JP2000271445A - Method of cleaning nitrogen oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To safely and efficiently reduce nitrogen oxide to nitrogen in the presence of excess oxygen by bringing the nitrogen oxide-containing gas whose oxygen concentration is a specified value into contact with a catalyst that platinum group metal and alkali metal are co-deposited on alumina within the specified temperature range taking methanol as a reducing agent. SOLUTION: After nitrogen oxide is adsorbed by adsorbent in the presence of excess oxygen, the nitrogen oxide is desorbed in inert gas atmosphere of oxygen concentration of less than 0.5%. Next, while methanol is added as a reducing agent to the nitrogen oxide, the nitrogen oxide is brought into contact with a catalyst that platinum group metal and alkali metal are co-deposited on alumina at 220-300 deg.C, thereby effectively reducing the nitrogen oxide to nitrogen. At this time, it is preferable that the deposited quantity of the alkali metal is made 0.5 to 6 wt.% and the deposited quantity of the platinum metal is made 0.3 to 3 wt.% and the deposited quantity ratio of the alkali metal to the platinum metal is made 0.2 to 10. Further, it is preferable that the used platinum group metal is palladium and/or platinum, and the used alkali metal is potassium and/or sodium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is used in the field of purifying nitrogen oxides contained in the atmosphere or combustion gas.

[0002]

2. Description of the Related Art In recent years, with the expansion of industry, environmental pollutants discharged annually are steadily increasing. In particular, nitrogen oxides show a remarkable increase due to a sharp increase in automobile demand and an increase in the amount of burning oil and coal in power plants and factories.
As a global source of pollution, such as air pollution and acid rain, reducing its emissions has become an urgent issue.

One of the problems to reduce the emission of nitrogen oxides into the atmosphere is to purify the nitrogen oxides contained in the ventilation gas of urban automobile tunnels in order to prevent urban air pollution. Attention has been paid.

Heretofore, methods of adsorbing and removing nitrogen oxides contained in such ventilation gas with an adsorbent have been studied. As the adsorbent, activated carbon, zeolite, alumina and the like are known.
No. 82, JP-A-1-155934, JP-A-6
This is exemplified in JP-A-114268.

On the other hand, the adsorbed nitrogen oxides must be desorbed at regular intervals and then reduced to nitrogen. This method is disclosed in Japanese Patent Application Laid-Open No. Hei 5-337339. SCR (Selective Catalytic Reductio) for large facilities such as thermal power plants
The method referred to as the n) method, that is, a method in which ammonia is added as a reducing agent in an atmosphere coexisting with oxygen, and selective reduction to nitrogen on a denitration catalyst is most widely studied.

As other methods, there are known a method of reducing nitrogen oxides by reaction with ammonia on a specific activated carbon fiber (JP-A-6-79176) and a method of irradiating an electron beam after adding ammonia. Have been.

However, the use of ammonia as a reducing agent has a safety problem as a method for reducing nitrogen oxides in tunnel ventilation gas in urban areas, and a safer and more efficient denitration method is required.

On the other hand, performing the step of desorbing nitrogen oxides in an inert gas atmosphere (to avoid depleting the adsorbent) is exemplified in, for example, JP-A-6-15136. However, also in this case, the desorbed gas containing nitrogen oxides is treated by a conventional denitration apparatus, so that oxygen or air is mixed again or ammonia is added again.

[0009]

The problem to be solved by the present invention is to provide a method for purifying nitrogen oxides, which safely and efficiently reduces nitrogen oxides in the presence of excess oxygen to nitrogen. is there.

[0010]

Means for Solving the Problems The present inventors have intensively studied to solve these problems, and as a result, after adsorbing nitrogen oxides in the presence of excess oxygen with an adsorbent, the oxygen concentration was 5,000 pP.
Desorption of nitrogen oxides under an inert gas atmosphere of pm or less,
Then, while adding methanol as a reducing agent, the catalyst is brought into contact with a catalyst in which a platinum group element and an alkali metal are co-supported on alumina at 220 ° C. or higher, so that nitrogen oxides can be safely and efficiently reduced to nitrogen. They found what they could do and completed the present invention.

That is, the present invention relates to (1) a catalyst comprising a nitrogen oxide-containing gas having an oxygen concentration of less than 0.5% and a platinum-group metal and an alkali metal co-supported on alumina using methanol as a reducing agent. And 220-300
C., a method for purifying nitrogen oxides that reduces nitrogen oxides to nitrogen by contacting at

(2) The amount of alkali metal carried is 0.5 to 6
% By weight, the supported amount of platinum group metal is 0.3 to 3% by weight, and the supported ratio of alkali metal / platinum group metal is 0.2 to 10%.
(1) The method for purifying nitrogen oxides according to (1),

(3) The method for purifying nitrogen oxides according to (1) or (2), wherein the platinum group metal is palladium and / or platinum, and the alkali metal is potassium and / or sodium.

(4) The nitrogen oxide-containing gas is obtained by adsorbing nitrogen oxide in an excess oxygen atmosphere and then desorbing it in an inert gas atmosphere. And the method for purifying nitrogen oxides described above.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The term "nitrogen oxide" as used in the present invention refers to nitric oxide, nitrogen dioxide and nitrous oxide. Nitric oxide is the most important and important reduction target near the emission source of combustion gas, and nitrogen dioxide is an air pollutant whose concentration in the atmosphere is always monitored. Nitrous oxide is the nitrogen oxide that has the greatest effect on global warming. The present invention is intended for those containing one or more of these, and has excellent reduction purification properties for any nitrogen oxide.

According to the purification method of the present invention, the concentration of nitrogen oxides in the nitrogen oxide-containing gas ranges from a low concentration of 1 ppm or less to 10 ppm.
It can be applied in a wide range up to a high concentration of 00 ppm or more. As such a nitrogen oxide-containing gas, a gas in the air atmosphere containing, for example, about 0.05 to 10 ppm of nitrogen oxide (eg, a tunnel ventilation gas for automobiles, a roadside atmosphere of an urban road, etc.) is passed through an adsorbent. After adsorbing nitrogen oxides, nitrogen oxides are desorbed by passing an inert gas such as nitrogen under heating.

The nitrogen oxide-containing gas to be treated here must be an inert gas atmosphere containing no oxygen or containing oxygen at a certain concentration or less. Oxygen contained therein must be less than 5000 ppm, more preferably 3000 ppm.
ppm or less, particularly preferably 1000 ppm or less. When the oxygen concentration is 5000 ppm or more, the efficiency of reducing nitrogen oxides to nitrogen in the present invention decreases.

In the present invention, the method for reducing nitrogen oxides to nitrogen requires the use of methanol as a reducing agent and the use of a catalyst in which a platinum group metal and an alkali metal are co-supported on alumina as a catalyst. Is what you do. As a reducing agent, ethane other than alcohols, propane, butane and other saturated hydrocarbons, and ethylene, propylene, and hydrocarbons containing double bonds such as butylene, etc., can be used to convert nitrogen oxides to nitrogen with high efficiency. Not effective for reduction.

In the present invention, when a lower alcohol other than methanol, such as ethanol, is used as a reducing agent, it is not effective because problems such as a high reduction temperature and formation of nitrous oxide occur. Further, the amount of the reducing agent to be used is preferably an amount calculated from the amounts of the nitrogen oxide and the oxygen contained by using the equations (1), (2), (3) and (4), respectively.

[0020] _{6NO + 2CH 3 OH → 3N 2} + 2CO 2 + 4H 2 O (1) 6NO 2 + 4CH 3 OH → 3N 2 + 4CO 2 + 8H 2 O (2) 3N 2 O + CH 3 OH → 3N 2 + CO ₂ + 2H ₂ O (3) 3O ₂ + 2CH ₃ OH → 2CO ₂ + 2H ₂ O (4)

On the other hand, it is necessary to use a catalyst in which a platinum group metal and an alkali metal are co-supported on alumina. Here, palladium or platinum is particularly effectively used as the platinum group metal, and potassium or sodium is particularly effectively used as the alkali metal. On the other hand, when only one of the two metals is supported alone,
Nitrous oxide is produced from nitric oxide and nitrogen dioxide,
Highly efficient reduction to nitrogen is not achieved.

The loading amount of a platinum group metal such as palladium is preferably from 0.3 to 3% by weight, more preferably from 0.5 to 2% by weight. The loading amount of alkali metal such as potassium is preferably 0.5 to 6% by weight, more preferably 0.8 to 4% by weight. If the loading amount is out of the above range, the reduction efficiency of nitrogen oxides decreases and the cost increases.

The alkali metal / platinum group metal loading ratio is preferably from 0.2 to 10, more preferably from 0.3 to 10.
5 If the loading ratio is out of this range, there arises a problem that the efficiency of reducing nitrogen oxides to nitrogen is reduced and that the reduction temperature is increased.

In the present invention, porous alumina (activated alumina) is the most effective as a carrier for co-supporting such a metal among inorganic porous materials, particularly from the efficiency of reduction to nitrogen. Although the surface area and pore size of the porous alumina are not particularly limited, for example, the specific surface area is 100 to 300 m ² /
g, and those having a pore diameter of 2 to 3 nm are used.

A denitration method for reducing nitrogen oxides to harmless nitrogen using alcohol as a reducing agent has been described in, for example, JP-A-6-47255, JP-A-8-150324, and JP-A-8-266868. Is disclosed. In JP-A-6-47255, a proton-type zeolite, alumina and alumina supporting a fourth-period transition metal are used as a catalyst. In JP-A-8-150324, a lower alcohol other than methanol is used as a preferable alcohol. I have.

In Japanese Patent Application Laid-Open No. 8-266868,
First, nitric oxide is oxidized to nitrogen dioxide by adding an oxidation catalyst or ozone, and then a reducing agent such as hydrocarbon or alcohol is added, and Al ₂ O ₃ , SiO ₂ , ZrO ₂ , T
By contacting one or more kinds of carriers selected from the group consisting of iO ₂ and zeolite with a denitration catalyst containing a compound of one or more kinds of metals selected from the group consisting of Ni, Zn, Mn, In, and Ag. It has been proposed to reduce nitrogen oxides to nitrogen.

In any case, the nitrogen oxide in the presence of excess oxygen is oxidized to nitrogen or directly to nitrogen dioxide and then reduced to nitrogen. Compared with the purification method of the present invention, nitrogen oxide is converted to nitrogen. The reduction efficiency is low or higher temperatures are required. The reduction temperature in the present invention is 220 ° C. or higher, preferably 220 to 300 ° C., and more preferably 230 to 280 ° C. If the temperature is lower than 220 ° C., the reduction efficiency decreases.

[0028]

The present invention will be further described with reference to examples. (Reference Example 1) FIG. 1 is a schematic view of an experimental apparatus (fixed-bed denitration reaction apparatus) for performing a nitrogen oxide purification test used in this example. In FIG. 1, (1) is a component gas supply section (raw material gas, helium gas base) prepared in advance with a known concentration, (2) is an electronically controlled gas mixer (including a water addition section), and (3) is Heating device, (4) reactor, (5) gas analyzer (measurement components are NOx, NO, N ₂ O, N ₂ , CO
₍₂ , CO, hydrocarbon, oxygen), (6) represents a bypass line for reference.

A mixed gas containing each component gas at a predetermined concentration was prepared by mixing a plurality of raw material gases (manufactured by Nippon Sanso Corporation) adjusted to an appropriate concentration using helium as a balance gas by an electronic control unit. The entire system was replaced with helium gas in advance, and it was confirmed before each experiment that there was no stagnation of unreplaced gas inside or no inflow of air from outside. The concentration on the inlet side was measured using a bypass line before and after the experiment. The temperature of the reaction section was controlled by a thermocouple set in the filled carbon material.
The gas composition in the mixed gas was analyzed by the following method.

(Gas analysis method) Nitrogen dioxide and nitric oxide: normal pressure chemiluminescence NOx
Total (produced by Horiba, PG-250) Nitrous oxide and carbon dioxide: non-dispersive infrared spectrometer (produced by Horiba, VIA-510)

Carbon monoxide: Non-dispersive infrared analyzer (PG-250, manufactured by Horiba, Ltd.) Hydrocarbon: Flame ionization analyzer (F, manufactured by Horiba, Ltd.)
IA-510) Oxygen: Electrochemical cell type trace oxygen meter (Moritz, EC
-180)

Example 1 Alumina having a specific surface area of 182 m ² / g and a pore diameter of 12.9 nm was immersed in an aqueous solution of palladium chloride (0.1 mol / L), and dried at 80 to 200 ° C. A supported alumina was prepared. This was further immersed in an aqueous potassium hydroxide solution (8 mol / L), and dried at 120 ° C. to obtain a palladium-potassium co-supported alumina having a palladium loading of 1.3% by weight and a potassium loading of 3.0% by weight. (Pd-K-Al2O
3) was prepared.

The obtained Pd-K-Al ₂ O ₃ was dried at 120 ° C. for 2 hours and charged in a fixed-bed flow type denitration reaction apparatus shown in FIG. Subsequently, helium substitution was performed, and it was confirmed that the detection of nitrogen was 0 ppm on both the entrance side and the exit side. The filling amount (dry weight) of Pd-K-Al ₂ O ₃ is 27
6.0 g, and the bulk density at the time of filling were 0.92 g / cm ³ .

The temperature of the filling section was set to 28 under the flow of helium gas.
After heating to 0 ° C., a mixed gas obtained by adding methanol at a flow rate of 0.040 cm ³ / min to a gas containing NO = 1000 ppm was passed at F = 50 L / min. Here, W / F =
0.33 g · s · cm ⁻³ and SV (space velocity) = 100
00h ^-1 . The concentration of each component on the outlet side is stable,
NO = 0 ppm, N ₂ = 495 pp on average for 5 hours
m, CO ₂ = 395 ppm. Other components such as nitrous oxide were not observed.

From the above results, it was shown that in this example, 100% of the nitric oxide was removed and 99% of the nitric oxide was reduced to nitrogen. Also, if methanol is 10
From the fact that 0% was consumed, it was estimated that the removal of nitric oxide in this example was mainly due to the reduction reaction of nitric oxide to nitrogen according to the reaction formula (1). In this example, 1% of nitric oxide was removed in addition to the reduction to nitrogen, but it is considered that this was adsorbed on alumina.

Example 2 The reaction temperature was 250 ° C., the composition of the mixed gas was NO = 1000 ppm, and O ₂ = 1.
000 ppm and the amount of methanol added is 0.08
A nitric oxide purification test was performed in the same manner as in Example 1 except that the flow rate was 7 cm ³ / min. The concentration of each component on the outlet side is
NO = 0 ppm, N ² = 498 ppm, CO ₂ = 970p
pm, hydrocarbons = 40 ppm, and no other components such as nitrous oxide were observed.

According to the above results, in this embodiment, oxygen is 10
Even in the presence of 00 ppm, 100% of nitric oxide was removed, and the amount of generated nitrogen showed that 99.6% of nitric oxide was reduced to nitrogen. The oxygen concentration decreased by 96%.

Example 3 The amount of Pd-K-Al ₂ O ₃ was 139.13 g, the reaction temperature was 280 ° C., the composition of the mixed gas was NO = 1000 ppm, and O ₂
= 1000 ppm, and the amount of methanol added is 0.1 ppm.
077 cm ³ / min, W / F = 0.17 g · s
A nitrogen monoxide purification test was performed in the same manner as in Example 1 except that cm ⁻³ and SV = 20,000 h ⁻¹ .

The concentration of each component on the outlet side is NO = 0 ppm, N
₂ = 465 ppm, N ₂ O = 29 ppm, O ₂ = 40 pp
m, CO ₂ = 934 ppm, CO = 20 ppm, hydrocarbon = 19 ppm, and no other components were detected. From the above results, in this example, SV = 20,000.
Even at h ^-1 , 100% of nitric oxide was removed, and the amount of generated nitrogen showed that 93% of nitric oxide was reduced to nitrogen. The rate of change to nitrous oxide was about 6%.

Example 4 The amount of Pd-K-Al ₂ O ₃ charged was 70.69 g, the reaction temperature was 300 ° C., the composition of the mixed gas was NO = 1000 ppm, and O
₂ = 1000 ppm, the amount of methanol added is 0.087 cm ³ / min, W / F = 0.85 ×
A nitric oxide purification test was performed in the same manner as in Example 1 except that 10 ⁻² g · s · cm ⁻³ and SV = 40000 h ⁻¹ .

The concentration of each component on the outlet side is NO = 0 ppm, N
₂ = 488 ppm, N ₂ O = 10 ppm, O ₂ = 40 pp
m, CO ₂ = 910 ppm, CO = 10 ppm, hydrocarbon = 18 ppm, and no other components were detected. From the above results, it was found that 100% of nitric oxide was removed even at SV = 40,000h ⁻¹ ,
It was shown that 7.6% was reduced to nitrogen. The rate of change to nitrous oxide was 2%.

(Example 5) The amount of Pd-K-Al ₂ O ₃ charged was 450.0 g, the reaction temperature was 230 ° C., the composition of the mixed gas was NO = 2033 ppm, and methanol was added. A nitric oxide purification test was performed in the same manner as in Example 1 except that the amount was 0.060 cm ³ / min. The concentration of each component on the outlet side is NO = 0 ppm, N ₂
= 1015ppm, a CO ₂ = 545ppm, other components such as nitrous oxide was not observed. From the above results, it was shown that 100% of nitrogen monoxide was removed even at 230 ° C., and from the amount of generated nitrogen, 99.9% of nitrogen monoxide was reduced to nitrogen.

(Examples 6 and 7) The amount of palladium supported was 1.9% by weight and the amount of potassium supported was 0.8% by weight (Example 6). The supported amount was 2.0% by weight (Example 7), the reaction temperature was 250 ° C., the composition of the mixed gas was NO = 1000 ppm, O ₂ = 1000 ppm, and the amount of methanol added was 0.1 ppm. A nitric oxide purification test was performed in the same manner as in Example 1 except that the flow rate was 080 cm ³ / min.

The concentration of each component on the outlet side is NO = 0 ppm, N
₂ = 498 ppm, CO ₂ = 975 ppm (Example 6) and NO = 0 ppm, N ₂ = 490 ppm, CO ₂ = 900
ppm (Example 7), and no other components were observed. From the above results, in this example, nitric oxide was 1
00% was removed, indicating that 99.6% (Example 6) and 98.0% (Example 7) of the nitric oxide had been reduced to nitrogen.

Example 8 The reaction temperature was 250 ° C., the composition of the mixed gas was NO = 1000 ppm, and O ₂ = 1.
000 ppm and the amount of methanol added is 0.08
A nitric oxide purification test was performed under the same conditions as in Example 1 except that the reaction time was 0 cm ³ / min and the reduction reaction time was 160 hours.

The concentration of each gas component on the outlet side is NO = 0 pp
m, N ₂ = 480 ppm, N ₂ O = 14 ppm, CO ₂ =
It was 980 ppm, and no other components were observed. From the above results, in this example, 100% of nitric oxide was removed even after 160 hours, and 9% of nitric oxide was removed.
It was shown that 6.0% had been reduced to nitrogen. The change to nitrous oxide was about 3%.

Example 9 The reaction temperature was 280 ° C., the composition of the mixed gas was NO ₂ = 442 ppm, and O ₂ = 10
00 ppm, and the amount of methanol added is 0.08
A nitrogen dioxide purification test was performed in the same manner as in Example 1 except that the flow rate was 0 cm ³ / min. The concentration of each component on the outlet side is NO ₂ = 0 ppm, N ₂ = 219 ppm, N ₂ O = 0 pp
m, CO ₂ = 996 ppm, and no other products were observed.

From the above results, in this embodiment, 100% of nitrogen dioxide was removed, and 99.1% of nitrogen dioxide was removed.
% Was reduced to nitrogen. Since 100% of the methanol was also consumed, it was concluded that the removal of nitrogen dioxide was due to the reduction reaction to nitrogen according to the reaction formula (2).

Example 10 The reaction temperature was 250 ° C., the composition of the mixed gas was N ₂ O = 1000 ppm, and O ₂ =
1000 ppm, and the amount of methanol added is 0.1 ppm.
A nitrous oxide purification test was performed in the same manner as in Example 1 except that the density was 080 cm ³ / min. The concentration of each component on the outlet side is N ₂ O = 38 ppm, N ₂ = 960 ppm, CO ₂ =
980 ppm, and no other products were observed.

From the above results, it was shown that in this example, 96.2% of nitrous oxide was removed, and 96.0% of nitrous oxide was reduced to nitrogen. Since methanol was also consumed by 100%, it was concluded that the removal of nitrous oxide was due to the reduction reaction to nitrogen according to the reaction formula (3).

Example 11 Purification test of nitric oxide under the same conditions as in Example 2 except that alumina supporting 3.0% by weight of sodium and 1.3% by weight of palladium was used instead of potassium. Was done. The concentration of each component on the outlet side is NO = 0 ppm, N ₂ = 490 ppm, CO ₂ = 920
ppm and no other products containing nitrous oxide were observed.

From the above results, it was shown that in this example, 100% of nitrogen monoxide was removed and 98% of nitrogen monoxide was reduced to nitrogen. Since 100% of the methanol was consumed, it was concluded that the removal of nitric oxide in this example was due to the reduction reaction to nitrogen according to the reaction formula (1).

(Comparative Example 1) A nitric oxide purification test was performed in the same manner as in Example 1 except that alumina not subjected to a metal supporting treatment was used. The concentration of each component gas on the outlet side is NO = 950 ppm, N ₂ = 0 ppm, CO ₂ = 0 pp
m, hydrocarbon = 460 ppm, and no other products were observed. From the result of the concentration change of each component gas,
It was shown that nitric oxide was not reduced at all.

(Comparative Examples 2 and 3)
Nitrogen monoxide was prepared in the same manner as in Example 2 except that alumina supporting 9% by weight was used (Comparative Example 2), or alumina only supporting 3.1% by weight of potassium was used (Comparative Example 3). Was subjected to a purification test. In Comparative Example 2,
The concentration of each component on the outlet side is NO = 30 ppm, N ₂ = 380
ppm, N ₂ O = 90 ppm, and CO ₂ = 900 ppm.

In Comparative Example 3, NO = 675 ppm and N ₂ =
30 ppm, N ₂ O = 100 ppm, CO ₂ = 30 pp
m, hydrocarbon = 533 ppm, and no other products were observed. From the above results, in Comparative Example 2, 18% of the nitric oxide was changed to nitrous oxide, the reduction and purification of nitric oxide was insufficient, and in Comparative Example 3, the reduction of nitric oxide hardly occurred.

Comparative Example 4 A nitric oxide purification test was performed in the same manner as in Example 2 except that the reaction temperature was set to 200 ° C. The concentration of each component on the outlet side is NO = 0 ppm, N ₂ = 32
0 ppm, N ₂ O = 150 ppm, CO ₂ = 962 ppm
And no other products were observed. From the above results, in this comparative example, 30.0% of the nitric oxide was changed to nitrous oxide, and the reduction purification of nitric oxide was insufficient.

Comparative Example 5 A nitric oxide purification test was carried out in the same manner as in Example 2 except that 0.040 cm ³ / minute of ethanol was added instead of methanol. The concentration of each component on the outlet side is NO = 0 ppm, N ₂ = 370 ppm,
N ₂ O = 104 ppm, CO ₂ = 1030 ppm, CO =
15 ppm and hydrocarbons were 45 ppm. From the above results, in this comparative example, 21% of the nitric oxide was changed to nitrous oxide, and the reduction purification of nitric oxide was insufficient.

(Comparative Example 6) The amount of Pd-K-Al ₂ O ₃ charged was 407.1 g, the reaction temperature was 240 ° C., and 352 ppm of propylene was used instead of methanol.
A nitric oxide purification test was carried out in the same manner as in Example 2 except that the addition was carried out and that SV = 2000 h ^-1 .

The concentration of each component on the outlet side is NO = 0 ppm, N
₂ = 340 ppm, N ₂ O = 150 ppm, CO ₂ = 51
0 ppm, and no other products were observed.
From the above results, in this comparative example, 30% of the nitric oxide was changed to nitrous oxide, and the reduction purification of nitric oxide was insufficient.

Comparative Example 7 A zeolite supporting 1.7% by weight of palladium and 1.0% by weight of potassium instead of Pd-K-Al ₂ O ₃ (specific surface area: 260 m ² / g, pore diameter: 4.0 nm) ), The composition of the mixed gas is NO = 2
Example 2 except that 000 ppm, O ₂ = 1000 ppm, and the amount of methanol added = 0.11 cm ³ / min.
In the same manner as in the above, a purification test of nitric oxide was performed.

The concentration of each component on the outlet side is NO = 828 pp
m, N ₂ = 320 ppm, N ₂ O = 220 ppm, CO ₂
= 655 ppm, hydrocarbons = 205 ppm, and no other products were observed. From the above results, in this comparative example, only 36.6% of the nitric oxide was removed, and thus the reduction purification of the nitric oxide was insufficient.

[0062]

According to the present invention, the coexisting oxygen concentration is 5,000 pp.
m can be reduced to nitrogen at a high efficiency, for example, at a space velocity of 10,000 h -1 and a temperature of 250 ° C. at an efficiency of almost 100% at a high efficiency, for example, nitrogen gas in an inert gas atmosphere of not more than m.
No harmful ammonia or ozone is used in the purification process. INDUSTRIAL APPLICABILITY The present invention is particularly effective in purifying nitrogen oxide-containing gas obtained by adsorbing nitrogen oxide in the presence of excess oxygen onto an adsorbent and then heating and desorbing with an inert gas having an oxygen concentration of a certain concentration or less. .

[Brief description of the drawings]

FIG. 1 is a schematic view of a nitrogen oxide purification test apparatus used for a nitrogen oxide purification test.

[Explanation of symbols]

(1) a component gas supply section (raw material gas, helium gas base) prepared in advance with a known concentration, (2) an electronically controlled gas mixer (including a water addition section), (3) a heating device,
(4) is a reactor, (5) is a gas analyzer (measurement component is NO
_X , NO, N ₂ O, N ₂ , CO ₂ , CO, hydrocarbon, oxygen) and (6) are reference bypass lines.

Continuation of the front page (72) Inventor Michiya Nakajima 1-28-304 Osakidai, Sakura-shi, Chiba F-term (reference) 3G091 AB04 BA14 BA39 CA16 FB10 GA20 GB01X GB02W GB06W GB07W GB10X GB16X 4D048 AA06 AA07 AB02 AC09 BA03X BA14X BA30Y BA31X BA32Y BA33Y BA41X BB01 DA01 DA10 EA07 4G069 AA03 BA01A BA01B BB02A BB02B BB04A BB04B BC01A BC02A BC02B BC03A BC03B BC69A BC72A BC72B BC75A CA02 CA03 CA08 CA13 EA02Y EC03Y

Claims (4)

[Claims] 1. A catalyst comprising a nitrogen oxide-containing gas having an oxygen concentration of less than 0.5%, methanol as a reducing agent, and a platinum group metal and an alkali metal co-supported on alumina.
A method for purifying nitrogen oxides in which nitrogen oxides are reduced to nitrogen by contacting at 00 ° C. 2. The alkali metal loading is 0.5 to 6% by weight, the platinum group metal loading is 0.3 to 3% by weight, and the alkali metal / platinum group metal loading ratio is 0.2%. The method for purifying nitrogen oxides according to claim 1, wherein the pressure is from 10 to 10. 3. The method for purifying nitrogen oxides according to claim 1, wherein the platinum group metal is palladium and / or platinum, and the alkali metal is potassium and / or sodium. 4. The gas according to claim 1, wherein the nitrogen oxide-containing gas is obtained by adsorbing nitrogen oxide in an excess oxygen atmosphere and then desorbing the nitrogen oxide-containing gas under an inert gas atmosphere. 5. A method for purifying nitrogen oxides according to any one of the above.