JPH1043550A - Purifying method of nitrogen oxides in waste gas and purifying catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain high NOX purifying performance and to improve heat resistance and anti-poisoning property by using a catalyst formed by carrying at least one kind of Rh, Pt or Pd, at least one kind of La or Ce and Mg and Na on a porous carrier. SOLUTION: The catalyst capable of withstanding the temp. change of a waste combustion gas or trace poisoning components (SOX, P, Pb) over a long period and excellent in heat resistance and anti-poisoning property is obtained by carrying at least one kind of Rh, Pt or Pd, at least one kind of La or Ce and Mg and Na on the porous carrier. The catalyst can be formed by carrying at least one kind of Rh, Pt or Pd, at least one kind of La or Ce, at least one kind of Sr or Ba and Mg and Na on the porous carrier. As the porous carrier, a carrier consisting of alumina and a carrier consisting of a multiple oxide of La and Al, in which the component ratio of La to Al is 1-20mol% and the sum of La and Al is 100mol%, are suitably used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently purifying nitrogen oxides from exhaust gas containing nitrogen oxides discharged from an internal combustion engine such as an automobile engine, and to a catalyst for purifying nitrogen oxides. .

The catalyst of the present invention has high nitrogen oxide purification performance not only for exhaust gas burned at the stoichiometric air-fuel ratio but also for exhaust gas containing oxygen burned in excess air.
Excellent heat resistance and poisoning resistance. Therefore, it is suitable as a catalyst for purifying exhaust gas emitted from a lean burn automobile engine.

[0003]

2. Description of the Related Art In recent years, in the course of resource saving and environmental protection,
There is a social demand to run a gasoline engine on a lean burn. Accordingly, development of a catalyst (lean NOx catalyst) for effectively purifying NOx in exhaust gas containing oxygen discharged from a lean burn engine has been promoted.

[0004] As an exhaust gas purifying catalyst for a lean burn engine, a particle size of an alkaline earth metal, an alkali metal or the like, which is a NOx absorbent that occludes lean NOx during lean burn and releases and reduces occluded NOx during stoichiometric combustion, is used. Numerous reports have been reported, such as a controlled catalyst (JP-A-8-24643) and a catalyst supporting an alkali metal oxide (JP-A-6-31139).

[0005]

As environmental regulations on automobiles are tightened, lean NOx catalysts are becoming increasingly expensive.
At the same time as the purification performance is required, heat resistance and poisoning resistance are required that can withstand the temperature change of the combustion exhaust gas due to various changing vehicle speeds and trace poisoning components (SOx, P, Pb) contained in the combustion exhaust gas for a long time. ing.

An object of the present invention is to solve the above technical problems,
An object of the present invention is to provide a catalyst material having high NOx purification performance and excellent heat resistance and poisoning resistance, and an exhaust gas purification method.

[0007]

According to a first aspect of the present invention, at least one of Rh, Pt, and Pd, at least one of La and Ce, and Mg and Na are contained in a porous carrier. It is to use a supported catalyst.

The catalyst has a structure in which an active ingredient is supported on a porous carrier, and can be particularly preferably implemented by using Pt, Rh, Ce, Mg, and Na.

Further, after Ce is supported on the porous carrier,
A suitable catalyst can be obtained by supporting Mg and Na, further supporting Pt and Rh, and finally supporting Mg.

[0010] Further, the second invention provides a porous carrier comprising Rh,
It is to use a catalyst that carries at least one of Pt and Pd, at least one of La and Ce, at least one of Sr and Ba, and Mg and Na.

The catalyst according to the second invention has a structure in which an active ingredient is supported on a porous carrier, and comprises Pt, Rh, Ce, and M.
It is particularly preferably carried out by using g, Sr and Na.

Further, after Ce is supported on the porous carrier,
A suitable catalyst can be obtained by supporting Mg, Na and Sr, further supporting Pt and Rh, and finally supporting Mg.

As the porous carrier, metal oxides or composite oxides such as titania, silica, silica-alumina, and magnesia can be used. Further, a composite oxide of Al having a high specific surface area even at a high temperature and a rare earth metal or an alkaline earth metal can also be used. Among these,
The carrier made of alumina or the composition ratio of La and Al is L
A carrier composed of a composite oxide of La and Al, in which a is 1 to 20 mol% and the total of La and Al is 100 mol%, is particularly preferred.

As a method for preparing the catalyst, any of a physical preparation method such as an impregnation method, a kneading method, a coprecipitation method, a sol-gel method, an ion exchange method, and a vapor deposition method, and a preparation method utilizing a chemical reaction can be applied.

As starting materials for preparing the catalyst, various compounds such as nitric acid compounds, acetic acid compounds, chlorides, sulfides, carbonate compounds, organic compounds and the like, metals and metal oxides can be used.

The loading amount of each component is as follows: Na is 5 to 20% by weight based on 100 parts by weight of the porous carrier;
0% by weight La, Ce is 5 to 30% by weight Pt is 0.5 to 3% by weight Rh is preferably 0.05 to 0.3% by weight Pd is preferably 0.5 to 15% by weight.

In the case where at least one of Sr and Ba is carried, it is desirable that the content is 1 to 20% by weight based on 100 parts by weight of the porous carrier.

The catalyst of the present invention creates a high affinity for lean NOx due to the combined effect of Na and the alkaline earth metal, and exhibits high NOx purification performance. further,
The complexing promotes the stabilization of the structure of Na and the alkaline earth metal, and develops heat resistance and poisoning resistance.

If the catalyst has been poisoned by use for a long period of time, it is preferable to reactivate the catalyst by heating the catalyst to 400 ° C. to 800 ° C. using a reducing atmosphere, ie, a combustion exhaust gas having a stoichiometric air-fuel ratio or less. . Even when the catalyst activity decreases, the catalyst can be reactivated by the same reactivation process.

By mounting the catalyst of the present invention in the exhaust system of an internal combustion engine, the emission of nitrogen oxides to the outside of the vehicle can be significantly suppressed.

The catalyst of the present invention is also effective for treating exhaust gas discharged from a diesel engine of a diesel vehicle. Diesel engines are operated at a high air-fuel ratio with excess oxygen, and the catalyst of the present invention exhibits excellent activity even in the presence of oxygen, so that even the exhaust gas discharged from the diesel engine can efficiently purify nitrogen oxides. can do.

The catalyst of the present invention has a temperature of 200 ° C. or more and 600 ° C.
Excellent activity in the following temperature range, especially 200 ° C
It has high activity in the temperature range of ~ 500 ° C. Therefore, it is effective to set the temperature at which the catalyst is brought into contact with the gas stream, the so-called reaction gas temperature, within the above temperature range.

[0023]

FIG. 1 is a system diagram of a fuel injection type automobile gasoline engine. In FIG. 1, air required for combustion is taken in from an intake port 2, passes through an air cleaner 1, a throttle valve 5 for controlling intake flow rate, is mixed with gasoline in an intake pipe 8, and is introduced into a cylinder.

Gasoline required for combustion is drawn from a fuel tank 9 by a fuel pump 10, pressurized, passes through a fuel damper 11 and a fuel filter 12, and flows from a fuel injection valve (injector) 13 into an intake pipe 8. It is injected.

The air mixed with gasoline in the intake pipe is
It burns by electric ignition in the cylinder.

Exhaust gas generated by the combustion is discharged to an exhaust pipe 19,
The exhaust gas is discharged outside the system through the exhaust gas purifying catalyst 20.

The combustion is controlled by controlling an intake air amount signal detected by the intake air flow meter 3, a valve opening signal from a throttle sensor 18 provided on the throttle valve 5, and a crank provided on a distributor 16. An angle signal from each sensor is input to the control unit 15 to calculate an appropriate fuel injection amount and ignition timing, and control the fuel injection valve 13 and the ignition device. At this time, precise control can be performed by detecting the combustion state in the cylinder based on the oxygen concentration signal from the oxygen sensor 51 provided in the exhaust pipe 19 and performing feedback control.

The control unit 15 for performing this control
2 is shown in FIG. The input signal is passed to the MPU via the I / O. In order to perform appropriate control, the MPU performs a calculation using an input signal and values of the ROM and the RAM, and outputs a calculation result via an I / O. This output becomes a control signal, and controls the fuel injection valve 13 and the ignition device.

According to this control method, the combustion state in the cylinder is controlled to any state of a stoichiometric air-fuel ratio (stoichiometric), an excess fuel state (rich), and an excess air state (lean). Here, since harmful components such as HC, CO, and NOx are contained in the exhaust gas discharged from the engine 7, the harmful components must be detoxified and then discharged outside the system.

Therefore, an exhaust gas purifying catalyst 20 is provided in the exhaust pipe 19. According to the present invention, lean exhaust gas can be newly purified in addition to conventional stoichiometric and rich combustion exhaust gas purification, and the combustion state of the combustion system shown in FIG. 1 can be arbitrarily set. In addition, the combustion system according to FIG. 1 can be operated stably by improving heat resistance and poisoning resistance.

Hereinafter, the present invention will be described with reference to specific examples.
The present invention is not limited by these examples.

Example 1 A nitric acid alumina slurry comprising alumina powder and its precursor was coated on a cordierite honeycomb (400 cells / inc ² ), and about 150 g of alumina was coated per liter of apparent honeycomb volume. The obtained alumina-coated honeycomb was obtained. The alumina-coated honeycomb was impregnated with a Ce nitrate solution, dried at 200 ° C, and fired at 600 ° C for 1 hour. Subsequently, impregnated with an aqueous solution of a mixture of Na nitrate and Mg nitrate,
Similarly, drying and firing were performed. Further, impregnated with a mixed solution of dinitrodiammine Pt nitric acid solution and Rh nitrate solution,
After drying at 0 ° C, baking was performed at 450 ° C for 1 hour. Finally,
It was impregnated with a Mg nitrate solution, dried at 200 ° C, and baked at 450 ° C for 1 hour. From the above, alumina 100% by weight
To 18% by weight of Ce, 12% by weight of Na and 1.
2% by weight, platinum 1.6% by weight, Rh 0.1
Example catalyst 1 was obtained which contained 5% by weight and 1.5% by weight of Mg.

In the same manner, rare earth metals are converted to Ce, La,
Noble metals are Rh, Pt, Pd, alkaline earth metals are Sr,
Example catalysts 2 to 5 in which Ba and Mg were obtained were obtained. In addition, a catalyst preparation method similar to that of Example Catalyst 1 was used, but Comparative Examples 1 and 2 with respect to Example 1 were obtained.

Table 1 summarizes the compositions of the prepared catalysts. In addition, the loading order in Table 1 is such that after loading the first component,
It shows that the second component is supported. The supported amount is indicated before the supported metal type.

[0035]

[Table 1]

(Experimental Example 1) Nitrogen oxide purifying performance experiments were conducted on the catalysts of Examples 1 to 6 and Catalysts 1 and 2 of Comparative Examples by the following experimental method.

Experimental method: (1) 6 cc (17 mm square × 21 mm length) of a honeycomb catalyst is charged into a Pyrex reaction tube.

(2) Put the reaction tube in an annular electric furnace,
Heat to 0 ° C. The temperature measures the honeycomb inlet gas temperature. When the temperature reaches 300 ° C. and stabilizes, the circulation of stoichiometric combustion model exhaust gas (referred to as stoichiometric model exhaust gas) is started. Three minutes after the circulation, the circulation of the stoichiometric model exhaust gas is stopped, and the circulation of the lean burn model exhaust gas (referred to as lean model exhaust gas) is started. NOx in the gas discharged from the reaction tube is measured by a chemiluminescence method, and HC is measured by a FID method. The NOx purification performance and HC purification performance at this time are defined as initial performance.

(3) The reaction tube filled with the honeycomb catalyst used in the above (2) is placed in an annular electric furnace and heated to 300 ° C. The temperature measures the honeycomb inlet gas temperature. When the temperature reaches 300 ° C. and becomes stable, the flow of SO ₂ -containing stoichiometric combustion model exhaust gas (referred to as poisoning gas) is started. The SO ₂ poisoning test is completed by passing poisoned gas for 5 hours. And the same tests as (2) using the SO ₂ honeycomb catalyst after poisoning, obtain NOx purification performance and HC purification performance after SO ₂ poisoning.

(4) The honeycomb catalyst used in (2) is placed in a firing furnace and fired at 800 ° C. for 5 hours in an air atmosphere. After cooling, the same NOx purification performance and H
C Measure the purification performance.

As the stoichiometric model exhaust gas, 0.1 vol% of NO, 0.05 vol% of C ₃ H ₆ and 0.6 vol of CO were used.
%, The O ₂ 0.6 vol%, the H ₂ 0.2 vol%, steam 1
A gas containing 0 vol% and the balance nitrogen was used. In addition, as a lean model exhaust gas, NO is 0.06 vol.
%, 0.04vol% of C ₃ H _6, 0.1vol% of CO, CO ₂
10 vol%, O _{2 5} vol%, water vapor 10 vol%, and the balance nitrogen was used. Further, as the poisoning gas, NO was 0.1 vol% and C ₃ H ₆ was 0.05 vol%.
%, CO was 0.6 vol%, O ₂ was 0.6 vol%, SO ₂ was 0.005 vol%, water vapor was 10 vol%, and the balance was nitrogen. The space velocity of the three gases is 30,000 / h for dry gas (not including water vapor).
And

Table 2 shows the NOx purification rate of the honeycomb catalyst at the initial stage and after the SO ₂ poisoning, after one minute from switching from the stoichiometric model exhaust gas to the lean model exhaust gas.
The NOx purification rate and the HC purification rate were calculated according to the following equations.

[0043]

(Equation 1)

[0044]

(Equation 2)

The catalysts of Examples 1 to 5 were higher in initial performance, heat resistance and SOx resistance than the catalysts of Comparative Example.

In Comparative Examples 1 and 2, in which only one type of the second component was used, the initial performance, heat resistance and SOx resistance were reduced.

[0047]

[Table 2]

"Example 2" The carrier of Example 1 catalyst was La
La and Al composite oxides in which the composition ratio of La and Al is 1 to 20 mol%, and the total of La and Al is 100 mol%.
An example catalyst 6 comprising (La-β-Al ₂ O ₃ ) was obtained. The results are shown in Table 3.

By making the carrier La-β-Al ₂ O ₃ ,
Heat resistance improved.

[0050]

[Table 3]

"Example 3"
N at 400 ° C when the amount of supported Na as a component was changed
The initial performance of the Ox purification rate was measured. The catalyst preparation method was the same as in Example Catalyst 1, and the experimental method was the same as Experimental Example 1. The results are shown in FIG. In order to obtain a high NOx purification rate, the amount of supported Na is 5 to 20 parts by weight per 100 parts by weight of the carrier.
It is preferable to set it as a percentage by weight.

"Example 4"
The amount of Mg supported in the component was calculated by dividing the amount of supported Mg / (amount of supported Na + M
g carrying amount), the initial NOx purification rate at 400 ° C. was measured. The results are shown in FIG. In order to obtain a high NOx purification rate, it is preferable to set the weight ratio of the supported amount of Mg / (the supported amount of Na + the supported amount of Mg) to 1 to 40% by weight.

"Example 5"
The initial NOx purification rate at 400 ° C. when the supported amount of the component Ce was changed was measured. The results are shown in FIG. In order to obtain a high NOx purification rate, the amount of Ce supported is preferably set to 1 to 40% by weight.

Example 6 In Example 1, Pt was used.
And the initial NOx purification rate at 400 ° C. when the supported amount of Rh was changed. The results are shown in FIG. The loading amount of Pt is 0.5-3% by weight, and the loading amount of Rh is 0.05-5%.
By setting it to 0.3% by weight, a high NOx purification rate can be obtained.

Example 7 In Example 1, Pt was used.
And the initial NOx purification rate at 400 ° C. when the amount of Pd carried was changed. The results are shown in FIG. The loading amount of Pt is 0.5 to 3% by weight, and the loading amount of Pd is 0.5 to 1%.
By setting the content to 5% by weight, a high NOx purification rate can be obtained.

"Example 8"
The NOx purification rate at the initial stage and at 400 ° C. after firing at 800 ° C. was measured when the amount of Sr carried as the component was changed with respect to 100 parts by weight of alumina. The results are shown in FIG. S
By setting the supported amount of r to 1 to 20% by weight, a high NOx purification rate and high heat resistance can be obtained.

Example 9 The catalyst of Example 1 was subjected to SO ₂ poisoning by the same method as (3) in the experimental method shown in Experimental Example 1, except that the SO ₂ treatment time was 3 hours. Then, the NOx purification rate after one minute of lean was measured. Next, the stoichiometric model exhaust gas having the composition described in Experimental Example 1 was subjected to stoichiometric treatment at 400 ° C. for 15 minutes. After cooling the temperature to 300 ° C., a lean model exhaust gas was flown, and the NOx purification rate after one minute was measured. The results are shown in Table 4. The catalyst performance was restored by the stoichiometric treatment.

[0058]

[Table 4]

Example 10 The NOx purification rate of the catalysts of Examples 1, 2, and 6 was measured one minute after switching the stoichiometric exhaust gas. Table 5 shows the results.

[0060]

[Table 5]

Example 11 The HC purification rates of the example catalysts 1, 2, and 6 and the comparative example catalyst 1 were measured. The results are shown in Table 6. The HC of the example catalyst was higher than that of the comparative example catalyst 1 in which the second component in Table 1 was only Na. Accordingly, the present invention provides a method for controlling the amount of HC,
It is suitable for detoxifying harmful components of CO and NOx and discharging them out of the system.

[0062]

[Table 6]

[0063]

According to the present invention, nitrogen oxides can be efficiently purified from exhaust gas containing oxygen, and the catalyst has heat resistance and resistance to catalyst poisoning substances contained in a trace amount in the exhaust gas. I was able to have the nature.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a NOx purification device.

FIG. 2 is a block diagram of a vehicle engine system control unit.

FIG. 3 is a diagram showing a NOx purification rate in optimizing the amount of Na carried.

FIG. 4 is a diagram showing a NOx purification rate in optimizing a Mg carrying amount.

FIG. 5 is a diagram showing a NOx purification rate in optimizing the amount of Ce carried.

FIG. 6 is a diagram showing a NOx purification rate in optimizing Rh and Pt carrying amounts.

FIG. 7 is a diagram showing a NOx purification rate in optimizing the Pd and Pt carrying amounts.

FIG. 8 is a diagram showing a NOx purification rate in optimizing the amount of Sr carried.

[Explanation of symbols]

1 ... air cleaner, 2 ... intake port, 3 ... intake flow meter,
5 throttle valve, 7 engine, 8 intake pipe, 9 fuel tank, 10 fuel pump, 11 fuel damper, 12 fuel filter, 13 fuel injection valve, 15 control unit, 16 distributor 18 ... Throttle sensor, 19 ...
Exhaust pipe, 20: exhaust gas purification catalyst, 51: oxygen sensor.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication B01D 53/36 102B 104A (72) Inventor Hiroshi Hanaoka 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Hitachi, Ltd.Hitachi Research Laboratories (72) Inventor Toshio Ogawa 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Hitachi, Ltd.Hitachi Research Laboratory (72) Inventor Hisao Yamashita 7-chome, Omikacho, Hitachi City, Ibaraki Prefecture No. 1-1 Inside Hitachi, Ltd. Hitachi Research Laboratories (72) Inventor Shigeru Azumahata 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd. Hitachi Research Laboratory Co., Ltd. (72) Inventor Yuichi Kitahara Hitachinaka City, Ibaraki Prefecture 2520 Oaza Takaba Inside the Automotive Equipment Division of Hitachi, Ltd.

Claims (5)

[Claims] 1. A method for purifying nitrogen oxides in combustion exhaust gas from an internal combustion engine with a reducing gas such as carbon monoxide and hydrocarbon contained in the exhaust gas in the presence of a catalyst.
At least one of Rh, Pt, and Pd on the porous carrier;
A method for purifying nitrogen oxides in exhaust gas, comprising using a catalyst supporting at least one of a and Ce, and Mg and Na. 2. A method for purifying nitrogen oxides in a combustion exhaust gas from an internal combustion engine with a reducing gas such as carbon monoxide and a hydrocarbon contained in the exhaust gas in the presence of a catalyst.
At least one of Rh, Pt, and Pd on the porous carrier;
A method for purifying nitrogen oxides in exhaust gas, comprising using a catalyst that carries at least one of a and Ce, at least one of Sr and Ba, and Mg and Na. 3. The method according to claim 1, wherein the porous carrier is (a) alumina, (b) La and A
1. A method for purifying nitrogen oxides in exhaust gas, characterized in that the composition ratio of La is 1 to 20 mol%, and the total of La and Al is 100 mol%. . 4. An amount of 5 to 20% by weight of Na and 1 to 40% by weight of La in a weight ratio of Mg loading / (Na loading + Mg loading) based on 100 parts by weight of the porous carrier. , Ce 5 to 30% by weight Pt 0.5 to 3% by weight Rh 0.05 to 0.3% by weight Pd in a range of 0.5 to 15% by weight in exhaust gas Nitrogen oxide purification catalyst. 5. The exhaust gas according to claim 4, wherein at least one of Sr and Ba is supported within a range of 1% by weight to 20% by weight based on 100 parts by weight of the porous carrier. Nitrogen oxide purification catalyst.