JP5299603B2 - Oxide complex precursor aqueous solution, oxide complex production method, oxide complex, exhaust gas purification catalyst including the oxide complex, and exhaust gas purification method using the exhaust gas purification catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxide composite precursor aqueous solution by which a metal element being a precursor for an oxide composite is stably incorporated into an aqueous solution with high concentration and in a stable state, and the sufficiently fined oxide composite is obtained. <P>SOLUTION: The oxide composite precursor aqueous solution contains a first compound containing at least one kind of a first metal element selected from a group comprising alkali metals and alkaline earth metals, a second compound containing at least one kind of a second metal element selected from a group comprising rare earth metals, a third compound having a multidentate ligand, and ammonia. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to an oxide complex precursor aqueous solution, a method for producing an oxide complex, an oxide complex, an exhaust gas purification catalyst including the oxide complex, and an exhaust gas purification method using the exhaust gas purification catalyst.

  Conventionally, in order to purify harmful nitrogen oxides (NOx) contained in exhaust gas of automobiles and the like, an oxide complex capable of storing and / or reducing NOx has been used as an exhaust gas purification catalyst (NOx storage reduction type catalyst). It has been used as a material. As such an oxide composite, an oxide composite of barium and cerium is known.

  For example, Japanese Patent Laying-Open No. 2005-21878 (Patent Document 1) discloses a catalyst including a carrier supporting barium and cerium. Furthermore, Patent Document 1 discloses a method for producing the catalyst by impregnating a support with an aqueous solution in which at least barium and cerium are mixed in an ionic state without impregnating barium and cerium and calcining. . However, in the method for producing a catalyst as described in Patent Document 1, an oxide composite of barium and cerium cannot be supported in a fine state on a carrier. In addition, when cerium acetate is used to mix cerium in an ionic state in the aqueous solution, the solubility of cerium acetate in water is as low as 20 g with respect to 100 g of water, so that cerium acetate is contained in a high concentration. (See Tokyo Chemical Doujin "Chemical Dictionary"). For this reason, when the above aqueous solution is used in the production of a catalyst having a high cerium loading, there is a problem in that the loading process and cost increase.

Further, in Japanese Patent 2000-262897 (Patent Document 2), the more the first composite oxide represented by _MgO-Al 2 _{O 3,} a second composite oxide represented by TiO 2 -ZrO ₂ An exhaust gas purifying catalyst comprising: a support; a NOx occlusion material supported on the support selected from alkali metals, alkaline earth metals and rare earth elements and containing at least sodium and barium; and a noble metal supported on the support. It is disclosed. However, the exhaust gas purifying catalyst described in Patent Document 2 is not always sufficient in heat resistance and sulfur poisoning durability.
Japanese Patent Laid-Open No. 2005-21878 JP 2000-262897 A

  The present invention has been made in view of the above-described problems of the prior art, and can contain a metal element that is a precursor of an oxide composite in an aqueous solution at a high concentration and in a stable state. An object of the present invention is to provide an oxide complex precursor aqueous solution capable of obtaining a refined oxide complex, a method for producing an oxide complex using the oxide complex precursor, and an oxide complex obtained thereby. And Further, the present invention comprises the above oxide composite of the present invention, has sufficiently high heat resistance and sulfur poisoning durability, and has sufficiently excellent catalytic activity even when exposed to sulfur or high temperature for a long period of time. An object of the present invention is to provide an exhaust gas purifying catalyst that can be exerted, and an exhaust gas purifying method using the exhaust gas purifying catalyst.

  As a result of intensive studies to achieve the above object, the present inventors have found that a first compound containing at least one metal element selected from the group consisting of alkali metals and alkaline earth metals, and a rare earth metal In the oxide complex precursor aqueous solution used when producing an oxide complex using a second compound containing at least one metal element selected from the group consisting of By containing the third compound having a polydentate ligand and ammonia together with the compound, the first and second compounds can be contained in an aqueous solution in a high concentration and in a stable state. It is found that it is possible to obtain a sufficiently refined oxide composite by firing, and the support, the oxide composite supported on the support, and the acid supported on the support. A catalyst containing a metal having a reducing ability has sufficiently high heat resistance and sulfur poisoning durability, and can exhibit excellent catalytic activity even when exposed to sulfur or high temperature for a long time. As a result, the present invention has been completed.

That is, the oxide complex precursor aqueous solution of the present invention is a compound containing a first compound that contains barium, which is the first metal element, and a compound containing cerium, which is the second metal element, and cerium acetate. It includes a certain second compound, a third compound having a polydentate ligand, and ammonia.

  Further, the third compound according to the present invention includes citric acid, oxalic acid, succinic acid, maleic acid, malic acid, adipic acid, tartaric acid, malonic acid, fumaric acid, aconitic acid, glutaric acid, ethylenediaminetetraacetic acid, It is preferably at least one selected from the group consisting of lactic acid, glycolic acid, glyceric acid, salicylic acid, mevalonic acid, ethylenediamine, ethyl acetoacetate, malonic acid ester, glycol and pinacol, more preferably citric acid. .

  In the oxide complex precursor aqueous solution of the present invention, the content of the third compound is 2 in terms of mole with respect to the content of the second metal element contained in the second compound. It is preferable that it is twice or more.

  Moreover, in the oxide complex precursor aqueous solution of the present invention, it is preferable that the content of ammonia is twice or more in terms of mole relative to the content of the third compound.

  In the oxide complex precursor aqueous solution of the present invention, the ammonia content is preferably 0.4 mol / L or more.

  Furthermore, the manufacturing method of the oxide composite of the present invention is a method characterized in that the oxide composite precursor aqueous solution of the present invention is fired to obtain an oxide composite.

The oxide complexes of the present invention, barium is the first metallic element, an oxide complex containing cerium and a second metal element,
It is obtained by firing the oxide complex precursor aqueous solution of the present invention, and
Of the first metal element relative to the sum of the peak area of the first metal element and the peak area of the second metal element obtained from TEM-EDX analysis at 20 or more measurement points of 10 nm square on the surface of the oxide composite. The standard deviation of the distribution of the ratio of peak areas ([peak area of the first metal element] / [sum of the peak area of the first metal element and the peak area of the second metal element]) is 10% or less ,
It is characterized by.

  The exhaust gas purifying catalyst of the present invention comprises a carrier, the oxide composite of the present invention carried on the carrier, and a metal having oxidation-reduction ability carried on the carrier. Is.

In the exhaust gas purifying catalyst of the present invention, the support preferably contains at least one oxide of a third metal element selected from the group consisting of aluminum, zirconium, alkaline earth metals, and rare earth metals. It is more preferable to contain a metal oxide represented by the composition formula: MgAl ₂ O ₄ .

  Furthermore, in the exhaust gas purifying catalyst of the present invention, it is preferable that the carrier further contains an oxide of a fourth metal element selected from the group consisting of titanium, silicon, iron, manganese and tungsten.

  The exhaust gas purification method of the present invention is a method characterized in that exhaust gas containing nitrogen oxides is brought into contact with the exhaust gas purification catalyst of the present invention to purify the exhaust gas in an oxygen-excess atmosphere.

  The reason why the above object is achieved by the oxide complex precursor aqueous solution and the oxide complex production method of the present invention is not necessarily clear, but the present inventors speculate as follows. That is, the oxide complex precursor aqueous solution of the present invention contains the third compound having a polydentate ligand and ammonia together with the first and second compounds. Therefore, in the aqueous solution, the first compound and the second compound interact with each other via the polydentate ligand and are held in close proximity. In addition, since the oxide complex precursor aqueous solution of the present invention contains ammonia, the aqueous solution containing the first compound, the second compound, and the multidentate ligand is used as an aqueous solution. The first compound and the second compound are maintained at a high concentration and in a stable state without causing precipitation. And when the oxide complex precursor aqueous solution of the present invention is fired, the bulky multidentate ligand existing as a ligand is oxidatively decomposed, and the first compound and the second compound are sufficiently fine. The present inventors infer that they are combined in a converted state. In addition, the oxide composite of the present invention includes the peak area of the first metal element and the second metal element determined by TEM-EDX analysis at 20 or more measurement points of 10 nm square on the surface of the oxide composite. Standard of the distribution of the ratio of the peak area of the first metal element to the sum of the peak area ([peak area of the first metal element] / [sum of the peak area of the first metal element and the peak area of the second metal element]) The deviation is 10% or less. Therefore, the oxide composite of the present invention is a mixture in which the first metal element and the second metal element are sufficiently uniformly mixed, and can exhibit sufficiently high catalytic activity when supported on a support. Become.

Further, in the exhaust gas purifying catalyst of the present invention, the present invention wherein the oxide of the first metal element and the oxide of the second metal element are uniformly mixed in the carrier and complexed in a fine state. The oxide composite is supported. When the oxide composite is supported in such a finely and sufficiently uniformly mixed state, the sulfate of the oxide composite is destabilized even if the support is strongly basic. Therefore, in this invention, the fall of the catalyst activity by sulfur poisoning is fully suppressed. In addition, a strongly basic carrier can keep the supported metal oxide component in a stronger base state. In general, since the NOx purification performance in a high temperature range is proportional to the amount of base points, the use of a stronger basic carrier for the catalyst tends to improve the NOx storage performance at high temperatures. In the present invention, since a sulfur poisoning of the oxide complex supported can be sufficiently prevented even when a strong basic support is used, a strong basic support containing MgAl ₂ O ₄ is preferably used. The present inventors infer that the NOx occlusion performance at a high temperature can be further improved by using a more basic carrier. The dispersibility of the oxide composite of the present invention on the carrier tends to be more excellent when a carrier having higher basicity is used. Accordingly, when a strongly basic carrier such as MgAl ₂ O ₄ is used as the carrier, the dispersibility of the oxide complex is particularly excellent, and the desorption rate of the sulfur component even after sulfur poisoning. It is presumed that this can be made sufficiently faster.

  According to the present invention, a metal element that is a precursor of an oxide composite can be contained in an aqueous solution at a high concentration and in a stable state, and a sufficiently fine oxide composite can be obtained. An object is to provide an aqueous oxide complex precursor aqueous solution, a method for producing an oxide complex using the same, and an oxide complex obtained thereby. Further, the present invention comprises the above oxide composite of the present invention, has sufficiently high heat resistance and sulfur poisoning durability, and has sufficiently excellent catalytic activity even when exposed to sulfur or high temperature for a long period of time. It is an object of the present invention to provide an exhaust gas purification catalyst that can be exhibited and an exhaust gas purification method using the exhaust gas purification catalyst.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

  First, the oxide complex precursor aqueous solution of the present invention will be described. That is, the oxide complex precursor aqueous solution of the present invention includes a first compound containing at least one first metal element selected from the group consisting of alkali metals and alkaline earth metals, and a group consisting of rare earth metals. And a second compound containing at least one second metal element selected from: a third compound having a polydentate ligand; and ammonia.

  Examples of the alkali metal that can be selected as the first metal element contained in the first compound include lithium, sodium, potassium, rubidium, and cesium. Examples of the alkaline earth metal that can be selected as the first metal element include barium, magnesium, calcium, and strontium. Examples of the first compound include alkali metal or alkaline earth metal hydroxides, acetates, carbonates, nitrates, and the like. As such a first compound, a compound containing barium (barium nitrate, barium acetate, etc.) has a high basicity and can exhibit a sufficiently high NOx occlusion ability when an oxide is formed. ) Is preferably used. In addition, you may use such 1st compound individually by 1 type or in mixture of 2 or more types.

  Examples of the rare earth metal that can be selected as the second metal element contained in the second compound include scandium, yttrium, lanthanum, cerium, praseodymium, and neodymium. Examples of the second compound include rare earth metal hydroxides, acetates, carbonates, nitrates, and the like. Such a second compound is preferably a compound containing cerium (cerium acetate, cerium nitrate, etc.), more preferably cerium acetate, from the viewpoint of having a relatively high specific surface area when an oxide is formed. . In addition, you may use such a 2nd compound individually by 1 type or in mixture of 2 or more types.

  The multidentate ligand that the third compound has is a ligand that can coordinate with two or more coordination groups. Examples of the third compound include polyvalent carboxylic acids such as citric acid and oxalic acid, diols such as glycol and pinacol, diamines such as ethylenediamine, and esters having two carbonyl groups such as ethyl acetoacetate. Is mentioned. Such third compounds include citric acid, oxalic acid, succinic acid, maleic acid, malic acid, adipic acid, tartaric acid, malonic acid, fumaric acid, aconitic acid, glutaric acid, ethylenediaminetetraacetic acid, lactic acid, glycolic acid. , Glyceric acid, salicylic acid, mevalonic acid, ethylenediamine, ethyl acetoacetate, malonic acid ester, glycol and pinacol are preferred, and among them, citric acid, lactic acid, malic acid, tartaric acid, glycol from the viewpoint of being a carboxylic acid having a hydroxy group. Acid and salicylic acid are more preferable, and citric acid is particularly preferable from the viewpoint that a bulky and finer oxide complex can be produced. In addition, you may use such 3rd compound individually by 1 type or in mixture of 2 or more types.

  In the present invention, the solvent containing the first compound, the second compound, the third compound, and the ammonia is water (preferably pure water such as ion-exchanged water and distilled water). .

  The content of the first compound in the oxide complex precursor aqueous solution of the present invention is preferably 0.05 mol / L or more, and preferably 0.2 mol / L to 2.0 mol / L. More preferred. Moreover, as content of a 2nd compound, it is preferable that it is 0.05 mol / L or more, and it is more preferable that it is 0.2 mol / L-1.0 mol / L. When the content of the first and second compounds is less than the lower limit, the concentrations of the first and second compounds tend to be too low and the production efficiency tends to decrease. When the concentrations of the first and second compounds become too high, the reaction does not occur uniformly when baked, and the oxide composite tends to be unable to be produced uniformly.

  Moreover, as content of the 2nd metal element in such a 2nd compound, it is 0.2-5 times in molar conversion with respect to content of the 1st metal element in a 1st compound. It is preferable to do. By including the first compound and the second compound so that the content ratio of the first and second metal elements is the above ratio, the obtained oxide composite exhibits a higher NOx storage capacity. It becomes possible to make it. Further, when the content of the second metal element in the second compound is less than 0.2 times in molar ratio with respect to the content of the first metal element in the first compound, the single phase of the first compound is The ratio of the resulting oxide composite decreases and the effect tends to decrease. On the other hand, if it exceeds 5 times, the single phase of the second compound increases, and the oxide composite obtained in the same manner The ratio tends to decrease.

  Furthermore, the content of the third compound is preferably 0.15 mol / L or more, and more preferably 0.7 mol / L to 2.0 mol / L. When the content of the third compound is less than the lower limit, the content of the polydentate ligand with respect to the first compound and the second compound is decreased. Therefore, in the aqueous solution, the first compound and the second compound are contained. It tends to be difficult to hold the compound in a close state. On the other hand, when the upper limit is exceeded, the concentration of the first compound and the second compound tends to decrease, and the supporting efficiency tends to decrease. .

  Moreover, as content of such a 3rd compound, it is 2 times or more (more preferably 2.5 to 10 times) in molar conversion with respect to content of the metal element contained in a said 2nd compound. It is preferable that When the content of the third compound is less than twice the molar content of the metal element contained in the second compound, it is difficult to form a complex with the second compound in an aqueous solution. Therefore, it becomes difficult to hold the first compound and the second compound in a close state, and the production of the oxide composite tends to be difficult.

  In addition, the ammonia content is preferably 0.4 mol / L or more, and more preferably 2.0 mol / L to 10 mol / L. When the ammonia content is less than the lower limit, precipitation tends to occur in the resulting aqueous solution. On the other hand, when the upper limit is exceeded, the concentration of the first compound and the second compound is decreased, thereby supporting efficiency. Tend to decrease.

  Furthermore, the ammonia content is preferably 2 times or more (more preferably 2.8 to 5 times) in terms of mole relative to the content of the third compound. If the ammonia content is less than twice the molar content of the third compound, it is difficult to contain the first compound and the second compound in a stable state, and precipitation tends to occur. There is a tendency.

  In addition, as a method for producing the aqueous oxide complex precursor solution of the present invention, the first compound, the second compound, the third compound, and ammonia can be dissolved in water. The method is not particularly limited. As a suitable method for producing such an oxide complex precursor aqueous solution of the present invention, for example, a third compound is dissolved in water, and then the second compound is added to form a precipitate. Then, ammonia is added to dissolve the precipitate again, and then the first compound is further added to the solution and stirred. After the precipitate is formed, the oxide complex precursor is dissolved again. The method of manufacturing body aqueous solution is mentioned. Alternatively, an oxide complex precursor aqueous solution may be manufactured using an ammonium salt (for example, ammonium citrate) obtained by combining a third compound and ammonia in advance.

  The oxide complex precursor aqueous solution of the present invention has been described above. Hereinafter, the method for producing the oxide complex of the present invention will be described.

  The method for producing an oxide complex of the present invention is a method for producing an oxide complex by firing the aqueous oxide complex precursor solution of the present invention.

  Such firing conditions are not particularly limited, but for example, heating in the air is preferably performed in a temperature range of 300 ° C. to 600 ° C., and more preferably heating is performed in a temperature condition of 300 ° C. to 500 ° C. Further, the heating time varies depending on the heating temperature and cannot be generally described, but it can be set to about 1 to 3 hours.

  An oxide composite can be produced by firing the aqueous oxide composite precursor solution of the present invention under such firing conditions. The oxide composite thus obtained has the peak area of the first metal element determined by TEM-EDX analysis at 20 or more measurement points of 10 nm square on the surface of the oxide composite. Ratio of the peak area of the first metal element to the sum of the peak areas of the two metal elements ([peak area of the first metal element] / [sum of the peak area of the first metal element and the peak area of the second metal element]) The standard deviation of the distribution is 10% or less. That is, using the oxide complex precursor aqueous solution of the present invention in which the first compound and the second compound are held in proximity to each other, the oxide complex obtained by firing the oxide complex is The one metal element and the second metal element are sufficiently uniformly mixed and sufficiently refined. Therefore, the obtained oxide composite can exhibit sufficiently high NOx occlusion performance, and a sufficient amount of NOx can be efficiently occluded by bringing NOx into contact therewith.

  As mentioned above, although the manufacturing method of the oxide composite of this invention was demonstrated, next, the oxide composite of this invention is demonstrated.

The oxide composite of the present invention includes at least one first metal element selected from the group consisting of alkali metals and alkaline earth metals, and at least one second metal element selected from the group consisting of rare earth metals. An oxide composite containing
Of the first metal element relative to the sum of the peak area of the first metal element and the peak area of the second metal element obtained from TEM-EDX analysis at 20 or more measurement points of 10 nm square on the surface of the oxide composite. The standard deviation of the distribution of the ratio of the peak areas ([peak area of the first metal element] / [sum of the peak area of the first metal element and the peak area of the second metal element]) is 10% or less. To do.

  The alkali metal and alkaline earth metal that can be selected as the first metal element according to the present invention, and the rare earth metal that can be selected as the second metal element according to the present invention are described in the above-described aqueous oxide composite solution of the present invention. The same as the first metal element and the second metal element. In addition, as such a first metal element, barium is preferable from the viewpoint of having a high basicity and capable of exhibiting a sufficiently high NOx occlusion ability when an oxide is formed. As the second metal element, From the viewpoint of having a relatively high specific surface area when the oxide is formed, cerium is preferable.

  Further, the combination of the first metal element and the second metal element contained in such an oxide composite is not particularly limited, but from the viewpoint of using it as a NOx storage material, Ba (first metal element), It is preferable to use a combination of Ce (second metal element), and from the viewpoint of use as a SOx storage material, Ba or Mg (first metal element) and Ce or Y (second metal element) are combined. It is preferable to use it.

In the TEM-EDX analysis employed in the present invention, a TEM-EDX apparatus in which a conventionally known transmission electron microscope (TEM) is equipped with a conventionally known energy dispersive X-ray spectrometer (EDX analyzer) as a measuring apparatus. Can be used. In such a TEM-EDX analysis, first, using a TEM-EDX apparatus, in an arbitrary region on the surface of the oxide composite, an energy dispersive X-ray fluorescence spectrum in a 10 nm square measurement point. Ask for. Next, from the obtained energy dispersive X-ray fluorescence spectrum, the peak area derived from the first metal element and the peak area derived from the second metal element are obtained, and the peak area of the first metal element is obtained. The ratio (area ratio) of the peak area of the first metal element to the sum of the peak area of the second metal element and the sum of the peak area of the second metal element is determined. In addition, such a peak area ratio is represented by the formula:
[Peak area ratio (%)] = ([Peak area of the first metal element] / [Sum of the peak area of the first metal element and the peak area of the second metal element]) × 100
Can be calculated by calculating. Further, the “peak” referred to here is one having a height difference of 1 cts or more from the baseline of the spectrum to the peak top. Further, such a peak appears at a position (BaLα line) where the energy is 4.5 KeV when the metal element is barium, for example, and a position (CeLα line) when the metal element is cerium. ).

  In addition, the standard deviation of the distribution of the peak area ratio is determined by performing a TEM-EDX analysis at any 20 or more measurement points to obtain the above peak area ratio at each measurement point. Based on the value, it can be obtained by calculating a standard deviation (%) of the distribution of the peak area ratio. In the oxide composite of the present invention, the standard deviation of such peak area ratio is 10% or less (more preferably 9% or less). Such an oxide composite having a standard deviation of more than 10% is not a sufficiently uniform mixture of the first metal element and the second metal element, and sufficiently suppresses sulfur poisoning. In addition, when the regeneration treatment is performed after sulfur poisoning, the desorption rate of the sulfur component is not sufficient.

  As a method for more reliably obtaining an oxide composite having a standard deviation of the peak area ratio distribution of 10% or less, the oxide composite precursor aqueous solution of the present invention is fired to obtain an oxide composite. A method can be mentioned. Therefore, the oxide composite of the present invention is preferably obtained by firing the aqueous oxide composite precursor solution of the present invention. An oxide complex obtained by firing such an oxide complex precursor aqueous solution contains the first compound and the second metal element containing the first metal element in the oxide complex precursor aqueous solution. Since the second compound to be contained is held at a high concentration and in a stable state, the first metal element and the second metal element are sufficiently uniformly mixed and refined. In addition, the conditions at the time of such baking are the same as the conditions at the time of baking demonstrated in the manufacturing method of the oxide composite of the said invention.

  Further, the shape of such an oxide composite is not particularly limited, and may be a powder shape, a pellet shape, or the like. Alternatively, the oxide composite precursor aqueous solution of the present invention may be supported on a carrier and then baked to support the oxide composite on the support.

  Moreover, when such an oxide composite is in a powder form, the average particle diameter of the powdered oxide composite particles is preferably 0.1 to 20 μm, and preferably 1 to 10 μm. Is more preferable. When the average particle size is less than the lower limit, handling tends to be difficult. On the other hand, when the upper limit is exceeded, the contact property with the reaction gas is lowered, and the NOx and SOx occlusion performance tends to be lowered. . In addition, such an average particle diameter can be calculated | required by observing with a scanning electron microscope (SEM), and taking the particle size distribution of arbitrary 100 particles.

Furthermore, when such an oxide composite is in powder form, the specific surface area is preferably ⁵ to 200 m ² / g. When such a specific surface area is less than the lower limit, the number of surface sites effective for the reaction tends to be insufficient. On the other hand, when the upper limit is exceeded, thermal stability is lowered and the specific surface area tends to be lowered.

Such an oxide composite can be suitably used as a material for an exhaust gas purification catalyst (for example, NOx storage material, SOx storage material, etc.). For example, in the case where the oxide composite is an oxide composite of barium (first metal element) and cerium (second metal element), the oxide composite is brought into contact with exhaust gas such as an automobile. Furthermore, NOx in the exhaust gas can be occluded as Ba (NO ₃ ) ₂ and removed to purify the exhaust gas. In addition, such oxide composites are excellent in sulfur poisoning durability and have excellent sulfur poisoning recovery properties, and are therefore used for purifying sulfur-containing gases such as exhaust gases from automobiles. In such a case, a sufficiently high NOx storage performance can be exhibited over a long period of time.

  The oxide composite of the present invention has been described above. Next, the exhaust gas purifying catalyst of the present invention will be described.

  An exhaust gas purifying catalyst of the present invention comprises a support, the oxide composite of the present invention supported on the support, and a metal having oxidation-reduction ability supported on the support. is there.

  Such a carrier is not particularly limited, but is preferably a basic carrier because the oxide composite can be supported in a highly dispersed state, and is preferably an aluminum, zirconium, alkaline earth metal and A support containing an oxide of at least one third metal element selected from the group consisting of rare earth metals is more preferable. By using such a basic support, it is possible to sufficiently suppress the decomposition of the oxide composite due to the reaction between the first metal element in the oxide composite and the support, which is sufficiently high. The catalyst activity tends to be maintained.

  Examples of the alkaline earth metal element that can be selected as the third metal element include magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). From the viewpoint that the basicity of the oxide is higher, the dispersibility of the oxide composite is further improved, and the interaction between the noble metal and its oxide tends to be strong and the affinity tends to be large, Mg, Ca, Ba Is preferable, and Mg is particularly preferable. As rare earth elements, yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), gadolinium (Ga), terbium (Tb), dysprosium (Dy) ), Ytterbium (Yb), lutetium (Lu), etc. Among them, La, Ce, Nd, Pr, Y, from the viewpoint that the interaction with the noble metal and its oxide tends to be strong and has a high affinity. Sc is preferable, and La, Ce, Y, and Nd are more preferable. Such rare earth elements and alkaline earth metal elements having low electronegativity have strong interactions with noble metals and the oxide composites, and thus suppress transpiration and sintering of the noble metals, Deterioration can be sufficiently suppressed.

In addition, as a carrier containing such an oxide of a third metal element, a composite oxide of zirconia and / or alumina and at least one element selected from the group consisting of alkaline earth metal elements and rare earth elements From the viewpoint that a support containing bismuth is preferred and a more basic support, a composite oxide of Mg and Al is still more preferred. Such a composite oxide of Mg and Al is represented by the formula: MgO—nAl ₂ O ₃ , and the value of n can be various numerical values. When n is less than 1, free MgO is present and the heat resistance tends to decrease. On the other hand, when n exceeds 1, the composite oxide of Mg and Al becomes a two-phase system of MgO—xAl ₂ O ₃ and yAl ₂ O ₃ (1 ≦ x, x + y = n), and Al ₂ O ₃ and The reaction with the first metal element in the composite oxide tends to occur easily. Therefore, as the carrier containing the oxide of the third metal element, a carrier containing a metal oxide represented by the composition formula: MgAl ₂ O ₄ is particularly preferable.

Further, when the carrier is a carrier containing a metal oxide represented by the composition formula: MgAl ₂ O ₄ , for example, the carrier in the high temperature region and the carrier are compared with the case where the carrier is made of Al ₂ O _3. The solid phase reactivity with the oxide complex becomes lower, and when the catalyst is exposed to a high temperature, the NOx occlusion ability tends to be sufficiently suppressed. In addition, since the support containing MgAl ₂ O ₄ has higher basicity than the support made of Al ₂ O ₃ as described above, the oxide complex can be held in a stronger base state. There is a tendency. In general, since the NOx purification performance in the high temperature range is proportional to the amount of base points, the use of a carrier containing MgAl ₂ O ₄ tends to increase the NOx storage performance in the high temperature range. In the conventional catalyst supporting conventional NOx-absorbing material to a carrier containing MgAl ₂ O _4, since the sulfate of the NOx storage material on the carrier containing MgAl ₂ O ₄ is more stabilized, The durability against sulfur poisoning was low. However, in the present invention, since the oxide composite is supported in a finely dispersed and highly dispersed state, the sulfate of the oxide composite is destabilized on the MgAl ₂ O ₄ support, Small decrease in activity due to sulfur poisoning. Further, since the dispersibility of the oxide composite is particularly excellent on a strongly basic carrier such as a carrier containing MgAl ₂ O ₄ , when a carrier containing MgAl ₂ O ₄ is used, When the regeneration treatment is performed after poisoning, the desorption rate of the sulfur component from the catalyst becomes faster, and the decrease in activity due to sulfur poisoning tends to be more sufficiently suppressed.

Further, the composition formula: In the carrier containing metal oxide represented by MgAl ₂ O _4, the content of metal oxide represented by MgAl ₂ O _4, 10 to 90 mass relative to the total weight of the carrier %, And more preferably 30 to 70% by mass. When the content of the metal oxide represented by MgAl ₂ O ₄ in such a support is less than the lower limit, the effect obtained by the metal oxide represented by MgAl ₂ O ₄ when the oxide composite is supported. On the other hand, if the upper limit is exceeded, there is a tendency that it is difficult to receive the merit of combined use with other carriers in terms of expansion of the active temperature range and improvement of sulfur poisoning durability.

Moreover, in such a support | carrier, in addition to the oxide of the said 3rd metal element, the oxide of another metal element can further be contained. Such other metal elements are not particularly limited, and known metal oxides that can be contained in the carrier of the exhaust gas purifying catalyst can be used as appropriate. Among these, titanium, silicon, iron, An oxide of a fourth metal element selected from the group consisting of manganese and tungsten is preferred. Therefore, the carrier according to the present invention may contain, for example, a composite oxide of titania (TiO ₂ ) and zirconia (ZrO ₂ ), a composite oxide of titania (TiO ₂ ) and ceria (CeO ₂ ), and the like. Good.

Further, if the carrier contains a metal oxide represented by MgAl ₂ O _4, it preferably contains a composite oxide of TiO ₂ and ZrO ₂ The _(TiO 2 -ZrO ₂₎ further. In such a composite oxide (TiO ₂ —ZrO ₂ ), ZrO ₂ is solid-solved in the anatase phase of TiO ₂ , and TiO ₂ is solid-solved in the tetragonal phase of ZrO ₂ , so that they are in solid solution with each other, and are thermally stable. High nature. Therefore, when such a composite oxide (TiO ₂ —ZrO ₂ ) is contained, the decrease in specific surface area tends to be suppressed even when exposed to high temperatures. Further, in such a composite oxide (TiO ₂ —ZrO ₂ ), since the solid solution as described above is formed, the solid phase reaction with the oxide composite is suppressed, and the function of TiO ₂ There is a tendency that a certain sulfur poisoning suppressing action is promoted. Therefore, it becomes possible to further improve heat resistance and sulfur poisoning durability by including a composite oxide of titania (TiO ₂ ) and zirconia (ZrO ₂ ). Although such TiO ₂ and the content ratio of TiO ₂ and ZrO ₂ in the composite oxide of ZrO ₂ is not particularly limited, the range of _{TiO 2 / ZrO 2 = 95 /} 5~5 / 95 in mass ratio Is preferred. When TiO ₂ is less than this range, the sulfur poisoning suppressing action is lowered, and when ZrO ₂ is less than this range, the heat resistance is lowered.

In addition, when a carrier in which a metal oxide represented by MgAl ₂ O ₄ and a composite oxide of TiO ₂ and ZrO ₂ are used as the carrier, a metal oxide represented by MgAl ₂ O ₄ and The mixing ratio with the composite oxide of TiO ₂ and ZrO ₂ is not particularly limited, but the ratio represented by the mass ratio of MgAl ₂ O ₄ : TiO ₂ —ZrO ₂ should be in the range of 4: 1 to 1: 4. Is preferred. If the content ratio of the metal oxide represented by MgAl ₂ O ₄ is less than the above lower limit, the heat resistance and catalytic activity tend to decrease. On the other hand, if the content exceeds the upper limit, the sulfur poisoning suppression effect tends to decrease. is there.

  Furthermore, the shape of the carrier according to the present invention is not particularly limited, but is preferably in the form of a powder because the specific surface area is improved and higher catalytic activity is obtained. When such a carrier is in powder form, the particle size (secondary particle size) of the carrier is not particularly limited, and is preferably 1 to 100 μm. If the particle diameter is less than the lower limit, it tends to be costly and difficult to handle, and on the other hand, if the upper limit is exceeded, the substrate for exhaust gas purification of the present invention will be described later. It tends to be difficult to stably form a catalyst coating layer.

The specific surface area of such carriers is preferably at ^{20 m} 2 / g or more, further preferably 50 to 300 m ² / g. If the specific surface area is less than the lower limit, it tends to be difficult to support a metal (preferably a noble metal) having an appropriate amount of redox ability to exhibit sufficient catalytic activity, while exceeding the upper limit. And, there is a tendency for the specific surface area to decrease due to thermal degradation. Such a specific surface area can be calculated as a BET specific surface area from an adsorption isotherm using a BET isotherm adsorption equation.

  Moreover, the manufacturing method in particular of the support | carrier concerning this invention is not restrict | limited, A well-known method can be employ | adopted suitably. For example, when producing a support containing two or more metal elements, an aqueous solution containing two or more metal elements containing at least a salt of the third metal element (for example, nitrate) is used. A method of producing a support containing the oxide of the third metal element by forming a coprecipitate of the metal element in the presence, filtering, washing and drying the obtained coprecipitate and further firing. Can be adopted.

  In the exhaust gas purifying catalyst of the present invention, the oxide composite of the present invention is supported on the carrier. Such an oxide composite can function as a so-called NOx occlusion material, SOx occlusion material, or the like by appropriately changing the combination of the first metal element and the second metal element in the catalyst. It is.

  As described above, such an oxide composite is preferably obtained by firing the aqueous oxide composite precursor solution of the present invention. In the oxide composite obtained by firing the aqueous oxide composite precursor solution of the present invention, the first metal element and the second metal element are finely composited, and are more uniform on the support. It tends to be more dispersed. In addition, the oxide complex obtained by firing the oxide complex precursor aqueous solution of the present invention is fired by the third compound having a polydentate ligand in the oxide complex precursor aqueous solution. By being oxidized and decomposed inside, the first metal element and the second metal element are uniformly mixed, and are supported in a highly dispersed state on the carrier, so that the NOx occlusion material and the SOx occlusion material It tends to be possible to keep the effective surface area as high enough.

  The oxide composite is preferably supported on the carrier in the form of finer particles. The average particle size of such oxide composite-supported particles is preferably 0.5 to 10 nm, and more preferably 0.5 to 5 nm. If the particle size of the oxide composite is less than the lower limit, a uniform composite tends to be difficult to obtain. On the other hand, if the upper limit is exceeded, the number of surface sites effective for storing NOx and SOx tends to decrease. . Note that the average particle diameter of such supported particles can be obtained by XRD measurement or TEM observation.

  The method for supporting the oxide composite on the support is not particularly limited as long as it is a method capable of supporting the oxide composite of the present invention on the support, but the oxide of the present invention is not particularly limited. It is preferable to employ a method of impregnating a carrier with an aqueous solution of a complex precursor and baking it. Such firing conditions are the same as the firing conditions described in the method for producing an oxide composite of the present invention.

  In the exhaust gas purifying catalyst of the present invention, a metal having oxidation-reduction ability is supported on the carrier. Examples of such a metal having redox ability include noble metals such as platinum, rhodium, palladium, osmium, iridium, and gold, silver, copper, cobalt, iron, and the like, but a catalyst having a higher exhaust gas purification catalyst is obtained. From the viewpoint of showing activity, noble metals such as platinum, rhodium and palladium are preferable.

  In the exhaust gas purifying catalyst of the present invention, the supported amount of the metal having oxidation-reduction ability is 0.05 to 10% by mass (more preferably 0.1 to 5% by mass) with respect to the mass of the catalyst. It is preferable. If the amount of the metal having the redox ability is less than the lower limit, the catalytic activity obtained by the metal having the redox ability tends to be insufficient, while if the upper limit is exceeded, the cost increases and the cost increases. Metal grain growth tends to occur easily.

  In the exhaust gas purifying catalyst of the present invention, it is preferable that the metal having oxidation-reduction ability is supported on a carrier in the form of finer particles. The particle diameter of the metal having such redox ability is more preferably 1 to 20 nm, and more preferably 1 to 10 nm. If the particle diameter of the metal having the redox capacity is less than the lower limit, it tends to react with the support and oxidize and deactivate, whereas if it exceeds the upper limit, it becomes difficult to obtain a high catalytic activity. There is a tendency.

  The method for supporting the metal having the oxidation-reduction ability on the carrier is not particularly limited. For example, when the metal having the oxidation-reduction ability is a noble metal, a salt of a noble metal (for example, a dinitrodiamine salt), A method in which an aqueous solution containing a complex (for example, a tetraammine complex) is brought into contact with the carrier, dried, and further baked can be employed.

  The form of the exhaust gas purifying catalyst of the present invention is not particularly limited, and may be a form of a honeycomb-shaped monolith catalyst, a pellet-shaped pellet catalyst, or the like. The substrate used here is not particularly limited, and is appropriately selected depending on the use of the obtained catalyst, etc., but a DPF substrate, a monolith substrate, a pellet substrate, a plate substrate, etc. are suitably employed. Is done. Also, the material of such a base material is not particularly limited, but a base material made of a ceramic such as cordierite, silicon carbide, mullite, or a base material made of a metal such as stainless steel including chromium and aluminum is suitably employed. Is done. Further, the method for producing the catalyst in the case of using such a substrate is not particularly limited. For example, after the carrier is supported on a monolithic substrate to form a coat layer made of the above carrier powder, the coat layer A method in which a metal having oxidation / reduction ability (preferably a noble metal) is supported and then an oxide composite is supported on the coating layer, or a carrier that has previously supported a metal having oxidation-reduction ability, is used as a monolith. For example, a method of supporting an oxide composite on the coating layer after the coating layer is formed on the substrate can be employed.

  The exhaust gas purifying catalyst of the present invention is preferably subjected to a regeneration treatment capable of desorbing a sulfur component when sulfur poisoning occurs due to long-term use. Such a regeneration treatment method is not particularly limited, and a known method such as a method of desorbing a sulfur component by bringing a predetermined lean gas and rich gas into contact with the catalyst alternately can be appropriately employed. In the exhaust gas purification catalyst of the present invention, by performing such regeneration treatment, the NOx purification performance in the low temperature region of the exhaust gas purification catalyst tends to be improved as compared with an unused exhaust gas purification catalyst. It is in. The reason why the NOx purification performance is improved in such a low temperature region is not necessarily clear, but the base strength of the oxide complex supported on the carrier is slightly weakened by performing the regeneration treatment after sulfur poisoning. The present inventors speculate that this is because the activity of the metal having oxidation-reduction ability supported on the carrier is improved.

  While the exhaust gas purification catalyst of the present invention has been described above, the exhaust gas purification method of the present invention will be described below.

  The exhaust gas purification method of the present invention is a method characterized by purifying exhaust gas by bringing exhaust gas containing nitrogen oxides into contact with the exhaust gas purification catalyst of the present invention in an oxygen-excess atmosphere.

The “oxygen-excess atmosphere” in the present invention refers to an atmosphere in which an oxidizing gas such as oxygen or nitrogen oxide is stoichiometrically excessive with respect to a reducing gas such as H ₂ , CO, or HC. In the present invention, the exhaust gas containing nitrogen oxides is brought into contact with the exhaust gas purifying catalyst of the present invention in such an oxygen-excess atmosphere. Thus, in the exhaust gas purification method of the present invention, since the exhaust gas purification catalyst of the present invention is used, NO _x is sufficiently removed even in an environment where the exhaust gas containing sulfur components (SO ₂ etc.) is exposed. It is possible to purify. Therefore, the exhaust gas purification method of the present invention can be employed in a method for purifying exhaust gas discharged from, for example, an internal combustion engine of an automobile.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
0.9 mol of citric acid (manufactured by Wako Pure Chemical Industries) was dissolved in 165 ml of ion exchange water and heated to 80 ° C., and then 0.3 mol of cerium acetate (manufactured by Wako Pure Chemical Industries) was added to the resulting solution and stirred. After producing a precipitate, 170 ml of 28% by mass NH ₃ water was added dropwise to dissolve the precipitate and cooled to room temperature to obtain an aqueous cerium citrate solution (content of cerium ammonium citrate: 0.65 mol / L). Prepared. Then, after adding 16 ml of 2.16 mol / L barium acetate aqueous solution to 54 ml of the obtained ammonium cerium citrate aqueous solution, the precipitate was stirred to form an oxide composite containing Ba and Ce by dissolving the precipitate again. A body precursor aqueous solution was prepared. The Ba / Ce molar ratio in the aqueous solution is 1, and the concentrations of Ba and Ce are 0.5 mol / L.

(Example 2)
Citric acid (manufactured by Wako Pure Chemical Industries) 0.9 mol was dissolved in 165 ml of ion exchange water, and 170 ml of 28% NH ₃ water was added to prepare an aqueous ammonium citrate solution. Next, 0.3 mol of cerium acetate (manufactured by Wako Pure Chemical Industries, Ltd.) was added to the obtained ammonium citrate aqueous solution and stirred, and an aqueous cerium citrate aqueous solution (content of cerium ammonium citrate: 0.65 mol / L) was added. Prepared. Subsequently, after adding 16 ml of 2.16 mol / L barium acetate aqueous solution to 54 ml of obtained cerium ammonium citrate aqueous solution, it stirred and the oxide complex precursor aqueous solution containing Ba and Ce was prepared. The Ba / Ce molar ratio in the aqueous solution is 1, and the concentrations of Ba and Ce are 0.5 mol / L.

(Comparative Example 1)
A BaCe-containing aqueous solution was prepared by dissolving 0.1 mol of cerium acetate (manufactured by Wako Pure Chemical Industries, Ltd.) and 0.1 mol of barium acetate in 300 ml of ion-exchanged water. The Ba / Ce molar ratio in the aqueous solution is 1, and the concentrations of Ba and Ce are 0.31 mol / L.

(Comparative Example 2)
An aqueous barium acetate solution was prepared by dissolving 0.3 mol of barium acetate in 114 ml of ion-exchanged water. The Ba concentration in the aqueous solution is 2.16 mol / L.

(Comparative Example 3)
0.9 mol of citric acid (manufactured by Wako Pure Chemical Industries) was dissolved in 165 ml of ion-exchanged water and heated to 80 ° C. to obtain a solution. Next, 0.3 mol of cerium acetate (manufactured by Wako Pure Chemical Industries, Ltd.) was added to the resulting solution and stirred to form a precipitate, and then 139 ml of an aqueous 2.14 mol / L barium acetate solution was further added. Thus, when citric acid, cerium acetate and barium acetate were added to ion-exchanged water, precipitation occurred and a stable aqueous solution could not be obtained.

(Comparative Example 4)
0.3 mol of cerium acetate (manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in 303 ml of ion-exchanged water. After the addition of the resulting solution to 2.14mol / L aqueous solution of barium acetate 139 ml, it was further added NH ₃ water 170ml of 28 wt%. Thus, when ammonia, cerium acetate, and barium acetate were added to ion-exchanged water, gelation proceeded and a stable aqueous solution could not be obtained.

(Synthesis Example 1: Preparation of Pt-supported catalyst)
First, 100 g of alumina, 100 g of titania-zirconia composite oxide, 50 g of zirconia carrying 0.5 g / 50 g of Rh, and 20 g of ceria-zirconia composite oxide are contained in a hexagonal cell cordierite monolith substrate having a diameter of 30 mm × 50 mmL. The carrier was coated at a rate of 270 g / L to obtain a carrier-supporting substrate. Next, using a dinitrodiammine platinum nitric acid solution, Pt was selectively adsorbed and supported at 2 g / L with respect to the carrier-supporting substrate to obtain a Pt-supporting substrate. Thereafter, the obtained Pt-supported base material was calcined in the atmosphere at a temperature condition of 300 ° C. for 3 hours to prepare a Pt-supported catalyst.

(Example 3)
The aqueous oxide complex precursor solution obtained in Example 1 was loaded on the Pt-supported catalyst obtained in Synthesis Example 1 with a supported amount of Ba and Ce of 0.2 mol / L (Ba) and 0.2 mol / L ( The Pt-supported catalyst is impregnated with the oxide composite precursor aqueous solution by impregnation so as to be Ce), and then calcined in the atmosphere at a temperature of 300 ° C. for 3 hours, and the Pt-supported catalyst An oxide composite was formed thereon to prepare an exhaust gas purification catalyst (NOx occlusion reduction type catalyst). In addition, when the method similar to the TEM-EDX analysis mentioned later was employ | adopted and the TEM-EDX analysis was performed with respect to the oxide composite in the exhaust gas purification catalyst obtained in the present Example, on the alumina support | carrier. The standard deviation of the distribution of the area ratio of the Ba peak area to the sum of the Ba peak area and the Ce peak area was 8.7%.

Example 4
A synthesis example using the same method as in Example 3 except that the oxide complex precursor aqueous solution obtained in Example 2 was used instead of the oxide complex precursor aqueous solution obtained in Example 1. An oxide complex was formed on the Pt-supported catalyst obtained in 1 to prepare an exhaust gas purifying catalyst (NOx occlusion reduction type catalyst). In addition, when the method similar to the TEM-EDX analysis mentioned later was employ | adopted and the TEM-EDX analysis was performed with respect to the oxide composite in the exhaust gas purification catalyst obtained in the present Example, on the alumina support | carrier. The standard deviation of the distribution of the area ratio of the Ba peak area to the sum of the Ba peak area and the Ce peak area was 8.6%.

(Comparative Example 5)
The same method as in Example 3 was adopted except that the BaCe-containing aqueous solution obtained in Comparative Example 1 was used instead of the oxide complex precursor aqueous solution obtained in Example 1, and obtained in Synthesis Example 1. An oxide composite was formed on the Pt-supported catalyst to prepare an exhaust gas purifying catalyst (NOx occlusion reduction type catalyst) for comparison. In addition, when the method similar to the TEM-EDX analysis mentioned later was employ | adopted and the TEM-EDX analysis was performed with respect to the oxide composite in the exhaust gas purification catalyst obtained by this comparative example, on an alumina support | carrier. The standard deviation of the distribution of the area ratio of the Ba peak area to the sum of the Ba peak area and the Ce peak area was 13.1%.

(Comparative Example 6)
The barium acetate aqueous solution obtained in Comparative Example 2 was used in place of the oxide complex precursor aqueous solution obtained in Example 1, and the amount of Ba supported on the Pt-supported catalyst obtained in Synthesis Example 1 was used. Except for impregnation so as to be 0.2 mol / L, the same method as in Example 3 was adopted to form barium oxide on the Pt-supported catalyst. NOx storage reduction catalyst) was prepared.

<Performance test of exhaust gas purifying catalyst (Examples 3 to 4 and Comparative Examples 5 to 6)>
[Durability test 1]
Using the exhaust gas purifying catalysts (NOx occlusion reduction type catalysts) obtained in Examples 3 to 4 and Comparative Examples 5 to 6, the compositions shown in Table 1 were used for each catalyst at a temperature of 750 ° C. Lean gas and rich gas were allowed to flow for 5 hours while varying at intervals of lean / rich = 110 seconds / 10 seconds.

[Durability test 2]
Using the exhaust gas purifying catalysts (NOx occlusion reduction type catalysts) obtained in Examples 3 to 4 and Comparative Examples 5 to 6, air was passed through each catalyst for 5 hours under a temperature condition of 750 ° C. Thereafter, pretreatment was performed by circulating a pretreatment rich gas having the composition shown in Table 2 for 10 minutes under a temperature condition of 650 ° C. Subsequently, the rich gas and the lean gas for sulfur poisoning treatment shown in Table 2 are changed at intervals of lean / rich = 120 seconds / 3 seconds with respect to each of the obtained pretreated catalysts under a temperature condition of 400 ° C. The mixture was allowed to flow for 41 minutes while supplying 3 g of sulfur per 2 L of catalyst to perform S poisoning treatment. Next, for each catalyst of the S poisoning treatment, a lean gas for S regeneration treatment having the composition shown in Table 2 was circulated for 5 minutes under a temperature condition of 600 ° C., and then the S regeneration having the composition shown in Table 2 was performed. A rich gas for treatment was circulated for 10 minutes to desorb the poisoned S, and the catalyst was regenerated.

[NOx purification test 1]
Using the exhaust gas purifying catalysts (NOx occlusion reduction type catalysts) obtained in Examples 3 to 4 and Comparative Examples 5 to 6 after the endurance test 1, each catalyst was subjected to a temperature condition of 400 ° C. in Table 3 The rich gas and the lean gas having the composition shown in FIG. 1 were circulated while varying at intervals of lean / rich = 120 seconds / 3 seconds, and the NOx purification rate in a steady state was measured. All space velocities (SV) were set to 51400 h ⁻¹ . Further, NOx purification rate, for each catalyst, the concentration of the NO _x contained in each of the front and rear of the gas that contacts the catalyst was measured to determine based on the value of the concentration of NO _x. The obtained results are shown in FIG.

[NOx purification test 2]
Except for using the exhaust gas purification catalysts (NOx storage reduction type catalysts) obtained in Examples 3 to 4 and Comparative Examples 5 to 6 after the durability test 2, the same method as in the NOx purification test 1 was adopted and NOx was used. The purification rate was measured. The obtained results are shown in FIG.

  As is apparent from the results shown in FIG. 1, the exhaust gas obtained by employing the oxide composite precursor aqueous solution of the present invention (Examples 1 and 2) and employing the method for producing the oxide composite of the present invention. The purification catalyst (NOx storage reduction catalyst: Examples 3 to 4) was excellent in NOx purification rate after the durability test. On the other hand, when the oxide complex precursor aqueous solution according to the present invention was not used (Comparative Examples 5 to 6), the NOx purification rate after the durability test of the NOx storage reduction catalyst was low. It was.

  From such a result, the exhaust gas purifying catalyst (NOx occlusion reduction type catalyst: Examples 3 to 4) in which the oxide complex was supported using the oxide complex precursor aqueous solution (Examples 1 and 2) of the present invention. ), It was confirmed that the obtained oxide composite was sufficiently refined, and the oxide composite was supported on the catalyst in a sufficiently dispersed state, so that high NOx purification performance could be exhibited. .

(Example 5)
First, a hexagonal cell cordierite monolith substrate having a diameter of 30 mm × 50 mmL was coated with alumina as a catalyst carrier at a rate of 200 g / L to obtain a carrier-supporting substrate. Next, using a dinitrodiammine platinum nitric acid solution, Pt was selectively adsorbed and supported at 2 g / L on the carrier-supporting substrate to obtain a Pt-supporting substrate. Thereafter, the obtained Pt-supported base material was calcined in the atmosphere at a temperature condition of 300 ° C. for 3 hours to prepare a Pt-supported catalyst. Next, with respect to the obtained Pt-supported catalyst, the oxide composite precursor aqueous solution obtained in Example 1 was loaded with 0.2 and 0.2 mol / L of Ba and Ce, respectively. After impregnating with L (Ce), the Pt-supported catalyst supports the oxide composite precursor aqueous solution, and then calcined in the atmosphere at a temperature of 300 ° C. for 3 hours. An oxide complex was formed on the supported catalyst to prepare an exhaust gas purifying catalyst (NOx occlusion reduction type catalyst) of the present invention.

(Comparative Example 7)
Exhaust gas purification for comparison using the same method as in Example 5 except that the BaCe-containing aqueous solution obtained in Comparative Example 1 was used instead of the oxide complex precursor aqueous solution obtained in Example 1 Catalyst (NOx occlusion reduction type catalyst) was prepared.

<Performance Test of Exhaust Gas Purification Catalyst (Example 5 and Comparative Example 7)>
[TEM-EDX analysis]
The catalyst powder scraped from the coating layer (the coating layer formed on the monolith substrate) of the exhaust gas purification catalyst obtained in Example 5 and Comparative Example 7 was observed with a transmission electron microscope (TEM), and EDX analysis was performed on 32 measurement points of 10 nm square on the surface of the oxide composite in the catalyst powder. For such EDX analysis, a trade name “JEM-2200FS” manufactured by JEOL Ltd. was used as a measuring device.

  As a result of such measurement, transmission electron microscope (TEM) photographs of the exhaust gas purification catalyst obtained in Example 5 are shown in FIGS. 2 to 4, and the transmission type of the exhaust gas purification catalyst obtained in Comparative Example 7 is shown. An electron microscope (TEM) photograph is shown in FIGS. A square of 10 nm square indicated by 001 to 032 on FIGS. 2 to 5 is a measurement point in EDX analysis. Further, FIG. 8 shows an energy dispersive X-ray fluorescence spectrum at measurement points 001 to 007 (see FIG. 2) on the surface of the oxide complex of the exhaust gas purifying catalyst obtained in Example 5, and Comparative Example 7 FIG. 9 shows an energy dispersive X-ray fluorescence spectrum at measurement points 001 to 006 (see FIG. 5) on the surface of the oxide complex of the exhaust gas purifying catalyst obtained in the above.

Further, from such an EDX analysis result, the peak area of Ba (peak area of BaLα line) and the peak area of Ce (peak area of CeLα line) at each measurement point are calculated, and the formula:
[Peak area ratio] = ([Ba peak area] / [Sum of Ba peak area and Ce peak area]) × 100
The area ratio of the peak area of Ba to the sum of the peak area of Ba and the peak area of Ce at each measurement point was calculated. And the standard deviation of the distribution of area ratio was calculated | required from the value of the area ratio calculated in this way. Table 4 shows the obtained results.

  As is apparent from the results shown in Table 4, in the exhaust gas purifying catalyst of the present invention (Example 5), the first obtained from the TEM-EDX analysis at the measurement point on the surface of the supported oxide composite. Ratio of the peak area of the first metal element to the sum of the peak area of the metal element (Ba) and the peak area of the second metal element (Ce) ([peak area of the first metal element] / [peak of the first metal element] The standard deviation of the distribution of the area and the sum of the peak areas of the second metal elements]) was confirmed to be 10% or less. From these results, it was found that in the exhaust gas purifying catalyst of the present invention (Example 5), an oxide composite in which Ba and Ce were sufficiently uniformly mixed was supported on the support. On the other hand, in the exhaust gas purifying catalyst for comparison (Comparative Example 7), the standard deviation was a value exceeding 10%, and it was found that the dispersion degree of Ba and Ce varied. .

  From the results of such TEM observation and EDX analysis, when the oxide composite was supported using the aqueous oxide composite precursor solution (Example 1) of the present invention (Example 5), It was confirmed that the supported oxide composite was sufficiently refined, and confirmed that the oxide composite had a uniform dispersion in the macro distribution in the coating layer and the micro distribution in the nm order on the carrier powder. It was done.

[NOx purification test 3]
First, except for using the exhaust gas purifying catalyst obtained in Example 5 and Comparative Example 7, the same method as in the durability test 1 described above was adopted, and the exhaust gas purifying obtained in Example 5 and Comparative Example 7 was used. Durability tests were performed on the catalyst. Next, the NOx of the exhaust gas purification catalyst obtained in Example 5 and Comparative Example 7 was adopted by adopting the same method as in the above NOx purification test 1 except that each exhaust gas purification catalyst after the durability test was used. The purification rate was measured. The results obtained are shown in Table 5.

  As apparent from the results shown in Table 5, the exhaust gas purifying catalyst of the present invention (NOx occlusion reduction type catalyst: Example 5) obtained using the oxide composite precursor aqueous solution of the present invention (Example 1). ) Was confirmed to have an excellent NOx purification rate after the durability test. In contrast, the exhaust gas purification catalyst for comparison (Comparative Example 7) that did not use the oxide complex precursor aqueous solution according to the present invention had a low NOx purification rate after the durability test. confirmed. From these results, it was found that the exhaust gas purifying catalyst of the present invention (Example 5) on which the oxide composite of the present invention was supported had sufficiently high heat resistance.

(Example 6)
After 0.9 mol of citric acid (Wako Pure Chemical Industries) was dissolved in 165 ml of ion-exchanged water, 170 ml of 28% by mass NH ₃ water was added to prepare an aqueous ammonium citrate solution. Next, 0.3 mol of cerium acetate (Wako Pure Chemical Industries, Ltd.) was added to the obtained ammonium citrate aqueous solution and stirred to prepare an aqueous solution of cerium ammonium citrate (0.67 mol / L). Then, 16 ml of 2.16 mol / L barium acetate aqueous solution was added to 52 ml of the ammonium cerium citrate aqueous solution and stirred to prepare an oxide complex precursor aqueous solution containing Ba and Ce. The Ba / Ce molar ratio in the aqueous solution was 1, and the concentrations of Ba and Ce were 0.51 mol / L.

(Synthesis Example 2: Preparation of Pt-supported catalyst)
First, a hexagonal cell cordierite monolith substrate having a diameter of 30 mm × 50 mmL, MgAl ₂ O ₄ 100 g, TiO ₂ and ZrO ₂ composite oxide 100 g, ZrO ₂ 50 g carrying Rh at a ratio of 0.5 g / 50 g, and A carrier containing 20 g of a composite oxide of CeO ₂ and ZrO ₂ was coated at a rate of 270 g / L to obtain a carrier-supporting substrate. Next, using a dinitrodiammine platinum nitric acid solution, Pt was selectively adsorbed and supported at 2 g / L on the carrier-supporting substrate to obtain a Pt-supporting substrate. Thereafter, the obtained Pt-supported base material was calcined in the atmosphere at a temperature condition of 300 ° C. for 3 hours to prepare a Pt-supported catalyst.

(Example 7)
The aqueous oxide complex precursor solution obtained in Example 6 was loaded on the Pt-supported catalyst obtained in Synthesis Example 2 with a supported amount of Ba and Ce of 0.2 mol / L (Ba) and 0.2 mol / L ( The Pt-supported catalyst is impregnated with the oxide composite precursor aqueous solution by impregnation so as to be Ce), and then calcined in the atmosphere at a temperature of 300 ° C. for 3 hours, and the Pt-supported catalyst An oxide composite was formed thereon to prepare an exhaust gas purifying catalyst (NOx storage reduction catalyst) of the present invention. In addition, when the same method as the above-mentioned TEM-EDX analysis was adopted, and the TEM-EDX analysis was performed on the obtained oxide composite in the exhaust gas purification catalyst, Ba of MgAl ₂ O ₄ was analyzed. The standard deviation of the distribution of the area ratio of the peak area of Ba to the sum of the peak area and the peak area of Ce was 8.1%.

(Comparative Example 8)
The barium acetate aqueous solution was used instead of the oxide complex precursor aqueous solution obtained in Example 6, and the amount of Ba supported on the Pt-supported catalyst obtained in Synthesis Example 2 was 0.2 mol / L. Exhaust gas purification catalyst (NOx occlusion reduction type catalyst) for comparison was prepared in the same manner as in Example 7 except that the impregnation was performed as described above.

<Performance Test of Exhaust Gas Purification Catalysts (Example 3, Example 7, Comparative Example 6 and Comparative Example 8)>
[Measurement of S Desorption]
Except for using the exhaust gas purifying catalyst obtained in Example 3, Example 7, Comparative Example 6 and Comparative Example 8, the same method as in the above durability test 1 was adopted, and Example 3, Example 7, Durability tests were performed on the exhaust gas-purifying catalysts obtained in Comparative Examples 6 and 8. Next, for each exhaust gas purifying catalyst (Example 3, Example 7, Comparative Example 6 and Comparative Example 8) after the endurance test, the composition shown in Table 2 above was obtained under the temperature condition of 650 ° C. Pre-treatment was performed by flowing a pre-treatment rich gas for 10 minutes. Next, for each of the catalysts after the pretreatment, the sulfur poisoning rich gas and the lean gas shown in Table 2 were added at an interval of lean / rich = 120 seconds / 3 seconds under the temperature condition of 400 ° C. The mixture was allowed to flow for 41 minutes while being fluctuated, and 3 g of sulfur (S) was supplied per 2 L of catalyst to perform S poisoning treatment. Next, for each catalyst after S poisoning treatment, a lean gas for S regeneration treatment having the composition shown in Table 2 above was circulated for 5 minutes under a temperature condition of 600 ° C., and then the composition shown in Table 2 above. A rich gas for S regeneration treatment was circulated for 10 minutes (hereinafter simply referred to as “S desorption test”). In this way, S is desorbed from each exhaust gas purification catalyst, and the S desorption amount of each exhaust gas purification catalyst for 3 minutes and 10 minutes from the time when the gas for S regeneration treatment is introduced, Each amount was determined by measuring the amount of SO _{2 in} the gas after contacting the exhaust gas purification catalyst. The obtained result is shown in FIG.

  As is clear from the results shown in FIG. 10, in the exhaust gas purifying catalysts (Examples 3 and 7) of the present invention, a sufficiently high sulfur (S) component desorption performance immediately after the start of circulation of the regeneration gas. It was confirmed that the S desorption rate was sufficiently faster than the exhaust gas purifying catalysts for comparison (Comparative Examples 6 and 8). From these results, it was found that the catalyst for exhaust gas purification of the present invention (Example 3 and Example 7) can sufficiently suppress a decrease in catalyst activity due to sulfur poisoning.

[NOx purification test 4]
Exhaust gas purification obtained in Example 3, Example 7, Comparative Example 6 and Comparative Example 8 after performing the durability test 1 and the S desorption test under the same conditions as those for measuring the amount of S desorption. Example 3, Example 7, Comparative Example 6 and Comparative Example were adopted using the same method as in the NOx purification test 1 except that the catalyst was used and the temperature condition was changed from 400 ° C. to 300 ° C. The NOx purification rate of the exhaust gas purification catalyst obtained in 8 was measured. The obtained results are shown in FIG.

[NOx purification test 5]
Exhaust gas purification obtained in Example 3, Example 7, Comparative Example 6 and Comparative Example 8 after performing the durability test 1 and the S desorption test under the same conditions as those for measuring the amount of S desorption. Example 3, Example 7, Comparative Example 6 and Comparative Example were adopted using the same method as in the above NOx purification test 1 except that the catalyst was used and the temperature condition was changed from 400 ° C. to 500 ° C. The NOx purification rate of the exhaust gas purification catalyst obtained in 8 was measured. The obtained result is shown in FIG.

As is clear from the results shown in FIGS. 11 to 12, in the exhaust gas purifying catalyst (Example 3 and Example 7) of the present invention, the exhaust gas purifying catalyst for comparison (Comparative Example 6 and Comparative Example 8). It was confirmed that it exhibits sufficiently high NOx purification performance as compared with the above. It was also found that the exhaust gas purifying catalyst obtained in Example 7 containing MgAl ₂ O ₄ in the support exhibits higher NOx purification performance.

[NOx purification tests 6 and 7]
<NOx purification test 6>
Except for using the exhaust gas purifying catalyst obtained in Example 3, Example 7, Comparative Example 6 and Comparative Example 8, the same method as in the above durability test 1 was adopted, and Example 3, Example 7, Durability tests were performed on the exhaust gas-purifying catalysts obtained in Comparative Examples 6 and 8. Next, the NOx described above was used except that the exhaust gas purifying catalysts after the endurance test (Example 3, Example 7, Comparative Example 6 and Comparative Example 8) were used and the temperature condition was changed from 400 ° C to 300 ° C. By adopting the same method as in the purification test 1, the NOx purification rate of the exhaust gas purification catalysts obtained in Example 3, Example 7, Comparative Example 6 and Comparative Example 8 was measured.

<NOx purification test 7>
Except for using the exhaust gas purifying catalyst obtained in Example 3, Example 7, Comparative Example 6 and Comparative Example 8, the same method as in the above durability test 1 was adopted, and Example 3, Example 7, Durability tests were performed on the exhaust gas-purifying catalysts obtained in Comparative Examples 6 and 8. Next, the NOx described above was used except that the exhaust gas purifying catalysts (Example 3, Example 7, Comparative Example 6 and Comparative Example 8) after the durability test were used and the temperature condition was changed from 400 ° C to 500 ° C. By adopting the same method as in the purification test 1, the NOx purification rate of the exhaust gas purification catalysts obtained in Example 3, Example 7, Comparative Example 6 and Comparative Example 8 was measured.

From the results obtained in the NOx purification tests 4 to 7, the NOx purification rate before and after the S desorption test of the exhaust gas purification catalysts obtained in Example 3, Example 7, Comparative Example 6 and Comparative Example 8 was obtained. The maintenance rate was determined. In addition, this maintenance factor is calculated | required for every temperature conditions (300 degreeC or 500 degreeC) in the case of a NOx purification test, Formula:
[Maintenance rate (%)] = [NOx purification rate after S desorption test] / [NOx purification rate before S desorption test] × 100
Calculated by The obtained result is shown in FIG.

  As is apparent from the results shown in FIG. 13, the exhaust gas purifying catalysts (Examples 3 and 7) of the present invention have a NOx purification rate maintenance rate of 80% or more regardless of temperature conditions. It was confirmed that it had sufficiently high heat resistance and sulfur poisoning durability. On the other hand, the exhaust gas purification catalyst obtained in Comparative Example 6 did not have a sufficient maintenance rate of the NOx purification rate. Further, in the exhaust gas purification catalyst obtained in Comparative Example 8, the maintenance rate of the NOx purification rate during the NOx purification test at a temperature condition of 300 ° C. is sufficient, but during the NOx purification test at 500 ° C. The maintenance rate of the NOx purification rate was 70% or less, and it was confirmed that the maintenance rate of the NOx purification rate was extremely lowered by increasing the temperature condition, and the heat resistance was not sufficient.

  As described above, according to the present invention, a metal element that is a precursor of an oxide complex can be contained in an aqueous solution at a high concentration and in a stable state, and a sufficiently miniaturized oxide complex. It is possible to provide an oxide complex precursor aqueous solution capable of obtaining a body and a method for producing an oxide complex using the same, and to provide an oxide complex obtained thereby. Further, according to the present invention, the catalyst is provided with the oxide composite of the present invention, has sufficiently high heat resistance and sulfur poisoning durability, and is sufficiently excellent even when exposed to sulfur or high temperature for a long period of time. It is possible to provide an exhaust gas purification catalyst capable of exhibiting activity and an exhaust gas purification method using the exhaust gas purification catalyst.

  As described above, since the oxide complex precursor aqueous solution of the present invention can efficiently produce a sufficiently miniaturized oxide complex, the oxide complex precursor aqueous solution of the present invention comprises: It is useful as a material for producing NOx storage materials, SOx storage materials, NOx storage reduction catalysts, and the like.

It is a graph which shows the NOx purification rate of the catalyst for exhaust gas purification obtained in Examples 3-4 and Comparative Examples 5-6. 6 is a transmission electron microscope (TEM) photograph showing the state of an oxide complex in a specific region on the surface of an exhaust gas purifying catalyst obtained in Example 5. FIG. 6 is a transmission electron microscope (TEM) photograph showing the state of an oxide complex in a specific region on the surface of an exhaust gas purifying catalyst obtained in Example 5. FIG. 6 is a transmission electron microscope (TEM) photograph showing the state of an oxide complex in a specific region on the surface of an exhaust gas purifying catalyst obtained in Example 5. FIG. 10 is a transmission electron microscope (TEM) photograph showing the state of an oxide complex in a specific region on the surface of an exhaust gas purifying catalyst obtained in Comparative Example 7. 10 is a transmission electron microscope (TEM) photograph showing the state of an oxide complex in a specific region on the surface of an exhaust gas purifying catalyst obtained in Comparative Example 7. 10 is a transmission electron microscope (TEM) photograph showing the state of an oxide complex in a specific region on the surface of an exhaust gas purifying catalyst obtained in Comparative Example 7. 6 is a graph showing an energy dispersive X-ray fluorescence spectrum at measurement points 001 to 007 on the surface of an oxide complex of an exhaust gas purifying catalyst obtained in Example 5. 6 is a graph showing an energy dispersive X-ray fluorescence spectrum at measurement points 001 to 006 on the surface of an oxide complex of an exhaust gas purifying catalyst obtained in Example 5. It is a graph which shows the sulfur (S) desorption amount of each exhaust gas purification catalyst obtained in Example 3, Example 7, Comparative Example 6 and Comparative Example 8 when the sulfur (S) desorption test was performed. It is a graph which shows the NOx purification rate of the exhaust gas purification catalyst obtained in Example 3, Example 7, Comparative Example 6 and Comparative Example 8 under a temperature condition of 300 ° C. It is a graph which shows the NOx purification rate of the exhaust gas purification catalyst obtained in Example 3, Example 7, Comparative Example 6 and Comparative Example 8 under a temperature condition of 500 ° C. It is a graph which shows the maintenance rate of the NOx purification rate of the exhaust gas purification catalyst obtained in Example 3, Example 7, Comparative Example 6 and Comparative Example 8 before and after the S desorption test.

Claims (13)

A first compound which is a compound containing barium which is a first metal element, a second compound which is a compound containing cerium which is a second metal element and is cerium acetate , and a multidentate ligand An aqueous oxide complex precursor solution comprising a third compound and ammonia. The third compound is citric acid, oxalic acid, succinic acid, maleic acid, malic acid, adipic acid, tartaric acid, malonic acid, fumaric acid, aconitic acid, glutaric acid, ethylenediaminetetraacetic acid, lactic acid, glycolic acid, glyceric acid 2. The aqueous oxide complex precursor solution according to claim 1, which is at least one selected from the group consisting of: salicylic acid, mevalonic acid, ethylenediamine, ethyl acetoacetate, malonic ester, glycol, and pinacol. The aqueous oxide complex precursor solution according to claim 1 or 2, wherein the third compound is citric acid. Wherein the content of the third compound, of claim 1 to 3, characterized in that said at second second metal element 2 times or more on a molar basis relative to the content of which is contained in the compound The oxide complex precursor aqueous solution according to any one of the above. The content of the ammonia, oxide composite according to any one of claims 1-4, characterized in that said at third 2 times or more on a molar basis relative to the content of the compound Precursor aqueous solution. Oxide composite aqueous precursor solution according to any one of claims 1-5 in which the content of the ammonia, and wherein the at 0.4 mol / L or more. A method for producing an oxide complex, wherein the oxide complex precursor aqueous solution according to any one of claims 1 to 6 is fired to obtain an oxide complex. An oxide composite containing barium as the first metal element and cerium as the second metal element,
It is obtained by firing the oxide complex precursor aqueous solution according to any one of claims 1 to 6, and
Of the first metal element relative to the sum of the peak area of the first metal element and the peak area of the second metal element obtained from TEM-EDX analysis at 20 or more measurement points of 10 nm square on the surface of the oxide composite. The standard deviation of the distribution of the ratio of peak areas ([peak area of the first metal element] / [sum of the peak area of the first metal element and the peak area of the second metal element]) is 10% or less ,
Oxide composite, wherein. An exhaust gas purifying catalyst comprising: a support; the oxide composite according to claim 8 supported on the support; and a metal having oxidation-reduction ability supported on the support. 10. The exhaust gas purifying apparatus according to claim 9 , wherein the carrier contains an oxide of at least one third metal element selected from the group consisting of aluminum, zirconium, alkaline earth metal, and rare earth metal. catalyst. The exhaust gas-purifying catalyst according to claim 9 or 10 , wherein the carrier contains a metal oxide represented by a composition formula: MgAl ₂ O ₄ . 12. The carrier according to claim 9 , further comprising an oxide of a fourth metal element selected from the group consisting of titanium, silicon, iron, manganese, and tungsten. Exhaust gas purification catalyst. An exhaust gas purification method comprising purifying exhaust gas by bringing exhaust gas containing nitrogen oxides into contact with the exhaust gas purification catalyst according to any one of claims 9 to 12 in an oxygen-excess atmosphere.