JPH02107340A - Catalyst for cleaning up diesel gaseous emission - Google Patents

Abstract

PURPOSE:To control exhaust backpressure at the time of mounting a catalyst and driving a vehicle by depositing a specific amount of catalytically active component over a seal type ceramic honeycomb structure and providing a catalyst having the sum of the volumes of pore exceeding a specific amount for cleaning up diesel gaseous emissions. CONSTITUTION:The catalytically active component consisting of catalytically active inorganic substance (alkali metals, alkaline earth metals, vanadium, tungsten, etc.) or porous inorganic substance (alumina, silica, zirconia, etc.) and catalytically active inorganic substance is deposited over a seal type ceramic honeycomb structure wherein gas is passable through only a partition wall with pores alternately closed at each end face thereof in an amount of 20-60g per liter of the aforesaid structure. At the time of depositing this catalytically active component on a plug honeycomb (seal type honeycomb monolith), the lowering of an engine output caused by a rise in exhaust backpressure can be prevented by summing up the volumes of the pores having a diameter of not less than 7mum of all the volumes of the pores in the plug honeycomb to not less than 0.11ml/g.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a catalyst for purifying diesel exhaust gas. More specifically, the present invention excels in purifying carbon monoxide (Go), gaseous hydrocarbons (HC), and carbonaceous particulates (particulates) in diesel exhaust gas, and improves the back pressure of engine exhaust gas when a catalyst is installed, and when driving. This invention relates to a catalyst for purifying diesel exhaust gas that extremely minimizes the increase in back pressure and suppresses the reduction in engine output caused by this increase in back pressure.

[Prior Art] In recent years, it has become a problem that CO18C and particulates contained in diesel exhaust gas are polluting the atmosphere. Various catalysts have been proposed as a countermeasure to this problem.

For example, a catalyst using vanadium and noble metals for purifying Co1)-1G in exhaust gas (Japanese Patent Application Laid-open No. 1206-1986)
No. 40), noble metals and alkaline earth metals (Japanese Patent Application Laid-open No. 60-23562) are used for purifying particulates.
There is a catalyst using the following.

[Problems to be Solved by the Invention] However, when these catalysts are installed in a diesel vehicle, the back pressure of the engine exhaust gas is high from the time of installation, and the back pressure increases even more during driving. As a result, the output of the engine decreases, making it difficult to actually install these catalysts.

However, currently, when installing an exhaust gas purification catalyst in a diesel vehicle, no catalyst has been proposed that suppresses the back pressure during installation and the increase in back pressure during driving, thereby minimizing the reduction in engine output. is the current situation.

Therefore, an object of the present invention is to provide a catalyst that reduces back pressure when the catalyst is mounted and suppresses an increase in back pressure during driving.

[Means for Solving the Problems] In order to achieve the above object, the present inventors discovered that when coating a structure with a catalytically active component, the structure has a pore diameter of 7 μm or more after coating. The volume is 0.11m! It has been found that by keeping the amount above /g, it is possible to suppress the back pressure caused by coating the catalytically active component, and also to suppress the increase in back pressure over time due to running.

That is, in a diesel exhaust gas purification catalyst in which a catalytically active component is coated and supported on a plugged ceramic honeycomb structure in which adjacent pores on both end faces are alternately closed to allow gas to pass through only from the partition walls, the structure 1
The sum of the volumes of pores in which the catalytic active component is coated and supported at 20 to 60 degrees per liter and has a pore diameter of 7 μm or more is 0.1
The present invention provides a catalyst for purifying diesel exhaust gas, which is characterized in that it has a concentration of 1 ml/g or more.

This structure is a plugged honeycomb monolith (hereinafter referred to as "plug honeycomb") in which adjacent pores on both end faces are alternately plugged with a honeycomb structure made of a refractory inorganic material to allow gas to pass through only from the partition walls. Although preferably used, in addition to this, carriers having a filtration function,
It goes without saying that, for example, a corrugated type honeycomb monolith exhibits a similar effect.

This catalytically active component is an inorganic substance that has catalytic activity, or is composed of a porous inorganic substance and an inorganic substance that has catalytic activity.

As inorganic substances having catalytic performance, alkali metals, alkaline earth metals, transition metals such as vanadium, tungsten, iron, zinc, manganese, nickel, noble metals, or oxides thereof are preferably used, but are not limited to these. It never happens.

The porous inorganic material refers to a heat-resistant porous inorganic material in which alumina, silica, zirconia, titania, a mixture thereof, or a composite oxide is used as a catalyst dispersion material, but is not limited thereto.

When a catalytic active component is supported on a plug honeycomb, by setting the sum of the volumes of pores with a diameter of 7 μm or more to 0.11 te/Q or more among the pore volumes of the plug honeycomb, back pressure of the catalyst and when the catalyst is installed can be reduced. The increase in back pressure can be suppressed to a low level. However, if the sum of the volumes is less than 0.11 d/Q, the back pressure of the catalyst and the increase in back pressure will be high, resulting in a catalyst with low practicality.

Therefore, the effects of the present invention can be obtained even when the supporting layers of the catalytically active component are the same or the total pore volume is the same.
It cannot be obtained unless the sum of pore volumes with pore diameters of 7 μm or more is 0.11 d/Q or more.

In addition, the supporting layer of the catalytically active component is 6 ts per liter.
If it exceeds 0g, the pore size will be 7μ even with the same supporting method.
In order to reduce the amount of pore volume of m or more, the back pressure of the catalyst and the increase in back pressure become high.

[Example] Below, Examples and Comparative Examples of the present invention will be shown, and the present invention will be explained in detail.

Example 1 206g of boehmite was dissolved in 750d of acidic aqueous solution,
A plug honeycomb made by Nippon Insulator ■ (144 holes φ, 152 holes, 100 cells/square inch) was immersed in it, pulled out, excess slurry was removed, dried at 120°C for 2 hours, and then dried at 500°C for 2 hours. Calcined, 77G in terms of alumina
A coated carrier was obtained.

A nitric acid solution of dinitrodiaminoplatinum containing 4.3 g of platinum was diluted with 2,500 d of ion-exchanged water and kept at 80° C. The resulting carrier was placed therein and moved up and down to adsorb platinum onto the carrier. Blow off excess water and heat to 120℃
After drying for 2 hours at
．． A catalyst body (A) carrying 3 g was obtained. The catalyst was loaded with 32.5 g of catalytically active material per liter of catalyst.

Example 2 500 g of alumina powder and 500 g of ion-exchanged water were placed in a ball mill, and 750Q of ion-exchanged water was added to the slurry obtained by grinding for 16 hours, and Example 1 was added to this slurry.
Soak the plug honeycomb, remove excess slurry,
After drying at 120°C for 2 hours, it was fired at 500°C for 2 hours. A carrier coated with 105a in terms of alumina was obtained.

Platinum was supported on this carrier in the same manner as in Example 1, and the catalyst body (8
) was obtained. The catalyst was loaded with 43.7 a of catalytically active material per liter of catalyst.

Comparative Example 1 A catalyst body (C) was obtained in the same manner as in Example 2 except that the slurry obtained by changing the wet grinding time of Example 2 to 2 hours was used.

45Q of catalytically active material was supported per liter of the catalyst.

Comparative Example 2 All samples were prepared by adding 160 g of ion-exchanged water to the slurry obtained by overnight wet grinding of Example 2.
A catalyst body (D) was obtained in the same manner as above.

This catalyst body was coated with 2000 alumina. The catalyst was loaded with 81.70 catalytically active substances per liter of catalyst.

Comparative example 3 The plug honeycomb was left untreated (E).

Example 3 Displacement 2.8j! The catalyst bodies (^) to (E) were mounted on a converter and evaluated at the exhaust port of a four-cylinder diesel engine.

(Measurement of Catalyst Back Pressure) A catalytic converter equipped with a catalyst is connected to the rear of the engine manifold, and a bypass pulp is provided on the inlet side of the catalytic converter. In order to prevent exhaust gas from flowing to the catalytic converter side, the bypass is opened at startup to allow all exhaust gas to exit the system.

The engine operating condition at this time is engine speed 270.
0 rpm, torque is 1.8 KfJ-m-r-. Operate in this state for 30 minutes. Next, close the bypass valve, introduce all the exhaust gas into the catalytic converter, and measure the differential pressure between the inlet and outlet of the catalyst. This is the pressure loss of the catalyst. The catalyst inlet temperature at this time was 290°C.

(Measurement of back pressure increase rate) Under the above conditions, let exhaust gas flow through the catalytic converter, measure the time for the pressure loss to increase by 6OImHg from the initial level,
The back pressure increase rate was calculated from the following formula.

Back pressure increase rate [mHg/fir] = 60am)l
(1/measurement time (Hr)) The results are shown in Table 1.

Example 4 The pore volume of catalyst bodies (A) to (E) was
(Shimadzu Corporation ■) and the results are shown in Table 2.

Table 1 table It is a highly versatile catalyst.

Claims (1)

[Claims] (1) A catalyst for diesel exhaust gas purification in which a catalytically active component is coated and supported on a plugged ceramic honeycomb structure in which adjacent holes on both end faces are alternately closed to allow gas to pass through only from the partition wall. 20 to 60 g of catalytic active component is coated and supported per liter of the structure, and the sum of the volumes of pores having a pore diameter of 7 μm or more is 0.11 m
A catalyst for purifying diesel exhaust gas, characterized in that it has a gas purification rate of 1/g or more.