JP3772478B2 - Regeneration method of exhaust gas purification catalyst for internal combustion engine - Google Patents

Description

【００６２】
【発明の効果】
本発明によれば、硫黄被毒によりＮＯｘ浄化性能の劣化した排ガス浄化触媒を再生することができる。
【図面の簡単な説明】
【図１】本発明の代表的な実施態様を示す排ガス浄化装置の構成図。
【図２】硫黄被毒により触媒中に亜硫酸塩が生成し該亜硫酸塩が転換されて生成する硫酸塩の量が予め設定された所定値に達する前の段階を検出する手段の一実施形態のフローチャート。
【図３】他の実施形態のフローチャート。
【図４】硫黄被毒によるＮＯｘ浄化性能の低下を示す図。
【図５】ＮＯｘ浄化性能の低下と亜硫酸塩及び硫酸塩の生成量の関係を示す図。
【図６】硫黄被毒により触媒中に亜硫酸塩が生成し該亜硫酸塩が転換されて生成する硫酸塩の量が予め設定された所定値に達する前の段階を検出する手段の一実施形態のフローチャート。
【図７】本発明による触媒再生方法を用いた運転における空燃比の変動の一例を示す図。
【図８】耐久試験後の触媒のＦＴ−ＩＲスペクトル。
【図９】耐久試験後再生処理した触媒のＦＴ−ＩＲスペクトル。
【図１０】亜硫酸塩の還元分解の熱特性を示す図。
【図１１】貴金属による亜硫酸塩の還元分解促進を示すＦＴ−ＩＲスペクトル。
【図１２】亜硫酸塩と硫酸塩の生成量の違いを示すＦＴ−ＩＲスペクトル。
【符号の説明】
１…エアクリーナー、２…エアフローセンサー、３…スロットルバルブ、５…インジェクター、６…点火プラグ、７…アクセルペダル、８…負荷センサー、９…吸気温度センサー、１２…燃料ポンプ、１３…燃料タンク、１８…窒素酸化物浄化触媒、１９…酸素濃度センサー、２０…触媒温度センサー、２１…排ガス温度センサー、２２…ＮＯｘ濃度センサー、２５…ＥＣＵ、２６…ノックセンサー、２８…水温センサー、２９…クランク角センサー、９９…エンジン、１００…ストイキ運転からリーン運転に切り換えてから所定時間経過した時点、１０１…硫黄被毒後の触媒Ｂ−１、１０２…硫黄被毒前の触媒Ｂ−１、１０３…再生処理後の触媒Ｂ−１、１０４…再生処理後のモデル触媒Ｃ−１、１０５…再生処理後のモデル触媒Ｃ−２、１０６…硫黄被毒後の触媒Ａ−１。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for regenerating a catalyst for purifying exhaust gas discharged from an internal combustion engine such as an automobile, and more particularly to an internal combustion engine operated at a lean air-fuel ratio (lean burn) and an automobile equipped with the internal combustion engine. The present invention relates to a method for regenerating a catalyst for purifying nitrogen oxides in exhaust gas.
[0002]
[Prior art]
Carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), etc. contained in exhaust gas discharged from internal combustion engines such as automobiles have been pointed out as adverse effects on the environment as air pollutants. Therefore, purification of these harmful components has been promoted conventionally, and in particular, exhaust gas purification methods that simultaneously oxidize CO and HC and reduce NOx by a three-way catalyst using noble metals such as Pt, Rh, and Pd as active components are widely used. Has been done.
[0003]
By the way, the exhaust gas purification performance of the three-way catalyst is greatly influenced by the air-fuel ratio (A / F) of the internal combustion engine, and all of CO, HC and NOx can be efficiently purified by burning near the stoichiometric air-fuel ratio (stoichiometric). Limited to the case. However, in recent years, automobiles have been developed that burn under conditions where the fuel is leaner than the stoichiometric air-fuel ratio due to social demands for improving fuel efficiency. In such a lean burn method, the oxygen concentration in the exhaust gas is stoichiometrically excessive compared to the reducing gas concentration, and the current three-way catalyst tends to oxidize CO and HC, but makes it difficult to reduce NOx. Become. Therefore, in order to promote the spread of the lean burn method, development of a new exhaust gas purification catalyst that promotes the reduction of NOx under excessive oxygen has been underway. In addition, it has been pointed out that a catalyst that purifies NOx under lean burn conditions is poisoned by sulfur oxides contained in exhaust gas, resulting in a decrease in NOx purification performance. Developments have also been made on methods for reducing poisoning.
[0004]
Japanese Patent Application Laid-Open No. 5-317652 proposes a catalyst supporting platinum and an alkaline earth metal such as barium. In this catalyst, barium acts as a NOx occlusion material in a lean atmosphere, reacts and occludes with NOx, and barium nitrate (Ba (NO_Three)₂Then, a reaction system has been proposed in which barium nitrate is reduced and decomposed by HC and CO in a rich atmosphere with stoichiometric or excessive fuel to purify NOx. By the way, SO contained in the exhaust gas from the internal combustion engine is burned and generated by sulfur contained in the fuel.₂Which reacts with barium to produce sulfate. Thus, the sulfated barium has a problem that the reactivity with NOx is lowered, and sufficient NOx purification ability as a catalyst cannot be maintained. This phenomenon is called sulfur poisoning, and has become a major issue in the development of exhaust gas purification catalysts as a cause of reducing the endurance activity of exhaust gas purification catalysts.
[0005]
JP-A-8-299793 proposes a catalyst carrying a strontium compound, platinum and a rare earth metal. In this catalyst, a reaction system has been proposed in which NOx is adsorbed by a strontium compound, transferred onto platinum existing in the vicinity of strontium, and reduced and purified. Even in this catalyst, SO contained in the exhaust gas is also present.₂Therefore, there is a problem that strontium is poisoned by sulfur and activity after durability is lowered.
[0006]
Japanese Patent Application Laid-Open No. 7-51544 proposes that at least two kinds of NOx occlusion materials are supported and complex sulfates are generated during sulfur poisoning. There is a description that this composite sulfate is easily decomposed because its decomposition temperature is lower than that of a single sulfate, and that it is easy to recover the reactivity with NOx even in a catalyst after sulfur poisoning.
[0007]
Japanese Patent Application Laid-Open No. 8-99034 proposes to use a material in which absorption of sulfur oxide is suppressed by combining titania or the like with alumina. There is a description that sulfite ions and sulfate ions are hardly adsorbed to such a composite carrier and sulfur poisoning does not proceed easily.
[0008]
As described above, in order to reduce sulfur poisoning in the exhaust gas purification catalyst, development has been widely promoted. In the above known example, there is a report on a method for facilitating regeneration from sulfur poisoning or suppressing sulfur poisoning. However, when sulfur poisoning has progressed sufficiently, the above method is not effective, and a sufficient sulfur poisoning reduction method has not yet been developed.
[0009]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for regenerating an exhaust gas purification catalyst whose NOx purification performance has deteriorated due to sulfur poisoning.
[0010]
[Means for Solving the Problems]
As a result of diligent investigations to solve the above problems, the present inventors have determined that the oxygen concentration is a stoichiometry compared to the reducing gas concentration as a method for removing sulfate and / or sulfite accumulated in the catalyst from the catalyst. It has been found effective to decompose by flowing a gas with a reducing atmosphere, ie rich or stoichiometrically equivalent, ie stoichiometric, through an exhaust gas flow path.
[0011]
Further, the present inventors decompose the sulfate and / or sulfite accumulated in the catalyst by flowing rich or stoichiometric gas into the exhaust gas flow path before the sulfite accumulated in the catalyst is converted into sulfate, We found that removal from the top was effective.
[0012]
In addition, the present inventors have found that the catalyst produces rich sulfite by sulfur poisoning, and when the amount of sulfate produced by conversion of the sulfite reaches a predetermined value set in advance, It has been found that a catalyst regeneration method in which NOx purification performance is deteriorated by sulfur poisoning can be obtained by creating a reducing atmosphere by flowing stoichiometric gas and reducing and decomposing sulfite.
[0013]
The present invention can be particularly preferably carried out when a catalyst containing a NOx adsorbent, a noble metal, and a component that suppresses the NOx adsorbent from being converted to sulfate by sulfur poisoning is used. The purpose of purifying nitrogen oxides in exhaust gas in a lean burn atmosphere is to reduce NOx adsorbed like platinum and components that adsorb NOx like strontium, as disclosed in, for example, Japanese Patent Laid-Open No. 8-299793. It can be realized by a combination with components to be purified. Here, it is necessary to prevent the performance deterioration of the NOx purification component due to sulfur poisoning.
[0014]
Sulfur poisoning is the SO produced by combustion of sulfur in fuel.₂And SO_ThreeIn addition, the active component in the catalyst under an oxygen-excess atmosphere causes SO₂Produced by oxidation of SO_ThreeOccurs by reacting with the NOx purification component in the catalyst in the presence of moisture to produce sulfite or sulfate. In addition, a reaction in which sulfite is further oxidized to become sulfate is also conceivable. Therefore, it is considered that there is a relatively large amount of sulfite in the early stage of sulfur poisoning, and the production of sulfate is gradually increased. These chemical reactions are roughly represented by the following reaction formulas.
[0015]
SO₂+ 1 / 2O₂ → SO_Three (1)
SO₂+ MCO_Three → MSO_Three+ CO₂ (2)
SO_Three+ MCO_Three → MSO_Four+ CO₂ (3)
MSO_Three+ 1 / 2O₂ → MSO_Four (4)
Here, M is an element that becomes a NOx trapping material by adsorption or absorption. The sulfite and sulfate produced here are decomposed in a stoichiometric or rich reducing atmosphere, and again SO2₂Was observed to be released. This chemical reaction is roughly represented by the following reaction formula.
[0016]
MSO_Four → MSO_Three+ [O] (5)
MSO_Three+ CO₂ → MCO_Three+ SO₂ (6)
Here, [O] is consumed by oxidation of the reducing component in the exhaust gas. Thus, it is considered that the sulfate produced by sulfur poisoning is decomposed via sulfite. Therefore, the rate of reductive decomposition is faster when the NOx trapping material is sulphated and when it is sulphited. This is also evident from the fact that when sulfur-poisoned catalysts are treated in a rich atmosphere, sulfite reduction is observed faster than sulfate reduction.
[0017]
In addition, when the standard heat of formation of sulfite and sulfate is compared, sulfate is generally larger. That is, sulfate is more stable and less susceptible to decomposition than sulfite. For example, the alkali metal element or alkaline earth metal element is as follows.
[0018]
Li₂SO_Three: -1177 kJ / mol, Li₂SO_Four: -1436 kJ / mol.
Na₂SO_Three: -1101 kJ / mol, Na₂SO_Four: -1387 kJ / mol.
K₂SO_Three: -1117 kJ / mol, K₂SO_Four: -1434 kJ / mol.
BaSO_Three: -1182 kJ / mol, BaSO_Four: -1465 kJ / mol.
[0019]
In addition, the value of standard heat of formation depended on the 4th edition of the Chemical Handbook Basic Edition (edited by the Chemical Society of Japan, published in 1993) and CRC Handbook of Chemstry and Physics, 61st Edition (CRC Press Inc, 1980).
[0020]
As described above, sulfite and sulfate produced by sulfur poisoning are more unstable, and they undergo reductive decomposition at a lower temperature more easily than sulfate. Further, considering reaction formulas (1) and (4), it is considered that the main product is sulfite at the initial poisoning stage, and the production of sulfate has not progressed sufficiently. As described above, since sulfite is more susceptible to reductive decomposition than sulfate, regeneration from sulfur poisoning of the NOx trapping material is effective by performing regeneration treatment in a stoichiometric or rich atmosphere at the initial stage of poisoning. Can be done.
[0021]
The eye of the present invention pays attention to the difference in susceptibility of sulfite and sulfate to reductive decomposition, and the NOx trapping material is regenerated from sulfur poisoning by treating it in a reducing atmosphere at the sulfite stage where reductive decomposition is easy It is easy to be done. The present invention can be particularly suitably carried out when a nitrogen oxide purification catalyst containing a component that suppresses sulfation of NOx adsorbent due to sulfur poisoning is used. In the above-mentioned known example, there is a description about the formation of sulfite and sulfate by sulfur poisoning, but for the sulfur poisoning reduction method focusing on the difference in susceptibility to reductive decomposition of sulfite and sulfate. It is not described at all.
[0022]
In the present invention, the time when the stoichiometric or rich atmosphere gas is flowed before the sulfite accumulated in the catalyst becomes sulfate can be determined by the following method, for example.
[0023]
The amount of sulfur oxide discharged into the exhaust gas can be estimated from the concentration of sulfur contained in the fuel and the amount of fuel consumed. Since the absorption rate of the sulfur oxide to the catalyst varies depending on the temperature and can be obtained experimentally in advance, the amount of sulfite produced by adsorption of the sulfur oxide on the catalyst is estimated from the exhaust gas temperature and / or catalyst temperature. can do. Here, the time required for the sulfite produced in the catalyst to be converted into sulfate by heat can be experimentally determined in advance, and this is based on conditions such as exhaust gas temperature and exhaust gas atmosphere, ie, lean, stoichiometric, rich, etc. It changes by etc. Thus, by monitoring the sulfur concentration in the fuel, fuel consumption, exhaust gas temperature and / or catalyst temperature, elapsed time, exhaust gas atmosphere, etc., the time when the sulfite accumulated in the catalyst is converted into sulfate. Can be expected. Prior to this point, the poisoned catalyst can be effectively regenerated by performing an operation of decomposing sulfite with stoichiometric or rich gas.
[0024]
Further, in the present invention, the method for detecting the stage where the catalyst produces sulfite by poisoning with sulfur oxide and the amount of sulfate produced by conversion of the sulfite reaches a predetermined value set in advance is as follows. It can be done by the method.
[0025]
Estimate the amount of sulfur oxide discharged into the exhaust gas from the concentration of sulfur contained in the fuel and the amount of fuel consumed, and the amount of sulfur oxide absorbed into the catalyst, the amount of sulfite produced, and sulfurous acid from the exhaust gas temperature or catalyst temperature The amount of conversion from salt to sulfate is estimated, and the time when the amount of sulfite or sulfate present in the catalyst estimated from these integrated values reaches a predetermined value set in advance is detected. Here, the absorption rate of the sulfur oxide into the catalyst varies depending on the exhaust gas temperature, and can be experimentally obtained in advance. The conversion rate from sulfite to sulfate varies depending on the temperature to which the sulfite is exposed, that is, the exhaust gas temperature, and can be experimentally obtained in advance. Therefore, the abundance of sulfite and sulfate in the catalyst can be determined by integrating the values calculated according to the temperature at each time point, and this is compared with a predetermined value set in advance. The timing at which reductive decomposition should be performed can be detected. Here, the predetermined value set in advance is a limit value at which sulfate produced in the catalyst is sufficiently small and reductive decomposition easily occurs, and is smaller than a value at which the production of sulfate proceeds and reduction becomes difficult. Is set. Although this value differs depending on the catalyst, according to the study by the present inventors, for example, the sulfite content is about 1 wt% or less with respect to the whole catalyst, and the sulfate content is relative to sulfite. About 10 wt% or less was suitable.
[0026]
Also, the absorption rate of sulfur oxides to the catalyst and the conversion rate from sulfite to sulfate vary depending not only on the exhaust gas temperature but also whether the exhaust gas is in an oxygen-excess atmosphere or a reducing atmosphere, Can be obtained. From the reaction formulas (1) to (6), the absorption of the sulfur oxide into the catalyst and the conversion from the sulfite to the sulfate easily proceed in an oxygen-excess atmosphere and hardly proceed in a reducing atmosphere. Therefore, the sulfite and sulfate abundance calculated according to the temperature at each time point from the absorption rate of the sulfur oxide to the catalyst and the conversion rate from sulfite to sulfate should be accumulated only for the oxygen-excess atmosphere. Can more accurately estimate the abundance of sulfite and sulfate in the catalyst.
[0027]
Further, in the present invention, the stage in which the nitrogen oxide purification catalyst produces sulfite by poisoning with sulfur oxide and the amount of sulfate produced by conversion of the sulfite reaches a predetermined value set in advance is detected. The following method can also be used as a method for this.
[0028]
Nitrogen oxidation in exhaust gas after a predetermined time after switching from operation under reducing atmosphere to operation under excess oxygen atmosphere by the signal of nitrogen oxide sensor placed downstream of nitrogen oxide purification catalyst in exhaust gas flow path When the concentration of sulfite or sulfate in the catalyst estimated from this is estimated, the rate of decrease in nitrogen oxide purification performance is estimated from the nitrogen oxide concentration To detect. Here, as the poisoning of the catalyst by sulfur oxide proceeds, the NOx purification performance decreases. That is, the amount of sulfite and sulfate present in the catalyst can be determined by detecting a decrease in NOx purification performance. The NOx purification performance is switched to operation in an oxygen-excess atmosphere after NOx trapped in the NOx trapping material by operation in a reducing atmosphere is reduced and detected, and the NOx concentration downstream of the catalyst after a predetermined time is detected. Can be estimated.
[0029]
In the present invention, the duration of the reducing atmosphere created for the reductive decomposition of the sulfite produced in the catalyst by poisoning with sulfur oxides is desirably 0.2 seconds or more and 10 minutes or less. Reductive decomposition of sulfite and sulfate produced in the catalyst is less likely than NOx reductive decomposition chemisorbed on the catalyst. Therefore, the reductive decomposition of sulfite and sulfate requires at least the same time as that for the reductive decomposition of NOx chemisorbed on the catalyst, and is preferably 0.2 seconds or longer. Further, since creating a reducing atmosphere lowers the air-fuel ratio and deteriorates fuel efficiency, it is desirable to make it within 10 minutes.
[0030]
The catalyst used in the present invention is a catalyst containing at least one or more of alkali metal or alkaline earth metal as a component for trapping nitrogen oxides by adsorption or absorption, and containing at least one or more of platinum, rhodium and palladium as noble metals. Preferably it is. In particular, a catalyst containing a component that suppresses the NOx adsorbent, the noble metal, and the NOx adsorbent from being converted to sulfate by sulfur poisoning is suitable. The NOx adsorbent is at least an alkali metal or an alkaline earth metal. One or more kinds, platinum, rhodium, or palladium as a noble metal, and titanium, zirconium, vanadium, niobium, chromium, molybdenum, tungsten as a component that inhibits NOx adsorbent from being converted to sulfate by sulfur poisoning At least one of these is desirable.
[0031]
The reason why the conversion of the NOx adsorbent into sulfate by the addition of a component that suppresses the NOx adsorbent from being converted into sulfate due to sulfur poisoning is not necessarily clear, but the following may be considered. .
[0032]
A component that suppresses the NOx adsorbent from being converted to sulfate by sulfur poisoning is supported together with the NOx adsorbing component, so that at least a part of the component is considered to be complex oxide. The composite oxide is more complex in crystal structure than the case of the NOx adsorbent alone by being composited. Therefore, a chemical reaction accompanied by a change in the crystal structure as in reaction formulas (2) and (3) is suppressed. In view of the size of sulfite ion, sulfate ion and carbonate ion, the reaction formula (3) is considered to have a larger crystal structure change than the reaction formula (2), and sulfation is suppressed more than sulfite. It is estimated to be. In addition, the NOx adsorbent alone has a strong solid basicity, but the composite basicity is lowered due to the composite oxide being complexed. Accordingly, the reaction with the acidic gas as in the reaction formulas (2) and (3) is suppressed, and the sulfite having a relatively low solid acidity is converted into a sulfate with a high solid acidity as in the reaction formula (4). Is estimated to be suppressed.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
EXAMPLES Hereinafter, although this invention is demonstrated with a specific example, this invention is not restrict | limited by these Examples.
[0034]
FIG. 1 is an overall configuration diagram showing an embodiment of a method for regenerating an exhaust gas purification catalyst of the present invention.
[0035]
The present invention includes an engine 99 capable of lean burn operation, an intake system having an air flow sensor 2, a throttle valve 3, and the like, an oxygen concentration sensor (or A / F sensor) 19, an exhaust gas temperature sensor 21, a nitrogen oxide purification catalyst 18, and the like. This is realized by an exhaust gas purifying apparatus having the exhaust system and the control unit (ECU) 25 and the like. The ECU includes an I / O LSI as an input / output interface, an arithmetic processing unit MPU, a storage device ROM and RAM storing a control program group, a timer counter, and the like.
[0036]
The above exhaust gas purification apparatus functions as follows. The intake air to the engine 99 is filtered by the air cleaner 1 and then measured by the air flow sensor 2. The fuel is then injected from the injector 5 through the throttle valve 3 and supplied to the engine 99 as an air-fuel mixture. The fuel is supplied from the injector 5 via the fuel pump 12 from the fuel tank 13. Sensor signals such as airflow sensor signals are input to the ECU 25. The ECU depresses the accelerator pedal 7 detected by the load sensor 8 and the control program group stored in advance and the sensor signals of the airflow sensor 2, the intake air temperature sensor 9, the knock sensor 26, the water temperature sensor 28, the crank angle sensor 29, etc. Based on such information, the operating state of the internal combustion engine and the state of the nitrogen oxide purification catalyst are evaluated to determine the operating conditions such as the operating air-fuel ratio, and the injector 5 and the spark plug 6 are controlled to mix under predetermined conditions. Burn your mind. The combustion exhaust gas is led to the exhaust system, and a nitrogen oxide purification catalyst 18 is provided in the exhaust system. During the stoichiometric operation, NOx, HC and CO in the exhaust gas are purified by the three-way catalyst function, and the lean operation is performed. Inside, NOx is adsorbed and purified, and HC and CO are purified by the combustion function. Further, when the NOx purification ability in the lean operation is reduced due to the determination and control signal of the ECU, the air-fuel ratio is shifted to the rich side to restore the NOx adsorption ability. By the above operation, the exhaust gas is effectively purified under all engine combustion conditions. The state of the catalyst can be monitored by the catalyst temperature sensor 20, the exhaust gas temperature sensor 21, the NOx concentration sensor 22, and the like.
[0037]
Here, SO contained in exhaust gas₂As a result, the catalyst is poisoned. Therefore, even if the air-fuel ratio is richly shifted and the NOx adsorption capacity is recovered as described above, the NOx adsorption capacity is not sufficiently recovered. In the present invention, since a component that suppresses the formation of sulfate by sulfur poisoning of the NOx adsorbing component is added to the catalyst material, the progress of sulfur poisoning is suppressed at the stage where sulfite that is easily reduced and decomposed is formed. Is done. However, if left as it is for a long time, conversion of sulfite to sulfate will eventually occur and it will be difficult for reductive decomposition. Therefore, by the method described later, the ECU detects a stage where sulfite is generated and the amount of sulfate generated by conversion of the sulfite reaches a predetermined value, and the air-fuel ratio is shifted to the rich side. Create a reducing atmosphere to reduce and decompose sulfites. By the above operation, the NOx adsorption capacity is sufficiently recovered, and an exhaust gas purification method in which deterioration of NOx purification performance due to sulfur poisoning is reduced can be obtained.
[0038]
FIG. 2 is a flowchart of an embodiment of means for detecting a stage in which the amount of sulfate produced by conversion of sulfite after the formation of sulfite in the catalyst due to sulfur poisoning reaches a predetermined value set in advance. Is shown.
[0039]
In step 1002, the SO released in the exhaust gas from the sulfur concentration in the fuel and the fuel consumption₂Estimate the amount of At step 1003, a signal such as exhaust gas temperature is read, and the released SO estimated at step 1002₂Of these, SO adsorbed on the catalyst₂The amount is estimated, and the amount of sulfite newly formed on the catalyst is estimated. In step 1003, the amount of sulfite accumulated on the catalyst to become sulfate by heating is estimated. This is the SO to the catalyst₂This is because both the absorption rate and the conversion rate from sulfite to sulfate change with temperature. The amounts of sulfite and sulfate estimated in step 1004 are integrated. It is determined whether or not the amount of sulfite or sulfate accumulated in step 1005 exceeds a predetermined value. If the predetermined value is not exceeded, the process is repeated from step 1002. If the predetermined value is exceeded, a reducing atmosphere is created in step 1006 to perform reductive decomposition of sulfur oxides and cancel the accumulation of sulfites and sulfates.
[0040]
FIG. 3 shows another embodiment of means for detecting a stage in which the amount of sulfate produced by conversion of sulfite after the formation of sulfite in the catalyst by sulfur poisoning reaches a predetermined value set in advance. This flowchart is shown.
[0041]
Differences from FIG. 2 are as follows. In step 1008, operating conditions are acquired from oxygen concentration, A / F, and other signals. In step 1009, it is determined whether the current operation condition is lean operation, stoichiometric operation or rich operation. In the case of lean operation, the process proceeds to step 1003 and proceeds to integration of the amount of sulfite and sulfate. In the case of the stoichiometric or rich operation, the integration after step 1003 is skipped and the process returns to step 1002. This is because sulfur poisoning occurs particularly strongly during lean operation, so it is more accurate to perform sulfite and sulfate accumulation only for lean operation than for total operation time. is there.
[0042]
FIG. 4 and FIG. 5 show other means for detecting a stage in which sulfite is produced in the catalyst by sulfur poisoning, and the amount of sulfate produced by conversion of the sulfite reaches a predetermined value set in advance. 1 illustrates the principle of one embodiment.
[0043]
As shown in FIG. 4, the NOx purification rate of the nitrogen oxide purification catalyst decreases as NOx adsorption progresses in lean operation, and the NOx purification rate is reduced by purging the stoichiometric or rich operation in a spiked manner to reduce the adsorbed NOx. Recover. However, the NOx purification rate becomes difficult to recover due to the progress of sulfur poisoning. The progress of the sulfur poisoning can be estimated by measuring the NOx purification rate at a time (100) after a predetermined time has elapsed since switching from the stoichiometric operation to the lean operation, for example, 30 seconds or 1 minute later. As shown in FIG. 5, the amount of sulfite and sulfate produced in the catalyst changes with a decrease in the NOx purification rate after the predetermined time due to sulfur poisoning, so the NOx purification rate after the predetermined time is measured. By doing so, it is possible to detect a stage in which the amount of sulfate produced by producing sulfite and converting the sulfite has reached a predetermined value.
[0044]
FIG. 6 detects the stage in which the sulfur poisoning shown in FIGS. 4 and 5 produces sulfite in the catalyst and the amount of sulfate produced by conversion of the sulfite reaches a predetermined value. 7 shows a flowchart of another embodiment of the means.
[0045]
In step 1010, lean operation is performed. In step 1011, the NOx adsorption capacity of the catalyst is estimated. In step 1012, it is determined whether it is necessary to purify the adsorbed NOx by richly shifting the A / F from the NOx adsorbing capacity. In step 1013, a rich shift is performed. In step 1014, the elapsed time after the rich shift is integrated. In step 1015, the end of the rich shift is determined. Next, at step 1016, a lean shift is performed, and at step 1017, the elapsed time after the lean shift is integrated. In step 1018, it is determined whether a predetermined time has elapsed after the lean shift. When the predetermined time is reached, the NOx purification rate is estimated from a signal from a NOx sensor or the like installed downstream of the catalyst in Step 1019. The amount of sulfite and sulfate produced in the catalyst is estimated from the NOx purification rate estimated in step 1020. It is determined whether the amount of sulfite or sulfate estimated in step 1021 has reached a predetermined value set in advance. When the amount of sulfite or sulfate exceeds a predetermined value, a reducing atmosphere is created in step 1022 to perform reductive decomposition of sulfur oxides.
[0046]
FIG. 7 shows an example of the fluctuation of the air-fuel ratio in the operation using the catalyst regeneration method according to the present invention.
[0047]
The sulfite or sulfate produced in the catalyst due to poisoning by sulfur oxide is reduced and decomposed in a reducing atmosphere, but this reaction is less likely to occur than the reaction for reducing and purifying NOx adsorbed on the NOx adsorbent. Therefore, the rich shift for reducing and decomposing sulfite and sulfate must be at least as long as or longer than the rich shift for reducing and purifying NOx adsorbed on the NOx adsorbent. However, since the fuel efficiency is deteriorated by performing the rich shift, the rich shift should not be performed for a longer time than necessary. As shown in FIG. 7, the rich shift is desirably 0.2 seconds or more and 10 minutes or less.
[0048]
Nitrogen oxide purification catalyst A-1 used in the present invention was prepared by the following method.
[0049]
Alumina sol as a binder obtained by nitric acid-separating alumina powder and boehmite was mixed to obtain a nitric acid acidic alumina slurry. After the honeycomb was immersed in the slurry, it was quickly pulled up, and the liquid blocked in the cells was removed by air blow, dried, and then fired at 450 ° C. This operation was repeated to coat 150 g of alumina per 1 L of the apparent volume of the honeycomb. The catalytically active component was supported on the alumina-coated honeycomb through the following steps. First, it was impregnated with a cerium nitrate solution, dried and then fired at 600 ° C. for 1 hour. Subsequently, it was impregnated with a mixed solution of a sodium nitrate solution, a magnesium nitrate solution, and a titania sol solution, and similarly dried and fired. Subsequently, it was impregnated with a mixed solution of dinitrodiammine platinum nitrate solution and rhodium nitrate solution, dried and baked at 450 ° C. for 1 hour. Finally, it was impregnated with a magnesium nitrate solution and dried and fired in the same manner. Thus, the nitrogen oxide purification catalyst A-1, that is, 2.1 Mg- (2.7 Pt, 0.2 Rh)-(18 Na, 4 Ti, 0.9 Mg) -27 Ce / Al₂O_ThreeGot. Where / Al₂O_ThreeIndicates that the active component was supported on alumina, and the numerical value before the element symbol is the number of grams of the display metal component supported per 1 L of honeycomb apparent volume, and Al₂O_ThreeThe component indicated near the symbol indicates that it was supported earlier, and the component enclosed in parentheses indicates that it was supported at the same time.
[0050]
Nitrogen oxide purification catalyst B-1 was prepared by the following method.
[0051]
Among the preparation methods in the catalyst A-1, the titania sol solution is not used, and the others are prepared in the same manner as A-1, and the nitrogen oxide purification catalyst B-1, that is, 2.1 Mg- (2.7 Pt, 0 .2Rh)-(18Na, 0.9Mg) -27Ce / Al₂O_ThreeGot.
[0052]
Further, model catalysts C-1 and C-2 simulating a state poisoned by sulfur oxide were prepared by the following method.
[0053]
An alumina-coated honeycomb prepared in the same manner as the catalyst A-1 was impregnated with a sodium sulfite solution, dried, and then fired at 450 ° C. for 1 hour to obtain a model catalyst C-2, ie, 18Na / Al₂O_Three(However, Na is present in sodium sulfite). Further, C-2 was further impregnated with a mixed solution of a dinitrodiammine platinum nitric acid solution and a rhodium nitrate solution, dried and then calcined at 450 ° C. for 1 hour, and model catalyst C-1, that is, (2.7 Pt, 0.2 Rh) − 18Na / Al₂O_Three(However, Na is present in sodium sulfite).
[0054]
FIG. 8 is a Fourier transform infrared absorption (FT-IR) spectrum showing the structural changes of the catalyst B-1 (101) after sulfur poisoning and the catalyst B-1 (102) before sulfur poisoning. The endurance test is conducted in standard lean composition gas₂The gas (SV = 30000 / h) added with 150 ppm of was introduced into the catalyst and poisoned at 300 ° C. for 1 hour. According to the durability test, sulfite ions and sulfate ions are accumulated in the catalyst, while carbonate ions are decreased. This result shows that the above reactions (1) to (4) occurred in the catalyst in the durability test.
[0055]
FIG. 9 is an FT-IR spectrum showing the structural change of the catalyst B-1 (103) after regeneration treatment, in which the catalyst B-1 (101) after sulfur poisoning was treated in a stoichiometric atmosphere. The treatment in the stoichiometric atmosphere was performed by flowing a standard stoichiometric composition gas (SV = 30000 / h) through the catalyst at 600 ° C. for 10 minutes. The sulphite ion and sulfate ion are decreased by the stoichiometric treatment, and the carbonate ion is increased. This result indicates that the above reactions (5) and (6) occurred in the catalyst by the stoichiometric treatment. Here, sulfite ions have a greater decrease in signal intensity than sulfate ions, indicating that sulfites are more susceptible to reductive degradation than sulfate.
[0056]
FIG. 10 is a diagram showing the generation amount of decomposition product gas when the model catalyst C-1 made of sulfite and noble metal is heated and reduced and decomposed in a hydrogen-helium stream. This result indicates that sulfite can be reductively decomposed at a low temperature of 400 ° C. or lower under appropriate conditions.
[0057]
FIG. 11 is an FT-IR spectrum showing that the ease of reductive decomposition differs between C-1 having a noble metal component and C-2 not containing a noble metal component in a model catalyst made of sulfite. In the model catalyst C-1 (104) after the regeneration treatment, sulfite is decomposed more than in the model catalyst C-2 (105) after the regeneration treatment. This result shows that the decomposition of sulfite is promoted by the coexistence of noble metal components. Therefore, in order to facilitate regeneration from sulfur poisoning, it is necessary that the noble metal component coexists in the NOx adsorbent.
[0058]
FIG. 12 is an FT-IR spectrum showing the difference in the presence state of poisoned sulfur oxides after endurance testing of the nitrogen oxide purification catalysts A-1 and B-1 used in the present invention. Compared to the catalyst B-1 (101) after sulfur poisoning, the catalyst A-1 (106) after sulfur poisoning has a weak signal indicating sulfate ions, and sulfation is suppressed in sulfur poisoning, and the main product is reduced. It was shown to be sulfite. Therefore, the catalyst A-1 is added to the catalyst B-1 by adding a component (titanium in this embodiment) that prevents the NOx adsorbent from producing sulfate by poisoning with sulfur oxides in the exhaust gas. In comparison, the sulfur compound is more easily reduced and decomposed by stoichiometric treatment after sulfur poisoning, and the activity is restored.
[0059]
Table 1 shows the effect of reducing NOx purification performance deterioration due to sulfur poisoning according to the present invention. Here, the durability treatment condition is SO in the standard lean composition gas.₂The gas (SV = 30000 / h) added with 150 ppm was introduced into the catalyst and poisoned at 300 ° C. In Regeneration 1, control was performed to perform the stoichiometric treatment at a stage before the amount of sulfate produced by the formation of sulfite in the catalyst and conversion of the sulfite reached a predetermined value. In regeneration 2, no such control was performed, and regeneration processing was performed after poisoning for a certain period of time. The stoichiometric condition was performed by flowing a standard stoichiometric composition gas (SV = 30000 / h) through the catalyst at 600 ° C. for 10 minutes. The above endurance treatment and stoichiometric regeneration processing were repeated several times, and the total duration of the endurance treatment was 10 hours, so that the reproduction 1 and the reproduction 2 were the same.
[0060]
Both the catalysts A-1 and B-1 have a reduced catalyst activity after the endurance in the regeneration 1 in which the control of the present invention is performed, compared to the regeneration 2 in which such control is not performed. It has been shown. Further, the activity of the catalyst B-1 is deteriorated in the regeneration 1 as compared with the catalyst A-1, and the catalyst used in the present invention is sulfated by the NOx adsorbing component due to sulfur poisoning like the catalyst A-1. It has been shown that ingredients that prevent the formation of are more suitable.
[0061]
[Table 1]

[0062]
【The invention's effect】
According to the present invention, it is possible to regenerate an exhaust gas purification catalyst whose NOx purification performance has deteriorated due to sulfur poisoning.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an exhaust gas purifying apparatus showing a typical embodiment of the present invention.
FIG. 2 shows an embodiment of a means for detecting a stage before sulfur sulfide is produced in a catalyst by sulfur poisoning and the amount of sulfate produced by conversion of the sulfite reaches a predetermined value set in advance. flowchart.
FIG. 3 is a flowchart of another embodiment.
FIG. 4 is a diagram showing a decrease in NOx purification performance due to sulfur poisoning.
FIG. 5 is a graph showing the relationship between the decrease in NOx purification performance and the amount of sulfite and sulfate produced.
FIG. 6 shows an embodiment of a means for detecting a stage before sulfur sulfide is generated in a catalyst due to sulfur poisoning and the amount of sulfate formed by conversion of the sulfite reaches a predetermined value set in advance. flowchart.
FIG. 7 is a diagram showing an example of air-fuel ratio fluctuation in operation using the catalyst regeneration method according to the present invention.
FIG. 8 is an FT-IR spectrum of the catalyst after the durability test.
FIG. 9 shows an FT-IR spectrum of a catalyst regenerated after the durability test.
FIG. 10 is a diagram showing thermal characteristics of reductive decomposition of sulfite.
FIG. 11 is an FT-IR spectrum showing acceleration of reductive decomposition of sulfite by a noble metal.
FIG. 12 is an FT-IR spectrum showing the difference in the amount of sulfite and sulfate produced.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Air cleaner, 2 ... Air flow sensor, 3 ... Throttle valve, 5 ... Injector, 6 ... Spark plug, 7 ... Accelerator pedal, 8 ... Load sensor, 9 ... Intake temperature sensor, 12 ... Fuel pump, 13 ... Fuel tank, DESCRIPTION OF SYMBOLS 18 ... Nitrogen oxide purification catalyst, 19 ... Oxygen concentration sensor, 20 ... Catalyst temperature sensor, 21 ... Exhaust gas temperature sensor, 22 ... NOx concentration sensor, 25 ... ECU, 26 ... Knock sensor, 28 ... Water temperature sensor, 29 ... Crank angle Sensor, 99 ... Engine, 100 ... When a predetermined time has elapsed since switching from stoichiometric operation to lean operation, 101 ... Catalyst B-1, after sulfur poisoning, 102 ... Catalyst B-1, 103 ... before sulfur poisoning ... Regeneration Catalyst B-1, 104 after treatment: Model catalyst C-1, after regeneration treatment 105, Model catalyst C-2 after regeneration treatment, 06 ... catalyst A-1 after the sulfur poisoning.

Claims (10)

A catalyst disposed in an exhaust gas flow path of an internal combustion engine and poisoned by sulfur compounds in the exhaust gas is removed by decomposing and removing the sulfur compounds on the catalyst by flowing a rich or stoichiometric gas through the flow path. A method for regenerating an exhaust gas purification catalyst for an internal combustion engine for regenerating a catalyst,
A method for regenerating an exhaust gas purification catalyst , comprising predicting a time point at which sulfite is converted to sulfate and decomposing sulfite with stoichiometric or rich gas before the predicted time point. A method for regenerating an exhaust gas purification catalyst for an internal combustion engine according to claim 1,
A method for regenerating an exhaust gas purification catalyst, characterized in that the predicted time is estimated from a sulfur concentration in fuel, fuel consumption, exhaust gas temperature and / or catalyst temperature, elapsed time, and exhaust gas atmosphere. A method for regenerating an exhaust gas purification catalyst for an internal combustion engine according to claim 1,
When the catalyst is poisoned with sulfur oxide to produce sulfite and the amount of sulfate produced by conversion of the sulfite reaches a predetermined value set in advance, rich or stoichiometric gas is introduced into the flow path. A method for regenerating an exhaust gas purification catalyst for an internal combustion engine, wherein a reducing atmosphere is created by flowing to reduce and decompose sulfite.   A catalyst disposed in an exhaust gas flow path of an internal combustion engine and poisoned by sulfur compounds in the exhaust gas is removed by decomposing and removing the sulfur compounds on the catalyst by flowing a rich or stoichiometric gas through the flow path. A method for regenerating an exhaust gas purification catalyst for an internal combustion engine that regenerates a catalyst, wherein the catalyst is poisoned with sulfur oxide to produce sulfite, and the amount of sulfate produced by converting the sulfite is preset. When a predetermined value is reached, rich or stoichiometric gas is allowed to flow through the flow path, and the sulfur oxide emission amount into the exhaust gas is estimated from the sulfur concentration and fuel consumption contained in the fuel, and the exhaust gas temperature and Estimate the amount of sulfur oxide absorbed into the catalyst, the amount of sulfite produced, and the amount converted from sulfite to sulfate from the catalyst temperature, and estimate the amount of sulfite present in the catalyst from these integrated values And the abundance is preset. Upon reaching a predetermined value, a method of reproducing an internal combustion engine exhaust gas purification catalyst which comprises reducing decomposing sulfite create a reducing atmosphere by flowing rich or Sutoikigasu the flow path.   A catalyst disposed in an exhaust gas flow path of an internal combustion engine and poisoned by sulfur compounds in the exhaust gas is removed by decomposing and removing the sulfur compounds on the catalyst by flowing a rich or stoichiometric gas through the flow path. A method for regenerating an exhaust gas purification catalyst for an internal combustion engine that regenerates a catalyst, wherein the catalyst is poisoned with sulfur oxide to produce sulfite, and the amount of sulfate produced by converting the sulfite is preset. When a predetermined value is reached, rich or stoichiometric gas is allowed to flow through the flow path, and the sulfur oxide emission amount into the exhaust gas is estimated from the sulfur concentration and fuel consumption contained in the fuel, and the exhaust gas temperature and The amount of sulfur oxide absorbed into the catalyst, the amount of sulfite produced, and the amount of sulfite converted to sulfate are estimated from the catalyst temperature, and the sulfite in the catalyst is calculated from these integrated values in an oxygen-excess atmosphere. Estimate the abundance of An exhaust gas purifying catalyst for an internal combustion engine characterized in that when the abundance reaches a predetermined value set in advance, a reducing atmosphere is created by flowing rich or stoichiometric gas through the flow path to reduce and decompose sulfite. Playback method.   A catalyst disposed in an exhaust gas flow path of an internal combustion engine and poisoned by sulfur compounds in the exhaust gas is removed by decomposing and removing the sulfur compounds on the catalyst by flowing a rich or stoichiometric gas through the flow path. A method of regenerating an exhaust gas purification catalyst for an internal combustion engine that regenerates a catalyst, wherein the catalyst is poisoned with sulfur oxide to produce sulfite, and the amount of sulfate produced by converting the sulfite is preset. When a predetermined value is reached, a rich or stoichiometric gas is allowed to flow through the flow path, and a signal from a nitrogen oxide sensor placed downstream of the exhaust gas purification catalyst in the exhaust gas flow path is used to start operation under a reducing atmosphere. Detecting the nitrogen oxide concentration in the exhaust gas after a predetermined time after switching to operation in an oxygen-excess atmosphere, estimating the rate of decrease in the purification performance of nitrogen oxide from the nitrogen oxide concentration, and estimating in the catalyst Of sulfite Regeneration of an exhaust gas purification catalyst for an internal combustion engine characterized in that when a quantity reaches a predetermined value set in advance, a reducing atmosphere is created by flowing rich or stoichiometric gas through the flow path to reduce and decompose sulfite. Method.   7. The reducing atmosphere created in any one of claims 4 to 6 for reducing and decomposing sulfite produced in a catalyst by poisoning with sulfur oxide is not less than 0.2 seconds and not more than 10 minutes. A method for regenerating an exhaust gas purification catalyst for an internal combustion engine.   8. The internal combustion engine according to claim 1, wherein the catalyst includes at least one of an alkali metal or an alkaline earth metal and a noble metal selected from at least one of platinum, rhodium, and palladium. Method for exhaust gas purification catalyst.   8. The catalyst according to claim 1, wherein a component that chemisorbs nitrogen oxides and a component that chemisorbs noble metals and nitrogen oxides are poisoned by sulfur oxides in exhaust gas to generate sulfate. A method for regenerating an exhaust gas purification catalyst for an internal combustion engine, comprising:   10. The catalyst according to claim 9, wherein the catalyst contains at least one or more of alkali metal or alkaline earth metal as a component that chemisorbs nitrogen oxide, and contains at least one or more of platinum, rhodium, and palladium as noble metals. It is characterized by containing at least one or more of titanium, zirconium, vanadium, niobium, chromium, molybdenum, and tungsten as a component that suppresses adsorbed components from being poisoned by sulfur oxides in the exhaust gas to produce sulfate. A method for regenerating an exhaust gas purification catalyst for an internal combustion engine.

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