JPH1066867A - Exhaust gas purification catalyst and exhaust gas purification method using the catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly active and stable catalyst mainly for removing nitrogen oxides in an oxygen-excess exhaust gas of a lean burn gasoline engine, a diesel engine, etc., and an exhaust gas purification method using the catalyst. Offer. SOLUTION: An exhaust gas purifying catalyst for removing nitrogen oxides from an oxygen-exhaust exhaust gas, comprising indium and / or gallium, cobalt, zirconia, zinc,
An exhaust gas purifying catalyst comprising at least one active component selected from titanium and a carrier component comprising an alumina-based oxide excluding zeolite.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the purification of exhaust gas discharged from internal combustion engines such as automobiles, boilers, industrial plants, etc., and more particularly, to excess oxygen such as exhaust gas from lean burn gasoline engines and diesel engines. The present invention relates to a catalyst for purifying exhaust gas by reducing or decomposing nitrogen oxides in exhaust gas, and a method for purifying exhaust gas using the catalyst.

[0002]

2. Description of the Related Art As a purification method by catalytic reduction of nitrogen oxides in an oxygen-excess atmosphere, a selective reduction method using ammonia as a reducing agent is well known, and nitrogen oxides in exhaust gas from boilers and industrial plants are well known. It is currently widely used for the removal of water. In this method, a vanadium catalyst supported on titanium oxide is usually used, but the use of ammonia is not desirable because of its toxicity, difficulty in handling, and the like.

On the other hand, exhaust gas from internal combustion engines such as automobiles uses a three-way catalyst mainly composed of a noble metal such as platinum-rhodium which simultaneously removes carbon monoxide, hydrocarbons and nitrogen oxides. However, in this case, control of the oxygen content (air / fuel ratio) in the exhaust gas is an essential condition. For example, in the state of excess oxygen, the reduction of nitrogen oxides is hardly performed, and it is completely effective as a denitration catalyst. It is known to go away.

[0004] In the object of the present invention, in the removal of mainly nitrogen oxides in an excess oxygen exhaust gas such as an exhaust gas from a lean burn gasoline engine or a diesel engine, a catalyst capable of purifying these gases without using ammonia. Has been rushed to develop and many proposals have already been made.

As an example, Japanese Patent Application Laid-Open No. 5-49933 discloses that a zeolite catalyst carrying an alkali metal and / or an alkaline earth metal and a zeolite catalyst carrying cobalt are provided on the exhaust gas inflow side. When the latter is disposed on the exhaust gas outlet side to purify the exhaust gas, it has been shown that the nitrogen oxide purifying activity does not decrease even if a hydrocarbon having a large carbon number is used as a reducing agent in an oxygen-excess atmosphere. It is described that it is used after being coated on a refractory base material such as a monolith, a pellet, or the like.

Japanese Patent Application Laid-Open No. 5-200255 discloses a catalyst in which at least one rare earth element and at least one of Cu, Co, Mn, and V are supported on a ceramic carrier, and a catalyst is provided upstream of the catalyst as a reducing agent. It is described that nitrogen oxides in exhaust gas can be reduced and removed by adding hydrocarbons to the exhaust gas.

[0007]

As described above, many purification catalysts have been proposed as purification catalysts in an oxygen-excess atmosphere, but none of them have been put to practical use. The reason for this is that no catalyst has been found which exhibits excellent activity not only in the high-temperature region but also in the low-temperature region and which satisfies the extremely difficult condition that the activity does not decrease under the use conditions.

[0008] Platinum-based catalysts generally exhibit excellent properties for low-temperature activity, but exhibit a rapid decrease in activity under the conditions of use, and show that saturated hydrocarbons and aromatic hydrocarbons are contained in exhaust gas. In the case of containing, there is a practical problem such as a very low removal rate of nitrogen oxides. Further, the catalyst comprising zeolite has a high initial activity, but has a serious problem in high-temperature durability in the presence of steam, and is considered to be difficult to put into practical use.

SUMMARY OF THE INVENTION An object of the present invention is to provide a catalyst for mainly removing nitrogen oxides in an exhaust gas of an oxygen-excessive exhaust gas, particularly a lean burn gasoline engine, a diesel engine or the like, and to provide an exhaust gas purifying method using the catalyst. .

[0010]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and have already disclosed in Japanese Patent Laid-Open No. 7-29936.
As disclosed in Japanese Unexamined Patent Publication No. 1 (1993), an exhaust gas purifying catalyst comprising an active component of indium and / or gallium and cobalt and a carrier component of an alumina-based oxide excluding zeolite has been developed. Research has been made to greatly improve the activity, and the present invention has been completed.

That is, the present invention provides indium and / or gallium for removing nitrogen oxides from an oxygen-excess exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons, cobalt, zirconia, zinc, The present invention discloses an exhaust gas purifying catalyst comprising at least one active component selected from titanium and a carrier component of an alumina-based oxide excluding zeolite.

The amount of the active component including the indium and the gallium is 0.05 to 30 watts relative to the carrier component.
t%, and the supported amount of the cobalt component is 0.01 to 30 wt% with respect to the carrier component, and the supported amount of at least one active component selected from zirconia, zinc, and titanium is 0.05% with respect to the carrier component. -20 wt%.

Further, the present invention provides a method for reducing nitrogen oxides in an oxygen-excess exhaust gas of a lean burn gasoline engine, a diesel engine or the like by using the catalyst of the present invention with a reducing agent such as hydrocarbons and / or alcohols. It also discloses a method for purifying exhaust gas which is reduced or decomposed into nitrogen and removed.

[0014] Then, nitrogen oxides in the exhaust gas are removed by introducing a reducing agent into the oxygen-excess exhaust gas, and the reducing agent is mainly hydrocarbons and / or alcohols. The exhaust gas is exhaust gas discharged from a lean burn gasoline engine or a diesel engine.

Exhaust gases containing nitrogen oxides, carbon monoxide and hydrocarbons include, for example, mobile source gases emitted from automobiles, such as exhaust gases from lean burn gasoline engines and diesel engines. The present invention is not limited to use with these exhaust gases only, but can also be used with fixed source gases such as boiler exhaust gases and exhaust gases from industrial plants. If the reducing agent is insufficient in the exhaust gas, a reducing agent such as hydrocarbons and / or alcohols may be added to the exhaust gas upstream of the catalyst layer.

[0016]

DETAILED DESCRIPTION OF THE INVENTION The main components of the catalyst of the present invention are as follows:
It comprises indium and / or gallium, cobalt, at least one active component selected from zirconia, zinc and titanium, and a carrier component composed of an alumina-based oxide excluding zeolite.

The carrier component is not particularly limited as long as it can stably hold indium and / or gallium, cobalt, and at least one selected from zirconia, zinc and titanium. -In addition to alumina, a porous carrier such as silica-alumina or β-alumina is used. Further, it may contain a component for stabilizing alumina, such as a co-catalyst component or lanthanum oxide.

Indium, gallium, cobalt, zirconia, zinc, and titanium are represented by element names, and are in the state of metal and / or oxide.

The combined amount of the indium and gallium components is preferably in the range of 0.05 to 30% by weight based on the carrier component.
Preferably, the range is 0.1 to 20 wt%.

The content of cobalt is preferably in the range of 0.01 to 30% by weight, preferably in the range of 0.1 to 20% by weight, and more preferably in the range of 1 to 10% by weight.

With respect to at least one component selected from zirconia, zinc and titanium, the combined amount of these components is preferably in the range of 0.05 to 20% by weight, preferably 0.1 to 10% by weight.
A good range is wt%.

If the amount is less than these ranges, the effect is not clear. If the amount is too large, the ratio of the effect is small, and furthermore, an economic problem is caused.

The indium and gallium used here behave very similarly under the conditions of use of the present catalyst. For example, gallium is inferior to indium, but shows a similar tendency with respect to a change in performance with respect to the supported amount.

In addition to these main components, there are many metals generally considered to have catalytic activity for the nitrogen oxide reduction reaction, for example, alkali metals, alkaline earth metals,
It may contain a metal such as a transition metal.

In preparing the catalyst of the present invention, each component may be supported on a carrier component by an impregnation method, or may be prepared by an alkoxide hydrolysis method or a coprecipitation method. Further, these may be dried and prepared by a method such as spray drying in a slurry state, or may be prepared by drying once after performing an operation such as filtration.

The raw material compound for supporting each component may be any compound, and is preferably a water-soluble chloride or nitrate. The method for producing the catalyst of the present invention is not limited to these methods.

The shape of the catalyst of the present invention can be various shapes such as a honeycomb shape, a foam shape, a granular shape and the like according to the purpose, but is not limited to these shapes. In taking these shapes, the catalyst itself may be directly formed into the shape described above, or the catalyst may be carried on a base material having a shape by a method such as coating.

[0028]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

[Examples Catalysts 1 to 13] γ-Al 2 O 3 powder was impregnated and supported by using an aqueous solution in which indium chloride, cobalt nitrate and zirconyl nitrate were dissolved. Thereafter, drying and firing were performed to obtain a catalyst powder. This catalyst was mixed with a nitric acid boehmite sol, and a cordierite honeycomb (20 cc, 400 ce) was used.
ll), dried and calcined to obtain Catalyst 1. The coating amount of the catalyst 1 thus prepared was such that
150 g / L, indium 0.15 g / L (0.1 wt.
%), Cobalt was 3 g / L (2 wt% based on alumina), and zirconia was 0.75 g / L (0.5 wt% based on alumina).

By the same preparation method, catalysts 2 to 13 having different loading components and loading amounts were prepared. The list is shown in Table 1 (% by weight based on Al2O3 support).

Comparative Catalysts A to C Impregnated on γ-Al 2 O 3 powder using an aqueous solution in which indium chloride, cobalt nitrate and zirconyl nitrate were dissolved. Thereafter, drying and firing were performed to obtain a catalyst powder. This catalyst was mixed with a nitric acid boehmite sol and a cordierite honeycomb (20 cc, 400 cels).
l), dried and calcined to obtain Comparative Example Catalyst A. The coating amount of Comparative Example Catalyst A thus prepared was
150 g / L for alumina, 0.075 g / L for indium (0.01 wt% based on alumina), 3 g / L for cobalt (2 wt% based on alumina)
%), And zirconia was 0.75 g / L (0.5 wt% based on alumina).

By the same preparation method, catalysts B to C having different loading components and different loading amounts were prepared. The list is shown in Table 1 (% by weight based on Al2O3 support).

[0033]

[Table 1] [Performance Evaluation Test] In the activity test, one honeycomb catalyst was set in a quartz tube. NO, C3H6, O2, H2O,
A gas containing N2 (Table 2) was introduced at a rate of 6,000 ml / min. NO was analyzed with a chemiluminescent NOx meter. C
3H6, C3H8, and CO were analyzed by TCD gas chromatography.

[0034]

[Table 2] The purification rates of NO and C3H6 were determined by analyzing the outlet gas concentration. The purification rate was determined from the following equation. “Purification rate = (inlet gas concentration−outlet gas concentration) ÷ inlet gas concentration × 100 (%)” The test results are summarized in Table 1.

As is evident from Table 1, the catalysts of Examples 1 to 3 exhibit excellent purification performance within the specified range of the amount of indium supported (Claim 2) with respect to Catalyst A of Comparative Example. Also,
The catalysts 4 to 5 show that even if indium is substituted for gallium or both are used, excellent purification performance is exhibited.

The catalysts 6 to 7 exhibit excellent purification performance with respect to the catalyst B within a specific range of the supported amount of cobalt (claim 2).

The catalysts 8 to 9 show excellent purification performance within the specific range of the amount of zirconium supported (Claim 2) with respect to the catalyst C. Further, the catalysts 10 to 11 replace zirconium with zinc and titanium, respectively. Also catalysts 12-13
Indicates that it is effective to use a combination of zirconium, zinc and titanium.

As can be seen from the above results, the catalyst comprising indium and / or gallium and cobalt may further include at least one selected from zirconium, zinc and titanium.
It is clear that the activity can be improved by adding seeds.

[0039]

According to the present invention, an exhaust gas purifying catalyst having improved activity is obtained by adding at least one active component selected from zirconium, zinc and titanium to a catalyst comprising indium and / or gallium and cobalt. And an excellent exhaust gas purification method using the catalyst is provided, which mainly contributes to the removal of nitrogen oxides in the exhaust gas containing excess oxygen such as lean-burn gasoline engines and diesel engines, and contributes to prevention of air pollution. The effect is achieved.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshihiko Nakano 1-9-13 Akasaka, Minato-ku, Tokyo Toyo CIA Co., Ltd. (72) Inventor Junji Ito 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Automobile Stock In-house (72) Inventor Yasuyuki Murofushi 2 Nihonsan Motor Co., Ltd., 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa

Claims (6)

[Claims] 1. An exhaust gas purifying catalyst for removing nitrogen oxides from an oxygen-excess exhaust gas, comprising at least one activity selected from indium and / or gallium, cobalt, zirconia, zinc and titanium. A catalyst for purifying exhaust gas, characterized by comprising a component and a carrier component composed of an alumina-based oxide excluding zeolite. 2. The supported amount of the active component including the indium and gallium is 0.05 to 30 wt% based on the carrier component, and the supported amount of the cobalt component is 0.01% based on the carrier component.
2 to 30 wt%, and the loading amount of at least one active ingredient selected from zirconia, zinc and titanium is 0.05 to 20 wt% based on the carrier component.
The exhaust gas purifying catalyst according to the above. 3. A method for purifying exhaust gas with an exhaust gas purifying catalyst for removing nitrogen oxides from an oxygen-excessive exhaust gas, wherein the purifying catalyst is the catalyst according to claim 1 or 2. A method for purifying exhaust gas, characterized by: 4. The exhaust gas purifying method according to claim 3, wherein a nitrogen oxide in the exhaust gas is removed by introducing a reducing agent into the exhaust gas having an excessive amount of oxygen. 5. The exhaust gas purifying method according to claim 4, wherein said reducing agent is mainly hydrocarbons and / or alcohols. 6. The exhaust gas purification method according to claim 3, wherein the exhaust gas is exhaust gas discharged from a lean burn gasoline engine or a diesel engine.