JP2004143940A - Exhaust emission control device and exhaust emission control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent condensation water form flowing in an NOx storage-reduction type catalyst as liquid water when starting an engine. <P>SOLUTION: A water absorbing member 3 is arranged on the upstream side of the NOx storage-reduction type catalyst 2. The condensation water in a pipe first flows to the water absorbing member 3, and is absorbed in the water absorbing member 3 at starting time. After starting, the condensation water absorbed in the water absorbing member 3 is evaporated by heat of exhaust gas, and flows in the NOx storage-reduction type catalyst 2 as steam. <P>COPYRIGHT: (C)2004,JPO

Description

【００３８】
表１より、実施例１及び比較例１ではほぼ同等のＮＯ_ｘ　浄化率を示しているが、実施例２では実施例１及び比較例１より高いＮＯ_ｘ　浄化率が発現されている。これは、吸水部材３にＲｈ／ＺｒＯ_２粉末を担持したものをＮＯ_ｘ　吸蔵還元型触媒２の上流側に配置した効果であることが明らかであり、水蒸気改質反応によって生成した水素によってＮＯ_ｘ　の還元活性が向上したと考えられる。
【００３９】
【発明の効果】
すなわち本発明の排ガス浄化装置及び排ガス浄化方法によれば、始動時に結露水がＮＯ_ｘ　吸蔵還元型触媒に流入するのが吸水部材によって未然に防止されているため、ＮＯ_ｘ　吸蔵材の移動あるいは流出を防止することができＮＯ_ｘ　吸蔵能の低下を防止することができる。
【００４０】
また水蒸気改質触媒をさらに配置すれば、吸水部材に吸水された水を水素に転化できるので、ＮＯ_ｘ　浄化能がさらに向上し、ＮＯ_ｘ　吸蔵材の硫黄被毒からの回復を促進することができる。
【図面の簡単な説明】
【図１】本発明の一実施例の排ガス浄化装置の構成を示す概略斜視図である。
【図２】実施例及び比較例の排ガス浄化装置の試験回数とＮＯ_ｘ　吸蔵量との関係を示すグラフである。
【図３】自動車の排気通路における堆積物の分析結果を示すグラフである。
【符号の説明】
１：触媒コンバータ　　２：ＮＯ_ｘ　吸蔵還元型触媒　　３：吸水部材[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purifying apparatus used for purification of various exhaust gases, more particularly to an exhaust gas purifying apparatus using the NO _x storage-and-reduction type catalyst.
[0002]
[Prior art]
In recent years, a lean burn engine that burns in an oxygen-excess atmosphere has been used for the purpose of reducing carbon dioxide (CO ₂ ). The lean burn engine is normally burned in oxygen excess lean conditions, and is driven by a system that reduces and purifies NO _x exhaust gas as a reducing atmosphere by a stoichiometric-rich condition of intermittent fuel excess. And as the best catalysts for this system, occludes NO _x in lean atmosphere, stoichiometric ~ _the NO _x storage-reduction type exhaust purifying catalyst is developing with _the NO _x storage material that releases occluded NO _x in a rich atmosphere Have been.
[0003]
Using this NO _x storage-and-reduction type catalyst, by controlling so that the stoichiometric-rich side in a pulsed manner the air-fuel ratio from the lean side, NO _x is occluded in _the NO _x storage material in the lean side, it is stoichiometric or to be released in the rich side are purified by reacting with reducing components such as HC and CO, can be efficiently purify NO _x even exhaust gas from a lean burn engine.
[0004]
The NO _x storage-and-reduction type catalyst is a porous carrier carrying the noble metal and _the NO _x storage material to the structure, such as alumina, for example, JP-A-05-317652, alkaline earth metals such as Ba metal and Pt NO _x storage-and-reduction type catalyst supported on a porous support such as alumina have been proposed. Also JP-A-06-031139, NO _x storage reduction catalysts of the alkali metal and Pt, such as carrying on a porous support such as alumina K has been proposed. More Hei 05-168860 discloses, NO _x storage-reduction catalyst carrying a rare earth element and Pt, such as La on a porous support such as alumina have been proposed.
[0005]
[Patent Document 1] Japanese Patent Application Laid-Open No. 05-317652 [Patent Document 2] Japanese Patent Application Laid-Open No. 06-031139 [Patent Document 3] Japanese Patent Application Laid-Open No. 05-168860
[Problems to be solved by the invention]
However, if the exhaust gas passage is allowed to cool after the engine is stopped, dew condensation occurs in the piping of the exhaust gas passage. Since exhaust gas remains in the pipe, a large amount of dew water is generated when a large amount of water vapor contained in the exhaust gas condenses. The condensed water is accumulated in the piping, flowing at once _the NO _x storage reduction catalyst as a liquid water at the next engine start. _The NO _x storage material that is supported on _the NO _x storage-reduction catalyst at this time, in order to have the property that easily dissolved in liquid water, and moves or flows out by flowed water, _the NO _x storage ability is decreased It is newly found that the problem occurs.
[0007]
For example equipped with NO _x storage-and-reduction type catalyst supporting potassium (K) as _the NO _x storage material, the analysis of the powder deposited on the downstream side of the pipe 50,000 km traveling vehicle NO _x storage-and-reduction type catalyst, FIG. As shown in FIG. 3, K was detected at a high concentration. This confirms the fact that K is spilled by the condensed water.
[0008]
Further, when the temperature of the exhaust gas flowing into the NO _x storage-and-reduction type catalyst is too high, the degradation due to grain growth of noble metal supported occurs also been possible to cool the exhaust gas by using a long pipe such as U-turn pipe are, but increases also the amount of dew condensation in the piping in such a case, at the time of start-up condensed water will flow to the large amount of NO _x storage-and-reduction type catalyst.
[0009]
The present invention has been made in view of such circumstances, and condensate water on the NO _x storage-and-reduction type catalyst during startup to prevent from flowing, the positively used to purifying performance condensed water It is intended to further improve.
[0010]
[Means for Solving the Problems]
Wherein the exhaust gas purifying apparatus of the present invention for solving the above-mentioned problems, the NO _x storage-and-reduction type catalyst arranged in the exhaust gas line, and the water absorption member disposed on the exhaust gas upstream side of NO _x storage-and-reduction type catalyst, composed of It is in.
[0011]
It is preferable that the water absorbing members are arranged in the same outer cylinder.
[0012]
It is desirable that this water absorbing member also serves as a steam reforming catalyst for generating hydrogen from hydrocarbon or carbon monoxide and steam. Furthermore, it is particularly preferable to further arrange the steam reforming catalyst for generating hydrogen from a hydrocarbon or carbon monoxide and water vapor to the downstream side and the upstream side of the NO _x storage reduction catalysts of the water-absorbing member.
[0013]
The exhaust gas purifying method of the present invention is characterized in that the water absorbing member of the exhaust gas purifying apparatus according to claim 3 of the present invention absorbs water, and water vapor and hydrocarbon or carbon monoxide generated from the absorbed water. preparative to produce hydrogen in contact with the steam reforming catalyst is a generated hydrogen and the exhaust gas to purify the exhaust gas is brought into contact with the NO _x storage-and-reduction type catalyst.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
In the exhaust gas purifying apparatus of the present invention is a water-absorbing member is disposed on the upstream side of the NO _x storage reduction catalyst. Therefore condensed water in the piping is absorbed in the water absorbing member is first flowed into the water-absorbing member at the time of startup, condensed water is prevented from flowing into the NO _x storage-and-reduction type catalyst. And after start-up exhaust gas is flowing into the NO _x storage-and-reduction type catalyst from the water-absorbing member, the condensed water absorbed in the water absorbing member flows into _the NO _x storage-reduction catalyst becomes water vapor evaporated by the heat of exhaust gas. Therefore, the problem that the NO _x storage material moves or flows out does not occur, and a decrease in the NO _x storage capacity can be prevented. The water-absorbing member recovers the water-absorbing ability and absorbs the dew water in the pipe at the next start.
[0015]
The NO _x storage reduction catalyst is composed of a porous carrier, a noble metal supported on the porous carrier, and a NO _x storage material supported on the porous carrier. As the porous carrier, alumina, silica, silica-alumina, zirconia, titania, ceria and the like can be used. One of these may be used, or a plurality of types may be mixed or combined for use. Among them, it is preferable to use γ-alumina having high activity.
[0016]
Examples of the noble metal used in the NO _x storage reduction catalyst include Pt, Rh, Pd, and Ir. Among them, Pt having high activity is particularly preferable. The amount of the noble metal carried is preferably 0.1 to 10 g per liter of the porous carrier. If the amount is less than this, the purification activity is insufficient, and if the amount is more than this, the effect is saturated and the cost becomes high.
[0017]
The _the NO _x storage material to be used in the NO _x storage-and-reduction type catalyst, it is possible to use at least one selected from alkali metals, alkaline earth metals and rare earth elements. Examples of the alkali metal include lithium, sodium, potassium, and cesium. Examples of the alkaline earth metal include barium, beryllium, magnesium, calcium, strontium and the like. Examples of the rare earth element include scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, dysprosium, and ytterbium. It is desirable to carry both alkali metals and alkaline earth metals.
[0018]
Loading amount of _the NO _x storage material in _the NO _x storage-reduction catalyst, it is desirable that the porous carrier per liter of 0.01 mols. _The NO _x purification performance for the supported amount is reduced less as _the NO _x storage amount than this range is decreased, the precious metal becomes more than this range is covered in _the NO _x storage material activity will be lowered.
[0019]
As the water-absorbing member, a member that can absorb and temporarily hold liquid water and has heat resistance and air permeability can be used. For example, zeolite is typically exemplified, and a pellet-shaped zeolite filled in a gas-permeable container, a monolith substrate having a honeycomb passage, a zeolite coated layer formed, or a zeolite molded product is used. Can be. The inlet side cell is formed from a heat-resistant ceramic such as cordierite and has a downstream end of the exhaust gas clogged, and an outlet cell adjacent to the inlet side cell and has an upstream end of the exhaust gas clogged. It is also possible to use a cell in which the cell partition partitioning the cell and the outflow side cell is porous having air permeability and water absorption (for example, a diesel particulate filter (DPF)). If the DPF is used, dew condensation water can be effectively absorbed, so that the total length can be shortened and the degree of freedom in mounting space is high.
[0020]
Although water-absorbing member is not particularly limited as long as it is upstream of the NO _x storage reduction catalysts, in order to prevent condensation in the piping between the water-absorbing member and the NO _x storage-and-reduction type catalyst, the position of the water-absorbing member is is desirable that the position close to the NO _x storage-and-reduction type catalyst. For example, as shown in Examples, for example, placing a water absorbing member to the cone portion of the catalytic converter, it is preferable to house the NO _x storage-and-reduction type catalyst and the water-absorbing member in the same outer tube. In this way, the space which has not been used in the past can be effectively used, and it is not necessary to newly provide a place for disposing the water absorbing member in the exhaust gas passage.
[0021]
It is preferable to arrange a steam reforming catalyst that generates hydrogen from hydrocarbon or carbon monoxide and steam on the upstream side of the NO _x storage reduction catalyst and on the downstream side of the water absorbing member.
[0022]
Exhaust gas oxygen excess lean atmosphere, contains SO _x, such as SO _2. For that reason such an exhaust gas touches the NO _x storage-and-reduction type catalyst, _the NO _x storage material and the SO _x reacts stable sulfates generated, _the NO _x storage ability of the NO _x storage material is lowered (sulfur Poisoning). However, if the steam reforming catalyst is disposed upstream of the NO _x storage reduction catalyst, the generated hydrogen can reduce and decompose the sulfate, and the NO _x storage capacity of the NO _x storage material can be easily restored. it can.
[0023]
As the steam reforming catalyst, a catalyst that generates hydrogen from hydrocarbon and steam or from carbon monoxide and steam by a steam reforming reaction or a water gas shift reaction can be used. A typical catalyst for carrying out the steam reforming reaction is a catalyst in which rhodium is supported on zirconia (Rh / ZrO ₂ ). As a catalyst for performing a water gas shift reaction, a Cu—Zn-based catalyst, a catalyst in which Cu is supported on γ-Al ₂ O ₃ , and the like are known.
[0024]
It is also preferable that the water absorbing member also serves as a steam reforming catalyst for generating hydrogen from hydrocarbon or carbon monoxide and steam. Even in this case, the water absorbed by the water-absorbing member is heated by the exhaust gas, becomes steam, flows into the steam reforming catalyst, and reacts with hydrocarbons or carbon monoxide in the exhaust gas to generate hydrogen, produced hydrogen flows into the NO _x storage-and-reduction type catalyst. Because a very high hydrogen reduction activity, reducing the NO _x on the NO _x storage-and-reduction type catalyst, NO _x purification performance is further improved.
[0025]
Examples of the water-absorbing member that also functions as a steam reforming catalyst include a monolith substrate having a honeycomb channel and a coat layer formed of a mixed powder of Rh / ZrO ₂ powder and zeolite powder formed thereon. With such a water-absorbing member, water absorption is exhibited by zeolite, and steam reforming reaction is exhibited by Rh / ZrO ₂ . Then, since the steam released from the zeolite is efficiently converted to hydrogen by the adjacent Rh / ZrO ₂ , the conversion rate of the steam to hydrogen is improved.
[0026]
【Example】
Hereinafter, the present invention will be specifically described with reference to examples.
[0027]
(Example 1)
FIG. 1 shows an automobile exhaust gas purifying apparatus of the present embodiment. The automobile exhaust gas purifying device, the NO _x storage-and-reduction type catalyst 2 arranged in the catalytic converter 1, _the NO _x storage-reduction catalyst 2 of the exhaust-gas upstream side water-absorbing member disposed in the cone portion 10 of the catalytic converter 1 with And 3.
[0028]
_The NO _x storage-reduction catalyst 2 comprises a honeycomb substrate made of cordierite, honeycomb substrate surface _{gamma-Al 2} O formed in 3 consists of a TiO ₂ and coating layer made of ZrO _2, the coating layer a noble metal of Pt and Rh, and the _the NO _x storage material consisting of Ba and K are carried in.
[0029]
The honeycomb substrate has a volume of 2.0 liters, and the coating layer is formed in an amount of 250 g per liter of the honeycomb substrate. The breakdown of the coat layer is 100 g of γ-Al ₂ O ₃ , 50 g of TiO ₂ , and 100 g of ZrO ₂ per liter of the honeycomb substrate. Further, 2.0 g of Pt is supported per liter of the honeycomb substrate, and 0.5 g of Rh is supported per liter of the honeycomb substrate. And 0.2 mol of Ba and 0.2 mol of K are supported per liter of the honeycomb substrate.
[0030]
The water absorbing member 3 includes a cordierite honeycomb substrate formed in a truncated cone shape, and a zeolite layer coated on the surface of the honeycomb substrate. The honeycomb substrate has a volume of 0.7 liter, and the zeolite layer is formed in an amount of 150 g per liter of the honeycomb substrate.
[0031]
(Comparative Example 1)
The NO _x storage-and-reduction type catalyst 2 on the upstream side, except that disposed water-absorbing member 3 on the downstream side of the same structure as in Example 1 to an exhaust gas purifying apparatus of Comparative Example 1.
[0032]
<Test / Evaluation>
The exhaust gas purifying devices of Example 1 and Comparative Example 1 were mounted on the exhaust passage of a 1.8 L lean burn engine, and 100 cc of water was stored in the exhaust passage on the upstream side of the catalytic converter 1, and the engines were started. Thereafter, in the same exhaust system (gas temperature 400 ° C. enters), it was measured _the NO _x storage amount in the lean. After the measurement, the engine was allowed to cool to room temperature. This test was repeated 30 times, and the obtained NO _x storage amounts are shown in FIG. Note that the space velocities are the same in Example 1 and Comparative Example 1.
[0033]
From FIG. 2, while the exhaust gas purifying device of Comparative Example 1 has decreased greatly _the NO _x storage amount when overlapping number of tests, the exhaust gas purifying apparatus of Example 1 30 times after the test also the initial and most comparable It can be seen that the NO _x storage amount is maintained. In the exhaust gas purifying apparatus of Comparative Example 1, in order to potassium from _the NO _x storage-reduction catalyst 2 is moved in or out, _the NO _x storage amount when Cumulative experience count can be considered to have significantly reduced.
[0034]
However, in the exhaust gas purifying apparatus of the first embodiment, the NO _x storage amount almost equal to the initial amount is maintained even after the 30 tests, which is due to the effect of disposing the water absorbing member 3 on the upstream side of the NO _x storage reduction catalyst 2. there it is apparent is the effect due to the _the NO _x storage material condensed water is absorbed by the water absorbing member 3 is moved or outflow is prevented.
[0035]
(Example 2)
Example 1 Example 1 except that the coating layer of the water absorbing member 3 used in Example 1 was formed from a mixed powder of 50% by weight of zeolite and 50% by weight of a catalyst (Rh / ZrO ₂ ) powder supporting rhodium on zirconia. The configuration was the same as described above. The coating layer is formed in an amount of 200 g per liter of the honeycomb substrate, and the amount of Rh carried is 0.5 g per liter of the honeycomb substrate.
[0036]
<Test / Evaluation>
Each of the exhaust gas purifying apparatuses of Examples 1, 2 and Comparative Example 1 was mounted on an exhaust passage of a 1.8 L lean burn engine, 100 cc of water was stored in an exhaust passage immediately below the engine, and the engine was started. The NO _x purification rate when the operation was alternately repeated for 2 minutes / rich 1 second was measured. Table 1 shows the results.
[0037]
[Table 1]

[0038]
From Table 1, it shows almost the same of the NO _x purification rate in Example 1 and Comparative Example 1, high _the NO _x purification rate than the Example 2 Example 1 and Comparative Example 1 are expressed. This is apparently the effect of arranging the Rh / ZrO ₂ powder on the water absorbing member 3 on the upstream side of the NO _x storage-reduction catalyst 2, and NO _x is generated by the hydrogen generated by the steam reforming reaction. It is considered that the reduction activity of the compound was improved.
[0039]
【The invention's effect】
That is, according to the exhaust gas purifying apparatus and an exhaust gas purifying method of the present invention, since the condensed water at the time of starting to flow into the NO _x storage-and-reduction type catalyst is prevented by the water-absorbing member, the movement or the outflow of the NO _x storage material it is possible to prevent a reduction of possible _the NO _x storage ability can be prevented.
[0040]
Further, if further arranged steam reforming catalyst, because the water absorption water in the water-absorbing member can be converted to hydrogen, can be further improved _the NO _x purification performance, promotes recovery from sulfur poisoning of the NO _x storage material it can.
[Brief description of the drawings]
FIG. 1 is a schematic perspective view showing a configuration of an exhaust gas purifying apparatus according to an embodiment of the present invention.
2 is a graph showing the relationship between the number of tests and _the NO _x storage amount of the exhaust gas purifying device of the Examples and Comparative Examples.
FIG. 3 is a graph showing an analysis result of deposits in an exhaust passage of an automobile.
[Explanation of symbols]
1: Catalytic converter 2: NO _x storage reduction type catalyst 3: Water absorption member

Claims (5)

A NO _x storage-and-reduction type catalyst arranged in the exhaust gas line, an exhaust gas purifying device comprising the water-absorbing member disposed on the exhaust gas upstream side of the NO _x storage-and-reduction type catalyst, in that it consists of. The exhaust gas purifying apparatus according to claim 1, wherein the water absorbing members are arranged in the same outer cylinder. 3. The exhaust gas purifying apparatus according to claim 1, wherein the water absorbing member also serves as a steam reforming catalyst that generates hydrogen from hydrocarbon or carbon monoxide and steam. 4. Downstream and in the NO _x storage-and-reduction type claims further disposed upstream of the catalyst 1 or claim 2 of a steam reforming catalyst to produce hydrogen from a hydrocarbon or carbon monoxide and water vapor and the water absorbing member An exhaust gas purifying apparatus as described in the above. Water is absorbed by the water absorbing member of the exhaust gas purifying apparatus according to claim 3 or 4, and steam generated from the absorbed water and hydrocarbon or carbon monoxide are brought into contact with a steam reforming catalyst to generate hydrogen. , the exhaust gas purification method, characterized in that the generated hydrogen and the exhaust gas is brought into contact with the NO _x storage-and-reduction type catalyst for purifying exhaust gas.

Images