FR3104037A1 - Impregnated monolith for a treatment device for a motor vehicle engine exhaust system and associated manufacturing process - Google Patents

Abstract

Impregnated monolith for a treatment device of a motor vehicle engine exhaust system, comprising a catalysis substrate (7) and an impregnation layer (8) comprising at least one metal compound of the PGM platinum group. Further, the impregnation layer (8) is unevenly distributed over the catalysis substrate (7) so that the amount of the PGM compound in a first area (9) of the catalysis substrate (7) is subject to a first exhaust gas flow temperature is greater than the amount of the PGM compound of a second zone (10) subject to a second exhaust gas flow temperature lower than the first temperature. Figure for the abstract: Fig 3

Description

Impregnated monolith for a device for treating a motor vehicle engine exhaust system and associated method of manufacture

The present invention relates, in general, to the reduction of pollutant emissions during the cold start of a motor vehicle internal combustion engine by reducing the priming time of the catalyst with which the vehicle is provided.

More particularly, the invention relates to an impregnated monolith for a device for treating a motor vehicle engine exhaust system and to a process for obtaining such an impregnated monolith.

Generally, at least one combustion gas treatment device, called catalytic brick, is mounted on the engine exhaust line and its operation makes it possible to reduce the emission of harmful particles, nitrogen oxides (NOx), carbon monoxide (CO) and unburnt hydrocarbons (HC) during the combustion of fuel (diesel or gasoline) at high temperatures. It can be a three-way catalyst or an impregnated filtering monolith (both for particulate filters, Nox-trap, HC-trap or other).

Conventionally, the treatment system comprises a plurality of catalysis substrates, monoliths, arranged between an intake manifold and an exhaust manifold, and each carrying out the conversion of a specific type of pollutant when the exhaust gases emerging of the intake manifold pass through them.

The efficiency of the catalyst is related to its temperature. When the catalyst is cold, i.e. at a temperature below its initiation temperature, it is not or only slightly active. Consequently, cold starting and operation during the first seconds of the engine generate a higher emission of pollutants into the atmosphere.

The performance of the treatment device and the initiation temperature depend on many parameters such as the properties of the monolith (the length, the thickness of the wall, the density of cells, etc.) but also the characteristics of the flow of gases d exhaust such as velocity, temperature and flow distribution. These factors also have an influence on the aging of the post-processing device.

In order to reduce the initiation temperature, it is known to apply an impregnation layer comprising a platinum group metal compound (PGM) to the catalysis substrate.

However, a poor gas velocity distribution can cause an inhomogeneous temperature distribution in the catalysis substrate. The catalysis substrate then rises in temperature less quickly in the zones where the speed of the flow of the exhaust gases is lower and, consequently, the ignition temperature is reached less quickly.

The object of the invention is therefore to remedy these drawbacks and to propose an impregnated monolith for a treatment device making it possible to reduce its priming time and consequently the emissions of pollutants, as well as reducing its premature aging.

There is therefore proposed an impregnated monolith, filtering or not, for a device for treating a motor vehicle engine exhaust system, comprising a catalyst substrate and an impregnation layer comprising at least one metal compound of the platinum group PGM .

Further, the impregnation layer is unevenly distributed over the catalyst substrate such that the amount of the PGM compound in a first region of the catalyst substrate subject to a first temperature of the exhaust gas stream is greater than the amount of the PGM compound of a second zone subject to a second temperature of the exhaust gas flow lower than the first temperature.

Advantageously, the engine is a gasoline engine.

According to one characteristic, the quantity of the PGM compound can be distributed unequally on the catalysis substrate in a transverse plane of the catalysis substrate.

Preferably, the impregnation layer is arranged over the entire length of the catalysis substrate.

Advantageously, the first zone is a zone subject to a temperature greater than or equal to a predetermined temperature.

The invention also relates to a treatment device for a motor vehicle engine exhaust system, comprising one or more impregnated monoliths arranged between an intake manifold and an exhaust gas exhaust manifold.

Furthermore, the treatment device comprises at least one impregnated monolith as described above.

Advantageously, the monolith impregnated as described previously can be placed facing said exhaust gas inlet manifold of the treatment device.

The invention also relates to a method of manufacturing an impregnated monolith for a device for treating a motor vehicle engine exhaust system, comprising the deposition on a catalysis substrate of an impregnation layer comprising a metal compound platinum group PGM.

Further, the impregnation layer is deposited unevenly on the catalyst substrate such that the amount of the PGM compound in a first area subject to a first temperature of the exhaust gas stream is greater than the amount of the PGM compound a second zone of the catalysis substrate subject to a second temperature of the flow of the exhaust gases lower than the first temperature.

Advantageously, the impregnation layer is deposited unevenly in a transverse plane of the catalysis substrate.

Preferably, the impregnation layer is deposited over the entire length of the catalysis substrate.

According to one embodiment, the deposition of the impregnation layer is carried out in at least two steps: the deposition of a first layer comprising a metal compound of the platinum group PGM on all of the first and second zones of the substrate of catalyzes then the deposition of a second layer comprising a metal compound of the platinum group PGM on the first zone only.

Other aims, advantages and characteristics will emerge from the following description, given for purely illustrative purposes and made with reference to the appended drawings in which:

is a schematic representation of a treatment device for the treatment of the exhaust gases of a motor vehicle, in accordance with the invention.

is a sectional view of a monolith impregnated according to a first embodiment of the treatment device illustrated in FIG. 1, according to the plane II-II, in accordance with the invention.

is a perspective view of an impregnated monolith according to a second embodiment, in accordance with the invention.

illustrates thermal distributions A and B at two different engine operating points.

FIG. 1 represents a device for processing a motor vehicle engine exhaust system, designated by the general reference 1.

The treatment device illustrated is a three-way catalyst for an internal combustion engine.

It comprises a plurality of impregnated monoliths arranged between an intake manifold 2 and an exhaust manifold 3.

In the example illustrated, the treatment device comprises first, second and third impregnated monoliths, respectively referenced 4, 5 and 6.

The exhaust gases treated by the treatment device 1, admitted by the intake manifold 2, pass through all of the impregnated monoliths 4, 5 and 6 and are evacuated by the exhaust manifold 3.

The first impregnated monolith 4, placed opposite the intake manifold 2, comprises a catalyst substrate 7, preferably a cylindrical monolith, for example made of ceramic or metal.

The velocity distribution of the exhaust gas flow exiting the intake manifold 2 is uneven and depends on the shape of the latter. However, the irregular shape of this collector 2 leads to an unequal distribution of the temperature of the exhaust gases so that different zones of the catalyst substrate subject to different temperatures can be identified.

As illustrated in Figures 2 and 3, the first impregnated monolith 4 comprises an impregnation layer 8 comprising at least one metal compound of the platinum group called "PGM" from the English Platinum Group Metals.

By metallic compound of the platinum group, we mean a compound comprising at least one element among the following elements: ruthenium, rhodium, palladium, osmium, iridium, platinum and rhenium.

The impregnation layer 8 is distributed unevenly in the catalysis substrate 7. Indeed, a first zone 9 of the catalysis substrate 7 is subject to a first temperature of the flow of the exhaust gases.

In the catalysis substrate 7 illustrated, two zones 9 and 10 subject to different exhaust gas flow temperatures can be identified.

The first zone 9 of the catalysis substrate 7 is subject to a first temperature of the flow of the exhaust gases and the second zone 10 is subject to a second temperature of the flow of the exhaust gases lower than the first temperature.

The quantity of the PGM compound in the first zone 9 of the catalysis substrate 7 is greater than the quantity of the PGM compound in the second zone 10.

Preferably, the quantity of the PGM compound is unevenly distributed on the catalysis substrate 7 when considering a transverse plane of the catalysis substrate 7.

Preferably again, the impregnation layer 8 is arranged over the entire length of the catalysis substrate 7.

Provision may be made for the first zone 9 at the level of which the impregnation layer 8 comprises a greater quantity of PGM compound than the second zone 10 to be a zone subject to a temperature greater than or equal to a predetermined temperature, for example a high temperature , advantageously between 250 and 450°C.

The amount of PGM compound in the impregnation layer 8 may be proportional to the temperature to which the zone to which the impregnation layer is applied is subjected, in particular from a threshold temperature of the order of 250° C. .

The shape and location of the first and second zones 9 and 10 depend on the shape of the intake manifold 2. According to the example of FIG. 2, the first zone 9 extends in the lower portion of the catalysis substrate 7, whereas in the example illustrated in FIG. 3, the first zone 9 extends in the central portion of the catalysis substrate 7.

Of course, the distribution of the quantity of PGM compound on the catalysis substrate 7 can be carried out over more than two zones, if the catalysis substrate 7 is for example subject to more than two different temperatures, due to a distribution of complex temperature with several areas of relative over-temperature due to the shape of the line of the exhaust duct.

The temperature distribution is known by three-dimensional fluid dynamics simulation or by test and depends on the exhaust duct but does not vary with time which allows, once the temperature distribution has been assessed, to define zones 8 and 9 , position them and calibrate their dimensions. In the case of different thermal distribution A and B depending on the operating point, that is to say the load and the engine speed, as illustrated in Figure 4, the distribution obtained for the most severe operating point will be selected. , namely the distribution which has a widest temperature zone >850°C, here that of case B, so as to further impregnate the high temperature zones, corresponding to low speeds, to reduce polluting emissions when cold and improve the aging of the brick.

To evaluate the thermal distribution, the coefficient γ gamma of watering between 0 and 1 can be used:

where S is the surface, [T] is the temperature at a cell level and [T]mean is the average temperature on the surface.

According to one embodiment, an impregnated monolith according to the invention can be manufactured by deposition on a catalysis substrate 7 of the impregnation layer 8 comprising a metal compound from the platinum group PGM.

The impregnation layer 8 is unevenly deposited on the catalysis substrate 7 depending on the temperature distribution of the substrate 7 so that the quantity of the PGM compound in a first zone subject to a first temperature of the gas flow of exhaust is greater than the amount of the PGM compound of a second region of the catalysis substrate subject to a second temperature of the flow of the exhaust gases lower than the first temperature.

Advantageously, the impregnation layer 8 can be deposited unevenly in a transverse plane of the catalysis substrate and, preferably, deposited over the entire length of the catalysis substrate.

In the example illustrated, the deposition of the impregnation layer 8 is carried out in two steps.

First of all, a first layer of an impregnation composition comprising a metal compound from the platinum group PGM is deposited on all of the first and second zones 9, 10 of the catalysis substrate.

Then, a second layer of impregnating composition comprising a metal compound from the platinum group PGM is deposited on the first zone 9 only.

Of course, provision could be made for the deposition to be carried out in a number of steps greater than two if it is desired to produce more than two zones whose quantity of PGM compound is different.

The amount of PGM compound in the first and second layers will be predetermined as a function of the temperature, the distribution of which will have been previously determined, to which the first and second zones 9 and 10 are subject.

Preferably, the first step of depositing a first layer of impregnating composition 8 is carried out over the entire length of the substrate 7 either in the direction of the exit towards the entrance of the monolith, or in the opposite direction, or even in alternating the two directions by turning over the monolith during the first step of deposition, while the second step of depositing a second layer of impregnating composition is carried out in the direction from the entry to the exit of the monolith with a system jet of impregnating liquid adapted to the thermal distribution, that is to say that the jet is distributed in a variable way according to the temperature of the zone, the shower head of distribution of the jet system therefore has a inhomogeneous distribution of the holes, a dimension and an inclination of each hole of the shower head shaped according to the thermal distribution so as to apply the second layer of impregnating composition in the predetermined zones of relative over-temperature of the substrate 7, the substrate being fixed.

As an alternative to impregnation by inhomogeneous jet of the shower head, the substrate 7 can also be dynamically oriented during the impregnation steps to distribute the layer differently depending on the positions of the zones 9, 10.

This process applies to any type of substrate 7, whether ceramic or metallic, regardless of the number of cells per unit area, the wall thickness or its porosity.

The zones comprising a greater quantity of PGM compound, the first zone 9 in the example illustrated, make it possible to lower the initiation temperature, which will therefore be reached more quickly, making it possible to reduce the emission of pollutants, in particular during the first seconds of starting the vehicle.

The verification of the correct distribution of the impregnation layer 8 on the substrate 7 can be made by material examination by controlling the mass of PGMs used locally on the zone with a higher density of PGMs and globally on the monolith via a control destructive, for example by inductive plasma emission spectroscopy or X-ray fluorescence, or by functional examination by controlling the initiation temperature obtained, for example on a synthetic gas bench.

Preferably, the process is at least applied to the first impregnated monolith 4 since it is the one which treats cold emissions and the most sensitive in terms of premature aging when its watering is not homogeneous. Thus, the quantity of PGM compound being adapted to the temperature to which the considered zone of the catalysis substrate 7 is subjected, the present invention makes it possible to prevent premature aging of the impregnated monolith 4.

Nevertheless, provision may be made for the impregnated monoliths 5 and/or 6 to be obtained according to one embodiment of the manufacturing process as described previously if the watering of these impregnated monoliths 5 and/or 6 is not homogeneous, it that is to say in particular that the thermal distribution in these impregnated monoliths is not homogeneous.

Provision may also be made for the impregnated monolith 4 to be adapted in a treatment device comprising impregnated monoliths in the so-called under-turbo position, or “close coupled” in English, on the exhaust line. Indeed, it is also possible to provide impregnated monoliths in the underfloor position (or "underfloor" in English), however in general the high temperatures are more linked to the position under turbo due to the difficulty of watering linked to architectures constrained in compactness.

The invention makes it possible to adapt the impregnated monolith 4 to the gas flow distribution, and in particular to the thermal inhomogeneity of the substrate 7, in particular in the form of a monolith, to improve the performance of the catalysis, with the geometry of the line existing exhaust without having to modify it, and using a single type of impregnation layer, which avoids the management of diversity and the potential difficulty of proximity between different types of impregnation layers.

Claims (10)

Impregnated monolith for a motor vehicle engine exhaust system treatment device, comprising a catalyst substrate (7) and an impregnation layer (8), said impregnation layer (8) comprising at least one metal of the platinum group PGM, characterized in that the impregnation layer (8) is unevenly distributed on the catalysis substrate (7) so that the amount of the PGM compound in a first region (9) of the catalysis substrate (7) subject to a first exhaust gas flow temperature is greater than the amount of the PGM compound of a second region (10) of the catalyst substrate (7) subject to a second exhaust gas flow temperature lower than the first temperature. Impregnated monolith according to Claim 1, characterized in that the quantity of the PGM compound is unevenly distributed on the catalysis substrate (7) in a transverse plane of the catalysis substrate (7). Impregnated monolith according to Claim 1 or 2, characterized in that the impregnation layer (8) is arranged over the entire length of the catalysis substrate (7). Impregnated monolith according to any one of the preceding claims, characterized in that the first zone (9) is subjected to a temperature greater than or equal to a predetermined temperature. Treatment device for a motor vehicle engine exhaust system, comprising one or more impregnated monoliths (4, 5, 6) arranged between an intake manifold (2) and an exhaust manifold (3) exhaust, characterized in that it comprises at least one impregnated monolith (4) according to any one of Claims 1 to 4. Treatment device according to Claim 5, characterized in that an impregnated monolith (4) according to any one of Claims 1 to 4 is arranged opposite the said inlet manifold (2) for the exhaust gases of the treatment device. . Method of manufacturing an impregnated monolith (4) for a motor vehicle engine exhaust system treatment device, comprising the deposition on a catalysis substrate (7) of an impregnation layer (8) comprising a platinum group metal compound PGM, characterized in that the impregnation layer (8) is unevenly deposited on the catalysis substrate (7) such that the amount of the PGM compound in a first region (9) subject to at a first exhaust gas flow temperature is greater than the amount of the PGM compound of a second region (10) of the catalyst substrate (7) subject to a second exhaust gas flow temperature lower than the first temperature. Manufacturing process according to Claim 7, characterized in that the impregnation layer (8) is deposited unevenly in a transverse plane of the catalysis substrate (7). Manufacturing process according to Claim 7 or 8, characterized in that the impregnation layer (8) is deposited over the entire length of the catalysis substrate (7). Manufacturing process according to any one of Claims 7 to 9, characterized in that the deposition of the impregnation layer (8) is carried out in at least two stages: the deposition of a first layer comprising a metal compound of the group platinum PGM on all of the first and second zones (9, 10) of the catalysis substrate (7) then the deposition of a second layer comprising a metal compound of the platinum group PGM on the first zone (9) only.