JP5939010B2 - Exhaust gas purification catalyst device - Google Patents

Description

  The present invention relates to an exhaust gas purifying catalyst device.

  HCCI (Homogeneous Charge Compression Ignition) combustion has attracted attention as a next-generation engine combustion technology. This HCCI combustion is also referred to as premixed compression self-ignition combustion, and in accordance with the operating state of the engine, the gasoline in the combustion chamber is compressed and self-ignited in a lean atmosphere for combustion. However, HCCI combustion is limited in knocking, so its operating range is limited. Therefore, development of an engine that switches the combustion mode is underway with the low load side of the engine as an HCCI operation region and the high load side as an SI (Spark Ignition) operation region in which fuel is burned with the assistance of a spark plug.

  With regard to such an HCCI / SI switching type engine, for example, Patent Document 1 discloses that in order to increase the exhaust gas temperature during HCCI operation while ensuring sufficient ignitability and fuel efficiency, fuel is put into the cylinder. It is described that split injection is performed. That is, it is known that HCCI combustion in the partial load region has an advantage that almost no NOx is discharged, but because of low temperature combustion, the exhaust gas temperature is considerably low. The invention described in Patent Document 1 has a problem that the exhaust gas temperature is low, and raises the exhaust gas temperature by split fuel injection during HCCI combustion, thereby promoting exhaust gas purification by the catalyst.

  Patent Document 2 does not describe HCCI combustion, but in order to avoid sintering and alloying of different kinds of catalyst noble metals, and to increase the degree of dispersion of each catalyst noble metal, two layers of upper and lower catalyst are formed on the honeycomb carrier. It is described that a layer is provided, an alumina supporting Pt on the upper layer, an alumina supporting Rh and an oxygen storage material supporting Rh are disposed, and an alumina supporting Pd and an oxygen storage material supporting Pd are disposed on the lower layer. Has been.

Although Patent Document 3 does not describe HCCI combustion, a first catalyst is provided upstream of the engine exhaust gas passage to efficiently purify exhaust gas when the air-fuel ratio of the engine fluctuates greatly. And an exhaust gas purifying catalyst device in which a second catalyst is provided downstream of the first catalyst. The first catalyst on the upstream side has upper and lower two catalyst layers provided on the substrate, the upper layer contains Rh-supported CeZrNd composite oxide and Rh-supported ZrO ₂ -coated alumina, and the lower layer is Pd-supported It contains alumina, Pd-supported CeZrYLa alumina, and CeZrNd composite oxide not supporting a catalyst metal. The second catalyst on the downstream side has a catalyst layer provided on the substrate, and the catalyst layer contains the Rh-doped CeZrNd composite oxide and the Pt-supported alumina.

JP 2011-214479 A JP 2006-297372 A JP 2008-062156 A

  By the way, there is still no specific report regarding the composition of the exhaust gas at the time of HCCI combustion described above. When the present inventor examined the exhaust gas composition of HCCI combustion, it was found that a large amount of saturated hydrocarbons (n-pentane, i-pentane) and CO having 5 carbon atoms were discharged. This is thought to be due to the fact that the fuel is gasoline and this is burned at a low temperature.

  As a result of further experiments and research conducted by the inventor, the conventional three-way catalyst did not provide satisfactory results for the purification of saturated HC (hydrocarbon) and CO.

That is, the conventional three-way catalyst has been developed for the purpose of purifying exhaust gas generated by combustion of fuel at stoichiometry. The hydrocarbons exhausted by such combustion often contain many unsaturated hydrocarbon species such as C ₃ H ₆ and aromatic hydrocarbons, and are easily oxidized and purified. On the other hand, unlike the exhaust gas of SI combustion, the exhaust gas of HCCI combustion contains a large amount of saturated hydrocarbons (pentanes) that are difficult to be oxidized as described above, and the exhaust gas temperature is low. Therefore, the conventional three-way catalyst has a problem that it is difficult to purify the exhaust gas of HCCI combustion.

  Therefore, the present invention provides a catalyst device that efficiently purifies engine exhaust gas. In particular, even when exhaust gas containing a large amount of pentanes and CO is discharged from the engine by HCCI combustion, it can be efficiently purified.

  In the present invention, in order to purify the exhaust gas of the engine, a first catalyst is provided upstream of the exhaust gas passage, a second catalyst is provided downstream of the first catalyst, and the Pt / Rh mass of the first catalyst. The ratio was 4 to 10 times the Pt / Rh mass ratio of the second catalyst.

That is, the exhaust gas purifying catalyst device presented here includes a first catalyst provided in an exhaust gas passage of an engine and a second catalyst provided in an exhaust gas passage downstream of the first catalyst. ing. Each of the first catalyst and the second catalyst contains Pt and Rh as catalyst metals, and as an oxide carrier supporting the catalyst metals, at least one of a Ce-containing oxide and a Ce-free oxide, activated alumina Containing. In the first catalyst and the second catalyst each, the Pt is supported only in the active alumina, at least a portion of the Rh being on at least one supported or doped Ce-containing oxide Mono及 beauty Ce-free oxide, Pt / Rh weight ratio is the ratio of Pt and Rh in the first catalyst, Ri 10x der than four times more Pt / Rh weight ratio is the ratio of Pt and Rh in the second catalyst, the first In the catalyst, the Pt content is higher than the Rh content, in the second catalyst, the Rh content is higher than the Pt content, and the Rh content of the first catalyst is the same as that of the second catalyst. It is characterized by being greater than the Rh content .

  According to such an exhaust gas purifying catalyst device, even exhaust gas containing a large amount of saturated HC and CO such as pentane generated by HCCI combustion can be efficiently purified. One of the reasons is considered to be that the Pt / Rh mass ratio of the first catalyst is set to 4 to 10 times the Pt / Rh mass ratio of the second catalyst.

  That is, the high Pt / Rh mass ratio of the upstream first catalyst means that the catalyst contains a relatively large amount of Pt component. This Pt is less likely to be oxidized than Rh, and the surface is in a reduced state, so that the dissociative adsorption of pentane, which is saturated HC, is promoted, and as a result, the reactivity of pentane is considered to be increased.

  On the other hand, in HCCI combustion, a relatively large amount of CO is exhausted from the engine. Rh, which is a noble metal active species, is effective for this CO purification reaction. That is, Rh is easy to oxidize on the surface, and is immediately reoxidized even when oxygen is supplied to CO, which is advantageous for CO oxidation purification. In particular, Rh is excellent in low temperature activity in the purification of CO.

In the exhaust gas purification catalyst device, since the upstream first catalyst contains Rh together with Pt, CO is oxidized and purified by the catalytic reaction by Rh even when the exhaust gas temperature is low. And, it is considered that the oxidation reaction of pentane by Pt is promoted by the combustion heat generated along with the oxidation reaction of CO. Furthermore, the temperature of the exhaust gas rises due to the combustion heat generated by the oxidation reaction of CO in the upstream first catalyst, and accordingly, the downstream second catalyst is heated, so that its early activation can be achieved. Here, the Rh content of the first catalyst is higher than the Rh content of the second catalyst, and the Pt content is higher than the Rh content in the first catalyst. The combustion heat generated by the oxidation reaction of CO by Rh of one catalyst has the effect of promoting the oxidation reaction of pentane by Pt of the first catalyst, and the second catalyst on the downstream side is heated, and its early activity The effect which becomes advantageous to crystallization is acquired.

  In addition, in each of the first catalyst and the second catalyst, all of Pt is supported on activated alumina having a large specific surface area and high heat resistance, so that the dispersibility of Pt is enhanced and oxidation of saturated HC containing the above pentane is performed. It becomes advantageous for purification. Further, even when exposed to high-temperature exhaust gas by SI operation at high engine load, there is little decrease in catalyst activity related to HC purification.

Thus, regarding the Pt / Rh mass ratio, the fact that the upstream first catalyst is higher than the downstream second catalyst means that the downstream second catalyst has a small amount of Rh. That is, in the second catalyst, the Rh content is higher than the Pt content. Therefore, CO that has not been purified in the first catalyst on the upstream side is efficiently purified by the Rh on the downstream side second catalyst, in addition, the purification of HC by the Pt is also promoted.

  As will be apparent from Examples and Comparative Examples described later, when the Pt / Rh mass ratio of the first catalyst is 4 to 10 times the Pt / Rh mass ratio of the second catalyst, the purification performance of pentane and CO A significant improvement is observed.

  Here, in one of the preferred embodiments of the present invention, the first catalyst has two upper and lower catalyst layers provided on a substrate, each of the upper layer and the lower layer contains the Pt, The mass ratio of Pt to lower layer Pt (upper layer Pt / lower layer Pt) is 75/25 or more and 95/5 or less. Thereby, the HC purification performance of the first catalyst is enhanced.

  This is presumably because not only HC in the exhaust gas contacts Pt in the upper layer, but also when the exhaust gas diffuses and moves from the upper layer to the lower layer, HC also contacts Pt in this lower layer. That is, it is presumed that the HC purification performance of the first catalyst is improved by increasing the chance of contact between HC and Pt. According to experiments, a high HC purification rate can be realized when the ratio of the Pt amount in the upper layer and the Pt amount in the lower layer (upper layer Pt / lower layer Pt) is 75/25 or more and 95/5 or less in mass ratio. It was recognized.

  Preferably, the first catalyst further contains Pd as a catalyst metal. That is, like Rh, Pd is easy to oxidize on the surface and is immediately reoxidized even when oxygen is supplied to CO, which is advantageous for CO oxidation purification. In particular, regarding CO purification, Pd has a good balance between low temperature activity and high temperature purification performance. Therefore, when the first catalyst contains Pd, the purification performance of HC and CO is further enhanced.

  The upper layer of the first catalyst may be configured to contain Pt and Rh as catalyst metals and not contain Pd, and the lower layer of the first catalyst may be configured to contain Pd as catalyst metals and not contain Rh. preferable. Thereby, it is avoided that Pd and Rh are alloyed and deteriorated when the first catalyst is exposed to high-temperature exhaust gas.

According to the present invention, each of the upstream first catalyst and the downstream second catalyst includes Pt and Rh as catalyst metals, and at least one of a Ce-containing oxide and a Ce-free oxide as an oxide support. , containing the active alumina, the first catalyst and the second catalyst each, Pt is supported only in the active alumina, at least one to the support of at least a part of Ce-containing oxide Mono及 beauty Ce-free oxide Rh or is doped, Pt / Rh weight ratio of the first catalyst Ri 10x der than four times more Pt / Rh weight ratio of the second catalyst, Pt content in the first catalyst becomes higher than Rh content and which, in the second catalyst has become higher than the Pt content Rh content, and because Rh content of the first catalyst that has become more than Rh content of the second catalyst, saturated HC by HCCI combustion And CO is released in large quantities Even if that is possible to purify the exhaust gas efficiently.

1 is a schematic diagram showing a configuration of an engine system according to an embodiment of the present invention. It is a figure which shows an example of the combustion mode map of an engine. It is a flowchart which shows the control action by an engine control unit. It is sectional drawing which shows the catalyst layer structure of a 1st catalyst. It is sectional drawing which shows the catalyst layer structure of a 2nd catalyst. It is a graph which shows the relationship between Pt / Rh mass ratio magnification and the light-off temperature regarding HC purification | cleaning. It is a graph which shows the relationship between Pt / Rh mass ratio magnification and the light-off temperature regarding CO purification. It is a graph which shows the relationship between the mass ratio of the upper layer Pt / lower layer Pt of a 1st catalyst, and the light-off temperature regarding purification | cleaning of HC and CO. It is a graph which shows the relationship between the mass ratio of the upper layer Pt / lower layer Pt of a 1st catalyst, and the purification rate of HC and CO.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the invention, its application, or its use.

<Engine>
An engine 1 according to the embodiment shown in FIG. 1 is a multi-cylinder gasoline engine whose combustion mode is switched between HCCI combustion and SI combustion according to an operating state, and is mounted on an automobile. In the figure, 3 is a cylinder block having a plurality of cylinders 2, 4 is a cylinder head, and 5 is a piston provided in each cylinder 2. A combustion chamber 6 is formed between the upper surface of the piston 5 and the lower surface of the cylinder head 4. The piston 5 is connected to the crankshaft 7 via a connecting rod 8.

  In the cylinder head 4, an intake port 9 and an exhaust port 10 are formed for each cylinder 2. An intake valve 11 and an exhaust valve 12 are provided in each of the intake port 9 and the exhaust port 10. Each of the intake valve 11 and the exhaust valve 12 is driven in synchronism with the rotation of the crankshaft 7 by a valve mechanism 13 including a pair of camshafts (not shown) disposed in the cylinder head 4.

  A variable valve lift mechanism (hereinafter referred to as “VVL”) 14 and a variable valve timing mechanism (hereinafter referred to as “VVT”) 15 are incorporated in each valve operating mechanism 13 of the intake valve 11 and the exhaust valve 12. . Each of the VVL 14 and the VVT 15 operates based on a command from the engine control unit 30, and the former changes the lift amount (opening amount) of the intake valve 11 and the exhaust valve 12, and the latter changes the intake valve 11 and the exhaust valve 12. Change the opening / closing timing (phase angle) of. The lift characteristics of the intake valve 11 and the exhaust valve 12 are changed according to the engine operating state by the VVL 14 and VVT 15. As a result, the amount of intake air into each cylinder 2 and the amount of residual burned gas (internal EGR) change. The VVL 14 and the VVT 15 are generally used and are known to those skilled in the art, and thus detailed description thereof is omitted.

  The cylinder head 4 is provided with a spark plug 16 so as to face the combustion chamber 6 of each cylinder 2. The spark plug 16 performs discharge (spark ignition) at a predetermined timing in response to power supply from the ignition circuit 17. Further, the cylinder head 4 is provided with a fuel injection valve 18 so as to face the combustion chamber 6 of each cylinder 2 from the side on the intake side. The fuel from the fuel tank is supplied to the fuel injection valve 18 by the high-pressure fuel pump 19 through the fuel passage. The high-pressure fuel pump 19 is driven by, for example, a spill valve, and can freely change the supply pressure of fuel to the fuel injection valve 18, that is, the fuel pressure, over a wide range from low pressure to high pressure. The fuel injection valve 18 directly injects fuel into the combustion chamber 6 at a predetermined injection timing (intake stroke or the like), and generates a predetermined air-fuel ratio mixture in the combustion chamber 6.

  An intake passage 20 is disposed on the intake side of the engine 1, and a surge tank 21 is provided in the middle of the intake passage 20. An electronically controlled throttle valve 22 is disposed in the intake passage 20 upstream of the surge tank 21. The intake passage 20 is branched for each cylinder 2 on the downstream side of the surge tank 21, and each downstream end is connected to the intake port 9 of each cylinder 2.

  An exhaust gas passage 25 is disposed on the exhaust side of the engine 1. The exhaust gas passage 25 branches at the upstream end side and is connected to the exhaust port 10 of each cylinder 2. An exhaust gas purifying first catalyst 27 for purifying harmful components in the exhaust gas is provided in an upstream portion of the exhaust gas passage 25, and the exhaust gas purifying is disposed in the exhaust gas passage 25 downstream of the first catalyst 27. A second catalyst 28 is provided. In the present embodiment, the first catalyst 27 is arranged in the engine room of the automobile directly connected to the collecting pipe portion of the exhaust manifold branched at the upstream end side, and the second catalyst 28 is arranged under the floor of the automobile.

  The engine control unit 30 is constituted by a computer having a central calculation processing device (CPU), various memories and the like. This control unit 30 changes the operation of the VVL 14, VVT 15, ignition circuit 17, fuel injection valve 18, high pressure fuel pump 19, throttle valve 22, etc. to the operating state of the engine 1 based on control information detected by various sensors. Control accordingly. For example, by controlling the VVL 14 and VVT 15 according to the operating state of the engine 1 to change the lift characteristics of the intake valve 11 and the exhaust valve 12, the operation related to intake and exhaust of the engine 1 is controlled, and the fuel injection valve The fuel injection amount 18, fuel pressure (fuel injection pressure), injection pulse width and fuel injection timing, driving state of the high-pressure fuel pump 19, discharge pressure, and the like are controlled.

  The sensor includes a crank angle sensor 31 that detects the rotation angle (crank angle) of the crankshaft 7, an airflow sensor 32 that detects the amount of air supplied to the engine 1, and an accelerator opening (accelerator pedal (not shown)) operation. An accelerator opening sensor 33 that detects the amount), an in-cylinder pressure sensor 34 that detects the in-cylinder pressure of each cylinder 2 (pressure in the combustion chamber 6), a vehicle speed sensor 35 that detects the speed of the automobile, and an intake air temperature (surge tank 21). There is an intake air temperature sensor 36 for detecting the temperature of the internal air) and a fuel pressure sensor 37 for detecting the pressure of the fuel supplied from the high-pressure fuel pump 19 to the fuel injection valve 18. These sensors 31 to 37 are electrically connected to the control unit 30. The in-cylinder pressure 34 sensor is integrally formed with the spark plug 16 and is built in the spark plug 16. The in-cylinder pressure sensor 34 may be formed integrally with the fuel injection valve 18.

  Here, based on the control information, the control unit 30 performs an HCCI combustion mode in which the air-fuel mixture generated during the intake stroke without using the spark plug 16 is compressed and self-ignited near the compression top dead center and burned. The combustion mode of the engine operation is switched between the SI combustion mode in which the air-fuel mixture is forcibly ignited by spark ignition using the spark plug 16 and burned.

  As shown in the combustion mode map in FIG. 2, in this embodiment, a predetermined low rotation / low load engine operation region is defined as an HCCI region, and a high rotation or high load engine operation region exceeding the HCCI region is defined as an SI region. It is set. This combustion mode map is obtained by experimentally finding and setting an optimal combustion mode corresponding to the engine rotation speed and the engine load in advance, and is electronically stored in the memory of the control unit 30.

  Further, in the memory of the control unit 30, a target torque map in which an optimum value of the target torque (engine load) is experimentally determined and recorded with respect to changes in the accelerator opening and the engine rotational speed, as well as the target torque and suction A fuel injection amount map in which the optimum fuel injection amount Qm determined experimentally according to changes in the air amount and the rotational speed is recorded and stored electronically. In the target torque map, the larger the accelerator opening and the higher the engine speed, the larger the target torque.

  Hereinafter, the combustion mode switching control by the control unit 30 will be described based on the flowchart of FIG. 3.

  In the first step S1, various signals for engine control including the detection signals of the sensors 31 to 37 are read. In the next step S2, the engine load (target torque) is calculated based on the accelerator opening from the accelerator opening sensor 33 and the engine speed determined from the crank angle from the crank angle sensor 31. In the next step S3, based on the engine speed and the engine load, it is determined whether the operating state of the engine 1 corresponds to the operating region of the HCCI region or the SI region in the combustion mode map shown in FIG. To do.

  In the next step S4, it is determined whether or not the operating state of the engine 1 is in the HCCI region. When the operation state is in the HCCI region, the process proceeds to step S5, the combustion mode is set to the HCCI combustion mode, and various controls of the engine 1 corresponding to the HCCI combustion mode based on the engine speed, the engine load, etc. Calculate the parameters. After step S5, the process returns.

  During operation in the HCCI combustion mode, the valve opening period of the exhaust valve 12 and the valve opening period of the intake valve 11 are close to the exhaust top dead center (top dead center between the exhaust stroke and the intake stroke). Are set so that there is a negative valve overlap period (NVO period) in which both are closed. Then, after the NVO period ends after the exhaust top dead center and the intake valve 11 is opened, fuel injection by the fuel injection valve 18 is performed. The injected fuel forms an air-fuel mixture in the combustion chamber 6, and the air-fuel mixture is compressed and self-ignited by itself near the compression top dead center (that is, without passing through other ignition means or ignition means). .

  When the determination in step S4 is NO, that is, when the operating state of the engine 1 is in the SI region, the process proceeds to step S6 to set the combustion mode to the SI combustion mode, and based on the engine speed, the engine load, and the like. Then, various control parameters of the engine 1 corresponding to the SI combustion mode are calculated. After step S6, the process returns.

  During operation in the SI mode, the opening period of the exhaust valve 12 and the opening period of the intake valve 11 slightly overlap each other in the vicinity of the exhaust top dead center in each cylinder cycle. It is set as follows. Then, after the intake valve 11 is opened, the fuel injection valve 18 performs normal fuel injection only once. Thereafter, the air-fuel mixture is ignited by the spark plug 16 in the vicinity of the compression top dead center (top dead center between the compression stroke and the expansion stroke), and the air-fuel mixture or fuel is burned by flame propagation.

  In the above-described HCCI combustion mode, the air-fuel mixture (fuel) burns rapidly without causing flame propagation. In this case, since the combustion temperature is lower than that in the case of spark ignition, the amount of NOx generated is greatly reduced. Thus, according to the study of the present inventor, it has been found that a large amount of saturated HC (n-pentane, i-pentane) and CO having 5 carbon atoms are discharged in this HCCI combustion mode. That is, when looking at the exhaust gas in the SI combustion mode, n-pentane and i-pentane were about 100 to 200 ppmC in total. On the other hand, when looking at the exhaust gas in the HCCI combustion mode, n-pentane and i-pentane were discharged together at about 1000 to 3000 ppmC, and the concentration was an order of magnitude higher than the concentration in the SI combustion mode. . Further, the CO concentration of the exhaust gas in the HCCI combustion mode was about 2000 to 4000 ppm.

<Exhaust gas purification catalyst device>
As described above, the engine device for purifying exhaust gas according to the present invention includes the first catalyst 27 on the upstream side and the second catalyst 28 on the downstream side, and the exhaust gas containing a large amount of the pentanes and CO by the HCCI combustion. Even when gas is discharged from the engine 1, it can be efficiently purified.

  FIG. 4 shows a catalyst layer configuration of the first catalyst 27. A catalyst layer 42 is formed on the exhaust gas passage wall of the substrate (honeycomb carrier) 41. The catalyst layer 42 includes an upper layer 43 and a lower layer 44, the lower layer 44 is formed on the exhaust gas passage wall surface of the carrier 41, and the upper layer 43 is overlaid on the lower layer 44. FIG. 5 shows a catalyst layer configuration of the second catalyst 28. A single catalyst layer 46 is formed on the exhaust gas passage wall of the substrate (honeycomb carrier) 45.

  The upper layer 43 of the first catalyst 27 contains Pt-supported La alumina composite oxide, Rh-supported CeZrNd composite oxide, and Rh-supported LaZr / La alumina composite oxide as catalyst components. The lower layer 44 contains, as a catalyst component, a Pd-supported CeZrNd composite oxide, a Pd-supported La alumina composite oxide, a Pt-supported La alumina composite oxide, and a CeZrNd composite oxide on which no catalyst metal is supported. Each of the upper layer 43 and the lower layer 44 contains a zirconia binder (Y-stabilized zirconia) as a binder.

  The catalyst layer 46 of the second catalyst 28 contains Pt-supported La alumina composite oxide and Rh-doped CeZrNd composite oxide as catalyst components, and zirconia binder (Y-stabilized zirconia) as a binder.

  The first catalyst 27 can be prepared by the following method. That is, the substrate 41 is made into a slurry obtained by mixing a Pd-supported CeZrNd composite oxide, a Pd-supported La alumina composite oxide, a Pt-supported La alumina composite oxide, a catalyst metal non-supported CeZrNd composite oxide and a binder with ion-exchanged water. Dip out. Excess slurry adhering to the base material 41 is removed by air blowing. Thereafter, in the air, the slurry adhering to the base material 41 is dried (150 ° C.) and fired (held at a temperature of 500 ° C. for 2 hours). Thereby, the lower layer 44 is formed on the base material 41. Next, the substrate 41 having the lower layer 44 is immersed in a slurry obtained by mixing Pt-supported La alumina composite oxide, Rh-supported CeZrNd composite oxide, Rh-supported La alumina composite oxide and binder with ion-exchanged water. Take out. Excess slurry adhering to the substrate is removed by air blowing. Thereafter, in the air, the slurry adhering to the lower layer 44 is dried (150 ° C.) and fired (held at a temperature of 500 ° C. for 2 hours). Thereby, the upper layer 43 is formed on the lower layer 44 of the base material 41.

  The second catalyst 28 can be prepared by the following method. That is, the base material 45 is dipped in a slurry formed by mixing a Pt-supported La alumina composite oxide, an Rh-doped CeZrNd composite oxide, and a binder with ion-exchanged water. Excess slurry adhering to the substrate is removed by air blowing. Thereafter, in the air, the slurry adhering to the base material 45 is dried (150 ° C.) and fired (held at a temperature of 500 ° C. for 2 hours). Thereby, the catalyst layer 46 is formed on the substrate 45.

[Catalyst component]
The catalyst component will be specifically described.

Each of the Pt-supported La alumina composite oxide, the Rh-supported La alumina composite oxide, and the Pd-supported La alumina composite oxide is an active alumina composite oxide powder containing 4% by mass of La ₂ O ₃ as an oxide carrier. , Pt, Rh, and Pd are supported by the evaporation to dryness method.

The Rh-supported CeZrNd composite oxide is obtained by supporting Rh on a CeZrNd composite oxide powder of CeO ₂ : ZrO ₂ : Nd ₂ O ₃ = 10: 80: 10 (mass%) by evaporation to dryness. The Pd-supported CeZrNd composite oxide is obtained by supporting Pd on a CeZrNd composite oxide powder of CeO ₂ : ZrO ₂ : Nd ₂ O ₃ = 23: 67: 10 (mass%) by evaporation to dryness. The composition of the catalyst metal non-supported CeZrNd composite oxide is CeO ₂ : ZrO ₂ : Nd ₂ O ₃ = 23: 67: 10 (mass%). The Rh-doped CeZrNd composite oxide is a CeZrNd composite oxide doped with Rh, and the composition excluding Rh is CeO ₂ : ZrO ₂ : Nd ₂ O ₃ = 23: 67: 10 (mass%).

The Rh-supported LaZr / La alumina composite oxide is obtained by supporting Rh on a LaZr / La alumina composite oxide powder by evaporation to dryness. The LaZr / La alumina composite oxide is obtained by supporting a LaZr composite oxide on the surface of a La alumina composite oxide containing 4% by mass of La ₂ O ₃ , and its composition is ZrO ₂ : La ₂ O ₃ : La alumina = 38: 2: 60 (mass ratio).

  The CeZrNd composite oxide powder can be prepared by a coprecipitation method. That is, mixing an 8 times diluted solution of 28% by mass ammonia water as a basic solution into a nitric acid solution obtained by mixing cerium nitrate hexahydrate, zirconyl oxynitrate solution, neodymium nitrate hexahydrate, and ion-exchanged water. To obtain a coprecipitate by neutralization. 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 coprecipitate after the final dehydration is dried at 150 ° C. in the air, pulverized, and fired at 500 ° C. for 2 hours in the air. Thereby, CeZrNd composite oxide powder can be obtained.

  The powder of Rh-doped CeZrNd composite oxide can also be prepared by a coprecipitation method. That is, an 8-fold diluted solution of 28% by mass ammonia water as a basic solution is added to a nitric acid solution obtained by mixing cerium nitrate hexahydrate, zirconyl oxynitrate solution, neodymium nitrate hexahydrate, rhodium nitrate and ion-exchanged water. By mixing, a coprecipitate is obtained by neutralization. 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 coprecipitate after the final dehydration is dried at 150 ° C. in the air, pulverized, and fired at 500 ° C. for 2 hours in the air. Thereby, a Rh-doped CeZrNd composite oxide powder can be obtained.

The LaZr / La alumina composite oxide can be prepared as follows. First, a powder of La alumina composite oxide containing 4% by mass of La ₂ O ₃ is dispersed in a mixed solution of zirconium nitrate and lanthanum nitrate, and ammonia water is added thereto to form a precipitate. The obtained precipitate is filtered, washed, dried at 200 ° C. for 2 hours, and calcined at 500 ° C. for 2 hours to obtain La alumina composite oxide powder having a ZrLa composite oxide supported on the surface. Can be obtained.

  In the exhaust gas purifying catalyst device, the first catalyst 27 has a Pt / Rh mass ratio that is a ratio of the total Pt amount of the upper layer 43 and the Pt amount of the lower layer 44 combined with the Pd amount of the upper layer 44 in the first catalyst 27. The Pt / Rh mass ratio, which is the ratio between the Pt amount and the Pd amount of the two catalysts 28, is 4 times or more and 10 times or less, and the exhaust gas containing a large amount of the pentanes and CO is efficiently purified. In this embodiment, the ratio (upper layer Pt / lower layer Pt) between the Pt amount of the upper layer 43 and the Pt amount of the lower layer 44 of the first catalyst 27 is 75/25 or more and 95/5 or less.

[Exhaust gas purification performance of exhaust gas purification catalyst device]
Hereinafter, the exhaust gas purification characteristics of the exhaust gas purification catalyst device will be described based on Examples and Comparative Examples.

-Examples 1-4, Comparative Examples 1-3
As catalyst components, a plurality of types of Pt-supported La alumina composite oxides with different Pt loadings, a plurality of types of Rh-supported CeZrNd composite oxides with different Rh loadings, and a plurality of types of Rh-supported LaZr / La aluminas with different Rh loadings A composite oxide, a Pd-supported CeZrNd composite oxide, a Pd-supported La alumina composite oxide, a Rh-doped CeZrNd composite oxide, and a catalyst metal-unsupported CeZrNd composite oxide were prepared.

Using these catalyst components, the Pt / Rh mass ratio of the first catalyst shown in Table 1 (the ratio between the total amount of Pt in the upper and lower two layers 43 and 44 and the amount of Rh in the upper layer 43) is shown in Table 1. In addition, Examples 1 to 4 and Comparative Examples 1 to 3 having different Pt / Rh mass ratio of the first catalyst to Pt / Rh mass ratio of the second catalyst (hereinafter referred to as “Pt / Rh mass ratio magnification”). Each catalyst set (first catalyst and second catalyst) was prepared. As the substrate, a cordierite honeycomb carrier (capacity 1 L) having a cell wall thickness of 3.5 mil (8.89 × 10 ⁻² mm) and 600 cells per square inch (645.16 mm ² ) was used. .

  In the first catalysts of Examples 1 to 4, the Pt / Rh mass ratio is 2/1 or more and 5/1 or less, and the Pt content is larger than the Rh content. In all of the second catalysts of Examples 1 to 4, the Pt / Rh mass ratio is 1/2, and the Rh content is larger than the Pt content.

−Exhaust gas purification performance evaluation test−
After bench aging the first catalyst and the second catalyst in each of Examples 1 to 4 and Comparative Examples 1 to 3, a core sample having a carrier capacity of about 25 mL was cut out from each catalyst. In bench aging, the catalyst was attached to the exhaust pipe of the engine, the engine speed was set so that the exhaust gas temperature at the catalyst inlet was 900 ° C., and the catalyst was exposed to the 900 ° C. exhaust gas for 50 hours. During the engine operation period, engine oil added with P was continuously supplied to the intake manifold by a pump.

  Then, the core sample of the first catalyst and the core sample of the second catalyst are attached to the model gas flow reactor so that the latter is located on the downstream side of the former, and each light-off temperature (HC) relating to the purification of HC and CO -T50 (° C), HC-T90 (° C), CO-T50 (° C), CO-T90 (° C)).

  That is, while the temperature of the model gas flowing into the first catalyst was gradually increased from the normal temperature, changes in the concentrations of HC and CO in the gas flowing out of the second catalyst were detected. HC-T50 (° C.) and CO-T50 (° C.) are the first catalyst inlet gas temperature when the purification rate of each component of HC and CO reaches 50%. HC-T90 (° C.) and CO-T90 (° C.) are the first catalyst inlet gas temperature when the purification rate of each component of HC and CO reaches 90%.

The composition of the model gas is i-pentane; 3000 ppmC, CO; 1900 ppm, O ₂ ; 10.8%, H ₂ O; 10%, remaining N ₂ . The gas flow rate is 26.1 L / min (space velocity SV = about 63000 h ⁻¹ ), and the gas heating rate is 30 ° C./min.

  Separately, only the core sample of the first catalyst of Example 1 is attached to the model gas flow reactor (without the second catalyst), and each light-off temperature (HC-T50 (° C.), CO-T50 for purification of HC and CO). And the purification rate (HC-C300 (%), CO-C300 (%)) at a catalyst inlet gas temperature of 300 ° C.

-Test results-
The results are shown in Table 2, FIG. 6 and FIG. Here, the fact that the light-off temperature difference (T90-T50) is small means that the exhaust gas purification rate rises rapidly as the temperature rises after the purification rate exceeds 50%. It means that it becomes high activity early.

  As shown in Table 2, only the first catalyst of Example 1 and Example 1 have the same values for HC-T50 and CO-T50. Therefore, regarding T50, it can be said that the effect of the second catalyst is hardly recognized. On the other hand, in the case of only the first catalyst of Example 1, HC-C300 is 65%, whereas HC-T90 of Example 1 is 305 ° C., so the effect of the second catalyst is recognized at T90. It is done. That is, with the first catalyst alone, the HC purification rate is about 65% at a catalyst inlet gas temperature of 300 ° C., but when a second catalyst is added, the HC purification rate reaches 90% at a catalyst inlet gas temperature of 305 ° C. Therefore, it can be said that the effect of the second catalyst is relatively large.

  Then, looking at the light-off temperature difference (T90-T50), when the Pt / Rh mass ratio magnification is in the range of 4 to 10 times, the light-off temperature difference is the same for both HC and CO. It is getting smaller. From this, it can be seen that by setting the Pt / Rh mass ratio magnification in this range, it is advantageous for early activation of the catalyst device.

<Mass ratio of first catalyst upper layer Pt / lower layer Pt>
-First catalyst examples A to E-
As catalyst components, multiple types of Pt-supported La alumina composite oxides with different Pt loadings, multiple types of Rh-supported CeZrNd composite oxides with different Rh loadings, and multiple types of Rh-supported La alumina composite oxides with different Rh loadings A plurality of Pd-supported CeZrNd composite oxides having different Pd loadings and a plurality of Pd-supporting La alumina composite oxides having different Pd loadings were prepared.

  Using these catalyst components, the first catalyst in which the mass ratio of upper layer Pt / lower layer Pt shown in Table 3 (the ratio of the Pt amount of the upper layer 43 to the Pt amount of the lower layer 44) shown in Table 3 differs depending on the catalyst preparation method described above. Each catalyst of Examples A to E was prepared.

−Exhaust gas purification performance evaluation test−
After bench-aging each catalyst of the first catalyst examples A to E, a core sample having a carrier volume of about 25 mL was cut out from each catalyst. This is attached to a model gas flow reactor, and each light-off temperature (HC-T50 (° C), CO-T50 (° C)) for purification of HC and CO and each purification rate of HC and CO (HC-C300 (%)) , CO-C300 (%)). In bench aging, the catalyst was attached to the exhaust pipe of the engine, the engine speed was set so that the exhaust gas temperature at the catalyst inlet was 800 ° C., and the catalyst was exposed to the 800 ° C. exhaust gas for 50 hours. The model gas used was the same as in the previous evaluation test. The gas flow rate and the gas heating rate are the same as in the previous evaluation test.

-Test results-
The results are shown in FIGS. It can be seen from FIG. 8 that HC-T50 and CO-T50 are affected by the mass ratio of upper layer Pt / lower layer Pt. That is, in the case of the above catalyst configuration, not only i-pentane comes into contact with the Pt component in the upper layer 43, but also when the exhaust gas diffuses and moves from the upper layer 43 to the lower layer 44, i-pentane also becomes the Pt component in the lower layer 44. You will be in contact and there will be more opportunities for contact. This is considered to affect the HC purification performance. Further, in the lower layer 44, not only the Pd component but also the Pt component works for CO oxidation purification. This is considered to affect the CO purification performance.

  Then, according to FIG. 8, when the mass ratio of upper layer Pt / lower layer Pt is 75/25 or more and 95/5 or less, it turns out that both HC-T50 and CO-T50 become a low value. Further, according to FIG. 10, when the mass ratio of upper layer Pt / lower layer Pt is 75/25 or more and 95/5 or less, C300 of HC and CO is high.

  As is apparent from the above description, the exhaust gas purifying catalyst device according to the present invention can efficiently purify the exhaust gas discharged from the engine. In particular, even an exhaust gas containing a large amount of pentane and CO discharged from HCCI combustion from a gasoline engine whose combustion mode is switched between HCCI combustion and SI combustion according to the operating state is applied to the present invention. It can be efficiently purified by such a catalyst device.

1 Engine 25 Exhaust gas passage 27 Exhaust gas purification catalyst 41 Base material (honeycomb carrier)
42 catalyst layer 43 upper layer 44 lower layer 45 base material (honeycomb carrier)
46 Catalyst layer

Claims (4)

An exhaust gas purifying catalyst device in which a first catalyst is provided in an exhaust gas passage of an engine, and a second catalyst is provided in an exhaust gas passage downstream of the first catalyst,
Each of the first catalyst and the second catalyst contains Pt and Rh as catalyst metals, and as an oxide carrier supporting the catalyst metals, at least one of a Ce-containing oxide and a Ce-free oxide, activated alumina And containing
In the first catalyst and the second catalyst each, the Pt is supported only in the active alumina, at least a portion of the Rh being on at least one supported or doped Ce-containing oxide Mono及 beauty Ce-free oxide,
Pt / Rh weight ratio is the ratio between the Pt and Rh in the first catalyst, Ri 10x der than four times more Pt / Rh weight ratio is the ratio between the Pt and Rh in the second catalyst ,
In the first catalyst, the Pt content is higher than the Rh content, in the second catalyst, the Rh content is higher than the Pt content, and the Rh content of the first catalyst is higher than that of the first catalyst. An exhaust gas purifying catalyst device characterized in that the Rh content of the two catalysts is larger . In claim 1,
The first catalyst has two upper and lower catalyst layers provided on a substrate, and each of the upper layer and the lower layer contains the Pt,
An exhaust gas purifying catalyst device, wherein a mass ratio (upper layer Pt / lower layer Pt) of the upper layer Pt and the lower layer Pt is 75/25 or more and 95/5 or less. In claim 1 or claim 2,
The exhaust gas purifying catalyst device, wherein the first catalyst further contains Pd as a catalyst metal. In any one of Claim 1 thru | or 3,
The exhaust gas purification catalyst apparatus according to claim 1, wherein the engine is switched between a compression self-ignition combustion and a spark ignition combustion for discharging an exhaust gas containing 1000 ppmC or more of pentane according to an operation region.

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