JPH06226105A - Catalyst for exhaust gas purification - Google Patents

Abstract

PURPOSE:To obtain a highly durable catalyst which has high activity in a wide temperature range and is capable of purifying NOx in an engine exhaust gas, especially in a lean-burn zone without any functional deterioration, if used at high temperature for a long time by improving a Cu-zeolite catalyst. CONSTITUTION:The catalyst for exhaust gas purification consists of copper and phosphorus and at least, one type of metal component selected from a group of calcium, magnesium, lithium and strontium added to an inorganic substance composed mainly of a crystalline aminosilicate.

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, and NOx The present invention relates to a catalyst that efficiently purifies from a low temperature range, has little deterioration even when used at a high temperature for a long time, and has excellent durability.

[0002]

2. Description of the Related Art Conventionally, as a catalyst for purifying exhaust gas from an internal combustion engine, activated alumina is generally used for palladium (P).
d), those carrying precious metal components such as platinum (Pt) and rhodium (Rh) are used. It contains hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (N
It is called a three-way catalyst because it can remove Ox) 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 when the internal combustion engine is operated under lean conditions with high oxygen content and better fuel economy. However, sufficient NOx removal performance cannot be 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, p71 (19
90); Held, A. Konig, T. Richter and L. Pupp
e, SAE Paper 900946 (1990)}. Especially Cu
The Cu-zeolite-based catalyst in which zeolite is supported by the ion exchange method exhibits high gas space velocity (GHSV) and excellent performance in a relatively wide temperature range. However, when the catalyst is exposed to high temperatures of 600 ° C or higher,
Ox removal performance deteriorates with time and cannot be used for a long time. Further, it cannot be said that the temperature range for maintaining high activity is sufficient, so that it has not yet been put to practical use.

The main cause of activity deterioration when the above catalyst is exposed to high temperature is C at the ion exchange site in zeolite.
It is considered that this is because u (active ingredient) moves out of the site due to heat and causes sintering.

Therefore, the following methods have been vigorously studied and proposed for stabilizing Cu by various additives. However, it is hard to say that all of them have obtained sufficiently satisfactory results.

According to Japanese Patent Laid-Open No. 3-131345,
It is said that a highly durable catalyst can be obtained by supporting zeolite with one or more alkaline earth metals selected from the group consisting of Cu, Sr and Ba (barium). In the patent publication, the catalyst has an air-fuel ratio (A / F) = 1.
8 shows the NOx purification rate of the catalyst at 400 ° C. in the model gas after holding at 800 ° C. in the model gas for 5 hours. For example, H type ZSM-5 with Cu
1.6% by weight, catalyst supporting 0.4% by weight of Ba and H type Z
A catalyst of 3.5% by weight of Cu supported on SM-5, 800
The NOx purification rates at 400 ° C after 5 hours at 45 ° C were 45% and 25%, respectively, and the catalyst containing Ba has a very low Cu content, which is considered to be the main active component, but is extremely low. Since it shows a high NOx purification rate, it can be seen that the effect of adding Ba is extremely remarkable. Further, the performance of the catalyst in which H type ZSM-5 carries 3.4 wt% of Cu and 1.0 wt% of Ca has reached 54%.

According to Japanese Patent Laid-Open No. 3-202157,
It is said that a highly durable catalyst can be obtained by supporting Cu and one or more alkaline earth metals and one or more rare earth metals on zeolite. The catalyst activity evaluation conditions of the publication are described in the publication (JP-A-3-13134).
The conditions are the same as those described in Japanese Patent No. 5). Here, the NOx purification rate of the catalyst in which 3 wt% of Cu, 2 wt% of Ba and 1 wt% of La were carried on the H-type ZSM-5 at 800 ° C. and 400 ° C. after 5 hours was 50%. Has reached On the other hand, a H-type ZSM is shown as a comparative example.
A catalyst in which 3 wt% of Cu is supported on -5, and H-type ZSM-5
Is a catalyst in which 3 wt% of Cu and 2 wt% of Ba are supported. The performances of these catalysts are 35% and 30%, respectively, and the addition of Ba, which showed a remarkable effect in the above-mentioned published patent publication, is regarded as an adverse effect in this published patent publication. That is, the effect of Ba is reversed between this publication and the publication.

In addition, the Cu disclosed in this publication is disclosed.
The supported amount (3% by weight) of Cu, which is the active component of the supported H-type ZSM-5 catalyst, is the same as that of the catalyst (3.
(5% by weight), but the catalytic performance is high. Furthermore, although the method of becoming the present patent publication is interpreted as an improvement of the method of the aforementioned patent publication,
In fact, the catalyst showing the highest performance is the H-type ZSM-5 catalyst in which Cu and Ca are combined and supported in the above-mentioned Japanese Patent Laid-Open Publication. Therefore, the effect of carrying a composite of an alkaline earth metal and a rare earth metal cannot be said to be clear.

According to Japanese Patent Laid-Open No. 3-135437, Cu is added to zeolite and Fe (iron), Co (cobalt), Ni (nickel), V (vanadium), Mn (manganese), W (tungsten). , Mo (molybdenum),
It is said that a highly durable catalyst can be obtained by supporting one or more valence variable metals selected from the group consisting of Cr (chromium), Ti (titanium) and Nb (neobium). The catalyst activity evaluation conditions in this patent publication are as described in 2 above.
It is almost the same as that of the two published patent publications (JP-A-3-131345 and JP-A-3-202157), except for the heat treatment conditions during the durability test of the catalyst. The heat treatment conditions in this publication are 700 ° C. and 5 hours, and the conditions relaxed from those in the above two publications (800 ° C., 5 hours) are adopted. In this publication, the NOx purification rate of the Cu-supported H-type ZSM-5 catalyst, which is a comparative example, after the durability test is 12%, but this performance is shown in the above-mentioned two publications. The catalyst performance of the comparative example is ambiguous, because the catalyst performance is significantly lower than the existing catalyst performance (25% and 35% after 5 hours at 800 ° C). Therefore, the performance evaluation results of the catalysts according to the examples in this patent publication are not clear, and the effect of adding the variable valence metal is unknown.

From the above, whether or not the durability of the catalyst can be truly improved by the method of the above-mentioned publication in which the alkaline earth metal, the rare earth metal, or the variable valence metal is added and supported on the Cu-zeolite catalyst. Is not clear,
A more effective catalyst improvement method has been desired.

[0010]

Therefore, an object of the present invention is to improve a Cu-zeolite type catalyst, to have high activity in a wide temperature range and to have less deterioration even if it is used at high temperature for a long time and has durability. It is to provide an excellent catalyst.

[0011]

The exhaust gas purifying catalyst of the present invention, which has achieved the above object, comprises an inorganic substance containing crystalline aluminosilicate as a main component and containing copper (Cu) and phosphorus (P), Furthermore, calcium (Ca), magnesium (M
g), lithium (Li) and strontium (Sr)
It is characterized by containing at least one metal component selected from the group consisting of

[0012]

[Operation] Next, the operation will be described. The Cu-zeolite catalyst can efficiently remove NOx even in the lean region, but when exposed to a temperature range of 600 ° C. or higher, Cu, which is an active component, causes sillinterring and the catalyst is short. It deteriorates with time. There are two possible factors for this Cu sintering. One is the ease of sintering of Cu itself, and the other is the force for holding Cu of the zeolite carrier. Regarding the former, Cu
It is necessary to stabilize itself. The latter is related to the dealumination phenomenon of zeolite, and the site that retains Cu (ion exchange site) is collapsed by this, so it is necessary to stably retain the aluminum atom in the zeolite skeleton.

The catalyst of the present invention comprises P, Ca, Mg and Li.
It is considered that the stabilization of Cu and the stabilization of the ion exchange site of the zeolite are efficiently realized by combining with one or more metal components selected from the group consisting of and Sr. P and the metal have the above-mentioned effects by themselves, but they are not sufficient by themselves, and their coexistence significantly promotes the mutual action. Further, the stabilization of Cu due to this coexistence has the effect of broadening the temperature range in which secondary high catalytic activity is exhibited.

Although the detailed mechanism described above is not clear, it can be considered as follows. The P component has an effect of suppressing dealumination of zeolite and a stabilizing effect of Cu ions, but this requires an appropriate number of P in an appropriate distance in the vicinity of Cu ions. The Ca, Mg, Li, and Sr components have the effect of facilitating the proper arrangement of Cu and P, and further exert the effect of suppressing the dealumination of the zeolite itself.

The crystalline aluminosilicate used in the present invention is a zeolite, and a pentasil type is effective. For example, mordenite, ferrierite, ZSM-5, ZSM-11, etc. are applicable. Among these, it is preferable that the molar ratio of SiO ₂ / Al ₂ O ₃ is 10 to 100 and the maximum cavity (pore) radius is 0.5 nm or more. Zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of less than 10 is liable to undergo dealumination and has insufficient thermal stability, resulting in poor catalyst durability. As a result, the amount of the active metal component supported becomes less and the catalytic activity becomes insufficient. Further, if the maximum cavity (pore) radius of zeolite is smaller than 0.5 nm, catalyst deterioration due to pore blockage due to carbonaceous coking cannot be ignored. In addition, zeolite is desirable because it is possible to obtain a catalyst having higher durability by improving the crystallinity or stabilizing it by hydrothermal treatment, resynthesis or the like.

In the present invention, the content of P is 0.1 to 4% by weight based on the crystalline aluminosilicate excluding the adsorbed water, and also Ca, Mg, Li and S.
The content of one or more metals selected from the group consisting of r is
0.01 to 5% by weight. Each of these contents is 0.1
And 0.01% by weight or more, the effect appears. However, in order to show a sufficient effect, 0.2% by weight or more is preferable for both P and Ca, Mg and the like. However, if the content of each of these exceeds the upper limit, in addition to Cu inactivation due to excessive stabilization of Cu, a decrease in activity due to Cu coating occurs.

As the raw material of P, inorganic phosphoric acid (orthophosphoric acid, etc.), inorganic phosphate, oxide (diphosphorus pentoxide, etc.),
Organic phosphoric acid, organic phosphate, chloride (phosphorus pentachloride, etc.),
Various compounds such as condensed phosphoric acid, condensed phosphates (sodium metaphosphate, etc.), ammonium phosphate salts (primary ammonium phosphate, etc.) can be used. Also, Ca, Mg, L
Various materials such as nitrates, acetates, carbonates and chlorides are used as the raw materials of i and Sr. In order to incorporate these into zeolite, it is also effective to make them into an aqueous solution and add them by an ion exchange method, an impregnation method, a kneading method, or physically mix the salt. Furthermore, a vapor deposition method or the like can also be used.

The loading amount of Cu on the zeolite is 2% by weight.
The above is preferable, but if it exceeds 8% by weight, copper oxide (CuO), which is not retained at the ion exchange sites and is excessive, becomes excessive, which causes adverse effects such as pore clogging of the zeolite. As the raw material of Cu, various materials such as acetate, nitrate, chloride, ammine complex compound are used.
Besides a general method such as an impregnation method, a vapor deposition method is also effective.

Cu, P, and Ca, M to zeolite
The order of supporting g, Li, and Sr is not particularly limited, and they may be added all at once.

The catalyst of the present invention may have any shape, but it is usually preferable to use it in the shape of a honeycomb, and the catalyst is applied to various honeycomb-shaped base materials. As this honeycomb material, a cordierite material is generally used, but the present invention is not limited to this, and the catalyst itself may be formed into a honeycomb shape.
It is also possible to use a honeycomb made of a metal material.

[0021]

EXAMPLES The present invention will be described below with reference to Examples, Comparative Examples and Test Examples. Example 1 Na-type ZSM-having a SiO ₂ / Al ₂ O ₃ molar ratio of about 30
5 Zeolite was impregnated with an aqueous solution containing orthophosphoric acid (H ₃ PO ₄ ) in an amount to achieve a loading amount of 0.5% by weight as P with respect to the zeolite (based on the state where adsorbed water was removed), and mixed well Then, it was dried at 150 ° C. for 8 hours or more. The obtained dry powder was stirred in a 0.1 M copper acetate aqueous solution for 12 hours, supported with Cu by an ion exchange method, and then dried in a dryer at 120 ° C. for 8 hours or more. The obtained dry powder was loaded with 1.0% by weight of Ca (based on zeolite excluding adsorbed water as Ca) by an impregnation method using an aqueous solution of calcium acetate, and dried at 150 ° C for 8 hours or more. After that, it was calcined in the air at 500 ° C. for 2 hours in an electric furnace to obtain a ZSM-5 catalyst powder containing Cu, P and Ca. The amount of supported Cu in this catalyst is 3.6 (as Cu).
% By weight. This catalyst is described as follows.

Embedded image Cu (3.6) -P (0.5) -Ca (1.0) / ZSM-5

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. Approximately 300 of this slurry per square inch cross section
Cordierite honeycomb carrier with individual channels (capacity
0.7 L), dried in a hot air drier at 120 ° C. for 1 hour, and then calcined at 400 ° C. for 1 hour to prepare catalyst 1 of Example 1.
Got The coating amount of the catalyst powder at this time was 170 g / L.

Example 2 The same Na-type ZSM-5 zeolite as in Example 1 was stirred for 8 hours in a 0.1 N calcium nitrate aqueous solution, and 0.27% by weight of Ca was carried by an ion exchange method, and then 24 hours at 150 ° C. in a dryer. Dried for hours. Then, the same method as in Example 1,
After replacing the P raw material with sodium pyrophosphate (Na ₄ P ₂ O ₇ ), 0.5% by weight of P was carried, and then Cu was similarly carried to obtain the following catalyst powder. In the same manner, a honeycomb catalyst 2 was obtained.

Embedded image Cu (3.3) -P (0.5) -Ca (0.27) / ZSM-5

Example 3 A honeycomb catalyst 3 was obtained in the same manner as in Example 1 except that the amount of P added was changed from 0.5% by weight to 0.1% by weight.

Embedded image Cu (3.1) -P (0.1) -Ca (1.0) / ZSM-5

Example 4 A honeycomb catalyst 4 was obtained in the same manner as in Example 1 except that the amount of P added was changed from 0.5% by weight to 0.9% by weight.

Embedded image Cu (3.8) -P (0.9) -Ca (1.0) / ZSM-5

Example 5 A honeycomb catalyst 5 was obtained in the same manner as in Example 1 except that the amount of P added was changed from 0.5% by weight to 2.0% by weight.

Embedded image Cu (3.8) -P (2.0) -Ca (1.0) / ZSM-5

Example 6 A honeycomb catalyst 6 was obtained in exactly the same manner as in Example 1 except that the amount of P added was changed from 0.5% by weight to 4.0% by weight.

Embedded image Cu (3.8) -P (4.0) -Ca (1.0) / ZSM-5

The amount of Ca added is 1.0% by weight to 0.1% by weight.
Honeycomb catalyst 7 was obtained in exactly the same manner as in Example 1 except that

Embedded image Cu (3.6) -P (0.5) -Ca (0.1) / ZSM-5

Example 8 A honeycomb catalyst 8 was obtained in exactly the same manner as in Example 1 except that the amount of Ca added was changed from 1.0% by weight to 4.0% by weight.

Embedded image Cu (3.6) -P (0.5) -Ca (4.0) / ZSM-5

Example 9 A honeycomb catalyst 9 was obtained in exactly the same manner as in Example 1 except that Ca was replaced with Mg and magnesium acetate was used instead of calcium acetate.

Embedded image Cu (3.6) -P (0.5) -Mg (1.0) / ZSM-5

Example 10 A honeycomb catalyst 10 was obtained in exactly the same manner as in Example 1 except that Ca was replaced by Li and lithium nitrate was used instead of calcium acetate.

Embedded image Cu (3.6) -P (0.5) -Li (1.0) / ZSM-5

Example 11 A honeycomb catalyst 11 was obtained in exactly the same manner as in Example 1 except that Ca was changed to Sr and therefore strontium nitrate was used instead of calcium acetate.

Embedded image Cu (3.6) -P (0.5) -Sr (1.0) / ZSM-5

Example 12 Na-type ZSM-having a SiO ₂ / Al ₂ O ₃ molar ratio of about 30
5 zeolite with a SiO ₂ / Al ₂ O ₃ molar ratio of about 34
A honeycomb catalyst 12 was obtained in exactly the same manner as in Example 1 except that the Na-type mordenite was replaced with.

Embedded image Cu (3.2) -P (0.5) -Ca (1.0) / mordenite

Comparative Example 1 The Na-type ZSM-5 of Example 1 was stirred in a 0.1 M copper acetate aqueous solution for 12 hours, supported with Cu by an ion exchange method, and then dried in a dryer at 120 ° C. for 8 hours or more. . The obtained dry powder was slurried in the same manner as in Example 1 to obtain a honeycomb catalyst 13.

[Image Omitted] Cu (3.2) / ZSM-5

Comparative Example 2 A honeycomb catalyst 14 was obtained in the same manner as in Example 1, except that Ca was not added.

Embedded image Cu (3.6) -P (0.5) / ZSM-5

Comparative Example 3 To the catalyst powder obtained in Comparative Example 1, Ca was added in the same manner as in Example 1 to obtain a honeycomb catalyst 15.

Embedded image Cu (3.2) -Ca (1.0) / ZSM-5

Test Example Table 1 shows the durability performance of the catalysts of the above Examples and Comparative Examples by a rapid durability test using an engine exhaust gas and an activity evaluation using an exhaust gas simulation.

Activity evaluation conditions Evaluation device: atmospheric pressure fixed bed flow type reaction device Catalyst capacity: 0.1 L (cut out from a 0.7 L size catalyst) Gas space velocity: Approximately 20000 h ^-1 Exhaust gas simulation gas composition: Total hydrocarbons = 3000 ppm (Cl terms) NO = 350ppm CO = 1000ppm O 2 = 4.5% CO 2 = 12% H 2 O = 8.5% N 2 = remainder

Rapid Endurance Treatment Conditions Catalyst Inlet Exhaust Gas Temperature: 610 ° C. Engine: V8 8-cylinder engine for President (manufactured by Nissan Motor Co., Ltd.) Average air-fuel ratio (A / F): Approx. 18 Fuel: Unleaded regular gasoline 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. With the Ca content in the catalyst fixed at 1.0% by weight, the NO removal rate when the P content was varied was observed, and when P content was 0.1% by weight or more, the effect appeared, and 0.3 to 3.0% by weight. It can be seen that a large effect is obtained in the range of, but when it exceeds 4.0% by weight, the opposite effect is obtained. Further, when the P content in the catalyst was kept constant at 0.5% by weight and the NO removal rate was changed when the Ca content was changed, the effect appeared when the Ca content was 0.01% by weight or more, and when the Ca content was 0.2 to 3.0% by weight. A clear effect can be obtained, but a content of 5.0% by weight or more has the opposite effect.

When the P content and Ca content coexist in the P content range of 0.3 to 3.0% by weight and the Ca content range of 0.2 to 3.0% by weight, the catalyst durability is greatly improved.

[0042]

[Table 1]

[0043]

EFFECTS OF THE INVENTION 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 period of time, and has excellent durability. Can provide a good car.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Hiroshi Akama 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (72) Goji Masuda 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd.

Claims (3)

[Claims] 1. An inorganic substance containing crystalline aminosilicate as a main component, containing copper (Cu) and phosphorus (P), and calcium (Ca), magnesium (Mg), lithium (L).
An exhaust gas purifying catalyst, characterized by containing at least one metal component selected from the group consisting of i) and strontium (Sr). 2. The exhaust gas purifying according to claim 1, wherein the content of P is 0.1 to 4% by weight with respect to the crystalline aminosilicate in a state where adsorbed water is removed. catalyst. 3. The crystalline aluminosilicate in a state in which water adsorbing the content of one or more metal components selected from the group consisting of Ca, Mg, Li and Sr is excluded,
The amount is 01 to 5% by weight.
Exhaust gas purification catalyst described.