulate solids. The exhaust gas purifier is equipped with the selective reduction type catalyst 24, a liquid injection nozzle 29 capable of injecting the urea liquid 32 to the catalyst, a diesel particulate filter 51 provided on the upstream thereof, and a filter temperature increasing means capable of increasing the temperature of the filter. In order to regenerate the selective reduction type catalyst wherein the ammonium nitrate of particulate solids are accumulated, the particulates accumulated on the filter 51 are combusted, thereby combusting the ammonium nitrate of particulate solids accumulated on the catalyst 24 by the heat of waste gas with increased temperatures to decompose. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a selective reduction catalyst that decomposes nitrogen oxides contained in exhaust gas of a diesel engine by reacting with a urea-based liquid and an exhaust gas purification device for an engine using the same.

Conventionally, as an exhaust gas purification device for reducing nitrogen oxides (hereinafter referred to as “NOx”) contained in exhaust gas of a diesel engine, a selective reduction catalyst is provided in the middle of an exhaust passage of the diesel engine, and the selective reduction catalyst An exhaust gas purification device for a diesel engine is known in which a liquid injection nozzle capable of injecting a urea-based liquid toward the selective reduction catalyst is provided in an exhaust pipe upstream of the exhaust gas (see, for example, Patent Document 1). . A conventional selective catalytic reduction catalyst includes a support having a plurality of through-holes formed in parallel to each other, and an active component having a catalytic action and supported on its partition walls. And in the exhaust gas purification apparatus of the conventional diesel engine provided with this selective reduction-type catalyst, the urea-type liquid injected from the liquid injection nozzle is heated with the heat | fever of exhaust gas, it hydrolyzes, and ammonia is produced. This ammonia functions as a reducing agent that purifies NOx in the exhaust gas by the selective reduction catalyst, and can reduce the amount of NOx discharged to the atmosphere.
JP 2004-239109 A (paragraph numbers [0012] to [0015], FIGS. 2 to 4)

However, when the temperature of the selective catalytic reduction catalyst is a relatively low temperature of about 80 to 200 ° C., NOx decomposition in the selective catalytic reduction catalyst is not effectively performed, and even when the selective catalytic reduction catalyst is provided, The problem to be solved still remains that NOx which is not decomposed is discharged into the atmosphere as it is.
An object of the present invention is to provide a selective reduction catalyst that can effectively prevent NOx from being released into the atmosphere even at a relatively low temperature, and an exhaust gas purification device for an engine using the same.

In the invention according to claim 1, as shown in FIG. 2, a carrier 26 in which a plurality of through-holes 26b partitioned by a porous partition wall 26a are formed in parallel with each other and a catalytic action carried on the partition wall 26a. This is an improvement of a selective catalytic reduction catalyst comprising an active component and configured to decompose nitrogen oxides in exhaust gas of the engine 11 by reacting with a urea-based liquid.
The characteristic configuration is that the inlet portions 26c and the outlet portions 26d adjacent to each other of the plurality of through holes 26b partitioned by the partition walls 26a are alternately sealed, and the partition walls 26a carrying the active ingredient have air permeability. The exhaust gas flowing in from the inlet portion 26c of the through hole 26b passes through the partition wall 26a and is discharged from the outlet portion 26d of the other through hole 26b adjacent to the one through hole 26b, and carries the active ingredient. The partition wall 26a is formed so as to be impermeable to particulate solid ammonium nitrate.
It has been found that when the temperature of the exhaust gas is relatively low, NOx in the exhaust gas reacts with ammonia to produce ammonium nitrate. This ammonium nitrate is a particulate solid at a temperature lower than the melting point of 210 ° C. It becomes a thing. Therefore, in the selective catalytic reduction catalyst described in claim 1, the ammonium nitrate produced when the temperature of the exhaust gas is relatively low is collected by being deposited on the partition walls 26a of the carrier 26, so that the exhaust gas is relatively low in temperature. At this time, NOx can be effectively prevented from being discharged into the atmosphere as it is.

As shown in FIG. 1, the invention according to claim 2 is the selective reduction catalyst 24 according to claim 1 provided in the exhaust pipe 16 of the diesel engine 11 and the exhaust pipe upstream of the selective reduction catalyst 24 from the selective reduction catalyst 24. 16, a liquid injection nozzle 29 capable of injecting the urea-based liquid 32 toward the selective reduction catalyst 24, a diesel particulate filter 51 provided in the exhaust pipe 16 on the exhaust gas upstream side of the selective reduction catalyst 24, The engine exhaust gas purification device includes a filter temperature increasing means configured to increase the temperature of the diesel particulate filter 51 to a predetermined value or more.
In the exhaust gas purification apparatus for an engine according to claim 2, particulates in the exhaust gas of the diesel engine 11 are collected by the particulate filter 51, and the particulates are effectively prevented from being discharged to the outside. be able to. Further, when the urea-based liquid is injected from the liquid injection nozzle, the urea-based liquid is hydrolyzed to generate ammonia, and when the exhaust gas is at a relatively high temperature, the ammonia purifies NOx in the exhaust gas by the selective reduction catalyst. And the amount of NOx discharged to the atmosphere can be reduced. On the other hand, when the exhaust gas is relatively low in temperature, NOx in the exhaust gas is collected by depositing particulate ammonium nitrate produced by reaction with ammonia on the partition walls 26a of the carrier 26 in the selective reduction catalyst, When the exhaust gas is at a relatively low temperature, NOx can be effectively prevented from being discharged into the atmosphere as it is.

The invention according to claim 3 is a method for regenerating the selective catalytic reduction catalyst 24 according to claim 1 provided in the exhaust pipe 16 of the diesel engine 11 and depositing particulate ammonium nitrate.
The characteristic point is that the temperature of the diesel particulate filter 51 provided in the exhaust pipe 16 on the exhaust gas upstream side of the selective catalytic reduction catalyst 24 is raised to burn the particulates deposited on the diesel particulate filter 51, and the particulates. The temperature of the exhaust gas passing through the diesel particulate filter 51 is increased by the combustion of the curate, and the particulate solid ammonium nitrate deposited on the selective catalytic reduction catalyst 24 is burned and decomposed by the heat of the exhaust gas whose temperature has increased. .
If the particulate solid ammonium nitrate is deposited on the selective catalytic reduction catalyst 24, the pores in the partition walls 26a may be clogged or the surface of the partition walls 26a may be blocked, thereby inhibiting the NOx purification reaction. Further, when the amount of particulates collected by the diesel particulate filter 51 increases, the flow passage resistance of the exhaust gas passing through the particulate filter 51 increases. For this reason, the selective catalytic reduction catalyst 24 and the diesel particulate filter 51 need to be regenerated periodically. In the catalyst regeneration method according to the third aspect, the particulate filter 51 is regenerated by raising the temperature of the particulate filter 51 to cause particulate combustion, and the selective reduction catalyst 24 can also be regenerated at the same time. This eliminates the need for a regenerator that independently regenerates the selective catalytic reduction catalyst 24, and makes the structure relatively simple.

  In the selective catalytic reduction catalyst of the present invention, adjacent inlet portions and outlet portions of a plurality of through holes partitioned by the partition walls are alternately sealed, and exhaust gas flowing from the inlet portion of one through hole passes through the partition walls. Since the partition wall in which the active component is supported is configured to be unable to pass through the particulate ammonium nitrate, the temperature of the exhaust gas is configured to be discharged from the outlet portion of the other through hole adjacent to the one through hole. Is collected by changing NOx in the exhaust gas to solid ammonium nitrate and depositing on the partition walls of the carrier when the temperature is relatively low, and when the exhaust gas is at a relatively low temperature, NOx is discharged into the atmosphere as it is To effectively prevent that.

  The selective reduction catalyst, a liquid injection nozzle provided in an exhaust pipe upstream of the selective reduction catalyst and capable of injecting urea-based liquid toward the selective reduction catalyst, and an exhaust gas upstream of the selective reduction catalyst In an exhaust gas purification apparatus for an engine comprising a diesel particulate filter provided in a pipe and a filter temperature increasing means configured to increase the temperature of the diesel particulate filter to a predetermined value or higher, the particulate matter in the exhaust gas of the diesel engine The curate is collected by the particulate filter, and the particulate can be effectively prevented from being discharged to the outside. Further, when the urea-based liquid is injected from the liquid injection nozzle, the urea-based liquid is hydrolyzed to generate ammonia, and when the exhaust gas is relatively high in temperature, the ammonia purifies NOx in the exhaust gas by the selective reduction catalyst. And the amount of NOx discharged to the atmosphere can be reduced. On the other hand, when the exhaust gas is at a relatively low temperature, the ammonium nitrate produced by the reaction of NOx in the exhaust gas with ammonia is collected by being deposited on the partition walls of the carrier in the selective catalytic reduction catalyst. It is possible to effectively prevent NOx from being discharged into the atmosphere as it is.

  Although the selective catalytic reduction catalyst on which particulate ammonium nitrate is deposited needs to be regenerated regularly, the temperature of the diesel particulate filter provided in the exhaust pipe upstream of the selective catalytic reduction catalyst is raised to increase the diesel Particulate solid deposited on the selective catalytic reduction catalyst by burning the particulates deposited on the particulate filter, increasing the temperature of the exhaust gas that passes through the diesel particulate filter due to the combustion of the particulates, and the heat of the exhaust gas whose temperature has increased If the ammonium nitrate is burned and decomposed, the particulate filter can be regenerated and the selective catalytic reduction catalyst can be regenerated at the same time, eliminating the need for a regenerator that independently regenerates the selective catalytic reduction catalyst. Can be made relatively simple.

Next, the best mode for carrying out the present invention will be described with reference to the drawings.
As shown in FIG. 1, an intake pipe 13 is connected to an intake port of a diesel engine 11 via an intake manifold 12, and an exhaust pipe 16 is connected to an exhaust port via an exhaust manifold 14. The intake pipe 13 is provided with a compressor 17a of the turbocharger 17 and an intercooler 18 for cooling the intake air compressed by the turbocharger 17, and the exhaust pipe 16 is provided with a turbine 17b of the turbocharger 17. Is provided. Although not shown, the rotor blades of the compressor 17a and the rotor blades of the turbine 17b are connected by a shaft. The compressor 17a is rotated by the energy of the exhaust gas discharged from the engine 11 through the turbine 17b and the shaft, and the intake air in the intake pipe 13 is compressed by the rotation of the compressor 17a.

  Although not shown, the engine 11 is provided with a fuel injection device. The fuel injection device according to this embodiment includes a cylinder injector capable of injecting light oil as fuel into the cylinder with the tip portion facing the cylinder, a common rail for accumulating light oil inside and pumping light oil to the injector, and light oil to the common rail. A feed pump. The in-cylinder injector is configured such that the injection amount and the injection timing of the light oil can be adjusted by a solenoid valve built in the injector. This fuel injection device is configured to be capable of post injection in which light oil as fuel is injected into the cylinder after the top dead center of the piston, and hydrocarbons supplied from the engine 11 to the exhaust pipe 16 depending on the presence or absence of this post injection. Can be increased or decreased. A selective catalytic reduction catalyst 24 is provided in the middle of the exhaust pipe 16. The selective catalytic reduction catalyst 24 is accommodated in a cylindrical converter 27 in which the diameter of the exhaust pipe 16 is enlarged.

  As shown in detail in FIG. 2, the selective catalytic reduction catalyst 24 includes a carrier 26 and an active component (not shown) having a catalytic action supported on the carrier 26. The carrier 26 is made of a porous body made of ceramic such as cordierite or silicon carbide, and a plurality of through holes 26b partitioned by the porous partition walls 26a are formed in parallel to each other. In this carrier 26, adjacent inlet portions 26c and outlet portions 26d of a plurality of through holes 26b partitioned by a partition wall 26a are alternately sealed, and an active component such as zeolite or alumina is sealed in the partition wall 26a of the porous body. Is coated on the partition wall 26a. That is, the selective catalytic reduction catalyst 24 is formed by immersing the carrier 26 in a liquid in which metal zeolite, metal alumina or the like is slurried, and then draining and drying and firing the active component on the carrier 26. Made. The partition wall 26a is configured to have air permeability in a state where the active component is supported, and the exhaust gas flowing in from the inlet portion 26c of one through hole 26b passes through the partition wall 26a as shown by the solid line arrow in the figure. It is configured to flow into the other through hole 26b adjacent to the one through hole 26b and to be discharged from the outlet portion 26d of the other through hole 26b. The active component carried on the partition wall 26a is configured to decompose NOx in the exhaust gas of the engine 11 by reacting with the urea-based liquid, and the active component in this example converts the NOx in the exhaust gas flowing into the exhaust pipe 16 into the exhaust gas. A zeolite or alumina that is reduced at a relatively low temperature, for example, 200 to 300 ° C., is used.

  Returning to FIG. 1, a liquid injection nozzle 29 is provided toward the selective reduction catalyst 24 at the exhaust pipe 16 on the exhaust gas upstream side of the selective reduction catalyst 24, that is, at the inlet of the selective reduction catalyst 24. One end of a liquid supply pipe 31 is connected to the liquid ejection nozzle 29, and the other end of the liquid supply pipe 31 is connected to a liquid tank 33 in which a urea-based liquid 32 is stored. The liquid supply pipe 31 is provided with a liquid adjustment valve 34 that adjusts the supply amount of the liquid 32 to the liquid ejection nozzle 29. The liquid supply pipe 31 between the liquid adjustment valve 34 and the liquid tank 33 is provided with the liquid tank 33. A pump 36 capable of supplying the liquid 32 in the liquid jet nozzle 29 is provided. The liquid regulating valve 34 is a three-way valve having first to third ports 34a to 34c, the first port 34a is connected to the discharge port of the pump 36, the second port 34b is connected to the liquid jet nozzle 29, and the first The 3 port 34 c is connected to the liquid tank 33 through a return pipe 37. The first and second ports 34a and 34b communicate with each other when the liquid regulating valve 34 is turned on, and the first and third ports 34a and 34c communicate with each other when the liquid adjustment valve 34 is turned off.

  On the other hand, the exhaust pipe 16 is provided with first and second temperature sensors 43 a and 43 b for detecting the exhaust gas temperature in the exhaust pipe 16. That is, a first temperature sensor 43 a that detects the exhaust gas temperature in the exhaust pipe 16 at the inlet is provided at the inlet of the selective reduction catalyst 24 between the liquid injection nozzle 29 and the selective reduction catalyst 24. On the other hand, a second temperature sensor 43b for detecting the exhaust gas temperature in the exhaust pipe 16 at the outlet is provided at the outlet of the selective catalytic reduction catalyst 24. The detection outputs of the first and second temperature sensors 43a and 43b are respectively connected to control inputs of a controller 44 composed of a microcomputer. Other detection outputs such as a rotation sensor 46 that detects the rotation speed of the engine 11 and a load sensor 47 that detects a load of the engine 11 are connected to the control input of the controller 44. In this embodiment, the load sensor 47 detects a displacement amount of a load lever of a fuel injection pump (not shown). The control output of the controller 44 is connected to the liquid regulating valve 34 and the pump 36, respectively. The controller 44 includes a memory 44a. In the memory 44a, the exhaust gas temperature at the inlet and outlet of the selective catalytic reduction catalyst 24, the on / off state of the liquid regulating valve 34 according to the engine rotation, the engine load, etc. Stored in advance.

  In addition, a diesel particulate filter 51 made of porous ceramics is provided in the exhaust pipe 16 upstream of the exhaust gas from the selective reduction catalyst 24, and an oxidation catalyst 53 is further provided upstream of the filter 51. The diesel particulate filter 51 and the oxidation catalyst 53 are accommodated side by side in a cylindrical converter 52 in which the diameter of the exhaust pipe 16 upstream of the selective reduction catalyst 24 is enlarged. Although not shown, the particulate filter 51 has a honeycomb shape in which a first passage with a plug on the upstream side and a second passage with a plug on the downstream side are alternately arranged, and the exhaust gas passes through the second passage. From the flow path wall surface of the porous ceramic to the first passage and to the downstream side. The particulates in the exhaust gas are collected by the porous ceramic, and are configured to prevent the particulates from being released into the atmosphere. On the other hand, the oxidation catalyst 53 has a monolithic carrier (material: cordierite) (not shown) in which lattice-like (honeycomb-like) passages are formed in the flow direction of the exhaust gas, and a platinum-zeolite catalyst or platinum-on the monolithic carrier. An alumina catalyst is coated. This coating imparts oxidizing power of soot and hydrocarbons (HC, etc.) to the oxidation catalyst 53.

  And the filter temperature raising means comprised so that the temperature of this diesel particulate filter 51 can be raised to a predetermined value is provided. The filter temperature raising means in this embodiment includes the above-described oxidation catalyst 53 and a fuel injection device (not shown). That is, light oil is post-injected into the cylinder by the fuel injection device, whereby hydrocarbons are increased in the exhaust gas and supplied from the engine 11 to the exhaust pipe 16 together with the exhaust gas. When the hydrocarbons increase in the exhaust gas, the increased hydrocarbons undergo an oxidation reaction in the oxidation catalyst 53 to increase the temperature of the exhaust gas itself, and increase the temperature of the diesel particulate filter 51 existing downstream thereof to a predetermined value. .

The operation of the apparatus for purifying exhaust gas of the engine configured as described above will be described.
When the engine 11 is started, the exhaust gas reaches the exhaust pipe 16 from the exhaust manifold 14, and reaches the diesel particulate filter 51 through the exhaust pipe 16. Particulates in the exhaust gas of the diesel engine 11 are collected by the diesel particulate filter 51. The exhaust gas from which the particulates have been collected and removed passes through the particulate filter 51 and reaches the selective catalytic reduction catalyst 24 existing on the downstream side thereof. The NOx in the exhaust gas is purified by the selective reduction catalyst 24.

That is, the controller 44 that has determined from the detection outputs of the first and second temperature sensors 43a and 43b that the temperature of the exhaust gas is relatively high turns on the liquid regulating valve 34 to turn the first and second in the liquid regulating valve 34 on. The ports 34 a and 34 b are communicated, and the urea-based liquid 32 is ejected from the liquid ejection nozzle 29. This is because a reducing agent is required to purify NOx in the exhaust gas by the selective reduction catalyst 24, and the urea-based liquid 32 that has been adjusted to a predetermined concentration in advance is stored in the liquid tank 33. The controller 44 estimates the NOx concentration in the exhaust gas from the operating state of the diesel engine 11 obtained based on the detection outputs of the rotation sensor 46 and the load sensor 47, and the amount of urea as a reducing agent necessary for purifying this NOx. Ask for. Then, the controller 44 determines a specific injection amount of the urea-based liquid 32 from the obtained urea amount necessary as the reducing agent, turns on the liquid adjustment valve 34, and optimizes the urea-based liquid from the injection nozzle 29. 32 is injected. The injected urea-based liquid is heated by the exhaust gas and hydrolyzed to produce ammonia. When this ammonia flows into the selective reduction catalyst 24, NO and NO ₂ in the exhaust gas are reduced and changed to N ₂ and H ₂ O, and the amount of NOx discharged into the atmosphere as it is is reduced.

  Here, it is known that when the temperature of the exhaust gas is relatively low, NOx generates ammonium nitrate by a reaction with ammonia supplied as a reducing agent. This ammonium nitrate becomes a solid at a temperature lower than 210 ° C., which is the melting point, and cannot pass through the partition walls 26a of the carrier 26 in the selective catalytic reduction catalyst 24, and is deposited on the partition walls 26a. The selective catalytic reduction catalyst 24 collects ammonium nitrate produced by the reaction of NOx with ammonia by depositing it on the partition wall, so that when the exhaust gas is at a relatively low temperature, NOx is discharged into the atmosphere as it is. Effectively prevent. For this reason, the controller 44 that has judged that the exhaust gas is relatively low temperature from the detection outputs of the first and second temperature sensors 43a and 43b turns on the liquid regulating valve 34 as necessary, and the first in the liquid regulating valve 34. In addition, the second ports 34 a and 34 b are communicated, and the urea-based liquid 32 is ejected from the liquid ejecting nozzle 29. The controller 44 is necessary for changing NOx in the exhaust gas to ammonium nitrate from the operation state of the diesel engine 11 obtained based on the detection outputs of the first and second temperature sensors 43a and 43b, the rotation sensor 46, and the load sensor 47. Find the correct amount of urea. Then, the controller 44 turns on the liquid regulating valve 34 from the necessary amount of urea and injects the optimal amount of urea-based liquid 32 from the injection nozzle 29, changes NOx to ammonium nitrate, and deposits it on the partition wall 26a in the catalyst 24. To reduce NOx emissions when the exhaust gas is at a relatively low temperature.

  On the other hand, if ammonium nitrate which is a particulate solid is excessively deposited on the selective catalytic reduction catalyst 24, the pores in the partition walls 26a of the catalyst 24 are clogged or the surface of the partition walls 26a is covered. May be disturbed. Further, even in the diesel particulate filter 51 provided on the upstream side of the selective catalytic reduction catalyst 24, if the amount of particulate collected by the diesel particulate filter 51 increases, the exhaust gas passing through the particulate filter 51 is exhausted. The flow path resistance increases. For this reason, it is necessary to periodically regenerate the selective catalytic reduction catalyst 24 and the diesel particulate filter 51 provided on the upstream side thereof. This reproducing method will be described below.

  The regeneration of the selective catalytic reduction catalyst 24 is performed together with the regeneration of the particulate filter 51. The regeneration of the particulate filter 51 is performed by post-injecting light oil, which is fuel, into the cylinder by a fuel injection device (not shown) that is a filter temperature raising means. By this post injection, hydrocarbons are increased in the exhaust gas and supplied from the engine 11 to the exhaust pipe 16 together with the exhaust gas. When the hydrocarbons increase in the exhaust gas, the increased hydrocarbons undergo an oxidation reaction in the oxidation catalyst 53 to increase the temperature of the exhaust gas itself, thereby increasing the temperature of the diesel particulate filter 51 existing downstream thereof. When the temperature of the particulate filter 51 rises and exceeds a temperature at which the particulates can be combusted, for example, 600 ° C., the particulates collected by the particulate filter 51 are combusted by the heat, and the particulate filter 51 is thereby heated. Reproduce.

When the temperature of the particulate filter 51 rises and the particulates burn, the temperature of the exhaust gas that has passed through the particulate filter 51 rises remarkably, and the exhaust gas whose temperature has increased is the selective catalytic reduction catalyst 24 provided downstream thereof. To reach. On the other hand, ammonium nitrate deposited on the selective catalytic reduction catalyst 24 burns at 210 ° C. or higher, and ammonium nitrate, which is a particulate solid deposited on the selective catalytic reduction catalyst 24 by the heat of exhaust gas whose temperature has risen, burns and decomposes. Thus, the selective catalytic reduction catalyst 24 can be regenerated.
In the embodiment described above, the turbocharged diesel engine is used as the engine. However, the apparatus for purifying exhaust gas of the present invention may be used for a naturally aspirated diesel engine.

  In the above-described embodiment, the post-injectable fuel injection device is used as the filter temperature increasing means. However, the filter temperature increasing means increases the temperature of the filter by increasing the temperature of the exhaust gas. For example, the engine load may be increased by closing the EGR control valve, the intake throttle valve or the exhaust brake valve, or increasing the nozzle vane opening of the VG (Variable Geometry) turbo, A nozzle capable of injecting hydrocarbons directly toward the filter may be provided immediately before the filter.

It is a block diagram which shows the structure of the exhaust gas purification apparatus of embodiment of this invention. It is an expanded sectional view of the selective reduction catalyst.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Diesel engine 16 Exhaust pipe 24 Selective reduction type catalyst 26 Carrier 26a Partition wall 26b Through hole 26c Inlet part 26d Outlet part 29 Liquid injection nozzle 32 Urea system liquid 51 Diesel particulate filter

Claims (3)

A carrier (26) in which a plurality of through-holes (26b) partitioned by a porous partition wall (26a) are formed in parallel with each other, and an active ingredient supported by the partition wall (26a) having a catalytic action, In the selective catalytic reduction catalyst configured to decompose nitrogen oxide in exhaust gas of the engine (11) by reacting with urea-based liquid,
The adjacent inlet portions (26c) and outlet portions (26d) of the plurality of through holes (26b) partitioned by the partition walls (26a) are alternately sealed,
The partition wall (26a) carrying the active ingredient has air permeability, and the exhaust gas flowing in from the inlet portion (26c) of one through hole (26b) passes through the partition wall (26a) and passes through the one through hole. It is configured to be discharged from the outlet portion (26d) of another through hole (26b) adjacent to the hole (26b),
In addition, the selective reduction catalyst, wherein the partition wall (26a) on which the active component is supported is configured not to pass particulate ammonium nitrate. The selective catalytic reduction catalyst (24) according to claim 1, provided in an exhaust pipe (16) of a diesel engine (11),
A liquid injection nozzle (29) provided in the exhaust pipe (16) upstream of the exhaust gas from the selective reduction catalyst (24) and capable of injecting a urea-based liquid (32) toward the selective reduction catalyst (24); ,
A diesel particulate filter (51) provided in the exhaust pipe (16) upstream of the exhaust gas from the selective catalytic reduction catalyst (24);
An exhaust gas purifying apparatus for an engine, comprising: a filter temperature increasing means configured to increase a temperature of the diesel particulate filter (51) to a predetermined value or more. A method for regenerating the selective catalytic reduction catalyst (24) according to claim 1, wherein the particulate solid ammonium nitrate is deposited on an exhaust pipe (16) of a diesel engine (11),
Particulates accumulated in the diesel particulate filter (51) by raising the temperature of the diesel particulate filter (51) provided in the exhaust pipe (16) on the exhaust gas upstream side of the selective catalytic reduction catalyst (24) Burn
Increasing the temperature of exhaust gas passing through the diesel particulate filter (51) by burning the particulates,
A method for regenerating a catalyst, comprising burning and decomposing ammonium nitrate of the particulate solid deposited on the selective catalytic reduction catalyst (24) by heat of exhaust gas whose temperature has increased.

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