DE4433120B4 - Heat-resistant catalytic converter to limit exhaust emissions - Google Patents

Abstract

Heat-resistant catalyst for converting NO _x in an exhaust gas containing hydrocarbons, the catalyst comprising a ZSM-5 zeolite and at least one catalytic element selected from the group consisting of Cu, Co, Fe and Pt in an amount C of the catalytic element , based on the zeolite in a range of 1 wt .-% ≤ C ≤ 10 wt .-%, characterized in that the ZSM-5 zeolite is a modified heat-resistant ZSM-5 zeolite, formed by an aluminum-removing Treatment of an unmodified ZSM-5 zeolite, whereby a molar ratio Mr2 of SiO ₂ / Al ₂ O _{3 of} the modified ZSM-5 zeolite in the range of 30 ≤ Mr2 ≤ 80 is achieved, and setting a ratio Mr2 / Mr1 of the molar ratio Mr2 to a molar ratio Mr1 of the unmodified ZSM-5 zeolite to ≥ 1.2.

Description

The invention relates to heat-resistant Exhaust emission control catalysts for use in one Exhaust system in a vehicle or the like.

They are catalysts for limiting exhaust emissions known, which are arranged in an exhaust system of a vehicle. However, a conventional one Exhaust emission control catalyst an emission by oxidation only in a high temperature range of an exhaust gas, e.g. at a Temperature of about 180 ° C and above limit, and therefore shows an extremely low emission control ability for a Exhaust gas with a low temperature and a high concentration of hydrocarbon immediately after starting an engine.

An exhaust emission control device was then installed known, which contains a hydrocarbon (HC) adsorber from zeolite, the is arranged upstream of a catalytic converter in an exhaust system, to hydrocarbons contained in a low temperature exhaust gas field (see e.g. Japanese Patent Laid-Open Publication No. 2-75327 (1990).

However, there is this exhaust emission control device a problem in that the Zeolite prefers water to be adsorbed in the exhaust gas and therefore its hydrocarbon adsorption capacity is considerable diminishes when the adsorption of water increases.

To avoid this problem developed an exhaust emission control device with a zeolite, which used as a water absorbent mordenite, which is a variety of Zeolite, in combination with a hydrocarbon adsorbent, the ZSM-5 zeolite contains as a main component (see e.g. Japanese Patent Laid-Open Publication No. 5-96182 (1993).

The temperature of one through the exhaust system flowing Exhaust gas is generally in the range of 1000 ° C, and therefore the water must be adsorbent and also the hydrocarbon adsorbent has sufficient heat resistance have to withstand the temperature mentioned.

However, the heat resistance temperature is for conventional, normal mordenite and ZSM-5 zeolite in the range of 700 ° C, and therefore exists with the conventional Water and hydrocarbon adsorbents have a problem in that they the mentioned temperature of the exhaust gas very little permanent and therefore are practically hardly usable.

It is further known to use a modified zeolite for a NOx (nitrogen oxide) converting catalyst, made by aluminum-removing treating (ie dealuminizing) unmodified zeolite to a range of the Mr2 mole ratio of SiO ₂ / Al ₂ O ₃ from 100 to 500 (see, for example, Japanese Patent Laid-Open Publication No. 2-126941 (1990).

However, a problem with this NOx (nitrogen oxide) converting catalyst is that if the molar ratio Mr2 of SiO ₂ / Al ₂ O _{3 of} the modified zeolite is set in a range of Mr2 ≥ 100, the modified zeolite has an improved heat resistance, but the catalytic activity of the NOx converting catalyst is reduced.

U.S. Patent 5,041,272 describes a process for removing nitrogen oxides from exhaust gases, in which hydrogenated zeolite catalysts, which can contain a catalytically active metal, are used. The according U.S. Patent 5,041,272 However, the catalysts formed are not subjected to any aluminum removal treatment and thus have a ratio of Mr2 / Mr1 = 1, which is why they only have a heat resistance up to a maximum of 600 ° C.

JP 2126941 A describes a NO _x converting catalyst comprising a zeolite modified by aluminum removal treatment.

A general overview of zeolites delivers natural science. 71 (1984) 192-198.

An object of the invention is to provide a heat-resistant exhaust emission control hydrocarbon adsorbent which has excellent heat resistance and NOx convertibility by specifying the SiO ₂ / Al ₂ O ₃ molar ratio of a modified zeolite.

This object is achieved according to the invention by a heat-resistant catalyst for converting NO _x in an exhaust gas which contains hydrocarbons, the catalyst comprising a ZSM-5 zeolite and at least one catalytic element selected from the group consisting of Cu, Co, Fe and Pt in one Quantity C of the catalytic element based on the zeolite in a range of 1 wt .-% ≤ CS 10 wt .-%, which is characterized in that the ZSM-5 zeolite is a modified heat-resistant ZSM-5 zeolite by aluminum removal treatment of an unmodified ZSM-5 zeolite, with a molar ratio Mr2 of SiO ₂ / Al ₂ O _{3 of} the modified ZSM-5 zeolite in the range of 30 ≤ Mr2 ≤ 80 and adjusting a ratio Mr2 / Mr1 of the molar ratio Mr2 to a molar ratio Mr1 of the unmodified ZSM-5 zeolite to ≥ 1.2.

To achieve this goal, a heat-resistant hydrocarbon adsorbent for limiting exhaust gas emissions is provided according to the invention, comprising a heat-resistant modified zeolite, obtained by dealuminization treatment of an unmodified zeolite with a dealuminization rate R of 10% R R 25 25% to obtain a molar ratio Mr2 of SiO ₂ / Al ₂ O _{3 set} to a range of 30 ≤ Mr2 ≤ 80 and at least one NOx converting catalytic element made of metal selected from Cu, Co, Fe and Pt or an oxide thereof, which is incorporated in the modified zeolite as a carrier, so that the adsorbent also acts as a catalyst.

The catalyst of the present invention comprises, as a component, a heat-resistant zeolite formed by aluminum removal or dealuminization treatment of an unmodified zeolite, the molar ratio Mr2 of SiO ₂ / Al ₂ O _{3 of} the modified zeolite being in a range of Mr2 ≥ 1.2 Mr1, where Mr1 represents a molar ratio of SiO ₂ / Al ₂ O _{3 of} the unmodified zeolite, and the modified zeolite has the same backbone structure as the unmodified zeolite.

When the molar ratio Mr2 of SiO ₂ / Al ₂ O _{3 of} the modified zeolite is set by the dealuminization treatment in the above manner, the modified zeolite has an improved hydrophobicity, and because the modified zeolite has the same skeleton structure as the unmodified zeolite, its specific surface is enlarged by the removal of aluminum. The modified zeolite therefore has an increased adsorption capacity as its property and therefore also shows a good hydrocarbon adsorption capacity in the presence of water.

Further, if the dealuminization treatment of the unmodified zeolite is carried out so that the modified zeolite has the above-mentioned skeleton structure and a molar ratio Mr2 of SiO ₂ / Al ₂ O _{3 of} the modified zeolite in the above range, the crystallinity of the modified zeolite can be improved, Prevent the formation of pyrolysis product cores and raise the heat resistance temperature of the modified zeolite to about 1000 ° C.

However, if the molar ratio Mr2 of SiO ₂ / Al ₂ O _{3 is} less than 1.2 Mr1, the modified zeolite has a low hydrophobicity and a smaller degree of increase in the specific surface area. Therefore, it has a reduced hydrocarbon adsorbability kit and, moreover, the improvement effect of the crystallinity and the prevention effect of the core formation are insufficient, with the result that the heat resistance temperature is about 800 ° C.

If the molar ratio Mr2 of SiO ₂ / Al ₂ O _{3 of} the modified zeolite is set in the range described above by the dealuminization treatment, the crystallinity of the modified zeolite can be improved and the pyrolysis product cores can be prevented from being formed, and therefore the heat resistance temperature can be raised to about Increase 1000 ° C, which improves the heat resistance of the catalyst.

The modified zeolite with the molar ratio Mr2 of SiO ₂ / Al ₂ O ₃ has a capacity for NOx-converting catalytic elements, which is improved by the dealuminization. If, for example, an ion exchange process is used as the uptake process, the amount of catalytic element that is carried up can be increased because of the large number of exchange sites. On the other hand, compared to unmodified zeolites, the modified zeolite has a high hydrocarbon adsorbability at low temperature and it activates adsorbed hydrocarbons at high and low temperatures of the exhaust gas, so that each activated hydrocarbon acts as a reducing agent against NOx and at the same time the NOx reducing effect by the catalytic element , for example Pt. This can improve the catalytic activity.

The dealuminization rate R is expressed as follows: R = {1 - (a 2 / a 1 )} × 100 (%) wherein a _{1 represents} an amount of aluminum in the unmodified zeolite and a _{2 represents} an amount of aluminum in the modified zeolite.

However, if the dealuminization rate R is less than 10%, the heat strength improvement effect of the modified zeolite is less. On the other hand, even if the dealuminization rate R is set to be more than 25%, the process is only complicated and the effect differs little from the case where the dealuminization rate R is equal to or less than 25%. If R ≥ 70%, the heat resistance of the modified zeolite is reduced. If the molar ratio Mr2 of SiO ₂ / Al ₂ O _{3 is} less than 30 at a dealuminization rate in the range described above, then the amount of aluminum originally contained in the unmodified zeolite is larger, and therefore the amount of aluminum removed is larger. Therefore, the absorption or carrying capacity and the hydrocarbon activation capacity are higher than for Mr2 ≥ 30, which leads to a further improved catalytic activity, but the improvement effect of the crystallinity of the modified zeolite and the prevention effect of the pyrolysis product arises hung reduces. On the other hand, if the molar ratio Mr2 of SiO ₂ / Al ₂ O _{3 is} more than 80 at a dealuminization rate in the range described above, the amount of aluminum originally contained in the unmodified zeolite is smaller, and therefore the amount of aluminum removed is smaller. Therefore, the absorption capacity and the hydrocarbon activation capacity are lower, which results in a lower catalytic activity.

These and other goals, characteristics and advantages of the invention will become apparent from the following description preferred versions in conjunction with the attached Drawings can be seen.

1 shows an X-ray diffraction pattern for an unmodified ZSM-5 zeolite;

2 shows an X-ray diffraction pattern for a modified ZSM-5 zeolite according to Example 1;

3 shows an X-ray diffraction pattern for a modified ZSM-5 zeolite according to a comparative example;

4 graphically shows the relationship between retention time and specific surface area;

5 shows in section an essential portion of an example of the catalyst;

6 shows in section an essential portion of another example of the catalyst;

7 graphically shows the relationship between the amount of modified ZSM-5 zeolite carried and the percent hydrocarbon adsorption;

8th graphically shows an example of the relationship between gas temperature and percent hydrocarbon conversion;

9 shows graphically the relationship between the molar ratio Mr2 of SiO ₂ / Al ₂ O ₃ and the percent NO conversion at a gas temperature of 400 ° C and the temperature at which the BET specific surface area is heated by 10% or more for 20 hours is reduced;

10 graphically shows the relationship between the Mr2 mole ratio of SiO ₂ / Al ₂ O ₃ and the percent conversion of NO at a gas temperature of 400 ° C;

11 shows graphically the relationship between the molar ratio Mr2 of SiO ₂ / Al ₂ O ₃ and the temperature at which the BET specific surface area is reduced by 10% by treatment for 20 hours.

12 shows graphically the relationship between the warming temperature and the percentage retention of the specific surface area in a first embodiment;

13 graphically shows the relationship between the gas temperature and the percentage conversion of NO before the heat destruction treatment in the first embodiment;

14 graphically shows the relationship between the gas temperature and the percentage conversion of NO after the heat destruction treatment in the first embodiment;

15 graphically shows the relationship between heating temperature and percent retention of specific surface area in a second embodiment;

16 graphically shows the relationship between the gas temperature and the percentage conversion of NO before a heat destruction treatment in the second embodiment;

17 graphically shows the relationship between the gas temperature and the percentage conversion of NO after the heat destruction treatment in the second embodiment;

18 graphically shows the relationship between heating temperature and percent retention of specific surface area in a third embodiment;

19 graphically shows the relationship between the gas temperature and the percentage conversion of NO before heat destruction treatment in the third embodiment;

20 graphically shows the relationship between the gas temperature and the percentage conversion of NO after the heat destruction treatment in the third embodiment;

21 shows graphically the relationship between the heating temperature and the percentage retention of the specific surface area in a fourth embodiment;

22 graphically shows the relationship between the gas temperature and the percentage conversion of NO before heat destruction treatment in a fourth embodiment; and

23 shows graphically the relationship between the gas temperature and the percentage conversion of NO after the heat destruction treatment in a fourth embodiment.

First execution (comparison)

A) Manufacturing and heat resistance of modified ZSM-5 zeolite

The modified ZSM-5 zeolite is by a predetermined modification treatment of unmodified ZSM-5 zeolite manufactured. While This treatment turns the unmodified ZSM-5 zeolite into impurities removed and a dealuminization of the unmodified takes place ZSM-5 zeolite instead.

• (a) Der unmodifizierte ZSM-5 Zeolith wurde in ein Wasser enthaltendes Behandlungsbad gegeben, und 12 Normale HCl-Lösung wurde allmählich hinzugegeben. Die Lösung wurde auf eine vorbestimmte Temperatur erwärmt, so daß die HCl-Lösung eine vorbestimmte Normalität erhielt.
• (b) Das unmodifizierte ZSM-5 Zeolith wurde bei dieser Temperatur für eine vorbestimmte Zeit gehalten, während gleichzeitig die HCl-Lösung umgerührt wurde. In diesem Fall wurde an das Behandlungsbad ein Kühlturm angeschlossen, um die Konzentration der HCl-Lösung bei der oben beschriebenen Normalität zu halten.
• (c) Die HCl-Lösung mit der vorbestimmten Normalität wurde auf Raumtemperatur abgekühlt.
• (d) Der somit hergestellte modifizierte ZSM-5 Zeolith wurde aus dem Behandlungsbad entfernt und mit reinem Wasser gewaschen, bis es einen pH-Wert von 5 oder mehr erreichte. Dann wurde der modifizierte ZSM-5 Zeolith getrocknet.

The modification treatment was carried out according to the following process.

• (a) The unmodified ZSM-5 zeolite was placed in a treatment bath containing water, and 12 normal HCl solution was gradually added. The solution was heated to a predetermined temperature so that the HCl solution became a predetermined normal.
• (b) The unmodified ZSM-5 zeolite was kept at this temperature for a predetermined time while stirring the HCl solution. In this case, a cooling tower was connected to the treatment bath in order to keep the concentration of the HCl solution at the normality described above.
• (c) The HCl solution with the predetermined normality was cooled to room temperature.
• (d) The modified ZSM-5 zeolite thus produced was removed from the treatment bath and washed with pure water until it reached pH 5 or more. Then the modified ZSM-5 zeolite was dried.

Table 1 shows the modification conditions for producing modified ZSM-5 zeolite in Examples 1, 2 and 3, these are the temperature and that reached by the HCl solution normality and the retention time at this temperature reached.

Table 1

As a comparison example, a unmodified ZSM-5 zeolite during a hydrothermal treatment 90 ° C for 10 hours exposed to produce a modified ZSM-5 zeolite.

Table 2 shows the molar ratio Mr1 of SiO ₂ / Al ₂ O _{3 of} the unmodified ZSM-5 zeolite, the molar ratio of SiO ₂ / Al ₂ O ₃ in Examples 1, 2 and 3 and the comparative example, the ratio of Mr2 to Mr1 and the percentage dealuminization.

Table 2

1 to 3 show results of X-ray diffraction, wherein 1 corresponds to the unmodified ZSM-5 zeolite, 2 the example 2 corresponds to and 3 corresponds to the comparative example.

The comparison of the 1 . 2 and 3 shows that the X-ray reflection intensity I (cps) on each crystal plane in the 1 to 3 is essentially identical and thus the dealuminization of the modification treatment is improved without destroying the basic structure of the ZSM-5 zeolite.

For Examples 1, 2 and 3, the comparative example and the unmodified ZSM-5 zeolite was subjected to a thermal destruction test in the atmosphere the conditions of a temperature of 600 to 1100 ° C and one heating time of 18 hours. Then, the example 1 and the like were powder X-ray diffraction using Cu-Kα rays exposed, and there was the destruction of a crystal on one (200) plane and a (020) plane observed due to heating to obtain the results shown in Table 3.

In Table 3, "O" means that there is no change even after the test the X-ray reflection intensity is present was; "☐" means the reduction the X-ray reflection intensity after Test is less than 10%, and "X" means the reduction the X-ray reflection intensity after Test is equal to or more than 10%.

Table 3

As can be seen from Table 3 Examples 1, 2 and 3 a heat resistance temperature from 1000 ° C, but the strength temperature of the unmodified ZSM-5 zeolite is only 700 ° C and the strength temperature of the comparative example with Mr2 <1.2 is Mr1 only 800 ° C. Therefore each of Examples 1, 2 and 3 has excellent heat resistance.

In addition, Examples 1, 2, and 3, the comparative example, and the unmodified ZSM-5 zeolite were kept at 900 ° C in the atmosphere, and the relationship between the retention time and the specific surface area of each of the examples was determined to obtain the values shown in Figs 4 results shown.

How out 4 as can be seen, the agglomeration of Examples 1, 2 and 3 is prevented by their excellent heat resistance, and therefore the decrease in their specific surface area is about 34%, and even when they are exposed to a high temperature of 900 ° C, their adsorptivity decreases little , In the comparative example and the unmodified ZSM-5 zeolite, however, due to the exposure to the high temperature of 900 ° C, the decrease in their specific surface area is about 80% or more and their adsorptivity decreases significantly.

B) HC adsorbability of modified ZSM-5 zeolite

• (1) The propylene gas (C ₃ H ₆ ) adsorbability of each of Examples 1, 2 and 3, the comparative example and the unmodified ZSM-5 zeolite was measured at room temperature using a porosimeter to obtain the results shown in Table 4. In this case, the purity of the propylene gas was 99.8%; the adsorption equilibrium time was 300 sec. and the adsorption temperature was 303 K. Table 4
  
  From Table 4 it can be seen that each of Examples 1, 2 and 3 has a higher HC adsorption capacity than the comparative example and the unmodified ZSM-5 zeolite.
• (2) A plurality of HC adsorbing parts 4 ₁ , each formed from a honeycomb 1 and an HC adsorbent 3 ₁ , as in 5 and with different thicknesses of HC adsorbents 3 ₁ and thus different amounts (g / l) of modified ZSM-5 zeolite carried therein were made using a process comprising the steps of: preparing a slurry of the modified ZSM-5 Zeolite in Example 2, immersing a cordierite honeycomb in the slurry to form an HC adsorbent 3 ₁ from the modified ZSM-5 zeolite with a single-layer structure on an inner surface of each cell 2 of the honeycomb 1, and drying them. Furthermore, a plurality of HC adsorption parts 4 ₂ were produced, each with an HC adsorbent 3 _{2 of} a two-layer structure, comprising a lower layer 5, which is formed from the modified ZSM-5 zeolite, and an upper layer 6, which consists of a heat-resistant , inorganic material is formed and has a water adsorption capacity, as in 6 shown. In this case, the amounts of modified ZSM-5 zeolite in the HC adsorption parts 4 ₂ each differ from one another.

γ-alumina particles with a water adsorption capacity were considered the heat-resistant, inorganic material used, and the top layer 6 was covered by formed a process comprising immersing the honeycomb 1 with the lower layer 5 in a slurry the γ-alumina particle. The amount of the upper layer 6 carried is in a range of 7 to 130 g / l appropriate and had a version of 20 g / l (corresponding a thickness of about 30 μm).

A gas was also prepared as a test gas containing: 10 wt% H ₂ O, 400 ppm C ₃ H ₆ , 0.5 wt% CO, 500 ppm NO, 0.17 wt% H _2, 14 wt .-% CO _2, 0.5 wt .-% O ₂ and the balance N _2.

The test gas flowed through the honeycomb 1 of each of the HC adsorption parts 4 ₁ and 4 ₂ at a flow rate of 25,000 ml / min for 30 seconds, while the HC adsorption rate was measured by the modified ZSM-5 zeolite.

7 shows the relationship between the amount of modified ZSM-5 zeolite carried in each of the HC adsorbing parts 4 ₁ and 4 ₂ , and the HC adsorption rate by the modified ZSM-5 zeolite.

Out 7 it can be seen that the HC adsorption rate increases as the amount of modified ZSM-5 zeolite carried is increased.

In addition, the HC adsorption rate that the HC adsorption part 4 ₂ with the upper layer having water adsorbability has is about 1.5 × higher than that that the HC adsorption part 4 _{1 has} no upper layer. This is because the lower layer capability degradation is extremely limited because water in the test gas is caught by the upper layer 6. The smaller thickness of the upper layer 6 has little influence on the HC adsorption capacity of the lower layer 5.

For the purpose of increasing the HC adsorption rate it is similar Way possible to granulate the modified ZSM-5 zeolite and the granulated, modified ZSM-5 zeolite to cover with a porous outer layer that from a heat-resistant, inorganic material such as γ-alumina particles water adsorption is formed.

C) HC adsorption part with HC oxidizing ability

If at least one in the HC adsorption part 4 ₁ with the HC adsorbent 3 _{1 of} the one-layer structure HC-oxidizing, catalytic element which is selected from the platinum group, ie from the group consisting of Ru, Rh, Pd, Os, Ir and Pt in the modified ZSM-5 zeolite as a carrier, the HC adsorption part 4 ₁ gain HC oxidation ability.

Similarly, such a catalytic element can either be contained in its modified ZSM-5 zeolite and / or the heat-resistant, inorganic material as a carrier in the HC adsorption part 4 ₂ with the HC adsorbent 3 _{2 of} the two-layer structure.

To demonstrate this, 3 g Palladium (Pd) in 80 g of the modified ZSM-5 zeolite from Example 2 through an impregnation process added using a palladium sulfate solution. For comparison were 3 g of palladium (Pd) in 80 g of the unmodified ZSM-5 zeolite as a thief recorded in the same way.

The modified ZSM-5 zeolite and the unmodified ZSM-5 zeolite as carrier with the palladium contained therein were subjected to the following HC conversion test to obtain the in 8th results shown.

The HC conversion test was carried out by Passing the test gas of the same composition as described above with a flow rate of 25.00 ml / min through the inside of an ambient pressure fixed bed reaction tube, that with 25 g Pd-bearing, modified or unmodified ZSM-5 Zeolite filled was, and increase the temperature of the test gas from ambient temperature to 400 ° C with a Rate 12 to 12.5 ° C increased per sec and measure the percent HC conversion during this time.

To 8th , The purification by the adsorption of HC takes place mainly at a gas temperature below a limit temperature of about 180 ° C, while the purification by the oxidation of HC mainly takes place at a temperature above the limit temperature of about 180 ° C. Out 8th it can be seen that when using the Pd-bearing, modified ZSM-5 zeolite, the adsorption of HC at low temperature and the oxidation of HC at the higher temperature can be realized with a high proportion.

Second embodiment (invention)

A heat-resistant HC adsorbent for Exhaust emission limitation according to the second execution is made from a modified ZSM-5 zeolite as a carrier copper (Cu) contained therein as a NOx-converting catalytic element formed an ion exchange process.

A) Manufacture of modified ZSM-5 zeolite

The modified ZSM-5 zeolite is by a predetermined dealuminization treatment of unmodified ZSM-5 zeolite manufactured. While This treatment removes impurities along with the aluminum removed from the unmodified ZSM-5 zeolite.

• (a) Der unmodifizierte ZSM-5 Zeolith wurde mit einem vorbestimmen Molverhältnis Mrl von SiO₂/Al₂O₃ in ein Wasser enthaltendes Behandlungsbad gegeben und es wurde 12 Normale HCl-Lösung allmählich zugegeben. Die Lösung wurde zum Erhalt einer 5 N HCl-Lösung auf 90°C erwärmt.
• (b) Der unmodifizierte ZSM-5 Zeolith wurde bei dieser Temperatur für 20 Stunden gehalten, während gleichzeitig die HCl-Lösung umgerührt wurde. In diesem Fall wurde an das Behandlungsbad ein Kühlturm angebracht, um die Konzentration der HCl-Lösung bei der genannten Normalität zu halten.
• (c) Die 5 N HCl-Lösung wurde auf Raumtemperatur abgekühlt.
• (d) Der somit hergestellte modifizierte ZSM-5 Zeolith wurde gefiltert und mit reinem Wasser gewaschen, bis es einen pH-Wert 5 oder mehr erreichte. Dann wurde der modifizierte ZSM-5 Zeolith bei 400°C für 24 Stunden getrocknet. Die durch diese Behandlung erlangte prozentuale Dealuminisierung R war nahe gleich 20%.

The dealuminization was carried out according to the following process:

• (a) The unmodified ZSM-5 zeolite was placed in a treatment bath containing water with a predetermined molar ratio Mrl of SiO ₂ / Al ₂ O ₃ , and 12 normal HCl solution was gradually added. The solution was heated to 90 ° C to obtain a 5N HCl solution.
• (b) The unmodified ZSM-5 zeolite was kept at this temperature for 20 hours while stirring the HCl solution. In this case, a cooling tower was attached to the treatment bath in order to keep the concentration of the HCl solution at the normality mentioned.
• (c) The 5 N HCl solution was cooled to room temperature.
• (d) The modified ZSM-5 zeolite thus produced was filtered and washed with pure water until it reached pH 5 or more. Then the modified ZSM-5 zeolite was dried at 400 ° C for 24 hours. The percentage dealuminization R obtained by this treatment was almost equal to 20%.

Table 7 shows the molar ratio Mr2 of SiO ₂ / Al ₂ O _{3 of} the modified ZSM-5 zeolite, the molar ratio Mr1 of SiO ₂ / Al ₂ O ₃ of the unmodified ZSM-5 zeolite used to produce the modified ZSM-5 and the ratio of Mr2 / M r1.

Table 7

B) Production of the HC adsorbent

50 g of the modified ZSM-5 zeolite in Example 1 were in 250 ml copper acetamine solution with a concentration of 0.2 mol / l. The resulting solution was at a temperature of 50 ° C for 18 hours for one Ion exchange left, followed by sequential filtering of solids, washing with water and baking at 400 ° C for 24 hours. This resulted in an HC adsorbent an example 1, formed from modified ZSM-5 zeolite with Cu supported in it. Copper (Cu) was modified in the ZSM-5 zeolites in Examples 2, 3 and 4 in the same way added to HC adsorbents of Examples 2, 3 and 4 to obtain.

Table 8 shows the amount C of in each of Examples 1, 2, 3 and 4 carrying Cu.

Table 8

The appropriate amount C of the ingested Cu is in a range of 1 wt% ≤ C ≤ 10 wt%. If C <1 wt%, that is NO versatility low. On the other hand, if C> 10 % By weight, the modified ZSM-5 zeolite is destroyed.

C)

• (1) For comparison, an unmodified ZSM-5 zeolite with a predetermined molar ratio Mr1 of SiO ₂ / Al ₂ O _{3 was} subjected to the same dealuminization treatment as that described above to obtain a modified ZSM-5 zeolite. Table 9 shows the molar ratio Mr2 of SiO ₂ / Al ₂ O _{3 of} the modified zeolites of Examples 1a, 2a, 3a and 4a, the molar ratio Mr1 of SiO ₂ / Al ₂ O ₃ of unmodified zeolites used to produce these modified zeolites and the ratio by Mr2 / Mr1. In this case the deal conversion rate R is about 20%. Table 9
  
  The modified ZSM-5 zeolites of Examples 1a to 4a were then used. In these modified ZSM-5 zeolites, copper (Cu) was taken up in the same manner as described above to obtain HC adsorbents of Comparative Examples 1a to 4a. Table 10 shows the amount of copper loaded in each of Comparative Examples 1a to 4a. Table 10
  
• (2) For comparison, unmodified ZSM-5 zeolites each having a predetermined molar ratio Mr1 of SiO ₂ / Al ₂ O _{3 were} used, and copper (Cu) was carried in these unmodified ZSM-5 zeolites in the same manner as described above, to obtain HC adsorbents of Comparative Examples 5a to 12a. Table 11 shows the molar ratio Mr1 of SiO ₂ / Al ₂ O ₃ and the amounts of copper supported in each of Comparative Examples 5a to 12a. Table 11
  
  By comparing Examples 1 to 4 with Comparative Examples 6a to 9a in Tables 7, 8 and 11, it can be seen that when the molar ratio Mr1 of the unmodified ZSM-5 zeolites is equal to the molar ratio Mr2 of the modified ZSM-5 zeolites, the in the catalysts of Examples 1 to 4, the amount of Cu carried by load is greater than that in the catalysts of Comparative Examples 6a to 9a. This is attributable to the fact that the number of ion exchange sites in each of the modified ZSM-5 zeolites was increased by the dealuminization treatment to a greater value than in each of the unmodified ZSM-5 zeolites.

D) Estimation of activity and heat resistance of the HC adsorbent

A gas with 10% by weight O ₂ , 10% by weight CO ₂ , 800 ppm C ₃ H ₆ , 1000 ppm CO, 1200 ppm NO, 500 ppm H ₂ , 10% by weight H ₂ O and the rest N ₂ was prepared as a test gas.

An NO conversion test was carried out by Passing the test gas at a flow rate of 25,500 ml / min. by the inside of an ambient pressure fixed bed reaction tube, the was filled with 20g of the HC adsorbent, Increase the temperature of the test gas from ambient temperature to 500 ° C with a Rate of 15 ° C per minute with one at the inlet of the Ambient pressure fixed bed reaction tube measured temperature and measurement the percentage conversion of NO during this time.

In a first heat resistance test, each of HC adsorbents for 20 hours at 550, 600, 650, 700, 750, 800 and 850 ° C in one Muffle furnace warmed, and the BET specific area was before and after heating measured.

9 shows the results of the NO conversion test and the first heat resistance test for Examples 1 to 4 and Comparative Examples 1a to 4a. The reference numerals in 9 give the numbers of the examples. The same applies in the following. Out 9 it can be seen that each of Examples 1 to 4 with the molar ratio Mr2 of the modified ZSM-5 zeolites, which is set in a range of 30 Mr Mr2 bei 80 with a percentage dealuminization R of approximately 20%, a high percentage NO conversion and shows excellent heat resistance.

Comparative example 1a shows one high percent NO conversion because the molar ratio Mr2 is <30, but poor heat resistance. Each of the comparative examples has good heat resistance because the molar ratio Mr2> 80, but shows a low percentage of NO conversion.

10 shows the comparison of the percent NO conversions and 11 shows the comparison of the thermal strengths, each for Examples 1 to 4, Comparative Examples 1a to 4a and Comparative Examples 5a to 12a. From the 1 and 11 it can be seen that using the modified ZSM-5 zeolite, the percentage conversion and the heat resistance can be improved compared to the unmodified ZSM-5 zeolite.

In a second heat resistance test, Example 2 and Comparative Examples 2a and 7a heated at 700, 800, 900 and 1000 ° C for 20 hours in a muffle furnace, and the BET specific surface area was measured before and after the heating to determine the percentage retention of the specific surface area of each of the HC adsorbents.

Table 12 shows the heating temperature, the specific surface and the percent retention of specific surface area for each of HC adsorbents.

Table 12

12 shows graphically the relationship between the heating temperature and the percentage retention of the specific surface according to Table 12. Aus 3 it can be seen that both example 2 and comparative example 2a have excellent heat resistance in comparison with comparative game 7a.

13 and 14 Figure 3 shows the percent NO conversion for Example 2 and Comparative Examples 2a and 7a, Figure shows the percent NO conversion before thermal destruction treatment, and 14 shows the percent NO conversion after the thermal destruction treatment. The thermal destruction treatment was carried out under a state in which each of the HC adsorbents was left to stand at 600 ° C for 20 hours in an atmosphere containing 10% by volume of water.

From the 13 and 14 It can be seen that Example 2 shows a high percentage conversion compared to Comparative Examples 2a and 7a, and the percentage conversion achieved by Example 2 was only slightly reduced by the thermal destruction treatment.

Third embodiment (invention)

An HC adsorbent to limit exhaust emissions according to the third execution is made from a modified ZSM-5 zeolite as a carrier cobalt (Co) incorporated therein as a NOx converting catalytic Element formed by an ion exchange.

A) Production of the HC adsorbent

50 g of the modified ZSM-5 zeolite (with a molar ratio Mr2 of SiO ₂ / Al ₂ O ₃ equal to 48) of the additive game 2 of the second embodiment was placed in 250 ml of cobalt acetate solution at a concentration of 0.2 mol / l. The resulting solution was then left at a temperature of 50 ° C for 18 hours for ion exchange, followed by sequentially filtering out solids, washing with water and baking at 400 ° C for 24 hours.

This results in an HC adsorbent Example 1 with incorporated in the modified ZSM-5 zeolite as a carrier Cobalt. The amount C of cobalt taken up by this HC adsorbent was 4.7% by weight. The appropriate amount C of cobalt taken up is in a range of 1% by weight s C s 10% by weight, for the same reason as described above.

B)

• (1) For comparison, an unmodified ZSM-5 zeolite with a Mr1 molar ratio of SiO ₂ / Al ₂ O ₃ equal to 48 was used, and cobalt was taken up in this unmodified ZSM-% zeolite in the same manner as described above to give an HC- To produce adsorbent of a comparative example 1a. The amount C of coabalt taken up as a carrier in this HC adsorbent was 2.9% by weight.
• (2) Also for comparison, the modified ZSM-5 zeolite (with a molar ratio Mr2 of SiO ₂ / Al ₂ O ₃ equal to 130) of Example 2a was used in the second embodiment, and in this modified ZSM-5 zeolite was used in the same way Cobalt added to produce a HC adsorbent of a comparative example 2a. The amount C of cobalt taken up as a carrier in this HC adsorbent was 2.0% by weight.

C) estimation of activity and heat resistance, of HC adsorbents

An NO conversion test was carried out in the same Way as described above using a test gas similar to that the second version carried out. A heat resistance test was also carried out in the same manner as in the second heat resistance test the second version carried out, a percentage retention of the specific surface area for each HC adsorbents in the same manner as in the second embodiment determine. Table 13 shows the heating temperature, the specific one surface and the percent retention of specific surface area for each of HC adsorbents.

Table 13

15 shows graphically the relationship between the heating temperature and the percentage retention of the specific surface according to Table 13. From Figure 15 it can be seen that both Example 1 and Comparative Example 2a have excellent heat resistance compared to Comparative Example 1a.

16 and 17 show the percent NO conversion for Example 1 and Comparative Examples 1a and 2a, 16 shows the percent NO conversion before thermal destruction treatment and 17 shows the percent NO conversion after the thermal destruction treatment. The thermal destruction treatment was carried out in the same manner as in the third embodiment.

Out 16 and 17 it can be seen that in comparison with comparative examples 1a and 2a, example 1 has an excellent NO convertibility and is less thermally destroyed and shows a relatively high percentage NO conversion.

Fourth embodiment (invention)

A heat-resistant HC adsorbent for Exhaust emission limitation according to the fourth execution is made from a modified ZSM-5 zeolite as a carrier absorbed iron (Fe) as a NOx converting catalytic Element produced by an ion exchange process.

A) Production of the HC adsorbent

The modified ZSM-5 zeolite of the Example 2 in the second version was in an amount of 50 g in 250 ml of iron nitrate with a concentration of 0.2 mol / l. The resulting solution was then at a temperature of 90 ° C for 18 Hours for left ion exchange, followed by sequential filtering of solids, washing with water and baking at 400 ° C for 24 hours.

This results in an HC adsorbent Example 1, the carrier from the modified ZSM-5 zeolite Fe is absorbed. The amount C of in this HC adsorbent Fe absorbed was 4.5% by weight.

The appropriate amount C of ingested Fe is in a range of 1% by weight ≤ C ≤ 10% by weight, namely from the same reason as described above.

B)

• (1) For comparison, an unmodified ZSM-5 zeolite with a Mr1 molar ratio of SiO ₂ / Al ₂ O ₃ equal to 48 was used, and iron (Fe) was taken up in this unmodified ZSM-5 zeolite in the same manner as described above, to produce a HC adsorbent of a comparative example 1a. The amount C of the iron taken up in this HC adsorbent as a carrier was 2.6% by weight.
• (2) Further for comparison, the modified ZSM-5 zeolite (with a molar ratio Mr2 of SiO ₂ / Al ₂ O ₃ equal to 130) of Example 2 was used in the second embodiment, and iron (Fe) was used in this unmodified ZSM- 5 supporting zeolite in the same manner to produce an HC adsorbent of a comparative example 2a. The amount C of Fe taken up in this HC adsorbent was 1.9% by weight.

C) Estimation of activity and heat resistance of HC adsorbents

A NO conversion test was carried out in the same way as described above using a test gas similar to that the second version carried out. A heat resistance test was also in the same manner as in the second heat resistance a second version carried out to determine a percentage retention of a specific surface area for each the HC adsorbents in the same way as in the second embodiment.

Table 14 shows the heating temperature, the specific surface and the percent retention of specific surface area for each of HC adsorbents.

Table 14

18 shows graphically the relationship between the heating temperature and the percentage Re tention of the specific surface according to Table 14. Aus 18 it can be seen that both Example 1 and Comparative Example 2a have excellent heat resistance compared to Comparative Example 1a.

19 and 20 show the percent NO conversion for Example 1 and Comparative Examples 1a and 2a, 19 shows the percent NO conversion before thermal destruction treatment and 20 shows the percent NO conversion after the thermal destruction treatment. The thermal destruction treatment was carried out in the same manner as in the embodiment.

From the 19 and 20 it can be seen that in comparison with comparative examples 1a and 2a, example 1 has excellent NO convertibility and is less thermally destroyed and shows a relatively high percentage NO conversion.

Fifth embodiment (invention)

A heat-resistant HC adsorbent for Exhaust emission limitation according to the fifth embodiment is canceled a modified ZSM-5 zeolite as a carrier with incorporated therein Platinum (Pt) as a NOx converting catalytic element formed an impregnation process.

A) Production of the HC adsorbent

The modified ZSM-5 zeolite (with a molar ratio of Mr2 SiO ₂ / Al ₂ O ₃ equal to 48) of Example 2 of the second embodiment was added in an amount of 50 g in 250 ml of a platinum chloride solution with a concentration of 0.05 mol / l. The resulting solution was then left at a temperature of 50 ° C for 18 hours for impregnation with platinum (Pt), followed by sequentially filtering out solids, washing with water and baking at 400 ° C for 24 hours.

This results in an HC adsorbent Example 1 with incorporated in the modified ZSM-5 zeolite as a carrier Pt. The amount C of Pt taken up in this HC adsorbent was 1.3% by weight. The appropriate amount C of Pt taken up is in a range of 1% by weight ≤ C ≤ 10% by weight, preferably in a range of C s 5% by weight, namely from the same Reason as described above.

• (1) For comparison, an unmodified ZSM-5 zeolite with a Mr1 molar ratio of SiO ₂ / Al ₂ O ₃ equal to 48 was used, and platinum (Pt) was taken up in this unmodified ZSM-5 zeolite in the same manner as described above, to produce a HC adsorbent of a comparative example 1a. The amount C of platinum taken up as a carrier in this HC adsorbent was 1.2% by weight.
• (2) Also for comparison, the modified ZSM-5 zeolite (with a molar ratio Mr2 of SiO ₂ / Al ₂ O ₃ equal to 130) of Example 2 was used in the second embodiment, and platinum (Pt) was used in this modified ZSM-5 Zeolite taken in the same way to produce a HC adsorbent of a comparison example 2a. The amount C of Pt taken up in this HC adsorbent was 1.2% by weight.

C) Estimation of activity and heat resistance of HC adsorbents

A NO conversion test was carried out in the same way as described above using a test gas similar to that the second version carried out. A heat resistance test was also carried out in the same manner as in the second heat resistance test the second version carried out, a percentage retention of the specific surface area for each HC adsorbents in the same manner as in the second embodiment determine.

Table 15 shows the heating temperature, the specific surface and the percent retention of specific surface area for each of HC adsorbents.

Table 15

21 shows graphically the relationship between the heating temperature and the percentage retention of the specific surface according to Table 15. Aus 21 it can be seen that both Example 1 and Comparative Example 2a have excellent heat resistance compared to Comparative Example 1a.

22 and 23 show the percent NO conversion for Example 1 and Comparative Examples 1a and 2a, 22 shows the percent NO conversion before thermal destruction treatment and 23 shows the percent NO conversion after the thermal destruction treatment. The thermal destruction treatment was carried out in the same manner as in the second embodiment.

From the 22 and 23 it can be seen that in comparison with comparative examples 1a and 2a, example 1 has excellent NO convertibility and is less thermally destroyed and shows a relatively high percentage NO conversion.

The conversion of NO through the example 1 receives one through a reducibility activated hydrocarbons through the modified ZSM-5 zeolite and a catalytic ability of platinum.

Example 1 is active at low temperature, as in the 22 and 23 shown, and therefore one can expand the active temperature range by combination with a catalyst active at high temperature.

In addition to the platinum group HC-oxidizing catalytic elements Ru, Rh, Pd, Os, Ir and Pt, as described above, other similarly oxidizing catalysts are also in execution usable of the invention. additionally to Cu, Co, Fe and Pt and their oxides as described above also similar ones Catalysts included in the catalytic elements used in the execution of the invention can be used.

A heat resistant exhaust emission control catalyst contains a heat resistant, modified zeolite. This modified zeolite is made by subjecting an unmodified zeolite to a dealuminization treatment. The molar ratio of SiO ₂ / Al ₂ O _{3 of} the unmodified zeolite is designated Mr1 and the molar ratio Mr2 of SiO ₂ / Al ₂ O _{3 of} the modified zeolite is equal to or greater than 1.2 Mr1 (Mr2 ≥ 1.2 Mr1). The modified zeolite has the same 1 framework structure as the unmodified zeolite. Such a catalyst has excellent heat resistance and a high hydrocarbon adsorption capacity ability.

Claims (5)

Heat-resistant catalyst for converting NO _x in an exhaust gas containing hydrocarbons, the catalyst comprising a ZSM-5 zeolite and at least one catalytic element selected from the group consisting of Cu, Co, Fe and Pt in an amount C of the catalytic element , based on the zeolite in a range of 1 wt .-% ≤ C ≤ 10 wt .-%, characterized in that the ZSM-5 zeolite is a modified heat-resistant ZSM-5 zeolite, formed by an aluminum-removing Treatment of an unmodified ZSM-5 zeolite, whereby a molar ratio Mr2 of SiO ₂ / Al ₂ O _{3 of} the modified ZSM-5 zeolite in the range of 30 ≤ Mr2 ≤ 80 is achieved, and setting a ratio Mr2 / Mr1 of the molar ratio Mr2 to a molar ratio Mr1 of the unmodified ZSM-5 zeolite to ≥ 1.2. Catalyst according to claim 1, characterized in that it has a two-ply layer, the bottom layer of which the modified zeolite and its upper layer made of a heat-resistant inorganic material with water adsorbability is formed. Catalyst according to claim 1, characterized in that the modified zeolite is formed as a granular mass and with an outer layer covered with heat-resistant, inorganic material with water absorption capacity is formed. A catalyst according to claim 2 or 3, wherein at least a hydrocarbon oxidizing catalytic element selected from the Platinum group in the modified zeolite and / or the heat-resistant inorganic Material is included. Catalyst according to one of the preceding claims, characterized characterized in that it was applied to a honeycomb structure is.