JP5594121B2 - Novel metallosilicate and nitrogen oxide purification catalyst - Google Patents

Description

  The present invention relates to a novel metallosilicate useful as a catalyst, an adsorbent, a separating agent, and the like. More specifically, the present invention is synthesized without using fluorine, which is difficult to industrially use, and has Al as a solid acid site and catalytic activity. The present invention relates to a highly crystalline β-type iron silicate that contains both Fe, which can serve as spots or adsorption points, in a crystal in a highly dispersed state and has high heat resistance.

  The present invention also relates to purification of nitrogen oxides exhausted from an internal combustion engine, a nitrogen oxide purification catalyst comprising a crystalline silicate having a β structure, and at least ammonia, urea, and organic amines using the catalyst. The present invention provides a method for purifying nitrogen oxides that reacts with one.

  β-type zeolite is a high-silica zeolite first disclosed by Patent Document 1, and is widely used as a catalyst, an adsorbent and the like.

  When using zeolite, chemical modification of the zeolite with metal is often performed for the purpose of imparting specific functions such as catalytic activity and adsorption selectivity. Commonly used methods include a method of supporting metal cations by ion exchange in the liquid phase utilizing the ion exchange ability of zeolite, and a method of supporting metals by impregnating zeolite with a solution containing a metal salt. There is a way.

  In the chemical modification of zeolite, in order to maximize the intended function, it is desirable that the supported metal is generally present in a highly dispersed state in the zeolite base material and is not aggregated as much as possible.

  However, in the above-described loading by ion exchange, for example, the amount of metal that can be exchanged depends on the ion exchange ability of the zeolite, and if it is attempted to carry more than that, metal aggregation tends to occur. Further, in the case of supporting by impregnation, there is a problem that the metal agglomeration is likely to occur as the amount of metal to be supported is increased, instead of easily controlling the amount of metal supported.

  Some metals can be introduced into the zeolite framework in the same manner as Si and Al by adding them as raw materials for the hydrothermal synthesis of zeolite. Since the metal introduced by such a method is taken into the Si network via oxygen atoms for each atom, the metal is in a very highly dispersed state. Known metals that can be introduced include B, Cr, V, Ge, Ga, Fe, Sn, and Zn. Among these metals, relatively many attempts have been made to introduce Fe.

  The following prior art has been disclosed for β-type iron silicate in which Fe is introduced into the framework of β-type zeolite.

  For example, Patent Document 2 discloses an adsorbent containing β-type iron silicate having both Al and Fe as a skeleton. Patent Document 3 discloses an adsorbent for purifying automobile exhaust gas containing β-type iron silicate defined by the half width of the X-ray diffraction peak. In addition, Patent Document 4 discloses an aluminosilicate zeolite containing skeletal iron and an iron cation at an ion exchange site.

  Further, for example, non-patent document 1 and non-patent document 2 also disclose β-type iron silicate. Further, Non-Patent Document 3 discloses β-type iron silicate synthesized by adding fluorine to the raw material. In general, it is known that by adding fluorine to a raw material in zeolite synthesis, a zeolite having good crystallinity with few lattice defects can be obtained as compared with the case where fluorine is not added. For example, non-patent document 4 discloses β-type zeolite.

  However, since the β-type iron silicates disclosed in these publications have a very small amount of Fe introduced, it is not always sufficient for use as an active point of a catalyst or the like, or the amounts of Al and Fe introduced are sufficient. Also, the crystallinity was not sufficient. In general, in hydrothermal synthesis of iron silicates containing Al, the smaller the Fe in the raw material, the closer the physical properties of the product are to those of ordinary aluminosilicate, which facilitates crystallization and at the same time the crystallinity of the crystals obtained. In contrast to the tendency to improve, when the amount of Fe in the raw material is increased, the crystal generation region is rapidly reduced, and the crystallinity of the obtained crystal is lowered. Such a tendency is considered to be caused by the instability of Fe with respect to Al in the alkaline raw material mixture and the increase in crystal distortion due to the presence of Fe having an ionic radius larger than that of Al in the zeolite framework.

  In addition, the use of fluorine in zeolite synthesis is industrially difficult from the viewpoint of equipment corrosion and the like, and there is also a problem that fluorine remaining in the produced zeolite adversely affects performance.

_Also, SiO 2 / _Fe 2 _{O 3} ratio of 20 to 300, the nitrogen oxide purification catalyst comprising a crystalline silicate having an iron isolated iron ion is more than 80% beta-type structure in containing iron (Patent Document 5) Has been reported. However, they have increased crystal grain size and improved crystallinity using fluorine raw materials.

In addition, a crystalline silicate having iron in a β skeleton structure having a SiO ₂ / Fe ₂ O ₃ molar ratio of 20 to 300 and a log (SiO ₂ / Al ₂ O ₃ ) of 2 or more (molar ratio) is excellent at a low temperature. It has been reported that it has decomposition performance and hydrothermal durability of nitrogen oxide (Patent Document 6). However, these particle sizes were as large as 5 μm or more.

  It has been synthesized without using fluorine, which has been difficult to use industrially, and contains both Al as a solid acid site and Fe that can act as a catalyst active site or adsorption site in a highly dispersed state in the crystal, and has high activity as a catalyst. No highly crystalline β-type iron silicate with high heat resistance in a particle size range in which mechanical performance can be expected has been known.

  A crystalline silicate having a skeletal structure substituted with a different element is expected to have characteristics different from those of ordinary aluminosilicate zeolites, and its use for catalytic reactions is being studied. For example, iron as a xylene isomerization catalyst using an iron silicate carrying platinum (Patent Document 7), a selective methylation catalyst of a naphthalene compound using an iron silicate (Patent Document 8), and a ring-opening polymerization catalyst of a cyclic ether A method for producing polyalkylene glycol using silicate (Patent Document 9) and the like are disclosed.

  On the other hand, nitrogen oxide purification technology using iron silicate is also being studied. For example, a catalyst for purifying exhaust gas containing nitrogen oxide in which a coprecipitation complex oxide of copper and gallium is dispersed and supported on ZSM-5 type iron silicate (Patent Document 10), in an atmosphere where excess oxygen exists, Nitrogen oxide purification method (patent document 11) in which an alkali metal exchanger of ZSM-5 type iron silicate is contacted with exhaust gas containing nitrogen oxide in the presence of hydrocarbons or oxygen-containing compounds, nitrogen oxide, oxygen gas, and Nitrogen oxide removal method (PTL 12) in which combustion exhaust gas containing sulfurous acid gas is contact-reacted in the presence of an iron silicate catalyst and a hydrocarbon reducing agent, if necessary, platinum, palladium, rhodium and cobalt on iron silicate Among them, an exhaust gas purification catalyst that mainly removes nitrogen oxide supporting at least one of them (Patent Document 13) has been reported. In addition, since the iron silicate described in patent documents 12 and 13 uses tetrapropylammonium salt at the time of synthesis, the skeleton structure of the obtained iron silicate is a ZSM-5 structure.

  As for the purification catalyst for nitrous oxide, a method for producing a catalyst containing β-type iron silicate supporting copper, cobalt, etc., used for direct decomposition of nitrous oxide (Patent Document 14), an iron silicate having a β structure is used. In addition, a method of directly decomposing nitrous oxide, a method of non-selective catalytic reduction of nitrous oxide using carbon monoxide as a reducing agent (Non-patent Document 3), and the like are disclosed.

  On the other hand, for the purification catalyst of nitrogen oxides in exhaust gas, with respect to the purification of nitrogen oxides of oxygen excess exhaust gas represented by lean burn combustion exhaust gas and diesel combustion exhaust gas, an aluminosilicate zeolite catalyst supporting iron or copper is used, A method of selective catalytic reduction (usually called SCR) with ammonia (Patent Document 15) is known.

_Also, SiO 2 / _Fe 2 _{O 3} ratio of 20 to 300, the nitrogen oxide purification catalyst comprising a crystalline silicate having an iron isolated iron ion is more than 80% beta-type structure in containing iron (Patent Document 5) Has been reported. However, in the nitrogen oxide (NOx) reduction method using ammonia as a reducing agent, the nitrogen oxide decomposition performance and hydrothermal durability at low temperatures were insufficient.

In addition, a crystalline silicate having iron in a β skeleton structure having a SiO ₂ / Fe ₂ O ₃ molar ratio of 20 to 300 and a log (SiO ₂ / Al ₂ O ₃ ) of 2 or more (molar ratio) is excellent at a low temperature. It has been reported that it has decomposition performance and hydrothermal durability of nitrogen oxide (Patent Document 6). However, these crystal particle diameters are as large as 5 μm or more, and problems remain in handling such as coating and molding.

U.S. Pat. No. 3,308,069 Japanese Patent No. 4044984 Japanese Patent No. 3986186 US Patent Application Publication No. 2009-048095 JP 2009-166031 A JP 2009-166032 A Japanese Patent No. 3269828 JP-T-2004-524142 Japanese Patent No. 3477799 JP-A-5-305240 Japanese Patent No. 2691643 JP-A-5-154349 Japanese Patent No. 2605956 US Patent Application Publication No. 2006-0088469 JP-A-2-2933021

ZEOLITES, Vol. 10 (1990), pages 85-89 Microporous Materials, Vol. 2 (1994) pp. 167-177 Journal of Catalysis, Vol. 232 (2005), pages 318-334 ZEOLITES, Vol. 12 (1992), pages 240-250

  The object of the present invention is to synthesize without using fluorine, which is difficult to use industrially, the fluorine content is 400 ppm or less, a highly crystalline β-type iron silicate containing both Al and Fe, and It is in providing the manufacturing method.

  In addition, while nitrogen oxides in exhaust gas are desired to be efficiently purified, conventionally, nitrogen oxides have high nitrogen oxide purifying activity and hydrothermal durability performance at a low temperature of 200 ° C. or lower, and excellent handling. An oxide purification catalyst was not obtained.

  An object of the present invention is a crystalline silicate having catalytic performance and hydrothermal durability for efficiently purifying nitrogen oxides in a wide temperature range, particularly in a relatively low temperature range of 200 ° C. or less, and excellent in handling. It is to provide a catalyst. Still another object is to provide a method for purifying nitrogen oxides using the above catalyst.

  In view of the situation as described above, the present inventors have intensively studied the production method and production conditions of β-type iron silicate, and as a result, have come to find the β-type iron silicate of the present invention.

  Hereinafter, the β-type iron silicate of the present invention will be described.

  First, the β-type iron silicate according to claims 1 to 5 of the claims will be described.

The composition of the β-type iron silicate of the present invention is:
(X + y) M _{(2 / n)} O.xFe ₂ O ₃ .yAl ₂ O ₃ .zSiO ₂ .wH ₂ O
(Where n is the valence of the cation M, x, y, and z are mole fractions of Fe ₂ O ₃ , Al ₂ O ₃ , and SiO ₂ , respectively, and x + y + z = 1. W is 0 or more. Number).

  The crystal structure of the β-type iron silicate of the present invention is β-type as confirmed by X-ray diffraction. β-type iron silicate is a metallosilicate having three-dimensional pores in which 0.76 × 0.64 nm and 0.55 × 0.55 nm pores composed of oxygen 12-membered rings intersect. The X-ray diffraction pattern of β-type iron silicate is characterized by the lattice spacing d (angstrom) shown in Table 1 below and its diffraction intensity.

  The β-type iron silicate of the present invention has a structure in which all or a part of Fe contained therein is connected to an oxygen atom as a skeleton atom of a tetracoordinate structure, and is derived from insufficient charge of the silicate skeleton as in the case of an aluminosilicate zeolite. It has solid acid properties. All of the Fe contained in the β-type iron silicate of the present invention is not necessarily present in the skeleton. This is because a part of Fe existing in the skeleton can be detached by a heat treatment such as a baking operation for removing the structure directing agent (hereinafter referred to as “SDA”).

SiO ₂ / Fe ₂ O ₃ of the β-type iron silicate composition of the present invention is 50 or more and 150 or less. When SiO ₂ / Fe ₂ O ₃ is less than 50, crystallization of the β-type structure becomes increasingly difficult, so that the crystallinity is lowered. When SiO ₂ / Fe ₂ O ₃ exceeds 150, the absolute amount of Fe decreases, leading to a decrease in catalytic activity and the like. From the viewpoint of crystallinity, the SiO ₂ / Fe ₂ O ₃ is preferably 100 or more and 150 or less, more preferably 130 or more and 150 or less.

Since both Al and Fe are introduced into the zeolite framework in a four-coordinate structure, crystallization is controlled not only by the individual composition of Al and Fe, but also by the total amount of these introduced. That is, the SiO ₂ / (Al ₂ O ₃ + Fe ₂ O ₃ ) of the β-type iron silicate of the present invention is 20 or more and 70 or less, preferably 25 or more and 70 or less, more preferably 30 or more and 70 or less from the viewpoint of crystallinity. is there.

  The β-type iron silicate of the present invention is synthesized without using fluorine as a raw material, and the fluorine content relative to the dry weight of the crystal is 400 ppm or less. In the β-type iron silicate synthesized using fluorine, fluorine remains even after SDA removal and baking. The fluorine content relative to the dry weight of the β-type iron silicate crystal of the present invention is preferably 200 ppm or less, more preferably 100 ppm or less, and even more preferably the detection limit or less.

  Quantification of fluorine in β-type iron silicate can be performed, for example, by lanthanum alizarin complexone spectrophotometry. Commercially available Alfusson (Dojindo Laboratories) can be used as the lanthanum alizarin complexone. In the analysis, as a pretreatment, the sample is alkali-dissolved, concentrated and distilled, Alfusson is added, and the absorbance at a wavelength of 620 nm is measured after pH adjustment.

  In the β-type iron silicate of the present invention, the full width at half maximum (FWHM) of the X-ray crystal diffraction (302) plane is 0.16 to 0.24 °.

  X-ray crystal diffraction is measured in the SDA-containing state after synthesis.

  The full width at half maximum (FWHM) is an index representing the state of the crystal, and represents the regularity of the crystal and the degree of distortion of the lattice. It can be said that the lower this value is, the higher the crystallinity is because the crystal maintains a long-period structure. When the half width exceeds 0.24 °, the crystallinity is not sufficient, and the crystal structure tends to collapse due to a high temperature hot water treatment or the like.

  The β-type iron silicate of the present invention contains all or part of iron in the β skeleton structure. The presence of Fe in the skeleton of β-type iron silicate can be confirmed by electron spin resonance measurement (measurement temperature 77K).

Paramagnetic Fe ions (Fe ³⁺ ) exhibit resonance absorption in electron spin resonance measurement, and have absorption peaks having at least three absorption peaks of g≈2.0, g≈4.3, and g> 4.3. (See Journal of Catalysis, 249 (2007) 67 et al.). Those having an absorption peak of g≈2.0 are isolated Fe ions having a symmetric tetrahedral structure (or highly symmetric multi-coordination structure), and Fe ions having absorption of g≈4.3 and g> 4.3 are It is attributed to isolated Fe ions having a distorted tetrahedral structure and a distorted multi-coordination structure.

  Fe existing in the silicate skeleton has an isolated and highly symmetric tetrahedral structure, and Fe outside the skeleton is considered to have an octahedral structure. Therefore, Fe exists in the skeleton of the β-type iron silicate of the present invention. This can be confirmed by the resonance absorption of g≈2.0 in the electron spin resonance measurement.

  Electron spin resonance measurement can be performed by a general method.

  For example, using an electron spin resonance apparatus (JES-TE200 manufactured by JEOL Ltd.), the measurement conditions are a measurement temperature of 77K, a microwave output of 1.0 mW, an observation range of 0 to 1000 mT, a modulation width of 0.32 mT, The time constant can be 0.3 sec. About 10 mg of the sample is weighed into a quartz sample tube, inserted into a liquid nitrogen temperature measurement dewar, and then measured.

  The presence of Fe in the skeleton of β-type iron silicate can also be confirmed by analyzing an X-ray absorption spectrum (XAFS). In this case, the pre-edge peak (7110 eV) appearing before the K absorption edge of Fe is attributed to the isolated Fe ions having a tetrahedral structure.

  The β-type iron silicate of the present invention is a so-called aluminosilicate containing Al. Since Al in the zeolite is a solid acid point and functions as an adsorption point in the catalytic reaction, it becomes an essential element depending on the chemical species to be adsorbed and the catalytic reaction to be applied. If the Al content is reduced, the hydrothermal durability of the zeolite is generally improved. On the other hand, the function of solid acid sites derived from Al is gradually lost.

  Incidentally, the hydrothermal durability of the zeolite means the hydrothermal durability of the zeolite skeleton itself.

  The β-type iron silicate of the present invention has high crystallinity and high hydrothermal durability while sufficiently containing Al acting as a solid acid point.

The SiO ₂ / Al ₂ O ₃ of the β-type iron silicate composition of the present invention is preferably 25 or more and 70 or less. When SiO ₂ / Al ₂ O ₃ is less than 25, crystallization of the β-type structure becomes increasingly difficult, so that the crystallinity is lowered. On the other hand, if SiO ₂ / Al ₂ O ₃ exceeds 70, the amount of solid acid becomes insufficient. From the viewpoint of crystallinity, SiO ₂ / Al ₂ O ₃ is preferably 35 or more and 70 or less, more preferably 45 or more and 70 or less.

  The crystal grain size in SEM observation of the β-type iron silicate of the present invention is preferably 0.2 μm or more and 2.0 μm or less.

  In the present invention, the crystal grain size means an average crystal grain size, and the measurement method is an arithmetic average value obtained by measuring the diameters of 50 primary particles at an SEM observation magnification of 15000 times. Since there are irregular shapes in the primary particles, the maximum horizontal diameter was uniformly measured for all the particles to obtain the diameter. The observation magnification can be arbitrarily selected as long as it is suitable for measuring the diameter.

  If it is less than 0.2 μm, the hydrothermal durability is low, and if it exceeds 2.0 μm, when used as a catalyst, the dynamic performance particularly when the flow rate is large is lowered. Furthermore, the particle size within the range of the present invention is preferable in handling properties such as coating and molding.

  Next, the manufacturing method of (beta) type iron silicate of this invention is demonstrated.

  The feed composition of the raw material mixture of β-type iron silicate of the present invention is exemplified as follows. However, these composition ranges are not limited, and can be arbitrarily set so that the final product composition falls within the composition range of the β-type iron silicate of the present invention. Moreover, you may add the component which has crystallization promotion effects, such as a seed crystal.

_{aM 2 O · SiO 2 · bFe} 2 O 3 · cAl 2 O 3 · dSDA · eH 2 O
here,
M = K ⁺ or Rb ⁺ or Cs ⁺
a = 0.005 to 0.10, preferably 0.01 to 0.05
b = 0.006 to 0.02, preferably 0.006 to 0.01
c = 0.014-0.04, preferably 0.014-0.028
d = 0.10 to 0.35, preferably 0.10 to 0.30
e = 7-15, preferably 9-13

The above-mentioned M ₂ O does not contain commonly used Na ⁺ . The presence of Na ⁺ stabilizes the negatively charged aluminosilicate species in the reaction solution and promotes crystallization. On the other hand, the increase in crystal nucleation often leads to the refinement of individual crystal grains. This is because sufficient crystallinity is difficult to obtain.

  The raw material for synthesis is composed of a silica source, an aluminum source, an iron source, SDA, an alkali metal source and water.

  Colloidal silica, amorphous silica, sodium silicate, tetraethylorthosilicate, iron aluminosilicate gel, etc. can be used as the silica source, and aluminum sulfate, sodium aluminate, aluminum hydroxide, aluminum nitrate, aluminosilicate gel can be used as the aluminum source. Metal aluminum or the like can be used. Further, as the iron source, iron nitrate, iron chloride, iron sulfate, metallic iron and the like can be used, and these raw materials are preferably those which can be sufficiently mixed with other components.

  As SDA raw materials, tetraethylammonium hydroxide having a tetraethylammonium cation (hereinafter referred to as “TEAOH”), tetraethylammonium bromide, octamethylenebiskinucridium, α, α′-diquinuclidium-p-xylene, α, α′-diquinuclidium-m-xylene, α, α′-diquinuclidium-o-xylene, 1,4-diazabicyclo [2,2,2] octane, 1,3,3, N, N-pentamethyl-6-azonium At least one or more of the group of compounds containing bicyclo [3,2,1] octane or N, N-diethyl-1,3,3-trimethyl-6-azonium bicyclo [3,2,1] octane cation are used. be able to.

  As the alkali metal source, potassium hydroxide, potassium sulfate, potassium chloride, potassium acetate, rubidium hydroxide, rubidium sulfate, rubidium chloride, rubidium acetate, cesium hydroxide, cesium sulfate, cesium chloride, cesium acetate, etc. can be used. These raw materials are preferably those that can be sufficiently uniformly mixed with other components.

  The β-type iron silicate of the present invention can be obtained by crystallizing a raw material mixture of water, silica source, aluminum source, iron source, SDA and alkali metal source in a sealed pressure vessel at a temperature of 100 to 180 ° C. it can.

  At the time of crystallization, the raw material mixture may be mixed and stirred or left standing. After completion of crystallization, the mixture is allowed to cool sufficiently, separated into solid and liquid, washed with a sufficient amount of pure water, and dried at a temperature of 110 to 150 ° C. to obtain the β-type iron silicate of the present invention.

For the SDA removal treatment, a liquid phase treatment using a chemical solution containing an acidic solution or an SDA decomposition component, an exchange treatment using a resin or the like, or a thermal decomposition treatment may be used, and these treatments may be combined. Furthermore, it can be used by converting into β-type or NH ₄ type by utilizing the ion exchange ability of β-type iron silicate.

  Since the β-type iron silicate of the present invention contains highly dispersed iron, it can be used as it is as a catalyst or an adsorbent, and its application is not particularly limited.

  The β-type iron silicate of the present invention may further support an active metal species. The metal species to be supported is not particularly limited.

  As the loading method, methods such as an ion exchange method, an impregnation loading method, an evaporation to dryness method, a precipitation loading method, and a physical mixing method can be used. As the raw material used for supporting the metal, nitrates, sulfates, acetates, chlorides, complex salts, oxides, complex oxides and the like can be used.

  The amount of metal supported is not limited, but a range of 0.1 to 10% by weight is particularly preferable.

  The β-type iron silicate of the present invention can be used after being mixed with a binder such as silica, alumina and clay mineral. Examples of the clay mineral used for molding include kaolin, attapulgite, montmorillonite, bentonite, allophane, and sepiolite. Moreover, it can also be used by wash-coating on a cordierite or metal honeycomb substrate.

  Next, a nitrogen oxide purification catalyst comprising the β-type iron silicate according to claims 6 to 13 of the claims, a method for producing the nitrogen oxide purification catalyst, and the nitrogen A method for reducing nitrogen oxides using an oxide purification catalyst will be described.

As a result of intensive studies on selective reduction catalysts for nitrogen oxides using ammonia or the like, the inventors of the present invention have a SiO ₂ / Al ₂ O ₃ molar ratio of 20 to 70, preferably 20 to 60, SiO ₂ / Fe. _In a crystalline silicate containing iron and aluminum in a β skeleton structure in which the ₂ O ₃ molar ratio is 50 to 200 and the half width (FWHM) of the crystal diffraction (302) plane is 0.30 to 0.40 ° In the selective reduction of nitrogen oxides using ammonia or the like as the reducing agent, the NOx reduction rate after hydrothermal endurance treatment in a 10% by volume water vapor atmosphere at 700 ° C. for 20 hours is excellent in the reaction temperature. The present inventors have found that it has excellent nitrogen oxide purification performance that is 45% or more and 60% or less at 200 ° C., and has completed the present invention.

  Hereinafter, the nitrogen oxide purification catalyst according to claims 6 to 13 of the present invention, the production method thereof, and the nitrogen oxide purification method using the catalyst will be described.

The nitrogen oxide purification catalyst of the present invention has a SiO ₂ / Al ₂ O ₃ molar ratio of 20 or more and 70 or less, a SiO ₂ / Fe ₂ O ₃ molar ratio of 50 or more and 200 or less, and a half of the crystal diffraction (302) plane. It is a β-type crystalline iron silicate (hereinafter referred to as “β-type iron silicate”) containing iron and aluminum in a β-skeleton structure having a value range (FWHM) of 0.30 to 0.40 °.

  The inclusion of iron and aluminum in the β skeleton structure means that not all iron is contained in the β skeleton structure, but part of iron is contained in the β skeleton structure, and the remaining iron is It refers to a state that does not exist as a constituent element and exists near an ion exchange site or surface silanol group that does not constitute a β skeleton structure.

The composition of β-type iron silicate is
(X + y) M _{(2 / n)} O.xFe ₂ O ₃ .yAl ₂ O ₃ .zSiO ₂ .wH ₂ O
(Where n is the valence of the cation M, x, y, and z are mole fractions of Fe ₂ O ₃ , Al ₂ O ₃ , and SiO ₂ , respectively, and x + y + z = 1. W is 0 or more. Number).

  The crystal structure of the β-type iron silicate of the nitrogen oxide purification catalyst of the present invention is β-type as confirmed by X-ray diffraction. β-type iron silicate is a metallosilicate having three-dimensional pores in which 0.76 × 0.64 nm and 0.55 × 0.55 nm pores composed of oxygen 12-membered rings intersect. The X-ray diffraction pattern of β-type iron silicate is characterized by the lattice spacing d (angstrom) shown in Table 2 below and its diffraction intensity.

The β-type iron silicate of the nitrogen oxide purification catalyst of the present invention has a structure in which tetracoordinate iron is linked to an oxygen atom as a skeleton atom, and is a solid derived from insufficient charge of the silicate skeleton similarly to an aluminosilicate zeolite. It has acid properties. The iron silicate of the present invention exists as isolated iron ions (Fe ³⁺ ) in which iron as a catalyst active metal is highly dispersed, and in a selective reduction reaction using ammonia or the like, iron aggregation is suppressed, Shows activity.

The β-type iron silicate of the nitrogen oxide purification catalyst of the present invention is a crystalline silicate having iron in the β skeleton structure, and the SiO ₂ / Al ₂ O ₃ molar ratio is in the range of 20 to 70, preferably 20 to 60. It is. If the SiO ₂ / Al ₂ O ₃ molar ratio is less than 20, the aluminum content increases, but if the amount of aluminum in the skeleton is too large, desorption and agglomeration of the metal from the skeleton such as dealumination and iron removal by hot water treatment. It becomes extremely easy to proceed, and it is difficult to sufficiently retain isolated Fe ³⁺ that contributes to activity. Therefore, a SiO ₂ / Al ₂ O ₃ molar ratio of 20 or more is preferable. On the other hand, when the SiO ₂ / Al ₂ O ₃ molar ratio is larger than 70, the amount of aluminum in the skeleton is reduced, and sufficient hydrothermal durability cannot be obtained. Further, since the amount of solid acid is reduced, sufficient catalytic activity cannot be obtained. In particular, the SiO ₂ / Al ₂ O ₃ molar ratio is preferably 60 or less, and more preferably 50 or less.

When the SiO ₂ / Fe ₂ O ₃ molar ratio is less than 50, the iron content increases. However, if the amount of iron in the skeleton is too large, metal removal from the skeleton such as dealumination and iron removal by a hot water treatment and aggregation It becomes difficult to keep the isolated Fe ³⁺ that contributes to the activity sufficiently. Therefore, the SiO ₂ / Fe ₂ O ₃ molar ratio is preferably 50 or more. In addition, when the SiO ₂ / Fe ₂ O ₃ molar ratio exceeds 200, the absolute iron ion amount is small and sufficient catalytic activity cannot be obtained. The SiO ₂ / Fe ₂ O ₃ molar ratio is preferably in the range of 50 to 200, more preferably 100 to 200.

The iron that contributes most to the reduction of nitrogen oxides in the β-type iron silicate of the nitrogen oxide purification catalyst of the present invention is present as dispersed iron ions (Fe ³⁺ ) in the silicate skeleton described later. Yes, it is not agglomerated as Fe ₂ O ₃ . Note that the SiO ₂ / Fe ₂ O ₃ molar ratio used in the definition of the composition of the β-type iron silicate of the present invention is a notation used for convenience in order to define the total iron content including isolated iron ions.

  The β-type iron silicate of the nitrogen oxide purification catalyst of the present invention has an X-ray crystal diffraction (302) plane half width (FWHM) of 0.30 to 0.40 °. The full width at half maximum (FWHM) is an index representing the state of the crystal, and represents the regularity of the crystal and the degree of strain of the lattice. The larger the value, the lower the regularity of the crystal and the stronger the distortion, and the stronger the interaction between the silica skeleton, iron and aluminum, and the higher the catalytic activity after hydrothermal treatment. It is done.

  X-ray crystal diffraction is measured after heat treatment for SDA removal.

  On the other hand, when the full width at half maximum (FWHM) is remarkably large, the zeolite structure itself is excessively collapsed, and the catalytic activity is considered to be significantly reduced. Therefore, when the full width at half maximum (FWHM) is less than 0.30 °, the strain is small, and the interaction between the silica skeleton, iron and aluminum is not sufficient, so that the catalytic activity after the hydrothermal treatment becomes low, and 0.40 ° Exceeding this causes the zeolite structure itself to collapse so much that the catalytic activity becomes low.

  The average crystal particle diameter of β-type iron silicate of the nitrogen oxide purification catalyst of the present invention is preferably in the range of 0.2 to 2.0 μm. The reason is that if it is less than 0.2 μm, the hydrothermal durability is low and the catalytic activity cannot be maintained, and if it exceeds 2.0 μm, the handling properties such as coating and molding are reduced, More preferably, it is 0.2-1.0 micrometer.

  The nitrogen oxide purification catalyst of the present invention is important as a nitrogen oxide purification catalyst after hydrothermal durability treatment at 700 ° C. for 20 hours in a 10 vol% steam atmosphere at a gas flow rate / zeolite volume ratio of 100 times / min. The NOx reduction rate at a reaction temperature of 200 ° C., which is an index for judging low temperature activity and hydrothermal durability, is 45% to 60% and exhibits excellent hydrothermal durability.

  Therefore, the nitrogen oxide purification catalyst of the present invention can stably treat NOx for a long time. The higher the NOx reduction rate after heat endurance, the better, but about 60% is the limit.

  Conventionally, nitrogen oxide purifying catalysts are generally evaluated by the performance after hydrothermal durability treatment, but there is no standardized hydrothermal durability treatment. The above hydrothermal durability test conditions are a category of conditions generally used as hydrothermal durability treatment conditions for the nitrogen oxide purification catalyst, and are not special conditions.

  In addition, not only β-type zeolite, but the thermal damage at 600 ° C. or higher exponentially increases in zeolite, so the hydrothermal durability treatment at 700 ° C. for 20 hours is 100 to 200 hours or longer at 650 ° C. If it is 800 degreeC, it is equivalent to the process for several hours.

  The nitrogen oxide purification catalyst of the present invention can be used after being mixed with a binder such as silica, alumina and clay mineral. Examples of clay minerals used for molding include kaolin, attapulgite, montmorillonite, bentonite, allophane, and sepiolite.

  The nitrogen oxide purification catalyst of the present invention has high performance as an exhaust gas purification catalyst.

  The nitrogen oxide purification catalyst of the present invention exhibits high NOx decomposability particularly at low temperatures after hydrothermal treatment by enhancing the interaction between iron and aluminum contained in the silica skeleton and part of the skeleton by heat treatment. The exhaust gas can be highly purified by contacting with exhaust gas containing oxide.

  Examples of nitrogen oxides purified by the present invention include nitric oxide, nitrogen dioxide, dinitrogen trioxide, dinitrogen tetroxide, dinitrogen monoxide, and mixtures thereof. Nitric oxide, nitrogen dioxide, and dinitrogen monoxide are preferred. Here, the nitrogen oxide concentration of the exhaust gas that can be treated by the present invention is not limited.

  The exhaust gas may contain components other than nitrogen oxides, and may contain, for example, hydrocarbons, carbon monoxide, carbon dioxide, hydrogen, nitrogen, oxygen, sulfur oxides, and water. Specifically, the method of the present invention can purify nitrogen oxides from a wide variety of exhaust gases such as diesel vehicles, gasoline vehicles, boilers, gas turbines and the like.

  The nitrogen oxide purification catalyst of the present invention can purify nitrogen oxide, particularly by using it as an SCR catalyst that purifies nitrogen oxide in the presence of a reducing agent.

  As the reducing agent, hydrocarbons, carbon monoxide, hydrogen, and the like contained in the exhaust gas can be used as the reducing agent. Further, if necessary, an appropriate reducing agent may be added to the exhaust gas to coexist. The reducing agent added to the exhaust gas is not particularly limited, and examples thereof include ammonia, urea, organic amines, hydrocarbons, alcohols, ketones, carbon monoxide, hydrogen, and the like, particularly improving the purification efficiency of nitrogen oxides. For this purpose, it is particularly preferable to use ammonia, urea or organic amines. By these reducing agents, nitrogen oxides are converted into harmless nitrogen, and the exhaust gas can be treated.

  The method of adding these reducing agents is not particularly limited, and a method of directly adding the reducing component in a gaseous state, a method of spraying and vaporizing a liquid such as an aqueous solution, a method of spraying pyrolysis, and the like can be employed. Moreover, the addition amount of these reducing agents can be arbitrarily set so that nitrogen oxides can be sufficiently purified.

The nitrogen oxide purification method using the nitrogen oxide purification catalyst of the present invention is not particularly limited as long as the nitrogen oxide purification catalyst of the present invention is used. For example, an SCR catalyst comprising the nitrogen oxide purification catalyst of the present invention It is preferable that the space velocity at the time of contacting the exhaust gas with the exhaust gas is 500 to 500,000 hr ⁻¹ , more preferably 2000 to 300,000 hr ⁻¹ on a volume basis.

  Next, the manufacturing method of the nitrogen oxide purification catalyst of this invention is demonstrated.

  The nitrogen oxide purifying catalyst of the present invention is obtained by calcining a compound obtained by crystallization from a reaction solution containing silica, aluminum, iron, and an organic structure directing agent (SDA) at 700 to 850 ° C. in an atmosphere having a water vapor concentration of 5 vol% or less. And can be produced by removing the organic structure directing agent.

Nitrogen oxide purification catalyst of the present invention, like the composition of the obtained β-type ferrosilicate is _SiO 2 / _Al 2 _{O 3 20~70} molar ratio and 50 to 200 at a _SiO 2 / _Fe 2 _{O 3} molar ratio, It can be produced by crystallization with a suitable charge composition. In crystallization under such conditions, it is possible to introduce isolated iron ions that are highly dispersed as isolated iron ions in the skeleton structure of β-type iron silicate and that have a highly symmetric tetrahedral structure. If the amount of iron is too large, aggregation is likely to proceed due to fresh baking or durability treatment, and isolated iron ions having an isolated symmetric tetrahedral structure are not sufficiently introduced, and the crystallinity of β-type iron silicate is likely to deteriorate.

  The raw material for synthesis is composed of a silica source, an iron source, an aluminum source, SDA, alkali and water, and a fluorine source is used as necessary. As the silica source, colloidal silica, amorphous silica, sodium silicate, tetraethylorthosilicate, aluminosilicate gel and the like can be used. As the iron source, iron nitrate, iron chloride, iron sulfate, metallic iron and the like can be used. These raw materials are preferably those that can be sufficiently uniformly mixed with other components.

  As SDA, tetraethylammonium hydroxide having tetraethylammonium cation, tetraethylammonium bromide, tetraethylammonium fluoride, octamethylenebiskinucridium, α, α′-diquinuclidium-p-xylene, α, α′-diquinuclidium-m -Xylene, α, α'-diquinuclidium-o-xylene, 1,4-diazabicyclo [2,2,2] octane, 1,3,3, N, N-pentamethyl-6-azonium bicyclo [3,2, 1] At least one of a group of compounds containing octane or N, N-diethyl-1,3,3-trimethyl-6-azonium bicyclo [3,2,1] octane cation can be used.

  Examples of alkali sources include sodium hydroxide, sodium sulfate, sodium chloride, sodium acetate, potassium hydroxide, potassium sulfate, potassium chloride, potassium acetate, rubidium hydroxide, rubidium sulfate, rubidium chloride, rubidium acetate, cesium hydroxide, cesium sulfate, Cesium chloride, cesium acetate, and the like can be used.

  As the aluminum source, aluminum sulfate, sodium aluminate, aluminum hydroxide, aluminum nitrate, aluminosilicate gel, metallic aluminum, or the like can be used.

  As the fluorine source, hydrofluoric acid, sodium fluoride, potassium fluoride, ammonium fluoride, tetraethylammonium fluoride, or the like can be used.

  These raw materials are preferably easy to mix uniformly with other components.

  The following composition range is illustrated as a preparation composition of a raw material mixture. However, these composition ranges are not limited, and can be arbitrarily set so that the final product composition falls within the composition range of the β-type iron silicate of the nitrogen oxide purification catalyst of the present invention. In addition, a component having a crystallization promoting action such as a seed crystal may be added, and conditions under which a large crystal particle diameter can be obtained are preferable.

SiO ₂ / _Al 2 _{O 3} molar ratio from 20 to 70, preferably 30 to 60, more preferably 30 to 50
SiO ₂ / Fe ₂ O ₃ molar ratio 50-200, preferably 100-200
H ₂ O / SiO ₂ molar ratio 5-50, preferably 5-10
SDA / SiO ₂ molar ratio of 0.1 to 5, preferably 0.1 to 1
Alkali / SiO ₂ molar ratio of 0 to 0.1
F / SiO ₂ molar ratio 0-5, preferably 0-1

  A raw material mixture of water, silica source, iron source, aluminum source, SDA, alkali source and, if necessary, a fluorine source is crystallized in a sealed pressure vessel at a temperature of 100 to 180 ° C. At the time of crystallization, the raw material mixture may be mixed and stirred or left standing. After completion of crystallization, the product is allowed to cool sufficiently, separated into solid and liquid, washed with a sufficient amount of pure water, dried at a temperature of 110 to 150 ° C., and then the SDA in the pores is removed by incineration. Iron silicate can be obtained.

  In general, it is considered that the heat treatment and removal of SDA in the pores of β-type iron silicate should be performed at a temperature as low as possible from the viewpoint of suppressing thermal deterioration of the silicate crystal, and a baking process at 550 to 650 ° C. in an air atmosphere. In addition, a liquid phase treatment using a chemical solution containing an acidic solution or a component that decomposes SDA, and an exchange treatment using a resin or the like have been performed.

  The nitrogen oxide purification catalyst of the present invention performs a heat treatment for removing SDA at a high temperature range of 700 to 850 ° C., which is not conventionally performed, so that the silica skeleton and a part of iron and aluminum in the skeleton are mutually bonded. The action becomes stronger and the low-temperature catalytic activity after hydrothermal durability treatment is improved.

  It is essential that the water vapor concentration during the heat treatment for the purpose of removing SDA in the production of the nitrogen oxide purification catalyst of the present invention is 5% by volume or less. In particular, it is preferable to perform the treatment at 1% by volume or less in order to suppress dealumination and iron removal from the skeleton by water vapor, and aggregation and inactivation of iron. When the water vapor concentration exceeds 5% by volume, the performance is not improved by the interaction between the skeleton silica and a part of the iron in the skeleton and the aluminum, and conversely, iron aggregation is promoted and the durability activity after the hydrothermal treatment is lowered.

  It is essential that the heat treatment temperature in the production of the nitrogen oxide purification catalyst of the present invention is 700 to 850 ° C. It is particularly preferable to carry out at 800 to 850 ° C. If the temperature is lower than 700 ° C., the interaction between the skeleton silica and a part of iron in the skeleton and aluminum is not sufficiently promoted, and the catalytic activity of the present invention cannot be obtained. The crystal disintegration of the ferrous iron silicate proceeds remarkably and the catalytic activity decreases.

  The heat treatment time is not particularly limited, but if the heat treatment time is too short, the interaction between iron and the silica skeleton of the β-type zeolite does not proceed sufficiently, and it is preferable to hold for 1 hour or longer.

  The crystal particle diameter (average crystal particle) observed with an electron microscope (SEM) of β-type iron silicate of the nitrogen oxide purifying catalyst of the present invention is 0.2 to 2 due to hot water resistance, ease of handling in coating, molding and the like. 0.0 μm, preferably 0.2 to 1.0 μm.

  Since the β-type iron silicate of the nitrogen oxide purification catalyst of the present invention contains active isolated iron ions, it can be used as it is as a nitrogen oxide purification catalyst, but further supports a catalytically active metal species. May be used.

  The metal species to be supported is not particularly limited, but is, for example, at least one selected from the group consisting of elements of groups 8, 9, 10, and 11, particularly iron, cobalt, palladium, iridium, platinum, copper, silver, and gold. In particular, at least one of iron, palladium, platinum, copper, and silver is preferable. In addition, a promoter component such as rare earth metal, titanium or zirconia can be additionally added.

  There are no particular limitations on the loading method when loading a catalytically active metal species. As the loading method, methods such as an ion exchange method, an impregnation loading method, an evaporation to dryness method, a precipitation loading method, and a physical mixing method can be employed. Nitrate, sulfate, acetate, chloride, complex salt, oxide, composite oxide and the like can be used as raw materials for metal loading. The amount of metal supported is not limited, but a range of 0.1 to 10% by weight is particularly preferable.

  The β-type iron silicate of the nitrogen oxide purification catalyst of the present invention can be used by mixing with a binder such as silica, alumina and clay mineral. Examples of clay minerals used for molding include kaolin, attapulgite, montmorillonite, bentonite, allophane, and sepiolite. Moreover, it can also be used by wash-coating on a cordierite or metal honeycomb substrate.

  The β-type iron silicate of the present invention is synthesized without using fluorine, which is difficult to use industrially, has high crystallinity, contains Fe in the crystal lattice, and has a fine crystal grain size of 2.0 μm or less. Has high heat resistance.

  The nitrogen oxide purification catalyst of the present invention has high nitrogen oxide purification performance, and can efficiently purify nitrogen oxide in a wide temperature range, particularly at a low temperature of 200 ° C. or lower. Moreover, it is excellent in durability and has high catalytic activity even after durability treatment.

2 is a diagram showing an electron spin resonance spectrum of β-type iron silicate obtained in Example 1. FIG. 6 is a diagram showing an X-ray diffraction pattern of a nitrogen oxide purification catalyst obtained in Example 12. FIG.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.

  Examples 1 to 11 and Comparative Examples 1 to 3 below relate to β-type iron silicates according to claims 1 to 5 of the present invention.

Example 1
No. 3 sodium silicate (SiO ₂ ; 30%, Na ₂ O; 9.1%, Al ₂ O ₃ ; 0.01%), 98% sulfuric acid, water, aluminum sulfate aqueous solution and iron nitrate nonahydrate And the produced gel was separated into solid and liquid and washed with pure water. A predetermined amount of water, 35% TEAOH, cesium hydroxide monohydrate and seed crystals were added to the washed gel, and the mixture was sufficiently stirred and mixed. The composition ratio of the reaction mixture _{SiO 2: 0.015Fe 2 O 3:} 0.026Al 2 O 3: 0.049Cs 2 O: 0.15TEAOH: was 10H ₂ O. The reaction mixture was sealed in a stainless steel autoclave and heated at 150 ° C. for 48 hours under a rotating condition to crystallize β-type iron silicate. The slurry-like mixture after crystallization was white, and the F content of the crystals was below the quantitative limit of analysis of 100 ppm and below the detection limit.

Example 2
A reaction mixture was prepared in the same manner as in Example 1. The composition ratio of the reaction mixture was SiO ₂ : 0.012Fe ₂ O ₃ : 0.025Al ₂ O ₃ : 0.015Cs ₂ O: 0.15TEAOH: 10H ₂ O. The reaction mixture was sealed in a stainless steel autoclave and heated at 150 ° C. for 48 hours under a rotating condition to crystallize β-type iron silicate. The slurry mixture after crystallization was white, and the F content of the crystals was below the detection limit.

Example 3
A reaction mixture was prepared in the same manner as in Example 1 except that 48% potassium hydroxide aqueous solution was used instead of cesium hydroxide monohydrate. The composition ratio of the reaction mixture was SiO ₂ : 0.010Fe ₂ O ₃ : 0.012Al ₂ O ₃ : 0.030K ₂ O: 0.14TEAOH: 10H ₂ O. The reaction mixture was sealed in a stainless steel autoclave and heated at 150 ° C. for 48 hours under a rotating condition to crystallize β-type iron silicate. The slurry mixture after crystallization was white, and the F content of the crystals was below the detection limit.

Example 4
A reaction mixture was prepared in the same manner as in Example 3. The composition ratio of the reaction mixture was SiO ₂ : 0.0062Fe ₂ O ₃ : 0.019Al ₂ O ₃ : 0.021K ₂ O: 0.15TEAOH: 10H ₂ O. The reaction mixture was sealed in a stainless steel autoclave and heated at 150 ° C. for 90 hours under a rotating condition to crystallize β-type iron silicate. The slurry mixture after crystallization was white, and the F content of the crystals was below the detection limit.

Example 5
A reaction mixture was prepared in the same manner as in Example 3. The composition ratio of the reaction mixture was SiO ₂ : 0.0067Fe ₂ O ₃ : 0.028Al ₂ O ₃ : 0.031K ₂ O: 0.15TEAOH: 10H ₂ O. The reaction mixture was sealed in a stainless steel autoclave and heated at 150 ° C. for 48 hours under a rotating condition to crystallize β-type iron silicate. The slurry mixture after crystallization was white, and the F content of the crystals was below the detection limit.

Example 6
A reaction mixture was prepared in the same manner as in Example 1 except that rubidium hydroxide n-hydrate was used instead of cesium hydroxide monohydrate. The composition ratio of the reaction mixture was SiO ₂ : 0.0069Fe ₂ O ₃ : 0.034Al ₂ O ₃ : 0.030Rb ₂ O: 0.15TEAOH: 10H ₂ O. The reaction mixture was sealed in a stainless steel autoclave and heated at 150 ° C. for 48 hours under a rotating condition to crystallize β-type iron silicate. The slurry mixture after crystallization was white, and the F content of the crystals was below the detection limit.

Comparative Example 1
A reaction mixture was prepared in the same manner as in Example 1 except that 48% aqueous sodium hydroxide solution was used instead of cesium hydroxide monohydrate. The composition ratio of the reaction mixture was SiO ₂ : 0.015Fe ₂ O ₃ : 0.026Al ₂ O ₃ : 0.049Na ₂ O: 0.15TEAOH: 10H ₂ O. The reaction mixture was sealed in a stainless steel autoclave and heated at 150 ° C. for 48 hours under a rotating condition to crystallize β-type iron silicate. The slurry mixture after crystallization was white, and the F content of the crystals was below the detection limit.

Comparative Example 2
After iron nitrate nonahydrate is dissolved in TEAOH, sodium aluminate and pure water are added thereto, and silica sol (SiO ₂ ; 40%, Na ₂ O; 0.5%, Al ₂ O ₃ is added under strong stirring. 0.00%) and seed crystals were added. The composition ratio of the reaction mixture was SiO ₂ : 0.0058Fe ₂ O ₃ : 0.038Al ₂ O ₃ : 0.077Na ₂ O: 0.12TEAOH: 7.7H ₂ O. The resulting gel was continuously stirred for 30 minutes, and then the reaction mixture was sealed in a stainless steel autoclave and heated at 160 ° C. for 48 hours under a rotating condition to crystallize β-type iron silicate. The slurry mixture after crystallization was white, and the F content of the crystals was below the detection limit.

Comparative Example 3
Iron nitrate nonahydrate was dissolved in TEAOH, tetraethylorthosilicate was added, and the mixture was thoroughly stirred and mixed to perform hydrolysis at room temperature to evaporate the produced ethanol. Subsequently, the required amount of water was evaporated. 48% hydrofluoric acid was added thereto and mixed in a mortar, and then the reaction mixture was filled in a stainless steel autoclave and heated at 150 ° C. for 240 hours for crystallization. The composition of the reaction mixture was SiO ₂ : 0.016Fe ₂ O ₃ : 0.50HF: 0.61TEAOH: 7.5H ₂ O. The slurry mixture after crystallization was white, and the F content of the crystals was 14000 ppm. This was calcined at 600 ° C. for 2 hours under air flow, and the F content of the crystals after removing SDA was 430 ppm.

Example 7
The crystal compositions of β-type iron silicates synthesized in Examples 1 to 6 and Comparative Examples 1 and 2 were analyzed by inductively coupled plasma emission spectrometry. The results are shown in Table 3 below.

Example 8
X-ray diffraction measurement of the β-type iron silicate synthesized in Examples 1 to 6 and Comparative Examples 1 and 2 was performed.

  The conditions for the X-ray diffraction measurement are shown below.

Target: Cu
Accelerating voltage: 40KV
Current: 30mA
Step width: 0.02 °
Sampling time: 1 second Divergence slit: 1 °
Anti-scattering slit: 1 °
Receiving slit: 0.3mm
The results are shown in Table 4. The full width at half maximum of the example was in the range of 0.16 to 0.24 °.

Example 9
The hot water resistance of the β-type iron silicate synthesized in Example 1 and Comparative Example 1 was evaluated. In the evaluation, a sample (fresh) from which SDA was burned and removed was used, and after pellet molding, the sample was crushed and subjected to evaluation. A sample was filled into a fixed bed flow type reaction tube, and a durability treatment was performed at a predetermined temperature for 5 hours under a flow of 10% by volume of H ₂ O. With respect to a fresh sample and a sample subjected to endurance treatment, the crystallinity of the sample was measured from the diffraction peak height of 2θ = 22.3 ° by powder X-ray crystal diffraction using a commonly used Cu—Kα ray source.

  The results are shown in Table 5 below.

  As described above, the β-type iron silicate of the present invention showed high hot water resistance compared to the comparative example under any treatment conditions.

Example 10
Table 6 below shows the average crystal grain sizes of β-type iron silicates obtained by observing the β-type iron silicates synthesized in Examples 1 to 6 and Comparative Examples 1 to 3 with a SEM at a magnification of 15000 times.

Example 11
Electron spin resonance measurement was performed on the β-type iron silicate synthesized in Example 1, and Fe present in the skeleton was confirmed.

  The conditions for electron spin resonance measurement are shown below.

Measurement temperature: 77K
Microwave output: 1.0 mW
Observation range: 0 to 1000 mT
Modulation width: 0.32 mT
Time constant: 0.3 sec
Sample amount: about 10mg

  The spectrum obtained by the measurement is shown in FIG.

  A large resonance absorption of g≈2.0 was observed, confirming the presence of Fe having a highly symmetric tetrahedral structure present in the silicate skeleton.

  The following Examples 12 to 14 and Comparative Examples 4 to 6 relate to a nitrogen oxide purification catalyst comprising another β-type iron silicate according to claims 6 to 9 of the present invention.

(Measurement of full width at half maximum (FWHM) by X-ray)
The full width at half maximum (FWHM) was determined using the main peak appearing in the vicinity of 2θ = 22.6 ° by powder X-ray crystal diffraction using a commonly used Cu—Kα radiation source. The X-ray diffraction measurement conditions are the same as those described in Example 8.

(Hydrothermal durability treatment conditions)
The nitrogen oxide purification catalyst was treated under the following conditions.

Temperature: 700 ° C
Time: 20 hours Gas concentration in gas: 10% by volume
Gas flow rate / zeolite volume ratio: 100 times / min

(Measurement of NOx reduction rate)
The NOx reduction rate was defined as the nitrogen oxide reduction rate when a gas having the following conditions was brought into contact at a predetermined temperature. The nitrogen oxide purification catalyst is generally evaluated by using a gas containing NO gas for reductive decomposition and ammonia as a reducing agent in a ratio of 1: 1. The NOx reduction conditions used in the present invention fall within the category of general conditions for evaluating the NOx reduction properties of ordinary nitrogen oxide purification catalysts, and are not special conditions.

Nitrogen reduction conditions employed in the evaluation of the present invention:
Process gas composition NO 200ppm
NH ₃ 200ppm
O ₂ 10% by volume
H ₂ O 3% by volume
Remaining N ₂ balance Process gas flow rate 1.5 l / min Process gas / catalyst volume ratio 1000 / min

Example 12
Using a sodium silicate aqueous solution, an aluminum sulfate aqueous solution, a ferric nitrate aqueous solution, and sulfuric acid, the reaction is performed with stirring so that the composition of the slurry product is SiO ₂ : 0.027Al ₂ O ₃ : 0.007Fe ₂ O ₃ The slurry was made into a slurry product, dehydrated, and washed to give a granular amorphous silicate.

Next, the reaction mixture was mixed so that the composition of SiO ₂ : 0.027Al ₂ O ₃ : 0.007Fe ₂ O ₃ : 0.060KOH: 0.15TEAOH: 10H ₂ O was further added to 100 parts of the composition. On the other hand, 1 part of seed crystals (Tosoh HSZ940NHA) was added and crystallized by hydrothermal synthesis at 150 ° C. for 60 hours in an autoclave (TEAOH: 35% aqueous solution of tetraethylammonium hydroxide).

  The slurry after crystallization was solid-liquid separated, washed with a sufficient amount of pure water, and dried at 110 ° C. The dried powder was calcined at 800 ° C. for 2 hours under a flow of dry air having a water vapor concentration of 0.05 vol% to obtain Catalyst 1.

As a result of ICP emission analysis, the composition of catalyst 1 was a SiO ₂ / Al ₂ O ₃ molar ratio of 35, a SiO ₂ / Fe ₂ O ₃ molar ratio of 144, and an average crystal particle diameter of 0.28 μm. The full width at half maximum (FWHM) of the X-ray crystal diffraction (302) plane is 0.36 °, and the NOx reduction rate after hydrothermal endurance treatment in a 10 vol% steam atmosphere at 700 ° C. for 20 hours is a reaction temperature of 200 ° C. 50%. Further, the NOx reduction rate before the durability treatment was 50% at a reaction temperature of 200 ° C.

  FIG. 2 shows an X-ray diffraction chart of the catalyst 1. The peak pattern coincides with the pattern of β-type zeolite, and it is clear that catalyst 1 has a β-type crystal structure.

Example 13
Using a sodium silicate aqueous solution, an aluminum sulfate aqueous solution, a ferric nitrate aqueous solution, and sulfuric acid, the composition of the slurry product is SiO ₂ : 0.035Al ₂ O ₃ : 0.007Fe ₂ O ₃ and the composition of the reaction mixture is SiO _2. : 0.035Al ₂ O ₃ : 0.007Fe ₂ O ₃ : 0.060KOH: 0.15TEAOH: 10H ₂ O and mixed to 100 parts of the composition, 0.5 parts of seed crystals (Tosoh Corporation) Catalyst 2 was obtained in the same manner as in Example 12 except that HSZ940NHA) was added.

As a result of ICP emission analysis, the composition of the catalyst 2 was a SiO ₂ / Al ₂ O ₃ molar ratio of 26, a SiO ₂ / Fe ₂ O ₃ molar ratio of 138, and an average crystal particle diameter of 0.26 μm. The full width at half maximum (FWHM) of the X-ray crystal diffraction (302) plane is 0.34 °, and the NOx reduction rate after hydrothermal endurance treatment in a 10 vol% steam atmosphere at 700 ° C. for 20 hours is a reaction temperature of 200 ° C. It was 47%. Further, the NOx reduction rate before the durability treatment was 47% at a reaction temperature of 200 ° C.

Example 14
Using a sodium silicate aqueous solution, an aluminum sulfate aqueous solution, a ferric nitrate aqueous solution, and sulfuric acid, the composition of the slurry product is SiO ₂ : 0.026Al ₂ O ₃ : 0.015Fe ₂ O ₃ and the composition of the reaction mixture is SiO _2. : 0.026 Al ₂ O ₃ : 0.015 Fe ₂ O ₃ : 0.100 KOH: 0.15 TEAOH: 10 H ₂ O The mixture was mixed so that 0.5 part of seed crystals (Tosoh) was added to 100 parts of the composition. Catalyst 3 was obtained in the same manner as in Example 12 except that HSZ940NHA) was added.

As a result of ICP emission analysis, the composition of catalyst 3 was a SiO ₂ / Al ₂ O ₃ molar ratio of 34, a SiO ₂ / Fe ₂ O ₃ molar ratio of 56, and an average crystal particle diameter of 0.24 μm. The full width at half maximum (FWHM) of the X-ray crystal diffraction (302) plane is 0.36 °, and the NOx reduction rate after hydrothermal endurance treatment in a 10 vol% steam atmosphere at 700 ° C. for 20 hours is a reaction temperature of 200 ° C. It was 46%. Moreover, the NOx reduction rate before the durability treatment was 55% at a reaction temperature of 200 ° C.

Comparative Example 4
Using a sodium silicate aqueous solution, an aluminum sulfate aqueous solution, a ferric nitrate aqueous solution, and sulfuric acid, the composition of the slurry product is SiO ₂ : 0.009Al ₂ O ₃ : 0.017Fe ₂ O ₃ and the composition of the reaction mixture is SiO _2. Comparative catalyst 1 was obtained in the same manner as in Example 12 except that 0.009Al ₂ O ₃ : 0.017Fe ₂ O ₃ : 0.050 KOH: 0.15 TEAOH: 10H ₂ O.

As a result of ICP emission analysis, the composition of Comparative Catalyst 1 was SiO ₂ / Al ₂ O ₃ molar ratio was 102, SiO ₂ / Fe ₂ O ₃ molar ratio was 49, and the average crystal particle diameter was 0.24 μm. The full width at half maximum (FWHM) of the X-ray crystal diffraction (302) plane is 0.34 °, and the NOx reduction rate after hydrothermal endurance treatment in a 10 vol% steam atmosphere at 700 ° C. for 20 hours is a reaction temperature of 200 ° C. It was 36%. Moreover, the NOx reduction rate before the durability treatment was 54% at a reaction temperature of 200 ° C.

Comparative Example 5
Using a sodium silicate aqueous solution, an aluminum sulfate aqueous solution, a ferric nitrate aqueous solution, and sulfuric acid, the composition of the slurry product is SiO ₂ : 0.009Al ₂ O ₃ : 0.027Fe ₂ O ₃ and the composition of the reaction mixture is SiO _2. : 0.009Al ₂ O ₃ : 0.027Fe ₂ O ₃ : 0.140KOH: 0.15TEAOH: 10H ₂ O The mixture was mixed so that 0.5 parts of seed crystals (Tosoh) was added to 100 parts of the composition. Comparative catalyst 2 was obtained in the same manner as in Example 12 except that HSZ940NHA) was added.

As a result of ICP emission analysis, the composition of Comparative Catalyst 2 was 88 / SiO ₂ / Al ₂ O ₃ molar ratio, 30 / SiO ₂ / Fe ₂ O ₃ molar ratio, and the average crystal particle diameter was 0.19 μm. The full width at half maximum (FWHM) of the X-ray crystal diffraction (302) plane is 0.38 °, and the NOx reduction rate after hydrothermal endurance treatment in a 10% by volume steam atmosphere at 700 ° C. for 20 hours is 200 ° C. 43%. Further, the NOx reduction rate before the durability treatment was 59% at a reaction temperature of 200 ° C.

Comparative Example 6
Comparative catalyst 3 was obtained in the same manner as in Example 12 except that the dried powder was calcined at 600 ° C. for 2 hours under a flow of dry air having a water vapor concentration of 0.05 vol%.

As a result of ICP emission analysis, the composition of the comparative catalyst 3 was a SiO ₂ / Al ₂ O ₃ molar ratio of 35, a SiO ₂ / Fe ₂ O ₃ molar ratio of 144, and an average crystal particle diameter of 0.28 μm. The full width at half maximum (FWHM) of the X-ray crystal diffraction (302) plane is 0.28 °, and the NOx reduction rate after hydrothermal endurance treatment in a 10 vol% steam atmosphere at 700 ° C. for 20 hours is a reaction temperature of 200 ° C. 38%. Further, the NOx reduction rate before the durability treatment was 77% at a reaction temperature of 200 ° C.

  Table 7 below shows the relationship between the physical properties of the nitrogen oxide purifying catalysts obtained in Examples 12 to 14 and Comparative Examples 4 to 6 and the NOx reduction rate at 200 ° C.

  As is clear from the table, the catalysts of Examples 12-14 have a higher NOx reduction rate at 200 ° C. after the endurance treatment than the catalysts of Comparative Examples 4-6.

  The highly crystalline β-type iron silicate of the present invention can be used, for example, as a nitrogen oxide purification catalyst, and is applied to the removal of nitrogen oxides from automobile exhaust gas.

  Further, the nitrogen oxide purification catalyst of the present invention can be used to purify nitrogen oxide in automobile exhaust gas in the presence of a reducing agent.

Claims (13)

The SiO ₂ / Fe ₂ O ₃ molar ratio is 50 or more and 150 or less, the fluorine content with respect to the dry weight of the crystal is 400 ppm or less, and the half width of the crystal diffraction (302) plane in powder X-ray crystal diffraction using a Cu—Kα radiation source (Beta) type | mold iron silicate which contains all or one part of iron in (beta) frame | skeleton structure whose (FWHM) is 0.16-0.24 degree. The β-type iron silicate according to claim 1, wherein the molar ratio of SiO ₂ / Al ₂ O ₃ is 25 or more and 70 or less.   The β-type iron silicate according to claim 1 or 2, wherein the crystal grain size is 0.2 µm or more and 2.0 µm or less.   The β-type iron silicate according to any one of claims 1 to 3, wherein the crystal grain size is 0.2 µm or more and 1.0 µm or less. The following fluorine containing no starting composition _{aM 2 O · SiO 2 · bFe} 2 O 3 · cAl 2 O 3 · dSDA · eH 2 O
here,
M = K ⁺ or Rb ⁺ or Cs ⁺
a = 0.005-0.10
b = 0.006-0.02
c = 0.014-0.04
d = 0.10-0.35
e = 7-15
The method for producing β-type iron silicate according to any one of claims 1 to 4, wherein crystallization is performed by hydrothermal treatment. It has iron and aluminum in a β-type skeleton structure, SiO ₂ / Al ₂ O ₃ molar ratio is 20 or more and 70 or less, and SiO ₂ / Fe ₂ O ₃ molar ratio is 50 or more and 200 or less, Cu—Kα radiation source A nitrogen oxide purification catalyst comprising β-type iron silicate, wherein the half-value width (FWHM) of the crystal diffraction (302) plane in powder X-ray crystal diffraction using is 0.30 to 0.40 °.   The nitrogen oxide purification catalyst according to claim 6, wherein the average crystal particle diameter is 0.2 to 2.0 µm.   The nitrogen oxide purification catalyst according to claim 6, wherein the average crystal particle diameter is 0.2 to 1.0 µm. The nitrogen oxide purification catalyst according to any one of claims 6 to 8, wherein the molar ratio of SiO ₂ / Fe ₂ O ₃ is 100 or more and 200 or less.   10. A β-type iron silicate crystallized from a reaction solution containing silica, aluminum, iron and an organic structure directing agent is heat-treated at 700 to 850 ° C. in an atmosphere having a water vapor concentration of 5% by volume or less. The manufacturing method of the nitrogen oxide purification catalyst in any one of.   The method for producing a nitrogen oxide purification catalyst according to claim 10, wherein the water vapor concentration is 1% by volume or less.   The method for producing a nitrogen oxide purification catalyst according to claim 10 or 11, wherein a holding time in firing at 700 to 850 ° C is 1 hour or more.   A method for reducing nitrogen oxides using the nitrogen oxide purification catalyst according to any one of claims 6 to 9.

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