FR3041032A1 - EXHAUST GAS POST-TREATMENT DEVICE OF A COMBUSTION ENGINE - Google Patents

Abstract

The invention relates to an aftertreatment device for the exhaust gas of a combustion engine (1) comprising: a DOC oxidation catalyst member (2) or a NOx LNT trap member; A mouth of a reducing agent introduction means (6) for the selective catalytic reduction of the SCR nitrogen oxides; SCR selective catalytic reduction means of the nitrogen oxides, said means comprising: a selective catalytic reduction member SCR of the nitrogen oxides NOx (3) dedicated; and / or - a selective catalytic reduction coating SCRF of NOx nitrogen oxides on a particulate filter member (4); • the particulate filter member (4); Means for treating the ammonia leaks (5) ASC by oxidation of the ammonia to NOx and then reducing said NOx to nitrogen, said means comprising a catalytic coating (s) and also incorporating a catalytic material passive adsorber of NOx.

Description

EXHAUST GAS POST-TREATMENT DEVICE

OF A COMBUSTION ENGINE

[001] The invention relates to means for treating pollutants from the exhaust gases of combustion engines.

[002] The pollutant emissions of combustion engines fitted to motor vehicles are regulated by standards. Regulated pollutants are, depending on the combustion engine technology considered, carbon monoxide (CO), unburnt hydrocarbons (HC), nitrogen oxides (NOx, ie NO and NO2) and particles (PM), which are formed during combustion of the fuel in the combustion chamber and then emitted to the exhaust.

[003] It is known to employ a number of pollution control means in the exhaust line of combustion engines to limit the emissions of regulated pollutants. An oxidation catalyst allows the treatment of carbon monoxide, unburned hydrocarbons, and under certain conditions nitrogen oxides; a particulate filter can be used for the treatment of soot particles.

[004] This type of device is generally referred to as the "after-treatment" device for the exhaust gases.

[005] To meet pollution control standards on nitrogen oxide (NOx) emissions, a specific post-treatment system can be introduced into the exhaust line of vehicles, including vehicles equipped with diesel engines. For the treatment of nitrogen oxides (NOx), selective catalytic reduction (SCR) technologies for Selective Catalytic Reduction (English) are known, which consist in reducing NOx by introducing a reducing agent (or a precursor of such a reducing agent) in the exhaust gas by catalyzed reactions. It may for example be a urea solution, the decomposition of which will make it possible to obtain ammonia which will serve as a reducing agent, but also of a reducing agent or a precursor of such a reducing agent. gaseous form. In the remainder of the present document, a "reducing agent" will generally be used to designate a reducing agent or a reducing agent precursor.

The reducing agent generated makes it possible to reduce the nitrogen oxides by reaction in an SCR catalyst, that is to say a substrate carrying a catalytic impregnation capable of promoting the reduction of NOx by the reducing agent.

[007] European standards, in particular, tend to become more and more severe. And solutions to reduce pollutant emissions at the end of the exhaust line to meet current standards will prove insufficient given the changes in standards planned beyond 2017.

[008] Indeed, the first step of the standard, Euro 6b (effective in September 2014) led car manufacturers to choose between different options to reduce NOx emissions more specifically: - the reduction of NOx "to the source ", at the level of the actual operation of the engine, via technologies of the exhaust gas recycling type in the engine, recycling also known as EGR technology according to the acronym for the English term corresponding to" Exhaust Gas Recirculation "high and low pressure, for example ; - the reduction of NOx at the exhaust line via a sequential catalytic treatment technology called "NOx trap"; the reduction of NOx at the level of the exhaust line also, via a continuous treatment technology called "selective catalytic reduction" as briefly described above (SCR); even by cumulating many of these solutions.

[009] If these solutions make it possible to satisfy this first step in the evolution of the standard (Euro6b), they are not necessarily capable of satisfying the second stage which promises to be even more severe (Euro 6c, entry into force foreseen in September 2017), with pollutant measurements on a new rolling cycle called "WLTC" (for "Worldwide Harmonized Light Vehicle Test Cycle" in English, or harmonized test cycle for light vehicles in French), containing more transient phases than the current approval cycle (known as "MVEG" for Motor Vehicle Emissions Group in English, or group of emissions for motorized vehicles in French), but also off-cycle measures (called "RDE" for Real Driving Emission or emissions in conditions driving practices) should be introduced.

[0010] In particular, to meet the risks of excessively high NOx emissions outside the cycle, various technological solutions and architectures can be envisaged. They have their advantages and disadvantages. But the most efficient nitrogen oxide treatment technology is selective catalytic reduction (SCR) because it is efficient in more extended temperature and gas flow ranges than a NOx trap, the other solution post-processing.

In addition, there are constraints of implantation of the post-processing device. In fact, in general, the catalytic systems used are all the more effective as the temperature of the exhaust gases passing through them is high (to a certain extent). They will then start all the more quickly after starting the engine as the temperature of the exhaust gas increases rapidly. It is therefore advantageous to implement the after-treatment devices as close to the engine, that is to say closer to the exhaust manifold, under hood, even though this environment is generally very crowded. The post-processing devices must therefore be as compact as possible without affecting their performance.

Throughout the present text, the terms "upstream" and "downstream" are understood as a function of the general direction of flow of the exhaust gases in the exhaust line integrating the post-processing units, since the engine to the end cannula of the exhaust line.

It is, for example, known from the patent application WO 2011/089330 a post-processing device grouping in the same envelope several bodies that will be successively traversed by the exhaust gas. It is proposed, in particular, a series of organs comprising upstream downstream: - an oxidation catalyst, - a urea reducing agent injector, - a mixer whose role is to intimately mix the droplets of urea injected into the envelope traversed by the gases, so as to decompose to ammonia as homogeneously as possible over the entire cross section of the envelope, - an organ SCR, - a particulate filter (called FAP by the after). It also proposes an alternative, consisting of replacing the SCR member and the FAP, with a FAP which is impregnated with a NOx reduction catalyst and which thus fulfills both the soot filter function and the reduction of the NOx (called SCRF later).

In addition, additional constraints arise when the motor vehicle is a vehicle called "heavy" (more than 1500 kg), whether a vehicle for private or utility type. In fact, under the same driving conditions as a lighter vehicle, the "heavy" vehicle will have higher temperature conditions in the exhaust to be managed, and larger quantities to process NOx generated in the engine. To compensate for these higher NOx emissions, the amounts of reducing agent to be injected into the exhaust line (for example urea decomposing to ammonia) will have to be larger too, since these quantities are dictated by the stoichiometry of the NOx reactions with ammonia. The higher temperatures of the gases at the engine outlet also favor the thermo-desorption of the ammonia stored in the SCR (and / or SCRF) members, and can furthermore contribute to the degradation of their active catalytic phases which can induce a decrease in their storage capacity in ammonia. The combination of higher temperatures and a higher amount of urea (or ammonia) to be injected on the line induces an increased risk of ammonia emissions that would not react at the end of the exhaust line. . Ammonia leaks at the end of the exhaust line are smelly, and can be inconvenient, especially if the vehicle is in a confined space of closed parking type.

The invention therefore aims to design a post-treatment of engine exhaust gas that overcomes the aforementioned drawbacks. One of its aims is to improve existing systems to meet higher standards for pollutant emissions, and more particularly for NOx emissions under unstabilized rolling conditions of the urban rolling type and / or an extended temperature range, while limiting as much as possible leakage of reducing agent NOx unreacted end of the exhaust line. Advantageously, it also aims to obtain a postprocessing device that is more efficient and which remains, in addition, compact.

The invention firstly relates to a device for post-treatment of the exhaust gas of a combustion engine, which comprises, from upstream to downstream: - a DOC oxidation catalyst member or a NOx trap organ LNT; a mouth of a reducing agent introduction means or a precursor of a reducing agent for the selective catalytic reduction of the SCR nitrogen oxides; SCR selective catalytic reduction means for the nitrogen oxides, said means comprising: a selective catalytic reduction member SCR of the nitrogen oxides NOx (6) dedicated, and / or a catalytic selective reduction coating SCRF of the oxides NOx nitrogen on a particulate filter member; the particulate filter element; means for treating ammonia leaks (so-called ASC) by oxidizing the ammonia to NOx and then reducing said NOx to nitrogen, said means comprising a catalytic coating (s) and also incorporating a passive catalytic adsorber material of NOx (called PNA), which is in a dedicated coating or is incorporated into one or more of the coatings.

"ASC" is the acronym for the term "Ammonia Slip Catalyst" or Catalyst leaking ammonia in French.

The invention therefore proposes to improve the means for treating ammonia leakage and adding a NOx passive adsorber function.

Thus, by their primary function, these processing means are capable of trapping excess ammonia at the end of the exhaust line, and to prevent it from being released. The treatment of ammonia is generally carried out in two stages, with, in one most common embodiment, a stack of two layers: the upper layer (that which is in contact with the exhaust gases), which corresponds to to a catalytic coating of SCR type and operates a reduction, and - the lower layer (that which is in contact with the walls of the substrate contains metals (deposited on alumina for example), which operates an oxidation. ASC is as follows: the residual ammonia enters the upper layer and stores in this layer in part.The rest of the ammonia passes through this upper layer and penetrates into the lower layer whose precious metals (Pd for example) favor the When the NOx come out of the SCR catalytic coating, they necessarily pass through the upper layer where the NH 3 is stored. NOx can then be carried out with NH3 and the NOx are converted to nitrogen (N2) before emerging from this catalyst.

However, if, in principle, these NH3 treatment means are effective, in practice they do not necessarily guarantee sufficient treatment of residual ammonia so that the NH3 emissions ultimately remain below the detectable level, whatever the operating conditions of the engine.

The invention therefore proposes to add a passive adsorber NOx material, whose usual English acronym is PNA for "Passive NOx Adsorber" to these residual NH3 treatment means. This type of PNA material has the ability to adsorb NOx in a certain temperature range (typically up to 150 or 200 ° C), and to desorb it further. It is thus known to place it in an exhaust aftertreatment device upstream of an organ SCR, so as to temporarily store the NOX at the start of the engine (when the exhaust gases are still "cold") for wait for the SCR unit to become effective (when the exhaust gases become sufficiently hot, for example from 200 or 300 ° C). The NOx stored "cold" in the PNA are then treated "hot" by the SCR organ.

But the present invention makes a different use, since the PNA is here disposed at the downstream end of the post-processing device, downstream of the SCR member therefore, and it is further integrated into the device treatment of residual NH3, which has very beneficial effects, jointly vis-à-vis the NOx and vis-à-vis the residual NH3. Indeed, with this configuration, the NOx that remain / would remain present in the exhaust gas at the downstream end of the post-treatment device can be stored in the PNA material, and thus be available to react with the residual NH 3 of the exhaust gases. exhaust that enters the NH3 treatment means or is already stored in the SCR layer. The ANP thus contributes to the removal of both residual NOx and residual NH3. Unlike the LNT type NOx traps discussed above, it does not require periodic passes from a lean engine speed to a rich engine speed. It works (adsorption / desorption of NOx) only depending on the temperature. By appropriately choosing the NOx desorption temperature of the PNA and that of the NH3 of the SCR layer, an optimal reaction can be achieved to treat them simultaneously. The selectivity of the conversion of NH3 to N2 in the presence of NOx, already existing in the known residual NH3 treatment devices, is significantly increased.

Overall, it can be noted that the four main reactions in an ASC are the following (expressed non-stoichiometrically): NH3 + O2 ~) N2 (major reaction) NH3 + O2 ~) N20 (reaction to avoid / limit) NH3 + 02 -) NOx (present reaction) NH3 + NOx ~) N2 (present reaction) The term "Passive NOx Adsorber" is to be understood in the invention broadly, to designate the storage function of the NOx in a DOC.

In ASC, there is a present reducer (NH3) in the ASC, which is capable of treating NOx. NH3 and HC are reducing agents that play the same role, which is to treat NOx.

Thus, the storage of NOx in an ASC according to the invention could also be called "active" rather than "passive", since the NOx are destroyed with a reducing agent, as in a NOx trap of type LNT (for Lean NOx Trap).

Advantageously, according to a first embodiment, the ammonia leak treatment means comprise a matrix on the walls of which is deposited a common coating comprising a first selective catalytic reduction material SCR and a second oxidation material. .

Advantageously, according to a second embodiment, the ammonia leak treatment means comprise a matrix on the walls of which is deposited a stack of coatings, a first coating, said top coating, comprising a first reduction material. selective catalytic converter SCR and a second coating, said lower coating, comprising a second oxidation material.

Whether with the first or second of these embodiments, the stack preferably comprises an additional dedicated coating comprising a passive adsorber NOx catalyst material, in particular disposed under the lower coating or under the common coating.

According to a variant of the second embodiment, the second coating comprising a second oxidation material is a common coating which also comprises the passive adsorber NOx catalyst material.

According to one or other of these embodiments, the coating or one of the coatings, in particular the coating comprising the catalytic passive adsorber material of NOx, may be deposited on only part of the walls of the matrix. , especially on a downstream part or on an upstream part. This is sometimes called "zoning" in English, to describe a coating deposit on a pre-defined area.

Similarly, the coating or one of the coatings, in particular the coating comprising the catalytic passive adsorber NOx material, may have a variable thickness, with in particular a thickness increasing or decreasing from upstream to downstream on the walls of the matrix.

Preferably, the NOx passive adsorber catalytic material of the ammonia leakage treatment means ASC comprises a nitrate or alkali metal oxide or alkaline earth metal or rare metal or transition metal oxide derivative, and comprises in particular a mixture of cerium and zirconium oxides and optionally barium.

[0034] Preferably, the SCR selective catalytic reduction material of the ASC ammonia leak treatment means comprises a zeolite with sites exchanged with iron or copper, such as copper-exchanged chabazite.

Preferably, the oxidation material of the ASC ammonia leak treatment means comprises a precious metal, in particular at least one of the metals Rh, Pt and Pd, optionally combined with a transition metal oxide or aluminum, and in particular comprises a mixture Rh Pt Pd.

Advantageously, the NOx desorption temperature of the NOx passive adsorber catalyst material is chosen to be less than or equal to, the NH3 desorption temperature of the ammonia leak treatment means. Thus, it increases the chances that NH3 and NOx react with each other in the ASC treatment means of the invention since they will desorb in the same temperature ranges.

Advantageously, the desorption temperatures of NOx and NH3 are at least 300 ° C.

The invention also relates to an exhaust line (of a heat engine), which comprises the post-processing device described above.

Optionally, the action of the ammonia leak treatment unit is completed by an ammonia leak treatment coating integrated with the particulate filter, preferably in its downstream portion.

The post-treatment device may also comprise a NOx sensor between the particulate filter member provided with a selective catalytic reduction catalyst coating SCRF NOx nitrogen oxides or the SCR member and the treatment means ammonia leaks ASC, and possibly another NOx sensor upstream of the DOC oxidation catalyst member / the LNT NOx trap, and / or another NOx sensor downstream of the leak treatment member ammonia. The "upstream" sensor, upstream of the DOC catalyst or the NOx trap, can also be replaced by modeling if necessary.

Preferably, the oxidation catalyst member has a catalyst whose quantity of noble metals is adjusted so as to obtain at the outlet of the organ exhaust gas whose ratio N02 / N0x is equal to or close to 0.5 ("neighboring" is understood to mean a variation of, for example, +/- 15% around this value).

Preferably, the catalyst of the particulate filter, when it is provided with, is based on zeolite (s) exchanged (s) copper.

It should be noted that the copper exchanged zeolites proposed for the SCRF and / or exchanged with iron for the catalyst of the catalytic reduction catalyst member SCR are for example based on zeolites of the chabazite, ferrierite or hydrated aluminosilicate type (ZMS5). ), and may also contain at least one of the following oxides: cerium (Ce) oxide, zirconium (Zr), or at least one of the following metals: niobium (Nb), tungsten (W), titanium ( Ti).

Advantageously, the after-treatment device according to the invention also comprises a mixing member of the exhaust gas and the reducing agent and / or the precursor of the gearbox between the mouth of the gearbox introduction means and / or precursor of a reducing agent for the selective catalytic reduction of SCR nitrogen oxides and the selective catalytic reduction catalytic converter of nitrogen oxides integrated in the SCRF particulate filter.

This mixer has the function of mixing as well as possible the exhaust with the reducing agent or reducing precursor, this being particularly useful when the precursor is of the liquid type, such as urea in aqueous phase.

The invention also applies to the direct injection of reducing gas, such as ammonia, which feeds the exhaust line from one or more salt cartridges (including SrCI2 type) suitable adsorbing the ammonia and releasing it by thermal activation, in a known manner (technology commonly called "solid" SCR), and in this case, the mixer is less necessary.

The invention also relates, in a first embodiment, to a motor vehicle defining a space under the hood, which contains what is usually referred to as the engine compartment, and a space under the box, and comprising a a heat engine connected to the preceding exhaust line, such that the engine and the aftertreatment device of the exhaust line are arranged in the space under the hood. In this way, all the depollution units are grouped compactly close to the engine.

The invention also relates, in a second embodiment, to a motor vehicle defining a space under the hood and a space under the body, and comprising a heat engine connected to the previous exhaust line, such as the engine. the DOC oxidation catalyst member or the LNT NOx trap, the mouthpiece, and the particulate filter member provided with a SCRF catalytic selective reduction catalyst coating of the NOx nitrogen oxides of the post-treatment device the exhaust line are arranged in the space under the hood, and such that the ammonia leak treatment member is disposed in the underbody space. This brings together the closer to the engine the pollution control organs needing a high exhaust gas temperature and away from the engine the ammonia leakage treatment member to preserve too severe heat that could cause a degradation of its effectiveness.

The invention also relates to a method of implementation of a motor vehicle comprising a heat engine connected to the exhaust line as described above, the treatment of NOx being provided by two systems, d ' on the one hand the NOx trapping member when it is used, and on the other hand the SCR and / or SCRF assembly, and, depending on the availability of the reducing agent on the vehicle, adjusting the NOx treatment weighting between the one or other of the systems. With the invention, the NOX treatment is further supplemented by the PNA material of the ammonia treatment unit.

The invention is described in more detail below with reference to the figures relating to a non-limiting example of embodiment relating to a device for the after-treatment of the exhaust gases of a diesel engine: FIG. 1 schematically represents a motor and its exhaust line of a motor vehicle comprising the after-treatment device according to an example of the invention; FIG. 2 represents a structural diagram of the processing means of the residual NFI3 of the post-processing device of FIG. 1; FIG. 3 is a graph showing the leakage of residual NH 3 as a function of temperature during operation under normal conditions of the aftertreatment device of the example according to the invention; FIG. 4 is a graph making it possible to display the gain in NOx emissions of the post-processing device of the example according to the invention.

The references taken from one figure to another designate the same components, and the various components shown are not necessarily scaled. The figures remain very schematic to facilitate reading.

FIG. 1 represents the post-processing device of the invention integrated in the exhaust line 10 of a heat engine 1. This device comprises a series of members that can be assembled in different configurations, either in a single common envelope connected to the line, or in several envelopes connected to the line and in which are distributed the different organs. The general flow of exhaust gas flow from the engine 1 to the end of the exhaust line 10 is symbolized by the arrow F, and it is with reference to this flow direction that the the terms "upstream" and "downstream" are used.

This post-treatment device comprises, from upstream to downstream, a first member 2 oxidation catalyst (DOC), an organ SCR 3, a particulate filter (FAP) 4 optionally provided with a catalytic coating SCR (It is then usually referred to as SCRF), and a residual NFI3 leak treatment catalyst member 5. It also comprises an injector 6 of ammonia precursor (in the form of urea in the aqueous phase) capable of injecting the precursor on the exhaust line 10 upstream of the SCR member 3 and, in known manner, in fluid connection with a precursor tank 7. It also comprises a not shown mixer (also called mixing box), already known, in particular from the patent application WO 2011/089330, which will ensure a sufficiently intimate mixture between the drops of urea and the exhaust gases to facilitate the decomposition of urea.

The oxidation catalyst 2 can be replaced / supplemented functionally by a NOx trap, for example consisting of a cordierite-type honeycomb support on which is deposited a catalytic phase comprising storage promoting elements. such as, but not limited to, simple or mixed oxides of barium and / or magnesium.

The piloting of the injection is done by the control unit 8 (of the onboard computer type), in particular using the information collected and reassembled to the control unit by the NOx sensors 9, 9 'and 9 ". It should be noted that at least one of these NOx sensors, and in particular the first one, 9, can be eliminated and replaced by means for estimating the NOx content in the exhaust gas stream, in particular by means of pre-established engine maps.

The control unit 8 also uses the pressure information collected and reassembled by pressure sensors 11, 11 'disposed on either side of the particulate filter 4, in particular for controlling the regeneration of the particulate filter. . It also uses the temperature information returned by the thermocouple 12 disposed between the DOC 2 and the SCR member 3.

If we detail the different bodies now, the first "brick" of this post-treatment device is the oxidation catalyst 2, which oxidizes the reducing species that are carbon monoxide (CO) and unburned hydrocarbons (HC).

It consists of a cordierite type honeycomb support on which is deposited a catalytic active phase ("washcoat") containing precious metals to catalyze the oxidation reactions of CO, HC and NO. This phase also comprises oxides such as alumina doped with various stabilizers (lanthanum, cerium, zirconium, titanium, silicon, etc.). On these oxides, precious metals (Pt, Pd, Rh, Ru, Re Au) are deposited in order to catalyze the oxidation reactions at low temperatures. Acidic compounds such as zeolites are also added. Their ability to store hydrocarbons at low temperatures and remove them from storage at high temperatures can improve the treatment of HC during cold phases. To these functions can be added (oxidation of carbon monoxide and unburned hydrocarbons and storage of these at low temperature) a storage function of nitrogen oxides, NOx also at low temperature. This storage function is ensured by the introduction of materials of simple or mixed oxides type basic type such as, for example, cerium oxides or barium among others.

The SCRF particle filter 4 also treats the nitrogen oxides and is also provided with a SCR coating, in addition to the dedicated SCR member 3.

The SCR catalyst of the dedicated SCR member 3 and / or the particulate filter 4 is based on copper zeolites, such as chabazite, β, copper-ferrierite, ZSM5 ... It is the best choice, in particular the SCRF 4, so that the catalyst of the particulate filter remains effective even at very high temperature (that it resists filter regenerations in particular). The porous support of the filter 4 is rather of SiC silicon carbide.

The ammonia leak treatment catalyst 5 is of the ASC type, the structure and mode of operation of which are illustrated in FIG. 2. It generally has two impregnation layers, when it does not include the modification proposed by the invention, namely a layer C2 which provides the oxidation function of NH3en NOx and a layer C1 which provides the NOx reduction function by NH3.

The composition of the ASC 5 member is thus as follows: the upper layer C1 (that which is in contact with the exhaust gas) corresponds to a catalytic coating SCR type (promoting the reduction reactions) and the lower layer C2 (that which is in contact with the walls of the substrate) promotes the oxidation reactions and contains precious metals (preferably palladium in a very small amount, between 0.5 and 5 g / ft3, ideally from 1 to 2) deposited on alumina. The operation of the unmodified ASC member 5 according to the invention is as follows: the residual ammonia enters the layer C1 and stores in this layer in part. The remainder of the ammonia passes through this layer C1 and enters the layer C2 whose precious metals (Pd) promote the oxidation of ammonia NH3 to NOx. When the NOx emerge from the catalytic coating SCR of the layer C2, they necessarily go through the layer C1 where the NH3 is stored. The NOx reduction reaction with NH3 can then take place. The NOx are thus converted into nitrogen (N2) before emerging from this catalyst 5.

The modification provided by the invention to the ASC 5 consists of adding to this stack of two layers a passive adsorber NOx material (PNA). Either we add a third layer, above the upper layer C1 or below the lower layer C2 or between the two layers, or we just integrate the PNA material in one of the C1 or C2 layers. Here, it was chosen in this example to integrate a PNA material in the oxidation-promoting layer, the lower layer C2 (alternatively, it can be integrated in the reducing layer, the upper layer C1).

Alternatively, there may be ASC monolayer bodies, where the reducing coating (SCR) and the oxidizing coating (noble metals) are associated in a common coating. In this case, the additional material PNA according to the invention can either be integrated in this common coating or be included in a dedicated coating, which is available on or under the common coating.

For the SCR material of the upper layer C1, it is possible to choose the SCR materials already mentioned for the dedicated SCR member 3.

For the oxidation material of the lower layer C2, one can choose a material from Al 2 O 3, TiO 2, ZrO 2, CeO 2, Y 2 O 3 with noble metals such as Pt, Pd, Rh, Ru, Re, Au, Ag, transition metals (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) and HC traps such as zeolites, alkali or alkaline earth metals, perovskites.

For the PNA material of the same lower layer, it is possible to choose (a) metal oxides such as alkali metals, alkaline earth metals, rare metals, transition metals or any mixed oxide of at least two of these metals. and (b) zeolites, in particular of metal doped preferentially with Al, Ce, Zr, Cu, Fe, Mn, W and copper oxides and their mixture. Other materials may be suitable, such as lanthanide oxides and / or actinides.

Here, the AUC of the example comprises a cordierite matrix, the oxidation material is chosen in a Pt-Pd mixture with a 1-1 ratio and is deposited on the matrix in a quantity corresponding to 10 grams. / foot 3, the SCR material is selected copper-exchanged chabazite in an amount corresponding to 10Og / l, and the material PNA is selected in a mixed oxide CeOx-ZrOx-BaOx in an amount corresponding to 10Og / l.

Figure 3 is a graph, with the abscissa time expressed in minutes, and ordinate (right axis) on the one hand the temperature in ° C measured by the thermocouple, on the other hand (left axis) the quantity expressed in ppm of residual NFI3 leak at the end of the exhaust line 10 under normal conditions of operation of the engine 1.

Curve A corresponds to the architecture of the post-processing device described above, but with a two-layer ASC (conventional) without PNA material, while curve B corresponds to the architecture according to the invention, where the ASC has been modified to include a PNA material. Curve A shows that there remains leakage of NH3 with a peak around 25 minutes but 50 ppm after 50 minutes. In contrast, the curve B of the example of the invention does not have such a peak and the residual NH3 leakage rate becomes zero or almost zero after 20 minutes. The CSA PNA material therefore has a measurable and highly effective effect on residual ammonia leaks, which it manages to suppress (or to render negligible).

FIG. 4 is a graph with the abscissa time expressed in seconds, and the ordinate (axis on the right) the temperature in ° C; and (left axis) the NOx level at the end of the exhaust line in ppm. Curve A 'corresponds to the architecture without PNA material in the residual NH3 treatment unit, curve B' corresponds to the architecture according to the invention: the hatched area which separates the two curves corresponds to the gain in emissions of NOx obtained with the invention: the exhaust line emits no more or almost no more NOx at low temperature, and emissions remain below 400 ° C.

In conclusion, the added PNA material in the downstream part of the post-treatment device has a very positive impact on ammonia leakage and NOx emissions over a wide temperature range. The invention makes it possible to increase the selectivity of the conversion of NH3 to N2 in the presence of NOx.

And its addition does not significantly complicate the manufacture (and implementation) of the residual NH3 treatment member, since it suffices to add one more component or one more coating in coatings existing / in an existing body.

Claims (10)

1. Apparatus for post-treatment of the exhaust gas of a combustion engine (1) characterized in that it comprises, from upstream to downstream: • a DOC oxidation catalyst member (2) or a trap member NOx LNT; A mouth of a means (6) for introducing a reducing agent or precursor of a reducing agent for the selective catalytic reduction of the nitrogen oxides SCR; SCR selective catalytic reduction means of the nitrogen oxides, said means comprising: a selective catalytic reduction member SCR of the nitrogen oxides NOx (3) dedicated, and / or a catalytic selective reduction coating SCRF of the oxides NOx nitrogen on a particulate filter member (4); The particulate filter element (4); means for treating the ammonia leaks (5) ASC by oxidation of the ammonia to NOx and then reducing said NOx to nitrogen, said means comprising a catalytic coating (s); ) (C1, C2) and also incorporating a passive catalytic adsorber material of NOx said PNA, which is in a dedicated coating or which is incorporated in one or more n coatings. 2. post-treatment device according to the preceding claim, characterized in that the ammonia leak treatment means (5) comprise a matrix on the walls of which is deposited a common coating comprising a first selective catalytic reduction material SCR and a second oxidation material. 3. post-treatment device according to claim 1, characterized in that the means for treating ammonia leaks (5) comprise a matrix on the walls of which is deposited a stack of coatings, a first coating, said upper coating , comprising a first selective catalytic reduction material SCR and a second coating, said lower coating, comprising a second oxidation material. 4. post-treatment device according to one of claims 2 or 3, characterized in that the stack comprises an additional dedicated coating comprising a passive adsorber NOx catalyst material, in particular disposed under the lower coating or under the common coating. The post-treatment device according to claim 3, characterized in that the second coating comprising a second oxidation material is a common coating which also comprises the NOx passive adsorber catalyst material. 6. post-treatment device according to one of claims 3 to 5, characterized in that the coating or one of the coatings, in particular the coating comprising the catalytic material adsorber passive NOx, is deposited on only part of the walls of the matrix, in particular on a downstream part or on an upstream part. 7. post-treatment device according to one of claims 2 to 6, characterized in that the coating or one of the coatings, including the coating comprising the catalytic material adsorber passive NOx, has a variable thickness, including a increasing or decreasing thickness from upstream to downstream on the walls of the matrix. 8. post-treatment device according to one of the preceding claims, characterized in that the NOx passive adsorber catalytic material of the ammonia leakage treatment means (5) ASC comprises a nitrate derivative or oxide of a alkali metal or alkaline earth metal or rare metal or transition metal, and comprises in particular a mixture of cerium oxides and zirconium and optionally barium. 9. post-treatment device according to claim 2, characterized in that the catalytic selective reduction material SCR ammonia leakage treatment means (5) ASC comprises a zeolite with sites exchanged with iron or copper, like chabazite exchanged with copper. 10. post-treatment device according to claim 2, characterized in that the oxidation material of the ammonia leak treatment means (5) ASC comprises a precious metal, in particular at least one of the metals Rh, Pt and Pd. , optionally combined with a transition metal oxide or aluminum, and in particular comprises a Rh Pt Pd mixture.