JP2009082880A - Exhaust gas cleaning catalyst apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas cleaning catalyst apparatus reducing an exhaust amount of H<SB>2</SB>S and exhibiting a high cleaning performance. <P>SOLUTION: In the exhaust gas cleaning catalyst apparatus, an upstream side catalyst 3 arranged in an upstream side in a circulation direction of the exhaust gas and a downstream side catalyst 4 arranged in a downstream side in the circulation direction of the exhaust gas are provided on an exhaust passage 2 of an engine 1. The downstream side catalyst 4 contains a rhodium-doped type composite oxide containing cerium (Ce) and a Ni component, and the upstream side catalyst 3 contains an oxygen occlusion material containing cerium (Ce) other than the rhodium-doped composite oxide and a Ni component. The exhaust gas cleaning catalyst apparatus is used, which is characterized in that a ratio of Ni relative to CeO<SB>2</SB>in the upstream side catalyst 3 is 15 mass% to 20 mass% and a ratio of Ni relative to CeO<SB>2</SB>in the downstream side catalyst 4 is 10 mass% to 60 mass%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust gas purifying catalyst device useful for purifying exhaust gas discharged from an internal combustion engine such as an automobile engine.

  As an exhaust gas purification catalyst device for purifying exhaust gas exhausted from an engine, for example, a manifold catalyst (directly connected catalyst, closed coupled catalyst) disposed directly connected to a joint part of exhaust gas in an engine manifold, The one provided with the underfloor catalyst arrange | positioned downstream is known. In this case, since the manifold catalyst is close to the engine, particularly when the exhaust gas temperature is low, such as when the engine is started, the exhaust gas is heated up as soon as possible so that hydrocarbons (HC), carbon monoxide (CO), etc. The exhaust gas is purified, and the underfloor catalyst purifies exhaust gas that could not be purified by the manifold catalyst, especially during normal operation or high speed operation.

  Each of these catalysts often contains an oxygen storage material. When the exhaust gas is in an oxygen-excess state (A / F lean state), it stores oxygen and is in an oxygen-deficient state (A / F rich state). In some cases, oxygen is released to bring the air-fuel ratio (A / F) of the exhaust gas into a substantially stoichiometric state, thereby increasing the catalytic activity and improving the purification performance.

  On the other hand, since gasoline (engine fuel) and engine oil (lubricant) contain sulfur (S), the exhaust gas discharged from the engine contains sulfur components such as sulfur oxides. ing. It is known that the exhaust gas purifying catalyst provided in the exhaust gas purifying catalyst device causes S poisoning due to the S component, and the catalytic activity is lowered.

Furthermore, this S component is easily adsorbed in the form of oxides on the oxygen storage / release material contained in the exhaust gas purification catalyst. When the exhaust gas is in an oxygen-deficient state, it is converted into hydrogen sulfide (H ₂ S) and discharged. H ₂ S is known as an off-flavor component and is required to reduce its emission amount. Further, the exhaust gas purifying catalyst is also poisoned by S due to this H ₂ S, and the catalytic activity is lowered.

Therefore, in order to suppress the generation of H ₂ S and reduce the H ₂ S emission amount and the S poisoning of the exhaust gas purification catalyst, nickel (Ni) which is a transition metal, its oxide (NiO), etc. The Ni component is contained in the exhaust gas purification catalyst. By doing so, it is known that the Ni component traps the S component, becomes Ni sulfide, and can suppress the generation of H ₂ S.

  As an example of such an exhaust gas purifying catalyst containing Ni or NiO, for example, Patent Document 1 discloses a support base material and an active alumina coating layer containing nickel oxide formed on the surface of the support base material. An exhaust gas purifying catalyst comprising a composite oxide of cerium oxide and zirconium oxide supported on the activated alumina coating layer and a noble metal catalyst supported on the activated alumina coating layer is disclosed.

Further, in Patent Document 2, in an exhaust gas purifying catalyst in which a plurality of catalyst layers are formed in layers on a carrier, a predetermined catalyst layer located on a lower layer side than the uppermost catalyst layer is oxidized. An exhaust gas purifying catalyst containing nickel and palladium is disclosed.
JP-A-1-242149 JP-A-8-290063

As described above, it is known that the exhaust gas purifying catalyst containing Ni or NiO as described above can suppress the generation of H ₂ S. Therefore, even when a manifold catalyst and an underfloor catalyst are provided, it is preferable to add a Ni component that traps the S component to each catalyst. Further, increasing the amount of Ni component added to further suppress the generation of H ₂ S is certainly effective in reducing the amount of H ₂ S discharged, but purification performance of HC, CO, NOx, etc. The problem of causing a drop in

It is an object of the present invention to provide an exhaust gas purification catalyst device that reduces H ₂ S emission and exhibits high purification performance.

The exhaust gas purifying catalyst device of the present invention includes an upstream catalyst disposed upstream of the exhaust gas flow direction and a downstream catalyst disposed downstream of the exhaust gas flow direction in the exhaust passage of the engine. An exhaust gas purification catalyst device provided, wherein the downstream catalyst is a rhodium-doped complex oxide in which rhodium is disposed between crystal lattice points or lattice points of an oxygen storage material containing cerium (Ce), and at least One of nickel (Ni) and nickel oxide (NiO), wherein the upstream catalyst contains cerium (Ce) other than the rhodium-doped composite oxide, and at least nickel (Ni) And nickel oxide (NiO), and the ratio of Ni to CeO ₂ in the upstream catalyst is 15 mass% or more and 20 mass% or less, The ratio of Ni to CeO ₂ in the downstream catalyst is 10% by mass or more and 60% by mass or less.

According to this configuration, the exhaust gas passes through the upstream side catalyst and the downstream side catalyst, and purifies HC, CO, NOx, etc. in both the upstream side catalyst and the downstream side catalyst. Even if the performance is somewhat lower than when nickel is not added, the final emission of HC, CO, NOx, etc. is small, and high purification performance is maintained. Moreover, since the generation of H ₂ S is suppressed in both the upstream catalyst and the downstream catalyst, the effect of suppressing the generation of H ₂ S in each catalyst is somewhat lower than when a large amount of Ni is added. However, the final H ₂ S emission can be reduced.

  The oxygen storage material contained in the downstream catalyst is a rhodium-doped complex oxide in which rhodium is disposed between crystal lattice points or lattice points. Such a complex oxide has a high oxygen storage / release rate and a large amount of oxygen storage, so even if the oxygen concentration of the exhaust gas fluctuates, a suitable oxygen concentration can be easily adjusted, and the downstream The side catalyst can work effectively. That is, exhaust gas that could not be purified by the upstream catalyst can be efficiently purified by the downstream catalyst. Also from this, high purification performance can be exhibited.

Therefore, the exhaust gas purification catalyst device of the present invention can exhibit high purification performance while reducing the discharge amount of H ₂ S.

  Moreover, it is preferable that the said complex oxide contained in the said upstream catalyst and the said downstream catalyst contains a zirconium and neodymium. Such a complex oxide has a large oxygen storage amount, and even if the oxygen concentration of the exhaust gas fluctuates, the catalyst can work effectively and the purification performance can be further improved.

The ratio of nickel to cerium oxide in the upstream catalyst is preferably larger than the ratio of nickel to cerium oxide in the downstream catalyst. According to this configuration, the upstream catalyst suppresses the generation of H ₂ S more effectively, thereby further suppressing the S-poisoning of the downstream catalyst. HC, CO, NOx, etc. that could not be purified by the above can be more efficiently purified by the downstream catalyst.

  Moreover, it is preferable that the composite oxide contained in the upstream catalyst and the downstream catalyst is a catalyst on which a catalyst noble metal is supported. According to this configuration, HC, CO, NOx, and the like can be purified more efficiently, and higher purification performance can be exhibited.

  Further, the catalyst noble metal supported on the composite oxide contained in the upstream catalyst is palladium and rhodium, and the catalyst noble metal supported on the composite oxide contained in the downstream catalyst is platinum. And rhodium are preferred.

According to the present invention, while reducing the emission of H 2 _S, it can exhibit high purifying performance.

  An exhaust gas purifying catalyst device according to an embodiment of the present invention will be described.

  FIG. 1 is a schematic view showing an exhaust gas purification catalyst device. The exhaust gas purification catalyst device is configured by filling an exhaust passage 2 connected to an engine 1 of an automobile with an upstream catalyst 3 and a downstream catalyst 4 respectively. The upstream catalyst 3 is disposed upstream of the exhaust gas flow direction, and the downstream catalyst 4 is disposed downstream of the exhaust gas flow direction. Further, the upstream catalyst 3 and the downstream catalyst 4 are provided apart from each other, and purify air pollutants such as HC, CO, and NOx present in the exhaust gas, respectively.

First, the upstream catalyst 3 will be described. The upstream catalyst 3 has an oxygen storage capacity, contains a composite oxide containing Ce, and at least a Ni component that is one of Ni and NiO, and the ratio of Ni to CeO ₂ is 15% by mass. It is 20 mass% or less. If this ratio is less than 15% by mass, the effect of suppressing the generation of H ₂ S is reduced, and the catalytic activity is reduced due to S poisoning of the catalyst noble metal supported on the upstream side catalyst 3 and the downstream side catalyst 4. There is a tendency to cause an increase in H ₂ S emissions. Moreover, when this ratio exceeds 20 mass%, it exists in the tendency for the catalytic activity of the upstream catalyst 3 to fall.

  The composite oxide is a composite oxide other than the Rh-doped composite oxide described later, and preferably further contains zirconium (Zr) and neodymium (Nd). In addition, the composite oxide preferably basically has a catalyst noble metal supported thereon. Examples of the catalyst noble metal supported on the upstream catalyst 3 include platinum (Pt), palladium (Pd), and rhodium ( Rh) and the like are exemplified, and it is particularly preferable that two types of Pd and Rh are supported.

The upstream catalyst 3 may be any catalyst as described above. Specifically, the following catalysts are exemplified. As the upstream catalyst 3, for example, a honeycomb-shaped carrier formed of heat-resistant ceramics such as cordierite or SiC, Si ₃ N ₄ is used as a catalyst carrier, and a lower catalyst layer (lower layer) is formed thereon. The upper catalyst layer (upper layer) is further formed on the lower catalyst layer. Here, a honeycomb carrier is used as the catalyst carrier, but any catalyst carrier may be used as long as it is used as a catalyst carrier, and the catalyst carrier is not limited to the honeycomb carrier.

The lower layer includes, for example, a catalyst base on which Pd which is a catalyst noble metal is supported. As the catalyst base, lanthanum (La) -containing alumina, Ce, Zr, La, yttrium (Y), and aluminum (Al) are included. A composite oxide containing Ce (Zr / La / Y / Al composite oxide) is used. Here, as the La-containing alumina, for example, _La 2 _{O 3} content include alumina is 4 wt%, as the Ce · Zr · La · Y · Al composite oxide, for example, CeO ₂ content 10% by mass and a composite oxide having an alumina content of about 80% by mass.

This lower layer is made of CeO ₂ and a composite oxide containing Zr, Ce and Nd (Zr · Ce · Nd composite oxide) as a co-catalyst (OSC) in order to enhance the exhaust gas purification performance and heat resistance of palladium. ) And zirconia as a binder for enhancing the binding of each component, and NiO as a Ni component for suppressing generation of H ₂ S, S poisoning of Pd, and the like. ZrO ₂ also has a function of increasing the heat resistance of CeO ₂ . Here, examples of the Zr / Ce / Nd composite oxide include a composite oxide having a CeO ₂ content of 35 mass%, and examples of NiO include NiO powder. In addition, although NiO was illustrated as Ni component, Ni, such as Ni powder, may be sufficient.

In addition, the above components of the lower layer are, for example, 45 g / L for La-containing alumina, 20 g / L for Ce · Zr · La · Y · Al composite oxide, 6 g / L for CeO ₂ , and Zr · Ce · Nd composite oxide. A product is contained so that it may become 6 g / L, NiO is contained so that it may become the said predetermined ratio, and the remainder is zirconia as a binder.

The upper layer includes, for example, a catalyst base on which Rh, which is a catalyst noble metal, is supported, and the catalyst base includes alumina containing a composite oxide of Zr and La (Zr / La composite oxide-containing alumina). And Zr / Ce / Nd composite oxides are used. Here, as the Zr / Ce / Nd composite oxide, for example, a composite oxide having a CeO ₂ content of 10 mass% can be cited.

And this upper layer further contains La-containing alumina, contains zirconia as a binder for enhancing the binding of each component, and further, as a Ni component for suppressing generation of H ₂ S, S poisoning of Pd, and the like. NiO is included. Here, as the La-containing alumina, for example, _La 2 _{O 3} content include alumina is 4 wt%, the NiO, NiO powders, and the like. In addition, although NiO was illustrated as Ni component, Ni, such as Ni powder, may be sufficient.

  In addition, each of the above components in the upper layer is contained so that, for example, La · Zr-containing alumina is 30 g / L, Zr · Ce · Nd composite oxide is 75 g / L, and La-containing alumina is 15 g / L. The above-mentioned predetermined ratio is included, and the balance is zirconia as a binder.

  Next, a method for manufacturing the above illustrated upstream catalyst 3 will be described.

First, Pd is supported (post-supported) on La-containing alumina and Ce · Zr · La · Y · Al composite oxide. Then, Pd-supported La-containing alumina and Ce · Zr · La · Y · Al composite oxide, CeO ₂ , Zr · Ce · Nd composite oxide, NiO, and zirconyl nitrate are mixed in a predetermined amount. Further, an appropriate amount of water is added to form a slurry. This slurry is wash-coated on the honeycomb carrier. The wash-coated honeycomb carrier is dried at 150 ° C. and sintered at 500 ° C. to form a lower layer on the honeycomb carrier.

  Next, Rh is supported (post-supported) on the La · Zr-containing alumina and the Zr · Ce · Nd composite oxide. Then, a predetermined amount of Rh-supported La · Zr-containing alumina and Zr · Ce · Nd composite oxide, La-containing alumina, NiO, and zirconyl nitrate is mixed, and an appropriate amount of water is added to form a slurry. . This slurry is wash-coated on the honeycomb carrier on which the lower layer is formed. The wash-coated honeycomb carrier is dried at 150 ° C. and sintered at 500 ° C. to form an upper layer on the lower layer.

  As described above, the upstream catalyst 3 is manufactured.

Next, the downstream catalyst 4 will be described. The downstream catalyst 4 has an oxygen storage capacity, contains a composite oxide containing Ce, and at least a Ni component that is one of Ni and NiO, and the ratio of Ni to CeO ₂ is 10% by mass. It is 60 mass% or less. When this ratio is less than 10% by mass, the effect of suppressing the generation of H ₂ S is reduced, and the catalytic activity decreases due to S poisoning of the catalyst noble metal supported on the downstream side catalyst 4 and the H ₂ S is discharged. There is a tendency to cause an increase in quantity. Moreover, when this ratio exceeds 60 mass%, it exists in the tendency for the catalyst activity of the downstream catalyst 4 to fall. Further, the ratio of Ni to CeO ₂ in the upstream catalyst 3 is preferably larger than the ratio of Ni to CeO ₂ in the downstream catalyst 4.

  The complex oxide containing Ce is a Rh-doped complex oxide in which Rh is arranged between crystal lattice points or between lattice points, and preferably further contains Zr and Nd. In addition, the composite oxide containing Ce is basically preferably a catalyst noble metal supported, and the catalyst noble metal supported on the downstream catalyst 4 is selected from, for example, Pt, Pd, Rh, and the like. At least one type is exemplified, and it is particularly preferable that two types of Pt and Rh are supported.

The downstream catalyst 4 may be any catalyst as described above. Specifically, the following catalysts are exemplified. As the downstream catalyst 4, for example, a honeycomb carrier formed of heat-resistant ceramics such as cordierite, SiC, Si ₃ N ₄ or the like is used as the catalyst carrier, as in the upstream catalyst 3, and on the catalyst, A layer is formed. Here, a honeycomb carrier is used as the catalyst carrier, but any catalyst carrier may be used as long as it is used as a catalyst carrier, and the catalyst carrier is not limited to the honeycomb carrier.

The catalyst layer contains, for example, La-containing alumina on which Rt, which is a catalyst noble metal, is supported, and an Rh-doped Zr / Ce / Nd composite oxide, on which Rh, which is a catalyst noble metal, is supported. The Rh-doped Zr / Ce / Nd composite oxide carrying Rh is obtained by further carrying (post-supporting) Rh on the Rh-doped Zr / Ce / Nd composite oxide described later. . Here, examples of the La-containing alumina include alumina having a La content of 4% by mass, and the Rh-doped Zr / Ce / Nd composite oxide is a composite having a CeO ₂ content of 22% by mass. An oxide etc. are mentioned.

Then, the catalyst layer contains zirconia as a binder for enhancing the binding properties of the components, further includes NiO as Ni component for suppressing the generation of H 2 _S. Here, NiO powder etc. are mentioned as NiO. In addition, although NiO was illustrated as Ni component, Ni, such as Ni powder, may be sufficient.

  Each component of the catalyst layer is contained so that, for example, La-containing alumina is 50 g / L, and Rh-doped Zr / Ce / Nd composite oxide is 110 g / L. The balance is zirconia as a binder.

  FIG. 2 is a schematic diagram showing the structure of a Rh-doped Zr / Ce / Nd composite oxide and a Zr / Ce / Nd composite oxide post-supported with Rh. 2A shows a Rh-doped Zr / Ce / Nd composite oxide, and FIG. 2B shows a Zr / Ce / Nd composite oxide post-supported with Rh.

  The Rh-doped Zr / Ce / Nd composite oxide has a structure as shown in FIG. In the Rh-doped Zr · Ce · Nd composite oxide, Rh is arranged at the crystal lattice point of the composite oxide in the same manner as Zr, Ce and Nd, in other words, RhMOx (M is another metal atom, x is in the form of oxygen atoms) and is strongly bonded to the complex oxide. Or Rh will be in the state arrange | positioned between the atoms of the said complex oxide. In any case, a composite oxide in which Rh is uniformly dispersed on the surface and inside of the composite oxide is obtained.

On the other hand, the Zr / Ce / Nd composite oxide after-supporting Rh has a structure as shown in FIG. The Zr / Ce / Nd composite oxide after supporting Rh is produced by, for example, forming a composite oxide containing Zr, Ce and Nd by an ammonia coprecipitation method, and then evaporating and drying Rh on the composite oxide. It is a composite oxide obtained by post-supporting. In this case, Rh is in a state of Rh ₂ O ₃ being unevenly distributed on the surface of the composite oxide.

  Therefore, the Rh-doped Zr · Ce · Nd composite oxide has the following two advantages compared to the Zr · Ce · Nd composite oxide after supporting Rh.

  In the Zr / Ce / Nd composite oxide post-supported with Rh, the bond between Rh and the composite oxide is weak, and Rh moves on the surface of the composite oxide by heating and is sintered. On the other hand, in the case of the Rh-doped Zr · Ce · Nd composite oxide, as shown in FIG. 2A, Rh existing between the lattice points or atoms of the composite oxide is As a result of the strong interaction, movement due to heating is less likely to occur. In addition, Rh inside the complex oxide is considered to act as a steric hindrance and suppress sintering of the complex oxide.

  In addition, the Rh-doped Zr / Ce / Nd composite oxide has a higher oxygen storage rate and a higher maximum value than the Zr / Ce / Nd composite oxide post-supported with Rh. In addition, the oxygen storage amount is also increasing. Such a difference in oxygen storage characteristics is considered to be due to the following reason. FIG. 3 is a schematic view schematically showing the estimated oxygen storage mechanisms of the Rh-doped Zr / Ce / Nd composite oxide and the Zr / Ce / Nd composite oxide after-supporting Rh. . 2A shows a Rh-doped Zr / Ce / Nd composite oxide, and FIG. 2B shows a Zr / Ce / Nd composite oxide after-supporting Rh. Illustration of atoms is omitted.

In the Zr / Ce / Nd composite oxide after supporting Rh, as shown in FIG. 3B, oxygen (O ₂ ) is present in oxygen deficient portions (O vacancies) existing near the surface inside the composite oxide. Is occluded as oxygen ions, but cannot reach the oxygen deficient part existing in a relatively deep part inside the complex oxide, and this oxygen deficient part is not used much for oxygen occlusion. it is conceivable that.

In contrast, as shown in FIG. 3A, in the Rh-doped Zr / Ce / Nd composite oxide, oxygen (O ₂ ) becomes an oxygen ion and is attracted to Rh existing in the composite oxide. It is considered that the oxygen atom instantaneously moves to the oxygen deficient portion inside the composite oxide through this Rh. In addition, since Rh is dispersed inside the complex oxide, oxygen ions hop through the complex oxide surface via a plurality of Rhs and enter oxygen deficient portions deep inside the complex oxide. it is conceivable that. For this reason, in the case of the Rh-doped complex oxide, the oxygen storage rate in an oxygen-excess atmosphere is quickly increased, and the maximum value of the oxygen storage rate is also increased. Since the oxygen deficient portion at a deep location is also used for oxygen storage, it is considered that the oxygen storage amount increases.

  Next, a method for producing the Rh-doped complex oxide will be described.

  First, a raw material preparation step for preparing an acidic solution containing Rh, Ce, and Zr is performed. The raw material preparation step can be prepared, for example, by mixing a solution of nitrate of each metal. If necessary, other metals such as Nd can be included.

  Next, a step of preparing a composite oxide precursor by an ammonia coprecipitation method is performed. In this step, while stirring the acidic solution as the starting material, excess ammonia water is quickly added and mixed, or the acidic solution and ammonia water are simultaneously supplied to a rotating cup-shaped mixer. And rapidly mixing to co-precipitate all the starting metal as a metal hydroxide to obtain an amorphous precursor.

  Then, the following steps are performed in order. The liquid in which the coprecipitation has occurred is allowed to stand for a whole day and night, and the precipitate obtained by removing the supernatant liquid is applied to a centrifuge and washed with water. A drying step is performed in which the cake washed with water is heated to a temperature of about 150 ° C. and dried. A baking step of heating and baking the dried cake is performed. This baking step is performed by holding the cake in an air atmosphere at, for example, a temperature of 400 ° C. for 5 hours and then holding the cake at a temperature of 500 ° C. for 2 hours. A reduction process is performed by holding the fired product at a temperature of about 500 ° C. in a reducing atmosphere.

  Through the above steps, the Rh-doped complex oxide is prepared.

  The downstream catalyst layer 4 is manufactured as follows using the Rh-doped composite oxide manufactured by the above-described manufacturing method.

  First, Pt is supported (post-supported) on La-containing alumina, and Rh is supported (post-supported) on the Rh-doped composite oxide. Then, a predetermined amount of La-containing alumina supporting Pt, Rh-doped composite oxide supporting Rh, NiO, and zirconyl nitrate as a binder raw material are mixed, and an appropriate amount of water is added to form a slurry. To do. This slurry is wash-coated on the honeycomb carrier. The wash-coated honeycomb carrier is dried at 150 ° C. and sintered at 500 ° C. to form a catalyst layer on the honeycomb carrier. As described above, the downstream catalyst 4 is manufactured.

  Examples of the exhaust gas purifying catalyst device according to the embodiment of the present invention will be described below. However, the present invention is not limited to the examples.

(Examples 1-7 and Comparative Examples 1-6)
Except for the Ni component and the binder material, the Ni component (NiO) has a mass ratio (mass%) shown in Table 2 so that the supported amount per liter of carrier (g / L) shown in Table 1 is obtained. The upstream catalyst and the downstream catalyst according to Examples 1 to 7 and Comparative Examples 1 to 6 were produced respectively.

  Moreover, the exhaust gas purification catalyst apparatus which concerns on Examples 1-7 and Comparative Examples 1-6 was manufactured by arrange | positioning the obtained upstream catalyst and downstream catalyst in the predetermined position shown in FIG.

The exhaust gas purifying catalyst devices according to Examples 1 to 7 and Comparative Examples 1 to 6 measured the light-off performance and the H ₂ S emission amount as follows. These results are shown in Table 2.

[Light-off performance]
First, an exhaust gas purification catalyst device is connected to a 2 L gasoline engine, the exhaust gas temperature at the upstream side catalyst inlet is adjusted to 900 ° C., the stoichiometric state is 60 seconds, the lean state is 10 seconds, the rich state Aging treatment was performed by repeating a 30-second cycle for 50 hours. At this time, the catalyst capacity is 1 L for both the upstream catalyst and the downstream catalyst.

  What was cut out from the upstream side catalyst and the downstream side catalyst subjected to the aging treatment as a cylindrical evaluation catalyst having a diameter of 25 mm and a height of 50 mm is set in a model gas flow catalyst evaluation device, and the simulated exhaust gas is placed in the space. The flow rate was 60,000 / h and the temperature was raised at a rate of 30 ° C./min. The concentration of HC, CO and NOx immediately after the catalyst outlet was 50% at the catalyst inlet side. The simulated exhaust gas temperature (light-off temperature T50) was measured. In addition, what was cut out as a cylindrical core sample having a diameter of 25 mm and a height of 50 mm from the upstream catalyst and the downstream catalyst subjected to the aging treatment was used as a catalyst. The simulated exhaust gas at this time was A / F = 14.9 ± 0.9. That is, the A / F is forced at an amplitude of ± 0.9 by adding a predetermined amount of fluctuation gas in a pulse form at 1 Hz while constantly flowing the main stream gas of A / F = 14.7. Vibrated. The light-off temperature T50 is an index for evaluating catalyst activity and exhaust gas purification performance. The lower the light-off temperature T50, the higher the catalyst activity and exhaust gas purification performance at low temperatures.

[H ₂ S emissions]
An exhaust gas purification catalyst device including an upstream side catalyst and a downstream side catalyst subjected to the same aging treatment as in the evaluation of the light-off performance was mounted on a 2L gasoline engine vehicle and traveled in the following travel pattern. This traveling pattern is traveling for 4 minutes at 30 km / h, traveling for 1 minute at 50 km / h, and then decelerating to 0 km / h. In this running pattern, after running at 50 km / h, the maximum H ₂ S concentration during the deceleration to 0 km / h was measured. The maximum H ₂ S concentration at this time is measured when S is attached to the catalyst during steady running such as running at 30 km / h and running at 50 km / h. This is because the fuel becomes rich when the fuel is restored, and H ₂ S is discharged at that time.

From Table 2, the ratio of Ni to CeO ₂ in the upstream catalyst is 15% by mass or more and 20% by mass or less, and the ratio of Ni to CeO ₂ in the downstream catalyst is 10% by mass or more and 60% by mass or less. In Comparative Examples 1 to 6, in which at least one of the ratios is out, the final H2S emission amount is relatively low, and the light-off temperatures of the upstream catalyst and the downstream catalyst are low.

It is the schematic which shows an exhaust-gas purification catalyst apparatus. It is the schematic diagram which showed the structure of Rh dope type | mold Zr * Ce * Nd complex oxide and Zr * Ce * Nd complex oxide which carry | supported Rh. It is the schematic which represented typically the oxygen storage mechanism by which Rh dope type | mold Zr * Ce * Nd complex oxide and the Zr * Ce * Nd complex oxide which carried Rh after carrying | support were each estimated.

Explanation of symbols

1 Engine 2 Exhaust passage 3 Upstream catalyst 4 Downstream catalyst

Claims (5)

An exhaust gas purification catalyst device in which an upstream catalyst disposed upstream in the exhaust gas flow direction and a downstream catalyst disposed downstream in the exhaust gas flow direction are provided in an exhaust passage of the engine. ,
The downstream catalyst is composed of a rhodium-doped complex oxide in which rhodium is arranged between crystal lattice points or lattice points of an oxygen storage material containing cerium (Ce), and at least nickel (Ni) and nickel oxide (NiO). Containing any one of them,
The upstream catalyst contains an oxygen storage material containing cerium (Ce) other than the rhodium-doped composite oxide, and at least one of nickel (Ni) and nickel oxide (NiO);
The ratio of Ni to CeO ₂ in the upstream catalyst is 15 to 20% by mass, and the ratio of Ni to CeO ₂ in the downstream catalyst is 10 to 60% by mass. Exhaust gas purification catalyst device.   The exhaust gas purification catalyst apparatus according to claim 1, wherein the composite oxide contained in the upstream catalyst and the downstream catalyst contains zirconium and neodymium. The exhaust gas purification catalyst apparatus according to claim 1 or ₂ , wherein a ratio of Ni to CeO ₂ in the upstream catalyst is larger than a ratio of Ni to CeO ₂ in the downstream catalyst.   The exhaust gas purifying catalyst device according to any one of claims 1 to 3, wherein the composite oxide contained in the upstream catalyst and the downstream catalyst carries a catalyst noble metal.   The catalyst noble metal supported on the composite oxide included in the upstream catalyst is palladium and rhodium, and the catalyst noble metal supported on the composite oxide included in the downstream catalyst is platinum and rhodium. The exhaust gas purification catalyst device according to claim 4.

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