FR2818163A1 - Catalyst preparation, for burning-off diesel soot, includes reaction between copper chloride and copper difluoride, followed by hot oxidation - Google Patents

Abstract

The present invention provides a process for preparing a catalyst, the catalyst thus obtained as well as the use of the catalyst, in particular, in the reduction of particles emitted in the exhaust gases of lean-burn engines, in particular of automobile engines.The present invention relates more particularly to the preparation of an active catalyst phase for the combustion of soot from a diesel engine.

Description

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"Process for the preparation of a catalyst, catalyst and use of a catalyst for the combustion of soot"
The present invention relates to a process for the preparation of a catalyst, the catalyst thus obtained and the use of the catalyst, in particular for the reduction of particles emitted in the exhaust gases of lean-burn engines, in particular of automobile engines.

 The present invention more particularly relates to the preparation of an active catalyst phase for the combustion of soot produced by a diesel engine.

 It is well known that gaseous emissions of hydrocarbons, carbon monoxide and other nitrogen oxides from gasoline engines from static sources or motor vehicles represent a serious health problem.

 In addition to these gaseous pollutants, lean-burn engines, particularly diesel engines, emit soot particles comprising carbonaceous substances which contain adsorbed hydrocarbons as well as inorganic compounds containing constituents which have been found to be carcinogenic.

 Also, particles from diesel engines are subject to increasingly stringent regulations from agencies or ministries of environmental protection. In the case of the European Union, for example, the 100 mg / km of particles authorized according to the Euro1996 standard will have to be reduced to 25 mg / km for Euro2005.

 To solve this problem of emission of soot particles by diesel engines, various processes have been proposed to date, in particular the filtration of exhaust gases by passing through a porous wall of a filter, metallic or based on cordierite type ceramic or silicon carbide, also called particle filter.

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However, in general, the use of conventional filter systems is not without inconvenience.

 Indeed, as and when the filter is loaded, the pressure drop of the latter increases as a function of the thickness of soot accumulated on the surface of its wall, resulting in overconsumption of fuel, with equal power output.

 Moreover, when the pressure drop becomes too great, the filter must be regenerated by burning soot.

However, the exhaust gas temperatures do not always make it possible to burn the soot and, in particular, the low load urban runs result in the clogging or complete clogging of the filters installed on the vehicles.

 To ensure regeneration in all cases of rolling, it has been envisaged to couple an external power source to increase the temperature of the gas to reach 600 C approximately, including electric heating or by additional fuel combustion.

 Still to regenerate the filters, it has also been envisaged to add one or more diesel additives to increase the kinetics of combustion to initiate regenerations at lower temperatures, about 500 C. Examples of additives currently marketed and which have received certain approvals, notably in Germany, may be mentioned iron and cerium.

 The techniques mentioned above, however, remain complex and expensive to implement on a vehicle.

 There is therefore a need for a catalyst that overcomes the difficulties encountered with current catalyst filter systems and that allows in particular to burn soot particles at temperatures of about 300 OC, that is to say at the usual temperatures of exhaust gas.

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 To satisfy such a need, the invention proposes, according to a first aspect, a process for preparing a catalyst comprising an active phase and a support comprising the following successive stages consisting of: (i) reacting cuprous chloride and bifluoride copper, - (ii) oxidize at a temperature of 600 C to 800 C under oxygen and then - (iii) cool, to room temperature under oxygen, the preceding mixture.

 Alternatively, the process according to the invention further comprises the following successive successive steps consisting in: (i) reacting iron chloride and aluminum chloride in aqueous solution, - (ii) adjusting the pH of the preceding mixture at a pH of 5 to 7 using an alkaline solution, and - (iii) extracting and then drying the precipitate thus obtained.

selon l'invention, de préférence une température d'environ 800 C est atteinte, à raison d'un accroissement d'environ 25 C par minute. During the oxidation step under pure oxygen of the process

according to the invention, preferably a temperature of about 800 ° C is reached, at an increase of about 25 C per minute.

 Even more advantageously, said temperature is maintained at about 800 ° C for about 2 hours.

 Preferably, the process according to the invention is further characterized by a deposition of said active phase of the catalyst on a support selected from ceramic filters such as, for example, oxide ceramics such as cordierite preferably, the ceramic filter used. is a ceramic monolith. As another useful support for the realization of the method according to the present invention, mention may be made of metal filters, such as H.sub.J filters. Preferably, filters based on micron iron powder are used.

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 According to a second aspect, the present invention relates to a catalyst comprising the following constituents: copper, iron, oxygen, chlorine and fluorine.

Advantageously, the catalyst according to the invention is such that the values of the mass percentages of its various constituents vary within the limits of the following intervals:
Copper from 5% m to 50% m
Iron from 10% m to 60% m
Oxygen from 30% m to 40% m
Chlorine from 1% m to 5% m
Fluorine from 0.1% m to 2% m.

 Alternatively, the catalyst according to the present invention further comprises alumina. According to this variant, advantageously, the values of the mass percentages of aluminum are in the range 5% m to 20% m.

 The present invention further relates, in a third aspect, to the use of a catalyst, as defined above or obtained by the process also mentioned above, for the combustion of soot.

 The present invention will now be described in more detail in its characteristics and other advantages with reference to the single appended figure which represents the evolution of the soot oxidation rate as a function of the temperature for a catalyst obtained according to a first and a second embodiment of the method according to the invention.

 The following examples are given purely by way of illustration and without any limitation of the invention.

Example 1
Process for the preparation of the active phase of the catalyst for depositing on a ceramic monolith

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1. 1. Preparation of the active phase
2.9 g of iron chloride (FeCl 3) and 10.5 g of aluminum chloride (AlCl 3) are dissolved in 70 ml of water, the operation being accompanied by a significant release of hydrochloric acid. The pH of the solution is adjusted to about 5 by adding 13 g of sodium hydroxide (NaOH) in 60 ml of distilled water. The precipitate obtained is dried on a sand bath with stirring.

This precipitate is then finely ground and added with 1.2 g of cuprous chloride (CuCl) and 0.1 g of copper bifluoride (CuF2).

pendant 2 h à environ 800 OC. Le refroidissement à température ambiante est également effectué sous oxygène pur. 1.2 Activation of the catalyst
The previously mixed mixture is placed in a ceramic reactor with an internal diameter of 12 mm countercurrently swept by a flow of 167 ml / min of pure oxygen and heated very rapidly to about 800 OC by introducing the reactor into the reactor. a preheated oven. The treatment is continued

for 2 hours at about 800 OC. Room temperature cooling is also performed under pure oxygen.

 The most active catalysts are obtained by carrying out heat treatment on small amounts of powder, typically 1 g to 2 g. These amounts can be increased by changing the characteristics of the reactor and the furnace.

1.3 Activity test
The soot oxidation rate curve on a mixture of 2 mg of soot per 98 mg of catalyst is shown in FIG.

 It is noted that between 220 OC and 300 OC, about 1 mg of soot is oxidized per g of catalyst per minute.

 This catalyst oxidized three charges of 2 mg of soot and a load of 20 mg of soot, without any notable change in its catalytic properties.

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 Another important advantage of this catalyst is that its catalytic properties are not affected by the addition of 10% water vapor to the reaction mixture.

constituants du catalyseur neuf

1.4 Microanalysis of the catalyst
Table 1: Percentages of different

constituents of the new catalyst

<Tb>
<tb> AI <SEP> Cu <SEP> Fe <SEP> 0 <SEP> CI <SEP> F
<tb> (% <SEP> m) <SEP> (% <SEP> m) <SEP> (% <SEP> m) <SEP> (% <SEP> m) <SEP> (% <SEP> m) <SEP> (% <SEP> m)
<tb> 21.4 <SEP> 21.5 <SEP> 16, <SEP> 8 <SEP> 37, <SEP> 8 <SEP> 1.4 <SEP> 1, <SEP> 0
<Tb>

Example 2
Process for preparing the active phase for deposition on a metal filter
2 1 Preparation of the active phase
An intimate mixture of 500 mg of 6- to 10-micron ferric iron powder of 600 mg of cuprous chloride (CuCl) and 50 mg of copper bi fluoride (CuF2) is ground in a mortar and placed in a reactor identical to that of Example 1. A stream of pure oxygen of 167 m 2 / min is set against the current and the temperature is raised from room temperature to about 800 ° C at about 25 ° C per minute. Cooling is carried out under pure oxygen.

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2. 2 Activity test The soot oxidation rate curve on a mixture of 2 mg of soot per 98 mg of catalyst is shown in Figure 2.

 It is noted that by limiting the operating temperature to 300 OC and even adding 10% of water vapor in the reaction mixture, the catalyst keeps its activity intact after combustion of 34 mg of total soot, added by 2 to 20 mg.

2.3 Basic analysis of the catalyst
Table 2: Percentages of the various constituents of the catalyst after tests.

<Tb>
<Tb>

Cu <SEP> Fe <SEP> 0 <SEP> CI <SEP> F
<tb> (% <SEP> m) <SEP> (% <SEP> m) <SEP> (% <SEP> m) <SEP> (% <SEP> m) <SEP> (% <SEP> m)
<tb> 32, <SEP> 8 <SEP> 37.2 <SEP> 27, <SEP> 0 <SEP> 1, <SEP> 6 <SEP> 0, <SEP> 1
<Tb>

mettre en évidence la formation d'une phase active associant le cuivre, le fer et ! e chiore (FenCuiOgOo 2 et 1 n5) Comparaisons des caractéristiques et avantages respectifs des deux catalyseurs illustrés à l'exemple 1. Anlayses XAS (X-ray absorption spectroscopy) and X-ray diffraction (XRD) allowed to

highlight the formation of an active phase involving copper, iron and! e chiore (FenCuiOgOo 2 and 1 n5) Comparisons of the characteristics and respective advantages of the two catalysts illustrated in Example 1.

 The catalysts have the same performance in soot oxidation. The choice of one or the other method of preparation will depend on the nature (ceramic or metallic) of the particulate filter selected for purification.

Claims (10)

 1. A process for preparing a catalyst, comprising an active phase and a support, comprising the following successive steps of: - (i) reacting cuprous chloride and copper bifluoride, - (ii) oxidizing to a temperature of 600oC at 800oC under oxygen and then (iii) cool to room temperature under oxygen the previous mixture.  2. Method according to claim 1, characterized in that it further comprises the following successive successive steps consisting in: (i) reacting iron chloride and aluminum chloride in aqueous solution, - (ii) adjusting the pH of the above mixture at a pH of 5 to 7 using an alkaline solution and (iii) extracting and then drying the precipitate thus obtained.  3. Method according to claim 1 or 2, characterized in that, during the oxidation step under pure oxygen, a temperature of about 800oC is reached, at an increase of about 25 C per min.  4. Method according to the preceding claim characterized in that one maintains the temperature of about 800 oC for about 2 hours.  5. Method according to any one of the preceding claims characterized in that said active phase is deposited on a support selected from ceramic filters, metal filters.  6. Catalyst comprising the following constituents: copper, iron, oxygen, chlorine and fluorine. <Desc / Clms Page number 9>  7. Catalyst according to the preceding claim characterized in that the values of the mass percentages of the various constituents vary within the limits of the following intervals: Copper from 5% m to 50% m Iron from 10% m to 60% m Oxygen from 30% m to 40% m Chlorine from 1% m to 5% m Fluorine from 0.1% m to 2% m.  8. Catalyst according to claim 6 or 7, characterized in that it further comprises alumina.  9. Catalyst according to the preceding claim characterized in that the values of the mass percentages of aluminum are in the range 5% m to 20% m.  10. Use of a catalyst according to any one of claims 6 to 9, or obtained by a process according to any one of claims 1 to 5, for the combustion of soot.