JPH06170173A - Use of catalyst for reducing amount and/or size of particulate in diesel exhaust gas - Google Patents

Abstract

PURPOSE: To use a catalyst that reduces the amount and/or size of particulates in diesel exhaust gas. CONSTITUTION: The catalyst brought into contact with exhaust gas of a diesel engine to reduce at least one of the amount and size of particulates in the exhaust gas contains a combination of a zeolite having acidic character and oxide of at least one transition metal or rare earth element. The formation of a sulfate by the oxidation of SO2 in the exhaust gas is prevented.

Description

Detailed Description of the Invention

The present invention relates to the use of a catalyst for reducing the amount and / or size of particles in diesel engine exhaust gas with a bifunctional catalyst containing a transition metal oxide and an acidic zeolite.

One of the problems with using diesel engines, and more particularly with driving motor vehicles, is that they emit particles that are difficult to prevent from entering the atmosphere. is there.

A well-known and widely used strategy for preventing particle emissions is the use of filters. The disadvantage of filters is that they have the risk of being blocked by particles even with relatively short run times. Therefore, it is necessary to take measures to regenerate the filter, for example by heating it for a short period of time to the ignition temperature of the deposited particles, using suitable equipment. Such a device is complicated and expensive, and is not a practical solution, for example for diesel powered vehicles.

It is also known that the amount of particles can be reduced catalytically. Oxidation catalysts containing platinum as the active ingredient on aluminum oxide have been used for this purpose. The disadvantage of this type of monofunctional noble metal catalyst is that they reduce the amount of particles in the exhaust gas, but they also show a strong oxidizing effect on the SO ₂ component of this exhaust gas. Is. The resulting formation of sulphate makes these particles hygroscopic and even increases the amount of particles under certain conditions. Moreover, the effectiveness of this catalyst is reduced as a result of the particles of sulphate deposited on the catalyst.

From the presently pending patent application Serial No. 836,043 filed on February 12, 1992, it was recognized that it is possible to reduce the amount of these particles without the additional generation of sulfate salts. ing. It has been found that zeolite-containing catalysts with acidic or degradative properties reduce the amount and / or size of particles and the amount of hydrocarbons without co-oxidizing SO ₂ in this exhaust gas to form sulfates. . The disadvantage of this is that small amounts of particles occur, especially at temperatures of ≦ 200 ° C.

The object of the present invention was therefore also to reduce the amount and / or size of the particles.

Zeolite-containing catalysts which have acidic or decomposing properties and additionally contain oxides of transition metals have been used in the prior art without the simultaneous oxidation of SO ₂ in the exhaust gas to form sulfates. It has been found here to significantly reduce the amount and / or size of the particles by comparison. Surprisingly, the zeolite catalysts containing these added metal oxides show no oxidizing effect on SO _{2 in} this exhaust gas, even at relatively high exhaust gas temperatures.

The addition of metal oxides also has a positive effect on particle depletion at relatively low temperatures, with the result that the particle depletion of acidic zeolite catalysts without metal oxide addition. 50% more than
It becomes very high.

The present invention is directed here to the use of a catalyst which is a combination of a zeolite having acidic properties with one or more transition metal oxides and / or rare earth oxides and the amount of particles in diesel engine exhaust gas and And / or the use of catalysts to reduce size.

The appropriately added metal oxides are preferably TiO ₂ , V ₂ O ₅ , Cr ₂ O ₃ , MnO ₂ , Fe ₂ O ₃ ,
CoO, NiO, CuO, Y ₂ O ₃ , ZrO ₂ , Nb
₂ O ₅ , Ta ₂ O ₅ , WO ₃ , MoO ₃ , La ₂ O ₃ , Ce
₂ O ₃ , WO _3, etc., or a mixture of these oxides.

These oxides are preferably 0.1 to 2
It is added in an amount of 0% by weight, more preferably 0.5 to 10% by weight.

A particularly suitable metal oxide added is Ti.
O ₂ , V ₂ O ₅ , WO ₃ , MoO ₃ , La ₂ O ₃ and Ce ₂ O
_{Is 3} .

Usually these metal oxides are added to the zeolite. In addition, an adhesive may be added to adhesively attach the mixture to a support (eg, cordierite or metal) or press to form a self-supporting structure. The mixture is homogenized by vigorous grinding, for example in a stirred ball mill. Next, these mixtures are dried to produce a water content suitable for granulation, and then press-molded with a suitable device such as a roller-type granulator or an extruder to give a molded structure. Suspensions of these active ingredients may, as already mentioned, be applied to supports, for example in the form of shaped structures or monolithic honeycombs.

It is also possible to coat these zeolite-containing catalysts with the salts of the transition metals or rare earths and then pyrolyze them.

Zeolites particularly suitable for use in accordance with the present invention include the following structural types: faujasite, pentasil, mordenite, ZSM 12, zeolite β, zeolite L, zeolite Ω, PSH-3, Z.
SM 22, ZSM 23, ZSM 48M, EU-1,
NU-86, offretith, ferrier stone, etc. are included.

The pentasil type zeolite is preferably 25 to 2000: 1, more preferably 40 to 60.
It has a SiO ₂ to Al ₂ O ₃ ratio of 0: 1.

Zeolites are represented by the following general formula (I)

[0018]

## STR00001 ## M ¹ _{2 / n} O.xM ² ₂ O ₃ .ySiO ₂ .qH ₂ O (I) [wherein, M ¹ is an equivalent amount of the exchangeable cation, and n
Represents the valence and number corresponding to the charge equalization of M ^2, M ² is a trivalent element which, together with the Si to form an oxide framework of the zeolite, y / x is SiO ₂ /
M ² ₂ O ₃ ratio, and q is the amount of adsorbed water].

Zeolites are crystalline aluminosilicates made from the viewpoint of their basic structure and having a network structure composed of SiO ₄ and M ² O ₄ tetrahedra. The individual tetrahedra are connected to each other by oxygen bridges on the corners of these tetrahedra, forming a three-dimensional network structure with uniformly distributed passages and voids. The individual zeolitic structures differ in the arrangement and size of these passages and voids and in their composition. The M ²
Exchangeable cations are incorporated for the purpose of equalizing the negative charge of the lattice arising from the components. Adsorbed water phase qH ₂ O
Can be reversibly removed without the scaffold losing its structure.

M ² is often aluminum, but it may be wholly or partly replaced by other specific trivalent elements.

A detailed description of zeolites is given, for example, in the title "Zeolite Molecular Sieves, Structure, C".
hemistry and use) by DW Breck (J. Wiley
& Sons, New York, 1974). For other explanations, especially for zeolites relatively rich in SiO ₂ which are of interest for catalytic applications, the title is “Synthesis of High Silica Aluminosilicate Zeolites” (Synths
is of High-Silica Aluminosilicate Zeolites)
Books by PA Jacobs and JA Martens (Studies in Su
rface Scienceand Catalysis, Volume 33, B. Delmon and
Edited by JI Yates, Elsevier, Amsterdam / Oxford / New Yor
k / Tokyo, 1987).

In the catalyst used according to the invention, M ²
Is one or more elements from the group consisting of Al, B, Ga, In, Fe, Cr, V, As and Sb, preferably A
represents one or more elements from the group consisting of l, B, Ga and Fe.

The above-mentioned zeolites may contain rare earths and / or protons as exchangeable cations M ¹ . Other suitable exchangeable cations are eg cations of Mg, Ca, Sr, Ba, Zn, Cd, and also transition metal cations such as Cr, M.
n, Fe, Co, Ni, Cu, V, Nb, Mo, Ru,
Cations of Rh, Pd, Ag, Ta, W, Re and Pt.

Suitable zeolites according to the present invention include zeolites of the structural type described above, and at least a portion, preferably 50 to 100%, more preferably of all of the original metal cations present. 80 to 100%
Is replaced by hydrogen ions and also contains an adduct of a metal oxide.

The acidic H ⁺ form of these zeolites is preferably produced by exchanging metal ions with ammonium ions and then calcining the zeolite thus exchanged. In the case of faujasite type zeolites, this dealumination (dealuminizat) can be performed by repeating the above exchange process and the subsequent firing under limited conditions.
This results in so-called ultra-stable zeolites that are thermally and hydrothermally stabilized during the ion) process and have a relatively low aluminum content. Another method to obtain SiO ₂ -rich faujasite-type zeolites is at relatively high temperatures (≧ 1
50 ° C.) subjected to a controlled treatment with SiCl ₄ on anhydrous zeolite. As a result of this treatment, aluminum is removed and at the same time silicon is incorporated into the lattice. Treatment with ammonium hexafluorosilicate under specific conditions also produces Si
This results in faujas stones rich in O ₂ .

Another method for replacing / exchanging protons is A
In the case of zeolites in which the ratio of SiO ₂ to l ₂ O ₃ is sufficiently high (> 5), the method with mineral acids is to be carried out. It is also possible to obtain dealuminated zeolites in this way.

Ion exchange with trivalent rare earth metal ions, which may be rich in lanthanum or cerium (in the form of individual and / or mixtures), leads to acidic centers, especially in the case of faujasite. Is also known. It is also known that when polyvalent metal cations are introduced into zeolites, acidic centers are generated.

The following examples illustrate the effectiveness of acidic zeolite-based or zeolite-containing catalysts additionally containing additional metal oxides in the conversion of particles and hydrocarbons in diesel engine exhaust gas. is there. These examples are not intended to limit the invention in any manner.

These results were obtained using a diesel engine under the conditions shown in the table. These catalysts were coated monoliths with a diameter of 102 mm and a length of 152 mm.

[0030]

EXAMPLE 1 SE Zeolite Y, a ratio of SiO ₂ to Al ₂ O ₃ of 4.9, a degree of exchange of about 90% and 2% of WO _{3 based} on this zeolite component. Containing, rare earth exchanged acidic zeolite Y.

Engine speed Pme Manifold temperature Hydrocarbon conversion rate Particle conversion rate [rpm] [bar] [° C] [%] [%] 2000 1 159 26.8 20.4 2000 6 425 33.4 34.9 Implementation Example 2 SE Zeolite Y, ie, the ratio of SiO ₂ to Al ₂ O ₃ is 4.9, the degree of exchange is about 90% and contains 2% MoO _{3 based} on this zeolite component, Acid zeolite Y exchanged with rare earth.

Engine speed Pme Manifold temperature Hydrocarbon conversion rate Particle conversion rate [rpm] [Bar] [° C] [%] [%] 2000 1 159 22.3 19.5 2000 6 425 30.6 36.1 Implementation Example 3 H Zeolite Y, a dealuminated acidic zeolite Y in which the ratio of SiO ₂ to Al ₂ O ₃ is 50 and WO ₃ is added at 2% based on this zeolite.

Engine speed Pme Manifold temperature Hydrocarbon conversion rate Particle conversion rate [rpm] [bar] [° C] [%] [%] 2000 1 159 34.3 26.3 2000 6 425 29.5 36.1 Implementation Example 4 H Zeolite Y, a dealuminated acidic zeolite Y in which the ratio of SiO ₂ to Al ₂ O ₃ is 50 and MoO ₃ is added at 2% based on this zeolite.

Engine speed Pme Manifold temperature Hydrocarbon conversion rate Particle conversion rate [rpm] [bar] [° C] [%] [%] 2000 1 159 30.9 21.5 2000 6 425 26.7 34.8 Comparison Example 5 SE Zeolite Y, a ratio of SiO ₂ to Al ₂ O ₃ of 4.9, and a degree of exchange of about 90% (no added metal oxide), acid exchanged with rare earths. Zeolite Y.

Engine speed Pme Manifold temperature Hydrocarbon conversion rate Particle conversion rate [rpm] [bar] [° C] [%] [%] 2000 1 159 20.6 15.1 2000 6 425 27.8 34.0 The specification and examples are illustrative and not limiting of the invention, and those skilled in the art will perceive other embodiments themselves within the spirit and scope of the invention. Will be understood.

The features and aspects of the present invention are as follows.

1. Of a zeolite having acidic properties and at least one oxide of a transition metal or rare earth in contacting a catalyst with exhaust gas of a diesel engine to reduce at least one of the amount and size of particles in the exhaust gas An improvement in which the catalyst comprises a combination.

2. The zeolite having the acidic property is
formula

[0039]

## STR00002 ## M ¹ _{2 / n} O.xM ² ₂ O ₃ .ySiO ₂ .qH ₂ O (I) [wherein M ¹ is the equivalent amount of the exchangeable cation, and this number is the content of M ^{2 as} a percentage. Equivalent to the quantity, where
n represents the valence of this cation, M ² is S
is a trivalent element that together with i forms the oxidized framework of this zeolite, y / x is the ratio SiO ₂ / M ² ₂ O ₃ and q is the amount of adsorbed water] The method according to item 1, which is

3. The method of claim 2 wherein the zeolite is of the faujasite type.

4. The method according to claim 3, wherein the zeolite is dealuminated faujasite.

5. The method according to claim 2, wherein the zeolite is of the pentasil type.

6. The method of claim 5 wherein said pentasil-type zeolite has a SiO ₂ to Al ₂ O ₃ ratio of 25 to 2000: 1.

7. The pentasil-type zeolite is 40:
Fifth with a SiO ₂ to Al ₂ O ₃ ratio of 1 to 600: 1
Method described in section.

8. The method of claim 2 wherein the zeolite is of the mordenite type.

9. 9. The method according to claim 8, wherein the zeolite is dealuminated mordenite.

10. The method of claim 1 wherein the zeolite comprises at least one element from the second major group of the Periodic System of Elements and a rare earth element as exchanged cations.

11. The method of claim 1 wherein the zeolite contains at least one transition element as an exchanged cation.

12. The transition element is Cu, Ni, Co,
First which is at least one of Fe, Cr, Mn and V
The method according to item 1.

13. The method according to claim 11, wherein the zeolite contains Cu as a transition element. 14. The transition element or rare earth oxide is TiO ₂ ,
V ₂ O ₅ , Cr ₂ O ₃ , MnO ₂ , Fe ₂ O ₃ , CoO, Ni
O, CuO, Y ₂ O ₃ , ZrO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ ,
The method according to claim 1, comprising at least one of WO ₃ , MoO ₃ , La ₂ O ₃ , Ce ₂ O ₃ , and WO ₃ .

15. The process of claim 1 wherein said oxide is present in about 0.1 to 20% by weight, based on zeolite.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ulrich-Dieter Schutant Germany Day 38527 Maine Bitten Azkar 5

Claims (1)

[Claims] 1. A zeolite having acidic properties and at least one transition metal or rare earth in contacting a catalyst with exhaust gas of a diesel engine to reduce at least one of the amount and size of particles in the exhaust gas.
An improvement in which the catalyst comprises a combination with a seed oxide.