JPH01151706A - Catalyst and filter for removing combustible fine particles and nitrogen oxide - Google Patents

Abstract

PURPOSE:To simultaneously remove both combustible particles and nitrogen oxides in exhaust gas by holding catalyst component composed of copper and zeolite by means of filter walls which partition intake and discharge passages of a filter. CONSTITUTION:A plurality of intake passages 2 and exhaust passages 3 are alternately formed on a filter 1 in the axial direction thereof. The passages 2, 3 are partitioned by a plurality of filter walls 10 extending in the axial direction. In this case, the passages 2, 3 are blocked checkerwise in every other opening by walls 31, on the intake side A of the respective passages 2, 3. On the other hand, they are blocked checkerwised by walls 22, on an exhaust side B thereof at outlets whose passages are not blocked on the intake side. As a result, the passages blocked on the exhaust side form the intake passages 2, and also, the passages blocked on the intake side form the discharge passages 3. Catalyst components composed of copper and zeolite is held by the filter walls 10.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a catalyst for simultaneously removing combustible particulates such as carbon and nitrogen oxides contained in the exhaust gas of internal combustion engines, particularly automobiles, and the catalyst. Regarding the filter used.

[Prior art]

It is known to use a filter in the exhaust system to remove combustible particulates such as carbon contained in the exhaust gas of a diesel engine. However, when used for a long time, combustible particles accumulate in this filter, causing it to become clogged and causing a pressure loss.

Therefore, conventional methods were used to solve this drawback.

A filter has been proposed in which a nichrome wire heater or a heat-generating metal layer is combined with a part of the filter that captures particulates to heat the part with electricity (Japanese Patent Application Laid-Open No. 74121/1983).
). There have also been proposals to inject fuel into the supplementary part and heat the combustible particulates with the combustion heat of the fuel, or to provide a high voltage electrode and heat it by spark discharge. these are,
The above heating incinerates combustible fine particles and prevents clogging; it also uses filters that support a silver vanadate catalyst (Japanese Patent Application Laid-open No. 58-84042), as well as filters containing lithium oxide, copper chloride, and alkali metals. A filter carrying one or more selected from vanadium oxide, lithium, sodium, potassium or cerium vanadate, or potassium or silver perrhenate has been proposed (Japanese Patent Laid-Open No. 59-49825). .

On the other hand, the exhaust gas also contains nitrogen oxides (NOx) in addition to the combustible particles, and efforts are being made to remove the nitrogen oxides.

C. Problems to be Solved] However, while these conventional techniques are effective in removing combustible particulates and nitrogen oxides individually, they are effective in removing both combustible particulates and nitrogen oxides. cannot be removed at the same time.

It has also been proposed to use a filter for removing combustible particulates and a catalytic converter for removing nitrogen oxides, and to sequentially feed exhaust gas through these to remove combustible particulates and nitrogen oxides, respectively. There is (Special Public Service 1986-4105)
4).

However, such means require two devices, a filter and a catalytic converter, and are compact.

This is not good news for automotive technology, which is moving towards weight reduction.

The present invention was made in view of this problem.

The present invention aims to provide a catalyst and a filter that can simultaneously remove combustible particulates and nitrogen oxides from exhaust gas.

[Means for solving problems]

The first invention of the present application is a catalyst for removing combustible particles and nitrogen oxides, which is characterized in that a catalyst component consisting of copper and zeolite is supported on a carrier. It is a catalyst for removing nitrogen oxides.

Copper (Cu) as the catalyst component may be in the form of metal Cu or copper oxide (Cub). Zeolite used with Cu is also called zeolite, and its chemical composition is similar to feldspars or quasi-feldspars (hereinafter referred to as zeolites).

General formula Wm Zn 02n-s H,O (where W is Na, Ca, K, Ba or Sr, Z is Si+Aj
2 (Si:A/!>1), s is not constant].

The catalyst is prepared by mixing zeolite and Cu, or by supporting Cu on zeolite by ion exchange. As shown in the examples, this ion exchange support is carried out by immersing the zeolite layer in a 114 aqueous solution of copper acetate, copper nitrate, etc. and drying it.
exchange ions with u. Further, the ion exchange rate at this time is preferably 50 to 100%. This is because if it is less than 50%, it is difficult to obtain the effects of the present invention.

Here, the ion exchange rate of Cu refers to the amount of Cu exchanged with elements such as Na or alkali in the zeolite when Cu is monovalent.

Next, as a carrier for supporting the above-mentioned catalyst component.

Cordierite, alumina, silica/alumina.

Porous sintered bodies such as subodumene are available. Also.

The shape of the carrier may be a single grain, a honeycomb shape, or a foam (porous) ring. However, in order to improve contact with the exhaust gas and improve the removal effect of combustible particulates and nitrogen oxides, a honeycomb shape is preferred. This integrated carrier, which is preferably an integrated carrier such as a body, is similar to the filter described below.

Further, the carrier can also be constructed by further adhering powder of alumina or the like to the surface of a cordierite carrier, which is an integral carrier, and firing the powder to form a porous body of the alumina or the like.

Furthermore, as a method for supporting the catalyst component on a carrier, for example, first, a porous layer of zeolite powder is coated on the carrier, and then, it is immersed in an aqueous copper solution such as copper acetate to support Cu by ion exchange. To do something, such as by doing something. Therefore, the amount of the catalyst component supported on the carrier is preferably 1 to 50 g per N of the carrier. Less than 1g.

It is difficult to obtain the effects of the present invention, and even if it exceeds 50 g, it is difficult to obtain the effects commensurate with that.

Note that the catalyst according to the present invention is preferably used at a temperature of 200 to 800°C. Further, the space velocity of the exhaust gas introduced into the catalyst layer is preferably GH3V1,000 to 10 force/hour.

Next, the second invention of the present application has a large number of passages separated by filter walls from the inflow side to the outflow side of exhaust gas, and the passages include a passageway whose outflow side is closed and a passageway whose inflow side is closed. and a discharge passageway with a closed discharge passageway, the passageway sharing the filter wall with at least one discharge passageway, and the filtering wall being configured to prevent combustible substances in the exhaust gas from passing from the passageway to the discharge passageway. It has holes that trap fine particles.

The present invention also provides a filter for removing combustible particulates and nitrogen oxides, characterized in that the filter wall supports a catalyst component consisting of copper and zeolite.

In the filter according to the second aspect of the invention, the passageway and the discharge passageway are separated by a large number of filter walls provided from the exhaust gas inflow side to the exhaust gas outflow side. That is, this filter is a cylindrical body having a large number of passages along its axial direction. and.

The passageway shares the filter wall with at least one discharge passageway. In other words, the structure is such that the exhaust gas that enters the passageway always passes through the filter wall and exits to the exhaust passageway. This filter wall is provided with a through hole for capturing combustible particulates in the exhaust gas when the exhaust gas passes through the filter wall.

However, what is the formation of the above-mentioned passageway and discharge passageway?

As shown in FIGS. 1 to 3 of the embodiment, first, a cylindrical body having a large number of passages was made, and one side of the passages was made.

For example, every other block is blocked in a so-called checkered pattern. Next, on the other side, the passages that were not closed are closed. As a result, the passage that is not blocked on the -blade side becomes a pass passage, and the passage that is not blocked on the other side becomes a discharge passage.

In addition, the above-mentioned filter wall can be called the skeleton of the filter of the present invention, and is composed of cordierite, alumina, alumina, etc.
It is composed of a sintered body of ceramic powder such as silica. Thus, such filter walls have small holes,
Supplement combustible particles as described above. The diameter of the through hole is preferably 5 to 50 μm. If the diameter is less than 5 μm, clogging due to combustible particles is large;
If it exceeds m, it becomes difficult to capture combustible particulates, and the nitrogen oxide removal (purification) effect also decreases.

Next, a catalyst component consisting of Cu and zeolite is supported on the filter wall. The supporting means is the same as in the case of supporting the catalyst component on the carrier in the first invention.

Further, the structure of the catalyst component is similar to the first invention, Cu
carried out by ion-exchange loading on zeolite, etc.
In addition, the ion exchange rate is 50 to 100% as mentioned above.
It is preferable that In addition, this catalyst component is supported by
It is preferable to set it as 1-50 g/l with respect to the filter IIl comprised by the said filtration wall.

In addition, in the first invention and the second invention, since the combustion removal of combustible particulates can be performed at a low temperature due to the presence of Cu and zeolite, the combustible particulates can be removed around the catalyst layer.

It is not necessary to provide a heater specifically for combustion heating around the filter, but such a heater can be provided if necessary.

[Action and effect]

In the first invention of the present application, since copper and zeolite are used as catalyst components, combustible particulates in the exhaust gas can be burned and removed at low temperatures, and the catalyst components can remove nitrogen oxides ( NOx) can be removed with high efficiency.

The above-mentioned combustible particulates are removed by combustion due to spontaneous ignition caused by the heat of the exhaust gas and the oxygen in the exhaust gas. The combustion temperature at this time can be as low as about 350°C. This is as above <,C
This is because u and zeolite are used as catalyst components.

The removal of NOx is performed mainly by reacting the hydrocarbons in the exhaust gas with NOx to form N, Co□.

This is done by decomposing it into components such as H and O.

Therefore, according to the first aspect of the invention, combustible particulates and nitrogen oxides in exhaust gas can be removed at the same time.

Moreover, its removal is possible at a low temperature of about 350'C. Also, for that purpose.

There is no need for two removal devices to remove combustible particulates and nitrogen oxides as in the past.

The device is compact and lightweight.

Further, since the combustible particulates are removed by reacting (combusting) with oxygen in the exhaust gas as described above, the reaction atmosphere is an oxygen-excessive atmosphere. On the other hand, since the removal of nitrogen oxides is a reduction reaction as is well known, it is usually not carried out satisfactorily under such an excess of oxygen. However, the present invention is noteworthy because it achieves the simultaneous removal of combustible particulates and nitrogen oxides under an excess of oxygen.

In addition, in the second invention of the present application, the inside of the filter is divided into an inlet passage and an outlet passage, and the exhaust gas that has entered the inlet passage is sent out to the outlet passage through the filtration wall. supports a catalyst component consisting of Cu and zeolite. Therefore, the combustible particulates in the exhaust gas can be reliably captured by the filter wall, and the captured combustible particulates can be burned and removed at low temperatures by the catalyst component, as in the case of the first invention. .

Furthermore, nitrogen oxides in the exhaust gas are efficiently decomposed and removed by the catalyst component to <Nt, etc., mainly when passing through the passage of the filter wall, as in the case of the first invention.

Therefore, according to the second invention, like the first invention, combustible particulates and nitrogen oxides in the exhaust gas can be removed simultaneously at low temperatures.

The device is also compact and lightweight. and.

Similar to the first invention, combustible particulates and nitrogen oxides can be simultaneously removed under excess oxygen.

Above 1st. In the second invention, the reason why the combustible particulates can be removed at low temperature is not clear.

This is thought to be because Cu and zeolite as catalyst components act to lower the ignition point of combustible particles.

〔Example〕

First example For filter walls of cordierite filter carriers.

A filter was prepared in which zeolite powder was supported and Cu was ion exchange supported, and exhaust gas from a diesel engine was then fed into the filter.

A test was conducted to remove combustible particulates and nitrogen oxides. Similar tests were also conducted for comparison filters.

That is, first, as shown in FIGS. 1 to 3.

The filter 1 has a large number of inlet passages 2 and discharge passages 3 alternately along the axial direction.

The filter 1 has a large number of passages formed by a large number of filtration walls 10 along the axial direction, and on the exhaust gas inflow side A of the passages, the entrances of the passages are arranged in a checkered pattern every other wall. 31 is occluded. Furthermore, on the exhaust gas outflow side B of the filter, the outlet of the passage that was not blocked on the inflow side A is blocked by the wall 22. Due to this.

The passage with the outflow side B closed forms the feed passage 2.

The passage with the inflow side A closed forms the discharge passage 3.

Therefore, the inlet passage 2 has an inlet 21 on the inlet side A and a wall 22 on the outlet side B.

On the other hand, the discharge passage 3 has a wall 31 on the inflow side A.

The outflow side B has a discharge port 32. The filter 1 has 70 of the catalyst components on its filter wall 10.

Thus, the gas 4 sent to the filter 1 from the inflow side A enters the inlet passage 2 of the filter l from the inlet 21, passes through the filter wall 10, is sent into the IJFIH passage 3, and is sent to the outlet. 32 and is discharged as a cleaning flux 41. The ηJ flammable particulates and nitrogen oxides in the exhaust gas 40 are removed as described above when passing through the filter wall 10.

The 11 filters are made of an integrated base material (carrier) made by molding and sintering cordierite powder.
and the cross-sectional area in the cross section perpendicular to the axial direction is 1 inch
The filter carrier has approximately 100 passages per unit.The average pore diameter of the filter wall L1 of the filter carrier is 30 μm.The filter has a diameter of 100 mm and a volume of 1.372.

Next, the catalyst component is placed on the filter carrier (existing method will be explained. First, 100 parts of zeolite powder with a particle size of 20 μm and 80 parts of silica sol are ball-milled together with water and nitric acid to produce a wash coat slurry. Then, the filter carrier was immersed in this. Excess liquid was then blown off with compressed air, and free water was removed by drying, followed by baking at 500°C for 1 hour.
A porous zeolite layer having a thickness of about 50 μm was coated on the filter carrier.

Next, the above filter carrier was mixed with 0.02 mol/l vinegar f.
i Soaked in a copper aqueous solution for 24 hours, dried, and then heated at 500°C for 1
The zeolite was calcined for a period of time to support CU on zeolite through ion exchange. The ion exchange rate of Cu at that time was 89%. Further, the amount of Cu supported on the filter carrier 12 was 20 g/l.

Subsequently, as shown in FIGS. 1 to 3, the inlet and outlet of the passage of the filter carrier are closed with walls 22 and 31, and the inlet passage 2. The filters 1 having the same number of discharge passages 3 were manufactured. This wall was made of alumina powder sintered body. This filter will be referred to as Sample Soil 1.

Ma? ,: For comparison, comparison filters (samples NQ and CL) not carrying the above catalyst components were prepared.

Next, the above filter was installed in the exhaust gas stream of Diesel Encia, and combustible particulates and nitrogen oxides (NOx) were removed.
) removal effect was tested. The effect of lowering the combustion temperature of combustible particles was evaluated by the rate of increase in pressure loss after 5 hours. That is, this evaluation method was used because combustible particles must be combusted at low temperatures and accumulate in the filter, causing clogging and increasing pressure loss.

The above diesel engine is a 4-cylinder injection type engine, stroke chamber volume 2200cc, rotation speed 250Orpm.
This is because a load of 5 kgf-m is used.

In addition, the temperature inside the Fifreku at the time of the test was approximately 45
0″C1 and space velocity (HSV was 30,000/hour).

The measurement results are shown in Table 1.

As is clear from Table 1, the filter (Nnl) according to the present invention has an extremely lower rate of increase in pressure loss than the comparative filter (NaC1), and effectively burns and removes combustible particulates at low temperatures. I understand that. Also, NOx
It can also be seen that the filter of the present invention exhibits an extremely high purification rate (removal rate) compared to the comparative filter.

As mentioned above, No. 1 of the present application. It can be seen that both the second invention exhibits excellent effects in removing combustible particulates and NOx.

Second Example A filter was prepared by supporting a catalyst component on the filter wall of a silicon carbide filter carrier in the same manner as in the first example.

Then, a test similar to that of the first example was conducted.

That is, as a filter carrier, 20
It has 0 passages. A filter carrier made of silicon carbide was used. Moreover, the filter carrier.

The average pore size of the filter wall is 4011 m, and the diameter is 100+ nm.
.

The volume is l, 3I! ,Met.

Next, 100 parts of zeolite powder having a particle size of 30 pm, 75 parts of silica sol, and 5 parts of alumina sol were ball milled together with water and nitric acid to produce a wash coat slurry, into which the filter carrier was immersed. Then, the same as in the first embodiment.

The excess liquid was blown off, the filter carrier was dried and fired, and the filter carrier was coated with 50 pm thick zeolite.

Thereafter, Cu was supported by ion exchange on one zeolite in the same manner as in the first example. This ion exchange rate is 90%
Also, the amount of Cu supported on the filter carrier 12 is 2
It was 0 g/Q. Also.

In the same manner as in the first embodiment, as shown in FIGS. 1 to 3 (1
A wall was installed at the entrance or exit of the passage to provide a passage for passage and a passage for discharge. As a result, a filter according to the present invention (sample Nα2) was produced.

Furthermore, for comparison, a comparative filter (sample N11C2) was prepared using the same filter carrier as above but without supporting the catalyst component.

Then, a test similar to that of the first example was conducted.

The results are shown in Table 2.

The filter known from the same table is <1 filter according to the present invention (
It can be seen that the filter 2) is more effective in removing combustible particulates and NOx than the comparative filter (NaC2).

Third Example Cordierite Foam Filter Carrier iIt
A filter was produced by supporting a catalyst component in the same manner as in the first example. Then, a test similar to that of the first example was conducted. ' That is, as a filter carrier, a diameter of 100 m.

A cordierite foam filter with a volume of 1.3Q was used. The carrier is a porous foam of cordierite with a three-dimensional network structure.

The number of mesh skeleton lattices was 15/inch.

Next, the same zeolite 9 silica sol as in the first example,
A wash coat slurry containing nitric acid, etc. is prepared, and the filter carrier is immersed in this slurry.

Excess liquid was blown off and dried in the same manner as in the first example.

Baked, about 200 g for the above filter carrier.

It was coated with zeolite having a thickness of 1100 II.

Thereafter, the filter carrier was immersed in a 0.02 mo171 copper nitrate aqueous solution for 24 hours, and Cu was supported by ion exchange on the zeolite on the filter carrier in the same manner as in the first example. The ion exchange rate of this Cu is 93%, and the filter carrier is 1! The amount of Cu supported is lOg/
It was Q.

Also, similar to the first embodiment, walls were provided at the entrances or exits of the nine passages to form passageways and discharge passages.

A filter according to the present invention (sample NL0L3) was produced.

For comparison, a comparison filter (Sample No. C3) was prepared using the same foam type filter carrier as above, but without supporting the catalyst component.

Then, a test similar to that of the first example was conducted.

The results are shown in Table 3.

As is known from the same table, nine filters according to the present invention (
It can be seen that Seed 3) exhibits superior effects in removing combustible particulates and NOx compared to the comparative filter (NαC3).

[Brief explanation of the drawing]

1 to 3 show a filter according to a first embodiment of the present invention, and FIG. 1 is a perspective view thereof. FIG. 2 is a sectional view of the main part, and FIG. 3 is a partially cutaway side view. 101. filter, io,, filtration wall. 231. Inlet passage, 3. ,,exhaust passage. 439. exhaust gas.

Claims (7)

[Claims] (1) A catalyst for removing combustible particulates and nitrogen oxides, characterized by supporting a catalyst component consisting of copper and zeolite on a carrier. Catalyst for removal. (2) The catalyst according to claim 1, wherein the copper is ion exchange supported on zeolite. (3) The catalyst according to claim 2, wherein the ion exchange rate of copper is 50 to 100%. (4) It has a large number of passages separated by filter walls from the inflow side to the outflow side of the exhaust gas, and the passages are separated from an inlet passage whose outflow side is closed and a discharge passage whose inflow side is closed. The inlet passage shares the filter wall with at least one outlet passage, and the filtration wall has a through hole for capturing combustible particulates in the exhaust gas when the exhaust gas passes from the inlet passage to the outlet passage. 1. A filter for removing combustible particulates and nitrogen oxides, characterized in that the filtration wall has a catalyst component made of copper and zeolite supported thereon. (5) The filter according to claim 4, wherein the steel is supported by ion exchange on zeolite. (6) The filter according to claim 5, wherein the ion exchange rate of copper is 50 to 100%. (7) The filter according to claim 4, wherein the pores in the filtration wall have a diameter of 5 to 50 μm.