SE537367C2

SE537367C2 - Catalyst for the treatment of exhaust gases and an exhaust system comprising such a catalyst

Info

Publication number: SE537367C2
Application number: SE1251420A
Authority: SE
Inventors: Björn Westerberg
Original assignee: Scania Cv Ab
Priority date: 2012-12-14
Filing date: 2012-12-14
Publication date: 2015-04-14
Also published as: EP2932057A1; EP2932057A4; CN104919152A; SE1251420A1; WO2014092638A1

Abstract

Sammandrag FOreliggande uppfinning avser en katalysator for behandling av avgaser fran en forbranningsmotor (1). Katalysatorn (5) innefattar vaggelement (5b) som formar ett flertal langstrackta kanaler (5a) hos katalysatom for mottagning av avgaser, varvid vaggelementen (5b) innefattar ett forsta yttre skikt (5bi) som tillhandahaller en utvandig yta i de langstrackta kanalerna (5a) och ett andra inre skikt (5b2) som anordnat invandigt om det forsta skiktet (5b1), varvid det forsta skiktet (5bi) innefattar ett forsta aktivt katalysatormaterial som framjar en katalytisk reaktion mellan kvaveoxid och ammoniak, och varvid det andra skiktet (5b2) innefattar ett material som har formaga att lagra kvaveoxid och ett andra aktivt katalysatormaterial som har en hOgre fOrmaga att framja oxidation av kvavemonoxid till kvavedioxid an det fersta katalysatormaterialet. Det andra skiktet (5b2) innefattar ett kvaveoxidlagrande material som bestar av en oxid av en alkalisk jordartsmetall eller en kombination av Adana oxider. Summary The present invention relates to a catalyst for treating exhaust gases from an internal combustion engine (1). The catalyst (5) comprises cradle elements (5b) forming a plurality of elongate channels (5a) of the exhaust gas receiving catalyst, the cradle elements (5b) comprising a first outer layer (5bi) providing an outer surface of the elongate channels (5a) and a second inner layer (5b2) disposed internally about the first layer (5b1), the first layer (5bi) comprising a first active catalyst material which promotes a catalytic reaction between nitrogen oxide and ammonia, and wherein the second layer (5b2) comprises a material capable of storing nitrogen oxide and a second active catalyst material having a higher capacity to promote oxidation of nitrogen monoxide to nitrogen dioxide than the first catalyst material. The second layer (5b2) comprises a nitrogen oxide storage material consisting of an oxide of an alkaline earth metal or a combination of Adana oxides.

Description

Katalysator for behandling av avgaser och ett avgassystem som innefattar en sadan katalysator UPPFINNINGENS BAKGRUND OCH KAND TEKNIK Foreliggande uppfinning avser en katalysator for behandling av avgaser enligt patentkravets 1 ingress och ett avgassystem som innefattar en sadan katalysator. BACKGROUND OF THE INVENTION AND PRIOR ART The present invention relates to a catalyst for the treatment of exhaust gases according to the preamble of claim 1 and an exhaust system comprising such a catalyst.

For att reducera utslappen av kvdveoxid NOx fran forbranningsmotorer anvands bl.a. en teknik som bendmns SCR (Selective Catalytic Reduction). Denna teknik innebar att en lOsning av urea tillfors i en bestamd dos till avgasema i en avgasledning. Urealosningen kan sprayas in i avgasledningen varefter den finfordelade urealosningen forangas i kontakt med de heta avgasema sâ att ammoniak bildas. Blandningen av ammoniak och avgaser leds darefter genom en SCR-katalysator. Kvavet hos kvdveoxiden i avgasema reagerar hdr med kvavet i ammoniaken sà att kvavgas bildas. Syret hos kvaveoxiden reagerar med vatet i ammoniaken sâ att vatten bildas. KvWeoxiden i avgasema reduceras saledes i katalysatom till kvavgas och vattenanga. In order to reduce the emissions of nitrogen oxide NOx from internal combustion engines, e.g. a technique called bendmns SCR (Selective Catalytic Reduction). This technique meant that a solution of urea was supplied at a certain dose to the exhaust gases in an exhaust line. The urea solution can be sprayed into the exhaust line, after which the finely divided urea solution is evaporated in contact with the hot exhaust gases so that ammonia is formed. The mixture of ammonia and exhaust gases is then passed through an SCR catalyst. The nitrogen of the nitrogen oxide in the exhaust gases reacts with the nitrogen in the ammonia so that nitrogen gas is formed. The oxygen of the nitrogen oxide reacts with the water in the ammonia to form water. The nitrogen oxide in the exhaust gases is thus reduced in the catalyst to nitrogen gas and water vapor.

Med en korrekt dosering av urea kan forbrdnningsmotoms utslapp av kvWeoxid i en stor utstrackning reduceras. With the correct dosage of urea, the emissions of carbon dioxide from the internal combustion engine can be greatly reduced.

En konventionell SCR- katalysators formaga att avlagsna kvaveoxid är relaterad till avgasemas temperatur. Den optimala temperaturen är beroende av vilken typ av aktivt katalysatormaterial som anviinds i SCR-katalysatom. Konventionella SCR- katalysatorers for-maga att avlagsna kvWeoxid frau avgaser är framfor alit ett problem vid lâga temperaturer. Kvaveoxid NOx i avgaser bestar av kvavemonoxid NO och kvavedioxid NO/. Konventionella SCR-katalysatorers formaga att avldgsna kvaveoxid fran avgaser är Wen beroende av forhallandet mellan kvavemonoxid NO och kvavedioxid NO/. En SCR-katalysators formaga att reducera mangden kvdveoxid i avgaser är optimal dâ avgasema innehaller lika mycket kvavemonoxid och 1 kvavedioxid. Avgaser fran i synnerhet dieselmotorer innehaller vanligtvis en betydligt mindre andel kvavedioxid an kvavemonoxid. Aven avgasflodet genom SCRkatalysatom är en faktor som paverkar SCR-katalysatoms kapacitet. The design of a conventional SCR catalyst is that nitrogen oxide precipitation is related to the temperature of the exhaust gases. The optimum temperature depends on the type of active catalyst material used in the SCR catalyst. The ability of conventional SCR catalysts to emit carbon dioxide from exhaust gases is above all a problem at low temperatures. Nitric oxide NOx in exhaust gases consists of nitrogen monoxide NO and nitrogen dioxide NO /. The ability of conventional SCR catalysts to emit nitrogen oxide from exhaust gases is Wen dependent on the ratio of nitrogen monoxide NO to nitrogen dioxide NO /. The ability of an SCR catalyst to reduce the amount of nitrogen oxide in exhaust gases is optimal as the exhaust gases contain the same amount of nitrogen monoxide and 1 nitrogen dioxide. Exhaust gases from diesel engines in particular usually contain a much smaller proportion of nitrogen dioxide than nitrogen monoxide. The exhaust flow through the SCR catalyst is also a factor that affects the capacity of the SCR catalyst.

For att Oka andelen kvavedioxid i avgasema som leds till en SCR-katalysator är det kant att anordna en oxidationskatalysator DOC (Diesel Oxidation Catalyst) i avgasledningen uppstroms SCR-katalysatom. En oxidationskatalysator oxiderar kvavemonoxid NO till kvavedioxid NO2. Darmed kan andelen kvavedioxid NO2 i avgasema hojas. En oxidationskatalysators formaga att oxidera kvavemonoxid NO till kvavedioxid NO2 varierar emellertid med avgasemas temperatur och flode. Darmed kan en oxidationskatalysator inte alltid leverera den onskade fordelningen mellan kvavemonoxid och kvavedioxid. En oxidationskatalysator skapar aven mottryck i avgasledningen. In order to increase the proportion of nitrogen dioxide in the exhaust gases which is led to an SCR catalyst, it is advisable to arrange an oxidation catalyst DOC (Diesel Oxidation Catalyst) in the exhaust line upstream of the SCR catalyst. An oxidation catalyst oxidizes nitrogen monoxide NO to nitrogen dioxide NO2. Thus, the proportion of nitrogen dioxide NO2 in the exhaust gases can be increased. However, the shape of an oxidation catalyst to oxidize nitrogen monoxide NO to nitrogen dioxide NO2 varies with the temperature and flow of the exhaust gases. Thus, an oxidation catalyst can not always deliver the desired distribution between nitrogen monoxide and nitrogen dioxide. An oxidation catalyst also creates back pressure in the exhaust line.

En SCR-katalysator ackumulerar i regel ammoniak som sedan reagerar med kvaveoxiden i avgasema. Vid laga temperaturer ackumuleras mer ammoniak i SCRkatalysatom an vid hoga temperaturer. Det innebar att ackumulerad ammoniak, vid snabba temperaturokningar hos avgaserna, kan frigOras och ledas ut fran SCRkatalysatom. For att eliminera sadana utslapp av ammoniaken kan en ammoniakslipkatalysator anordnas nedstroms SCR-katalysatom i avgasledningen. En ammoniakslipkatalysator innefattar i regel en belaggning av en adelmetall sasom platina som oxiderar ammoniak till kvavgas, kvaveoxid och lustgas. Lustgas är en stark vaxthusgas. En ammoniakslipkatalysator skapar aven ett mottryck i avgasledningen. An SCR catalyst usually accumulates ammonia which then reacts with the nitrogen oxide in the exhaust gases. At low temperatures more ammonia accumulates in the SCR catalyst than at high temperatures. This meant that accumulated ammonia, at rapid temperature rises in the exhaust gases, could be released and discharged from the SCR catalyst. To eliminate such ammonia emissions, an ammonia grinding catalyst can be provided downstream of the SCR catalyst in the exhaust line. An ammonia abrasive catalyst usually comprises a coating of a noble metal such as platinum which oxidizes ammonia to nitrogen gas, nitrogen oxide and nitrous oxide. Nitrous oxide is a strong greenhouse gas. An ammonia grinding catalyst also creates a back pressure in the exhaust line.

I ett konventionellt avgassystem med en oxidationskatalysator DOC, ett partikelfilter DPF, en SCR-katalysator och en ammoniakslipkatalysator ASC tar det en relativt Lang tid efter en kallstart innan en temperatur uppnas vid vilken urealosningen kan borja tillsattas. Under denna uppvarmningsperiod sker ingen eliminering av kvaveoxid fran avgasema. In a conventional exhaust system with an oxidation catalyst DOC, a particulate filter DPF, an SCR catalyst and an ammonia abrasive catalyst ASC, it takes a relatively long time after a cold start before a temperature is reached at which the urea solution can begin to be added. During this heating period, no nitrogen oxide is eliminated from the exhaust gases.

US 7,431,895 visar ett avgassystem som innefattar en SCR-katalysator med aktiva katalysatormaterial som är anordnade i tva. skikt. En SCR-komponent kan vara anordnad i ett yttre skikt och en kvaveoxidlagrande komponent kan vara anordnad i ett inre skikt. Med hjalp av den kvaveoxidlagrande komponenten kan kvaveoxid lagras temporart i SCR-katalysatorn dâ avgaserna har en lag temperatur och frigoras dâ 2 avgaserna erhaller en hogre temperatur. En forutsattning for att denna SCR-katalysator ska fungera val är dock forekomsten av en oxidationskatalysator som forser SCRkatalysatorn med kvaveoxid med vasentligen lika stora andelar av kvavemonoxid och kvavedioxid. Om det Over tiden genomsnittligt fader ett overskott av kvavedioxid, kommer lagringsformagan inte att utnyttjas effektivt, eftersom den i regel kommer att vara fylld och inte ha formagan att lagra ytterligare. US 7,431,895 discloses an exhaust system comprising an SCR catalyst with active catalyst materials arranged in two. layer. An SCR component may be arranged in an outer layer and a nitric oxide storage component may be arranged in an inner layer. With the aid of the nitrogen oxide storage component, nitrogen oxide can be stored temporarily in the SCR catalyst when the exhaust gases have a low temperature and are released when the 2 exhaust gases reach a higher temperature. A prerequisite for this SCR catalyst to function, however, is the presence of an oxidation catalyst which supplies the SCR catalyst with nitrogen oxide with substantially equal proportions of nitrogen monoxide and nitrogen dioxide. If it over time fathers an excess of nitrogen dioxide on average, the storage form will not be used efficiently, as it will usually be filled and not have the form to store further.

SAMMANFATTNING AV UPPFINNINGEN Det framsta syftet med foreliggande uppfinning är att tillhandahalla en katalysator som har kapacitet att lagra kvaveoxider reducera utslappen av kvaveoxid vid kallstarter. Andra syften är att tillhandahalla en god eliminering av kvaveoxid yid vasentligen alla driftstemperaturer samt att vasentligen forhindra utslapp av ammoniak, s.k. ammoniaks lip. SUMMARY OF THE INVENTION The primary object of the present invention is to provide a catalyst having the capacity to store nitrogen oxides to reduce nitrogen oxide emissions during cold starts. Other objects are to provide a good elimination of nitrogen oxide yid substantially all operating temperatures and to substantially prevent the emission of ammonia, so-called ammonia lip.

Dessa syften uppnas med katalysatorn av det inledningsvis namnda slaget, vilket kannetecknas av de sardrag som anges i patentkravets 1 kannetecknande del. Insprutningen av ett reduktionsmedel startar forst efter att en viss temperatur uppnatts i avgassystemet. Vid kallstarter strommar saledes avgasema inledningsvis genom katalysatorn utan flagon tillsats av ammoniak. Det andra inre skiktet innefattar saledes ett kvaveoxidlagrande material och ett katalysatormaterial som har en god formaga att oxidera kvavemonoxid till kvayedioxid. En sa.dan katalysator kan anvandas som en ammoniakslipkatalysator (ASC) i ett system med en uppstroms placerad oxidationskatalysator, ett efterfOljande partikelfilter och SCR-katalysator. Vid kallstart varms forst oxidationskatalysatorn upp varpa den borjar producera kvavedioxid. I detta skede är fortfarande partikelfiltret, SCR-katalysatorn och ammoniakslipkatalysatorn kalla. Kviivedioxid lagras da in i det kviiveoxidlagrande materialet. När partikelfiltret blivit varmt och SCR-katalysatorn borjat bli varm kan urea borja doseras och kvaveoxiderna kan borja reduceras. Nar varmen nar ammoniakslipkatalysatorn kan inlagrad kviiveoxid reduceras. Denna katalysator kan Liven anyandas som SCR- katalysator i motsvarande system. I detta fall uppnas en stone kapacitet att lagra kvaveoxider vid kallstart. Med en sadan kvaveoxidlagrande funktion kan utslappen av kvaveoxid reduceras under en kallstart innan en temperatur uppn'atts vid vilken det är mojligt att tillfora ett reduktionsmedel. 3 Sâ snart en lagsta erforderlig driftstemperatur uppnatts sà startar insprutningen av reduktionsmedlet sâ att ammoniak bildas i avgaserna. Reduktionsmedlet är med fordel en urealosning. Avgaser och ammoniaken som nar katalysatorn kommer inledningsvis i kontakt med det yttre forsta skiktet. Ammoniaken diffunderar in i det forsta skiktet och adsorberas pa s.k. aktiva saten. Kvaveoxiden i avgaserna diffunderar Wen in i det forsta skiktet dar den reagerar med ammoniak pa namnda aktiva saten sa att vatten och kvavgas bildas. Koncentrationen av ammoniak och kvaveoxid avtar med avstandet fran det fcirsta skiktets yta. Koncentrationen av ammoniak avtar dock snabbare med avstandet fran ytan an koncentrationen av kvWeoxid eftersom ammoniaken adsorberas pa namnda saten medan kvaveoxiden kan diffundera vasentligen fritt i det ffirsta skiktet sâ lange som den inte reagerar med ammoniak. En del av kvaveoxiden tranger Wen in i det andra skiktet. These objects are achieved with the catalyst of the kind mentioned in the introduction, which can be characterized by the features stated in the characterizing part of claim 1. The injection of a reducing agent only starts after a certain temperature has been reached in the exhaust system. Thus, in cold starts, the exhaust gases initially flow through the catalyst without flaking addition of ammonia. The second inner layer thus comprises a nitrogen oxide-storing material and a catalyst material which has a good ability to oxidize nitrogen monoxide to nitrogen dioxide. Such a catalyst can be used as an ammonia abrasive catalyst (ASC) in a system with an upstream oxidation catalyst, a subsequent particulate filter and SCR catalyst. At a cold start, the oxidation catalyst first warms up and begins to produce nitrogen dioxide. At this stage, the particulate filter, SCR catalyst and ammonia abrasive catalyst are still cold. Nitrogen dioxide is then stored in the nitrogen oxide storage material. When the particle filter has become hot and the SCR catalyst has started to get hot, urea can start to be dosed and the nitrogen oxides can start to be reduced. When the heat reaches the ammonia abrasive catalyst, the stored nitrogen oxide can be reduced. This catalyst can be Liven anyandas as SCR catalyst in the corresponding system. In this case, a stone capacity is achieved to store nitrogen oxides at cold start. With such a nitrogen oxide storage function, the emissions of nitrogen oxide can be reduced during a cold start before a temperature is reached at which it is possible to supply a reducing agent. 3 As soon as a minimum required operating temperature has been reached, the injection of the reducing agent starts so that ammonia is formed in the exhaust gases. The reducing agent is advantageously a urea solution. Exhaust gases and the ammonia reaching the catalyst initially come into contact with the outer first layer. The ammonia diffuses into the first layer and is adsorbed on so-called active saten. The nitrogen oxide in the exhaust gases diffuses Wen into the first layer where it reacts with ammonia on the said active compound so that water and nitrogen gas are formed. The concentration of ammonia and nitrogen oxide decreases with distance from the surface of the first layer. However, the concentration of ammonia decreases more rapidly with the distance from the surface than the concentration of nitric oxide because the ammonia is adsorbed in the said way while the nitrogen oxide can diffuse substantially freely in the first layer as long as it does not react with ammonia. Some of the nitrogen oxide penetrates Wen into the second layer.

Vid driftstillfallen da ammoniak tillsatts i avgaserna vid en relativt lag temperatur är kvaveoxidens och ammoniakens benagenhet att reagera lag. Kvaveoxiden i det ffirsta skiktet reagerar damned i betydligt mindre utstrackning med ammoniak som adsorberats pa namnda saten. Relativt mycket kvaveoxid diffunderar darmed in i det andra skiktet dar en del av kvavemonoxiden oxideras till kvavedioxid av det aktiva katalysatormaterial som framjar oxidation av kvavemonoxid till kvavedioxid i det andra skiktet. Kvavedioxiden i det andra skiktet diffunderar tillbaka till det forsta skiktet vilket resulterar i ett kraftigt okat antal reaktioner mellan ammoniak och kvaveoxid pa ett relativt stort djup i det forsta skiktet. Vid tillfallen da avgaserna har en lag temperatur bidrar det andra skiktet till aft Oka katalysatorns formaga markant och att eliminera kvaveoxid fran avgaserna. Da avgaserna har en lag temperatur är detta mycket onskvart och det resulterar i att katalysatorn kan ha en hog kapacitet att eliminera kvaveoxid Wen vid laga driftstemperaturer. In the case of operation when ammonia is added to the exhaust gases at a relatively low temperature, the tendency of nitrogen oxide and ammonia to react is low. The nitrogen oxide in the first layer reacts with the dam to a much lesser extent with ammonia adsorbed on the said seed. Relatively much nitrogen oxide thus diffuses into the second layer where a part of the nitrogen monoxide is oxidized to nitrogen dioxide by the active catalyst material which promotes oxidation of nitrogen monoxide to nitrogen dioxide in the second layer. The nitrogen dioxide in the second layer diffuses back to the first layer, which results in a greatly increased number of reactions between ammonia and nitrogen oxide at a relatively large depth in the first layer. In cases where the exhaust gases have a low temperature, the second layer contributes significantly to shaping the catalyst and eliminating nitrogen oxide from the exhaust gases. As the exhaust gases have a low temperature, this is very unfavorable and it results in the catalyst having a high capacity to eliminate nitric oxide Wen at low operating temperatures.

Vid driftstillfallen da reduktionsmedlet sprutas in avgaserna och det raider en hog temperatur är kvaveoxidens och ammoniakens benagenhet att reagera hog. In operational cases when the reducing agent is injected into the exhaust gases and it raids a high temperature, the tendency of nitrogen oxide and ammonia to react is high.

Kvaveoxiden som diffunderar in i det ffirsta skiktet reagerar &armed niistan omedelbart med den ammoniak som adsorberats i det forsta skiktet. Reaktionerna sker har huvudsakligen nara det forsta skiktets yta. Endast en mindre del av kvaveoxiden nar det andra skiktet. Det andra skiktet mottar i detta fall endast en relativt liten mangd kvaveoxid. I detta fall bidrar forekomsten av det andra skiktet endast i en utstrackning till att Oka katalysatorns formaga aft eliminera kvaveoxid fran avgaserna. The nitrogen oxide which diffuses into the first layer reacts immediately with the ammonia adsorbed in the first layer. The reactions take place mainly near the surface of the first layer. Only a small part of the nitrogen oxide reaches the second layer. The second layer in this case receives only a relatively small amount of nitric oxide. In this case, the presence of the second layer contributes only to an extent to the Oka catalyst's ability to eliminate nitrogen oxide from the exhaust gases.

Eftersom en katalysator normalt redan har en hog kapacitet att eliminera kvaveoxid ur 4 avgaserna vid en hog temperatur är detta inte nodvandigt. Katalysatorn har saledes en god kapacitet att eliminera kvaveoxid fran avgaserna vid bade laga och hoga avgastemperaturer. Since a catalyst normally already has a high capacity to eliminate nitric oxide from the 4 exhaust gases at a high temperature, this is not necessary. The catalyst thus has a good capacity to eliminate nitrogen oxide from the exhaust gases at both low and high exhaust gas temperatures.

Vid driftstillfallen da ett reduktionsmedel sprutas in och det rader en lag temperatur i katalysatorn kan relativt stora mangder ammoniak lagras i det fOrsta skiktet. Eftersom katalysatorn innefattar ett andra skikt med ett kvaveoxidlagrande material och ett katalysatormaterial som har formagan att framja oxidation av kvavemonoxid till kvavedioxid kan det andra skiktet samtidigt innehalla en stor mangd lagrad kvavedioxid. Vid driftstillfallen som avgasernas temperatur hastigt hojs, pa grund av ett motorpadrag, minskar katalysatorns formaga aft adsorbera ammoniak. Ackumulerad ammoniak kommer darmed att frigOras fran satena i det forsta skiktet. En del av den frigjorda ammoniaken diffunderar i riktning mot det andra skiktet dar den reagerar med den lagrade kvaveoxiden som har en hog andel kvavedioxid. Det innebar att en vasentlig del av den temporart frigjorda ammoniaken kan elimineras och clamed utslappet av ammoniak nedstroms katalysatorn. Att forhindra ammoniakslip med hjalp av lagrad kvaveoxid har fordelen att ammoniak elimineras utan att lustgas skapas. In the case of operation when a reducing agent is injected and it radiates a low temperature in the catalyst, relatively large amounts of ammonia can be stored in the first layer. Since the catalyst comprises a second layer with a nitrogen oxide storage material and a catalyst material having the ability to promote oxidation of nitrogen monoxide to nitrogen dioxide, the second layer may simultaneously contain a large amount of stored nitrogen dioxide. In operating cases where the temperature of the exhaust gases rises rapidly, due to an engine path, the ability of the catalyst to adsorb ammonia decreases. Accumulated ammonia will thus be released from the satin in the first layer. Some of the released ammonia diffuses towards the other layer where it reacts with the stored nitrogen oxide which has a high proportion of nitrogen dioxide. This meant that a substantial portion of the temporarily released ammonia could be eliminated and the ammonia emission downstream of the catalyst clambered. Preventing ammonia grinding with the help of stored nitric oxide has the advantage that ammonia is eliminated without creating nitrous oxide.

Enligt en foredragen utforingsform av uppfinningen innefattar det andra skiktet en adelmetall. Adelmetaller har i regel en god formaga att fungera som katalysator vid oxidering av kvavemonoxid till kvavedioxid. Det andra skiktet innefattar med fordel platina. Platina är en mycket god katalysator for detta andamal Andra alternativa adelmetaller är palladium och rodium. De har dock an klart samre formaga att oxidera kvaveoxid an platina. Adelmetaller anvands i konventionella ammoniakslipkatalysatorer for att oxidera ammoniak till kvavgas, lustgas och kviivemonoxid. I de fall da den lagrade kviiveoxid inte racker till for att eliminera ett temporart overskott pa ammoniak kan adelmetallen hjalpa till med detta. According to a preferred embodiment of the invention, the second layer comprises a noble metal. Noble metals generally have a good ability to act as a catalyst in the oxidation of nitrogen monoxide to nitrogen dioxide. The second layer advantageously comprises platinum. Platinum is a very good catalyst for this andamal Other alternative precious metals are palladium and rhodium. However, they have a much better ability to oxidize nitric oxide than platinum. Noble metals are used in conventional ammonia abrasive catalysts to oxidize ammonia to nitrogen gas, nitrous oxide and nitrogen monoxide. In cases where the stored nitrogen oxide is not sufficient to eliminate a temporary excess of ammonia, the noble metal can help with this.

Enligt en foredragen utforingsform av uppfinningen innefattar det andra skiktet ett kvaveoxidlagrande material som bestar av en eller en kombination av oxider av alkaliska jordartsmetaller. Oxider av alkaliska jordartsmetaller har i regel en mycket god formaga att lagra kvaveoxid. Lampliga sidana oxider är magnesiumoxid MgO, Kalciumoxid CaO, Strontiumoxid Sr0 och Barium Oxid BaO. According to a preferred embodiment of the invention, the second layer comprises a nitrogen oxide storage material consisting of one or a combination of oxides of alkaline earth metals. Oxides of alkaline earth metals generally have a very good ability to store nitrogen oxide. Suitable side oxides are Magnesium Oxide MgO, Calcium Oxide CaO, Strontium Oxide SrO and Barium Oxide BaO.

Enligt en utforingsform av uppfinningen innefattar det forsta skiktet ett aktivt katalysatormaterial som framjar den katalytiska reaktionen mellan ammoniak och kvaveoxid. Det forsta aktiva katalysatormaterialet bor aven ha fOrmagan att ackumulera ammoniak. Det forsta katalysatormaterialet innefattar med fordel Vanadinpentoxid V205. Vanadinpentoxid har till skillnad fran andra katalysatormaterial, sasom zeoliter, en relativt god formaga att framja den katalytiska reaktionen mellan ammoniak och kvaveoxid vid relativt laga temperaturer och dâ det rader ett underskott pa kvavedioxid. SCR-katalysatorer baserad jarn-zeolit har samre prestanda an en vanadinbaserad SCR-katalysator vid laga temperaturer. SCR- katalysatorer baserad pa koppar-zeolit har samre selektivitet an vanadinbaserad SCR- katalysatorer vid hoga temperaturer, da den i mycket hogre utstrackning oxiderar ammoniak. Bada typerna av zeloitkatalysator producerar mer lustgas, och i synnerhet den koppar-zeolitbaserade, an en vanadinbaserad SCR-katalysator. Det forsta aktiva katalysatormaterialet innefattar med fordel alien volframoxid. Darmed erhaller det forsta katalysatormaterialet ytterligare fOrbattrade egenskaper att katalysera reaktionen mellan ammoniak och kvaveoxid i det forsta skiktet. According to one embodiment of the invention, the first layer comprises an active catalyst material which promotes the catalytic reaction between ammonia and nitrogen oxide. The first active catalyst material should also have the capacity to accumulate ammonia. The first catalyst material advantageously comprises Vanadium pentoxide V205. Unlike other catalyst materials, such as zeolites, vanadium pentoxide has a relatively good ability to promote the catalytic reaction between ammonia and nitrous oxide at relatively low temperatures and then there is a deficit of nitrogen dioxide. Iron-zeolite-based SCR catalysts have a better performance than a vanadium-based SCR catalyst at low temperatures. SCR catalysts based on copper zeolite have a lower selectivity than vanadium-based SCR catalysts at high temperatures, as it oxidises ammonia to a much greater extent. Both types of zelite catalyst produce more nitrous oxide, and in particular the copper-zeolite-based, vanadium-based SCR catalyst. The first active catalyst material advantageously comprises alien tungsten oxide. Thereby, the first catalyst material acquires further improved properties to catalyze the reaction between ammonia and nitrous oxide in the first layer.

Enligt en utforingsform av uppfinningen är namnda vaggelement formade av en barande kropp som bar upp de tva skikten. I regel är de tva skikten inte sjalva kapabla att forma katalysatoms struktur. En sadan barande kropp bestar med fordel av en monolitstruktur som formar ett stort antal langsgaende parallella kanaler i en sammanhallen struktur. Den barande kroppen kan bestâ av ett keramiskt material som kan vara kordierit (en blandoxid av magnesium, kisel och aluminium) eller av en metall. Altemativt sâ kan den barande kroppen innefattar atminstone ett av de tva skikten. Det kan ske genom att den barande kroppen är extruderad av det aktiva materialet i nagot av skikten eller att det aktiva materialet applicerats pa en korrugerad hoprullad glasfiberyily och ett bindemedel. According to an embodiment of the invention, said cradle elements are formed by a supporting body which carried the two layers. As a rule, the two layers themselves are not capable of shaping the structure of the catalyst. Such a bearing body advantageously consists of a monolith structure which forms a large number of longitudinal parallel channels in a cohesive structure. The bearing body may consist of a ceramic material which may be cordierite (a mixed oxide of magnesium, silicon and aluminum) or of a metal. Alternatively, the bearing body may comprise at least one of the two layers. This can be done by the bearing body being extruded from the active material in some of the layers or by the active material being applied to a corrugated rolled fiberglass and a binder.

Enligt en utforingsform av uppfinningen innefattar det andra skiktet ett barmaterial i form av aluminiumoxid. Aluminiumoxid har Liven en viss fOrmaga att lagra kvaveoxid. According to an embodiment of the invention, the second layer comprises a bare material in the form of alumina. Aluminum oxide, Liven has a certain ability to store nitrogen oxide.

De forsta och andra skikten innefattar forutom en eller flera aktiva material aven ett porost barmaterial. Syftet med barmaterialet ar att tillhandahalla en stor total kontaktyta mellan det forsta skiktet och avgasema. F6r ett normalt barmaterial ar kontaktytan i storleksordningen 100 m2/g. Det aktiva materialet ar utspritt som ett tunt lager eller som manga sma partiklar i barmaterialets porer. Barmaterialet i det forsta skiktet kan utgoras av titandioxid eller anatas. 6 Enligt en annan utforingsform av uppfinningen är det forsta skiktet är dimensionerat sa att det har kapacitet att mottaga all ammoniak under normal drift sâ att ammoniak endast tranger in i det andra skiktet vid driftstillfallen da det uppstar ett temporart overskott pa ammoniak. I detta fall kommer alla reaktioner mellan ammoniak och kvaveoxid att ske i det forsta skiktet under normal drift. Da ett Overskott av ammoniak uppkommer, vid exempelvis en hastig hajning av avgasernas temperatur, kan frigjord ammoniak reagera med lagrad kvaveoxid. Frigjord ammoniak kan Wen oxideras i det andra skiktet av det andra aktiva katalysatormaterialet da det bestar av en adelmetall. The first and second layers comprise, in addition to one or more active materials, also a porous bar material. The purpose of the bare material is to provide a large total contact area between the first layer and the exhaust gases. For a normal bare material, the contact surface is in the order of 100 m2 / g. The active material is spread as a thin layer or as many small particles in the pores of the bare material. The bare material in the first layer may be titanium dioxide or anatase. According to another embodiment of the invention, the first layer is dimensioned so that it has the capacity to receive all ammonia during normal operation so that ammonia only penetrates into the second layer during operating cases when a temporary excess of ammonia arises. In this case, all reactions between ammonia and nitric oxide will take place in the first layer during normal operation. When an excess of ammonia arises, for example at a rapid rise in the temperature of the exhaust gases, liberated ammonia can react with stored nitrogen oxide. Released ammonia, Wen can be oxidized in the second layer of the second active catalyst material as it consists of a noble metal.

Katalysatorn kan utgora en SCR-katalysator i ett avgassystem. Materialet i det forsta skiktet sakerstaller att katalysatorn har en motsvarande funktion som en konventionell SCR-katalysator. Materialet i det andra skiktet som framjar oxidationen av kvavemonoxid till kvavedioxid gör att katalysatorns behov av en uppstroms anordnad oxidationskatalysator elimineras eller atminstone reduceras. Materialet i det andra skiktet som framjar lagring av kvaveoxid resulterar Wen i att katalysatorn erhaller en mycket god formaga att reducera temporara overskott av ammoniak. Darmed elimineras eller atminstone reduceras behovet av en nedstroms anordnad ammoniakslipkatalysator. The catalyst may be an SCR catalyst in an exhaust system. The material in the first layer ensures that the catalyst has a corresponding function as a conventional SCR catalyst. The material in the second layer which promotes the oxidation of nitrogen monoxide to nitrogen dioxide eliminates or at least reduces the catalyst's need for an upstream oxidation catalyst. The material in the second layer which promotes the storage of nitric oxide results in Wen obtaining a very good catalyst to reduce temporary excess ammonia. This eliminates or at least reduces the need for a downstream ammonia abrasive catalyst.

Enligt en annan utfOringsform utgor katalysatorn en ammoniakslipkatalysator. I och med att katalysatorn har sâ goda egenskaper att eliminera temporara overskott av ammoniak kan den anvandas som en ammoniakslipkatalysator och placeras nedstroms en konventionell SCR-katalysator. Katalysatorn har fordelen i forhallande till en konventionell ammoniakslipkatalysator att den kan utnyttja lagrad kvaveoxid for att eliminera ett temporart overskott pa ammoniak utan att bilda lustgas. According to another embodiment, the catalyst is an ammonia abrasive catalyst. Because the catalyst has such good properties to eliminate temporary excess ammonia, it can be used as an ammonia abrasive catalyst and placed downstream of a conventional SCR catalyst. The catalyst has the advantage in relation to a conventional ammonia abrasive catalyst that it can use stored nitrogen oxide to eliminate a temporary excess of ammonia without forming nitrous oxide.

KORT BESKRIVNING AV RITNINGARNA I det foljande beskrivs, sasom exempel, fOredragna utforingsformer av uppfinningen med hanvisning till bifogade ritningar, pa vilka: Fig. 1visar en del av en avgasledning som innefattar en katalysator enligt foreliggande uppfinningen i form av en SCR-katalysator, Fig. 2visar en langsgaende tvarsnittsvy av en del av katalysatorn i Fig. 1 och, 7 Fig. 3visar en del av en avgasledning som innefattar en katalysator enligt fcireliggande uppfinningen i form av en ammoniakslipkatalysator. BRIEF DESCRIPTION OF THE DRAWINGS In the following, by way of example, preferred embodiments of the invention are described with reference to the accompanying drawings, in which: Fig. 1 shows a portion of an exhaust line comprising a catalyst of the present invention in the form of an SCR catalyst; Fig. 2 shows a longitudinal cross-sectional view of a part of the catalyst in Fig. 1 and.

DETALJERAD BESKRIVNING AV FOREDRAGNA UTFORINGSFORMER AV 5 UPPFINNINGEN Fig. 1 visar en forbranningsmotor i form av en dies elmotor 1. Dieselmotorn 1 kan vara avsedd som drivmotor for ett tyngre fordon. Dieselmotorn 1 är forsedd med en avgasledning 2 som innehaller en behallare 3 for avgasbehandlande komponenter. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Fig. 1 shows an internal combustion engine in the form of a diesel electric motor 1. The diesel engine 1 may be intended as a drive motor for a heavier vehicle. The diesel engine 1 is provided with an exhaust line 2 which contains a container 3 for exhaust gas treatment components.

Behallaren 3 kan vara en ljuddampare. Behallaren 3 innehaller i detta fall en forsta avgasbehandlande komponenter i form av ett partikelfilter 4 som kan benamnas DPF (Diesel Particulate Filter). Ett partikelfilter 4 innefattar langstrackta parallella kanaler med stoppytor anordnade pa lampliga stallen. Stoppytorna tvingar avgaserna att ledas in i angransande langstrackta kanaler i partikelfiltret 4. Kanalernas vaggar är 1tillverkade av ett porost material med fina kanaler som tinker passage av avgaser men inte av sotpartiklar. Sotpartiklarna fastnar darvid inuti partikelfiltret 4. Partikelfiltret 4 regenereras kontinuerligt utan aktiva atgarder genom att sotpartiklarna oxideras med NO2 ochleller aktivt genom varmehojande &Order som paskyndar oxidationen med antingen NO2 eller syre. Behallaren 3 innehaller en andra avgasrenande komponent i form av en katalysator 5 enligt foreliggande uppfinning. Katalysatorn utgor har en SCR-katalysator for katalytisk avgasrening enligt den metod som benamns SCR (Selective Catalytic Reduction). Denna metod innebar att ett reduktionsmedel i form av en urealosning sprutas in i avgaserna. I detta fall lagras urealosning i en tank 6 och leds, via en ledning 7, till ett insprutningsorgan 8 som sprutar in urealosningen i ett utrymme 3a i behallaren. En styrenhet 9 styr tillforseln av urealosningen med information avseende specifika motorparametrar 10. En pump 11 transporterar ureakisningen till insprutningsorganet 8. The container 3 can be a muffler. The container 3 in this case contains a first exhaust gas treatment components in the form of a particle filter 4 which can be called DPF (Diesel Particulate Filter). A particle filter 4 comprises elongate parallel channels with stop surfaces arranged on suitable stalls. The stop surfaces force the exhaust gases to be led into adjacent elongate channels in the particulate filter 4. The cradles of the channels are made of a porous material with fine channels that tinker the passage of exhaust gases but not of soot particles. The soot particles then get stuck inside the particle filter 4. The particle filter 4 is regenerated continuously without active action by oxidizing the soot particles with NO2 and / or actively by heat-raising & Orders which accelerate the oxidation with either NO2 or oxygen. The container 3 contains a second exhaust gas purifying component in the form of a catalyst 5 according to the present invention. The catalyst consists of an SCR catalyst for catalytic exhaust gas purification according to the method called SCR (Selective Catalytic Reduction). This method meant that a reducing agent in the form of a urea solution was injected into the exhaust gases. In this case, urea discharge is stored in a tank 6 and is led, via a line 7, to an injection means 8 which injects the urea discharge into a space 3a in the container. A control unit 9 controls the supply of the urea discharge with information regarding specific motor parameters 10. A pump 11 transports the urea indentation to the injection means 8.

Fig. 2 visar ett langsgaende snitt av tva. kanaler 5a hos SCR-katalysatorn 5. Kanalerna 5a definieras av vaggelement 5b. Vaggelementen 5b innefattar av ett fOrsta yttre skikt 5bi som definierar en yta hos kanalen 5a, ett andra inre skikt 5b2 och en barande kropp 51); som bar upp det forsta skiktet 5b1 och det andra skiktet 5b2. Det forsta skiktet 5bi innefattar ett forsta aktivt katalysatormaterial som har formagan att ackumulera ammoniak och att framja en katalytisk reaktion mellan kvaveoxid och ammoniak. Det forsta skiktet bestar med fordel av vanadinpentoxid och av volframtrioxid pa ett barmaterial besfaende av titandioxid. Det andra skiktet 5b2bestar av ett material som 8 har kvaveoxidlagrande egenskaper och ett aktivt katalysatormaterial som framjar oxidation av kvavemonoxid till kvavedioxid. Det andra siktet kan innehalla en blandning av en eller flera oxider av alkaliska jordartsmetaller som har kvaveoxidlagrande egenskaper och en adelmetall sasom platina som framjar oxidation av kvavemonoxid till kvavedioxid pa ett bararmaterial bestaende av aluminiumoxid. Fig. 2 shows a longitudinal section of two. channels 5a of the SCR catalyst 5. The channels 5a are defined by cradle elements 5b. The cradle elements 5b comprise of a first outer layer 5bi defining a surface of the channel 5a, a second inner layer 5b2 and a bearing body 51); which carried the first layer 5b1 and the second layer 5b2. The first layer 5bi comprises a first active catalyst material which has the ability to accumulate ammonia and to promote a catalytic reaction between nitrogen oxide and ammonia. The first layer consists advantageously of vanadium pentoxide and of tungsten trioxide on a bare material containing titanium dioxide. The second layer 5b2 consists of a material 8 having nitrogen oxide storage properties and an active catalyst material which promotes oxidation of nitrogen monoxide to nitrogen dioxide. The second sieve may contain a mixture of one or more oxides of alkaline earth metals having nitrogen oxide storing properties and a noble metal such as platinum which promotes oxidation of nitrogen monoxide to nitrogen dioxide on a bar material consisting of alumina.

Aven aluminiumoxid har en viss egenskap att lagra kvaveoxid. Den barande kroppen 51); bestar av kordierit eller annat lampligt keramiskt material. Alumina also has a certain property of storing nitric oxide. The bearing body 51); consists of cordierite or other suitable ceramic material.

Under drift av fOrbranningsmotorn 1 beraknar styrenheten 9 med hjalp av information avseende motorparametrar 10 som belastning och varvtal den mangd av urealosningen som behover tillsattas for att kvaveoxiden i avgasema ska reduceras pa ett optimalt sat. Styrenheten 9 aktiverar pumpen 11 som transporterar urealosningen i den beralmade mangden till insprutningsorganet 8 som sprutar in urealosningen i avgasema. Den tillforda urealosningen upphettas av avgasema i behallaren 3 sa att den forangas och omvandlas till ammoniak. Blandningen av ammoniak och avgasema leds in katalysator 5. I katalysatom 5 reagerar kvavet hos kvaveoxiden i avgasema med kvavet i ammoniaken sâ att kvavgas bildas. Syret hos kvaveoxiden reagerar med vatet i ammoniaken sâ att vatten bildas. Kvaveoxiden i avgasema reduceras saledes i katalysatom 5 till kvavgas och vattenanga. During operation of the internal combustion engine 1, the control unit 9 calculates with the aid of information regarding engine parameters 10 such as load and speed the amount of urea solution that needs to be added in order for the nitrogen oxide in the exhaust gases to be reduced in an optimal way. The control unit 9 activates the pump 11 which transports the urea solution in the grounded quantity to the injector 8 which injects the urea solution into the exhaust gases. The supplied urea solution is heated by the exhaust gases in the container 3 so that it evaporates and is converted to ammonia. The mixture of ammonia and the exhaust gases is introduced into catalyst 5. In catalyst 5, the nitrogen of the nitrogen oxide in the exhaust gases reacts with the nitrogen in the ammonia so that nitrogen gas is formed. The oxygen of the nitrogen oxide reacts with the water in the ammonia to form water. The nitrogen oxide in the exhaust gases is thus reduced in the catalyst to nitrogen gas and water vapor.

UrealOsningen borjar dock fOrst sprutas in i avgasema efter att en lagsta acceptabel driftstemperatur uppnatts. Vid, exempelvis, en kallstart dâ en lagre temperatur rader i avgassystemet leds saledes avgaser till katalysatom 5 utan nagon tillsats av ammoniak. Kvaveoxiden i avgasema diffunderar har in det forsta skiktet 5bi och det andra skiktet 5b2 hos SCR-katalysatom 5. Eftersom det andra skiktet 5b2 innefattar ett material med kvaveoxidlagrande egenskaper blir aiminstone en del av avgasema som nar SCRkatalysatom 5 kvar i det andra skiktet 5b2. However, the Ureal solution only begins to be injected into the exhaust gases after a minimum acceptable operating temperature has been reached. Thus, for example, in a cold start when a lower temperature rows in the exhaust system, exhaust gases are thus led to the catalyst 5 without any addition of ammonia. The nitrogen oxide in the exhaust gases diffuses has the first layer 5bi and the second layer 5b2 of the SCR catalyst 5. Since the second layer 5b2 comprises a material with nitrogen oxide storage properties, it becomes at least a part of the exhaust gases which the SCR catalyst 5 remains in the second layer 5b2.

Nar en driftstemperatur uppnas startar insprutningen av urealosningen sâ att ammoniak bildas i avgasema. Avgaser och ammoniak kommer inledningsvis i katalysatom 5 i kontakt med det forsta skiktet Sbi som innehaller det forsta aktiva katalysatormaterialet. Ammoniaken diffunderar in i det forsta skiktet 5b1 och adsorberar pa aktiva saten. Kvaveoxid diffunderar aven in i det forsta skiktet 5bi. Kvaveoxiden reagerar dar med ammoniak pa namnda aktiva saten sa att vatten och kvavgas bildas. Koncentrationen av ammoniak och kvaveoxid avtar med avstandet fran det forsta skiktets 5bi yta. Koncentrationen av ammoniak avtar snabbare med avstandet 9 fran ytan an koncentrationen av kvaveoxid eftersom ammoniaken adsorberas pa namnda saten medan kvWeoxiden kan diffundera fritt i det forsta skiktet sâ lange som den inte reagerat med ammoniak. Kvaveoxid tranger Wen in i det andra skiktet 5130. When an operating temperature is reached, the injection of the urea solution starts so that ammonia is formed in the exhaust gases. Exhaust gases and ammonia initially come into contact with the catalyst 5 in the first layer Sbi which contains the first active catalyst material. The ammonia diffuses into the first layer 5b1 and adsorbs on the active seeds. Nitric oxide also diffuses into the first layer 5bi. The nitrogen oxide reacts there with ammonia on the said active way so that water and nitrogen gas are formed. The concentration of ammonia and nitrogen oxide decreases with distance from the surface of the first layer 5bi. The concentration of ammonia decreases more rapidly with the distance 9 from the surface than the concentration of nitric oxide because the ammonia is adsorbed in the said way while the nitrogen oxide can diffuse freely in the first layer as long as it has not reacted with ammonia. Nitric oxide penetrates Wen into the second layer 5130.

Vid driftstillfallen da urealosningen sprutas in och det fader en relativt lag temperatur i katalysatom är kvaveoxidens och ammoniakens benagenhet att reagera lag. Kvaveoxiden som tranger in i det forsta skiktet 5bi reagerar darmed i betydligt mindre utstrackning med den ammoniak som adsorberats i det forsta skiktet 5b1. Eftersom det andra skiktet 5b2 innefattar ett katalysatormaterial som framjar oxidation av kvavemonoxid till kvavedioxid sâ skapas en relativt stor mangd kvavedioxid i det andra skiktet 5b2. Efter en kallstart kan det Wen finnas en relativt stor mangd lagrad kvavedioxid i det andra skiktet 5b2. KvWedioxiden i det andra skiktet 5b2 diffunderar sâ smaningom tillbaka till det forsta skiktet 5b1 vilket resulterar i ett kraftigt okat antal reaktioner mellan ammoniak och kvaveoxid pa ett relativt stort avstand fran ytan hos det forsta skiktet 5bi. I de fall da avgasema har en lag temperatur bidrar det andra skiktet 5b2 till att markant Oka katalysatorns5 formaga att eliminera kvWeoxid frail avgasema. Det resulterar i att katalysatom 5 kan ha en hog kapacitet att eliminera kvaveoxid vid 18ga driftstemperaturer. In operating cases when the urea solution is injected and it fades a relatively low temperature in the catalyst, the tendency of the nitrogen oxide and ammonia to react is low. The nitrogen oxide penetrating into the first layer 5b1 thus reacts to a much lesser extent with the ammonia adsorbed in the first layer 5b1. Since the second layer 5b2 comprises a catalyst material which promotes oxidation of nitrogen monoxide to nitrogen dioxide, a relatively large amount of nitrogen dioxide is created in the second layer 5b2. After a cold start, there may be a relatively large amount of nitrogen dioxide stored in the second layer 5b2. The nitrogen dioxide in the second layer 5b2 then gradually diffuses back to the first layer 5b1, which results in a greatly increased number of reactions between ammonia and nitrogen oxide at a relatively large distance from the surface of the first layer 5bi. In cases where the exhaust gases have a low temperature, the second layer 5b2 helps to significantly shape the catalyst 5 to eliminate the nitric oxide from the exhaust gases. As a result, the catalyst 5 may have a high capacity to eliminate nitric oxide at 18ga operating temperatures.

Vid driftstillfallen da reduktionsmedlet sprutas in avgasema och det fader en relativt hog temperatur i katalysatom 5 är kvaveoxidens och ammoniakens benagenhet att reagera hog. KvWeoxiden som diffunderar in i det forsta skiktet 5bi reagerar armed nastan omedelbart med den ammoniak som adsorberats i det forsta skiktet 5b1. Reaktionema sker har huvudsakligen nara ytan hos det forsta skiktet 5bi. Endast en mindre del av kvaveoxiden nar det andra skiktet 5b2. Det andra skiktet 5b2 mottar i detta fall endast en liten mangd kvavemonoxid som kan oxideras till kvWedioxid. I detta fall bidrar fOrekomsten av det andra skiktet 5b2 endast i en liten utstrackning till att Oka katalysatoms 5 formaga att eliminera kvaveoxid fran avgasema. Eftersom katalysator 5 redan har en hog kapacitet att eliminera kvaveoxid ur avgasema da en hEig temperatur rader är detta heller inte nOdvandigt. In the case of operation when the reducing agent is injected into the exhaust gases and it fades a relatively high temperature in the catalyst, the tendency of nitrogen oxide and ammonia to react is high. The kvWe oxide which diffuses into the first layer 5bi reacts almost immediately with the ammonia adsorbed in the first layer 5b1. The reactions take place substantially near the surface of the first layer 5bi. Only a small part of the nitrogen oxide reaches the second layer 5b2. The second layer 5b2 in this case receives only a small amount of nitrogen monoxide which can be oxidized to nitrogen dioxide. In this case, the presence of the second layer 5b2 contributes only to a small extent to the shape of the Oka catalyst 5 to eliminate nitrogen oxide from the exhaust gases. Since catalyst 5 already has a high capacity to eliminate nitric oxide from the exhaust gases at a high temperature range, this is not necessary either.

Vid driftstillfallen dâ urealosningen sprutas in och det fader en lag temperatur i katalysatom 5 kan relativt stora mangder ammoniak lagras i det forsta skiktet 5bi. In operating cases when the urea solution is injected and it has a low temperature in the catalyst 5, relatively large amounts of ammonia can be stored in the first layer 5bi.

Eftersom katalysatom 5 innefattar ett andra skikt 5b2 med ett kvWeoxidlagrande material och eft katalysatormaterial som har formagan att framja oxidation av kvavemonoxid till kvWedioxid kan det andra skiktet 5b2 innehalla en stor mangd lagrad kvavedioxid. Vid driftstillfallen som avgasemas temperatur hastigt hojs, pa grund av exempelvis ett motorpadrag, minskar katalysatoms 5 formaga att adsorbera ammoniak. Ackumulerad ammoniak i det fOrsta skiktet 5bikommer darmed att frigoras och diffundera i olika riktningar. Ammoniak som diffunderar i riktning mot det andra skiktet 5b2reagerar med kvaveoxiden i det andra skiktet 5b2 som har en lampligt hog andel kvavedioxid. Det innebar att en vasentlig del av den temporart frigjorda mangden ammoniak kan reduceras med hjalp av lagrad kvaveoxid vilket eliminerar utslapp av ammoniak nedstroms katalysatom 5. I detta fall da. katalysatom 5 utgOrs av en SCR-katalysator behOys ingen ammoniakslipkatalysator anordnas nedstroms katalysatom 5. Since the catalyst 5 comprises a second layer 5b2 with a nitrous oxide storage material and after catalyst material which is capable of promoting oxidation of nitrous oxide to nitrous oxide, the second layer 5b2 may contain a large amount of stored nitrogen dioxide. In the case of operation where the temperature of the exhaust gases rises rapidly, due to, for example, an engine path, the ability of the catalyst 5 to adsorb ammonia decreases. Accumulated ammonia in the first layer 5 thus becomes released and diffuses in different directions. Ammonia which diffuses in the direction of the second layer 5b2 reacts with the nitrogen oxide in the second layer 5b2 which has a suitably high proportion of nitrogen dioxide. This meant that a substantial part of the temporarily released amount of ammonia can be reduced with the aid of stored nitrogen oxide, which eliminates the emission of ammonia downstream of the catalyst 5. In this case then. Catalyst 5 is an SCR catalyst, no ammonia abrasive catalyst is provided downstream of catalyst 5.

Fig. 3 visar en altemativ utforingsform av katalysatom 5. I detta fall är avgasledningen 3 forsedd med en konventionell oxidationskatalysator 12, ett partikelfilter 4, en konventionell SCR-katalysator 13 och en ammoniakslipkatalysator i form av den uppfinningsenliga katalysatom 5. Katalysatorn 5 är har placerad nedstrOms SCR- katalysator som pa konventionellt satt är utformad med ett skikt av ett aktivt katalysatormaterial. Katalysatom 5 är aven har utformad med kanaler 5a som definieras av vaggelement 5b som innefattar ett fOrsta yttre skikt 5bi, ett andra inre skikt 5b3 och en barande kropp 5b3 pa samma satt som i Fig. 2. Fig. 3 shows an alternative embodiment of the catalyst 5. In this case the exhaust line 3 is provided with a conventional oxidation catalyst 12, a particulate filter 4, a conventional SCR catalyst 13 and an ammonia abrasive catalyst in the form of the catalyst 5 according to the invention. The catalyst 5 is located downstream SCR catalyst which is conventionally formed with a layer of an active catalyst material. The catalyst 5 is also formed with channels 5a defined by cradle elements 5b which comprise a first outer layer 5bi, a second inner layer 5b3 and a supporting body 5b3 in the same manner as in Fig. 2.

Eftersom katalysatom 5 kan har lagra kvaveoxid kan den reducera utslappen av kvaveoxid vid kallstarter innan urealosning har(5b1) borjat sprutas in i avgasema. Vid driftstillfallen dâ urealosning sprutas in och dâ avgasema har en lag temperatur har den en betydligt hogre kapacitet att eliminera kvaveoxid an den konventionella SCR- katalysatom 13 och den utgor damned ett mycket gott komplement till den konventionella SCR-katalysator 13. Eftersom SCR-katalysatom 13 har en konventionell utformning shipper den igenom ammoniak vid hastiga temperaturokningar hos avgasema. Katalysatom 5 eliminerar har det temporara overskott pa ammoniak med hjalp av lagrad kvaveoxid i det andra skiktet. Eftersom det andra aktiva katalysatormaterialet innehaller en adelmetall kan den Liven reducera overskottet pa ammoniak som tranger in i det andra skiktet. Since the catalyst 5 may have stored nitric oxide, it can reduce the emission of nitric oxide at cold starts before urea release (5b1) has started to be injected into the exhaust gases. In operational cases where urea discharge is injected and when the exhaust gases have a low temperature, it has a much higher capacity to eliminate nitrogen oxide than the conventional SCR catalyst 13 and it is therefore a very good complement to the conventional SCR catalyst 13. Since the SCR catalyst 13 has a conventional design, it ships through ammonia at rapid temperature rises in the exhaust gases. The catalyst 5 eliminates the temporary excess of ammonia by means of stored nitrogen oxide in the second layer. Since the second active catalyst material contains a noble metal, it can reduce the excess ammonia that penetrates into the second layer.

Vid design av katalysatom 5 da den utgors av en ammoniakslipkatalysator med kvaveoxidlagringsfunktion behover nagra avvagningar goras. Formagan att lagra NOx ska avta och vara liten Over temperaturer dâ kvaveoxidreduktionen uppnas i SCR- katalysatorn och ammoniakslipkatalysator. Detta uppnas genom val av material eller 11 kombination av material for kvaveoxidlagring (den termiska stabiliteten for nitrater av alkaliska jordartsmetaller avtar uppat i periodiska systemet). Efter ett tags varm drift är den kvaveoxidlagrande komponenten tOmd och den kan ater lagra kvaveoxid vid nasta kallstart. Vid design av katalysatom 5 da den utgor en SCR-katalysator med kvaveoxidlagringsfunktion behover ytterligare avvagningar goras. Forhallandet mellan skiktens tjocklek och adelmetallhalten i det inre skiktet bOr vara valda sa att reaktionen mellan ammoniak och NOx i det yttre skiktet vid de fiesta driftfall forbrukar all ammoniak. Det inre skiktets tjocklek kan ligga i intervallet 5-50% av summan av bada skiktens tjocklek. Adelmetallhalten kan ligga i intervallet 0.25-10 g/ft3. When designing the catalyst 5 as it consists of an ammonia abrasive catalyst with a nitrogen oxide storage function, some balances need to be made. The capacity to store NOx must decrease and be small. Over temperatures when the nitrogen oxide reduction is achieved in the SCR catalyst and ammonia abrasive catalyst. This is achieved by the choice of material or combination of materials for nitrogen oxide storage (the thermal stability of nitrates of alkaline earth metals decreases upwards in the periodic table). After a while of hot operation, the nitrogen oxide storage component is empty and it can store nitrogen oxide again at the next cold start. When designing the catalyst 5 as it constitutes an SCR catalyst with a nitrogen oxide storage function, further balances need to be made. The ratio between the thickness of the layers and the noble metal content in the inner layer should be chosen so that the reaction between ammonia and NOx in the outer layer in most operating cases consumes all ammonia. The thickness of the inner layer can be in the range 5-50% of the sum of the thickness of both layers. The noble metal content can be in the range 0.25-10 g / ft3.

Uppfinningen är inte begransad till den ovan beskrivna utforingsformen utan den kan varieras fritt Mom patentkravens ramar. 12 The invention is not limited to the embodiment described above, but it can be varied freely within the scope of the patent claims. 12

Claims

PatentkravPatent claims

1. Katalysator fcir behandling av avgaser frau en forbranningsmotor (1), varvid katalysatorn (5) innefattar vaggelement (5b) som formar ett flertal langstrackta kanaler (5a) hos katalysatorn fcir mottagning av avgaser, varvid vaggelementen (5b) innefattar ett forsta yttre skikt (5b1) som tillhandahaller en utvandig yta i de langstrackta kanalerna (5a) och ett andra inre skikt (5b2) som anordnat invandigt om det forsta skiktet (5b1), varvid det forsta skiktet (5b1) innefattar ett forsta aktivt katalysatormaterial som framjar en katalytisk reaktion mellan kvaveoxid och ammoniak, och varvid det andra skiktet (5b2) innefattar ett material som har formaga att lagra kvaveoxid och ett andra aktivt katalysatormaterial som har en hogre formaga att framja oxidation av kvavemonoxid till kvavedioxid an det fOrsta katalysatormaterialet, kannetecknad av att det andra skiktet (5b2) innefattar ett kvaveoxidlagrande material som bestar av en oxid av en alkalisk jordartsmetall eller en kombination av sadana oxider.A catalyst for treating exhaust gases from an internal combustion engine (1), the catalyst (5) comprising rocker elements (5b) forming a plurality of elongate channels (5a) of the catalyst for receiving exhaust gases, the rocker elements (5b) comprising a first outer layer (5b1) providing an outer surface of the elongate channels (5a) and a second inner layer (5b2) disposed internally about the first layer (5b1), the first layer (5b1) comprising a first active catalyst material which promotes a catalytic reaction between nitrogen oxide and ammonia, and wherein the second layer (5b2) comprises a material capable of storing nitrogen oxide and a second active catalyst material having a higher capacity to promote oxidation of nitrogen monoxide to nitrogen dioxide than the first catalyst material, characterized in that the second the layer (5b2) comprises a nitrogen oxide-storing material consisting of an oxide of an alkaline earth metal or a combination of sa dana oxides.

2. Katalysator for rening av avgaser enligt krav 1, kannetecknad av att det andra skiktet (5b2) innefattar ett aktivt katalysatormaterial i form av en adelmetall.Catalyst for exhaust gas purification according to claim 1, characterized in that the second layer (5b2) comprises an active catalyst material in the form of a noble metal.

3. Katalysator enligt krav 2, kannetecknad av att det andra skiktet (5b2) innefattar ett aktivt katalysatormaterial i form platina.Catalyst according to claim 2, characterized in that the second layer (5b2) comprises an active catalyst material in the form of platinum.

4. Katalysator enligt dagot av foregaende krav, kannetecknad av att det forsta katalysatormaterialet i det fcirsta skiktet (5b1) innefattar vanadinpentoxid.Catalyst according to the preceding claim, characterized in that the first catalyst material in the first layer (5b1) comprises vanadium pentoxide.

5. S. Katalysator enligt krav 4, kannetecknad av att det forsta katalysatormaterialet i det forsta skiktet (5b1) Liven innefattar volframoxid.S. Catalyst according to claim 4, characterized in that the first catalyst material in the first layer (5b1) of the Life comprises tungsten oxide.

6. Katalysator enligt nagot av foregaende krav, kannetecknad av aft namnda vaggelement (5b) är formade av en barande kropp (5b3) som bar upp de tvii skikten (5bi, 5b2).Catalyst according to any one of the preceding claims, characterized in that said rock element (5b) is formed by a supporting body (5b3) which supported the two layers (5bi, 5b2).

7. Katalysator enligt nagot av foregaende krav, kannetecknad av att materialet i atminstone ett av skikten innefattas i en barande kropp (5b3). 13Catalyst according to any one of the preceding claims, characterized in that the material in at least one of the layers is included in a bearing body (5b3). 13

8. Katalysator enligt nagot av foregaende krav, kannetecknad av att det andra skiktet (5b2) innefattar ett bdrmaterial i form av aluminiumoxid.Catalyst according to one of the preceding claims, characterized in that the second layer (5b2) comprises a support material in the form of alumina.

9. Katalysator enligt nagot av foregaende krav, kannetecknad av att det forsta skiktet (5b1) är dimensionerat sa att det har kapacitet att mottaga all ammoniak under normal drift sa att ammoniak endast tranger in i det andra skiktet (5b2) vid driftstillfallen da det uppstar ett temporart overskott pa ammoniak.Catalyst according to any one of the preceding claims, characterized in that the first layer (5b1) is dimensioned so that it has the capacity to receive all ammonia during normal operation so that ammonia only penetrates into the second layer (5b2) at operating times when it arises a temporary excess of ammonia.

10. Avgas system for en fOrbranningsmotor, kannetecknad av att det innefattar en katalysator (5) enligt nagot av kraven 1-10.Exhaust system for an internal combustion engine, characterized in that it comprises a catalyst (5) according to any one of claims 1-10.

11. Avgas system for en fOrbranningsmotor enligt kravet 10, kannetecknad av att katalysatorn (5) utgor en SCR-katalysator i avgassystemet.Exhaust system for an internal combustion engine according to claim 10, characterized in that the catalyst (5) constitutes an SCR catalyst in the exhaust system.

12. Avgassystem for en fOrbranningsmotor enligt kravet 10, kannetecknad av att katalysatorn (5) utgor en ammoniakslipkatalysator i avgassystemet. 14 1 4 8 A... '4 33a zak'Stak'S,MM'aa::,> A U L., 13 6 7 9 ............ 11Exhaust system for an internal combustion engine according to claim 10, characterized in that the catalyst (5) constitutes an ammonia abrasive catalyst in the exhaust system. 14 1 4 8 A ... '4 33a zak'Stak'S, MM'aa ::,> A U L., 13 6 7 9 ............ 11