JP4586293B2 - NOx occlusion agent, NOx occlusion reduction type catalyst and method for producing the same - Google Patents

Description

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次に、実施例１〜３で得られたＮＯｘ吸蔵還元型触媒における粒子（ＢａＺｒＯ₃、ＺｒＯ₂及びＢａＣＯ₃）の平均粒径を透過型電子顕微鏡観察により求めた。また、実施例１〜３で得られたＮＯｘ吸蔵還元型触媒について、エネルギー分散型Ｘ線分析装置（ＥＤＸ）を用いて、５ｎｍのスポットで元素分析を行った。かかる分析において５ｎｍのスポットでジルコニウム及びバリウムが観察されるかどうかを測定した。これらの結果をまとめて表４に示す。
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【表４】

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【発明の効果】
以上説明したように、本発明によれば、自動車の排気ガス等に含まれるＮＯｘの吸蔵性能の優れたＮＯｘ吸蔵剤、ＮＯｘ吸蔵還元性能が充分に高く、硫黄被毒を受けた場合であっても高いＮＯｘ吸蔵性能を発揮するＮＯｘ吸蔵還元型触媒、及びかかるＮＯｘ吸蔵剤及びＮＯｘ吸蔵還元型触媒の製造方法が提供される。
【図面の簡単な説明】
【図１】実施例１〜３及び比較例１〜２で得られたＮＯｘ吸蔵還元型触媒のＲＳＮＯｘ吸着量を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a NOx storage agent, a NOx storage reduction catalyst, and a production method thereof. More specifically, the present invention relates to NOx storage agent excellent in storage performance of NOx contained in exhaust gas of automobiles, etc., and NOx efficiently. The present invention relates to a NOx occlusion reduction type catalyst capable of achieving the above and a production method thereof.
[0002]
[Prior art]
The exhaust gas of automobiles and the like contains harmful nitrogen oxides (NOx), and in order to purify this, a material capable of storing and / or reducing NOx is used as a catalyst (NOx storage reduction catalyst). This has been done conventionally. A barium compound is known as a material capable of occluding NOx, and a material in which a barium compound is supported alone or together with a noble metal catalyst is used as a catalyst.
[0003]
By the way, in the exhaust gas of automobiles, in addition to the above NOx, sulfur oxide (SO) generated by combustion of sulfur (S) present in the fuel.₂) Is also included and this SO₂Is oxidized in the exhaust gas and becomes sulfuric acid by reacting with water vapor, etc., so that it reacts with the barium compound in the catalyst to produce barium sulfite and barium sulfate, so the NOx storage and / or reduction action of the barium compound May be inhibited (deterioration of sulfur poisoning).
[0004]
In order to reduce this sulfur poisoning deterioration, various attempts have been made to devise the composition of the catalyst. For example, Japanese Patent Laid-Open No. 7-136514 proposes that a barium compound is mixed with titania powder and heated to form a solid solution, which is supported on a support together with a noble metal catalyst, and used as a NOx occlusion reduction type catalyst. Has been.
[0005]
Further, International Publication No. 99/33560 discloses a carrier containing rutile-type titania, a NOx occlusion agent supported on the carrier made of at least one selected from alkali metals, alkaline earth metals and rare earth elements, An exhaust gas purification catalyst comprising a noble metal supported on a carrier is disclosed.
[0006]
[Problems to be solved by the invention]
However, since the storage agent and catalyst disclosed in the above publication are obtained by solid solution of titania powder and NOx storage agent such as barium compound, the formed complex oxide is formed on the surface of the titania powder. It was only a part and it was difficult to obtain a fine composite oxide. For this reason, there existed a problem that NOx occlusion performance and NOx occlusion reduction performance could not be made high. Further, in such a storage agent and catalyst, the sulfur compound formed when subjected to sulfur poisoning is coarse, so it is difficult to recover to the state before poisoning and high sulfur poisoning durability cannot be obtained. There was also a problem.
[0007]
The present invention has been made in view of the problems of the prior art, and an object of the present invention is to provide a NOx occlusion agent having excellent NOx occlusion performance contained in automobile exhaust gas or the like. It is another object of the present invention to provide a NOx occlusion reduction type catalyst that has sufficiently high NOx occlusion reduction performance and exhibits high NOx occlusion performance even when it is subjected to sulfur poisoning. Furthermore, it aims at providing the manufacturing method of this NOx occlusion agent and NOx occlusion reduction type catalyst.
[0008]
[Means for Solving the Problems]
As a result of intensive studies to achieve the above object, the present inventors have found that a NOx occlusion agent containing a complex oxide containing zirconium and a specific metal compound has excellent NOx occlusion performance, and the NOx occlusion agent. It has been found that a NOx occlusion reduction catalyst in which a noble metal is added exhibits high NOx occlusion reduction performance and is also excellent in sulfur poisoning durability.
[0009]
In addition, a method of obtaining a coprecipitate from a solution containing a zirconium compound and a specific metal oxide and baking the coprecipitate, preparing a solution containing an alkoxide containing zirconium and a specific alkoxide, and then hydrolyzing it. A method for firing, an organic salt mixture was obtained from a solution containing a zirconium organic salt and a specific metal organic salt, and a method for firing this resulted in a NOx storage agent having the above characteristics, and these methods were carried out. Later, it was found that a NOx occlusion reduction type catalyst having the above characteristics can be obtained by further supporting a noble metal, and the present invention has been completed.
[0010]
That is, the NOx storage agent of the present invention comprises (A) a composite oxide of zirconium and a metal other than zirconium selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals, and (B) zirconium oxide, It contains at least one metal compound selected from the group consisting of oxides of metals other than zirconium and carbonates of metals other than zirconium.
[0011]
Moreover, the NOx occlusion reduction type catalyst of the present invention is characterized by comprising the NOx occlusion agent and (C) a noble metal. In such a NOx occlusion reduction type catalyst, the composite oxide is composite oxide particles having an average particle size of 30 nm or less, the metal compound is metal compound particles having an average particle size of 30 nm or less, and at least a part of the noble metal is present. The composite oxide particles and / or the metal compound particles are preferably supported. By setting the average particle size of the composite oxide and the metal compound to the above values, the NOx occlusion reduction performance and the sulfur poisoning durability can be further improved.
[0012]
The present invention further provides the following production methods (i), (ii) and (iii) of the NOx storage agent.
[0013]
Production method( i )
(1) A solution preparation step in which a zirconium compound and a compound containing a metal other than zirconium selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals are dispersed and / or dissolved in a solvent to obtain a solution; 2) A method including a coprecipitate forming step of forming a coprecipitate by adding a precipitant to the solution, and (3) a firing step of firing the coprecipitate to obtain a fired product.
[0014]
Production method( ii )
(1) A solution in which a first alkoxide containing zirconium and a second alkoxide containing a metal other than zirconium selected from the group consisting of alkali metals, alkaline earth metals and rare earth metals are dispersed and / or dissolved in a solvent. (2) Hydrolysis step of removing the solvent and hydrolyzing the first alkoxide and the second alkoxide to obtain a hydrolyzate, and (3) the hydrolyzate And a firing step for obtaining a fired product.
[0015]
Production method( iii )
(1) A solution preparation step in which a zirconium organic salt and an organic salt of a metal other than zirconium selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals are dispersed and / or dissolved in a solvent to obtain a solution; (2) A method including a solvent removal step of removing the solvent to obtain an organic salt mixture, and (3) a firing step of firing the organic salt mixture to obtain a fired product.
[0016]
The present invention further provides the following production methods (I), (II) and (III) of the NOx occlusion reduction catalyst shown below.
[0017]
Production method( I )
A method of performing a precious metal supporting step of supporting a precious metal on a fired product obtained in the firing step after the firing step in the production method (i).
[0018]
Production method( II )
A method of performing a precious metal supporting step of supporting a precious metal on a fired product obtained in the firing step after the firing step in the production method (ii).
[0019]
Production method( III )
A method of performing a precious metal supporting step of supporting a precious metal on a fired product obtained in the firing step after the firing step in the production method (iii).
[0020]
In the production methods (I) to (III), it is preferable to further disperse and / or dissolve the porous carrier in the solvent in the solution preparation step. By adding the porous carrier, the NOx occlusion reduction type catalyst can be supported on the porous carrier.
[0021]
The present invention further provides the following method for producing NOx occlusion reduction catalyst (IIa), (IIb), (IIIa) and (IIIb) using a supercritical fluid or a subcritical fluid.
[0022]
Production method( IIa )
(1) A first solvent comprising a first alkoxide containing zirconium, a second alkoxide containing a metal other than zirconium selected from the group consisting of alkali metals, alkaline earth metals and rare earth metals, and a porous carrier. A solution preparation step for obtaining a solution by dispersing and / or dissolving in (2), and (2) a support in which the first solvent is removed and the first alkoxide and the second alkoxide are supported on the porous carrier. (3) a contact step of bringing the second solvent into contact with the support in a state where the solvent becomes a supercritical fluid or a subcritical fluid; and (4) the contact is performed. A firing step of firing the supported product to obtain a fired product, and (5) a precious metal support step of supporting the precious metal on the fired product.
[0023]
Production method( IIb )
(1) A solution in which a first alkoxide containing zirconium and a second alkoxide containing a metal other than zirconium selected from the group consisting of alkali metals, alkaline earth metals and rare earth metals are dispersed and / or dissolved in a solvent. (2) contacting the solution with the porous carrier in a state where the solvent becomes a supercritical fluid or a subcritical fluid, whereby the first alkoxide and the first alkoxide are added to the porous carrier. A method comprising: a supporting step of supporting a alkoxide of 2 to obtain a supported product; (3) a firing step of firing the supported product to obtain a fired product; and (4) a precious metal supporting step of supporting a precious metal on the fired product.
[0024]
Production method( IIIa )
(1) A zirconium organic salt, an organic salt of a metal other than zirconium selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals, and a porous carrier are dispersed and / or dissolved in a first solvent. A solution preparation step for obtaining a solution; (2) a mixture carrying step for removing the first solvent to obtain a carrying product in which an organic salt mixture is carried on the porous carrier; and (3) for the carrying product A contact step of bringing the second solvent into contact with the solvent in a state of becoming a supercritical fluid or a subcritical fluid, and (4) a firing step of firing the supported material subjected to the contact to obtain a fired product, 5) A method including a noble metal supporting step of supporting a noble metal on the fired product.
[0025]
Production method( IIIb )
(1) A solution preparation step in which a zirconium organic salt and an organic salt of a metal other than zirconium selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals are dispersed and / or dissolved in a solvent to obtain a solution; (2) a supporting step of supporting the organic salt mixture on the porous carrier by bringing the solution into contact with the porous carrier in a state where the solvent becomes a supercritical fluid or a subcritical fluid; and (3) the solvent. Removing the solvent to obtain a supported product in which the organic salt mixture is supported on the porous carrier, (4) a firing step of firing the supported product to obtain a fired product, and (5) the fired product. And a noble metal supporting step for supporting the noble metal on the substrate.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in more detail.
[0027]
The NOx storage agent of the present invention includes the following components (A) and (B), and the NOx storage reduction catalyst of the present invention further includes the component (C).
[0028]
(A) Complex oxide of zirconium and a metal other than zirconium (provided that the metal other than zirconium is a metal selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals);
(B) at least one metal compound selected from the group consisting of zirconium oxide, oxides of metals other than zirconium and carbonates of metals other than zirconium;
(C) Noble metal.
[0029]
Examples of the alkali metal in the component (A) include lithium, sodium, potassium, and cesium. Examples of the alkaline earth metal include barium, magnesium, calcium, and strontium. Examples of the rare earth metal include scandium, yttrium, and lanthanum. , Cerium, praseodymium, neodymium. In the present invention, the metal other than zirconium is particularly preferably barium, potassium or lithium. As the component (A) (composite oxide), a composite oxide containing zirconium and barium as metal elements is particularly preferable. The composite oxide in the present invention may be a mixture of different types.
[0030]
The component (B) (metal compound) includes at least one of zirconium oxide, an oxide of a metal other than zirconium, and a carbonate of a metal other than zirconium, but the component (B) Preferably, at least two of them are included. In the present invention, the component (B) particularly preferably contains barium oxide and / or barium carbonate and zirconium oxide. The metal oxides other than zirconium and the metal carbonates other than zirconium may be different types of mixtures.
[0031]
Examples of the noble metal include platinum group noble metals such as ruthenium, rhodium, palladium, iridium, and platinum, and platinum is particularly preferable. The noble metal in the present invention may be a mixture of different types.
[0032]
Since the NOx storage agent of the present invention contains the above components (A) and (B) as essential components, it exhibits excellent NOx storage performance. In the NOx storage agent of the present invention, the component (A) is a composite oxide particle having an average particle size of 30 nm or less, and the component (B) is preferably a metal compound particle having an average particle size of 30 nm or less. By setting both the average particle diameters of the component (A) and the component (B) to 30 nm or less, it is possible to make both of them close to each other in the NOx storage agent, and therefore the NOx storage performance can be further improved. .
[0033]
The NOx occlusion reduction catalyst of the present invention is obtained by further adding the component (C) to the NOx occlusion agent of the present invention, and by adding the component (C), it is possible to have a high NOx occlusion reduction performance. Even when it is subjected to sulfur poisoning, it is possible to exhibit excellent NOx storage performance. In the present invention, the component (A) in the NOx occlusion reduction catalyst is a composite oxide particle having an average particle size of 30 nm or less, the component (B) is a metal compound particle having an average particle size of 30 nm or less, and the component (C). It is preferable that at least a part of is supported on the composite oxide particles and / or the metal compound particles. By adopting such a configuration, the (A) component, the (B) component, and the (C) component can be present close to each other, so that the NOx occlusion reduction performance and sulfur poisoning durability can be further improved. It becomes possible.
[0034]
The NOx occlusion reduction in the NOx occlusion reduction type catalyst of the present invention is considered to be caused by the mechanism described below. That is, in the case where a composite oxide of zirconium and barium is included as the component (A), NOx in the exhaust gas reacts with a noble metal to form nitrate ions and the like, and comes into contact with the composite oxide of zirconium and barium. Ba (NO_Three)₂The stored NOx is stored in the exhaust gas atmosphere when the air-fuel ratio becomes rich due to fluctuations in engine operation or the like.₂It is thought that it is reduced and released.
[0035]
The NOx occlusion reduction type catalyst of the present invention preferably comprises the NOx occlusion reduction type catalyst having the above structure and a porous carrier carrying the NOx occlusion reduction type catalyst. Examples of the porous carrier include alumina, titania, zirconia, magnesia, and a composite oxide containing at least one of these. When the NOx occlusion reduction type catalyst of the present invention is supported on a porous carrier, it is preferably supported on the inside and on the surface of the porous carrier. In the present invention, the NOx storage reduction catalyst supported on 100 g of the porous carrier is preferably 0.03 to 1.0 mol.
[0036]
The NOx storage agent of the present invention can be produced by the above production methods (i) to (iii), and the NOx storage reduction catalyst of the present invention is produced by the above production methods (I) to (III). be able to. Since the production methods (i) and (I) are both methods using a coprecipitation agent, the production method (i) is hereinafter referred to as a NOx storage agent production method by the “coprecipitation method”, and the production method (I) Hereinafter, it is referred to as a method for producing a NOx occlusion reduction type catalyst by the “coprecipitation method”. In addition, since the production methods (ii) and (II) are both methods using alkoxide, the production method (ii) is hereinafter referred to as a NOx storage agent production method by the “alkoxide method”, and the production method (II) is described below. This is referred to as a NOx occlusion reduction type catalyst production method by the “alkoxide method”. Furthermore, since the production methods (iii) and (III) are both methods using an organic salt, the production method (iii) is hereinafter referred to as “NOx storage agent production method by the“ organic salt method ”, and the production method (III) Is hereinafter referred to as a method for producing a NOx occlusion reduction type catalyst by the “organic salt method”.
[0037]
First, the manufacturing method of the NOx storage agent by the coprecipitation method and the manufacturing method of the NOx storage reduction type catalyst will be described.
[0038]
The zirconium compound used in the solution preparation step in the coprecipitation method is not particularly limited as long as it is a compound containing zirconium. An example of such a compound is zirconium oxynitrate. As the compound containing a metal other than zirconium selected from the group consisting of alkali metals, alkaline earth metals and rare earth metals, metal compounds containing barium, potassium and lithium are preferred. Such compounds include barium nitrate, barium acetate and acetic acid. Examples include potassium and lithium acetate. Moreover, water (preferably ion-exchange water) is mentioned as a solvent used in a solution preparation process.
[0039]
In the solution preparation step, a zirconium compound is added so that the zirconium atoms are 0.005 to 0.1 mol per 1000 mL of solvent, and the metal atoms other than zirconium are 0.005 to 0.1 mol. Thus, it is preferable to introduce a compound containing a metal other than zirconium. When either one of the number of moles exceeds 0.1 mole, the solution concentration becomes too high and the reaction tends to be difficult to occur uniformly. On the other hand, when either one of the number of moles is less than 0.005 mole, the solution concentration is too dilute and the production efficiency tends to decrease.
[0040]
In the solution preparation step, it is preferable to further add a porous carrier. By adding the porous carrier, the NOx occlusion reduction type catalyst can be supported on the porous carrier. Here, examples of the porous carrier include those made of alumina, titania, zirconia, magnesia, and a composite oxide containing at least one of these. In the solution preparation step, it is preferable to add the porous carrier so that the porous carrier becomes 100 g with respect to 0.03 to 1.0 mol of the NOx storage reduction catalyst finally obtained. .
[0041]
Examples of the precipitant used in the coprecipitate formation step in the coprecipitation method include ammonium bicarbonate, aqueous ammonia, and a mixture thereof. The amount of the precipitant added is preferably 1.2 times or more the equivalent of the zirconium compound and the compound containing a metal other than zirconium used in the solution preparation step.
[0042]
When the number of moles of zirconium atoms with respect to 1000 mL of solvent is 0.005 to 0.1 mole, the number of metal atoms other than zirconium is 0.005 to 0.1 moles, and the amount of the precipitant added is as described above. In particular, a very fine coprecipitate can be obtained due to a large pH change upon addition of the precipitant.
[0043]
In the firing step in the coprecipitation method, the coprecipitate obtained in the coprecipitate formation step is fired. Here, the coprecipitate to be baked may contain components other than the coprecipitate, for example, a solvent used in the solution preparation step, or may be obtained by removing the solvent. Moreover, what is necessary is just to implement baking at 200-700 degreeC (preferably 300-500 degreeC) in the air, for example, and heating time can be made into 1-3 hours, for example.
[0044]
By performing the firing step, the coprecipitate is selected from the group consisting of a composite oxide of zirconium and a metal other than zirconium; zirconium oxide, an oxide of a metal other than zirconium, and a carbonate of a metal other than zirconium. And at least one metal compound. In this case, by adopting the above preferred reaction conditions, each component in the fired product can have an average particle size of 30 nm or less. In addition, when a porous carrier is added in the solution preparation step, the fired product can be carried on the porous carrier.
[0045]
For example, when zirconium oxynitrate and barium nitrate are used in the solution preparation process, a fired product containing a composite oxide of zirconium and barium, zirconium oxide, and barium oxide is obtained in the firing process. At least a part is further changed to barium carbonate by contact with carbon dioxide or the like.
[0046]
In the case of obtaining a NOx storage reduction catalyst in the coprecipitation method, after the firing step in the production method of the NOx storage agent, a precious metal supporting step is performed in which the precious metal is supported on the fired product obtained in the firing step. Is preferably a platinum group noble metal such as ruthenium, rhodium, palladium, iridium or platinum. In the noble metal carrying step, the fired product obtained in the firing step is immersed in a solution containing a noble metal precursor, heated to remove the solvent, and further subjected to a reduction treatment to carry the noble metal. it can. The reduction process is, for example, H₂(5%) / N₂It is possible by treating at 500 ° C. for 1 hour in an atmosphere. Here, the noble metal precursor refers to a substance that generates a noble metal by reduction treatment. Examples of such noble metal precursors include platinum halides, platinum nitrates, and platinum acetylacetonate.
[0047]
By adopting the above preferred conditions, both the component (A) and the component (B) in the NOx occlusion reduction catalyst are particles having an average particle size of 30 nm or less, and at least part of the component (C) is composed of the component particles (A) and / Or (B) It can carry | support to a component particle. For example, when zirconium oxynitrate and barium nitrate are used in the solution preparation process and a platinum precursor is used in the noble metal supporting process, as described above, in the firing process, a composite oxide of zirconium and barium, zirconium oxide, A NOx occluding agent containing barium oxide and / or barium carbonate is obtained, and platinum is supported on the occluding agent in the noble metal supporting step.
[0048]
Next, the manufacturing method of the NOx storage agent by the alkoxide method and the manufacturing method of the NOx storage reduction type catalyst will be described.
[0049]
Examples of the first alkoxide containing zirconium used in the solution preparation step in the alkoxide method include zirconium methoxide, ethoxide, and isopropoxide. Specifically, zirconium tetramethoxide, zirconium tetraethoxide, zirconium tetra An example is isopropoxide.
[0050]
The second alkoxide containing a metal other than zirconium is an alkoxide containing at least one metal selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals, and as the alkoxide, barium alkoxide is preferable. Examples of barium alkoxides include barium methoxide, ethoxide, and isopropoxide, and specific examples include barium dimethoxide, barium diethoxide, and barium diisopropoxide.
[0051]
Examples of the solvent used in the solution preparation step include alcohols such as methanol, ethanol and isopropanol; ketones such as acetone and acetylacetone; ethers such as dimethyl ether. In the alkoxide method, the alcohol is preferably used as a solvent.
[0052]
In the solution preparation step, the first alkoxide is added so that the zirconium atom is 0.005 to 0.1 mol per 1000 mL of solvent, and the metal compound containing a metal other than zirconium is 0.005 to 0. It is preferable to add the second alkoxide so as to be 1 mol. When either one of the number of moles exceeds 0.1 mole, the solution concentration becomes too high and the hydrolysis reaction tends to hardly occur. On the other hand, when either one of the number of moles is less than 0.005 mole, the solution concentration is too dilute and the production efficiency tends to decrease.
[0053]
In the solution preparation step in the alkoxide method, it is preferable to further add a porous carrier. By adding the porous carrier, the NOx occlusion reduction type catalyst can be supported on the porous carrier. Here, examples of the porous carrier include those made of alumina, titania, zirconia, magnesia, and a composite oxide containing at least one of these. In the solution preparation step, it is preferable to add the porous carrier so that the porous carrier becomes 100 g with respect to 0.03 to 1.0 mol of the NOx occlusion reduction catalyst finally obtained.
[0054]
In the hydrolysis step in the alkoxide method, the solvent is removed and the first alkoxide and the second alkoxide are hydrolyzed. Hydrolysis can be performed in the process of removing the solvent, but can also be performed by contacting with water or the like, if necessary, after removing the solvent. The temperature for hydrolysis is preferably room temperature to 70 ° C.
[0055]
By carrying out the hydrolysis step, the first alkoxide becomes a hydrolyzate (including a hydrolysis condensate), and the second alkoxide also becomes a hydrolyzate (including a hydrolysis condensate). In this case, one condensate may be produced from the hydrolyzate of the first alkoxide and the hydrolyzate of the second alkoxide.
[0056]
In the firing step in the alkoxide method, the hydrolyzate is fired, but the firing conditions and the like are the same as in the coprecipitation method. By calcining the hydrolyzate, at least one selected from the group consisting of a composite oxide of zirconium and a metal other than zirconium; zirconium oxide, an oxide of a metal other than zirconium, and a carbonate of a metal other than zirconium A fired product containing a metal compound is obtained. Moreover, the average particle diameter of each component in a baked product can be 30 nm or less by employ | adopting the said suitable conditions. Zirconium oxide is derived from the hydrolyzate of the first alkoxide, and the oxide of the metal other than zirconium is derived from the hydrolyzate of the second alkoxide. The complex oxide of zirconium and a metal other than zirconium is considered to be derived from the first and second hydrolysates and / or the condensate of the first and second hydrolysates.
[0057]
For example, when the first alkoxide used in the solution preparation step is zirconium tetraisopropoxide and the second alkoxide is barium diisopropoxide, the hydrolyzate of zirconium tetraisopropoxide is used in the hydrolysis step. A hydrolyzate containing a hydrolyzate of barium diisopropoxide (including a hydrolyzed condensate) is obtained (including hydrolyzed condensate), and the hydrolyzate is composed of zirconium tetraisopropoxide. It may contain a condensate generated from the hydrolyzate and the hydrolyzate of barium diisopropoxide. By calcining this hydrolyzate, a calcined product containing a composite oxide of zirconium and barium, zirconium oxide, and barium oxide is obtained, and at least a part of the barium oxide is carbonated by contact with carbon dioxide or the like. Further changes to barium.
[0058]
In the case of obtaining a NOx storage reduction catalyst in the alkoxide method, a precious metal supporting step of supporting the precious metal on the fired product obtained in the calcining step is performed after the calcining step in the method of producing the NOx storage agent. This is equivalent to the coprecipitation method. Moreover, the noble metal carrying | support process in an alkoxide method can be performed similarly to the noble metal carrying | support process in a coprecipitation method.
[0059]
Moreover, by adopting the above preferred conditions, both the component (A) and the component (B) in the NOx storage reduction catalyst are particles having an average particle size of 30 nm or less, and at least a part of the component (C) is converted to the component (A). It can carry | support to particle | grains and / or (B) component particle | grains. For example, when zirconium tetraisopropoxide and barium diisopropoxide are used in the solution preparation process, and a platinum precursor is used in the noble metal supporting process, the composite oxide of zirconium and barium and A NOx occlusion agent containing zirconium oxide and barium oxide and / or barium carbonate is obtained, and platinum is supported on the occlusion agent in the noble metal supporting step.
[0060]
Next, the manufacturing method of the NOx storage agent by the organic salt method and the manufacturing method of the NOx storage reduction type catalyst will be described.
[0061]
As the zirconium organic salt used in the solution preparation step in the organic salt method, for example, SYM-ZR04 provided as a solution from High Purity Chemical Co. can be used. The organic salt of a metal other than zirconium is an organic salt of at least one metal selected from the group consisting of an alkali metal, an alkaline earth metal, and a rare earth metal. For example, a barium organic salt provided as a solution from High Purity Chemical Co., Ltd. SYM-BA05 can be used. As the metal other than zirconium, barium, potassium, and lithium are preferable. Moreover, organic solvents, such as ethanol, hexane, xylene, are mentioned as a solvent used in a solution preparation process.
[0062]
In the solution preparation step, a zirconium organic salt is added so that the zirconium atoms are 0.005 to 0.1 mol per 1000 mL of solvent, and the metal atoms other than zirconium are 0.005 to 0.1 mol. It is preferable to add an organic salt of a metal other than zirconium. When either one of the number of moles exceeds 0.1 mole, the solution concentration becomes too high and mixing tends not to occur sufficiently. On the other hand, when either one of the number of moles is less than 0.005 mole, the solution concentration is too dilute and the production efficiency tends to decrease.
[0063]
In the solvent removal step, the solvent is removed to obtain an organic salt mixture (a mixture of zirconium organic salt and organic salt of metal other than zirconium). The removal of the solvent can be performed at room temperature to the boiling point of the solvent, and if necessary, the removal can be made efficient by reducing the pressure. In the solvent removal step, it is preferable to remove all the solvent, but a part of the solvent may remain as long as no problem occurs in the subsequent baking step.
[0064]
In the firing step in the organic salt method, the organic salt mixture is fired, and the firing conditions and the like are the same as in the coprecipitation method. By firing the organic salt mixture, at least one selected from the group consisting of a composite oxide of zirconium and a metal other than zirconium; zirconium oxide, an oxide of a metal other than zirconium, and a carbonate of a metal other than zirconium A fired product containing a metal compound is obtained. Moreover, the average particle diameter of each component in a baked product can be 30 nm or less by employ | adopting the said suitable conditions.
[0065]
In the case of obtaining a NOx storage reduction catalyst in the organic salt method, a precious metal supporting step for supporting a precious metal on the fired product obtained in the calcining step is performed after the calcining step in the production method of the NOx storage agent. Is equivalent to the coprecipitation method. The noble metal supporting step in the organic salt method can be performed in the same manner as the noble metal supporting step in the coprecipitation method. By adopting the above preferred conditions, both the component (A) and the component (B) in the NOx occlusion reduction catalyst are particles having an average particle size of 30 nm or less, and at least a part of the component (C) is composed of the component (A). It can carry | support to particle | grains and / or (B) component particle | grains.
[0066]
When a porous carrier is used in the alkoxide method and organic salt method of the present invention, it is preferable to prepare a NOx occlusion reduction type catalyst using a supercritical fluid or a subcritical fluid. In the present invention, a supercritical fluid means a fluid heated to a critical temperature or higher, and a subcritical fluid means a fluid heated to 0.8 times or more lower than the critical temperature. Although there is no restriction | limiting in particular regarding the pressure of a solvent, It is preferable to set it as a critical pressure or more. Supercritical fluids and subcritical fluids have the same dissolving ability as liquids, diffusivity and viscosity close to those of gases, and therefore hydrolyze even deep pores of porous carriers and pores with very fine diameters. Compounds such as organic compounds and organic salt mixtures can be easily and rapidly permeated.
[0067]
First, a case where a supercritical fluid or a subcritical fluid is applied in the alkoxide method will be described. In the alkoxide method, when a NOx occlusion reduction type catalyst is produced by applying a supercritical fluid or a subcritical fluid, it is preferably carried out according to the following production methods (IIa) and (IIb).
[0068]
Production method( IIa )
(1) A first solvent comprising a first alkoxide containing zirconium, a second alkoxide containing a metal other than zirconium selected from the group consisting of alkali metals, alkaline earth metals and rare earth metals, and a porous carrier. A solution preparation step for obtaining a solution by dispersing and / or dissolving in (2), and (2) a support in which the first solvent is removed and the first alkoxide and the second alkoxide are supported on the porous carrier. (3) a contact step of bringing the second solvent into contact with the support in a state where the solvent becomes a supercritical fluid or a subcritical fluid; and (4) the contact is performed. A firing step of firing the supported product to obtain a fired product, and (5) a precious metal support step of supporting the precious metal on the fired product.
[0069]
The first alkoxide, the second alkoxide, the porous carrier and the noble metal in the production method (IIa) are the same as the first alkoxide, the second alkoxide, the porous carrier and the noble metal in the alkoxide method. Moreover, the 1st solvent in manufacturing method (IIa) is the same as the solvent in the solution preparation process of the said alkoxide method.
[0070]
That is, in the production method (IIa), a solution in which the first alkoxide, the second alkoxide, and the porous carrier are dispersed and / or dissolved in a solvent under the same conditions as in the solution preparation step of the alkoxide method. In the subsequent solvent removal step, the solvent used in the solution preparation step is removed to obtain a support in which the first alkoxide and the second alkoxide are supported on the porous carrier.
[0071]
Next, in the contacting step, the support is brought into contact with a solvent. In the case of contacting, the solvent is brought into a supercritical fluid or subcritical fluid state. For example, when the solvent is methanol (critical temperature: 239 ° C.), contact in the supercritical fluid state is possible by bringing methanol to 239 ° C. or higher and bringing it into contact with the support. The solvent used in the contact step may be the same as or different from the solvent in the solution preparation step, and the solvent is preferably an organic solvent such as alcohol. The support that has been contacted with the solvent in a supercritical fluid or subcritical fluid state is subjected to firing in the firing step, and the obtained fired product carries the noble metal in the noble metal support step. The firing step and the noble metal supporting step can be performed in the same manner as the firing step and the noble metal supporting step in the alkoxide method. By bringing the solvent into contact with the support in a supercritical fluid or subcritical fluid state, the supported hydrolyzate can reach deeper in the pores of the porous support. The support area of the hydrolyzate on the carrier is improved, the specific surface area of the NOx storage reduction catalyst finally obtained is increased, and the catalyst performance is improved.
[0072]
In addition, after carrying out the solvent removal step, hydrolyzing the first alkoxide and the second alkoxide, and carrying out a hydrolysis step to obtain a support in which these hydrolysates are supported on a porous carrier, You may implement a contact process using the support material obtained by this hydrolysis process.
[0073]
Production method( IIb )
(1) A solution in which a first alkoxide containing zirconium and a second alkoxide containing a metal other than zirconium selected from the group consisting of alkali metals, alkaline earth metals and rare earth metals are dispersed and / or dissolved in a solvent. (2) contacting the solution with the porous carrier in a state where the solvent becomes a supercritical fluid or a subcritical fluid, whereby the first alkoxide and the first alkoxide are added to the porous carrier. A method comprising: a supporting step of supporting a alkoxide of 2 to obtain a supported product; (3) a firing step of firing the supported product to obtain a fired product; and (4) a precious metal supporting step of supporting a precious metal on the fired product.
[0074]
The first alkoxide, the second alkoxide, the solvent, the porous carrier and the noble metal in the production method (IIb) are the same as the first alkoxide, the second alkoxide, the solvent, the porous carrier and the noble metal in the alkoxide method. . In the production method (IIb), unlike the production method (IIa), the solution obtained in the solution production step is converted into a porous carrier under the condition that the solvent used for producing the solution becomes a supercritical fluid or a subcritical fluid. Make contact.
[0075]
That is, after performing the solution preparation step in the same manner as the solution preparation step in the alkoxide method, the obtained solution is brought into contact with the porous carrier under the condition that the solvent becomes a supercritical fluid or subcritical fluid, and the first alkoxide is obtained. The second alkoxide is supported on the porous carrier (supporting step). Next, the firing step and the noble metal supporting step are carried out, and the conditions of the step can be the same as those in the alkoxide method. By carrying out the production method (IIb), the specific surface area of the obtained NOx storage reduction catalyst can be increased, so that the catalyst performance can be improved.
[0076]
Next, a case where a supercritical fluid or a subcritical fluid is applied in the organic salt method will be described. In the organic salt method, when a NOx occlusion reduction type catalyst is produced by applying a supercritical fluid or a subcritical fluid, it is preferably carried out according to the following production methods (IIIa) and (IIIb).
[0077]
Production method( IIIa )
(1) A zirconium organic salt, an organic salt of a metal other than zirconium selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals, and a porous carrier are dispersed and / or dissolved in a first solvent. A solution preparation step for obtaining a solution; (2) a mixture carrying step for removing the first solvent to obtain a carrying product in which an organic salt mixture is carried on the porous carrier; and (3) for the carrying product A contact step of bringing the second solvent into contact with the solvent in a state of becoming a supercritical fluid or a subcritical fluid, and (4) a firing step of firing the supported material subjected to the contact to obtain a fired product, 5) A method including a noble metal supporting step of supporting a noble metal on the fired product.
[0078]
The zirconium organic salt in the production method (IIIa), the organic salt of a metal other than zirconium, the porous carrier and the noble metal are the same as the zirconium organic salt in the organic salt method, the organic salt of a metal other than zirconium, the porous carrier and the noble metal. is there. Moreover, the 1st solvent in manufacturing method (IIIa) is the same as the solvent in the solution preparation process of the said organic salt method.
[0079]
That is, in the production method (IIIa), a zirconium organic salt, an organic salt of a metal other than zirconium, and a porous carrier are dispersed in a solvent and / or under the same conditions as in the solution preparation step of the organic salt method. In the subsequent mixture supporting step, the solvent used in the solution preparing step is removed under the same conditions as the solvent removing step in the organic salt method, so that the organic salt mixture becomes a porous carrier. A supported product is obtained.
[0080]
Next, in the contacting step, the support is brought into contact with a solvent in the same manner as in production method (IIa). The solvent used in the contact step may be the same as or different from the solvent in the solution preparation step, and the solvent is preferably an organic solvent such as alcohol. The support that has been contacted with the solvent in a supercritical fluid or subcritical fluid state is subjected to firing in the firing step, and the obtained fired product carries the noble metal in the noble metal support step. The firing step and the noble metal supporting step can be performed in the same manner as the firing step and the noble metal supporting step in the organic salt method. By bringing the solvent into contact with the support in a supercritical fluid or subcritical fluid state, the supported organic salt mixture can reach deeper in the pores of the porous support. The carrying area of the organic salt mixture on the carrier is improved, the specific surface area of the NOx storage reduction catalyst finally obtained is increased, and the catalyst performance is improved.
[0081]
Production method( IIIb )
(1) A solution preparation step in which a zirconium organic salt and an organic salt of a metal other than zirconium selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals are dispersed and / or dissolved in a solvent to obtain a solution; (2) a supporting step of supporting the organic salt mixture on the porous carrier by bringing the solution into contact with the porous carrier in a state where the solvent becomes a supercritical fluid or a subcritical fluid; and (3) the solvent. Removing the solvent to obtain a supported product in which the organic salt mixture is supported on the porous carrier, (4) a firing step of firing the supported product to obtain a fired product, and (5) the fired product. And a noble metal supporting step for supporting the noble metal on the substrate.
[0082]
Zirconium organic salt in production method (IIIb), organic salt of metal other than zirconium, solvent, porous carrier and noble metal are zirconium organic salt in the organic salt method, organic salt of metal other than zirconium, solvent, porous carrier and Similar to precious metals.
[0083]
In the production method (IIIb), after performing the solution preparation step in the same manner as the solution preparation step in the organic salt method, the obtained solution is converted into a porous carrier under the condition that the solvent becomes a supercritical fluid or subcritical fluid. Contact is made, and the organic salt mixture is supported on the porous carrier (supporting step). Then, the solvent is removed in the subsequent solvent removal step. The conditions for the solvent removal step are the same as those for the solvent removal step in the organic salt method. Next, the firing step and the noble metal supporting step are carried out, and the conditions of the step can be the same as in the organic salt method. By carrying out the production method (IIIb), the specific surface area of the obtained NOx storage reduction catalyst can be increased, so that the catalyst performance can be improved.
[0084]
【Example】
Hereinafter, preferred examples of the present invention will be described in more detail, but the present invention is not limited to these examples.
[0085]
(Example 1: Coprecipitation method)
A dispersion was obtained by adding 8.9 g of zirconium oxynitrate, 8.7 g of barium nitrate, and 20.0 g of γ-alumina powder to 1500 mL of ion-exchanged water and stirring. Separately from this, 3.80 g of ammonium bicarbonate and 25.0 g of aqueous ammonia (25% aqueous solution) were dissolved in ion-exchanged water to make 100 mL, which was used as a precipitant. The entire amount of this precipitating agent was charged into the dispersion, the precipitate obtained by coprecipitation was filtered, and the obtained solid content was again dispersed in a solution in which 3.80 g of ammonium bicarbonate was dissolved in 1500 mL of ion-exchanged water. Then, filtration was performed to obtain a coprecipitate.
[0086]
The obtained coprecipitate was calcined in air at 300 ° C. for 3 hours and then cooled to obtain a composite oxide of zirconium and barium (BaZrO_Three), Zirconium oxide (ZrO)₂), Barium carbonate (BaCO)_Three) Was supported on the γ-alumina powder (NOx storage agent). In the supported product, the number of moles of zirconium relative to 200 g of γ-alumina powder was 0.2 mole, and the number of moles of barium was 0.2 mole. Next, this support was immersed in platinum P salt (platinum nitrate) to support platinum nitrate. At this time, the weight of platinum was set to 2 g with respect to 200 g of γ-alumina powder. Next, this is H₂(5%) / N₂The mixture was fired at 500 ° C. to change the platinum nitrate to platinum. Thereby, zirconium-barium composite oxide (BaZrO_Three), Zirconium oxide (ZrO)₂), Barium carbonate (BaCO)_Three), A NOx occlusion reduction type catalyst having platinum and γ-alumina as constituent components was obtained.
[0087]
(Example 2: Alkoxide method)
5.1 g of barium diisopropoxide, 6.6 g of zirconium tetraisopropoxide and 20.0 g of γ-alumina powder were put into 1000 mL of isopropanol and stirred to obtain a dispersion. Isopropanol was evaporated from this dispersion at 60 ° C. and 130 Torr using an evaporator, and the hydrolysis reaction was advanced to obtain a composite in which the hydrolyzate was supported on an alumina carrier.
[0088]
The obtained composite was fired in air at 300 ° C. for 3 hours and then cooled to obtain a composite oxide of zirconium and barium (BaZrO_Three), Zirconium oxide (ZrO)₂), Barium carbonate (BaCO)_Three) Was obtained on the γ-alumina powder (NOx storage agent). In the supported product, the number of moles of zirconium relative to 200 g of γ-alumina powder was 0.2 mole, and the number of moles of barium was 0.2 mole. Next, this support was immersed in platinum P salt (platinum nitrate) to support platinum nitrate. At this time, the weight of platinum was set to 2 g with respect to 200 g of γ-alumina powder. Next, this is H₂(5%) / N₂The mixture was fired at 500 ° C. to change the platinum nitrate to platinum. Thereby, zirconium-barium composite oxide (BaZrO_Three), Zirconium oxide (ZrO)₂), Barium carbonate (BaCO)_Three), A NOx occlusion reduction type catalyst having platinum and γ-alumina as constituent components was obtained.
[0089]
(Example 3: Organic salt method)
30.0 mL of zirconium organic salt solution (manufactured by Koyo Chemical Co., Ltd., SYM-ZR04, oxide concentration: 0.4 mol / 1000 mL) and barium organic salt solution (manufactured by Koyo Chemical Co., Ltd., SYM-BA05, oxide concentration: 0) 0.5 mol / 1000 mL) 37.5 mL and 20.0 g of γ-alumina powder were put into 1500 mL of n-hexane and stirred to obtain a dispersion. Using an evaporator, n-hexane was evaporated from this dispersion at 70 ° C. and 60 Torr to obtain an organic salt mixture.
[0090]
The obtained organic salt mixture was calcined in air at 300 ° C. for 3 hours and then cooled to obtain a composite oxide of zirconium and barium (BaZrO_Three), Zirconium oxide (ZrO)₂), Barium carbonate (BaCO)_Three) Was supported on the γ-alumina powder (NOx storage agent). In the supported product, the number of moles of zirconium relative to 200 g of γ-alumina powder was 0.2 mole, and the number of moles of barium was 0.2 mole. Next, this support was immersed in platinum P salt (platinum nitrate) to support platinum nitrate. At this time, the weight of platinum was set to 2 g with respect to 200 g of γ-alumina powder. Next, this is H₂(5%) / N₂The mixture was fired at 500 ° C. to change the platinum nitrate to platinum. Thereby, zirconium-barium composite oxide (BaZrO_Three), Zirconium oxide (ZrO)₂), Barium carbonate (BaCO)_Three), A NOx occlusion reduction type catalyst having platinum and γ-alumina as constituent components was obtained.
[0091]
(Comparative Example 1)
Barium nitrate 5.2g was disperse | distributed to 500 mL ion-exchange water, and the dispersion liquid was obtained.
This dispersion was evaporated to dryness, mixed with 20.0 g of γ-alumina powder, dispersed in a solution of 3.80 g of ammonium bicarbonate in 1500 mL of ion-exchanged water, and filtered.
[0092]
The solid content obtained by filtration was fired in air at 300 ° C. for 3 hours and then cooled to obtain a supported material in which the fired product was supported on γ-alumina powder. In the supported product, the number of moles of barium with respect to 200 g of γ-alumina powder was 0.2 mol. This support was immersed in platinum P salt (platinum nitrate) to support platinum nitrate. At this time, the weight of platinum was set to 2 g with respect to 200 g of γ-alumina powder. Next, this is H₂(5%) / N₂The mixture was fired at 500 ° C. to change the platinum nitrate to platinum.
[0093]
(Comparative Example 2)
Dispersion liquid was obtained by dispersing 5.2 g of barium nitrate and 1.6 g of titania powder in 500 mL of ion exchange water. This dispersion was evaporated to dryness, mixed with 20.0 g of γ-alumina powder, dispersed in a solution of 2.82 g of ammonium bicarbonate in 1500 mL of ion-exchanged water, and filtered.
[0094]
The solid content obtained by filtration was fired in air at 300 ° C. for 3 hours and then cooled to obtain a supported material in which the fired product was supported on γ-alumina powder. The number of moles of barium and titanium with respect to 200 g of γ-alumina in the supported material was 0.2 moles. This support was immersed in platinum P salt (platinum nitrate) to support platinum nitrate. At this time, the weight of platinum was set to 2 g with respect to 200 g of γ-alumina powder. Next, this is H₂(5%) / N₂The mixture was fired at 500 ° C. to change the platinum nitrate to platinum.
[0095]
The NOx occlusion reduction type catalysts obtained in Examples 1 to 3 and Comparative Examples 1 and 2 were pulverized by a pressure molding machine and then pulverized to obtain 300 to 700 μm pellets. The sulfur-poisoned gas shown in Table 1 below was circulated at 600 ° C. at a flow rate at which the S / Ba molar ratio was about 2 with respect to this pellet, and then the recovery treatment gas shown in Table 2 below was passed at 700 ° C. Circulated for 5 minutes. Using 0.5 g of pellets subjected to sulfur poisoning and regeneration in this manner, the RSNOx occlusion amount (rich spike) at the measurement temperatures of 300 ° C., 400 ° C. and 500 ° C. under the NOx occlusion amount evaluation conditions shown in Table 3 below. NOx occlusion amount) was measured. The measurement results are shown in FIG.
[0096]
[Table 1]

[0097]
[Table 2]

[0098]
[Table 3]

[0099]
Next, particles (BaZrO) in the NOx occlusion reduction type catalysts obtained in Examples 1 to 3 were used._Three, ZrO₂And BaCO_Three) Was determined by observation with a transmission electron microscope. Further, the NOx occlusion reduction type catalysts obtained in Examples 1 to 3 were subjected to elemental analysis at a spot of 5 nm using an energy dispersive X-ray analyzer (EDX). In this analysis, it was determined whether zirconium and barium were observed at a 5 nm spot. These results are summarized in Table 4.
[0100]
[Table 4]

[0101]
【The invention's effect】
As described above, according to the present invention, the NOx occlusion agent having excellent NOx occlusion performance contained in the exhaust gas of automobiles, the NOx occlusion reduction performance is sufficiently high, and it has been subjected to sulfur poisoning. Provided are a NOx occlusion reduction type catalyst that exhibits a high NOx occlusion performance, and a method for producing such a NOx occlusion agent and NOx occlusion reduction type catalyst.
[Brief description of the drawings]
FIG. 1 is a graph showing the amount of RSNOx adsorbed by NOx storage reduction catalysts obtained in Examples 1-3 and Comparative Examples 1-2.

Claims (7)

Zirconium organic salt, a solution preparation step of obtaining an alkali metal, solution and metal organic salts other than zirconium selected from the group consisting of alkaline earth metals and rare earth metals, is dispersed and / or dissolved in a solvent, the zirconium organic A solvent removing step of obtaining the organic salt mixture by removing the solvent from the solution in which the organic salt of the metal other than the salt and the zirconium is dispersed and / or dissolved, and the firing to obtain the fired product by firing the organic salt mixture And a process for producing the NOx storage agent. A method for producing a NOx occlusion reduction catalyst, comprising carrying out a noble metal supporting step of supporting a noble metal on a calcined product obtained in the calcining step after the calcining step in the method for producing an NOx storage agent according to claim 1 . The method for producing a NOx storage reduction catalyst according to claim 2 , wherein a porous carrier is further dispersed and / or dissolved in the solvent in the solution preparation step. (A) a composite oxide of zirconium and a metal other than zirconium selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals; (B) zirconium oxide, oxides of metals other than zirconium, and zirconium At least the one metal compound, containing, NOx occluding agent characterized Rukoto can be produced by the method of claim 1 wherein is selected from the group consisting of metal carbonates other than. A NOx storage-reduction catalyst comprising the NOx storage agent according to claim 4 and (C) a noble metal. The composite oxide is a composite oxide particle having an average particle size of 30 nm or less, the metal compound is a metal compound particle having an average particle size of 30 nm or less, and at least a part of the noble metal is the composite oxide. 6. The NOx occlusion reduction type catalyst according to claim 5, which is supported on the particles and / or the metal compound particles. And claim 5 or 6 NOx occlusion reduction type catalyst according, NOx storage reduction catalyst, wherein the porous carrier carrying the NOx storage reduction catalyst, in that it consists of.

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