JP2009133247A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control system dispensing with a process for removing sulfur component adhering on a lean NOx catalyst and capable of efficiently purifying exhaust gas with a small volume. <P>SOLUTION: SOx trap material for removing the sulfur component is employed in this exhaust emission control system, and a SOx oxidation function is given to the SOx trap material. The exhaust emission control system is provided with a three-way catalyst or an oxidation catalyst, the SOx trap material with SOx oxidation function, and the lean NOx catalyst. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification system that purifies exhaust gas from an internal combustion engine, and also relates to a sulfur-capturing material that removes sulfur-containing components from the exhaust gas.

For the purpose of improving the environment, reduction of carbon monoxide (CO), nitrogen oxides (NOx), and hydrocarbons (HC), which are harmful substances in exhaust gas from internal combustion engines, is required. Furthermore, reduction of carbon dioxide (CO ₂ ), which is a greenhouse gas, is required to prevent global warming.

  In order to improve fuel efficiency and reduce carbon dioxide, an engine (lean burn engine) that operates in a fuel atmosphere (hereinafter lean) leaner than the theoretical air-fuel ratio (about 14.6) has been developed. A lean NOx purification catalyst that reduces and purifies nitrogen oxides in an oxygen atmosphere has been developed.

  In a lean NOx purification catalyst, a trapping point of nitrogen oxide in the catalyst is poisoned by sulfur components such as fuel and sulfur oxide (SOx) derived from lubricating oil contained in exhaust gas (hereinafter referred to as S poison). Happens. In order to recover the performance of the S-poisoned lean NOx purification catalyst, it is necessary to eliminate the S-poisoning by a process of raising the temperature of the exhaust gas and desorbing the SOx from the catalyst (hereinafter referred to as a regeneration process).

  In order to prevent S poisoning, it has been studied to prevent S poisoning of the lean NOx purification catalyst by disposing a capturing material that captures a sulfur component upstream of the lean NOx purification catalyst. Japanese Patent Laying-Open No. 2004-84502 (Patent Document 1) describes an exhaust purification catalyst carrying an SOx trap catalyst.

JP 2004-84502 A

  In the regeneration of the lean NOx purification catalyst by the regeneration process, a heating means for raising the temperature of the exhaust gas is required. In addition, since fuel is excessively supplied for increasing the temperature, fuel efficiency is deteriorated. Furthermore, thermal deterioration of the lean NOx catalyst becomes a problem due to heat during regeneration.

  On the other hand, when the SOx trapping material is arranged, for the purpose, it is desirable to trap all the sulfur contained in the exhaust gas. However, since the trapping efficiency of sulfur is low and a large-capacity trapping material is required, it is difficult to arrange in practice.

  Therefore, an object of the present invention is to improve the performance of the SOx trapping material and reduce the volume of the SOx trapping material. As a result, in the exhaust gas purification system, the heating means for the regeneration process can be omitted, and the deterioration of the fuel consumption and the catalyst can be prevented.

The present invention that solves the above problems comprises a SOx trapping component and a SOx oxidizing component, wherein the SOx trapping component is a composite oxide containing an alkali metal or alkaline earth metal element, and the SOx oxidizing component is at least one of Fe, Mn, and Ce. It is in the SOx trapping material using this. The feature of the present invention is that the SOx trapping material has an SOx oxidation function for oxidizing SO ₂ to SO ₃ . In addition, in order to impart this oxidation function, it is characterized by using non-noble metals such as Fe, Mn, and Ce instead of a general noble metal as an oxidation catalyst. The SOx trapping material can trap SOx as sulfate. When noble metal is present in the SOx trapping material, the noble metal has both functions of reduction and oxidation. Therefore, when the exhaust gas atmosphere becomes a reducing atmosphere, SOx may be detached from the SOx trapping material. By using Fe, Mn, and Ce, an SOx trapping material that suppresses the inflow of SOx into the lean NOx catalyst can be provided.

  The SOx trapping component contained in the SOx trapping material is preferably a composite oxide containing an alkali metal or an alkaline earth metal. This is because the composite oxide containing an alkali metal or an alkaline earth metal has a high SOx trapping amount and stability. In particular, it is preferably a composite oxide composed of lithium and titanium.

  Another invention of the present application is an exhaust gas purification system using an SOx trap.

  As for the arrangement of the catalyst in the exhaust gas purification system, an oxidation catalyst or a three-way catalyst, a SOx trapping material, and a lean NOx catalyst are arranged in the exhaust pipe from the side near the engine. The SOx trapping material has an SOx trapping component made of a composite oxide containing an alkali metal or alkaline earth metal element as described above, and at least one oxidizing component of Fe, Mn, and Ce that are non-noble metals.

  In addition, it is also known that the exhaust gas purification system uses not only a lean NOx catalyst but also other NOx catalysts. The SOx trapping material is not limited to the prevention of sulfur poisoning of the lean NOx catalyst, but can be applied to any NOx purification catalyst whose NOx purification performance is reduced by SOx. Hereinafter, a lean NOx catalyst will be described as an example of a representative NOx purification catalyst, but the present invention is not limited thereto.

As the SOx trapping component of the SOx trapping material, those containing at least one of LiTiO ₂ , Li ₂ TiO ₃ , and Li ₄ TiO ₄ are suitable.

  By using a base material as the SOx trapping material and holding the SOx trapping component and the SOx oxidation component on the base material, handling and arrangement in the system become easy. The SOx trapping component and the SOx oxidizing component can be applied to the wall surface of the honeycomb-shaped substrate having through holes, or the SOx trapping component and SOx oxidizing component formed into a granular shape can be filled in the opening of the honeycomb substrate.

  Further, the present invention is suitable for an internal combustion engine having a diesel engine. A diesel particulate filter is often provided in an exhaust gas purification system of a diesel engine. A diesel particulate filter can be filled with the SOx trapping material of the present invention.

  In the present invention, as described above, the SOx trapping component and the SOx oxidizing component are substantially free of noble metals. “Substantial” means that a trace amount of inevitable precious metals that are contained in the raw material or mixed with precious metals in the manufacturing process are not taken into consideration.

  The SOx trapping material of the present invention has high sulfur trapping performance. In the exhaust gas purification system of the present invention, the NOx purification performance can be maintained for a long time.

  The present invention will be described in further detail. As described above, the SOx trapping material of the present invention has the SOx trapping component and the SOx oxidizing component as main components.

As the SOx trapping component of the SOx trapping material, alkali metal or alkaline earth metal elements are known. These SOx trapping components are usually used by being supported on a carrier such as alumina or silica. In the present invention, the SOx trapping component of the SOx trapping material is a complex oxide containing an alkali metal or alkaline earth metal element. Among them, in the LiTi composite oxide, the number of moles of titanium can be 1 to 4 with respect to the number of moles of titanium. Examples of the composite oxide of lithium and titanium include LiTiO ₂ , Li ₂ TiO ₃ , and Li ₄ TiO ₄ . Therefore, the composition of Li / Ti has a composition of 1 to 4, and in particular, the higher the proportion of Li, the greater the amount of sulfur trapped per unit weight, so the composite oxidation with a Li / Ti ratio of 2 or more. It is preferable that a thing is included.

  The SOx trapping component functions in any use form such as application to a substrate or filling into a container or the like. Even if it is used by mixing with a carrier such as alumina or silica, it has the effect of increasing the SOx trapping ability. As the SOx trapping material of the present invention, it is preferable to use a honeycomb-structured carrier that is used in general exhaust gas purification catalysts for automobiles. In the honeycomb carrier having the through holes, the exhaust gas flowing into the cell flows out in contact with the SOx trapping component layer containing the SOx oxidizing component applied to the wall. Moreover, it is also preferable to use with the diesel particulate filter (DPF) used for the soot removal of a diesel engine. The DPF is an exhaust gas purification honeycomb carrier in which the cells on the inflow surface and the outflow surface are alternately sealed so that the gas flowing in from one side passes through the cell wall and flows out from the adjacent cell to the other surface. Since it has many cells and each cell has an open hole on the inflow side / outflow side, either side is filled with SOx trapping material. As a result, the sulfur component in the exhaust gas can be removed at a high ratio, and the volume of the SOx trapping material can be reduced.

It is possible to increase the amount of sulfur trapped by the SOx trapping material by sufficiently oxidizing the sulfur component to SO ₃ . Therefore, in the purification system of the present invention, in addition to the oxidation catalyst installed in the exhaust flow path, the SOx trapping material is given a SOx oxidation function, thereby promoting the oxidation of SOx and increasing the SOx trapping amount. it can. One of Fe, Mn, and Ce is used as the SOx oxidation component. Further, the oxidation catalyst is effective for removing components such as carbon monoxide and hydrocarbons contained in the exhaust gas. A three-way catalyst may be used as the oxidation catalyst. In the case where the oxidation catalyst contains a noble metal, it is preferable to provide it physically separated from the SOx trapping material for the reasons described above to prevent reduction of the trapped sulfate.

  Further, the SOx trapping material of the present invention is characterized in that it contains substantially no precious metal. When the exhaust gas is in an oxidizing atmosphere under lean conditions, the sulfate captured on the SOx capturing material is difficult to be decomposed. However, when the exhaust gas is in a reducing atmosphere under rich conditions, the sulfate on the SOx trapping material is likely to be reduced. Since the noble metal has both oxidation and reduction functions, when the noble metal is included on the SOx trapping material, the sulfate may be reduced and released as a gas under reducing conditions.

  In particular, in an exhaust gas purification system that uses a lean NOx catalyst, NOx adsorbed on the lean NOx catalyst is reduced and purified, so that the reducing atmosphere is adjusted at regular intervals. Accordingly, in a system in which the SOx trapping material is exposed to a reducing atmosphere, the noble metal contained in the SOx trapping material can be eliminated to prevent the trapped sulfur component from being released and the SOx flow into the lean NOx catalyst.

  According to the SOx trapping material of the present invention, when the exhaust gas discharged from the internal combustion engine is only in the lean condition or when lean / rich control is performed, SOx can be efficiently captured and the sulfur component can be removed from the exhaust gas. Further, when the lean NOx catalyst is arranged downstream of the SOx trapping material, the NOx purification catalyst can be prevented from being poisoned, and the NOx purification performance can be maintained for a long time.

  In addition, an exhaust gas purification system for an internal combustion engine that solves the above problem captures a sulfur component including an oxidation catalyst and a SOx oxidation component of the non-noble metal of the present invention from an upstream side in an exhaust gas passage on the downstream side of the internal combustion engine. It has a SOx trap and a lean NOx catalyst that reduces and purifies nitrogen oxides in the exhaust gas from which sulfur components have been removed to nitrogen gas. According to the said structure, the harmful component in waste gas can be removed efficiently. Further, another oxidation catalyst or a three-way catalyst may be arranged upstream of the SOx trap. By improving the oxidation rate of SOx, there is an advantage that the SOx trapping rate is improved and S poisoning of the lean NOx catalyst can be prevented for a longer period of time.

  Further, the internal combustion engine provided with the above system has a significantly reduced or unnecessary frequency of S regeneration, so that it is excellent in fuel efficiency and environmental performance.

  The details of the present invention will be described.

(About SOx trapping component)
As the SOx trapping component of the SOx trapping material, alkali metal or alkaline earth metal elements are known. The SOx trapping component is usually used by being supported on a carrier such as alumina or silica. In order to realize a high SOx trapping amount, a carrier itself having a SOx trapping capability, that is, an alkali metal or alkaline earth metal compound is suitable. Among these, the action of capturing sulfur of the composite oxide of lithium and titanium, which has a particularly high SOx capturing ability, will be described. The LiTi composite oxide reacts with SOx to become a sulfate, thereby trapping SOx in the catalyst. Furthermore, the amount of SOx trapped can be further increased by supporting an alkali metal or alkaline earth metal having a SOx trapping action on the LiTi composite oxide.

  The capturing material of the present invention is substantially free of noble metals. Further, when a noble metal is used as the oxidation catalyst, it is preferable to avoid providing the capturing material in contact with a component containing the noble metal.

(About SOx oxidation component)
Fe, Mn, and Ce are known as non-noble metal elements having an oxidation function. Since these components are fired in air, they are supported as oxides. A desirable addition amount is 0.05 mol / L to 1 mol / L as an element amount per honeycomb volume. If it is less than 0.05 mol / L, the oxidation function is not sufficient, and if it exceeds 1 mol / L, the exposure amount of the SOx trapping material may be reduced. By containing these SOx oxidation components in the SOx trapping material, the SOx trapping material itself has SOx oxidation capability, so that the oxidation of SOx can be promoted and the SOx trapping rate in the SOx trapping material can be increased. As a result, the effect of preventing the SOx poisoning of the lean NOx catalyst can be maintained for a long time. Further, when the amount of S to be captured is the same amount, the volume of the SOx trapping material necessary for SOx trapping can be reduced. When these components are used as oxidizing components, the release of SOx is suppressed even under rich conditions.

(How to use SOx trapping material)
An SOx trapping material can be applied to the honeycomb. The honeycomb material used may be cordierite, silicon carbide, or metal. When filling the honeycomb with the SOx trapping material, one side of the cell is partially plugged, and the SOx trapping material is filled into the plugged portion.

  In general, a honeycomb used as a DPF has the cell ends of the honeycomb alternately sealed, and the inflowing exhaust gas always flows out through the honeycomb wall. It is particularly preferable to fill this cell with a SOx trap. The SOx trapping material can be filled on either or both of the outflow surface side and the inflow surface side of the DPF.

  FIG. 1 is a schematic cross-sectional view when a SOx trapping material is filled in a cell having an open hole on the outflow side of the DPF. The SOx trapping material is formed into a granular shape. After the exhaust gas flows into a cell having an open hole on the inflow side and passes through the wall of the DPF to remove the soot in the exhaust gas, it flows to the cell having an open hole on the adjacent outflow side, and the SOx trapping material The gas from which the sulfur content has been removed through the particles flows out from the open holes.

  Similarly, FIG. 2 is a schematic cross-sectional view in the case where a cell having an open hole on the inflow side of the DPF is filled with a SOx trapping material formed into a granular shape. The exhaust gas passes through the SOx trap, the DPF wall, and the unfilled DPF cell in this order. The exhaust gas flows into the cell filled with the SOx trapping material particles, passes through the SOx trapping material particles, and then flows through the DPF wall to the adjacent cell having an open hole on the outflow side.

  In addition, as shown in FIG. 1, it is desirable to fill the SOx trapping material on the exhaust gas outflow surface side. This is because unburned carbides (diesel particulates, hereinafter referred to as PM) in the exhaust gas are filtered by DPF, so that PM does not block between SOx trapping particles and increase pressure loss.

  The method for producing the SOx trapping material integrated with the DPF is as follows. The raw material powders are mixed and fired to produce SOx trapping component powders. After granulating the powder, the SOx oxidizing component is impregnated to produce SOx trapping material particles. A cell is filled with particles of SOx trapping material from one side of the DPF. After filling, it is impregnated with a binder and heated to solidify. When filling both sides of the DPF, the cells are filled with the SOx trapping material particles from the side opposite to the side already filled with the SOx trapping material particles, and after the filling, the binder is impregnated. Heat to solidify the binder.

(Purification system with SOx trapping material)
FIG. 3 is a diagram illustrating a configuration example of an exhaust gas purification system. The exhaust gas purification system of FIG. 3 purifies exhaust gas emitted from the diesel engine 3d. In the exhaust gas flow path of the engine, a three-way catalyst or an oxidation catalyst 3a is disposed from the upstream side, the SOx trapping material 3b of the present invention is disposed downstream, and a NOx purification catalyst 3c is disposed further downstream.

  The three-way catalyst is a catalyst that purifies exhaust gas from an internal combustion engine such as a gasoline engine that is operated at a stoichiometric air-fuel ratio. It is possible to simultaneously oxidize CO and HC and reduce NOx using exhaust gas components.

A lean NOx catalyst that is one of NOx purification catalysts will be described as an example. The lean NOx catalyst is a catalyst that purifies nitrogen oxides of an internal combustion engine that is operated by alternately controlling lean conditions with a large amount of oxygen and rich conditions with a large amount of fuel as compared with the stoichiometric air-fuel ratio. During lean, NOx in the exhaust gas is trapped on the catalyst, and the lean / rich control is performed to temporarily make the air / fuel ratio (hereinafter rich) the fuel is larger than the stoichiometric air-fuel ratio, and the adsorbed NOx is HC, CO in the rich gas. , H ₂ or other reducing gas. As a trapping method, there are a case where NOx is occluded in the catalyst (NOx occlusion catalyst) and a case where it is adsorbed on the catalyst surface (NOx adsorption catalyst). In addition, when using the said adsorption | suction and occlusion without distinguishing, it describes as capture | acquisition. Alternatively, a catalyst having a function of capturing NOx in exhaust gas at the time of lean is described as a lean NOx catalyst.

  The SOx trapping material provided with the SOx oxidation function is installed upstream of the lean NOx catalyst. SOx is oxidized and trapped on the SOx trapping material to prevent the SOx from flowing into the lean NOx catalyst. Since the SOx trapping material itself has SOx oxidation capability, the exhaust purification system as a whole exhibits high SOx oxidation performance together with the SOx oxidation capability of the oxidation catalyst, and a high SOx trapping rate can be realized. Further, by using a SOx trapping material having a high capability of trapping SOx, the activity of the lean NOx catalyst is not inhibited by sulfur, and the removal of sulfur from the lean NOx catalyst during the exhaust gas purification treatment (NOx catalyst Reproduction processing) is also unnecessary.

〔Example〕
Examples of the present invention are shown below. In this embodiment, an example in which a LiTi composite oxide is used as the SOx trapping component of the SOx trapping material with an SOx oxidation function will be described. In addition, this invention is not limited to a present Example.

  Example 1 shows an example in which an SOx trapping material is prepared using iron (Fe) as an SOx oxidation component. In this example, the wall surface of a honeycomb having openings at both ends is coated with a SOx trapping material. FIG. 4 shows a schematic cross-sectional view. As shown in the figure, the SOx trapping material layer 4b provided with the SOx oxidation function is coated on the honeycomb 4a.

The SOx trapping material of this example is made of Fe and LiTi composite oxide. The LiTi composite oxide was produced by the following procedure. 50.98 g of lithium acetate dihydrate was dissolved in 60 ml of water to prepare an aqueous lithium acetate solution, to which 33.29 g of TiO ₂ sol was added and mixed and dispersed. While stirring with a stirrer, 5 ml of 25% ammonia solution was added. Then, it dried at 150 degreeC for 6 hours, and baked at 600 degreeC for 1 hour, and obtained LiTi complex oxide powder.

The LiTi composite oxide was prepared by adjusting the amount of raw materials so that the ratio of Li and Ti was 4, but it was determined from X-ray diffraction of the prepared powder that LiTiO ₂ , Li ₂ TiO ₃ , Li ₄ It was a mixture of TiO ₄ . In addition to the crystalline structure, it contains an amorphous compound that is not detected by X-rays.

A slurry obtained by mixing 14.4 g of LiTi composite oxide powder, 7.2 g of silica sol (Nissan Chemical Co., Ltd., colloidal silica O), and 7.74 g of water for 15 minutes with a cracking machine was used as a cordierite honeycomb (400 cells, 7.2 mil, 17 × 17 × 75 mm) and applied. Excess slurry was blown with air, dried at 150 ° C. for 15 minutes, and fired at 600 ° C. for 1 hour. The application amount of the LiTi composite oxide powder is 300 g / L. Next, iron was supported on the LiTi composite oxide as an SO ₂ oxidation component by an impregnation method. An aqueous solution of iron nitrate was prepared according to the water absorption amount of the honeycomb coated with the LiTi composite oxide, and sucked up. The amount of Fe supported was 0.1 mol / L as Fe element. After drying at 150 ° C. for 1 hour, the honeycomb was fired at 600 ° C. for 1 hour, and a honeycomb coated with an SOx trapping material made of LiTi composite oxide impregnated and supported was obtained.

  Example 2 is an example in which the SOx trapping material is made granular and filled from the gas outflow side of the DPF. The component of the SOx trapping material is obtained by impregnating Fe into a LiTi composite oxide in the same manner as in Example 1. The LiTi composite oxide was produced in the same manner as in Example 1. First, 100 ml of a polyvinyl alcohol aqueous solution was added to 1 kg of LiTi composite oxide powder, and granulation was performed with a bread granulator to obtain LiTi composite oxide particles.

  Using a sieve, the LiTi composite oxide particles were classified to 0.5 to 1.0 mm (average particle size of 0.75 mm). 140 g of these particles were sucked and impregnated with Fe in a proportion of 0.1 mol. An iron nitrate aqueous solution was used for the impregnation. The impregnated particles were dried at 150 ° C. for 1 hour, and calcined at 600 ° C. for 1 hour to obtain LiTi composite oxide particles impregnated with Fe. The amount of Fe impregnation was the same as in Example 1 and was 0.1 mol / L.

The particles were filled from the gas outflow side into a DPF with a porosity of 42% (1 cell opening 1.17 × 1.17 mm, 300 cells, made of SiC, length 75 mm). A cell having an open hole on the gas inflow side was not filled with LiTi composite oxide particles. The filling amount is 140 g / L per DPF honeycomb volume. Thereafter, it poured the solids concentration (600 solids weight / solution weight ℃ after firing) 3% TiO ₂ sol and mixed aqueous solution of a solid concentration of 3% SiO ₂ sol from DPF outlet side as a binder. Drying was performed at 150 ° C. for 1 hour, and calcination was performed at 600 ° C. for 1 hour.

  In this way, an SOx trapping material made of a LiTi composite oxide impregnated with Fe was produced and filled in a DPF.

  Example 3 shows an example in which the Fe of Example 1 is changed to Mn to create a SOx trap. In the same manner as in Example 1, the honeycomb was coated with LiTi composite oxide, and an aqueous manganese nitrate solution was sucked and impregnated into the honeycomb. After drying at 150 ° C. for 1 hour and firing at 600 ° C. for 1 hour, a honeycomb coated with a SOx trapping material in which Mn was impregnated into a LiTi composite oxide was obtained. The amount of Mn supported was 0.1 mol / L as Mn element.

  Example 4 shows an example in which the Fe of Example 1 is changed to Ce to create a SOx trap. In the same manner as in Example 1, the honeycomb was coated with LiTi composite oxide, and the honeycomb was sucked and impregnated with an aqueous cerium nitrate solution. After drying at 150 ° C. for 1 hour and firing at 600 ° C. for 1 hour, a honeycomb coated with a SOx trapping material in which Mn was impregnated with LiTi composite oxide was obtained. The supported amount of Ce was 0.1 mol / L as Ce element.

(Comparative Example 1)
Comparative Example 1 shows an example in which an SOx trapping material that does not contain an SOx oxidation component is created. As in Example 1, the honeycomb was coated with LiTi composite oxide. The coating amount of LiTi oxide is 300 g / L. The SOx oxidation component was not carried, and the SOx trapping material of Comparative Example 1 was used.

(Comparative Example 2)
In Comparative Example 2, as in Comparative Example 1, an example is shown in which a SOx trapping material that does not contain an SOx oxidizing component is prepared and used in a form in which the same SOx trapping material as in Example 2 is filled in the form of particles. As in Example 2, the DPF was filled with LiTi composite oxide particles as an SOx trap. The filling amount is 140 g / L per DPF honeycomb volume. The SOx oxidation component was not supported.

(Example of sulfur component capture test)
A SOx trapping test was performed in which the SOx trapping material obtained in Examples 1 to 4 and Comparative Examples 1 and 2 was subjected to SOx trapping after measuring the amount of SOx trapped after flowing sulfur-containing gas into the honeycomb. It was. Table 1 shows the model gas composition containing SO ₂ used in the SOx trapping test.

The performance tests of the examples and comparative examples were performed according to the test outline of FIG. An exhaust gas purification system of a diesel engine was simulated, and the reaction tube 5a was filled with the oxidation catalyst 5b and the SOx trapping material 5c from upstream. The model gas 5d shown in Table 1 was circulated, and water was dropped with a water pump 5e and supplied with water vapor. The sample size is 17 × 17 × 75 mm (volume 21.7 cm ³ ) for both the oxidation catalyst and the SOx trapping material. It is distributed for 8 hours at SV47000h ⁻¹ , and the amount of supplied S is 1.13 g. The catalyst inlet temperature was adjusted to 300 ° C. in the electric furnace 5f. The SOx trapping amount was measured by using a S analyzer to measure the amount of S after pulverizing the SOx trapping material after the sulfur gas was absorbed into the SOx trapping material by the model gas containing SO ₂ . The SOx trapping performance of the SOx trapping material was expressed by the SOx trapping rate (Formula 1). The SOx capture rate is desirably 100%.

    SOx trapping rate = SOx trapping amount / SOx supply amount × 100 (Equation 1)

  The results of the SOx capture test are shown in Table 2.

  Examples 1, 3, and 4 and Comparative Example 1 are examples in which a honeycomb is coated and a SOx trapping material is used. In contrast to the SOx trapping rate of 54% in Comparative Example 1, Examples 1, 3, and 4 using the SOx oxidation component were 61, 63, and 62%, respectively, improving 6 to 8 points. Comparative Example 2 and Example 2 are examples in which the DPF is filled with the SOx trapping material. In contrast to the SOx trapping rate of 56% in Comparative Example 2, it was 63% in Example 2, an improvement of 7 points. In either case, the influence of the SOx oxidation component on the SOx trapping rate is observed. Further, in the case of Fe, Mn, and Ce, the effect of Mn was the highest than those of Examples 1, 3, and 4.

  Thus, the SOx trapping rate was increased by using the SOx trapping material imparted with the SOx oxidation function of the present invention. Next, this SOx trapping rate improvement effect was compared as a catalyst volume necessary for the exhaust gas purification system. The amount of sulfur emitted from an internal combustion engine, such as an automobile engine, is estimated from the concentration of sulfur components in the fuel, the fuel consumption of the vehicle, and the travel distance during which the trapping material is used. For example, in the case of a diesel passenger car, the specific gravity of the fuel (light oil) is 850 g / L, the sulfur concentration in the fuel is 15 ppm, the fuel consumption is 16 km, and the mileage until the vehicle is disposed (or until the trapping material is replaced) is 190,000. If km, the amount of sulfur emission is about 150 g.

  The volume of the SOx trapping catalyst necessary for trapping the sulfur content with a sulfur emission of 150 g was calculated from the SOx trapping rate. When the SOx trapping material per honeycomb volume described in the examples and comparative examples is coated (or filled), the volume of the SOx trapping material necessary to capture 150 g of the estimated sulfur emission amount during vehicle running is the case of the honeycomb coat. Comparative Example 1 was suppressed to 4.6 to 4.8 L in Examples 1, 3 and 4 as compared to 5.3 L. Similarly, when the DPF was filled, the comparative example 2 was 5.1 L while the example 2 was 4.6 L. The volume can be reduced by about 10% in any form of the SOx trapping material filled in the honeycomb coat or DPF.

  The SOx trapping material traps SOx as sulfate. When the exhaust gas is in a lean condition (oxidizing atmosphere), the sulfate trapped on the SOx trapping material is difficult to be decomposed. However, when the exhaust gas is rich (reducing atmosphere), the sulfate on the SOx trapping material is likely to be reduced and released. Since noble metals such as Pt have a function of promoting both oxidation and reduction, when the SOx trapping material contains a noble metal, the sulfate may be reduced and released as a gas under reducing conditions. Since the SOx trapping material of the present invention does not contain a noble metal, the release of SOx due to the reduction of sulfate under rich conditions can be suppressed as compared with the case of containing a noble metal. As a result, the SOx poisoning rate of the lean NOx catalyst can be greatly suppressed by increasing the SOx trapping rate under lean conditions and by suppressing the reduction of sulfate from containing no precious metals under rich conditions. In addition, the NOx purification performance of the lean NOx catalyst can be maintained for a long time.

  In particular, it can be used for purification of exhaust gas from internal combustion engines including diesel engines.

The cross-sectional schematic diagram of the SOx trapping material filled with SOx trapping material particles from the exhaust gas outflow side. The cross-sectional schematic diagram of the SOx trapping material filled with SOx trapping material particles from the exhaust gas inflow side. System diagram of diesel engine exhaust gas treatment (1). The cross-sectional schematic diagram of the honeycomb which apply | coated SOx trapping material. Example of sulfur component capture test.

Explanation of symbols

1a SOx trapping material particle 1b Seal 1c DPF wall 1d Exhaust gas flow 3a Oxidation catalyst or three-way catalyst 3b, 5c SOx trapping material 3c NOx purification catalyst 3d Engine 4a Honeycomb 4b SOx trapping material layer 5a Reaction tube 5b Oxidation catalyst 5d SO Model gas including ₂ 5e Water pump 5f Electric furnace

Claims (12)

An exhaust gas purification system that is installed in an exhaust passage of an internal combustion engine and purifies at least nitrogen oxides and sulfur oxides in exhaust gas, and is disposed downstream of an SOx trapping material that traps sulfur components and an SOx trapping material And a NOx purification catalyst for purifying nitrogen oxides,
The SOx trapping material has a SOx trapping component and a SOx oxidizing component,
The SOx trapping component has a complex oxide containing an alkali metal or alkaline earth metal element,
The exhaust gas purification system, wherein the SOx oxidation component contains at least one of Fe, Mn, and Ce.   2. The exhaust gas purification system according to claim 1, wherein at least one of an oxidation catalyst and a three-way catalyst is disposed upstream of the SOx trap. 3. The exhaust gas purification system according to claim 1, wherein the SOx trapping component contains at least one of LiTiO ₂ , Li ₂ TiO ₃ , and Li ₄ TiO ₄ . An exhaust gas purification system according to any one of claims 1 to 3,
The exhaust gas purification system, wherein the SOx trapping material is applied to a honeycomb-shaped substrate wall surface having a through hole. An exhaust gas purification system according to any one of claims 1 to 3,
The exhaust gas purification system, wherein the SOx trapping material has a particle shape, and the particulate SOx trapping material is filled in an opening of a honeycomb-shaped base material having a through hole. An exhaust gas purification system according to any one of claims 1 to 3,
The exhaust gas purification system has a diesel particulate filter, and the SOx trapping material is filled in the diesel particulate filter. An exhaust gas purification system according to any one of claims 1 to 5,
The exhaust gas purification system, wherein the SOx trapping material contains substantially no precious metal. An SOx trapping material that is installed in an exhaust passage of an internal combustion engine and traps sulfur oxide in exhaust gas,
The SOx trapping material has a SOx trapping component and a SOx oxidizing component,
The SOx trapping component has a complex oxide containing an alkali metal or alkaline earth metal element,
The SOx trapping material, wherein the SOx oxidation component contains at least one of Fe, Mn, and Ce.   9. The SOx trapping material according to claim 8, wherein the SOx trapping component includes a composite oxide composed of lithium and titanium, and a molar ratio of lithium is 1 to 4 with respect to titanium of the composite oxide. A SOx trapping material characterized by being. The SOx trapping material according to claim 9, wherein
The SOx trapping material is characterized in that an alkali metal or alkaline earth metal element is supported on a composite oxide composed of lithium and titanium.   11. The SOx trapping material according to any one of claims 8 to 10, wherein the SOx trapping material does not substantially contain a noble metal.   12. The SOx trapping material according to any one of claims 8 to 11, wherein the SOx trapping component and the SOx oxidizing component are supported on a carrier.

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