JP3352473B2 - Exhaust gas purification device - Google Patents

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 apparatus having improved exhaust gas purifying efficiency by eliminating the influence of a shift in the maximum activation temperature of exhaust gas, particularly a catalyst for purifying NOx.

[0002]

2. Description of the Related Art Since the exhaust gas of a lean burn engine has a high concentration of oxygen, a three-way catalyst which simultaneously oxidizes HC and CO and reduces NOx cannot effectively remove NOx. As a catalyst capable of decomposing and purifying NOx in exhaust gas into N ₂ and O ₂ under a high-concentration atmosphere, a so-called zeolite catalyst obtained by supporting an active species such as Cu on a metal-containing silicate is promising. Have been. Therefore, it is known to apply the zeolite catalyst to an exhaust gas purifying device provided in an engine, particularly an exhaust system of a lean burn engine.

[0003] At the same time, the zeolite catalyst itself needs to be selected in various forms, such as selection of active species, starting from selection of active species, in order to always provide an exhaust gas purifying catalyst having excellent NOx removal capability in response to various conditions of exhaust gas. Measures are being considered.

For example, Japanese Patent Application Laid-Open No. 3-202157 proposes a technique for efficiently removing NOx in an oxygen-rich atmosphere. The technology disclosed in the above-mentioned publication is to provide a catalyst in which zeolite supports Cu and at least one kind of alkaline earth metal and one or more kinds of rare earth metals, thereby obtaining excellent NOx in a temperature range of 800 ° C. or less. An object of the present invention is to obtain a catalyst having a purifying ability and durability that can be used for a long time.

[0005]

However, Cu ion-exchanged zeolite catalysts, which are typical zeolite catalysts, provide excellent NOx purification rates, but are inferior in heat resistance.
In particular, when the temperature of the gas at the catalyst inlet becomes 750 ° C. or higher, the catalyst rapidly deteriorates. Further, although the Cu ion exchanged zeolite catalyst can obtain an excellent NOx purification rate, the actual operation of the catalyst increases the catalyst inlet gas and exposes the exhaust gas to the exhaust gas for a long time.
After the so-called heat resistance of the catalyst, there is a problem that the maximum activation temperature at which the above-mentioned excellent NOx purification rate is obtained tends to shift to a higher temperature side.

Further, when the engine is operated at a low load, the catalyst temperature in the low-temperature region is required to be improved because the catalyst inlet gas temperature of the exhaust gas is lowered so that the catalyst is required to be improved in the low-temperature region. What has an excellent purification rate is needed. However, Japanese Unexamined Patent Publication No. Hei.
No. 57, a catalyst in which Cu and a metal of an alkaline earth metal and a rare earth element are supported on a metal-containing silicate has been found to have improved heat resistance, but it has been recognized that NO There is a problem that the purification rate in a low temperature range such as 300 ° C. or lower is inferior, and it is not possible to meet the demand for a catalyst having an excellent purification rate in the low temperature range.

In general, a type of N having a high activity in a low temperature region
Although it has been recognized that the Ox purification catalyst exhibits an excellent NOx purification rate even in an oxygen-rich atmosphere at the time of lean burn, since the NOx purification temperature range is narrow, the catalyst inlet gas temperature (accurately, the catalyst temperature) is high. If it is too low or too low, the above-mentioned excellent NOx purification rate cannot be obtained. Furthermore, such a catalyst is exposed to the exhaust gas atmosphere of a so-called actual operation for a long time under the condition of lean burn operation in an actual vehicle,
Since the maximum activation temperature at which the NOx purification characteristics are effectively exhibited shifts to a lower temperature side, the NOx purification rate apparently decreases.

As a result, when the exhaust gas purifying catalyst is exposed to the exhaust gas atmosphere of the actual operation for a long time, not only the catalyst whose maximum activation temperature shifts to the above-mentioned high temperature side, but also the above-mentioned low temperature activation catalyst which shifts to the low temperature side. Even when the catalyst is excellent in catalyst efficiency, the catalyst inlet gas temperature (catalyst temperature) does not match the maximum activation temperature of the exhaust gas purifying catalyst practically, and efficient exhaust gas purification, particularly NOx purification, is performed. There is a problem that there is no.

Therefore, the present inventor has developed a precious metal-supported metal-containing silicate from a lean-burn engine exhaust gas as a NOx catalyst having an excellent purification activity in a high oxygen concentration atmosphere in an exhaust gas and in a relatively low temperature range of the exhaust gas. As a result of intensive research focusing on the exhaust gas purifying catalyst, it was confirmed that the catalyst composed of the metal-containing silicate supporting the noble metal can obtain an excellent NOx purification rate as expected.

In particular, a catalyst in which Pt and Ir are indispensably supported as a noble metal active species on a metal-containing silicate has a remarkable effect of exhibiting NOx purification activity from a low temperature range, and the NOx purification rate in a fresh state is reduced. Can be further improved. Further, in addition to the above Pt and Ir, R
When an active species to which h or the like is added is used, results such as improvement in heat resistance have been obtained.

[0011] Therefore, in a catalyst in which a Pt-Ir-based active species having excellent NOx purification characteristics as described above is supported on a metal-containing silicate under a high oxygen concentration atmosphere in exhaust gas, the function of this catalyst is the most. We continued research on practical means that can be used efficiently.

As a result, a catalyst made of a Pt-Ir-based metal-containing silicate having excellent NOx purification characteristics is also used.
Due to the characteristics of Pt and Ir applied as active species, it was recognized that the maximum active temperature shifted to a lower temperature side by actual operation as described above.

On the other hand, in order to reduce the emission of the harmful substances as much as possible in consideration of the regulations on the emission of the harmful substances in the exhaust gas of the engine, the temperature at which the characteristics of the catalyst can be effectively utilized from the beginning of operation is considered. Considering the part of the engine exhaust system where the region is obtained as the optimal position for exhaust gas, especially NOx purification,
It is widely practiced to dispose an exhaust gas purifying catalyst in such a portion.

In view of this, for example, a catalyst comprising a metal-containing silicate carrying a Pt-Ir-based active species is disposed at a position considered to be the above-mentioned optimum position in the engine exhaust system based on the characteristics indicated by the data at the time of preparation. In this case, an excellent exhaust gas purifying ability is exhibited in the early stage of the actual operation. However, the maximum activation temperature shifts to, for example, a lower temperature side with the progress of the actual operation, so that the condition of purifying the exhaust gas in the best exhaust gas purification activation temperature range of the catalyst is not satisfied, and the exhaust gas purification ability is reduced. There is a contradiction.

In view of the above, according to the present invention, even if the exhaust gas purifying catalyst provided in the engine exhaust system is a catalyst having a tendency to shift the maximum active temperature by the operation of the actual machine, the shift of the maximum active temperature causes the shift. It is an object of the present invention to provide an exhaust gas purifying apparatus that eliminates the influence that occurs and that permanently retains the excellent exhaust gas purifying ability provided by the inherent excellent characteristics of the catalyst.

[0016]

Here, the present inventor has determined that the above-mentioned situation is the same as the maximum activation temperature after the maximum activation temperature is shifted by the actual operation of the engine exposed to the exhaust gas of the engine. If the conditions for the catalyst inlet gas temperature are determined, and the exhaust gas can be purified while satisfying such conditions, at the stable maximum activation temperature after shifting by the actual operation, the actual operation of the actual Through the knowledge that an efficient exhaust gas purification ability can be obtained throughout the continuation, the present invention has been completed.

Therefore, the above-mentioned object is achieved by the present invention having the following configuration. The invention of claim 1 is to prevent the shift of the maximum activation temperature caused by the actual operation of the apparatus in advance for NOx purification. By causing the catalyst to occur, the effect of the shift of the maximum activation temperature caused by the actual operation of the NOx purification catalyst is intended to be eliminated.

Specifically, a solution taken by the invention of claim 1 is directed to an exhaust gas purifying apparatus provided with a catalyst for purifying NOx in an engine exhaust system. aging process of shifting within a predetermined temperature range the highest activation temperature of the catalyst to the high temperature side or the low temperature side is given in advance in an atmosphere of the corresponding gas composition, the engine
The catalyst inlet gas temperature in the exhaust system is the highest after the shift
It is configured to be installed at a site where the activation temperature is reached .

In the exhaust gas purifying catalyst of the present invention, the metal-containing silicate on which active species such as Pt and Ir are supported is an aluminosilicate (zeolite) using Al as a metal forming a crystal skeleton. Is preferable, and instead of the above Al or Al
In addition, a metal-containing silicate using a metal such as Ga, Ce, Mn, or Tb as a skeleton forming material can be applied. As the metal-containing silicate, A-type, X-type, Y-type, mordenite, ZSM-5 and the like are preferable.

As the metal-containing silicate, Na-type ZSM-5 in which the cationic species is Na and H-type ZSM-5 in which the cationic species is H + are preferably used.

Further, about 20% by weight of a hydrated alumina or silica sol or the like is added as a binder to the above-mentioned catalyst, and for example, it is used as a monolith type catalyst device by wash-coating a cordierite honeycomb carrier. Can also.

In the exhaust gas purifying apparatus of the present invention, the catalyst for purifying NOx disposed in the engine exhaust system is one whose maximum activation temperature is shifted by actual operation. Further, as described above, when the catalyst purifies NOx, when the catalyst is made of a metal-containing silicate supporting a noble metal such as a Pt-Ir based catalyst having an excellent NOx purifying activity in a low temperature range of exhaust gas, the above-mentioned maximum is considered. The activation temperature shifts to a lower temperature.

According to the structure of the present invention, as described in detail below, the highest activation temperature of the NOx purifying catalyst after the shift by the actual operation is matched with the catalyst inlet gas temperature to achieve the highest. Since the maximum NOx purification rate at the activation temperature can be effectively utilized, basically, in the effective and permanent NOx purification activation temperature range after the shift in the catalyst, NO
An effect of purifying x can be obtained, and thereby an exhaust gas purifying device with improved purification efficiency can be obtained.

According to the structure of the first aspect of the present invention, an aging treatment catalyst in which a shift in the maximum activation temperature similar to the shift in the maximum activation temperature caused by the actual operation of the engine is previously given to the NOx purification catalyst is required in the engine exhaust system. Department , that is,
Part where the catalyst inlet gas temperature becomes the highest active temperature after the shift
Since the provided position, aging the catalyst after the activation temperature was shifted decrease in the NOx purification characteristic of the post-installed vehicle is prevented.

[0025]

Embodiments of the present invention will be described below with reference to the drawings.

Exhaust gas applied to the exhaust gas purifying apparatus according to the present invention, particularly a catalyst for purifying NOx, comprising a silicate containing a noble metal-supporting metal, which exhibits excellent NOx purifying characteristics in a low temperature region of the gas temperature at the catalyst inlet. , A Pt-Ir-based active species-supported metal-containing silicate catalyst was selected. This Pt-Ir-based active species-supporting metal-containing silicate catalyst is an effective catalyst for improving NOx purification characteristics in the low temperature range because the maximum activation temperature shifts to a low temperature side by actual operation.

First, the Pt-Ir-based active species is a ternary active species of Pt-Ir-Rh to which Rh is added.
The H-type metal-containing silicate (S) supported so that the supporting ratio of r-Rh becomes a molar ratio of 30: 10: 1
iO ₂ / Al ₂ O ₃ = 70) catalyst was prepared, and this catalyst was loaded on a 1.3 liter cordierite honeycomb support (1).
(400 cells per square inch) and Pt-Ir-
An Rh-based catalyst device was prepared. Then, a plurality of catalyst samples having different capacities were prepared from the catalyst device.

Each of these catalyst samples was mounted on an exhaust gas conducting device 1 as shown in FIG. 1, and a heat treatment was performed with exhaust gas of an actual engine. The exhaust gas used for this heat treatment has an air-fuel ratio (A / F) of 22 and HC: 6000.
ppmC, CO: 0.12%, NOx: 2000 pp
_{m, H 2: 650ppm, CO} 2: 10%, N 2: it had a composition of balance, such exhaust gas SV = 550
00h-1, the catalyst inlet gas temperature is about 300 ° C.,
The Pt-Ir-Rh-supported H-type metal-containing silicate catalyst is heated by passing it through a catalyst sample supported on the honeycomb carrier.

The exhaust gas conducting device 1 illustrated in FIG. 1 has a gas branch box 3 communicating with the engine 2 and a gas collecting box 4 provided opposite the gas branch box 3. By sandwiching the catalyst sample 5 between the gas branch box 3 and the gas collecting box 4, exhaust gas discharged from the engine 2 is sent to the catalyst sample 5 via the gas branch box 3 and contacted with the catalyst sample 5. The later exhaust gas is put together in the gas collecting box 4 and the exhaust pipe 6
It is structured to be discharged from. Further, the properties of the exhaust gas sent out from the engine 2 can be detected by an air-fuel ratio sensor 7 provided on the upstream side of the gas branch box 3.

Next, the NOx purification characteristics of the catalyst sample in a fresh state where the above-mentioned heat treatment was not performed and the catalyst sample which was subjected to the above-mentioned heat treatment and after heating in a so-called actual machine were evaluated, and the results were evaluated. As shown in FIG.
According to the results shown in FIG. 2, the Nt in the catalyst sample of the Pt-Ir-Rh-based active species after the actual heating by the heat treatment was performed.
It was also confirmed that the maximum activation temperature including the excellent range of the Ox purification characteristics shifted to the lower temperature side as expected, and that the NOx purification characteristics hardly fluctuated after the shift.

When the NOx purification characteristics in such a fresh state and after heating the actual machine were evaluated for each of other conventional catalysts, for example, FIG. 3 shows the results for a Cu ion exchanged zeolite catalyst. Thus, the maximum activation temperature has shifted to the higher temperature side. It is clear that such a catalyst in which the maximum activation temperature range shifts to the high temperature side is not an advantageous shift for the purpose of obtaining excellent NOx purification characteristics in the low temperature range.

Next, the maximum activation temperature from the shift state of the NOx purification characteristics as shown in FIG. 2 to the initial stage of use of the catalyst which is advantageously applied to the present invention and after a lapse of time is 240 ° C. As shown in FIG. 4 using the above catalyst sample, ± 240 ° C.
The gas (exhaust gas of the actual engine) used in the heat treatment is applied under the same conditions while oscillating the catalyst inlet gas temperature so that the catalyst inlet gas temperature repeatedly rises and falls within the range of 20 ° C. It was applied to the above catalyst sample, and the NOx purification rate at each rising point and each falling point was measured.

Similarly, the catalyst inlet gas temperature is set to 200 ° C., 2
The temperature was set to 20 ° C. and 260 ° C., and the NOx purification rate at each rising point and each falling point of each temperature was measured while oscillating within ± 20 ° C. based on each set temperature. Table 1 shows the maximum NOx purification rate and the average NOx purification rate at the oslate temperature.

[0034]

[Table 1]

According to the results shown in Table 1, the average NOx
It is noted that high values of the purification rate are not obtained at 240 ° C. where the highest maximum NOx purification rate is obtained at each temperature, but rather are obtained at 220 ° C. where the maximum NOx purification rate obtained is somewhat lower. From the tendency of each measured value shown in Table 1,
The average value of the NOx purification rate obtained under the mode in which the catalyst inlet gas temperature is oscillated with an appropriate temperature gradient based on a certain temperature sequentially increases the catalyst inlet gas temperature straight up to the same temperature as the above temperature. It was found that the average value of the NOx purification rate obtained in the mode in which the NOx purification was performed did not match.

[0036] Such a phenomenon can be solved by establishing a portion having a temperature suitable for disposing a catalyst for purifying NOx in the engine exhaust system in a specific example described later, and thereby setting an effective N2.
This significantly contributes to obtaining Ox purification characteristics.

On the other hand, the catalyst inlet gas temperature and N
In order to observe the trend of the relationship with the Ox purification rate, the exhaust pipe of the engine was adjusted to change the catalyst inlet gas temperature, and the NOx purification rate at each temperature was measured. The results are shown in Table 2.

[0038]

[Table 2]

According to the results shown in Table 2, the average NOx purification rate measured in the mode in which the catalyst inlet gas temperature is oscillated as shown in Table 1 is very similar to the NOx purification rate in an actual vehicle. It was confirmed that the average NOx purification rate measured in the mode in which the inlet gas temperature was oscillated could be used as a highly accurate NOx purification rate as a simulation test of an actual vehicle. <
Specific Example> In this specific example , the shift of the maximum activation temperature caused by the actual operation of the engine exposed to the exhaust gas of the engine is caused in the NOx purification catalyst in advance so that the NOx purification in the NOx purification catalyst is performed. The characteristics are improved.

That is, a catalyst prepared as specified (for example, a catalyst in which Pt-Ir-Rh is supported on an H-type metal-containing silicate in a molar ratio of 30: 10: 1) is mixed with a catalyst carrier (for example, cordierite). After being supported on a honeycomb carrier, the sample was aged for a certain period of time at a temperature within + 50 ° C. of the maximum activation temperature before the shift in a gas atmosphere furnace adjusted to the composition conditions of the exhaust gas of the actual vehicle to be used. In this specific example, the aging treatment was performed by heating at 350 ° C. for about 10 hours.

[0041] Thus, the aging treatment catalyst applied definitive exhaust gas purifying device a specific example of the present invention,
a-active species loading, b-dry, c-wash coat, d
~ Drying, e ~ firing, and in addition to the usual preparation steps, f ~ gas atmosphere furnace aging and g ~ drying.

The aging process catalyst strained facilities such aging, the catalyst inlet further that put the engine exhaust system
The outlet gas temperature is set at the highest active temperature after the shift, so that the N
The excellent purification characteristics were permanently maintained without the Ox purification characteristics decreasing.

[0043] In the present invention, as a comparative example to other upper Kigu body examples, such as the maximum activation temperature by a real machine operation is temperature that matches the maximum activation temperature after the shift, the temperature-optimal in the engine exhaust system By arranging the exhaust gas purifying catalyst at an appropriate portion, it is possible to maintain excellent NOx purifying characteristics.

That is, from the viewpoint of effectively utilizing the maximum activation temperature after shifting by actual operation, the most suitable part for the catalyst device in the engine exhaust system is as follows:
As described above, this is a portion where the catalyst inlet gas temperature at which the best average NOx purification characteristics are obtained is obtained. Therefore, the average NOx purification rate is measured in the mode in which the catalyst inlet gas temperature is oscillated, and the exhaust gas purification section having the temperature corresponding to the temperature at which the highest average NOx purification rate is obtained is obtained. A catalyst was provided.

As a result, the maximum activation temperature after the shift by the actual operation can be matched with the temperature of the disposed part, in other words, the catalyst inlet gas temperature. It is possible to permanently maintain excellent purification characteristics without lowering the purification performance.

Next, the NOx purification rate obtained by the exhaust gas purifying apparatus as shown in Kigu body above example according to the present invention, conventional exhaust gas purification which does not consider the shift of the exhaust gas purification activity temperature ranges by actual operation NO obtained by the device
x purification rate.

In the prior art, the above-mentioned Pt-Ir-Rh-based catalyst is disposed in a portion of the engine exhaust system which has a temperature that matches a temperature range in which the catalyst can obtain a maximum NOx purification characteristic in a fresh state. Things.

Regarding this conventional exhaust gas purifying apparatus,
Initially applied to actual vehicle, when traveling 5000 km and 10,000 km
A test for measuring the NOx purification rate was performed for each run, and the results are shown in Table 3.

[0049]

[Table 3]

According to the results shown in Table 3, the conventional example shows an excellent NOx purification rate at the beginning of the test,
After the activation temperature range was shifted by the actual operation, the NOx purification rate deteriorated with time.

From the test results shown in Table 3, it is determined that the shift of the maximum activation temperature has already occurred because the NOx purification rate has decreased at the stage when the actual vehicle has traveled 5000 km. It can be understood that when the shift of the maximum activation temperature occurs due to the fact that the actual vehicle travels 5000 km.

Next, the above-mentioned P is added to a portion showing a temperature matching the active temperature range after the maximum active temperature is shifted by the actual operation of the engine, that is, an optimally disposed portion in the engine exhaust system.
With respect to the exhaust gas purifying apparatus of the comparative example in which the t-Ir-Rh-based catalyst is provided, the same test as that of the conventional example was performed. The results are shown in Table 4.

[0053]

[Table 4]

According to the results shown in Table 4, in the case of the comparative example, the maximum activation temperature in the NOx purification characteristics in the fresh state does not match the temperature of the disposition portion at the beginning.
Ox purification rate is poor. However, after the maximum activation temperature shifts due to the actual operation, in other words, after traveling 5000 km, the maximum activation temperature after the shift matches the temperature of the disposition portion, so that an excellent NOx purification rate can be achieved over time. Obtained permanently.

Further, a portion showing a temperature matching the active temperature range after the maximum active temperature has been shifted by actual operation,
That is, for the exhaust gas purifying device according to the present invention in which the aging treatment catalyst is disposed at the optimally disposed portion in the engine exhaust system, the same test as that of the conventional example was performed, and the results are shown in Table 5. Indicated.

[0056]

[Table 5]

According to the results shown in Table 5, it can be seen that in the example, an excellent NOx purification rate was obtained permanently from the beginning of the actual operation to the lapse of time.

[0058]

As described above, according to the exhaust gas purifying apparatus according to the first aspect of the present invention, a shift of the highest active temperature similar to the shift of the highest active temperature range caused by the operation of the actual machine is given to the catalyst in advance. Activation temperature of exhaust gas purifying catalyst in engine exhaust system
Because it is provided in the best position to be established in consideration of the shift of the band, since there is no low under the NOx purification characteristic by also shifting the maximum activation temperature after use predetermined time, the NOx purification characteristic of a Kaname Tokoro is permanently can get.

[Brief description of the drawings]

FIG. 1 is a front view illustrating an exhaust gas conducting device used in the present invention.

FIG. 2 shows NO in an exhaust gas purifying catalyst applied to the present invention.
It is a graph which shows x purification characteristic.

FIG. 3 is a graph showing a NOx purification characteristic of a conventional example of the present invention.

FIG. 4 is a diagram exemplifying a pattern of an oslate temperature for obtaining a suitable catalyst inlet gas temperature in the present invention.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Takemoto 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Inside Mazda Co., Ltd. (56) References JP-A-4-265414 (JP, A) JP-A-4 -63140 (JP, A) JP-A-3-281929 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 53/86 F01N 3/00

Claims (1)

(57) [Claims] 1. An exhaust gas purifying apparatus provided with a catalyst for purifying NOx in an engine exhaust system , wherein the catalyst has a maximum activation temperature of the catalyst in an atmosphere having a gas composition corresponding to the exhaust gas of the engine. Aging treatment for shifting the temperature within a predetermined temperature range to a high temperature side or a low temperature side is performed in advance, and the catalyst inlet gas temperature in the engine exhaust system is reduced.
The exhaust gas purifying apparatus is provided at a position where the maximum activation temperature is obtained after the shift .