JP3395525B2 - Internal combustion engine exhaust gas purification catalyst and purification method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to nitrogen oxides (hereinafter NOx) in exhaust gas discharged from internal combustion engines of automobiles and the like.
The present invention relates to a catalyst material for purifying exhaust gas, which is excellent in durability against sulfur oxides (hereinafter referred to as SOx), and an exhaust gas purification method using the same.

[0002]

2. Description of the Related Art Carbon monoxide (hereinafter CO), hydrocarbons (hereinafter HC), NOx, etc. contained in exhaust gas discharged from an internal combustion engine of an automobile or the like adversely affect the human body as air pollutants, and plants Cause problems such as hindering the growth of. Therefore, many researches have been conducted to reduce the emission of these harmful substances, such as reduction of the amount of harmful substances generated by improving combustion conditions in internal combustion engines, purification of discharged harmful substances with a catalyst, etc. Development has been advanced.
At present, in the case of automobile exhaust gas, a method of oxidizing HC and CO with a three-way catalyst containing a noble metal such as Pt, Rh, and Pd as a main component and simultaneously reducing NOx to render it harmless is predominant.

Generally, a three-way catalyst has a low oxygen concentration at a theoretical air-fuel ratio (A (weight of air) / F (weight of fuel) = 14.7).
Effective only in the vicinity to purify harmful substances. Therefore, in the case of an ordinary automobile engine, the air-fuel ratio has been controlled to be close to the stoichiometric air-fuel ratio to suppress the emission of harmful substances into the atmosphere.

However, since fuel consumption can be improved by operating at an air-fuel ratio leaner than the stoichiometric air-fuel ratio, in recent years, lean burn vehicles operating at lean air-fuel ratio have been developed.
This lean-burn vehicle has a high concentration of oxygen (3
In the conventional three-way catalyst, HC
Although CO and CO can be detoxified by oxidation, they have poor ability to reduce NOx and cannot be detoxified. Therefore, as a NOx purification technology for lean burn, NOx can be used even in the presence of oxygen.
Research is progressing on catalysts that can reduce and purify air (hereinafter referred to as lean NOx catalysts). As one example, Japanese Patent Laid-Open No. 1-13
No. 0735 and JP-A-1-266854 disclose zeolite catalysts carrying a transition metal such as copper.

[0005]

Problems to be solved by the invention include the improvement of activity, the improvement of heat resistance, and the improvement of resistance to poisoning. Above all, poisoning of the catalyst by the sulfur content contained in gasoline is a big problem, and improvement of SOx resistance is an important issue.

In general, catalysts are more susceptible to poisoning with SO ₃ than SO ₂ . In lean burn exhaust gas, high concentration of oxygen coexists, so SO ₂ is easily oxidized to SO ₃ ,
The catalyst is more likely to be poisoned than the conventional engine exhaust gas operated at the theoretical air-fuel ratio. Therefore, in the lean NOx catalyst, it is essential to improve the SOx resistance.

A method for producing a complex sulfate which is easily decomposed in JP-A-7-51544, and an S-method in JP-A-171349 has been disclosed.
A method for suppressing the oxidation of O ₂ has been proposed. The present invention provides a NOx purification catalyst in an exhaust gas of an internal combustion engine having excellent SOx resistance, which belongs to these categories, and an exhaust gas purification method using the same.

[0008]

Means for Solving the Problems As a result of intensive studies on the method for improving the SOx resistance of an exhaust gas purifying catalyst, the present inventors have found that S poisoning is suppressed by supporting titanium with an alkaline earth metal. At the same time, it was found that the NOx purification performance was restored when exposed to a reducing atmosphere at 300 ° C or higher.

A feature of the present invention is an exhaust gas purifying catalyst having improved SOx resistance by supporting an alkaline earth metal and titanium as active components on a porous carrier.

[0010] As a method for carrying the alkaline earth metal and titanium on a porous support, after carrying A alkaline earth metal, it supported titanium.

The present inventors have found that the catalyst activity for NOx purification is improved by further supporting a noble metal on the exhaust gas purification catalyst excellent in SOx resistance.

Therefore, another feature of the present invention resides in that an alkaline earth metal and titanium as active ingredients are carried on a porous carrier, and a noble metal is further carried thereon.

Furthermore, the present inventors have found that an alkaline earth metal,
It has been found that the catalyst activity is further improved by supporting the rare earth metal on the exhaust gas purifying catalyst supporting titanium and noble metal.

A further feature of the present invention is that a rare earth metal, an alkaline earth metal and titanium as active ingredients are carried on a porous carrier, and a noble metal is further carried thereon.

The present invention does not limit the supported amounts of alkaline earth metal and titanium, but the alkaline earth metal is contained in an amount of 3 to 40% by weight and the titanium content is in the range of 0.1 to 0.1 with respect to the porous carrier.
When the amount is in the range of 30% by weight, a better catalytic activity can be obtained.

As the alkaline earth metal supported in the present invention, magnesium, calcium, strontium and barium can be used, but particularly good results can be obtained by using strontium.

When a precious metal is supported on the exhaust gas purifying catalyst, platinum, rhodium, palladium or the like can be used as the precious metal, but platinum and rhodium are particularly preferable. The amount of the noble metal supported is not limited in the present invention, but is preferably 0.2 to 4% by weight of platinum and 0.05 to 1% by weight of rhodium with respect to the porous carrier.

[0018] The present invention is not intended to limit the carrying amount of the rare earth metals, it is preferable rare earth metal with respect to the porous support is in the range of 5 to 40 wt%.

As the rare earth metal supported in the present invention, cerium, lanthanum, yttrium or the like can be used, but particularly good results can be obtained by using cerium.

Alumina, silica and the like can be used as the porous carrier in the above-mentioned exhaust gas purifying catalyst, but alumina can be used particularly favorably.

The above exhaust gas purifying catalyst is CO or HC.
As long as it is an exhaust gas containing at least one or more reducing agents, the composition of the exhaust gas that can be purified is not limited, and even if oxygen is present at a high concentration, it has a good NOx purification activity. A method for purifying exhaust gas from an internal combustion engine in which oxygen coexists at 2% by volume or more using the catalyst is also a feature of the present invention.

The above exhaust gas purifying catalyst is used in the exhaust gas of various internal combustion engines in the presence of SOx such as in boilers and automobiles.
Although Ox can be satisfactorily purified, it is particularly effective to mount it on an automobile. It can also be mounted on a lean-burn automobile with high oxygen concentration in the exhaust gas.

In general, the exhaust gas purifying catalyst is often used as a honeycomb catalyst, and most of the automobile catalysts are practically used as a honeycomb catalyst. When the present invention is applied to a honeycomb-shaped catalyst, a powdery catalyst can be prepared in advance and made into a honeycomb by a usual wash coating method or the like. It is also possible to first coat the honeycomb with the porous carrier and then impregnate it with the active ingredient to obtain a honeycomb catalyst. Besides, the catalyst itself can be formed into a honeycomb shape by extrusion molding or the like. The present invention does not prevent the catalyst from being formed into a honeycomb shape and used.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Examples of the present invention will be shown below.
The invention is not limited by these examples.

Example 1 Water and dilute nitric acid were added to boehmite powder and mixed by stirring to obtain a coating slurry.
The cordierite honeycomb was wash-coated with the slurry, 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 above alumina-coated honeycomb was dipped in an aqueous cerium nitrate solution, dried, and then fired at 600 ° C. for 1 hour. Then, soak in an aqueous strontium nitrate solution,
After drying, it is baked at 600 ° C. for 1 hour, further dipped in an aqueous solution of titania sol as a precursor of titanium, and dried,
It was baked at 00 ° C. for 1 hour. Next, it is immersed in an aqueous solution containing dinitrodiamine platinum and rhodium nitrate, dried, and then
Calcination was performed for 1 hour. Finally, it was immersed in an aqueous magnesium nitrate solution, dried, and then baked at 450 ° C. for 2 hours to obtain a honeycomb catalyst A. The catalyst composition of the honeycomb catalyst A is such that Mg: 1 wt% (wt%), Rh: 0.15 with respect to alumina.
wt%, Pt: 1.9 wt%, Ti: 5 wt%, Sr:
15 wt% and Ce: 18 wt%, which are the standards for the catalysts of other Examples.

As a method of manufacturing the honeycomb catalyst,
In addition to the method of impregnating the alumina coating honeycomb with the catalyst component as described above, a method of slurrying the catalyst powder prepared by impregnating the alumina powder with the catalyst component and then coating the honeycomb powder is also possible. The titanium precursor may be an organic titanium compound, titanium sulfate, titanium chloride, or the like, in addition to the titania sol.

Example 2 A honeycomb catalyst B was obtained in the same manner as in Example 1 except that barium nitrate was used instead of strontium nitrate as the alkaline earth metal. Similarly, a honeycomb catalyst C was obtained using calcium nitrate.

[Example 3] A honeycomb catalyst D was obtained in the same manner as in Example 1 except that lanthanum nitrate was used instead of cerium nitrate as the rare earth metal. Similarly, a honeycomb catalyst E was obtained using yttrium nitrate.

[Example 4] By changing the concentration of the titania sol used in Example 1, three types of honeycomb catalysts F to H having different titanium loadings were obtained.

[Example 5] By changing the concentration of the strontium nitrate aqueous solution used in Example 1, three types of honeycomb catalysts I to
I got K.

[Example 6] By changing the concentration of the dinitrodiamine platinum aqueous solution used in Example 1,
Three types of honeycomb catalysts L to N having different platinum loadings were obtained.

[Example 7] By changing the concentration of the aqueous rhodium nitrate solution used in Example 1, three types of honeycomb catalysts O to Q having different amounts of supported rhodium were obtained.

[Example 8] By changing the concentration of the cerium nitrate aqueous solution used in Example 1, three types of honeycomb catalysts R to T having different amounts of cerium supported were obtained.

Comparative Example 1 An alumina-coated honeycomb obtained by the same method as in Example 1 was impregnated with cerium and strontium by the same operation as in Example 1. Subsequently, without supporting titanium, platinum, rhodium and magnesium were impregnated by the same operation as in Example 1 to obtain a honeycomb catalyst U. The composition of the honeycomb catalyst U was the same as that of the honeycomb catalyst A except that titanium was not contained.

Table 1 shows the catalyst compositions of the honeycomb catalysts A to U obtained by the above-mentioned example and comparative example catalysts.

"Test Example 1" With respect to the honeycomb catalysts A to U obtained by the above-mentioned Examples and Comparative Examples, under the following conditions,
The NOx purification reaction activity was evaluated. 6 cc of the honeycomb catalyst was filled in a quartz reaction tube having an inner diameter of 25 mm and placed in an annular electric furnace. The gas at the inlet of the reaction tube was heated in an electric furnace at a constant temperature of 300 ° C., and the following model gas was passed.
As assumed exhaust gases when operating an internal combustion engine at the stoichiometric air-fuel _{ratio, NO: 0.1%, C 3} H 6: 0.05%, CO:
0.6%, O ₂ : 0.5%, H ₂ : 0.2%, H ₂ O: 10
%, N ₂ : The model gas with the balance of composition is space velocity 30,000 /
It was distributed at h. Further, as exhaust gas assuming that the internal combustion engine is operated at a lean air-fuel ratio, NO: 0.06%, C ₃ H ₆ :
0.04%, CO: 0.1%, O ₂ : 5%, H ₂ O: 10
%, N ₂ : The model gas with the balance of composition is space velocity 30,000 /
It was distributed at h. The model gas assuming the stoichiometric air-fuel ratio and the lean air-fuel ratio was alternately flowed every 3 minutes.

The NOx concentrations at the catalyst inlet and outlet at this time were measured by a chemiluminescence type NOx analyzer, and after switching from the theoretical air-fuel ratio model exhaust gas to the lean air-fuel ratio model exhaust gas, 1
The NOx purification rate after minutes was calculated by the following formula.

[0039]

[Equation 1] NOx purification rate (%) = 100− (outlet NOx concentration)
/ (Inlet NOx concentration) × 100 “Test Example 2” NOx purification reaction for honeycomb catalysts A to U was performed in the same manner as in Test Example 1 except that the inlet gas temperature was kept constant at 400 ° C. in an electric furnace. The activity was evaluated.

[Test Example 3] As in Test Example 1, the inlet gas temperature was heated to 300 ° C. at a constant temperature in an electric furnace, and SO ₂ was added to the model gas assuming a lean air-fuel ratio operation at 0.002.
The gas added with 5% was circulated for 3 hours at a space velocity of 30,000 / h. Then, in the same manner as in Test Example 1, the honeycomb catalysts A to U were evaluated for NOx purification reaction activity at an inlet gas temperature of 300 ° C.

[0041] Similar to the "Test Example 4" Test Example 3, SO ₂ 0.
Dilute air-fuel ratio model gas with 005% added at 300 ℃ 3
After circulating for a period of time, the honeycomb catalysts A to U were subjected to NO at an inlet gas temperature of 400 ° C. by the same method as in Test Example 2.
x Purification reaction activity was evaluated.

With respect to the honeycomb catalysts A to U, the results evaluated in Test Examples 1 and 3 are shown in Table 1, and the results evaluated in Test Examples 2 and 4 are shown in Table 2.

The catalysts A to T of the examples all have a higher NOx purification rate after SO ₂ durability than the catalyst U of the comparative example, and are resistant to SO.
It can be seen that the x property is strong.

[Test Example 5] With respect to the honeycomb catalysts A and U, X-ray diffraction spectra were measured to identify their crystal structures. The results are shown in FIGS. 1 and 2. Honeycomb catalyst A X
The line diffraction spectrum has no peak due to titanium, and it is considered that titanium is supported in an amorphous state. It can be seen that strontium as an alkaline earth metal is supported by carbonate.

FIG. 3 shows an example of an exhaust gas purifying system using the exhaust gas purifying catalyst to which the present invention is applied. The exhaust gas discharged from the lean burn engine 1 contains oxygen, sulfur compounds (SO ₂ , SO ₃ , H ₂ S, etc.) in addition to harmful substances such as CO, HC and NOx. The exhaust gas passes through the exhaust pipe 2, flows through the exhaust gas purifying catalyst 3 of the present invention to purify harmful substances, and then is exhausted from the muffler 5 to the outside of the vehicle via the silencer 4.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

EFFECTS OF THE INVENTION By supporting an alkaline earth metal and titanium as an active component on a porous carrier, it becomes possible to prepare a catalyst having a low affinity for SO ₂ and a high affinity for NOx. That is, it has excellent SOx resistance and N
An exhaust gas purification catalyst having high Ox purification performance can be obtained.

[Brief description of drawings]

FIG. 1 is a honeycomb catalyst A as an example of the catalyst of the present invention.
2 is an X-ray diffraction spectrum of

FIG. 2 is an X-ray diffraction spectrum of a honeycomb catalyst U as a comparative example.

FIG. 3 is a configuration diagram showing an example of an automobile engine system to which an internal combustion engine exhaust gas purification catalyst according to the present invention is applied.

[Explanation of symbols]

1 ... lean burn engine, 2 ... exhaust pipe, 3 ... exhaust gas purifying catalyst, 4 ... silencer, 5 ... muffler.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hidehiro Iizuka, 1-1 1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Toshio Ogawa 7-chome, Omika-cho, Hitachi-shi, Ibaraki No. 1 Hitachi Ltd. within Hitachi Research Laboratory (72) Inventor Toshio Yamashita 7-1 Omika-cho, Hitachi City, Ibaraki Prefecture Hitachi Ltd. within Hitachi Research Laboratory (72) Inventor Shigeru Shodohata Seven Omika-cho, Hitachi City, Ibaraki Prefecture 1-1-1, Hitachi Ltd., Hitachi Research Laboratory (72) Inventor Yuichi Kitahara 2520, Takaba, Hitachinaka City, Ibaraki Prefecture Hitachi, Ltd. Automotive Equipment Division, Hitachi Ltd. (72) Toshifumi Hiratsuka, Takahata, Ibaraki Prefecture Address 2520 Hitachi, Ltd. Automotive Equipment Division (56) References -57314 (JP, A) JP-A-8-192051 (JP, A) JP-A-7-102958 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B01J 21/00- 37/36 B01D 53/86

Claims (7)

(57) [Claims] 1. A catalyst for purifying nitrogen oxides in a lean-burn exhaust gas, wherein the active component is supported on a porous carrier selected from alumina and silica, wherein the alkaline earth metal is used as the active component. And titanium , the titanium is amorphous after supporting the alkaline earth metal.
A catalyst for purifying exhaust gas from an internal combustion engine, which is supported in a state of being. 2. A catalyst for purifying nitrogen oxides in a lean burn exhaust gas, wherein the active component is supported on a porous carrier selected from alumina and silica, wherein a rare earth metal and an alkali are used as the active components. It has an earth metal, titanium, and a precious metal, and carries an alkaline earth metal.
A catalyst for purifying exhaust gas from an internal combustion engine, characterized in that titanium is supported in an amorphous state . 3. The method according to claim 2, wherein the amount of alkaline earth metal supported is 3 to 40% by weight of the porous carrier, and the amount of titanium supported is 0.1 to 30% by weight of the porous carrier. A catalyst for purifying exhaust gas from an internal combustion engine, wherein the amount of metal supported is in the range of 5 to 40% by weight with respect to the porous carrier. 4. The noble metal according to claim 2, wherein the noble metal is platinum and rhodium, and the loading amount thereof is within the range of 0.2 to 4% by weight of platinum and 0.05 to 1% by weight of rhodium with respect to the porous carrier. A catalyst for purifying exhaust gas from an internal combustion engine, characterized in that 5. A method for purifying exhaust gas from an internal combustion engine, comprising purifying lean burn exhaust gas using the catalyst according to claim 1. 6. A method for purifying exhaust gas of an internal combustion engine by bringing it into contact with a purification catalyst, wherein the catalyst according to any one of claims 1 to 4 is arranged in an exhaust gas passage of the internal combustion engine, and lean burn exhaust gas is provided in the catalyst. And then
A method for purifying exhaust gas from an internal combustion engine, which comprises exposing the catalyst to a reducing atmosphere. 7. A method for purifying an exhaust gas of an internal combustion engine by bringing it into contact with a purification catalyst, wherein the catalyst according to any one of claims 1 to 4 is arranged in an exhaust gas passage of the internal combustion engine, and lean burn exhaust gas is provided in the catalyst. And a method for purifying exhaust gas of an internal combustion engine, characterized in that exhaust gas having a stoichiometric air-fuel ratio is alternately flowed.