JP6149757B2 - Engine exhaust gas purification catalyst material and particulate filter - Google Patents

Description

  The present invention relates to a catalyst material for purifying engine exhaust gas and a particulate filter carrying the same.

Ce-containing oxides are commonly contained in three-way catalysts, diesel oxidation catalysts, lean NOx storage reduction catalysts, diesel particulate combustion catalysts, and the like, which are exhaust gas catalysts for engines. This is because the CeO ₂ material has oxygen storage / release ability and NOx adsorption ability. A CeO ₂ material (CeZr composite oxide) in which zirconia is compounded is also known. Combining zirconia can greatly improve the thermal stability of ceria. For such a CeO ₂ material, various studies have been made such as improving the durability of the CeO ₂ material itself, improving the durability of the supported catalyst metal, or improving the oxygen storage / release capability. (Patent Documents 1 and 2).

For example, Patent Document 1 discloses a catalyst supporting Rh with a Ce oxide as a nucleus and a coating of an oxide of at least one metal selected from Zr, Ti, La and Y. This is a technique for suppressing the deactivation of supported Rh. Patent Document 2 discloses that CeO ₂ is supported on the surface of a solid solution of CeO ₂ —ZrO ₂ to exhibit excellent oxygen storage ability over a wide temperature range from a low temperature to a high temperature.

JP 2007-144290 A JP2012-228628A

However, in the examination of Patent Documents 1 and 2, it has not been clarified by what mechanism the oxygen storage / release ability of the CeO ₂ material is specifically reduced. Therefore, the conventional technique has become a symptomatic therapy technique. The inventors of the present application investigated the oxygen storage / release mechanism of the CeO ₂ material and the inhibition mechanism thereof, and studied to improve the oxygen storage / release capability of the CeO ₂ material based on the mechanism.

  This invention is made | formed in view of this point, The place made into the objective is to provide the catalyst material for engine exhaust gas purification | cleaning which has the outstanding oxygen storage-release capability.

An engine exhaust gas purification catalyst material according to the present invention includes Ce-containing oxide particles supporting Pt and a support material mainly composed of an oxide of a rare earth metal other than Ce, and oxidizing the rare earth metal other than Ce. The material has a lattice constant of 90% or more and 110% or less of the lattice constant of CeO ₂ , and the support material is supported on the surface of the Ce-containing oxide particles and at least a part thereof is a solid solution. It is characterized by that.

  According to this engine exhaust gas purifying catalyst material, the generation of carbonate on the surface of the Ce-containing oxide particles and the decrease in oxygen storage / release ability, the support material mainly composed of oxides of rare earth metals other than Ce prevent. A support material mainly composed of an oxide of a rare earth metal other than Ce means that the content of the oxide of the rare earth metal other than Ce in the support material is larger than 50% by mass. It is preferable that a thing is not substantially contained. In addition, the support material is supported on the surface of the Ce-containing oxide particles and at least a part thereof is in solid solution. This means that at least the interface between the support material is dissolved and the support state is maintained. means. The lattice constant is represented by the oxygen-oxygen distance on the (110) plane.

  Preferably, the rare earth metal other than Ce is at least one selected from La, Nd, Y and Pr. Thereby, it can prevent more efficiently that the oxygen storage-release capability of Ce containing oxide particle falls.

  In the particulate filter of the present invention, the engine exhaust gas purification catalyst material is supported on the exhaust gas flow passage wall surface.

  According to the engine exhaust gas purifying catalyst material of the present invention, oxygen storage and release ability is achieved by supporting a support material mainly composed of an oxide of a rare earth metal other than Ce on the surface of Ce-containing oxide particles supporting Pt. It is possible to prevent the deterioration and to exert an excellent exhaust gas purification action.

The surface of the CeO ₂ material carrying Pt is a diagram schematically showing. It is the figure which showed the absorption spectrum of FT-IR under CO distribution | circulation conditions. It is the figure which showed the change of the absorption spectrum of FT-IR under oxygen circulation conditions. It is the figure which showed the change of the absorption spectrum of FT-IR in 500 degreeC. It is the bar graph which showed T10 and T50 of an Example and a comparative example. It is a typical figure showing a particulate filter concerning an embodiment.

  Before describing the embodiments of the present invention, the background to the present invention will be described.

As described above, the CeO ₂ material has an oxygen storage / release capability and NOx adsorption capability, and is used as a catalyst material for engine exhaust gas purification. However, a phenomenon has been found that the oxygen storage / release ability of the CeO ₂ material decreases during use, and the present inventors have sought to prevent the decrease in oxygen storage / release ability by exploring the mechanism of this phenomenon. As a result of various investigations on the active sites on the surface of the CeO ₂ material, the present invention shows that one of the causes of the decrease in the ability to store and release oxygen is that the carbonates block the sites that store and release oxygen. They found for the first time. The following shows this mechanism and the experiment that led to it.

FIG. 1 schematically shows the surface of a CeO ₂ material supporting Pt. A large number of sites 100 and 101 for storing and releasing oxygen exist on the surface of the CeO ₂ material. As shown on the left side of FIG. 1, for example, when CO reaches the surface of the CeO ₂ material supporting Pt, CO is once adsorbed on the surface of the Pt or CeO ₂ material and stored in the site 100. Oxygen is bound to the adsorbed CO and becomes CO ₂ away. Here, if there is a site (oxygen defect portion) 101 in which oxygen is not occluded, one oxygen of CO ₂ is trapped in this oxygen defect portion 101 as shown on the right side of FIG. Binds to CO ₂ to form carbonate 90. This carbonate 90 will block the two sites 102, 102. Since the site 100 is a place where the oxygen is stored and released and is an important part of the oxidation catalyst, if the sites 90 are blocked by the carbonate 90, the oxygen storage / release capability is lowered, and the performance of the oxidation catalyst is lowered. Resulting in.

The absorption spectrum of FT-IR in FIG. 2 indicates that the carbonate is adsorbed on the surface of the CeO ₂ material supporting Pt. 1a is CeO ₂ material (no Pt supported), 1b is CeO ₂ material supported Pt, 2a is Zr _0.54 Nd _0.18 Pr _0.28 O ₂ material (no Pt supported), 2b is Pt the absorption spectrum of loaded with _Zr 0.54 _Nd 0.18 _{Pr 0.28} O ₂ material surface. In the measurement, each material was treated as a pretreatment at 600 ° C. for 10 minutes in a state of O ₂ at 50 Torr, and then evacuated at room temperature, and then kept at room temperature for 30 minutes in a state of CO at 50 Torr, and then CO It was performed in the state of.

CeO ₂ material 1a, the absorption derived from carbonate both of Bidentate type 1b (1650,1538cm ^-1) is appears large, the absorption derived from carbonate of Unidentate type (1429,1336cm ^-1) also appear. In FIG. 1, only the Bidentate-type carbonate 90 is shown for the sake of simplification, but there is also an Unidentate-type carbonate produced by combining CO ₂ with the stored oxygen in the site 100, and this carbonate is also present. Will also block the site 100.

  On the other hand, in the ZrNdPr composite oxide materials 2a and 2b, absorption derived from Bidentate type carbonate is slightly observed, but absorption derived from Unidentate type carbonate is not observed.

Next, oxygen was supplied for the purpose of eliminating the adsorption of carbonate from the states 1b and 2b. The result is shown in FIG. In the CeO ₂ material, evacuation was performed once from the state of 1b, and O ₂ was held at room temperature for 10 minutes at room temperature, but no change was observed in the absorption derived from the carbonate. Therefore, when the temperature was raised to 200 ° C. (1c), absorption from the carbonate carbonate of Bidentate type shifted to 1560 cm ⁻¹ , but absorption from the carbonate remained almost as it was, and there was almost no change in the adsorption state of the carbonate on the surface. I understand that there is no. On the other hand, in the ZrNdPr composite oxide material, the absorption derived from the carbonate was lost in 2c, which was once evacuated from the state of 2b and kept O ₂ at 50 Torr for 10 minutes at room temperature. This indicates that the adsorption of carbonate has been eliminated.

Furthermore, the adsorption situation of carbonate at higher temperature was investigated. The samples used were CeO ₂ material supporting Pt (same as 1b) and Zr _0.54 Nd _0.18 Pr _0.28 O ₂ material supporting Pt (same as 2b). These samples are first heated to 500 ° C. while flowing He at 50 ml / min. Then, 1% CO was added to He and flowed at 500 ° C. for 10 minutes, and then FT-IR spectrum was measured (1d, 2d). Then, the gas to be flowed was changed to He added with 1% O ₂ and flowed at 500 ° C. for 10 minutes, and then the FT-IR spectrum was measured (1e, 2e).

CeO ₂ material Pt carrying is, 1298cm ^-1 (Bidentate type) as indicated by 1d of FIG. 4 after passing a CO mixed He and 1460,1385Cm ^-1 absorption from large and broad carbonate to (Polydentate type) Was observed. After that, when the gas was switched to O ₂ mixed He, the absorption derived from the carbonate decreased as shown by 1e, but it was not completely lost but partially remained. The polydentate type is one in which the three oxygen atoms forming the carbonate are each bonded to a metal ion on the oxide surface.

On the other hand, ZrNdPr composite oxide material Pt supported thereon over the 1568Cm ^-1 from 1331cm ^-1 as indicated by 2d in Figure 4 after passing a CO mixed He, absorption of a small carbonate from at Bidentate type broad is observed It was. The gas was then switched to O ₂ mixed He and the carbonate-derived absorption disappeared as shown by 2e.

From this result, the Pt-supported CeO ₂ material adsorbs a large amount of carbonate by flowing CO even at a high temperature of 500 ° C. where the exhaust gas catalyst functions, and even if oxygen is flowed, some adsorption of the carbonate remains. It became clear that. On the other hand, the Pt-supported ZrNdPr composite oxide material adsorbs a little carbonate by flowing CO at 500 ° C., but the adsorption of carbonate disappeared by flowing oxygen thereafter.

In this way, the CeO ₂ material is impregnated with oxygen, because the sites that store and release oxygen are blocked by the carbonate, regardless of whether or not Pt is supported, and once they are blocked, they do not desorb easily. The mechanism became clear. Therefore, the inventors of the present application have made various studies based on this mechanism and have arrived at the present invention. Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following drawings, components having substantially the same function are denoted by the same reference numerals for the sake of brevity.

<Examples and Comparative Examples>
Ce-containing oxide particles (CeO ₂ material, wherein the _{CeO 2 -ZrO 2 -Nd 2 O 3} ) supporting Pt on as support material _La 2 _{O 3} and loaded with the catalyst material of Example 1 for an engine exhaust gas purification A catalyst material was obtained. Similarly, those using Nd ₂ O ₃ , Y ₂ O ₃ and Pr ₆ O ₁₁ as the support materials were used as the catalyst materials of Example 2, Example 3 and Example 4, respectively. Further, only the CeO ₂ material carrying Pt was used as the catalyst material of Comparative Example 1, and the material carrying Sc ₂ O ₃ as the carrying material was used as the catalyst material of Comparative Example 2. Specific amount ratios and adjustment methods for each catalyst material are as follows.

<Adjustment of catalyst material>
-Preparation of Ce-containing oxide particles (CeO ₂ material) supporting Pt-
The Ce-containing oxide particles (CeO ₂ material) according to the embodiment can be prepared, for example, by a coprecipitation method. That is, cerium nitrate, zirconyl oxynitrate, and neodymium nitrate are dissolved in ion-exchanged water at a mass ratio of 2: 7: 1. A coprecipitate (CeO ₂ material precursor) is obtained by mixing and neutralizing this nitrate solution with an 8-fold diluted solution of 28% by mass ammonia water as a basic solution. The solution containing this coprecipitate is centrifuged to remove the supernatant (dehydration), and ion-exchanged water is further added and stirred (water washing). Remove basic solution. The co-precipitate after the final dehydration is dried in the air at a temperature of 150 ° C. for a whole day and night, pulverized, and then fired in the air at a temperature of 500 ° C. for 2 hours. Thereby, Ce containing oxide particles (CeO ₂ material) can be obtained.

Thereafter, Pt is supported on the CeO ₂ material. Pt was supported by a dinitrodiamine platinum nitric acid solution by evaporation to dryness. The amount of Pt supported is 1% by mass.

-Supporting a support material mainly composed of oxides of rare earth metals other than Ce-
In Example 1, lanthanum nitrate and urea (2-fold molar amount of lanthanum nitrate) were dissolved in ion-exchanged water to form an aqueous solution, and the above CeO ₂ material supporting Pt was added thereto at 100 ° C. for 8 hours. Stirring was performed. This slurry-like stirring product was filtered, and ion-exchanged water was added to the solid for washing, followed by filtration again. This washing was repeated twice. This solid was dried at 150 ° C. for 24 hours and then calcined at 800 ° C. for 2 hours to obtain a catalyst material. The carrying amount of the carrying material (La ₂ O ₃ ) is 5% by mass. The particles of the support material supported on the surface of the CeO ₂ material by firing were in solid solution with the CeO ₂ material at the support interface.

  In Example 2, a catalyst material was prepared in the same manner as in Example 1 using neodymium nitrate instead of lanthanum nitrate.

  In Example 3, a catalyst material was prepared in the same manner as in Example 1 using yttrium nitrate instead of lanthanum nitrate.

  In Example 4, a catalyst material was prepared in the same manner as in Example 1 using praseodymium nitrate instead of lanthanum nitrate.

  In Comparative Example 2, a catalyst material was prepared in the same manner as in Example 1 using scandium nitrate instead of lanthanum nitrate.

<Measurement of carbon combustion performance>
In order to know and compare the degree of oxygen storage / release capacity of each catalyst material, carbon combustion performance was measured using each catalyst material prepared. Specifically, first, each catalyst material was subjected to atmospheric aging at 800 ° C. for 24 hours.

  Then, a carbonate generation treatment was performed on each catalyst material as follows. 100 mg of the catalyst material granulated to 1 to 0.5 mm was weighed and packed in a sample tube, placed in a He gas stream mixed with 1% CO, and heated to 600 ° C. at a rate of 10 ° C./min. The temperature was kept for 30 minutes and then cooled to room temperature.

  Thereafter, the performance of carbon combustion was measured for each catalyst material as follows. First, each catalyst material for which the carbonate generation process was completed was pulverized in an agate mortar. Carbon black was added at a weight ratio of 4: 1 to each pulverized catalyst material and mixed in an agate mortar. 5 mg of this mixture was weighed, and a temperature increase test was performed to 700 ° C. at a rate of 10 ° C./min in an air stream (100 ml / min) by TG-DTA. From the TG curve, the temperature when carbon black burned 10% (T10) and the temperature when burned 50% (T50) were determined. These are shown in Table 1 and FIG. In FIG. 5, among the two bar graphs of each comparative example and each example, the left side is T10 and the right side is T50.

  The above-mentioned carbon combustion test is conducted for the purpose of measuring the performance of oxidizing the carbon powder contained in the exhaust gas particulates to carbon dioxide by the catalyst material. It can be said that the smaller the values of T10 and T50, the higher the performance of oxidation.

Only CeO ₂ material carrying Pt as compared with Comparative Example 1 in which a catalyst material, Examples 1-4 T10 is 18 to 23 ° C. reduced, T50 small 10 to 15 ° C.. Comparative Example 2 has substantially the same values of T10 and T50 as Comparative Example 1. Therefore, the catalyst materials according to Examples 1 to 4 have higher performance of oxidizing than Comparative Example 1. This is because the sites on the surface of the catalyst material that occludes and releases oxygen are blocked by carbonate in Comparative Example 1, whereas in Examples 1 to 4, this site is not blocked by carbonate or is blocked. This is probably because the carbonate is easily decomposed even if it is peeled off.

The difference between Comparative Example 1 and Examples 1 to 4 is presumed to be largely influenced by the number of sites that are oxygen deficient portions and the amount of O ²⁻ present on the catalyst material surface. It is known that other rare earth oxides such as lanthanum, neodymium, yttrium, and praseodymium are less likely to produce oxygen defects as compared with cerium oxide. The rare earth oxide has a property of having O ²⁻ on the surface, and CO ₂ is attracted thereto. Cerium oxide has more O ²⁻ on the surface than other rare earth oxides, and when CO ₂ is attracted to it, if there is an oxygen defect near it, it becomes carbonate and is easily trapped. In Comparative Example 1, both of these two steps are likely to occur.

On the other hand, in Examples 1 to 4, rare earth (La, Nd, Y, Pr) oxides other than cerium are supported on the surface of the CeO ₂ material, thereby reducing oxygen defects and solidifying the interface. Since it melts, the surface characteristics of the CeO ₂ material are changed, and the adsorption of O ²⁻ is suppressed. Furthermore, there is a function of passing oxygen to a carbonate in which a rare earth (La, Nd, Y, Pr) oxide other than cerium is trapped, and the oxygen is decomposed by the oxygen and desorbed from the catalyst material as CO _2. .

In Examples 1 to 4, the lattice constant of a rare earth (La, Nd, Y, Pr) oxide other than cerium is 90% (3.474) or more 110% (4.246) of the lattice constant 3.86 of CeO _2. Since it is below, the distortion at the crystal interface with CeO ₂ is small. Therefore, the crystal interface is easily dissolved, and the ability to pass oxygen to the carbonate is large. On the other hand, scandium oxide of Comparative Example 2, the lattice constant is above 115% of the lattice constant of CeO _2, strain in the crystal interface between CeO ₂ and scandium oxide is large. Therefore, it is considered that the ratio at which the interface dissolves is lowered, and the function of passing oxygen to the carbonate is inhibited.

<Supporting on particulate filter>
The particulate filter carrying the catalyst material according to Examples 1 to 4 is shown in FIG. The particulate filter 10 has a honeycomb structure, is provided with a large number of exhaust gas passages extending in parallel to each other, and is disposed in the exhaust gas passage 11. And the catalyst material which concerns on Examples 1-4 is carry | supported by the wall surface of the exhaust gas flow path. With such a configuration, the particulates collected by the particulate filter 10 are oxidized and decomposed by the catalyst materials according to the first to fourth embodiments.

(Other embodiments)
The above-described embodiments and examples are examples of the present invention, and the present invention is not limited to these examples, and these examples may be combined or partially replaced with known techniques, common techniques, and known techniques. Good. Also, modified inventions easily conceived by those skilled in the art are included in the present invention.

  The Ce content in the Ce-containing oxide particles, the types of other constituent elements, and the content thereof are not limited to the above-described examples, and may be any configuration as long as they can function as a catalyst. Further, the amount of Pt supported on the Ce-containing oxide particles is not particularly limited as long as it can exhibit a function as a catalyst. The amount of the support material supported is not particularly limited as long as it can function as a catalyst. A plurality of types of rare earth oxides may be used as the support material. A known method can be used as a method for preparing and adjusting the catalyst material. Furthermore, the support material may contain a substance other than the main component of a rare earth metal oxide other than Ce.

10 Particulate filter

Claims (1)

A particulate filter in which a catalyst material for engine exhaust gas purification is supported on the wall surface of the exhaust gas flow path ,
The engine exhaust gas purification catalyst material is
Ce-containing oxide particles supporting Pt;
A supporting material mainly composed of an oxide of a rare earth metal other than Ce;
Including
The rare earth metal oxide other than Ce has a lattice constant of 90% to 110% of the lattice constant of CeO ₂ ,
The support material is supported on the surface of the Ce-containing oxide particles and at least a part thereof is in solid solution,
The rare earth metal other than Ce is at least one selected from La, Nd, Y and Pr,
A particulate filter in which the Ce-containing oxide particles contain a Zr oxide and an Nd oxide .

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