JP2006326578A - Catalyst for decomposing ammonia and nitrogen oxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst capable of restraining ammonia from leaking to the atmosphere while keeping a high denitrification rate even under such a condition that the concentration of nitrogen oxide fluctuates. <P>SOLUTION: The catalyst for deoxidizing nitrogen oxide in the presence of ammonia is composed of sulfated zirconia containing at least a manganese component. The ratio of the manganese component in terms of Mn is around 0.1-10 parts weight based on 100 parts weight zirconia. The catalyst can furthermore contain an iron component. The ratio of the iron component in terms of Fe can be around 0.1-10 parts weight based on 100 parts weight zirconia. When the gas to be treated is brought into contact with this catalyst at around 350-550°C, the nitrogen oxide in the gas to be treated can be deoxidized and removed and the unreacted ammonia therein can also be decomposed and removed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a reduction catalyst (or purification catalyst) useful for reducing nitrogen oxides contained in combustion exhaust gas and the like, and a method for removing nitrogen oxides (or a purification method for combustion gases, etc.). The present invention also relates to a catalyst useful for decomposing ammonia into nitrogen (a catalyst for decomposing ammonia) and a method for decomposing (or removing) ammonia.

Nitrogen oxides (NOx: x is usually 1 or 2, that is, nitric oxide and nitrogen dioxide in many cases) contained in combustion exhaust gas and nitric acid production process exhaust gas, acid rain, photochemical smog, respiratory disease The amount of emissions is strictly regulated. Nitrogen oxides in exhaust gas discharged from boilers, diesel engines, etc. contain excessive oxygen. This nitrogen oxides are selectively contacted by adding ammonia as a reducing agent and reducing the nitrogen oxides to nitrogen for denitration. It has been removed by the reduction method. In this selective catalytic reduction method, a titanium oxide-vanadium oxide catalyst or a catalyst composed of titanium oxide-vanadium oxide-tungsten oxide is widely used. For example, JP-A-50-51966 (Patent Document 1) discloses catalytic reductive decomposition of nitrogen oxide in which nitrogen oxide is contacted with a catalyst in which vanadium oxide is supported on titanium oxide or zirconium oxide in the presence of ammonia. The law is disclosed. Other than titanium oxide, it is known that a catalyst in which vanadium oxide is supported on zirconium oxide (such as the catalyst of Patent Document 1) and a catalyst in which sulfate radical and tungsten oxide are supported on zirconium oxide can be used as the catalyst for the selective catalytic reduction method. It has been. For example, Japanese Patent Application Laid-Open No. 2003-326167 (Patent Document 2) discloses a catalyst comprising zirconium oxide and SO ₃ or SO ₄ ²⁻ , and having a solid acid strength (Ho) of Ho ≦ −11.93. A high-temperature denitration catalyst used in a high temperature range of reaction temperature 450 to 800 ° C. is disclosed.

  The selective catalytic reduction method is characterized in that a denitration rate close to 100% can be obtained if the molar ratio between nitrogen oxides in the exhaust gas and ammonia to be added is strictly controlled. However, when the concentration of nitrogen oxides in the exhaust gas varies with time, it is extremely difficult to inject the ammonia amount necessary for denitrating nitrogen oxides without excess or deficiency. Therefore, in order to maintain a high denitration rate, it is necessary to add an excessive amount of ammonia with respect to nitrogen oxides. As a result, unreacted ammonia remains in the denitrated gas, and ammonia is discharged to the atmosphere. Therefore, for the purpose of reducing the amount of ammonia leaked into the atmosphere (leak ammonia concentration), it has a method of attaching a catalyst having an ammonia decomposition action downstream of a conventional catalyst, and an ammonia decomposition action and a nitrogen oxide reduction action. A method using a catalyst is shown.

For example, Japanese Patent Application Laid-Open No. 2002-336699 (Patent Document 3) describes a carrier having an acid site having a decomposing action of ammonia (a specific site on a solid surface involved in acid expression) (for example, zeolite, ZrO ₂ , A catalyst having ruthenium supported on SiO ₂ .Al ₂ O ₃ or the like is disclosed. When ammonia is treated using this catalyst, nitrogen is produced without producing nitrogen oxide, and ammonia is decomposed and removed, which is useful for reducing leaked ammonia after the ammonia denitration reaction.

  On the other hand, JP-A-5-146634 (Patent Document 4) and JP-A-8-290062 (Patent Document 5) disclose catalysts having an ammonia decomposition action and a nitrogen oxide reduction action. In the former, a catalyst in which a first component composed of titanium oxide-vanadium oxide-tungsten oxide and a second component in which platinum is supported on mordenite is proposed, and in the latter, the former is improved, A catalyst in which platinum and iridium are supported on silica as two components has been proposed. Both of these catalysts have an ammonia decomposing action by adding a small amount of noble metal and reduce leaked ammonia.

However, these catalysts are both expensive because they contain precious metals, and since precious metals generally have high oxidation activity, they are explosive when contacted with a gas containing a high concentration of hydrocarbons due to poor combustion or the like. It causes a catalytic oxidation reaction and the activity is significantly reduced. Further, for the same reason, the ammonia decomposition reaction proceeds vigorously at a high temperature of 450 ° C. or higher, and the denitration rate is significantly reduced.
JP-A-50-51966 (Claims) JP 2003-326167 A (Claims) JP 2002-336699 A (Claims) JP-A-5-146634 (Claims) JP-A-8-290062 (Claims)

  An object of the present invention is to reduce a nitrogen oxide (or purify a gas to be treated) that can suppress leakage (exhaust) of ammonia into the atmosphere while maintaining a high denitration rate even under conditions in which the concentration of nitrogen oxides varies. And a method for producing the same and a method for removing nitrogen oxides.

  Another object of the present invention is to remove a nitrogen oxide reduction catalyst or a treatment gas purification catalyst and a nitrogen oxide removal or treatment gas that can maintain high denitration activity even if the treatment gas contains hydrocarbons. It is to provide a purification method.

  Still another object of the present invention is to provide a highly durable reduction catalyst for nitrogen oxide and a method for removing nitrogen oxide that do not require a noble metal and can maintain high catalytic activity over a long period of time.

  Another object of the present invention is to provide a catalyst capable of efficiently decomposing ammonia into nitrogen and an ammonia decomposing method.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventor used a catalyst composed of sulfate zirconia containing a manganese component as a catalytic reduction catalyst, over a long period of time even under conditions in which the concentration of nitrogen oxides fluctuated, It has been found that the leakage (discharge) of ammonia into the atmosphere can be suppressed while maintaining a high denitration rate, and that the ammonia can be efficiently decomposed (or converted) into nitrogen when the catalyst is brought into contact with ammonia. Was completed.

  That is, the catalyst of the present invention is a catalyst for decomposing ammonia and / or nitrogen oxide, and is composed of sulfate zirconia containing at least a manganese component. In the catalyst, the ratio of the manganese component may be about 0.1 to 10 parts by weight with respect to 100 parts by weight of zirconia in terms of manganese Mn. The catalyst may further contain an iron component. In the catalyst containing such an iron component, the ratio of the total amount of the iron component and the manganese component may be about 1 to 10 parts by weight in total in terms of iron Fe and manganese Mn with respect to 100 parts by weight of zirconia. The ratio between the iron component and the manganese component may be about the former / the latter (weight ratio) = 95/5 to 10/90 in terms of iron Fe and manganese Mn.

  The catalyst of the present invention can be used as a catalyst for treating (decomposing) a gas to be treated containing ammonia. For example, the catalyst of the present invention is useful for reducing nitrogen oxides in the presence of ammonia. Therefore, the catalyst of the present invention may be a catalyst (reduction catalyst) used for reducing nitrogen oxides in the presence of ammonia. Such a catalyst of the present invention may usually have a reduction function for nitrogen oxides and a decomposition function for ammonia. The catalyst of the present invention can reduce nitrogen oxides at a high denitration rate, and can suppress the discharge of leaked ammonia into the atmosphere even if excess ammonia is used.

  The catalyst of the present invention can efficiently decompose ammonia into nitrogen. Therefore, the catalyst of the present invention may be a catalyst used for decomposing ammonia into nitrogen (a catalyst for decomposing ammonia).

  In the present invention, a method for removing (or decomposing) nitrogen oxides in which a gas to be treated containing nitrogen oxides is brought into contact with the catalyst (a catalyst composed of sulfate zirconia containing at least a manganese component) in the presence of ammonia. Method). In this method, the gas to be treated may be brought into contact with the catalyst at a temperature of about 350 to 550 ° C. Further, the amount of ammonia may be about 0.9 to 1.5 mol with respect to 1 mol of nitrogen oxide in the gas to be treated. When the gas to be treated is brought into contact with the catalyst of the present invention, nitrogen oxides in the gas to be treated can be efficiently reduced and removed, and unreacted ammonia that has not been used in the denitration reaction can also be decomposed and removed. Furthermore, even if the gas to be treated contains components such as hydrocarbons, a high denitration rate can be maintained over a long period of time.

  As described above, the catalyst of the present invention has a function of decomposing ammonia into nitrogen. Therefore, in the present invention, a gas to be treated containing ammonia [for example, a gas to be treated containing ammonia and (substantially) free from nitrogen oxide] is brought into contact with the catalyst to decompose ammonia into nitrogen. A method for decomposing ammonia is also included.

  The present invention also includes a method for producing the catalyst (a catalyst composed of sulfate zirconia containing at least a manganese component) by containing at least a manganese component in sulfate zirconia. In such a method, typically, a solution containing at least sulfate ions and manganese ions may be impregnated with zirconium hydroxide, dried, and fired. In this method, since the iron component is supported on zirconia (or sulfate zirconia), the solution may further contain iron ions.

In this specification, the nitrogen oxide is a general term for nitrogen oxides such as NO and NO ₂ represented by NO _x .

  According to the present invention, since a specific catalyst is used, the discharge of ammonia into the atmosphere can be suppressed while maintaining a high denitration rate even under conditions where the nitrogen oxide concentration varies. Moreover, even if the gas to be treated contains hydrocarbons, high catalytic activity can be maintained. Furthermore, since no precious metal is required, not only is it inexpensive, but high catalytic activity can be maintained over a long period of time, and durability is high. The catalyst of the present invention can efficiently decompose ammonia into nitrogen.

[catalyst]
The catalyst of the present invention is composed of sulfate zirconia containing a manganese component.

The sulfate radical zirconia constituting the catalyst is composed of a sulfate radical and zirconia (ZrO ₂ ). The sulfate group zirconia may have any crystal structure (crystal system) as long as it has catalytic activity. However, the sulfate group is usually formed on the surface of tetragonal zirconium oxide (IV) (zirconia, ZrO ₂ ). In many cases, (SO ₄ ²⁻ ) is present, and a small amount of monoclinic zirconia may be included. Zirconia (or zirconium) is not limited to being included as an oxide (zirconia), and is a compound (for example, hydroxide, halide, oxyacid salt, organic acid salt) as long as the activity of the catalyst is not hindered. May be included. The sulfate radical zirconia may contain a sulfate radical as a coordination or salt.

The ratio of sulfate radicals to zirconia may be in a range that does not hinder the activity of the catalyst. The ratio of sulfate radicals (in terms of sulfur S) is, for example, 0.1 parts per 100 parts by weight of zirconia (ZrO ₂ ). -10 parts by weight (eg, 0.2-10 parts by weight), preferably 0.2-8 parts by weight [eg, 0.3-8 parts by weight (eg, 0.5-7 parts by weight)], more preferably May be about 1 to 5 parts by weight (for example, 2 to 4 parts by weight), and usually 0.2 to 5 parts by weight (for example, 0.3 to 4 parts by weight, preferably 0.4 to 2.5 parts by weight). Part by weight).

In the manganese component constituting the catalyst, the valence of manganese is not particularly limited, and may be divalent manganese Mn (II) or trivalent manganese Mn (III). Further, the manganese component may be contained in the form of a manganese compound as long as it does not affect the activity of the catalyst. For example, oxides (eg, MnO, Mn ₂ O ₃ , MnO ₂ ), hydroxides (eg, Mn (OH) ₂ ), inorganic acid salts [eg, sulfates (eg, MnSO ₄ , Mn ₂ (SO _{4 3} )] etc. may exist.

The ratio of the manganese component in the catalyst is, for example, 0.05 to 10 parts by weight (for example, 0.1 to 10 parts by weight), preferably 0 in terms of manganese Mn, with respect to 100 parts by weight of zirconia (ZrO ₂ ). 0.1-5 parts by weight (eg 0.2-5 parts by weight), more preferably 0.2-4 parts by weight (eg 0.3-2 parts by weight), in particular 0.3-4 parts by weight (eg 0.5-3 parts by weight). If the proportion of the manganese component is too small, the catalytic activity may be reduced. If the proportion of the manganese component is too large, coarse manganese oxide particles are formed, and the oxidation of ammonia is excessively promoted. There is a possibility that the nitrogen oxide removing performance of the catalyst may be lowered.

  The catalyst of the present invention only needs to contain at least a manganese component, and may further contain an iron component. That is, the catalyst of the present invention may be composed of sulfate zirconia containing a manganese component and an iron component.

In the iron component constituting the catalyst, the valence of iron is not particularly limited, and may be divalent iron Fe (II) or trivalent iron Fe (III). Furthermore, the iron component may be contained in the form of an iron compound as long as it does not affect the activity of the catalyst. For example, iron oxide (for example, FeO, Fe ₃ O ₄ , Fe ₂ O ₃ ), iron hydroxide (for example, Fe (OH) ₂ ), inorganic acid salt [for example, sulfate (for example, FeSO ₄ , Fe ₂ ( SO ₄ ) ₃ ) etc.] may be included.

The ratio of the iron component in the catalyst is, for example, 0.1 to 10 parts by weight, preferably 0.2 to 8 parts by weight, more preferably 0, in terms of iron Fe, with respect to 100 parts by weight of zirconia (ZrO ₂ ). It may be about 5 to 7 parts by weight (for example, 1 to 5 parts by weight). If the ratio of the iron component is too small, there is a possibility that a sufficient addition effect cannot be obtained. If the ratio of the iron component is too large, coarse iron oxide particles are formed, and oxidation of ammonia is excessively promoted. The nitrogen oxide removal performance of the catalyst of the present invention may be reduced.

  In the catalyst, the ratio of the iron component and the manganese component may be in a range that can provide sufficient catalytic activity. The former / the latter (weight ratio) = 98/2 to 5/95 in terms of iron Fe and manganese Mn. The range can be selected from, for example, 95/5 to 10/90, preferably 90/10 to 30/70, and more preferably 85/15 to 50/50 (for example, 80/20 to 60/40). There may be.

The ratio of the total amount of iron component and manganese component, the sum of iron Fe and manganese Mn in terms of zirconia _(ZrO 2) with respect to 100 parts by weight, for example, 0.5 to 20 parts by weight, preferably 1 to 10 The weight may be about 1.5 to 8 parts by weight (for example, 1.5 to 6 parts by weight).

  Moreover, the ratio of the total amount of an iron component and a manganese component is the sum of iron Fe and manganese Mn conversion, and is 10-200 weight part with respect to 100 weight part of sulfate radicals (sulfur S conversion), Preferably it is 20-150. It may be about parts by weight (for example, 20 to 120 parts by weight), more preferably about 25 to 100 parts by weight (for example, 30 to 50 parts by weight).

  The manganese component (and iron component) constituting the catalyst may be included in the catalyst in any form. In particular, it is desirable that at least a part of each of the iron component and the manganese component (for example, a part of the manganese component) is exposed on the surface of the sulfate zirconia. Further, the manganese component (and iron component) is preferably present in a uniformly dispersed state on the catalyst surface, and at least a part thereof may be dissolved in the sulfate radical zirconia.

In addition, the said catalyst may contain other atoms (a metal atom etc.), such as titanium, silicon, rare earth, etc. in the range which does not reduce catalyst activity. Such other atoms may be contained as a simple substance, or may be contained as a compound (for example, an oxide such as TiO ₂ ). In particular, commercially available zirconia and its precursors often contain a small amount of hafnium (for example, about 5% by weight with respect to zirconia). The catalyst of the present invention does not adversely affect the catalytic activity even if such a small amount of atoms (hafnium or the like) is contained.

  The catalyst of the present invention is a very useful catalyst excellent in (1) activity, (2) selectivity, and (3) durability, which are three elements of the catalyst function. That is, (1) a high denitration rate can be realized even under conditions where the nitrogen oxide concentration fluctuates, and the discharge of leaked ammonia into the atmosphere is suppressed, and (2) the nitrogen oxide concentration is extremely low (for example, 10 to 10%). 3000ppm) and can be selectively denitrated even in the presence of a large amount of other component gases other than nitrogen oxides. (3) Since it has moderate activity in the oxidation reaction of hydrocarbons, degradation due to explosive reactions It is suppressed and accumulation of catalyst poison can be suppressed.

  The shape of the catalyst of the present invention is not particularly limited, and examples thereof include powder, granule (or granule), pellet, and honeycomb. Of these shapes, the honeycomb shape is preferable from the viewpoint of reducing the pressure loss during the treatment of the gas to be treated. The catalyst may be non-porous or porous.

The BET specific surface area of the catalyst is usually 10 m ² / g or more, and may be, for example, about 10 to 300 m ² / g, preferably about 50 to ²⁰⁰ m ² / g, and more preferably about 80 to 160 m ² / g. .

  In addition, if necessary, various conventional additives may be blended in the catalyst as long as the activity of the catalyst is not impaired.

  The catalyst of the present invention can be produced by adding at least a manganese component (for example, a manganese component, a manganese component, an iron component, etc.) to sulfate zirconia. This production method is not particularly limited as long as it can contain a manganese component (and iron component) in sulfate zirconia, and the manganese component (and iron component) can be added to sulfate zirconia simultaneously or separately ( It may be contained individually), or may be contained in a lump (or once) or divided into a plurality of times. When the iron component and the manganese component are contained separately, the order is not particularly limited.

  In the above production method, the manganese component (and iron component) may be contained in any stage of the catalyst preparation step as long as it can be contained in sulfate zirconia. For example, zirconium component, zirconia, and sulfate zirconia You may make it contain in any of the components selected from (sulfate radical zirconia source). In addition, when making it contain in a zirconium component or a zirconia, the process of containing a sulfate radical is needed. Such a step of containing a sulfate group can also be performed at an appropriate stage of the catalyst preparation step. For example, a sulfate group may be contained together with a manganese component (and an iron component), or a manganese component (and an iron component). After the component) is contained, a sulfate radical may be contained.

  Typically, for example, (1) zirconium hydroxide or a precursor thereof (hereinafter simply referred to as a zirconium component) and a solution containing sulfate ions and manganese ions (and iron ions) are mixed, dried, and fired. The catalyst of the present invention can be produced by a method, (2) a method of supporting a manganese component (and an iron component) on sulfate zirconia as a support, and the like. Usually, in many cases, a sulfate component zirconia source is impregnated (or immersed) or treated with a manganese component (and an iron component) and fired. Hereinafter, these production methods (1) and (2) will be described in detail.

[Production Method (1)]
As the production method (1), for example, (i) a zirconium component (particularly zirconium hydroxide) is impregnated in a solution (particularly an aqueous solution) containing sulfate ions, manganese ions (and iron ions as required) ( In the case of a catalyst containing an iron component, (ii) a zirconium component is impregnated in a solution (especially an aqueous solution) containing sulfate ions and iron ions, dried, baked, and then manganese. After impregnating a solution containing ions (especially an aqueous solution), drying and firing, (iii) After impregnating (or immersing) the zirconium component in a solution containing sulfate ions and manganese ions (particularly an aqueous solution), and drying and firing. And a method of impregnating this in a solution containing iron ions (particularly, an aqueous solution), drying and firing. The method (i) is efficient and preferable.

  The zirconium component is a general term for zirconium hydroxide or a precursor thereof, and the precursor of zirconium hydroxide is a compound (particularly a water-soluble compound) capable of forming zirconium hydroxide, and an inorganic acid salt (sulfuric acid). Zirconium, zirconium nitrate, etc.), halides (zirconium chloride, etc.), organic acid salts (zirconium acetate, etc.) and the like can be exemplified. These zirconium components can be used alone or in combination of two or more. Of these zirconium components, zirconium hydroxide and the like are preferable.

  The solution containing sulfate ions may be prepared, for example, by dissolving sulfuric acid or various sulfates (ammonium sulfate, titanium sulfate, etc.) as long as the activity of the catalyst is not affected. These can be used alone or in combination of two or more. Of these, ammonium sulfate is preferred because the remaining cation does not adversely affect the activity of the catalyst.

  Solutions containing manganese ions (especially aqueous solutions) may be used in various manganese compounds such as inorganic acid salts (eg, sulfates such as manganese (II) sulfate, manganese (III) sulfate, and the like) as long as they do not affect the activity of the catalyst. Double salt of sulfate; nitrates such as manganese (II) nitrate), chlorides (such as manganese (II) chloride), organic acid salts (eg acetates such as manganese (II) acetate, manganese (III) acetate), A complex (for example, a manganese carbonyl compound) or the like may be prepared by dissolving in water. These manganese compounds can be used alone or in combination of two or more. Of these manganese compounds, manganese sulfate is preferred.

  Solutions containing iron ions (especially aqueous solutions) can be used for various water-soluble iron compounds such as inorganic acid salts (for example, sulfuric acid such as iron (II) sulfate and iron (III) sulfate) as long as they do not affect the activity of the catalyst. Salts and sulfate double salts; nitrates such as iron (II) nitrate and iron (III) nitrate), chlorides (such as iron (II) chloride and iron (III) chloride), organic acid salts (eg iron acetate (III) )), Complexes (for example, iron carbonyl compounds, etc.) and the like may be dissolved in water. These iron compounds can be used alone or in combination of two or more. Of these iron compounds, iron sulfate is preferred.

  In addition, in the said manufacturing method, the solvent which comprises a solution will not be specifically limited if it is a solvent which can melt | dissolve each component (a manganese compound, an iron compound, a sulfuric acid component, etc.), Water, organic solvents (alcohols, ketones) And esters). These solvents may be used alone or in combination of two or more. Usually, the solution is often an aqueous solution because each component is often water-soluble and is environmentally advantageous. The aqueous solution may contain other solvents (alcohols and the like).

The proportion of the zirconium component, sulfate ion, iron ion and manganese ion is not particularly limited as long as the catalyst having the component proportion can be produced. Components that volatilize by firing (such as sulfate ions) may be added in a greater amount than the final catalyst. For example, the ratio of sulfate ion (in terms of SO ₄ ²⁻ ) is, for example, 1 to 100 parts by weight, preferably 3 to 50 parts by weight, and more preferably 5 to 30 parts per 100 parts by weight of the zirconium component (in terms of zirconia). It may be about parts by weight (particularly 10 to 30 parts by weight).

  The impregnation temperature of the zirconium component is usually room temperature (about 15 to 25 ° C.), but may be heated (for example, about 30 to 80 ° C., particularly about 50 to 80 ° C.).

  The drying conditions are not particularly limited, and may be dried by heating (for example, about 100 to 150 ° C.) under normal pressure or reduced pressure, or may be evaporated to dryness.

  The calcination temperature can be selected from about 300 to 800 ° C. as long as the catalytic activity is not impaired. For example, 350 to 750 ° C. (for example, 350 to 700 ° C.), preferably 400 to 700 ° C. (for example, 400 to 650 ° C., preferably 450 to 550 ° C.), particularly 500 to 600 ° C., usually about 500 to 730 ° C. (for example, 550 to 700 ° C.). If the firing temperature is too high, the sulfate radicals may volatilize and disappear. If it is too low, there will be no firing effect and stable crystals will not be formed. The firing time is usually selected from the range of about 10 minutes to 100 hours (for example, 1 to 80 hours), for example, 1 to 50 hours (for example, 1 to 20 hours), preferably about 3 to 10 hours. is there.

[Production method (2)]
The sulfate radical zirconia may be prepared by a conventional method, and for example, it can be obtained by impregnating a zirconium component in a solution containing sulfate ions, drying and firing. In addition, the solution containing the zirconium component and sulfate ion illustrated by the term of the manufacturing method (1) can respectively be used for the solution containing a zirconium component and a sulfate ion. These solutions containing zirconium components and sulfate ions can also be used alone or in combination of two or more. Among these, it is preferable to use a combination of zirconium hydroxide and an ammonium sulfate solution from the viewpoint of not adversely affecting the activity of the catalyst.

  In the production method (2), an aqueous solution can be suitably used as described above.

  The impregnation temperature at which the zirconium component is impregnated with the solution containing sulfate ions, the drying conditions, the firing temperature, the firing time, and the like are the same as those in the production method (1).

  For example, (i) Sulfate zirconia is impregnated in a solution containing manganese ions (and iron ions as required) and dried. , A method of firing, and a catalyst containing an iron component, (ii) impregnating (or immersing) sulfate radical zirconia in a solution containing iron ions, drying, firing, impregnating this in a solution containing manganese ions, and drying A method of firing, (iii) a method of impregnating (or immersing) sulfate zirconia in a solution containing manganese ions, drying and firing, then impregnating the solution in a solution containing iron ions, drying, and firing. It is done. The method (i) is efficient and preferable. The iron compound and manganese compound used in the solution containing iron ions and the solution containing manganese ions are not particularly limited, and the iron compounds and manganese compounds exemplified in the section of production method (1) can be used. These iron compounds or manganese compounds can be used alone or in combination of two or more.

  The catalyst of the present invention can also be produced by methods other than the production methods (1) and (2). When the production methods (1) and (2) are compared, the production method (1) is economically advantageous because a catalyst can be prepared with a smaller number of steps.

Examples of the method for molding the catalyst include conventional methods such as a kneader, a molding machine (such as an extrusion molding machine and a compression molding machine), and a method using a tableting machine. Examples of the method for forming the catalyst into a honeycomb shape include a method of coating the catalyst on a honeycomb-like refractory ceramic, a method of adding a binder as necessary, and a method of extrusion forming into a honeycomb shape. As a method of forming into a honeycomb shape, an extrusion method is preferable from the viewpoint of the performance of the catalyst. The number of cells of the honeycomb can be selected within a range in which an increase in pressure loss during the treatment of the gas to be treated can be suppressed. For example, 1 to 250 cells / cm ² , preferably 5 to 150 cells / cm ² , more preferably 10 to 100. It may be about pieces / cm ² . The aperture ratio of the honeycomb may be about 50 to 80%, preferably about 55 to 75%.

  The catalyst of the present invention can be used as a catalyst for decomposing ammonia and / or nitrogen oxides. For example, the catalyst of the present invention is useful as a catalyst (reduction catalyst) for reducing nitrogen oxides in the presence of ammonia. Such a nitrogen oxide reduction catalyst usually has not only a reduction function for nitrogen oxides but also a decomposition function for ammonia, so even if excess ammonia is used, the amount of ammonia leaking can be reduced. . The catalyst of the present invention is also useful as a catalyst for decomposing ammonia into nitrogen regardless of whether the gas to be treated contains nitrogen oxides. That is, the catalyst acts as a nitrogen oxide decomposition catalyst (or reduction catalyst) (and ammonia decomposition catalyst), but ammonia decomposition catalyst (specifically, ammonia in the gas to be treated containing at least ammonia). It functions also as a catalyst for decomposing | disassembling. Hereinafter, a method for decomposing nitrogen oxides and / or ammonia using the catalyst of the present invention will be described in detail.

[Nitrogen oxide removal method]
In the present invention, by treating the gas to be treated in the presence of ammonia using the catalyst of the present invention, nitrogen oxides contained in the gas to be treated can be removed with a high denitration rate. The gas to be treated in the present invention refers to a nitrogen oxide-containing gas that can be purified by the catalyst of the present invention. Examples thereof include combustion exhaust gas and nitric acid production process gas. The nitrogen oxide concentration in the gas to be treated may be 5000 ppm or less (for example, 1 to 5000 ppm) in volume ratio, and is usually about 5 to 4000 ppm, preferably about 10 to 3000 ppm.

  In addition to nitrogen oxides, the gas to be treated may contain oxygen, water vapor, carbon dioxide and the like. The ratio of oxygen is, for example, about 0.1 to 30% by volume, preferably 1 to 20% by volume, and more preferably about 2 to 15% by volume in the gas to be treated. The ratio of water vapor is, for example, about 0.1 to 50% by volume, preferably 1 to 30% by volume, and more preferably about 2 to 20% by volume in the gas to be treated. The ratio of carbon dioxide is, for example, about 0.1 to 20% by volume, preferably about 0.5 to 15% by volume, and more preferably about 1 to 10% by volume in the gas to be treated.

  Further, the combustion exhaust gas often contains sulfur oxides that deteriorate the subsequent equipment, and the catalyst of the present invention can also be applied to gases containing sulfur oxides. About 0.1-100 ppm (for example, 1-70 ppm) may be sufficient as the density | concentration of the sulfur compound in to-be-processed gas by volume ratio.

  Furthermore, the removal method of the present invention can be applied even if the gas to be treated contains a combustible component such as hydrocarbon or carbon monoxide that reduces the activity in a general-purpose catalyst. Even if the concentration of these components is contained in the gas to be treated at a relatively high concentration, for example, about 500 to 3000 ppm (for example, 1000 to 2000 ppm) by volume, the present invention reduces the activity of the catalyst. Can be prevented.

  In the method for removing nitrogen oxides of the present invention, the gas to be treated containing nitrogen oxides in the presence of ammonia is composed of sulfate zirconia containing the catalyst (manganese component (and iron component as required)). Nitrogen oxide is removed from the gas to be treated by contacting with the catalyst. Ammonia may be present in the gas treatment system to be treated, and may be present in the system by applying a known method. For example, not only a method of adding gaseous ammonia using liquefied ammonia, but also a method of generating ammonia in the system, such as a method of spraying an aqueous solution of a compound that generates ammonia by thermal decomposition of urea or ammonium carbonate. And ammonia may be present. The amount of ammonia before the start of treatment may be adjusted as appropriate according to the type of gas to be treated. For example, 0.9 to 1.5 moles (for example, 1 to 1 mole of nitrogen oxide in the gas to be treated). About 1.0 to 1.5 mol), preferably about 1.0 to 1.3 mol, and more preferably about 1.1 to 1.2 mol. In particular, in the present invention, since ammonia is converted to nitrogen, in particular, 1 mol or more (for example, about 1.1 to 1.5 mol) of ammonia is contained with respect to 1 mol of nitrogen oxide in the gas to be treated. Even so, the amount of ammonia leakage can be suppressed to a sufficiently low level. If the amount of ammonia is too small, a sufficient denitration rate cannot be obtained. If the amount is too large, the amount of leaked ammonia may increase, and the economy will also decrease.

  The contact temperature between the nitrogen oxide-containing gas to be treated and the catalyst can be selected from a range in which the denitration rate is not impaired and the amount of leaked ammonia can be suppressed, and is, for example, 300 ° C. or higher, preferably 350 ° C. or higher (for example, 350 ˜650 ° C.), more preferably 400 ° C. or more (for example, 400 to 600 ° C.), still more preferably about 450 ° C. or more (for example, 450 to 550 ° C.). If the temperature is too low, the catalytic activity decreases, which is accompanied by a decrease in the denitration rate and an increase in the leak ammonia concentration. On the other hand, if it is too high, the denitration rate is lowered, and the durability of the catalyst is lowered. In particular, in order to remove nitrogen oxide with high efficiency, the contact may be performed at a temperature not exceeding 500 ° C. (for example, 320 to 470 ° C., preferably 350 to 450 ° C., more preferably about 370 to 430 ° C.).

In the gas-treated system, the gas space velocity per hour (GHSV) is preferably in a range that achieves both economic efficiency and denitrification, for example, 500 to 200000 h ⁻¹ , preferably 1000 to 150,000 h ⁻¹ , more preferably. Is about 2000 to 100000 h ⁻¹ , particularly about 5000 to 30000 h ⁻¹ . The linear velocity (LV) of the gas to be treated with respect to the catalyst can be selected, for example, from a range of about 0.02 to 20 m / second, preferably 0.05 to 5 m / second, and more preferably about 0.3 to 3 m / second.

  The length as a catalyst layer can be selected in the range which does not impair catalyst activity, for example, 0.01-10 m, Preferably it is 0.05-5 m, More preferably, about 0.1-1 m may be sufficient.

[Ammonia decomposition method]
In the ammonia decomposition method of the present invention, the gas to be treated (ammonia-containing gas to be treated) containing ammonia is composed of sulfate zirconia containing the catalyst (manganese component (and iron component as required)). The ammonia is decomposed (converted) into harmless nitrogen and removed. The ammonia concentration in the gas to be treated may be 5000 ppm or less (for example, 1 to 5000 ppm) in volume ratio, and usually 5 to 4000 ppm, preferably about 10 to 3000 ppm. Note that the gas to be processed may contain nitrogen oxides as described above, and may contain oxygen, water vapor, carbon dioxide, hydrocarbons, carbon monoxide, and the like as described above. In addition, the content rate of these gas in to-be-processed gas can be selected from the same range as the case of the said nitrogen oxide removal method. The gas to be processed may be a gas to be processed that does not substantially contain nitrogen oxides. For example, in the ammonia decomposing method of the present invention, a gas to be treated which is reduced and removed from nitrogen oxides and does not substantially contain nitrogen oxides and which contains ammonia may be used.

  The contact temperature between the ammonia-containing gas to be treated and the catalyst is, for example, 350 ° C. or higher, preferably 400 ° C. or higher (eg 400 to 600 ° C.), more preferably 450 ° C. or higher (eg 450 to 550 ° C.). It is. If the temperature is too low, the catalytic activity is lowered and the decomposition rate is lowered. On the other hand, if it is too high, a part of ammonia may be converted to nitrogen oxide, and the durability of the catalyst may be lowered. Note that the gas space velocity, the length of the catalyst layer, and the like can be selected from the same ranges as in the case of the nitrogen oxide removing method.

  The nitrogen oxide removal method and the ammonia decomposition method may be combined with other methods, or the nitrogen oxide removal method and the ammonia decomposition method may be combined. For example, in the presence of ammonia, a gas to be treated containing nitrogen oxide is brought into contact with the catalyst or a conventional catalyst (for example, a titanium oxide catalyst) to reduce and remove the nitrogen oxide, and then the nitrogen oxide is removed. Further, the gas to be treated containing ammonia may be further brought into contact with the catalyst on the downstream side to decompose ammonia into nitrogen.

  The present invention is not only a gas to be treated containing nitrogen oxides from various sources, for example, a discharge system in which the concentration of nitrogen oxides is constantly stable (for example, gas discharged from a power plant, etc.) It can also be applied to exhaust systems in which the concentration of nitrogen oxides fluctuates in time series (for example, combustion exhaust gas discharged from boilers and prime movers and nitric acid production process exhaust gas). Available for removal). The present invention can reduce the amount of leaked ammonia even if an excessive amount of ammonia is added to the nitrogen oxide, so that it is particularly useful for the treatment of combustion exhaust gas and process exhaust gas in which the nitrogen oxide concentration tends to fluctuate greatly in time series. It is. The catalyst of the present invention has a function of decomposing ammonia itself. For this reason, leak ammonia can be efficiently converted into harmless nitrogen by a method such as disposing the catalyst of the present invention downstream of the general-purpose catalyst (titanium oxide catalyst, etc.) relative to the gas stream. In general, it is easy to achieve a high denitration rate and a low ammonia leak which are incompatible with each other.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. The denitration rate and the leaked ammonia concentration in the examples and comparative examples were calculated from the following equations based on the concentrations of nitrogen oxides and ammonia contained in the gas to be treated before and after the treatment with the catalyst. The “pre-catalyst concentration” indicates the concentration upstream of the gas flow to be processed with respect to the catalyst, and the “post-catalyst concentration” indicates the concentration downstream of the gas flow with respect to the gas to be processed. In the examples, all units are based on volume unless otherwise specified.

Denitration rate (%) = 100 × {1- (post-catalyst NOx concentration) / (pre-catalyst NOx concentration)}
Leak ammonia concentration (ppm) =
{(Pre-catalyst NOx concentration (ppm)) + (Pre-catalyst ammonia concentration (ppm)) − 2 × (Post-catalyst nitrogen concentration (ppm)) − (Post-catalyst NOx concentration (ppm))}
The NOx concentration in the gas was measured with a chemiluminescent NOx analyzer, and the nitrogen concentration was measured with a gas chromatograph.

  Further, the decomposition rate in the ammonia decomposition reaction was calculated from the following equations for the nitrogen generation reaction and the nitrogen oxide generation reaction, respectively.

Nitrogen (decomposition rate due to nitrogen generation) (%) =
200 × (nitrogen concentration after catalyst) / (ammonia concentration before catalyst)
Nitrogen oxide (decomposition rate due to formation of nitrogen oxide) (%) =
100 × (NOx concentration before catalyst) / (Ammonia concentration before catalyst).

Example 1
Zirconium hydroxide; and (Mitsuwa Chemicals Co., Ltd. as ZrO ₂ 79 wt% content) 120 g, ammonium sulfate 18 g, iron sulfate _{(III) (Fe 2 (SO} 4) 3 · 15H 2 O) 6.0g and sulfuric acid It was immersed for 15 hours in a 100 ml aqueous solution in which 2.0 g of manganese (MnSO ₄ .5H ₂ O) was dissolved. After evaporating to dryness on a hot plate having a temperature of 120 ° C. under normal pressure (atmospheric pressure), the mixture was calcined in air at 550 ° C. for 6 hours to obtain a Fe—Mn-supported sulfate zirconia catalyst (1.1 Fe—0.5 Mn). / SZ). As a result of fluorescent X-ray analysis, the iron content of this catalyst was 1.1% by weight with respect to zirconia in terms of Fe. The manganese content was 0.5% by weight with respect to zirconia in terms of Mn. As a result of ICP analysis, the sulfate group content was 4.8% by weight as a weight ratio to the whole catalyst in terms of S. The BET specific surface area of the catalyst was 139 m ² / g. As a result of X-ray diffraction analysis, the crystal form of the catalyst was found to be mainly tetragonal.

The catalyst was compression-molded to prepare a granulated product having a particle size of 1 to 2 mm, and 4.5 ml of the granulated product was filled in a quartz reaction tube (inner diameter 14 mm). The temperature of the catalyst was maintained at 350 ° C., 400 ° C., 450 ° C. or 500 ° C., and the gas to be treated was circulated at a flow rate of 1.2 liters per minute (volume at 0 ° C., 1 atm) (GHSV = 16000 h ^−1). ).

As the gas to be treated, nitrogen monoxide NO, ammonia NH _3, oxygen _{O 2,} water _H 2 O, composed of sulfur dioxide SO _2, and the balance helium, NH ₃ concentration of two different gas to be treated It was used. Regarding the ratio of each component contained in the gas to be treated, the ratio (volume ratio) of NO, O ₂ , H ₂ O, and SO ₂ is 320 ppm for NO, 10% for O ₂ , and H _{2 for} any gas to be treated. O is 10%, SO ₂ is 1 ppm, and the ratio (volume ratio) of NH ₃ is 250 ppm and 320 ppm (in order, [NH ₃ ] / [NO] (molar ratio) is 0.78, 1. 00).

Then, the temperature of each catalyst is kept at 550 ° C., and the gas to be treated is circulated for 10 hours at a flow rate of 1.2 liters per minute (volume at 0 ° C., 1 atm), and high temperature treatment (high temperature durability treatment, high temperature degradation). Treatment). In the high-temperature treatment, the gas to be treated was 320 ppm NO, 320 ppm NH ₃ , 10% O ₂ , 10% H ₂ O, and 1 ppm SO ₂ .

Subsequently, the gas to be treated was circulated through the catalyst after the high temperature treatment. That is, the temperature of each catalyst is kept at the same temperature (350 ° C., 400 ° C., 450 ° C. or 500 ° C.) as before the high temperature treatment, and the gas to be treated is 1.2 liters per minute (0 ° C., 1 atm volume) ) (GHSV = 16000 h ⁻¹ ). As the gas to be treated, nitrogen monoxide NO, ammonia NH _3, oxygen _{O 2,} water _H 2 O, is composed of sulfur dioxide SO _2, and the balance helium was used four different gas of NH ₃ concentration . Regarding the ratio of each component contained in the gas to be treated, the ratio (volume ratio) of NO, O ₂ , H ₂ O, and SO ₂ is 320 ppm for NO, 10% for O ₂ , and H _{2 for} any gas to be treated. O is 10%, SO ₂ is 1 ppm, and the ratio (volume ratio) of NH ₃ is 250 ppm, 320 ppm, 400 ppm, and 480 ppm (in order, [NH ₃ ] / [NO] (molar ratio) is 0.00). 78, 1.00, 1.25, 1.50).

  Table 1 shows the denitration rate before the high temperature treatment (the upper part of Table 1) and the denitration rate after the high temperature treatment (the lower part of Table 1).

As is clear from the results in Table 1, a denitration rate substantially corresponding to the ammonia concentration is obtained at 400 ° C. or higher. That is, when [NH ₃ ] / [NO] (molar ratio) is less than 1, the denitration rate is [NH ₃ ] / [NO] × 100%, and [NH ₃ ] / [NO] (molar ratio) is In the case of 1 or more, it was found that the denitration rate was 100%.

  In addition, the catalyst still showed excellent denitration performance even after high temperature treatment at about 550 ° C. Its denitration performance was improved compared to that before high temperature treatment. For example, a denitration rate corresponding to the ammonia concentration was obtained even at 350 ° C., and the performance was almost unchanged up to 500 ° C.

Furthermore, the leaked ammonia concentration after the high temperature treatment was 10 ppm or less even under the conditions where the catalyst temperature was 500 ° C. and the NH ₃ ratio (volume ratio) was 480 ppm. This means that most of the excess ammonia (160 ppm) has been converted to nitrogen. Therefore, unlike the conventional catalyst, the catalyst of Example 1 can reduce the leaked ammonia concentration even when ammonia is excessively added, and has durability against high temperature treatment.

(Comparative Example 1)
180 g of zirconium hydroxide (manufactured by Mitsuwa Chemicals Co., Ltd .; containing 79% by weight as ZrO ₂ ) was immersed in a 150 ml aqueous solution in which 27 g of ammonium sulfate was dissolved for 15 hours. After evaporating to dryness on a hot plate having a temperature of 120 ° C. under normal pressure (atmospheric pressure), the mixture was calcined in air at 550 ° C. for 6 hours to obtain a sulfate radical zirconia catalyst (SZ). As a result of ICP analysis, the sulfate group content was 2.1% by weight in terms of S, based on the total catalyst.

  For this catalyst (SZ), the catalyst was evaluated before and after the high temperature treatment in the same manner as in Example 1. The results are shown in Table 2.

  As is apparent from Table 2, this catalyst had a significantly low denitration rate or a negative value. This is presumably because ammonia did not reduce NOx, but was oxidized by oxygen to produce NOx.

(Comparative Example 2)
150 ml of zirconium hydroxide (manufactured by Mitsuwa Chemicals Co., Ltd .; containing 79 wt% as ZrO ₂ ), 18 ml of ammonium sulfate and 14 g of iron (III) sulfate (Fe ₂ (SO ₄ ) ₃ · 15H ₂ O) For 15 hours. After evaporating to dryness on a hot plate having a temperature of 120 ° C. under normal pressure (atmospheric pressure), the mixture was calcined in air at 550 ° C. for 6 hours to obtain an iron-supported sulfate zirconia catalyst (1.5Fe-SZ). . As a result of fluorescent X-ray analysis, the iron content of this catalyst was 1.5% by weight with respect to zirconia in terms of Fe. As a result of the ICP analysis, the sulfate group content was 3.3% by weight in terms of S, based on the entire catalyst. The BET specific surface area of the catalyst was 140 m ² / g. As a result of X-ray diffraction analysis, the crystal form of the catalyst was found to be mainly tetragonal.

  For this catalyst (1.5Fe-SZ), the catalyst was evaluated before and after the high temperature treatment in the same manner as in Example 1. The results are shown in Table 3.

As is apparent from Table 3, the denitration performance is high at 400 ° C. or higher, but the denitration rate is only 84% at 350 ° C. even under the condition of excess ammonia. Further, the leaked ammonia concentration after the high-temperature treatment was 55 ppm under the conditions of the catalyst temperature of 500 ° C. and the NH ₃ ratio (volume ratio) of 480 ppm, which was 5.5 times that of Example 1.

(Comparative Example 3)
150 ml of zirconium hydroxide (manufactured by Mitsuwa Chemicals Co., Ltd .; containing 79% by weight as ZrO ₂ ) is dissolved in 7 g of ammonium sulfate and 7 g of iron sulfate (III) (Fe ₂ (SO ₄ ) ₃ · 15H ₂ O) For 15 hours. After evaporating to dryness on a hot plate having a temperature of 120 ° C. under normal pressure (atmospheric pressure), it was calcined in air at 550 ° C. for 6 hours to obtain an iron-supported sulfate radical zirconia catalyst (2.9Fe-SZ). . As a result of fluorescent X-ray analysis, the iron content of this catalyst was 2.9% by weight based on zirconia in terms of Fe. As a result of ICP analysis, the sulfate group content was 3.8% by weight with respect to the total catalyst in terms of S. The catalyst had a BET specific surface area of 148 m ² / g. As a result of X-ray diffraction analysis, the crystal form of the catalyst was found to be mainly tetragonal.

  For this catalyst (2.9Fe-SZ), the catalyst was evaluated before and after the high temperature treatment in the same manner as in Example 1. The results are shown in Table 4.

As is clear from Table 4, compared with Comparative Example 2, the amount of iron supported increased, so that the denitration performance at a low temperature was somewhat improved, but still not as good as the Examples. The concentration of leaked ammonia after the high-temperature treatment was 30 ppm under the conditions of the catalyst temperature of 500 ° C. and the NH ₃ ratio (volume ratio) of 480 ppm, which was three times that of Example 1.

(Example 2)
15 g of zirconium hydroxide (manufactured by Mitsuwa Chemicals Co., Ltd .; containing 79 wt% as ZrO ₂ ) is dissolved in 110 ml of an aqueous solution in which 13.5 g of ammonium sulfate and 7.8 g of manganese sulfate (MnSO ₄ .5H ₂ O) are dissolved. Soaked for hours. After evaporating to dryness on a hot plate having a temperature of 120 ° C. under normal pressure (atmospheric pressure), it was calcined in air at 700 ° C. for 6 hours to obtain a Mn-supported sulfate radical zirconia catalyst (1.6Mn / SZ). . As a result of fluorescent X-ray analysis, the manganese content of this catalyst was 1.6% by weight with respect to zirconia in terms of Mn. As a result of ICP analysis, the sulfate group content was 0.43% by weight as a weight ratio to the whole catalyst in terms of S. The BET specific surface area of the catalyst was 61 m ² / g. As a result of X-ray diffraction analysis, it was found that the crystal form of the catalyst was composed of 75% tetragonal crystal and 25% monoclinic crystal.

The catalyst was compression-molded to prepare a granulated product having a particle size of 1 to 2 mm, and 4.5 ml of the granulated product was filled in a quartz reaction tube (inner diameter 20 mm). The temperature of the catalyst is kept at 300 ° C., 350 ° C., 400 ° C., 450 ° C., 500 ° C. or 550 ° C., and the gas to be treated having the composition shown in Table 5 is 1.2 liters per minute (volume at 0 ° C. and 1 atm). ) (GHSV = 16000 h ⁻¹ ), and the denitration rate (treated gases 5A and 5B) was measured.

Next, the temperature of the catalyst is maintained at 550 ° C., and the gas to be treated is circulated for 12 hours at a flow rate of 1.2 liters per minute (volume at 0 ° C., 1 atm) to perform high temperature treatment (high temperature durability treatment, high temperature degradation treatment). ) In the high temperature treatment, the gas to be treated 5B (NH ₃ /NO=1.0) shown in Table 5 was used as the gas to be treated.

Subsequently, the gas to be treated was circulated through the catalyst after the high temperature treatment. That is, the temperature of the catalyst is kept at the same temperature (300 ° C., 350 ° C., 400 ° C., 450 ° C., 500 ° C. or 550 ° C.) as that before the high temperature treatment, and again the gas to be treated having the composition shown in Table 5 is 1. Circulates at a flow rate of 2 liters (volume at 0 ° C. and 1 atm) (GHSV = 16000 h ⁻¹ ), denitration rate (treated gases A to D), leaked ammonia concentration (treated gases 5C and 5D), and The ammonia decomposition rate (treated gas 5E) in the ammonia decomposition reaction was measured.

  Table 5 shows the composition of the gas to be treated, and Table 6 shows the result. In Table 5, the unit without display is “ppm”.

  As is apparent from Table 6, the catalyst of Example 2 shows little deterioration even when exposed to a relatively high temperature of 550 ° C., and when used in the denitration reaction, it exhibits sufficient denitration performance even at about 300 ° C. Even when excess ammonia was injected relative to NOx at a temperature higher than 0 ° C., the leakage of ammonia could be remarkably suppressed and a sufficient denitration rate was obtained up to about 500 ° C. Moreover, even when used for the decomposition of ammonia, it was possible to effectively decompose into nitrogen with a small amount of nitrogen oxide by-products.

(Example 3)
135 g of zirconium hydroxide (manufactured by Mitsuwa Chemicals Co., Ltd .; containing 79% by weight as ZrO ₂ ), 0.9 g of ammonium sulfate, 7.8 g of manganese sulfate (MnSO ₄ .5H ₂ O) and iron (III) sulfate (Fe ₂ (SO ₄ ) ₃ · 15H ₂ O) was immersed in 110 ml of an aqueous solution dissolving 21.4 g for 15 hours. After evaporating to dryness on a hot plate having a temperature of 120 ° C. under normal pressure (atmospheric pressure), the mixture was calcined in air at 700 ° C. for 6 hours to obtain an Fe—Mn-supported sulfate zirconia catalyst (3.0 Fe—1.6 Mn). / SZ). As a result of fluorescent X-ray analysis, the manganese content of this catalyst was 1.6% by weight with respect to zirconia in terms of Mn, and the iron content was 3.0% by weight with respect to zirconia in terms of Fe. It was. As a result of ICP analysis, the sulfate group content was 0.42% by weight as a weight ratio to the whole catalyst in terms of S. The BET specific surface area of the catalyst was 62 m ² / g. As a result of X-ray diffraction analysis, it was found that the crystal form of the catalyst was composed of 95% tetragonal crystal and 5% monoclinic crystal.

  A granulated product having a particle diameter of 1 to 2 mm is prepared by tableting the catalyst, and 4.5 ml of the granulated product is filled in a quartz reaction tube (inner diameter 20 mm). The catalyst was evaluated before and after the treatment.

  The results are shown in Table 7.

  As is apparent from Table 7, the catalyst of Example 3 is also less deteriorated when exposed to a relatively high temperature of 550 ° C. as in the catalyst of Example 2, and even when used in a denitration reaction, even at about 300 ° C. In addition to exhibiting sufficient denitration performance, particularly at 400 ° C. or higher, leakage of ammonia could be remarkably suppressed even when excess ammonia was injected relative to NOx.

Example 4
135 g of zirconium hydroxide (manufactured by Mitsuwa Chemicals Co., Ltd .; containing 79 wt% as ZrO ₂ ), 15.6 g of manganese sulfate (MnSO ₄ .5H ₂ O) and iron (III) sulfate (Fe ₂ (SO ₄ )) ₍₃ · 15H ₂ O) was immersed in 110 ml of an aqueous solution dissolving 21.4 g for 15 hours. After evaporating to dryness on a hot plate having a temperature of 120 ° C. under normal pressure (atmospheric pressure), the mixture was calcined in air at 700 ° C. for 6 hours to obtain a Fe—Mn-supported sulfate radical zirconia catalyst (3.0Fe-3.2Mn). / SZ). As a result of X-ray fluorescence analysis, the manganese content of this catalyst was 3.2% by weight with respect to zirconia in terms of Mn, and the iron content was 3.0% by weight with respect to zirconia in terms of Fe. It was. As a result of ICP analysis, the sulfate group content was 0.61% by weight as a weight ratio to the whole catalyst in terms of S. The BET specific surface area of the catalyst was 50 m ² / g. As a result of X-ray diffraction analysis, it was found that the crystal form of the catalyst was composed of 93% tetragonal crystal and 7% monoclinic crystal.

  A granulated product having a particle diameter of 1 to 2 mm is prepared by tableting the catalyst, and 4.5 ml of the granulated product is filled in a quartz reaction tube (inner diameter 20 mm). The catalyst was evaluated before and after the treatment.

  The results are shown in Table 8.

  As is apparent from Table 8, the catalyst of Example 4 is also less deteriorated when exposed to a relatively high temperature of 550 ° C. as in the catalyst of Example 2, and even at about 300 ° C. when used in a denitration reaction. In addition to exhibiting sufficient denitration performance, particularly at 400 ° C. or higher, leakage of ammonia could be remarkably suppressed even when excess ammonia was injected relative to NOx.

(Example 5)
The catalyst (3.0Fe-3.2Mn / SZ) obtained in Example 4 was compression-molded to prepare a granulated product having a particle size of 1 to 2 mm, and 4.5 ml of the granulated product was added to a quartz reaction tube. The catalyst was evaluated before and after the high temperature treatment in the same manner as in Example 2 except that (inner diameter 20 mm) was filled and the gas to be treated was changed to the gas to be treated shown in Table 9. In Table 9, the unit without display is “ppm”.

  The results are shown in Table 10. The ethylene decomposition rate and CO removal rate were calculated by the following formulas.

Ethylene decomposition rate (%) = 100 × {1- (ethylene concentration after catalyst) / (ethylene concentration before catalyst)}
CO decomposition rate (%) = 100 × {1- (post-catalyst CO concentration) / (pre-catalyst CO concentration)}
The ethylene concentration and the CO concentration before and after the catalyst were each measured by a gas chromatograph.

  As is apparent from Table 10, the catalyst of Example 4 has little influence on the denitration performance and ammonia decomposition performance even when hydrocarbons and carbon monoxide coexist, and removes hydrocarbons and carbon monoxide. It was also possible. In addition, it is thought that the removal rate of carbon monoxide becomes a negative value around 400 ° C. because ethylene is partially (incompletely) oxidized to generate carbon monoxide. Further, at 350 to 400 ° C., the denitration rate is slightly improved as compared with the case where ethylene and carbon monoxide do not coexist, but ethylene and carbon monoxide may also contribute to the reduction of NOx.

(Comparative Example 4)
A catalyst (1.5Fe / SZ (700)) was prepared in the same manner as in Comparative Example 2 except that the calcination temperature was changed from 550 ° C to 700 ° C. As a result of fluorescent X-ray analysis, the iron content of this catalyst was 1.5% by weight with respect to zirconia in terms of Fe. As a result of ICP analysis, the sulfate group content was 0.40% by weight with respect to zirconia in terms of S. The BET specific surface area of the catalyst was 71 m ² / g. As a result of X-ray diffraction analysis, it was found that the crystal form of the catalyst was composed of 82% tetragonal crystal and 18% monoclinic crystal.

  A granulated product having a particle diameter of 1 to 2 mm is prepared by tableting the catalyst, and 4.5 ml of the granulated product is filled in a quartz reaction tube (inner diameter 20 mm). The catalyst was evaluated before and after the treatment.

  The results are shown in Table 11.

  As is apparent from Table 11, even when the calcination temperature was increased, the performance of the catalyst hardly changed, and was inferior to the performance of the catalyst obtained in the examples.

(Comparative Example 5)
A catalyst (2.9Fe / SZ (700)) was prepared in the same manner as in Comparative Example 3 except that the calcination temperature was changed from 550 ° C to 700 ° C. As a result of fluorescent X-ray analysis, the iron content of this catalyst was 2.9% by weight based on zirconia in terms of Fe. As a result of ICP analysis, the sulfate group content was 0.43% by weight with respect to zirconia in terms of S. The BET specific surface area of the catalyst was 75 m ² / g. As a result of X-ray diffraction analysis, it was found that the crystal form of the catalyst was composed of 95% tetragonal crystal and 5% monoclinic crystal.

  A granulated product having a particle diameter of 1 to 2 mm is prepared by tableting the catalyst, and 4.5 ml of the granulated product is filled in a quartz reaction tube (inner diameter 20 mm). The catalyst was evaluated before and after the treatment.

  The results are shown in Table 12.

  As is apparent from Table 12, even if the calcination temperature was increased, the performance of the catalyst was hardly changed and was inferior to the performance of the catalyst obtained in the examples.

(Comparative Example 6)
The catalyst was evaluated before and after the high temperature treatment in the same manner as in Example 5 except that the catalyst was changed to the catalyst (2.9Fe / SZ (700)) obtained in Comparative Example 5. The results are shown in Table 13.

  As is clear from Table 13, compared with Example 5, the NOx removal reaction by hydrocarbons and / or carbon monoxide was observed at low temperatures (300 ° C.), and the removal performance of hydrocarbons and carbon monoxide was inferior. It was.

(Comparative Example 7)
80 g of zirconium hydroxide (manufactured by Hayashi Junyaku Kogyo Co., Ltd .; containing 84 wt% as ZrO ₂ ) and 10 g of tungstic acid (H ₂ WO ₄ , manufactured by Mitsuwa Chemicals Co., Ltd.) are mixed, and further 100 g of water And wet-kneaded for 6 hours using a stirrer. The obtained mixture was evaporated to dryness on a hot plate having a temperature of 120 ° C. under normal pressure (atmospheric pressure), and then calcined in air at 700 ° C. for 6 hours to obtain a tungsten oxide-supported zirconia catalyst (WZ). Got. The BET specific surface area of the catalyst was 60 m ² / g. As a result of X-ray diffraction analysis, it was found that the crystal form of the catalyst was composed of 71% tetragonal crystal and 29% monoclinic crystal.

A granulated product having a particle diameter of 1 to 2 mm is prepared by tableting the catalyst, and 4.5 ml of the granulated product is filled in a quartz reaction tube (inner diameter 20 mm). The catalyst was evaluated before and after the treatment. The results are shown in Table 14. In Table 14, since the nitrous oxide (N ₂ O) was contained in the gas after the catalyst of the denitration reaction at 400 ° C., 450 ° C. and 500 ° C. (after the reaction), the denitration rate and leak In calculating the ammonia concentration, the total concentration of the nitrogen concentration and the nitrous oxide concentration was used instead of the nitrogen concentration.

Tungsten oxide-supported zirconia is known as a zirconia-based oxide having strong solid acidity. As is clear from Table 14, the denitration performance and the ammonia decomposition rate are very low compared to the catalysts obtained in the examples. In addition, it has been found that there is a risk of producing nitrous oxide, which has a high global warming effect, as a by-product.

Claims (14)

  A catalyst for decomposing ammonia and / or nitrogen oxides, which is composed of sulfate zirconia containing at least a manganese component.   The catalyst according to claim 1, wherein the ratio of the manganese component is 0.1 to 10 parts by weight with respect to 100 parts by weight of zirconia in terms of manganese Mn.   Furthermore, the catalyst of Claim 1 or 2 containing an iron component.   The total of iron Fe and manganese Mn conversion in terms of 100 parts by weight of zirconia, including 1 to 10 parts by weight of iron component and manganese component, the ratio of iron component and manganese component in terms of iron Fe and manganese Mn, the former The catalyst according to claim 3, wherein / the latter (weight ratio) = 95/5 to 10/90.   The catalyst according to any one of claims 1 to 4, which is used for reducing nitrogen oxides in the presence of ammonia.   The catalyst according to claim 5, which has a reducing function for nitrogen oxides and a decomposition function for ammonia.   The catalyst according to any one of claims 1 to 4, which is used for decomposing ammonia into nitrogen.   The removal method of the nitrogen oxide which makes the to-be-processed gas containing nitrogen oxide contact the catalyst in any one of Claims 1-4 in presence of ammonia.   The method according to claim 8, wherein the gas to be treated is brought into contact with the catalyst at a temperature of 350 to 550 ° C.   The method according to claim 8 or 9, wherein the amount of ammonia is 0.9 to 1.5 mol per mol of nitrogen oxide in the gas to be treated.   A method for decomposing ammonia in which ammonia is decomposed into nitrogen by bringing a gas to be treated containing ammonia into contact with the catalyst according to claim 1.   The method for producing a catalyst according to any one of claims 1 to 4, wherein the sulfate component zirconia contains at least a manganese component.   The production method according to claim 12, wherein a solution containing at least sulfate ions and manganese ions is impregnated with zirconium hydroxide, dried and fired.   The production method according to claim 13, wherein the solution further contains iron ions.