JP2012159053A - Exhaust gas purification apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas purification apparatus which can generate ammonia from urea at a high conversion rate to improve purification performance of a selective reduction catalyst unit on the downstream side even when urea is injected, in close range, from an urea supply device into a diesel particulate filter device, can improve the purification performance of the selective reduction catalyst device, can reductively purify NOx even when the temperature of exhaust gas passing through the exhaust gas purification apparatus is low, and can be downsized.SOLUTION: In the exhaust gas purification apparatus placed in a discharge passage of an internal combustion engine wherein an urea supply apparatus, a diesel particulate filter device and a selective reduction catalyst device are disposed in this order from the upstream side, a hydrolysis catalyst layer 12 is provided on a filter wall surface on the exhaust gas inlet side of the diesel particulate filter device, and an ammonia absorption layer 13 is provided on a filter wall surface on the exhaust gas outlet side.

Description

  The present invention relates to an exhaust gas purification device that purifies harmful substances such as particulate matter, nitrogen oxides, carbon monoxide, and hydrocarbons in exhaust gas of an internal combustion engine such as a diesel vehicle.

  For the purpose of purifying harmful substances such as particulate matter (PM), nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HC) in the exhaust gas of engines (internal combustion engines) of diesel engine-equipped vehicles Reduction of the generation of harmful substances by improving the combustion state in the engine cylinder, oxidation catalyst device (DOC), diesel particulate filter device (DPF), urea selective reduction catalyst (urea SCR) provided in the exhaust passage of the engine Removal of harmful substances is progressing by mounting multiple exhaust gas purification devices such as (catalyst) devices.

  For example, an oxidation catalyst, a urea injection device, a diesel particulate filter device, a selective reduction type NOx catalytic converter, and an oxidation catalyst are arranged in this order from the upstream side of the exhaust passage, and the diesel particulate filter device has an oxidation function. An exhaust gas purification system that supports a urea decomposition catalyst without supporting a catalyst has been proposed (see, for example, Patent Document 1).

  However, as a result of improving the combustion state of the engine, the exhaust gas temperature has been reduced to 30 ° C. to 50 ° C. or higher than before, and the exhaust gas purification devices have become more and more large in size. Therefore, it has become difficult to ensure the activation temperature of the catalyst due to an increase in heat capacity. Moreover, since the exhaust gas purification device is disposed farther from the exhaust port of the engine due to the increase in size, it tends to be more difficult to maintain the catalyst at the activation temperature. Therefore, there is a problem that the effect of reducing harmful substances in each exhaust purification device is reduced.

  In addition, in the urea selective reduction type catalyst (urea SCR) device, in order to diffuse the urea water uniformly and to promote the decomposition of urea into ammonia, the urea supply device such as a urea water injection nozzle is used. In addition, it is difficult to shorten the distance to the urea selective reduction catalyst device, which is also a major factor in increasing the size of the exhaust purification device.

JP 2010-242515 A

  The present invention has been made in view of the above-described situation, and an object of the present invention is to generate ammonia from urea at a high conversion rate even when urea is injected from a urea supply device to a diesel particulate filter device at a short distance. Thus, the purification performance of the downstream selective reduction catalyst device can be improved, and the diesel particulate filter device can be used as a buffer material for supplying ammonia, and the temperature of the exhaust gas passing through the exhaust gas purification device is low. It is another object of the present invention to provide an exhaust gas purification device that can improve the purification rate of the selective catalytic reduction device, reduce and purify NOx, and can be made compact.

  An exhaust emission control device of the present invention for achieving the above object is arranged in an exhaust passage of an internal combustion engine, and a urea supply device, a diesel particulate filter device, and a selective catalytic reduction device are arranged in this order from the upstream side. In the exhaust gas purifying apparatus, a hydrolysis catalyst layer is provided on the filtration wall surface on the exhaust gas inlet side of the diesel particulate filter device, and an ammonia adsorption layer is provided on the filtration wall surface on the exhaust gas outlet side.

  According to this configuration, even when urea is injected from the urea supply device to the diesel particulate filter device (DPF) at a short distance, ammonia can be generated from urea at a high conversion rate by the hydrolysis catalyst layer on the inlet side. Therefore, the purification performance of the downstream selective reduction catalyst device can be improved.

  In addition, since a diesel particulate filter device having an ammonia adsorption layer formed on the outlet side can be used as a buffer material for supplying ammonia, the purification rate of the selective catalytic reduction catalyst can be obtained even when the temperature of the exhaust gas passing through the exhaust gas purification device is low. And NOx can be reduced and purified.

  Furthermore, when the urea hydrolysis layer is formed of a porous layer formed of nano-order particles, the pressure loss when collecting particulate matter (PM) with a diesel particulate filter device and the variation in collection are reduced. be able to.

  According to the exhaust gas purification apparatus for an internal combustion engine according to the present invention, even when urea is injected from the urea supply device to the diesel particulate filter device at a short distance, the hydrolysis catalyst layer on the inlet side converts the ammonia from urea to a high level. Can be generated at a rate. Therefore, the purification performance of the downstream selective reduction catalyst device can be improved.

  In addition, since a diesel particulate filter device having an ammonia adsorption layer formed on the outlet side can be used as a buffer material for supplying ammonia, the purification rate of the selective catalytic reduction catalyst can be obtained even when the temperature of the exhaust gas passing through the exhaust gas purification device is low. And NOx can be reduced and purified.

It is a figure which shows the structure of the filtration wall part of the diesel particulate filter apparatus of embodiment of this invention. It is a figure which shows the ammonia change rate in an Example, the comparative example 1, and the comparative example 3. FIG. It is a figure which shows the NOx average purification rate (average temperature of 200 degreeC) in the JE05 mode in an Example, the comparative example 1, the comparative example 2, and the comparative example 3. FIG. It is a figure which shows the NOx average purification rate (average temperature of 250 degreeC) in the JE05 mode in an Example, the comparative example 1, the comparative example 2, and the comparative example 3. FIG.

  Hereinafter, an exhaust gas purifying apparatus according to an embodiment of the present invention will be described with reference to the drawings. This exhaust gas purification device for an internal combustion engine is a device that is disposed in the exhaust passage of the internal combustion engine, and in that order from the upstream side, a urea supply device, a diesel particulate filter (DPF) device, a selective reduction catalyst (SCR catalyst) device. Arranged. In this exhaust gas purification device, a hydrolysis catalyst layer is provided on the filtration wall surface on the exhaust gas inlet side of the diesel particulate filter device, and an ammonia adsorption layer is provided on the filtration wall surface on the exhaust gas outlet side.

The filtration wall 10 is formed of nano-order DPF constituent particles 11 such as silicon carbide (SiC) or cordierite, and a porous layer is formed by an aggregate of the DPF constituent particles 11. For the hydrolysis layer, a rare earth oxide having a large basicity such as titanium dioxide (TiO ₂ ) or zirconium dioxide (ZrO ₂ ) is used. In addition, a material having an acid point such as zeolite is used for the ammonia adsorption layer.

  A cross section of this filtration wall is shown in FIG. The filtration wall 10 has a porous layer formed of aggregates of DPF constituent particles 11, a hydrolysis catalyst layer 12 is formed on the filtration wall surface on the inlet side of the exhaust gas G, and a filtration wall surface on the exhaust gas outlet side. An ammonia adsorption layer 13 is provided.

  By the porous layer of the nano-order DPF constituent particles 11 on the surface of the filtration wall 10, it is possible to reduce the pressure loss and the collection variation at the time of PM collection.

Urea sprayed in the exhaust gas G is mainly decomposed by thermal decomposition of urea ((NH ₂ ) ₂ CO → NH ₃ + HNCO) and hydrolysis of isocyanic acid generated by thermal decomposition (HNCO + H ₂ O → NH _3+). Ammonia (NH ₃₎ is generated via CO ₂ ). This hydrolysis has a slower reaction rate than thermal decomposition, and in a vehicle selective reduction catalyst device with limited layout, conversion to ammonia is sufficient by simply uniforming the diffusion of urea water. It will not be a thing.

  However, in the present invention, even when urea is injected from the urea supply device to the diesel particulate filter device at a short distance by the hydrolysis catalyst layer 12 on the inlet side, ammonia can be generated from urea at a high conversion rate. Therefore, the purification performance of the downstream selective catalytic reduction catalyst can be improved.

  In addition, since a diesel particulate filter device having an ammonia adsorption layer formed on the outlet side can be used as a buffer material for supplying ammonia, purification of the selective catalytic reduction catalyst device is possible even when the temperature of the exhaust gas passing through the exhaust gas purification device is low. The rate can be improved and NOx can be reduced and purified.

  Furthermore, since the ammonia adsorption layer 13 can be used as an ammonia supply buffer on the outlet side, even when the temperature of the exhaust gas passing through the exhaust gas purification device is low, the purification rate of the selective catalytic reduction catalyst device can be improved, and NOx is reduced. Reduce and purify.

  2 to 4 show the ammonia conversion rate and the NOx average purification rate in the JE05 mode in Examples of the present invention and Comparative Examples 1, 2, and 3 related thereto. The embodiment is a case where the above-described exhaust gas purifying apparatus of the present invention is used. Comparative Example 1 is a diesel particulate filter device in which a ceramic carrier carrying platinum (Pt), platinum-palladium (Pt-Pd), etc. is coated on the filtration wall surface. The comparative example 3 is a case where the ammonia adsorption layer 13 is not provided on the surface of the filtration wall on the exhaust gas outlet side in the example.

  In this example, comparative example 1, and comparative example 3, each device is arranged in the order of an oxidation catalyst device, a urea supply device, a diesel particulate filter device, and a selective reduction catalyst device. Using the diesel particulate filter device of Example 1, each device is arranged in the order of an oxidation catalyst device, a urea supply device, a selective reduction catalyst device, and a diesel particulate filter device.

  FIG. 2 shows the ammonia change rate (%) at the inlets of the selective catalytic reduction devices of Examples, Comparative Examples 1 and 3. According to FIG. 2, Example and Comparative Example 3 show a high ammonia conversion rate even at 200 ° C. On the other hand, in Comparative Example 1, ammonia generated by thermal decomposition is oxidized on the surface of the noble metal, so the ammonia conversion rate decreases as the temperature increases.

  3 and 4 show the average purification rate of NOx when the JE05 mode test is performed. FIG. 3 shows a case where the mode average temperature of the inlet of the diesel particulate filter device is 200 ° C., and FIG. 4 shows a case where the mode average temperature of the inlet of the diesel particulate filter device is 250 ° C. As a result of this JE05 mode test, when the average temperature is 200 ° C., Example> Comparative Example 3> Comparative Example 2 >> Comparative Example 1; when the average temperature is 250 ° C., Example≈Comparative Example 3> Comparative Example 2 >> Comparative Example 1 was obtained.

  According to the exhaust gas purification apparatus for an internal combustion engine of the present invention, even when urea is injected from a urea supply device to a diesel particulate filter device at a short distance, ammonia can be generated from urea with a high conversion rate, and downstream selective reduction The purification performance of the selective catalyst can be improved, and the diesel particulate filter device can be used as a buffer material for supplying ammonia, so that the purification rate of the selective catalytic reduction catalyst can be improved even when the temperature of the exhaust gas passing therethrough is low. Reduce and purify. Therefore, it can be used as an exhaust gas purification device for an internal combustion engine mounted on an automobile or the like.

DESCRIPTION OF SYMBOLS 10 Filtration wall 11 DPF constituent particle 12 Hydrolysis catalyst layer 13 Ammonia adsorption layer G Exhaust gas

Claims (2)

  In an exhaust gas purification device that is disposed in an exhaust passage of an internal combustion engine and sequentially arranges a urea supply device, a diesel particulate filter device, and a selective reduction catalyst device from the upstream side, the exhaust gas inlet side of the diesel particulate filter device An exhaust gas purification apparatus comprising a hydrolysis catalyst layer on the filtration wall surface and an ammonia adsorption layer on the exhaust wall outlet side filtration wall surface.   The exhaust gas purification device according to claim 1, wherein the urea hydrolysis layer is formed of a porous layer formed of nano-order particles.

Images