JPH10231720A - Regenerating method of exhaust emission control catalyst of internal combustion engine in automobile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce sulfur poisoning resistance by automatically stopping an engine after an engine switch is turned off and then regenerating operation of an exhaust emission control catalyst is carried out. SOLUTION: A lean NOx catalyst A is arranged on the way of an exhaust pipe, and a material added thiophene of 400ppm as sulfur in gasoline is used as fuel. An automobile is traveled for 10 hours at 50km per hour and in a lean operating condition, the engine switch is turned off, and regenerating treatment of an exhaust emission control catalyst is carried out by automatic control. The regenerating treatment is controlled in such a way that operation of engine only is changed from 5 seconds to 10 minutes without traveling the automobile in a condition of an stoichiometric air-fuel ratio or in a fuel excessive condition, and the temperature of the exhaust emission control catalyst is set to 250 to 600 deg.C. When the regenerating treatment time is set to 1 minute and the air-fuel ratio is set to 14.0, the more the regenerating treatment temperature is high, the more a NOx purifying ratio is high, and also the sulfur rate in the catalyst is reduced. It is thus possible to separate and reduce sulfur in the exhaust emission control catalyst, and it is also possible to suppress deterioration of the exhaust emission control catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for regenerating an exhaust gas purifying catalyst of an automobile internal combustion engine from deterioration caused by sulfur compounds.

[0002]

2. Description of the Related Art Carbon monoxide (hereinafter referred to as CO), hydrocarbons (hereinafter referred to as HC), NOx, and the like contained in exhaust gas discharged from an internal combustion engine of an automobile or the like have an adverse effect on the human body as air pollutants and plants. Causes problems such as hindering the growth of Therefore, a number of studies have been conducted to reduce the emission of these harmful substances, such as reducing the amount of harmful substances generated by improving combustion conditions in internal combustion engines, and purifying exhausted harmful substances with catalysts. Development has been advanced.
Currently, in the case of automobile exhaust gas, a method of oxidizing HC and CO and reducing NOx to make it harmless at the same time as a three-way catalyst containing a noble metal such as Pt, Rh, and Pd as a main component is mainly used.

In general, a three-way catalyst has a low stoichiometric air-fuel ratio (A (weight of air) / F (weight of fuel) = 14.7).
) Effective only for purification of harmful substances nearby.
For this reason, in the case of a normal automobile engine, the air-fuel ratio has been controlled to be close to this stoichiometric air-fuel ratio to suppress emission of harmful substances into the atmosphere.

However, fuel efficiency can be improved by operating at an air-fuel ratio leaner than the stoichiometric air-fuel ratio. Therefore, in recent years, lean burn vehicles operating at a lean air-fuel ratio have been developed.
In this lean burn vehicle, high concentration of oxygen (3
Therefore, with the conventional three-way catalyst, HC and CO can be oxidized and made harmless, but the ability to reduce NOx is poor and cannot be made harmless. Therefore, as a NOx purification technology corresponding to lean burn, research is currently being conducted on a catalyst capable of reducing and purifying NOx even in the presence of oxygen (hereinafter, lean NOx catalyst). As an example, see JP-A-6-3
No. 1139 and JP-A-8-24643 disclose a catalyst supporting an alkaline earth metal and the like.

[0005]

SUMMARY OF THE INVENTION A three-way catalyst or lean NO
Common problems of exhaust gas purifying catalysts such as x catalysts include improving activity, improving heat resistance, and improving poisoning resistance. Above all, poisoning of the catalyst by sulfur contained in gasoline is a major problem, and improving sulfur poisoning resistance has become an important issue.

In general, catalysts are more susceptible to poisoning by SO ₃ than SO ₂ . In lean burn exhaust gas, high concentration of oxygen coexists, so SO ₂ is easily oxidized to SO ₃ , and is more likely to poison the catalyst than conventional engine exhaust gas operated at a stoichiometric air-fuel ratio. Therefore, especially in a lean NOx catalyst, improvement of sulfur poisoning resistance is indispensable.

Until now, from the viewpoint of catalyst materials, Japanese Patent Application Laid-Open
Japanese Patent Application Laid-Open No. 5-51544 proposes a method of producing a complex sulfate which is easily decomposed, and Japanese Patent Application Laid-Open No. 7-171349 proposes a method of suppressing the oxidation of SO ₂ . The present invention provides a means for regenerating an exhaust gas purifying catalyst that has been poisoned and degraded by a sulfur compound. The present invention can reduce the sulfur poisoning resistance of a conventional exhaust gas purifying catalyst.

[0008]

Means for Solving the Problems The present inventors have made intensive studies on a method for regenerating the catalytic activity degraded by poisoning by sulfur in the conventional three-way catalyst and lean NOx catalyst, and as a result, switched off the engine switch. At that time, it was found that it is effective to automatically stop the engine after performing the regeneration operation of the exhaust gas purification catalyst instead of immediately stopping the engine. A feature of the present invention resides in a method of regenerating an exhaust gas purifying catalyst of an automobile internal combustion engine in which an engine switch is turned off, an exhaust gas purifying catalyst is regenerated, and then the engine is automatically stopped.

The present inventors have found that it is effective as a means for regenerating sulfur poisoning to operate at a stoichiometric air-fuel ratio or in an excessive fuel state to desorb sulfur compounds contained in an exhaust gas purification catalyst. I found it. Another feature of the present invention is a method of regenerating an exhaust gas purifying catalyst for an automobile internal combustion engine, which operates in a stoichiometric air-fuel ratio or an excessive fuel state and desorbs sulfur compounds contained in the exhaust gas purifying catalyst.

The above-described method for regenerating an exhaust gas purifying catalyst from a sulfur compound is also effective as a regenerating operation after an engine switch is turned off. Another feature of the present invention is that after turning off the engine switch, the engine is operated in the stoichiometric air-fuel ratio or in the state of excessive fuel,
The present invention relates to a method for regenerating an exhaust gas purifying catalyst for an automobile internal combustion engine, which automatically stops the engine after desorbing sulfur compounds contained in the exhaust gas purifying catalyst.

Further, the present inventors have found that the regeneration of the sulfur-poisoned exhaust gas purifying catalyst proceeds advantageously in a temperature range of 400 ° C. or higher. A further feature of the present invention is that after turning off the engine switch, the temperature of the exhaust gas purifying catalyst is 400 ° C.
A method for regenerating an exhaust gas purifying catalyst of an automobile internal combustion engine, in which the engine is automatically stopped after the engine is operated in a stoichiometric air-fuel ratio or a state in which the amount of fuel is higher than the stoichiometric air-fuel ratio in a state controlled as described above. In order to control the temperature of the exhaust gas purifying catalyst to 400 ° C. or higher, it is possible to increase the engine speed, but it is also possible to use an external heating device. The present invention is not limited by the means for controlling the temperature of the exhaust gas purifying catalyst to 400 ° C. or higher.

Any of the above-mentioned regenerating operations of the exhaust gas purifying catalyst is an effective method using a conventional three-way catalyst or lean NOx catalyst. However, the exhaust gas purifying catalyst is a heat-resistant catalyst supporting a noble metal, an alkaline earth metal and a rare earth metal. By being a metal oxide, it can be exhibited as an extremely effective means.
The present invention is also characterized in that the exhaust gas purifying catalyst is a heat-resistant metal oxide supporting a noble metal, an alkaline earth metal and a rare earth metal, but the present invention is not limited to this.

[0013]

Embodiments of the present invention will be described below.

"Catalyst Example 1" Water and diluted nitric acid were added to boehmite powder and mixed with stirring to obtain a slurry for coating.
The slurry was wash-coated on a cordierite honeycomb, dried, and fired at 600 ° C. for 1 hour to obtain an alumina-coated honeycomb. The coating amount of alumina was 150 g per liter of honeycomb.

The alumina coated honeycomb was immersed in an aqueous cerium nitrate solution, dried, and fired at 600 ° C. for 1 hour. Subsequently, it was immersed in an aqueous solution containing strontium nitrate and titania sol, dried, and fired at 600 ° C. for 1 hour. Next, it was immersed in an aqueous solution containing dinitrodiamine platinum and rhodium nitrate, dried, and baked at 450 ° C. for 1 hour. Finally, immerse in magnesium nitrate aqueous solution, and after drying,
The mixture was calcined at 450 ° C. for 2 hours to obtain a lean NOx catalyst A. The catalyst composition of the lean NOx catalyst A was: Mg: 1 wt%, Rh: 0.15 wt%, Pt: 1.
9 wt%, Ti: 5 wt%, Sr: 15 wt%, Ce:
18 wt%.

"Catalyst Example 2" A conventional general three-way catalyst was used. (Three-Way Catalyst B) Example 1 A vehicle equipped with a 1.8-liter lean burn engine was equipped with a lean NOx catalyst A shown in Catalyst Example 1.
Was installed in the middle of the exhaust pipe. As the fuel, gasoline obtained by adding 400 ppm of thiophene as a sulfur content to gasoline was used. The initial state before the endurance running test is defined as (I). Subsequently, the state after traveling for 10 hours in a lean operation state at about 50 km / h is defined as (II). Further, the state after the engine switch is turned off and the regeneration processing of the exhaust gas purifying catalyst is performed by the automatic control is defined as (III). The regeneration process was performed in a state of a stoichiometric air-fuel ratio (stoichiometric ratio) or an excessive amount of fuel (rich) by changing the operation of only the engine from 5 seconds to 10 minutes without running the automobile. Further, the temperature of the exhaust gas purifying catalyst was controlled to be 250 to 600 ° C.

The same method as in Example 1 was carried out except that the three-way catalyst B of Catalyst Example 2 was provided in the middle of the exhaust pipe instead of the lean NOx catalyst A of Catalyst Example 1.

"Test Example 1" In each of the conditions (I) to (III),
The engine was operated at a stoichiometric air-fuel ratio at a speed of about 40 km / h, switched to a lean burn operation, and the NOx purification rate after one minute was measured. In the state of (I), the NOx purification rate was 90% in Example 1 and 30% in Example 2. In the state (II), the NOx purification rate was 41% in Example 1 and 3% in Example 2.

"Test Example 2" A part of the exhaust gas purifying catalyst corresponding to each of the states (I) to (III) was cut out and pulverized, and the sulfur concentration in the exhaust gas purifying catalyst was analyzed. The sulfur concentration in the state of (I) was 0% by weight in both Examples 1 and 2.
Met. The sulfur concentration in the state (II) was determined in Example 1.
Was 2.1% by weight and Example 2 was 1.2% by weight.

In the first and second embodiments, the regeneration processing temperature, the regeneration processing time, and the air-fuel ratio (weight ratio) at the time of the regeneration were changed, and (III)
The NOx purification rate and sulfur concentration in the state of were measured.
FIG. 1 shows that the catalyst A was used, the regeneration processing time was 1 minute, and the air-fuel ratio was 14.
This is the dependence of the regeneration processing temperature on the case of 0. It was found that the higher the regeneration treatment temperature, the higher the NOx purification rate and the lower the amount of sulfur in the catalyst. FIG. 2 shows the case where the catalyst A was used and the regeneration treatment temperature was 4
This is the dependence of the regeneration processing time at 50 ° C. and an air-fuel ratio of 14.0. The effect is higher as the playback processing time is longer. FIG.
Uses catalyst A, regeneration processing time 1 minute, regeneration processing temperature 45
This is the dependence of the air-fuel ratio at 0 ° C. The more fuel is switched from the stoichiometric air-fuel ratio to the state of excessive fuel (the lower the air-fuel ratio), the higher the regeneration effect. FIG. 4 shows that the catalyst B was used and the regeneration treatment temperature 4
This is the dependence of the regeneration processing time at 50 ° C. and an air-fuel ratio of 14.0. It has been found that the present invention is also effective for sulfur poisoning of a conventional general three-way catalyst.

[0021]

According to the present invention, by using a regeneration means for a certain period of time after the engine switch is turned off, the sulfur content in the exhaust gas purification catalyst is desorbed and reduced, and the deterioration of the exhaust gas purification catalyst can be suppressed. That is, the life of the catalyst can be extended.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram of a regeneration test result of an exhaust gas purifying catalyst as one example of the present invention.

FIG. 2 is a characteristic diagram of a regeneration test result of an exhaust gas purifying catalyst as one example of the present invention.

FIG. 3 is a characteristic diagram of a regeneration test result of an exhaust gas purifying catalyst as a second embodiment of the present invention.

FIG. 4 is a characteristic diagram of a regeneration test result of an exhaust gas purifying catalyst as a third embodiment of the present invention.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F01N 3/10 ZAB F02D 29/02 321C 3/24 41/04 305A ZAB B01D 53/36 ZAB F02D 29/02 321 102E 41/04 305 102H (72) Inventor Hidehiro Iizuka 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd. Hitachi Research Laboratory (72) Inventor Toshio Ogawa 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Hitachi, Ltd., Hitachi Research Laboratories (72) Inventor Toshio Yamashita 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd. Hitachi Research Laboratory (72) Inventor Shigeru Azuhata 7-1, Omika-cho, Hitachi City, Ibaraki Prefecture No. 1 Inside Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Yuichi Kitahara 2520 No. Odaiba, Hitachinaka City, Ibaraki Prefecture Hitachi, Ltd. Automotive Equipment Division (72) Inventor Toshifumi Hiratsuka 2520, Oaza Takaba, Hitachinaka City, Ibaraki Prefecture Hitachi, Ltd. Automotive Equipment Division

Claims (5)

[Claims] 1. A method for regenerating an exhaust gas purifying catalyst for an automobile internal combustion engine, comprising: after turning off an engine switch, performing an operation for regenerating the exhaust gas purifying catalyst, and then automatically stopping the engine. 2. A method for regenerating an exhaust gas purifying catalyst for an automobile internal combustion engine, comprising operating the engine at a stoichiometric air-fuel ratio or an excessive amount of fuel to desorb sulfur compounds contained in the exhaust gas purifying catalyst. . 3. An internal combustion engine for an automobile, wherein after the engine switch is turned off, the engine is operated with a stoichiometric air-fuel ratio or an excessive amount of fuel to desorb sulfur compounds contained in the exhaust gas purification catalyst, and then the engine is automatically stopped. A method for regenerating an exhaust gas purifying catalyst for an automobile internal combustion engine, comprising: 4. An automobile internal combustion engine is operated with the stoichiometric air-fuel ratio or in a state where the fuel is more than the stoichiometric air-fuel ratio in a state where the temperature of the exhaust gas purifying catalyst is controlled to be 400 ° C. or higher after the engine switch is turned off. A method for regenerating an exhaust gas purifying catalyst for an automobile internal combustion engine, comprising automatically stopping the engine. 5. A method for regenerating an exhaust gas purifying catalyst for an automobile internal combustion engine according to claim 1, wherein said exhaust gas purifying catalyst is a heat-resistant metal oxide carrying a noble metal, an alkaline earth metal and a rare earth metal. .