JP2004283738A - Exhaust gas purification method and exhaust gas purification device - Google Patents

Abstract

Disclosed is a time average in an oxygen excess in the exhaust gas, with sufficiently reduce and purify NO _x from a low temperature range, also inhibits discharge of NH _3.
A adsorbs NO _x to _the NO _x adsorption and reduction catalyst 3 for reducing the _{N 2} is reacted with NH ₃ adsorbed NO _x arranged in the exhaust gas line, at the upstream side, _{R =} NH 3 / NO _x Is alternately repeated between an exhaust gas atmosphere in which the molar ratio R defined by R <1 and an exhaust gas atmosphere in which R> 1.
In an exhaust gas atmosphere of R <1, NO _x is adsorbed and accumulated in the NO _x adsorption reduction catalyst 3, and in an exhaust gas atmosphere of R> 1, excess NH ₃ reacts with NO _x adsorbed on the NO _x adsorption reduction catalyst 3. and to reduce and remove, _the NO _x adsorption and reduction catalyst 3 recovers _the NO _x adsorbing capacity again.
[Selection diagram] Fig. 1

Description

【００６２】
表１より、本実施例の排ガス浄化装置によれば、ＮＯ_ｘ の排出量を９１％程度低減することができることが明らかであり、ＮＯ_ｘ の排出を大幅に抑制することができた。またＨＣ及びＣＯも十分に浄化でき、アンモニア臭も感知されなかった。
【００６３】
（実施例３）
図４に本実施例の排ガス浄化装置を示す。この装置は、ＮＯ_ｘ 吸着還元触媒３の下流側にＮＯ_ｘ センサ３０を配置したこと以外は実施例１と同様である。ＮＯ_ｘ センサ３０はＰｔとＷＯ_３ 系ｎ型半導体からなり、その検出信号は、ＮＨ_３ 添加装置２における圧縮空気導入装置２１の駆動を制御する制御装置７に入力されている。
【００６４】
以下、図５に示すフローチャートを参照しながら、この排ガス浄化装置の作用を説明する。
【００６５】
先ずステップ １０１では、圧縮空気導入装置２１の駆動が停止され、Ｒ≦１の排ガスがＮＯ_ｘ 吸着還元触媒３に導入される。すると排ガス中のＮＯ_ｘ はＮＯ_ｘ 吸着還元触媒３に吸着され、ＮＯ_ｘ 吸着還元触媒３にはＮＯ_ｘ が徐々に蓄積される。
【００６６】
次にステップ １０２では、ＮＯ_ｘ センサ３０の検出信号が制御装置７に入力され、ＮＯ_ｘ 吸着還元触媒３からの出ガス中のＮＯ_ｘ の有無が判別される。ここでＮＯ_ｘ が検出されなかった場合には、何もせず処理はステップ １０３に進む。しかしＮＯ_ｘ が検出された場合には、ＮＯ_ｘ 吸着還元触媒３のＮＯ_ｘ 吸着余力が少ないと判断されるため、処理はステップ １０３をジャンプしてステップ １０４へ進み、Ｒ＞１とされて多くのＮＨ_３ が添加される。
【００６７】
ステップ １０３では、タイマーによって圧縮空気導入装置２１の駆動が３０秒未満の範囲で行われる。そして３０秒経過後に、処理はステップ １０４に進む。
【００６８】
ステップ １０４では、圧縮空気導入装置２１が駆動され、排ガス中にＮＨ_３ が添加されて、Ｒ＞１の排ガスがＮＯ_ｘ 吸着還元触媒３に導入される。すると過剰のＮＨ_３ によってＮＯ_ｘ 吸着還元触媒３に吸着蓄積されているＮＯ_ｘ がＮ_２に転換され、同時にＮＨ_３ が消費されて消滅する。これによりＮＯ_ｘ 吸着還元触媒３のＮＯ_ｘ 吸着能が回復する。
【００６９】
そしてステップ １０５では、再びＮＯ_ｘ センサ３０の検出信号が制御装置７に入力され、ＮＯ_ｘ 吸着還元触媒３からの出ガス中のＮＯ_ｘ の有無が判別される。ここでＮＯ_ｘ が検出された場合には、ＮＨ_３ の添加量がまだ少なく、ＮＯ_ｘ 吸着還元触媒３のＮＯ_ｘ 吸着余力がまだ少ないことを意味するので、処理はステップ １０７へ進み、ＮＨ_３ が継続して添加される。一方ＮＯ_ｘ が検出されなかった場合には、処理はステップ １０６へ進み、経験則に基づいてＮＨ_３ の生成量が過剰であるか否かが判別される。ＮＨ_３ の生成量が過剰であった場合には、所定の補正処理が行われ、処理はステップ １０１に戻って圧縮空気導入装置２１の駆動が停止されＮＨ_３ の添加が停止される。またＮＨ_３ の生成量が適切であった場合には、何もせず処理はステップ １０７へ進む。
【００７０】
ステップ １０７では、タイマーによって圧縮空気導入装置２１の駆動停止が３０秒未満の範囲で継続され、３０秒経過後に処理はステップ １０１に戻ってＮＨ_３ の添加が停止される。
【００７１】
したがって本実施例の排ガス浄化装置では、圧縮空気導入装置２１を必要十分な時間で駆動することができ、無駄な駆動を不要とすることができる。またＮＯ_ｘ 及びＮＨ_３ の排出をさらに抑制することができる。
【００７２】
【発明の効果】
すなわち本発明の排ガス浄化方法及び排ガス浄化装置によれば、ＮＯ_ｘ 及びＮＨ_３ の排出を大きく抑制することができる。また各成分が高濃度で反応するため、通常の排ガス中での反応に比べて反応効率が約１０００倍に向上し、ひいては触媒の低容量化も可能となる。
【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模式的に示すブロック図である。
【図２】実施例１及び比較例１の排ガス浄化装置からの出ガス中のＮＯ_ｘ 濃度をブランクと共に示すグラフである。
【図３】本発明の第２の実施例の排ガス浄化装置の構成を模式的に示すブロック図である。
【図４】本発明の第３の実施例の排ガス浄化装置の構成を模式的に示すブロック図である。
【図５】本発明の第３の実施例の排ガス浄化装置の制御内容を示すフローチャートである。
【符号の説明】
１：エンジン ２：ＮＨ_３ 添加装置 ３：ＮＯ_ｘ 吸着還元触媒
４：エンジン ５：ＮＨ_３ 生成触媒[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purifying method and an exhaust gas purifying apparatus, and more particularly to a method for purifying NO in exhaust gas having an oxygen excess on a time average. _x To NH ₃ The present invention relates to an exhaust gas purifying method and an exhaust gas purifying apparatus for purifying by reducing in an exhaust gas.
[0002]
[Prior art]
NO emitted from power plants, various chemical factories or automobile engines _x Is considered to be the cause of the occurrence of photochemical smog and acid rain, and the development of effective removal means is desired. These NO _x Exhaust gas containing oxygen often contains several volume% or more of oxygen. _x It is necessary to use a treatment method that can efficiently purify the wastewater.
[0003]
As such a processing method, for example, NO in which zeolite supports Cu _x There is a method using a selective reduction catalyst. But the current NO _x For selective reduction catalyst, practically enough NO _x Nothing satisfies purification performance and durability performance. Also NO _x Requires a large excess of HC, there is a risk that excess HC will be discharged.
[0004]
Also, the exhaust gas is converted to NH ₃ NH contacted with ₃ A denitration method is known. This NH ₃ With NH as a reducing agent ₃ In the denitration method, even if oxygen is present in the exhaust gas at 1% by volume or more, NH ₃ Is NO _x Reacts selectively with _x It is considered to be an advantageous method in terms of the purification rate and the use efficiency of the reducing agent.
[0005]
This NH ₃ NH used for denitration ₃ As the denitration catalyst, for example, V catalyst as described on page 248 of “Catalysis Course 7 (Basic Industrial Catalyst Reaction)” (published by Kodansha) ₂ O ₅ -TiO ₂ Examples thereof include catalysts and catalysts described in JP-A-53-030995.
[0006]
However, such NH ₃ In the denitration catalyst, high activity is obtained in a wide temperature range in purifying a gas having a small space velocity such as SV = 10000 / h, but sufficient activity cannot be obtained at a space velocity exceeding this. Therefore, there is a drawback in that if a sufficient activity is to be obtained, the required amount of catalyst increases, and the size of the catalyst device increases.
[0007]
Japanese Patent Application Laid-Open No. Hei 10-146528 discloses alumina (Al ₂ O ₃ ) NH having at least palladium (Pd) and zinc (Zn) supported on a carrier ₃ A denitration catalyst is disclosed. This NH ₃ According to the denitration catalyst, even in a high space velocity region exceeding SV = 10000 / h, high NO at a low temperature of 300 to 400 ° C. _x Purification activity is obtained. Therefore, even if the catalyst amount is small, sufficient NO _x Since purification activity is obtained and the size of the catalyst device can be reduced, it can be used as a catalyst for purifying exhaust gas of automobiles.
[0008]
However, NH ₃ When using a denitration catalyst, NO _x NH in an amount corresponding to the amount ₃ Need to be added, and the excess NH ₃ Has the disadvantage that it is discharged as it is. NO _x And NH ₃ Is represented by the following reaction formula.
[0009]
NO + NH ₃ + (1/4) O ₂ → N ₂ + (3/2) H ₂ O
Therefore NH ₃ NO added _x However, such control is difficult in the case of an automobile engine whose exhaust gas composition varies greatly depending on the driving conditions. NO in total _x : NH ₃ = 1: 1 but momentarily NO _x Or NH ₃ Will be discharged. Further NH ₃ Since the denitration catalyst contains a heavy metal such as vanadium, it is not preferable as an exhaust gas purifying catalyst for automobiles.
[0010]
In addition, as described in Japanese Patent Application Laid-Open No. 05-317652, _x It is also conceivable to use a storage reduction catalyst. NO _x NO stored in the storage material _x To NH ₃ It is reduced with. However, NO consisting of alkali metal or alkaline earth metal _x Since the occluding material is supported separately from a noble metal such as Pt, the occluding portion and the reacting portion are separated from each other. _x Have to move. Therefore, its reactivity is low, especially in the low temperature range below 300 ° C. _x Is difficult to reduce.
[0011]
Further NO _x Since the storage material is basic, the same basic substance, NH, is used. ₃ NO that is difficult to access _x Low reactivity with SO in exhaust gas _x Is NO _x Reacts with storage material, NO _x There is also a problem that the storage capacity is lost.
[0012]
[Patent Document 1] JP-A-53-030995
[Patent Document 2] Japanese Patent Laid-Open No. 05-317652
[Patent Document 3] JP-A-10-146528
[Non-Patent Document 1] "Catalyst Course 7 (Basic Industrial Catalytic Reaction)" (Kodansha Publishing), p. 248
[0013]
[Problems to be solved by the invention]
The present invention has been made in view of such circumstances, and NO _x Is sufficiently reduced and purified from a low temperature range and NH ₃ The purpose is to suppress the emission of carbon dioxide.
[0014]
[Means for Solving the Problems]
The feature of the exhaust gas purifying method of the present invention that solves the above problems is that NO _x NO adsorbed _x To NH ₃ And react with N ₂ NO to reduce to _x An adsorption reduction catalyst is arranged in the exhaust gas flow path, and NO _x NH upstream of the adsorption reduction catalyst ₃ And NH ₃ At least one of the precursors is supplied and the NO _x And NH ₃ An exhaust gas purification method for purifying by reacting
NO _x In the gas entering the adsorption reduction catalyst, R = NH ₃ / NO _x An exhaust gas atmosphere in which the molar ratio R defined by R is R <1 and an exhaust gas atmosphere in which R> 1 are alternately repeated.
[0015]
Another feature of the exhaust gas purifying apparatus of the present invention is that the exhaust pipe of at least one control cylinder of the internal combustion engine having a plurality of cylinders has NH. ₃ Supply NH ₃ Supply means is arranged and NH ₃ In the exhaust gas passage where exhaust pipes of a plurality of cylinders are gathered on the downstream side of the supply means, _x NO adsorbed _x To NH ₃ And react with N ₂ NO to reduce to _x The point is that an adsorption reduction catalyst is arranged.
[0016]
Still another feature of the exhaust gas purifying method of the present invention is that, using the exhaust gas purifying apparatus of the present invention described above, the control cylinder is operated alternately in an air-deficient atmosphere and an air-excess atmosphere for a predetermined time, and other cylinders other than the control cylinder are used. Is to operate in an excess air atmosphere.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
NO _x And NH ₃ Reacts with a molar ratio of 1: 1. On the other hand, NO in automobile exhaust gas _x Since the concentration is about 500 ppm at most from about 10 ppm at idle, _x NH required for the reduction of ₃ The amounts are in the same range. As a result, NH ₃ To supply NH ₃ NO by denitration catalyst _x In the method of purifying NO, NO _x And NH ₃ At the same time at such low concentrations is extremely low. Therefore, even if a catalyst having excellent activity is used, the reaction efficiency is extremely low because the concentration of the reaction components is extremely low. In addition, since the probability of coexistence at the same time at a molar ratio of 1: 1 is low, unreacted NO _x Or NH ₃ Is discharged.
[0018]
Therefore, NO _x Or NH ₃ If one of them can be fixed by some means, the NO accumulated in the fixing means _x Or NH ₃ One of them becomes a high concentration at that site, so that the reaction efficiency is expected to be improved.
[0019]
Therefore, in the exhaust gas purification method of the present invention, NO _x NO adsorbed _x To NH ₃ And react with N ₂ NO to reduce to _x Using an adsorption reduction catalyst, R = NH ₃ / NO _x The exhaust gas atmosphere in which the molar ratio R defined by R is R <1 and the exhaust gas atmosphere in which R> 1 are alternately repeated. In the exhaust gas atmosphere of R <1, NO _x The amount is NH ₃ NH3 ₃ Remaining without reduction _x Is NO _x It is adsorbed and accumulated on the adsorption reduction catalyst. If the exhaust gas atmosphere is R> 1, NH ₃ Is NO _x Excess NH3 ₃ Is NO _x NO adsorbed on the adsorption reduction catalyst _x Reacts with N ₂ Converted to NO _x Is reduced and removed. NH ₃ Disappears. Therefore NO _x The adsorption reduction catalyst returns NO _x If the adsorption capacity is restored and then R <1, excess NO _x To adsorb.
[0020]
By such an action, the exhaust gas atmosphere in which R> 1 and the exhaust gas atmosphere in which R <1 are alternately repeated, so that NO _x Emissions can be suppressed, and NH ₃ Emissions can also be suppressed.
[0021]
Further, in an exhaust gas atmosphere of R <1, NO in the exhaust gas _x Is NO _x NO adsorbed and accumulated on the adsorption reduction catalyst _x NO on adsorption reduction catalyst _x Becomes high concentration. Therefore, NH supplied in an exhaust gas atmosphere of R> 1 ₃ And the molar ratio of 1: 1 is easy, so that unreacted NO _x Or NH ₃ Can be suppressed from being discharged.
[0022]
NO _x NO as an adsorption reduction catalyst _x NO adsorbed _x To NH ₃ And react with N ₂ A substance which reduces heat to heat is preferably used. As such a catalyst, a catalyst supporting a noble metal such as Rh or Pd as a catalyst component is preferable. _x And NH ₃ It is particularly desirable to include Rh which is effective in the reaction with Examples of the carrier supporting the noble metal include alumina, titania, and zirconia, and an oxide having a high specific surface area including ceria is particularly preferable. NO by interaction of precious metal and ceria _x Is likely to be adsorbed, and high activity is expressed.
[0023]
NO _x In the adsorption reduction catalyst, the oxide having a high specific surface area containing ceria is CeO. ₂ , CeO ₂ -ZrO ₂ A composite oxide is exemplified. It is desirable that the composition contains at least 50 mol% of ceria. The amount of the noble metal carried is preferably in the range of 0.05 to 10% by weight based on the metal oxide containing ceria. If the content is less than 0.05% by weight, it becomes difficult to exhibit the activity, and even if the content exceeds 10% by weight, the activity is saturated, the cost is increased, and the noble metal undergoes grain growth at high temperatures.
[0024]
R (NH) ₃ / NO _x ) Can be adjusted by adding NH ₃ , Urea, NH ₃ (NH) ₃ Precursor), or by adjusting the A / F to oxygen deficiency and using a catalyst in combination with NH3 in the exhaust gas. ₃ Can also be generated. NO _x And NH ₃ Is characterized in that it reacts at a molar ratio of 1: 1. ₃ The amount of NO flowing into the catalyst during one addition (generation) time _x Amount and NO _x NO adsorbed on the adsorption reduction catalyst _x It must be less than or equal to the sum of the quantities. If NH ₃ NO _x Exceeds the total amount of ₃ Is discharged.
[0025]
NH ₃ To control the quantity, the operating conditions of the engine and the NO _x If the relationship with the emission amount is obtained in advance and used as a map, the NO generated during actual operation _x Since the amount can be estimated, NH ₃ What is necessary is just to determine the addition amount (production amount). A particularly simple method is to use NH only when the exhaust gas atmosphere is R> 1. ₃ Is added (generated) in a pulsed manner. NO that can be removed with one pulse _x NO NO _x NO of adsorption reduction catalyst _x If the saturation value of the amount of adsorption is set as the upper limit, the time of one pulse can be adjusted so that the adsorbed NO _x Can be reduced and removed, and NH 3 ₃ Almost all is consumed in the reaction.
[0026]
However, even with this method, NO _x NO adsorbed on the adsorption reduction catalyst _x Estimated timing and NH ₃ Unreacted NO due to deviation from the addition (generation) time of _x Or NH ₃ Could be emitted. So NH ₃ NO (addition amount) _x Saturated NO of adsorption reduction catalyst _x It is particularly desirable to set it to 10 to 50% based on the amount of adsorption. In this case, NO _x NO of adsorption reduction catalyst _x When the amount of adsorption reaches 10 to 50% of the saturation value, NH ₃ Is added (generated), so that NO _x Adsorption reduction catalyst is always NO _x It becomes a state where the remaining power of adsorption is left, and NO _x Or NH ₃ Can be further suppressed.
[0027]
NH ₃ Can be determined from the above-described map by monitoring the operating condition of the engine. However, for higher accuracy, _x NO downstream of the adsorption reduction catalyst _x Arrange the sensor, NO _x NO in outgas of adsorption reduction catalyst _x Is detected when NH is detected. ₃ Is desirably added (produced). That is, NO _x NO during sensor outgassing _x Is detected, NO _x NO of adsorption reduction catalyst _x Since it means that the adsorption amount is approaching saturation, a predetermined amount of NH ₃ Is added (generated) to give NH ₃ NO without worrying about emission of NO _x Can be reduced and removed.
[0028]
NH in exhaust gas ₃ Is added with NH ₃ Gas addition method, ammonia water spray addition method, or decomposition of urea or hexamethylenetetramine to NH ₃ (NH) ₃ (Precursor) as it is or as a solution. In the case of the exhaust gas purification method of the present invention, NO _x NO adsorbed and accumulated on the adsorption reduction catalyst _x NH in an amount corresponding to the amount ₃ , A relatively high concentration solution can be used and control is easy.
[0029]
NH in the exhaust gas ₃ A / F is adjusted to oxygen deficiency and NH ₃ It can be carried out by using the produced catalyst in combination. That is, NO _x NH upstream of the adsorption reduction catalyst ₃ The production catalyst is arranged, and at least one cylinder of the multi-cylinder engine is operated for a predetermined time under a slightly excessive fuel condition with respect to air. Then NH ₃ CO, HC, H ₂ Products such as incomplete combustion and water vapor and NO _x Reacts with NH ₃ Is generated and the pulse is NO _x It is supplied to the adsorption reduction catalyst. And NO _x NO adsorbed and accumulated on the adsorption reduction catalyst _x Reacts with NO _x And reducing NH ₃ It is consumed and disappears.
[0030]
This NH ₃ As the generated catalyst, a known catalyst can be used, but a catalyst in which at least one of Pt and Pd is supported on a metal oxide carrier is preferable. Examples of the metal oxide carrier include alumina, titania, zirconia, and ceria. The amount of the noble metal supported is preferably in the range of 0.05 to 10% by weight based on the metal oxide carrier. If the content is less than 0.05% by weight, it becomes difficult to exhibit the activity, and even if the content exceeds 10% by weight, the activity is saturated, the cost is increased, and the noble metal undergoes grain growth at high temperatures.
[0031]
Such NH ₃ The generated catalyst has high efficiency and NO _x To NH ₃ Harmful components such as unburned HC or CO discharged at the time of oxygen excess, and NO _x Since it is disposed on the upstream side of the adsorption reduction catalyst, it is suitable in that it is exposed to relatively high temperatures but has excellent heat resistance. NH ₃ If a production catalyst is used, NH ₃ Has the advantage that a device for adding NO is not required, and the NO in the exhaust gas _x Amount and NH generated ₃ NO, regardless of driving conditions _x NH according to quantity ₃ There is also an effect that the amount of generation is automatically adjusted and troublesome control is not required.
[0032]
NH ₃ In the case of using the generated catalyst, it is necessary to perform control to adjust the A / F to a pulsed oxygen deficiency. However, when the A / F is adjusted to be short of oxygen, there is a problem that fuel efficiency deteriorates. We examine this problem below.
[0033]
Defining S = (the actual amount of air supplied to the engine / the amount of air required for complete combustion of fuel), the NO emitted by normal oxygen excess combustion where S is 1.5 or more _x The amount is NO where S is around 1.0 _x It is generally about 1/5 to 1/10 of the discharge amount. NO emitted even if S is less than 0.8 _x The amount drops. Therefore NH ₃ NH generated by generated catalyst ₃ Is preferably in the range of 0.8 to 1.0 in order to efficiently generate.
[0034]
If the time during which the oxygen deficiency condition in which S is in the range of 0.8 to 1.0 is set to 10 to 20% of the total operation time, the exhausted NO _x Is mostly NH ₃ And NO during excessive oxygen combustion _x NO adsorbed on the adsorption reduction catalyst _x Sufficient amount of NH to reduce and remove all of the amount ₃ Is generated. Accordingly, lean combustion with excess oxygen can be performed for 80 to 90% of the entire operation time, and combustion with excess oxygen occurs on a time average, so that fuel consumption hardly deteriorates. Note that NH ₃ NH generated by generated catalyst ₃ In order to generate more efficiently, it is preferable that S is closer to 1.0, and as S is closer to 1.0, deterioration of fuel efficiency can be further suppressed.
[0035]
As described above, S is usually set to 1.5 or more, and NO _x NO for adsorption reduction catalyst _x May be intermittently controlled to be 0.8 to 1.0 when accumulated, all the cylinders of the multi-cylinder engine may be so controlled. It is preferable to install a fuel supply device and an intake control valve that can be controlled independently for each cylinder.
[0036]
In the exhaust gas purifying apparatus of the present invention, the exhaust pipe of at least one control cylinder of the internal combustion engine having a plurality of cylinders has NH ₃ Supply NH ₃ Supply means is arranged and NH ₃ In the exhaust gas passage where exhaust pipes of a plurality of cylinders are gathered on the downstream side of the supply means, _x And NH ₃ NO that promotes the reaction with _x An adsorption reduction catalyst is provided.
[0037]
For example, NO _x NO for adsorption reduction catalyst _x Is controlled such that S becomes 1.5 or more for all cylinders of the multi-cylinder engine. Then the exhaust gas is first NH ₃ Through the production catalyst, in this case NH 3 ₃ No generation of NO _x Is NO _x NO flowing into the adsorption reduction catalyst _x It is adsorbed and accumulated on the adsorption reduction catalyst.
[0038]
At some point, S of at least one cylinder of the multi-cylinder engine is controlled to be 0.8 to 1.0, and the other cylinders are controlled so that S is 1.5 or more. In a control cylinder in which S is controlled to be 0.8 to 1.0, oxygen-deficient combustion occurs and NH ₃ NO by generated catalyst _x To NH ₃ Is generated. NH generated ₃ Is NO _x NO flowing into the adsorption reduction catalyst and accumulated in high concentration _x To N ₂ To remove. Depending on the number and / or time of the control cylinders for performing the oxygen-deficient combustion control, the generated NH ₃ The amount can be adjusted.
[0039]
According to the exhaust gas purifying apparatus of the present invention, the NO. _x Emissions are determined and the NO _x NH corresponding to the amount of emissions ₃ If the number of control cylinders and the time ratio required to generate the air current are calculated and controlled based on the obtained empirical rule, 95% or more of HC and CO can be obtained even in actual running. _x 80-90% can be purified. NO _x In order to further reduce the amount of emissions, appropriate feedback control is required.
[0040]
In this case, NO _x NO downstream of the adsorption reduction catalyst _x It is desirable to arrange sensors. NO _x Sensor is NO for the first time _x Is detected, NO _x NO of adsorption reduction catalyst _x Adsorption capacity is small, that is, NH ₃ It is determined that the generation amount is insufficient. NO _x Is not detected, appropriate control conditions or NH ₃ It is determined that the amount of generation is excessive. If the above rule of thumb is corrected based on these determinations, NO _x Emission can be further suppressed.
[0041]
Also NO _x Adsorption reduction catalyst and NO _x Placing an oxidation catalyst between the sensor and NO with an oxidation catalyst added _x It is also preferable to use a sensor. In this case, NO _x NH from adsorption reduction catalyst ₃ Is discharged, the oxidation catalyst causes NO _x To be converted to NH ₃ Can be prevented from being discharged. Also NO _x NO because it can be detected by a sensor _x What is necessary is just to control so that the detection value of a sensor may become minimum.
[0042]
【Example】
Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.
[0043]
(Example 1)
FIG. 1 schematically shows the exhaust gas purifying apparatus of the present embodiment. This exhaust gas purifying apparatus includes an NH 1 disposed in an exhaust system of the engine 1. ₃ Addition device 2 and NH ₃ NO arranged at a position of 0.8 m downstream of the addition device 2 _x And an adsorption reduction catalyst 3.
[0044]
The engine 1 is a 2.2-liter, 4-cylinder turbocharged diesel engine.
[0045]
NH ₃ The addition device 2 includes a tank 20 into which a 30% by weight aqueous solution of urea is charged, and a compressed air introduction device 21. The compressed air introduced from the compressed air introduction device 21 converts the urea water in the tank 20 into exhaust gas. Sprayable.
[0046]
NO _x The adsorption-reduction catalyst 3 is a catalyst in which a coat layer made of ceria is formed on a cordierite honeycomb substrate, and Rh is carried on the coat layer. Hereinafter, this NO _x A method for producing the adsorption reduction catalyst 3 will be described, and a detailed description of the configuration will be substituted.
[0047]
A coat layer made of ceria was formed on a cordierite cylindrical honeycomb substrate (2 L, 400 mesh) by a wash coat method. 400 g of the coat layer was formed. Next, using a rhodium nitrate aqueous solution, 4 g of Rh was supported on the coat layer, and NO _x Adsorption reduction catalyst 3 was prepared.
[0048]
Using this exhaust gas purifier, the engine 1 was operated at 1700 rpm and 68 Nm, ₃ 0.42 ml of aqueous urea was sprayed into the exhaust gas from the addition device 2 every 30 seconds for 0.5 seconds. R (NH) in exhaust gas atmosphere when urea water is not added ₃ / NO _x ) Is almost zero, and R (NH) in the exhaust gas atmosphere when urea water is added ₃ / NO _x ) Is about 5.
[0049]
While driving in this state, _x The average NOx concentration in the gas emitted from the adsorption reduction catalyst 3 was measured, and the results are shown in FIG. Note that NO _x The temperature of the gas entering the adsorption reduction catalyst 3 was 270 ° C. NO in exhaust gas from the engine 1 _x The concentration was 150 ppm, which is shown as a blank in FIG.
[0050]
(Comparative Example 1)
NO of Example 1 _x Instead of the adsorption reduction catalyst 3, a commercially available VW / TiO of the same size ₂ An exhaust gas purifying apparatus similar to that of Example 1 was used except that a system ammonia denitration catalyst was used. Then, in the same manner as in Example 1, the average NO _x The concentration was measured and the results are shown in FIG.
[0051]
<Evaluation>
From FIG. 2, in the exhaust gas purifying apparatus of Comparative Example 1, NO _x Emissions have hardly been reduced. In addition, ammonia odor is also detected from exhaust gas, and NH ₃ Had also been discharged. On the other hand, according to the exhaust gas purifying apparatus of this embodiment, the average NO in the exhaust gas _x The concentration can be reduced by 93%, NO _x Emissions were significantly reduced. Also, no ammonia odor was detected.
[0052]
(Example 2)
FIG. 3 schematically shows the exhaust gas purifying apparatus of the present embodiment. This exhaust gas purifying apparatus includes an NH 4 disposed in an exhaust system of the engine 4. ₃ Generation catalyst 5 and NH ₃ NO similar to that of Example 1 disposed downstream of the generation catalyst 5 _x An A / F sensor 6 is provided between the engine 4 and the NH3 generating catalyst 5.
[0053]
The engine 4 is a 2.0-liter, 4-cylinder gasoline engine with a total displacement of 2.0 L. Each cylinder is provided with a fuel supply device and an intake control valve (not shown) that can be independently controlled.
[0054]
NH ₃ The generated catalyst 5 is one in which a coat layer made of γ-alumina is formed on a cordierite honeycomb substrate, and Pt is carried on the coat layer. Hereinafter, this NH ₃ A method for producing the production catalyst 5 will be described, and the detailed description of the configuration will be substituted.
[0055]
A coat layer made of γ-alumina was formed on a cordierite cylindrical honeycomb substrate (0.5 L, 400 mesh) by a wash coat method. 80 g of the coat layer was formed. Next, 0.8 g of Pt was supported on the coat layer using an aqueous dinitrodiammine platinum solution, ₃ Production catalyst 5 was prepared.
[0056]
First, from this exhaust gas purifying device, NH ₃ Generation catalyst 5 and NO _x The first step is to supply 1.6 times more fuel to one control cylinder of the engine 4 than the other three cylinders while detecting the signal of the A / F sensor 6 using the device excluding the adsorption reduction catalyst 3. Controlled to. The other three cylinders are adjusted so that the S value is 1.5, and the exhaust gas from the control cylinder is about 7% oxygen deficient.
[0057]
The composition of the exhaust gas from the engine 4 in the first process was measured, and the results are shown in Table 1.
[0058]
Next, similarly from the exhaust gas purifying apparatus, NH ₃ Generation catalyst 5 and NO _x As a second step, all the cylinders of the engine 4 were operated so as to have an S value of 1.5 while detecting the signal of the A / F sensor 6 using the apparatus excluding the adsorption reduction catalyst 3. At this time, the composition of the exhaust gas from the engine 4 was measured, and the results are shown in Table 1.
[0059]
Further, similarly from the exhaust gas purifying apparatus, NH ₃ Generation catalyst 5 and NO _x Using the apparatus excluding the adsorption reduction catalyst 3, as a third step, the first step and the second step were alternately and repeatedly performed for 30 seconds each, and the average composition of the exhaust gas from the engine 4 was measured. 1 is shown.
[0060]
Next, NH was placed 50 cm downstream from the outlet of the engine 4. ₃ The production catalyst 5 is arranged, and NO _x The exhaust gas purifying apparatus of the present embodiment was provided by disposing the adsorption reduction catalyst 3. Then, the operation is performed in the same manner as in the third step, and NO _x The average composition of the gas emitted from the adsorption reduction catalyst 3 was measured, and the results are shown in Table 1.
[0061]
[Table 1]

[0062]
From Table 1, according to the exhaust gas purifying apparatus of the present embodiment, NO _x It is clear that the emission amount of NO can be reduced by about 91%. _x Emissions were greatly reduced. In addition, HC and CO were sufficiently purified, and no ammonia odor was detected.
[0063]
(Example 3)
FIG. 4 shows an exhaust gas purifying apparatus of the present embodiment. This device has NO _x NO on the downstream side of the adsorption reduction catalyst 3 _x It is the same as the first embodiment except that the sensor 30 is arranged. NO _x Sensor 30 is Pt and WO ₃ And the detection signal is NH ₃ It is input to the control device 7 that controls the driving of the compressed air introduction device 21 in the addition device 2.
[0064]
Hereinafter, the operation of the exhaust gas purifying apparatus will be described with reference to the flowchart shown in FIG.
[0065]
First, in step 101, the drive of the compressed air introduction device 21 is stopped, and the exhaust gas of R ≦ 1 is NO. _x It is introduced into the adsorption reduction catalyst 3. Then NO in the exhaust gas _x Is NO _x NO adsorbed on the adsorption reduction catalyst 3 _x NO in the adsorption reduction catalyst 3 _x Gradually accumulates.
[0066]
Next, in step 102, NO _x The detection signal of the sensor 30 is input to the control device 7, and _x NO in gas emitted from adsorption reduction catalyst 3 _x Is determined. NO here _x If is not detected, the process proceeds to step 103 without doing anything. But no _x Is detected, NO _x NO of adsorption reduction catalyst 3 _x Since it is determined that the residual capacity for adsorption is small, the process jumps from step 103 to step 104, where R> 1 and many NHs are set. ₃ Is added.
[0067]
In step 103, the timer drives the compressed air introduction device 21 for less than 30 seconds. After a lapse of 30 seconds, the process proceeds to step 104.
[0068]
In step 104, the compressed air introduction device 21 is driven, and NH4 is contained in the exhaust gas. ₃ And the exhaust gas of R> 1 is NO _x It is introduced into the adsorption reduction catalyst 3. Then excess NH ₃ By NO _x NO adsorbed and accumulated in the adsorption reduction catalyst 3 _x Is N ₂ And at the same time NH ₃ Is consumed and disappears. This makes NO _x NO of adsorption reduction catalyst 3 _x The adsorption capacity is restored.
[0069]
Then, in step 105, NO _x The detection signal of the sensor 30 is input to the control device 7, and _x NO in gas emitted from adsorption reduction catalyst 3 _x Is determined. NO here _x Is detected, NH ₃ Is still small and NO _x NO of adsorption reduction catalyst 3 _x Since it means that the remaining adsorption capacity is still small, the processing proceeds to step 107, where NH ₃ Is continuously added. NO _x If is not detected, the process proceeds to step 106, where NH is set based on an empirical rule. ₃ It is determined whether or not the generation amount of is excessive. NH ₃ Is excessive, a predetermined correction process is performed, and the process returns to step 101, in which the driving of the compressed air introduction device 21 is stopped and NH ₃ Is stopped. NH ₃ If the generation amount is appropriate, the process proceeds to step 107 without doing anything.
[0070]
In step 107, the timer stops the driving of the compressed air introduction device 21 for less than 30 seconds, and after 30 seconds, the process returns to step 101 to set the NH ₃ Is stopped.
[0071]
Therefore, in the exhaust gas purifying apparatus of the present embodiment, the compressed air introduction device 21 can be driven in a necessary and sufficient time, and unnecessary driving can be eliminated. Also NO _x And NH ₃ Can be further suppressed.
[0072]
【The invention's effect】
That is, according to the exhaust gas purifying method and the exhaust gas purifying apparatus of the present invention, NO _x And NH ₃ Can be greatly suppressed. Further, since each component reacts at a high concentration, the reaction efficiency is improved about 1000 times as compared with the reaction in a normal exhaust gas, and the capacity of the catalyst can be reduced.
[Brief description of the drawings]
FIG. 1 is a block diagram schematically showing a configuration of an exhaust gas purifying apparatus according to one embodiment of the present invention.
FIG. 2 shows NO in gas emitted from exhaust gas purifying apparatuses of Example 1 and Comparative Example 1. _x It is a graph which shows a density with a blank.
FIG. 3 is a block diagram schematically showing a configuration of an exhaust gas purifying apparatus according to a second embodiment of the present invention.
FIG. 4 is a block diagram schematically showing a configuration of an exhaust gas purifying apparatus according to a third embodiment of the present invention.
FIG. 5 is a flowchart showing control contents of an exhaust gas purifying apparatus according to a third embodiment of the present invention.
[Explanation of symbols]
1: Engine 2: NH ₃ Addition device 3: NO _x Adsorption reduction catalyst
4: Engine 5: NH ₃ Generated catalyst

Claims (9)

The _the NO _x adsorption reduction catalyst for reducing NO _x adsorbs the adsorbed NO _x to N ₂ is reacted with NH ₃ is arranged in the exhaust gas line, upstream of the _the NO _x adsorption and reduction catalyst in an oxygen excess in the exhaust gas at the time average An exhaust gas purification method for supplying at least one of NH ₃ and an NH ₃ precursor to the exhaust gas side and reacting NO _x in the exhaust gas with NH ₃ to purify the exhaust gas,
In entering gas to the _the NO _x adsorption and reduction catalyst, characterized in that the molar ratio R defined by R = NH 3 _/ NO _x is repeated and the exhaust gas atmosphere is 1 <exhaust gas atmosphere and R 1> R alternately Exhaust gas purification method. Wherein _the NO _x adsorption reduction catalyst, the exhaust gas purifying method according to claim 1, wherein at least Rh is supported on the metal oxide. The exhaust gas purification method according to claim 2, wherein the metal oxide contains at least ceria. Exhaust gas to NH ₃ supply means for supplying NH ₃ is arranged in an exhaust pipe of the at least one control cylinder of an internal combustion engine having a plurality of cylinders, the exhaust pipes of the plurality of the gas cylinder downstream of the NH ₃ supply means is set exhaust gas purification apparatus characterized by comprising placing the _the NO _x adsorption and reduction catalyst for reducing the N ₂ adsorbed NO _x adsorbs NO _x in the flow path is reacted with NH _3. 5. The exhaust gas purifying apparatus according to claim 4, wherein the NH ₃ supply unit is a NH ₃ generating catalyst that supports at least one of Pt and Pd on a metal oxide carrier and converts NO _x in exhaust gas to NH ₃ . The NH ₃ supply means, at least an exhaust gas purifying apparatus according to a substance to produce a NH ₃ in the exhaust gas to claim 4 is NH ₃ addition device to be added to the exhaust gas. Wherein _the NO _x adsorption and reduction catalyst is at least Rh exhaust gas purifying apparatus according to claim 4 comprising supported on a metal oxide. The exhaust gas purifying apparatus according to claim 7, wherein the metal oxide contains at least ceria. The exhaust gas purifying apparatus according to any one of claims 4 to 8, wherein the control cylinder is alternately operated in an air-deficient atmosphere and an air-excess atmosphere for a predetermined time, and the other cylinders than the control cylinder are operated in an air-excess atmosphere. An exhaust gas purification method characterized by operating.

Images