JP2554340B2 - Exhaust gas purification device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an exhaust gas purification device that reduces nitrogen oxides in exhaust gas discharged from a combustion device such as a diesel engine.

(Prior Art) Generally, in a diesel engine, it is difficult to purify nitrogen oxides because the combustion gas is in an oxidizing atmosphere. Also,
Even in a gasoline engine, when the air-fuel ratio is set to a lean state in order to improve fuel economy, it becomes difficult to reduce the amount of nitrogen oxides in the exhaust gas because the combustion gas is in an oxidizing atmosphere.

Therefore, for example, as shown in JP-A-61-185612, by adding a reducing substance product mainly composed of water to the exhaust gas to cause a water-gas reaction, the exhaust gas is reduced to a reducing atmosphere. After that, a technique for reducing nitrogen oxides using a three-way catalyst is known. However, in the above-mentioned conventional technique, it is necessary to maintain the exhaust gas at a high temperature of 800 ° C. or higher in order to cause the water-gas reaction, the use conditions are limited, and a large-scale product containing a large amount of reducing substance products is stored. Since it is necessary to provide a container, there is a problem that the device becomes large. Further, when water is used as the reducing substance product, there are problems that rust is likely to occur in the device and that oxygen generated by the decomposition of the water oxidizes and deteriorates the catalyst.

(Object of the Invention) The present invention has been made in order to solve the above problems, and can change exhaust gas from an oxidizing atmosphere to a reducing atmosphere without adding a reducing substance product, and has a simple configuration. The present invention provides an exhaust gas purification device that can effectively reduce nitrogen oxides in exhaust gas.

(Structure of the Invention) The present invention provides a reducing component generating part in which zinc is supported on the surface of a carrier, and an exhaust gas outlet of this reducing component generating part is a nitrogen oxide for purifying nitrogen oxides under a reflux atmosphere. It is connected to the exhaust gas inlet of the substance purification catalyst.

According to the above configuration, the sulfuric acid produced by the reaction of sulfur dioxide in the exhaust gas with oxygen and moisture reacts with the reducing component product zinc to produce hydrogen and zinc sulfate. Exhaust gas becomes a reducing atmosphere of oxygen lean state and is supplied to the nitrogen oxide purification catalyst,
With this nitrogen oxide purification catalyst, the nitrogen oxides in the exhaust gas are effectively reduced in the relatively low temperature region and purified.

(Embodiment) FIG. 1 shows an embodiment of an exhaust gas purifying apparatus according to the present invention. This exhaust gas purifying apparatus includes an oxidation catalyst 1 installed in an exhaust passage of a diesel engine, a nitrogen oxide purification catalyst 2 including a reduction catalyst installed on the downstream side of the oxidation catalyst 1, and the nitrogen oxide. The exhaust gas outlet 4 of the reducing component generating unit 3 and the exhaust gas inlet 5 of the nitrogen oxide purifying catalyst 2 are provided with a communication pipe 6. Connected through.

The oxidation catalyst 1 is one in which a catalyst component made of platinum, palladium, an alloy of platinum and palladium, or the like is supported on a carrier, and the hydrocarbon and carbon monoxide in the exhaust gas are oxidized and purified, It is configured to produce sulfuric acid by oxidizing sulfur dioxide in the exhaust gas and then reacting with water.

To produce this oxidation catalyst 1, for example, γ-alumina is used.
100g, boehmite (hydrated alumina) 100g, 240cc of water, 1.6cc of nitric acid was added to the slurry, and the mixture was stirred and mixed. Let After removing excess slurry by high pressure blow etc., 150
Dry for about 30 minutes at a temperature of ℃, then about 1.5 at a temperature of 550 ℃
By firing for a time, an alumina coat layer is formed on the surface of the carrier. Next, the carrier is immersed in an aqueous solution in which palladium chloride or the like is dissolved, and the alumina coating layer is impregnated with a catalyst component such as palladium. In this way, the alumina coating layer is coated and formed on the carrier at a ratio of about 2 wt%, and the catalyst component such as palladium is supported on the carrier at a ratio of about 1.6 to 2.0 g /.
Is formed.

The nitrogen oxide purification catalyst 2 is a platinum rhodium-based reduction catalyst component supported on a carrier, and reduces nitrogen oxides such as nitrogen monoxide or nitrogen dioxide in exhaust gas for purification treatment. Is configured. In order to produce this nitrogen oxide purifying catalyst 2, an alumina coat layer is formed on a carrier in the same manner as in the above-mentioned oxidation catalyst 1, and then this alumina coat layer is impregnated with a platinum rhodium-based catalyst component. To do. The carrier amount of this catalyst component is about 1.6 to 3.0 g / carrier, and the ratio of platinum to rhodium is in the range of about 3: 1.

Further, the reducing component producing section 3 is one in which zinc is supported on a carrier, and this zinc reacts with sulfuric acid in the exhaust gas discharged from the oxidation catalyst 1 to generate hydrogen and zinc sulfate. Then, the hydrogen is used to make the exhaust gas a reducing atmosphere in an oxygen-lean state. This reducing component producing part 3 has about 82 g of zinc sulfate (ZnSO ₄ .7H
₂ O) is dissolved in about 180 cc of water and the foam type carrier with a capacity of about 0.5 to 1.0 is immersed in the solution, and the zinc sulfate is attached to the surface of the carrier, then at a temperature of about 150 ° C. Zinc is supported on the carrier by drying for about 30 minutes and baking at a temperature of about 500 ° C. for about 1 hour. The amount of zinc supported is about 2 to 10 wt% with respect to the carrier.

The exhaust gas purifying apparatus having the above-mentioned configuration supplies the sulfuric acid produced in the oxidation catalyst 1 to the reducing component producing part 3 and reacts this sulfuric acid with zinc carried by the carrier of the reducing component producing part 3 As shown in the following formula (1), hydrogen is generated to make the exhaust gas a reducing atmosphere.

H ₂ SO ₄ + Zn → ZnSO ₄ + H ₂ (1) Then, the exhaust gas containing hydrogen is supplied to the exhaust inlet 5 of the nitrogen oxide purifying catalyst 2 through the communication pipe 6.
Since the nitrogen oxide purification catalyst 2 is in a reduced state of oxygen lean state, it is possible to effectively reduce the nitrogen oxides in the exhaust gas for purification treatment in the low temperature region as shown in the following formula (2). it can.

NO + H ₂ → 1 / 2N ₂ + H ₂ O NO ₂ + 2H ₂ → 1 / 2N ₂ + 2H ₂ O (2) Next, the exhaust gas purifying apparatus of the present invention having the reducing component generation part 3 and the reducing component generation part An exhaust gas purification test performed to compare the performance with a conventional device that does not have the above will be described. The exhaust gas purifying apparatus of the present invention has a capacity of 1.0
The alumina coating layer was coated at a ratio of 21 wt% on the carrier and the catalyst component composed of palladium was 1.6 g.
The oxidation catalyst 1 supported at a ratio of /, the alumina coating layer was coated at a ratio of 21 wt% with respect to the carrier having a capacity of 1.0, and the catalyst component composed of platinum and rhodium at a ratio of 5: 1 was used as a carrier. On the other hand, a catalyst comprising a catalyst 2 for purifying nitrogen oxides, which is supported at a ratio of 2.0 g /, and a reducing component generator 3 in which 10 wt% of zinc is supported on a carrier having a capacity of 0.8 are used. did.

As the conventional device, the device of the present invention from which the reducing component producing section 3 is removed is used. The test gas introduced into both devices was a mixture of air-fuel ratio of 35 burned by an engine with a displacement of 2000cc.

Then, as a result of measuring the nitrogen oxide purification rate of the exhaust gas purifying apparatus according to the present invention and the conventional apparatus, the data as shown in FIG. 2 were obtained. From this data, it can be seen that the purification performance of the device of the present invention shown by line a is improved as compared with the conventional device shown by line b. In particular, it was confirmed that the purification performance of the device of the present invention was good in the region where the catalyst inlet temperature was about 400 ° C.

Next, the results of tests conducted under the temperature condition of 400 ° C. in order to select an appropriate value of the amount of zinc carried on the carrier of the reducing component producing part 3 will be shown. That is, as shown in FIG. 3, the purification performance of nitrogen oxides becomes good when the amount of zinc supported on the carrier is 2 wt% or more. Further, the amount of zinc peeled off can be suppressed to a small value by setting the amount of zinc supported on the carrier to 10 wt% or less, as shown in FIG. Therefore, the amount of zinc loaded on the carrier is 2-10 wt.
% Is preferable.

In the above embodiment, the nitrogen oxide purifying catalyst 2 and the reducing component generator 3 are installed in parallel, but both are arranged in series and the hydrogen produced in the reducing component generator 3 is exhausted through the exhaust passage. Alternatively, the nitrogen oxide purifying catalyst 2 may be directly supplied to the nitrogen oxide purifying catalyst 2. However, when the nitrogen oxide purifying catalyst 2 and the reducing component generator 3 are installed in series,
Since the back pressure of the engine increases and the output decreases, it is desirable to install both in parallel.

Further, when the nitrogen oxide purifying catalyst 2 and the reducing component generating part 3 are installed in parallel and only a part of the exhaust gas is introduced into the reducing component generating part 3, the reducing component generating Since the part 3 can be prevented from being excessively heated by the exhaust gas, there is an advantage that the function of the reducing component generating part 3 can be effectively prevented. That is,
The zinc sulfate attached to the carrier of the reducing component producing part 3 is
When the temperature is 740 ° C. or higher, zinc is oxidized to become zinc oxide, impairing the hydrogen generating action represented by the above formula (1), but when the introduction amount of exhaust gas is limited as described above, The reducing component generator 3 is 740 ° C due to exhaust gas
Since the heating above can be prevented, the hydrogen generating function can be maintained in a good state.

A radiating fin or the like may be provided upstream of the reducing component generator 3 to forcibly reduce the exhaust gas temperature to prevent the oxidation of zinc.

(Effects of the Invention) As described above, the present invention provides a reducing component generation part in which zinc is supported on the surface of a carrier, and hydrogen is generated by reacting sulfuric acid in the exhaust gas with the zinc. Since it is supplied to the exhaust gas inlet of the nitrogen oxide purifying catalyst, the nitrogen oxide purifying catalyst becomes a reducing atmosphere in an oxygen-lean state to effectively purify nitrogen oxides in a low temperature region. it can.

In addition, there is an advantage that the structure can be simplified without adopting a complicated structure such as a conventional device for adding a reducing substance such as water, and generation of rust and deterioration of the catalyst can be prevented.

[Brief description of drawings]

FIG. 1 is an overall schematic view showing an embodiment of an exhaust gas purifying device of the present invention, FIG. 2 is a graph showing the results of a purifying performance test of the above purifying device, and FIGS. 3 and 4 are zinc loading rates, respectively. It is a graph which shows the purification rate and the amount of exfoliation when it changes variously. 2 ... Nitrogen oxide purifying catalyst, 3 ... Reducing component generation unit,
4 ... Exhaust outlet, 5 ... Exhaust inlet.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiromi Oishi 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (56) References JP-A-49-131950 (JP, A) JP-A-49 -114571 (JP, A)

Claims (1)

(57) [Claims] 1. A catalyst for purifying nitrogen oxides, which comprises a reducing component generating part in which zinc is supported on the surface of a carrier, and an exhaust gas outlet of the reducing component generating part purifies nitrogen oxides under a reflux atmosphere. An exhaust gas purifying device, characterized in that it is connected to the exhaust inflow port.