JP2008272760A - Porous material, method, and device for catalytic conversion of exhaust gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a porous material for the catalytic conversion of exhaust gas. <P>SOLUTION: An oxidizing catalyst capable of catalyzing the oxidation of nitrogen monoxide to nitrogen dioxide, and catalyzing the oxidation of a reducing agent is included. The oxidation of the reducing agent is inhibited because of sterically preventing the reducing agent from contacting the oxidizing catalyst. The porous material also preferably contains a carrier with a reducing agent having a capability of selectively catalyzing the reduction of nitrogen dioxide to nitrogen, (thereby the reducing agent is at least partially consumed). The invention also relates to a method and a device using the porous material, and a useful use of the porous material. The invention can be applied to the field of the catalytic conversion of an exhaust gas generated from an internal combustion engine, particularly a lean-burn engine, and a diesel engine. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

(Technical field)
The present invention relates to a porous material for catalytic conversion of exhaust gas. The porous material contains a carrier having a first porous structure and an oxidation catalyst having the ability to catalytically oxidize nitric oxide to nitrogen dioxide in the presence of oxygen. The oxidation catalyst itself has the ability to catalyze the oxidation of the reducing agent, but according to the invention, the oxidation of the reducing agent is prevented by the oxidation catalyst enclosed inside the first porous structure, The first porous structure has such a size as to sterically prevent the reducing agent from coming into contact with the oxidation catalyst.

  Preferably, the porous material also contains a carrier having a second porous structure and a reduction catalyst, which in the presence of a reducing agent is capable of selectively catalytic reduction of nitrogen dioxide to nitrogen, The reducing agent is at least partially consumed. The reduction catalyst is thereby arranged in a second porous structure having a size such that the reducing agent can contact the reduction catalyst. The present invention also relates to methods and apparatus that utilize this porous material and demonstrates the advantageous use of the porous material.

  The invention can be applied in the field of catalytic conversion of exhaust gases generated from internal combustion engines, in particular lean burn engines (LC-engines) and diesel engines.

  The present invention may also utilize other exhaust gases, including nitrogen oxides and having excess oxygen, generated from fixed exhaust sources such as gas turbines, power plants, and the like.

(Background of the Invention)
In an attempt to reduce nitrogen oxide (NO _x ) emissions from internal combustion engines, many efforts have been made to reduce NO _x -emissions while further maintaining combustion efficiency at satisfactory levels. It has been made to improve.

Among the traditional techniques for reducing NO _x -emissions, mention may in particular be made of exhaust gas recirculation (EGR) and special design techniques for fuel injection and combustion chambers. Other important parameters are compression, fuel injection time and fuel injection pressure. Techniques relating to water injection, the use of fuel / water emulsions and so-called selective catalytic reduction (SCR) with ammonia can also be used. Thereby, it has been found that unilateral optimization of combustion efficiency often results in increased NOx emissions.

  Today, both fuel consumption and NOx-exhaust reduction are required. There is also a strong demand to reduce emissions of other chemical compounds that are potentially hazardous to the environment, such as hydrocarbons.

  Accordingly, there is an increasing need for catalytic converters that can also treat exhaust gases from so-called lean burn (LC) engines. A number of different catalytic converters have therefore been developed and are well known for commercial use, for example in automobiles.

  Typically, conventional catalytic converters contain one or several matrices, or monolith bricks (often referred to as such). Such bricks or monoliths are in the form of a ceramic honeycomb substrate with through passages and cells and may be provided with a porous surface coating. Appropriate catalyst particles are embedded in the surface of the matrix and the design of the matrix has been optimized to maximize the surface area at which the catalytic reaction occurs. Common catalysts are noble metals such as silver (Ag), platinum (Pt), palladium (Pd), rhodium (Rh), gallium (Ga) or ruthenium (Ru) or mixtures thereof. In addition, there are many other metals and metal oxides that can be used as catalysts. Such catalysts can have the ability to catalyze oxidation or reduction reactions, or both.

  The use of crystalline aluminum silicates, so-called zeolites, filled with suitable catalysts has also been known for some time. The use of celite in connection with catalytic conversion of exhaust gases is disclosed, for example, in EP 0 499 931 Al and EP 0 445 408 A.

  Furthermore, it has also been known for some time to combine several different catalyst matrices or to arrange so-called afterburners in the catalytic conversion process. Such a device is disclosed in US Pat. No. 5,465,574.

  It has also been previously known to use corrugated metal foil honeycomb monoliths with suitable catalysts held or supported on the surface.

  For example, in EP 0 483 708 Al, it is also proposed to combine a conventional ceramic catalytic converter with an electrically heatable catalytic converter to ensure that the optimum temperature for catalytic conversion is maintained. It has been.

  Accordingly, a number of different catalyst materials, devices and arrangements for catalytic conversion of exhaust gases have been described in the art.

Thus, for example, simultaneous release of nitrogen oxides (NO _x ) and hydrocarbons (H _x C _y ) over Ag-catalysts may occur and follow the following (simplified) chemical reaction:
A) NO _x + H _x C _y → N ₂ + H ₂ O + CO ₂ + CO
And B) O ₂ + H _x C _y → H ₂ O + CO ₂
In practice, however, we find that the following reactions are dominant:
C) NO ₂ + H _x C _y → N ₂ + H ₂ O + CO ₂
The term H _x C _y in the chemical reactions herein not only refers to a hydrocarbon, it should further be noted also relevant that the oxygen and / or other reducing agents containing sulfur. Accordingly, the reducing agent H _x C _y can also be expressed as _{H x C y O z S w} . Examples of reducing agents that may be present in the exhaust gas are alkanes, alkenes, paraffins, alcohols, aldehydes, ketones, ethers or esters and various sulfur-containing compounds. CO or H ₂ can also act as a reducing agent. The reducing agent in the exhaust gas can come from fuel or combustion air, or can be deliberately added to the exhaust gas.

It has been previously discovered that the above reaction according to C) is very fast, for example on Ag-catalysts. Acid catalysts (H ⁺ ) and acidic zeolites doped with Ag or other suitable catalysts have been found to be selective in the sense that NO ₂ is easily converted (NO is not converted). . This can be a major disadvantage because, for example, NO dominates in “lean” exhaust gases from LC-engines. Another problem is that the effective amount of NO ₂ can be limited with respect to the regulation of hydrocarbons (H _x C _y ) or other unwanted compounds.

To solve this problem (i.e., it can reduce both the amount of NO and H _x C _y amount in the exhaust gas), Ag- combination of zeolite catalyst and Pt- catalyst is suggested more sleeping pre Yes.

  Usually, the following main reactions occur over conventional Pt-catalysts:

Ｅ）Ｏ₂＋Ｈ_xＣ_y→Ｈ₂Ｏ＋ＣＯ₂
Ｆ）２ＮＯ＋Ｈ_xＣ_y→Ｎ₂Ｏ＋Ｈ₂Ｏ＋ＣＯ₂
従来のＡｇ−ゼオライト触媒を従来のＰｔ−触媒と組み合わせて使用する場合、
４つの反応、Ｃ）、Ｄ）、Ｅ）およびＦ）の全てが起こる。しかしながら、炭化水素（Ｈ_xＣ_y）が、化学反応Ｅ）およびＦ）において消費されるため、十分な量の炭化水素（Ｈ_xＣ_y）が、二酸化窒素（ＮＯ₂）との反応（反応Ｃ）に対応）に残されていないという危険をはらむ。これによって、所望されない二酸化窒素（ＮＯ₂）残留分が触媒的に転換された排気ガス中に発生する（反応Ｄ由来）。

E) O ₂ + H _x C _y → H ₂ O + CO ₂
F) 2NO + H _x C _y → N ₂ O + H ₂ O + CO ₂
When using a conventional Ag-zeolite catalyst in combination with a conventional Pt-catalyst,
All four reactions, C), D), E) and F) occur. However, hydrocarbon (H _x C _y) is, for consumption in a chemical reaction E) and F), a sufficient amount of hydrocarbon (H _x C _y) is reacted with nitrogen dioxide (NO ₂₎ (reaction There is a risk that it is not left in (C)). This produces unwanted nitrogen dioxide (NO ₂ ) residue in the catalytically converted exhaust gas (from reaction D).

  Previous attempts to solve this problem with different types of catalysts combine different catalysts to provide a sufficient amount of hydrocarbons for reaction C), and additional amounts of hydrocarbons in this exhaust gas. Was carried out by adding

However, many previous solutions are associated with the problem of unwanted oxidation of hydrocarbons (H _x C _y ) on at least some surfaces of the oxidation catalyst. Preferably, this catalyst should only catalyze the oxidation of nitric oxide (NO) to nitrogen dioxide (NO ₂ ) (corresponding to reaction D).

Another problem associated with many previously known catalysts is that under certain conditions, these catalysts catalyze reaction F), which produces dinitrogen monoxide (N ₂ O). This reaction is undesirable and nitrogen oxides (NO _x ) in the exhaust gas are converted to nitrogen (N ₂ ) at the highest possible rate, not to dinitrogen monoxide (N ₂ O). It is preferable.

(Technical problem)
Accordingly, there is a need for new, selective oxidation catalyst materials that catalyze the oxidation of nitric oxide (NO) to nitrogen dioxide (NO ₂ ) and do not catalyze the oxidation of hydrocarbons.

There is also a need for effective combinations. For example, selective oxidation catalyst materials (catalyzing reactions that produce nitrogen dioxide (NO ₂ )) and reduction catalyst materials (nitrogen dioxide (NO ₂ ) are converted to nitrogen (N ₂ ) by hydrocarbons or other reducing agents. A catalyst that catalyzes the reaction to be reduced).

(Summary of the Invention)
Accordingly, a first object of the present invention is to provide a porous material that catalytically converts exhaust gas, which oxidizes nitric oxide (NO) to nitrogen dioxide (NO ₂ ). Can be selectively catalyzed and catalytic oxidation of hydrocarbons (H _x C _y ) or other reducing agents can be avoided.

  The first object of the present invention is achieved by the use of a porous material for catalytic conversion of exhaust gases. According to claim 1, the porous material includes a carrier having a first porous structure and an oxidation catalyst. In the presence of oxygen, this oxidation catalyst has the ability to catalyze the oxidation of nitric oxide to nitrogen dioxide (corresponding to the first reaction). Furthermore, the oxidation catalyst itself has the ability to catalyze the oxidation of the reducing agent (corresponding to the second reaction). In accordance with the present invention, the oxidation catalyst is enclosed within a porous structure. This porous structure has dimensions that prevent the reducing agent from sterically contacting the oxidation catalyst. Thereby, first of all, the first reaction of the first reaction and the second reaction can occur on the oxidation catalyst mainly during the catalytic conversion of the exhaust gas.

Furthermore, a second object of the present invention is to provide a porous material for catalytically converting exhaust gas, where only the desired reaction takes place, resulting in catalytic activity. converted NO in the exhaust gas, the amount of NO ₂ and H _x C _y is effectively reduced and mainly resulting conversion products is N _2, CO ₂ and H ₂ O, N ₂ O is not.

  The second object of the present invention is achieved using a porous material according to claim 1, which according to claim 2 further comprises a carrier having a second porous structure and a reduction catalyst. In the presence of a reducing agent, the reduction catalyst can selectively catalyze the reduction of nitrogen dioxide to nitrogen (corresponding to the third reaction), thereby precipitating the reducing agent in the third reaction. , And the reducing agent is at least partially consumed. This reduction catalyst is therefore located in the second porous structure. This porous structure has dimensions such that the reducing agent can come into contact with the reduction catalyst, thereby allowing the third reaction to proceed.

  A third object of the present invention is to provide a method for catalytic conversion of exhaust gases, where a porous material according to the present invention is utilized.

  The third object of the present invention is achieved using a method for catalytically converting exhaust gases. According to claim 23, the method comprises the oxidation of nitric oxide to nitrogen dioxide on an oxidation catalyst (corresponding to the first reaction), whereby the oxidation catalyst is also capable of catalyzing the oxidation of the reducing agent. (Corresponding to the second reaction) However, according to the present invention, this reducing agent is prevented from sterically contacting the oxidation catalyst. As a result, the first reaction mainly occurs on the oxidation catalyst among the first reaction and the second reaction.

  The fourth object of the invention is to show the advantageous use of the porous material according to the invention.

  According to the invention, the fourth object is achieved by using a porous material according to the invention. This porous material provides functions for both the oxidation of nitrogen monoxide to nitrogen dioxide and the reduction of nitrogen dioxide to nitrogen for the catalytic conversion of exhaust gases containing excess oxygen.

  Finally, a fifth object of the present invention is to provide an advantageous arrangement for the catalytic conversion of exhaust gases utilizing the porous material according to the present invention.

  In accordance with the present invention, a fifth object of the present invention is achieved by an arrangement comprising a porous material according to the present invention for catalytically converting exhaust gases from an internal combustion engine.

Detailed Description of Preferred Embodiments
Below, it demonstrates with reference to drawings which affixed the porous material according to this invention.

The porous material 1 in FIG. 1 comprises a carrier having a first porous structure 2, 2 ′. The oxidation catalyst (OX) is surrounded inside the first porous structure 2, 2 ′. In the presence of oxygen (O ₂ ), this oxidation catalyst (OX) has the ability to catalyze the oxidation of nitric oxide (NO) to nitrogen dioxide (NO ₂ ) (corresponding to the first reaction 3). Furthermore, the oxidation catalyst (OX) itself has the ability to catalyze the oxidation of the reducing agent (HC) (corresponding to the second reaction (not present in FIG. 1)).

  However, according to the present invention, such oxidation of the reducing agent according to the second reaction is not desirable because the reducing agent (HC) is more useful in the third reaction as shown below.

  In order to prevent unwanted second reactions from occurring, the oxidation catalyst (OX) is enclosed within the first porous structure 2, 2 '. This structure is characterized in that the reducing agent (HC) is sterically prevented from contacting the structures 4, 4 'and the oxidation catalyst (OX). Thereby, the desired first reaction 3 out of the first reaction and the second reaction can take place on the oxidation catalyst (OX) during catalytic conversion of the exhaust gas. In the present specification, the term “first porous structure” mainly means internal micropores in a carrier material or micropores between carrier particles or carrier grains.

Preferably, the porous material 1 further comprises a carrier having a second porous structure 5, 5 ', in which a reduction catalyst (RED) is located. As used herein, the term “second porous structure” can include internal micropores in the carrier material, or cavities or channels between carrier particles, as well as through the porous material, into the cavity interior or channels, ie macropores. Can be included. In the presence of a reducing agent (HC), this reduction catalyst (RED) can selectively catalyze the reduction of nitrogen dioxide (NO ₂ ) to nitrogen (N ₂ ) (corresponding to the third reaction 6). And is schematically shown in FIG. Therefore, the reducing agent (HC) precipitates in the third reaction 6 and is at least partially consumed.

  In accordance with the present invention, the reduction catalyst (RED) is located in the second porous structure 5, 5 ', and this structure has dimensions such that the reducing agent (HC) can contact the reduction catalyst (RED). Thereby, the desired third reaction 6 can occur during the catalytic conversion of the exhaust gas.

  According to one embodiment of the porous material according to the present invention, the average first porous structure 2, 2 ′ is smaller than the second porous structure 5, 5 ′ with respect to the reducing agent (HC). 7 is shown. In this way, the reducing agent (HC) is prevented from coming into contact with the oxidation catalyst (OX). The oxidation catalyst (OX) is surrounded by the first porous structure 2, 2 ′, but does not prevent the second porous structure 5, 5 ′ from contacting the reduction catalyst (RED). These pores of the first porous structure 2, 2 ′ should preferably have an effective size mainly between 3 and 6 Å.

  According to another embodiment of the porous material, both the first porous structure 2, 2 'and the second porous structure 5, 5' are provided in the same layer or coating of porous material.

  However, if desired, the first porous structure 2, 2 'and the second porous structure 5, 5' can be provided in different layers / coating of the porous material. This can be an advantage and depends on the composition of the exhaust gas to be converted catalytically.

  In one embodiment of the porous material, the carrier having the second porous structure 5, 5 ′ is the size of the molecule and / or of the reducing agent (HC) (s) expected to be generated in the exhaust gas. Adapted to absorption characteristics.

In another embodiment of the porous material, the ratio between the oxidation catalyst (OX) and the reduction catalyst (RED) substantially corresponds to the consumption of (NO ₂ ) of nitrogen dioxide (corresponding to the third reaction 6). Then, it is optimized to generate nitrogen dioxide (NO ₂ ) (corresponding to the first reaction 3).

In yet another embodiment of the present invention (FIG. 4A), the porous material further comprises a first portion 10 and a second portion 11, wherein the first portion 10 is more than the second portion 11 during catalytic conversion. It is intended to catch the exhaust gas 12 before. Therefore, the first portion 10 includes a larger volume of oxidation catalyst (OX) than the second portion 11. Here, the second portion 11 includes a reduction catalyst (RED) having a larger capacity than the first portion 10. Thus, when the outflow of the exhaust gas, the first reaction 3 of generating NO _2, takes place upstream of the third reaction 6 (consumption of NO _2). Also contemplated is an embodiment in which, as shown in FIG. 4B, as long as the first part and the second part are used for catalytic conversion in the same conversion process, they are separated from one another.

  According to one embodiment of the present porous material, the first porous structure 2, 2 'and / or the second porous structure 5, 5' is provided in a carrier having a zeolite crystal structure.

  Furthermore, both the first porous structure 2, 2 'and the second porous structure 5, 5' can be provided in a zeolite type carrier. Here, preferably the first porous structure 2, 2 ′ is provided in the first zeolite 14 and the second porous structure is provided in the second zeolite 15.

  Thus, as described above, the first porous structure 2, 2 'and the first zeolite 14 according to the present invention should also provide suitable properties to prevent the aforementioned unwanted second reaction from occurring. It is.

  There are many different ways of combining various zeolites in the porous material according to the present invention. Thus, the porous material may include a physical mixture 13 of the first zeolite 14 and the second zeolite 15 (FIG. 3A).

  In addition, the porous material includes a layered structure 16 of the first zeolite and a layered structure 17 of the second zeolite (FIGS. 3B and 3C). Different layers may also be applied or coated on various support substrates 18 or various surfaces of the substrate 18.

In certain applications, it may be preferred to arrange a layered structure 17 so that upon exhaust gas outflow, this second zeolite contacts the exhaust gas before the first zeolite. This may be the case, for example, when the exhaust gas to be converted moderately contains a high content of NO ₂ but contains a low content of NO.

In other applications, for example, if the content of NO in the exhaust gas is reasonably high but the content of NO ₂ is low, this layered structure 16 is oriented in the opposite direction, ie outside the second zeolite. It may be desirable to place

  According to one embodiment of the present porous material, the layered structure comprises a second porous structure 5, 5 ′ crystallized on a first zeolite 14 comprising a first porous structure 2, 2 ′. This is achieved using the second zeolite 15. This can be done by means called overgrowth.

  Another embodiment of the present porous material aims to further reduce the occurrence of the aforementioned unwanted second reaction. In this embodiment, the oxidation catalyst (OX) content was reduced outside the first zeolite layer 8 using partial ion exchange (shown in FIG. 1). Methods for converting penetration depth and catalytically active metal dispersion are well known to those skilled in the art and will not be described in more detail.

  In another embodiment of the present porous material, an additional zeolite catalyst layer with a reduced content of oxidation catalyst (OX) was crystallized on the first zeolite by a means called obbergulose. Therefore, the additional layer advantageously contains a zeolite with a porous structure having even smaller pores / inlets than the first zeolite. In this way, unwanted reducing agents are prevented more effectively from approaching the inside of the internal pore structure of the first zeolite, and at the same time, nitric oxide (NO) enters, It can move freely inside.

  Also, the size of the crystal grains in the zeolite crystal structure can be used to promote desired chemical reactions and to prevent unwanted chemical reactions. Different crystal structures can be achieved in a variety of different ways (eg by selection of crystal conditions and selection of zeolite type). Also, the internal pore structure of this zeolite is affected by the choice of zeolite type.

Thus, according to one embodiment of the present porous material, the crystal grain size 9 and shape in the crystal structure of the first zeolite both prevent access to the reducing agent (HC) and oxidize NO to NO ₂ . Objective and optimized. It is important to optimize the grain size. This is because it can maximize the oxidation of NO to NO ₂ and minimize the oxidation of HC.

  In another embodiment of the porous material, the relatively small pore size is such that in the crystal structure of the first zeolite providing the first porous structure 2, 2 ′, for example ferrierite-zeolite rather than mordenite-zeolite. Or achieved by selecting chabazite-zeolite.

As mentioned above, the porous material according to the present invention has the ability to catalyze the oxidation of nitric oxide (NO) to nitrogen dioxide (NO ₂ ), and preferably also in the presence of a reducing agent (HC). And has the ability to selectively catalyze the reduction of nitrogen dioxide (NO ₂ ) to nitrogen (N ₂ ). Thus, the reducing agent (HC) can be any suitable reducing agent present or added in the exhaust gas that is catalytically converted.

However, it is advantageous if the reducing agent (HC) in the exhaust gas is a hydrocarbon (H _x C _x ) or a chemical compound containing oxygen and sulfur (H _x C _y O _z S _w ). These compounds can come from fuel, which is consumed and at least partially consumed according to the third reaction 6 with the reduction catalyst (RED) as described above. Alternative fuels (eg rapeseed methyl ether) can produce oxygen-containing compounds, while sulfur is frequently present in most fuels.

  The reduction catalyst (RED) in the second porous structure 5,5 'can be of any suitable and known type. However, in the porous material according to the present invention, the reduction catalyst (RED) is preferably a Bronsted acid site, and silver (Ag), copper (Cu) or rhodium (Rh), cobalt (Co), indium (In). , Iridium (Ir) or a combination thereof. In the porous material according to the present invention, an acidic zeolite catalyst is preferred as a reduction catalyst (RED).

  The oxidation catalyst (OX) can be of any type suitable for this purpose, but preferably contains platinum (Pt) and / or palladium (Pd).

  The term “porous material” as used herein should be considered as containing the total structure / mass that may be present in a unit for catalytic conversion of exhaust gases. Thus, the term “porous” should be understood in both a microscopic and macroscopic sense, i.e. porous materials contain elements within themselves that are not porous to the exhaust gas. obtain. However, this material structure as a whole, ie the “porous material” according to the invention, allows the exhaust gas to be contact-converted to pass through. It should also be noted that embodiments in which the porous material consists of several separated parts with different structures and functions are conceivable as long as they are used within the same catalytic conversion process. is there.

  The porous material of the present invention can be coated on one or several suitable substrates 18 or matrices to provide a carrier having a first or / and second porous structure. Substrates suitable for this purpose are well known from the prior art and are not so important to the invention, so they will not be described in particular detail.

  Thus, the substrate 18 can be a metal substrate of a known type. The substrate 18 can also be a support, an already known, honeycomb structure of a suitable material, with or without catalytic activity.

  It should also be noted that the term “porous structure” as used herein should be understood as containing both micropores and macropores of the porous material. Thus, internal micropores, cavities between carrier particles, channels in or through the porous material, etc. are all included within the scope of “porous structure”.

  For example, the second porous structure 5, 5 need not be an internal micropore structure in the carrier material, but the second porous structure 5, 5 ′ is instead an opener, macroscopic structure May be provided by the body. However, the first porous structure 2, 2 ′ is preferably a carrier material in order to provide sufficient steric hindrance against (undesirable) incorporation of the reducing agent at the site where the oxidation catalyst is located. It is an internal microstructure inside.

In the following, the method for catalytic conversion of exhaust gases will be described in more detail with reference to the attached FIGS. 1 and 5 according to the present invention. The process according to the invention comprises the oxidation of nitric oxide (NO) to nitrogen dioxide (NO ₂ ) with an oxidation catalyst (OX) according to the first reaction 3 (FIG. 1). The oxidation catalyst (OX) by itself has the ability to catalyze the oxidation of the reducing agent (HC) according to a second reaction (not shown in FIG. 1). However, according to the present invention, the reducing agent (HC) is 4,4 ′ that is sterically hindered from contacting the oxidation catalyst (OX). As a result of this, the main first reaction 3 from the first and second reactions takes place on the oxidation catalyst (OX).

According to one embodiment of the present invention, the method of the present invention comprises, according to the third reaction 6, carbon dioxide to nitrogen (N ₂ ) over a reducing catalyst (RED) in the presence of a reducing agent (HC). Further included is the reduction of nitrogen (NO ₂ ). For this reason, the reducing agent (HC) contributes to the third reaction 6 and is at least partially consumed. In this way, catalytically converted exhaust gas 12 ′ (FIG. 5) is obtained, which includes reduced amounts of nitric oxide (NO), nitrogen dioxide (NO ₂ ) and reducing agent (HC) and comparisons. Contains a low amount of dinitrogen monoxide (N ₂ O). Furthermore, the converted exhaust gas contains a reduced amount of carbon monoxide (CO).

  If desired, according to the third reaction 6 (FIGS. 1 and 5), an additional amount of 19, 19 ′, 19 ″ of reducing agent (HC) is suitable before reduction takes place on the reduction catalyst (RED). Can be added using a simple injection device 28. Thus, the stoichiometry of the resulting chemical reaction can be affected, so that the catalytic conversion is as complete as possible. It is also possible to increase or adjust the amount of available reducing agent in the internally consumed engine by so-called engine parameter tuning methods. This can be implemented, for example, by fuel injection timing, valve timing, post injection, supply pressure and / or control of fuel injection pressure, EGR, transmission ratio, etc.

Advantageously, an additional amount of 19, 19 ′, 19 ″ of reducing agent (HC) is measured of the reducing agent (HC) and / or nitrogen oxides (NO _x ) in the exhaust gas 12, 12 ′. Or may be adjusted based on a pre-mapped amount 20.

A measured amount 20 of reducing agent (HC) or nitrogen oxide (NO _x ) in the catalytically converted exhaust gas (12 ′) can also be used in the diagnostic control system 22 to provide an indication of this catalytic conversion status. provide.

The exhaust gas 12 can also be passed through a device having the capacity to store and, if necessary, release nitrogen oxides (NO _x ) prior to oxidation on the oxidation catalyst (OX) according to the first reaction 3 Can do. Such NO _x -absorbers are well known to those skilled in the art and are not described in further detail herein. Prior to oxidation, the exhaust gas 12 can also pass through previously known devices that have the ability to store and release reductant (HC) (eg, hydrocarbons) when necessary. This embodiment is useful, for example, for a cold start of an internal combustion engine.

  In order to ensure that the oxidation catalyst (XO) and / or the reduction catalyst (RED) function in the most possible way, i.e. in the active temperature interval, the temperature of the exhaust gas is adjusted to the porous material 21 according to the invention. It can be controlled before passing. This can be done using any known device 23 that is suitable for this purpose.

  To further improve catalytic conversion, the exhaust gas may allow passage through the second dioxide catalyst 24, on which oxidation of the reducing agent and / or carbon monoxide residue may occur. In this way, it is ensured that the exhaust gas (which is at least partially catalytically converted on the porous material 21) reaches a sufficiently high degree of catalytic conversion.

Exhaust gas 12 originates from the internal combustion engine 25 and the reducing agent (HC) is a hydrocarbon (H _x C _y ) and / or a chemical compound containing oxygen and / or sulfur (H _x C _y O _z S _w ) Is beneficial to the method of the present invention.

Furthermore, the fuel 26 consumption of the internal combustion engine 25 affects the chemical composition of the exhaust gas 12. Legal regulations, imposed on both the residual content of the fuel consumption and contact converted nitrogen oxides of the exhaust gases 12 'in (NO _x). In one embodiment of the invention, the fuel consumption of the internal combustion engine and the residual content of nitrogen oxides (NO _x ) in the catalytically converted exhaust gas 12 ′ are regulated to meet relevant legal regulations.

  In one preferred embodiment of the method according to the invention, the internal combustion engine 25 is a diesel engine and the reducing agent (HC) arises from internal combustion within the diesel engine.

  When referring to a diesel engine, an additional amount of 19 reducing agent (HC) can be effectively supplied to the engine through the fuel injector of the diesel engine and / or through an isolated injector for additional reducing agent.

The use of the porous material according to the present invention has oxygen sulfide and is therefore catalytic conversion of exhaust gas 12 that is difficult to convert with conventional catalytic conversion (eg, three-way converter). preferred. in such use, the porous material, for the oxidation of nitrogen monoxide (NO) into nitrogen dioxide (NO _2), and nitrogen reduction of nitrogen dioxide (N ₂₎ to (NO ₂₎ For providing both functions.

  In accordance with the invention, it is also preferred to use an arrangement 27 for the catalytic conversion of the exhaust gas originating from the internal combustion engine 25. This arrangement thus comprises a porous material 21 according to the invention and further operates through a method according to the invention.

(Example)
To more clearly illustrate the basic principles of the present invention, a number of porous samples, i.e. model catalyst materials, were run in a series of laboratory trials.

  In laboratory trials, basic types of zeolites, mordenite, ferrierite and chabazite were used to provide the catalyst carrier.

Different zeolite types have the following channel / pore dimensions:
Mordenite: free diameter: 12 rings 6.5 × 7.0 Å, 8 rings 2.6 × 5.7 Å
Ferrierite: Effective diameter: 10 rings 4.2 x 5.4 mm, 8 rings 3.5 x 4.8 mm
Chabazite: Effective diameter: 8-ring 3.8 x 3.8 mm
As is clear from the above, the selected zeolites have either eight, ten or twelve rings and provide entry into their internal micropore structure. The selected zeolite crude material was provided in the form of NH ₄ -zeolite.

(Preparation of platinum-zeolite (Pt))
Samples of different NH ₄ -zeolites were calcined at 500 ° C. for 1 hour under a stream of oxygen in order to convert the zeolite to the acid form, ie H-zeolite. 0.5 wt%, a 1.0 wt% or 1.5 wt% of the amount of platinum (Pt), by contacting them with an aqueous solution of _{Pt (NH 3) 4 (OH} ) 2, was loaded onto H- zeolites . Therefore, a 0.01 MPt solution was added dropwise to the zeolite dispersed in water. The resulting mixture was stirred for 24 hours at room temperature, filtered, washed with H ₂ O, and dried at 60 ° C. overnight. The sample was then calcined in dry air at 450 ° C. for 2 hours at a rate of 0.5 ° C. × min ⁻¹ , after which the sample was cooled in a N ₂ stream.

  The method for Pt-loading is described in the publication J.I. Catal. 113 (1988), pages 220-235 (Tzou et al.) And J. Am. Catal. 117 (1989), 91-101 (Homeyer et al.).

(Preparation of silver-zeolite (Ag))
Ag-zeolite was produced using a so-called “incipient wetness” method by loading ₅ wt-% Ag onto a different NH ₄ -zeolite by soaking in AgNO ₃ . Thus, the metal salt (AgNO ₃ ) was dissolved in a minimum amount of water (1 ml / gram zeolite) and then the resulting solution was mixed with the zeolite powder. Finally, the sample was calcined at 550 ° C. for 16 hours in a muffle furnace and stored in the dark until evaluation was performed.

(Evaluation of contact conversion efficiency)
Prior to evaluation, the resulting Pt-Zeolite and Ag-Zeolite, and their physical mixtures, were compressed into pellets, i.e. model porous materials, and the catalytic conversion efficiency of these different porous samples was evaluated.

In a preferred porous sample, Pt-zeolite is intended to provide the NO oxidation function as described above, while Ag-zeolite is intended to provide the NO ₂ reduction function as described above.

Evaluation of catalytic conversion efficiency was performed by inserting a small amount of porous sample (0.3 ml) into a device suitable for the purpose of evaluating catalytic conversion efficiency. A gas flow of 300 ml / min (containing a composition of 500 ppm NO, 350 ppm C ₈ H ₁₈ , 6% O ₂ , 12% H ₂ O, 10% CO ₂ and 350 ppm CO) is then applied to the porous material sample. Passed through the sample chamber where it was placed. The temperature was increased stepwise from 140 ° C. to 500 ° C. while simultaneously detecting the catalytically converted exhaust gas composition from the sample chamber.

The catalytic conversion efficiency for several different porous samples (containing different zeolites and their physical mixtures) is evident from Table 1 below. Table 1 shows the temperature at which maximum conversion of NO to N ₂ was obtained, the total NO _x -conversion at this temperature, and the formation of N ₂ and N ₂ O, respectively, at this temperature. It should be noted that in this case, conversion to N ₂ is desirable, but conversion to N ₂ O is not desirable.

表１の結果は、最も高い総ＮＯ_x−変換が、Ｐｔ−モルデナイトタイプのゼオライトを含有する多孔質サンプルによって達成されることを示す。しかし、Ｐｔ−モルデナイトを用いる一酸化二窒素（Ｎ₂Ｏ）の強力な形成は、不利益である。組み合わせたＰｔ−ＣＲＡ／Ａｇ−ＭＯＲサンプルは、Ｎ₂へのＮＯｘの非常に高い変換を示した。Ａｇ−ＣＨＡサンプルはまた、Ｎ₂へのＮＯ₂の非常に高い変換を示したが、これは非常に高温（５００℃）においてのみであり、多くの適用には実施不可能である。

The results in Table 1 show that the highest total NO _x -conversion is achieved with a porous sample containing a Pt-mordenite type zeolite. However, the strong formation of dinitrogen monoxide (N ₂ O) using Pt-mordenite is disadvantageous. Combined Pt-CRA / Ag-MOR sample exhibited very high conversion of NOx into N _2. Ag-CHA sample also showed a very high conversion of NO ₂ to N _2, which is only very at high temperature (500 ° C.), for many applications it is not feasible.

In Table 2 below, the catalytic conversion efficiency is shown from further evaluation of different zeolites and their physical mixtures. This catalytic conversion efficiency is achieved when the hydrocarbon (C ₈ H ₁₈ ) in the supplied gas mixture is a linear alkane, ie n-octane, and when the hydrocarbon (C ₈ H ₁₈ ) is clearly branched. Both are shown for paraffin, ie iso-octane (more particularly 2,2,4-tri-methylpentane).

表２から明らかであるように、Ｐｔ−フェリエライトのみ（Ｐｔ−ＦＥＲ）を含有するサンプルは、供給された炭化水素が直鎖炭化水素、すなわちｎ−オクタンである場合、非常に高い総ＮＯ_x−変換を提供した。このことは、前述の反応Ｆ：
Ｆ）２ＮＯ＋Ｈ_xＣ_y→Ｎ₂Ｏ＋Ｈ₂Ｏ＋ＣＯ₂
に従った、Ｐｔ−触媒上の直鎖炭化水素の反応の結果である。

As is apparent from Table 2, the sample containing only Pt-ferrierite (Pt-FER) is very high in total NO _x when the feed hydrocarbon is a straight chain hydrocarbon, ie n-octane. -Provided conversion. This is due to the aforementioned reaction F:
F) 2NO + H _x C _y → N ₂ O + H ₂ O + CO ₂
Is the result of the reaction of linear hydrocarbons on the Pt-catalyst.

As a result of this reaction, the formation of undesired dinitrogen monoxide N ₂ O is very high when fed with linear hydrocarbons.

  Instead, total NOx-conversion is dramatically reduced when clearly branched iso-octane is fed to the Pt-FER sample. The reason for this is that the distinctly branched iso-octane is sterically hindered from contact with the Pt-catalyst, and this is due to the rather small entrance of the Pt-ferrierite internal pore structure. And the main part of the Pt-catalyst is arranged inside this. On the other hand, linear hydrocarbons are not sterically hindered from contacting the Pt-catalyst within the internal pore structure, and (thus reaction F) can occur and consume NO.

As is also apparent from Table 2, the porous sample containing only Ag-mordenite provides much lower total NO _x -conversion and conversion efficiency when n-octane and iso-octane are fed, respectively. There is no difference. This result shows that the clearly branched iso-octane is not sterically hindered from contacting the Ag-catalyst to a higher degree than the linear n-octane. The reason for the low total NO _x -conversion in this case is that the amount of nitrogen dioxide (NO ₂ ) in the test gas is too small to allow the aforementioned reaction C) to take place on the Ag-catalyst. is there.
C) NO ₂ + H _x C _y → N ₂ + H ₂ O + CO ₂
From these results, it can be concluded that ferrierite-zeolite accepts linear hydrocarbons into their internal pore structure, but does not accept clearly branched hydrocarbons. Furthermore, it can be concluded that mordenite-zeolites accept both linear and well-branched hydrocarbons into their internal pore structure.

  Thus, a mixture of Pt-ferrierite and Ag-ferrierite accepts linear hydrocarbons (eg, n-octane) and that the following four reactions occur on the combined Pt / Ag-catalyst sample: Enable:

Ｅ）Ｏ₂＋Ｈ_xＣ_y→Ｈ₂Ｏ＋ＣＯ₂（Ｐｔ上）
Ｆ）２ＮＯ＋Ｈ_xＣ_y→Ｎ₂Ｏ＋Ｈ₂Ｏ＋ＣＯ₂（Ｐｔ上）
Ｃ）ＮＯ₂＋Ｈ_xＣ_y→Ｎ₂＋Ｈ₂Ｏ＋ＣＯ₂（Ａｇ上）
分岐イソ−オクタンが、代わって供給される場合、分岐イソ−オクタンは、少なくとも部分的に、関与することを立体的に妨げられるので、反応Ｅ）、Ｆ）およびＣ）による反応がより少なくなる。この結果は、表２（Ｐｔ−ＦＥＲ／Ａｇ−ＦＥＲ）から明らかであるように、分岐イソ−オクタンを供給する場合、総ＮＯ_x−変換が降下するということである。これは、添付のグラフ１Ａおよび１Ｂによってさらに例示される。

E) O ₂ + H _x C _y → H ₂ O + CO ₂ (on Pt)
F) 2NO + H _x C _y → N ₂ O + H ₂ O + CO ₂ (on Pt)
C) NO ₂ + H _x C _y → N ₂ + H ₂ O + CO ₂ (on Ag)
If branched iso-octane is supplied instead, the branched iso-octane is sterically hindered from participating, at least in part, resulting in fewer reactions due to reactions E), F) and C). . The result is that, as is apparent from Table 2 (Pt-FER / Ag-FER), the total NO _x -conversion decreases when supplying branched iso-octane. This is further illustrated by the accompanying graphs 1A and 1B.

When using a porous material containing a combination of Pt-ferrierite and Ag-mordenite (Pt-FER / Ag-MOR), the linear n-octane is the internal pore of both Pt-ferrierite and Ag-mordenite. Approach the structure. Thus, all four reactions D, E, F and C can occur. Thus, as can be seen from the results in Table 2, a fairly high total NO _x -conversion occurs when linear n-octane is fed.

  As described above, branched iso-octane is sterically hindered from entering the ferrilite-zeolite pore structure, but not from entering the mordenite-zeolite pore structure. Thus, when a branched hydrocarbon, such as iso-octane, is fed to the physical mixture of Pt-ferrierite and Ag-mordenite, reactions D and C are dominant:

Ｃ）ＮＯ₂＋Ｈ_xＣ_y→Ｎ₂＋Ｈ₂Ｏ＋ＣＯ₂（Ａｇ上）
このことは、直鎖ｎ−オクタンの代わりに分枝イソ−オクタンが供給される場合、総ＮＯ_x−変換の驚くべき増加、および相対的Ｎ₂Ｏ−形成の著しい減少として、表２（Ｐｔ−ＦＥＲ／Ａｇ−ＭＯＲ）に示される。この効果は、接触変換効率を改善するのに非常に有用であり、そして添付のグラフ２Ａおよび２Ｂにさらに例示される。

C) NO ₂ + H _x C _y → N ₂ + H ₂ O + CO ₂ (on Ag)
This is shown in Table 2 (Pt) as a surprising increase in total NO _x -conversion and a significant decrease in relative N ₂ O-formation when branched iso-octane is provided instead of linear n-octane. -FER / Ag-MOR). This effect is very useful in improving the contact conversion efficiency and is further illustrated in the accompanying graphs 2A and 2B.

  Thus, according to the present invention, it is beneficial to sterically hinder hydrocarbons or other reducing agents from being oxidized by reactions E) and / or F). A number of further conclusions can be drawn from this fact. This is also the basic principle on which the present invention is based, as has become clear from the above description.

  The present invention should not be considered limited to the embodiments described herein, but numerous further changes and modifications are considered to be within the scope of the appended claims.

Hereinafter, the present invention will be described in more detail with reference to the attached drawings and graphs.
FIG. 1 shows a schematic view of a portion of a porous material according to the present invention, with an enlarged view of the pores of this porous material as viewed from the inside. It also shows the main chemical reactions that occur during the catalytic conversion of exhaust gases. FIG. 2 schematically illustrates an embodiment of a porous material according to the present invention, with a detailed enlarged view of a portion of the porous material including a support substrate. FIG. 3A schematically shows a detailed enlarged view of a portion of the detailed enlarged view of FIG. 2 and shows different porous materials containing a physical mixture of two different zeolite carriers according to the present invention. FIG. 3B schematically shows another detailed enlarged view of a portion of the detailed enlarged view of FIG. 2 and shows another different porous material comprising a layered structure of two different zeolite carriers according to the present invention. . FIG. 3C schematically shows an alternative layered structure in FIG. 3B. FIG. 4A schematically illustrates an embodiment of a porous material having a first portion and a second portion according to the present invention. FIG. 4B schematically shows another embodiment of the present invention, in which a porous material according to the present invention is divided into two parts (intended to be used together in a single catalytic conversion process). Including different parts. FIG. 5 shows a schematic process diagram of an arrangement for catalytic conversion of exhaust gas according to the present invention. FIG. 6A shows the results of a laboratory evaluation of a porous sample containing a physical mixture of Pt-ferrierite and Ag-ferrierite when linear hydrocarbons are fed to the catalytically converted gas. . FIG. 6B shows the results of a laboratory evaluation of the same porous sample as in FIG. 6A when branched hydrocarbons are fed to the catalytically converted gas. FIG. 7A shows the results of a laboratory evaluation of a porous material containing a physical mixture of Pt-ferrierite and Ag-mordenite according to the present invention when linear hydrocarbons are added to the catalytically converted gas. Indicates. FIG. 7B shows the results of a laboratory evaluation of the same porous sample as in FIG. 7A, according to the present invention, when branched hydrocarbons are fed to the catalytically converted gas.

Claims (1)

Invention described in the specification.

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