JP3507538B2 - Exhaust gas purification catalyst and purification method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention relates to medium and purifying methods catalyst purification of exhaust gas, more particularly nitrogen oxides in the exhaust gas (NOx), the purification of carbon monoxide (CO) and ammonia (NH ₃₎ suitable for waste gas purification of catalysts and purification
Regarding the method .

[0002]

2. Description of the Related Art Nitrogen oxide (NOx) in combustion exhaust gas discharged from a boiler is a causative substance of photochemical smog and acid rain. Therefore, as a method of removing NOx, it was added to exhaust gas using a catalyst. A catalytic reduction method of selectively reducing with ammonia (NH ₃ ) is widely adopted. As the catalyst, various denitration catalysts based on titanium oxide, for example, a catalyst in which the catalyst component is formed into a honeycomb shape or a spherical shape, or a catalyst whose catalyst usage amount is reduced by coating the catalyst component on a ceramic honeycomb or a metal substrate Have been put into practical use (Japanese Patent Laid-Open No. 50-128681, Japanese Laid-Open Patent Publication No.
3-28148, JP-A-2-83086).

On the other hand, in recent years, not only NOx in the exhaust gas, and the reduction of unreacted NH ₃ outflow of the NH ₃ injected is obtained as removing or reducing agents CO in the exhaust gas simultaneously these components At the same time, the development of catalysts and purification methods for purifying is ongoing. For example, Japanese Patent Laid-Open No. 5-329334
Japanese Patent Laid-Open Publication No. 2003-242242 discloses a catalyst capable of removing NOx and CO and reducing the outflow amount of unreacted ammonia, specifically, silica or mordenite carrying platinum and a titanium oxide-based denitration catalyst component in combination. Other catalysts are disclosed.

[0004]

However, in the above catalyst, the removal reaction of NOx and NH ₃ is carried out by the reaction of the following formulas (1) and (2), and NH ₃ comes into contact with the platinum catalyst in the catalyst surface layer. As a result, the generated NO is less likely to react with the residual NH ₃ because it is oxidized to generate NO, and as a result, the NO concentration in the exhaust gas is not lowered and the denitration performance is deteriorated. . NO + NH ₃ + 3/4 O ₂ → N ₂ + 3/2 H ₂ O (1) NH ₃ + 5/4 O ₂ → NO + 3/2 H ₂ O (2)

That is, NOx in the exhaust gas becomes N ₂ and H ₂ O in the reaction of the formula (1) by the titanium oxide type denitration catalyst component in the catalyst in the presence of NH ₃ as a reducing agent. On the other hand, unreacted NH ₃ not used in the reaction of the formula (1)
Is oxidized to NO by the formula (2) in the presence of a platinum catalyst in the catalyst. The generated NO is brought into contact with the denitration catalyst particles adjacent to the platinum catalyst particles and the remaining NH ₃ to become N ₂ and H ₂ O by the reaction of the formula (1), and as a result, unreacted N 3
The amount of H ₃ flowing out of the system will be reduced. However, in the above-mentioned conventional catalyst in which a mixture of a platinum catalyst and a denitration catalyst component is molded or coated on a substrate, NH ₃ comes into contact with the platinum catalyst on the catalyst surface to generate NO on the catalyst surface, It is considered that this NO reduces the chances of contacting the remaining NH ₃ with the reaction of the above (1) to reduce the denitration rate.

An object of the present invention shows the above-mentioned solution to the problems of the prior art, a small amount of catalyst used, Kiyoshi exhaust gas to a reduction in the outflow of removal and unreacted NH ₃ in NOx and CO can be efficiently and to provide a reduction catalytic and purification method.

[0007]

The inventions claimed in this application are as follows. (1) on a metal substrate, a nitrogen acid which is characterized in that the platinum component layer and the denitration catalyst component layer is sequential carried from the metal substrate
Products, waste gas <br/> purification of catalysts containing carbon monoxide and ammonia. (2) The denitration catalyst component according to (1) is characterized in that it is a mixture of titanium oxide, molybdenum oxide and vanadium oxide, a mixture of titanium oxide, tungsten oxide and vanadium oxide or a mixture of titanium oxide and vanadium oxide.
Nitrogen oxides, purification of catalytic material discharge <br/> gas containing carbon monoxide and ammonia. (3) Contains nitrogen oxide, carbon monoxide and ammonia
Exhaust gas purification method that purifies the exhaust gas in the presence of a catalyst
Therefore, as the catalyst, the purification according to (1) or (2)
A method for purifying exhaust gas, which comprises using a oxidization catalyst.

FIG. 1 is a schematic sectional view showing an example of an exhaust gas purifying catalyst of the present invention. In the figure, the exhaust gas-purifying catalyst 1 has a platinum particle layer 3 and a denitration catalyst particle layer 4 in this order on a metal substrate 2. NOx in the exhaust gas first contacts the denitration catalyst particle layer 4 on the catalyst surface and reacts with NH ₃ to become N ₂ and H ₂ O. Since the denitration catalyst particle layer 4 has no platinum particles, NH ₃ is not oxidized to NO. The unreacted NH _{3 that} has not reacted with NOx diffuses inside the denitration catalyst particle layer 4 and comes into contact with the platinum particle layer 3 to generate N.
Oxidized to O. The generated NO reacts with the remaining NH _{3 in} contact with the denitration catalyst particles adjacent to the platinum particles, and N ₂
And H ₂ O. On the other hand, since CO in the exhaust gas has a property of easily diffusing in the catalyst, it is quickly contacted with the platinum oxidation catalyst component 3 and is oxidized to CO ₂ .

As described above, in the exhaust gas purifying catalyst of the present invention, unlike the conventional catalyst, the platinum particles do not appear on the catalyst surface, and NH ₃ is not oxidized to NO in the catalyst surface layer. However, it is possible to obtain a high denitration rate without being discharged to the outside of the system as it is, and moreover, CO in the exhaust gas can be easily oxidized and the outflow amount of unreacted NH ₃ can be greatly reduced. Further, the exhaust gas purifying catalyst of the present invention,
Since it can be obtained by thinly coating each catalyst component on a metal substrate, the amount of catalyst used can be reduced. For example, when the expanded metal is coated, the amount of the catalyst used can be reduced to 1/10 or less, which is economically superior to the conventional plate-shaped catalyst in which the openings of the expanded metal are filled with the catalyst.

The metal substrate used in the present invention is not particularly limited, and any of stainless steel, mild steel and the like can be used, and the shape thereof can also be any of flat plate, net, expanded metal and the like. A metal substrate having a rough surface formed by subjecting the metal surface to a metal spray treatment with aluminum or the like is preferable because the contact between the metal surface and the catalyst is strengthened, the catalyst surface area is increased, and the activity is improved. The platinum component layer in the present invention is, for example, a chloride of platinum, a metal substrate is immersed in an aqueous solution dissolved in the form of a soluble salt such as nitrate or an amine complex, or the aqueous solution is applied to the metal substrate, and the metal surface is coated on the metal surface. It is obtained by carrying out ion exchange of platinum, supporting it, and drying.

The denitration catalyst component in the present invention is a mixture of titanium oxide, molybdenum oxide and vanadium oxide, a mixture of titanium oxide, tungsten oxide and vanadium oxide or an oxide, from the viewpoints of activity, dispersibility and peel strength of the catalyst component. A mixture of titanium and vanadium oxide is used.
For the denitration catalyst component layer, for example, a mixed powder of the above oxide is suspended in water to form a slurry, which is applied onto a metal substrate having the above platinum component layer to support it to a thickness of several tens of μm, and then a known method is used. It is obtained by drying and baking by the method of.

[0012]

EXAMPLES The present invention will be described in detail below with reference to examples. Example 1 1 m of SUS304 expanded metal with a thickness of 0.2 mm
² is immersed in an aqueous solution of chloroplatinic acid having a concentration of 20 mg / l,
Platinum was ion-exchanged and supported on the surface of the expanded metal. This substrate was washed with water and dried to give a catalyst substrate. To 50 kg of metatitanic acid containing 30% by weight of titanium oxide, 3.81 kg of ammonium molybdate and 1.04 kg of ammonium metavanadate are added and kneaded by heating with a kneader,
A paste having a water content of 35% by weight was obtained. This paste was granulated by an extrusion granulator, dried, and calcined at 550 ° C for 2 hours.
100 granules 90 of the obtained granules with a hammer hull
Crushed to over%. Water (4.6 kg) was added to and suspended in 5.4 kg of this powder to obtain a slurry of a denitration catalyst. The platinum-supported substrate was immersed in this slurry to remove excess slurry, dried and calcined at 500 ° C. for 2 hours to obtain a catalyst having a supported amount of 150 g / m ² .

Example 2 The same as Example 1 except that the aqueous solution of chloroplatinic acid was applied to the expanded metal, dried and then baked at 500 ° C. for 2 hours to support platinum on the expanded metal. A catalyst was prepared by the method. Example 3 A catalyst was prepared in the same manner as in Example 2 except that an aqueous dinitrodiammine platinum solution was used instead of the chloroplatinic acid aqueous solution. Example 4 In Example 2, SU in which aluminum was sprayed at 50 g / m ² instead of the SUS304 expanded metal
A catalyst was prepared in the same manner as in Example 2 except that the expanded metal manufactured by S304 was used.

Comparative Example 1 To 5 kg of silica powder was added an aqueous solution of chloroplatinic acid in which 6.64 g of chloroplatinic acid was dissolved in 8 l of water, and the mixture was stirred with heating to obtain silica powder carrying chloroplatinic acid. The silica powder carrying chloroplatinic acid was dried and then calcined at 500 ° C. for 2 hours to obtain silica carrying 0.05% of platinum. The silica powder supporting 0.05% of platinum and the powder of the denitration catalyst composed of the oxides of titanium, molybdenum and vanadium used in Example 1 were mixed at a weight ratio of 2:98 and mixed with water. Was added, and the mixture was stirred and suspended to obtain a catalyst slurry. A 0.2 mm-thick SUS304 expanded metal was immersed in this slurry, and the catalyst substrate was dried and calcined in the same manner as in Example 1 to obtain a catalyst having a catalyst loading of 150 g / m ² .

<Test Example> Exhaust gas treatment was performed using each of the catalysts obtained in Examples 1 to 4 and Comparative Example 1, and N
The removal rate of O, the removal rate of CO, and the outflow amount of NH ₃ were examined. The exhaust gas components and treatment conditions used are shown in Table 1,
The obtained results are shown in Table 2.

[Table 1]

[0016]

[Table 2]

From Table 2, platinum is supported on a metal substrate,
The catalyst having a structure in which a thin layer of the denitration catalyst is coated thereon (Examples 1 to 4) has the same NH as that of the catalyst coated with the platinum-supported silica and the denitration catalyst component (Comparative Example 1). _It can be seen that the decomposition rate is ₃ and the denitrification rate is much higher than that of a catalyst obtained by simply mixing platinum-supported silica and a denitration catalyst component and coating the mixture.

[0018]

EFFECT OF THE INVENTION Exhaust gas purifying catalyst and purifying method of the present invention
According to the method , since the oxidation reaction of NH ₃ to NO does not occur in the surface layer of the catalyst, and after the unreacted NH ₃ is oxidized to NO by the platinum particles on the substrate surface, the NO is adjoined to the NOx removal catalyst. Since it reacts with the residual NH ₃ to form N ₂ and H ₂ O above, it does not deteriorate the denitration performance, and the unreacted NH
The outflow amount of ₃ can be reduced. Also, C in the exhaust gas
O is also oxidized and removed by CO ₂ due to the platinum component in the catalyst. Therefore, the denitration apparatus using the catalyst of the present invention can suppress outflowing NH ₃ at low cost and can achieve a high denitration rate and CO removal. It is possible to reduce the or catalytic amount, excellent economy.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an example of an exhaust gas purifying catalyst of the present invention.

[Explanation of symbols]

1 ... Exhaust gas purifying catalyst, 2 ... Metal substrate, 3 ... Platinum particle layer, 4 ... Denitration catalyst particle layer.

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B01J 21/00-38/74 B01D 53/00-53/96

Claims (3)

(57) [Claims] To 1. A metal substrate, <br/> containing nitrogen oxides, characterized in that the platinum component layer and the denitration catalyst component layer is sequential carried from the metal substrate, the carbon monoxide and ammonia exhaust gas for purification of catalysts. 2. The denitration catalyst component according to claim 1, which is a mixture of titanium oxide, molybdenum oxide and vanadium oxide, a mixture of titanium oxide, tungsten oxide and vanadium oxide or a mixture of titanium oxide and vanadium oxide. Nitrogen oxides, carbon monoxide and ammonia
Waste gas purification of catalysts containing. 3. Nitrogen oxides, carbon monoxide and ammonia
Exhaust gas purification that purifies exhaust gas containing a in the presence of a catalyst
The method of claim 1, wherein the catalyst is used as the catalyst.
Exhaust gas purification characterized by using the purification catalyst described in 2.
Method.