JP4889585B2 - Internal combustion engine exhaust gas purification method - Google Patents

Description

  The present invention relates to a method for purifying internal combustion engine exhaust gas. More specifically, the present invention relates to a purification method that is excellent in removing particulates and the like from exhaust gas from an internal combustion engine such as a diesel engine and removing sulfur compounds and the like in a NOx storage catalyst.

  Diesel particulate filters are used to collect PM (particulate matter) such as black smoke and SOF discharged from internal combustion engines such as diesel engines, and PM accumulates in the filters as they are used. There is a problem that the pressure loss becomes large.

  Therefore, conventionally, for PM deposition, a heating device such as an electric heater is disposed in the filter, and the filter is regenerated by burning and removing the PM by heating (Patent Document 1).

  However, such a reproduction method has a problem that power consumption is large and running cost is high. In addition to the filter, the heater occupies a large volume, and there is a problem that the installation location is limited when installing in a vehicle. In order to solve these problems, a filter for collecting diesel engine particulates, a catalytic converter active on hydrocarbons (HC) provided upstream of the exhaust pipe of the filter, and a catalytic converter A diesel exhaust gas purification device including an HC control means capable of supplying a large amount of HC has been proposed, and platinum, palladium, rhodium and the like are disclosed as the catalyst (Patent Document 2).

  A diesel exhaust particle filter in which a catalyst component is coated on a filter is also disclosed (Patent Document 3).

  Furthermore, a regenerative diesel particulate filter is provided in the exhaust passage of the internal combustion engine, and regeneration mode operation is performed when the collected amount of particulate matter in the filter for collecting particulate matter exceeds a predetermined judgment value. In the exhaust gas purification system for an internal combustion engine that removes the collected particulate matter, the collected amount estimating means for estimating the collected amount of the particulate matter collected by the filter, and the collected amount estimating means An exhaust gas purification system for an internal combustion engine is also proposed that includes a maximum injection amount control means for limiting the maximum injection amount of the internal combustion engine when the particulate matter estimated by the above is greater than or equal to a predetermined determination value (Patent Document 4). .

  In addition, in the nitrogen oxide removal method, it is known that the NOx storage catalyst used for the removal of NOx and the like absorbs sulfur oxides such as SOx, thereby reducing the catalyst performance. In addition, a method of regenerating by introducing a large amount of hydrocarbons and raising the temperature has been proposed. However, this method has a limited temperature range suitable for regeneration (Patent Document 5).

Further, it is disclosed that hydrocarbons discharged in a low temperature range at the time of engine start can be efficiently purified using catalysts carrying different catalyst amounts and catalyst compositions on the inflow side and the outflow side on the same catalyst. In this catalyst, the HC adsorbent is temporarily adsorbed by the HC adsorbent at a low temperature where the catalytic activity is not manifested in the engine starting region, and is purified when the catalytic activity is manifested due to the temperature rise, and the oxygen release amount from the downstream side. However, the precious metal content is preferably higher on the outflow side than on the exhaust gas inflow side. However, when the precious metal content is higher on the outflow side than on the exhaust gas inflow side as described above, as shown in FIGS. Further, as shown in FIGS. 4 and 5, in the present invention, the CO ₂ concentration increases as the amount of decrease in the HC concentration increases, so that the combustion reaction represented by the formula (A) is not temporarily adsorbed by HC. is happening. (Patent Document 6).

Japanese Patent No. 2953409 JP 60-043113 A US Patent Publication No. 5100632 JP 2004-108207 A Japanese Patent No. 3747639 JP 2003-200049 A

  The method described in the above document has the advantage that the manufacturing cost is low and the restriction on the installation place is relaxed compared to the method using an electric heater, etc., but on the other hand, a large amount of hydrocarbon needs to be supplied. The poisoning of hydrocarbons adhering to the catalyst due to the supply of hydrogen is a problem. This hydrocarbon poisoning is likely to occur when hydrocarbons are supplied at a temperature of the temperature raising catalyst portion at the time of supplying hydrocarbons that is lower than the boiling point of the supplied hydrocarbons, and also more likely to occur as the concentration of hydrocarbons increases. This is because the hydrocarbon combustion reaction rate is slow when the temperature of the temperature raising catalyst portion is low, and when the hydrocarbon concentration is high, the hydrocarbon feed rate is higher than the combustion treatment rate of the temperature raising catalyst. This is because it is faster. For this reason, in the conventional method, after the temperature is increased to a temperature at which the combustion speed of hydrocarbons is high by control on the engine side, control is required such as supplying hydrocarbons or supplying a small amount capable of sufficiently burning hydrocarbons. there were. However, when such control is performed, the time until regeneration becomes longer, which adversely affects running performance and the environment. On the other hand, when a large amount of hydrocarbon is supplied at a low temperature without performing such control, hydrocarbon poisoning tends to occur on the catalyst, and when hydrocarbon poisoning occurs and the catalyst performance decreases, Since the hydrocarbons introduced thereafter do not burn, a large amount of hydrocarbons are discharged. As a result, when a diesel particulate filter is installed in the latter stage, high temperature exhaust gas is not supplied, so PM repaired in the diesel particulate filter does not burn, soot accumulation proceeds, As a result, the engine may be stopped. In addition, when a NOx storage catalyst is installed in the subsequent stage, it is necessary to remove sulfur oxide accumulated on the NOx storage catalyst with high-temperature exhaust gas. However, since high-temperature exhaust gas is not supplied, The accumulated state continues and the state in which the NOx purification performance deteriorates continues, causing NOx emission. For these reasons, it is a problem to improve the exhaust gas temperature rise performance by improving the combustibility with respect to high-concentration hydrocarbons at low temperatures.

  Therefore, an object of the present invention is to provide a novel method for raising the temperature of exhaust gas from an internal combustion engine.

  Another object of the present invention is to provide a purification method excellent in removing particulates and the like from exhaust gas from an internal combustion engine, particularly a diesel engine.

  Still another object of the present invention is to provide an exhaust gas purification method that is excellent in removing sulfur oxides when using a NOx storage catalyst.

  Still another object of the present invention is to provide an internal combustion engine exhaust gas purification method that enables stable regeneration of a filter for a long period of time in a system that supplies a high-concentration hydrocarbon fuel.

  The above objects are achieved by the following (1) to (13).

  (1) An internal combustion engine exhaust gas temperature raising catalyst is provided upstream of the exhaust gas purification catalyst in the exhaust gas passage of the internal combustion engine along the flow of the exhaust gas, and upstream of the temperature raising catalyst. The exhaust gas purifying method comprises introducing 1,000 to 40,000 ppm of hydrocarbons in terms of methane from the exhaust gas inflow side on the refractory three-dimensional structure. A method for purifying internal combustion engine exhaust gas, wherein a catalytically active component is supported with a concentration gradient that becomes lower toward the outflow side.

  (2) A catalyst active component (A) made of at least one noble metal selected from the group consisting of platinum, palladium and rhodium is supported on the refractory inorganic oxide powder (B). The method according to (1) above, wherein the catalyst component is supported on the refractory three-dimensional structure.

  (3) The method according to (1) or (2), wherein the concentration gradient is formed stepwise.

  (4) The supported amount of the catalytically active component (A) in the temperature increasing catalyst is 0.2 to 20 g / liter, and the supported amount of the refractory inorganic oxide powder (B) is 10 to 300 g / liter. Item 4. The method according to Item 2 or 3.

  (5) The supported amount of the catalytic active component (A) is 20 to 80% in the total length of 10 to 66.7% from the exhaust gas inflow side on the fire-resistant three-dimensional structure of the catalyst component in the temperature increasing catalyst. The amount of the catalytically active component (A) supported at 50% of the length on the inflow side is larger than the amount of the catalytically active component (A) supported on 50% on the outflow side. The method as described in any one of -4.

  (6) The catalyst active component (A) is supported in an amount of 50 to 80% in 30 to 66.7% of the total length from the exhaust gas inflow side on the refractory three-dimensional structure in the temperature increasing catalyst. 5. The supported amount of the catalytically active component (A) at 50% of the length on the inflow side is larger than the supported amount of the catalytically active component (A) at 50% on the outflow side. The method as described in any one of.

  (7) The method according to any one of (1) to (6), wherein the introduction temperature of the hydrocarbon is 200 to 350 ° C.

  (8) The method according to any one of (1) to (7), wherein an introduction amount of the hydrocarbon is 5,000 to 30,000 ppm in terms of methane with respect to the exhaust gas.

  (9) The method according to any one of (1) to (8), wherein the exhaust gas temperature raising catalyst also has an exhaust gas purification capability.

  (10) The method according to any one of (1) to (9), wherein an exhaust gas purifying catalyst is installed downstream of the exhaust gas temperature raising catalyst with respect to the flow of the exhaust gas.

  (11) The method according to (10), wherein the exhaust gas purification catalyst is at least one selected from the group consisting of a diesel particulate filter, an oxidation catalyst, and a NOx storage catalyst.

  (12) The method according to any one of (1) to (11), wherein the three-dimensional structure of the exhaust gas temperature raising catalyst is a honeycomb and / or a plug honeycomb or a pellet.

  (13) The method according to any one of (1) to (12), wherein the three-dimensional structure of the exhaust gas purifying catalyst is a honeycomb and / or a plug honeycomb or a pellet.

  The present invention has a configuration as described above, and further, as a temperature raising catalyst, a catalytic active component having a concentration gradient that becomes lower from the exhaust gas inflow side to the outflow side on the refractory three-dimensional structure. Since it is supported, a high concentration of the catalytically active component is present in the inflow portion, thereby suppressing hydrocarbon poisoning in the inflow portion due to high concentration hydrocarbons, and a part of the introduced hydrocarbons It burns and the catalyst temperature rises. Also, in the part that enters the exhaust gas outflow side from the inflow part, hydrocarbons burned in the inflow part, so the hydrocarbon concentration in that part decreases, and the exhaust gas temperature rises due to combustion in the inflow part. Therefore, it is considered that the combustion of hydrocarbons is more likely to proceed than the inflow portion. Therefore, in this part, hydrocarbon poisoning is suppressed with a smaller amount of catalytic active component than in the inflow part, hydrocarbons burn, and the exhaust gas temperature is further increased. Similarly, by supporting the catalytically active component with a concentration gradient that becomes lower toward the outflow side than the inflow side, it is possible to suppress hydrocarbon poisoning and raise the exhaust gas temperature. There is.

  On the other hand, when the catalytic active component is supported with a concentration gradient that becomes lower toward the inflow side than the outflow side, the exhaust gas temperature hardly rises as shown in FIGS. . For this reason as well, the effect of efficiently burning high-concentration hydrocarbons on the inflow side is an important issue. Since the present invention has a remarkable effect on this issue, the combustion of hydrocarbons is stable and long. Even after a period of use or when exposed to high-temperature exhaust gas, the exhaust gas temperature can be stably increased. For this reason, when a diesel particulate filter is installed at the subsequent stage of the temperature increasing catalyst, the filter can be stably regenerated for a long period of time. Similarly, the NOx storage catalyst is disposed at the subsequent stage of the temperature increasing catalyst. Is installed, combustion removal of the accumulated sulfur oxide is stably performed. Also, even when the concentration of hydrocarbons flowing into the temperature rising catalyst does not exceed 1000 ppm, when the catalytic active component is supported with a concentration gradient that becomes lower toward the outflow side than the inflow side, Compared with the case where the catalytic active component is supported without a concentration gradient, the exhaust gas purification performance is equal to or higher than that.

  Next, the present invention will be described in more detail with reference to the drawings. That is, FIG. 1 shows a schematic diagram of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention.

  That is, the exhaust pipe 2 that communicates with the internal combustion engine 1, for example, a diesel engine, further communicates with the temperature raising area 5 that is filled with the catalyst for raising the temperature, and the filtration area that communicates with the downstream side of which the particulate filter is installed. 6 are provided. The exhaust pipe 2 on the exhaust gas inflow side of the temperature raising area 5 is provided with a fuel supply nozzle 4 provided with a reverse valve or the like (not shown) as necessary as means for supplying the hydrocarbon liquid fuel for temperature raising. A fuel supply pump 3 communicating with the nozzle 4 is attached.

  The exhaust gas purification apparatus configured as described above is provided with a temperature sensor 7 and a pressure sensor 10 at the inlet of the catalyst so that the temperature and pressure at the inlet and outlet of the catalyst can be measured if necessary. A temperature sensor 8 and a pressure sensor 11 are respectively provided at the output section, and a temperature sensor 13 and a pressure sensor 12 are respectively provided at the outlet of the filtration zone 6 provided with a filter as necessary. Each temperature sensor and pressure sensor signal is connected to the controller 9, and the controller 9 signal is connected to the pump 3.

  Further, as another embodiment of the present invention, the pump 3 and the fuel supply nozzle 4 can be directly supplied to the internal combustion engine 1, for example, a cylinder of a diesel engine by a signal from the controller 9. For example, the hydrocarbon-based liquid (for example, fuel) may be supplied after the combustion of the fuel in the cylinder of the internal combustion engine is completed and before the exhaust process is completed.

  Next, the operation of the exhaust gas purification apparatus configured as described above will be described. That is, as shown in FIG. The exhaust gas of the internal combustion engine 1, for example, a diesel engine, passes through the exhaust pipe 2, and in the temperature rising region 5 filled with the catalyst for raising the temperature, the high-concentration unburned hydrocarbons contained in the exhaust gas ( HC) is combusted to become water and carbon dioxide, and is discharged out of the system through a filter area 6 filled with a filter, a muffler (not shown), and the like.

  On the other hand, the particulates contained in the exhaust gas are collected by the particulate filter in the filtration zone 6, but gradually accumulate, so that the pressure applied to the filter rises and the pressure value reaches a constant value. When the filter temperature reaches a certain temperature, the hydrocarbon liquid fuel is injected from the nozzle 4 and supplied onto the temperature raising catalyst 5 in the temperature raising region 5. Since the pressure sensor 11 provided between the temperature raising area 5 and the filtration area 6 measures the pressure in the filtration area 6, the received value is obtained when the measured value is equal to or higher than a predetermined pressure. Thus, the fuel supply pump 3 is operated by the command of the controller 9, and if the pressure is lower than the predetermined pressure, the operation of the pump 3 is stopped by the command of the controller 9.

  Further, if the temperature sensor 8 provided between the temperature raising zone 5 and the filtration zone 6 exceeds a predetermined value, for example, if it exceeds 700 ° C., the operation of the fuel supply pump 3 is stopped by a command from the controller 9, Further, for example, in the case of light oil, 90% or more of the components have a boiling point or higher at about 330 ° C. However, if the temperature is lower than 330 ° C., the high boiling fraction in the light oil is liquid and is introduced into the temperature raising zone 5. Adhesion on the catalyst surface is likely to occur, and a small amount is supplied from the pump 3 in accordance with a command from the controller 9. Further, for example, when the temperature is lower than 200 ° C., the operation of the fuel supply pump 3 is stopped by a command from the controller 9. On the other hand, if it is 330 degreeC or more and less than 500 degreeC, for example, the supply amount of hydrocarbon fuel will be adjusted so that the target temperature may be reached.

  The pressure sensor 10 at the inlet of the temperature raising zone 5 is installed when the pressure sensor 11 provided between the normal temperature raising zone 5 and the filtration zone 6 is not installed, and detects the pressure applied to the temperature raising zone 5 and the filtration zone. The pressure applied to the temperature rising catalyst and the filtration zone is measured from the difference between the pressure sensor 10 and the pressure sensor 12.

  In general, after measuring the pressure applied to the filter, the control unit 9 sends the temperature and pressure information before and after the filter (or inside the filter) to the control unit, and when a certain value is exceeded, a fuel supply signal is sent to the fuel injection device. The filter regeneration control (fuel supply) is started. During the fuel supply, the pressure value of the filter is sent to the control unit by the pressure sensor, and the regeneration control is stopped when the pressure value drops to a certain value.

  In this case, the hydrocarbon may be a hydrocarbon that generates heat by a combustion reaction, and includes methane, ethane, propane, gasoline, methanol, ethanol, dimethyl ether, light oil, and the like, preferably light oil. The amount used is 1,000 to 40,000 ppm, preferably 5,000 to 30,000 ppm, more preferably 5,000 to 20,000 ppm, and most preferably 5,000 to 15 ppm in terms of methane with respect to the exhaust gas. 1,000 ppm. If the amount of hydrocarbon used is small, a plurality of additions are required to raise the temperature to the target temperature, and there is a problem that rapid temperature rise cannot be performed. Further, as shown in FIG. 9, the effect of the present invention cannot be obtained when the total hydrocarbon concentration supplied is 1,000 ppm or less. On the other hand, if the amount of hydrocarbon used is large, there is a problem that hydrocarbon poisoning is likely to occur as described above, and the catalyst performance is likely to deteriorate, and control such as increasing the exhaust gas temperature when supplying hydrocarbons by engine control is performed. It is necessary to carry out or increase the amount of the catalytically active component, resulting in problems such as high costs.

  In the present invention, the upstream of the exhaust gas may be upstream of the rising catalyst, but preferably upstream of the rising catalyst after combustion of the engine. Further, “after combustion of the engine” may be a wake of the engine exhaust gas or may be in the engine.

  Thus, the introduction temperature of the hydrocarbon is 200 ° C. to 600 ° C., preferably 200 ° C. to 350 ° C., more preferably 200 ° C. to 300 ° C.

  The same applies to the case where the hydrocarbon liquid (fuel) is directly supplied to the internal combustion engine.

The temperature increasing catalyst used in the present invention is obtained by supporting a catalytically active component on a refractory three-dimensional structure with a concentration gradient that decreases toward the exhaust gas inflow side.
The temperature increasing catalyst is a catalyst in which a catalytic active component (A) made of at least one noble metal selected from the group consisting of platinum, palladium and rhodium is supported on a refractory inorganic oxide powder (B). Contains ingredients. That is, the temperature increasing catalyst according to the present invention includes a refractory three-dimensional structure, a catalytically active component (A), and a refractory inorganic oxide powder (B).

  The supported amount of the catalytically active component (A) in the temperature increasing catalyst is 0.2 to 20 g / liter, preferably 1 to 15 g / liter, and the supported amount of the refractory inorganic oxide powder (B) is 10 to 300 g / liter, preferably 20 to 200 g / liter.

  Of the noble metals, platinum is preferred, and may be platinum-palladium and / or rhodium. The mass ratio is 20/1 to 1/1, preferably 5/1 to 2/1.

  Examples of platinum starting materials include inorganic compounds such as platinum nitrate, dinitrodiammine platinum, and chloroplatinic acid, and organic compounds such as bisplatinum. Examples of rhodium starting materials include rhodium nitrate, rhodium chloride, and rhodium acetate. There are palladium starting materials such as palladium nitrate, palladium chloride, and palladium acetate.

  As the refractory inorganic oxide component used in the present invention, any component can be used as long as it is usually used as a catalyst carrier. For example, α-alumina, activated alumina such as γ, δ, η, θ, zeolite, Titania, or zirconia, titania, silicon oxide or a composite oxide thereof such as alumina-titania, alumina-zirconia, titania-zirconia, etc. can be used, and activated alumina powder is preferable. The amount of the refractory inorganic oxide used is usually 10 to 300 g, preferably 50 to 150 g, per liter of the integral structure. If it is less than 10 g, the precious metal cannot be sufficiently dispersed and durability is not sufficient. On the other hand, if it exceeds 300 g, the contact state between the noble metal and the hydrocarbon introduced for temperature rise is poor and temperature rise hardly occurs. Therefore, it is not preferable.

The refractory inorganic oxide has a BET specific surface area of 50 to 750 m ² / g, preferably 150 to 750 m ² / g. The average particle size of the refractory inorganic oxide powder is 0.5 to 150 μm, preferably 1 to 100 μm.

  An example of the catalyst component in the catalyst includes, for example, platinum and palladium as the catalyst active component (A) and active alumina and β-zeolite as the refractory inorganic oxide powder (B).

  The preparation method of the catalyst for raising the temperature according to the present invention will be specifically described. In the slurry containing the catalytic active component having a predetermined concentration composed of the catalytic active component and the refractory inorganic oxide powder, the three-dimensional structure is It is obtained by soaking.

  (A) When the three-dimensional structure is a honeycomb type, after the three-dimensional structure is entirely immersed, the three-dimensional structure is pulled up and dried, and then fired in an air atmosphere. Next, the catalytically active component-coated three-dimensional structure thus obtained is partially immersed, dried and fired. Further, the catalytically active component-coated three-dimensional structure having a large thickness is sequentially repeated as many times as necessary, whereby the coating thickness is the largest at one end, and the other end is sequentially reached according to the number of repetitions of the dipping and drying. Thus, a catalyst with a reduced coating thickness can be obtained.

  (B) A method in which when the three-dimensional structure is a honeycomb type, only the base substrate is coated with the catalyst component, and then the catalyst active component solution is partially coated sequentially.

  (C) When the three-dimensional structure is a honeycomb type, the slurry containing the high concentration catalytic active component is partially coated, for example, up to 1/3, and the slurry containing the low concentration catalytic active component is opposed to the remaining portion, for example, 2/3 Method of coating from the side.

(D) When the three-dimensional structure is a honeycomb type, the high-concentration catalytic active component-containing slurry is partially covered, for example, 1/3, and the low-concentration catalytic active component-containing slurry is partially applied from the other, for example, 1 from the other end. / 3 Method of coating. (It is important that a large amount of catalytically active components exist on the inflow side.)
(E) Dividing the three-dimensional structure into a plurality of parts, sequentially changing the concentration of the catalytically active component in the catalytic component, immersing and drying, respectively, and preparing different loaded amounts of the catalytically active component, These are sequentially arranged in series so that the paths communicate with each other and the high concentration is on the exhaust gas inflow side.

  (F) When the three-dimensional structure is a pellet type, a plurality of different types of catalyst active component supported are prepared. Fill.

  In the above method, the catalytically active component is supported with a concentration gradient that becomes lower from the inflow side to the outflow side of the exhaust gas, and the amount of the catalytically active component on the inflow side 50% It is important to make the amount larger than the amount, but preferably the amount of the catalytically active component in the total length of 10 to 66.7% from the inflow side is 20 to 80% (when the amount of all the catalytically active components is 100%). More preferably, the amount of the catalytically active component at 30 to 66.7% of the total length from the inflow side is supported at 50 to 80%. When the amount of the catalytically active component supported is increased only in the inflow portion, it is not preferable because the hydrocarbon does not sufficiently burn on the outflow side from the inflow portion, and the catalytic active component necessary for the combustion of the hydrocarbon and the continuous combustion is required. As a result, hydrocarbon poisoning is suppressed, hydrocarbons burn, and the exhaust gas temperature rises. Further, as described above, the amount of the catalytically active component may be supported with a concentration gradient that becomes lower toward the outflow side than the inflow side, and the amount of the catalytic component excluding the catalytically active component is more on the outflow side than the inflow side. The concentration gradient is such that the amount of the catalyst component excluding the catalytically active component becomes lower from the inflow side to the outflow side at the same ratio as the catalytically active component. It is supported by.

  These catalyst component-coated three-dimensional structures are preferably dried at 300 to 1200 ° C., more preferably 300 to 800 ° C., and still more preferably 400 to 600 ° C. for 15 minutes to 2 hours, preferably 30 minutes. A catalyst for raising the temperature is obtained by calcination for ˜1 hour.

  Zeolite used as necessary includes BEA type, MFI type, FER type, FAU type, MOR type and the like, and the preferred crystal structure varies depending on the purpose, and is not particularly limited.

  Examples of the fire-resistant three-dimensional monolithic structure covering the catalyst component include a heat-resistant carrier such as a honeycomb carrier, but a monolithic honeycomb structure is preferable. For example, a monolith honeycomb carrier, a metal honeycomb carrier, a plug honeycomb carrier, etc. In addition, a pellet carrier or the like can be used instead of a three-dimensional integrated structure.

  As the monolithic carrier, what is usually called a ceramic honeycomb carrier may be used. A honeycomb carrier made of a material such as cordierite is particularly preferable. In addition, an integrated structure using an oxidation-resistant heat-resistant metal such as stainless steel or Fe—Cr—Al alloy is used.

  When a pellet carrier is used as the refractory three-dimensional structure, a catalyst with a large amount of the catalytically active component supported on the pellet carrier of the above material is placed on the exhaust gas inflow side, and a catalyst with a small amount of the catalytically active component supported on the exhaust gas inflow side. It is desirable to sequentially fill the gas so as to be on the exhaust gas inflow side.

  These monolith carriers are manufactured by an extrusion molding method or a method of winding and solidifying a sheet-like element. The shape of the gas passage port (cell shape) may be any of a hexagon, a square, a triangle, and a corrugation. A cell density (number of cells / unit cross-sectional area) of 100 to 600 cells / square inch can be sufficiently used, and preferably 200 to 500 cells / square inch.

In the present invention, the method for coating the NO _x storage catalyst is not particularly limited, but usually an impregnation method is suitably used.

  There are various types of plug honeycombs used in the present invention, and known ones can be used. Examples thereof include cordierite filters and silicon carbide filters having high heat resistance.

Further, as the post-stage catalyst, a particulate material can be collected by a three-dimensional structure such as cordierite, silicon carbide, stainless steel, such as a honeycomb carrier, and a catalyst component is not coated, such as a diesel catalyst. There are a curate filter, a plug filter and the like, a filter coated with the same catalyst component as the temperature raising catalyst, and a filter that requires a high temperature in the process of using the catalyst. Further, as the stage catalyst, there is an oxidation catalyst, NO _X storage catalyst and the like.

  Next, the method of the present invention will be described in more detail with reference to examples.

Comparative Example 1
120 g of dinitrodiammine platinum aqueous solution equivalent to 2 g of platinum and palladium nitrate aqueous solution equivalent to 0.5 g of palladium, activated alumina (γ-Al ₂ O ₃ , BET specific surface area 200 m ² / g, average primary particle size 6 μm) A total of 300 g of the aqueous slurry (A) was prepared by wet pulverizing the mixture with a ball mill. As shown in FIGS. 2 (A) and 6 (A), this slurry was applied to a honeycomb carrier 101 made of cordierite having a diameter of 24 mm and a length of 50 mm having 400 cells per square inch of cross-sectional area of 122. The catalyst layer 102 was formed by coating (wash coat) so as to be 5 g, dried at 120 ° C. for 8 hours, and then calcined at 500 ° C. for 1 hour to obtain Catalyst A.

Example 1
As shown in FIG. 2 (B), the slurry (A) obtained by the method of Comparative Example 1 was placed on the cordierite honeycomb carrier 101 similar to Comparative Example 1 so that the total amount was 61.25 g per liter. (Catalyst layer 102), dried and fired at 500 ° C. for 1 hour, and using the same slurry (A), 66.7% of the total length from the inflow side to 61.25 g per liter of honeycomb carrier Covered to the length (catalyst layer 103), dried and calcined at 500 ° C. for 1 hour to obtain catalyst B in which the amount of the catalytically active component on the inflow side 50% was larger than the amount of the catalytically active component on the outflow side 50% .

Example 2
As shown in FIG. 2C, the slurry (A) obtained by the method of Comparative Example 1 is placed on the cordierite honeycomb carrier 101 similar to Comparative Example 1 so that the amount is 40.8 g per liter. After coating (catalyst layer 102), firing and firing at 500 ° C. for 1 hour, coating (catalyst layer 103) to a length of 66.7% of the total length, drying and firing at 500 ° C. for 1 hour, and further honeycomb support 1 Cover the catalyst from the inflow side to a length of 33.3% of the total length (catalyst layer 104) so as to be 40.8 g per liter, and after drying, calcinate for 1 hour at 500 ° C. Catalyst C was obtained in which the amount was greater than the amount of catalytically active component at 50% on the outflow side.

Example 3
As shown in FIG. 2 (D), the slurry (A) obtained by the method of Comparative Example 1 is entirely coated on a cordierite honeycomb carrier 101 similar to Comparative Example 1 so that the amount is 108.9 g per liter. (Catalyst layer 102), and after baking for 1 hour at 500 ° C. after drying, the same slurry A was used to cover 12.5% of the total length from the inflow side to 13.6% per liter of honeycomb carrier ( The catalyst layer 103) was dried and calcined at 500 ° C. for 1 hour to obtain a catalyst D in which the amount of the catalytically active component on the inflow side 50% was larger than the amount of the catalytically active component on the outflow side 50%.

Example 4
Catalysts A, B, C and D having a diameter of 24 mm and a length of 50 mm were calcined at 800 ° C. for 16 hours, and then exhausted as NO 500 ppm, CO 300 ppm, O ₂ 10%, CO ₂ 6%, H ₂ O 6% and The remaining nitrogen gas is converted to S.P. V. (Space velocity) circulated at 50,000 hr ⁻¹ , and when the catalyst layer temperature became 200 ° C. and stabilized, propane 2,000 ppm (methane conversion, the same applies hereinafter) and propylene 8,000 ppm hydrocarbon were circulated (conditions 1) When the temperature of the catalyst outlet at this time was measured over time, the result of FIG. 3 was obtained. Further, when the hydrocarbon concentration at the catalyst layer outlet at this time was measured over time, the result of FIG. 4 was obtained. Furthermore, when the concentration of CO ₂ at the catalyst layer outlet at this time was measured over time, the result of FIG. 5 was obtained.

Comparative Example 2
The slurry (A) obtained by the method of Comparative Example 1 is coated on the entire cordierite honeycomb carrier 201 similar to Comparative Example 1 so as to give 40.8 g per liter as shown in FIG. 6 (E). (Catalyst layer 202), dried, and calcined at 500 ° C. for 1 hour, and using the same slurry (A), 66.7% of the total length from the outflow side to 40.8 g per liter of honeycomb carrier Coating (catalyst layer 203), followed by drying at 500 ° C. for 1 hour, and further coating (catalyst catalyst) from the outflow side to a length of 33.3% of the total length so as to be 40.8 g per liter of honeycomb carrier. Layer 204) and dried and calcined at 500 ° C. for 1 hour to obtain catalyst E in which the amount of catalytically active component on the inflow side 50% is smaller than the amount of catalytically active component on the outflow side 50%.

Comparative Example 3
The slurry (A) obtained by the method of Comparative Example 1 was coated on the entire cordierite honeycomb carrier 201 similar to Comparative Example 1 so that the slurry (A) was 108.9 g per liter, as shown in FIG. 6 (F). (Catalyst layer 202) After drying, it was fired at 500 ° C. for 1 hour, and 12.5% of the total length from the outflow side to 13.6 g per liter of honeycomb carrier using the same slurry (A). The catalyst F was further coated (catalyst layer 203), dried and then calcined at 500 ° C. for 1 hour to obtain a catalyst F in which the amount of catalytically active component on the inflow side 50% was smaller than the amount of catalytically active component on the outflow side 50%.

Comparative Example 4
Catalysts A, E, and F were calcined at 800 ° C. for 16 hours, and then NO, 500 ppm, CO 300 ppm, O ₂ 10%, CO ₂ 6%, H ₂ O 6%, and the remaining nitrogen were used as exhaust gases. V. (Space velocity) circulated at 50,000 hr ⁻¹ . When the catalyst layer temperature became 200 ° C. and stabilized, 2,000 ppm of propane (converted to methane, the same applies hereinafter) and 8,000 ppm of propylene were circulated (Condition 1). When measured over time, the results of FIG. 7 were obtained.

Comparative Example 5
After the catalysts A and C were calcined at 800 ° C. for 16 hours, NO 500 ppm, CO 300 ppm, O ₂ 10%, CO ₂ 6%, H ₂ O 6%, and the remaining nitrogen were used as the exhaust gas. V. (Space velocity) circulated at 50,000 hr ⁻¹ . When the catalyst layer temperature reached 250 ° C. and was stabilized, 10,000 ppm (converted to methane) of light oil was allowed to flow (Condition 2), and the hydrocarbon concentration at the catalyst outlet at this time was measured over time. The result of FIG. 8 was obtained.

Comparative Example 6
After the catalysts A and C were calcined at 800 ° C. for 16 hours, NO 500 ppm, CO 300 ppm, O ₂ 10%, CO ₂ 6%, H ₂ O 6%, and the remaining nitrogen were used as the exhaust gas. V. (Space velocity) circulated at 50,000 hr ⁻¹ . When the temperature of the catalyst layer reaches 200 ° C., a hydrocarbon composed of 200 ppm of propane (converted to methane) and 800 ppm of propylene (converted to methane) is allowed to flow (condition 3), and the hydrocarbon concentration at the catalyst outlet at this time is set to the time. 9 was obtained, and the results of FIG. 9 were obtained. Comparative Example 7 Catalysts A and C were calcined at 800 ° C. for 16 hours, and then exhausted as NO 500 ppm, CO 300 ppm, O ₂ 10%, CO _{2, respectively.} 6%, 6% H ₂ O and the remaining nitrogen V. (Space velocity) circulated at 50,000 hr ⁻¹ . When the catalyst layer temperature reaches 200 ° C. and stabilizes, hydrocarbons consisting of 600 ppm of propane (converted to methane) and 2400 ppm of propylene (converted to methane) are allowed to flow (Condition 4). As a result of measurement, the result of FIG. 10 was obtained.

It is the schematic which shows the outline of an exhaust-gas purification apparatus by this invention. (A)-(D) are sectional drawings which show the model of the catalyst for a temperature rise used in the comparative example 1 and Examples 1-3, respectively. It is a graph which shows the relationship between the temperature of the catalyst exit at the time of hydrocarbon addition of the temperature raising catalyst used by this invention, and time. It is a graph which shows the relationship between the hydrocarbon density | concentration discharged | emitted from the catalyst exit at the time of hydrocarbon addition of the temperature rising catalyst used by this invention, and time. Is a graph showing the relationship between been CO ₂ concentration and time discharged from the catalyst outlet when the hydrocarbon addition of temperature increase for the catalyst used in the present invention. It is sectional drawing which shows the model of the catalyst of a comparative example. It is a graph which shows the relationship between the temperature of the catalyst exit at the time of hydrocarbon addition using the catalyst of a comparative example, and time. It is a graph which shows the relationship between the hydrocarbon density | concentration discharged | emitted from the catalyst exit at the time of the hydrocarbon addition using the catalyst of a comparative example, and time. It is a graph which shows the relationship between the hydrocarbon concentration discharged | emitted from the catalyst exit at the time of the hydrocarbon addition using the catalyst of a comparative example, and time. It is a graph which shows the relationship between the hydrocarbon density | concentration discharged | emitted from the catalyst exit using the catalyst of a comparative example, and time.

Claims (11)

An internal combustion engine exhaust gas temperature raising catalyst is provided upstream of the exhaust gas purification catalyst along the flow of the exhaust gas in the exhaust gas passage of the internal combustion engine, and converted into methane from the upstream side of the temperature raising catalyst. A method for purifying the exhaust gas comprising introducing 1,000 to 40,000 ppm of hydrocarbon,
A catalyst component in which the catalyst for raising temperature is supported on a refractory inorganic oxide powder (B) with a catalytically active component (A) made of at least one noble metal selected from the group consisting of platinum, palladium and rhodium. Is supported on a fire-resistant three-dimensional structure,
The catalytically active component (A), is responsible lifting with a concentration gradient such that lower toward the outlet side of the exhaust gas inlet side on the refractory three-dimensional structure,
The catalyst active component (A) is supported at 20 to 80% of the total length of 10 to 66.7% from the exhaust gas inflow side of the catalyst component in the temperature increasing catalyst from the exhaust gas inflow side on the refractory three-dimensional structure. And the amount of the catalytically active component (A) supported at 50% of the length on the inflow side is larger than the amount of the catalytically active component (A) supported on 50% on the outflow side .
An internal combustion engine exhaust gas purification method. The refractory inorganic oxide powder (B) is supported on the refractory three-dimensional structure with a concentration gradient that becomes lower from the exhaust gas inflow side to the outflow side. The method described. The method according to claim 1 or 2 , wherein the introduction temperature of the hydrocarbon is 200 to 600 ° C. The method according to any one of claims 1 to 3, wherein the temperature raising catalyst is obtained by calcining a fire-resistant three-dimensional structure coated with a catalyst component at 300 to 1200 ° C. The method according to any one of claims 1 to 4 , wherein the concentration gradient is formed stepwise. Supporting amount of the catalytically active components (A) in the temperature raising catalyst with 0.2 to 20 g / l, and supporting amount of the refractory inorganic oxide powder (B) is 10 to 300 g / liter claim 1 6. The method according to any one of 5 above.   The method according to any one of claims 1 to 6, wherein an introduction amount of the hydrocarbon is 5,000 to 30,000 ppm in terms of methane with respect to the exhaust gas.   The method according to any one of claims 1 to 7, wherein the exhaust gas temperature raising catalyst has an exhaust gas purification capability.   The method according to any one of claims 1 to 8, wherein an exhaust gas purification catalyst is installed downstream of the exhaust gas temperature raising catalyst with respect to the flow of the exhaust gas.   The method according to claim 9, wherein the exhaust gas purification catalyst is at least one selected from the group consisting of a diesel particulate filter, an oxidation catalyst, and a NOx storage catalyst.   The method according to any one of claims 1 to 10, wherein the three-dimensional structure of the exhaust gas purifying catalyst is a honeycomb and / or a plug honeycomb or a pellet.

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