JPH09125931A - Diesel particulate filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To arrest diesel particulates and absorb NOx concurrently without causing any increase of pressure loss by forming a diesel particulate filter out of a material containing porous oxide with an NOx absorbent carried thereon. SOLUTION: Regarding the structure of this diesel particulate filter(DPF), a DPF forming material with an NOx absorbent carried thereon is used to form DPF. In other words, this DPF is made to carry the NOx absorbent on the division surface thereof and the surface of a fine hole in the division, thereby applying both NOx absorbing and particulate arresting functions to a single compact without any increase in pressure loss. In this case, one material selected from lithium, sodium, potassium. calcium, lanthanum and the like are, for example, mentioned as the NOx absorbent. Also, alumina, silica-alumina, zeolite and the like are used as the porous oxide.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to particulate matter and NO _x contained in exhaust gas of a diesel engine.
The present invention relates to a diesel particulate filter (hereinafter referred to as DPF) capable of effectively removing components.

[0002]

2. Description of the Related Art A diesel engine operates in a region where the air-fuel ratio is very high, that is, a so-called lean region.
Although the emission amount of O and HC is small, the emission amount of NO _x and particulates is large, and reducing these is an issue.

This NO_xAs a way to reduce
NO when the air-fuel ratio of lean is lean _xAbsorbs and exhausts
NO absorbed when the oxygen concentration of the gas decreases_xRelease N
O_xThe absorbent should be placed in the exhaust passage of the diesel engine.
And is known. That is, this NO_xExhaust to absorbent
NO in gas_xTo absorb NO_xThe absorption efficiency of the absorbent
When it falls, cut off the inflow of exhaust gas and NO_xAbsorbent
Supply reducing gas to NO_xNO absorbed from absorbent_x
And the released NO_xReduction purification of
Is going.

As a method of reducing the particulate matter, it is known to arrange a DPF as shown in FIG. 1 in the exhaust passage of the diesel engine to collect the particulate matter in the exhaust gas. In this filter, plugs 2 are alternately plugged at one of both ends of a large number of cells (through holes), and a cell 3 plugged at an exhaust gas inlet end is opened at an outlet end. On the contrary, the cell 4 opened at the inlet end has a structure in which it is plugged at the outlet end. The partition walls 5 of the cells adjacent to each other have pores that allow the exhaust gas to pass but not the particulates. When the exhaust gas flows into the filter having such a structure, as shown in FIG. 1b, the exhaust gas 6 that has flowed into the exhaust gas inlet side cell 4 whose inlet end is open must be the partition wall 5 as shown in FIG.
The particulate matter is collected on the partition wall of the cell on the exhaust gas inlet side because the particulate matter passes therethrough. The collected particulates are removed by igniting combustion by heating with a heater or the like, or by self-combustion by the action of the catalyst carried on the filter.

[0005] in JP-A-6-272541 is, DPF configurations was supported through the coating layer _the NO _x absorbent on the surface of the partition wall of the DPF as described above is disclosed. By using such a filter, with collecting particulates in the exhaust gas, it absorbs NO _x, thereby enabling a reduction in particulate and NO _x.

[0006]

The functions required for the DPF include high particulate collection efficiency, low pressure loss, high durability, mass productivity, and the like. In the case of the DPF having a structure in which the NO _x absorbent is supported via the coat layer, the pressure loss becomes large, which leads to a decrease in fuel consumption and is not preferable. It is also conceivable to combine the NO _x absorbent with the DPF as a separate unit, but it is known that the pressure loss increases as the number of catalytic converters that pass exhaust gas increases, and the device becomes bulky and costly. May increase, and it is not preferable to combine them as separate units.

In view of the above problems, the present invention collects particulates and NO _x without causing an increase in pressure loss.
It is an object of the present invention to provide a DPF that can simultaneously absorb the above.

[0008]

According to the present invention, NO _x
There is provided a diesel particulate filter formed of a material containing a porous oxide supporting an absorbent. The NO _x absorbent is supported on the DPF forming material before the DPF is formed, and the DPF is formed by using this material, so that the NO _x absorbent is not provided with the coating layer as in the conventional case, but the partition surface of the DPF is formed. Also, it can be supported on the surface of the pores through which the exhaust gas in the partition wall passes. As a result, since no coat layer is provided, one molded article can have two functions of NO _x absorption capacity and particulate collection capacity without increasing pressure loss.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The NO _x absorbent used in the present invention has been conventionally used for purifying exhaust gas of an internal combustion engine, and when the air-fuel ratio of the inflowing exhaust gas is lean, NO _x is removed. The absorbed NO _x is released when the oxygen concentration of the inflowing exhaust gas decreases. Examples thereof include lithium, sodium, potassium,
At least one selected from alkali metals such as cesium, alkaline earth metals such as calcium and barium, and rare earth elements such as lanthanum and yttrium can be given.

As the porous oxide supporting the NO _x absorbent, various oxides conventionally used for catalyst carriers, such as alumina, silica-alumina, zeolite, cordierite, layered oxide, etc., can be used. Can be used. This porous oxide preferably has pores with a pore size of 50 Å or less. This is because if the pore size is larger than 50Å, the surface area is not sufficient and the amount of NO _x absorbent to be carried cannot be made sufficient. Further, since the NO _x absorbent is carried in the pores, the pore diameter of the pores needs to be larger than the size of the alkali metal element as the NO _x absorbent, that is, 2 to 3 Å, and 10 Å The above is preferable.

The diameter of the pores of commonly used zeolite is less than 10Å, which is not preferable for use in the present invention. Therefore, in the present invention, when zeolite is used as the porous oxide, it is disclosed in
It is preferable to use the layered silica-metal oxide porous body (hereinafter referred to as FSM) described in JP-A-238810. This FSM has a structure in which inter-layer cross-linking of SiO ₄ is formed by dehydration condensation of silicic acid between layered crystals of silicon tetrahedron SiO ₄ , and has a large number of pores with a pore diameter of 10 Å or more, and the layered crystals are It has a solid acidity that is developed by the bonding of a metal atom different from silicon. This FS
M is produced by introducing an organic substance having a size corresponding to a desired size of pores between the layers of the layered crystal of silicon tetrahedron SiO ₄ and firing it, so that the size of the formed pores is arbitrary. Can be designed to.

As a method for supporting the NO _x absorbent on the porous oxide, a usual method for supporting the catalyst on the carrier, for example, an impregnation method, an ion exchange method, an adsorption method or the like can be used. In addition to this NO _x absorbent, a noble metal conventionally used as an exhaust gas purifying catalyst, such as platinum, palladium or rhodium, may be supported. By supporting this noble metal, the obtained DPF can oxidize and purify HC and CO in the exhaust gas while collecting particulates and absorbing NO _x .

Thus, using the porous oxide supporting the NO _x absorbent, if necessary, an inorganic binder such as alumina sol, water glass, aluminum phosphate, silica sol, etc. is added, and a honeycomb filter is formed by a usual extrusion molding method,
As shown in FIG. 1, every other inlet and outlet of each cell is plugged with a plug to form the DPF of the present invention.

FIG. 2 shows an embodiment of an exhaust emission control device for an internal combustion engine using the DPF of the present invention. In FIG. 2, 7 is a diesel engine, 8 is an intake passage, and 9 is an exhaust passage. An intake throttle valve 10 is provided in the intake passage 8, and the intake throttle valve 10 is normally fully opened.
The valve is closed when the O _x absorbent is regenerated, and the intake air amount of the engine 7 is throttled to reduce the exhaust flow rate flowing into the NO _x absorbent. As a result, the amount of reducing agent required to consume oxygen in the exhaust gas and reduce the oxygen concentration in the NO _x absorbent atmosphere is reduced. In the figure, reference numeral 11 indicates the intake throttle valve 1.
It is an actuator that drives 0.

A DPF 1 is arranged in the exhaust passage 9. Reference numeral 12 is a reducing agent supply device for supplying a reducing agent to the exhaust passage 9 on the upstream side of the DPF 1 to make the exhaust air-fuel ratio flowing into the NO _x absorbent rich. As the reducing agent, a gas such as hydrogen and carbon monoxide, a liquid or gaseous hydrocarbon such as propane, propylene and butane, a liquid fuel such as gasoline, light oil and kerosene can be used. Here, light oil, which is a fuel of a diesel engine, is used as a reducing agent, and the reducing agent supply device 12 includes a nozzle that atomizes the fuel supplied from the engine fuel system into the exhaust passage 9.

An exhaust temperature sensor 13 is arranged in the exhaust passage 9 between the DPF 1 and the reducing agent supply device 12, and a detection signal of the exhaust temperature sensor 13 is an electronic control unit (ECU) 1.
4 is input. The ECU 14 includes a CPU (central processing unit), RAM (random access memory), ROM
(Read-only memory), becomes the output port from the known type of digital computer connected by a bi-aromatic bus, in addition to performing the basic control of the engine fuel injection control and the like, regeneration of _the NO _x absorbent in the present embodiment, party combustion curated, also performs the control of the poisoning recovery etc. of the NO _x absorbent. In order to perform these controls, the ECU 14 controls the actuator 11 that drives the intake body throttle valve 10 and the reducing agent supply device 12 to open / close the intake body throttle valve 10 and supply the reducing agent from the reducing agent supply device 12. Adjustment.

The DPF 1 is manufactured as described above, and the NO _x absorbent is carried in the pores on the partition walls. N fuel ratio of _the NO _x absorbent inflow exhaust gas is absorbed NO _x when the lean, the oxygen concentration in the inflowing exhaust gas to release the absorbed NO _x when lowered
It acts to absorb and release O _x .

In this embodiment, since the diesel engine is used, the exhaust air-fuel ratio at normal times is lean and N
The O _x absorbent absorbs NO _{x in} the exhaust gas. Also,
When the reducing agent is supplied from the reducing agent supply device 12 to the exhaust passage on the upstream side of the DPF 1 and the air-fuel ratio of the inflowing exhaust gas becomes rich, the NO _x absorbent releases the absorbed NO _x . The released NO _x reacts with unburned HC or CO in the exhaust gas and is reduced and purified to N ₂ .

Next, the exhaust air-fuel ratio is made lean and the DPF
The particulates collected in 1 are burned, and D
PF1 becomes hot. At this time, NO _x absorbent becomes high. In general, _the NO _x absorbent becomes so NO _x is released from the NO _x absorbent even under lean atmosphere becomes a high temperature, combustion of particulates is carried out after the NO _x is released from _the NO _x absorbent Therefore, nO _x during combustion of the particulates are not released, thus unpurified of the nO _x is prevented from being released into the atmosphere.

[0020]

EXAMPLE A DPF according to the present invention was manufactured as follows. 16% by weight of potassium and 3.2% by weight of platinum were loaded on the above FSM having a pore size of 25 liters, and 12% by weight of alumina sol, 8% by weight of water glass, and 4% by weight of ethyl cellulose as a plasticizer were added thereto, and extrusion molding was performed. It was formed into a honeycomb filter. Dry it at 200 ℃,
Every other inlet and outlet of the cell was plugged with a plug and then sintered at 900 ° C. to obtain a DPF of the present invention. This DP
F is the number of cells 23 cells / cm ² (150 cells / square inch), wall thickness
200 μm, average pore size of partition walls is 45 μm, diameter 200 mm
The length was 180 mm.

This DPF was mounted on a 2.4 liter engine as shown in FIG. 3, and the engine was operated for 10 hours at a constant engine speed of 2000 rpm and a torque of 80 nm, and the exhaust gas purification rate and system pressure were determined by the routine shown in the flow chart of FIG. The loss was measured. In addition, for comparison, a combination of the unplugged honeycomb filter manufactured above and a conventionally used cordierite DPF was attached to an engine as shown in FIG. 5 and exhausted in the same manner as above. The gas purification rate and system pressure drop were measured. Table 1 shows the results.

[0022]

[Table 1]

As is clear from the results of the above table, the DPF of the present invention can achieve the same degree of exhaust gas purification rate in one unit as compared with the conventional device in which the DPF and the catalytic converter are combined. The pressure loss can be significantly reduced.

[0024]

The DPF of the present invention constitutes this DPF.
The material itself is NO_xExhaust gas because it has an absorbent
In the exhaust gas at the same time as collecting the inside particulates
NO _xCan be absorbed, and DP as before
NO after molding F through the coating material_xSupport the absorbent
Instead of holding,
The form itself is NO_xIncreases pressure loss as it becomes an absorbent
Can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic view showing the structure of a DPF, where a is a front view,
b is a cross-sectional view.

FIG. 2 is a diagram showing an exhaust emission control device using the DPF of the present invention.

FIG. 3 is a diagram of an exhaust gas purification system used for evaluating the DPF of the present invention.

FIG. 4 is a flowchart showing an operation in DPF evaluation.

FIG. 5 is a diagram of an exhaust gas purification system using a conventional DPF and a catalytic converter containing a NO _x absorbent.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Diesel particulate filter 2 ... Plug 3 ... Exhaust gas inflow cell 4 ... Exhaust gas outflow cell 5 ... Partition wall 6 ... Exhaust gas 7 ... Diesel engine 8 ... Intake passage 9 ... Exhaust passage 10 ... Intake throttle valve 11 ... Actuator 12 ... Reductant supply device 13 ... Exhaust temperature sensor 14 ... Electronic control unit 15 ... Reformer 16 ... Cordierite DPF 17 ... NO _x storage catalytic converter

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seiji Okawara 1 Toyota-cho, Toyota-shi, Aichi Toyota Automobile Co., Ltd.

Claims (1)

[Claims] 1. A diesel particulate filter formed of a material containing a porous oxide supporting an NO _x absorbent.