JP3291316B2 - Exhaust gas purification catalyst - 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 catalyst.

[0002]

2. Description of the Related Art As a catalyst for purifying exhaust gas of an engine,
Oxidation of CO (carbon monoxide) and HC (hydrocarbon) and N
Three-way catalysts that simultaneously reduce Ox (nitrogen oxide) are known. As a three-way catalyst, a catalyst in which Pt (platinum), Pd (palladium), and Rh (rhodium) are supported on γ-alumina is known.
/ F) is around 14.7, which is the stoichiometric air-fuel efficiency, and high purification efficiency is obtained.

[0003] Among the exhaust gases of the above engines, NOx
Due to the great potential for adverse effects on human bodies and ecosystems, their release into the atmosphere must be minimized. There are several methods for preventing the emission, but in the case of a mobile engine, it is practical to purify the exhaust gas with a catalyst installed at the latter stage of the engine.

On the other hand, in the field of automobiles, lean burn engines, so-called lean burn engines, have been put to practical use in order to comply with fuel regulations for engines. But,
In the case of the lean-burn engine, since the exhaust gas is in an oxygen-excess atmosphere due to a high air-fuel ratio, even if CO and HC can be oxidized and purified by the above three-way catalyst, reduction of NOx It cannot be purified.

[0005] Therefore, even in an atmosphere of excess oxygen in the exhaust gas, NOx is directly or directly reduced by a reducing agent (eg, CO,
As a catalyst that can be catalytically decomposed into N ₂ and O ₂ by the presence of HC or the like, a catalyst composed of a zeolite carrying a transition metal, for example, by ion exchange is widely used. Furthermore, various proposals have been made for this transition metal-supported zeolite catalyst in order to increase the NOx purification rate and improve the activity of the catalyst.

For example, there is a catalyst for decomposing NOx described in Japanese Patent Application Laid-Open No. 2-251247. According to the publication, there is disclosed a NOx decomposition catalyst in which Cu and one or more metals of Co, Ni, La, and Ce are supported on zeolite, and Cu and Co are supported on zeolite by ion exchange. It is intended to increase the activity and obtain effective NOx decomposition even when the NOx concentration is low.

[0007]

However, the preferred use temperature at which the purifying activity of the NOx decomposition catalyst described in Japanese Patent Application Laid-Open No. 2-251247 is obtained is 400 to 700 ° C. Transition metal ion exchanged zeolite catalysts have a problem that their low-temperature activity is poor.

A Cu ion exchanged zeolite catalyst, which is a practical catalyst capable of effectively removing NOx,
In general, when a NOx purification rate exceeding 90% is exhibited at a laboratory level and NOx is to be purified in an oxygen-excess atmosphere by being installed in an actual vehicle equipped with a lean burn engine, a model gas in the laboratory and an exhaust gas in the actual vehicle are used. It is inevitable that the NOx purification rate decreases due to the difference between the gas and the gas. Further, in such a Cu ion exchanged zeolite catalyst, the temperature at which the NOx purifying function is exhibited is 350 to 450.
Since the temperature is high, the total NOx purification rate is low when the NOx purification rate in an oxygen-excess atmosphere is evaluated.

In view of the above, the present invention is intended to improve the purification efficiency of an exhaust gas purification catalyst so that NOx can be efficiently purified in an oxygen-excess atmosphere.

[0010]

In order to achieve the above object, the invention of claim 1 is directed to a metal-containing silicide.
In order to enhance the NOx purification function in a practical zeolite-based catalyst in which Cu is supported as a transition metal on a kate , the metal-containing silicate is combined with Cu , which is a transition metal , by V
It is intended to improve the purification efficiency of the zeolite catalyst by supporting Bi which is a Group B metal.

Specifically, a solution taken by the invention of claim 1 is that a metal-containing silicate is made of a transition metal such as Cu and VB.
Bi , which is a group metal , is carried on each.

Further, the invention according to claim 2 is a catalyst for efficiently purifying NOx by using a zeolite catalyst comprising Bi and Cu supported on a metal silicate, wherein each of the supported amounts of Cu and Bi is set to an appropriate value. In this case, the metal-containing silicate is made of VB group metal.
Only Bi is supported as a genus, and the supported weight ratio of Bi / Cu when the Cu and Bi are supported on the metal-containing silicate, respectively, is in the range of 0.1 to 2.0. Things.

In the exhaust gas purifying catalyst of the present invention,
When the metal species is supported on the metal-containing silicate , Cu
And Bi are used in combination to support the catalyst body, so that the exhaust gas compared with the conventional Cu ion-exchanged zeolite catalyst in which only Cu is supported as shown in the following Examples It has excellent NOx purification rate and high activity over a wide temperature range. As a result, the NOx purification rate particularly in a low temperature range has been significantly improved, and the purification efficiency can be improved.

The reason why the above-mentioned effect is brought about is that B supported on the above metal-containing silicate together with Cu
It is presumed to be due to the characteristics of the behavior shown for the gas i .
In other words , Bi has a characteristic of being rich in gas activity, such as gas adsorbability and gas desorption, regardless of the temperature atmosphere. Therefore, the exhaust gas is used as a metal-containing silicate catalyst in which Bi is supported together with Cu. Sufficiently adsorbed and easily desorbed.

As a result, a large amount of exhaust gas is ensured in the catalyst, and a large amount of NOx is purified by reducing and purifying NOx by the combustion to sufficiently perform the reduction purification action by HC. become.

Further, since each component generated by purifying the exhaust gas is quickly desorbed by the above-mentioned characteristics of Bi, the unit amount of the catalyst according to the present invention can be purified. Is an amount larger than the purification amount of the exhaust gas purifying catalyst according to the related art in unit amount. As a result, it is recognized that the purification efficiency can be improved because the amount of NOx that passes through the catalyst unpurified without involving the catalyst is reduced.

The metal-containing silicate body is preferably an aluminosilicate (zeolite) using Al as the metal forming the skeleton of the crystal.
Alternatively, a metal-containing silicate using another metal such as Ga, Ce, Mn, or Tb together with Al as a skeleton forming material can be applied. Type A zeolite,
X-type, Y-type, mordenite, ZSM-5 and the like are preferred.

Complex with metal-containing silicate of the present invention
And combination of Cu and Bi carried by the practical
It is easy to improve the purification efficiency when purifying NOx
It is a thing. When the Cu and Bi are supported on the metal-containing silicate, the supported weight ratio Bi / Cu of Bi and Cu is 0.1 / 1.0 to 2.0 / 1.0.
(In other words, the supported weight ratio is in the range of 0.1 to 2), in particular, Bi / Cu is 0.5 /
When it is within the range of 1.0 to 1.0 / 1.0 (the range of the supported weight ratio of 0.5 to 1), the effect of improving the purification efficiency is large.

Further, VB group metal supported on the metal-containing silicate with Cu is not limited to Bi type, Bi
A plurality of metals selected from the group VB metals, such as a combination of Sb and Sb, may be combined. Even in such a case, the supported weight ratio between Cu and the transition metal when supported on the metal-containing silicate is such that the ratio between the total amount of each metal in the VB group metal and Cu is equal to or less than the above. It is preferable to set the catalyst body in such a range as described above.

The catalyst according to the present invention is obtained by carrying Cu and Bi on the above metal-containing silicate, for example, by ion exchange. The catalyst is used as a binder with about 20% by weight of an inorganic material such as hydrated alumina or silica sol. A monolith type catalyst can also be prepared by adding a binder and wash-coating the carrier.

When the above catalyst is prepared by wash coating, the carrier is preferably a cordierite honeycomb, but other inorganic porous bodies can also be used.

[0022]

Embodiments of the present invention will be described below.

As the metal-containing silicate, Na-type ZSM-
5 was used. The SiO ₂ / Al ₂ O ₃ ratio is preferably in the range of 20 to 200, and a ratio of 30 to 50 in that range was used. The cationic species may be other alkali metals, alkaline earth metals, H ⁺ or NH ₄ ⁺ in addition to Na. (Examples 1 to 4) The powder of the metal-containing silicate is immersed in a mixture of an aqueous solution of a nitrate or acetate of Cu and an aqueous solution of a nitrate or sulfate of Bi, or each metal salt of Cu and Bi Dipping in a separate aqueous solution in turn. Then, from room temperature to about 8
Stir at 0 ° C, preferably 40-60 ° C for 24 hours. Then, after washing with water and drying at 150 ° C. for 10 hours, 500
Calcination was performed in air at ℃ for 2 hours. In the above immersion process,
By adjusting the concentration of the Bi salt aqueous solution, as shown in Table 1, the supported amounts of Bi and Cu and Bi and Cu
The catalysts of Examples 1 to 4 in which the supported amount ratio changes stepwise were obtained. ( Reference Example 1 ) An aqueous solution of chloride of As was used in place of the aqueous solution of nitrate or sulfate of Bi in Examples 1 to 4, and otherwise shown in Table 1 in the same manner as in Examples 1 to 4. Thus, the catalyst of Reference Example 1 having the supported amounts of As and Cu and the supported amount ratio of As and Cu was obtained. ( Reference Example 2 ) An aqueous solution of acetate or chloride of Sb was used instead of the aqueous solution of nitrate or sulfate of Bi in Examples 1 to 4, and the other conditions were the same as in Examples 1 to 4. Sb and Cu as shown in FIG. 1 and Sb and Cu
The catalyst of Reference Example 2 having a supported amount ratio of (Conventional example) The above metal-containing silicate powder is immersed in an aqueous solution of a nitrate or acetate of Cu, and is heated from room temperature to about 80 ° C.
Stirred at 0-60 <0> C for 24 hours. After washing with water 150
After drying at 10 ° C. for 10 hours, it was calcined at 500 ° C. for 2 hours in the air to obtain a conventional catalyst having a supported amount of Cu as shown in Table 1.

The method in which a metal selected from the group VB metals or Cu alone is supported together with Cu as a transition metal on the metal-containing silicate in each of the examples, reference examples, and conventional examples is described by ion exchange method, impregnation method. And a common supporting method such as a coprecipitation method.

[0025]

[Table 1]

Each of the catalysts shown in Table 1 above (Examples 1-4
In addition, hydrated alumina, silica sol and the like were added as binders to each of Reference Examples 1 and 2 and Conventional Example) so that the weight was 20%, and then an appropriate amount of water was added to prepare a coating slurry. This slurry was added to a cordierite honeycomb (1
(400 cells per square inch) is immersed, the excess slurry is blown off by air blow, dried and calcined at 500 ° C. for 2 hours in the atmosphere to obtain the exhaust gas purifying catalyst according to the embodiment of the present invention and the conventional catalyst. Was. At this time, the amount of the catalyst carried on the honeycomb carrier was adjusted to 20% by weight of the honeycomb carrier.

Each of the exhaust gas purifying catalysts having the compositions shown in Table 1 and the conventional catalysts were mounted on a normal-pressure fixed-bed flow reactor, and the NOx purification rate was determined by a well-known method. Was measured respectively. That is, NO: 2000 ppm, HC: 5500 ppm, O
_{2: 8%, H 2:} 650ppm, CO: 0.2%, C
O ₂ : 10%, N ₂ : Using a model gas with the remaining amount,
This gas was flowed from the upstream side to the downstream side of each of the above-mentioned catalysts so as to have an SV of 55000 hr ^-1, and the NOx purification rate at each temperature was measured. The results are shown in FIGS.
FIG. 2 shows Reference Examples 1 and 2 in comparison with the conventional example.

According to the results shown in FIG. 1, the conventional C
Bi of Examples 1-4 according to the present invention compared to u / ZSM-5
-Cu / ZSM-5 each have high initial activity. That is, as for the supported amounts of Bi and Cu, Bi / Cu in the VB group metal / Cu in Table 1 was 0.1%.
/ 1 in the range from Example 1 where the ratio is 1.0 / 1.0 to Example 4 where the ratio is 2.0 / 1.0 (the weight ratio supported is 0.1 to 2), particularly 0.5 / 1. 0.0 to 1.0 / 1.0
When the supported amount ratio (supported weight ratio is 0.5 to 1), the effect of improving the purification efficiency is great.

According to the results shown in FIG.
As-Cu / ZSM- of Reference Example 1 compared to u / ZSM-5
5 and Sb-Cu / ZSM-5 of Reference Example 2 each have high purification efficiency.

[0030]

As described above, according to the exhaust gas purifying catalyst according to the first aspect of the present invention, Cu as a transition metal and Bi as a VB group metal are supported on the metal-containing silicate in a complex manner. Is used,
Since the gas adsorbing property and the gas desorbing property of Bi make the catalyst body actively absorb and desorb the exhaust gas, the purification efficiency of the exhaust gas purifying catalyst is improved.

[0031] According to the second aspect of the present invention, excellent exhaust gas purifying catalyst of the purification efficiency can be obtained practically by the supported amount ratio of B i and Cu in the range of 0.1 to 2.0 It will be easier.

[Brief description of the drawings]

FIG. 1 is a graph showing a result of measuring a NOx purification rate of a combination of Cu and Bi in an example of the present invention.

FIG. 2 is a graph showing the results of measuring the NOx purification rate of a combination of Cu and a VB group metal other than Bi.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-40238 (JP, A) JP-A-4-16239 (JP, A) JP-A-58-156508 (JP, A) 4045 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B01J 21/00-37/36 B01D 53/86

Claims (2)

(57) [Claims] 1. The metal-containing silicate is transition metal C
An exhaust gas purifying catalyst, wherein u and Bi , a VB group metal , are respectively supported. 2. The method according to claim 2, wherein said metal-containing silicate is composed of a VB group metal.
And only Bi is supported, and the supported weight ratio of Bi / Cu when the Cu and Bi are supported on the metal-containing silicate, respectively, is 0.1 to
The exhaust gas purifying catalyst according to claim 1 , wherein the range is 2.0.