FR2995349A1 - Device i.e. solid particle filter, for processing e.g. carbon monoxide emissions, in diesel engine exhaust line of car, has reducer compensating on-board reducer in its action of nitrogen oxide catalytic reduction during reduction catalysis - Google Patents

Abstract

The device has porous filtration walls for filtering solid particles. An upstream selective catalytic reduction catalyst (15) is arranged in a flow direction of gases from an engine (20) toward an exhaust exit (21) of a vehicle. A nitrogen oxide reducer formation catalyst (16) is used for formation of reducer of nitrogen oxides from a gas mixture to be processed. The formed reducer compensates an on-board reducer in its action of catalytic reduction of nitrogen oxides during selective catalytic reduction catalysis. The catalysts are impregnated on the walls. An independent claim is also included for an exhaust line.

Description

DEVICE FOR TREATING POLLUTING EMISSIONS OF A THERMAL MOTOR BY CATALYTIC REDUCING, REDUCING THE INPUT REDUCER FEEDING [0001] The context of the invention is that of automotive pollution control and more specifically that of the reduction of pollutant emissions from engines. including diesel, such as carbon monoxide (CO), unburned hydrocarbons (HO) and nitrogen oxides (NOx). Pollutant emission standards will see the introduction of new approval cycles measuring the effectiveness of pollution control systems in very varied engine operating conditions, such as a cold start, a city taxi slow and aggressive driving. However, in some of these conditions, the temperature in the combustion chamber increases, favoring the unwanted NOx emissions (Zeldovich mechanism called "thermal NO"), making them reach hard to treat quantities. Today, the preferred device for the treatment of pollutant emissions of a diesel engine is the oxidation catalyst or DOC, but it is likely to only partially meet these standards. It is certainly effective in treating carbon monoxide (CO) and unburned hydrocarbon (HO) emissions when the temperature inside it allows (ie> 150 - 200 ° C) but not during a cold start. And concerning emissions of nitrogen oxides (NOx) that can be very high in aggressive driving and therefore more problematic to treat, it is totally ineffective. It is therefore known, particularly from US 2011/0162347, to couple the DOC with an additional device for treating these NOx emissions: [0005] Two types of these additional devices are commonly used: - a NOx trap with treatment of trapped NOx to transform them into non-polluting species such as N2, OR - an SCR catalyst (Selective Catalytic Reduction), which transforms NOx into N2 in a continuous way thanks to a specific reducing agent which may consist of hydrocarbons or ammonia (NH3), or an intermediate reducer (liquid or gaseous) which will generate ammonia (NH3) in fine in this catalyst. This latter device is preferred to the NOx trap because it remains effective even beyond 450 ° C. [0007] Despite everything, an SCR catalyst does not make it possible to efficiently treat the NOx emissions in large quantities over the entire range of operating conditions of the engine provided by the forthcoming standards without consuming very high quantities of on-board gearboxes. vehicle. A solution envisaged is to make the reducer refill between two revisions of the vehicle but this would be done by the customer, with the risk of negligence or forgetfulness, and the car manufacturers should, in addition, support the extra cost and inconvenience of a filling system via an easily accessible chute (fuel door ...). There is therefore no simple solution to cover the entire engine operating field in terms of NOx treatment without having to significantly increase the onboard volume of additive (SCR reducer), which represents an increase in the cost , mass and space constraints in the vehicle or to ask the customer to refill himself. The invention aims to overcome this disadvantage. For this purpose the invention relates to a device forming a particulate filter and a catalyst for removing nitrogen oxides contained in a gaseous mixture from a combustion engine of a motor vehicle, and conveyed to an outlet exhaust system of the vehicle, comprising an SCR catalyst implementing a selective catalytic reduction of nitrogen oxides by a gearbox on board the vehicle, characterized in that it comprises, upstream of the catalyst SCR in the direction of travel of the gases from the engine towards the exhaust outlet of the vehicle, a catalyst for forming a second reducing agent of the nitrogen oxides from the gaseous mixture to be treated, the second reducing agent being formed to supplement the on-board gearbox in its catalytic reduction action of oxides of nitrogen during SCR catalysis. The invention thus makes it possible, by producing in situ a second gearbox, to comply with the emission emission standards set for very varied engine operating conditions, without requiring a large volume of onboard gearbox, thus allowing a filling of the reducer tank only during the revisions of the vehicle, that is to say approximately every 20 000 to 30 000 km even in the case of extreme driving generating a lot of NOx to be treated. Advantageously, but optionally, the device comprises at least one of the following technical characteristics: the particulate filter comprises porous filtration walls of the solid particles, the SCR catalyst and the formation catalyst of the second reducing agent being impregnated on at less some of the porous walls of the filter; the particulate filter comprises inbound and outgoing channels alternately in pairs, an inbound channel being separated from the adjacent outgoing channel by one of the porous walls of the filter, the partition wall layer closest to the incoming channel being impregnated with the catalyst for forming the second reducer, and the layer of the partition wall closest to the outlet channel being impregnated with the SCR catalyst; the formation catalyst of the second reducing agent is a hydrogen formation catalyst H2. ; the hydrogen-forming catalyst H2 comprises rhodium on cerium oxides or on any other reducible support, and / or platinum on cerium oxides, and / or cobalt on alumina or on ceria and / or copper on hO 2. ; and the SCR catalyst comprises zeolites exchanged with iron, with copper, and / or simple or mixed acid oxides such as acidic zirconias. The invention also relates to an exhaust line of a motor vehicle with a combustion engine, allowing the evacuation of a gaseous mixture produced by the engine in operation, comprising an oxidation catalyst, and arranged downstream. of this oxidation catalyst in the direction of flow of gas from the engine to the exhaust outlet of the vehicle, a particulate filter comprising a catalyst for removing nitrogen oxides contained in the gas mixture as defined above. Advantageously, but optionally, the exhaust line according to the invention comprises at least one of the following technical characteristics: the exhaust line comprises an injection of the on-board gearbox upstream of the particulate filter; and it comprises a fuel injection upstream of the oxidation catalyst and therefore upstream of the particulate filter Finally, the invention also relates to a motor vehicle comprising a diesel engine, a storage tank of a on-board gearbox and an exhaust line as defined above. Other features and advantages of the invention will become apparent from the following description given with reference to the accompanying drawings: - Figure 1 is a schematic view of a particle filter device according to the invention; FIG. 2 is an enlargement of the zone of the filter marked "II" in FIG. 1; - Figure 3 is an enlargement of the area marked "Ill" in Figure 2; FIG. 4 schematically illustrates a heat engine and an exhaust line of a motor vehicle equipped with the particulate filter of FIG. 1. Selective catalytic reduction or SCR catalysis makes it possible to treat NOx by reacting them with a reducing agent such as gaseous ammonia NH3 according to the following chemical equations: (1 b) 4 NO + 02 + 4 NH3 -) 4 N2 + 6 H20 (standard SCR) (2b) NO + NO2 + 2 NH3 -) 2 N 2 + 3 H 2 O (fast kinetic SCR) (3b) 6 NO 2 + 8 NH 3 -) 7 N 2 + 12 H 2 O (high temperature SCR) In the case where the reducing agent is not gaseous ammonia but a intermediate reducer such as a liquid solution such as urea, it is necessary to transform the urea into NH3 first by thermolysis and then by hydrolysis: (4b) (NH2) 200 -) NH3 + HNCO Urea thermolysis (5b ) HNCO + H20 -) NH3 + CO2 Hydrolysis of isocyanic acid [0020] This transformation of urea into NH 3 requires that the exhaust gases to be treated have reached a total of higher than 180 - 200 ° C. By integrating a particulate filter SCR catalyst, it makes possible compliance with standards on pollutant emissions with a very compact architecture: a first "brick" DOC oxidation catalyst, as shown in Figure 4 which catalyzes CO and hydrocarbon oxidation reactions ("HO") and a second "brick" particulate filter impregnated with SCR catalyst (SCRF), schematically shown in Figure 4 and in detail in Figure 1 or 2, which provides both NOx reduction and solid particle filtration by porous walls. When SCR catalysis is impregnated on a particulate filter, it is deposited on the walls of the particulate filter and the gaseous reductant (NH3) or a liquid reductant for forming gaseous NH3 is injected upstream of the particulate filter. but downstream of the DOC in the flow direction of the gases formed by the engine to the exhaust (Figure 4). A particulate filter, such as that indicated by 1 in FIG. 1, comprises incoming channels 2 in which the gaseous mixture to be treated is admitted via an inlet 3, the opposite end of the channel being closed off by an impervious plug at gas 7, and outgoing channels 4 through which the treated gas mixture is delivered through an outlet 8, the opposite end of the outgoing channel being plugged by a shutter plug 9. The incoming channels 2 and the outgoing channels 4 are superposed alternately two two, each inlet channel 2 being separated from the adjacent outflow channel 4 by a porous wall 5 which can be impregnated with a catalyst. The gaseous mixture 11 admitted into the incoming channels 2 is forced through the porous walls 5 to reach the outgoing channels 4 because of the plugs 7 closing the incoming channels 2, and it is impossible for the gaseous mixture that reaches the outgoing channels 4 to return. to the motor because of the plugs 9 closing the outgoing channels. They can only be transported once processed to the exhaust outlet. The fact that the SCR catalysis is in the close position of the engine since deposited in the particulate filter, compensates for the thermal inertia of the filter media of the particulate filter compared to that of a cordierite support typical of the automotive catalysis which would be located at a location further from the engine (and this, even if the filter media of the particulate filter is cordierite) However, it should be noted that the catalyst SCR impregnating the filter is not able to treat engine emissions, as long as the temperature of the exhaust gas does not reach 150 to 200 ° C. SCR catalysis is therefore effective for temperatures above at least 150 ° C. However, its efficiency is also related to the relative amount of reducing agent relative to that of the NOx to be treated: the greater the amount of NOx to be treated, the greater the amount of reducing agent to be injected. However, it is not satisfactory to have to increase the amount of NH3 or urea embedded in the vehicle because it increases the cost, mass and congestion in particular. The heart of the invention lies precisely in the fact of generating a second reducer within the particulate filter, from species present in the exhaust gas, and which will complete the urea or NH3 as reagent for SCR catalysis, to avoid increasing or even reducing the amount of urea or NH3 used and therefore that embedded in the vehicle. Vehicles whose exhaust lines will be equipped with a particulate filter of this type can thus meet the standards for polluting emissions including those providing extreme engine operating conditions such as aggressive driving. , without the need to increase the onboard volume of the first reducer or the frequency of its filling. For this purpose, the invention provides that a second reducer is produced in the channels 2 of the particle filter, located upstream of the channels provided with the catalyst SCR 4, that the second reducer passes through the walls of the filter to achieve these channels provided with the SCR catalyst, and that it comes to supplement the first reducer injected at these SCR catalyst channels and reacts in combination with the first NOx to reduce, during SCR catalysis. According to a preferred embodiment of the invention, only the outgoing channels of the particulate filter are impregnated with the SCR catalyst and only the incoming channels of this filter are impregnated with a catalyst allowing the formation of the second reducer, which is ideally hydrogen H2. Hydrogen, H2 was chosen on purpose because its reducing power is significantly higher than that of HO and even that of CO. Moreover, the SCR by HO is not very effective and it is preferred by far that by NH3. Once the hydrogen is produced in the incoming channels, it passes through the walls of the filter to reach the outgoing channels, in order to reduce NOx on the catalytic sites impregnated on these outgoing channels, according to the following reaction (3). (3) NO + H2 Y 2 N 2 ± H 2 O Impregnation of the incoming channels of the FAP is a catalytic impregnation for producing hydrogen when the temperature and richness conditions are met. More specifically, with reference to Figures 2 and 3, the wall 5 separating an outgoing channel 4 of the adjacent incoming channel 2 is provided with a double impregnation: a first thickness 15 of this wall, the closest to the outgoing channel 4 , is impregnated with the SCR catalyst and a second thickness 16, the closest to the inlet channel 2, is impregnated with one or more catalysts for the steam reforming of the hydrocarbons and / or the so-called "water gas" reaction. In the example shown, the SCR impregnation is carried out on about 2/3 of the thickness of the wall of the filter and the impregnation to produce H2 on the remaining 1/3 thickness but the distribution between both impregnations should be optimized according to the desired efficiency and technical constraints. This particular structure of the particulate filter allows, in accordance with Figure 3, to treat a gaseous mixture containing NOx nitrogen oxides which is admitted into the inlet channel 2 at first, through the portion 16 of the wall separation zone 5 impregnated by the catalysts for producing H2 from the hydrocarbons and / or CO, then, in a second step, the additive gas mixture of the H2 that has just been produced passes through the remaining portion 15 of the impregnated partition wall 5 of SCR catalyst allowing the NOx reaction of the gaseous mixture with the H2 hydrogen produced in situ and NH3 ammonia injected or derived from urea. The gaseous mixture freed of NOx is then discharged to the exhaust outlet. According to a first variant embodiment of the production of hydrogen, it is a question of performing the steam reforming of unburned hydrocarbons (HO) also called "Steam Reforming" (SR): (1) CH y + 2xH 2 O xCO 2 + (2x) + Y /) H2 [0040] To produce H2 by this reaction, it is therefore necessary to have unburned hydrocarbons HO in large quantities. Two solutions can be envisaged to produce these hydrocarbons: - either by fuel injection in the line, which is then decomposed and converted to H2 in accordance with the reaction (1) above, - or by combustion in the chamber engine that can generate a lot of HC (post-injection type) but with the disadvantage of having a DOC upstream of the SCRF which will largely consume the reducers. Another solution may be to alternatively use a fuel vaporization reactor located upstream of the injection to the exhaust. This solution makes it possible to inject gaseous hydrocarbons into the exhaust by supplying electrical energy (heating the vaporization reactor). The advantage is then to lower the fuel injection temperature in the exhaust line. According to a second variant embodiment of the production of hydrogen, it is a question of carrying out the so-called "gas-to-water" reaction, also called "Water-Gas-Shift" (WGS in FIG. 2). ): (2) CO + H 2 CO 2 + H 2 [0044] According to a third variant embodiment, the two reactions (1) and (2) are carried out simultaneously. The reactions (1) and (2) require temperature to be effective (200 to 300 ° C for the "WGS" and even 400 to 500 ° C for the steam reforming HO and therefore the production of hydrogen) . This is a solution that comes in addition to the first reducer (liquid or gaseous) embedded, the latter dealing with lower temperatures. Thus, the large amounts of NOx emitted during high loads generated for example by aggressive driving, will be partly processed by the first onboard gearbox and for the rest by the hydrogen produced in situ (in the FAP). It is for this reason that according to the preferred embodiment of the invention, the dedicated impregnation "steam reforming HO" and / or "WGS" is positioned on and in the wall of the incoming channels, the impregnation SCR being positioned on and in the outgoing channels of the FAP. Thus the gearboxes, whether NH3 or H2, will pass through the SCR impregnation of the outgoing channels and convert the NOx emitted by the engine. An example of an SCR catalyzed particulate filter according to the invention comprises, ideally: an incoming and outgoing channel structure consisting of a filter media made of silicon carbide (SiC), cordierite, mullite, metal or the like the outgoing channels of the filter are impregnated at the surface or in their thickness with a catalyst SCR of the zeolite type exchanged (with iron, with copper, or others) or with the type simple or mixed acid oxides such as acid zirconias or other - the Incoming channels are impregnated at the surface or in their thickness with a rhodium type "steam reforming" type catalyst on cerium oxides or on any other reducible support, and / or with a "WGS" type catalyst of the Platinum type on oxides of cerium, cobalt on alumina or on ceria, copper on TiO 2, etc. [0050] In accordance with FIG. 4, a FAP of this type equips the exhaust line 18 of a motor vehicle with a diesel engine, downstream d a DOC oxidation catalyst relative to the path of the gases produced by the engine and heading towards the exhaust. An injection of urea 19 is provided between the DOC and the FAP and an injection diesel fuel IGE, upstream of the DOC. As indicated above, thanks to this solution, it is possible to maintain an average consumption of gear (the lowest possible to reduce the amount shipped) while ensuring the treatment of NOx for very varied engine operating conditions, the H2 production reactions making it possible as soon as the temperature conditions allow it, which is the case as soon as the amounts of NOx are large, to take over the relay of the first reducing agent, in this case NH3. It may even be envisaged, from a certain temperature, not to inject the first reductant (urea or NH3 for example) namely the temperature at which the production of H2 by the impregnation dedicated "steam reforming HC "and / or" WGS "is sufficient to ensure the treatment of NOx in the SCR impregnation of the outgoing channels of the FAP. The advantage is to reduce in this case the onboard gearbox volume. The determination of said temperature may be performed on synthetic gas bench. It will then take into account the steam reforming activity of HC and WGS to nine but also after aging, even to determine the evolution of H2 production as a function of aging and the temperature of the SCRF. These maps will be integrated into the computer which will stop the injection of the on-board gearbox as soon as the conditions are met. Finally, the particulate filter will benefit from the presence on and in the wall of the incoming channels of the precious metals (Platinum and / or Rhodium) useful for the formation catalyst of the second reducing agent (H2) since the latter will also contribute to the combustion of stored soot (regeneration aid). The particulate filter according to the invention (SCRF-H2 filter) can be integrated into one or the other of the following configurations: ENGINE DOC SCRF-H2 EXHAUST ENGINE DOC INJECTOR HC SCRF-H2 EXHAUST

Claims (10)

REVENDICATIONS1. Device forming a particulate filter and a catalyst for removing nitrogen oxides contained in a gaseous mixture resulting from a heat engine of a motor vehicle, and conveyed to a vehicle exhaust outlet, comprising a SCR catalyst setting Selective catalytic reduction of the nitrogen oxides by an on-board gearbox in the vehicle, characterized in that it comprises, upstream of the SCR catalyst (15) in the direction of flow of the gases from the engine (20) towards the exhaust outlet (21) of the vehicle, a catalyst (15) for forming a second reducing agent of the nitrogen oxides from the gaseous mixture to be treated, the second reducing agent being formed to supplement the on-board gearbox in its catalytic reduction action oxides of nitrogen during SCR catalysis. 2. Device according to claim 1, characterized in that it comprises porous walls (5) for filtering solid particles (10), the SCR catalyst (15) and the catalyst for forming the second reducer (16) being impregnated onto at least some of the porous walls (5) of the filter. 3. Device according to claim 2, characterized in that it comprises incoming channels (2) and outgoing channels (4) alternately in pairs, an incoming channel (2) being separated from the adjacent outgoing channel (4) by one of the porous walls (5) of the filter, the layer of the partition wall closest to the inlet channel being impregnated with the formation catalyst of the second reducer (16), and the layer of the partition wall closest to the outlet channel being impregnated with the SCR catalyst (15). 4. Device according to one of the preceding claims, characterized in that the catalyst for forming the second reducer (16) is an H2 hydrogen formation catalyst. 5. Device according to claim 4, characterized in that the H2 hydrogen-forming catalyst comprises rhodium on cerium oxides or on any other reducible support, and / or platinum on cerium oxides, and / or cobalt on alumina or on ceria and / or copper on h02. 6. Device according to one of the preceding claims, characterized in that the SCR catalyst comprises zeolites exchanged with iron, copper, and / or single or mixed acid oxides such as acidic zirconia. 7. Exhaust line of a motor vehicle with a combustion engine, allowing the evacuation of a gaseous mixture produced by the engine in operation, comprising an oxidation catalyst (DOC), and disposed downstream of this catalytic converter. oxidation in the direction of flow of gases from the engine to the vehicle exhaust outlet, a device forming a particulate filter (9) and a catalyst for removing nitrogen oxides contained in the gas mixture according to one of claims 1 to 6. 8. Exhaust line according to claim 7, characterized in that it comprises an injection (19) of the on-board gearbox upstream of the particulate filter. 9. Exhaust line according to claim 8, characterized in that it comprises a fuel injection (IGE) upstream of the particulate filter and upstream of the oxidation catalyst. 10. Motor vehicle comprising a diesel engine (20) including a storage tank of a gearbox on board the vehicle and an exhaust line (18) according to one of claims 7 to 915.