JP3660080B2 - Nitrogen oxide adsorbent and method for removing nitrogen oxide - Google Patents

Description

【００７０】
【表２】

【００７１】
【表３】

【００７２】
【表４】

【００７３】
【発明の効果】
本発明の主たる効果を列挙すると次のとおりである。
【００７４】
（１）本発明の吸着剤は窒素酸化物、特に二酸化窒素の吸着能に優れている。
【００７５】
（２）本発明の吸着剤は低濃度の窒素酸化物の吸着能に優れている。
【００７６】
（３）本発明の吸着剤は処理すべき排ガス中の共存ガス（例えば、水蒸気、硫黄化合物（二酸化硫黄および／または三酸化硫黄））によって影響を受けることが少なく、安定して窒素酸化物を吸着除去することができる。
【００７７】
（４）本発明の吸着剤はオゾン分解能も有し、オゾンを用いて一酸化窒素を酸化して二酸化窒素に変換し、これを吸着除去する場合、過剰のオゾンがそのまま流出するのを防止することができる。
【００７８】
（５）本発明の吸着剤は硫黄化合物（二酸化硫黄および／または三酸化硫黄）を同時に吸着する性能を有する。
【００７９】
（６）本発明の吸着剤は容易に再生することができる。
【００８０】
（７）本発明の方法によれば、排ガス中の窒素酸化物、特に低濃度の二酸化窒素を効率よく吸着除去することができる。
【００８１】
（８）本発明の方法によれば、排ガス中の一酸化窒素を予めオゾンなどの酸化剤で酸化して二酸化窒素とし、この排ガスを吸着剤と接触させることにより、排ガス中の窒素酸化物を一段と効率よく吸着除去することができる。[0001]
[Industrial application fields]
The present invention relates to a nitrogen oxide adsorbent and a method for removing nitrogen oxide using the adsorbent. More specifically, the present invention relates to an adsorbent suitable for removing low-concentration nitrogen oxides (NOx: nitrogen monoxide and / or nitrogen dioxide) contained in exhaust gas, particularly nitrogen dioxide, and using the adsorbent. The present invention relates to a method suitable for efficiently adsorbing and removing low-concentration nitrogen oxides in exhaust gas, particularly nitrogen dioxide.
[0002]
[Prior art]
Regarding the removal method of nitrogen oxides from stationary nitrogen oxide sources such as boilers, conventionally, ammonia is used as a reducing agent to selectively reduce nitrogen oxides and convert them into harmless nitrogen and water. The catalytic reduction method is widely used as the most economical method.
[0003]
By the way, the concentration of nitrogen oxides contained in ventilation gas or air at road tunnels, roads with shelters, deep underground spaces, road intersections, etc., and gases discharged from combustion equipment used in the home is about 5 ppm. And the nitrogen oxide concentration in the boiler exhaust gas is remarkably low, the gas temperature is normal, and the amount of gas is enormous. For this reason, for example, in order to efficiently remove nitrogen oxides by applying the catalytic reduction method to the ventilation gas of a road tunnel, the temperature of the ventilation gas needs to be 300 ° C. or higher. Since a great deal of energy is required, there is an economical problem in applying the catalytic reduction method as it is. Under such circumstances, it is desired to efficiently remove nitrogen oxides from exhaust gas having a low nitrogen oxide concentration, for example, about 5 ppm or less, such as the above-mentioned road tunnel ventilation gas.
[0004]
Therefore, the present inventors previously proposed an adsorbent suitable for adsorbing and removing nitrogen oxides from the low-concentration nitrogen oxide-containing exhaust gas as described above (see JP-A-7-88363). .
[0005]
[Problems to be solved by the invention]
When the nitrogen oxide adsorbent is used to treat the gas after tunnel ventilation, the gas needs to be treated in the tunnel, so that the installation space is limited and the apparatus itself needs to be compact. For this reason, it is desirable that the adsorbent used has an excellent nitrogen oxide adsorption ability.
[0006]
In addition, since exhaust gas contains sulfur compounds (sulfur dioxide and / or sulfur trioxide), water vapor, etc. in addition to nitrogen oxides, the nitrogen oxide adsorbent used is affected by these coexisting gases. What is difficult to receive is desirable.
[0007]
Thus, the present invention is a nitrogen oxide adsorbent that is excellent in nitrogen oxide adsorbing ability, is not easily affected by the coexisting gas, and can maintain high performance over a long period of time, particularly low concentration nitrogen oxide of about 5 ppm or less in exhaust gas. An object of the present invention is to provide a nitrogen oxide adsorbent suitable for adsorbing and removing substances.
[0008]
[Means for Solving the Problems]
As a result of intensive studies, the present inventors have found that an adsorbent having the following composition can solve the above-mentioned problems, and have completed the present invention based on this finding.
[0009]
That is, this invention relates to the nitrogen oxide adsorbent containing the following A component, B component, and C component.
[0010]
Component A: At least one selected from platinum (Pt), gold (Au), ruthenium (Ru), rhodium (Rh) and palladium (Pd), and compounds of these metals.
[0011]
Component B: at least one selected from oxides of manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), lead (Pb) and cerium (Ce) seed.
[0012]
Component C: At least one selected from alkaline earth metal compounds.
However, adsorbents containing ruthenium and cerium, and adsorbents made of platinum, barium and iron are excluded.
[0013]
The present invention also relates to a nitrogen oxide removal method in which exhaust gas is brought into contact with the nitrogen oxide adsorbent and the nitrogen oxide in the exhaust gas is adsorbed and removed.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The component A constituting the adsorbent of the present invention is at least one selected from platinum, gold, ruthenium, rhodium and palladium, and compounds of these metals. These metal compounds are starting materials appropriately selected from compounds containing the metal such as oxides, hydroxides, carbonates, ammonium salts, nitrates, sulfates, acetates, oxalates and halides. Is obtained by firing at a temperature in the range of 300 to 600 ° C. The type of the metal compound in the adsorbent is determined by the starting material used and the preparation conditions of the adsorbent, and what type of compound is present in the adsorbent is the content of the compound. Since the amount is small, it cannot be analyzed and cannot be specifically identified. For example, when a metal oxide is used as a starting material, the metal is present in the form of an oxide in the adsorbent obtained, but in the case of a metal halide (such as a chloride), a partial halide It is thought that it exists in the form of
[0015]
The B component is at least one selected from oxides of manganese, iron, cobalt, nickel, copper, zinc, lead and cerium. The starting material for component B can be appropriately selected from oxides, hydroxides, carbonates, ammonium salts, nitrates, sulfates, acetates, oxalates, halides, and the like of each metal.
[0016]
Further, the alkaline earth metal compound as the C component means an alkaline earth metal carbonate, sulfate, oxide and hydroxide. The starting material of component C can be appropriately selected from oxides, hydroxides, carbonates, ammonium salts, nitrates, sulfates, acetates, oxalates, halides, and the like of each metal.
[0017]
About the ratio of each component in the adsorption agent of this invention, A component is 0.01-10 weight% in conversion of a metal, Preferably it is 0.01-1 weight%, B component is 5-95 weight%, Preferably it is 10-10 weight%. 80% by weight, and C component is 5 to 95% by weight, preferably 10 to 80% by weight (total 100% by weight).
[0018]
The nitrogen oxide adsorbing ability of the adsorbent of the present invention is particularly effectively exhibited when the proportions of the A component, B component and C component are in the above ranges. Nitrogen oxide adsorption capacity is low when the proportion of A component (converted to metal) is less than 0.01% by weight. On the other hand, even if A component is used in a proportion of more than 10% by weight, further improvement in adsorption capacity can be achieved. In fact, the raw material cost is high and it is not practical. Similarly, when the ratios of the B component and the C component are each less than 5% by weight, sufficient nitrogen oxide adsorption ability cannot be obtained.
[0019]
The nitrogen oxide referred to in the present invention means nitrogen monoxide and nitrogen dioxide, and the adsorbent of the present invention has an adsorbing ability for both nitrogen monoxide and nitrogen dioxide. Excellent adsorption capacity. The adsorbent of the present invention is particularly suitable for adsorption of nitrogen oxides having a low concentration of 5 ppm or less.
[0020]
The adsorbent containing the A component, B component and C component of the present invention may be supported on a carrier. As this carrier, those generally used as a carrier can be used. Specifically, alumina, silica, titania, zirconia, alumina-silica, titania-silica, titania-zirconia, zeolite, diatomaceous earth, soda Lime, activated carbon, etc. can be used. The specific surface area of these carriers is usually 10 m ² / g or more, particularly preferably 20 m ² / g or more.
[0021]
In particular, titanium-silicon composite oxide (titania-silica: TiO ₂ —SiO ₂ ) is an amorphous composite oxide with a high surface area and has excellent properties as a support. Preferably used.
[0022]
The titanium-silicon composite oxide can be prepared, for example, by the following method. The titanium source can be appropriately selected from inorganic titanium compounds such as titanium chloride and titanium sulfate, organic titanium compounds such as tetraisopropyl titanate, and the like. Moreover, as a silicon source, it can select and use suitably from inorganic silicon compounds, such as colloidal silica, water glass, and silicon tetrachloride, organosilicon compounds, such as tetraethyl silicate. These raw materials may contain trace amounts of impurities, contaminants, etc., but if they are of a certain amount, they will not significantly affect the physical properties of the target titanium-silicon composite oxide. So it can be used without problems.
[0023]
(1) Titanium sulfate is mixed with silica sol, ammonia is added to cause precipitation, and the resulting precipitate is washed and dried, and then calcined at 300 to 650 ° C.
[0024]
(2) A sodium silicate aqueous solution is added to titanium tetrachloride and reacted, and the resulting precipitate is washed and dried, and then calcined at 300 to 650 ° C.
[0025]
(3) To a water-alcohol solution of titanium tetrachloride, ethyl silicate ((C ₂ H ₅ O) ₄ Si) is added and then hydrolyzed to form a precipitate, and the resulting precipitate is washed. Dry and then fire at 300-650 ° C.
[0026]
(4) Ammonia is added to a water-alcohol solution of titanium oxide chloride (TiOCl ₂ ) and ethyl silicate to cause precipitation, and the resulting precipitate is washed and dried, and then calcined at 300 to 650 ° C.
[0027]
Among the above methods, the method (1) is particularly preferable, and specifically, an acidic aqueous solution or sol having a concentration of 1 to 100 g / L (liter) (as oxide) for each of the compounds as a titanium source and a silicon source. In this state, the co-precipitate of titanium and silicon is produced by maintaining the pH at 2 to 10 at 10 to 100 ° C., and the precipitate is filtered, washed thoroughly, and then dried at 80 to 140 ° C. for 10 minutes to 3 hours. And then calcined at 400 to 700 ° C. for 1 to 10 hours to obtain a titanium-silicon composite oxide.
[0028]
The amount of the adsorbent containing the A component, B component and C component of the present invention supported on the carrier is not particularly limited, and is usually 5 to 50% by weight based on the weight of the carrier.
[0029]
Next, a typical method for preparing the adsorbent of the present invention will be described with reference to the case of using a carrier, but the method for preparing the adsorbent of the present invention is not limited to these methods. (1) The aqueous solution containing the A component and the powder containing the B component and the C component are mixed well with a mixer such as a kneader and formed into a desired shape. You may mix and shape | mold the powder which is a support | carrier simultaneously. After molding, the product is dried as necessary and then fired at 300 to 600 ° C.
[0030]
(2) An aqueous solution containing each metal of A component, B component and C component is impregnated into powder as a carrier, evaporated and dried, then fired at 300 to 600 ° C., and then molded into a desired shape To do. A powder that is a carrier may be formed in advance, and the molded body may be impregnated with the aqueous solution.
[0031]
(3) Add an aqueous solution containing the metals of component A, component B and component C to the aqueous solution of the starting material of the carrier, mix well, and then add an alkaline solution such as ammonia, sodium hydroxide, potassium hydroxide, etc. After adding and coprecipitating, the obtained precipitate is washed with water and dried, then calcined at 300 to 600 ° C., and then formed into a desired shape.
[0032]
(4) After adding powder as a carrier to an aqueous solution containing each metal of component A, component B, and component C to form a slurry, an alkaline solution such as ammonia, ammonium hydroxide, or potassium hydroxide is added. Each component is deposited on a carrier, washed with water, dried, fired at 300 to 600 ° C., and then formed into a desired shape.
[0033]
Regardless of the method (1) to (4), the firing is preferably performed at a temperature in the range of 300 to 600 ° C, particularly preferably at a temperature in the range of 350 to 550 ° C. .
[0034]
The shape of the adsorbent of the present invention is not particularly limited, and can be appropriately selected from a columnar shape, a cylindrical shape, a spherical shape, a plate shape, a honeycomb shape, and other integrally formed ones. The adsorbent can be molded by a general molding method such as a tableting method or an extrusion method. In the case of a spherical adsorbent, the average particle size is usually 1 to 10 mm. In the case of a honeycomb-like adsorbent, it is the same as a so-called monolithic carrier, and is manufactured by an extrusion molding method or a method of winding a sheet-like element. The shape of the gas passage port (cell shape) may be hexagonal, quadrangular, triangular or corrugated. The cell density (number of cells / unit cross-sectional area) is usually 25 to 800 cells / in 2, preferably 25 to 500 cells / in 2.
[0035]
The specific surface area and pore volume of the adsorbent of the present invention are not particularly limited, but when no carrier is used, the specific surface area of the adsorbent is in the range of 10 to 100 m ² / g, particularly 10 to 80, and the pores. The volume is preferably in the range of 0.2 to 0.6 cc / g, particularly 0.2 to 0.5 cc / g. When a support is used, the adsorbent has a specific surface area of 10 to 400 m ² / g, particularly 10 to 300 m ² / g, and a pore volume of 0.2 to 0.6 cc / g, particularly 0.2. It is preferably in the range of -0.5 cc / g.
[0036]
According to the method for removing nitrogen oxides of the present invention, exhaust gas is brought into contact with the adsorbent to remove nitrogen oxides in the exhaust gas by adsorption. The exhaust gas here means nitrogen gas (nitrogen monoxide and / or nitrogen dioxide), which means ventilation gas or atmospheric gas from the road tunnel or the like, and the method of the present invention is particularly nitrogen oxide. It is suitably used for adsorption removal of nitrogen oxides, particularly nitrogen dioxide, from exhaust gas having a low nitrogen oxide concentration of 5 ppm or less.
[0037]
There is no restriction | limiting in particular about the contact method of the adsorbent of this invention, and waste gas, Usually, exhaust gas is introduce | transduced in the layer which consists of this adsorbent. About this process condition, since it changes with the properties of exhaust gas, etc., it cannot be specified unconditionally, but the temperature of the supplied exhaust gas is usually 0 to 100 ° C., particularly preferably in the range of 0 to 50 ° C. Also, the space velocity of the exhaust gas supplied (SV) is usually a 500~50000hr ^-1 (STP), preferably in the range of 2000~30000hr ^-1 (STP).
[0038]
Since the adsorbent of the present invention is particularly effective for adsorbing and removing nitrogen dioxide among nitrogen oxides, nitrogen monoxide is pre-oxidized with an oxidizing agent such as ozone when adsorbing and removing nitrogen oxide in exhaust gas. Then, after converting to nitrogen dioxide, when it is brought into contact with the adsorbent, nitrogen oxides in the exhaust gas can be more effectively removed. Of course, the exhaust gas may be directly brought into contact with the adsorbent of the present invention to mainly remove nitrogen dioxide from the nitrogen oxides.
[0039]
Therefore, according to a preferred embodiment of the present invention, an oxidizing agent such as ozone is added to the exhaust gas to convert nitrogen monoxide in the exhaust gas to nitrogen dioxide, and then the exhaust gas is contacted with the adsorbent of the present invention. By adsorbing nitrogen dioxide, nitrogen oxides in the exhaust gas can be efficiently removed.
[0040]
In the above method, ozone is preferably used as the oxidizing agent, but the amount of ozone used is preferably 0.5 to 5 times the molar amount of nitrogen monoxide in the exhaust gas. If the amount of ozone used is less than 0.5 times mol, oxidation of nitrogen monoxide to nitrogen dioxide will not proceed sufficiently, while if it is used more than 5 times mol, harmful ozone will flow out undecomposed. Absent. In addition, since the adsorbent of the present invention also has ozone resolving power, if the amount of ozone used is within the above range, excessive ozone can be decomposed and removed, and ozone can be effectively prevented from flowing out as it is. .
[0041]
The adsorbent of the present invention can be easily regenerated by introducing heated air after use to release nitrogen oxides adsorbed on the adsorbent. Further, the adsorbent of the present invention is not affected by the gas coexisting in the exhaust gas, and also has a function of adsorbing it together with nitrogen oxide in the case of a sulfur compound (sulfur dioxide and / or sulfur trioxide). .
[0042]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples.
[0043]
Example 1
80 g of aqueous platinum nitrate solution (produced by Tanaka Kikinzoku Co., Ltd., containing 3.75% by weight of platinum metal), 675.1 g of manganese carbonate (MnCO ₃ ) and 500 g of magnesium carbonate (MgCO ₃ ) are mixed well with a kneader to obtain an appropriate amount of water. After further mixing, the mixture was molded into a pellet having a diameter of 5 mm and a length of 5 mm with an extruder. The pellet was dried at 100 ° C. for 10 hours and then calcined at 350 ° C. for 3 hours in an air atmosphere.
[0044]
The composition of the adsorbent thus obtained was Pt: MnO ₂ : MgCO ₃ = 0.3: 49.7: 50 (% by weight).
[0045]
Examples 2-4
In Example 1, adsorbent pellets having the composition shown in Table 1 were obtained in the same manner as in Example 1 except that calcium carbonate, strontium carbonate and barium carbonate were used instead of magnesium carbonate.
[0046]
Examples 5-20
In Examples 1 to 4, an adsorbent having the composition shown in Table 1 was used in the same manner as in Examples 1 to 4 except that an aqueous gold chloride solution, an aqueous ruthenium nitrate solution, an aqueous rhodium nitrate solution and an aqueous palladium nitrate solution were used instead of the platinum nitrate aqueous solution. Pellets were obtained.
[0047]
Example 21
71.4 g of ruthenium nitrate aqueous solution (Tanaka Kikinzoku Co., Ltd., containing 4.20% by weight of ruthenium metal), 553.3 g of iron hydroxide (FeO (OH)) and 500 g of barium carbonate (BaCO ₃ ) with appropriate amounts of water The mixture was mixed well with a kneader while being added, and then molded into a pellet having a diameter of 5 mm and a length of 5 mm with an extruder. The pellet was dried at 100 ° C. for 10 hours and then calcined at 350 ° C. for 3 hours in an air atmosphere.
[0048]
The composition of the adsorbent thus obtained was Ru: Fe ₂ O ₃ : BaCO ₃ = 0.3: 49.7: 50 (% by weight).
[0049]
Examples 22-27
In Example 21, the same procedure as in Example 21 was used except that basic cobalt carbonate, basic nickel carbonate, basic copper carbonate, basic zinc carbonate, basic carbonate and cerium carbonate were used instead of iron hydroxide. Adsorbent pellets having the compositions shown in Table 2 were obtained.
Example 28
71.4 g of ruthenium nitrate aqueous solution (Tanaka Kikinzoku Co., Ltd., containing 4.20% by weight of ruthenium metal), 264.4 g of manganese carbonate (MnCO ₃ ), basic cobalt carbonate (containing 42% by weight of cobalt metal) 349. 6 g and 597 g of magnesium carbonate (MgCO ₃ ) were mixed well with a kneader while adding an appropriate amount of water, and then formed into pellets having a diameter of 5 mm and a length of 5 mm by an extruder. The pellet was dried at 100 ° C. for 10 hours and then calcined at 350 ° C. for 3 hours in an air atmosphere.
[0050]
The composition of the adsorbent thus obtained was Ru: MnO ₂ : Co ₃ O ₄ : MgCO ₃ = 0.3: 20: 20: 59.7 (% by weight).
[0051]
Examples 29-31
In Example 28, pellets having the compositions shown in Table 2 were obtained in the same manner as in Example 28 except that calcium carbonate, strontium carbonate, and barium carbonate were used instead of magnesium carbonate.
[0052]
Comparative Example 1
A suitable amount of 71.4 g of ruthenium nitrate aqueous solution (Tanaka Kikinzoku Co., Ltd., containing 4.20% by weight of ruthenium metal), 1053.8 g of manganese carbonate, and 349.6 g of basic cobalt carbonate (containing 42% by weight of cobalt metal) The mixture was mixed well with a kneader while adding water, and then formed into pellets having a diameter of 5 mm and a length of 5 mm with an extruder. The pellet was dried at 100 ° C. for 10 hours and then calcined at 350 ° C. for 3 hours in an air atmosphere.
[0053]
The composition of the adsorbent thus obtained was Ru: MnO ₂ : Co ₃ O ₄ = 0.3: 79.7: 20 (% by weight).
[0054]
Example 32
About the adsorption agent obtained in Examples 1-31, the nitrogen oxide adsorption ability was evaluated by the following method.
[0055]
(Evaluation methods)
76 mL of adsorbent was filled in a glass reaction tube having an inner diameter of 30 mm. A synthesis gas having the following composition was introduced into the adsorbent layer under the following conditions.
[0056]
Synthesis gas composition <br/> nitric oxide (NO): 3 ppm, sulfur dioxide _{(SO 2): 0.15ppm, H} 2 O: 2.5 % by volume, remainder: air
Treatment conditions Gas amount: 15.2 NL / min, treatment temperature: 25 ° C., space velocity (SV): 1200 hr ⁻¹ (STP), gas humidity: 85% RH
Three hours after the synthesis gas was introduced, the nitrogen oxide (NOx) concentration in the synthesis gas at the inlet and outlet of the adsorbent layer was measured with a chemiluminescent NOx meter, and the NOx removal rate according to the following formula: Was calculated.
[0057]
NOx removal rate (%) = [(inlet NOx concentration−outlet NOx concentration) / (inlet NOx concentration)] × 100
The results of the evaluation test are shown in Table 3.
[0058]
Example 33
In Example 32, the nitrogen oxide adsorption performance (NOx removal rate) was evaluated in the same manner as in Example 32 except that the composition of the synthesis gas was changed as follows.
[0059]
Synthesis gas composition <br/> nitric oxide (NO): 3 ppm, sulfur dioxide _{(SO 2): 0.15ppm, H} 2 O: 2.5 % by volume, ozone (O _3): 3 ppm, remainder: air. However, nitrogen monoxide was all nitrogen dioxide (NO ₂ ) by adding ozone.
[0060]
After 20 hours and 40 hours have passed since the synthesis gas was introduced, the nitrogen oxide (NOx) concentration in the synthesis gas at the inlet and outlet of the adsorbent layer was measured with a chemiluminescence NOx meter. The removal rate was calculated and the results are shown in Table 3.
[0061]
Example 34
In Example 32, the nitrogen oxide adsorption performance (NOx removal rate) was evaluated in the same manner as in Example 32 except that the composition of the synthesis gas was changed as follows.
[0062]
Synthesis gas composition <br/> nitric oxide (NO): 3 ppm, sulfur dioxide _{(SO 2): 0.15ppm, H} 2 O: 2.5 % by volume, ozone (O _3): 4.5 ppm, the remainder: air . However, nitrogen monoxide (NO) was all nitrogen dioxide (NO ₂ ) by adding ozone. Excess ozone (O ₃ ) remained at 1.5 ppm.
[0063]
After 20 hours and 40 hours have passed since the synthesis gas was introduced, the nitrogen oxide (NOx) concentration in the synthesis gas at the inlet and outlet of the adsorption layer was measured with a chemiluminescent NOx meter. The removal rate was calculated and the results are shown in Table 3.
[0064]
Example 35
The SO ₂ resistance of the adsorbents of Examples 28, 29, 30, 31 and Comparative Example 1 was evaluated by the following method.
[0065]
(Evaluation methods)
76 ml of adsorbent was packed into a 30 mm inner diameter glass reactor. A synthesis gas having the following composition was introduced into the adsorbent layer under the following conditions.
[0066]
Syngas <br/> nitric oxide (NO): 20 ppm, sulfur dioxide _{(SO 2): 1ppm, H} 2 O: 2.5 % by volume, ozone (O _3): 30 ppm, remainder: air. However, nitrogen monoxide (NO) was all nitrogen dioxide (NO ₂ ) by adding ozone. Excess ozone (O ₃ ) remained at 10 ppm.
[0067]
Processing conditions The same as in Example 32.
[0068]
After 100 hours, 200 hours and 300 hours have passed since the synthesis gas was introduced into the reactor, the nitrogen oxide (NOx) concentration in the synthesis gas at the inlet and outlet of the adsorption layer was chemically determined under the same conditions as in Example 34. The NOx removal rate was measured with a luminescent NOx meter, and the NOx removal rate was calculated according to the previous formula. The results are shown in Table 4. From this result, it can be seen that the adsorbent containing no C component of the present invention is inferior in SO ₂ resistance.
[0069]
[Table 1]

[0070]
[Table 2]

[0071]
[Table 3]

[0072]
[Table 4]

[0073]
【The invention's effect】
The main effects of the present invention are listed as follows.
[0074]
(1) The adsorbent of the present invention is excellent in the ability to adsorb nitrogen oxides, particularly nitrogen dioxide.
[0075]
(2) The adsorbent of the present invention is excellent in the ability to adsorb a low concentration of nitrogen oxides.
[0076]
(3) The adsorbent of the present invention is less affected by the coexisting gas (for example, water vapor, sulfur compound (sulfur dioxide and / or sulfur trioxide)) in the exhaust gas to be treated, and stably absorbs nitrogen oxides. It can be removed by adsorption.
[0077]
(4) The adsorbent of the present invention also has ozone resolving power. When ozone is oxidized to convert nitric oxide into nitrogen dioxide and this is adsorbed and removed, it prevents the excess ozone from flowing out as it is. be able to.
[0078]
(5) The adsorbent of the present invention has the ability to adsorb sulfur compounds (sulfur dioxide and / or sulfur trioxide) simultaneously.
[0079]
(6) The adsorbent of the present invention can be easily regenerated.
[0080]
(7) According to the method of the present invention, nitrogen oxides in exhaust gas, particularly low-concentration nitrogen dioxide, can be efficiently adsorbed and removed.
[0081]
(8) According to the method of the present invention, nitrogen monoxide in the exhaust gas is oxidized beforehand with an oxidizing agent such as ozone to form nitrogen dioxide, and the exhaust gas is brought into contact with the adsorbent to thereby convert the nitrogen oxide in the exhaust gas. Adsorption and removal can be performed more efficiently.

Claims (6)

An adsorbent for adsorbing and removing nitrogen oxides at a temperature of 0 to 100 ° C, comprising the following A component, B component and C component.
Component A: at least one selected from platinum (Pt), gold (Au), ruthenium (Ru), rhodium (Rh) and palladium (Pd), and compounds of these metals.
Component B: at least one selected from oxides of manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), lead (Pb) and cerium (Ce) seed.
Component C: At least one selected from alkaline earth metal compounds.
However, an adsorbent containing ruthenium and cerium and an adsorbent composed of platinum, barium and iron are excluded.   The nitrogen oxide adsorbent according to claim 1, which is an adsorbent for adsorbing and removing nitrogen oxide from exhaust gas having a nitrogen oxide concentration of 5 ppm or less. A method for removing nitrogen oxides , comprising contacting exhaust gas with the nitrogen oxide adsorbent of claim 1 or 2 at a temperature of 0 to 100 ° C to adsorb and remove nitrogen oxides in the exhaust gas. The method for removing nitrogen oxides according to claim 3 , wherein the nitrogen oxide concentration in the exhaust gas is 5 ppm or less. The method for removing nitrogen oxides according to claim 3 or 4 , wherein the exhaust gas is contacted with a nitrogen oxide adsorbent after oxidizing nitric oxide in the exhaust gas to nitrogen dioxide. 6. The method for removing nitrogen oxides according to claim 5 , wherein ozone is added to the exhaust gas to oxidize nitric oxide in the exhaust gas to nitrogen dioxide.