WO2019086385A1

WO2019086385A1 - Use of a colloidal dispersion as a gpf regeneration additive

Info

Publication number: WO2019086385A1
Application number: PCT/EP2018/079586
Authority: WO
Inventors: Thierry Seguelong; Antoine LACARRIERE
Original assignee: Rhodia Operations
Priority date: 2017-11-01
Filing date: 2018-10-29
Publication date: 2019-05-09
Also published as: FR3072968A1

Abstract

The present invention relates to the use of a colloidal dispersion comprising particles as a regeneration additive for a particulate filter of a direct- or indirect-injection petrol engine. The invention also relates to a method for regenerating the particulate filter.

Description

Use of a colloidal dispersion as a GPF regeneration additive

This application claims priority to French patent application No. 1760308 filed on November ^1, 2017 and whose contents are fully incorporated by reference. In case of inconsistency between the text of the present application and the text of the French patent application which affects the clarity of a term or expression, reference will be made to this application only.

Technical area

The present invention relates to the use of a colloidal dispersion as a regeneration additive of a particulate filter of a gasoline engine with direct or indirect injection. The invention also relates to a regeneration process of said particulate filter.

Technical problem

The automotive market is currently experiencing the commercial development of new gasoline engines called direct injection that have reduced fuel consumption and better driving pleasure (low-end torque). To improve performance, these new engines operate with high fuel injection pressure and fuel injectors with the right geometry. The air / fuel mixture is obtained in the combustion chamber. In fact, this particular operation can lead to heterogeneities in the combustion and the formation of carbonaceous particles for which environmental standards, be they European, Asian or American, impose increasingly strict limits. This particular operation also generates the formation of deposits at the fuel injectors themselves and downstream of them. This fouling has an impact on the combustion and therefore on the primary emissions (that is to say the emissions in motor output), in particular those of the carbonaceous particles, which become important. A similar phenomenon with gasoline combustion systems with indirect injection could also be observed.

To meet the regulations and the durability of emissions, we associate with gasoline engines with direct or indirect injection, a particulate filter suitable for these gasoline engines, also called GPF (Gasoline Particulate Filter). The operation of the GPF is known: the carbonaceous particles emitted by the engine accumulate on the filter and during the regeneration phase (so-called purge), for example when the amount of accumulated particles has reached a given threshold, the Carbonaceous particles are burned inside the filter and vented to the atmosphere as carbon dioxide. If the operation resembles that of a DPF, it differs however because unlike diesel engines, gasoline engines operate with a lower air / fuel ratio, which therefore limits the presence of oxygen downstream of the combustion chamber. Therefore, it is more difficult to oxidize the carbonaceous particles that would be deposited on the walls of the GPF.

It is therefore necessary to develop a solution that aims to effectively burn the carbon particles that have been deposited on a particulate filter of a direct or indirect injection gasoline engine whatever the driving configuration of the vehicle ( altitude, cold climate, ...).

Brief description of the invention

The invention relates to the use of a colloidal dispersion comprising particles consisting of an oxide and / or a hydroxide and / or an oxyhydroxide:

- iron and / or cerium; or

cerium and an element E selected from the group consisting of Al, Cu, Ti, Zr, La, Pr, Nd and Y;

dispersed in a liquid organic phase,

as a regeneration additive for a particulate filter of a direct or indirect injection gasoline engine.

The term "colloidal dispersion" is used to describe particles dispersed in a liquid phase and having a size of between 1 and 100 nm.

The invention also relates to a method of regenerating a GPF of an internal combustion engine operating with gasoline consisting of using a gasoline to which has been added a colloidal dispersion comprising particles consisting of an oxide and / or or a hydroxide and / or an oxyhydroxide:

- iron and / or cerium; or

cerium and an element E selected from the group consisting of Al, Cu, Ti, Zr, La, Pr, Nd and Y. The invention therefore also relates to a method for regenerating a GPF of a gasoline internal combustion engine consisting in using a gasoline in which particles consisting of an oxide and / or a hydroxide and / or a oxyhydroxide:

- iron and / or cerium; or

- cerium and an element E selected from the group consisting of Al, Cu, Ti, Zr, La, Pr, Nd and Y. The regeneration consists of burning the carbonaceous particles that have deposited on the walls of the GPF . The invention can be applied to a direct injection gasoline engine in which the gasoline is injected directly into the combustion chamber of the engine or to an indirect injection gasoline engine in which gasoline is injected upstream into the intake manifold upstream of the intake valve. In direct or indirect injection engines, the fuel injection is frequently controlled by an electronic unit according to predefined parameters (eg engine speed, engine temperature, engine load, etc.). Technical background

Dispersions based on iron or cerium are already known as additives for diesel under the term BCF for "Fuel Borne Catalyst". The role of the iron or cerium particles present in diesel is to catalyze, in the presence of oxygen, the combustion of soot deposited on a DPF (Diesel Particulate Filter) type particle filter. Thus, for example, WO 2008/1 16550 describes the use of a colloidal dispersion of an iron compound used to reduce the fouling of injectors of a diesel engine. The use and the method described in the present application are therefore different because the particulate filter is different and operates differently from a DPF.

detailed description

The particles consist of an oxide and / or a hydroxide and / or an oxyhydroxide:

- iron and / or cerium; or

cerium and at least one element E selected from the group consisting of Al, Cu, Ti, Zr, La, Pr, Nd and Y. It can be considered that the composition of the particles is essentially an oxide and / or hydroxide and / or an oxyhydroxide of iron and / or cerium or cerium and an element E. The term "essentially" means that the particles are consisting of an oxide and / or hydroxide and / or a hydroxide and may also contain residual compounds from the particle preparation process. For example, in the case of precipitating the particles from an aqueous solution of nitrate or chloride, the particles may contain nitrate or chloride ions. Similarly, in the case where an iron or cerium complexing agent is used in the precipitation as taught in application WO 2003/053560, the particles may contain residues of said complexing agent.

In the case of mixed particles based on iron and cerium, the proportion of iron in the particles can vary from 0.5% to 50%, more particularly from 0.5% to 25%, this proportion being expressed by weight of iron oxide relative to the total weight of the particles. In the case of mixed particles based on E and cerium, the proportion of the element E or the total proportion of the elements E in the particles may vary from 0.5% to 50%, more particularly from 0.5% to 25%, this proportion being expressed by weight of the oxide or oxides of E relative to the total weight of the particles. The proportion of cerium in the mixed particles may vary from 50% to 99.5%, more particularly from 75% to 99.5%, this proportion being expressed by weight of cerium oxide relative to the total weight of the particles. It will be noted that in the case where E is zirconium, hafnium is generally also present. These proportions are given by weight of oxide unless otherwise indicated. For these calculations it is considered that the cerium oxide is in the form of ceric oxide (CeO 2) and that the other elements are in the following forms: Al 2 O 3, Fe 2 O 3, CuO, Al 2, ZrO 2, HfO 2, La 2 O 3, P 2 O 3, Nd2O3, Y2O3. The proportions of the elements can be obtained using the usual analysis techniques in laboratories, in particular X-ray fluorescence.

In the dispersion, the particles are dispersed in a liquid organic phase. Preferably, the liquid organic phase is chosen to be compatible with the gasoline used. However, it should be noted that the problem of compatibility or interference with gasoline is generally not to be feared when the amount of dispersion that is added to gasoline is low, which is usually the case. The liquid organic phase may be an apolar hydrocarbon that is to say which has a dipole moment resulting zero. As an example of liquid organic phase, there may be mentioned aliphatic hydrocarbons such as hexane, heptane, octane, nonane; cycloaliphatic hydrocarbons such as cyclohexane, cyclopentane or cycloheptane; aromatic hydrocarbons such as benzene, toluene, ethylbenzene, xylenes, liquid naphthenes. Also suitable are petroleum fractions containing a mixture of iso- and cyclo-paraffinic hydrocarbons such as Isopar ^® or Herbal ^®. For example, it is possible to use Isopar ^® L, Tisane ^® 175 or Tisane ^® 185. Also suitable are petroleum fractions containing a mixture of alkylbenzenes in particular dimethylbenzene and tetramethylbenzene, such as Solvesso ^® .

The particles of the dispersion according to the invention can be amorphous or crystallized.

According to another characteristic of the invention, at least 85%, more particularly at least 90% and even more particularly at least 95% of the particles of the dispersion are primary particles. The term "primary particle" means a particle that is perfectly individualized and that is not aggregated with another or more other particles. This characteristic can be demonstrated by the method of counting by MET (high resolution transmission electron microscopy) described later. The% given here is a% by number.

The particles of the dispersion may have at least one of the following characteristics:

^■ when the particles are crystallized, a mean size ÔDRX determined by diffraction technique of less than X-ray or equal to 10 nm;

^■ a mean size DMET determined using the lower MET or equal to 10 nm;

^■ a hydrodynamic diameter D _h measured by dynamic light scattering, less than or equal to 30 nm. dDRx is the size t of the coherent domain calculated according to the Scherrer model from the width of one or more diffraction peaks most intense oxide. It is possible to use several characteristic peaks (2 or 3) to calculate ÔDRX- In this case, ÔDRX corresponds to the arithmetic mean of the corresponding t-sizes. According to Scherrer's model, a size t is determined by the following formula:

t: size at the angle 2Θ (theta);

k: form factor equal to 0.89;

λ (lambda): wavelength of the incident beam 1, 54 Å;

H: width at half height of a characteristic peak;

s: width due to instrument optics defect which depends on the instrument used and angle Θ (theta);

Θ: Bragg angle.

The instrumental width can be determined in a manner known to those skilled in the art by LaBe analysis.

The particles may consist of an oxide, especially an iron oxide, in particular a crystallized iron oxide. When the iron oxide is magnetite and / or maghemite and the diffraction peaks (440) described respectively in sheets 01 -088-0315 and 00-039-1346 and the ICDD (International Center for Diffraction Data). When the iron oxide is poorly crystallized, it is possible to retain the wide diffraction peak located between 35 ° and 61 °.

The particles may consist of a cerium oxide. In this case, we can retain the diffraction peaks described in ICDD file 01-089-8436. In particular, the peaks can be selected at the following angles: 28.5 ° ± 0.1; 47.5 ± 0.1 and 56.3 ± 0.1.

When the particles are based on iron and cerium or E and cerium, especially when the particles consist of a mixed oxide of iron and cerium or a mixed cerium oxide and the element (s) E, the characteristic peaks that can be retained can correspond to those of the iron oxide or cerium or the element E or may be offset with respect thereto.

The DRX analysis may be carried out, for example, on a commercial apparatus of the X'Pert PRO MPD PANalytical type comprising in particular a g-Θ goniometer, allowing the characterization of liquid samples. The sample remains horizontal during the acquisition and it is the source and the detector that move. This installation is driven by the X'Pert Datacollector software provided by the manufacturer and the exploitation of the diffraction diagrams obtained can be carried out using the software X'Pert HighScore Plus version 2.0 or higher (PANalytical supplier). di iET is calculated from a particle size distribution determined using TEM. The particles have a dMET of less than or equal to 10 nm, dMET being calculated from a particle size distribution determined using TEM. The method for obtaining the distribution consists in measuring the diameter of at least 300 particles on one or more electron microscope slides (after depositing the dispersion on a membrane and allowing the liquid organic phase to evaporate). The enlargement of the microscope which is retained must make it possible to clearly distinguish the images of the particles on a snapshot. The enlargement can be for example between 50 000 and 1 000 000. The diameter of a particle which is retained is that of the minimum circle allowing to circumscribe the entirety of the image of the particle as it is visible on a MET snapshot. The term "minimum circle" has the meaning given to it in mathematics and represents the circle of minimum diameter to contain a set of points of a plane. Only particles with at least half of the perimeter are defined. ImageJ software can be used to do more simple processing; this open access software was originally developed by the NIH American Institute and is available at http://rsb.info.nih.gov or http://rsb.info.nih.gov/ii/ download.html. After determining the diameters of the particles retained by the above method, said diameters are grouped into several size classes ranging from 0 to 300 nm, the width of each class being 1 nm (it being understood that for dispersions having a tight distribution , some of the classes may be empty). The number of particles in each class is the basic data to represent the (cumulative) number distribution. From the distribution, the mean diameter dMET is determined which corresponds to the median diameter as conventionally understood in statistics. dMET is such that 50% of the particles (in number) taken into account on the plate (s) MET have a diameter smaller than this value. The hydrodynamic diameter D _h (median diameter) is measured by dynamic light scattering from a number distribution of particle sizes. The measurement is made in the liquid organic phase of the dispersion.

As examples of colloidal dispersions, mention may be made of those described in the following patent applications and patents: US Pat. No. 6,210,451, EP 671,205, WO 97/19022, WO 01/10545 and WO 03/053560, the latter two notably describing dispersions based on of cerium and iron compounds respectively and additionally containing an amphiphilic agent. Applications WO 2012/084838 and WO 2012/084851 also describe dispersions of an iron compound in crystallized form which can also be used. EP 2129751 B1 describes iron oxide particles on which is grafted a long chain polycarboxylic acid.

The particles may consist of an oxide and / or a hydroxide and / or an iron oxyhydroxide. These particles can be prepared according to the teaching of the international application WO 03/053560. The particles may consist of an oxide and / or a hydroxide and / or a cerium oxyhydroxide. These particles may be prepared according to the teaching of US Pat. No. 6,210,451 or EP 0671205. More particularly, the particles may be based on cerium dioxide and may be in the form of crystallite aglomerates whose d80 (number distribution) is at most equal to 10 nm, d80 being determined by high transmission electron microscopy counting.

The particles may be in the form of cerium oxide. These particles can be prepared according to the teaching of international applications WO 97/19022 or WO 01/10545.

To ensure stability of the dispersion, it advantageously comprises at least one amphiphilic agent whose function is to stabilize the particles. The amphiphilic agent may be a carboxylic acid comprising from 7 to 50 carbon atoms, preferably from 7 to 25 carbon atoms. The carboxylic acid may be a monoacid or a diacid. This acid can be linear or branched. It can be chosen from aryl, aliphatic or arylaliphatic, optionally carrying other functions provided that these functions are stable in the environments where it is desired to use the dispersions according to the present invention. Thus, it is possible to use, for example, aliphatic carboxylic acids, whether natural or synthetic.

By way of example of acids, mention may be made of tall oil fatty acids, soya oil, tallow, linseed oil, oleic acid, linoleic acid, stearic acid and its isomers , in particular isostearic acid, pelargonic acid, capric acid, lauric acid, myristic acid, dodecylbenzenesulfonic acid, ethyl-2-hexanoic acid, naphthenic acid, acid hexoic. Oleic or isostearic acid are two acids that may be suitable for stabilizing particles. It may also be succinic acids substituted with polybutenyl groups, for example PIBSA of formula (I) in which PIB denotes a polybutenyl group:

The amphiphilic agent may also be the compound of formula (II):

(II) or the diacid derived from the compound of formula (II).

In the case of amphiphilic agents of formula (I) or (II), the agent can graft chemically on the particles. For this purpose, a dispersion of an iron compound which is prepared from iron (III) chloride and sodium bicarbonate and the compound of formula (I) of formula ( II) or the diacid derived from said compound of formula (II), following the teaching of example 1 of EP 2129751 B1. Mixtures of acids may also be used, particularly acid mixtures which contain chain length distributions. For example, Prisorine 3501 from Croda corresponds to a mixture of C16-C22 acids.

The amphiphilic agent may also be chosen from polyoxyethylenated alkyl ether phosphates. Phosphates of formula

R 1 -O- (CH ₂ -CH ₂ -O) n P (= O) (OM) ₂

or else the polyoxyethylenated dialkoyl phosphates of formula:

R3-O- (CH 2 CH ₂ O) nP (X) (= O) (OM) where X = R ₂ -O- (CH ₂ CH ₂ O) _n - wherein:

^■ R, R _2, R 3, identical or different, represent a linear or branched alkyl group, which may comprise from 2 to 20 carbon atoms; a phenyl radical; an alkylaryl radical, more particularly an alkylphenyl radical, especially having an alkyl chain group of 8 to 12 carbon atoms; an arylalkyl group, more particularly a phenylaryl radical;

^■ n is an integer representing the number of ethylene oxide ranging from ranging from 0 and 12;

^■ M represents a hydrogen atom, sodium or potassium.

The radical R 1 may especially be a hexyl, octyl, decyl, dodecyl, oleyl or nonylphenyl radical.

One example is of this type of amphiphilic compounds marketed under the trademarks ^® and Lubrophos Rhodafac ^® marketed by Rhodia and especially the products below:

- poly-oxy-ethylene alkyl (Cs-Cio) ether phosphates Rhodafac ^® RA 600;

- the poly-oxyethylene tridecyl ether phosphate Rhodafac ^® RS 710 or RS 410;

- poly-oxy-ethylene oleocetyl ether phosphate Rhodafac ^® PA 35;

poly (oxy) ethylene nonyl phenyl ether phosphate Rhodafac ^® PA 17;

Rhodafac ^® RE 610 poly (ethylene oxide) nonyl (branched) ether phosphate.

The amphiphilic agent may also be chosen from polyoxyethylenated alkyl ether carboxylates of formula: R ₄ - (OC ₂ H ₄ ) _n -OR ₅ in which R ₄ is a group linear or branched alkyl may include in particular 4 to 20 carbon atoms, n is an integer of up to 12 for example and R ₅ is a carboxylic acid residue such as -CH ₂ COOH. As an example may be mentioned for this type of amphiphilic compound those marketed under the brand AKIPO ^® by Kao Chemicals.

In addition to the particles previously described, the dispersion may also comprise at least one other additive selected from the group consisting of corrosion inhibitors, additives improving the lubricating power, detergents, defoamers, antifreezes, antioxidants, dyes, stabilizing additives, additives improving the octane number. These additives are used to prevent wear or seizure of high pressure pumps including injectors. This other additive can be added directly to the colloidal dispersion. According to one variant, the combination of the particles and the other additive can be obtained by separately introducing said additive into the gasoline.

Thus, the dispersion comprises:

the particles as previously described, in particular the particles of iron oxide, cerium oxide, mixed iron oxide and cerium oxide or mixed cerium oxide and element E;

at least one amphiphilic agent;

the liquid organic phase;

optionally an additive selected from the group consisting of corrosion inhibitors, additives improving the lubricating power, detergents, defoamers, antifreezes, antioxidants, colorants, stabilizing additives, additives improving the index of octane.

According to one embodiment, the dispersion does not include the additive. According to another embodiment, the dispersion consists of the particles, at least one amphiphilic agent and a liquid organic phase.

The dispersion is used as a regeneration additive for a particulate filter of a direct or indirect injection gasoline engine. This particle filter (commonly called GPF) is placed on the exhaust line and its function is to reduce the number of carbon particles emitted by the engine of the engine. vehicle, in order to meet environmental standards on carbon emissions.

The GPF is a porous device that reduces, by a filter mechanism, emissions of carbonaceous particles below a regulatory limit, for example 6.0 x 10 ⁺¹¹ particles / km when considering the vehicle or 6.0 x 10 ⁺¹¹ particles / kW.h when considering only the motor, especially in dynamic cycle (eg according to the cycle "World Harmonized Transient Cycle - WHTC - or the recent cycle" European Transient Cycle "- This particulate filter is therefore suitable for the filtration of carbonaceous particles from the combustion of gasoline and differs from conventional particulate filters used to filter soot particles from diesel combustion (also commonly known as diesel fuel). DPF) The GPF can be made of a porous ceramic, a ceramic or metallic foam, or an entanglement of ceramic or metallic threads The geometry of the filter (size, filtration area, porosity and distribution) pore size reduction) is variable and depends on the solution chosen by the manufacturer whose constraints are as follows:

- a reduction in emissions of carbonaceous particles below the regulatory value;

- a limitation of the fuel consumption of the vehicle;

- maintain a filter efficiency even in the presence of residues from the consumption of oil or other fluids and other organs used by the engine.

The particles of the dispersion have the function of catalyzing the combustion of the carbonaceous particles which have deposited on the walls of the filter. The particles of the dispersion make it possible to burn the carbonaceous particles at a lower temperature and / or for a shorter regeneration time than in the absence of particles of the dispersion. The regeneration is carried out in order to burn all the carbonaceous particles present on the walls of the filter. The regeneration is generally caused that is to say triggered by an engine injection calculator when a parameter representative of the amount of carbonaceous particles in the GPF is reached. Each car manufacturer can choose the appropriate trigger mode. Thus, to trigger the regeneration, one can inject gasoline at the entrance of the GPF or in the cylinders of the engine at the end of the compression time so that the gasoline does not participate in combustion and is exhausted. It is also possible to regulate the operation of the engine by adjusting the ignition and / or phasing of the fuel injection in the combustion cycle so as to degrade the combustion efficiency and thus increase the heat losses at the engine. exhaust. The duration of the regeneration is therefore variable, it being understood that it is preferable that this duration be as short as possible. It is also possible that the GPF will operate continuously and that the carbonaceous particles will be burned as they accumulate on the filter walls.

In general, the exhaust gas temperature for a gasoline engine is higher than for a diesel engine. The exhaust gas temperatures of a gasoline engine can be in the range of 550 ° C to 670 ° C. During regeneration, the temperature of the GPF must be sufficient for the carbonaceous particles to be burned efficiently whether for triggered regeneration or for continuous regeneration. Preferably, for an effective combustion of the carbonaceous particles, the temperature of the GPF is at least 200 ° C., or even at least 400 ° C., or even at least 450 ° C. The GPF may be disposed at several points in the exhaust line. It can be in the "close-coupled" (ie close to the engine) or "sub-floor" position (ie in a position on the exhaust line farther than the position close-coupled). The "close-coupled" position is advantageous because, as a result, the GPF can benefit more effectively from the caloric energy provided by the combustion gases.

Note that in addition to the GPF, the exhaust line may also include at least one other device for reducing other pollutants such as CO, unburned hydrocarbons or NO _x . This other device can be arranged on the exhaust line before or after the GPF in the direction of flow of the exhaust gas. Fig. 1 shows several examples of combinations of such a device type TWC ("Three-Way Catalyst" or catalyst 3-way) with the GPF.

Modes of introduction of dispersion

Addition of dispersion in gasoline: Dispersion can be added to gasoline in several ways. It can be added to gasoline continuously or discontinuously. The dispersion is added in the gasoline either at the tank level of gasoline either in the low-pressure gas line (eg in the outbound line, the return line, or at the fuel filter). The dispersion is contained in an on-board tank. The batch introduction is an intermittent addition of the dispersion in the gasoline, which saves dispersion. It can be added to gasoline using a metering pump that can be controlled by an on-board electronic system (ECU). The addition of the dispersion is controlled according to several parameters of the ECU, for example the quantity of carbonaceous particles in the GPF, the temperature of the GPF, the moment when the regeneration is triggered, etc.

The dispersion can also be added manually and batchwise to the fuel tank. The dispersion is then contained in doses and pods that are generally marketed in networks accessible to the general public.

Whatever the method of adding the dispersion to gasoline, the proportion of the dispersion in gasoline is generally less than or equal to 100 ppm, or even less than or equal to 50 ppm, this proportion being expressed in weight by weight particles constituting the dispersion with respect to the gasoline just before its injection into the combustion chamber. This proportion may be more particularly between 1 and 50 ppm.

Introduction of the dispersion in the exhaust line: the dispersion can also be introduced into the exhaust line, that is to say between the exhaust manifold and the GPF, from an onboard tank containing the dispersion. The point of introduction of the dispersion can be optimized to reduce fouling of mechanical parts on the exhaust line, such as EGR valves, or carbon deposits that could poison TWC catalysts upstream of the GPF . The dispersion can be introduced by an injection means, such as for example an injector. This introduction mode has the advantage of effectively using the dispersion because the dispersion can be introduced only when necessary, which allows to limit the consumption. Here too, the dispersion can be introduced into the exhaust line continuously or discontinuously. Here too, it can be added to gasoline using a metering pump that can be driven by an ECU. The introduction is controlled according to several parameters of the ECU, for example the quantity of carbonaceous particles in the GPF, the temperature of the GPF, the moment when the regeneration is triggered, ...

The gasoline engine operates with a lower oxygen content than a diesel engine. Generally, the stoichiometric air / fuel mass ratio is 14.7: 1. In operation, the ratio can be between 10: 1 and 70: 1. The factor λ can be between 0.9 and 1.10.

The engine equipped with a GPF operates with an injection of petrol under pressure. The fuel injection pressure can be at least 100 bar. This pressure can reach 500 bar, current technical limitation but which could become higher with the technological progress to come.

Examples

Carbonaceous (soot) particles are first impregnated with a colloidal dispersion of CeO ₂ in water (15% by weight of Ce oxide with respect to soot). The soot combustion temperature is then determined using thermogravimetric analysis (ATD-ATG). A Mettler TGA / DCS3 + LF1 thermobalance 100 connected directly at the furnace outlet to a Bruker IR spectrometer for analyzing the flue gases is used for this purpose.

The program used for ATG is as follows: rise in ambient temperature to 150 ° C at 5 ° C / min; isothermal at 150 ° C for 1 h; temperature rise from 150 ° C to 1000 ° C to 10 ° C / min. The sample is flushed with a gas at a flow rate of 50 mL / min which is either nitrogen or a mixture of nitrogen + 2% O ₂ (representative of the composition of an exhaust gas from a gasoline engine which does not contains only a few hundred ppm of 0 ₂ ). The sample is contained in a 70 μΙ alumina crucible with a lid. The mathematical compensation of Archimedes' thrust (equivalent to the subtraction of a blank test under the same conditions) is used.

Fig. 2 represents the weight loss in% relative to the temperature in ° C for two samples under a nitrogen sweep:

- soot without cerium oxide (white);

- the same soot with cerium oxide. Fig. 3 represents the weight loss in% with respect to the temperature in ° C for two samples under a purge of the nitrogen + O ₂ mixture:

- soot without cerium oxide (white);

- the same soot with cerium oxide. These two figures show that soot combustion is initiated at a lower temperature in a low O ₂ atmosphere.

Claims

1. Use of a colloidal dispersion comprising particles consisting of an oxide and / or a hydroxide and / or an oxyhydroxide:

- iron and / or cerium; or

dispersed in a liquid organic phase,

2. Use according to claim 1 wherein the particles have at least one of the following characteristics:

^■ a mean size ÔDRX determined by diffraction technique of less than X-ray or equal to 10 nm;

^■ a mean size DMET determined using the lower MET or equal to 10 nm;

^■ a hydrodynamic diameter D _h measured by dynamic light scattering, less than or equal to 30 nm.

3. Use according to one of the preceding claims wherein the dispersion comprises:

- the particles ;

at least one amphiphilic agent;

a liquid organic phase;

4. Use according to claim 3 wherein the amphiphilic agent is a carboxylic acid comprising from 7 to 50 carbon atoms, preferably from 7 to 25 carbon atoms.

5. Use according to claim 3 or 4 wherein the amphiphilic agent is selected from tall oil fatty acids, soybean oil, tallow oil, linseed oil, oleic acid, linoleic acid, stearic acid and its isomers, in particular isostearic acid, pelargonic acid, capric acid, lauric acid, myristic acid, dodecylbenzenesulfonic acid, 2-ethylhexanoic acid, naphthenic acid, hexoic acid.

6. Use according to one of the preceding claims wherein the particles consist of iron oxide, cerium oxide, a mixed oxide of iron and cerium or a mixed cerium oxide and the one or more element (s) E.

7. Use according to one of the preceding claims characterized in that at least 85%, more particularly at least 90% and even more particularly at least 95% of the particles of the dispersion are primary particles.

8. Use according to one of the preceding claims wherein the particles are amorphous or crystallized.

9. Use according to one of the preceding claims wherein:

dispersion is added to the gasoline continuously or discontinuously; or

the dispersion is introduced into the exhaust line.

10. A method of regenerating a GPF of an internal combustion engine operating with gasoline consisting in using a gasoline to which has been added a colloidal dispersion as described in one of claims 1 to 8.

1 1. A method of regenerating a GPF of a gasoline internal combustion engine comprising using a gasoline in which particles as described in one of claims 1 to 8 are dispersed.

12. The method of claim 10 or 11 wherein:

dispersion is added to the gasoline continuously or discontinuously; or

the dispersion is introduced into the exhaust line.

13. The method of claim 10 to 12 wherein the GPF temperature is at least 200 ° C, or even at least 400 ° C, or even at least 450 ° C.

14. Method according to one of claims 10 to 13 wherein the GPF is arranged in "close-coupled" position.

15. Method according to one of claims 10 to 14 wherein the exhaust line also comprises at least one other device for reducing pollutants other than carbonaceous particles such as CO, unburned hydrocarbons or NO _x .