FR2694598A1 - Use of a catalyst to reduce the amount of particles or their diameter or both in the exhaust gas of a diesel engine. - Google Patents

Abstract

The invention relates to the use of a catalyst for reducing the mass and / or the diameter of particles in the exhaust gas of a diesel engine. The catalyst used is a bifunctional catalyst which contains a transition metal oxide and an acidic zeolite. Application: reduction of atmospheric pollution by particles contained in the exhaust gas of diesel engines, in particular of motor vehicles.

Description

The present invention relates to the use of a catalyst for reducing

mass and / or diameter of

  particles in the exhaust gas of a diesel engine by means of a bifunctional catalyst which contains a transition metal oxide and an acidic zeolite.

  It is known that when using diesel engines, particularly as motor vehicle engines, a disadvantage lies in the fact that these engines emit

  particles of lampblack whose release into the atmosphere

  phere can only be prevented with difficulty.

  Another conventional measure known to prevent the escape of black-light particles is to use filters. The disadvantage of such filters is the danger of blocking by black-smoke particles after a relatively short period of use. Therefore, to regenerate the particulate filters, one must

  take measures which consist, for example, in heating

  shortage of these filters by means of appropriate devices, up to the ignition temperature of the deposited black smoke particles Such devices expend energy and are expensive and therefore do not constitute a technical solution for example for cars

diesel tourism.

  It is also known to catalytically reduce the mass of particles. For this purpose, oxidation catalysts are used which contain as a component

  active ingredient of platinum deposited on aluminum oxide

  However, these monofunctional catalysts based on noble metals have the advantage that although they reduce the mass of particles in the exhaust gases, they also exert a strong oxidizing action on the constituent 502 of these gases. The formation of bound sulphate This oxidation makes the mass of particles hygroscopic and leads to an elevation of this mass under specific conditions. In addition, there must be a deposit of sulphate particles.

  on the catalyst, which can affect the efficiency.

  According to the German patent application P 41 05 534 without prior publication, it is known that the

  particle mass can be reduced without adequate training

  It has been found that catalysts containing a zeolite and having acidic properties or cracking properties reduce the mass and / or the particle diameter and the quantity of hydrocarbons without, however, oxidizing the 502 contained in the gas to sulphates. exhaust. The disadvantage is that small amounts of particles are always formed, mainly at high temperatures.

<200 'C.

  The problem was therefore to further reduce the

  mass and / or particle diameter.

  The Applicant has just found that catalysts

  However, those containing zeolites having acidic properties and cracking properties, which additionally contain transition metal oxides, reduced the mass and / or the particle diameter relative to the prior art without, however, oxidizing the sulfates to 502. It is surprising to note that zeolitic catalysts containing additions of metal oxides do not exert any oxidative effect on the 502 contained in the exhaust gas even when the latter is in the exhaust gas.

at high temperatures.

  The addition of metal oxides is particularly advantageous in reducing the particles to lower temperatures, so that in this case the particle reduction is up to 50% higher than that provided by a catalyst. The object of the present invention resides in the use of a catalyst for reducing the mass and / or the particle diameter in the exhaust gas of a diesel engine by means of a catalyst which is a combination of a zeolite having acidic properties and one or more

  transition metal oxides and / or rare earth oxides.

  Metal oxides which are suitable as additives are preferably TiO 2, V 205, Cr 203, MnO 2, Fe 2 O 3, CoQ, NiO, CuO, Y 203, ZrO 2, Nb 2 O 5, Ta 205. , W 03, Mo O 3, La 2 O 3,

  This 203, W 03, among others, or mixtures of these oxides.

  Oxides are advantageously used in quantitative

  from 0.1 to 20% by weight, especially from 0.5 to 10% by weight. The metal oxides which constitute the particularly preferred additives are Ti O 2, V 205, W 03,

Mo O 3, La 203 and Ce 203.

  The metal oxide additives are usually mixed with the zeolite, and then a binder is added so that this mixture can adhere to the support on which it is deposited (for example cordierite,

  metal) or can be pressed into self-supporting shaped bodies.

  The mixture is homogenized by intensive grinding, for example using ball mills. Then, the mixtures are brought by drying to the degree of humidity allowing the granulation and they are pressed into agglomerated bodies by means of Suitable apparatuses, for example roll granulators It is also possible to carry out, as already mentioned above, a coating of supports, for example of agglomerated bodies or of monolithic bodies.

  alveolar, with a suspension of the active components.

  It is also possible to impregnate zeolitic catalysts with salts of the transition metals or rare earths, which can then be thermally decomposed. Zeolites which are particularly suitable for use according to the invention include the following structural types: faujasites, pentasils, mordenites, ZSM 12, zeolite 3, zeolite L, zeolite n, PSH-3, ZSM 22,

  ZSM 23, ZSM 48, EU-1, NU-86, offretite, ferrierite, etc. Zeolites of the pentasil type

  a report Si O 2 / A 1203 from 25 to 2000, in particular

between 40 and 600.

  The zeolites are characterized by the general formula (I) M 12 ## STR2 ## In this formula: M 1 denotes an equivalent of an exchangeable cation, n denoting the valence and the number corresponding to the charge equivalence of M 2; M 2 is a trivalent element which together with silicon forms the oxide framework of the zeolite; y / x is the ratio Si O 2 / M 2203;

  q is the amount of water adsorbed.

  By their basic structure, zeolites are crystalline aluminosilicates which are formed of a network of SiO 4 and M 204 tetrahedra. The individual tetrahedra are bound together at their angles by oxygen bridges and form a spatial network which is uniformly The individual zeolitic structures are distinguished by the arrangement and size of the channels and cavities as well as by their composition Exchangeable cations are incorporated to compensate for the negative charge of the network, which comes from the proportion of M 2 The adsorbed aqueous phase can be reversibly removed without the framework losing its

structure.

  M 2 is frequently aluminum, but it can be partly or completely replaced by some others

trivalent elements.

  A description of zeolites is given by

  example in the monograph of D W Breck entitled "Zeolite Molecular Sieves, Structure, Chemistry and Use", J.

  Wiley & Sons, New York, 1974 A further description is given

  especially in the case of SiO 2 -rich zeolites of interest for catalytic applications, in the PA Jacobs and JA Martens monograph entitled "Synthesis of High-Silica Aluminosilicate Zeolites", Volume 33, published in Studies in Surface Science and Catalysis. under the

  direction of B Delmon and J I Yates, Elsevier, Amsterdam-

Oxford-New York-Tokyo, 1987.

  In the zeolites used according to the invention, M 2 designates one or more elements of the group

  Al, B, Ga, In, Fe, Cr, V, As and Sb, they represent preferably

  One or more elements of group Al, B, Ga and Fe. As exchangeable cations Mi, the zeolites mentioned may contain rare earths and / or protons. Exchangeable cations which are also suitable are, for example, those of Mg, Ca, Sr, Ba, Zn, Cd as well as transition metals such as, for example, Cr, Mn, Fe, Co,

  Ni, Cu, V, Nb, Mo, Ru, Rh, Pd, Ag, Ta, W, Re or Pt.

  In accordance with the invention,

  catalysts which contain zeolites of the structural types

  mentioned above in which at least a portion of the metal cations have been exchanged for hydrogen ions, preferably 50 to 100%, especially 80 to 100% of all the metal cations initially present, and

  additionally contain the metal oxide additives

lic.

  The acidic H + forms of the zeolites are advantageously

  are prepared in such a way that the metal ions are exchanged for ammonium ions and the

  zeolite thus treated by exchange A repetition of the

  Suspended exchange followed by calcination under defined conditions leads in the case of zeolites of the faujasite type to so-called ultrastable zeolites, depleted in aluminum, which are rendered thermally and hydrothermally more stable by this process of dealumination Another possibility for obtaining faujasite type zeolites rich in SiO 2 is to conduct the appropriate treatment of the anhydrous zeolite with Si C 14 at elevated temperatures (2 1500 C). Aluminum is then removed together with

  silicon is incorporated into the network

  ammonium fluorosilicate also leads to a faujasite

  rich in Si O 2 under specified conditions.

  Another possibility of incorporation / exchange of protons is to use the process with mineral acids in the case of zeolites which have a SiO 2 / A 1203 ratio which is sufficiently high (> 5).

  also obtain aluminum depleted zeolites.

  It is also known that ion exchange with trivalent metal ions of the rare earths, individually and / or in mixtures, which can preferably be rich in lanthanum and cerium, leads to acidic centers mainly in the case of Faujasite It is further known that when incorporating multivalent metal cations into zeolites, acidic centers are produced. The following examples illustrate the activity of zeolitic or zeolite-containing acid catalysts, which additionally contain metal oxide additives, with respect to reducing the amount of particles.

  and the conversion of hydrocarbons in the exhaust gases

  DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments given by way of example do not constitute a limitation of the invention. The results are obtained for a diesel engine

  under the conditions mentioned in the Tables

  the dimensions of which are 102 mm in diameter and one

  152 mm These are coated monoliths.

Example 1

  Zeolite Y containing rare earths: zeolite Y acid treated by exchange with rare earths, having an SiO 2 / A 1203 ratio of 4.9 and an exchange degree of about% and also containing 2% by weight of W 03 compared to the

fraction of zeolite.

  Number of pressure revolutions effective ltr / minl average lbarsl

2000

Transfor Transfor-

  at the level of the nation of collec hydro particles teur lOCl carbures l% l l% l 26,8 33,4, 4 34,9

Example 2

  Zeolite Y containing rare earths: zeolite Y acid treated by exchange with rare earths, having a ratio Si O 2 / A 1203 of 4, 9 and an exchange degree of about 90%, with 2% Mo O 3 with respect to the zeolite fraction. Number of revolutions ltr / minl

2000

Mean Effective Pressure lbarsl

tempera-

at collector level lICl

Transfor Transfor-

  tion of carbolic hydrocarbon particles 1% l l% l

22.3 19.5

, 36.1

Example 3

  Y-zeolite in H-form: zeolite Y dealuminated acid having an SiO 2 / A 1203 molar ratio equal to 50 and containing an addition of 2% of W 03 relative to the zeolite. Number of revolutions ltr / minl Average effective pressure lbarsl

tempera-

at collector lo Cl

trans-

of

hydro-

carbides l% l

trans-

particle formation l% l

2000

34.3 29.5 26.3 36.1

Example 4

  Y zeolite in the H form: zeolite Y dealuminated acid having an SiO 2 / A 1203 molar ratio equal to 50 and containing an addition of 2% MoO 3 with respect to the

zeolite.

  Number of revolutions ltr / minl Average effective pressure lbarsl

tempera-

ture at collector level l o Cl

trans-

of

hydro-

carbides l% l

trans-

particle formation l% l

2000

  Comparative Example 5 Zeolite Y containing rare earths: zeolite Y acid treated with rare earth exchange, having an SiO 2 / Al 203 ratio of 4.9 and a degree of exchange of about

  90% (without addition of metal oxide).

  Number of revolutions ltr / minl Average effective pressure lbarsl

tempera-

at collector lo Cl

trans-

of

hydro-

carbides l% l, 6

trans-

particle formation l% l, 1

2000 6

34.0

425 27.8

Claims (9)

  1 Use of a catalyst to reduce the mass and / or diameter of particles in the exhaust gas   A diesel engine is characterized in that the catalyst is an association between a zeolite having acidic properties and one or more transition metal oxides and / or rare earth oxides. 2 Use of a catalyst according to claim 1, characterized in that the zeolite having acidic properties has the general formula: M 2 / no y Si O 2 q H 20 (I) wherein m 1 is an equivalent of one exchangeable cation whose number corresponds to the fraction of M 2, n denoting the valence of the cation; M 2 is a trivalent element which together with silicon forms the oxide framework of the zeolite; y / x is the ratio Si O 2 / M 2203; q is the amount of water adsorbed.   3 Use according to one of the claims   1 and 2, characterized in that the zeolite is of the faujasite type. 4 Use according to claim 3,   characterized in that the zeolite is a malfunctioning faujasite undermined.   Use according to one of the claims   1 and 2, characterized in that the zeolite is of the pentasil type. 6 Use according to claim 5, characterized in that the pentasil type zeolite has an SiO 2 / A 1203 ratio of 25 to 2000, preferably between and 600.   7 Use according to one of the claims   1 and 2, characterized in that the zeolite is a zeolite of type of mordenite.   8 Use according to claim 7,   characterized in that the zeolite is a mordenite   undermined. 9 Use according to one or more of   Claims 1 to 8, characterized in that the zeolite   contains as exchanged cations one or more elements of the group of elements of the second subgroup of the System   Periodic Elements and / or rare earth elements.   Use following one or more of   Claims 1 to 8, characterized in that the zeolite   contains as exchanged cations one or more transition elements. Use according to claim 10, characterized in that the transition elements are Cu, Ni, Co, Fe, Cr, Mn and / or V. Use according to claim 10, characterized in that the zeolite contains copper as transition element.   13 Use according to claim 1, characterized in that as transition metal oxides and / or rare earth oxides Ti O 2, V 205, Cr 203, Mn O 2, Fe 203, Coo O, Ni O are used as rare earth oxides. , Cu O, Y 203, Zr O 2, Nb 205, Ta 203,   W 03, MO 3, La 203, Ce 203, WO 3 or mixtures of these oxides.   Use according to claim 1, characterized in that the oxides are used in amounts   from 0.1 to 20% by weight relative to the zeolite.