JP2015181971A - Catalyst and method for treating marine exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for treating marine exhaust gas which is used for treating exhaust gas generated by a marine diesel engine, more specifically, for stably treating NOx contained in exhaust gas over a long time even when the temperature of the exhaust gas is low and particularly even when sulfur oxide is contained in the exhaust gas.SOLUTION: A catalyst for treating marine exhaust gas which is used for treating exhaust gas generated by a marine diesel engine, contains: a catalyst A component comprising a compound oxide and/or a mixed oxide of titanium, silicon and tungsten, which are obtained from compounds of titanium, silicon and tungsten by a coprecipitation method; and a catalyst B component comprising a compound of at least one element of vanadium, niobium and tantalum.

Description

  The present invention relates to a catalyst for treating exhaust gas generated from marine diesel engines, and to treatment of exhaust gas using the catalyst. In particular, it relates to treatment of exhaust gas containing sulfur oxides.

  In general, a diesel engine is an oxygen-excess type internal combustion engine, and its exhaust gas contains a relatively large amount of nitrogen oxide (hereinafter also referred to as NOx). Since this NOx can cause pollution and environmental destruction, a method for removing NOx from exhaust gas is indispensable for diesel engines. As the method, a selective catalytic reduction method (SCR method) in which nitrogen oxide in exhaust gas is catalytically reduced on a catalyst using a reducing agent such as ammonia or urea and decomposed into nitrogen and water is generally used. Yes.

  As an exhaust gas treatment catalyst used in the SCR method, for example, a catalyst containing titanium oxide, vanadium oxide and tungsten oxide (Patent Document 1), or a catalyst containing titanium oxide, vanadium oxide and molybdenum oxide (Patent Document 2) and the like have been proposed.

  On the other hand, in ships and the like, there are many examples of mounting an SCR internal combustion engine on a ship equipped with a medium-speed diesel engine, and studies are being made on mounting an SCR internal combustion engine in a low-speed diesel engine. The catalyst used to purify exhaust gas from marine diesel engines is selected from zeolite with a high silica / alumina ratio, vanadium, tungsten, molybdenum, niobium, or titanium as a catalyst component with excellent sulfur poisoning resistance. The use of one or more oxides is disclosed (Patent Document 3).

The most notable problem in mounting SCR on ships is poisoning of the catalyst by sulfur contained in fuel oil. Ammonia used as a reducing agent reacts with sulfur oxides (hereinafter also referred to as SOx) in exhaust gas to produce acidic ammonium sulfate (ammonium hydrogen sulfate: NH ₄ HSO ₄ ), which adheres to the surface of the catalyst. In particular, this problem is considered to be remarkable in an atmosphere having an exhaust gas temperature of about 300 ° C. or lower. In medium-speed diesel engines, this problem is mitigated because the exhaust gas temperature in most engines is above 300 ° C.

On the other hand, in most low speed diesel engines, the exhaust gas temperature is 300 ° C. or lower in most engines, and in particular, the latest models with excellent engine performance are below 250 ° C. In a low-speed diesel engine, a low exhaust gas temperature means that the amount of heat to be discarded is small, and it is also a testament to high efficiency, low fuel consumption, and low CO ₂ emissions. On the other hand, since the exhaust gas treatment temperature is 300 ° C. or less, poisoning such as SOx becomes remarkable, and there is a problem in terms of durability of the catalyst. Therefore, even if the catalyst is superior in sulfur poisoning resistance described in Patent Document 3 above, NOx is efficiently removed while maintaining high efficiency, low fuel consumption, and low CO ₂ emission performance, and further, SOx, etc. There was room for improvement in maintaining durability against poisoning.

Japanese Patent No. 3337634 Japanese Patent No. 3749078 JP 2011-32953 A

  An object of the present invention is a marine diesel capable of removing nitrogen oxides in exhaust gas over a longer period of time even in a low temperature range of exhaust gas, with less performance degradation due to sulfur oxide or the like than conventional catalysts. An object of the present invention is to provide a catalyst for treating exhaust gas from an engine and a method for treating exhaust gas generated from a marine diesel engine using the catalyst.

  As a result of intensive studies in order to solve the above problems, the present inventor has found that a catalyst having the following composition is effective.

  That is, according to the first aspect of the present invention, a catalyst for treating exhaust gas generated from a marine diesel engine is a composite oxide obtained by a coprecipitation method from three compounds of titanium, silicon and tungsten as a catalyst A component. And / or a mixed oxide and a catalyst B component containing a compound of at least one element of vanadium, niobium and tantalum, and the content of the catalyst B component is 0 with respect to the total of the catalyst A component and the catalyst B component .2 to 10% by mass (as oxide).

  A second invention of the present invention is a method for treating exhaust gas from a marine diesel engine characterized by using the catalyst of the first invention.

  By using the present invention, it becomes possible to suppress the performance deterioration due to sulfur oxide even in the low temperature range, particularly in the temperature range of 300 ° C. or less, and the NOx contained in the exhaust gas can be stabilized for a long time. Can be processed automatically.

  The exhaust gas treatment catalyst of the present invention is a composite oxide and / or mixed oxide obtained by coprecipitation from three compounds of titanium, silicon and tungsten as the catalyst A component, and vanadium, niobium and tantalum as the catalyst B component. And at least one elemental compound of at least one elemental compound.

  The composition of the catalyst A component greatly affects the NOx removal performance and durability. Specifically, the catalyst A component essentially includes elements of titanium, silicon and tungsten, and a composite oxide obtained from a compound of these elements by a coprecipitation method. And / or mixed oxides. The content of titanium in the catalyst A component is 70 to 98% by mass in terms of oxide, preferably 75 to 95% by mass, and more preferably 80 to 93% by mass. When the content of titanium in the catalyst A component exceeds 98% by mass in terms of oxide, sufficient durability cannot be obtained, and when it is less than 70% by mass, the NOx removal performance decreases. The content of silicon in the catalyst A component is preferably 1 to 20% by mass in terms of oxide, preferably 1.5 to 15% by mass, and more preferably 2 to 10% by mass. . When the content of silicon in the catalyst A component exceeds 20% by mass in terms of oxide, the NOx removal performance decreases, and when it is less than 1% by mass, sufficient durability cannot be obtained. Content of tungsten should just be 1-20 mass%, Preferably it is 2-15 mass%, More preferably, it is 4-12 mass%. This is because if it exceeds 20% by mass, the initial performance is remarkably deteriorated, and if it is less than 1% by mass, sufficient durability cannot be obtained. The content of the catalyst A component in the catalyst is preferably 90 to 99.8% by mass in terms of oxide with respect to the total of the catalyst A component and the catalyst B component, and more preferably 91 to 99.7. It is good that it is mass%, More preferably, it is 91.5-99.6 mass%. When the content of the catalyst A component is less than 90% by mass or exceeds 99.8% by mass, the NOx removal performance or durability is lowered.

  In addition, as starting materials for preparing the catalyst A component, oxides, hydroxides, inorganic salts, organic salts and the like of each element are used. For example, titanyl sulfate, titanium tetrachloride, tetraisopropyl titanate, etc. are used as the titanium source, silica sol, water glass, silicon tetrachloride, etc. are used as the silicon source, and ammonium metatungstate, For example, ammonium paratungstate can be used.

  Furthermore, the catalyst A component in the present invention is prepared by a coprecipitation method. Specifically, the catalyst A component is added by adding an acidic solution of a titanium source to a basic solution of a mixture of a silicon source and a tungsten source. It is good to obtain the precursor of a component. By preparing in this way, each component of titanium, silicon, or tungsten is in a highly dispersed state, and a catalyst having high NOx removal performance and durability can be obtained. In this case, the pH after the coprecipitation reaction is preferably controlled to 4 to 10, more preferably 6 to 8 in the case of a ternary oxide of titanium, silicon and tungsten. By controlling in this way, a catalyst excellent in performance and durability can be obtained. Furthermore, the temperature of the liquid or slurry during the coprecipitation reaction is preferably controlled between 5 and 60 ° C, more preferably between 10 and 50 ° C, and even more preferably between 15 and 45 ° C. . This is because if the temperature of the liquid or slurry during the coprecipitation reaction exceeds the range of 5 to 60 ° C., the NOx removal performance or durability of the catalyst is lowered.

  Even if it is a complex oxide containing titanium, silicon and tungsten, the effect of the invention cannot be obtained even if a complex oxide prepared without using the coprecipitation method is used instead of the component A of the present invention.

  The catalyst B component of the present invention is a compound of at least one element selected from the group 5 elements of vanadium, niobium and tantalum, but is contained in the catalyst in the form of an oxide from the viewpoint of removal performance. preferable. In particular, it is preferable to contain vanadium oxide, and a catalyst excellent in NOx removal performance and durability can be obtained.

The content of the catalyst B component also greatly affects the removal performance and durability. In the present invention, it is 0.2 to 10% by mass in terms of oxide with respect to the total of the catalyst A component and the catalyst B component, but more preferably Is 0.3 to 9% by mass, more preferably 0.4 to 8.5% by mass. If the content of the catalyst B component is less than 0.2% by mass, sufficient removal performance cannot be obtained, and if it exceeds 10% by mass, the performance may be deteriorated due to sintering of metal species. This is because the oxidation of SO ₂ to SO ₃ is promoted to increase the accumulation of acidic ammonium sulfate, which may adversely affect the catalyst life. In addition, when using the compound of a some element from vanadium, niobium, and a tantalum as a catalyst B component, it is good that the total amount in conversion of the oxide of each compound exists in the said range. Further, as starting materials for preparing the catalyst B component, oxides, hydroxides, inorganic salts, organic salts, and the like of each element are used. For example, ammonium metavanadate is preferably used as the vanadium source. As a source, niobium oxalate or its ammonium salt can be used.

  The method for adding the catalyst B component is not particularly limited, and there are a method for adding the catalyst A component after it is obtained by the coprecipitation method and a method for obtaining the catalyst B component by mixing the raw materials of the catalyst A component and the catalyst B component.

  In addition, another compound can also be added as long as the performance of the catalyst according to the present invention is not impaired.

  The pore volume of the denitration catalyst used in the present invention is such that the total pore volume is in the range of 0.20 to 0.70 mL / g, more preferably 0.25 to 0.60 mL / g, Preferably it is in the range of 0.28 to 0.50 mL / g. If the pore volume of the catalyst is too small, sufficient catalyst performance will not be obtained, and if it is too large, the catalyst performance will not improve so much, but the mechanical strength of the catalyst will be reduced, causing handling problems and wear resistance This is not preferable because there is a risk of adverse effects such as lowering.

  As the catalyst preparation method according to the present invention, (1) after obtaining the composite oxide or mixed oxide related to the catalyst A component by the above procedure, the aqueous solution of the catalyst B component is added and sufficiently mixed with a kneader or the like, (2) The catalyst A component and the catalyst B component raw materials are mixed at once, and the pH is adjusted to obtain a precipitate. Then, the precipitate is dried and fired, and further an aqueous medium. The slurry obtained in (3) and (2) can be coated on a carrier usually used as a catalyst carrier. (4) In addition, when forming by (1) and (2), it can also be formed into honeycombs, pellets and granules, dried and fired to form a catalyst.

  In the catalyst preparation method described above, the drying conditions are not particularly limited, and the temperature is 50 to 100 ° C., preferably 60 to 80 ° C. in hydrogen, nitrogen, air or a mixed gas thereof, preferably 20 to 500 minutes, preferably 30. Can be done in ~ 100 minutes. Also, the firing conditions are not particularly limited, and hydrogen, nitrogen, air, or a mixed gas thereof is 300 to 600 ° C, preferably 400 to 550 ° C, and 2 to 50 hours, preferably 3 to 10 hours. It can be carried out.

  The catalyst according to the present invention can be formed into a saddle, pellet, sphere, or honeycomb by extrusion molding, tableting, rolling granulation, or the like. Further, a saddle-shaped, pellet, sphere, or honeycomb-shaped carrier can be used by coating the components of the denitration catalyst. A honeycomb shape is preferable for reducing the pressure loss of the exhaust gas treatment apparatus. Further, in the preparation, a general preparation method using various metal compounds can be used. For example, a method of impregnating a molded product of the catalyst A component with a solution of the catalyst B component, or a powder of the catalyst A component Although the method of kneading after mixing the solution or powder of the catalyst B component is mentioned, the kneading method is suitably used from the viewpoint of controlling the pore volume.

  The exhaust gas treatment method of the present invention is an exhaust gas treatment method for removing NOx in the exhaust gas using the catalyst of the present invention. At this time, the treatment temperature of the exhaust gas is 180 to 330 ° C, preferably 200 to 300 ° C. More preferably, it should be in the range of 220 to 290 ° C, more preferably 230 to 270 ° C. If the treatment temperature of the exhaust gas is less than 180 ° C, sufficient removal efficiency of NOx cannot be obtained, and the accumulation of acidic ammonium sulfate increases, resulting in a large decrease in catalyst performance. If the treatment temperature exceeds 330 ° C, the catalyst is thermally damaged. This is because performance may be degraded. About the deterioration of the catalyst performance due to the poisoning of SOx, an effect that the performance degradation is suppressed in the temperature range of the exhaust gas treatment is shown. In particular, in the temperature range where the temperature of the exhaust gas is 300 ° C. or lower, the treatment method using the catalyst of the present invention shows an effect superior in durability against poisoning such as SOx than the treatment method using the conventional catalyst.

  The exhaust gas to be treated by the catalyst according to the present invention contains nitrogen oxides (NOx), and the NOx concentration in the exhaust gas is preferably 5 to 1000 ppm (volume basis), more preferably 10 to 500 ppm, More preferably, it is in the range of 20 to 300 ppm. If the NOx concentration in the exhaust gas is less than 5 ppm, sufficient NOx removal performance will not be exhibited. On the other hand, if it exceeds 1000 ppm, if sulfur compounds are contained in the exhaust gas, the amount of acidic ammonium sulfate will increase and the performance will deteriorate significantly This is because it is not preferable.

  Although the exhaust gas may contain an organic compound, the concentration of the organic compound is preferably 3000 ppm or less (volume basis), more preferably 1000 ppm or less, and even more preferably 500 ppm or less. This is because if the concentration of the organic compound in the exhaust gas exceeds 3000 ppm, heat generated by the reaction increases and the catalyst may be thermally damaged.

  In the method for treating exhaust gas of the present invention, a form in which ammonia or urea (also referred to as ammonia or the like) is added to the exhaust gas is preferably used. The addition amount of ammonia or the like is 0.2 to 2.0 mol, preferably 0.5 to 1. mol in terms of ammonia (1/2 mol in the case of urea) with respect to 1 mol of nitrogen oxide (in terms of NOx). 0 mole.

  In addition, when an organic halogen compound is contained in the exhaust gas, it is not necessary to add ammonia or the like, but even if ammonia or the like is added to the exhaust gas, the effect of the catalyst according to the present invention is not impaired.

Furthermore, oxygen, water, SOx, etc. are contained in the exhaust gas. For example, it is preferably used under conditions where oxygen is present in the exhaust gas. In this case, the oxygen concentration is preferably in the range of 0.1 to 50% by volume, more preferably 0.3 to 20% by volume. More preferably, it is in the range of 0.5 to 16% by volume. If the oxygen concentration is less than 0.1% by volume, the removal efficiency decreases, and if it exceeds 50% by volume, SO ₂ oxidation as a side reaction is promoted, which is not preferable. When the exhaust gas contains moisture, the concentration is preferably 50% by volume or less, more preferably 40% by volume or less, and further preferably 30% by volume or less. This is because when the moisture concentration in the exhaust gas exceeds 50% by volume, the removal efficiency is lowered and, in some cases, the performance is greatly lowered.

The exhaust gas treatment method of the present invention can be suitably used when sulfur oxide (SOx) is contained in the exhaust gas. The SOx concentration in the exhaust gas at that time should be in the range of 5 to 5000 ppm (volume basis), preferably 10 to 2000 ppm, more preferably 50 to 1000 ppm, and still more preferably 100 to 500 ppm. The effect of the present invention is exhibited in the treatment of exhaust gas having a SOx concentration of 0.1 ppm or more. On the other hand, if the SOx concentration in the exhaust gas exceeds 2000 ppm, performance degradation due to SOx becomes large, which is not preferable. In addition, among SOx, SO ₃ contributes particularly greatly to performance degradation, but its concentration is in the range of 0.1 to 200 ppm, preferably 0.5 to 100 ppm, more preferably 1 to 50 ppm, and even more preferably 2 to 30 ppm. There should be. If the SO ₃ concentration in the exhaust gas exceeds 200 ppm, the performance degradation due to SOx increases, which is not preferable.

Also, space velocity during the exhaust gas treatment of the present invention, 100~100,000h ^-1 (STP), preferably 200~50,000h ^-1 (STP), more preferably 500~20,000h ^-1 (STP) It is good to be in the range. Not sufficient removal efficiency is obtained of the space velocity exceeds 100,000h ^-1 (STP) NOx and organic halogen ^compounds, removal efficiency but does not change significantly the pressure loss of the exhaust gas treatment device is less than ^100h -1 (STP) This is because the height of the apparatus becomes large and the apparatus itself becomes large, which hinders mounting on a ship. Furthermore, the linear velocity of the gas passing through the catalyst layer in the exhaust gas treatment of the present invention is 0.1 to 10 m / s (Normal), preferably 0.5 to 7 m / s (Normal), more preferably 0.7. It should be in the range of ˜4 m / s (Normal). If the linear velocity is less than 0.1 m / s (Normal), sufficient removal efficiency cannot be obtained, and if it exceeds 10 m / s (Normal), the removal efficiency does not change greatly, but the pressure loss of the exhaust gas treatment device increases. is there.

  The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the following examples as long as the effects of the present invention are achieved.

(Example 1)
<Preparation of Ti-Si-W ternary oxide (WO ₃ content: 6% by mass)>
A uniform solution was prepared by mixing and dissolving 1.3 kg of ammonium paratungstate (containing 90 wt% as WO ₃ ) and 0.6 kg of monoethanolamine in 10 liters of water (hereinafter referred to as L). This tungsten-containing solution, silica sol (Snowtex-30 (product name), manufactured by Nissan Chemical Industries, containing 30% by mass in terms of SiO ₂ ) 3.3 kg, industrial ammonia water (containing 25% by mass NH ₃ ) 134 kg, To a mixed solution with 100 L of water, 254 L of a sulfuric acid solution of titanyl sulfate (manufactured by Teika, containing 70 g / L as TiO _{2 and} 287 g / L as H ₂ SO ₄ ) was gradually added dropwise with stirring to form a precipitate. It was. At this time, the temperature of the liquid or slurry was controlled to be in the range of 15 to 45 ° C. Thereafter, an appropriate amount of aqueous ammonia was added to adjust the pH to 7. The coprecipitated slurry was allowed to stand for about 20 hours, washed thoroughly with water, filtered, and dried at 100 ° C. for 1 hour. Furthermore, it was fired at 500 ° C. for 5 hours in an air atmosphere, further pulverized using a hammer mill, and classified with a classifier to obtain a Ti—Si—W ternary oxide powder. The composition of the Ti—Si—W ternary oxide powder thus prepared was TiO ₂ : SiO ₂ : WO ₃ = 89: 5: 6 (mass ratio).
<Addition of vanadium oxide>
A homogeneous solution was prepared by mixing and dissolving 1.29 kg of ammonium metavanadate, 1.54 kg of oxalic acid, and 0.3 kg of monoethanolamine in 7 L of water. After 19.0 kg of the Ti-Si-W ternary oxide powder prepared earlier was put into a kneader, a vanadium-containing solution was added together with a molding aid such as an organic binder, followed by thorough stirring. Further, after mixing well with a blender while adding an appropriate amount of water, the mixture was sufficiently kneaded with a continuous kneader and extruded into a honeycomb shape having an outer diameter of 80 mm square, a length of 500 mm, an aperture of 3.2 mm, and a wall thickness of 0.5 mm. The obtained molded product was dried at 60 ° C. for 50 minutes while ventilating air, and then calcined at 500 ° C. for 5 hours in an air atmosphere to obtain Catalyst A. The composition of the catalyst A is TiO ₂ : SiO ₂ : WO ₃ : V ₂ O ₅ = 84.5: 4.8: 5.7: 5.0 (mass ratio), and the total pore volume is 0.8. It was 43 mL / g.

(Example 2)
In 0.5 L of water, 0.10 kg of ammonium metavanadate, 0.12 kg of oxalic acid, and 0.03 kg of monoethanolamine were mixed and dissolved to prepare a uniform solution. Next, 19.9 kg of the Ti—Si—W ternary oxide powder prepared in Example 1 was put into a kneader, and the vanadium-containing solution prepared earlier was added together with a molding aid such as an organic binder, and the mixture was stirred well. . Further, after mixing well with a blender while adding an appropriate amount of water, the mixture was kneaded, extruded, dried and fired in the same manner as in Example 1 to obtain Catalyst B. The composition of the catalyst B is TiO ₂ : SiO ₂ : WO ₃ : V ₂ O ₅ = 88.6: 5.0: 6.0: 0.4 (mass ratio), and the total pore volume is 0.00. It was 41 mL / g.

(Example 3)
In 11 L of water, 2.19 kg of ammonium metavanadate, 2.62 kg of oxalic acid, and 0.5 kg of monoethanolamine were mixed and dissolved to prepare a uniform solution. Next, 18.3 kg of the Ti—Si—W ternary oxide powder prepared in Example 1 was put into a kneader, and the vanadium-containing solution prepared earlier was added together with a molding aid such as an organic binder, and the mixture was stirred well. . Furthermore, after mixing well with a blender while adding an appropriate amount of water, the mixture was kneaded, extruded, dried and fired in the same manner as in Example 1 to obtain Catalyst C. The composition of the catalyst C is TiO ₂ : SiO ₂ : WO ₃ : V ₂ O ₅ = 81.4: 4.6: 5.5: 8.5 (mass ratio), and the total pore volume is 0.8. It was 45 mL / g.

(Comparative Example 1)
In 0.1 L of water, 0.03 kg of ammonium metavanadate and 0.03 kg of oxalic acid and 0.01 kg of monoethanolamine were mixed and dissolved to prepare a uniform solution. Next, 20.0 kg of the Ti—Si—W ternary oxide powder prepared in Example 1 was put into a kneader, and the vanadium-containing solution prepared earlier was added together with a molding aid such as an organic binder, followed by thorough stirring. . Further, after mixing well with a blender while adding an appropriate amount of water, the mixture was kneaded, extruded, dried and fired in the same manner as in Example 1 to obtain Catalyst D. The composition of the catalyst D is TiO ₂ : SiO ₂ : WO ₃ : V ₂ O ₅ = 88.9: 5.0: 6.0: 0.1 (mass ratio), and the total pore volume is 0.00. It was 41 mL / g.

(Comparative Example 2)
In 16 L of water, 3.09 kg of ammonium metavanadate, 3.70 kg of oxalic acid, and 0.7 kg of monoethanolamine were mixed and dissolved to prepare a uniform solution. Next, 17.6 kg of the Ti—Si—W ternary oxide powder prepared in Example 1 was put into a kneader, and the vanadium-containing solution prepared earlier was added together with a molding aid such as an organic binder, followed by thorough stirring. . Further, after mixing well with a blender while adding an appropriate amount of water, the mixture was kneaded, extruded, dried and fired in the same manner as in Example 1 to obtain Catalyst E. The composition of the catalyst E is TiO ₂ : SiO ₂ : WO ₃ : V ₂ O ₅ = 78.3: 4.4: 5.3: 12.0 (mass ratio), and the total pore volume is 0.8. It was 46 mL / g.

(Comparative Example 3)
A homogeneous solution was prepared by mixing and dissolving 1.29 kg of ammonium metavanadate, 1.54 kg of oxalic acid, and 0.3 kg of monoethanolamine in 7 L of water.

Next, instead of using the Ti—Si—W ternary oxide powder prepared in Example 1, 16.9 kg of TiO ₂ powder (DT-51 (product name), manufactured by Cristal Global) and SiO ₂ 1.0 kg of powder (nip seal LP (product name), manufactured by Tosoh Silica Co., Ltd.) and 1.3 kg of ammonium paratungstate (containing 90% by weight as WO ₃ ) are put into a kneader, together with molding aids such as an organic binder. The vanadium containing solution prepared previously was added and stirred well. Further, after mixing well with a blender while adding an appropriate amount of water, the mixture was kneaded, extruded, dried and fired in the same manner as in Example 1 to obtain Catalyst F. The composition of the catalyst F is TiO ₂ : SiO ₂ : WO ₃ : V ₂ O ₅ = 84.5: 4.8: 5.7: 5.0 (mass ratio), and the total pore volume is 0.8. It was 24 mL / g.

(NOx removal test)
Using the catalysts A to F obtained in Examples 1 to 3 and Comparative Examples 1 to 3, the NOx removal performance was evaluated under the following conditions.

[Supply gas composition]
_{NOx: 200ppm, NH 3: 200ppm} , SO 2: 200ppm, SO 3: 10ppm, O 2: 13 _volume%, H 2 O: 10 _volume%, N 2: balance
[Processing conditions]
Gas temperature: 265 ° C., space velocity: 18,000 h ⁻¹ (STP), gas linear velocity: 1.0 m / s (Normal)
Next, the NOx concentrations at the catalyst inlet and the catalyst outlet were measured, and the NOx removal rate was calculated according to the following equation (Equation 1). The measurement was performed 10 hours and 200 hours after the start of the reaction. The results are shown in Table 1.

  It can be seen that the catalyst D in which the amount of the component B is 0.1% by mass has inferior initial performance, and the catalyst E having 12% by mass has the same initial performance as the catalysts A to C but inferior in durability.

[Formula 1]

  The present invention stably treats NOx over a long time even when the temperature of the exhaust gas is low, in the treatment of exhaust gas containing sulfur oxides and nitrogen oxides (NOx) in the exhaust gas generated from marine diesel engines. In particular, even when sulfur oxide is contained in the exhaust gas, NOx contained in the exhaust gas can be treated stably over a long period of time.

Claims (2)

A catalyst for treating exhaust gas from a marine diesel engine, a composite oxide and / or mixed oxide obtained by a coprecipitation method from three compounds of titanium, silicon and tungsten as a catalyst A component, a catalyst As the B component, a compound of at least one element of vanadium, niobium and tantalum is contained, and the content of the catalyst B component is 0.2 to 10% by mass (oxidation with respect to the total of the catalyst A component and the catalyst B component) A catalyst for treating exhaust gas from a marine diesel engine. A method for treating exhaust gas from a marine diesel engine, comprising using the catalyst according to claim 1.