JP5573453B2 - Nitrogen oxide purification catalyst and method for producing the same - Google Patents

Description

  The present invention relates to a catalyst for purifying nitrogen oxides, particularly a catalyst containing zeolite capable of purifying nitrogen oxides contained in exhaust gas discharged from an internal combustion engine such as a diesel engine, and the zeolite catalyst efficiently. Regarding the method.

Nitrogen oxides contained in exhaust gas from an internal combustion engine, factory exhaust gas, and the like have been purified by selective catalytic reduction (SCR) using a V ₂ O ₅ —TiO ₂ catalyst and ammonia. However, since the V ₂ O ₅ —TiO ₂ catalyst sublimes at high temperatures and the catalyst component may be discharged from the exhaust gas, it is not particularly suitable for exhaust gas purification of moving bodies such as automobiles.

Therefore, in recent years, a metal-supported zeolite catalyst has been proposed as a catalyst for performing the selective catalytic reduction (hereinafter sometimes referred to as “SCR catalyst”) in automobiles, particularly diesel cars in which it is difficult to purify nitrogen oxides. . Copper and iron are generally used as the supported metal, but iron is generally used in countries and regions where the use of copper is restricted, such as Japan.
In recent years, in accordance with stricter exhaust gas regulations, it is necessary to use a filter called DPF (Diesel particulate filter) together with the SCR catalyst in order to remove particulate matter (hereinafter referred to as PM) contained in exhaust gas. PM trapped in the DPF is usually removed by burning at a high temperature of 600 to 700 ° C. Studies are being made to mount the SCR catalyst immediately after the DPF or to carry the SCR catalyst on the DPF. In this case, however, the SCR catalyst also rises to a temperature close to 700 ° C. during PM combustion. Therefore, β-type and MFI-type aluminosilicate zeolite catalysts used for conventional SCR catalysts have insufficient heat resistance and can be used. Have difficulty.

  In recent years, as a zeolite, a zeolite containing at least an aluminum atom, a phosphorus atom and a silicon atom in its skeleton structure (hereinafter sometimes referred to as “silicoaluminophosphate” or “SAPO”) and a metal-supported catalyst are used. It is known that a catalyst having a high durability can be obtained. For example, Non-Patent Document 1 proposes a nitrogen oxide purification catalyst using a hydrocarbon in which a metal such as copper or iron is supported on SAPO as a reducing agent. Further, Patent Document 1 proposes a nitrogen oxide purifying catalyst in which a metal is supported on SAPO which does not decrease the specific surface area even if it is subjected to steam treatment at 700 to 900 ° C.

In addition, as a method for producing an iron-supported zeolite catalyst, a method of supporting iron by an ion exchange method using an inorganic acid salt such as nitrate or sulfate is generally used as disclosed in Patent Document 2 regarding aluminosilicate zeolite. Used.
In order to further improve the purification performance, as a method for producing an iron-supported aluminosilicate zeolite catalyst, there is a method in which solid ion exchange is performed with iron chloride and zeolite and heat treatment is performed in a reducing atmosphere or an inert atmosphere as described in Patent Document 3, etc. It is disclosed.

US Pat. No. 7,645,718 JP 2008-81348 A JP 2007-24450 A

J. et al. Catal. 169 (1997), 93-102

  However, the SAPO catalyst described in Non-Patent Document 1 has a problem in that the performance deteriorates in an endurance test under steam at 700 ° C. or higher. This is considered to be caused by the fact that the structure of SAPO is decomposed under high-temperature steam in addition to the poor crystallinity of SAPO and the insufficient dispersion of iron. The SAPO catalyst described in Patent Document 1 has good performance when copper is supported and durability under high-temperature steam, but when iron is supported, a general ion exchange method is used. The iron loading was very low at 0.4% by weight or less, and there was a problem that the nitrogen oxide purification performance was insufficient for practical use.

Further, SAPO is generally unstable when it is in an acidic state as compared with aluminosilicate, and there has been a problem that sufficient performance cannot be obtained when an acidic inorganic salt conventionally used is used as an iron source.
Furthermore, when iron chloride is used as an iron source, corrosive chlorine gas is generated, and firing in a reducing atmosphere such as hydrogen has a risk of explosion, and industrialization is very difficult. there were.

  An object of the present invention is to provide a nitrogen oxide purification catalyst having high durability under high-temperature steam without using copper, which is a regulated substance, and to provide a method for producing the nitrogen oxide purification catalyst.

  As a result of intensive studies, the present inventors have found that the amount of iron supported on iron-supported silicoaluminophosphate is 1% by weight or more of the total weight of the zeolite, and the height of a specific peak in X-ray diffraction measurement. When the ratio is within a specific range, the nitrogen oxide purification performance is high, the durability under high steam is good, and it is found that the present invention is suitable as an SCR catalyst for nitrogen oxide purification. It came to complete.

That is, the first gist of the present invention is a nitrogen oxide purification catalyst in which iron is supported on a zeolite containing at least an aluminum atom, a phosphorus atom, and a silicon atom in a skeleton structure,
(1) The amount of iron supported is 1% by weight or more of the total weight of the zeolite,
(2) When the catalyst is measured by X-ray diffraction using CuKα as an X-ray source, the diffraction peak height observed at a diffraction angle (2θ) in the range of 21.2 to 21.6 degrees is 0.01. That's it,
(3) When the catalyst was steamed at 800 ° C. for 5 hours and then subjected to X-ray diffraction measurement using CuKα as an X-ray source, the diffraction angle (2θ) was observed in the range of 20.6 to 21.0 degrees. that for the diffraction peak height state, and are the ratio of the diffraction peak height is 0.01 to 1.0 the diffraction angle (2 [Theta]) is observed in the range of 21.2 to 21.6 degrees,
(4) structure of the zeolite containing at least aluminum atom and a phosphorus atom and a silicon atom in the skeleton structure, CHA Ru der code represented by IZA, nitrogen oxide purification catalyst (hereinafter, "the present invention Sometimes referred to as “catalyst for nitrogen oxide purification”.

  The present invention provides a nitrogen oxide purification catalyst having high nitrogen oxide purification performance and high durability under high-temperature steam without using copper, which is a regulated substance. Also, the nitrogen oxide purification catalyst can be produced by a simple method.

2 is an XRD chart before steam treatment of the catalyst 1 described in Example 1. FIG. 2 is an XRD chart after steam treatment of the catalyst 1 described in Example 1. FIG.

Hereinafter, embodiments of the present invention will be described in detail. However, the following description is an example (representative example) of an embodiment of the present invention, and the contents thereof are not specified.
(1) Nitrogen oxide and purification thereof Nitrogen monoxide, nitrogen dioxide, nitrous oxide and the like are listed as nitrogen oxides purified by the nitrogen oxide purification catalyst of the present invention. Hereinafter, these may be collectively referred to as NOxs. In this specification, purifying nitrogen oxides means that nitrogen oxides are reacted on a catalyst and converted to nitrogen, oxygen, or the like.
In this case, nitrogen oxides may react directly, but a reducing agent may coexist in the catalyst for the purpose of increasing purification efficiency. As the reducing agent, ammonia, urea, organic amines, carbon monoxide, hydrocarbons, alcohol, hydrogen and the like are used, and preferably ammonia and urea are used.

(2) Nitrogen oxide purifying catalyst The nitrogen oxide purifying catalyst catalyst of the present invention refers to the above-described catalyst capable of purifying nitrogen oxide, and specifically has the following properties. It is.
(I) The iron loading is 1% by weight or more of the total weight of the zeolite,
(II) When the catalyst is measured by X-ray diffraction using CuKα as an X-ray source, the diffraction peak height observed at a diffraction angle (2θ) in the range of 21.2 to 21.6 degrees is 0.01. That's it,
(III) When the X-ray diffraction measurement using CuKα as an X-ray source was performed after steaming the catalyst at 800 ° C. for 5 hours, the diffraction angle (2θ) was observed in the range of 20.6 to 21.0 degrees. The ratio of the diffraction peak height observed in the diffraction angle (2θ) range of 21.2 to 21.6 degrees with respect to the diffraction peak height is 0.01 or more and 1.0 or less.

The above-mentioned zeolite refers to zeolites defined by International Zeolite Association (hereinafter referred to as IZA). Specific zeolites include at least oxygen, aluminum (Al), phosphorus (P), silicon (as atoms constituting the framework structure) Si) -containing materials (hereinafter sometimes referred to as silicoaluminum phosphates).
The composition ratio (molar ratio) of Si, Al, and P constituting the skeleton structure of silicoaluminophosphates is not particularly limited, but silicon atoms, aluminum atoms included in the skeleton structure in the zeolite, X1 is usually 0.06 or more and 0.15 or less, and y1 is usually 0, where x1 is the silicon atom content ratio relative to the total phosphorus atoms, y1 is the aluminum atom content ratio, and z1 is the phosphorus atom content ratio. 0.3 or more and 0.6 or less and z1 is usually 0.3 or more and 0.6 or less. Further, x1 is preferably 0.07 or more, more preferably 0.08 or more, and it is preferably a zeolite that is usually 0.14 or less, preferably 0.13 or less, more preferably 0.12 or less.

  In the zeolite framework of the present invention, elements other than silicon, aluminum, and phosphorus may be contained. Examples of other elements include lithium, magnesium, titanium, zirconium, vanadium, chromium, manganese, iron, cobalt, nickel, palladium, copper, zinc, gallium, germanium, arsenic, tin, calcium, and boron. Preferably, iron, copper, and gallium are used. The content of other elements is preferably 0.3 or less, and more preferably 0.1 or less, in terms of the molar ratio to the total of silicon, aluminum and phosphorus in the zeolite skeleton.

The ratio of the above elements is determined by elemental analysis. Elemental analysis in the present invention can be obtained by inductively coupled plasma (hereinafter referred to as ICP) emission spectroscopic analysis by heating a sample with an aqueous hydrochloric acid solution.
The structure of the zeolite is an X-ray diffraction method (for example, a measurement method described in Atlas of Zeolite framework types, Ch. Baerlocher et.al 2007, Elsevier) (X-ray diffraction, hereinafter sometimes referred to as “XRD”). ) The structure of the zeolite is not particularly limited, but when indicated by a code defined by the International Zeolite Association (IZA), it is usually AEI, AFR, AFS, AFT, AFX, Afy, AHT, CHA, DFO, ERI, Any of FAU, GIS, LEV, LTA, and VFI, and any of AEI, AFX, GIS, CHA, VFI, AFS, LTA, FAU, and AFY is preferred, and CHA is less likely to adsorb fuel-derived hydrocarbons. Zeolite having a structure is more preferable.

When measured by XRD, it is preferable that all have the above-mentioned zeolite structure, but if the CHA structure is the main component, an amorphous component or a small amount of other skeleton structures may be included. These zeolites are referred to herein as “zeolite”.
The zeolite may contain a cation species that can be ion-exchanged with other cations, in addition to the component constituting the skeleton structure as a basic unit. The cations in that case are not particularly limited, and examples include protons, alkaline elements such as Li, Na, and K, alkaline earth elements such as Mg and Ca, and rare earth elements such as La and Ce. Among them, protons and alkaline elements Alkaline earth elements are preferred.

The framework density of the zeolite (hereinafter sometimes abbreviated as FD) is not particularly limited, but is usually 13.0 T / nm ³ or more, preferably 13.5 T / nm ³ or more, more preferably Is 14.0 T / nm ³ or more, usually 20.0 T / nm ³ or less, preferably 19.0 T / nm ³ or less, more preferably 17.5 T / nm ³ or less. The framework density (T / nm ³ ) means the number of T atoms (atoms of elements other than oxygen constituting the skeleton of the zeolite) present per unit volume nm ³ of the zeolite, and this value is the structure of the zeolite. It is determined by. If the amount is less than the lower limit value, the structure may become unstable or the durability tends to decrease. On the other hand, if the upper limit value is exceeded, the amount of adsorption, the catalytic activity may decrease, May not be suitable for use.

  The zeolite preferably has a characteristic that the adsorption amount of water largely changes within a specific relative vapor pressure range as the adsorption characteristic of water vapor. When evaluated by the adsorption isotherm, the water adsorption amount change is usually observed in the water vapor adsorption isotherm at 25 ° C. when the relative vapor pressure changes by 0.05 within the range of the relative vapor pressure of 0.03 or more and 0.25 or less. It is 0.10 g / g or more, and preferably 0.15 g / g or more. A preferable range of the relative vapor pressure is 0.035 or more and 0.15 or less, more preferably 0.04 or more and 0.09 or less. Further, the greater the change in the amount of adsorption of water, the greater the difference in the amount of adsorption, which is preferable, but it is usually 1.0 g / g or less.

  One feature of the nitrogen oxide purifying catalyst of the present invention is that the iron is supported on the zeolite at 1% by weight or more of the total weight of the zeolite. The supported amount of iron used in the present invention is usually 1% or more, preferably 1.5% or more, more preferably 2% or more by weight ratio to the zeolite, and the upper limit is not particularly limited. However, it is usually 10% or less, preferably 8% or less, and more preferably 5% or less. If it is less than the lower limit, the active sites tend to decrease, and sufficient catalytic performance is not exhibited. If the upper limit is exceeded, metal agglomeration tends to be remarkable, and the catalyst performance may be lowered.

The ratio of iron supported on the catalyst for purifying nitrogen oxides of the present invention can be determined by dissolving an iron-supported catalyst and conducting elemental analysis by ICP emission spectroscopic analysis, similarly to the elemental composition in zeolite.
The supported metal may be iron only, but may be used in combination with a metal other than iron. In that case, the metal is not particularly limited, but is preferably a group 13 metal of the periodic table such as aluminum, gallium, indium, cobalt, palladium, iridium, platinum, copper, silver, gold, cerium, lanthanum, praseodymium, titanium. , Selected from the group among zirconia and the like. Of these, a group 13 metal of the periodic table is preferable, and aluminum is more preferable.

In the present invention, the term “metal” is not necessarily limited to an element having a zero-valent state. Reference to “metal” includes the presence state supported in the catalyst, eg, the presence state as ionic or other species.
The catalyst for purifying nitrogen oxides according to the present invention comprises (II) a diffraction angle (2θ) in the range of 21.2 to 21.6 degrees when X-ray diffraction measurement is performed using CuKα as an X-ray source. The observed diffraction peak height is 0.01 or more, and (III) Cu is treated with water vapor at 800 ° C. for 5 hours and then Cu is added.
When X-ray diffraction measurement is performed using Kα as an X-ray source, the diffraction angle (2θ) is 21.21 with respect to the diffraction peak height observed in the diffraction angle (2θ) range of 20.6 to 21.0 degrees. One of the characteristics is that the ratio of the diffraction peak heights observed in the range of 2 to 21.6 degrees is 0.01 or more and 1.0 or less.

  The water vapor concentration of the steam treatment at 800 ° C. for 5 hours (hereinafter sometimes referred to as “high temperature steam treatment”) is preferably 5% by volume to 20% by volume which is the water vapor concentration in diesel engine exhaust gas. Most preferred is 10% by volume. The method of the high-temperature steam treatment is not particularly limited, and a general firing furnace can be used, but a method of steam treatment by circulating the gas is desirable. The gas flow rate is not particularly limited, but the gas flow rate per gram of powder is usually 0.1 ml / min or more, preferably 5 ml / min or more, usually 100 ml / min or less, preferably 20 ml / min or less. Distribution speed.

  The high-temperature steam treatment assumes the following situation. The nitrogen oxide purifying catalyst needs to have durability at a temperature equal to or higher than the temperature of exhaust gas emitted when PM is burned with DPF. At the time of PM combustion, the exhaust gas becomes 600 to 700 ° C. When the catalyst is applied onto the DPF and PM burns on the catalyst, the temperature may locally rise to 800 ° C. In addition, although the exhaust gas contains water vapor, zeolite is likely to decompose under high temperature conditions under water vapor, so it is important to have heat resistance under these conditions.

  When the nitrogen oxide purification catalyst of the present invention was subjected to XRD measurement using CuKα as the X-ray source, in addition to the peak derived from zeolite, the diffraction peak at a diffraction angle (2θ) of 21.2 to 21.6 degrees Is observed. The ratio of the diffraction peak height observed in the range of 21.2 to 21.6 degrees to the peak height of the diffraction peak observed in the range of 20.6 to 21.0 degrees derived from zeolite is 0. 01 or more, preferably 0.02 or more, more preferably 0.05, 1.0 or less, preferably 0.6 or less, more preferably 0.3 or less. Here, “diffraction peak height” refers to the height from the baseline where no diffraction peak exists to the peak top.

  The ratio of the diffraction peak heights represents the following state in the nitrogen oxide purifying catalyst of the present invention. When iron is supported in zeolite at 1% by weight or more of the total weight of the zeolite to disperse the iron, in addition to the iron being dispersed in the zeolite, some iron reacts with the zeolite. When iron partially reacts with zeolite, a diffraction peak appears at 21.2 to 21.6 degrees as the amount of the reacted material. On the other hand, since the peak height of the diffraction peak observed at 20.6 to 21.0 degrees represents the amount of zeolite, the diffraction observed at 20.6 to 21.0 degrees derived from the zeolite at the height of this peak. The ratio of the peak to the peak height being 0.01 or less means that the nitrogen oxide purification performance is insufficient because the iron dispersion is insufficient. In addition, when the ratio of the peak height is 1.0 or more, it means that the zeolite structure is largely destroyed, the adsorption power of the reducing agent such as ammonia in the zeolite is lowered, and the nitrogen oxide purification performance is lowered. To do.

Further, the nitrogen oxide purifying catalyst of the present invention is 5 at 800 ° C. when the X-ray diffraction measurement is performed.
The ratio of the diffraction peak height observed in the diffraction angle (2θ) range of 21.2 degrees or more and 21.6 degrees or less after the time steam treatment to the peak height before the steam treatment is 2 or less. preferable. When the peak height ratio exceeds the upper limit, the zeolite structure is greatly broken under high-temperature steam, and the diffraction peak observed in the diffraction angle (2θ) range of 21.2 to 21.6 degrees increases. The purification performance is greatly reduced. A diffraction peak having a diffraction angle (2θ) of 21.2 to 21.6 degrees is usually 1 or more because it does not decrease by treatment under high-temperature steam.

  The particle diameter of the catalyst for purifying nitrogen oxides of the present invention means an average value of primary particle diameters of arbitrary 10 to 30 zeolite particles when the catalyst is observed with an electron microscope, and is usually 1 μm or more. Preferably it is 2 micrometers or more, More preferably, it is 2.5 micrometers or more, Usually, 15 micrometers or less, Preferably it is 10 micrometers or less. When the particle size is small, the crystallinity is low and the durability under high-temperature steam is lowered. When the particle size is too large, it becomes difficult to support the metal, and when a catalyst is used, it is difficult to apply the catalyst to a substrate or the like. If necessary, dry pulverization such as a jet mill or wet pulverization such as a ball mill may be performed.

(2) Durability under high steam of the catalyst for purifying nitrogen oxides of the present invention The catalyst for purifying nitrogen oxides of the present invention has an effect of being excellent in durability under high steam. Specifically, in the water vapor repeated adsorption / desorption test measured at 90 ° C. described below, the adsorption maintenance rate is high, that is, the adsorption maintenance rate is 80% or more, preferably 90% or more, more preferably 95% or more. Yes, the upper limit is not particularly limited, but usually shows a maintenance rate of 100% or less.

The nitrogen oxide purification catalyst of the present invention has a water adsorption amount after a water vapor repeated adsorption / desorption test measured at 90 ° C. of 70% or more with respect to the water adsorption amount at a relative vapor pressure of 0.2. Preferably, it is 80% or more, more preferably 90% or more. The upper limit is not particularly limited, but is usually 100% or less, preferably 95% or less.
In the repeated water vapor adsorption / desorption test, the sample is held in a vacuum vessel maintained at T ° C. and subjected to a 90 ° C. saturated water vapor atmosphere and a T 2 ° C. saturated water vapor atmosphere for 90 seconds each (T1 <T <T2). . At this time, part of the water adsorbed on the sample when exposed to the saturated water vapor atmosphere at T2 ° C. is desorbed in the saturated water vapor atmosphere at T1 ° C. and moves to the water reservoir maintained at T1 ° C. From the m-th adsorption to the n-th desorption, the average amount of adsorption per one time based on the total amount of water (Qn; m (g)) transferred to the 5 ° C sump and the dry weight of the sample (W (g)) (Cn; m (g / g)) is determined as follows.

[Cn; m] = [Qn; m] / (n−m + 1) / W
Usually, absorption and desorption are repeated 1000 times or more, preferably 2000 times or more, and the upper limit is not particularly limited.
(The above process is referred to as “T-T2-T1 water vapor repeated adsorption / desorption test”.)
In the water vapor repeated adsorption / desorption test of the zeolite used in the present invention, the operation of holding the zeolite sample in a vacuum vessel maintained at 90 ° C. and exposing it to a 5 ° C. saturated water vapor atmosphere and an 80 ° C. saturated water vapor atmosphere for 90 seconds respectively. repeat. The average adsorption amount per time (Cn; m (g / g)) is determined from the above-obtained numerical values (90-80-5 water vapor repeated adsorption / desorption test).
(The above process may be referred to as “water vapor repeated adsorption / desorption test when measured at 90 ° C.”.)

  The maintenance rate of the desorption test is a ratio of the average adsorption amount from 1001 to 2000 times to the average adsorption amount from 1 to 1000 times in the water vapor repeated adsorption / desorption test. A high retention rate of the average adsorption amount indicates that the zeolite does not deteriorate even if the adsorption / desorption of water is repeated. The maintenance ratio is 80% or more, preferably 90% or more, more preferably 95% or more. The upper limit is 100% at which no deterioration occurs.

Changes in zeolite due to repeated adsorption and desorption of water vapor can be observed by changes in the water vapor adsorption isotherm of the zeolite before and after the test.
If there is no change in the structure of the zeolite due to repeated adsorption and desorption of water, there is no change in the water vapor adsorption isotherm, and a decrease in the amount of adsorption is observed when the structure of the zeolite is changed. Water vapor adsorption is usually 70% or more, preferably 80% when the relative vapor pressure at 25 ° C. after the test is 0.2 after the test is repeated 2000 times at 90 ° C. More preferably, it is 90% or more.

  Zeolite having the above structure is excellent in the purification of nitrogen oxides because of its high adsorption retention rate in the water vapor repeated adsorption / desorption test. When the catalyst of the present invention is mounted and used in an automobile or the like, it is considered that water adsorption / desorption is actually repeated and purification of nitrogen oxides is performed, so that it does not deteriorate during repeated adsorption / desorption of water. Is considered to have a structure excellent in exhaust gas purification ability and practically superior nitrogen oxide purification ability.

  As with the catalyst of the present invention, the zeolite used in the present invention preferably has a higher adsorption maintenance rate in the repeated vapor adsorption / desorption test measured at 90 ° C., and usually the adsorption maintenance rate is 80% or more, preferably Is 90% or more, more preferably 95% or more, and the upper limit is not particularly limited, but is usually 100% or less.

  Further, the zeolite used in the present invention has a water adsorption amount after a water vapor repeated adsorption / desorption test measured at 90 ° C. of 70% or more with respect to the water adsorption amount at a relative vapor pressure of 0.2. Preferably, it is 80% or more, more preferably 90% or more. The upper limit is not particularly limited, but is usually 100% or less, preferably 95% or less.

(3) Nitrogen oxide purifying catalyst production method of the present invention The nitrogen oxide purifying catalyst of the present invention is a mixing step of mixing the zeolite and the carbon-containing iron salt, and drying the mixture obtained in the mixing step. And a baking step of baking the dried material obtained in the drying step.

  The carbon-containing iron salt is not particularly limited as long as it contains carbon and iron in the structure, but preferably an organic acid salt of iron such as acetate, oxalate, or citrate. Specific examples include basic iron acetate, iron oxalate, ammonium iron oxalate, iron citrate, iron octylate, iron fumarate, iron lactate, iron maftenate, iron stearate, and iron tartrate. The iron raw material may be soluble or insoluble in the dispersion medium described later.

The carbon-containing iron salt is added so that the amount of iron supported on the catalyst finally becomes 1% by weight or more and 10% by weight or less of the total weight of the zeolite. Specifically, the molar ratio of iron to silicon in the zeolite skeleton is 0.1 or more and 2.0 or less, preferably 0.2 or more and 1.0 or less.
In general, when iron is supported on zeolite of aluminosilicate, it is easily available, so it is supported by ion exchange using an iron raw material such as iron nitrate or iron sulfate. However, when iron is supported on SAPOs, since SAPOs are weakly acidic, if strong acid strength nitrates, sulfates, etc. are used, the zeolite structure will be damaged during loading, and sufficient catalytic performance will not be achieved. . For this reason, it is important to use a carbon-containing iron raw material with low acid strength.

  In addition, when iron is supported in an amount of 1% by weight or more of the total weight of the zeolite using ordinary nitrates and sulfates, the iron is supported as aggregates, resulting in insufficient dispersion and insufficient purification performance. This is considered to be because iron is oxidized during heat treatment and does not disperse any more. On the other hand, when a carbon-containing iron salt is used as an iron raw material and heat treatment is performed, it is considered that the carbon-containing portion can be easily dispersed by reducing iron when the carbon-containing portion burns.

  As a method for producing the catalyst of the present invention, it is preferable to add a Group 13 metal of the periodic table such as aluminum, gallium and indium in addition to the carbon-containing iron salt. Aluminum and gallium are preferable, and aluminum is more preferable. The raw material of the Group 13 metal to be supported on the zeolite in the present invention is not particularly limited, but metal salts, metal complexes, simple metals, metal oxides and the like are used, and preferably inorganic such as nitrates, sulfates, and hydrochlorides. Organic acid salts such as acid salts or acetates are used. In the case of aluminum, specifically, aluminum nitrate, aluminum sulfate, polyaluminum chloride, ammonium aluminum sulfate, aluminum acetate, basic aluminum acetate, aluminum chloride, aluminum lactate, aluminum stearate, aluminum oleate, aluminum oxalate, lauric acid Examples thereof include aluminum and aluminum benzoate. The metal source may be soluble or insoluble in the dispersion medium described below.

  The Group 13 metal raw material is added so that the supported amount of the Group 13 metal catalyst in the finally produced catalyst is 1% by weight or more and 10% by weight or less of the total weight of the zeolite. Preferably they are 1.5 weight% or more and 8 weight% or less, More preferably, they are 2 weight% or more and 5 weight% or less. The specific mixing ratio is 0.3 or more and 4 or less, preferably 0.5 or more and 3.5 or less, more preferably 0.7 or more, in terms of the molar ratio of the group 13 metal added to silicon in the zeolite skeleton. It is as follows.

  When iron is supported, when a group 13 metal is simultaneously supported and heat-treated, when iron element reacts and diffuses with zeolite, iron forms a complex with group 13 element and promotes the dispersion of iron. It is thought that it has the effect of suppressing attacks on new zeolite. Therefore, in the heat treatment at the time of zeolite synthesis, while suppressing excessive reaction of zeolite and iron, even in the heat treatment under high temperature steam used in the durability test, nitrogen oxide purification with excellent durability without damaging the zeolite A catalyst can be produced.

The method for supporting the metal species on the zeolite when producing the catalyst of the present invention is not particularly limited, but generally used ion exchange method, impregnation support method, precipitation support method, solid phase ion exchange method, CVD method Etc. are used. The ion exchange method and the impregnation support method are preferable. It is difficult to disperse and support iron in zeolite, and impregnation support is preferable because only a very small amount may be supported by a normal ion exchange method.
When performing impregnation support, it is preferable to dry in a short time from the slurry state, and it is more preferable to dry using the spray drying method described below.

  First, a mixture of zeolite, metal source, and dispersion medium (hereinafter sometimes simply referred to as a mixture) is prepared. The dispersion medium in the present invention refers to a liquid for dispersing zeolite. The mixture used in the present invention is usually in the form of a slurry or cake, but is preferably in the form of a slurry in view of operational applicability. The type of the dispersion medium used in this production method is not particularly limited, but usually water, alcohol, ketone, etc. are used, and from the viewpoint of safety during heating, the dispersion medium should use water. Is desirable.

  The mixing order of the mixture in the mixing step of the production method is not particularly limited, but usually, a metal source is first dissolved or dispersed in a dispersion medium, and zeolite is mixed therewith. The ratio of the solid content in the slurry prepared by mixing the above components is 5% by mass to 60% by mass, preferably 10% by mass to 50% by mass. When the ratio of the solid content is less than the lower limit, the amount of the dispersion medium to be removed is large, which may hinder the dispersion medium removal step. Moreover, when the ratio of solid content exceeds the said upper limit, there exists a tendency for a metal to become difficult to disperse | distribute uniformly on a zeolite.

The preparation temperature of the mixture used in the present invention is usually 0 ° C. or higher, preferably 10 ° C. or higher, usually 80 ° C. or lower, preferably 60 ° C. or lower.
Zeolite usually generates heat when mixed with a dispersion medium, and if the blending temperature exceeds the upper limit, the zeolite itself may be decomposed by acid or alkali. The lower limit of the preparation temperature is the melting point of the dispersion medium.

  The pH of the mixture used in the present invention is not particularly limited, but is usually 3 or more, preferably 4 or more, more preferably 5 or more, usually 10 or less, preferably 9 or less, more preferably 8 or less. is there. If the pH is adjusted to be lower than the lower limit or higher than the upper limit, the zeolite may be destroyed.

  Various additives may be added to the mixture used in the present invention for adjusting the viscosity of the mixture or controlling the particle shape and particle size after removal of the dispersion medium. The type of the additive is not particularly limited, but an inorganic additive is preferable, and examples thereof include an inorganic sol and a clay-based additive. As the inorganic sol, silica sol, alumina sol, titania sol and the like are used, and silica sol is preferable. The average particle size of the inorganic sol is 4 to 60 nm, preferably 10 to 40 nm. Sepiolite, montmorillonite, kaolin and the like are used as the clay additive.

The addition amount of the additive is not particularly limited, but is 50% or less, preferably 20% or less, more preferably 10% or less by weight ratio to the zeolite. If the weight ratio exceeds the upper limit, the catalyst performance may be reduced.
As a method for mixing the mixture used in the present invention, any method that sufficiently mixes or disperses the zeolite and the metal source may be used, and various known methods can be used. Specifically, stirring, ultrasonic waves, homogenizer, etc. Is used.

  Next, the dispersion medium is removed from the mixture used in the present invention (drying step). The method for removing the dispersion medium is not particularly limited as long as it can remove the dispersion medium in a short time, but it is preferably a method that can be removed in a short time after being uniformly sprayed, and more preferably uniformly. It is a method of removing by contacting with a high-temperature heat medium through a sprayed state, and more preferably by uniformly removing by removing it by contacting with hot air as a high-temperature heat medium after spraying uniformly. It is a method that can obtain a fine powder, “spray drying”. When spray drying is applied, as a spraying method, centrifugal spraying using a rotating disk, pressurized spraying using a pressure nozzle, spraying using a two-fluid nozzle, four-fluid nozzle, or the like can be used.

  The dispersion medium is removed from the sprayed slurry by coming into contact with a heated metal plate or a heat medium such as a high-temperature gas. In either case, the temperature of the heat medium is not particularly limited, but is usually 80 ° C. or higher and 350 ° C. or lower. If the amount is less than the lower limit, the dispersion medium may not be sufficiently removed from the slurry, and if the upper limit is exceeded, the metal source may decompose and the metal oxide may aggregate.

In the case of using spray drying, the drying conditions are not particularly limited. Usually, the gas inlet temperature is about 200 to 300 ° C, and the gas outlet temperature is about 60 to 200 ° C.
The time required for removing the dispersion medium from the mixture in the present invention refers to the time until the amount of the dispersion medium in the mixture becomes 1% by mass or less, and the drying time when water is the dispersion medium is the temperature of the mixture. Refers to the time from when the temperature becomes 80 ° C. or higher until the amount of water contained in the mixture becomes 1% by mass or less in the obtained mixture. The drying time in the case of a dispersion medium other than water is 1% by mass of the dispersion medium contained in the mixture from the time when the temperature becomes 20 ° C. lower than the boiling point at normal pressure of the dispersion medium. Time until the following. The removal time of the dispersion medium is 60 minutes or less, preferably 10 minutes or less, more preferably 1 minute or less, still more preferably 10 seconds or less, and it is desirable to dry in a shorter time, so the lower limit is particularly limited. Although it is not a thing, it is 0.1 second or more normally.

  If the dispersion medium is removed from the mixture over a time exceeding the upper limit, the metal source is aggregated and supported unevenly on the surface of the zeolite on which the metal is supported, which causes a decrease in catalyst activity. In general, metal sources are acidic or alkaline, so if they are exposed to high-temperature conditions for a long time in the presence of a dispersion medium, the structure of the zeolite loaded with metal atoms is decomposed. Will be promoted. Therefore, it is considered that the catalyst activity decreases as the drying time becomes longer.

The average particle size of the dry powder obtained after removal of the dispersion medium is not particularly limited, but is usually 1 mm or less, preferably 200 μm or less, and usually 2 μm or more so that drying can be completed in a short time. It is preferable to remove the dispersion medium.
When a metal is supported by spray drying, there is an advantage that it is easy to increase the amount of metal supported. In particular, in the case of a metal that is difficult to disperse in zeolite by a technique such as an ion exchange method such as iron, it is difficult to increase the amount of metal supported only by the ion exchange method. When spray drying is used, the drying time is fast, so even if the metal loading is increased, the acid from the metal source does not damage the zeolite skeleton or the metal is agglomerated, resulting in higher crystallinity. Thus, a catalyst with good metal dispersion can be obtained.

  After removing the drying step, the obtained dry powder (dried product) is calcined to obtain the catalyst of the present invention. The firing atmosphere is not particularly limited, but a low oxygen atmosphere is preferable. In a low oxygen atmosphere, the oxygen concentration is preferably 10% by volume or less, more preferably 5% by volume or less. The lower limit is not particularly limited, and may be an inert atmosphere where the oxygen concentration is 0%. The inert atmosphere is not particularly limited as long as oxygen is not included, but nitrogen and argon are preferable. Water vapor may be contained in the atmosphere. If the oxygen concentration is too high, when the carbon-containing iron salt is burned, the iron is oxidized to a state where it is difficult to disperse, so that the iron is not sufficiently dispersed and the purification performance is lowered. When firing in a low oxygen atmosphere or in an inert atmosphere, the iron is more easily dispersed without further iron oxidation, and the iron dispersion progresses and exhibits good purification performance.

Since some carbon components may remain in the catalyst after firing in a low oxygen atmosphere or in an inert atmosphere, an additional heat treatment may be performed in air.
The temperature at which the calcination is carried out in the present invention is not particularly limited, but is usually 500 ° C. or higher, preferably 700 ° C. or higher, usually 1000 ° C. or lower, preferably 900 ° C. or lower, in order to increase metal dispersion and enhance the interaction with the zeolite surface. To implement. If it is less than the lower limit, the metal source may not be decomposed, and if it exceeds the upper limit, the structure of the zeolite may be destroyed.

There are no particular limitations on the firing method, and a muffle furnace, kiln, fluidized firing furnace, or the like can be used, but a method of firing by circulating the above gas is desirable. The flow rate of the gas is not particularly limited, but the flow rate of the gas per 1 g of the powder is usually 0.1 ml / min or more, preferably 5 ml.
/ Min or more, usually 100 ml / min or less, preferably 20 ml / min or less, and heat treatment under a gas flow to obtain a catalyst obtained by the present invention.

If the flow rate of gas per gram of powder is less than the lower limit value, the acid remaining in the dry powder may not be removed during heating and the zeolite may be destroyed, and the flow rate exceeds the upper limit value. Then, powder may be scattered.
The firing time is 1 second to 24 hours, preferably 10 seconds to 8 hours, and more preferably 30 minutes to 4 hours. The catalyst may be pulverized after calcination.

  The zeolite used in the present invention is a compound known per se, and can be produced according to a commonly used method. The method for producing zeolite in the present invention is not particularly limited. For example, Japanese Patent Publication No. 4-37007, Japanese Patent Publication No. 5-21844, Japanese Patent Publication No. 5-51533, US Pat. No. 4,440,871. It can manufacture according to the method as described in gazette, Japan Unexamined-Japanese-Patent No. 2003-183020, etc.

The zeolite used in the present invention is usually mixed with an aluminum atom raw material, a phosphorus atom raw material, a silicon atomic raw material (if other atomic Me is included, another atomic (Me) atomic raw material) and a template, and then hydrothermally. It is obtained by synthesizing and removing the template.
Hereinafter, specific examples of the method for producing zeolite will be described.

<Aluminum atomic material>
The aluminum atom raw material of the zeolite in the present invention is not particularly limited, and is usually pseudoboehmite, aluminum alkoxide such as aluminum isopropoxide, aluminum triethoxide, aluminum hydroxide, alumina sol, sodium aluminate, etc. preferable.

<Raw material>
The phosphorus atom raw material of the zeolite used in the present invention is usually phosphoric acid, but aluminum phosphate may be used.
<Raw material of silicon atoms>
The silicon atom raw material of zeolite in the present invention is not particularly limited, and is usually fumed silica, silica sol, colloidal silica, water glass, ethyl silicate, methyl silicate, etc., and fumed silica is preferable.
<Template>
As a template (structure directing agent) used in the production of the zeolite of the present invention, various templates used in a known method can be used, and are not particularly limited, but the following templates are preferably used. .

As the template used in the present invention, one or more compounds are selected and used from each of two groups: (1) an alicyclic heterocyclic compound containing nitrogen as a heteroatom, and (2) an alkylamine.
(1) Alicyclic heterocyclic compound containing nitrogen as a heteroatom The heterocyclic ring of an alicyclic heterocyclic compound containing nitrogen as a heteroatom is usually a 5- to 7-membered ring, and preferably a 6-membered ring. The number of heteroatoms contained in the heterocycle is usually 3 or less, preferably 2 or less. Heteroatoms other than nitrogen are optional, but those containing oxygen in addition to nitrogen are preferred. The positions of the heteroatoms are not particularly limited, but those where the heteroatoms are not adjacent to each other are preferable.
The molecular weight of the alicyclic heterocyclic compound containing nitrogen as a hetero atom is usually 250 or less, preferably 200 or less, more preferably 150 or less, and usually 30 or more, preferably 40 or more, and more preferably 50. That's it.

  Examples of the alicyclic heterocyclic compound containing nitrogen as a hetero atom include morpholine, N-methylmorpholine, piperidine, piperazine, N, N′-dimethylpiperazine, 1,4-diazabicyclo (2,2,2) octane, N-methylpiperidine, 3-methylpiperidine, quinuclidine, pyrrolidine, N-methylpyrrolidone, hexamethyleneimine and the like can be mentioned, morpholine, hexamethyleneimine and piperidine are preferable, and morpholine is particularly preferable.

(2) Alkylamine The alkyl group of the alkylamine is usually a chain alkyl group, and the number of alkyl groups contained in one amine molecule is not particularly limited, but three is preferable. Moreover, the alkyl group of the alkylamine of the present invention may partially have a substituent such as a hydroxyl group. The number of carbon atoms in the alkyl group of the alkylamine of the present invention is preferably 4 or less, and the total number of carbon atoms of all alkyl groups in one molecule is more preferably 10 or less. The molecular weight is usually 250 or less, preferably 200 or less, more preferably 150 or less.

  Examples of such alkylamines include di-n-propylamine, tri-n-propylamine, tri-isopropylamine, triethylamine, triethanolamine, N, N-diethylethanolamine, N, N-dimethylethanolamine, N- Examples include methyldiethanolamine, N-methylethanolamine, di-n-butylamine, neopentylamine, di-n-pentylamine, isopropylamine, t-butylamine, ethylenediamine, di-isopropyl-ethylamine, N-methyl-n-butylamine. Di-n-propylamine, tri-n-propylamine, tri-isopropylamine, triethylamine, di-n-butylamine, isopropylamine, t-butylamine, ethylenediamine, diisopropyl-ethyl Amine, N- methyl -n- butylamine are preferred, triethylamine being particularly preferred.

A preferred combination of the templates (1) to (2) is a combination containing morpholine and triethylamine. The mixing ratio of the templates needs to be selected according to conditions.
When mixing two templates, the molar ratio of the two templates to be mixed is usually 1:20 to 20: 1, preferably 1:10 to 10: 1, more preferably 1: 5 to 5: 1. It is.

When mixing three templates, the molar ratio of the third template is usually from 1:20 to 20: 2 with respect to the sum of the two templates (1) and (2) mixed above. 1, preferably 1:10 to 10: 1, more preferably 1: 5 to 5: 1.
The mixing ratio of the two or more templates is not particularly limited and can be appropriately selected according to the conditions. For example, when morpholine and triethylamine are used, the molar ratio of morpholine / triethylamine is usually 0.05. Above, preferably 0.1 or more, more preferably 0.2 or more, usually 20 or less, preferably 10 or less, more preferably 9 or less.

Other templates may be contained, but the other templates are usually 20% or less in molar ratio to the whole template, and preferably 10% or less.
When the template in the present invention is used, the Si content in the zeolite can be controlled, and the Si content and Si existing state preferable as a catalyst for purifying nitrogen oxides can be obtained. The reason is not clear, but the following can be inferred.

  For example, when synthesizing a SAPA having a CHA type structure, an alicyclic heterocyclic compound containing nitrogen as a hetero atom, such as morpholine, can synthesize a SAPO having a high Si content relatively easily. However, when trying to synthesize SAPO with a low Si content, there are many dense components and amorphous components, and crystallization is difficult. Further, alkylamines such as triethylamine can be synthesized under limited conditions, but SAPOs with various structures are usually mixed together. However, conversely, it is not a dense component or an amorphous component, and tends to have a crystalline structure. That is, each template has characteristics for deriving a CHA structure, characteristics for promoting SAPO crystallization, and the like. By combining these features, it seems that a synergistic effect was exhibited, and an effect that could not be realized by itself was exhibited.

<Synthesis of zeolite by hydrothermal synthesis>
The above silicon atom raw material, aluminum atom raw material, phosphorus atom raw material, template and water are mixed to prepare an aqueous gel. The order of mixing is not limited and may be appropriately selected depending on the conditions to be used. Usually, however, a phosphorus atom raw material and an aluminum atomic raw material are first mixed with water, and then a silicon atom raw material and a template are mixed therewith.

The composition of the aqueous gel is such that when the silicon atom raw material, the aluminum atom raw material and the phosphorus atom raw material are represented by the molar ratio of the oxide, the value of SiO 2 / Al 2 O 3 is usually greater than 0, preferably 0
. 02 or more, and usually 0.7 or less, preferably 0.6 or less, more preferably 0.4 or less. Further, the ratio of P2O5 / Al2O3 on the same basis is usually 0.6 or more, preferably 0.7 or more, more preferably 0.8 or more, usually 1.3 or less, preferably 1.2 or less, more preferably Is 1.1 or less.

  The composition of the zeolite obtained by hydrothermal synthesis has a correlation with the composition of the aqueous gel, and the composition of the aqueous gel may be appropriately set in order to obtain a zeolite having a desired composition. The total amount of the template is usually 0.2 or more, preferably 0.5 or more, more preferably 1 or more in terms of the molar ratio of the template with respect to Al2O3 when the aluminum atom raw material in the aqueous gel is represented by an oxide. 4 or less, preferably 3 or less, more preferably 2.5 or less.

The order of mixing one or more templates selected from each of the two or more groups is not particularly limited, and after preparing the template, it may be mixed with other substances, and each template may be mixed with other substances. May be mixed with.
The proportion of water is usually 3 or more, preferably 5 or more, more preferably 10 or more, and usually 200 or less, preferably 150 or less, more preferably 120 or less, in molar ratio with respect to the aluminum atom raw material. .

The pH of the aqueous gel is usually 5 or more, preferably 6 or more, more preferably 6.5 or more, and is usually 10 or less, preferably 9 or less, more preferably 8.5 or less.
In addition, the aqueous gel may contain components other than the above as desired. Examples of such components include hydrophilic organic solvents such as hydroxides and salts of alkali metals and alkaline earth metals, and alcohols. The amount of hydroxide or salt of alkali metal or alkaline earth metal is usually 0.2 or less, preferably 0.1 or less, in terms of molar ratio with respect to the aluminum atom raw material. A solvent is 0.5 or less normally by molar ratio with respect to water, Preferably it is 0.3 or less.

  The obtained aqueous gel is put into a pressure vessel, and hydrothermal synthesis is performed by maintaining a predetermined temperature under stirring or standing under self-generated pressure or gas pressurization that does not inhibit crystallization. The reaction temperature of hydrothermal synthesis is usually 100 ° C. or higher, preferably 120 ° C. or higher, more preferably 150 ° C. or higher, and is usually 300 ° C. or lower, preferably 250 ° C. or lower, more preferably 220 ° C. or lower. In this temperature range, in the process of raising the temperature to the highest temperature which is the highest temperature, it is preferably placed in a temperature range from 80 ° C. to 120 ° C. for 1 hour or more, and more preferably for 2 hours or more. If the temperature rising time in this temperature range is less than 1 hour, the durability of the zeolite obtained by calcining the obtained template-containing zeolite may be insufficient. Further, it is preferable in terms of durability that the temperature is in the temperature range from 80 ° C. to 120 ° C. for 1 hour or longer. More preferably, it is 2 hours or more.

On the other hand, the upper limit of the time is not particularly limited, but if it is too long, it may be inconvenient in terms of production efficiency, and is usually 50 hours or less, and preferably 24 hours or less in terms of production efficiency.
The temperature raising method between the temperature regions is not particularly limited. For example, various methods such as a method of increasing monotonously, a method of changing in a stepped manner, a method of changing up and down such as vibration, and a method of combining these methods. Can be used. Usually, from the viewpoint of ease of control, a method of monotonically increasing the temperature while maintaining the temperature increase rate below a certain value is preferably used.

Further, in the present invention, it is preferable to hold for a predetermined time in the vicinity of the highest temperature, and the vicinity of the highest temperature means a temperature 5 ° C. lower than the temperature or the highest temperature, and the time for holding at the highest temperature is: It affects the ease of synthesis of the desired product, and is usually 0.5 hours or more, preferably 3 hours or more, more preferably 5 hours or more, usually 30 days or less, preferably 10 days or less, more preferably 4 days. It is as follows.

  The method of changing the temperature after reaching the maximum temperature is not particularly limited, and there are various methods such as a method of changing in steps, a method of changing up and down such as vibration below the maximum temperature, and a combination of these. This method can be used. Usually, from the viewpoint of ease of control and durability of the obtained zeolite, it is preferable to lower the temperature from 100 ° C. to room temperature after maintaining the maximum temperature.

<Zeolite containing template>
After hydrothermal synthesis, the product-containing template-containing zeolite is separated from the hydrothermal synthesis reaction solution, but the template-containing zeolite separation method is not particularly limited. Usually, the product can be obtained by separation by filtration or decantation, washing with water, and drying at room temperature to 150 ° C. or lower.

  Next, the template is usually removed from the zeolite containing the template, but the method is not particularly limited. Usually contained in air or oxygen-containing inert gas, or by baking in an atmosphere of inert gas at a temperature of 400 ° C. to 700 ° C. or by extraction with an extraction solvent such as an ethanol aqueous solution or HCl-containing ether. Organic matter can be removed. Preferably, removal by firing is preferable in terms of productivity.

  In the production of the catalyst of the present invention described above, the metal may be supported on the zeolite from which the template is removed, or the template may be removed after the metal is supported on the zeolite containing the template. It is preferable to remove the template after supporting the metal because it is advantageous in terms of manufacturing.

  When a metal is supported on zeolite, a generally used ion exchange method uses zeolite from which the template has been removed by baking. This is because an ion exchange zeolite is produced by ion exchange of metal into the pores from which the template has been removed, and the zeolite containing the template cannot be ion exchanged, and thus is not suitable for the production of a catalyst. In the production method of the present invention, the catalyst is produced by using the zeolite containing the template without removing the ion exchange method, removing the dispersion medium from the mixed dispersion with the metal, and performing the following calcination simultaneously with the template removal. This is advantageous in terms of manufacturing.

In addition, a reducing atmosphere is created when the template is combusted during firing, and this reduces iron and makes it easier to disperse the iron, thus improving purification performance.
When carrying the metal after removing the template, usually a method of firing at a temperature of usually 400 ° C. or more and 700 ° C. or less in an atmosphere of air or oxygen-containing inert gas or inert gas, an aqueous ethanol solution, The contained template can be removed by various methods such as extraction with an extracting agent such as HCl-containing ether.

The catalyst for removing nitrogen oxides of the present invention is usually obtained by supporting a metal having catalytic activity on zeolite.
The above-described method for producing a catalyst for purifying nitrogen oxides of the present invention is generally effective in realizing a high supported amount of 1 to 10% by weight with respect to the total amount of zeolite.
(4) Method of using the catalyst for purifying nitrogen oxides of the present invention The catalyst for purifying nitrogen oxides of the present invention can be used as it is in a powder form, or mixed with a binder such as silica, alumina, clay mineral, etc. It can also be used after molding. Further, when used as an exhaust gas catalyst for automobiles or the like, it can be formed by using a coating method or a forming method, and preferably formed into a honeycomb shape.

  When obtaining a molded article of a nitrogen oxide purification catalyst of the present invention (hereinafter sometimes simply referred to as an element) by a coating method, a zeolite catalyst is usually mixed with an inorganic binder such as silica or alumina to prepare a slurry. The honeycomb-shaped catalyst is obtained by applying to a surface of a molded body made of an inorganic material such as cordierite and firing, and preferably applying to the honeycomb-shaped molded body at this time.

When the molded product of the catalyst catalyst for nitrogen oxide purification of the present invention is obtained by a molding method, usually zeolite is kneaded with inorganic binders such as silica and alumina, inorganic fibers such as alumina fibers and glass fibers, an extrusion method, a compression method, etc. The honeycomb-shaped element is obtained by forming into a honeycomb shape, and preferably by forming into a honeycomb shape at this time.
The catalyst for purifying nitrogen oxides of the present invention purifies nitrogen oxides by contacting exhaust gas containing nitrogen oxides. 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, in the method of the present invention, diesel vehicles, gasoline vehicles, stationary power generation / ships / agricultural machinery / construction machinery / motorcycles / various diesel engines for aircraft, boilers, gas turbines, etc. Nitrogen oxide contained can be purified.

  The contact condition between the catalyst and the exhaust gas when using the catalyst for purifying nitrogen oxides of the present invention is not particularly limited, but the space velocity is usually 100 / h or more, preferably 1000 / h or more, The temperature is usually 500,000 / h or less, preferably 100,000 / h or less, and the temperature is usually 100 ° C. or higher, preferably 150 ° C. or higher, usually 700 ° C. or lower, preferably 500 ° C. or lower.

  Using the catalyst for purifying nitrogen oxides of the present invention, a catalyst that oxidizes excess reducing agent that has not been consumed in the purification of nitrogen oxides is mounted in the subsequent stage of purifying the nitrogen oxides, and in the exhaust gas The reducing agent can be reduced. In that case, a catalyst in which a metal such as a platinum group is supported on a support such as a zeolite for adsorbing a reducing agent as an oxidation catalyst can be used, and the zeolite of the present invention and the catalyst are used as the zeolite and the oxidation catalyst. be able to.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples.
(Steam treatment)
The catalyst was hydrothermally treated at 800 ° C. and 10% by volume of water vapor for 5 hours in an atmosphere having a space velocity of SV = 3000 / h.
(Measurement method of XRD)
X-ray source: Cu-Kα ray output setting: 40 kV, 30 mA
Optical conditions during measurement:
Divergent slit = 1 °
Scattering slit = 1 °
Receiving slit = 0.2mm
Diffraction peak position: 2θ (diffraction angle)
Measurement range: 2θ = 3 to 50 degrees Scan speed: 3.0 ° (2θ / sec), continuous scan Sample preparation: About 100 mg of a sample pulverized manually using an agate mortar using a sample holder of the same shape The sample amount was made constant.

The peak height is the peak height from the baseline where no diffraction peak exists.
The peak height of the diffraction peak observed in the range of 21.2 degrees or more and 21.6 degrees or less with respect to the diffraction peak height of the diffraction angle (2θ) in the range of 20.6 degrees or more and 21.0 degrees or less. The ratio was calculated. Further, the ratio of the diffraction peak height observed in the range of diffraction angle (2θ) of 21.2 degrees or more and 21.6 degrees or less after steam treatment at 800 ° C. for 5 hours to the peak height before steam treatment is Asked.
(Composition analysis and measuring method of iron loading)
The sample was alkali-melted and then dissolved in acid, and the resulting solution was analyzed by inductively coupled plasma emission spectrometry (ICP-AES method).

<Water vapor repeated adsorption / desorption test ("90-80-5 repeated durability test")>
In the water vapor repeated adsorption / desorption test, an operation of holding a sample in a vacuum vessel maintained at 90 ° C. and exposing each sample to a 5 ° C. saturated water vapor atmosphere and an 80 ° C. saturated water vapor atmosphere for 90 seconds is repeated. At this time, part of the water adsorbed on the sample when exposed to a saturated water vapor atmosphere at 80 ° C. is desorbed in a saturated water vapor atmosphere at 5 ° C. and moves to a water reservoir maintained at 5 ° C. From the m-th adsorption to the n-th desorption, the average amount of adsorption per one time based on the total amount of water (Qn; m (g)) transferred to the 5 ° C sump and the dry weight of the sample (W (g)) (Cn; m (g / g)) is determined as follows.

[Cn; m] = [Qn; m] / (n−m + 1) / W
Usually, absorption and desorption are repeated 1000 times or more, preferably 2000 times or more, and the upper limit is not particularly limited.
(The above process is referred to as “repeated adsorption / desorption test of water vapor at 90 ° C.”)
(Water vapor adsorption isotherm)
The sample was evacuated at 120 ° C. for 5 hours, and then a water vapor adsorption isotherm at 25 ° C. was measured with a water vapor adsorption measuring device (Belsorb 18: manufactured by Nippon Bell Co., Ltd.) under the following conditions.

Air temperature chamber temperature: 50 ° C
Adsorption temperature: 25 ° C
Initial introduction pressure: 3.0 torr
Introduced pressure setting points: 0
Saturated vapor pressure: 23.755 torr
Equilibrium time: 500 seconds

(Method for evaluating catalytic activity after endurance test)
The catalyst activity of the prepared catalyst was evaluated based on the following method.
The prepared catalyst was press-molded, crushed, passed through a sieve, and sized to 0.6 to 1 mm. The rectified catalyst was subjected to an endurance test under the conditions of the above-described 800 ° C. steam treatment.
After completion of the durability test, 1 ml of each catalyst was filled into a normal pressure fixed bed flow type reaction tube. The catalyst layer was heated while flowing the gas having the composition shown in Table 1 through the catalyst layer at a space velocity SV = 100000 / h. When the outlet NO concentration becomes constant at 250 ° C,
(NO purification rate) = {(Inlet NO concentration) − (Outlet NO concentration)} / (Inlet NO concentration)
The value of the catalyst was used to evaluate the nitrogen oxide removal activity of the catalyst.

Example 1
To 253 g of water, 101 g of 85% phosphoric acid and 68 g of pseudo boehmite (containing 25% water, manufactured by Sasol) were slowly added and stirred. This was designated as liquid A. Separately from Liquid A, a liquid was prepared by mixing 7.5 g of fumed silica (Aerosil 200: manufactured by Nippon Aerosil Co., Ltd.), 43.5 g of morpholine, 55.7 g of triethylamine, and 253 g of water. This was slowly added to the liquid A and stirred for 3 hours to obtain an aqueous gel. The aqueous gel is charged into a 1 L stainless steel autoclave containing a fluororesin inner cylinder, and is heated linearly from 30 ° C. to 190 ° C. at a heating rate of 16 ° C./hour while being stirred. For 50 hours. In the process of raising the temperature to the highest temperature, the time in the range of 80 ° C. to 120 ° C. was 2.5 hours. After the reaction, the reaction mixture was cooled and the supernatant was removed by decantation to collect a precipitate. The precipitate was washed with water three times, filtered off and dried at 120 ° C. The obtained zeolite was pulverized to a median diameter of 3 μm by a jet mill to obtain a zeolite containing a template.
The zeolite containing the template was calcined at 560 ° C. in an air stream to remove the template.

The XRD of the zeolite thus obtained was measured based on the above-described measurement method, and was found to have a CHA structure (framework density = 14.6T / 1,000Ｔ ³ ). In addition, when elemental analysis was performed by ICP analysis after heating and dissolving in an aqueous hydrochloric acid solution, the composition ratio (molar ratio) of each component to the total of silicon, aluminum, and phosphorus in the skeleton structure was 0.088 for silicon and 0 for aluminum. .500 and phosphorus was 0.412.

When the water vapor adsorption isotherm of this zeolite at 25 ° C. was measured, the amount of adsorption change at a relative vapor pressure of 0.04 to 0.09 was 0.17 g / g.
Further, when the water vapor adsorption isotherm at 25 ° C. was measured, the water adsorption amount when the relative vapor pressure was 0.2 was 0.28 g / g.

  When this zeolite was subjected to repeated water vapor repeated adsorption / desorption tests (90-80-5 water vapor repeated adsorption / desorption test) at 90 ° C., the retention rate was 100%. Further, when the water vapor adsorption isotherm at 25 ° C. of the sample after 2000 times was measured, the water adsorption amount when the relative vapor pressure was 0.2 was 0.27 g / g, which was 96% before the repeated adsorption / desorption test. It became.

  Next, 40 g of pure water was added to and dissolved in 4.6 g of ammonium iron oxalate trihydrate (manufactured by Kishida Chemical Co., Ltd.), 20 g of the zeolite was added, and the mixture was further stirred to obtain a water slurry. This water slurry was sprayed onto a 170 ° C. metal plate and dried to obtain a catalyst precursor. The time required for drying was 10 seconds or less. The catalyst precursor was calcined at 700 ° C. for 4 hours in a nitrogen flow of 12 ml / min per gram of catalyst to obtain Catalyst 1. The amount of iron supported was determined by ICP analysis and found to be 2.8% by weight. The molar ratio of iron to silicon in the zeolite skeleton was 0.52.

  About the catalyst 1, the steam process of 800 degreeC was performed, the XRD measurement was performed, and ratio with respect to each peak height was calculated | required by said method. An XRD chart before and after the steam treatment is shown in FIGS. Further, the NO purification rate was evaluated based on the above-mentioned catalyst evaluation conditions. The evaluation results are shown in Table 2.

(Example 2)
A template-containing zeolite was synthesized by the same method as in Example 1. The template-containing zeolite contained a total of 20% by weight of the template.
Next, 40 g of pure water was added to 4.6 g of ammonium iron oxalate trihydrate (manufactured by Kishida Chemical Co., Ltd.), dissolved, 25 g of the above-mentioned template-containing silicoaluminophosphate zeolite was added, and the mixture was further stirred, It was. This water slurry was sprayed onto a 170 ° C. metal plate and dried to obtain a catalyst precursor. The catalyst precursor is calcined at 700 ° C. for 4 hours in a mixed gas flow of oxygen and nitrogen containing 6.7 ml / min of 5% oxygen per gram of the catalyst, and the catalyst is removed while the catalyst is calcined to obtain the catalyst 2 It was. The evaluation results are shown in Table 2.

(Example 3)
To 4.6 g of ammonium iron oxalate trihydrate (manufactured by Kishida Chemical Co., Ltd.) 40 g of pure water was added and dissolved, and then 8.3 g of aluminum nitrate nonahydrate (manufactured by Kishida Chemical Co., Ltd.) was added. A mixed solution of iron salt and aluminum salt was obtained. 25 g of the template-containing zeolite described in Example 2 was added to the above mixed solution of iron salt and aluminum salt (hereinafter referred to as “iron aluminum salt mixed solution”) and further stirred to obtain a water slurry. This water slurry was spray-dried and calcined in the same manner as in Example 2 to obtain Catalyst 3. The evaluation results are shown in Table 2.

(Example 4)
To 7.7 g of ammonium iron oxalate trihydrate (manufactured by Kishida Chemical Co., Ltd.) 40 g of pure water was added and dissolved, and then 8.3 g of aluminum nitrate nonahydrate (manufactured by Kishida Chemical Co., Ltd.) was added. An iron aluminum salt mixture is obtained. 25 g of the template-containing zeolite described in Example 2 was added with a mixed solution of iron aluminum salt and further stirred to obtain a water slurry. This water slurry was spray-dried and calcined in the same manner as in Example 2 to obtain catalyst 4. The evaluation results are shown in Table 2.

(Example 5)
40 g of pure water was added to 7.7 g of ammonium iron oxalate trihydrate (manufactured by Kishida Chemical Co., Ltd.) and dissolved, and then 10.7 g of polyaluminum chloride (Al2O3: 10.5%, manufactured by Daimei Chemical Co., Ltd.) Addition to obtain a mixed solution of iron aluminum salt. A mixed solution of iron aluminum salt was added to 25 g of the zeolite described in Example 2, and the mixture was further stirred to obtain a water slurry. This water slurry was spray-dried and calcined in the same manner as in Example 2 to obtain catalyst 5. The evaluation results are shown in Table 2.

(Example 6)
2.0 g of basic iron acetate (manufactured by Kishida Chemical Co., Ltd.) and 20 g of the zeolite described in Example 1 were added to 40 g of pure water and further stirred to obtain a water slurry. This water slurry was spray-dried and calcined in the same manner as in Example 1 to obtain catalyst 6. The evaluation results are shown in Table 2.
(Example 7)
3.5 g of iron citrate (manufactured by Showa Kako Co., Ltd., Fe content: 17.2 wt%) and 25 g of the zeolite described in Example 2 were added to 40 g of pure water and further stirred to obtain a water slurry.
This water slurry was spray-dried and calcined in the same manner as in Example 2 to obtain catalyst 7. The evaluation results are shown in Table 2.

(Comparative Example 1)
BEA type aluminosilicate zeolite was synthesized by the synthesis method described in Microporous and Mesoporous Materials 116 (1-3), 2008, 188-195. The silica / alumina ratio was 40.
An aqueous solution of 25.7% by mass of iron nitrate nonahydrate (manufactured by Kishida Chemical Co., Ltd.) was added to the above BEA zeolite for impregnation. Thereafter, the dried powder was calcined in the same manner as in Example 1 to obtain catalyst 8. The evaluation results are shown in Table 2.

(Comparative Example 2)
To 4.3 g of iron nitrate nonahydrate (manufactured by Kishida Chemical Co., Ltd.), 40 g of pure water was added and dissolved, and 20 g of the zeolite of Example 1 was added and further stirred to obtain a water slurry. The catalyst 9 was obtained by spray drying and calcining in the same manner as in Example 1. The evaluation results are shown in Table 2.

(Comparative Example 3)
40 g of pure water was added and dissolved in 7.2 g of iron sulfate heptahydrate (manufactured by Kishida Chemical Co., Ltd.), 15 g of the zeolite of Example 1 was added and further stirred to obtain a water slurry. The catalyst 10 was obtained by spray drying and calcining in the same manner as in Example 1. For the catalyst 10, the NO purification rate was evaluated under the same conditions as in Example 1. The results are shown in Table 2.

(Comparative Example 4)
Based on the method described in example 2 of US Pat. No. 7,645,718, SAPO was synthesized using TEAOH as a template and calcination to remove the template. When this zeolite was subjected to repeated water vapor repeated adsorption / desorption tests (90-80-5 water vapor repeated adsorption / desorption test) at 90 ° C., the retention rate was 63%.

  Ion exchange was performed by adding 6 g of SAPO to a solution obtained by adding 40 g of pure water to 4.3 g of iron nitrate nonahydrate (manufactured by Kishida Chemical Co., Ltd.). Thereafter, the catalyst 11 was obtained by firing in the same manner as in Example 1. The iron loading was 0.1% by weight. The evaluation results are shown in Table 2.

(Comparative Example 5)
To 18.4 g of ammonium iron oxalate trihydrate (manufactured by Kishida Chemical Co., Ltd.) 40 g of pure water was added and dissolved, and 25 g of the zeolite of Example 2 was added and further stirred to obtain a water slurry. This water slurry was spray-dried and calcined in the same manner as in Example 2 to obtain catalyst 13. The evaluation results are shown in Table 2.

If the nitrogen oxide purification catalyst of the present invention is used, the nitrogen oxide contained in the exhaust gas discharged from a diesel engine or the like can be efficiently purified, and the amount of catalyst is reduced because it does not deteriorate even in high temperature exhaust gas. can do.
Moreover, the manufacturing method of the catalyst for nitrogen oxide purification of this invention can provide a highly active catalyst for nitrogen oxide purification by a simple method.

Claims (8)

A catalyst for purifying nitrogen oxides in which iron is supported on a zeolite containing at least an aluminum atom, a phosphorus atom and a silicon atom in a skeleton structure,
(1) The amount of iron supported is 1% by weight or more of the total weight of the zeolite,
(2) When the catalyst is measured by X-ray diffraction using CuKα as an X-ray source, the diffraction peak height observed at a diffraction angle (2θ) in the range of 21.2 to 21.6 degrees is 0.01. That's it,
(3) When the catalyst was steamed at 800 ° C. for 5 hours and then subjected to X-ray diffraction measurement using CuKα as an X-ray source, the diffraction angle (2θ) was observed in the range of 20.6 to 21.0 degrees. that for the diffraction peak height state, and are the ratio of the diffraction peak height is 0.01 to 1.0 the diffraction angle (2 [Theta]) is observed in the range of 21.2 to 21.6 degrees,
And,
(4) The structure of the zeolite containing at least an aluminum atom, a phosphorus atom and a silicon atom in the skeleton structure is CHA in a code represented by IZA.
Nitrogen oxide purification catalyst. A catalyst for purifying nitrogen oxides in which iron is supported on a zeolite containing at least an aluminum atom, a phosphorus atom and a silicon atom in a skeleton structure,
(1) The amount of iron supported is 1% by weight or more of the total weight of the zeolite,
(2) When the catalyst is measured by X-ray diffraction using CuKα as an X-ray source, the diffraction peak height observed at a diffraction angle (2θ) in the range of 21.2 to 21.6 degrees is 0.01. That's it,
(3) When the catalyst was steamed at 800 ° C. for 5 hours and then subjected to X-ray diffraction measurement using CuKα as an X-ray source, the diffraction angle (2θ) was observed in the range of 20.6 to 21.0 degrees. The ratio of the diffraction peak height observed in the range of the diffraction angle (2θ) from 21.2 to 21.6 degrees with respect to the diffraction peak height of 0.01 to 1.0,
(4) The structure of the zeolite containing at least an aluminum atom, a phosphorus atom and a silicon atom in the skeleton structure is CHA in a code represented by IZA,
And,
( 5 ) When the X-ray diffraction measurement using CuKα as an X-ray source was performed before and after steaming the catalyst at 800 ° C. for 5 hours, the diffraction angle (2θ) was in the range of 21.2 to 21.6 degrees. The ratio of the diffraction peak height observed in the measurement after the water vapor treatment to the diffraction peak height observed in the measurement before the water vapor treatment is 2 or less.
Nitrogen oxide purification catalyst. A mixing step of mixing a zeolite containing at least an aluminum atom, a phosphorus atom, and a silicon atom in the skeleton structure with a carbon-containing iron salt, a drying step of drying the mixture obtained in the mixing step, and a dried product obtained in the drying step claim 1 or 2 method for producing a nitrogen oxide purifying catalyst according to, characterized in that it comprises a firing step of firing. The method for producing a nitrogen oxide purifying catalyst according to claim 3 , wherein the carbon-containing iron salt is an iron organic acid salt. Substances to be mixed in the mixing step, the zeolite containing at least aluminum atom and a phosphorus atom and a silicon atom in the backbone structure, and carbon-Mototetsu salt, according to claim 3 or, characterized in that further a Group 13 metal of the Periodic Table 5. A method for producing a nitrogen oxide purification catalyst according to 4 . The method for producing a nitrogen oxide purifying catalyst according to any one of claims 3 to 5 , wherein the Group 13 metal in the periodic table is aluminum. The method for producing a nitrogen oxide purifying catalyst according to any one of claims 3 to 6 , wherein the calcination step is performed at 500 ° C or higher in a low oxygen atmosphere containing 10% by volume or less of oxygen. A zeolite containing at least an aluminum atom, a phosphorus atom and a silicon atom in the skeletal structure is produced by hydrothermal synthesis after mixing a silicon atom raw material, an aluminum atom raw material, a phosphorus atom raw material and a template, and as the template alicyclic heterocyclic compounds containing nitrogen as a hetero atom, and two groups of alkylamine to any one of claims 3 to 7, characterized by using a template that selects one or more compounds per group The manufacturing method of the nitrogen oxide purification catalyst of description.

Images