JP2012067641A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine that is provided at upstream of an exhaust emission control catalyst with a small oxidation catalyst and a fuel supply valve, and is capable of preventing the small oxidation catalyst from deteriorating, and improving exhaust emission control performance by improved low temperature ignition performance.SOLUTION: An upstream portion 14a which is a portion corresponding to 35-90% of the length of the base material from an upstream end 14c to downstream of the base material of the small oxidation catalyst 14, contains an amount of platinum equivalent to 55-85 mass% of all the precious metal at the upstream end 14a. A downstream portion 14b which is a portion other than the upstream portion 14a of the small oxidation catalyst 14, contains an amount of platinum equivalent to 0-50 mass% of the amount of all the precious metal of the downstream portion 14b.

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  Conventionally, as an apparatus for purifying exhaust gas of an internal combustion engine, an exhaust purification catalyst having an oxidation function disposed in an exhaust passage, an oxidation catalyst disposed on the upstream side of the exhaust purification catalyst in the exhaust passage, and this oxidation 2. Description of the Related Art An exhaust emission control device that includes a fuel supply valve that supplies fuel to a catalyst is known (see, for example, Patent Documents 1 and 2).

  In the exhaust purification device disclosed in Patent Document 1, a small-sized oxidation catalyst having a smaller volume than the exhaust purification catalyst is disposed upstream of the exhaust purification catalyst. According to this exhaust purification apparatus, activation of the exhaust purification catalyst is promoted by the small oxidation catalyst, and the exhaust gas purification performance is improved. That is, when fuel is supplied from the fuel supply valve to the small oxidation catalyst, the fuel is oxidized in the small oxidation catalyst. At this time, heat of oxidation reaction occurs in the small oxidation catalyst, and the temperature of the small oxidation catalyst rises rapidly. As a result, the exhaust gas is heated by the small oxidation catalyst, and higher temperature exhaust gas is supplied to the exhaust purification catalyst. Therefore, the temperature of the exhaust purification catalyst also rises and the activation of the exhaust purification catalyst is promoted. If more fuel is supplied to the small oxidation catalyst while the exhaust purification catalyst is activated, a part of the supplied fuel is reformed by the small oxidation catalyst. The reformed fuel is supplied to the exhaust purification catalyst and oxidized. As a result, the temperature of the exhaust purification catalyst further increases, and the activation of the exhaust purification catalyst is further promoted.

JP 2009-156168 A JP 2005-127257 A

  As described above, when an oxidation reaction occurs in the small oxidation catalyst, the temperature of the small oxidation catalyst rapidly increases. However, if the temperature of the small oxidation catalyst becomes too high, the catalyst is deteriorated (sintered), and the reactivity of the small oxidation catalyst is lowered. In that case, the necessary reaction heat may not be obtained unless more fuel is supplied to the small oxidation catalyst. That is, if the temperature of the small oxidation catalyst becomes too high, there is a possibility that the amount of fuel consumption necessary to raise the temperature of the exhaust purification catalyst will increase.

  Further, when the temperature of the exhaust gas discharged from the internal combustion engine is relatively low, the time until the fuel starts to oxidize in the small oxidation catalyst becomes long. That is, the time until the fuel is ignited becomes longer. However, if the time until the fuel is ignited becomes long, the temperature rise of the small oxidation catalyst is delayed, and as a result, the time until the exhaust purification catalyst is activated becomes long. Therefore, the exhaust gas may be discharged without being sufficiently purified for a certain period of time.

  Therefore, the present invention provides an exhaust gas purification apparatus for an internal combustion engine that includes a small oxidation catalyst and a fuel supply valve upstream of an exhaust purification catalyst, and suppresses deterioration of the small oxidation catalyst and improves low temperature ignition performance. The purpose is to improve gas purification performance.

  The inventor has paid attention to the fact that when the temperature of the small oxidation catalyst is raised, the temperature of the downstream portion of the small oxidation catalyst is higher than that of the upstream portion. In view of this, the inventors considered a configuration in which the downstream portion is less susceptible to catalyst deterioration due to temperature rise than the upstream portion. Further, the ignition of fuel in the small oxidation catalyst occurs in the upstream portion of the small oxidation catalyst. In view of this, the inventors have considered that the upstream portion is superior in low-temperature ignition performance to the downstream portion.

  An exhaust gas purification apparatus for an internal combustion engine according to the present invention is disposed in an exhaust passage of the internal combustion engine, and has an exhaust purification catalyst having an oxidation function, and is disposed upstream of the exhaust purification catalyst in the exhaust passage. A small oxidation catalyst having a volume smaller than that of the purification catalyst, and a fuel supply valve for supplying fuel to the small oxidation catalyst. The small oxidation catalyst has a base material and a plurality of types of noble metals supported on the base material. In the upstream side portion, which is a portion corresponding to 35% to 90% of the length of the base material from the upstream end of the base material toward the downstream side of the small oxidation catalyst, platinum accounts for the total noble metal amount of the upstream side portion. On the other hand, in the downstream portion that is a portion other than the upstream portion of the small oxidation catalyst, the amount of platinum in the total amount of noble metals in the downstream portion is 0% by weight. -50 mass%.

  In the exhaust emission control device, the downstream portion of the small oxidation catalyst contains 0% by mass to 50% by mass of platinum with respect to the total noble metal amount, so that noble metal particle growth is effectively suppressed. For this reason, deterioration of the catalyst is suppressed in the downstream portion where the temperature tends to be high. On the other hand, since the upstream side portion of the small oxidation catalyst contains 55% to 85% by mass of platinum based on the total amount of noble metals, the ignition performance at low temperature is excellent. By making a portion corresponding to 35% to 90% of the length of the base material from the upstream end to the downstream side of the base material of the small-sized oxidation catalyst as an upstream side portion, suppression of catalyst deterioration in the downstream side portion and upstream side portion Improvement in low-temperature ignition performance in can be effectively achieved. Therefore, according to the exhaust gas purification apparatus, the exhaust gas purification performance is improved.

  In a preferable aspect of the exhaust gas purification apparatus for an internal combustion engine disclosed herein, the small-sized oxidation catalyst contains platinum and palladium. According to such a small oxidation catalyst, deterioration of the catalyst in the downstream side portion at the time of temperature rise is effectively suppressed. Further, after the fuel is ignited in the upstream portion, the temperature in the upstream portion is quickly increased. Therefore, the exhaust purification catalyst can be activated well and the purification performance can be improved.

  In another preferred embodiment, the internal combustion engine is a diesel engine. In a diesel engine, the temperature of the exhaust gas is relatively low. Therefore, when the internal combustion engine is a diesel engine, the effect of improving the low-temperature ignition performance of the small oxidation catalyst described above is more effectively exhibited.

1 is an overall view of a diesel engine. It is a block diagram in an exhaust pipe. It is the IIB-IIB sectional view taken on the line of FIG. 2A. It is a schematic diagram of a small oxidation catalyst. It is a graph which shows the relationship between Pt ratio, HC-T50, and CO adsorption amount. It is a time chart for demonstrating the pattern of fuel addition. It is a figure which shows the temperature profile of the upstream center temperature and downstream center temperature of a small oxidation catalyst. It is a graph which shows the relationship between the Pt ratio and the temperature rising effect at the time of fuel addition. It is a graph which shows the relationship between the length ratio of the upstream part of a small oxidation catalyst, and the temperature rising effect at the time of fuel addition with respect to inflow gas. It is the graph which compared the temperature rising effect at the time of the fuel addition with respect to inflow gas about an Example and a comparative example. It is a time chart for demonstrating engine European mode driving | running | working. It is a graph which shows the relationship between the temperature rising effect at the time of fuel addition with respect to inflow gas, and the improvement rate of the CO purification rate of an exhaust purification catalyst about an Example and a comparative example.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

<Exhaust gas purification device>
As shown in FIG. 1, the exhaust emission control device according to this embodiment is applied to a diesel engine 1 as an internal combustion engine. First, the configuration of the diesel engine 1 will be briefly described. In addition, the diesel engine 1 demonstrated below is only an example of the internal combustion engine which concerns on this invention. The exhaust emission control device according to the present invention can also be applied to an internal combustion engine (for example, a gasoline engine) other than the diesel engine 1 described below.

  The diesel engine 1 includes a plurality of combustion chambers 2 and a fuel injection valve 3 that injects fuel into each combustion chamber 2. Each combustion chamber 2 communicates with an intake manifold 4 and an exhaust manifold 5. The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 through the intake duct 6. An inlet of the compressor 7 a is connected to an air cleaner 9 via an intake air amount detector 8. A throttle valve 10 is disposed in the intake duct 6. Around the intake duct 6, a cooling device 11 for cooling the air flowing in the intake duct 6 is arranged. The exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 b of the exhaust turbocharger 7. The outlet of the exhaust turbine 7 b is connected to the exhaust pipe 12.

  The exhaust manifold 5 and the intake manifold 4 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 18. An electronically controlled control valve 19 is disposed in the EGR passage 18. A cooling device 20 for cooling the EGR gas flowing in the EGR passage 18 is disposed around the EGR passage 18.

  Each fuel injection valve 3 is connected to a common rail 22 via a fuel supply pipe 21. The common rail 22 is connected to the fuel tank 24 via the fuel pump 23. Here, the fuel pump 23 is an electronically controlled fuel pump with variable discharge amount. However, the configuration of the fuel pump 23 is not particularly limited.

  As shown in FIG. 2A, in the exhaust pipe 12, the fuel supply valve 15, the small oxidation catalyst 14, and the exhaust purification catalyst 13 are sequentially arranged from the upstream side (left side in FIG. 2A) to the downstream side (right side in FIG. 2A). Is arranged. Although illustration is omitted, another catalyst or the like may be arranged on the downstream side of the exhaust purification catalyst 13. For example, a particulate filter for collecting particulates in the exhaust gas, a NOx storage catalyst, or the like may be disposed on the downstream side of the exhaust purification catalyst 13.

  The exhaust purification catalyst 13 is a catalyst having an oxidation function. The exhaust purification catalyst 13 is formed of a monolith catalyst carrying a noble metal catalyst such as Pt (platinum). However, the type of the exhaust purification catalyst 13 is not particularly limited.

  The small oxidation catalyst 14 is an oxidation catalyst having a volume smaller than that of the exhaust purification catalyst 13. Here, the “small size” of the small oxidation catalyst 14 merely means that it is smaller than the exhaust purification catalyst 13, and does not limit the absolute dimensions at all.

  2B is a cross-sectional view taken along the line IIB-IIB in FIG. 2A. The small oxidation catalyst 14 according to the present embodiment has a base material having a laminated structure of a thin metal plate and a thin metal corrugated plate. A catalyst carrier layer made of alumina, for example, is formed on the surface of the substrate. A plurality of types of noble metal catalysts including Pt (platinum) are supported on the catalyst carrier. As a noble metal other than Pt, for example, Pd (palladium), Rh (rhodium) or the like can be used. For the substrate, for example, a honeycomb body made of ceramics such as cordierite or a heat-resistant alloy can be used.

  As can be seen from FIGS. 2A and 2B, the cross-sectional area of the small oxidation catalyst 14 is smaller than the cross-sectional area of the exhaust pipe 12. Further, the cross-sectional area of the small oxidation catalyst 14 is smaller than the cross-sectional area of the exhaust purification catalyst 13. The small oxidation catalyst 14 is formed in a substantially cylindrical shape extending in the exhaust gas flow direction (left-right direction in FIG. 2A). The small oxidation catalyst 14 is disposed in a cylindrical outer frame 16. The outer frame 16 is supported in the exhaust pipe 12 by a plurality of stays 29. However, the arrangement of the small oxidation catalyst 14 is not limited at all. In this embodiment, the small oxidation catalyst 14 is disposed at the center of the exhaust pipe 12, but the small oxidation catalyst 14 may be disposed at a position shifted from the center of the exhaust pipe 12. Further, the shape of the small oxidation catalyst 14 is not limited to the cylindrical shape, and various other shapes can be adopted.

  Although the arrangement mode of the fuel supply valve 15 is not limited at all, in the present embodiment, the fuel supply valve 15 is arranged so that the nozzle port is located at the center in the exhaust pipe 12. The fuel supply valve 15 injects diesel fuel (light oil) as the fuel F from the nozzle port toward the upstream end face of the small oxidation catalyst 14.

<Details of small oxidation catalyst>
The small oxidation catalyst 14 mainly promotes activation of the exhaust purification catalyst 13. When fuel is supplied from the fuel supply valve 15 to the activated small oxidation catalyst 14, the fuel ignites and the small oxidation catalyst 14 rises in temperature. That is, the fuel is oxidized in the small oxidation catalyst 14, and the temperature of the small oxidation catalyst 14 is increased by the oxidation reaction heat generated at this time. Then, the exhaust gas is heated by the small oxidation catalyst 14, and the temperature of the exhaust gas supplied to the exhaust purification catalyst 13 rises. As a result, the temperature of the exhaust purification catalyst 13 is raised and its activation is promoted.

  Further, when a larger amount of fuel is supplied to the small oxidation catalyst 14, a part of the fuel is reformed in the small oxidation catalyst 14. The reformed fuel is supplied to the exhaust purification catalyst 13 and oxidized in the exhaust purification catalyst 13. Thereby, the temperature of the exhaust purification catalyst 13 is further increased.

  Since the flow resistance in the small oxidation catalyst 14 is large, the amount of exhaust gas flowing through the small oxidation catalyst 14 is relatively small. Further, when an oxidation reaction occurs in the small oxidation catalyst 14, the gas expands and the viscosity of the gas increases, so that the amount of exhaust gas flowing in the small oxidation catalyst 14 further decreases. Therefore, the flow rate of the exhaust gas in the small oxidation catalyst 14 is considerably slower than the flow rate of the exhaust gas flowing in the exhaust pipe 12. As described above, since the flow rate of the exhaust gas in the small oxidation catalyst 14 is slow, once the oxidation reaction occurs in the small oxidation catalyst 14, the oxidation reaction becomes active. Moreover, since the small-sized oxidation catalyst 14 has a small volume, its heat capacity is small. Therefore, when the fuel is supplied, the temperature of the small oxidation catalyst 14 rapidly rises to a relatively high temperature.

  However, when the catalyst is exposed to a high temperature, the noble metals contained in the catalyst aggregate and grain growth occurs (sintering). As a result, the surface area of the particles is reduced and the number of contact points with the exhaust gas is reduced. As a result, the purification performance of the catalyst decreases. That is, the catalyst deteriorates when exposed to high temperatures.

  By the way, the temperature distribution of the small-sized oxidation catalyst 14 at the time of temperature rise is not constant, and the temperature tends to be higher toward the downstream side. Therefore, a larger heat load is applied to the downstream portion of the small oxidation catalyst 14 than to the upstream portion. Therefore, in order to suppress the deterioration of the small oxidation catalyst 14, it is effective to suppress the deterioration of the downstream portion.

  As described above, the small oxidation catalyst 14 rises in temperature when the supplied fuel is ignited. However, if the temperature of the exhaust gas discharged from the internal combustion engine is low, it takes a certain amount of time for the fuel supplied from the fuel supply valve 15 to ignite by the small oxidation catalyst 14. That is, even if the small-sized oxidation catalyst 14 is easily heated, if the temperature of the exhaust gas is low, the time until the fuel is ignited becomes long. Generally, when the internal combustion engine is a diesel engine, the temperature of the exhaust gas is low. Therefore, it takes time until the fuel is ignited by the small oxidation catalyst 14, and during that time, the exhaust purification catalyst 13 is not sufficiently activated, and the exhaust gas may be exhausted without being sufficiently purified. .

  The fuel is ignited in the upstream portion of the small oxidation catalyst 14. Therefore, in order to improve the low temperature ignition performance of the small oxidation catalyst 14, it is effective to improve the low temperature ignition performance of the upstream portion.

  Therefore, the present inventor makes the upstream portion of the small-sized oxidation catalyst 14 have a property of easily igniting the fuel by making the Pt ratio different between the upstream portion and the downstream portion, and the downstream portion is caused by temperature increase. It was decided to have the property that the catalyst would not easily deteriorate.

  As schematically shown in FIG. 2C, the small oxidation catalyst 14 includes an upstream portion 14a and a downstream portion 14b. The upstream portion 14a is a portion that corresponds to 35% to 90% of the length of the base material from the upstream end 14c of the base material (the left end in FIGS. 2A and 2C) toward the downstream side. The downstream portion 14b is a portion other than the upstream portion 14a. That is, the downstream portion 14b is a portion located on the downstream side of the upstream portion 14a. When the total length of the small oxidation catalyst 14 is L, the total length of the upstream portion 14a is La, and the total length of the downstream portion 14b is Lb, La = 0.35L to 0.90L, and La + Lb = L. The length of the substrate can be measured with a known length measuring device such as a gauge scale.

  The upstream portion 14a is configured to include Pt in an amount corresponding to 55% by mass to 85% by mass of the total noble metal amount of the upstream side portion 14a in order to improve the ignitability at a low temperature. On the other hand, the downstream portion 14b is configured to include an amount of Pt corresponding to 0% by mass to 50% by mass of the total amount of noble metal in the downstream side portion 14b in order to suppress deterioration of the catalyst due to high temperature. The amount of each noble metal can be measured by, for example, a plasma emission analyzer (ICP).

  According to the small-sized oxidation catalyst 14, it is possible to effectively achieve suppression of catalyst deterioration in the downstream portion 14b and improvement in low temperature ignition performance in the upstream portion 14a. Therefore, according to the exhaust gas purification apparatus, the exhaust gas purification performance is improved. Further, since the small oxidation catalyst 14 is less deteriorated, the exhaust purification catalyst 13 can be efficiently heated with a smaller amount of fuel supply. Therefore, the effect which suppresses the fall of a fuel consumption can also be acquired as an accompanying effect.

<Production method of small oxidation catalyst>
The small oxidation catalyst 14 can be produced, for example, as follows. Note that the method described below is merely an example of a method for producing the small-sized oxidation catalyst 14. The small oxidation catalyst 14 can be produced by other methods.

  First, a predetermined amount of alumina and a binder such as aluminum hydroxide, alumina sol, or titanium oxide are mixed by a wet process to prepare a slurry. Thereafter, using this slurry, a metal substrate or a substrate made of cordierite or the like is subjected to a wash coat, and dried and fired to form a coat layer on the surface of the substrate. Next, a portion corresponding to 35% to 90% of the total length from one end in the axial direction of the base material is immersed in a solution of Pt and other noble metals (Pd, etc.), and 55 wt% to 85 wt% of the total noble metal amount in the portion. % Of Pt and other noble metals occupying the remaining content are supported, dried and fired. This portion is an upstream portion 14 a of the small oxidation catalyst 14. Next, the remaining part of the base material is immersed in a solution of Pt and other noble metals, and the part occupies an amount corresponding to 0 to 50% by mass of the total noble metal amount and the remaining content. Other noble metals are supported, dried and fired. This portion becomes the downstream portion 14 b of the small oxidation catalyst 14. As described above, the small oxidation catalyst 14 having the upstream portion 14a and the downstream portion 14b can be obtained.

<Reason for setting upstream and downstream parts>
Next, the reason why the ratio of Pt in the downstream part, the ratio of Pt in the upstream part, and the ratio of the length of the upstream part are set to the values in the above range will be sequentially described.

<Pt ratio in downstream part>
The present inventor conducted an experiment for examining HC-T50 and CO adsorption amount (PGM active site amount) using a plurality of small oxidation catalyst samples having different Pt ratios. Here, “HC-T50” means that when exhaust gas is passed through a small oxidation catalyst, the HC concentration in the exhaust gas on the outlet side of the small oxidation catalyst is half the HC concentration in the exhaust gas on the inlet side. Is the temperature of the small oxidation catalyst. This HC-T50 represents the purification performance of a small oxidation catalyst. The lower the HC-T50, the higher the purification performance.

  In this experiment, the CO adsorption amount was measured by the CO pulse adsorption method. The HC concentration was measured by a flame ionization detection method.

  In this experiment, a small oxidation catalyst having a diameter of 45 mm and a length of 30 mm was used as each sample. The volume of each sample is about 48 mL. Each sample carries Pt and / or Pd as a noble metal catalyst.

  The production method of each sample is as follows. That is, first, alumina and a binder are mixed by a wet process to prepare a slurry. Thereafter, a wash coat is applied to the cordierite base material using this slurry, followed by drying and firing. Thereby, 150 g of alumina is supported per 1 L of the volume of the cordierite base material (hereinafter, the supported amount may be expressed as 150 g / L or the like). Next, the base material is immersed in a solution of noble metal (Pt and / or Pd), and 1.8 g / L of the noble metal is supported on the base material. Thereafter, the substrate carrying the noble metal is dried and fired.

The experimental conditions are as follows.
Gas composition: lean atmosphere (CO ₂ : O ₂ : NO: CO: C ₃ H ₆ : H ₂ O = 10%: 10%: 200 ppm: 350 ppm: 3500 ppm: 10%. Others are N ₂ )
Gas flow rate: 15L / min
Temperature rising condition: 150 ° C. to 500 ° C. (temperature rising rate is 20 ° C./min)

図３から、Ｐｔ割合が０質量％〜５０質量％の場合、ＣＯ吸着量が高く、貴金属粒成長を効果的に抑制できることが分かった。また、Ｐｔ割合が０質量％〜５０質量％の場合、ＨＣ−Ｔ５０が低く、ＨＣに対する活性が高いことが分かった。このことにより、小型酸化触媒の下流側部分のＰｔ割合として、０質量％〜５０質量％が好ましいことが分かった。 The experimental results are shown in Table 1 and FIG. The “Pt ratio” is the mass% of Pt in the total precious metal catalyst.

From FIG. 3, it was found that when the Pt ratio is 0% by mass to 50% by mass, the CO adsorption amount is high and the growth of noble metal particles can be effectively suppressed. Moreover, when Pt ratio was 0 mass%-50 mass%, it turned out that HC-T50 is low and the activity with respect to HC is high. Thus, it was found that 0% by mass to 50% by mass is preferable as the Pt ratio in the downstream portion of the small oxidation catalyst.

<Pt ratio of upstream part>
The present inventor conducted an experiment to examine the low temperature ignition performance of a small oxidation catalyst using a plurality of samples having different Pt ratios. Also in this experiment, a small oxidation catalyst having a diameter of 45 mm and a length of 30 mm was used as each sample. The method for producing each sample is the same as in the above-described experiment. Each sample carries Pt and / or Pd as a noble metal catalyst. The total amount of precious metals is 1.8 g / L.

  In this experiment, a diesel engine with a displacement of 2.2 L was set on an engine bench, and a fuel supply valve, each sample of a small oxidation catalyst, and an exhaust purification catalyst were sequentially arranged in the exhaust passage of the diesel engine (see FIG. 2A). ). The endurance test was conducted by repeating the fuel addition of the pattern as shown in FIG. 4 from the fuel supply valve. The “upstream center temperature” on the vertical axis in FIG. 4 is a temperature measured by a thermocouple arranged at a position 16% of the total length from the upstream end of the small oxidation catalyst. The fuel addition was performed by giving a periodic pulse signal to the fuel supply valve and periodically turning the fuel supply valve on and off. That is, a certain amount of fuel is periodically and continuously added. In this pattern, the fuel is so maintained that the upstream center temperature is maintained at 720 ° C. for 5 minutes, the state at 750 ° C. for 3 minutes, the state at 780 ° C. for 3 minutes, and the state at 810 ° C. for 3 minutes. The amount of addition is increased stepwise. Thereafter, the state in which no fuel is supplied (that is, fuel cut) is continued for 10 seconds, and then the above pattern is repeated again. In this experiment, the above pattern was repeated 400 cycles.

  FIG. 5 shows a temperature profile of the upstream center temperature and the downstream center temperature of the small oxidation catalyst. The “downstream center temperature” is a temperature measured by a thermocouple disposed at a position 83% of the total length from the upstream end of the small oxidation catalyst. FIG. 5 shows that the temperature of the small oxidation catalyst is higher on the downstream side than on the upstream side. As a result of the durability test, the durability of each sample was confirmed.

About each sample, the test (henceforth a temperature rising effect confirmation test) which investigates the temperature rising effect at the time of fuel addition was done. In this test, a pulse signal was continuously given to the fuel supply valve under a condition where the inlet side gas temperature was constant (280 ° C.), and a predetermined amount of fuel was intermittently supplied from the fuel supply valve. Specifically, the injection amount per one time of the fuel supply valve is set to 115 mm ³ , the injection time per one time is set to about 70 milliseconds, and the fuel is injected at a rate of about once every 1.47 seconds. In this way, a predetermined amount of fuel is periodically and continuously added by periodically turning on and off the fuel supply valve. Thermocouples are placed at 33%, 50%, and 67% of the total length from the upstream end of the small oxidation catalyst (referred to as “upstream position”, “intermediate position”, and “downstream position”, respectively), and fuel is injected Then, the temperature at each position when the temperature was stabilized was measured. And the temperature rising effect at the time of fuel addition in each position (the difference between the temperature at the time of fuel addition and the temperature at the time of no fuel addition) was determined. The result is shown in FIG.

  From FIG. 6, it can be seen that in the range where the Pt ratio is 55% by mass to 85% by mass, a higher temperature raising effect is obtained than when the Pt ratio is 0% by mass to 50% by mass. Further, it can be seen that when the Pt ratio is 70% by mass to 80% by mass, a higher temperature increase effect is obtained, and when the Pt ratio is 75% by mass, the highest temperature increase effect is obtained. From the above, when the Pt ratio is 55% by mass to 85% by mass, the time until the fuel ignites is shorter and the low temperature ignitability is better than when the Pt ratio is 0% by mass to 50% by mass. Presumed. Accordingly, it was found that 55% to 85% by mass is preferable as the Pt ratio in the upstream portion of the small oxidation catalyst.

<Length ratio of upstream part>
Next, the inventor conducted an experiment for examining a suitable length ratio of the upstream portion. In the experiment, a plurality of samples having different length ratios in the upstream portion were used. Also in this experiment, a small oxidation catalyst having a diameter of 45 mm and a length of 30 mm was used as each sample. The upstream portion was loaded with 1.5 g / L Pt and 0.3 g / L Pd. The Pt ratio in the upstream portion is about 83% by mass. In Samples B1 to B5, 1.8 g / L of Pd was supported on the downstream portion. The Pt ratio in the downstream portion is 0% by mass. In samples C1 to C5, 0.9 g / L Pt and 0.9 g / L Pd were supported on the downstream portion. The Pt ratio in the downstream portion is 50% by mass. The method for producing each sample is the same as in each of the above-described experiments.

  As a comparative example, a sample having a constant Pt ratio (that is, a sample having the same Pt ratio in the upstream portion and the downstream portion) was used. In Comparative Example 1, 1.8 g / L of Pd was supported, and the Pt ratio was 0% by mass. In Comparative Example 2, 1.8 g / L of Pt was supported, and the Pt ratio was 100% by mass. In Comparative Example 3, 0.9 g / L Pt and 0.9 g / L Pd were supported, and the Pt ratio was 50% by mass.

  Also in this experiment, a 2.2 L diesel engine was set on the engine bench, and a fuel supply valve, small oxidation catalyst samples, and an exhaust purification catalyst were sequentially arranged in the exhaust passage of the diesel engine (FIG. 2A). reference). Durability tests similar to those described above were performed, and the durability of each sample was confirmed.

About each sample, the temperature rising effect confirmation test was done on the conditions similar to the above-mentioned temperature rising effect confirmation test. In this test, thermocouples were respectively arranged in the space on the inlet side (upstream side) and the space on the outlet side (downstream side) of the small oxidation catalyst in order to measure the temperature of the exhaust gas. Then, by calculating the difference between the temperature of the exhaust gas on the outlet side and the temperature of the exhaust gas on the inlet side, the temperature of the exhaust gas increases due to passing through the small oxidation catalyst, that is, the increase in fuel addition to the inflow gas. The temperature effect was determined. The results are shown in Table 2 and FIG.

  From FIG. 7, it is understood that when the length ratio of the upstream portion is 35% to 90%, the heating effect is higher than Comparative Example 3 (Comparative Example having the highest heating effect among Comparative Examples 1 to 3). . Further, when the length ratio of the upstream portion is 50% to 60%, the temperature rising effect is very high, and particularly when the length ratio of the upstream portion is 55%, the highest temperature rising effect can be obtained. I understand.

  From the above, 35% to 90% of the total length from the upstream end is the upstream part, and the other part is the downstream part, and Pt contained in the upstream part is 55% to 85% by mass and the downstream part It was found that when the contained Pt was 0% by mass to 50% by mass, a small oxidation catalyst with little catalyst deterioration due to temperature rise and excellent low temperature ignition performance could be obtained.

  Examples will be described below. However, the present invention is not limited to the following examples.

<Example 1>
Alumina and a binder were mixed by a wet method to prepare a slurry. The binder material is aluminum hydroxide, alumina sol, and titanium oxide. Thereafter, using this slurry, a cordierite base material having a diameter of 45 mm and a length of 30 mm was wash-coated, dried and fired, and 150 g / L of alumina was supported on the base material. Next, 50% of the base material in the length direction was immersed in a solution of Pt and Pd, and 1.5 g / L of Pt and 0.3 g / L of Pd were supported, dried and fired. Next, the remaining 50% of the substrate was immersed in a Pd solution, and 1.8 g / L of Pd was supported on the portion, followed by drying and firing.

<Example 2>
Alumina and a binder were mixed by a wet method to prepare a slurry. Thereafter, using this slurry, a cordierite base material having a diameter of 45 mm and a length of 30 mm was wash-coated, dried and fired, and 150 g / L of alumina was supported on the base material. Next, 50% of the base material in the length direction was immersed in a solution of Pt and Pd, and 1.5 g / L of Pt and 0.3 g / L of Pd were supported, dried and fired. Next, the remaining 50% of the substrate was immersed in a solution of Pt and Pd, 0.9 g / L of Pt and 0.9 g / L of Pd were supported on the part, and dried and fired. .

  For performance evaluation of Examples 1 and 2, a comparison with a comparative example was performed. Comparative Examples 1 to 3 are as follows.

<Comparative Example 1>
Alumina and a binder were mixed by a wet method to prepare a slurry. Thereafter, using this slurry, a cordierite base material having a diameter of 45 mm and a length of 30 mm was wash-coated, dried and fired, and 150 g / L of alumina was supported on the base material. Next, the entire base material was immersed in a Pd solution to support 1.8 g / L of Pd, and dried and fired.

<Comparative example 2>
Alumina and a binder were mixed by a wet method to prepare a slurry. Thereafter, using this slurry, a cordierite base material having a diameter of 45 mm and a length of 30 mm was wash-coated, dried and fired, and 150 g / L of alumina was supported on the base material. Next, the entire base material was immersed in a Pt solution, loaded with 1.8 g / L of Pt, dried and fired.

<Comparative Example 3>
Alumina and a binder were mixed by a wet method to prepare a slurry. Thereafter, using this slurry, a cordierite base material having a diameter of 45 mm and a length of 30 mm was wash-coated, dried and fired, and 150 g / L of alumina was supported on the base material. Next, the entire base material was immersed in a solution of Pt and Pd to carry 0.9 g / L of Pt and 0.9 g / L of Pd, followed by drying and firing.

<Performance confirmation test>
The following tests were conducted on the exhaust emission control devices provided with the small oxidation catalysts of Examples 1-2 and Comparative Examples 1-3. As in the previous experiment, a diesel engine with a displacement of 2.2 L was set on the engine bench, a fuel supply valve, a small oxidation catalyst (Examples 1-2, Comparative Examples 1-3) in the exhaust passage of the diesel engine, And an exhaust purification catalyst were sequentially arranged (see FIG. 2A). As the exhaust purification catalyst, a 1.1 L monolith catalyst in which Pt and Pd were supported on alumina was used. A durability test similar to the above-described durability test was performed to confirm the durability of the small oxidation catalyst.

  About the small-sized oxidation catalyst of Examples 1-2 and Comparative Examples 1-3, the temperature rising effect confirmation test was done on the same conditions as the above-mentioned temperature rising effect confirmation test. The result is shown in FIG. As can be seen from FIG. 8, in Examples 1 and 2, it was confirmed that the temperature rising effect at the time of fuel addition was higher than in Comparative Examples 1 to 3.

  Next, a test for examining the improvement rate of the CO purification rate of the exhaust purification catalyst was conducted. The improvement rate of the CO purification rate of the exhaust purification catalyst refers to the CO purification rate of the exhaust purification catalyst when the small oxidation catalyst is arranged on the basis of the CO purification rate of the exhaust purification catalyst when the small oxidation catalyst is not arranged. It indicates whether the rate has risen at a certain rate. In the test, the European mode running shown in FIG. 9 was performed on the engine bench. Similar to the temperature increase effect confirmation test, a predetermined amount of fuel was supplied from the fuel supply valve to the small oxidation catalyst. The test results are shown in FIG.

  FIG. 10 shows the relationship between the temperature rise effect at the time of fuel addition and the improvement rate of the CO purification rate of the exhaust purification catalyst. As can be seen from FIG. 10, in Examples 1 and 2, it was confirmed that the CO purification rate of the exhaust purification catalyst was further improved as compared with Comparative Examples 1 to 3.

1 Diesel engine (internal combustion engine)
4 Intake manifold 5 Exhaust manifold 7 Exhaust turbocharger 12 Exhaust pipe (exhaust passage)
13 Exhaust purification catalyst 14 Small oxidation catalyst 15 Fuel supply valve

Claims (3)

An exhaust purification catalyst disposed in the exhaust passage of the internal combustion engine and having an oxidation function;
A small-sized oxidation catalyst that is disposed upstream of the exhaust purification catalyst in the exhaust passage and has a smaller volume than the exhaust purification catalyst;
An exhaust purification device for an internal combustion engine, comprising a fuel supply valve for supplying fuel to the small oxidation catalyst,
The small oxidation catalyst has a base material and a plurality of kinds of noble metals supported on the base material,
In the upstream portion which is a portion corresponding to 35% to 90% of the length of the base material from the upstream end of the base material toward the downstream side of the small oxidation catalyst, The amount is 55% to 85% by weight,
An exhaust gas purification apparatus for an internal combustion engine, wherein the amount of platinum in the total amount of noble metals in the downstream portion is 0 mass% to 50 mass% in a downstream portion other than the upstream portion of the small oxidation catalyst.   2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the plurality of types of noble metals include at least platinum and palladium.   The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2, wherein the internal combustion engine is a diesel engine.

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