JPH07144134A - Exhaust gas purification catalyst - Google Patents

Abstract

(57) [Abstract] [Purpose] Effectively works even when the air-fuel ratio of an internal combustion engine such as an automobile engine is in the lean combustion (lean) region, and shows little deterioration even after long-term use at high temperature, and has low temperature activity and A catalyst with excellent durability is obtained. [Structure] An inorganic material containing crystalline aluminosilicate as a main component, copper, and at least one component selected from the group consisting of boron, phosphorus, antimony and bismuth, and an alkaline earth metal or a rare earth metal. It comprises a compound with one or more components selected from the group.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst for an internal combustion engine such as an automobile engine, and in particular, it works effectively even when the air-fuel ratio of the internal combustion engine is in a lean burn region. The present invention relates to a catalyst having excellent durability.

[0002]

2. Description of the Related Art Conventionally, as a catalyst for purifying exhaust gas from an internal combustion engine, palladium (P
d), those carrying precious metal components such as platinum (Pt) and rhodium (Rh) are used. This is called a three-way catalyst because it can remove hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx) at once. However, this is effective only when the internal combustion engine is operated under conditions near the stoichiometric air-fuel ratio (stoichiometric ratio), and is sufficient when operating the internal combustion engine under lean conditions where the oxygen concentration is high and fuel consumption is better. NOx removal performance is not obtained. It is known that a catalyst composed of a metal ion-exchanged zeolite is effective for removing NOx under such lean conditions. {Iwamoto, Small Discussion "Catalyst Technology for Nitrogen Oxide Reduction" Preliminary Report Shu, p. 71 (1990); W. Held, A. Konig, T. Richter and L.
Puppe, SAE Paper 900496 (1990)}. In particular, the Cu-zeolite catalyst obtained by supporting copper (Cu) on zeolite by the ion exchange method shows excellent performance even at high gas space velocity (GHSV). However, when such a catalyst is exposed to high temperatures of 600 ° C or higher,
The NOx removal performance deteriorates with time and cannot be used for a long time.

The main cause of deterioration of the above-mentioned catalyst when exposed to high temperature is Cu at the ion exchange site in zeolite,
It is thought to be because the heat moves out of the site and causes sintering. For this reason,
As disclosed in JP-A-131345, JP-A-3-202157, JP-A-3-135437, JP-A-4-4045, etc., Cu-zeolite-based catalysts include alkaline earth metals and rare earth metals. A method of stabilizing Cu in the catalyst by adding various metals has been vigorously studied and proposed. However, it is difficult to say that any of these conventional methods has obtained sufficient results for practical use, and there is a long-felt need for a more effective catalyst improvement and a catalyst having practically sufficient heat resistance. It was

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned drawbacks of conventional catalysts and to provide a catalyst which is less deteriorated even when used at high temperature for a long time and which has excellent durability.

[0005]

The exhaust gas purifying catalyst of the present invention, which has achieved the above object, comprises an inorganic material mainly composed of crystalline aluminosilicate containing copper, and is composed of boron, phosphorus, antimony and bismuth. And a compound of one or more components selected from the group consisting of calcium, magnesium, strontium, barium, lanthanum, cerium and yttrium, and one or more alkaline earth or rare earth metal components. It is characterized by

Here, boron, phosphorus, antimony and
One or more ingredients selected from the group consisting of bismuth and al
For example, a compound with a potash or rare earth metal component
For example, the group consisting of boron, phosphorus, antimony and bismuth
Based on oxo acid salt of one or more components selected from
Compound, specifically Ca (BO₂), Ca₂B₆O₁₁, Mg
₃(BO₃)₂, Mg₂B₂O_Five, LaBO₃, Ca₃(PO_Four)₂, Ca (P
O₃)₂, Ca (H₂PO₂)₂, Ca (H₂PO_Four)₂, CaHPO_Four, Ca_Ten(PO_Four)₆(O
H)₂, Mg₃(PO_Four)₂, MgHPO_Four, Ba (H₂PO_Four)₂, Ba₃(PO_Four)₂, B
a (PO₃)₂, Ba (PO₃)₂, Ca₂Sb₂O₇, Mg₂Sb₂O₇, Mg (BiO₃)₂
Etc. Alkali complex derived from the compound
Salt and ammine complex salt are the
Potassium or rare earth metal is Na, Li, K, NH_FourBy
Are partially replaced.

The crystalline aluminosilicate used in the present invention is a zeolite, preferably a pentasil type. For example, moldenart, ferrierite, ZSM-5, ZSM-11, etc. are applicable. Zeolite is desirable because it is possible to obtain a catalyst with higher heat resistance by improving crystallinity or stabilizing it by hydrothermal treatment, resynthesis, or the like.

In the present invention, the content of the above compound is preferably 0.2 to 10% by weight based on the crystalline aluminosilicate in a state where the adsorbed water is removed. Since the compounds have different actions on the ion-exchange sites of zeolite, some effects may be significant at 0.2% by weight or more, while several% by weight may be necessary to sufficiently bring out the expected effect.
For some, addition of is required. However, if the content of the compound exceeds 10% by weight, the zeolite catalyst portion is relatively decreased, which causes a decrease in activity.

The Cu content is 1.
0 to 20% by weight is effective, but practically 2.0 to 8.
0% by weight is preferred. If it is less than 2.0% by weight, the catalytic activity becomes insufficient, while if it exceeds 8.0% by weight, excess Cu is added.
It is not preferable because the NOx removal reaction is hindered by the generation of O near the pore inlet of the zeolite and on the outer surface.

In order to support the compound of one or more components selected from the group consisting of boron, phosphorus, antimony and bismuth and the alkaline earth or rare earth metal component on the zeolite, the impregnation method, the dipping method, A wet method such as a kneading method is used, but the effect can be obtained by carrying out an appropriate heat treatment after supporting by a dry method such as a powder mixing method.
Further, when the compound is supported on the zeolite in the form of a slurry or a solution, it is preferable that the compound which is hardly soluble in water is converted into a compound in a more soluble form. For example, tricalcium phosphate _{((Ca 3 PO 4) 2} ) Because less soluble in water,
It is effective when used as calcium dihydrogen phosphate (Ca (H ₂ PO ₄ ) ₂ ). Further, such a solution can achieve more effective loading by appropriately adjusting the pH.

[0011]

[Operation] Next, the operation will be described. The Cu-zeolite catalyst can efficiently remove NOx even in lean exhaust gas, but when exposed to a temperature of 600 ° C or higher, the catalyst deteriorates in a short time. this is,
This is because copper has a relatively low melting point and is easily reduced, so that sintering easily occurs when exposed to high temperature in an oxidizing-reducing atmosphere. Therefore, in order to solve the above-mentioned problem, it is indispensable to stabilize copper which is an active ingredient. Therefore, as a result of extensive and intensive search for components effective for copper stabilization, the present inventors have found that certain specific compounds, that is, one or more components selected from the group consisting of boron, phosphorus, antimony and bismuth. It was found that a catalyst obtained by supporting a compound of an alkaline earth metal component or a rare earth metal component on zeolite together with copper has high NOx removal activity and excellent heat resistance.

Although the detailed mechanism described above is not clear, it is presumed that the compound acts to reinforce the Cu ion retention of the zeolite and stabilizes the Cu state. Further, as another action of the compound, the effect of stabilizing aluminum in the zeolite skeleton to suppress dealumination, and further, the acid strength of the zeolite matrix is made mild and the catalyst durability is improved by suppressing carbonaceous coking. The effect of improvement can be considered.

The catalyst of the present invention may have any shape, but it is usually preferable to use it in a honeycomb shape, and the catalyst powder is applied to various honeycomb-shaped carrier base materials and used. As the honeycomb material, a cordierite material is generally used in many cases, but the present invention is not limited to this, and the catalyst powder itself may be formed into a honeycomb shape. It is also possible to use the following honeycomb carrier. By making the shape of the catalyst honeycomb, the catalyst area of the catalyst and exhaust gas is increased,
Since pressure loss can also be suppressed, it is extremely advantageous when used for automobiles. Further, since it is an integral type, it has an effect that it is not worn by vibration.

[0014]

EXAMPLES The present invention will be described in detail below with reference to Examples, Comparative Examples and Test Examples.

Example 1 A powder of H-type ZSM-5 zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of about 30 was contacted with an aqueous solution of calcium dihydrogen phosphate (Ca (H ₂ PO ₄ ) ₂ ), The compound was supported on zeolite by drying and firing. The supported amount of the compound is converted to Ca (based on the zeolite in a state where the adsorbed water is removed) and is 0.1.
It was 25% by weight. This powder was dispersed in a 0.05 M copper acetate aqueous solution, stirred, and then filtered, dried, and calcined to obtain a catalyst powder. The Cu content in the catalyst was 3.7% by weight (based on the zeolite without adsorbed water).

2250 g of this catalyst powder was placed in a ball mill pot together with 1250 g of silica sol (solid content 20%) and 1500 g of water and pulverized for 4 hours to obtain a slurry. About 40 of this slurry per square inch of cross section
Cordierite honeycomb with 0 channels (capacity 0.
1 L) coated on a carrier and dried with hot air at 120 ° C, then 500
The catalyst (1) of Example 1 was obtained by calcination for 1 hour. The amount of catalyst powder applied to this honeycomb was 180 g / L.

Example 2 Water was added to the H-type ZSM-5 zeolite powder of Example 1 to form a slurry, which was mixed with hydroxyapatite (Ca ₁₀ (PO ₄ ) ₆ (O
H) ₂ ) was thoroughly mixed with the slurry and dried. The amount of the compound added was 0.34% by weight in terms of Ca (based on the zeolite excluding the adsorbed water). This powder was dispersed in a 0.1 M aqueous copper acetate solution, stirred, and then filtered, dried, and calcined to obtain a catalyst powder. The Cu content in the catalyst was 3.8% by weight (based on the zeolite without adsorbed water). Using this catalyst powder as a honeycomb catalyst in the same manner as in Example 1, a catalyst (2) of Example 2 was obtained.

Examples 3, ₄ , _{5 In} the same manner as in Examples 3, ₄ except that Ca (H ₂ PO ₄ ) ₂ in Example 1 was replaced with BaHPO ₄ , Ca ₂ B ₆ O ₁₁ and Mg ₂ B ₂ O _5. , 5 catalysts (3),
(4) and (5) were obtained. The supported amount of the compound (based on the zeolite excluding the adsorbed water) was 0.3% by weight converted to Ba in the catalyst (3), and 0.28% by weight converted to Ca in the catalyst (4). In 5), converted to Mg 0.32
% By weight. Catalyst powder was obtained through the steps of drying and firing. The Cu content in the catalyst is 3.3, 3.6 and 3. (based on the zeolite without adsorbed water).
It was 6% by weight.

Example 6 In Example 2, H type ZSM-5 zeolite was mixed with H type model.
Rudenite (SiO₂/ Al ₂O₃Change the molar ratio to about 24),
Similarly, a catalyst (6) of Example 6 was obtained. To mordenite
Ca_Ten(PO_Four)₆(OH)₂The added amount of is converted to Ca (adsorbed water
0.29% by weight (based on zeolite excluding)
there were. In addition, the content of Cu in the catalyst (excluding adsorbed water
4.2% by weight (based on the zeolite in the
It was

Example 7 Ca ₂ B ₆ O was added to the H-type ZSM-5 zeolite powder of Example 1.
_After the aqueous solution of ₁₁ was contacted and dried, the aqueous solution of Ca (H ₂ PO ₄ ) ₂ was further contacted, and the compound was supported on zeolite by drying and firing. The supported amounts of the compound were 0.21% by weight and 0.25% by weight, respectively, in terms of Ca (based on the zeolite in the state where adsorbed water was removed). The following is
A catalyst (7) of Example 7 was obtained in the same manner as in Example 1. The Cu content in this catalyst was 4.4% by weight (based on the zeolite without adsorbed water).

Example 8 Instead of Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ in Example 2, Na ₄ Ca ₈ (PO ₄ ) ₆
A catalyst (8) of Example 8 was obtained in the same manner by using (OH) ₂ . The amount of the compound supported was 0.29% by weight in terms of Ca (based on the zeolite excluding the adsorbed water). The Cu content in this catalyst was 3.6% by weight (based on the zeolite excluding the adsorbed water).

Example 9 A catalyst (9) of Example 9 was obtained in the same manner by using LaBO ₃ instead of Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ of Example 2. The loaded amount of the compound was 0.31% by weight in terms of La (based on the zeolite excluding the adsorbed water). The Cu content in this catalyst was 3.5% by weight (based on the zeolite excluding the adsorbed water).

Example 10 Instead of Ca ₁₀ (PO ₄ ) ₅ (OH) ₂ of Example 2, Ca ₈ Y ₂ (PO ₄ ) ₆ O was used.
A catalyst (10) of Example 10 was obtained in the same manner using ₂ . The amount of the compound supported was 0.21% by weight in terms of Y (based on the zeolite excluding the adsorbed water). The Cu content in the catalyst was 3.7% by weight (based on the zeolite excluding the adsorbed water).

Example 11 Instead of Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ of Example 2, Ca ₈ La ₂ (PO ₄ ) _{6 was used.}
A catalyst (11) of Example 11 was obtained in the same manner by using O ₂ . The supported amount of the compound was 0.27% by weight in terms of La (based on the zeolite excluding the adsorbed water). The Cu content in this catalyst was 3.5% by weight (based on the zeolite excluding the adsorbed water).

Example 12 Instead of Ca ₁₀ (PO ₄ ) ₈ (OH) ₂ of Example 2, Ca ₈ Ce (PO ₄ ) 2 was used.
Similarly using ₆ (OH) ₂ , the catalyst of Example 12 (12)
Got The supported amount of the compound was 0.22% by weight in terms of Ce (based on the zeolite excluding the adsorbed water). The Cu content in the catalyst was 3.5% by weight (based on the zeolite excluding the adsorbed water).

COMPARATIVE EXAMPLE 1 The powder of Na-type ZSM-5 zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of Example 1 was agitated with a 0.1 M copper nitrate aqueous solution for 12 hours or more, and the zeolite was prepared by an ion exchange method. Cu
Was carried. Then, it is dried in a drier at 120 ° C. for 8 hours or more, and the obtained dry powder is calcined in an electric furnace at 500 ° C. in the atmosphere for 2 hours, whereby Cu is added to the zeolite (zeolite in a state where adsorbed water is removed). A catalyst powder supporting 3.3% by weight was obtained. This was slurried in the same manner as in Example 1 to obtain a honeycomb catalyst (13).

Comparative Example 2 A powder of H-type ZSM-5 zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of Example 1 was brought into contact with an aqueous solution of calcium acetate and dried.
Calcination supported calcium on the zeolite. Ca
The loading was 0.3% by weight (based on the zeolite without adsorbed water). Thereafter, the same procedure as in Example 1 was carried out to obtain a catalyst (14) of Comparative Example 2. The amount of Cu supported in this catalyst is (based on the zeolite excluding adsorbed water)
It was 2.8% by weight.

Comparative Example 3 A catalyst (15) was obtained in the same manner as in Comparative Example 2 except that the calcium acetate aqueous solution was changed to magnesium nitrate. The supported amounts of Mg and Cu on this catalyst were 0.3 and 3.2 wt% (based on the zeolite excluding the adsorbed water), respectively.

Test Example The durability performance of the catalysts of Examples 1 to 12 and Comparative Examples 1 to 3 above was evaluated by rapid durability using engine exhaust gas and activity evaluation using simulated exhaust gas, and the results are shown in Table 1. Show.

Activity evaluation conditions Evaluation device: atmospheric pressure fixed bed flow type reaction device Catalyst capacity: 0.1 L Gas space velocity: about 26000 h ^-1 Exhaust gas simulation gas composition: Total hydrocarbon = about 2500 ppm (Cl conversion) NO = about 500 ppm CO = 1000 ppm O ₂ = 6.5% CO ₂ = 12% H ₂ O = 10% N ₂ = balance

Rapid Durability Treatment Conditions Catalyst Inlet Exhaust Gas Temperature: 610 ° C. Engine: Nissan Motor Co., Ltd. V type 6 cylinder 3000 cc
Engine average air-fuel ratio (A / F): About 15 Fuel: Unleaded regular gasoline (with fuel cut) Processing time: 50h

Table 1 shows the NO removal performance of the catalysts of Examples and Comparative Examples at the catalyst inlet temperature of 400 ° C. The catalyst of the present invention maintains high NOx removal activity even after the rapid durability treatment, and is excellent in durability.

[0033]

[Table 1]

[0034]

As described above, the catalyst of the present invention can efficiently purify NOx in engine exhaust gas in the lean region, has little deterioration even when used for a long time, and has excellent durability. It is possible to provide a vehicle with excellent fuel efficiency and low environmental pollution.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C01B 39/36 7202-4G B01D 53/36 102 H (72) Inventor Toshiaki Hayasaka Sodegaura City, Chiba Prefecture Izumi 1280 Idemitsu Kosan Co., Ltd. (72) Inventor Hiroshi Akama 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (72) Inventor Goji Masuda 2 Takara-cho, Kanagawa-ku, Yokohama, Nissan Nissan Motor Co., Ltd. (72) Inventor Hiroyuki Kanasaka 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd.

Claims (4)

[Claims] 1. An inorganic material containing a crystalline aluminosilicate as a main component containing copper, which is selected from the group consisting of boron (B), phosphorus (P), antimony (Sb) and bismuth (Bi). An exhaust gas purifying catalyst comprising a compound of the above components and one or more components selected from the group consisting of alkaline earth metals and rare earth metals. 2. Calcium (C as the alkaline earth metal
a), magnesium (Mg), strontium (S
r) and barium (Ba), and lanthanum (La), cerium (Ce), and yttrium (Y) as rare earth metals.
The exhaust gas purifying catalyst according to claim 1, wherein the catalyst is used. 3. The exhaust gas purification according to claim 1, wherein the compound is borate, phosphate, antimonate, bismuthate, or an alkali complex salt or ammine complex salt of the compound. Catalyst. 4. An exhaust gas purifying catalyst, characterized in that the catalyst according to claim 1 is provided as a coat layer on a honeycomb-shaped carrier substrate or is formed into a honeycomb shape.