JP2022073362A - Adsorption material of nitrogen oxide, and catalyst for automobile exhaust gas - Google Patents

Abstract

To provide an adsorption material of nitrogen oxides that efficiently collects by adsorption nitrogen oxides in an automobile exhaust gas and efficiently supplies the same by surface diffusion to a noble metal catalyst in the low temperature range where the catalyst is active, thereby to promote low-temperature removal of the nitrogen oxides, and to provide a catalyst for cleaning automobile exhaust gas made of the adsorption material.SOLUTION: A part of the cations (preferably, 4-34 mol% of a total amount of the cations) of a cerium oxide or a zirconium oxide are substituted with substituent ions composed of one or two of Nd3+ ion and Gd3+ ion. An adsorption material of nitrogen oxides has a structure that the substituent ions are present in an oxygen polyhedron location of a cubic crystal. The adsorption material of nitrogen oxides has an adsorption power that at least nitrogen monoxide among the nitrogen oxides adsorbed by the adsorption material of nitrogen oxides is desorbed in the temperature range of 275°C or higher and 325°C or lower.SELECTED DRAWING: Figure 1

Description

The present invention relates to an automobile exhaust gas catalyst containing a nitrogen oxide adsorbing material and a nitrogen oxide adsorbing material.

Conventionally, a three-way catalyst has been used as a method for purifying nitrogen oxides (NOx), which is a harmful substance in the exhaust gas of automobiles. The exhaust gas is purified by simultaneously oxidizing carbon monoxide (CO) and hydrocarbon (HC) and reducing nitrogen oxides (NOx) with a three-way catalyst. As a three-way catalyst, a noble metal (for example, Pt, Rh, Pd, Ir, Ru, etc.) is supported on a fire-resistant oxide porous body such as an alumina porous body having a high surface area, and this is used as a base material, for example, fire resistant. A material that is supported on a honeycomb structure base material made of ceramic or metal, or supported on fire-resistant particles is generally used.

In the three-way catalyst used for exhaust gas purification of a gasoline engine, in order to efficiently remove nitrogen oxides in the exhaust gas, it is necessary to keep the catalyst temperature at the activation temperature of the noble metal (about 250 ° C.) or higher. That is, the nitrogen oxides in the exhaust gas are discharged without being purified for several tens of seconds immediately after the engine is started. In particular, nitrogen oxide emissions are high in cold regions and in winter. Therefore, while the catalyst temperature immediately after starting the engine does not reach the activation temperature for purifying nitrogen oxides in the exhaust gas, the nitrogen oxides are once occluded or adsorbed, and the NOx occlusal is occluded after reaching the activation temperature. Reduction catalysts have been proposed. As the NOx storage reduction catalyst, a NOx storage material composed of a noble metal (for example, Pt, Rh, etc.) and an alkaline earth metal element such as barium is supported on a fire-resistant oxide porous body such as an alumina porous body having a high surface area. The one that has been made is used.

However, in the NOx storage reduction catalyst, there is a limit amount (saturation amount) in the amount of NOx that can be stored in the NOx storage material. It is discharged. Therefore, it is required to improve the low-temperature catalytic activity so that high purification activity can be obtained even when the temperature of the exhaust gas is in the low-temperature region.

As an adsorbent that functions in a low temperature range from nitrogen oxides contained in automobile exhaust gas, Patent Document 1 contains zeolite, Patent Document 2 contains hollandite-type metal oxides, and Patent Document 3 contains ceria, magnesia, and alumina. An adsorbent having two types of nitrogen oxide adsorbent layers, that is, a porous carrier made of the above, a carrier supporting an active metal element, and a porous carrier containing ceria as a main component has been proposed.

Further, as a nitrogen oxide adsorbing material suitable for a lean burn engine, Patent Document 4 describes a material having a magnet plumbit structure, and Patent Document 5 describes a composite oxide in which titanium, cerium and copper are solid-dissolved. Reference numeral 6 is a catalyst in which a composite oxide containing ceria and rare earth oxides is supported with a noble metal and a solid acid, and at least one metal oxide selected from vanadium, tungsten, molybdenum, copper, iron, cobalt, nickel and manganese. Have been proposed respectively.

Japanese Unexamined Patent Publication No. 2008-36544 Japanese Unexamined Patent Publication No. 2011-115782 Japanese Unexamined Patent Publication No. 2009-82846 Japanese Unexamined Patent Publication No. 2004-12202077 Japanese Unexamined Patent Publication No. 2016-43310 Japanese Unexamined Patent Publication No. 2008-62235

As mentioned above, various materials are known as nitrogen oxide adsorbing materials, and so far, high nitrogen oxide adsorption amount and thermal durability in the low temperature region are required for automobile exhaust gas purification catalysts, and development corresponding to them has been developed. It has been done. However, the requirements for nitrogen oxide purification catalysts also change as the components and temperature emitted from the engine change in order to improve fuel efficiency. Specifically, it not only adsorbs nitrogen oxides at low temperatures, but also improves the purification performance of nitrogen oxides at low temperatures (low-temperature decomposition of nitrogen oxides, low-temperature reduction decomposition).

Therefore, until now, the development of nitrogen oxide adsorbing materials has mainly focused on improving adsorption or occlusion performance in the low temperature range. Patent Documents 1 to 3 aim at adsorbing nitrogen oxides at 150 ° C. or 200 ° C. or lower, or improving storage performance, and Patent Documents 3 to 6 adsorb nitrogen oxides from a low temperature range to a high temperature range so as to be compatible with a lean burn engine. The purpose is to improve performance. Therefore, it has hardly been attempted so far to promote low temperature purification (low temperature decomposition) of nitrogen oxides by improving the supply performance of the adsorbed component to the noble metal catalyst in the vicinity of the catalytic activity temperature.

The present invention has been made in view of the above circumstances, and efficiently adsorbs and collects nitrogen oxides in automobile exhaust gas in a low temperature region where catalytic activity occurs, and efficiently diffuses them to a noble metal catalyst on the surface. It is an object of the present invention to provide a nitrogen oxide adsorbing material capable of promoting low temperature purification of nitrogen oxides and an automobile exhaust gas purification catalyst using the same.

The present inventors have studied diligently to solve the above problems, and as a result, one or two kinds of Nd ³⁺ ion (neodymium ion) and Gd ³⁺ ion (gadrinium ion) are added to cerium oxide or zirconium oxide. It has been found that when the substituted ion composed of the above is substituted and solid-dissolved so that the substituted and solid-dissolved ion is present in the oxygen polyhedron structure of the cubic crystal, these act as effective adsorption points for the nitrogen oxide. In particular, if the adsorbing force of the nitrogen oxide adsorbed by the adsorption mechanism is such that the nitrogen oxide is desorbed in the range of 275 ° C to 325 ° C, the nitrogen oxide in the automobile exhaust gas is efficiently adsorbed and collected, and the noble metal. Since it can be surface-diffused to the catalyst and efficiently supplied, it has been found that low-temperature purification of nitrogen oxides is promoted, and the present invention has been completed.

That is, the gist of the present invention is as follows.

(1) A nitrogen oxide adsorbing material in which a part of the cation of the oxide is substituted with a substituted ion consisting of one or two kinds of Nd ³⁺ ion and Gd ³⁺ ion in cerium oxide or zirconium oxide. Therefore, the substituted ion has a structure in which it exists at the position of a cubic oxygen polyhedron, and at least nitrogen monoxide among the nitrogen oxides adsorbed by the nitrogen oxide adsorbent material is removed in a temperature range of 275 ° C. or higher and 325 oC or lower. A nitrogen oxide adsorbing material characterized by having an adsorbing power to separate.

(2) The nitrogen oxide according to (1), wherein the total content of the substituted ions is 4 mol% or more and 34 mol% or less with respect to the total cation amount of the nitrogen oxide adsorbing material. Adsorption material.

(3) The nitrogen oxide adsorbing material according to (1) or (2), wherein the specific surface area is 30 m ² / g or more and 70 m ² / g or less.

(4) The nitrogen oxide adsorbing material according to any one of (1) to (3), wherein the noble metal is supported.

(5) The nitrogen oxide according to any one of (1) to (4), which has both an oxygen absorption / release function and a nitrogen oxide adsorption function by being mixed with an oxygen absorption / release material. Adsorption material.

(6) An automobile exhaust gas purification catalyst comprising the nitrogen oxide adsorbing material according to any one of (1) to (5).

As described above, according to the present invention, nitrogen oxides (for example, nitrogen monoxide) contained in automobile exhaust gas are efficiently collected and adsorbed, and the adsorbed nitrogen oxides are collected on the catalyst noble metal by surface diffusion. Since it can be efficiently supplied to, the low temperature purification performance of automobile exhaust gas containing nitrogen oxides can be improved.

One embodiment of the nitrogen oxide adsorbing material of the present invention is shown, and in (a), a part of Ce ⁴⁺ ion which is a cation of cerium oxide is derived from one or two kinds of Nd ³⁺ ion and Gd ³⁺ ion. It is a schematic schematic diagram substituted with a substituted ion (indicated by "Ln ³⁺ " in the figure), and in (b), the Ln ³⁺ ion adsorbs a nitrogen oxide such as nitrogen monoxide (NO). It is a schematic schematic diagram which shows the state which acts as a point and adsorbs nitrogen monoxide (NO). It is a schematic schematic diagram explaining the mechanism that nitric oxide (NO) is adsorbed and stabilized by the coordination stabilization energy in the nitrogen oxide adsorbing material of this invention. It is an X-ray diffraction chart which shows that Nd ³⁺ ion and Gd ³⁺ ion which are substitution ions exist in the oxygen polyhedron position of a cubic crystal in the nitrogen oxide adsorbing material of this invention.

In the present invention, a part of the cation of cerium oxide or zirconium oxide is replaced with Nd ³⁺ ion (neodim ion), Gd ³⁺ ion (gadrinium ion), or both Nd ³⁺ ion and Gd ³⁺ ion. Further, the nitrogen oxide adsorbing material has a structure in which the substituted ion is present at the position of the oxygen polyhedron of the cubic crystal, and if this is used as an automobile exhaust gas catalyst, the catalytic activity in the low temperature region can be improved.

As shown in FIG. 1 (a), Nd ³⁺ ions (neodymium ions) and Gd ³⁺ ions (gadolinium ions) are present at the oxygen polyhedron positions of cubic crystals (note that in FIG. 1, Nd ³⁺ ions). Ions and Gd ³⁺ ions are indicated by "Ln ³⁺ ions") and, as shown in FIG. 1 (b), this acts as an adsorption point for nitrogen oxides (nitrogen monoxide, etc.) and is a catalyst noble metal. The reactants can be efficiently supplied to. As a result, the catalytic reaction occurs efficiently, that is, the low temperature purification ability is improved.
As shown in FIG. 2, this is filled in the f orbital splitting formed by the existence of f-electrons of Nd ³⁺ ions (neodymium ions) and Gd ³⁺ ions (gadolinium ions) in the coordinated polyhedron of cubic crystals. This is due to the fact that the coordination is stabilized.
Looking at the ligand, O ^2- ion (oxygen ion) becomes the ligand in the oxide crystal lattice, but when the stronger ligand N (N of nitrogen oxide) approaches, O ^2- ion (oxygen) The ligand N is coordinated in place of the ion) to further increase the f orbital splitting, that is, the coordination stabilizing energy is increased.
This is a mechanism that acts as an adsorption point for nitrogen oxides, and is different from a mechanism that adsorbs by mere electrostatic attraction. By such a different adsorption mechanism, nitrogen oxides contained in automobile exhaust gas can be efficiently collected without causing chemical changes such as oxidation, and surface diffusion easily occurs, so that the adsorbed nitrogen oxides occur. The substance can be efficiently supplied onto the catalyst noble metal. Further, since the nitrogen oxides adsorbed by the coordination can promote the reduction decomposition with the catalytic noble metal, the low temperature purification performance of the automobile exhaust gas can be improved.
As shown in the X-ray diffraction chart of FIG. 3, in the nitrogen oxide adsorbing material of the present invention, Nd ³⁺ ions (neodymium ions) and Gd ³⁺ ions (gadolinium ions) are located at cubic oxygen polyhedron positions. Confirmed to exist.
That is, the substitution ions Nd ³⁺ ion (neodymium ion) and Gd ³⁺ ion (gadolinium ion) in the nitrogen oxide adsorbing material of the present invention are substituted even though the substitution amount may be considerably large. The peak of the oxide element derived from the element could not be confirmed, and it is a single phase. From this, it can be said that the substituted ion is substituted at the position of Ce or Zr, in other words, the substituted ion has a structure existing at the oxygen polyhedral position of the cubic crystal.

Further, the nitrogen oxide adsorbing material of the present invention has an adsorbing power to desorb at least nitrogen monoxide NO among the nitrogen oxides adsorbed in the above-mentioned coordination adsorption mechanism in a temperature range of 275 ° C. or higher and 325oC or lower. As a result, the effect of the present invention is exhibited, in which the adsorbed nitrogen oxides are efficiently supplied onto the catalyst noble metal by surface diffusion to improve the low temperature purification performance of automobile exhaust gas.
However, if the desorption temperature is less than 275 ° C, the adsorbing power of nitrogen oxides is too weak to obtain the effect of the present invention, while if the desorption temperature exceeds 325 ° C, the adsorbing power of nitrogen oxides is not obtained. Is too strong to obtain the effect of the present invention.

In the nitrogen oxide adsorbing material of the present invention, it is more preferable that the sum of the substituted ions of Nd ³⁺ ions and Gd ³⁺ ions contains 4 mol% or more and 34 mol% or less with respect to the total cation amount.

Nitric oxide can be more effectively adsorbed and diffused more efficiently onto the noble metal catalyst by dissolving Nd ³⁺ ions or Gd ³⁺ ions in the above range as substitution ions in cerium oxide or zirconium oxide. Can be made to. If Nd ³⁺ ions and Gd ³⁺ ions are substituted and solid-solved, the effects of the present invention can be obtained. For example, when the solid solution amount is 1 mol% or more, a certain degree of action and effect can be obtained, but when the solid solution amount is 4 mol% or more, a more remarkable action and effect can be obtained. That is, if the amount of the substituted solid solution of the ion is increased, a more effective action and effect can be obtained, but if the amount of the solid solution is increased too much, the substituted solid solution ion is not uniformly dispersed (aggregated). The effects are saturated and become almost constant. For example, if it is 45 mol% or more, the action and effect are saturated as described above, so it is preferably 34 mol% or less. If it exceeds 34 mol%, the solid solution that maintains the oxygen polyhedral structure of the cubic crystal may not be possible due to the above-mentioned reason. The amount of the substituted solid solution is more preferably 10 mol% or more, and further preferably 21 mol% or more, still more preferably 28 mol% or more in order to obtain a larger effect of this action.

From the viewpoint of more effectively collecting nitric oxide, the nitrogen oxide adsorbing material of the present invention preferably dissolves Gd ³⁺ ions (gadolinium ions). Nd 3+ ion (Nd ³⁺ ion (gadolinium ion) because 7 electrons enter the lower level of the 4f split orbital of Gd ³⁺ ion (gadolinium ion) created by the oxygen polyhedron by dissolving Gd ³⁺ ion (gadolinium ion). Larger coordination stabilizing energy can be obtained as compared with the case of using neodymium ion), and nitrogen monoxide can be adsorbed more effectively.

The oxide that dissolves the substituted ions (Nd ³⁺ ion, Gd ³⁺ ion) as a solid solution can obtain the effects of the present invention with either cerium oxide or zirconium oxide, but zirconium oxide is preferable. By using zirconium oxide, the lattice constant is smaller than that of cerium oxide, so the oxygen polyhedron around Nd ³⁺ ion (neodymium ion) and Gd ³⁺ ion (gadolinium ion) becomes smaller, which results in coordination stabilization energy. As a result, nitrogen monoxide can be adsorbed more effectively.

The nitrogen oxide adsorbing material of the present invention preferably has a specific surface area of 30 m ² / g or more and 70 m ² / g or less. In order to obtain the action and effect of the present invention, any specific surface area may be used, but the above range is more effective. Since the present invention is an action and effect related to the surface, if the specific surface area is less than 30 m ² / g, it may be insufficient or require a complicated design depending on the application due to differences in engine and engine management. Further, since the nitrogen oxide adsorbing material of the present invention exerts its action and effect by the mechanism as described above, it is preferable that the specific surface area is large, but a sufficient action and effect can be obtained if it is about 70 m ² / g. Therefore, 70 m ² / g or less is more preferable from the viewpoint of manufacturing cost and ease of handling, but a larger specific surface area may be used if the above-mentioned problems do not occur.

It is more preferable that the nitrogen oxide adsorbing material of the present invention carries a noble metal. The adsorbed nitrogen oxide may be decomposed on the catalytic noble metal supported on another carrier oxide, but considering the action and effect of the present invention as described above, the nitrogen oxide adsorbing material of the present invention is used. , It is more preferable that a noble metal is supported. The noble metal is, for example, platinum Pt, palladium Pd, rhodium Rh, silver Ag, or the like. Rhodium Rh and platinum Pt are preferable as the purification catalyst for nitrogen oxides. It is better to carry palladium Pd in the sense that it improves the purification ability of the nitrogen oxides of palladium Pd used as a purification catalyst for hydrocarbons and carbon monoxide.

The amount of the noble metal supported is not particularly limited as long as it is an amount that can obtain the action and effect of the present invention, but is, for example, the amount carried in a normal three-way catalyst. Specifically, for example, the mass ratio of the noble metal to the carrier is 0.01% by mass or more and 20% by mass or less, more preferably 0.1% by mass or more and 10% by mass or less, and further preferably 0.4% by mass or more 6 It is mass% or less.

Since the composite oxide obtained by substituting Nd ³⁺ ion (neodymium ion) or Gd ³⁺ ion (gadrinium ion) with the above-mentioned cerium oxide or zirconium oxide and solidifying it does not have oxygen absorption / release ability, it is an oxygen absorption / release material. When used in a ternary catalyst, it exhibits exhaust gas purification ability more effectively. The oxygen absorbing / releasing material used in the present invention may be any material as long as it can absorb / release oxygen, and examples thereof include metals, oxides, and sulfates. Of these, ceria-zirconia composite oxides and iron-based oxides are preferable. The iron-based oxide is, for example, a composite oxide containing strontium ion and iron ion.
The amount of the oxygen absorbing / releasing material to be mixed may be appropriately determined according to the engine management, and may be, for example, 3% by mass or more and 60% by mass or less. It is preferably 10% by mass or more and 48% by mass or less.
The mass% here means the mass ratio of the oxygen absorbing / releasing material to the whole of the cerium oxide or zirconium oxide and the oxygen absorbing / releasing material.

Further, the nitrogen oxide adsorbing material of the present invention can be incorporated into a conventional three-way catalyst to obtain a higher-performance automobile exhaust gas purification catalyst.

The method for producing the nitrogen oxide adsorbing material of the present invention may be produced by any production method as long as the requirements of the present invention can be satisfied. Examples thereof include a gas phase synthesis method such as PVD and CVD, a solid phase reaction method, a wet method such as a coprecipitation method and a sol-gel method, and the like. As an example, a synthetic example of the wet method is shown below.
When wet synthesis is carried out in an aqueous system, the raw material is not limited as long as it is soluble in water, but for example, nitrates, acetates, chlorides and the like can be used. The raw materials of cerium, zirconium, neodymium and gadolinium are dissolved in water to prepare a raw material liquid. The precipitation method from the raw material liquid is not particularly limited, but for example, a method of obtaining a hydroxide by raising the pH, a method of precipitating as an organic acid salt with citric acid or the like, a method of precipitating by complex polymerization, etc. There is. Here, a method of obtaining a hydroxide by increasing the pH will be described as an example. Examples of the base used for adjusting the pH include sodium hydroxide, urea, ammonia and the like, and when these bases are added, a hydroxide precipitate can be obtained by setting the pH to 8.5 or higher. Here, the dehydration condensation reaction may be promoted by stirring while heating. After filtering the precipitate thus obtained, washing and filtration are repeated to obtain a cake. The cake is dried and crushed. The crushing method is not particularly limited, but for example, there is a method of crushing in a mortar. A nitrogen oxide adsorbing material can be obtained by calcining the crushed powder (for example, at 700 ° C. for 3 hours). Here, in order to more uniformly dissolve neodymium ions and gadolinium ions, conditions for uniform precipitation may be sufficient. In particular, when the precipitation pH of each cation is significantly different, a rapid pH change is caused to suppress heterogeneous precipitation. Further, in order to obtain a large specific surface area, conditions may be set to promote uniform nucleation in precipitation formation, for example, precipitation is performed from a large degree of supersaturation.

In the supported form according to the present invention, the noble metal is typically placed directly on the carrier material or may be supported directly on the carrier material, for example, the noble metal can be dispersed on the carrier material. The method for supporting the noble metal is not particularly limited, but for example, it can be carried out by the impregnation-supporting method. There is a method of obtaining a catalyst by adding a noble metal salt to the slurry and then removing the excess liquid.

The method of mixing with the oxygen absorbing / releasing material according to the present invention is not particularly limited, but for example, after putting the nitrogen oxide adsorbing material powder and the oxygen absorbing / releasing material in an aqueous medium, a wet crusher such as a ball mill is used. By using it, it can be made into a slurry. Further, in the case of producing an automobile exhaust gas purification catalyst, a method of immersing a honeycomb in the slurry, removing excess slurry, drying and firing may be mentioned.

Hereinafter, the present invention will be specifically described with reference to Examples (Invention Examples) and Comparative Examples, but the present invention is not limited thereto.

The adsorbed amount of nitric oxide measured in the present invention was carried out by using the thermal desorption method. As a pretreatment, after 60 minutes of treatment at 200 ° C. under He flow, the mixture was held at 100 ° C. for 15 minutes under He flow, and then 4% NO / Hebalance was circulated at 100 ° C. for 30 minutes to adsorb NO. The temperature rise desorption was performed at a temperature rise rate of 10 ° C./min under the carrier gas He flow, and the amount of NO desorption was measured at m / z = 30 using a quadrupole mass spectrometer.
The measurement of the specific surface area is as follows.
As a pretreatment, about 0.3 g of a sample is placed in a flask-shaped sample cell, degassed at 370 ° C. for 40 minutes under nitrogen gas flow using a FloVac degassing device (manufactured by Anton Paar Japan), and then the surface area is measured. The specific surface area was measured by the BET method (one-point method) by adsorbing nitrogen gas using an apparatus (NOVAtouch NX-4LX-1 manufactured by Anton Paar Japan).

(Example 1)
An aqueous solution of cerium nitrate and neodymium nitrate at a molar ratio of Ce: Nd = 67.0: 33.0 was prepared, and aqueous ammonia was added to bring the pH to 8 or more to cause precipitation. After adding 9.8 g of lauric acid to the solution, the solution was heated to 80 ° C. and stirred for 6 hours. The obtained precipitate was filtered-washed once with 2.5% aqueous ammonia to obtain a cerium-neodymium composite oxide cake. The obtained composite oxide cake was dried at 120 ° C. to form a powder, which was packed in a crucible and baked at 700 ° C. for 3 hours in a crucible, and replaced with a ceria-neodymium-based composite oxide (replaced with neodymium ion) shown in Table 1. A solid-dissolved cerium oxide) powder was obtained.

The NO adsorption amount of the obtained powder was measured and found to be 2.21 μmol. The specific surface area (SSA) of the obtained powder was 45 m ² / g, and the amount of NO adsorption per unit area was 0.49 μmol / g. Here, the temperature of the NO desorption peak was 280 ° C.

(Example 2)
As shown in Table 1, the ceria-neodymium-based composite oxide (neodymium ion-substituted and solid-dissolved) was obtained in the same manner as in Example 1 except that the compounding composition was Ce: Nd = 96.0: 4.0 in terms of molar ratio. Cerium oxide) powder was obtained.

When the NO adsorption amount of the obtained powder was measured in the same manner as in Example 1, it was 1.08 μmol. The specific surface area (SSA) of the obtained powder was 41 m ² / g, and the amount of NO adsorption per unit area was 0.26 μmol / g. Here, the temperature of the NO desorption peak was 280 ° C.

(Example 3)
As shown in Table 1, a ceria-gadolinium-based composite oxide (substituted and solid-dissolved with gadolinium ions) was used in the same manner as in Example 1 except that the compounding composition was Ce: Gd = 67.0: 33.0 in terms of molar ratio. Cerium oxide) powder was obtained.

When the NO adsorption amount of the obtained powder was measured in the same manner as in Example 1, it was 1.99 μmol. The specific surface area (SSA) of the obtained powder was 39 m ² / g, and the amount of NO adsorption per unit area was 0.51 μmol / g. Here, the temperature of the NO desorption peak was 290 ° C.

(Example 4)
As shown in Table 1, the zirconia-neodymium-based composite oxide (neodymium ion-substituted and solid-dissolved) was obtained in the same manner as in Example 1 except that the compounding composition was Zr: Nd = 67.0: 33.0 in terms of molar ratio. Zirconia oxide) powder was obtained.

When the NO adsorption amount of the obtained powder was measured in the same manner as in Example 1, it was 3.07 μmol. The specific surface area (SSA) of the obtained powder was 61 m ² / g, and the amount of NO adsorption per unit area was 0.50 μmol / g. Here, the temperature of the NO desorption peak was 310 ° C.

(Example 5)
As shown in Table 1, a zirconia-gadolinium-based composite oxide (substituted and solid-dissolved with gadolinium ions) was used in the same manner as in Example 1 except that the compounding composition was Zr: Gd = 67.0: 33.0 in terms of molar ratio. Zirconium oxide) powder was obtained.

When the NO adsorption amount of the obtained powder was measured in the same manner as in Example 1, it was 3.04 μmol. The specific surface area (SSA) of the obtained powder was 57 m ² / g, and the amount of NO adsorption per unit area was 0.53 μmol / g. Here, the temperature of the NO desorption peak was 315 ° C.

(Example 6)
As shown in Table 1, a ceria-neodymium-based composite oxide (substituted and solid-dissolved with neodymium ion) was obtained in the same manner as in Example 1 except that the compounding composition was Ce: Nd = 96.0: 4.0 in terms of molar ratio. Cerium oxide) powder was obtained.

When the NO adsorption amount of the obtained powder was measured in the same manner as in Example 1, it was 1.23 μmol. The specific surface area (SSA) of the obtained powder was 42 m ² / g, and the amount of NO adsorption per unit area was 0.29 μmol / g. Here, the temperature of the NO desorption peak was 275 ° C.

(Example 7)
As shown in Table 1, a ceria-gadolinium-based composite oxide (substituted and solid-dissolved with gadolinium ions) was obtained in the same manner as in Example 1 except that the compounding composition was Ce: Gd = 96.0: 4.0 in terms of molar ratio. Cerium oxide) powder was obtained.

When the NO adsorption amount of the obtained powder was measured in the same manner as in Example 1, it was 1.30 μmol. The specific surface area (SSA) of the obtained powder was 43 m ² / g, and the amount of NO adsorption per unit area was 0.30 μmol / g. Here, the temperature of the NO desorption peak was 285 ° C.

(Example 8)
As shown in Table 1, a ceria-neodymium-based composite oxide (cerium substituted with neodymium ion) was used in the same manner as in Example 1 except that the compounding composition was a molar ratio Ce: Nd = 66.0: 34.0. Oxide) powder was obtained.

When the NO adsorption amount of the obtained powder was measured in the same manner as in Example 1, it was 2.59 μmol. The specific surface area (SSA) of the obtained powder was 47 m ² / g, and the amount of NO adsorption per unit area was 0.55 μmol / g. Here, the temperature of the NO desorption peak was 280 ° C.

(Comparative Example 1)
As shown in Table 1, a ceria-zirconia-based composite oxide powder was obtained in the same manner as in Example 1 except that the compounding composition was Ce: Zr = 50: 50 in terms of molar ratio.

When the NO adsorption amount of the obtained powder was measured in the same manner as in Example 1, it was 2.08 μmol. The specific surface area (SSA) of the obtained powder was 79 m ² / g, and the amount of NO adsorption per unit area was 0.26 μmol / g. Here, the temperature of the NO desorption peak was 270 ° C.

(Comparative Example 2)
As shown in Table 1, ceria powder was obtained in the same manner as in Example 1 except that the compounding composition was 100.0 in terms of molar ratio and Ce.

When the NO adsorption amount of the obtained powder was measured in the same manner as in Example 1, it was 1.81 μmol. The specific surface area (SSA) of the obtained powder was 72 m ² / g, and the amount of NO adsorption per unit area was 0.25 μmol / g. Here, the temperature of the NO desorption peak was 260 ° C.

Further, by performing X-ray diffraction for each of Examples 1 to 8, it was confirmed that the substituted ion had a crystal structure existing at the position of the oxygen polyhedron of the cubic crystal.
FIG. 3 shows, for example, X-ray diffraction charts measured for Examples 1, 3, 4, and 5, but according to FIG. 3, the amount of substituted ions is as large as 0.33 in terms of molar ratio. However, since the peak of the oxide element derived from the substitution element is not confirmed, it can be seen that the phase is monophasic. That is, it can be said that the substituted ion is substituted at the position of Ce or Zr and has a structure in which the substituted ion exists at the position of the oxygen polyhedron of the cubic crystal.
The X-ray diffraction conditions are as follows.
The sample was placed in a sample holder, and X-ray diffraction measurement was performed using a Rigaku desktop X-ray diffractometer MiniFlex 600 under the conditions of 20 to 70 °, step 0.02 °, and 10 ° C./min.

From Table 1, when Comparative Example 1 and Comparative Example 2 are compared with Example 1 and Example 4, it is found that the amount of NO adsorption per unit area is improved by solid-solving Nd in the ceria lattice and the zirconia lattice. Understand. That is, it can be seen that when Nd is solidly dissolved in a cubic oxygen polyhedron in the ceria lattice and the zirconia lattice, these act as adsorption points for nitrogen oxides and exert the action and effect of the present invention.
Further, in Comparative Examples 1 and 2, the nitrogen oxide desorption temperature is 270 ° C. or 265 ° C., whereas in Examples 1 to 8, the nitrogen oxide desorption temperature is 275 ° C. It can be seen that the temperature is within the range of 325 ° C.

From Table 1, when Example 1, Example 2, Example 6 and Example 8 are compared, it can be seen that the amount of NO adsorption per unit area is improved by dissolving Nd in a solid solution of 4 mol% to 34 mol%. .. That is, it can be seen that when Nd is solidly dissolved in the cubic oxygen polyhedron in the ceria lattice, these act as adsorption points for nitrogen oxides and effectively exert the action and effect of the present invention.

From Table 1, when Comparative Example 1 is compared with Example 3, Example 5, and Example 7, it is found that the amount of NO adsorption per unit area is improved by solid-solving Gd in the ceria lattice and the zirconia lattice. Understand. That is, it can be seen that Gd is dissolved in a cubic oxygen polyhedron in the ceria lattice and the zirconia lattice, and these act as adsorption points for nitrogen oxides to exert the action and effect of the present invention.

From Table 1, when comparing Examples 1 and 3, it is found that the desorption temperature of NO is improved by solid-solving Gd in the ceria lattice as compared with the case where Nd is solid-solved in the ceria lattice. Understand. That is, when Gd is solid-dissolved in a cubic oxygen polyhedron in the ceria lattice, nitrogen oxides are more effectively adsorbed than when Nd is solid-dissolved, thereby exhibiting the effects of the present invention. You can see that it is doing.

As described above, according to the present invention, a ceria-based composite oxide and a zirconia-based composite oxide characterized by efficiently adsorbing nitrogen oxides and desorbing them in the temperature range of 275 ° C. to 325 ° C. are obtained. It was confirmed that it was done.
Further, when the noble metals of Rh, Pd and Pt were supported on the nitrogen oxide adsorbing material of the present invention and the reduction activity of the nitrogen oxide was examined, the catalytic activity was better than that of the noble metal catalyst supported on the alumina carrier. Indicated. In the comparative example, no catalytic activity exceeding that of the example was obtained.

If the material having high HC oxidation and NOx reduction activity of the present invention is used as an auxiliary catalyst for an automobile exhaust gas purification catalyst, it helps to purify nitrogen oxides discharged when the engine is started in a low temperature region, and nitrogen of a noble metal is more than ever. The oxide component purification performance can be improved.

Claims (6)

A nitrogen oxide adsorbing material in which a part of the cation of the oxide is substituted with a substitution ion consisting of one or two kinds of Nd ³⁺ ion and Gd ³⁺ ion in a cerium oxide or a zirconium oxide. Adsorption in which the substituted ion exists at the position of the oxygen polyhedron of the cubic crystal, and at least nitrogen monoxide among the nitrogen oxides adsorbed by the nitrogen oxide adsorbent material is desorbed in the temperature range of 275 ° C. or higher and 325 oC or lower. A nitrogen oxide adsorbing material characterized by having power. The nitrogen oxide adsorbing material according to claim 1, wherein the total amount of the content ratio of the substituted ions is 4 mol% or more and 34 mol% or less with respect to the total cation amount of the nitrogen oxide adsorbing material. The nitrogen oxide adsorbing material according to claim 1 or 2, wherein the specific surface area is 30 m ² / g or more and 70 m ² / g or less. The nitrogen oxide adsorbing material according to any one of claims 1 to 3, wherein the noble metal is supported. The nitrogen oxide adsorbing material according to any one of claims 1 to 4, wherein the mixed oxygen absorbing / releasing material has both an oxygen absorbing / releasing function and a nitrogen oxide adsorbing function. An automobile exhaust gas purification catalyst comprising the nitrogen oxide adsorbing material according to any one of claims 1 to 5.

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