JP4985423B2 - Exhaust gas component purification catalyst material and exhaust gas component purification catalyst - Google Patents

Description

  The present invention relates to an exhaust gas component purification catalyst material and an exhaust gas component purification catalyst provided with a catalyst carrier base material having a catalyst layer containing the exhaust gas component purification catalyst material.

  For example, in a vehicle such as an automobile, an exhaust gas component purification catalyst is provided in the exhaust gas path of the engine in order to purify the exhaust gas discharged from the engine. In particular, in vehicles equipped with diesel engines or lean-burn gasoline engines, exhaust gas components that reduce unburned carbon-like substances (so-called particulate matter: PM) and nitrogen oxides (NOx) in exhaust gases as exhaust gas component purification catalysts There is a need for a purification catalyst.

  For example, there is a concern that PM contained in exhaust gas of a diesel engine may lead to environmental pollution, and its emission is regulated. For this reason, a diesel particulate filter (DPF) is mounted in the exhaust gas path in a vehicle equipped with a diesel engine. DPF is a heat-resistant ceramic material made of silicon carbide (SiC), cordierite, etc., formed into a shape called a three-dimensional network type or wall flow type. PM in exhaust gas passes through the DPF. It is supposed to be collected.

  By the way, the collected PM gradually accumulates in the DPF according to the operation time, so that there is a problem that the back pressure increases, the engine output decreases and the fuel consumption deteriorates. Then, excessively flowing HC component (for example, fuel) from the exhaust upstream side, burning the HC component with the catalyst disposed upstream of the DPF, and raising the temperature of the DPF using the combustion heat, the PM Methods for promoting ignition and combustion are known. Further, in recent years, in order to effectively promote the ignition and combustion of PM, a catalyst layer containing an oxygen storage material together with alumina or the like is provided on the exhaust gas passage surface of the DPF, and the oxygen component stored in the oxygen storage material is reduced. Proposed to use.

This oxygen storage material has the characteristic of storing oxygen when the exhaust gas atmosphere is in an excess oxygen state and releasing the stored oxygen when the exhaust gas atmosphere is in a state of oxygen shortage (so-called oxygen storage and release capability). ) has, by this property, HC in the exhaust gas, CO, air-fuel ratio spread that can purify NO _X, the exhaust gas purifying performance can be improved.

  Conventionally, a composite oxide containing Ce and Zr is known as the oxygen storage material. For example, in the following Patent Document 1, the applicant of the present application relates to such a composite oxide, between its crystal lattices or lattice points. An oxygen storage material in which a catalytic metal (strictly a catalytic noble metal) is arranged and an exhaust gas purification catalyst including the oxygen storage material are proposed. Patent Document 1 discloses a technique in which a catalyst noble metal is arranged between crystal lattices or lattice points of a complex oxide containing Ce and Zr. According to such a technique, the oxygen storage capacity is improved, and sintering of the catalyst noble metal is prevented. As a result, it is possible to maintain high purification performance over a long period of time. In addition, Patent Document 1 below discloses an oxygen storage material containing neodymium (Nd) in addition to Ce, Zr, and a catalyst noble metal.

  On the other hand, in the catalyst layer formed on the wall surface of the exhaust gas flow path of the DPF body, a catalytic noble metal for oxidizing and burning PM and a complex oxide not containing Ce, containing Zr and rare earth metal Y And the catalyst containing the complex oxide which acts as an oxygen ion conductive material is proposed (for example, refer to the following patent document 2). In this catalyst, unlike the oxygen storage material described above, if there is a difference in oxygen concentration in the vicinity of the oxygen ion conductive material particles, oxygen ions pass from the high oxygen concentration portion to the low oxygen concentration portion through the particles, and active oxygen Is sent out. As a result, after generation of a fire type for oxidizing and burning PM, expansion of the combustion region is promoted, and PM can be efficiently oxidized and burned.

  In addition, NOx contained in the exhaust gas of a diesel engine or lean-burn gasoline engine that burns in an oxygen-excess state is also concerned with environmental pollution, and its emission is regulated. For this reason, a NOx storage / reduction catalyst is provided in the exhaust gas path of a diesel engine or lean-burn gasoline engine, and NOx in the exhaust gas is stored when leaning during normal operation, and is stored in the NOx storage / reduction catalyst when it is temporarily created. It is known to reduce NOx and purify NOx in exhaust gas.

  In this NOx occlusion reduction catalyst, there is a problem that the performance deteriorates due to the reaction with the sulfur component contained in the fuel. For example, Patent Document 3 discloses ceria, praseodymium oxide, or cerium. Presence of sulfur oxides using a catalyst having an oxide catalyst component comprising a mixture of oxides of at least two elements selected from zirconium, praseodymium, neodymium, terbium, samarium, gadolinium and lanthanum and / or composite oxides Below, a method for catalytic reduction of nitrogen oxides is also described.

JP 2004-174490 A JP 2005-262184 A JP 2006-043533 A

  By the way, when a particulate filter is provided in a vehicle equipped with a diesel engine or a lean-burn gasoline engine, an oxidation catalyst that oxidizes HC or the like is often provided upstream of the particulate filter. In this case, measures are taken to increase the temperature of the exhaust gas introduced into the particulate filter by burning the fuel increased by the oxidation catalyst, etc. to promote PM combustion. It is inevitable that extra fuel is consumed for combustion. In order to reduce such an increase in fuel, a composite oxide that further improves the combustion rate of PM is used rather than a composite oxide containing Zr and rare earth metal Y as disclosed in Patent Document 2 above. It is desirable. On the other hand, there is concern that the amount of carbon monoxide (CO) emission may increase due to incomplete combustion of PM as the amount of PM combustion increases, and measures against this incomplete combustion of PM may be taken. Desired.

  Further, in a vehicle equipped with a diesel engine or a lean combustion gasoline engine, further improvement in NOx purification performance is required in addition to PM reduction. Although Patent Document 3 describes a catalyst for catalytic reduction of nitrogen oxides, a composite oxide that realizes further improvement in NOx purification performance in exhaust gas is desired.

  The present invention has been made in view of the above technical problem, and can oxidize and burn PM in a shorter time, suppress CO emission during PM combustion, and further purify NOx. An object of the present invention is to provide a catalyst material for exhaust gas component purification and a catalyst for exhaust gas component purification.

Therefore, the invention according to claim 1 of the present application contains a complex oxide containing zirconium (Zr) and neodymium (Nd) as essential components, and further containing a rare earth metal R other than cerium (Ce) and neodymium (Nd). The zirconium, neodymium, and rare earth metal R constituting the composite oxide are oxides, and the Nd ₂ O ₃ / (ZrO ₂ + Nd ₂ O ₃ + RO) ratio is 3 mol%. in the conjunction is _{more, (Nd 2 O 3 + RO} ) / (ZrO 2 + Nd 2 O 3 + RO) ratio Ri der less 33 mol%, _{and, RO / (ZrO 2 + Nd} 2 O 3 + RO) ratio of 12 mol% or more contained in a certain way, the rare earth metal R is yttrium (Y), ytterbium (Yb), scandium (Sc), lanthanum (La), Pra Ojimu (Pr), at least one metal selected from samarium (Sm), the composite oxide of platinum (Pt) is supported as a catalyst metal, which is contained in the catalyst layer on the particulate filter, it It is characterized by.

According to the invention of claim 1 of the present application, as the exhaust gas component purification catalyst material, a rare earth metal R other than zirconium (Zr), neodymium (Nd) and cerium (Ce) is used as an oxide, and Nd ₂ O ₃ / ( with _{ZrO 2 + Nd 2 O 3 +} RO) ratio is not less than _{3mol%, (Nd 2 O 3} + RO) / (ZrO 2 + Nd 2 O 3 + RO) ratio Ri der less 33 mol%, and, RO / (ZrO ₂ By using a Zr—Nd—R composite oxide that is contained so that the ratio of + Nd ₂ O ₃ + RO is 12 mol% or more , zirconium (Zr) and neodymium (Nd) or other rare earth metals are contained. Compared with binary composite oxides, carbon can be oxidized and burned in a shorter time, and CO emissions during carbon combustion can be effectively suppressed. Further, the Zr—Nd—R-based composite oxide has a small reduction rate of the BET specific surface area, and as a result, the supported catalytic noble metal can be suppressed from being buried in the composite oxide, and also during high-temperature aging. The crystal form is maintained and the catalytic function contributing to the exhaust gas purification reaction is larger, and as a result, better exhaust gas purification performance can be realized. Further, as will become clear from the data described later, since it has a high oxygen storage / release capability in a temperature range useful as a catalyst, which is different from the oxygen storage materials containing ceria known so far, a three-way catalyst and lean NOx It can also be used as a catalyst.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 shows a state in which a DPF 3 is assembled in an exhaust passage 1 of a diesel engine. In this figure, an exhaust pipe constituting the exhaust passage 1 is connected to a diesel engine body (not shown) via an exhaust manifold (not shown) on the upstream side (left side in the figure). And the exhaust gas discharged | emitted from a diesel engine main body will flow in the direction shown by the arrow in FIG.

A DPF 3 for collecting PM in the exhaust gas is mounted in the exhaust passage 1. 2 and 3 are both explanatory diagrams schematically showing the DPF 3. In the present embodiment, the DPF 3 is a so-called wall flow type filter having an outer diameter formed in a cylindrical shape. The DPF ₃ is made of a large number of flow holes 5a (by heat resistant ceramics such as cordierite, SiC, Si ₃ N _4, etc. 4) and a filter body 6 formed in a honeycomb shape having a large number of cells 4 (passages) extending in parallel with each other along an exhaust path, and a part in a zigzag shape. A plugging portion 15 for plugging the upstream end side of the cell 4b and the downstream end side of the other cell 4a.

  In the DPF 3 having such a structure, as indicated by an arrow in FIG. 3, the exhaust gas flowing in from the upstream cell 4a opened on the upstream end side flows through the porous wall to the downstream cell 4b opened on the downstream end side. In the meantime, PM is collected. Instead of this DPF 3, a conventionally known three-dimensional network structure carrier using a heat resistant material such as silicon carbide may be adopted.

FIG. 4 is an enlarged sectional view showing the porous wall 5. As shown in FIG. 4, an oxidation catalyst layer 8 is formed in the internal flow path of the DPF 3 through which the exhaust gas flows by coating the inner wall surface with a particulate oxidation catalyst for burning PM. In the present embodiment, the particulate oxidation catalyst includes a catalytic noble metal such as platinum (Pt), palladium (Pd), or rhodium (Rh) for burning PM, and zirconium (Zr) as a carrier supporting the catalytic noble metal. ), Neodymium (Nd), and zirconium-neodymium-rare earth metal R-based composite oxide (hereinafter referred to as Zr-Nd-R-based composite oxide) containing rare earth metal R other than cerium (Ce) and neodymium (Nd) Alumina (Al ₂ O ₃ ) is included as oxide particles having a high specific surface area. Alumina stabilized with a rare earth metal such as La is preferable from the viewpoint of heat resistance, and further, an alumina having a specific surface area of 250 m ² / g or more is preferable for preventing sintering of the catalyst noble metal.

  When the Zr—Nd—R composite oxide and alumina described above are mixed and used, both of these Zr—Nd—R composite oxide and alumina are contained in the range of 10 g / L to 150 g / L. It is preferable to make it. This is because when the content of the Zr—Nd—R composite oxide is below the above range, the PM combustion performance is not sufficiently exhibited, and when the content of alumina is below the above range, the catalyst noble metal is supported. In this case, the degree of dispersion of the catalyst noble metal is lowered, and as a result, the improvement degree of the light-off performance and the purification performance of carbon monoxide generated at the time of PM combustion becomes poor. Further, Zr-Nd-R This is because if the contents of the system complex oxide and alumina are in the above range or more, the back pressure becomes high when particulates are collected and deposited on the DPF 3. These alumina and Zr—Nd—R composite oxides are coated on the internal flow path of DPF 3 mixed after a predetermined amount of catalyst noble metal is supported. Further, the oxidation catalyst layer 8 composed of the particulate oxidation catalyst may be formed over the entire area of the internal flow path of the filter body 6, or may be upstream of the internal flow path, particularly on the upstream side. It may be formed on the inner wall surface of the cell 4a and the flow hole 5a.

The catalyst noble metal is exemplified by at least one selected from platinum (Pt), palladium (Pd), rhodium (Rh), and the like. For example, with respect to platinum (Pt), a dinitrodiamine platinum nitric acid solution is added to the above complex oxide and mixed. The composite oxide is supported by evaporation to dryness. Each of the Zr—Nd—R composite oxide and alumina (Al ₂ O ₃ ) carries a catalyst noble metal, for example, platinum (Pt) in each of the examples described later. The amount of the catalyst noble metal supported on the composite oxide can be adjusted, for example, by adjusting the concentration and amount of dinitrodiamine platinum nitrate solution for platinum (Pt). The supported catalyst noble metal may be different.

Here, the reason why Zr and Nd are contained as essential components in the Zr—Nd—R composite oxide will be described. Table 1 below shows the BET specific surface area after heat treatment of various composite oxides. Specifically, three kinds of zirconium-based composite oxides (ZrO ₂ − after heat treatment at various temperatures in the atmosphere). 8 mol% Nd ₂ O ₃ , ZrO ₂ -8 mol% Y ₂ O ₃ , ZrO ₂ -8 mol% Yb ₂ O ₃ ).

  As can be seen from Table 1, the zirconium-based composite oxide containing Nd has a larger BET specific surface area than the zirconium-based composite oxide containing Y and Yb after passing through the thermal history. In other words, the large BET specific surface area means that there are many pores, and in addition to the merit that oxygen storage and release is performed smoothly, the supported catalyst noble metal is buried in the composite oxide. Therefore, the catalytic function contributing to the exhaust gas purification reaction is increased, and as a result, the exhaust gas purification performance is improved.

  Further, the zirconium-neodymium composite oxide contains rare earth metals excluding cerium (Ce) and neodymium (Nd). The rare earth metal contained in the zirconium-neodymium composite oxide is Sc, Y, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, excluding the cerium (Ce). , Yb, Lu, among which at least one metal selected from yttrium (Y), ytterbium (Yb), scandium (Sc), lanthanum (La), praseodymium (Pr), and samarium (Sm) is preferable. . Note that cerium (Ce) is excluded from the rare earth metal contained in each composite oxide because it does not exhibit oxygen ion conductivity as described later under predetermined conditions and may function as an electron transfer medium. This is because it is difficult to effectively exhibit oxygen ion conductivity.

  In order to form the oxidation catalyst layer 8, as described above, a Zr—Nd—R composite oxide and alumina are loaded with a catalyst noble metal (for example, platinum), and then Zr—Nd— supporting this catalyst noble metal. R-type composite oxide and alumina supporting catalytic noble metal are mixed and this mixture is mixed with water and a binder to form a slurry. The slurry is coated on the inner wall surface of the internal flow path of the filter body 6 and air blown. After removing the excess slurry, dry and fire. The thickness and the like of the oxidation catalyst layer 8 can be adjusted by the viscosity and concentration of the slurry.

  The Zr—Nd—R composite oxide contained in this particulate oxidation catalyst has oxygen ion conductivity. The mechanism by which PM is oxidized by the particulate oxidation catalyst using the complex oxide having oxygen ion conductivity is assumed as follows. FIG. 5 is an explanatory view showing the oxidation mechanism of PM.

  When exhaust gas is discharged from the diesel engine main body and PM is collected in the DPF 3, carbon 9 as PM is deposited on the oxidation catalyst layer 8. Since the carbon 9 is porous and has a characteristic of being easily bonded to oxygen, release / desorption of oxygen occurs in the surface portion of the oxidation catalyst layer 8 on which the carbon 9 is deposited. The oxygen concentration is lowered, and a microscopic difference in oxygen concentration is produced with respect to other portions.

Thus, when the oxygen concentration of a portion of the surface of the oxidation catalyst layer 8 is lowered, the Zr—Nd—R-based composite oxide constituting the oxidation catalyst layer 8 has oxygen ion conductivity, so that the composite having a high oxygen concentration From inside the oxide, oxygen ions O ²⁻ move to the surface portion where the oxygen concentration is lowered. This oxygen ion O ²⁻ reaches the surface of the oxidation catalyst layer 8 to become active oxygen, and as a result, a place where a carbon oxidation reaction is likely to occur on the composite oxide surface locally occurs.

  Then, the oxidation reaction of the carbon 9 starts at the site where the reaction conditions are the best. When this oxidation reaction starts, a fire type 10 is generated there, and oxygen around it is depleted by this fire type 10 to form an oxygen-deficient space 11. In an oxygen deficient state, the oxidation reaction of carbon 9, that is, the fire is weakened, and the fire type 10 disappears eventually. However, in the DPF 3 according to this embodiment, the particulate oxidation catalyst constituting the oxidation catalyst layer 8 is oxygen ion conductive. Since the active oxygen is continuously supplied to the oxygen-deficient space 11 by the action of the composite oxide, the oxidation reaction of the carbon 9 is performed. Is promoted, and the combustion area expands around the fire type 10.

  In other words, in an oxygen-excess atmosphere, an oxygen concentration difference is generated between the oxygen-deficient space 11 and its surroundings. A balance is generated, and oxygen ions are moved from the high oxygen concentration portion to the oxygen-deficient space 11 through the Zr—Nd—R-based composite oxide of the oxidation catalyst layer 8. The oxygen ions are released as active oxygen into the oxygen-deficient space 11, thereby promoting the combined combustion of carbon 9 and active oxygen, that is, oxidation. Therefore, since the fire type 10 generated on a part of the surface of the oxidation catalyst layer 8 is not lost, the combustion region is expanded, so that the PM that is the carbon 9 can be burned and purified efficiently and in a short period of time. For this reason, the combustion rate of PM can be substantially improved.

  Here, since rare earth metals are contained in the Zr—Nd—R composite oxide, inside the Zr—Nd—R composite oxide, as shown in FIG. Nd) and other rare earth metals (both are indicated by black circles in the figure), whereby oxygen ion vacancies exist and oxygen ions are transported through the vacancies. In FIG. 5, alumina is omitted.

  By the way, the DPF 3 is often provided with an oxidation catalyst that oxidizes HC or the like upstream thereof, and the exhaust gas introduced into the DPF 3 by burning the fuel increased by the post-injection control or the like in the diesel engine with the oxidation catalyst. A means for increasing the temperature of the gas and promoting carbon combustion is taken, but in such a case, there is a possibility that extra fuel may be consumed due to oxidation combustion of PM.

  However, the inventor of the present application adopts the Zr—Nd—R composite oxide according to the present embodiment, so that the conventional cerium composite oxide or composite oxide containing Zr and one kind of rare earth metal Y is used. As a result, it has been found through experiments that a further improvement in the carbon burning rate can be realized, and as a result, an increase in fuel can be reduced.

  In order to confirm such an effect, an experiment conducted for evaluating PM combustion performance in the DPF and the result thereof will be described below.

(A) Carbon burning rate evaluation experiment For the evaluation experiment of the carbon burning rate in the Zr-Nd-R composite oxide, the components and the content ratio of the Zr-Nd-R composite oxide contained in the particulate oxidation catalyst were determined. Several modified samples were prepared. More specifically, 26 types of samples of the Zr—Nd—R-based composite oxide, and carbon black, which is simulated PM, are deposited on the catalyst layer surfaces of the four types of samples for comparison, and the catalyst inlet is used for these. An experiment was conducted to measure the carbon burning rate at a gas temperature of 590 ° C.

Here, a material in which the total amount of the catalyst noble metal is supported on the composite oxide contained in the particulate oxidation catalyst without mixing alumina (Al ₂ O ₃ ) is used. In addition, as a DPF carrier (filter body 6) of this experiment, a sample of a cylindrical test sample having a volume of 25 ml is cut out from a DPF carrier made of silicon carbide having a cell structure of 12 mil / 300 cpsi (cell per square inch). used.

(Sample preparation method)
A method for preparing each sample will be described.
In preparing the Zr—Nd—R-based sample, the content of neodymium oxide (Nd ₂ O ₃ ) relative to zirconium oxide (ZrO ₂ ), and the rare earth metal R other than cerium (Ce) and neodymium (Nd) A total of 26 types of Zr—Nd—R composite oxides having different oxide (RO) contents are prepared. As the rare earth metal other than neodymium (Nd), any one of yttrium (Y), ytterbium (Yb), scandium (Sc), lanthanum (La), praseodymium (Pr), and samarium (Sm), or lanthanum (La) ) And praseodymium (Pr). These Zr-Nd-R composite oxides dissolve nitrates of each metal mixed in ion-exchanged water, drop an alkaline solution adjusted with ammonia to form a precipitate containing each metal element, filter, wash with water , Dried and fired at 500 ° C. for 2 hours. Then, platinum (Pt) is supported as a catalyst noble metal on these Zr—Nd—R composite oxides. The supported amount of platinum is set to 0.5 g / L with respect to a Zr—Nd—R-based composite oxide of 50 g / L (50 g per 1 L of DPF3).

That is, each of the complex oxide powders having different contents of Nd ₂ O ₃ and RO is mixed with a dinitrodiamine platinum nitric acid solution, and platinum (Pt) is converted into a zirconium-neodymium complex oxide by evaporation to dryness. It was made to carry on.

  After drying this, it is pulverized in a mortar, heated and fired in an electric furnace at 500 ° C. in an air atmosphere for 2 hours, and a Zr—Nd—R-based catalyst powder comprising a Pt-supported Zr—Nd—R-based composite oxide ( Pt-supported composite oxide powder) was obtained. By mixing the obtained Pt-supported composite oxide with water and a binder to make a slurry, and sucking the slurry into the filter body 6 plugged by the plugging portion 15 and removing excess slurry by air blowing Zr-Nd-R system in which an oxidation catalyst layer 8 is formed over substantially the entire internal flow path of the filter main body after being washed and dried and then heated in an electric furnace at 500 ° C. in an air atmosphere for 2 hours and fired. A sample of was obtained.

As a sample for comparison, four kinds of Zr—Nd-based oxides each containing no rare earth metal R other than cerium (Ce) and neodymium (Nd) and having different contents of Nd ₂ O ₃ were added to the aforementioned Zr. As in the case of the —Nd—R-based composite oxide, platinum (Pt) is supported, and this Pt-supported oxide is used as a slurry, which is sucked, removed, dried, and baked. A sample in which an oxide catalyst layer was formed was obtained.

(Carbon burning rate evaluation experiment)
Each sample obtained in this manner was subjected to an aging treatment that was allowed to stand for 24 hours in the atmosphere at 800 ° C., and was set in a model gas flow catalyst evaluation apparatus for flowing simulated exhaust gas. A carbon burning rate evaluation experiment was conducted to examine the evaluation.

In this experiment, carbon black powder (manufactured by Sigma-Aldrich) was deposited on DPF3 instead of PM as an index for calculating PM combustion performance, and when the temperature was raised while flowing simulated exhaust gas, Evaluation was performed using the concentration of CO ₂ and CO discharged by combustion. In the deposition of the carbon black powder, 10 cc of ion exchange water is added to the carbon black powder equivalent to 10 g / L, and the mixture is stirred and mixed for 5 minutes using a stirrer to sufficiently disperse the carbon black powder. The upstream end side of the filter body 6 as a sample was immersed in this, and at the same time, suction was performed by an aspirator from the opposite side to the immersed end surface. Moisture that could not be removed by this suction was removed by air blowing from the soaked end face side, and dried at 150 ° C. for 2 hours with a dryer.

In the model gas flow catalyst evaluation apparatus, oxygen gas and water vapor are each 10% by volume with respect to the total gas flow rate and NO (nitrogen monoxide) is contained at 300 ppm while the temperature is raised to 600 ° C. at a rate of 15 ° C./min. Then, the simulated exhaust gas in which the remainder was nitrogen gas or the like was circulated so that the space velocity was 80000 / h, and the CO and CO ₂ concentrations immediately after the outlet portion of the DPF 3 were measured. Then, the CO, was based on the CO ₂ concentration determined a carbon burning rate defined by the following equation. The carbon burning rate indicates the amount of carbon burned per 25 ml of the test DPF carrier.

  FIG. 6 corresponds to a sample (Examples 1 to 26) corresponding to a total of 26 types of various Zr—Nd—R-based composite oxides obtained based on the above formula and a total of 4 types of Zr—Nd composite oxides. It is a table | surface showing the measurement result of the carbon combustion rate of the made sample (Comparative Examples 1-4). This table also shows the CO generation amount. FIG. 7 is a graph showing the measurement result of the carbon burning rate shown in FIG. 6. Among the Zr—Nd—R composite oxides, praseodymium (Pr) or lanthanum (La) is used as the rare earth metal R. It is a graph showing the change of the carbon combustion rate accompanying the change of the content of neodymium (Nd) in the Zr—Nd composite oxide when used.

  As can be seen from FIGS. 6 and 7, the Zr—Nd—R sample in which the particulate oxidation catalyst is constituted by the Zr—Nd—R composite oxide is better than each Zr—Nd sample as a comparative example. Carbon burning rate was realized.

Specifically, each sample of Zr, which is a comparative example, is contained for a sample in which the content of neodymium (Nd) is such that the Nd ₂ O ₃ / (ZrO ₂ + Nd ₂ O ₃ + RO) ratio is 3 mol% or more. A better carbon burning rate was achieved than the -Nd sample. As is apparent from FIG. 6, the Nd ₂ O ₃ / (ZrO ₂ + Nd ₂ O ₃ + RO) ratio is more preferably 6 mol% or more, and further preferably 12 mol% or more.

_{Also, Nd 2 O 3 / (ZrO} 2 + Nd 2 O 3 + RO) ratio is 12.0 mol%, _{and, La 2 O 3 / (ZrO} 2 + Nd 2 O 3 + La 2 O 3) ratio is 3 mol% In addition, in Example 20 in which the ratio of Pr ₂ O ₃ / (ZrO ₂ + Nd ₂ O ₃ + Pr ₂ O ₃ ) is 18 mol%, the amount of CO generated during carbon combustion is increased as compared with other samples. From this tendency of increasing the amount of generated CO, it was estimated that it is not preferable that the (Nd ₂ O ₃ + RO) / (ZrO ₂ + Nd ₂ O ₃ + RO) ratio exceed 33 mol%. In the table of FIG. 6, “−” in the CO generation amount is less than 1 ppm.

That is, zirconium, neodymium, and rare earth metal R have an Nd ₂ O ₃ / (ZrO ₂ + Nd ₂ O ₃ + RO) ratio of 3 mol% or more, and (Nd ₂ O ₃ + RO) / (ZrO ₂ + Nd _2). By being contained so that the O ₃ + RO) ratio is 33 mol% or less, the carbon 9 can be oxidized and burned in a shorter time, and the emission of CO during carbon combustion can be effectively suppressed.

Furthermore, as can be seen from FIG. 7, when the content of the rare earth metal R is contained so that the RO / (ZrO ₂ + Nd ₂ O ₃ + RO) ratio is 12 mol% or more, the carbon is surely better. Burning rate was realized.

(B) Catalyst physical property evaluation experiment In addition to the above-described carbon combustion performance evaluation, the present inventor contains lanthanum (La) and praseodymium (Pr) as rare earth metals other than cerium (Ce) and neodymium (Nd), respectively. An experiment for evaluating the physical properties of the catalyst by X-ray structural analysis of two types of Zr—Nd—R composite oxides was conducted.

8 and 9 are respectively ZrO ₂ -12 mol% Nd ₂ O ₃ -6 mol% La ₂ O ₃ (hereinafter simply referred to as Zr-12Nd-6La according to Example 7. Other composite oxides are also the same). .) It is a chart showing the X-ray diffraction measurement of the composite oxide and the Zr-12Nd-6Pr composite oxide. These samples are subjected to aging treatment at 800 ° C. for 24 hours in the air. In these graphs, sharp peaks appear, and it can be seen that the crystal form of each composite oxide is retained. In other words, the Zr—Nd—R composite oxide can maintain a crystal structure even when subjected to high temperature aging corresponding to the environment exposed to engine exhaust gas, thereby maintaining oxygen ion conductivity. Performance degradation can be suppressed.

  In the present embodiment, as described above, since the zirconium-neodymium-based composite oxide is selected as the composite oxide, in addition to the reduction rate of the BET specific surface area being reduced, the crystal form is maintained in this way. The catalyst function contributing to the exhaust gas purification reaction is larger, and as a result, better exhaust gas purification performance can be obtained.

(C) Oxygen storage / release capability evaluation experiment Further, in addition to the above-described carbon combustion performance evaluation and catalyst physical property evaluation, the present inventor has two types of Zr—Nd—R-based composite oxides (in Example 13 in FIG. 6). The oxygen storage / release capability evaluation was performed on the corresponding Zr-6Nd-6Pr and Zr-12Nd-18Pr-3La) corresponding to Example 20 in FIG.

The oxygen storage / release capability was measured as follows.
Each sample was previously loaded with platinum (Pt) at 1.0 wt%, and was subjected to an aging treatment in which the sample was allowed to stand for 24 hours at 800 ° C. under atmospheric pressure. 100 mg of this was taken and set in a fixed bed flow type reactor, and in order to occlude oxygen, a He balance gas containing 5% by volume of oxygen gas was flowed at a flow rate of 100 cc / min from room temperature to 600 ° C. The temperature was raised at 30 ° C./min.

Then, after hold | maintaining at 600 degreeC for 5 minute (s), it cools under the same gas distribution to room temperature. Subsequently, the balance is switched to He balance gas containing 2% by volume of CO gas, and the temperature is raised from room temperature to 600 ° C. at 20 ° C./min at a flow rate of 100 cc / min. As a result, oxygen is released and reacts with CO to generate CO ₂ . The graph shown in FIG. 10 summarizes the amount of CO ₂ generated at this time.

FIG. 10 is a graph showing the relationship between temperature and oxygen storage / release capability for various composite oxides. Here, as a comparative example, zirconium-yttrium composite oxide (Zr-8Y) and cerium-based oxide (complex oxide containing 90 mol% Ce and 10 mol% Pr as metal elements; Ce _0.9 Pr _{0 .1} O ₂ ) temperature and oxygen storage / release capacity are also shown.

  According to this data, it can be seen that the two types of Zr—Nd—R-based composite oxides have a larger oxygen storage / release capability in the entire temperature range than Zr—Y used as a comparative example. Further, Zr-6Nd-6Pr corresponding to Example 13 in FIG. 6 is in a temperature range of about 220 to 330 ° C., and Zr-12Nd-18Pr-3La corresponding to Example 20 in FIG. In the temperature range of ˜300 ° C., an oxygen storage / release capacity higher than that of the cerium-based oxide, which is known to have an oxygen storage / release capacity, was confirmed. This temperature range is a range in which the catalytic noble metal gradually increases in activity, and the inclusion of a complex oxide having a high oxygen storage / release capability in such a range is an exhaust gas component purification catalyst for HC, CO, NOx. Useful. In other words, the exhaust gas component purification catalyst material containing the Zr—Nd—R composite oxide such as Examples 13 and 20 is not limited to the use of carbon combustion, but also a three-way catalyst, a lean NOx catalyst, and a diesel oxidation catalyst. It can be said that it is a useful catalyst material.

(D) NOx purification performance evaluation experiment Furthermore, in addition to the above-mentioned carbon combustion performance evaluation, catalyst physical property evaluation, and oxygen storage / release capacity evaluation, the inventor of the present application has five types of Zr—Nd—R-based composite oxides (see FIG. 6 Zr-3Nd-6La corresponding to Example 1, Zr-12Nd-12La corresponding to Example 8, Zr-12Nd-12Pr corresponding to Example 17, Zr-12Nd-18Pr corresponding to Example 18 The NOx purification performance evaluation regarding Zr-12Nd-18Pr-3La) corresponding to Example 20 was performed.

The NOx purification performance measurement was performed as follows.
Each Zr—Nd—R composite oxide is mixed with a 1: 1 mass ratio of alumina (alumina: Zr—Nd—R composite oxide = 1: 1 (mass ratio)), water, and a binder to form a slurry. The slurry is sucked into the honeycomb carrier formed from cordierite as the filter body 6 and is washed by removing excess slurry by air blow, dried and fired to form the first on the honeycomb carrier. A washcoat layer was formed. The first washcoat layer was set to 270 g / L (270 g per liter of honeycomb carrier), and the honeycomb carrier having a cell density of 4.5 mil / 400 cpsi was used.

  Next, Rh-supported alumina supporting catalyst metal Rh, water and a binder are mixed to produce a slurry, and this slurry is sucked into the honeycomb carrier on which the first washcoat layer is formed, and excess air is blown by air blow. The slurry was removed to wash coat, and dried and fired to form a second wash coat layer on the first wash coat layer formed on the honeycomb carrier. The supported amount of catalyst metal Rh supported on alumina was set to 0.5 g / L, and the second washcoat layer was set to 50 g / L.

  Then, the honeycomb carrier on which the first washcoat layer and the second washcoat layer are formed is immersed in an aqueous acetic acid solution containing barium and strontium as a NOx trap material for trapping NOx in the exhaust gas. After impregnating the coat layer and the second washcoat layer with barium acetate and strontium acetate, drying and firing were performed to form a first catalyst layer and a second catalyst layer on the honeycomb carrier. Further, the honeycomb carrier on which the first catalyst layer and the second catalyst layer are formed is dipped in a dinitrodiamine platinum nitric acid solution, and then dried and fired to obtain a Zr—Nd—R composite oxide and alumina. Platinum was supported as a catalyst metal. The catalyst metal Pt content was set to 2 g / L, the barium content was set to 30 g / L, and the strontium content was set to 10 g / L.

  FIG. 11 is a cross-sectional explanatory view schematically showing a two-layer catalyst layer formed on a honeycomb carrier of a sample for NOx purification performance evaluation. In the NOx purification performance evaluation sample 20 prepared as described above, as shown in FIG. 11, the catalyst layer 22 formed on the honeycomb carrier 21 has the first catalyst layer 23 on the honeycomb carrier 21 side, The first catalyst layer 23 includes an alumina 25 as oxide particles having a high specific surface area, platinum 26 as a catalyst metal, and Zr—Nd—. The R-based composite oxide 27 and the NOx trap material 28 are contained, and the Zr—Nd—R-based composite oxide 27 and the alumina 25 carry platinum 26 and the NOx trap material 28. The second catalyst layer 24 contains alumina 25, Rh29 and Pt26 as catalyst metals, and a NOx trap material 28. The alumina 25 carries Rh29, Pt26, and the NOx trap material 28. .

  As a sample for comparison, one kind of Zr-based oxide (Zr-20Pr) and three kinds of Zr-Nd-based oxides (Zr-12Nd corresponding to Comparative Example 3 in FIG. Corresponding Zr-20Nd and Zr-1Nd-8La) are used in place of the aforementioned Zr-Nd-R-based composite oxide, and samples are prepared in the same manner as the aforementioned Zr-Nd-R-based composite oxide sample. Was prepared.

(NOx purification performance evaluation experiment)
Each sample for evaluation thus obtained was subjected to aging treatment in the atmosphere at 750 ° C. for 24 hours, and set in a model gas flow catalyst evaluation apparatus for flowing simulated exhaust gas. An NOx purification performance evaluation experiment was conducted to examine the purification performance evaluation.

  As the simulated exhaust gas, a lean gas having a gas component shown in Table 2 below and having an air-fuel ratio of 28 (A / F = 28) and a rich gas having an air-fuel ratio of 14 (A / F = 14) are used. While maintaining the predetermined temperature and flowing alternately every minute, the NOx purification rate when the simulated exhaust gas was lean was measured. Here, the space velocity SV was 30,000 / hour, and 200 ° C., 250 ° C., and 300 ° C. were used as predetermined gas temperatures.

  FIG. 12 shows the measurement results of the NOx purification performance. As shown in FIG. 12, regarding the NOx purification performance, Examples A, B, C, D, and E were respectively Comparative Examples A, B, C, and D at 200 ° C., 250 ° C., and 300 ° C. Compared to the above, it was confirmed that the NOx purification rate during lean was high and the NOx purification performance in exhaust gas was excellent.

Thus, the Nd ₂ O ₃ / (ZrO ₂ + Nd ₂ O ₃ + RO) ratio is 3 mol% or more, and the (Nd ₂ O ₃ + RO) / (ZrO ₂ + Nd ₂ O ₃ + RO) ratio is 33 mol. % Of the exhaust gas component purification catalyst provided with a catalyst carrier base material having a catalyst layer containing a Zr—Nd—R-based composite oxide contained so as to be less than or equal to 1%. The Zr—Nd—R composite oxide is contained in the first catalyst layer, and alumina, Pt, NOx trap material are included in each of the first catalyst layer and the second catalyst layer. By containing, NOx at the time of lean can be effectively purified.

  In the exhaust gas component purification catalyst, the Zr—Nd—R composite oxide contained in the first catalyst layer has high oxygen ion conductivity, and takes in oxygen in the atmosphere and releases active oxygen when lean. Since it excels in the oxygen exchange reaction, the oxidation reaction of trapped NOx can be promoted and trapped as nitrate, so the NOx purification performance can be improved. In addition, since the Zr—Nd—R composite oxide has basic properties, it is easy to attract NOx, and NOx can be trapped effectively.

  On the other hand, when the exhaust gas component purification catalyst reduces the trapped NOx when rich, the Zr-Nd-R composite oxide has a smaller oxygen release amount than the Ce composite oxide. Therefore, NOx can be effectively purified without inhibiting the NOx reduction reaction.

  Further, when NOx trapped in the second catalyst layer is desorbed by supporting rhodium and platinum on alumina contained in the second catalyst layer, most of the NOx is in the first catalyst layer. Thus, efficient reduction and purification of desorbed NOx can be promoted by Rh that promotes the NOx reduction reaction, and the above-described effects can be more effectively achieved.

  In the present embodiment, the Zr—Nd—R composite oxide is contained only in the first catalyst layer below the exhaust gas passage side, but the Zr is also contained in the second catalyst layer on the exhaust gas passage side. You may make it contain -Nd-R type complex oxide. In addition, barium and strontium are used as the NOx trap material, but alkaline earth metals other than barium and strontium, alkali metals such as potassium, lithium and sodium, and rare earth metals such as cerium, lanthanum and praseodymium are used. it can.

  Further, in the present embodiment, two catalyst layers are formed on the catalyst carrier base material. However, even when three or more catalyst layers are formed, at least the exhaust gas passage side of the plurality of layers is used. NOx trap material that traps NOx trapping oxide particles having a high specific surface area, platinum (Pt) as the catalyst metal, and NOx in each of the plurality of layers, the layer below the layer containing the composite oxide The same effect can be acquired by including.

As described above, the present invention is not limited to the illustrated embodiments, and it goes without saying that various improvements and design changes can be made without departing from the gist of the present invention.
For example, in the above-described embodiment, the wall flow type particulate filter is used as the DPF. However, the present invention is not limited to this, and a three-dimensional mesh type particulate filter may be employed. Alternatively, since the composite oxide according to the present invention has oxygen ion conductivity, it is effective for the above PM combustion, and also has oxygen storage capacity, so that PM is deposited upstream of the DPF. It may be contained in a diesel oxidation catalyst or a lean NOx catalyst on a straight flow type honeycomb carrier.

It is explanatory drawing which shows the state which assembled | attached DPF and the oxidation catalyst in the exhaust passage of the diesel engine. It is a front view which shows typically DPF of this embodiment. It is a longitudinal cross-sectional view which shows the said DPF typically. It is sectional drawing which expands and shows the porous wall of the said DPF. It is explanatory drawing which shows the combustion mechanism of PM. It is a table | surface showing the carbon combustion rate of various Zr-Nd-R type complex oxide (Example) and Zr-Nd complex oxide (comparative example). It is a graph showing the change of the carbon combustion rate accompanying the change of content (Zr + Nd + R) of Nd in Zr-Nd-R type complex oxide and Zr-Nd complex oxide. It is a Xr-ray-diffraction measurement chart figure of Zr-12Nd-6La-O. It is a X-ray-diffraction measurement chart figure of Zr-12Nd-6Pr-O. It is a graph showing the relationship between the temperature and oxygen storage / release capability for various composite oxides. FIG. 3 is an explanatory cross-sectional view schematically showing a two-layer catalyst layer formed on a honeycomb carrier of a sample for NOx purification performance evaluation. It is a table | surface showing the measurement result of the purification performance of NOx.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Exhaust passage, 3 ... DPF, 6 ... Filter body, 8 ... Oxidation catalyst layer, 9 ... Carbon, 20 ... Catalyst material for exhaust gas component purification, 21 ... Honeycomb carrier, 22 ... Catalyst layer, 23 ... First catalyst layer , 24 ... second catalyst layer

Claims (1)

A catalyst material for exhaust gas component purification containing a complex oxide containing zirconium (Zr) and neodymium (Nd) as essential components, and further containing a rare earth metal R other than cerium (Ce) and neodymium (Nd),
The zirconium constituting the composite oxide, as neodymium and rare earth metal R _oxides, with _{Nd 2 O 3 / (ZrO 2} + Nd 2 O 3 + RO) ratio is not less than _{3mol%, (Nd 2 O 3} + RO) _{/ (ZrO 2 + Nd 2 O} 3 + RO) ratio Ri der less 33 mol%, _{and, RO / (ZrO 2 + Nd} 2 O 3 + RO) ratio are contained such that the above 12 mol%,
The rare earth metal R is at least one metal selected from yttrium (Y), ytterbium (Yb), scandium (Sc), lanthanum (La), praseodymium (Pr), and samarium (Sm),
A catalyst material for purifying exhaust gas components, wherein the composite oxide carries platinum (Pt) as a catalyst metal and is contained in a catalyst layer on a particulate filter .

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