JPH07102323B2 - Catalyst for removing carbon monoxide or carbon monoxide and nitrogen oxides in exhaust gas - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a catalyst for removing carbon monoxide (CO) or carbon monoxide (CO) and nitrogen oxides (NOx) in exhaust gas, and in particular, The present invention relates to a catalyst suitable for reducing CO in an exhaust gas containing oxygen or simultaneously reducing CO and NOx.

[Background of the Invention]

The combustion exhaust gas discharged from the boiler and the gas turbine contains a large amount of NOx and CO, which causes air pollution, which is a serious problem for environmental protection.

As a method for removing NOx in exhaust gas, a specific selective catalytic reduction method using hydrocarbon, carbon monoxide or hydrogen as a reducing agent is known, but in the case of exhaust gas containing oxygen, this method is used. Until NO is consumed for CO oxidation
Since the reduction reaction of x does not proceed, application to oxygen-containing exhaust gas is practically impossible. On the other hand, the selective catalytic reduction method using NH ₃ as a reducing agent is the most effective method for removing NOx in exhaust gas because NH ₃ selectively reacts with NOx. Various catalysts showing high activity for the reaction have been studied, and Ti
Ti-based catalysts such as O ₂ / V ₂ O ₅ and TiO ₂ / M ₀ O ₃ , or mordenite-based catalysts obtained by substituting mordenite with a metal (JP-A-51-
69476) has been developed and put into practical use.

Regarding removal of CO in exhaust gas, it is known that a noble metal catalyst such as Pt exhibits high activity as a catalyst for purifying automobile exhaust gas. However, a catalyst that removes CO and NOx at the same time has not been put into practical use, and by combining a Pt-based catalyst with the above denitration catalyst, CO and NOx in exhaust gas are removed at the same time. This method has a high catalyst cost and cannot be practically applied to the treatment of a large amount of exhaust gas such as boiler exhaust gas.

Therefore, for a large amount of exhaust gas sources such as boilers,
A low-cost catalyst that can simultaneously remove CO and NOx is desired.

[Object of the Invention]

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and provide a low-cost catalyst that can efficiently remove CO and NOx in exhaust gas at the same time.

[Outline of Invention]

In the method of reducing NOx using CO as a reducing agent, the reaction proceeds when oxygen does not coexist, and CO becomes harmless CO ₂ and NOx
Becomes N ₂ , but in the coexistence of oxygen, CO
It is known that NOx reduction does not proceed by reacting with O ₂ .

Therefore, as a method for simultaneously removing CO and NOx, the present inventors selectively react with NOx for removal of NOx.
NH ₃ is injected and added as a reducing agent to make NOx harmless N ₂ .
On the other hand, for removal of CO, CO and O ₂ contained in exhaust gas
Consider a method of making harmless CO ₂ by reacting
We searched for a catalyst with high activity in both of these reactions. As a result, it is a hydrogen substitution product of mordenite, and is SiO ₂ / Al ₂ O ₃
With respect to mordenite having a molar ratio of 10 or more, a catalyst in which a part or all of hydrogen in the mordenite is replaced with copper or copper is carried is active in both CO removal and NOx removal reactions and particularly CO removal. Regarding the rate, the amount of injected NH ₃ and the N in the exhaust gas
The present invention has been achieved by finding that a high value is exhibited regardless of the ratio with O (NH ₃ / NO).

In the present invention, the hydrogen substitution product of mordenite is obtained by a known method from synthetic mordenite or naturally occurring mordenite ore. This hydrogen substitution product of mordenite has a composition represented by H ₂ · Al ₂ O ₃ · nSiO ₂ —xH ₂ O, and n in this composition is often 10 in pure mordenite. ₂ minutes a lot. In the case of mordenite having a relatively low SiO ₂ content, naturally occurring mordenite ore or synthetic mordenite is treated with a mineral acid such as hydrochloric acid, sulfuric acid or nitric acid, or an organic acid such as oxalic acid, acetic acid or ethylenediaminetetraacetic acid. The SiO ₂ / Al ₂ O ₃ molar ratio can be adjusted by removing an appropriate amount of Al ₂ O ₃ in mordenite.

In the present invention, the SiO ₂ / Al ₂ O ₃ molar ratio needs to be 10 or more. If this molar ratio is 10 or more,
Even if SOx is contained, the removal rate of CO and NOx is high, but if the molar ratio is smaller than 10, the catalyst deteriorates due to SOx in the exhaust gas, making it difficult to maintain the catalyst activity at a high level for a long period of time. Become.

Next, the present invention is a Sio ₂ / Al ₂ O ₃ molar ratio is a certain mordenite hydrogen part or all of the hydrogen is replaced with Cu or mordenite Cu
Is carried. Mordenite catalysts substituted with Fe, Co, and Ni are active in the denitration reaction, but not in the CO oxidation reaction. In the mordenite catalyst with Cu substituted or supported, the denitration reaction and CO oxidation reaction proceed simultaneously,
High activity for both NOx removal. Cu for mordenite
To replace or carry Cu, ion exchange method, impregnation method,
A method such as a kneading method can be adopted. Compounds used at this time include copper nitrate, sulfate, chloride,
Examples thereof include oxalate.

In the present invention, the amount of Cu substituted or supported in the mordenite is preferably 0.1 atom to 10 atoms with respect to the Si atom of the mordenite. If the amount of Cu is within this range, both the CO removal rate and the NOx removal rate in the exhaust gas can be increased.

When treating the exhaust gas using the catalyst of the present invention, the reaction temperature is preferably 350 to 450 ° C. From the exhaust gas
When removing only CO, the higher the reaction temperature from 350 ℃, the higher the CO removal rate.
At the same time, when removing NOx, the NO removal rate decreases from around 450 ° C, so 350 to 450 ° C is desirable.

The amount of NH ₃ injected into the exhaust gas is preferably such that the molar ratio of NH ₃ / NO to NO in the exhaust gas is 1.0 or less. NH ₃
If the molar ratio of / NO exceeds 1.0, the N ₂ O production rate tends to increase as the reaction temperature increases.

Example of Invention

Example 1 Hydrogen-substituted mordenite SiO ₂ / Al _{2 as} mordenite
Using O _{3 having} a molar ratio of 30, stir-suspend in a 3% copper nitrate solution for about 5 hours to replace H in mordenite with Cu, and then wash with ion-exchanged water, Cu-substituted mordenite powder Got A molding aid and water were added to this powder and kneaded, and a 6φ round bar was extruded.
This molded product was calcined at 500 ° C. for 2 hours and then sized to 10 to 20 mesh to obtain a test catalyst. The amount of copper supported on this catalyst was 0.2 atom based on 1 Si atom in mordenite. The CO removal rate of this catalyst was measured under the reaction conditions shown below.

SV: 80,000 ^-1 Temperature: 250 to 400 ° C. Gas _{composition: CO: 1% CO 2:} 10% O 2: 10% N 2: shows the temperature characteristics of the remaining CO removal rate in the first FIG. Under this condition, the CO removal rate showed a high value at 350 ° C. or higher, and the catalyst according to this example exhibited a very high activity for the CO oxidation reaction.

Example 2 The same test catalyst as in Example 1 was used, and the CO removal rate and NOx removal rate were measured under the reaction conditions shown below.

SV: 150,000h ^-1 Temperature: 200 to 500 ° C. Gas composition: NO: 200ppm CO: 12% CO: 500ppm H 2 O: 12% O 2: 10% NH 3: 240ppm N 2: the remaining CO removal rate, NO The removal rate and the N ₂ O production rate are shown in FIG. N
The O 2 removal rate showed a high value from the reaction temperature of 200 ℃ to 450 ℃, but under the condition of NH ₃ / NO molar ratio of 1.2, the formation of N ₂ O was observed in the temperature range above 350 ℃. Also, when the temperature rises above 450 ° C
It was found that the NO removal rate was decreasing. On the other hand, the CO removal rate increases from a reaction temperature of about 350 ° C,
It became clear that the oxidation reaction of O proceeded. From the results of the above temperature characteristics, it was found that the reaction temperature between 350 ° C. and 450 ° C. is most effective for simultaneously removing CO and NOx.

Example 3 test catalyst using the same as in Example 1, the same except that the reaction conditions were 1.0 mole ratio of NH ₃ / NO and the concentration of NH ₃ and 200ppm and conditions of Example 1 As a result, the removal rates of CO and NO were measured. The results are shown in FIG. The CO and NO removal rates were the same as in Example 2, and good results were obtained. In addition, in the case of this Example, the NH ₂ / NO molar ratio was 1 or 2, compared to the case of N ₂ O. The production amount of was decreased. Thus injection of NH ₃ is required to be a molar ratio of NH ₃ / NO is applied at 1.0 or less.

Example 4 A catalyst was prepared in the same manner as in Example 1 except that the SiO ₂ / Al ₂ O ₃ molar ratio of 30 in Example 1 was changed to 10. The amount of copper supported on this catalyst was 1.2 atoms with respect to 1 Si atom in mordenite.

Example 5 A catalyst was prepared in the same manner as in Example 1 except that the SiO ₂ / Al ₂ O ₃ molar ratio of 30 in Example 1 was changed to 20. The amount of copper supported on this catalyst was 0.8 atom with respect to the Si atom in mordenite.

Comparative Example 1 A catalyst was prepared in the same manner as in Example 1 except that the SiO ₂ / Al ₂ O ₃ molar ratio of 30 in Example 1 was changed to 5. The amount of copper supported on this catalyst was 1.5 atoms with respect to 1 Si atom in mordenite.

Regarding each catalyst of Examples 1 and 4.5 and Comparative Example 1, Example 1
500 ppm of SO ₂ was injected into the gas under the activity measurement conditions, and the change in the activity of the catalyst with time was measured. The results are shown in FIG. As shown in Fig. 4, SOx has a SiO ₂ / Al ₂ O ₃ molar ratio of 10 or more.
It was clarified that the decrease in activity due to

Comparative Example 2 A catalyst was prepared by kneading TiO ₂ powder with ammonium metavanadate so that the atomic ratio of Ti and V would be 3%.
CO and NO removal rates were measured under the same reaction conditions as above. The result is shown in FIG. In the case of this catalyst, as is clear from FIG. 5, the NO removal rate showed a high value, but it showed almost no activity against the CO removal reaction.

Comparative Example 3 TiO ₂ powder was mixed with copper nitrate to obtain an atomic ratio of Ti and Cu of 3%.
A catalyst was prepared so as to obtain, and CO and NO removal rates were measured under the same reaction conditions as in Example 1. The result is shown in FIG. As is clear from FIG. 5, this catalyst showed a high activity for the CO removal reaction, but had a very low activity for the NO removal reaction.

Comparative Example 4 The hydrogen of the hydrogen-substituted mordenite used in Example 1 was replaced with Fe to prepare an Fe-mordenite catalyst, and the CO and NO removal rates were measured under the same reaction conditions as in Example 1. The result is shown in FIG. As is clear from FIG. 5, this catalyst showed high activity for the NO removal reaction on the high temperature side (400 ° C. or higher), but showed almost no activity for the CO removal reaction.

Comparative Example 5 A Co-mordenite catalyst in which hydrogen in the hydrogen-substituted mordenite used in Example 1 was replaced with Co was prepared, and CO and NO removal rates were measured. The result is shown in FIG. As is clear from FIG. 5, this catalyst exhibited much lower activity than the catalyst shown in Example 1 for CO removal reaction and NO removal reaction.

Comparative Example 6 A Ni-mordenite catalyst in which hydrogen in the hydrogen-substituted mordenite used in Example 1 was replaced with Ni was prepared, and CO and NO removal rates were measured. The result is shown in FIG. As is clear from FIG. 5, this catalyst showed almost the same low activity as the Co-mordenite catalyst shown in Comparative Example 5.

〔The invention's effect〕

As described above, according to the present invention, without using a noble metal such as Pt, CO in exhaust gas that does not contain NOx by an inexpensive catalyst composed of Cu-mordenite catalyst, or NOx in exhaust gas,
Even if it contains both CO, CO and NOx can be removed efficiently, and it is highly practical as a catalyst for treating a large volume of gas such as boiler exhaust gas. Further, since the SiO ₂ / Al ₂ O ₃ molar ratio of mordenite is selected to be 10 or more, CO or CO and NOx can be efficiently removed without degrading the catalyst for SOx-containing exhaust gas.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the reaction temperature and the CO removal rate of the catalyst of Example 1, and FIG. 2 is the NH ₃ /NO=1.2 in the catalyst of Example 1.
NH at the reaction temperature and the CO and NO removal rate, shows the relationship between the N ₂ O formation rate, FIG. 3 is the same catalyst as in Example 1 when the ₃ /
FIG. 4 is a diagram showing the relationship between the reaction temperature and the removal rates of CO and NO, and the production rate of N ₂ O when NO = 1.0. FIG. 4 shows SiO _{2 in} Cu-mordenite.
Fig. 5 is a diagram showing the relationship between the reaction time and the denitration rate of each catalyst with varying the / Al ₂ O ₃ ratio, and Fig. 5 shows the relationship between the reaction temperature, the NO removal rate, and the CO removal rate in catalysts other than Cu-mordenite. FIG.

Claims (2)

[Claims] 1. A hydrogen-substituted form of mordenite and having SiO ₂ / A
Carbon monoxide in exhaust gas, or carbon monoxide and nitrogen oxides in which a part or all of the hydrogen thereof is replaced with copper or supported on mordenite having a molar ratio of l ₂ O ₃ of 10 or more. Removal catalyst. 2. Copper is added to Si atoms in the mordenite.
The catalyst for removing carbon monoxide or carbon monoxide and nitrogen oxides in exhaust gas according to claim 1, wherein 0.1 to 10 atoms are added.